Production Of Methanol From Natural Gas

Production Of Methanol From Natural Gas

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Production Of Methanol From Natural Gas

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Methanol Methanol is an Alcohol whose chemical formula can be written as CH 3OH. It is a clear, colourless liquid with a mild odour, and dissolves readily in most common organic solvents. Methanol is one of the largest volume chemicals produced, with a world wide annual production of about 13 million tons. Methanol was first obtained commercially some 150 years ago by the destructive distillation of wood. Today it is produced mainly from the steam reforming of natural gas via a synthesis gas intermediate. Methanol can and is , however also being produced from such alternative feed stocks as coal and residual fuel oil. Methanol has been traditionally used as a chemical intermediate for the production of formaldehyde, solvents, methyl derivatives(chemical groups containing CH3) and increasingly acetic acid. Recently methanol has gained importance as a clean burning fuel and fuel additive in such diverse uses as a boiler fuel for NOx control , as an octane booster for gasoline by direct blending or as a methyl tertiary butyl ether derivative and for fuel cell application . 1.1 Physical Properties.Methanol (CH3OH) is an alcohol fuel. Methanol is the simplest alcohol, containing one carbon atom. It is a colorless, tasteless liquid with a very faint odor and is commonly known as "wood alcohol."As engine fuels, ethanol and methanol have similar chemical and physical characteristics. Methanol is methane with one hydrogen molecule replaced by a hydroxyl radical (OH).

Physical Properties Molecular weight

32.04

Boiling point

64.7°C

Vapor pressure

97 Torr at 20°C

Formula

CH3OH

Freezing point

-97.68°C

Refractive index

1.3284 at 20°C

Density

0.7913 g/mL (6.603 lb/gal) at 20°C 0.7866 g/mL (6.564 lb/gal) at 25°C

Production Of Methanol From Natural Gas

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Dielectric constant

32.70 at 25°C

Dipole moment

2.87 D at 20°C

Solvent group

2

Polarity index (P')

5.1

Eluotropic value on alumina

0.95

Eluotropic value on octadecylsilane

1.0

Viscosity

0.59 cP at 20°C

Surface tension

22.55 dyn/cm at 20°C

Solubility in water

Miscible in all proportions

Melting Point

-97.7 0C

Flash point

11 oC

Auto ignition temperature

455 oC

Explosive limits

7-36 %

Heat of Formation

-201.3 MJ/kmol

Gibbs Free Energy

-162.62 MJ/kmol

Critical temperature

512.6 K

Critical pressure

81 bar abs

Critical volume

0.118 m³/kmol

Heat of Vaporization

35278 kJ/kmol

Regulatory and Safety Data Acute effects

Poisonous by ingestion or inhalation, may cause respiratory failure, kidney failure, blindness.

Chronic effects

As acute. Skin contact can cause dermatitis.

.

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1.2 Reactions Of Methanol Methanol is the 1st in a series of aliphatic, monohydric alcohols and undergoes many of the reactions typical of this class of chemical compound , Methanol is also a typical member of this series since it contains only one carbon atom . Methanol, for example can not undergo elimination of the hydroxyl group and hydrogen to form the analogous olefins as do many of the higher alcohols. The reactions of the aliphatic alcohols including methanol generally involve hydroxyl group, either through breaking of the C-O bond or O-H bond and substitution or displacement of the – H or _OH group, . the O-H and C-O bonds in alcohols are relatively strong, albeit polar and kinetically labile. Hemolytic bond dissociation energies are in the order of 90 – 100 Kcal/ mole. Because of this bond strength in alcohols, some activation of these bonds is often necessary to achieve acceptable reaction rates.

1.3 CHEMICAL PROPERTIES OF METHANOL: CH3OH Combustion of Methanol: Methanol burns with a pale-blue, non-luminous flame to form carbon dioxide and steam. 2CH3OH

+

302 ===>

2CO2 +

4H2O

Oxidation of Methanol: Methanol is oxidized with acidified Potassium Dichromate, K2Cr2O7, or with acidified Sodium Dichromate, Na2Cr2O7, or with acidified Potassium Permanganate, KMnO4, to form formaldehyde. CH3OH

===>

Methanol 2H2 + O2 ===>

HCHO

+

H2

Formaldehyde 2H2O

If the oxidizing agent is in excess, the formaldehyde is further oxidized to formic acid and then to carbon dioxide and water. HCHO ===> HCOOH ===> CO2 + H2O Formaldehyde Formic Acid

Catalytic Oxidation of Methanol: The catalytic oxidation of methanol using platinum wire is of interest as it is used in model aircraft engines to replace the sparking plug arrangement of the conventional petrol engine. The heat of reaction is sufficient to spark the engine.

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Dehydrogenation of Methanol: Methanol can also be oxidized to formaldehyde by passing its vapor over copper heated to 300 °C. Two atoms of hydrogen are eliminated from each molecule to form hydrogen gas and hence this process is termed dehydrogenation. Cu 300°C CH3OH ===> HCHO + Methanol Formaldehyde

H2

Dehydration of Methanol: Methanol does not undergo dehydration reactions. Instead, in reaction with sulphuric acid the ester, dimethyl sulphate is formed.

2 CH3OH Methanol

Conc H2SO4 ===> (CH3)2SO4 Dimethyl Sulphate

+ H2O Water

Esterification of Methanol Methanol reacts with organic acids to form esters.

CH3OH Methanol

H(+) + HCOOH ===> Formic Acid

HCOOCH3 Methyl Formate

+ H2O Water

Substitution of Methanol with Sodium Methanol reacts with sodium at room temperature to liberate hydrogen. This reaction is similar to the reaction of sodium with ethanol. 2 CH3OH + Methanol

2 Na ===> Sodium

2CH3ONa Sodium Methoxide

+ H2 Hydrogen

Substitution of Methanol with Phosphorus Pentachloride Methanol reacts with phosphorus pentachloride at room temperature to form hydrogen chloride, methyl chloride, (i.e. chloroethane) and phosphoryl chloride. CH3OH Methanol

+

PCl5 ===>

HCl

+

Phosphorus Hydrogen

CH3Cl Methyl

+

POCl3 Phosphoryl

Production Of Methanol From Natural Gas Pentachloride Chloride

Chloride

6 Chloride

Substitution of Methanol with Hydrogen Chloride Methanol reacts with hydrogen chloride to form methyl chloride (i.e. chloromethane) and water. A dehydrating agent (e.g. zinc chloride) is used.

CH3OH + Methanol

HCl

ZnCl2 ===>

CH3Cl Methyl Chloride

+

H2O

1.4 USES OF METHANOL:The major portion of the methanol produced is used for making formaldehyde and a number of chemical derivatives. Other applications include its use as solvents extractant and air automation antifreeze. .

Methanol As A Solvent:Methanol is miscible with most organic liquids and is a solvent for variety of substance like dyes, nitro cellulose, polyvinyl, butyl ethyl cellulose, Shellac and modified resin. It is used in the manufacturing of wood and metal polishes. Water proofing formulation, coated fabrics, aniline, and other inks, and duplicator fluids. Its solution have lower viscosities than similar solution, made from other alcohols, methanol is uses in combination with 5 to 10 % of polyhydroxy alcohol as a solvent for water soluble aniline dyes in the manufacture of non=grain-raising wood-stain, it is also used as a solvent for aniline dyes for leather and is especially useful where uniform colour development is essential. Other application of this products include its addition to asphalts paints to decrease their drying time and its use in both natural and synthetic rubber solutions to lower the viscosity during processing . Methanol does not dissolve cellulose acetate and acetate butyrate, polystyrene, polyethene, methylcrylate resin, polyvinyl chloride, and co-polymers.

Methanol As An Extractant:Methanol is employed in a large scale in many industrial chemical processes as an extractant. In the refining of gasoline and heating oil. The unisol process use caustic methanol solutions to remove undesirable mercaptan impurities. Methanol may also be used to extract the aromatic potion of petroleum form other hydrocarbons and patent literature describe its use in extraction organic nitrites. From non polar hydrocarbon in the secondary recovery of crude oil by th miscible phase method using alcohol methanol is the least expensive and most easy recovered. A process has been developed to use a solvent of methanol and hexane in the extraction of tars from Texas Lignite deposits. Methanol is also uses for removing acid impurities from vegetable oils, dewaxing dimmer gum, flash washing water soluble crystals, extracting inorganic salt such as potassium iodide and barium and strontium halides, purifying hormones and crystallizing steroid.

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Methanol As A Ceansing Agent:Methanol is used in many cleansing operations such as in washing steel surfaces before coatings are applied , rinsing the interiors of electronic tubes before they are evacuated , cleaning resin sheets before further processing , It is employed as a reducing agent in the vapor phase cleaning of copper, the bright annealing of brass and in soldering fluxes. Its is also used in special preparation for dry cleaning leather goods, in glass cleaners and in flushing fluids for hydraulic brake system.

Methanol As An Anti Freezing Agent Methanol offers the advantages of low molecular weights, low costs and high efficiency when used as an automotive or industrial antifreeze. The pressure up cap on the radiator of the modern engine cooling system prevent losses by evaporations. Methanol-antifreeze solutions are considered less result of internal leakage then the high boiling type. Fuel system antifreeze and windshield washer fluid based on methanol add to the dependability and convenience of motor transport in methyl ester of 2-4 D is a selective weed killer, methyl salicylate is used in medicines flavorings and perfumes., dimethylpthalate is as insect repellent and a plasticizer for cellulose acetate methyl P=hydroxyl benzoate is a mold inhibitor for aqueous preparations, containing starch guans and oil. Methylcrylate polymerizes readily to form clear plastics.

Formaldehyde:Worldwide, the largest amount of formaldehyde is consumed in the production of ureaformaldehyde resins, the primary end use of which is found in building products such as plywood and particle board .The demand for these resins, and consequently methanol, is greatly influenced by housing demand. In the United States, the greatest market share for formaldehyde is again in the construction industry. However, a fast-growing market for formaldehyde can be found in the production on acetylenic chemicals, which is driven by the demand for 1, 4 butanediol and its subsequent downstream product, spandex fibers.

Methyl T-Butyl Ether:MTBE is used as an oxygen additive for gasoline. Production of MTBE in the United States ha increased due to the requirements of the 1990 Clean Air Act amendments, and has surpassed formaldehyde as the largest domestic consumer of methanol. Projection for this use of methanol are difficult to estimate due to the varying political and environmental considerations that promote the use of cleaner burning motor fuels.

ACIDS:Methanol carbonylation has become the process of choice for production of this staple of the organic chemical industry, which is used in the manufacture of acetate fibers, acetic anhydride, and terephthalic acid, and for fermentation,

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Methanol As An Alternative Fuel Utilization of methanol as alternative fuel can be done through two different ways that is by using directly in an internal combustion engine or by implementing methanol fuel cell powered vehicles. Pure methanol (M100) has been used in heavy-duty trucks and transit buses equipped with compression-ignition diesel engines. Since 1965, M100 has been the official fuel for Indianapolis 500 race cars. (The last time gasoline was used in the Indianapolis 500 was in 1964, when the race suffered a pile-up of cars that resulted in a gasoline fire and deaths.) Typically, a blend of 85 percent methanol and 15 percent gasoline (M85) is used in cars and light trucks. Pure methanol can also be reformed in fuel cells into hydrogen, which is then used to power electric vehicles. Methanol-powered vehicles have been found largely in the West, primarily in California. They can also be seen in the fleets of the federal government and the New York

STORAGE AND SAFETY Because methanol is corrosive to some metals and damaging to rubber and some plastics, fuel storage tanks and dispensing equipment must be corrosion and damage resistant. California requires that underground storage tanks for methanol be double walled. Because methanol is water soluble, it could be quickly diluted in large bodies of water to levels that are safe for organisms. Environmental recovery rates for methanol spills are often faster than for petroleum spills. As with gasoline, methanol can be fatal when ingested. Inhalation of fumes and direct contact with skin can also be harmful. Because pure methanol flames are nearly invisible in daylight, gasoline is added as a safety precaution to provide color to a flame. Added gasoline also serves to add a smell to this otherwise odorless liquid. Because of its high flash point, methanol is less volatile than gasoline. It burns more slowly and at a lower temperature. Methanol is transported by barge, truck, or rail. In the event of an

EMISSIONS The methanol molecule has a simple chemical structure, which leads to clean combustion; reports from emissions studies, however, vary more widely for methanol than for other fuels probably because of differences among fuel blends used across the country and because vehicles may not be optimized for using methanol. Comparisons of M100 with gasoline and diesel have shown these results: Carbon monoxide: Emissions vary — sometimes lower, but are usually equal or slightly higher. Ground-level-ozone-forming potential: 30 to 60 percent less. (In order to take advantage of this characteristic, vehicles must be properly adjusted.) Nonmethane evaporative hydrocarbons: Usually less. Toxics: M100 contains none of the carcinogenic ingredients such as benzene, 1,3-butadiene, and acetaldehyde. M85 (with 15 percent gasoline) has 50 percent fewer toxic air pollutants than gasoline.

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Formaldehyde levels: Much higher, although still low. The toxicity of formaldehyde is lower than that of other toxics, and formaldehyde emissions can be reduced dramatically with new technology, such as improved catalytic converters. Nitrogen oxides: Usually comparable or less. Greenhouse gases: Comparable to gasoline. Particulate matter: Buses using M100 emit significantly less than diesel-fueled buses.

Internal Combustion Engines Using Methanol Several factors effect the use and selection of any fuel. Among the important ones are engine design, net energy per pound, net energy per gallon and the sulfur content of alternative fuel properties. a-Pure methane b-Octane rating above 100 are correlated with given conc. Of tetra ethyl lead in 150 octane. c-Natural sulfur content very low but measurable. Measuring a fuel‘s selective potential energy can easily be done by defining that fuel‘s BTU content. A Btu defined as the amount of heat necessary to raise one pound of water, onedegree Fahrenheit. At ambient temperature and atmospheric pressure, liquid methanol is basically similar to gasoline or diesel fuel. Therefore methanol is easy to be stored and transported compared to CNG & LNG. These characteristics make the price of methanol vehicles and refueling station lower than the price of CNG or LNG vehicles and refueling station. For a certain type, methanol vehicle is offered at lower price than gasoline vehicles, for the purchase of certain No. OF vehicles. Present design internal combustion engines run on liquid fuels. Methanol required few of any engine modification to extract the maximum power from this fuel. As compared to gasoline, methanol lowers some tailpipe emissions, namely the sulfur based HC, CO, as well as NOx. Methanol contains only half the energy per gallon of gasoline but has a very high octane rating. Increased compression ratios could yield 5-20 %. More power. When methanol is used as a gasoline additive antiknock compound and fuel extender, it becomes economical with very positive results especially from the emissions stand point. It contains zero sulfur thereby reducing tailpipe acid significantly. Of the six most popular attractive fuels presently available methanol has the second lowest Btu/lb, net energy yield. As a result, fuel tanks will need to be enlarged for vehicles that run on pure methanol.

1.5 A Historical Overview In their embalming process, the ancient Egyptians used a mixture of substances, including methanol, which they obtained from the pyrolysis of wood. Pure methanol, however, was first isolated in 1661 by Robert Boyle, who called it spirit of box, because he produced it via the distillation of boxwood. It later became known as pyroxylic spirit. In 1834, the French chemists Jean-

Production Of Methanol From Natural Gas

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and Eugene Peligot determined its elemental composition. They also introduced the word methylene to organic chemistry, forming it from the Greek words methu, meaning "wine," and hyle, meaning "wood". The term methyl was derived in about 1840 by back-formation from methylene, and was then applied to describe methyl alcohol. This was shortened to methanol in 1892 by the International Conference on Chemical Nomenclature. Baptiste Dumas

In 1923, the German chemist Matthias Pier, working for BASF developed a means to convert synthesis gas (a mixture of carbon monoxide and hydrogen derived from coke and used as the source of hydrogen in synthetic ammonia production) into methanol. This process used a zinc chromate catalyst, and required extremely vigorous conditions—pressures ranging from 30–100 MPa (300– 1000 atm), and temperatures of about 400 °C. Modern methanol production has been made more efficient through the use of catalysts capable of operating at lower pressures. . The first large scale commercial synthetic methanol process was introduced by BASF in 1923. The process was based on the reaction of synthesis gas (a mixture of hydrogen and carbon oxides) over a zinc chromite catalyst at relative high temp (300 to 400 Co) and high pressure (250-350 atm). The synthesis gas was derived from coal via the water gas reaction. The first synthetic methanol unit in the USA was located at Belle, West Virginia, at the ammonia plant of Lazote, Inc, a subsidiary of Dupont and began operation in 1927. The unit was actually installed to remove the 1 to 2 % carbon monoxide impurity in the ammonia synthesis gas by utilizing the methanol synthesis reaction as purification step. Up till the end of World War II, methanol was mainly produced as a co product using synthesis gas from coke via the water gas or blue gas reactions as well as using off-gases form fermentation, coke ovens and steel furnaces. These methanol units were relatively small (less than 200 thousand tons per year, most in the 30 to 90 thousand tons per year range). One of the major technological changes often overlooked in the methanol industry was conversion from water-gas to natural gas as a source of synthesis gas for feed to the methanol converters. Natural gas derived synthesis gas was much higher quality , contained much less impurities and catalyst poisons , and was readily available in nearly unlimited quantity. 71% of the carbon monoxide uses for the synthesis of methanol was obtained form coke or coal , where as by 1948 about 77% was derived from natural gas. In 1966 , Imperial Chemical Industries (ICI) in England announced the second major break through in methanol technology , the ICI low pressure process for synthesis of methanol using a propri9etary copper based catalyst. The high activity copper based catalyst allowed the methanol synthesis reaction to proceed at commercially acceptable levels tat relatively low temp. (22-280 oC) thus allowing operation at significantly reduced pressure (50 atm) from that needed for the high pressure process (350 atm ). A number of improvements have been made in these early methanol process, principally in the area of improved energy efficiency. Subsequent low pressure process have revolutionized the industry and have allowed for the construction of more energy efficient and cost effective plant. Now a days, modern low pressure methanol units have a capacity of about 400-1000 thousand tons per year, operates at 50 to 100 atm.

Production Of Methanol From Natural Gas

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Production Of Methanol From Natural Gas

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RAW MATERIALS Long-term availability energy consumption and environmental aspects are all considered in choosing a raw material, however financial consideration are of primary importance. Keeping above described factors in view, a fuel containing sufficient amount of hydrogen and carbon monoxide is a possible raw material commonly known as synthesis gas for methanol production. Major resources from which synthesis gas be produced are 1. Natural Gas 2. Coal 3. Naphtha 4. Heavy hydrogen feed stock. Extraction of synthesis gas from these sources is further described here:

2.1 SYNTHESIS GAS FROM COAL:The production of gaseous fuel from coal has been practiced for 100 of years but most of the process for gasification was gradually replaced in the 1950s and 1960s by processes based on low cost petroleum hydrocarbons. The oil shortage of the 1970 renewed a worldwide interest in coal as chemical feedstock. However, recent falling prices of oil in the world have moderated that short lived interest. During gasification, falling ground coal reacts with oxygen and steam at elevated temp. to form a synthesis gas comprised mainly of carbon monoxide and hydrogen, with lesser amount of carbon-dioxide, methane, nitrogen, argon, hydrogen sulphide, tar and phenols. The quantities of the lesser components depend on the amount of impurities found in the coal and in the amount of oxygen fed to the gasifier. The heart of the coal based partially oxidation process in the gasification step. To achieve maximum efficiency, a gasifier should operate at an elevated pressure, have low oxygen and steam demand, have high carbon conversions and have low heat losses. It is also desirable to achieve high reliability, to minimize or eliminate by-product formation and to accept a wide variety of coals. Low temperature gasifiers produce considerably more methane, oils, phenols and tar than high temperature ones. A slagging gasifier operated at temperature above the fusion point so that ash is removed in the molten form; that temperature is typically b/w 24002700 oC. Selecting the best gasifier for a particular operation is usually a matter of compromise, since the designer must weigh many variables including the type of coal available, capacity, byproduct rates, and capital investment efficiency and so on. Most gasifiers fall into one of three general categories atmospheric or low pressure, high pressure and second generation.

2.2 The Koppers-Totzok (K-T):Gasifier is an atmospheric process with extensive commercial experience in Europe, Asia and South Africa. It will handle all coals; make virtually no by-products operate with high thermal efficiency and high conversion. However, there is an extra cost associated with this

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process (Low Pressure Process), because it operates at atmospheric pressure; the product synthesis gas must be compressed before introduction to methanol synthesis loop. THE WINKLER GASIFIER is another low pressure process widely used in Europe, Japan and India. However, as a low-pressure process, it has the same advantages and disadvantages as the K-T process A high pressure process, the LURGIDRY ASH GASIFIER is the most widely used commercial process. It has even more disadvantages than K-T process, forms numerous by-products, has a limited ability to handle caking coals, and produces as large amount of methane (which must be purged from the converter loop, if the gas is used for the methanol synthesis).

2.3 The British Gas Council Lurgi (BGC-Lurgi):Gasifier is another high pressure process, more efficient than LURGI DRY ASH PROCESS. Due to reduced steam usage and higher capacity, however, it produces great amount of byproducts and has only a limited ability to handle caking coals.

The Texaco and Shell-Koppers:Gasifiers are two of the most promising second-generation process. Both offer many of the similar advantages as the atmospheric gasifiers, but both are high pressure operations, that accept all coals and make virtually no by- products. A large number of purification steps are necessarily required to produce methanol synthesis gas from the crude product gas leaving the gasifier since the raw gases contain no large number of undesirable by-products. Some or all of the following process steps may be required. Cooling with steam generation, water washing, compression, sulfur removal, shift conversion of carbon monoxide and after that hydrogen and carbon dioxide removal. Kopper Totzek Pressure(atm) 1.4 Temp.(oC) 1500 OxygenReqd. High Steam Reqd. Low Capacity 850 (tons/day) Raw Product ---gas analysis Vol% Carbon 58.1 monoxide Hydrogen 29.3 Carbon 11.0 dioxide Methane 0.1 Hydrocarbon ---Inerts (N2, Ar) 1.5

Winkler

Lurgi

BGC Lurgi

Taxaco

1.4 – 2.1 930 Medium Medium 1000

20 -27 540-590 Low High 500

20 - 27 480-540 Low Low 1250

21 - 83 1290 High None 2000

Shell Kopper 31 1480 High Low 1000

----

----

----

----

----

35.0

24.6

60.6

46.3

67.7

40.8 22.0

39.8 24.6

27.8 2.6

35 17

29.9 1.1

1.2 Trace 1.0

8.7 1.1 1.2

7.6 0.4 1.0

0.2 ---1.5

0.2 ---1.1

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2.4 SYNTHESIS GAS FROM NAPHTHA During the 1950s an oversupply situation in Europe made naphtha an economical feed stock for steam reforming. A series of alkali promoted catalyst was developed specifically for naphtha, and by the early 1960s many European procedures where preparing synthesis gas from light distillate naphtha. At the present time the price of the naphtha feedstock and mixing it with a hydrogen stream so that the combined stream contain approximately 5% hydrogen stream so that the combined stream contain nickel molybdate catalyst to convert organic sulfur compounds to hydrogen sulfide and also to saturate alkenes. Desulphurization is then conducted as described above for hydrogenation. The sulfur free gas is fed to a reformer which contains catalyst specially designed for naphtha reforming. A stream to carbon ratio as lo as 2 is used, where pressure range from 1500-4000 Kpa (200 to 575 Lb/in2g). Small amount of carbon dioxide can be added optionally to yield synthesis gas composition similar to those obtained via hydrocarbon reforming.

2.5 SYNTHESIS GAS FROM NATURAL GAS:The majority of methanol synthesis plants now use catalytic reforming of natural gas for the production of synthesis gas. The process consists of two steps Desulphurization and the steam reforming section.

a) Desulphurization:Natural gas contains both organic and inorganic sulfur compounds that must be improved to protect the both reforming and down stream methanol synthesis catalysts. They can position the catalyst even as low as 0.5 PPM. Hydrodesulphurization across a cobalt or nickel molybdenum zinc oxide fixed bed sequence is the basis for an effective purification system. The temperature in the range of 340-370 0C may be necessary.

R-SH + H2

R.H + H2S

ZnO + H2S

ZnS + H2O

Zinc oxide is capable to reduce the H2S concentration down to 0.3 PPM.The disadvantages are that it is non-regenaratable must eventually be replaced. To have the advance warning before the ZnO bed is completely converted to ZnS at this point is provided at 755 of bed depth. When the ZnO changes to ZnS at this point, it is the time to renew the bed.Chlorides and mercury may also be found in natural gas, particularly from off shore reservoirs.Activated alumina or carbon beds can remove these poisons.

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b. STEAM REFORMING:Once the sulphur has been removed from the hydrocarbon feed stream, the gas is mixed with steam and reform to produce methanol synthesis gas. The following reactions occur in the reformer.

CnH2n+2 + nH2O

nCO + (2n+1) H2

CnH2n+2 + 2nH2O

-1

nCO2 + (2n+1) H2

CnH2n+2 (n-1/2) H2O

-2

(3n-1)/4 CH4 + (n-1)4 CO2

-3

All three of these reactions are endothermic, and in full scale commercial reformer, all three proceed essentially to completion. The primary reforming equilibrium reaction involves methane and steam:

CH4 + H2O

CO + 3H2

H298 = 206.08 KJ/g

-4

The equilibrium reaction of carbon monoxide with steam, often referred to as the water gas shift reaction, is also a significant contributor in this process.

CO + H2O

CO2 + H2

H298 = - 41.17 KJ/g

-5

Note that the reforming reaction (4) is endothermic and the water gas shift reaction (5) is exothermic. Undesirable reactions may occur in the reformer, resulting in deposition o carbon on the reactor walls, on the catalyst surface, or in the pores of the catalyst. This reduces the catalyst activity.

CnH2n+2

nC + (n – 1) H2

-6

CH4

C + 2H2

-7

2CO

C + CO2

-8

CO + H2

C + CO2

-9

CO + 2H2

C + 2H2O

-10

A critical examination of the equations presented above allows one to make some preliminary conclusions concerning reformer operation. Since reforming reaction (4) is endothermic and the water gas shift reaction (5) is exothermic , it is obvious that less methane and more carbon monoxide and hydrogen would be obtained at higher temperature. It is also suggested that decreasing pressure would decrease the amount of methane in the reformer product stream.

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In a similar manner , increasing the partial pressure of the steam would result in a decrease in the amount of methane in the product. A set of equations , which is used to calculate the composition of exit stream, is eq.(4),(5) and eq.(8). Carbon composition via eq-8 can theoretically be prevented by ensuring that steam is present in excess of some minimum amount calculated using the equilibrium equations. Any increase in steam also has the effect of increasing methane conversion. Most Commertial reformers operate safely with steam carbon ratio in the range of 3 to 4.5. Reforming catalysts contain from 12 to 25 % nickel as nickel oxide supported on calcium aluminate , alumina or calcium titanate .Alkali metal compounds added to prevent carbon formation and increase catalyst durability. The feed stream to the reformer is distributed over hundreds of parallel catalyst filled tubes, the tubes are subjected to a temperature range of 860 to 950 oC, wit process gas exit temperature in the range of 750 to 850 oC & pressure range from 4 to 35 atm (450 to 3550 Kpa). Gas hourly space velocities are usually on the order of 5000 to 8000 based on wet feed. The flue gases temperatures are in the range of 980 to 1040 oC. These hot flue gases are transferred to a convection section where they are cooled and used to super heat steam for provide motive power for compressors and large pumps, process steam for reforminf and reboil duty for distillation.

2.6 SELECTION OF RAW MATERIAL Natural gas is the only most convenient and economical raw material available in Pakistan. This God gifted treasure is found in large reserves at Sui, Mari and some other areas. Natural gas is easily available , cheap raw material , containing low impurities and there are no transportation and storage costs involved. Hence natural gas is the most economically suitable raw material for synthesis gas. Coal is another source for the Sun. gas production in Pakistan. Coal available in Pakistan at MAkerwal, Dhodak and Kalabagh but its quality is very poor. However , the largest reservoirs of coal in world now found in Pakistan at Thar. No doubt, these reservoirs contain small amounts of sulfur about 0.1-0.7% but there are some other factors involved in degrading the coal selectivity for Syn. Gas production , such as high transportation cost , handling and storage cost , further more additional equipment (gasifier etc) and process costs. Coal contains much impurities and mineral materials (as compared to the natural gas) lead to the formation of the various pollutants during combustion having adverse environmental impacts when emitted into the atmosphere. The environmental aspects that are associated with the use of coal are, the formation of pollutants such as fly ash , sulfur oxides, nitrogen oxides and other mineral materials. Also coke formation occur and this is higher compared to the natural gas and this reduces the activity of catalyst and may stick to the walls of steam reformer which reduce the heat transfer rate. Naphtha is not economically viable for Syn gas production in Pakistan, its reservoirs are limited in Pakistan and do not meet sufficiently the other demands (motor fuels). Its costs are too much as compared to the natural gas, hence it is not usable , same is the matter involved in selection of heavy hydrocarbons.

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Capacity Selection As mentioned earlier that currently thee is no methanol producing plant in Pakistan and all is being imported from other countries (see in table).Major exporters are Saudi Arabia and Iran. Methanol consumption in Pakistan is about 26800 tons / year (90 tons /day), report issued by Federal Bureau of Statistics 2004-2005. Lets take a look to the international market ; methanol production is going to increase and foreign methanol producers are extending their capacities in order to meet the growing demand (as shown in the tables, where world methanol plants capacities supply /demand by the year 1998- 2007 are given , which contains the previous , present and anticipated capacities and shows comprehensive increasing trend in demand).

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Also rising image so methanol as an ―Alternative Fuel ― for motor vehicles is a matter of great consideration for scientists. As far as Pakistan is concerned , gasoline and diesel prices are high and unstable. CNG and LPG are used as alternative fuels but methanol is easy to be stored and transported compared to CNG and LPG (it is a liquid fuel. These characteristics make the prices of methanol vehicles and refueling stations cheaper than the price of CNG and LPG vehicles and refueling stations. These methanol based vehicles will be available by the year 2005 in foreign markets and some major motor manufacturing companies may also invest in Pakistan, Raw material foe methanol synthesis (N.G) is cheaper here in Pakistan, which is a primary factor involved in reducing it‘s price ,also methanol is environmental friendly. In Pakistan , methanol is being employed in making urea formaldehyde , acetic acid and methalated spirit for pharmaceutical and dyes etc. industries. Now a new formaldehyde plant is being installed by Dyno chemicals at Hub Industrial And Trading Estate. Super Chemicals (Karachi) , Wah Nobel Chemicals (Wah Cantt.) and Pakistan Resins (Azad Kashmir) are also manufacturing urea formaldehyde. As A result of this brief discussion , we may say that our capacity of 150 tons/ day is reasonable , where 90 tons / day is present consumption in Pakistan and remaining 60 tons/ day could be exported and If demand of Pakistani market increases , we may reduce or stop its export to fulfill out demand.

3.1 Methanol Imports In Pakistan Countries

Asian Countries NS Bangladesh China Dubai Germany Indonesia Iran Kuwait Laos Malaysia Natherland New Zealand Saudi Arabia Singapore

2002-2003

2003-2004 3

2004-2005 3

LTR

Rs * 10 LTR

Rs * 10 LTR

Rs * 103

18000

336

26800

610

-

-

210000 13040 373651 690180 254266 -

2140 200 3094 10042 213426 -

200000 132040 450000 9751 26080 101570 100000 13040 281600 13040 31965758 440000

2700 5217 5434 534 647 1662 2892 328 11671 249 394528 11410

2309723 58612 4099556 114338 101100 27093185 13040

23752 2478 41170 1934 4481 298683 273

Production Of Methanol From Natural Gas South Africa 14768 Rep Spain Turkey 25600 Thailand U.S.A 424633 U.K Total (LTR) 27196520 Tons 26800

20

148

-

-

104

40

386 2863 232635

3000 33762679 36559

145 438026

79200 200000 34068859 43800

1024 2033 375831

Production Of Methanol From Natural Gas

21

Production Of Methanol From Natural Gas

22

Production Of Methanol From Natural Gas

23

Production Of Methanol From Natural Gas

24

Production Of Methanol From Natural Gas

25

Production Of Methanol From Natural Gas

26

4.1 Methanol Manufacturing Process The Methanol Industry in Trinidad began with the construction of a 1,200 MT state-owned methanol plant in 1983 (Trinidad and Tobago Methanol Company‘s first plant). Since that time, the industry has expanded to include four larger plants with an annual production capability close to 3 million MT of methanol. At the MHTL Point Lisas Methanol Complex, methanol is made using the ICI Low Pressure Methanol Synthesis Process. The two main raw materials used are natural gas (96% methane) received from the National Gas Company (NGC) to provide the carbon and hydrogen components and water from the Water and Sewerage Authority (WASA) to provide the oxygen component. These raw materials undergo a series of chemical reactions to produce crude methanol which is then purified to yield refined methanol, having a purity exceeding 99.9%. The plants operate continuously 24 hours a day in a production process that can be divided into four main stages: Feed Purification, Reforming, Methanol Synthesis and Methanol Purification as shown in the flow sheet below:

STEP1 FEED PURIFICATION The two main feed stocks, natural gas and water, both require purification before use. Natural Gas contains low levels of sulphur compounds and undergo a desulphurization process to reduce, the sulphur to levels of less than one part per million. Impurities in the water are reduced to undetectable or parts per billion levels before being converted to steam and added to the process. If not removed, these impurities can result in reduced heat efficiency and significant damage to major pieces of equipment.

Production Of Methanol From Natural Gas

27

STEP 2: REFORMING Reforming is the process which transforms the methane (CH4) and the steam (H2O) to intermediate reactants of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO). Carbon dioxide is also added to the feed gas stream at this stage to produce a mixture of components in the ideal ratio to efficiently produce methanol. This process is carried out in a Reformer furnace which is heated by burning natural gas as fuel.

STEP 3 : METHANOL SYNTHESIS After removing excess heat from the ―reformed gas‖ it is compressed before being sent to the methanol production stage in the synthesis reactor. Here the reactants are converted to methanol and separated out as as crude product with a composition of methanol (68%) and water (31%). Traces of byproducts are also formed. Methanol conversion is at a rate of 5% per pass hence there is a continual recycling of the unreacted gases in the synthesis loop.

This continual recycling of the synthesis gas however results in a build-up of inert gases in the system and this is continuously purged and sent to the the reformer where it is burnt as fuel. The crude methanol formed is condensed and sent to the methanol purification step which is the final step in the process.

STEP 4 : METHANOL PURIFICATION The 68% methanol solution is purified in two distinct steps in tall distillation columns called the topping column and refining column to yield a refined product with a purity of 99% methanol classified as Grade AA refined methanol.The methanol process is tested at various stages and the finished product is stored in a large secured tankage area off the plant until such time that it is ready to be delivered to customers. Since

4.2 Methanol Process Description The Leading Concept Methanol process in use at the Coogee Methanol Plant has various advantages compared to the conventional methanol processes. Some of those advantages are that it is efficient and compact and substantially reduces waste through the internal recycling of process effluents.

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28

Natural gas feedstock is delivered to the plant via a pipeline from the main Sui to plant location carrying Bass Strait gas. The gas is first compressed and then purified by removing sulphur compounds. The purified natural gas is saturated with heated and recycled process waste water. The mixed natural gas and water vapour then goes to the gas heated reformer to be partially converted to synthesis gas, a mixture of carbon dioxide, carbon monoxide and hydrogen. This partially converted gas is then completely converted to synthesis gas by reaction with oxygen in the secondary reformer. The synthesis gas is then converted to crude methanol in the catalytic synthesis converter. The crude methanol is purified to standard quality specifications by removing water and organic impurities through distillation. The water and organic impurities are recycled.

Process Description The Coogee Energy plant is designed to produce 164 tones per day of methanol from about 5 TJ/day of Bass Strait natural gas. The plant consists of four main process steps : feed gas preparation, synthesis gas generation, methanol synthesis and distillation supported by utilities and offsite units.

Feedgas Preparation Natural gas is compressed to about 45 bar and sulphur removed by hyrodesulphurisation in the purifier. The desulphurising gas is cooled and flows to the saturator where it contacts with hot water over a bed of packing. The saturated gas leaving the vessel contains about 92% of the steam required for reforming. Saturator make up is 90% process condensate and the balance refining column bottoms water. Prior to leaving the saturator the gas stream is contacted with recycled fusel oil where waste products from methanol synthesis are stripped off. A blow down stream is required to control dissolved solids. Additional steam generated in the boiler is made up to the gas stream to achieve 3.0:1 steam to carbon ratio for reforming. The total feed stream is then heated in the gas heated reformer preheated. Both the preheated and boiler are fired with a mixture of synthesis loop purge gas and natural gas.

4.3 Synthesis Gas Generation Reactions There are three main chemical reactions which occur in this process step : Steam reformingCH4 + H2O = CO + 3H2 Shift reaction -

CO + H2O = CO2 + H2

Production Of Methanol From Natural Gas

29

The net effect of these reactions is the production of a synthesis gas stream which is composed of carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2).

Description Preheated gas flows from the preheater to the tube side of the advanced gas heated reformer (AGHR). The feedstock is heated from the feed temperature of 425° C as it passed down through the catalyst and the reforming reactions start. The AGHR contains 19 reforming tubes which contain the reforming catalyst. Hot reformed gas exits the bottom of the reforming tubes and flows to the tube side exit of the AGHR at about 700°C. The heat required for the endothermic reforming reaction is derived from cooling the secondary reformer effluent in the shell side of the AGHR. About one quarter of the methane is reformed in the AGHR. The partly formed gas flows from the AGHR to the combustor/secondary reformer where the bulk of the reforming takes place. The heat required for the endothermic reforming in both the AGHR and secondary reformer is provided by partially burning the AGHR effluent with pure oxygen in the combustor located integrally at the top of the secondary reformer. Oxygen is injected into the gas via a specially designed gun. About 0.50 tonne of oxygen per tonne of methanol is required. The oxygen is completely consumed and the resulting hot gas stream passes over the secondary reforming catalyst. Reforming reactions continue and the gas leaves the secondary reformer at up to 1000°C with less than 0.5% methane slip. The secondary effluent passes to the AGHR shell and thence through the heat recovery train to provide heat for the saturator circuit and distillation reboilers. The process condensate which condenses out of the reformed gas is recycled back to the saturator. After heat recovery the reformed gas is finally cooled and then compressed to about 70 barg in the synthesis gas compressor to be fed as synthesis gas to the synthesis loop. Bass Strait natural gas contains about 93.6 mol% of methane, 3.5 mol% of ethane with the balance being predominantly propane, nitrogen and carbon dioxide. On an offshore facility with less sophisticated gas separation facilities there may be higher levels of higher hydrocarbons such as components but the oxygen consumption would increase. The synthesis gas joins the synthesis loop recycle gas from the circulator to pass through the loop interchanger and be fed to the methanol converter at about 130° C. The converter is a tubular cooled converter design where the gas is preheated to reaction temperatures inside the tubes as it flows up through the hot catalyst bed. This type of converter maximizes catalyst efficiency as it enables a temperature profile to be maintained inside the converter that is close to the maximum reaction rate curve. The hot reacted gas leaves the converter and provides heat to the saturator water circuit and the loop interchanger before finally being cooled. Crude methanol is separated from the uncondensed gases in the loop catch pot and the gases recirculated back to the converter via the circulator.

Production Of Methanol From Natural Gas

30

Distillation Crude methanol from the loop catch pot is filtered to remove traces of wax, let down in pressure and fed to the product purification section. This section consists of a topping column and a refining column. Unlike most methanol distillation columns these columns are packed with structured packing. Reboiler duty is provided by reformed gas. The product methanol specification is for a water content of less that 0.10 wt %. The water bottoms from the refining column has a specification of less than 100 ppm of methanol and is recycled back to the saturator. Other synthesis byproducts such as higher alcohols are collected as fusel oil and recycled back the saturator.

4.4 LCM -The Low Cost Methanol Technology Introduction The emphasis on reducing the cost of production of methanol is nothing new. Aside from a short period after the invention and commercial introduction of the Low Pressure Methanol Process by ICI in the mid-1960s, that pressure has always been present. ICI itself was no stranger to this as many of its older businesses were in commodity products whose profitability relied critically on minimizing the cost of production in order to maintain acceptable margins. However, cost of production is not just a case of reducing capital cost, although undoubtedly this is an important part of the total picture. Often the installed cost of the plant appears to be given greater weighting than is justified from a simple economic assessment. It is understandable, though, that at the time of selection of the technology vendor, everyone's mind tends to be focused on the need to raise the money, and fixed and variable costs of operation can recede into the distance. Methanex and Synetix have been working together for some time to identify the optimum route for syngas generation for the manufacture of methanol and other GTL products. Many options were investigated, but it was determined that the Synetix Syngas Generation (SGG) process offered the most economic route and the methanol process based on SGG, the LCM Process, was the most attractive option at high capacities.

Historical Perspective It was against a background of intense competitive pressure on its Fertilizer Business that ICI mandated its Catalyst and Technology Licensing Department (now a part of Synetix) to develop a compact reforming process to revolutionize the manufacture of ammonia. In many

Production Of Methanol From Natural Gas

31

ways, the process that was developed, LCA, was revolutionary and ahead of its time, but the fundamental principles behind the project were similar to those operators need to adopt to prosper in today's highly competitive methanol industry.The legacy of ICI's commitment in building the LCA plants at its Severnside Works in the late 1980s is that the Synetix Gas Heated Reformer (GHR) can no longer be thought of as new technology. It is well-proven now, with over 30 operating years experience spread over the 4 plants that have been built around the technology. These plants are: Absolutely key to the successful operation of these units has been the adoption of the correct metallurgy to withstand the conditions within the reformer. There can be no doubt whatsoever, that metal dusting has been overcome as an issue within the range of operating conditions of these plants. However, without detracting from the importance of the metallurgy, it is the mechanical design of the reformer that turns concept into reality. With the introduction of the Advanced Gas Heated Reformer (AGHR) into the Coogee Energy MRP in April 1998, Synetix incorporated a number of novel features that significantly simplified the compact reformer in terms of design,construction, maintenance and operation.

Key Success Factors Clearly, many factors are important to an operator/investor in making a project successful. A number of these factors is listed below. Selling price Financing costs Gas price Import tariffs Delivery costs Maintenance costs Manpower costs Plant installed cost Plant efficiency Plant reliability Items 1-3 are commercial issues over which the operating company has varying degrees of influence. Items 4 and 5 will be very location specific, with the latter being a key factor as methanol is transported from more remote locations to the consuming markets. Items 6-10 are influenced by location, but it is in these aspects that choice of technology and the standard of engineering design can have a major impact. The focus of the rest of the paper will be mainly on these areas.

Compact Reforming The term "Compact Reforming" implies that the main aim of the new technology is to reduce the size. This was indeed a consideration, and it may be the only benefit offered by certain types of compact reforming device. However, when Synetix was developing the syngas process for the new ammonia plants for ICI, there was a much broader goal, which included the complete elimination of steam generation and the steam system. This required a complete

Production Of Methanol From Natural Gas

32

rethink and a major simplification of the whole heat recovery scheme. The intention was to use the hot reformed gas from the Secondary Reformer to provide the heat directly for the methane steam reaction in a heat exchanger reformer. It was not the first time such an idea had been proposed, but the major stumbling block was always the fact that metal dusting conditions were present on the hot side of the heat exchanger. Many options had been considered by others, including approaches that would avoid metal dusting by, for example, using ceramic tubes, but none had been successful. The breakthrough by Synetix came in first identifying materials that were resistant to metal dusting under the conditions envisaged and then in proving that they were resistant in a full-scale, single-tube reformer operating under real process conditions. This trial unit was built and operated on ICI's Bellingham, UK site and provided essential process design data, but more importantly verified the selection of metallurgy. The first successful implementation of compact, heat exchange reforming on the industrial scale was in the GHRs installed on the LCA plants at Severnside, UK in 1988. The first successful deployment of the AGHR was at Laverton, Australia in 1998.

Operability of the LCM Process The absence of steam raising and a steam system offers many benefits, but it does mean that there is no obvious source for the process steam required for the methane steam reforming reaction. Fortunately, this is an easy issue to address since Synetix have used a saturator circuit for many years as a way of recovering low grade heat and turning it into process steam without raising steam directly. Water is pumped through a set of heat exchangers and warmed up before being contacted in a packed tower with the natural gas feed from the Purification section. The saturator typically provides J to ½ of the process steam required in a conventional plant, but this concept can easily be extended to provide all of the steam needed for the methane steam reforming reaction in the AGHR. Of course, as this is the only source of steam, the saturator circuit assumes a greater importance than before. In the LCM Process, between 30 and 40% of the heat being supplied into the saturator circuit comes from the methanol synthesis loop. So, if the synthesis loop were not running, there would be a significant shortfall of heat that would need to be acquired from elsewhere or the whole plant would have to shut down. Normally, whenever there is a trip on a plant, everything is done to try to maintain flow through the reformer and firing on it in order to avoid a temperature cycle. This is where another valuable feature of the LCM Process becomes important, and that is the ease of start-up and shut-down, which means that a temperature cycle on the reformer is of rather less concern. The AGHR can be thought of as simply a feed effluent exchanger around the Secondary Reformer. Start-up then requires nothing more than a mechanism to get the Secondary above the auto-ignition temperature of the feed gas and the whole unit will come on stream very quickly. Following a plant trip, heat is trapped within the Secondary by the feed effluent exchangers preventing it cooling too much. From a cold restart, heating is achieved using a simple catalytic combustor as a start-up heater generating hot syngas. On the LCM Process it may take up to 12 hours from introduction of feed gas before the plant is making methanol, whereas on a warm restart (which could occur even after several days off line) the time taken can be 6 hours or less.

Production Of Methanol From Natural Gas

33

Production Of Methanol From Natural Gas

34

METHANOL SYNTHESIS The heart of any Methanol synthesis process is Methanol converter. The converter contains the catalyst over which synthesis gas is converted to methanol. The main difference between competing methanol process today lies in the converter and its method of temperature control and heat recovery.

5.1 TYPES OF CONVERTER:The four basic types of converters are    

Quench Converter Multiple Adiabatic Converter Tube-cooled Converter Steam Raising Converter

1. QUENCH CONVERTER:The quench converter was the basis for the initial ICI low pressure methanol process. Quench type converters used multiple catalyst beds, typically contain three to six catalyst beds. Bed volumes are sized to help control the exothermic methanol synthesis reaction. Additionally, cool feed gas is injected between beds to control or quench catalyst bed inlet temperature. Reaction heat is recovered through added heat recovery exchangers located downstream of the converter.

2. MULTIPLE ADIABATIC CONVERTER:The adiabatic converter system employs heat exchanger rather than quench gas for introduce cooling. Because the beds are adiabatic, temperature profile exhibits still the same saw tooth approach to maximum reaction rate, but catalyst productivity is somewhat improved because all of the gas passes through the entire catalyst volume. Costs for vessels and exchangers are generally higher than for quench converter system.

3. TUBE-COOLED CONVERTER:The tube cooled converter functions as interchanger, consisting of a tube filled vessel containing catalyst on the shell side. The combined synthesis and recycle gas enters the bottom of the reactor tubes, where it is heated by reaction taking place in the surrounding catalyst bed. The gas turns at the top of the tubes and passes down through the catalyst bed. The principle advantage of this reactor is in the reduced catalyst volume, since the reduction path move closely follows the maximum rate line. Converter performance can further be enhanced by extending the catalyst below the tube cooled area to act as a further adiabatic reaction zone.

Production Of Methanol From Natural Gas

35

4. STEAM RAISING CONVERTER:There are varieties of tubular steam raising converters available, which feature radial or axial flow, with the catalyst on either shell or tube side. The near isotherm reaction of this rector type is the most thermodynamically efficient of the types used, requiring the least catalyst volume, lower catalyst peak temperatures also results in reduced by-product formation and longer catalyst life.

Production Of Methanol From Natural Gas

36

 Low pressure drop, both in converter and heat exchanger equipment, to minimize recycle compression energy.  High conversion per pass that reduces required cycle, minimizes synthesis loop capital cost & maximizes reaction heat recovery.  Efficient recovery of exothermic reaction heat of methanol synthesis.  Corrosion resistance to formation of iron carbonyls that can poison the catalyst and promote formation of undesirable hydrocarbon by-products.  A high yielding, commercially proven, long life synthesis catalyst to minimize costly catalyst replacement.  Low capital cost.  Good economy of scale, high capacity single train converter.

5.2 METHANOL SYNTHESIS TECHNOLOGY TODAY Different companies have been involved in practicing their technologies for methanol synthesis. But the question is which company offers the most dependable and economically viable process. This is visualized by the percentages obtained by evaluating their practical applications as shown below: Company Name

Production Rate

Imperial Chemical Industry (ICI)

61%

LURGI CORP.

27%

Mitsubishi Gas Chemicals (MGS)

8%

KELLOGG

3%

5.3 ICI LOW PRESSURE METHANOL PROCESS Most of the difficulties involved in developing the new ―Low Pressure‖ methanol process were successfully overcome by the ICI 50atm process. Methanol was first synthesized commercially at low pressure when ICI commissioned its 300tons/dayplant at Birmingham in December, 1966. a copper based catalyst, more active and selective was used. The greater activity of this catalyst permits the synthesis of methanol from gaseous mixture of hydrogen and carbon dioxide at much lower pressure and temperature of the order of 50 atm and 250 oC respectively. Several innovatory features were incorporated in the design. They include a new simple type of quench bed converters, larger in diameter then conventional converters and easy catalyst charging and discharging procedure. The use of rotary machine of synthesis gas compression which was significant, because it demonstrated the concept of single stream unit, well known in large scale ammonia plant, was now a practical proposition for small methanol production units.

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37

In 1972 ICI commissioned a 1100 tons/day plant based on their latest technology. It operates at 100 atm and uses a modified version of original low-pressure methanol synthesis catalyst. For capacity greater than 500 tons/day, the 100 atm process plants are adopted, whereas for smaller plants of outputs from 150-500 tons/day, the 50 atm process is used.

5.4 LURGI LOW PRESSURE METHANOL PROCESS At the end of fifties, Lurgi began development of a low pressure methanol process, using highly active copper catalyst at 50 atm pressure. At that time, the space time yield and catalyst life was not satisfactory (Sulfur Poisoning) which resulted in the suspension of further development work.

Production Of Methanol From Natural Gas

38

In 1964 research work was resumed. At that time the purification of synthesis gas (Using Lurgi Rectisol (50 atm process) was no longer a problem. Several years of development work required in selecting from numerous catalysts available a suitable catalyst. Because of Lurgi‘s experience in Fisher Tropsch synthesis reactor, the methanol reactor was based on a design worked out of Fisher Tropsch Synthesis. This reactor is similar to a vertical and tube heat exchanger and was a promising solution, to both reactor design and heat recovery problem. The tubes closed at their lower end by the hinged grid with boiling water, maintaining a substantially uniform catalyst temperature over the reactor cross section and over the full length of the tubes. Early 1970 Lurgi decided to build its own methanol plant with a small capacity to serve mainly for demonstration purposes and also to study the problems which might come up in the large scale plants. The first commercial plant with a capacity of 4000 tones/yr was built at wesseting (West Germany) in April, 1971. This plant was built in two days, was designed on the basis of a computer programme.

5.5 ADVANTAGES OF THE LOW PRESSURE METHANOL PROCESS  Reduced by-product formation resulting in lower feed stock consumption per ton of methanol.  Reduced compression cost due to lower operating pressure.  The ability to use steam directory compressors on small plants.  Lower steam pressure through out the plant.  The avoidance of CO2 addition in natural gas based plant without incurring large financial penalties.  Simplicity in design and low-pressure equipment, suitable for large and small plant.  Commissioning period.  Proved in wide practical services.

PROCESS SELECTION In 1966, an Imperial Chemical Industry (ICI) is the first, which announced the low pressure process for synthesis of methanol using proprietary copper based catalyst.

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39

A number of other companies in the late 1960‘s and early 1970‘s announced their own low pressure processes and proprietary copper-based catalyst; these companies included Lurgi, Mitsubishi etc. Today two processes are mostly used. 1) ICI low pressure (61%) 2) Lurgi low pressure process (27%) ICI process used Cu-Zn-Al catalyst while Lurgi process used CU-Zn-V or Cu-Mn-V catalyst. Besides the catalyst, these processes differ in their method of temperature control and heat recovery. ICI use quench type adiabatic converter with multiple catalytic beds. Bed volumes are sized to help control the exothermic methanol synthesis reaction. Additionally, cool feed gas is injected between beds to control or quench catalyst bed inlet temperature. Reaction heat is typically recovered through added heat recovery exchangers located downstream of the converter. Whereas Lurgi used shell and tube (Isothermal type) converter with boiling water for temperature controls. Overall results of quench type converter is best than other type of converter. The main drawback of water cooled tubular (Isothermal) converter is that internal tube sheets have failed in some tubular isothermal methanol converter design. The long down times associated with a catastrophic converter failure could financially devastate most procedures. In addition converter internal baffles, expansion joints, gas distributors and internal exchangers can fail and cause internal leaks. These components should be extremely rugged to withstand the operating abuse imposed by actual commercial operation. Cost is another major factor for the selection of process. ICI process has low cost as compare to the other processes. Therefore the ICI process is also called ICI LCM (Low Cost Methanol) process. That‘s reason ICI LCM process is mainly used in the world. Considering these entire factor we select the ICI LCM process.

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40

Production Of Methanol From Natural Gas

41

6.1 DESULPHERIZER CATALYST Hydrocarbon feeds for steam reforming must have a very low sulfur contents, since nickel reforming catalysts are quite susceptible to poisonings even by levels as low as 0.5PPM. In many cases, sulfur can be removed b y adsorption over a bed of activated carbon at 15-500C. Frequent regeneration may be necessary; which can be accomplished by heating the bed and for stripping it with steam or hot gases. The activated carbon bed adsorbs high boiling sulfur compounds such as mercaptans, much more rapidly than low boiling compounds such as H 2S .As a result, adsorption over a sacrificial guard bed of zinc oxide at temperature in the range of 340-370 0C. Hydrodesulphurization may be necessary for organic sulfur compounds that are not removed by either zinc oxide or carbon bed. This is accomplished by mixing the sulfur containing steam with hydrogen, so that the hydrogen contents are approximately 5%, the resulting mixture is passed over a bed of cobalt or nickel molybdate catalyst at temperature of 290-370oC. Under these conditions, sulfur compounds are conditions, sulfur compounds are converted to hydrogen sulfide, which can be removed in a zinc oxide bed. Now a days, codes are used to represent the catalysts shown here: The KATALCO range of absorbents and hydrogenation catalysts ensures an optimized system for meeting individual plant requirements. Sulfur Removal Catalysts Hydrodesulphurization Catalyst. KATALCO32-4 KATALCO 41-6 KATALCO 61-1 PURASPEC 2570 These catalysts are used by ICI.

6.2 STEAM REFORMING CATALYST Reforming catalyst usually contain from 12-25% nickel oxide supported on calcium aluminate titanate. Calcium aluminate has generally replaced calcium aluminum silicate, has support material to avoid the problem of silica migration encountered in earlier catalyst formulation. Alkali metal compounds added to prevent carbon formation and to increase catalyst durability include potassium aluminum silicate, potassium carbonate and potassium poly aluminate, sulfur chlorine and arsenic compounds. Poison the catalyst, sulfur poisoning is reversible, but chlorine and arsenic poisonings are severe and generally irreversible. Synetix has been associated with pre-reforming catalysts since the 1960‘s and together with kvaerner process technology recently launched the new CRGLH series of catalysts. These have been demonstrated to be the most active and robust commercially available product for this application. KATALCO

25-4

KATALCO

57-4

KATALCO

23-4

KATALCO

46-Serie

KATALCO

23-4Q

KATALCO

25-4Q

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42

6.3 METHANOL SYNTHESIS CATALYST High Pressure Catalyst Zinc Chromite catalyst, reduced zinc oxide promoted with Chromia was the catalyst used in the 1st large scale commercial methanol process developed by BASF in Germany in 1920‘s. The zinc Chromite catalyst with improvements over the years was only the catalyst of consequence used for the high process methanol process, up until the high pressure process was phased out in 1970‘s. Although BASF is credited with a 1st commercial methanol process generally attributed to G. TART in FRANCE in 1921. He defined his methanol catalyst has being all metal, oxides and salt active in hydrogenation. Small unit was built near Paris to test catalyst for PARTARTS process and began operation in 1923. The unit was designed to operate at 150-200 atm pressure. 300-6000C, with hydrogen to carbon monoxide feed gas ratio of 2:1. The BASF high pressure methanol process was operated at 250-3500 C, similar to the conditions purposed by PARTART. Now low pressure, process commonly called ICI low pressure process is used because of its practical feasibility.

6.4 LOW PRESSURE CATALYST Early in the developing methanol industry, it was recognized that to significantly improve the high pressure methanol process, a much more active catalyst than zinc chromite was needed. A more active catalyst would permit operation at lower temperatures and pressures, yet still allow acceptable production rates to be mentioned. Copper based catalysts known from the 1920‘s have been more active than zinc chromite. Copper based catalysts, however, were also known to be much more susceptible to poisoning by sulfur, chlorine, etc. than zinc Chromite, Zinc Chromite, for example, could tolerate sulfur levels of more than PPM in the feed gas, whereas for copper based catalysts, sulfur must be kept below 1 PPM. Generally poor quality of synthesis gas and the limited purification techniques available at that time resulted in an unacceptably short operating life for the copper based, catalysts and precluded their commercial use. A second breakthrough in the methanol technology occurred in 1966 with the introduction of ICI‘s low-pressure process for the production of methanol. This was made possible by a major improvement in synthesis gas quality from the introduction of hydrocarbon steam reforming and improved purification techniques for the hydrocarbon feed stock. The synthesis gas from steam reforming contained only trace quantities of impurities and proved ideal for methanol synthesis with a copper catalyst. The ICI process, using a much more active copper based catalyst could operate efficiently at 50 atm pressure and at temp. of 220-280oC. The copper based catalyst developed by ICI was also more selective than the high pressure zinc chromite catalyst and operated at a much lower temp. Consequently, it produced a significantly lower of impurities than zinc Chromite as shown in following table.

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LEVEL OF IMPURITES PRODUCED BY MS CATALYSTS Impurity

ZnO/Cr2O3 catalyst

Cu/ZnO catalyst

Dimethyl ether

5000-10000ppm

20-150ppm

Carbonyl compds

80-220ppm

10-35ppm

Higher alcohols

3000-5000ppm

100-2000ppm

Methane

Variable

None

6.5 SOME OTHER SALIENT FEATURES Copper based catalyst produced no methane. The possibility of a highly exothermic runaway methanation reaction leading to catalyst sintering and possible converter damage was a continual threat in the high pressure process. This improvement is selectivity for the copper based catalyst over zinc Chromite was estimated to reduce feed stock requirements from 5-10% for the equivalent amount of methanol produced. Hence ICI methanol catalysts were both active and long lived and generally considered a benchmark in industry and represented a significant achievement in heterogeneous catalysis. Catalysts used by ICI in methanol synthesis in accordance with SYNETIX are:KATALCO 51-8 PPT for ARC-Reactors. KATALCO 51-8 PPT for Tubular and quench type reactors.

6.6 RECENT CATALYST DEVELOPMENTS Following ICI‘s breakthrough in methanol technology in 1966, other companies quickly followed with their own alternative low-press. Methanol processes and catalysts. Companies that currently have both a methanol process and catalysts, include ICI, Lurgi, Haldor Topsoe, BASF, Ammonia Casale and Mitsubishi Gas Chemical. A patent survey of representative copper based methanol catalysts is shows in following table. Company Ammonia casale BASF

DUPONT HALDOR TOPSOPE ICI

Catalyst system Cu-Zn-Al-Cr Cu-Zn-Al Cu-Zn-Al-CrMn Cu-Zn-Al Cu-Zn- Cr Cu-Zn-Al Cu-Zn-Al

Typaical atomic ratio 29:47:6:18 32:42:36 38:38:0.4:12:12 50:19:31 37:15:48 61:30:9 64:23:13

Production Of Methanol From Natural Gas LURGI

Cu-Zn-V Cu-Mn-V MITSUBISHI GAS Cu-Zn-MP CHEMICAL Cu-Zn- Cr Cu-Zn-B SHELL Cu-Zn-Ag Cu-Zn-Re UNITED CATALYSTS Cu-Zn-Al

44 61:30:9 48:30:22 55:43:2 55:43:2 61:38:1 61:24:15 71:24:5 62:21:17

6.7 CURRENT CATALYST COMPOSITION All commercial low-pressure methanol catalyst contains copper and zinc oxides together with one or more additional promoters, usually aluminum or chromium oxide. ICI, for example, reports a standard industrial catalyst to contain copper oxide, zinc oxide and Alumina in a ratio of 60:30:10, respectively.

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45

Production Of Methanol From Natural Gas

46

Balance Around Distillation Column A = 150 Tons/day

Light ends (L)

Distillation Column

A4

Distillation Column

CH3OH 99.85% 149.775 H2O 0.14% 0.216 HCHO 0.003% 0.0045 CH3COOH 0.003% 0.0045

(2) (1) CH3OH H2O CO2 HCHO CH3OCH3 C2H5OH C3H7OH C5H11OH CH3COOH

80% wt % 18% 0.20% 0.40% 0.40% 0.30% 0.20% 0.20% 0.30%

W Waste Water

Basis:- One day Operation Methanol Balance:0.8 A4 =

0.9985 A

A4

=

187.21

CH3OH in A4

=

149.775 tons

H2O in A4

=

33.69

CO2 in A4

=

0.3748 tons

HCHO in A4

=

0.748

tons

CH3OCH3 in A4

=

0.748

tons

tons

tons

Total light ends in A4

=

1.87

C2H5OH in A4

=

0.561 tons

C3H7OH in A4

=

0.374 tons

C5H11OH in A4

=

0.374 tons

CH3COOH in A4

=

0.561 tons

Total Heavy ends in A4 =

tons

1.872 tons

tons tons tons tons

Production Of Methanol From Natural Gas

47

Calculation of W:Water in W

= =

CH3COOH in W

= CH3COOH in A4 = = 0.557 tons

C2H5OH in W

= =

C2H5OH in A4 0.561 tons

C3H7OH in W

= =

C3H7OH in A4 0.374 tons

C5H11OH in W

= =

C5H11OH in A4 0.374 tons

=

35.35 tons

So,

W

Water in A4 - Water in A 33.48 tons CH3COOH in M

Now, % of H2O

=

94.71 %

% of CH3COOH

=

1.57

%

% of C2H5OH

=

1.58

%

% of C3H7OH

=

1.05

%

% of C5H11OH

=

1.05

%

HCHO in L

= =

HCHO in A4 - HCHO in A 0.744 tons

CO2 in L

= =

CO2 in A4 0.374 tons

Calculation of L:-

CH3OCH3 in L

= =

CH3OCH3 in A4 0.748 tons

Total L

= 1.86 tons

% of HCHO

=

39.85 %

% of CO2

= 20.04 %

% of CH3OCH3

= 40.09 %

Production Of Methanol From Natural Gas

Now as

A4

=

A4

= 7800.78 Kg/hr

48

187.21 tons/day

&1 day = 24 hrs 1 ton = 1000 kg

So,

Now arranging the whole data in a tabular form,

Component

So,

Wt %

Wt

Mol.Wt k.Mole Mole %

CH3OH H2O CO2 HCHO CH3OCH3 C2H5OH C3H7OH C5H11OH CH3COOH

80% 18% 0.2% 0.4% 0.4% 0.2% 0.3% 0.3% 0.2%

6240.6 1404.1 15.60 31.20 31.20 23.40 15.60 15.60 23.40

32 18 44 30 46 46 60 88 60

A4

276.43 K.Mole/hr

=

195.0 78.0 0.35 1.04 0.67 0.50 0.26 0.17 0.39 276.4

70.54 28.21 0.128 0.376 0.245 0.184 0.094 0.064 0.141

Balance Around Converter:Basis:-

1 hr Operation Recycle stream H2 75% Mol % CO 13% Mol % CO2 9% Mol % N2 3% Mol %

A6

A2

B

A7

A3 Reactor

A1

Separator

M H2 76.68% CO 13.78% CO2 9.41% N2 0.13%

Mol % Mol % Mol % Mol %

A4 276.43 K.Mol /hr CH3OH 70.54 H2O 28.21 CO2 0.128 HCHO 0.376 CH3OCH3 0.245 C2H5OH 0.184 C3H7OH 0.0940 C5H11OH 0.0641 CH3COOH 0.1410

C Balance:23.19% A1

=

22% A7

+ 72.79611 * A4/100

23.19% A1

=

22% A7

+ 201.235

mol % mol % mol % mol % mol % mol % mol % mol % mol %

(1)

Production Of Methanol From Natural Gas

49

N2 Balance:0.13%

A1

=

A1

3% A7

=

2307.69% A7

(2)

Putting Eq (2) in (1), 535.15% A7

=

513.15% A7

= 201.23

A7

=

22%

A7

+ 201.235

39.21 K.Mol /hr

So, H2 in A7 CO in A7 CO2 in A7 N2 in A7

= = = =

29.41 5.09 3.52 1.17

K.Mol /hr K.Mol /hr K.Mol /hr K.Mol /hr

So Eq(2) becomes, A1

= 904.96

K.Mol /hr

Now, H2 in A1 CO in A1 CO2 in A1 N2 in A1

= = = =

693.93 124.70 85.15 1.176

K.Mol /hr K.Mol /hr K.Mol /hr K.Mol /hr

Reactor:Now suppose,

50%

conversion of CO & CO2 per pass

50%

* {( 124.70 + 13% * A6 )

+ ( 85.15 + 9% * A6)} = 195.0

50%

* {( 209.86 + 22% * A6 )} = 195.0 209.86 + 22% * A6 = 390.03 22% * A6 A6

= 180.17 = 818.98 K.Mol /hr

So, H2 in A6 CO in A6 CO2 in A6 N2 in A6

= = = =

614.23 K.Mol /hr 106.46 K.Mol /hr 73.70 K.Mol /hr 24.56 K.Mol /hr

Balance at point M:A=

=

A1 + A 6

Production Of Methanol From Natural Gas A2

=

1723.95 K.Mol /hr

A5

=

A6 + A 7

A5

=

858.20 K.Mol /hr

50

Balance at point B:-

Balance Around the Separator:A3

=

A4

+

A5

A3

=

1134.63 K.Mol /hr

Balance Around the Separator1:-

D2

H2 57.42% CO 10.32% CO2 7.04% N2 0.10% H2O 25.11%

Separator

A1 = 904.96 K.Mol /hr H2 CO CO2 N2

By vol By vol By vol By vol By vol

76.68% 13.78% 9.41% 0.13%

Mol % Mol % Mol % Mol %

W1 H2O 100%

Overall Balance:D2 D2

= =

W 1 + A1 W1 + 904.96

(3)

H2O Balance:25.11% * D2

=

W1

(4)

Putting (4) in (3), D2 = 25.11% * D2 + 74.89% * D2 = 904.96 D2 = 1208.39 K.Mol /hr So, H2 in D2 CO in D2 CO2 in D2 N2 in D2 H2O in D2

= = = = =

693.86 K.Mol /hr 124.70 K.Mol /hr 85.07 K.Mol /hr 1.18 K.Mol /hr 303.4 K.Mol /hr

Now putting value of D2 in Eq(4) , we get, W1

= 303.4 K.Mol /hr

904.96

Production Of Methanol From Natural Gas

51

Balance Around Heat Exchanger:-

D1

D2 = 1208.39 K.Mol /hr

Heat Exchanger

As No mass transfer take place in Heat Exchanger, So D1

= D2

= 1208.39 K.Mol /hr

and D1 has the same composition as the D2.

Balance Around the Steam Reformer:Natural gas Steam Reformer

D

CH4 C2H6 C3H8 CO2 N2

93.40% By vol 3.50% By vol 1.50% By vol 1% By vol 0.60% By vol

D1 = 1208.39 K.Mol /hr

H2 CO CO2 N2 H2O

S H2O 100 %

57.42% 10.32% 7.04% 0.10% 25.11%

By vol By vol By vol By vol By vol

Steam

C - Balance:105.9% * D D

= 209.77 = 198.09 K.Mol /hr

H2 - Balance:402.7

+ S = 997.29 S

= 594.57 K.Mol /hr

Natural gas to steam ratio:S/D = 3.00 This ratio matches with the value given in literature , which proves it to be right. So, CH4 in D C2H6 in D C3H8 in D CO2 in D N2 in D

K.Mol /hr

Mol. Wt Kg / hr

= = = = =

16 30 44 44 28

185.0 6.93 2.97 1.98 1.18

2960.25 207.99 130.73 87.15 33.27

Production Of Methanol From Natural Gas

Total

52

= 3419.439 Kg / hr

So finally, 3419.4 Kg / hr

= 82.06 tons/day

& S

= 594.57 K.Mol /hr = 256.85 tons/day

1 k.mol H2O = 18 Kg

Production Of Methanol From Natural Gas

53

Production Of Methanol From Natural Gas

54

Energy Balance Balance Around Steam Reformer:S H2O = 1 450 oC F

= 198.08 K.mol/hr 855 oC

S.R Kmol/hr CH4 = C2H6 = C3H8 = CO2 = N2 =

Mol Fractions 0.934 185.01 0.035 6.93 0.015 2.97 0.01 1.98 0.006 1.18

H2 = CO = CO2 = N2 = H2O =

F1 =1208.39 K.mol/hr

Kmol/hr Mol Fractions 0.574 693.85 0.103 124.70 0.070 85.07 0.00098 1.18 0.251 303.42

Heat In By F:Cp of CH4

= ( 34.31 + 5.47E-02 T + 0.934

*

=

32.045 + 5.11E-02 T + 3.42E-06 T2

=

0.035

Cp of CO2

Cp of N2

=

1.020

+ 2.26E-01 T * ( 68.032 +

2

0.01

* ( 36.11 +

=

0.361 +

= ( 29 + 0.006 *

4.23E-04

2.26E-01

3.17E-08 T )

T - 1.31E-04 T

2

3

+ 3.17E-08 T )

T2 + 4.76E-10 T3)

T - 2.89E-05

T2 + 7.46E-09 T3 )

4.23E-02 T -

2.89E-05 T

T -

2.20E-03 T + ( 29 +

3

1.31E-04 T +

+ 3.39E-03 T - 1.97E-06

=

= CP Net

( 49.37 + 1.39E-01 T - 5.82E-05 T2 +7.28E-09 T3)

= ( 36.11 + 4.23E-02

=

- 1.03E-08 T3)

+ 4.87E-03 T - 2.04E-06 T2 + 2.55E-10 T3)

= ( 68.032 0.015

- 1.10E-08 T3)

1.39E-01 T - 5.82E-05 T2 + 7.28E-09 T3) *

= 1.72

=

T3)

- 1.10E-08

( 34.31 + 5.47E-02 T + 3.66E-06 T2

=

Cp of C2H6 = ( 49.37 +

Cp of C3H8

3.66E-06 T2

2.89E-07 T 5.72E-06

2

+

2

3

+ 7.46E-09 T )

7.46E-11

3

T )

T2 - 2.87E-09 T3 )

2.20E-03 T + 5.72E-06 T

0.174 + 1.32E-05 T + 3.43E-08 T 2

2

2

-

3

2.87E-09 T ) 3

- 1.72E-11 T )

= (35.32 + 5.98E-02 T -8.37E-07 T -9.49E-09 T3)

Production Of Methanol From Natural Gas

Heat In by F = 198.08 = = =

=

∫m Cpnet dt

55

RANGE = 25 to 450 oC

*1000 / 3600 [ 35.32907 * 425 + 5.98E-02 * 100937.5 - 3.43E-08 * 30369791.67 - -9.49E-09 * 10251464844 ] 55.024 * 2.11E+04 1.16E+06 Watts 1.16E+03 KW

Heat In By S:Cp of Steam

Heat In By S

=

= 33.46

+ 6.88E-03

∫mCpsteam dt

+ 7.60E-06T2 - 3.59E-09 T3

RANGE =

25 to 450 oC

= 594.57 * 1000/3600 * [ 33.46 * 425 + 6.88E-03 * 100937.5 + 7.60E-06 * 30369791.67 - 3.59E-09 *10251464844 ] = 165.15 * 1.51E+04 = 2.50E+06 Watt = 2.50E+03 KW Total Heat of Reactant = ∆HR = 3.66E+03 KW

Heat Out By F1 :Cp of H2 = 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 = 0.574 * ( 28.84

+ 7.65E-05 T

+3.29E-06 T2 - .70E-10 T3 )

= 16.55 + 4.39E-05 T + 1.89E-06 T2 - 4.99E-10 T3 Cp of CO = 28.95 = 0.1032

+ 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 )

* ( 28.95

+ 3.66E-07 T2 - 2.29E-10 T3

= 2.98 + 4.24E-04 T

Cp of CO2 = 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 = 0.0704

* ( 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 )

= 2.54 + 2.98E-03 T - 2.03E-06 T2 + 5.25E-10 T3 Cp of N2

= ( 29 + 2.20E-03 T = 0.00098 * ( 29

+ 5.72E-06 T2 - 2.87E-09 T3)

+ 2.20E-03 T + 5.72E-06 T2

= 0.028 + 2.16E-06 T + 5.61E-09 T2 Cp of H2Og

=

33.46

= 0.2511

- 2.87E-09 T3)

- 2.81E-12 T3

+ 6.88E-03 T + 7.60E-06 T2 - 3.59E-09 T3 * (33.46

+ 6.88E-03 T +7.60E-06 T2 - 3.59E-09 T3

Production Of Methanol From Natural Gas

56

= 8.40 + 1.73E-03 T + 1.91E-06 T2 - 9.02E-10 T3 Cp Net

Heat Out By F1

= 30.51994 + 5.18E-03 T

∫mCpnet dt

=

= 1208.391 *

= = =

+ 2.14E-06 T2

- 1.09E-10 T3

RANGE = 25

to

855oC

1000/3600 [ 30.51 * 830 + 5.18E-03 * 365200 + 2.14E-06 * 208336916.7 - 1.09E-10 * 1.33599E+11 ]

335.66 * 2.77E+04 9.28E+06 Watts 9.28E+03 KW

Heat of reaction:CH4

+

C2H6

+

H2O 2H2O

C3H8 CO

+ +

CO

+

2CO

3H2O

3H2

(1)

+ 5H2

(2)

3CO +

H2O

CO2

Heat of formation of CH4 Heat of formation of CO Heat of formation of H2O Heat of formation of CO2 Heat of formation of C2H6 Heat of formation of C3H8

= = = = = =

+

-74.84 -110.52 -241.82 -393.51 -84.66 -119.84

7H2

H2

(4)

Kj/g.mol Kj/g.mol Kj/g.mol Kj/g.mol Kj/g.mol Kj/g.mol

SO, ∆H1 ∆H1 ∆H2 ∆H2 ∆H3 ∆H3 ∆H4

∆H4

= = = = = = =

206.14 206146 347.27 347279 513.75 513758 -41.164

Kj/g.mol Kj/K.mol Kj/g.mol Kj/K.mol Kj/g.mol Kj/K.mol Kj/g.mol

=

-41164

Kj/K.mol

From eq 1 :-

X1 =

185.05

K.mol of CO per hr

From eq 2 :From eq 3 :From eq 4 :-

X2 = X3 = X4 =

13.8 8.91 83.1

K.mol of CO per hr K.mol of CO per hr K.mol of CO2 per hr

Total Heat of reaction = = =

44113745 12253.82 12253.82

Kj/hr Kj/sec KW

(3)

Production Of Methanol From Natural Gas

57

So,

Heat Required

=

Hin

- Hout

= =

+

6.63E+03 2.39E+07

Hreaction Kj/sec Kj/hr

Natural Gas Required:Calorific value So, Natural Gas Required

= =

=

975

Btu/ft3

=

36351607.5

Kj/m3

Heat Req / C.V 6.57E-01 m3/hr

Energy Balance Around Heat Exchanger:o

354 C

4.8 Mpa F1

= 1208.391 K.mol/h

= 376 o C

F2

o

855 C

o

B.F.W (AT 80 C)

Heat In By F1

= 9.28E+03

Kj/sec

Heat Out By F2 :Cp Net = 30.51 + 5.18E-03 T + 2.14E-06 T2 - 1.09E-10 T3 Heat Out By F2 = ∫mCpnet dt RANGE = 25 to 376 oC = 1208.39 * 1000/3600 [ 30.519938 * 351 + 5.18E-03 * 70375.5 + 2.14E-06 * 17713917 - 1.09E-10 * 4996695688 ] = 335.6642 * 1.11E+04 = 3.73E+06 Watts = 3.73E+03 KW

Heat Transfer

= =

Heat in - Heatout 5.55E+03 KW

Water Required: T1 T1 T2 T2

= = = =

30 o C 303 K 361 oC 634 K

HL

=

125.7

Kj/kg

HV

=

3104.35

Kj/kg

Production Of Methanol From Natural Gas

58

So, ∆H = ∆H =

HV - HL 2978.65

Kj/kg

Now, Q = m * ∆H m = Q/∆H Avg Mol. Wt = 9.93 m = 1.86E+00 Kg/sec m = 6.71E+03 Kg/hr = 8133.07 Kg/hr

Energy Balance Around point "A" M6

M1

=

904.96 K.mol/hr

H2 CO2 CO N2

= = = = =

8660.50 K.g/hr 16.03% 43.27% 40.32% 0.38%

= =

819.041 K.mol/hr 8133.07 Kg/hr H2 = 15.10% CO2 = 39.89% CO = 36.62%

N2

=

A 100 oC

8.45% M2 = 1724.0 K.mol/hr H2 = 15.57% CO2 = 41.61% CO = 38.53% N2 = 4.29%

Heat In by M1:M1 = Avg. Cp = T =

=

Q1

8660.505 K.g/hr 2.727 Kj/Kg.K 100 oC (373K)

t =

298 K

m Cp ∆T

= 1771290

Kj/hr

Heat In by M6:M6 = 8133.07 Avg. Cp = 2.727 T = 35 o C = 308 K =

Kg/hr Kj/Kg.K

Q6 = mCp ∆T 221789 KJ/hr

So,

Total Heat In:Qt = = 1993079

=

Q 1 + Q6 1993079 Heat In mCp∆T

KJ/hr =

Heat Out

Production Of Methanol From Natural Gas 1993079 1993079 43.48 T

= = = = =

59

16809.05 * 2.727 * ( T - 298 ) 45838.28 * ( T -298 ) ( T -298 ) 341.48 K 68.48 o C

Energy Balance Around Reactor :230 oC M2 =

1724.005 K.mol/Hr

=

0.5

16809.05 K.g/hr

M3 =1134.69K.mol/hr

Reactor

0.5

o

75 C

Heat In By M2 Stream:Avg. Cp =

2.727

Kj/Kg.K

Qin = = =

mCp dt

+ Kj/hr KW

In M2

CO = 13.39%

Heat Of Reaction:CO

=

4698423.28 5844380.18 1623.43

1145956.8

CO2 = 9.10%

+ 2H2

CH3OH ∆H = ∆H =

-90.77 -90770

CO2

KJ/g.mol KJ/K.mol

+ 3H2

∆H = ∆H =

-49.58 -49580

(1)

CH3OH KJ/hr KJ/K.mol

+ H2O

(2)

Conversion =

So, X1 X2 X3

= 115.4 K.mol of CH3OH per hour = 78.44 K.mol of CH3OH per hour = 78.44 K.mol of H2O per hour

Total Heat Of Reaction

= -10476867 + -7778331 = -18255198 Kj/hr = -5070.888 KW

Heat Out By M3 Stream:Cp of H2

= 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 = 0.567 * [ 28.84 +7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 ]

50%

Production Of Methanol From Natural Gas = 16.36 + Cp of CO

= 28.95

60 + 1.87E-06 T2 - 4.93E-10 T3

4.34E-05 T

+ 3.55E-06 T2 - 2.22E-09 T3

+ 4.11E-03 T

= 0.098 * [ 28.95 + 4.11E-03 T

+ 3.55E-06 T2 - 2.22E-09 T3

= 2.84 + 4.04E-04 T + 3.49E-07 T2 - 2.18E-10 T3 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3

Cp of CO2 = 36.11

0.068 *[ 36.11+ 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3

=

2.89E-03 T -1.97E-06 T2 + 5.10E-10 T3

= 2.46 + Cp of N2

+ 5.72E-06 T2

= ( 29

+ 2.20E-03 T

= 0.022 * [ 29

+ 2.20E-03 T

+ 5.72E-06 T2 -

33.46 + 6.88E-03 T + 7.60E-06 T2 -

=

+ 7.60E-06 T

= 0.0687 * [ 33.46 + 6.88E-03 T =

- 2.87E-09 T3)

+ 1.30E-07 T2

= 0.651 + 4.99E-05 T Cp of H2Og

- 2.87E-09 T3)

2.300375

+ 4.73E-04 T

Cp of CH3OH = ( 42.93 = 0.17187 * [ 42.93 = 7.378379

3.59E-09 T3

2

- 3.59E-09 T3

+ 5.23E-07 T2 - 2.47E-10 T3

+ 8.30E-02 T +

6.51E-11 T3

8.30E-02 T

+ 1.43E-02 T

- 1.87E-05 T2 - 8.03E-09 T3 ) - 1.87E-05 T2 - 8.03E-09 T3 )

- 3.21E-06 T2 - 1.38E-09 T3

Cp of HCHO = ( 34.28 + 4.27E-02 T + 0 - 8.69E-09 T3 ) = 9.16E-04 * [ 34.28 + 4.27E-02 T + 0 - 8.69E-09 T3 ) = 3.14E-02

+ 3.91E-05 T + 0.00E+00 - 7.96E-12 T3

Cp of C2H5OH = ( 61.34 + 1.57E-01 T -

8.75E-05 T

= 4.48E-04 * [ 61.3 + 1.57E-01 T -

Cp NET

Qout

=

2

8.75E-05 T

3

+ 1.98E-08 T ) 2

3

+ 1.98E-08 T ) 2

= 2.75E-02 + 7.04E-05

T - 3.92E-08 T

= 3.21E+01 + 1.82E-02

T - 2.36E-06 T - 9.06E-10

∫mCpnet dt

Range :-

+ 8.88E-12 T

2

25

to

315.19 2.89E+06

*

9.17E+03 Watts

T

3

290 oC

= 1134.69 * 1000/3600 [ 3.21E+01 * 2.65E+02 + 1.82E-02 * 3.61E+04 -2.36E-06 * 6555792 + -9.06E-10 * 5314019375 ] = =

3

Production Of Methanol From Natural Gas =

∆H

2.89E+03

= Qin =

61

KW

- Qout

+

-6.14E+03

Qreacion KW

Heat Balance Around Separator:o

35 C o

o

Separator

35 C

Heat transfer =

35 C

0

Energy Balance Around Distillation(Light Ends)

o

40 C V

Qv

L =1.8695 tons/day = 1869.5 Kg/day

Distillation column

M4 = 187.22 tons/day = 187220 Kg/day 35 oC 308 K 70 C

CH3OH = 80% H2O =18% CO2 =0.20% HCHO = 0.40% CH3OCH3 = 0.40% C2H5OH = 0.30% CH3COOH = 0.30% C5H11OH = 0.20% C3H7OH = 0.20%

Heat In By M4 Stream: Cp of CH3OH = 80%* 2.95 = 2.36 KJ/Kg.K Cp of H2O

=

18% * 4.18

W = 185.35 tons/day Qb = 185350 Kg/day

Production Of Methanol From Natural Gas = Cp of CO2

62

0.7524 KJ/Kg.K

= 0.20% * 1.09 = 0.0021 KJ/Kg.K

Cp of HCHO = 0.40% * 1.192 = 0.0047 KJ/Kg.K Cp of CH3OCH3 Cp of C2H5OH

= 0.40% * 1.75 = 0.007 KJ/Kg.K = 0.30% * 2.5 = 0.0075 KJ/Kg.K

Cp of CH3COOH = 0.30% * 2.05 = 0.0061 KJ/Kg.K Cp of C3H7OH

= 0.20% * 2.41 = 0.0048 KJ/Kg.K = 0.20% * 2.26 = 0.00452 KJ/Kg.K

Cp of C5H11OH Cp NET

= 3.149 KJ/Kg.K = mCp∆T = 245674.6 KJ/hr

QM4

Heat Renoved In Condenser:In this column , we saparate the dissolve gases from crude methanol mixture.The gases pass through the condenser.Here the purpose of condenser is to condense the vapor of methanol if it passes with gas stream.As such , there is no reflux. we assume, Temp of "V" stream = 40 oC = 313 K Temp of "L" stream = = Input

Qv

=

Qc

=

=

Ql Qv

Cp of HCHO = 0.39877 * 1.256 = 0.500 KJ/KG.K Cp of CO2

= 0.2 * 1.09 = 0.218 KJ/KG.K

Cp of CH3OCH3 = 0.401 * 1.88

25 oC 298 K Output

+ -

Ql

Qc (1)

Production Of Methanol From Natural Gas

63

= 0.75 KJ/KG.K Cp NET

= 1.47

KJ/KG.K

Substituting the values in Eq (1), Qc = =

1721.19 1721.19

Kj/hr

* KJ/Kg.K * KJ/Kg.K * KJ/Kg.K * KJ/Kg.K * KJ/Kg.K KJ/Kg.K

2.85

0 = 0.478 KW

Heat Added By Reboile Qb:Cp of CH3OH

= = Cp of H2O = = Cp of HCHO = = Cp of C2H5OH = = Cp of CH3COOH = = Cp NET =

0.80807 2.30 0.181 0.75 2.40E-05 3.01E-05 0.00302 0.0047 0.00302 0.0061 3.07E+00

4.18 1.25 1.56 2.05

So, Heat Out by stream. Q

= mCp∆T = 1068261

Kj/hr

Balance Qb + QM4 Qb

Input = Output = Qc +QP + QL = QC + Qp + QL - QM4 = 824307.5 Kj/hr = 228.97 KW

Steam required:Qb is supplied by super heated steam. P = 4800 Kpa λ = 1654 KJ/Kg Q = mλ m = Q/λ = 498.37 Kg/hr

Water Required:Qc is removed by cooling water with a termperature risse of 15 oC. Qc m

= = =

m Cp∆T Qc / Cp∆T 27.45 Kg/hr

Production Of Methanol From Natural Gas

64

Energy balance of distillation (Heavy ends) Column:65 oC Hv V

Qv Distillation column

P = 185.35 tons/day =185350 Kg/day

53 oC L Hl

M =150 tons/day HM = 150000 Kg/day

95 oC Qb Heat In By "P" stream:= 1068261 KJ/hr

W = 35.3475 ons/day = 35347.5 kg/day

Heat Removed By Condenser Qc:R L V

= = = = = =

L/M 158.01 158010 L+M 308.01 308010

1.0534 tons/day Kg/day tons/day Kg/day

At steady State:Input = Output VHv = MHm + LHl + Qc Qc = VHv -MHm - LHl (2) At 65 oC or 338 K Enthalpy of vapors = Hv = 1804.8 Kj/Kg At 53 oC or 326 K Enthalpy of Condensate Hl = Hm = 670.5

Kj/Kg

Substituting the values in eq (2)..we get

Qc = Qc = =

V = 3.08E+05 Kg/day L = 1.58E+05 Kg/day 5.56E+08 - 100575000 - 1.06E+08 3.49E+08 Kj/day 1.46E+07 Kj/hr = 4055.56 KW

Production Of Methanol From Natural Gas

Heat Added By Reboiler Qb:Heat Out By "W" Stream: Qw = mCp∆T = 10194219 Kj/day = 424759.1 kKj/hr Balance:Input QB + Q p

= =

Output Qc + Qw + Qm

Qb = Qc + Qw + QM - Qp = 1.50E+07 + 4190625 - 1068260.964 = 1.81E+07 Kj/hr = 5027.78KW

Steam Required:Qb is supplied by super heated steam . P = 4800 Mpa λ = 1654 KJ/Kg Q = mλ m = Q/λ = 1.09E+04 Kg/hr

Water required In condenser: Qc is removed by cooling water with a termperature risse of 15 oC. Qc = mCp∆T m = Qc/Cp∆T =

232174.2

Kg/hr

65

Production Of Methanol From Natural Gas

66

Production Of Methanol From Natural Gas

67

Production of Hydrogen Hydrogen has been produced and used for industrial purposes for over one hundred years. Of the world’s total hydrogen production of approximately 45 mill. tons, over 90% comes from fossil raw materials. The largest producers of hydrogen are the fertiliser and petroleum industries. Sale of hydrogen has increased by 6% annually in the last five years. This is closely related to the increased use of hydrogen in oil refineries, which is a result of the strict requirements on the quality of fuels. This development is expected to increase. Hydrogen is used elsewhere in many other process industries and laboratories, and compressed hydrogen gas can be bought from most gas retail stores. Many renewable energy sources vary considerably on a daily and seasonal basis. An energy system based on such sources must be able to store energy to balance out variations. Correspondingly, the great distances usually seen between the energy sources and the consumers necessitates transportation of the energy. For both these purposes it may be practical to convert the energy to hydrogen. It should be noted that as an energy carrier, hydrogen is ―neutral‖ as to the actual source of energy. One could, for instance, envision large scale electrolysis based on nuclear power. Due to the environmental problems surrounding nuclear power, such a solution would, in our view, defeat the purpose.

Production of hydrogen based on fossil raw materials Strongly simplified, the majority of the processes described below are based on heating up hydrocarbons, steam and in some instances air or oxygen, which are then combined in a reactor. Under this process, the water molecule and the raw material are split, and the result is H 2, CO and CO2. In other words, the hydrogen gas comes from both the steam and the hydrocarbon compound. Another method is to heat up hydrocarbons without air until they split into hydrogen and carbon.

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68

Gasification of coal Gasification of coal is the oldest method of producing hydrogen. In the old gas plants, the original gas piped in to cities was produced this way. This gas contained up to 60% hydrogen, but also large amounts of CO. Typically, the coal is heated up to 900ºC where it turns into a gaseous form and is then mixed with steam. It is then fed over a catalyst – usually nickel. There are also other more complex methods of gasifying coal. The common factor is that they turn coal, treated with steam and oxygen at high temperatures, into H 2, CO and CO2. In addition, sulphur is released from the raw material and creates sulphur and nitrogen compounds. As with CO and CO2, these compounds must be handled in an environmentally friendly way.[Winter et al 1988] Today there are large coal gasification plants in Europe, South Africa and the USA, and technologies for gasification of coal is the object of a great deal of R & D within the coal industry.

Steam reforming of natural gas Natural gas consists mainly of methane, mixed with some heavier hydrocarbons and CO 2. By applying high temperature steam to the methane, hydrogen and carbon oxides are created. Steam reforming is the most common method of producing hydrogen today. The formula for the chemical reaction is: CH4 + H2O -> CO + 3H2 And for the following ―shift reaction‖:

CO + H2O -> CO2 + H2 Which produces: 1 mol methane =-> 4 mol hydrogen The percentage of hydrogen from water is 50%. Steam reforming of natural gas is currently the cheapest way to produce hydrogen, and accounts for about half of the world‘s hydrogen production. Steam, at a temperature of 7001000 ºC, is fed methane gas in a reactor with a catalyst, at 3-25 bar pressure. In addition to the natural gas being part of the reaction process, an extra 1/3 natural gas is used as energy to power the reaction. New methods are constantly being developed to increase the efficiency, and maximising the heat process makes it possible to increase the utilisation to over 85% and still make a profit. A large steam reformer which produces 100,000 tons of hydrogen a year can, roughly speaking, supply one million fuel cell cars which have an annual average driving distance of 16,000 km. Steam reforming of natural gas produces 7.05 kg CO2 per kilogram of hydrogen.

Production Of Methanol From Natural Gas

69

There are two main types of steam reformers for small scale hydrogen production: conventional, down-sized reformers, and specially constructed reformers for fuel cells. The latter operates under lower pressure and temperature than conventional reformers, and are more compact. Work is under way to build a modified steam reformer with a built-in CO2 remover. This will make it possible to produce hydrogen at a lower temperature than regular steam reformers. These reformers will reduce the cost of hydrogen production by 25-30% compared to conventional technology, mainly due to reduced capital and operating expenses. The most common method of "on-purpose" hydrogen production is the steam reforming process. The main process step involves the reaction of steam with a hydrocarbon over a catalyst at around 750-8000C (1380-1470ºF) to form hydrogen and carbon oxides. However, there are several other steps to remove impurities and maximize hydrogen production. The main steps involved are as follows: Feedstock purification - removal of poisons such as sulphur and chloride to maximize the life of the downstream steam reforming and other catalysts

Feedstock Purification The catalysts used in the steam reforming process are poisoned by trace components in the hydrocarbon feed, particularly sulphur, chlorine and metal compounds. Sulphur is the commonest problem, the nature and level of sulphur species being dependent on the source, pre-treatment and molecular weight of the hydrocarbon. Chlorine compounds are less common and metal compounds are typically found in some heavier LPG and naphtha feeds. The best way to remove sulphur compounds is to convert the organic sulphur species to H2S over a hydrodesulphurization catalyst. The HDS catalyst removes organic-sulphur compounds by reaction with hydrogen to convert the sulphur to H2S. The next step is sulphur removal with an absorbent. The same catalyst similarly converts any organic-chloride species to give HCl and also acts as an absorbent for most problematic metal

Production Of Methanol From Natural Gas

70

species. A second absorbent is used for chloride removal. CO + 3H2 «=» CH4 +H2O CO2 + 4 H2 «=» 2CH4 + 2H2O Most catalysts are formulated on a calcium aluminate base with the active nickel incorporated in a NiO/MgO solid solution. This results in negligible nickel sintering during operation. Deactivation mostly results from solvent carry over from the upstream CO 2 removal section.

Steam Reforming Catalysts This is the heart of the hydrogen generation process. The main steam reforming reactions are: CH4 + H2O «=» CO + 3 H2 CxHy + H2O «=» x CO + (x + 0.5y) H2 and CO + H2O «=» CO2+H2 The reaction takes place across a nickel catalyst packed in tubes in a fired furnace. An excess of steam is used to promote the reforming reaction and avoid carbon deposition on the catalyst. Some flowsheets may have pre or post-reforming in addition to the conventional steam reformer. Newer plants tend to be PSA-based, with typically only a High Temperature Shift bed rather than both High and Low Temperature Shift. This selection considers the feedstock types and operating conditions. The selection is usually dictated by the heaviest hydrocarbon feed and may involve two or three catalyst types in order to obtain optimum performance. The main categories of catalyst are as follows.

Burner Combustion Efficiency Conserving fuel in heating operations such as melting or heat treating is a complex operation. It requires careful attention to the following:  Refractories and insulation  Scheduling and operating procedures  Preventative maintenance  Burners  Temperature controls  Combustion controls

Production Of Methanol From Natural Gas

71

Furnace Efficiency Conventional refractory linings in heating furnaces can have poor insulating abilities and high heat storage characteristics. Basic methods available for reducing heat storage effect and radiation losses in melt and heat treat furnaces are: 1. Replace standard refractory linings with vacuum-formed refractory fiber insulation material. 2. Install fiber liner between standard refractory lining and shell wall. 3. Install ceramic fiber linings over present refractory liner.

The advantages?  R  efractory fiber materials offer exceptional low thermal conductivity and heat storage.  These two factors combine to offer very substantial energy savings in crucible, reverberatory and heat treat furnaces.  With bulk densities of 12-22 lbs/cu ft, refractory fiber linings weigh 8% as much as equivalent volumes of conventional brick or castables.  Refractory fibers are resistive to damage from drastic and rapid changes in temperature.  Fiber materials are simple and fast to install.  The density of fiber refractory is low, so there is very little mass in the lining, therefore  much less heat is supplied to the lining to bring it to operating temperature. This results in rapid heating on the startup. Conversely, cooling is also rapid, since there is less heat stored in the lining.

The steam reformer with cold outlet manifold system The steam reformer is a furnace in which a multiplicity of tubes filled with catalyst are heated by

Production Of Methanol From Natural Gas

72

burning fuel. The process gas temperature required at the outlet of the catalyst-filled tubes is about 740 - 880C at a pressure of up to 40 bar. lnevitably, the service life of components such as the reformer tubes is limited. Material deterioration occurs by the combined effect of creep, alternating thermal and mechanical stresses, external and internal oxidation and carburisation. Inlet manifold Burners Reformer tubes Cold outlet manifold system.

Advantages: • A uniform mixture of gas and oxygen along with sufficient reaction space to ensure equalised gas temperatures prior to contact with the catalyst. • Safe burner design. • No metallic internals in the combustion zone.

The Combustion Process The combustion in fired heaters takes place in the burner. The types of burners and how they function are not covered in detail in this section. The amount of heat released can be easily calculated for a gas when we know the composition of the fuel and the heating values of the various components. For liquid fuels, the heating values are obtained by a calorimeter test. From these values and using the standard combustion equation, we can determine the composition of the flue gas. As an example, the combustion of methane could be stated :

CH4 + 2O2 --- > CO2 + 2H2O Of course for fuel gases containing many more components and burning in air rather than pure oxygen, the equation gets more complicated. Therefore, a task that in itself is quite simple, becomes a burden to do by hand, but can be easily accomplished by a simple computer program. The heating values normally used in fired heater design are the LHV.

Production Of Methanol From Natural Gas

73

Burner Types & Selection Burners for fired heaters can be generally divided into two categories, natural draft and forced draft. The natural draft type burner requires less pressure differential to provide the required air for combustion then the forced draft burner. Air pressure differential, or pressure drop, across a natural draft burner would normally fall in the 0.1 to 1.0 in H 2O range, where the forced draft burner would normally require 0.3 to 4.0 in H2O. Burner combustion air can also be induced by the fuel gas flowing through a venturi section. Also burners have different air registers for primary and secondary air intake. The air may be delivered to the registers by an air plenum. In addition to burners being classified by the draft requirements, they are also described by the fuel they burn such as oil or gas or combination. There are numerous fuels which may be burned including: Refinery Gas Propane or Heavier Gas Natural Gas

High Hydrogen Gas

Waste Gas

No. 2 Fuel Oil

No. 6 Fuel Oil Other Liquids Burners may be of the low NOx which may incorporate staged air or fuel designs. These burner types have become almost standard in the developed world where environmental air standards demand the best combustion technology available. Burners may be designed for mounting in the heater floor, side walls, or end walls. The burner tips can be designed for various shapes or flame patterns. In conclusion, there is such a wide variety of types and configurations of burners available from the many manufacturers, that selecting a particular burner for a design requires that the designer work closely with the burner manufacturer to assure the correct selection

Burning with low excess air: For many years, it was not uncommon to see furnaces operating with 50 to 100% excess air. It was simply easier for the operator to just make sure there was plenty of air. Of course this method of operation also resulted in reduced efficiency and more NO x generation. As fuel costs and environmental concerns has risen, these practices have changed. With the excess air at levels of 15 to 30%(lower for gas and higher for oil), the furnace could be operated with a minimum of monitoring. In recent years, development of advanced instrumentation has allowed continuous automatic furnace monitoring and control of excess air, and the percent excess air can now be reduced below the 10-30% limit. EPA tests concluded that a 19% average reduction of NOx can be achieved by reducing the percent excess air from an average of 20% to an average of 14%. This method is somewhat limited since it can cause other problems such as carbon monoxide and soot emissions..

Production Of Methanol From Natural Gas

74

Purpose Of Excess Air Perfect combustion is achieved when all the fuel is burned using only the theoretical amount of air. Perfect combustion cannot be achieved in a fired heater. Complete combustion is achieved when all the fuel is burned using the minimal amount of air above the theoretical amount of air needed to burn the fuel. With complete combustion, the fuel is burned at the highest combustion efficiency. Incomplete combustion occurs when all the fuel is not burned, which results in the formation of soot and smoke. Oxygen for combustion is obtained from the atmosphere, which is about 21% oxygen by volume or 23% by weight. About 2000 cubic feet of air is required to burn one gallon of fuel oil at 80% efficiency at sea level. About 15 cubic feet of air is required to burn one cubic foot of natural gas at 75% at sea level. Most of the 79% of air that is not oxygen is nitrogen, with traces of other elements. Nitrogen is inert at ordinary flame temperature and forms few compounds as the result of combustion. Nitrogen is an unwanted "parasite" that must be accepted in order to obtain the oxygen. It contributes nothing to combustion, it increases the volume of combustion products to be vented, it steals heat from the reaction and now creates a growing environmental problem as well. Air required in combustion is classified as:

Primary Air Primary air controls the rate of combustion, which determines the amount of fuel that can be burned.

Secondary Air Secondary air controls combustion efficiency by controlling how completely the fuel is burned.

Excess Air Excess air is air supplied to the burner that exceeds the theoretical amount needed to burn the fuel. Combustion air requirements are based on the composition of the fuel used and the design of the burner. Fuels commonly used contain nitrogen, ash, oxygen, sulfur, carbon and hydrogen. When a fuel has a large volume of nitrogen that must be accepted along with the desired oxygen, more excess air should be provided. That excess air has a chilling effect on the flame. Some fuel particles fail to combine with oxygen and pass out of the stack unburned. Natural gas contains more hydrogen and less carbon per unit of heat content than oil and consequently its combustion produces a great deal more water vapor which withdraws a greater amount of heat from the flame. Therefore gas efficiency is always slightly less than oil efficiency. Air requirements for combustion are generally expressed in cubic feet of air per gallon of oil or per cubic foot of gas for convenience because fans, ducts and other air moving devices are

Production Of Methanol From Natural Gas

75

rated in cubic feet per minute or cubic feet per hour. The Fuel/Air Ratio for combustion is actually a weight ratio based on the required weight of oxygen for a given weight of fuel.

Preheated Combustion Air There are basically two ways to obtain preheated combustion air and reduce the amount of fuel required. One process would use heat from an external source to preheat the combustion air, such as waste steam or flue gases from other sources. The other method would be to utilize the flue gas from the heater to preheat the combustion air. In either case, the heat available in the preheated air is taken into account in the radiant heat transfer as described in section 4, Heat Transfer Concepts. In the second case, the additional heat removed from the flue gas in the air heater is taken into account when calculating the overall efficiency of the heater. The amount of heat available in the flue gas can be calculated using the enthalpy of the flue gas at the entering and exiting temperatures.

Cylindrical Radiant Section The radiant section in a vertical tube, cylindrical fired heater contains tubes in a vertical position. The tubes may be along the refractory wall, as in a circular pattern, or they may be exposed to the radiating flame from both sides, as in a cross or octagonal pattern.

Shield Section The shield section contains the tube rows that "shield" the convection rows from the direct radiant heat. Just below the shield tubes are two important monitoring points. The first is the "bridgewall" temperature which is the temperature of the flue gas after the radiant heat is removed including the radiant heat to the shield tubes above, but before the convective heat to the shield tubes. The other is the draft measurement at this point, since for most heater designs, if it is negative at this point, it is negative throughout the furnace.

Convection Section The convection section is located in the cooler flue gas stream. It often contains rows of extended surface tubes to improve the efficiency of the furnace. The flue gases can be cooled to a very low temperature, but caution must be used to avoid going below the dew point of the flue gas with the metal temperature of the tubes or surface, since this could cause corrosion.

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76

Flue Stack The flue stack on the heater is very important for several reasons. In addition to just getting the flue gasses up and out of the way where they won't endanger people, they also perform other functions. In the example shown, draft or flow of the flue gas is controled by an induced draft fan. In a natural draft furnace, the draft created in the stack is what "pulls' the flue gasses through the furnace convection

Damper The main damper in the stack is used to control draft in the furnace. It is normal adjusted to achieve a negative 0.05 inches H2O pressure at the bridgewall. It is not used to control combustion air which is controlled by air plenum dampers or air registers at the burner(s). In the example used herein, it is used to redirect the flue gasses to the air preheat system.

DESIGNING OF STEAM REFORMER Radiant Section:1)

Assumed average heat flux = 10,000 Bto/hr /ft2

2)

ACP

=2

average flux

=2

10,000

= 20,000 Btu/hr/ft2 3)

Overall Exchange factor f = 0.6 (assumed)

4) 5)

ACP f

= 33333.33 Btu/hr ft

Tube surface temperature:Ts = 700 F

6)

Evaluate Ta from fig 19.14 kern Ta = 1571 F Ta

7)

Q = 2.38

8)

QF = /

107 kj/nr

= 855s

C

Production Of Methanol From Natural Gas

2.38 10 7 = 0.85

77

kj/hr

= 28000000 kj/hr 28000000 Btu/hr 1.055

QF

=

QF

= 26540284.36 Btu/hr

Fuel consumption qF =

QF Btu / hr lower heateing value at full Btu / hr

Methane is fuel and lower heating value of methane = 21500 Btu/lb

26540284.36 21500

qF

=

qF

= 1234.43 lb/hr

From Graph given in nelson . lb air lb fuel

as oxygen used in 20% Excess II)

qA

= Amount of w.r used

= qF

lb air lb fuel

= 1234.43

18

qA = 22219.77 lb/nr. Entering temp of air = 357 C = 674.6 F = 1134.6 R Enthalpy of entering air HA

= 4711.49 Btu/lb uel = 162.49 Btu/lb.

QA

=

HA

= 162.49

QA

qA 22219.77

= 3610490.43 Btu/hr

18

Production Of Methanol From Natural Gas III)

78

QW = 2% at QF QW =

2.0 100

3610490.43

QW = 72209.80 Btu/lb IV)

Amount at fuel consumed

QF = 1234.43 16

= 77.2 moles From equation

CH4 + 2O2

Oxygen Consumed = 77.2

2

= 154.3 Moles As oxygen is supplied in 20% excess so Oxygen supplied = 154.3

1.2

= 185.2 moles Oxygen in flue gas = 185.2 – 154.3 = 30.9 moles Nitrogen in flue gas = 185.2

0.79 0.21

= 696.7 moles CO2 in flue gases = 77.2 moles H2O in flue gases = 2

77.2

= 154.4 moles Ta = 1610 F = 2070 F From Himmelblau

qN2 = 696.7

11570

= 8060819 Btu/hr

qO2 = 30.9

12100

= 373890 Btu/hr

qX120 = 13100

154.8

= 2027880 Btu/hr

CO2 + 2H2O

Production Of Methanol From Natural Gas

qCO2 = 17900

79

77.2

= 1381880 Btu/hr

Qa = q N2 + qO2 =

qHW - qCO2

8060819 + 373890 –2027880 –1381880

Qa = 5024949 Btu/hr. Now Net heat load Q = QF + QA – QW – Qa Q = QNet – Qa Q = 26540284.36 + 3610490.43 – 72209.80 – 4392522.6 = 2.56

107 Btu/hr

(It is very closed to actual heat load i,e. 2.65 8)

Assume tube length =30ft Dia of tubes = 5 = 5/12 ft. Centre to centre distance = 10/12 ft

As our furnace is vertical tube single layer Height at furnace = length – at tubes = 30ft 9)

Surface area at tubes = Dl =

0.416

30

As = 39.28 ft2 Heat transferred part tube Qtube = are flux

surface annex at tube

= 10,000

39.28

Qtube = 392814 Btu/hr No at tubes =

Q ( Btu / hr ) Qtube

=

2.65 10 7 = 68 tubes 392814

107 Btu/hr)

Production Of Methanol From Natural Gas Ntube = 68 tubes 10)

Diameter of furnace 2

C – C distance

R = No of tubes

10 12

= 68

56.66 2

R=

R = 9.02 ft D = 18.04 ft 11)

(effectiveness factor ) =

=

C

C dis tan ce 0 . D at tubes

10 =2 5

From Fig 19.11 Kern = 0.87 12)

Ac Ac p = (no at tubes) (length at each tube) (C – C distance) = 68

30

10/12

Ac p = 1700 ft2 13)

AT = Total area at furnace =

18.04

30

AT = 1700.23 ft2 14)

AR = A T -

Acp

= 1700.23 – (0.87

1700)

= 221 ft2 15)

AR ACP

221 0.87 1700

AF ACP

0.149

This factor is used to evaluate if

16)

Mean beam length.

0.149

80

Production Of Methanol From Natural Gas

81

Using table 19.1 kern at page # 691, L = 2/3 ( 30 * 29.753 * 20.085)1/3 (For dimension ratio 1:1:1) L = 17.4 ft

17)

Emissivity at Gas: EG

i)

From Graph given in Nelson (18 . 16) For 20% Excess air at H2O + CO2 = 0.178 atm

From reaction CH4 + 2O2

CO2 + 2H2O

at CO2 = 1/3

= 1/3

0.178

= 0.0593 at H2O = 2/3 = 2/3

0.178

at H2O = 0.118 atm. ii)

From Fig 19.12 Kern For CO2 using PP at CO2 = 0.0593 atm

TS = 806 F

Ta = 1571 F

qCO2 = 300 Btu/hr.ft2

qCO2 = 1780 Btu/hr ft2

qCO2

L = 300

qCO2

L = 1780

qCO2

L = 5220 Btu/hr.ft

qCO2

L = 30972 Btu/hr ft

17.4

17.4

From Fig 19.13 kern for H2O cap using pp at H2O cap = 0.118 atm. At

iv)

TS = 806 F

Ta = 1571 F

qH2O = 280 Btu/hr.ft2

qH2O = 1600 Btu/hr ft2

qH2O

L = 280

qH2O

L = 1600

qH2O

L = 4872 Btu/hr.ft

qH2O

L = 27840 Btu/hr ft

AT

Ta

17.4

17.4

Production Of Methanol From Natural Gas

82

at CO2 CO2 H 2O

0.0593 0.178

= 0.333 PHO

L + PCO2

= (0.118

L

6.9) + (0.0593

6.9)

= 1.2213 From Fig 19.12 kern % correction = 6 %

v)

qb = 0.173 Eb

T 100

4

6b = 1

qb at Ta = 0.173

1571 460 100

1

4

= 29436.47 Btu/hr ft2

qb at Ts = 4444.07 Btu/hr ft2

vi) EG = EG =

Ea = Emissivity at Gas qCO 2

QH 2O Ta qb Ta

30972 27840 29436.47

EG = 0.689

qCO 2

QH 2O TS

qb TS

5220 4872 4444.07

100

% cor 100

100 6 100

94 100

EG = 0.648 18)

From Fig 19.15 kern At AF/ Acp = 0.149 EG = 0.648 f = 0.61 (Which is very close to true assumed value at f = 0.6)

Production Of Methanol From Natural Gas

(a):-

83

ACP f 25600000 0.87 1700 0.61

ACP f

= 28375.4 20)

Calculate actual Ta: From Fig 19.14 kern Using

ACP f

= 28375.4 And town made at Ts = 800 F Ta = 1550 F (Assumed made at Ta was 1571 F which is not far away from 1560 F.

Hence we can consider our calculation and assumptions correct.) Moreover the convection section is also designed according to the exit temperature of the gaseous stream from the radiant section.

Specification Sheet Type Process Item Required Item No. Heat Required Efficiency Furnace Duty Inlet Temperature Outlet Temperature Pressure Standard length of each tube No. of tubes No. of rows Volume of reformer Material of Construction of tube No of burners

Radiant Section of Steam Reformer Continuous 1 S-1 2.257 * 107 Btu/hr 87% 2.594 * 107 Btu/ hr 842 oF 1571 oF 1.6 Mpa 30 ft 45 5 558.85 m3 HK-40,25% Cr , 20% Ni 22

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84

Types of Heat Recovery Equipment Choosing the type of heat recovery device for a particular application depends on a number of factors. For example air-to-air equipment is the most practical choice if the point of recovery and use are close+ coupled. Air-to-liquid equipment is the logical choice if longer distances are involved. Included in this section are five types of heat recovery systems.  Economizers  Heat pipes  Shell and tube heat exchangers  Regenerative units  Recuperators

Heat Exchanger As Waste Heat Boiler : A heat exchanger is a device for transferring heat from one fluids are separated by a solid wall so that they never mix

fluid

to another, where the

Definition of heat exchanger : ―A heat exchanger is a heat transfer device that is used for transfer of internal thermal energy between two or more fluids available at different temperatures.‖ In most of the exchangers the fluids are separated by a heat transfer surface and ideally they don‘t mix. The word ‗exchanger‘ really applies to all type of equipment in which heat is exchanged but is often used specifically to denote equipment in which heat is exchanged between two process fluids. Such as:

Classification of Heat Exchanger      

: In general industrial heat exchangers are classified according to there Construction: Transfer processes Degrees of surface compactness Flow arrangements Pass arrangements Phase of the process fluid Heat transfer mechanism

Production Of Methanol From Natural Gas

Parallel flow heat exchanger: In parallel-flow heat exhangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. Parallel-flow Heat Exchanger

Figure shows a fluid flowing through a pipe and exchanges heat with another fluid through an annulus surrounding the pipe. In a parallel-flow heat exchanger fluids flow in the same direction. If the specific heat capacity of fluids is constant, it can be shown that:

where, dQ/dt= Rate of heat transfer between two fluids U= Overall heat transfer coefficient A= Area of the tube ΔT= Logarithmic mean temperature difference defined by:

Heat Exchanger Selection Criteria : When selecting a heat exchanger for a given duty the following points must be considered 

Material of construction



Operating pressure and temperature



Flow rates



Flow arrangements



Performance parameters--thermal effectiveness and pressure drops



Fouling tendencies



Types and phases of fluids



Maintenance, inspection, cleaning, extension, and repair possibilities



Overall economy



Fabrication technique



Intended application

85

Production Of Methanol From Natural Gas

86

Failures of Heat Exchangers : Damage to heat exchangers is frequently difficult to avoid. Some common causes of failures in heat exchangers are listed below:           

Pipe and tubing imperfections Welding Fabrication Improper design Improper materials Improper operating conditions Pitting Stress-corrosion cracking (SCC) Corrosion fatigue General corrosion Crevice corrosion

Shell And Tube Heat Exchanger: The most commonly used heat exchanger is shell and tube type. It is the ―work horse‖ of industrial process heat transfer. These exchangers are being used in 90% of the process industries now days.

Advantages of Shell and Tube Exchanger than other Exchangers :    

It is used for high heat transfer duties. It occupies less space. Its compactness is more. Its maintenance is easy.



It can be fabricated with any type of material depend up fluid properties.

Classification of Shell and tube heat exchanger: Shell and tube (or tubular) heat exchangers are used in applications where high temperature and pressure demands are significant. Shell and tube heat exchangers consist of a bundle of parallel sanitary tubes with the ends expanded in tube sheets. The bundle is contained in a cylindrical shell. Connections are such that the tubes can contain either the product or the media, depending upon the application. The major limitation is that they cannot be used to regenerate, but they can transfer lots of heat due to the surface area. There are many different types or designs of shell and tube

Production Of Methanol From Natural Gas

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heat exchangers to meet various process requirements. Shell and Tube heat exchangers can provide steady heat transfer by utilizing multiple passes of one or both fluids. Tubular heat exchangers are also employed when fluid contains particles that would block the channels of a plate heat exchanger. There are several types of shell and tube heat exchangers including U-tube, straight, spiral, and finned tube. Figure:

shell and tube heat exchanger with countercurrent flow

Figure 1. Shell-and-tube-heat exchanger with one shell pass and one tube pass; crosscounterflow operation

Maintenance aspects: Special consideration shall be given to determine if the heat exchanger shall be located in a horizontal or vertical position due to maintenance and inspection requirements. Space for tube bundle withdrawal, access for platform crane, inspection requirements may also affect the choice of heat exchanger type.

Tubeside and shellside fluid allocation:     

The criteria for fluid allocation shall be: The most corrosive to be tubeside. The higher pressure fluid to be tubeside. Severe fouling fluids shall be allocated the side which is accessible. Shellside boiling or condensation is usually preferred. • Specific pressure drop.

MAIN PARTS OF SHELL AND TUBE HEAT EXCHANGER: The principal components of an STHE are: • shell; • shell cover; • tubes;

Production Of Methanol From Natural Gas

88

• channel; • channel cover; • tube sheet; • baffles; • nozzles.

DESIGNING OF WASTE HEAT BOILER Designing of 1–2 counter flow shell & tube heat exchange in which 31095.68 lb/hr (14134.4 kg/sec) of hot Synthesis Gases leaving the bottom of a Steam Reformer at 1571oF (855 oC) and will be cooled to 725 oF (385 oC) by 13566.49 lb/hr (6166.58 kg/sec) of water coming from Steam Drum at 80 oF(176 oC) and heated to 669.2 oF (354 oC) to convert into superheated steam at 50psi. T1 = 1571 oF(855 oC) T2 = 725 oF (385 oC) t1 = 176 oF(80 oC)

t2 = 280.4 oF(138 oC) (It is the Saturation temp at 50psi)

t3 = 669.2 oF(354 oC) Steps involved in the designing are:

STEP 1:-(Heat Balance) To complete the specification, the duty (heat transfer rate) needed to be calculated. Now, For hot Synthesis Gases, The heat duty or heat transfer rate

= WCp

T

= 14134.4 x 0.707 x (1128 – 658) = 5450.54 kW (18599012 Btu/hr) Now as the a huge amount of energy is transferred to water which is converted into steam. So, here we shall consider the heat transfer with phase change. And there occurs three zones through which the water is converted into steam which are given below, 1. Pre heating zone 2. Vaporizing 3. Superheating Cp of water at 109 oC = 1 Btu/lb. oF Latent heat of vaporization = = 922.6 Btu/lb (2144kJ/Kg) Cp of steam at 246 oC

= 1.59 Btu/lb.oF

(3.7 kJ/Kg.K)

Production Of Methanol From Natural Gas Cp(t2-t1) Cp(t3 - t2)

89

= 104.4 Btu/lb (242.31kJ/Kg) = 343.9 Btu/lb. (798.42kJ/Kg)

Ti

T2

t2

t1

Now, Qcold

= m * (cp(t2 - t1)+ +Cp * (t3 - t2)) m = 13566.49 lb/hr (6166.58 kg/hr)

Now, For Pre heating zone q1 = mCp∆T = 1416342 Btu/hr For Vaporizing zone q2 = m*

= 12516868 Btu/hr For Superheating zone = q3 = mCp∆T = 4665803 Btu/hr Qcold

= 18599012 Btu/hr (5450.544 kW)

STEP :- (Weighted ∆t) ∆t1

= LMTD1 = [(T1 - t2) - (T2 - t1)] / [ ln(T1-t2) / (T2-t1)] = 867.61 oF (464.22 oC)

∆t2

= LMTD2 = [(T1 - t3) - (T2 - t2)] / [ln(T1 - t3) / (T2 - t2)] = 646.78 oF (341.38 oC)

∆t3

= LMTD3 = [(T1 - t2) - (T2 - t2)] / [ln(T1 - t2) / (T2 - t2)] = 793.85 oF (423.25 oC)

q1/∆t1 = 1632.47 Btu/hr. oF q1/∆t2 = 19361.61 Btu/hr. oF q1/∆t3 = 5877.41 Btu/hr. oF ∑ q/∆t = 26871.54 Btu/hr. oF So, Weighted ∆t = Q/∑ q/∆t = 692.15 oF (366.75 oC)

Production Of Methanol From Natural Gas

STEP 3:- (Selection of Ud (Overall design coefficient) From D.Q.Kern, Page -840 And Table #8 Or (fig 12.1 and Table 12.1 coulson – 6) Our Hot fluid is the combination of different gases i. e; gases (75%) and steam(25%) For gases to water system Ud range is: 2 to 50 Btu/hr.ft2.F (6.31 to 157.64 W/m2.K) Ud for gases = 37.5 Btu/hr.ft2.F (118.23 W/m2.K) Now For steam to water system Ud range is : 200 to 700 Btu/hr.ft2.F (630.56 to 2206.96W/m2.K) So, max Ud for hot fluid = 212.5 Btu/hr.ft2.F (669.97W/m2.K) And we select, Ud = 70 (220.69 W/m2.K)

STEP 4:- ( Total Surface Area) Q = ud A A = Q / ud

Tw Tw

A = 35.681 m2 (383.88 ft2)

Using a spilt ring floating heat exchanger for efficiency and ease of cleaning. Assume From D.Q.Kern , Page -843 And Table #10 Tube outside dia (do) = l in = 0.0254m 16 BWG, Tube inside dia (di) = 0.022 m (0.870in) From Coulson Vol. 6 & Peter & Timmerhaus 5th edition The standard length of tubes in

shell & tube exchanger is 6,8,12,16,20&24ft.

We select length of tube = 14ft = 4.268m

STEP 5:- No. of tubes: At = (area of one tube)

=

do L

= 3.14 x 0.0254 x 4.268 = 0.3406m2 (3.655ft2)

90

Production Of Methanol From Natural Gas Nt

= no of tubes = Ao / At = 35.68 / 0.3406 = 104.361

Nt

≡ 104 tubes

Tube Pitch Pt

= 1.25 do = 1.25 x 0.0254 = 0.3175 m

For 2 tubes passes, tube per pass = 52 Tube cross sectional area = At

=

/ 4 (di2)

= /4 x (0.022)2 = 0.000384 m2 (0.594 in2) So area per pass

= 52 x 3.84 x 10-4 = 0.01994 m2 (0.214 ft2)

Mass Velocity = G = W c / At = 85.89 kg/sec.m2 (63229.3 lb/hr.ft2) ut = tube side velocity = G/3600* ro = 1.769 m/sec The velocity is satisfactory between 1 to 2 m/sec.

STEP 6:- (TUBE BUNDLE AND SHELL DIA) From table 12.4 for 2 tube passes and square pitch (Coulson 6) K1 = 0.156 n1 = 2.291

91

Production Of Methanol From Natural Gas

92

For square pitch Pt = 1.25 do Db = do (Nt / K1)1/n1 = 0.0254 (104 / 0.156) 1/2.291 Tube bundle dia (Db ) = 0.434m (1.4237ft) For a spilt ring floating head exchanger the typical shell clearance from (fig 12.10 coulson 6) Shell clearance = 57 mm = 0.057m (2.204 in) So, Ds = Shell inside dia = 0.434 + 0.057 = 0.490 m

STEP 7:Re = G x di /

c

µ (water at 109 oC ) = 0.36cp (0.8712 lb/hr.ft) µ (steam at 138 OC) = 0.0324 lb/hr.ft (13.42 kg/m.sec) µ (steam at 246 OC) = 0.026 lb/hr.ft (11.1 kg/m.sec ) So, NRe1 = 5261.852 NRe2 = 141466.2 NRe3 = 171033.9

PRANDTLE NUMBER:Pr = C x

/k

C (Btu/lb. oF)

K (Btu/hr.ft. oF)

Water

1.1

0.0187

Steam

1.41

0.0241

Superheated Steam

1.59

0.0282

Production Of Methanol From Natural Gas

93

Pr1 = 51.25 Pr2 = 1.89 Pr3 = 1.51 From Kern page # 834,fig # 25 L / di = 193.10 JH1 = 320

JH2 = 640

JH3 = 570

Heat transfer Coefficient :hi = JH Re Pr1/3 (K / do) hi 1= 1493.94 w/m2.Co (263.25Btu/hr.ft2.F) hi 2 = 1299.744 W/m2.C (229.03 Btu/hr.ft2.F) hi 3 = 1256.58 W/m2.C (221.42 Btu/hr.ft2.F) Now,

hio = hi*ID/OD hio 1= 1299.73 W/m2.C

So,

hio 2 = 1130.78 W/m2.C hio 3 = 1093.23 W/m2.C

SHELL SIDE HEAT TRANSFER COEFFICIENT (Ds)

= inside dia of shell = 0.490 m

From Coulson Vol.6 Page # 650 The baffle spacing is used range from 0.2 to 1 times the shell dia. Assume take a baffle spacing = Ds * 0.8 = 0.490 * 0.8 = 0.392m This baffle spacing give good heat transfer with out too much high-pressure drop.

No. of baffles

= length of tube / baffle spacing

Production Of Methanol From Natural Gas

94

= 4.268 / 0.392 = 10.86 As

Flow Area = As = ID*C*B / 144*Pt Where, C = (Pt - OD ) = 0.0063m (0.25in) = 0.0384 m2 (0.413ft2)

As

SHELL SIDE EQUIVALENT DIA : de

= 1.27 / do (pt2 – 0.785 do2)

de

= 0.0251 (or From Fig 28 Kern)

Mass Velocity G

= W / As = 102.16 Kg/m2.sec (75214.23 lb/hr.ft2)

REYNOLD NO : Re

= Ds * G / = 77700.65

( = 0.033cp = 0.0798 lb/ft.hr)

PRANDTL NO:Pr

=C* /K C = 0.707 Btu/lb.F K = 0.12 Btu/hr.ft.F Pr = 0.471 Use 25% Cut Segmental Baffles

From fig 28 Kern JH

= 170

ho

= jH x Re x Pr1/3 (k/de)

ho

= 192.81 Btu/hr.ft2.F (1094.192 w/m2Co)

CLEAN OVERALL COEFFICIENT:Uc = (hio * ho) / (hio + ho) Uc1 = 104.68 Btu/hr.ft2.F

Production Of Methanol From Natural Gas

Uc2 = 97.98 Btu/hr.ft2.F Uc3 = 96.36 Btu/hr.ft2.F Now, A1 = q1 / (Uc1*dt1) = 15.59 ft2 A2

= q2/(Uc2*dt2) = 197.59 ft2

A3

= q3/(Uc3 * dt3) = 60.99 ft2 At = 195.56 ft2

Weighted clean overall coefficient Uc:- ∑q/At = 98.007 Btu/hr.ft2.F

DESIGN OVERALL COEFFICIENT:-

Area of heat exchanger: Surface area per linear feet = 0.2618 ft2/ft As = Nt * L * as = 381.18 ft2 (35.43 m2) Q = Ud *A*∆tm uo required

= Q / Ao

uo required

= 70.49 Btu/hr.ft2.F (222.25 w/m2.K )

Uo estimated

= 70

Btu/hr.ft2.F (220.69 W/m2.K)

Rd = (Uc - Ud) / (Uc * Ud)

= 0.006 Btu/hr.ft2.F

PRESSURE DROP: TUBE SIDE PRESSURE DROP:-

95

Production Of Methanol From Natural Gas

96

Fanning

Specific

∆Pt (psi) =

friction

Gravity (s)

(f*G2*L*n)/(5.22*E10*D*s*Φt)

factor (f) ft2/in2 Water (pre heating

0.0003

0.0179

0.495

0.00015

0.00186

0.0000377

0.00013

0.000023

0.00264

zone) at Nre1 Steam( Vaporizing Zone) at NRe2 Superheated Steam(superheating zone) at NRe3

So,

Total Pressure Drop = 0.498 psi

PRESSURE DROP FOR SHELL SIDE:For

NRe = 77700.65

From kern Fig # 29, f = 0.0004 ft2 / in2 N + 1 = 12 * L / B = 10.88 S

= 0.00529

∆Ps

= (f*Gs * 62 * Ds * (N+1)) / (5.22*E10*De * s *Φ) = 1.737 psi

SPECIFICATION SHEET Identification Item:

Heat Exchanger (WHB)

No. Required =

1

Production Of Methanol From Natural Gas

97

Function: To produce super heated steam by using the high temperature of Synthesis gas. Operation: Continuous Type: 1-2 Horizontal Shell and Tube Heat Exchanger Tube side Boiling Heat Duty = 18599012 Btu/hr Material of construction= carbon steel

Tube Side:

Tubes OD: 1 in, 16 BWG

Fluid handled cold water

104 tubes each 14 ft long

Flow rate = 13566.49 lb/hr

2 passes

Pressure = 50 lbf/in2

Square pitch

Temperature = 80oF to 669.2oF

Pressure drop = 0.498psi

Shell Side:

Shell ID =19.29 in 1 passes

Fluid handled: Synthesis Gas

Baffles spacing = 19.29 in2.

Flow rate = 31095.68 lb/hr Pressure = 7 atm Temperature = 1571oF to 725 oC

Pressure drop = 1.737 psi 25% cutoff segmented baffle

Utilities: Cold water Ud assumed = 70 Btu/hr.ft2.0F

Ud calculated = 70.49 Btu/hr.ft2.0F

Uc calculated = 98.01 Btu/hr.ft2.0F

Allowed dirt factor = Rd = 0.006

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Air-Cooled Heat Exchangers Purpose The purpose of this paper is to provide some general information on air-cooled heat exchangers and answer some of the commonly heard questions. This is a mixture of fact and opinion. Wherever the opinion is obvious to me, I have attempted to show it by use of italics.

Why use an air-cooled heat exchanger? Air-cooled heat exchangers are generally used where a process system generates heat which must be removed, but for which there is no local use. A good example is the radiator in your car. The engine components must be cooled to keep them from overheating due to friction and the combustion process. The excess heat is carried away by the water/glycol coolant mixture. A small amount of the excess heat may be used by the car's radiator to heat the interior. Most of the heat must be dissipated somehow. One of the simplest ways is to use the ambient air. Air-cooled heat exchangers (often simply called air-coolers) do not require any cooling water from a cooling tower. They are usually used when the outlet temperature is more than about 20 deg. F above the maximum expected ambient air temperature. They can be used with closer approach temperatures, but often become expensive compared to a combination of a cooling tower and a water-cooled exchanger.

Types of coolers  Water-Coolers. These coolers use a tube and shell heat exchanger .  Air-Coolers. These coolers use a fined tubed heat exchanger and motor driven fans or centrifugal blowers to move air through the cooler

SELECT A WATER-COOLER IF:     

Adequate water supplies are available from tower, city or well sources. Water supply is of good quality. Heat recovery is not practical or unimportant. Plant ambient temperatures consistently exceed 95°F. Ambient air is polluted with large dust and dirt particles

Production Of Methanol From Natural Gas

99

Water Cooler (ADVANTAGES & DISADVANTAGES)     

Offer lower capital investment. Operates more efficiently on hot summer days. Easier to operate. Does not offer summer ventilation. But cost expensive

SELECT AN AIR COOLER IF:      

Adequate water supply not available from tower or well sources. Water supply is not of good quality. Heat recovery is practical and important. Plant ambient temperature will not consistently exceed 95°F. Ambient air is not polluted with large dust and dirt particles. To make the process economic.

Air Cooler (ADVANTAGES & DISADVANTAGES)      

Somewhat more costly to purchase and operate but cheaper than water cooler. Gives less cooling on hot summer days. Consumes more electricity. Offers summer ventilation and winter supplement heating. No problem arising for thermal and chemical pollution of cooling fluids. Flexibility for any plant location and plot plan arrangement like installation over other units  Reduction of maintenance costs such as cleaning limited, when needed, to the inside of exchanger tubes.  No need of over sizing of the equipment due to tube fouling.  Easy installation by bolted assembly

What are headers? Headers are the boxes at the ends of the tubes which distribute the fluid from the piping to the tubes.

Why are some coolers forced draft and some induced draft? Which is better? It depends. The majority of air-cooled exchangers is of forced draft construction. Forced draft units are easier to manufacture and to maintain. The tube bundle is mounted on top of the plenum, so it can be easily removed and replaced. The fan shaft is short, since it does not have to extent from the drive unit through the tube bundle and plenum to the fan, as in an induced draft design. Forced draft units require slightly less horsepower since the fan are moving a lower volume of air at the inlet than they would at the outlet. If the process fluid is very hot, the cooling air is hot at the outlet. This could cause problems with some fans or fan

Production Of Methanol From Natural Gas

100

pitch actuators if the fan is exposed to very hot exhaust air. Since forced draft coolers do not have the fans exposed to hot exhaust air, they are a better choice in such cases. However, induced draft units have some advantages, too. A common problem with forced draft coolers is accidental warm air recirculation. This happens when the hot exhaust air is pulled back in to the fans. Since a forced draft cooler has a low air velocity at the exhaust from the bundle and a high velocity through the fan, a low pressure area is created around the fan, causing the hot air to be pulled over the side or end of the bay. For this same reason, there should never be a small space between the bays of a bank of forced-draft cooler. Induced draft cooler have a high exhaust air velocity through the top-mounted fan, and a lower velocity into the face of the tube bundle below. This tends to minimize the probability of accidental air recirculation. Also an induced draft plenum does not have to support the tube bundle so some weight can often be saved in this area.

Plenums, dispersion angle, and fan coverage: The API specification includes a number of paragraphs about fan coverage and dispersion angle. This is for a very good reason. The actual air coming from a fan does not distribute itself evenly at first. The most air flow is seen around the fan tip area. If you measure the air flow across the face of a tube bundle, it is often very different around the fan blade tip as opposed to the center of the fan or the corner of the bundle. However, as the plenum becomes deeper, this localized effect is diminished as the air becomes more evenly distributed. All of the heat transfer programs assume that the air is distributed perfectly evenly. The fan coverage is the ratio of the fan area to the bundle face area. The higher this ratio, the better the fan coverage. The API minimum is 40% with a 45 degree maximum dispersion angle from the fan ring to the middle of the tube bundle at the middle of the sides or the middle of the ends of each fan chamber. More fan coverage or a lower dispersion angle can improve the air distribution. (See Figure 6 on Page 14 of API 661for a sketch of this.)

What kinds of controls are used? As one might expect the best kind of control scheme depends on the application. Does the process require a very tight control on the process outlet temperature, or is it better to allow the process temperature to go down with the ambient air temperature. Is there a possibility of

Production Of Methanol From Natural Gas

101

freezing the process? Is there a pour-point problem? Is the cost of operating the fan motors a significant factor? The following is a list of some of the commonly used control devices for air coolers, but in no particular order. 1. Manually operated louvers. 2. Electrically or pneumatically operated louvers. 3. Pneumatically actuated automatic variable-pitch fans. 4. Variable-frequency fan drives. 5. Warm-air recirculation systems for freezing/pour point control in cold climates. 6. Steam coils.

Design of Air Cooler Hot fluid = Synthesis gas Cold fluid = Air P = 90 psi Mass flow rate = 28655.24 lb/hr At 90psi, dew point = 320.27 oF Inlet temp = T1 = 320.27 oF = 160.15 oC Outlet temp. = T2 = 203.41 oF o

=

95.23 C

Mean Temp. = 261.84 oF Total pressure = 90 psi = 6.12 atm Partial pressure of water = 19.03 psi = 1.29 atm

Entering Molar Composition Components

Mol %

H2

57.42

CO

10.32

CO2

7.041

N2

0.104

H2O

25.1

Weighted Temperature differnce Overall Balances: Water Vapor Pressure,pv = 19.03 psi =

1.29 atm

Production Of Methanol From Natural Gas Inert Pressure , pg

102

= 70.96 psi =

4.82 atm

Exit : Partial pressure of water at 203.4 oF = 11 psi Vapor pressure = 11 psi Inert Pressure = 79 psi Lb mol steam inlet = 534.03 Remaining lb moles = 1990.6 Lb mol steam exit = 277.17 lb moles of steam condensed = 256.85 Heat Load ; For interval 320 to 203 oF: = 894.97 Btu/lb o cp at 261 F = 0.46 Btu/lb. oF Heat of condensation = Latent heat = m* = 4137894 Btu sensible heat = m cp ∆T = 248529.4 Btu Heat from uncondensed steam = 268183.1 Btu Heat from non condensibles

= 4806459

Btu

Qc = 4137894 Qs = 5323172

So, total heat load

= 9461065

Btu/hr

Heat Duty: Q

= mcp(T1 - T2) Mean Cp = 0.71ss

Q

=

9461065

Btu/hr

Now, For gases and air system , the overall heat transfer coefficient U = 17 53 Btu/hr.ft2.F From Coulson & Richardson ,6th Vol.

Bundle Selection:First Assumption : From Table # 2.17, page #82 Bundle size.(ft) 4 * 24

Air Data:-

No of tubes 74

Face Area (ft2),FA 70

Frank L Evans Vol-2 And 2nd Edition Inside Effective Surface area(ft2) 378

Production Of Methanol From Natural Gas

103

Inlet temp. of air = 25 oC t1 = 77 oF Density at 25C & 14.7psia = 0.0716 lb/ft3 Specific heat of air = Cp = 0.55 Air face velocity = Fa = 675

Btu/lb. oF ft/min At page #82

Calculating Air Flow Rate: w = =

* Fa * FA * 60 202986 lb/hr

Average Temp. Difference of Air: (t2 - t1)avg = t2 t2

o

Q / wCp

= 84.74 F = t1 + 84.74 o = 161.74 F

LMTD: ∆t1 =

T 1 - t2 LMTD

= 158.5 oF = (∆t1 - ∆t2)/ln(∆t1/∆t2) = 141.86 oF

∆t2 = T2 - t1 = 126.4 oF

LMTD Correction:R P Correction factor Ft

= (t2 - t1)/(T1 - T2) = 0.72 oF = (T1 - T2)/(T1 - t1) = 0.48 =a/b

Where, a = {(R2 + 1)0.5/ (R - 1)] * ln[(1 - P)/(1 - RP)] b = ln [2/P - 1 - R + (R2 + 1)1/2] / {2/P - 1 - R - (R2 + 1)1/2] (1 - P)/(1 - RP) = ln[(1 - P)/(1 - RP)] = (R2 + 1)0.5/(R - 1) = [2/P - 1 - R + (R2 + 1)1/2] = {2/P - 1 - R - (R2 + 1)1/2] = So,

Ft

0.797 -0.22 -4.49 3.67 1.20

= 0.91

LMTD corrected: LMTD(cor.) = LMTD * Ft o = 129.3 F Overall Heat Transfer Coefficient:

Production Of Methanol From Natural Gas

104

Q = UaA LMTD Ua = Q/A*LMTD = 193.55 Btu/hr.ft2. oF As it is above the range mentioned,So another set of bundle is considered.

2nd Assumption: Bundle size.(ft) One 4 * 24 One 8 * 24 Total

No of tubes 74 166 148

Face Area (ft2),FA 70 181 251

Inside Effective Surface area(ft2) 378 849 1227

Now, Calculating Air Flow Rate: w = =



* Fa * FA * 60 727849.8 lb/hr

Average Temp. Difference of Air: (t2 - t1)avg = Q/wCp = 23.63 oF t2 = t1 + 23.63 t2 = 100.6 oF LMTD: ∆t1 = T1 - t2 = 219.6 oF ∆t2 = T2 - t1 = 126.4 oF LMTD = (∆t1 - ∆t2)/ln(∆t1/∆t2) = 168.7 oF LMTD Correction:R = = P = =

(t2 - t1)/(T1 - T2) 0.202 (T1 - T2)/(T1 - t1) 0.48

Correction factor Ft = (1 - P)/(1 - RP) = ln[(1 - P)/(1 - RP)] = (R2 + 1)0.5/(R - 1) = [2/P - 1 - R + (R2 + 1)1/2] = {2/P - 1 - R - (R2 + 1)1/2] = So, LMTD corrected:

Ft = 0.983 oF

0.57 -0.55 -1.279 3.98 1.94

Production Of Methanol From Natural Gas

105

LMTD(cor.) = LMTD * Ft = 165.9 oF Overall Heat Transfer Coefficient: Q = Ua A LMTD Ua = Q / A*LMTD = 46.46 Btu/hr.ft2.F It is quite satisfactory and within the range , so our 2nd assumption is right.

Heat Transfer Coefficient Calculations: Inside Film Coefficient(Tube Side) Inside film coefficients based on the number of bundles calculated are determined from,

hic = his =

0.76 (k/di) *(di3 ro2 g2 * n * L/ μ m)1/3 0.0225 (k/di)*(di G/ μ)0.8 *(cp μ /k)0.4

hic = his = k = di = ro = g = n = L =

Inside film coefficient for condensation Btu/hr.ft2.F Inside film coefficient for subcooling Btu/hr.ft2.F thermal conductivity Btu/hr.ft2.F Inside tube diameter,ft density ,lb/ft3 = 60.5 lb/ft3 Acceleration of gravity ,4.18E08,ft/hr2 No. of tubes in paralllel Length of the heat transfer ,ft

where,

Μ = μ = Viscosity ,lb/hr.ft2 m = Flow rate lb/hr G = Mass velocity ,lb/hr.ft2 Cp = Specific heat ,Btu/lb.F The outside film coefficient based on the inside surface area for the described bundle is 180Btu/hr.ft2.F at a face velocity of 675 ft/min. Using 316SS,1in. OD for 18 BWG tubes OD = = ID = =

1 in 0.083 ft 0.902 in 0.075 ft

Wall thickness = 0.049 in = 0.004 ft

G

= m * 4/ π * di2 * n = 43653.80 lb/hr.ft2

Avg. Cp = 0.71

L = 12 ft

Production Of Methanol From Natural Gas Avg. Avg. K

= 0.122 = 0.06

rmi =

xdi / km dm

rmi = x = km = dm = = km =

inside metal resistance to heat transfer Tube wall thickness,in Metal thermal conductivity ,Btu/hr.ft.oF Mean tube diameter, in 0.951 in = 0.079 ft 9.4 Btu/hr.ft.F

rmi =

0.00041 hr.ft2.oF/Btu

his = ha =

72.75 Btu/hr.ft2.F 180 Btu/hr.ft2.F

where,

So,

1/Us = 1/his + 1/ha + rmi + x/ k + f 1/Us = 1/his + 1/ha + rmi + x/k + f1 + fo where, ha = Air film Coefficient for heat transfer (based on inside surface) f = Fouling factors Inside fouling factor = fi = 0.0001 hr.ft2.F/Btu Outside fouling factor = fo = 0.001 hr.ft2.F/Btu 2 f = 0.0011 hr.ft .F/Btu So, 1/Us = Us =

0.0208 48.047 Btu/hr.ft2.F This is closed to the above determined

Now calculating corrected area,

hic

= 0.76 k/di [di3 ro2*g2 * n * L / μ *W)0.333 =

493.66 Btu/hr.ft2.F

For condensing:

1/Uc = 1/hic + 1/ha + rmi + x/k + f 1/Uc = 1/hic + 1/ha + rmi + x/k + f1 + fo 1/Uc = Uc =

0.009 109.97 Btu/hr.ft2.F

Area Requirment Determination: Ac / As = (Qc/Qs) * (Us/Uc) * (LMTDs cor./LMTDc cor.) Qc = 4137894 Btu/hr

106

Production Of Methanol From Natural Gas

107

Qs

= 5323172 Btu/hr

Ac/As

= 0.33 * (LMTDs cor./LMTDc cor.)

First Assumption : 70% of total area is used for condensation 30% of total area is used for subcooling of fluid Air Flow = 727849.8 lb/hr Air Flowc = 509494.9 lb/hr Air Flows = 218354.9 lb/hr (t2 - t1) c avg = =

Q/wCp 14.76 oF

(t2 - t1) s avg = =

Q/wCp 44.32 oF

LMTDc

= =

(∆t1 - ∆t2)/ln(∆t1/∆t2) 172.45 oF

LMTDs

= =

(∆t1 - ∆t2)/ln(∆t1/∆t2) 159.94 oF

So, Ac/As = 0.339 * (LMTDs cor./LMTDc cor.) Ac/As = 0.314 42.85% not equal to 0.314

Area Requirment Determination: Ac/As = Qc = Qs =

(Qc/Qs) * (Us/Uc) * (LMTDs cor./LMTDc cor.) 4137894 Btu/hr 5323172 Btu/hr

Ac/As =

0.339

* (LMTDs cor./LMTDc cor.)

2nd Assumption : 76% 24% Air Flow = Air Flowc = Air Flows =

of total area is used for condensation of total area is used for subcooling of fluid Q = UaA LMTD lb/hr 3144799 lb/hr 1277561 lb/hr

(t2 - t1) c avg = =

Q/wCp 2.39 oF

(t2 - t1) s avg =

Q/wCp

t2 =

2.39 oF

Production Of Methanol From Natural Gas =

7.57 oF

108 7.57 oF

t2 =

(∆t1 - ∆t2)/ln(∆t1/∆t2) 207.63 oF

LMTDc

= =

LMTDs

= (∆t1 - ∆t2)/ln(∆t1/∆t2) = 205.6 oF

So, Ac/As = 0.339 * (LMTDs cor./LMTDc cor.) Ac/As = 0.336 31.57% almost equal to 0.336425 So, Ac = 356.24 As = 856.63 Total = 1212.87

ft2

The total area caculated is 15 ft2 less than the total area of the set of bundle assumed.This is acceptable .Additional subcooling will be expected.

Tube side Pressure Drop Calculation G

= 43653.80 lb/hr.ft2

Avg μ = 0.122 a

= Outside Surface area per lin ft = 0.2618 = Inside Dia = 0.902 in = 0.075 ft Re = D * G / Avg μ = 26893.6 f = 0.00017

From Kern Table 10

D

ft2 / in2

Density of air = PM/RT = 90*29/10.726*721.8 Desity of feed = PM/RT

= 90*11.35025 / 10.726*721.8

s = Specific Gravity = Desity of feed / Desity of air = L = length of Tube

=

0.391279

24 ft

∆Pt = f * G2 * L n / 5.22*10110 *D*s* π Volumetric Flow Rate = nRT/P = 6157.1 m3/hr = P = 90 psi

216262.5

Velocity = Volumetric flow rate / area * No.of tubes

ft3/hr

Production Of Methanol From Natural Gas = 3441.9 ft/hr

109

= 0.956 ft/s

T = 721.8 oR ∆Pr = =

4n/s*(V2/2g)(62.5/144) 0.062 psi

∆PT = =

∆Pt + ∆ Pr 1.28E+00 psi

Spaecification Sheet Item No

A-1

Type

Forced Draft

No. of item

1

Function

To condense water vapors from gases

Operation

Continuous

Heat Duty

2772.6 KW

No. of tubes

240

Face Area

241 ft2

Face Velocity

675 ft/min

LMTD Corrected

74.4oC

Supposed Ud

0.074 to 0.32 KW/m2.oC

Calculated Ud

0.26 KW/m2.oC

Gases Mass Flow Rate

13025 Kg/hr

Air Flow Rate

330840 Kg/hr

Inside Effective Area

114.1m2

Calculated Area

112.7 m2

Production Of Methanol From Natural Gas

110

THEORY OF REACTOR Reactor selection criteria 1- conversion 2- selectivity 3- productivity 4- safety 5- economics 6- availability 7- flexibility 8- compatibility with processing 9- energy utilization 10- feasibility 11- investment operating cost 12- heat exchange and mixing

Reacti on rate Volume of reactor

Volume flow rate

Model

Outlet concent ration

Inlet concentr ation Contacti ng pattern

Selected Reactor: Catalytic Packed Bed Reactor Heterogeneous catalytic reactors are the most important single class of reactors utilized by chemical industry. Whether their importance is measured by the whole sale value of goods produced, the processing capacity or the overall investment in the reactors and associated peripheral equipment, there is no doubt as to prime economic role that reactors of this type play in modern technology society. Commercially significant types of Heterogeneous Catalytic Reactors. The types of reactors used in industry for carrying out heterogeneous catalytic reactions may be classified in terms of relatively small numbers of categories. One simple means of classification is in terms of relative motion of the catalyst particles or lack there of we consider.

Production Of Methanol From Natural Gas

111

Reactors in which the solid catalyst particles remain in a fixed position relative to one another (fixed bed, trickle bed and moving bed reactors). Reactors in which the particles are suspended in a fluid and are constantly moving about (fluidized bed and slurry reactors).

Fixed Bed Reactors. In its most basic form a fixed bed reactor consists of a cylindrical tube filled with catalyst pellets. Reactants How through the catalyst bed and are converted in to products. Fixed bed reactors are often revered to as packed bed reactors. They may be regarded as the work horse of the chemical industry with respect to number of reactors employed and the economic value of materials produced. Ammonia synthesis, sulphuric acid production (by oxidation of SO2 to SO3) and nitric acid production (by ammonia oxidation) are only a few of the extremely high tonnage process that make extensive use of various forms of packed bed reactors. The

catalyst

constituting

the

fixed

bed

will

generally

be employed in one of the

following configurations A single large bed Multiple horizontal beds supported on trays arranged in a Vertical stack Multiple parallel packed tubes in a single shell Multiple beds each in their own shell The use of multiple catalyst sections usually arises because of the need to maintain adequate temperature control with in the system. Other constraints leading to the use of multiple beds include those of pressure drop or adequate fluid distribution. In addition to the shell and tube configuration, some of possibilities for heat transfer to or from fixed bed reactors include the use of internal heat exchangers, annular cooling spaces or cooling thimbles are circulation of a portion of the reacting gases through an external heat exchanger. The packing itself may consist of spherical, cylindrical or randomly shaped pellets, weir screens or gauzes, crushed particles or a variety of other physical configurations. The particles usually are 0.25 to 1.0 cm in diameter. The structure of the catalyst pellets is such that the internal surface area far exceeds the superficial (external) surface area so that the contact area is in principle, independent of pellet size. To make effective use of the internal surface

Production Of Methanol From Natural Gas

112

area, one must use a pellet size that minimizes diffusional resistance with in the catalyst pellet but that also gives rise to an appropriate pressure drop across the catalyst bed. Some considerations which are important in the handling and use of catalysts for fixed bed operation in industrial situations are discussed in the catalyst hand books.

Advantages: A fixed bed reactor has many unique and value able advantages relative to other reactor types. One of its prime attributes is its simplicity, with the attendant consequence of low costs for construction, operation and maintenance relative to moving bed or (fluidized bed operation. It requires a minimum of auxiliary equipment and is particularly appropriate for use in small commercial units when investments of large sums for control, catalyst handling and supporting facilities would be economically prohibitive-. Another major advantage of this mode of Advantages Catalytic Fixed Bed Reactor

Disadvantages

The fluid flow regimes approach plug flow, so high conversion can be achieved.

The intra-particle diffusion resistance is very high.

Pressure drop is low.

Comparatively low Heat and mass transfer rates

Owing to the high holdup there is better radial mixing and channeling is not encountered. High catalyst load per unit of reactor volume

Catalyst replacement is relatively hard and requires shut down.

operation is implicit in the- u.-e of the term "fixed bed reactor" (i.e.) there are no problems in separating the catalyst from the reactor effluent stream. (In many fluidized bed systems catalyst recovery can be quite troublesome and require substantial equipment costs). An other important attribute of fixed bed reactors is the wide variation in space times at which they can be operated. This flexibility is extremely important in situations where one is likely lo encounter wide variations in the quantity or quality of the feed stock to be processed. For example high temperatures or high pressure reactions employing solid catalyst, economic considerations usually dictate that the process becomes commercially viable only when a fixed bed reactor is employed.

Production Of Methanol From Natural Gas

113

HEAD AND CLOSURE OF REACTOR The ends of cylindrical vessels are closed by heads of various types .The principle types are as follows; 1.

Flat plates and flat heads

2.

Hemispherical heads

3.

Ellipsoidal heads

4.

Torispherical heads Hemispherical, elilipsoidal and torispherical heads are collectively referred to as

domed heads. Torispherical heads are often referred to as dished ends. Torispherical heads are most commonly used end closure for vessel up to operating pressure 15 bars. Flat ends are not a structurally efficient form, and very thick plates would be required for high pressure or large diameter. A hemispherical head having cost higher than torispherical heads and are used for high pressure. Closure to 10 bar ellipsoidal heads will prove to be most economical closure to use. Ellipsoidal head is selected because pressure is 8 bars so it is more economical. Type of Reactor

Characteristics

Tubular fixed bed Reactor

Tubular reactor that is paced with solid catalyst particles

Kinds of Phases Present

Usage

Advantages

Disadvantages

1. Gas phase/ solid catalyzed

1. Used primarily in heterogeneous has phase reactions with a catalyst

1. High conversion per unit mass of catalyst

1. Undesired thermal gradients may exist

2. Gassolid rxns

2. Low operating cost 3. Continuous operation

2. Poor temperature control 3. Channeling may occur 4. Unit may be

Production Of Methanol From Natural Gas

114

difficult to service and clean

Comparison Of Continuous & Batch Packed Bed Reactors A continuous packed bed reactor has the following advantages over a batch packed bed reactor: 1. 2. 3. 4.

Easy, automatic control and operation Reduction of labor costs Stabilization of operating conditions Easy quality control of products

Chemical Kinetics Chemical kinetics is the study and discussion of chemical reactions with respect to reaction rates, effect of various variables, re-arrangement of atoms, formation of intermediates etc. There are many topics to be discussed, and each of these topics is a tool for the study of chemical reactions. By the way, the study of motion is called kinetics, from Greek kinesis, meaning movement. At the macroscopic level, we are interested in amounts reacted, formed, and the rates of their formation. At the molecular or microscopic level, the following considerations must also be made in the discusion of chemical reaction mechanism. Molecules or atoms of reactants must collide with each other in chemical reactions. The molecules must have sufficient energy (discussed in terms of activation energy) to initiate the reaction. In some cases, the orientation of the molecules during the collision must also be considered.

Reaction Rates Chemical reaction rates are the rates of change in concentrations or amounts of either reactants or products. For changes in amounts, the units can be one of mol/s, g/s, lb/s, kg/day etc. For changes in concentrations, the units can be one of mol/(L s), g/(L s), %/s etc. With respect to reaction rates, we may deal with average rates, instantaneous rates, or initial rates depending on the experimental conditions. Thermodynamics and kinetics are two factors that affect reaction rates. The study of energy gained or released in chemical reactions is called thermodynamics, and such energy data are called thermodynamic data. However, thermodynamic data have no direct correlation with reaction

Production Of Methanol From Natural Gas

115

rates, for which the kinetic factor is perhaps more important. For example, at room temperature (a wide range of temperatures), thermodynamic data indicates that diamond shall convert to graphite, but in reality, the conversion rate is so slow that most people think that diamond is forever.

Factors Influence Reaction Rates Many factors influence rates of chemical reactions, and these are summarized below. Much more extensive discussion will be given in other pages. 1. Nature of Reactants Acid-base reactions, formation of salts, and exchange of ions are fast reactions. Reactions in which large molecules are formed or break apart are usually slow. Reactions breaking strong covalent bonds are also slow. 2. Temperature Usually, the higher the temperature, the faster the reaction. The temperature effect is discussed in terms of activation energy. 3. Concentration Effect The dependences of reaction rates on concentrations are called rate laws. Rate laws are expressions of rates in terms of concentrations of reactants. Keep in mind that rate laws can be in differential forms or integrated forms. They are called differential rate laws and integrated rate laws. The following is a brief summary of topics regarding rate laws. o rate laws: differential and integrated rate laws. o Integrated rate laws: First Order Reactions Second Order Reactions Rate laws apply to homogeneous reactions in which all reactants and products are in one phase (solution). 4. Heterogeneous reactions: reactants are present in more than one phase For heterogeneous reactions, the rates are affected by surface areas. 5. Catalysts: substances used to facilitate reactions By the nature of the term, catalysts play important roles in chemical reactions.

Production Of Methanol From Natural Gas

116

Design Calculations For Packed Bed Reactor (Quench Type)

1 50 % of feed i.e ; 862.005Kmol/hr

at 230C & 50 atm H2 = CO = CO2 = N2 =

76.68% 13.78% 9.41% 0.13%

3

2

50 % of feed i.e ; 862.005 Kmol/hr at 75C H2 = CO = CO2 = N2 =

F= 1724.01Kkol/hr = 16809.05 Kg/hr

4

P = 1473.863 Kmol/hr CO CH3OH H2O CO2 HCHO N2 C2H5OH H2 C3H7OH C5H11OH CH3OCH3 CH3COOH

76.68% 13.78% 9.41% 0.13%

0.120661 0.065684 0.027296 0.082785 0.003053 0.00152 0.003814 0.693739 0.000342 0.00057 0.000457 7.87E-05

Production Of Methanol From Natural Gas

117

Heat in at Point 1:Cp of H2

= 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 = 0.766 * [ 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 ] = 22.11 + 5.87E-05 T + 2.52E-06 T2 - 6.67E-10 T3

Cp of CO

= 28.95 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 = 0.138 * [ 28.95 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09T3 = 3.98 + 5.66E-04 T + 4.89E-07 T2 - 3.06E-10 T3

Cp of CO2

= 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 = 0.094 * [ 36.11 + 4.23E-02 T - 2.89E-05 T2 +7.46E-09 T3 = 3.397 + 3.98E-03 T - 2.72E-06 T2 + 7.02E-10 T3

Cp of N2

= ( 29 + 2.20E-03 T + 5.72E-06 T2 - 2.87E-09 T3) = 0.0013 * [ 29 + 2.20E-03 T+ 5.72E-06 T2 - 2.87E-09 T3) = 0.037 + 2.86E-06 T + 7.44E-09 T2 - 3.73E-12 T3 = 29.53 + 4.61E-03 T + 3.01E-07 T2 - 2.74E-10 T3

Total

(2 230 oC 503 K Reference Temperature = 25 oC = 298 K Temperatures =

Qin

=

m1Cp dt

= 1724.01 * 0.5 *1000/3600 [ 2.95E+01 * 2.05E+02 + 4.61E-03 * 2.61E+04 + 3.01E-07 * 4050458 - 2.74E-10 * 699504844 ] = 239.44 * 6.18E+03 = 1.48E+06 Watts = 1.48E+03 KW

Heat of Reaction;CO

+

2H2

∆H = ∆H = CO2

+

CH3OH -90.77 -90770

3H2

∆H = ∆H =

KJ/g.mol KJ/K.mol CH3OH

-49.58 -49580

KJ/hr KJ/K.mol

So, X1 X2 X3

= 34.62 = 23.53 = 23.53

Total Heat Of Reaction

K.mol of CH3OH per hour K.mol of CH3OH per hour K.mol of H2O per hour =

=

(1)

-3143060 - 2333499 -5476560 Kj/hr

+ H2O

(2)

Conversion = 30%

Production Of Methanol From Natural Gas =

118

-1521.27 KW

Heat out by stream 3:Cp of H2

= 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 = 0.69 * [ 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3] = 19.98 + 5.30E-05 T + 2.28E-06 T2 - 6.03E-10 T3

Cp of CO = 28.95 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 = 0.112 * [ 28.95 + 4.11E-03 T +3.55E-06 T2 - 2.22E-09 T3 = 3.26 + 4.64E-04 T + 4.00E-07 T2 - 2.50E-10 T3 Cp of CO2 = 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 = 0.076 * [ 36.11 + 4.23E-02T - 2.89E-05 T2 +7.46E-09 T3 = 2.747 + 3.22E-03 T -2.20E-06 T2 + 5.68E-10 T3 Cp of N2

= ( 29 + 2.20E-03 T + 5.72E-06 T2 - 2.87E-09 T3) = 0.0015 * [ 29 + 2.20E-03 T + 5.72E-06 T2 - 2.87E-09 T3) = 0.0435 + 3.30E-06 T + 8.58E-09 T2 - 4.31E-12 T3

Cp of H2Og = 33.46 + 6.88E-03 T + 7.60E-06 T2 -3.59E-09 T3 = 0.031 * [33.46 + 6.88E-03 T + 7.60E-06 T2 -3.59E-09 T3 ] = 1.057 + 2.17E-04 T + 2.40E-07 T2 - 1.14E-10 T3 Cp of CH3OH = ( 42.93 + 8.30E-02 T - 1.87E-05 T2 - 8.03E-09 T3 ) = 0.077*[ 42.93 + 8.30E-02 T -1.87E-05 T2 - 8.03E-09 T3 ] = 3.344 + 6.47E-03 T - 1.46E-06 T2 - 6.26E-10 T3 Cp of HCHO

= ( 34.28 + 4.27E-02 T + 0 - 8.69E-09 T3 ) = 3.20E-03 * [ 34.28 + 4.27E-02 T + 0 - 8.69E-09 T3 ) = 1.10E-01 + 1.37E-04 T + 0.00E+00 - 2.78E-11 T3

Cp of C2H5OH = ( 61.34 + 1.57E-01 T - 8.75E-05 T2 + 1.98E-08 T3 ) = 3.80E-03*[ 61.34 + 1.57E-01 T- 8.75E-05 T2 +1.98E-08 T3 ] = 2.33E-01 + 5.97E-04 T -3.32E-07 T2 + 7.54E-11 T3 Cp NET

=

Qout

= 3.08E+01 + 1.12E-02 T - 1.06E-06 T2 + 2.24E-10 T3

∫mCpnet dt

Range :-

25

290oC

= 745.526* 1000/3600 * [ 3.08E+01 *2.65E+02 + 1.12E-02 * 3.61E+04 - 1.06E-06 * 6555792 + 2.24E-10 * 5314019375 ] = 207.0905556 * 8.55E+03 = 1.77E+06 Watts = 1.77E+03 KW

Total Heat out:∆H

= Q in

- Q out

= -1.23E+03 KW

+

Q reacion

Production Of Methanol From Natural Gas

119

Now, this is the amount of heat which should b e removed to bring the stream # 3 , again at the reaction temperature of 230C.And it is achieved by quenching with the help of stream # 2.Now it is required to find out the temperature at which stream #2 should be added . Cp of H2 = 28.84 + 7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 = 0.766 * [ 28.84 +7.65E-05 T + 3.29E-06 T2 - 8.70E-10 T3 ] = 22.114 + 5.87E-05 T + 2.52E-06 T2 - 6.67E-10 T3 Cp of CO = 28.95 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 = 0.137 * [ 28.95 + 4.11E-03 T + 3.55E-06 T2 - 2.22E-09 T3 = 3.98 + 5.66E-04 T + 4.89E-07 T2 - 3.06E-10 T3 Cp of CO2 = 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 = 0.094 * [ 36.11 + 4.23E-02 T - 2.89E-05 T2 + 7.46E-09 T3 = 3.397 + 3.98E-03 T - 2.72E-06 T2 + 7.02E-10 T3 = ( 29 + 2.20E-03 T + 5.72E-06 T2 - 2.87E-09 T3 ) = 0.0013 * [ 29 + 2.20E-03 T + 5.72E-06 T2 - 2.87E-09 T3] = 0.037 + 2.86E-06 T + 7.44E-09 T2 - 3.73E-12 T3

Cp of N2

= 29.53 + 4.61E-03 T + 3.01E-07 T2 - 2.74E-10 T3

Total Temperatures =

75 348

Qin

290 563

=

o

C k

mCp dt

= 862.005 *1000/3600 [ 2.95E+01 * -1.55E+02 + 4.61E-03 * -2.36E+04 + 3.01E-07 * -3915042 + -2.74E-10 * -691692344 ] = 239.4458 * -4.69E+03 = -1.12E+06 Watts = -1.12E+03 KW So if the feed stream #2 is added at temperature of 75 oC , then the reaction temperature of 230C is again achieved .

Energy Balance Around 2nd Bed :Outlet stream from 1st bed plus feed stream #2 will be total feed for the 2nd bed.So,

Total amount of heat in Bed # 2: Qin

= =

Heat Of Reaction:-

mCp dt 2126 KW CO = CO2 =

13.39% 9.10%

Production Of Methanol From Natural Gas CO

+ 2H2 ∆H = ∆H =

CO2

CH3OH -90.77 -90770

(1)

KJ/g.mol KJ/K.mol

+ 3H2 ∆H = ∆H =

120

CH3OH -49.58 -49580

KJ/hr KJ/K.mol

+ H2O

(2)

Conversion =

20%

So, X1 X2 X3

= 23.08 = 15.68 = 15.68

Total Heat Of Reaction

K.mol of CH3OH per hour K.mol of CH3OH per hour K.mol of H2O per hour =

= =

-2095373 -3651040 -1014.18

+ Kj/hr KW

-1555666

Heat Out By Stream 4:-

2

3

Cp of H2

= 28.84 + 7.65E-05 T + 3.29E-06 T - 8.70E-10 T 2 3 = 0.692 * [ 28.84 + 7.65E-05 T + 3.29E-06 T - 8.70E-10 T ] 2 3 = 19.98 + 5.30E-05 T + 2.28E-06 T - 6.03E-10 T

Cp of CO

= 28.95 + 4.11E-03 T + 3.55E-06 T - 2.22E-09 T 2 3 = 0.112 * [ 28.95 + 4.11E-03 T + 3.55E-06 T - 2.22E-09 T 2 3 = 3.265 + 4.64E-04 T + 4.00E-07 T - 2.50E-10 T

2

3

2

3

Cp of CO2

= 36.11+ 4.23E-02 T - 2.89E-05 T + 7.46E-09 T 2 3 = 0.0761 * [ 36.11 + 4.23E-02 T - 2.89E-05 T + 7.46E-09 T 2 3 = 2.747971 + 3.22E-03 T - 2.20E-06 T + 5.68E-10 T

Cp of N2

= ( 29 + 2.20E-03 T + 5.72E-06 T - 2.87E-09 T ) 2 3 = 0.0015 * [ 29 + 2.20E-03 T + 5.72E-06 T - 2.87E-09 T ) 2 3 = 0.0435 + 3.30E-06 T + 8.58E-09 T - 4.31E-12 T

Cp of H2Og

= 33.46 + 6.88E-03 T + 7.60E-06 T - 3.59E-09 T 2 3 = 0.0316 * [ 33.46 + 6.88E-03 T + 7.60E-06 T - 3.59E-09 T 2 3 = 1.057 + 2.17E-04 T + 2.40E-07 T 1.14E-10 T

2

3

2

3

2

3

Cp of CH3OH = ( 42.93 + 8.30E-02 T - 1.87E-05 T - 8.03E-09 T ) 2 3 = 0.077 * [ 42.93 + 8.30E-02 T - 1.87E-05 T - 8.03E-09 T ) 2 3 = 3.344 + 6.47E-03 T 1.46E-06 T - 6.26E-10 T Cp of HCHO

3

= ( 34.28 + 4.27E-02 T + 0 - 8.69E-09 T ) 3 = 3.20E-03 * [ 34.28 + 4.27E-02 T + 0 - 8.69E-09 T ) 3 = 1.10E-01 + 1.37E-04 T + 0.00E+00 - 2.78E-11 T 2

3

Cp of C2H5OH = ( 61.34 + 1.57E-01 T - 8.75E-05 T + 1.98E-08 T ) 2 3 = 3.80E-03 * [ 61.34 + 1.57E-01 T - 8.75E-05 T +1.98E-08 T ) 2 3 = 2.33E-01 + 5.97E-04 T - 3.32E-07 T + 7.54E-11 T Cp NET

= 3.08E+01 + 1.12E-02 T - 1.06E-06 T

2

+ 2.24E-10 T

3

Production Of Methanol From Natural Gas

=

Qout

∫mCpnet dt

= = = =

∆H

= Qin

- Qout

121 o

Range :-25 to 290 C 728.33 * 1000/3600 [ 3.08E+01 * 2.65E+02 +1.12E-02 * 3.61E+04 - 1 .06E-06 *6555792 + 2.24E-10 * 5.31E+09 ] 202.3139 * 8.55E+03 1.73E+06 Watts 1.73E+03 KW

+

Qreacion

= -1.37E+03 KW

So Total Heat Out At Point 4 :-1.37 + -1.12 = -2.53E+03 KW

Reactor Design With Space Velocity:Type:Catalyst: Catalyst size : Bed Void Fraction Bulke density ;

Packed Bed Reactor Cu-Zn-Al 3 mm 0.5 1120 Kg/m3

Operating Conditions:Temperature = To = 230 o C = 503 K Pressure = P = 50 atm Mass flow rate in = 16800.64 Kg/hr = 1732.025 K.mol/hr Average Mol.wt = 9.7 Density = Density =

PM/RT 11.30216 Kg/m3

R =

0.08205 m3*atm/k-mol*K

Now, The compositions of the components entering into the reactor are: molar flow rate conc.(K.mol/m3) H2 CO CO2 N2

= = = =

76% 13.50% 9% 1.50%

1316.33 233.82 155.88 25.98

k.mol/hr k.mol/hr k.mol/hr k.mol/hr

Space Velocity = 250 hr-1 = 0.069 sec-1 Residence time = 14.4 sec Now Volumetric Flow Rate = q = Mass flow rate/density

0.885 0.157 0.104 0.017

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122

= 1429.65 m3/hr = 50481.0 ft3/hr Volume of bed

= Vol. flow rate * residence time = 201.92 ft3 = 5.71 m3

And finally, Toal reactor volume

= Vol.of bed * (1+ void fraction) = 403.84 ft3 = 11.43 m3

Diameter and Length of reactor:We assume, L/D = 5 L = 5 *D Volume = Area * Length

Area

= 0.785 D2

403.84 = 0.785 D2 * 5 * D 403.84 = 3.925 D3 D3 = 102.89 ft3 D = 4.67 ft radius = r = 2.339 ft r2 = 5.47 ft2 L = 23.39 ft And = 7.13 m Extra length added for ceramic balls to support the catalyst & gap between the beds = 20% So, Total Length = 28.07 ft = 8.56 m Area

= 0.785 * 21.88 = 17.18 ft2 = 1.59 m2 Total Volume = 1.59 * 8.56 = 13.67 m3 Weight of Catalyst

= Vol. of bed * bulk density of catalyst

Taking no of beds So, Catalyst per bed

= =

226155.2 lb 2

=

113077.57 lbs

Wall thickness for cylendrical shell:t = Working pressure Design pressure

= =

Pi*Di /(2fJ - Pi) + c 50 1.1

atm * 50

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123

= 55 atm = 5.57 N/mm2 Inside Dia (without wall thickness) = 4.68 ft = 142.60 cm = 1426.05 mm Effiiciency of joint = j = 0.85 Corrosion Allowance = 0.3 mm Allowable Working stress = 107 N/mm2 = 1056.00 atm So, t = 45.07 + 0.3 = 45.37 mm = 4.53 cm = 0.148 ft

Weight of reactor Weight of shell = pi * dia * length * thickness * desnity Density of Stainless steel 316 = 498 lb/ft3 = 25476.32 lbs Weight of heads

= 2*[2*pi * r2 *thickness * density] = 2547.6 * 2 = 5095.26 lbs

so, wt of catalyst = 226155.16 lb Total weight = 256726.7 lbs = 116693.97 Kg Now, Extra weight due to nozzles, amnholes , saddles etc. For vertical position = 20% increase So, Actual total weight = 308072.09 lbs = 140.03 tons

Calculation of Pressure Drop: From Ergun’s Equation

P L

G 1 gc Dp

3

150 1 Dp

1.75G

Where mass velocity of feed = G = Mass flow rate / Cross sectional area = 10520.20 kg/hr.m2 = 0.597 lb/ft2.sec Partical diameter = DP = 3 mm = 0.0098 ft = 0.003 m gc = 1.30E+07 m.Kgm/hr2.Kgf = 9.81 lbm*ft/lbf*sec2 Avg, viscosity =

1.12E-05 lb/ft.sec = 0.060 kg/m.sec

Production Of Methanol From Natural Gas Avg . Density = =

124

11.751 Kg/m3 0.732 lb/ft3

So, after putting all the values in the formula, we get Pressure drop = ∆P = 70.61 lb/ft2 = 0.033 atm

= 0.490 psi

Design With Kinetics: Now if the kinetics from the literature is available and in the following form,

-r co = k pco pH2 2 Order of Reaction = 3 Then first convert it into the concentration form by using the ideal gas relation and for the gases variable volume factor ―ε ‗ is used, and final relation for the above equation takes the shape like this,

r co =

kR3T3 Cco3[(1 - Xa)/(1 + ε Xa)*(M- 2Xa)2/(1 + ε Xa)2 * (To/T)

Where To / T is added to count for the temperature variations. More the value of K is also given with the kinetics in the literature as such, k =

7.60E-06 mol (kg cat.)-1 min-1 atm-3 at 230ºC

Ao = CO Bo = H2 M = Bo/Ao = CH2/Cco Now , the design equation for the packed bed is ,

C Ao

W FAo

(From Octave Levenspiel. Page # 46)

XA

dX A rA 0

Now putting the all values in the above equation and getting the area under the curve for solving the complex equation. And finally the value of the wight of the catalyst is obtained and further procedure is same as above mentioned.

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125

Specification Sheet Equipment no.

R-1

No. of Units

1

Material of construction

Carbon steel

Type

Catalytic fixed bed

Process

Adiabatic

Operation

Continuous

Catalyst Size

3mm

Catalyst porosity

0.5

Catalyst Type Shape

Cu– ZnO– Al(60%-30%10%) Cylindrical

Residence Time

0.033 hr

Space Velocity

30.3 hr-1

Conversion

50%

Fluid handled

Synthesis Gas

Operating Pressure

50 atm

Operating Temp.

230oC

Length

15.92 m

Shell Diameter

2.65 m

Thickness

6.9 cm

Volume

88.04 m3

Head thickness

6.9 cm Torispherical

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126

Basic principle and objective The primary job of the gas liquid separators is to separate vapor and liquid, but they may also serve as liquid surge drums. The basic design principle of a vapor liquid separator is to provide a sufficiently low gas velocity so that liquid and vapor will separate. The separation of the mixture is actually done due to the actions of gravity and impaction and also on density basis.

Types of the vapor liquid separators Knockout drums. Vertical gas liquid separator. Horizontal gas liquid separator.

Selection criteria Length to diameter ratio. Separator liquid surge characteristics. Gas to liquid ratio. Space limitations.

Types OF Mist Eliminator The mist eliminators are of two types Knitted wire mesh Vane type mist eliminator

Vane Type Mist Eliminators Vane eliminators consists of closely spaced plates mist strikes on adjacent vane there they held by surface force.

Production Of Methanol From Natural Gas

Mesh Eliminators Mesh eliminators are made up of plastic or stainless steel wire with diameter of 0.006-0.011 inch

Application of mist eliminators Proper application of mist eliminator is based on understanding how they work. Vane and mesh devices both employ the same mechanism—known as inertial impaction

127

Production Of Methanol From Natural Gas

128

Selection of mist eliminator The efficiency of vane mist eliminators is generally acceptable only for droplets larger than 10 or 20 microns. A vane unit is generally more expensive than a mesh pad in the same application.

Separator design Diagram of separator

Production Of Methanol From Natural Gas

Design considerations Pressure = 50atm Temperature=308.15 K Mass flow rate of liquid,ML=7817.45 Kg/hr Mass flow rate of vapor,MV = 8545.48 Kg/hr Liquid Density, ρ = 811.09 kg/m3 L

Vapor Density, ρV = 19.34 kg/m3 Volumetric flow rate of vapors = Qv =.122 m3/sec Volumetric flow rate of liquid = QL = 0.0027 m3/sec

Step 1: Vapor liquid separation factor: The term used for the separation factor is (ML/ MV). (ρV / ρL)0.5 =0.142 From fig find ―K‖ = 0.27 ft/sec = 0.082m/sec

Step 2: Calculate the maximum velocity for the system: Vmax

0.50

= K [(ρL - ρV) / ρV] 0.50 = 0.082 [(811.09 – 19.34)/19.34 ] = 0.524 m/sec

Step 3: Minimum vessel cross-sectional area Amin = QV/ Vmax = 0.122 / 0.524 = 0.235 m2

Step 4: Diameter of the vessel is calculated as

129

Production Of Methanol From Natural Gas

130

0.5

= [4 Amin / ρ] = 0.547 m D = Dmin + 0.1524 = 0.547 + 0.1524 = 0.7 m Dmin

Step 5: Liquid level Assume residence time = 4min Vessel volume, V = QL ( residence time) = 0.0027 60 4 = 0.643 m3/sec LL = V 4/( D2) = 1.51 m

Step 6: The height of separator can be calculated by following formula L = LL+ 1.5D + 0. 46 = 3.07 m

Step 7: Calculate L/D ratio L/D = 3.07 / .70 = 4.38

Specification sheet Unit name

Liquid-gas separator

No. required

1

Material of construction

Stainless steel

Type of Mist Eliminator

Mesh Pad

Diameter

0.7m

Length

3.07m

Pressure

50 atm

Temperature

308.15K

Fluid handled

Liquid gas mixture

Liquid level

1.51 m

Holding Time

4 min

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131

DISTILLATION ―A process in which liquid and vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat.‖ Distillation is based on the fact that the vapor of a boiling mixture will be richer in the components that have lower boiling points. Therefore, when this vapor is cooled and condensed, the condensate will contain more volatile components. At the same time, the original mixture will contain more of the less volatile material. All distillation involve two processes: vaporization followed by condensation. In a distillation a liquid mixture is heated until it is boiled, then the vapor above the boiling liquid is removed, condensed and collected as a liquid distillate. The molecules in a liquid are in constant motion and have a tendency to escape from the liquid‘s surface and enter the gaseous phase. The pressure exerted by these gaseous molecules is called the vapor pressure of the liquid. The temperature at which the liquid‘s vapor pressure is equal to external pressure over the liquid is called the boiling point of a liquid. Separation of components from a liquid mixture via distillation depends on the differences in boiling points of the individual components. also, depending upon the concentrations of the components present; the liquid mixture will have different boiling point characteristics. Therefore, distillation depends upon the vapor pressure of liquid mixtures. Distillation columns are designed to achieve this separation efficiently. Although many people have a fair idea what ―distillation‖ means, the important aspects that seem to be missed from the manufacturing point of view are that:Distillation is the most common separation technique.It can contribute to more than 50% of plant operating costs. It consumes enormous amounts of energy, both in terms of cooling and heating requirements.

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132

The best way to reduce operating costs of existing units is to improve their efficiency and operation via process optimization and control. To achieve this improvement, a thorough understanding of distillation principles and how distillation systems are designed is essential.

TYPES OF DISTILLATION Extractive distillation:Extractive distillation is defined as distillation in the presence of a miscible, high boiling, relatively non-volatile component, the solvent, that forms no azeotrope with the other components in the mixture. Used for mixtures having a low value of relative volatility, nearing unity. Mixtures having a low relative volatility can not be separated by simple distillation because the volatility of both the components in the mixture is nearly the same causing them to evaporate at nearly the same temperature to a similar extent, whereby reducing the chances of separating either by condensation.

Flash Distillation In the flash evaporation process is when the liquid is preheated and is then subjected to a pressure below its vapor pressure causing boiling or flashing to occur. Sea water is first heated in tubes and is then put in a chamber with a vapor pressure lower than in the heating tubes and the liquid evaporates. The vapors flash off the warm liquid and the salts exit with the remaining water. The process seems inefficient because the evaporation of a small amount causes the temperature to drop dramatically. For example, when only 7.1% of the liquid is evaporated off, the temperature drops 40 degrees, from 100 to 60 degrees Celcius. However, since the design is so simple, it has become a close competitor to multiple-effect evaporation economically. This is true especially in larger plants.

Steam distillation:Steam distillation is a special type of distillation (a separation process) for temperature sensitive materials like natural aromatic compounds. Steam distillation is employed in the manufacture of etherial oils for, for instance, perfumes. In this method steam is guided over the plant material containing the desired oils. It is also employed in the synthetic procedures of complex organic compounds.

Vacuum distillation:Vacuum distillation is a method of distillation whereby the pressure above the solution to be distilled is reduced to less than one Atmosphere (unit) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points.) Vacuum distillation is used with or without heating the solution; some distillation processes use both vacuum and thermal action. Vacuum distillation works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure (atmospheric pressure above it or pressure in the

Production Of Methanol From Natural Gas

133

distillation apparatus.) In standard thermal distillation, the vapor pressure is increased. In vacuum distillation, the ambient pressure is decreased.

Azeotropic distillation:Azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. A common distillation with an azeotrope is the distillation of ethanol and water. Using normal distillation techniques, ethanol can only be purified to approximately 95% (hence the 95% (190 proof) strength of some commercially available grain alcohols).

PLATE/TRAY TYPE COLUMNS :To optimize the mass transfer between vapor and liquid in thermal separations, various types of plates are used. Usually, trays are horizontal, flat, perforated to offer vapor passages, specially prefabricated metal circular sheets, which are placed at a regular in a vertical cylindrical column. On these elements, the reflux liquid and encounters the vapor which must pass through it.

distance circulates

Trays have two main parts: 1) The part where vapor (gas) and liquid are being contacted; the contacting area. And 2) The part where vapor and liquid are separated, after having been contacted; the down comer area.

TRAY DEVICES:In the design of the distillation column, the most important step is estimation of number of

Production Of Methanol From Natural Gas

134

stages (plates) or trays.

CLASSIFICATION OF TRAYS:Classification of trays is based on:     

Type of plate used in the contacting area Type and number of down comers making up the down comer area Direction and path of the liquid flowing across the contacting area of the tray Vapor (gas) flow direction through the (orifices in) the plate Presence of baffles, packing or other additions to the contacting area to improve the separation performance of the tray.

Selection Criteria of any tray:The principal factors to consider when comparing performance of three types of plate i.e., sieve plate, valve tray, bubble-cap tray are as follows:-

Cost:Cost of plate depends upon material of construction used. For mild steel, the ratio of cost between plates is Sieve plate 3

:

valve plate

:

1.5

:

bubble-cap plate :

1.0 .

Capacity:There is little difference in the capacity rating of the three types (the diameter of the column required for a given flow rate).The ranking is Sieve tray

>

valve tray

>

bubble-cap tray

Operating Range:Operating range means the range of vapor and liquid rates over which the plate will operate satisfactorily. Bubble-cap plates have a positive seal for liquid and so operate at very low vapor flow rates. Sieve trays rely on the vapor flow rate through holes to hold the liquid on the plate. And cannot operate at very low vapor rates. But with good design, it will give satisfactorily results.

Pressure drop:It is an important parameter for plate design, particularly for vacuum process. It depends upon the plate design.On the basis of pressure drop the ranking is

Production Of Methanol From Natural Gas

Bubble-cap tray >

valve tray

>

135

sieve tray

. Type Of Plates Used In The Contacting Area:There are mainly three types of trays. 1. Sieve Trays. 2. Valve Trays. 3. Bubble Cap Trays.

Sieve Trays :-( Perforated Trays):Advantages:They are simple to design. These trays are very cheap. Sieve trays give lower pressure drop. It gives high efficiency. They give us efficient mass transfer.

Disadvantages:When misoperation occurs, mass transfer ceases. Due to misoperation, efficiency drops because of weeping. Misoperations are foaming and forth formation depending upon the nature of liquid. It is also sometimes unacceptable for low liquid loads when weeping has to be minimized.

Valve Trays:Advantages:Although slightly more expensive than Sieve Trays. They can operate over a wide range of pressure. It gives low pressure drop. Valve trays may be uses for a wide range of flow rates. Because of their flexibility and price, they are replacing bubble cap trays. It can operate at large capacities. Their cost is less than bubble cap trays. In this, entrainment and weeping are controllable.

Production Of Methanol From Natural Gas

136

Disadvantages:It pressure drop is greater than sieve tray. Their cost is 20% higher than sieve plates.

Bubble Caps:Advantages:It is widely used due to its performance. Entrainment is controlled here. They are capable of dealing with very low liquid rates. Weeping is also controlled in bubble cap trays. They are useful for operation at low reflux. They are required to provide maximum tray flexibility.

Disadvantages:Bubble Caps are a relatively high cost than both sieve and valve trays. Capacity of bubble cap trays is also lower than both sieve and valve trays. It gives high pressure drop. They cause problems in large columns. Their construction is very complicated.

BASIC DISTILLATION EQUIPMENT AND OPERATION Main Components of Distillation Columns Distillation columns are made up of several components, each of which is used either to transfer heat energy or enhance material transfer. A typical distillation contains Column internals such as trays/plates and/or packings which are used to enhance component separations everal major components a vertical shell where the separation of liquid components is carried out a reboiler to provide the necessary vaporisation for the distillation process a condenser to cool and condense the vapour leaving the top of the column a reflux drum to hold the condensed vapour from the top of the column so that liquid (reflux) can be recycled back to the column

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137

The vertical shell houses the column internals and together with the condenser and reboiler, constitute a distillation column. A schematic of a typical distillation unit with a single feed and two product streams is shown below: Basic Operation and Terminology

The liquid mixture that is to be processed is known as the feed and this is introduced usually somewhere near the middle of the column to a tray known as the feed tray. The feed tray divides the column into a top (enriching or rectification) section and a bottom (stripping) section. The feed flows down the column where it is collected at the bottom in the reboiler. Thus, there are internal flows of vapour and liquid within the column as well as external flows of feeds and product streams, into and out of the column. The vapour moves up the column, and as it exits the top of the unit, it is cooled by a condenser. The condensed liquid is stored in a holding vessel known as the reflux drum. Some of this liquid is recycled back to the top of the column and this is called the reflux. The condensed liquid that is removed from the system is known as the distillate or top product. Heat is supplied to the reboiler to generate vapour. The source of heat input can be any suitable fluid, although in most chemical plants this is normally steam. In refineries, the heating source may be the output streams of other columns. The vapour raised in the reboiler is reintroduced into the unit at the bottom of the column. The liquid removed from the reboiler is known as the bottoms product or simply, bottoms..

Packings Packings are passive devices that are designed to increase the interfacial area for vapourliquid contact. The following pictures show 3 different types of packings

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138

These strangely shaped pieces are supposed to impart good vapour-liquid contact when a particular type is placed together in numbers, without causing excessive pressure-drop across a packed section. This is important because a high pressure drop would mean that more energy is required to drive the vapour up the distillation column.

Packings versus Trays A tray column that is facing throughput problems may be de-bottlenecked by replacing a section of trays with packings. This is because: packings provide extra inter-facial area for liquid-vapour contact efficiency of separation is increased for the same column height packed columns are shorter than trayed columns Packed columns are called continuous-contact columns while trayed columns are called staged-contact columns because of the manner in which vapour and liquid are contacted.

DISTILLATION COLUMN DESIGN Feed Components wt% CH3OH H2O

=

7722.917 Kg/hr

Kg/hr 6240.6 1404.02

Mol. Wt. 32 18

=

274.36 K.mole/hr K.mole 195.02 78

Mole% 71.08 28.60

About (71.08 + 28.43 = 99.51%) of the feed consists of methanol and water. Thus binary distillation can be assumed. Distillate = 6238 Kg/hr = 195.53 K.mole/hr Component wt% CH3OH H2O

Kg/hr

Mol. Wt.

K.mole

Mole%

6228.18 9

32 18

194.63 0.5

99.65 0.348

Production Of Methanol From Natural Gas

139

Waste = 1484.68 Kg/hr = 78.84 K.mole Component wt% H2O CH3COOH

Kg/hr

Mol. Wt

K.mole

Mole%

1395.166 23.1526

18 60

77.51 0.3858

98.31 0.49

We get Xf = 0.71 Xd = 0.9974 Xw = 0.005 From Unit Operation by McCabe &Smith (page # 583) Equilibrium Data for Methanol – Water is given as follows: X Y

0.1 0.2 0.3 0.4 0.5 0.417 0.579 0.669 0.729 0.78

0.6 0.7 0.8 0.9 1.0 0.825 0.871 0.915 0.9591 1.0

Where X = Mole fraction of M.V.C in Liquid phase Y = Mole fraction of M.V.C in Vapor phase Now after drawing equilibrium curve

Xd - Yf Yf - Xf Minimum Reflux Ratio = Rm = = (0.9974 – 0.874)/(0.874 – 0.7) = 0.75244 Reflux Ratio = R = 1.5* Rm = 1.5 * 0.75244 =1.13 The Points Of Top Operating Line:(0 , Xd/(R+1)) (0 , 0.486)

; (Xd , Xd) ; (0.9974 , 0.9974)

The Bottom Operating Line Points :-

(Xw , Xw)

=

(0 , 0)

This point joins where the top operating line cut the feed line

Production Of Methanol From Natural Gas

140

From Graph

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

q. l i ne T op Oper at i ong Li ne

x=y

B ot t om Oper at i ng Li ne

0

0.2

0.4

0.6

0.8

1

The ideal number of plates / stages = 11

Efficiency And Total Number Of Real Stages From PETER and TIMMERHAUS (page # 665) Eo = 17 – 61.1 Log μf, avg Where Eo = Overall column efficiency percent. Average temperature of column = 87.5 oC = 189.5 oF Viscosity of Methanol

=

0.257 cp

Viscosity of Water

=

0.325 cp

μ

= =

(0.7108 * 0.257)

0.257 cp

Now Eo

= =

17 – 61.1 Log (0.257) 55.25 %

Actual number of trays in column = 11 / 0.5525 = 20

+

(0.2843 * 0.325)

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141

Feed should be entered on plate # 7 Maximum vapor flow rate in rectifying section = Vn = 416.46 kg mole/hr Maximum liquid flow rate in rectifying section = Ln = 220.7 kg mole/hr Maximum vapor flow rate in stripping section = Vm = 416.47 kg mole/hr Maximum liquid flow rate in stripping section = Lm = 495.31 kg mole/hr Plate spacing initial estimate = 0.5m = 18in Calculation of column diameter based on flooding velocity Calculate FLV = liquid vapor flow factor FW

LW VW

V L

LW = liquid mass flow rate kg/s VW = vapor mass flow rate, kg/s

FWTop

220.7 1.15 416.46 750 = 0.022

FLV Bottom

495.31 .5 416.47 962 = 0.04

From figure 11.27 Coulson and Richardson vol.6 t1 = a constant obtained from fig 11.27 K1 Top = 0.08

K1 Bottom = 0.085

Flooding Velocity: Uf = flooding velocity 0.2

Uf

K1

L

V V

20

Production Of Methanol From Natural Gas

U f bottom

0.085

142 0.2

962 0.5 58 0.5 20

= 4.3 m/s

U f Top

750 1.15 19 0.08 1.15 20

0.2

= 2.17 m/s Based on 85% flooding velocity

Superficial Vapor Velocity

Maximum volumetric Flow rate

Uˆ base

4.3 0.85 3.5 7 m/s

Uˆ v,top

2.17 0.85 1.9 m/s

=

V/

Top

=

3.21 m3/sec

Bottom

=

6.5 m3/sec

V

Net Area Required Maximum volume metric flow rate / superficial velocity Top

=

3.21/1.9

Bottom

=

6.5/3.57

=

1.6m2

= 1.8 m2

As first trial take down comer area as 12% of the total. Column cross sectional area Base

=

1.8/0.88

=

2.01 m2

Top

=

1.6/0.88

=

1.8 m2

Column Diameter Diameter =√ (4 × Area / ) Area =

4

d2

1.81 4 Top

2.01 4 ,

Bottom

Production Of Methanol From Natural Gas = 1.5 m

143 = 1.60 m

From fig.11.28 Coulson Volume no.6

Our required flow pattern is single pass Provisional Plate Design Column diameter (base)

=

Column Area Ac

1.6 m

4

Ac

d2 2.01 m2

=

0.12 2.01

Downcomer area Ad

Net area An

Active area Aa

Hole area Ah take 10% Aa

=

0.23 m2

=

Ac – Ad

=

2.01– 0.23

=

1.78 m2

=

Ac – 2Ad

=

2.01 – 2(0.23)

=

1.55m2

=

0.1 × 1.55 = 0.155 m2

Weir length Ad / Ac = 0.23 / 2.01 = 0.12 (From figure 11.31 vol.6) lw / dc

=

lw

0.76

1.6 lw

0.76

=

1.22 m

Take weir height , hw

=

50 mm

Hole diameter, dh

=

5 mm

Plate thickness

=

5 mm

Production Of Methanol From Natural Gas

144

Check Weeping Lm’

Maximum liquid rate

=

Minimum liquid rate at 70% turn down

495.31× 18 / 3600 = 2.48 kg/sec 0.7 2.48

= 1.74s kg/sec how

= weir crust Maximum how

2.48 750 962 1.22

2/3

= 12.45 mm liquid Minimum how

750

1.74 962 1.22

2/3

= 9.8 mm liquid At minimum hw + how = 50 + 9.8 = 59.8 mm liquid From fig 11.30, Coulson and Richardson Vol.6 K2 = 30.4

 U min

K2

 U min

30.4 0.9 25.4 5 1/ 2 0.5

0.9 25.4 d h v

1/ 2

= 14.2 m/s Actual minimum vapour velocity

min. vapour rate Ah 0.70 6.5 0.155 = 28.1 m/s

So minimum vapor rate will be well above the weep point.

Production Of Methanol From Natural Gas

145

Plate Pressure Drop Dry Plate Drop Max. Vapour velocity through holes

Uˆ h = Volumetric Flow Rate / Hole Area 6.5 0.155

Uˆ h

38m / s

Fom fig. 11.43 for plate thickness/hole dia = 5/5 = 1 and

Ah Ap Co

Ah Aa

.155 1.55

0.1

= 0.84

From Eq.11.88 Coulson vol.6

Uˆ 51 h Co

hd

hd

38 51 0.84

2

2 V L

0.5 = 40.2 mm liquid 962

Residual Head hr

12.5 10 3 962

12.9mm liquid mm liquid

Total Pressure Drop ht = hd + (hw + how) + hr Total pressure drop = 40.2+ (50 + 12.45) + 12.9 ht = 115.55 mm liquid

Production Of Methanol From Natural Gas

146

Down comer Liquid Backup Take hap = hw – 10 = 40 mm Area under apron ―Aap‖ 1.22 40 10

3

= 0.0488 m2 As this is less than Ad use Aap in eq. 11.92 coulson vol.6 i.e, 2

hdc

hdc

166

l wd L Aap

2.48 166 962 0.0488

2

= 0.463 mm liq.

Backup in down comer hb

= (hw + how) + ht + hdc

hb

=(50 + 12.45) + 155.55 + 0.463 = 218.46 mm liq. = 0.218 m liq.

hb < ½ (Tray spacing + weir height) 0.218<1/2(0.5+0.05) So tray spacing is acceptable

Check Residence Time tr

tr

Ad

hbc  L Lwd

0.23 0.218 962 2.48 = 12.8 sec > 3 sec. so, result is satisfactory

Check Entrainment Uv

= Maximum Volumetric Flow Rate of vapors/Net Area

Production Of Methanol From Natural Gas

147

UV

=

6.5/ 1.78

=

3.42 m/s

Percent flooding

=

3.42/4.3

=

0.795 = 79.5 %

FLV(base) = 0.04

From fig. 11.29 coulson vol.6

Fractional Entrainment

= 0.076 well below 0.1 Satisfactory

Trial Lay Out Use cartridge type construction. Allow 50 mm imperforated strip round plate edge; 50 mm wide calming zone. From fig. 11.32

Lw/Dc =

0.76

Q

99o

=

Angle subtended at plate edge by imperforated strip = 180 – 99 = 81o Mean length, imperforated edge strip:

tr

1.175 50 10

81 180

3

50 10

3

1.175 50 10

3

Area of imperforated edge strip Ap/ Mean length of calming zone Area of calming zone Acal

1.59

2 0.83 50 10

3

1.59) sin

99 2

0.0168m2 0.83m

0.080m2

Total area of perforations, Ap = Aa – Ap/ - Acal = 0.859 – 0.016 – 0.080 =0.763 m2 Ah Ap

0.0859 0.763

0.112

From fig. 11.33 Coulson vol.6 lp/dh = 2.7

Satisfactory within 2.5 - 4.0

No of Holes Area of one hole

1.964 10

5

Number of Holes = Hole Area / Area of one hole

Production Of Methanol From Natural Gas

No. of holes

0.155 1.964 10

= 6620

5

Specification Sheet • Equipment

=

Distillation column

• Operation

=

Continuous

• Function

=

Final production of Methanol

• No.of Trays

=

20

• Efficiency

=

55.25%

• R

=

1.13

• Top Diameter

=

1.5 m

• Bottom Dia.

=

1.6 m

• Height

=

10.06 m

• No. of Holes

=

6620

• Superficial velocity =

80% of Flooding velocity

• No weeping • Fractional entrainment =

0.076

• Pressure Drop

=

115.55 mm liquid

• Tray Thickness

=

5mm

• Weir Height

=

50 mm

• Weir Length

=

1.2 m

• Tray Spacing

=

1.5ft

• Area of one Hole = • Total Hole Area

0.0000196 m2

= 0.115 m2

• Down Comer Area = 0.23 m2

148

Production Of Methanol From Natural Gas

149

Production Of Methanol From Natural Gas

150

Compressor Selection A compressor selection study shall be made in the conceptual engineering phase i.e. by use of computerised selection programs and data bases. The results from the preliminary selection may include some or all of the following variables: Number and types of compressor casings. Number of impellers in each casing. Rotational speeds. Type of seals. Frame size. Performance data. Rating and operating conditions. Rotor stability. Rotor dynamic and aerodynamic behaviour. Sparing alternatives. Re-wheeling strategy. Advanced seals and bearings. Type of base plate. Weight & space requirements. Normally we use centrifugal or reciprocating compressor in our refrigeration process. For high pressure requirement we usually use reciprocating compressors and for low pressure requirement we prefer centrifugal compressor. Over reciprocating compressor due to its some advantages We selected centrifugal compressor because here we need a low pressure for saturation of our refrigerant. The Centrifugal Compressor forRefrigeration system was designed and developed by Dr. Willis H.Carrier in 1922.this compressor increases the pressure of low pressure vapor refrigerant to a high pressure by centrifugal force.

Hermetic sealed compressors:When the compressor and motor operate on the same shaft and are enclosed in a common casing, they are known as HERMETIC SEALED COMPRESSORS. The advantages of the hermetic sealed compressors are: The leakage of refrigerant is completely prevented It is less noisy It requires small space because of compactness The lubrication is simple as the motor and compressor operate in a sealed space with lubricating oil.

Advantages of Centrifugal Compressor over Reciprocating Compressor

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151

Since the centrifugal compressors have no valves, cylinders, connecting rod etc therefore the working life of these compressors is more as compared to reciprocating compressors. These compressors operate with little or no vibrations as there are no unbalanced masses. The operation of centrifugal compressor is quiet and clean The centrifugal compressor run at high speeds (3000 r.p.m), therefore these can be directly connected to electric motors or steam turbines Because of high speed, these compressors can handle large volumes of vapors refrigerants, as compared to reciprocating compressors. The centrifugal compressors are especially adapted for systems ranging from 50 to 5000 tones. They are also used for temperature range between -900 C and 100C The efficiency of these compressors is considerably high.

Compresor Selection:Inlet pressure P1 = = = = = =

1.6 Mpa 232.12 psi 15.79 atm 33425.9 lb/ft2 246.82 psia 35542.7 lb/ft2

Outlet Pressure = P2 = 5.065 Mpa = 734.81 psi = 49.98766 atm = 105813.8 lb/ft2 = 749.51 psia = 107930.6 lb/ft2 Compression ratio = P2 / P1 = 3.03 From “Plant Design & Economics For Chemical Engineering” By Timmerhous K.D , page # 524, 4th edition, If P2/P1 > 5 ,then there can be multistage compressor, but in our case it is 3.03 which < 5, so Single stage compressor Avg.Mol.wt of gases = R Inlet Temp. T

Density = PM/RT

9.7 gm/gmol

= 0.00008206 m3.atm/gmol.K = 35o C = 308 K = 6.060 Kg/m3

Production Of Methanol From Natural Gas

152

Now, Molar flow rate of gases

= 904.964 kmol/hr = 8778.15 kg/hr

Volumetric flow rate

= 1448.47 m3/hr = 851.88 ft3/min

So,

From Compressor selection Diagram , Coulson vol-6,page # 432, Selected Compressor: Centrifugal Compressor Power Calculations: From Timmerhous Page # 524,edition # 4th Single Stage Compressor Eq.

hp =

3.03*E-5 K * P1 * qfm1 * [(P2/P1)(K-1)/K - 1]/(K - 1)

where, hp = Horse power requirement, ft-lbf/lnm P1 = Intake pressure ,lbf/ft2 P2 = Final delivery pressure, lbf/ft2 qfm1 = Cubic feet of gas per minute at intake conditions Ratio of specific heat at constant pressure to constant volume K

= Cp / Cv

(Average value since for gases the value of γ lies between 1.2-1.4) So, Hp = 1.09 E+03 Efficiency = 70% So, Hp

= = =

1.56E+03 1.16E+06 watts 1.16E+03 Kw

Specification Sheet: Type

Centrifugal Compressor

Feed flow rate

8778.15

Inlet Pressure

33425.90 lbf/ft2

Outlet Pressure

105813.8 lbf/ft2

Compression Ratio

3.036

Material construction Power

Kg/hr

of Carbon steel 1.56E+03 hp

Production Of Methanol From Natural Gas

153

Fan Selection Flow rate of air Density of air at 35C

= =

qA = 22219.77 lb/nr 0.0716 lb/ft3

So, Volumetric Flow rate of air = 310332 ft3/hr = 5172.2 ft3/min Discharge pressure = 14.7 psig = 29.4 psia The head = 29564.25 ft-lbf / lbm Now, Hp = 1.57E-04 Q * p From Perry 6-21 , 5th edition Where, Q = Fan volumetric discharge, ft3/min p = Fan operating pressure,inches of water column Convert the pressure units into inches of water column, So,

p =

407.16 in.of water

Finally, Hp = 3.31E+02 The operating efficiencies of fans range from 40-70% Form Perry, 6-21 We select the efficiency i.e; 70% Therefore, hp = 4.72E+02

Specification Sheet: Type Fan Volume Temperature of air Fan Operating Pressure Head Power required

Centrifugal Axial Flow 5172.2 ft3/min 35 oC 407.16 in.of H2O 29564.25 ft-lbf/lbm 4.72E+02 hp

Production Of Methanol From Natural Gas

154

Introduction A condenser is a two-phase flow heat exchanger in which heat is generated from the conversion of vapor into liquid (condensation) and the heat generated is removed from the system by a coolant. Condensers may be classified into two main types: those in which the coolant and condensate stream are separated by a solid surface, usually a tube wall, and those in which the coolant and condensing vapor are brought into direct contact. The direct contact type of condenser may consist of a vapor which is bubbled into a pool of liquid, a liquid which is sprayed into a vapor, or a packed-column in which the liquid flows downwards as a film over a packing material against the upward flow of vapor. Condensers in which the streams are separated may be subdivided into three main types: air-cooled, shelland-tube, and plate. In the air-cooled type, condensation occurs inside tubes with cooling provided by air blown or sucked across the tubes. Fins with large surface areas are usually provided on the airside to compensate for the low airside heat transfer coefficients. In shelland-tube condensers, the condensation may occur inside or outside the tubes. The orientation of the unit may be vertical or horizontal. In the refrigeration and air-conditioning industry, various types of two-phase flow heat exchangers are used. They are classified according to whether they are coils or shell-and-tube heat exchangers. Evaporator and condenser coils are used when the second fluid is air because of the low heat transfer coefficient on the air side. In the following sections, the basic types of condensers are shown:

Types of Condensers Tubular condensers Plate-type Condensers Air-Cooled Condensers Direct Contact Condensers

Selection of condenser One of the more important actions taken by the design engineer in arriving at a satisfactory solution for a specific heat exchange is the careful selection of the condenser type that should be used. In the chemical industry the preferred choice in the past has been the tubular condensers for which there are well-established codes and standards prepared by TEMA (Tubular Exchanger Manufacturers Association) and ASME (American Society for Mechanical Engineers). However, to attain higher thermal efficiencies while minimizing capital costs, the use of other types of condensers has received considerable attention in both the chemical industry and other manufacturing industries.

Production Of Methanol From Natural Gas

155

The selection process normally includes a number of factors, all of which are related to the heat-transfer application. These factors include, but are not limited to, the following items: 1. Thermal and hydraulic requirements 2. Material compatibility 3. Operational maintenance 4. Environmental, health, and safety considerations and regulations 5. Availability 6. Cost

Condensers desired properties Any condenser selected must be able to provide a specified heat transfer, often between a fixed inlet and outlet temperature, while maintaining a pressure drop across the exchanger that is within the allowable limits dictated by process requirements or economics. The exchanger should be able to withstand the stresses due to fluid pressure and temperature differences. The material or materials selected for the exchanger must be able to provide protection against excessive corrosion. The propensity for fouling in the exchanger must be evaluated to assess the requirements for periodic cleaning. The exchanger must meet all the safety codes. Potential toxicity levels from all fluids must be assessed, and appropriate types of condenser selected to eliminate or minimize the human and environmental effects in the event, of an accidental leak or failure of the exchanger. Finally, to meet construction time constraints and project cost controls, the design engineer may have to select a heat exchanger based on a standard design used by the fabricator to maintain timeliness and reduce costs.

Note that heat exchangers often do not operate at the conditions for which they were designed. For example, if fouling allowances are included in the design, the heat exchanger will be over-designed initially and under-designed prior to shutdown for periodic cleaning. As a consequence, the outlet conditions from the exchanger will vary, with possible downstream effects.

Production Of Methanol From Natural Gas

156

Four Condenser Configuration are Possible 1) 2) 3) 4)

Horizontal with condensation is shell side and cooling medium in the tubes. Horizontal with condensation in tube side cooling medium in shell side. Vertical with condensation in the shell. Vertical with condensation in the tubes.

Horizontal shell side and vertical tube side are the most commonly used types of condensers. In this process we have used the normal mechanism for heat transfer in commercial condenser, which film wise condensation. Since vapor-liquid heat transfer changes usually occur at constant or really constant pressure in industry, the vaporization or condensation of a single compared normally occurs isothermally. If a mixture of vapors instead of a pure vapor is condensed at constant pressure, the change does not take place isothermally in most instances.

Fixed tube type condenser Fixed tube type condenser is probably used more often than any other type. The construction is simple and economical. The inside of the tubes can be cleaned mechanically or chemically, while the outside of the tubes requires chemical cleaning. An expansion bellows is often used to accommodate excessive stresses caused by thermal expansion

DESIGN CALCULATIONS OF CONDENSER Mass flow rate of the process stream (Methanol) = m = 28268.17 lb/hr Condensation takes place at Temperature = 1490F Pressure = 1atm Latent heat of vaporization = 488 Btu/lb Heat Load Qc = m = 28268.17 488

Production Of Methanol From Natural Gas = 13794866.96 Btu/hr

Water Flow rate Use 25oF rise in temperature of water

Qc C p Δt

m

13794866.96 1 25 = 551794.68 lb/hr =

551794.68 = 1104.03gpm 8.33 60 1104.03 ft3/sec = = 2.46 ft3/sec 7.48 (60) g.p.m =

LMTD = 50 oF

Water Flow Area Set minimum water tube velocity = 5.5 ft/sec Then, Total tube Cross-section flow area = 2.46/5.5 = 0.4473 ft2

No of Tubes Use 1 ¼ -inch 16 BWG tube Tube flow area = 0.985 / 144= 0.00684 ft2/tube No of Tubes = 0.4473 / 0.00684 = 65 tubes per pass Value of UD Assumed UD =140 Btu/hr.ft2 oF

Heat Transfer Area A

13794866.96 50 140

= 1970 ft2

Tube Length Required:Out side area / tube = 0.3271 ft2/ft Total tube Footage = 1970 / 0.3271 = 6025 ft Tube length =16 ft

157

Production Of Methanol From Natural Gas

6025 65 16 =5.8 use six pass No. of tubes= 390 No. of passes =

Shall Diameter Use 39-inch I.D shell with 6 tube pass with 390 tubes total, 16 ft long on 1× 9/16 -inch triangular pitch. Trial area = 390 × 0.3271 ×16 = 2041 ft2

Flow Area Flow area per pass= 65× .00684 = 0.4446 ft2/pass Baffle spacing = B = 39 in Tube pitch = 1.5625 in Clearance = 0.3125 in

Water Velocity Water velocity in tubes = 2.46/0.4446 = 5.53 fps/pass

Shell Side Calculations Flow Area

ID C B 144Pr

as as

39 0.3125 39 144 1.5625 = 2.1125 ft2

Mass Velocity Gs

Gs

m as

28268.17 2.1125

= 13381.4 lb/hr ft2

Condensing Loading

158

Production Of Methanol From Natural Gas m LN1/3 t 28268.17

G

G

2/3

15.5 390 = 34.16 lb/hr

Physical Properties Thermal conductivity kf = 0.11 Btu/hr-ft-oF Specific gravity sf = 0.76 lb/hr-ft Viscosity f = 0.33 cp

Value of film coefficient From Figure (literature) ho = 260 Btu/hr-ft2-oF

Tube Side Calculations for Film Coefficient Mean water Temperature = 97.5 oF Velocity in tubes = 5.53 fps From graph (literature) value of hi = 1260 Btu/hr-ft2-oF Correction factor for 1 ¼ -inch tube Fw = 0.87 Correction to outside of tube: hio = hi

I.D × Fw O.D

hio = 1260

1.12 × 0.87= 980 Btu/ hr-ft2-oF 1.25

Overall heat transfer coefficient 1 1 1 ro rio U D ho hio Put values 1 1 1 0.001 0.001 U 260 980 UD = 145.68 Btu/ hr-ft2-oF

Area Required Qc T UD 13794866.96 = 1877.25 ft2 A 145.68 50.47

A

159

Production Of Methanol From Natural Gas

160

Overall Clean Coefficient

h ioh o h io h o

UC UC

260 980 260 980 = 205 Btu/hr-ft2 oF

Dirt Factor Rd Rd

UC U D UCUD 205 145.45 = 0.002 hr-ft2-oF / Btu 145.45 205

Pressure Drop (Shell Side) Reynolds No. = 0.011 2.42 = 0.0266 lb/ft hr De = 0.07584 ft Res = DeGs/ = 0.07584 13381.4 /0.0266 = 3.8 For Res = 3.8 104 Friction factor for shell side f = 0.0016 No. of crosses, N + 1 = 5 Specific gravity = Sv = 0.001173 Shell I.D = 39/12 = 3.25 ft

Kern fig 15

vap

Pressure Drop

Ps

fG s2 D s N

1

2 5.22 1010 D e s 2

0.0016 13381.4 3.25 5 = 5.22 1010 0.07584 0.0011733 2 = 0.7 psi

Pressure Drop (Tube Side) Tube flow area = 0.985 in2 aL =

390 0.985 144 6

= 0.4446 ft2

Kern fig 28 104 Kern fig 29

Production Of Methanol From Natural Gas Gt = w/aL = 551794.68/.4446 = 1241103.64 lb/hr ft2 = 0.72 2.42 =1.74 lb/hr ft2 Ret =

1.12 1241103.64 =6.66 104 12 1.74

From fig 26 (Kern) f = 0.00013

Pt

fG 2t Ln 5.22 1010 D s 0.00013 (1241103.64)2 16 6

Pt

5.22 1010 0.0933 1 1

=3.95psi

End return loss from graph 27 (kern) V2/2g =.21

Pr = (94n/s)(V2/2g) Pr = 5.04 psi Total Pressure, Tube side PT Pt Pr = 5.04+3.95 = 9 psi

SPECIFICATION SHEET Identification Item: condenser No. Required = 1 Function: Condense vapors of methanol by removing the latent heat of vaporization Operation: Continuous Type: 1-6 Horizontal Condenser Shell side condensation Heat Duty = 13794866.96 Btu/hr Material of construction= carbon steal

161

Production Of Methanol From Natural Gas Tube Side:

Tubes OD: 1.25 in2, 16 BWG

Fluid handled cold water

390 tubes each 16 ft long

Flow rate = 551794.68 lb/hr

6 passes

Pressure = 14.7 lbf/in2

1× 9/16 triangular pitch

Temperature = 85oF to 110oF

Pressure drop = 9.54psi

Shell Side:

Shell ID =39 in2 1 passes

Fluid handled: Methanol

Baffles spacing = 39 in2.

Flow rate = 28268.17 lb /hr Pressure = 14.7 psi Temperature = 149oF

Pressure drop = 0.7 psi 25% cutoff segmented baffle

Utilities: Cold water Ud assumed = 140 Btu/hr.ft2.0F

Ud calculated = 145.68 Btu/hr.ft2.0F

Uc calculated = 205 Btu/hr.ft2.0F

Allowed dirt factor = Rd = 0.002

162

Production Of Methanol From Natural Gas

163

Production Of Methanol From Natural Gas

164

MECHANICAL DESIGN: 1

SHELL THICKNESS: ts =

P*D 2 fJ P

Where, ts = Shell thickness =? P = Design Pressure = 1.76 N/mm2 Di = Inner diameter of shell = 0.70m = 695.12mm Permissible strength for carbon steel = 95 N/mm2 J = Joint factor = 85% ts = [1.76 x 695.12/ (2 x 95 x .85 – 1.76)] = 1223.41/ 159.74 = 7.66 mm So, minimum shell thickness is = 7.66 mm ( including corrosion allowance)

NOZZLE DIAMETER: Material used = carbon steel Feed nozzle for Gases, Mass flow rate of shell side fluid = m = ρA v = 31095.68 lb/hr = 14134 kg/hr Density of gases = 5.27 kg/m3 Velocity of gases = 27641.36 m/hr A = m / ρv = 14134 / 5.27 * 27641.36 = 0.097 m2 Diameter of the nozzle = [0.097 x 4 / pi]1/2 = 0.352 m = 13.85 in. = 352 mm Feed nozzle outlet also has the same diameter.

NOZZLE THICKNESS: Corrosion allowance = C =2 mm

tn =

P * Dn C 2* f * J P

= [1.76 x 352/ {(2 x 95 x 0.85) – 55.445}] + 2 = 3.8 + 2 = 5.8 mm

Production Of Methanol From Natural Gas

165

HEAD THICKNESS: Take a floating head, the thickness can be calculated as: th = PRcW / 2fJ where , th = thickness of head

P = 1.76 N/mm2

W = ¼ ( 3 +√ Rc / Rk) Rc = Crown radius = outer radius of shell = 7.66 + 695.12 = 702.78 mm Rk = Knuckle radius = 0.06 Rc = 42.16 mm So, W = 1.52  th = (1.76 x 702.78 x 1.52)/(2 x 95 x 0.85) = 11.64 mm Taking.002mm corrosion allowance we have, th = 11.64 +.002 = 11.643 mm

The Rods & Spacers: The rods and spacers shall be provided to retain all cross baffles and tube support plates accurately in position from Ludwig (2nd edition , vol, 3 ,page # 26) table # 10.6 For shell diameter 864-1220 mm Diameter of tie rod is 12.8 and number of rods = 8 Spacers diameter = 12 mm

Baffle Detail : Baffle cut : 25% cut (the length of the baffle from the shell to the flat edge of the baffle is 75% of the diameter of the shell)

Baffle diameter:

From Coulson & Richardson (vol 6, 3rd edition ,page # 651) For shell diameter of 886 to 1067 mm , baffle diameter is given by the relation, Db = Ds – 4.8 mm = 695.12 + 4.8 = 699.92 mm Baffle spacing : According to TEMA standard should not less than 1/5(shell diameter) , So B = 0.696 m = 696 mm Number of baffles = N + 1 = Lt / B Where , Lt = 10ft = 3.048 m So no of baffles = 3.048 / 0.696 = 4.38 = 5

Production Of Methanol From Natural Gas

166

Let thickness of the baffles = 0.5 in = 12.7 mm From Ernest Ludwig ,TEMA standard 1978, page # 11 Height of baffle = 0.75 * Ds = 0.75 * 695.12 = 521.34 mm = 0.52 m

TUBE SIDE: Material used = Stainless Steel 316 No. of tube passes = 2 Number of tubes = 100 Allowable stress = 0.0001 N/mm2 Outside diameter

= 1.5 in = 0.038 m

Inside diameter

= 1.37 in = 0.034 m

Wall thickness of tubes = 0.065 in. = 0.00165m Length of tubes = Lt = 10ft = 3.048 m For Square pitch ,Pt = 1.875 in = 0.048 m Here the feed is

= water

Working Pressure

= 1.6Mpa = 15.8 atm = 232.12 psi = 1.6 N/mm2

Design Pressure

= 1.1 * 1.6 =1.76 N/ mm2

Inlet temp.

= 30 oC

Outlet temp.

= 354 oC

TUBE SHEET THICKNESS: tts

=

0.25 * P F *G * f

0.5

= 1 x 0.40 (0.25 x 1.76 / 95)0.5 = 0.027 m

CHANNEL DESIGN: a. Channel Length = 1.3 x (cross sectional area of tube/pass)/Ds

Production Of Methanol From Natural Gas = 1.3 x 0.5 * pi /4 x (0.038)2 / 0.696 =.0.0011 m

b. Channel thickness: tc = Gc (kP/f)1/2 = 0.40 x (0.3 x 1.76 / 95)1/2 = 0.0298 m

NOZZLE DESIGN FOR TUBE SIDE: Now nozzle design for water inlet: Material used Is Stainless Steel 316 Mass flow rate of water = 14769.34 lb/hr = 6713.33 Kg/hr Density of water = 1000 kg / m3 Velocity of tube side fluid = v = 0.0798 ft/sec = 87.585 m/hr m = ρA v A = m/ρv = 6713.33/(1000 x 87.585) = 0.076 m2 Diameter of the nozzle = d = (0.076 x 4/ π)1/2 = 0.31 m = 12.2 in = 309.88 mm

Nozzle Thickness:tn =

Pd * Dn 2* f * J P

=(1.76 * 309.88)/(2* 95 *0.85 – 1.76) = 3.41mm Now, nozzle thickness with corrosion allowance = 5.41 mm

SUPPORT DESIGN: For this shell and tube heat exchanger, we use a saddle type of support. Material used : low carbon steel Diameter of shell = Ds = 695.12 mm Working Pressure = 15.8 atm Shell thickness = 7.66 mm Head Thickness = 11.643 mm Corrosion Allowance = 2mm

167

Production Of Methanol From Natural Gas Permissible stress = 95 N/mm2 Rc = Crown radius = outer radius of shell = 7.66 + 695.12 = 702.78 mm Rk = Knuckle radius = 0.06 Rc = 42.16 mm R = Ds/2 = 695.12/2 = 347.6 mm = 0.347 m Distance of saddle canter from shell end = A = 0.5 R =173.8 mm Total depth of head (H) = (Ds Rc / s)1/2 = (695.12* 702.78/2)1/2 = 494.22 mm

SHELL WEIGHT: Ws = π * (r20-ri2)*L*ρof shell material

ρ of shell material = 7700 Kg/m3 Ws = π * (0.7022 – 0.6952) x 3.7 x 7700 / 4 = 218.7 kg

TUBE WEIGHT: Wt = π/4 x [Do2-Di2] * L *.nt * ρ

Density of tube material = 7800 kg/m3 = π /4 x [(0.038)2 – (0.0348)2] x 3.7 x 100 x 7800 = 526.68 kg

Fluid load in the shell: W1 = (shell volume – tube volume) ρ gases = [πDs2 L/4 – n π do2 l/4] * 5.27 kg/m3 = [π* 0.6952 * 3.7/4 -100 * 0.0382 * 3.04 /4] * 5.27 = 6.82 kg

Fluid load in the tube : W2 = n * π di2 l * ρ liquid / 4

= 100 * 3.14 * 0.0342 * 3.04 *1000 /4 = 275.86 kg Now, Total Weight = Wt = Ws + Wt + W1 + W2 ` = 526.68 + 218.7 + 6.82 + 275.86 = 1028.06 kg

WEIGHT OF TIE ROD, END COVERS, BAFFLES: WA = 500 kg Total weight = 500 + 1028.06 = 1528.06 kg

LONGITUDINAL BENDING MOMENT: The bending moment at the support is:

168

Production Of Methanol From Natural Gas M1 = Q*A[ 1 – {(l – A/L + (R2 – H2)/2A L)/(1 + 4/3 H/L)}] Q = W/2 [L + 4/3 H] L = 3.7 m, H = 494.22 mm = 0.494 m Q = 1528.06 / 2 [3.7 + 4/3 x 0.494] = 1861.99 kg` Let us take A = 0.25 m M1 = 1861.99 x 0. 25 * [1 – {1 – 0.25/3.7 + (0.3472 – 0.4942)/(2 x 0.25 x 3.7)}/{1 + 4/3 x 0.494/3.7}] = 1239.6 x 0.25 [1 – (0.437 /1.1780)] = 1239.6 x 0.25 * (0.6288) = 194.88 kg m The bending moment at the center of span is calculated by:s M2 = QL/4 [ {1 + 2(R2 – H2)/L2}/{1 + 4/3 H/L} – 4A/L] = 1861.99 x 3.7 /4 [{1+2(0.3472 – 0.4942)/3.72}/{1+4/3x 0.494/3.7} – .025 x 4/3.7] = 1861.99 x 3.7 /4 (0.83 - 0.27) = 970.65 kg m

STRESSES IN SHELL AT THE SADDLE: f1 = M1 / k1 π R2t k1 = 0.107 m = 194.88 /(0.107 x 3.14 x 0.3472 * 0.01) = 481720 kg/m = 48.17 kg / cm2 f2 = M1 / (k2 π R2t) k2 = 0.192 m = 194.88/(0.192 x 3.14 x 0.3472 * 0.01) = 268458.67 kg/m2 = 26.84 kg/cm2 And stress in the shell at mid point: F3 = M2/ ( π * R2 t) F3 = 970.65/(3.14*0.3472 * 0.01) = 256728.48 kg/m2 = 25.67 kg/ cm2 The stresses are well within the permissible limit. Hence design support is acceptable.

169

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Instrumentation and Control The main objective of specifying and using of instruments and controls systems are  To safe the plant operation by keeping the process variables within the operating limits and detects the dangerous situations since developed.  To control the product rate and quality within the specified quality.  To operate the process at the lowest production cost.

11.1 Final Control Elements Is the mechanism which alters the value of the manipulated variable in response to the output signal from and automatic controller. In a majority of systems the final control element is and automatic control valve which throttles the flow of a manipulative variable.

Controller The job of the controller is to compare te process signal from the transmitter with the set point signal and to send out an appropriate signal to the control valve. There are three basic types of controllers which are  Proportional action which moves the control valve indirect proportional to the magnitude of the error.  Integral action (reset) which moves the control valve based on the time integral of the error and the purpose of integral action is to drive the process back to its set point when it has been disturbed.  Ideal derivative action and its purpose is to anticipate where the process is heading by looking at the time a rate of change of the error.

11.2 Commercial Controllers The three actions are used individually or combined in three basic controllers.  Proportional  Proportional – integral (P.L)  Proportional – Integral – derivative (P.I.D)

11.3 Transmitters Is the interface between the process and it‘s control system and it‘s job is to convert the sensor signal into a control signal.

Sensors The instruments on the process which measure the properties and important variables such as temperature, pressure, flow rate and level.

11.4 Typical control Systems Level Control

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In any equipment where an interface exists between two phases (e.g. liquid- vapor), some means of maintaining the interface at the required level must be provided. This may be incorporated in the design of the equipment as is usually done for decanters or by automatic control of the flow from the equipment. Figure shows a typical arrangement for the level control at the base of a column. The control valve should be placed on the discharge line from the pump.

Pressure Control Pressure control will be necessary for most systems handling vapor or gas. The method of control will depend on the nature of the process.

Flow Control Flow control is usually associated with inventory control in a storage tank or other equipment. There must be a reservoir to take up the changes in flow rate. To provide flow control in a compressor or pump running at a fixed speed and supply a near constant volume output, a bypass control would be used.

Alarms, Safety Trips, And interlocks Alarms are used to alert operators of serious, and potentially hazardous, deviations in process conditions. Key instruments are fitted with switches and relays to operate audible and visual alarms on the control panels and enunciator panels. Where delay, or lack of response, by the operator is likely to lead to the rapid development of a hazardous situation, the instruments would be fitted with a trip system to take action automatically to avert the hazard, such as shutting down pumps, closing valves, operating emergency systems. The basic components of an automatic trip system are 1. A sensor to monitor the control variable and provide and output signal when a preset values exceeded (The instrument). 2. A link to transfer the signal to the actuator, usually consisting of a system of pneumatic or electric relays. ‗ 3. Ana actuator to carry out the required action, close or open a valve, switch off motor.

Interlocks Where it is necessary to follow a fixed sequence of operations – for example, during a plant start-up and shut –down, or in batch operations – interlocks are included to prevent operators departing from the required sequence, they may be incorporate in the control system design. Various proprietary special lock and key systems are available.

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11.5 CONTROL SCHEMES OF DISTILLATION COLUMN GENERAL CONSIDERATION Objective In distillation column control any of following may be the goals to achieve    

Over head composition. Bottom composition Constant over head product rate. Constant bottom product rate.

.

Manipulated Variables Any one or any combination of following may be the manipulated variables     

Steam flow rate to reboiler. Reflux rate. Overhead product withdrawn rate. Bottom product withdrawn rate Water flow rate to condenser.

LOADS OR DISTURBANCES  Flow rate of feed  Composition of feed.  Temperature of feed.  Pressure drop of steam across reboiler  Inlet temperature of water for condenser.

CONTROL SCHEME Overhead product rate is fixed and any change in feed rate must be absorbed by changing bottom product rate. The change in product rate is accomplished by direct level control of the reboiler if the stream rate is fixed feed rate increases then vapor rate is approximately constant & the internal reflux flows must increase.

ADVANTAGE Since an increase in feed rate increase reflux rate with vapor rate being approximately constant, then purity of top product increases.

DISADVANTAGE The overhead reflux change depends on the dynamics of level control system that adjusts it.

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HAZOP STUDY 12.1 INTRODUCTION A HAZOP survey is one of the most common and widely accepted methods of systematic qualitative hazard analysis. It is used for both new or existing facilities and can be applied to a whole plant, a production unit, or a piece of equipment It uses as its database the usual sort of plant and process information and relies on the judgment of engineering and safety experts in the areas with which they are most familiar. The end result is, therefore reliable in terms of engineering and operational expectations, but it is not quantitative and may not consider the consequences of complex sequences of human errors. The objectives of a HAZOP study can be summarized as follows:  To identify (areas of the design that may possess a significant hazard potential.  To identify and study features of the design that influence the probability of a hazardous incident occurring.  To familiarize the study team with the design information available.  To ensure that a systematic study is made of the areas of significant hazard potential.  To identify pertinent design information not currently available to the team.  To provide a mechanism for feedback to the client of the study team's detailed comments. A HAZOP study is conducted in the following steps: 1)

Specify the purpose, objective, and scope of the study. The purpose may he the analysis of a yet to be built plant or a review of the risk of un existing unit. Given the purpose and the circumstances of the study, the objectives listed above can he made more specific. The scope of the study is the boundaries of the physical unit, and also the range of events and variables considered. For example, at one time HAZOP's were mainly focused on fire and explosion endpoints, while now the scope usually includes toxic release, offensive odor, and environmental end-points. The initial establishment of purpose, objectives, and scope is very important and should be precisely set down so that it will be clear, now and in the future, what was and was not included in the study. These decisions need to be made by an appropriate level of responsible management.

2)

Select the HAZOP study team. The team leader should be skilled in HAZOP and in interpersonal techniques to facilitate successful group interaction. As many other experts should be included in the team to cover all aspects of design, operation, process chemistry, and safety. The team leader should instruct the team in the

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HAZOP procedure and should emphasize that the end objective of a HAZOP survey is hazard identification; solutions to problems are a separate effort. 3)

Collect data. Theodore16 has listed the following materials that are usually needed:  Process description  Process flow sheets  Data on the chemical, physical and toxicological properties of all raw materials,, intermediates, and products.  Piping and instrument diagrams (P&IDs)  Equipment, piping, and instrument specifications  Process control logic diagrams  Layout drawings  Operating procedures  Maintenance procedures  Emergency response procedures  Safety and training manuals

Table-: HAZOP Guide Words and Meanings Guide Words Meaning No Negation of design intent Less Quantitative decrease More Quantitative increase Part of Qualitative decrease As well as Qualitative Increase Reverse Logical opposite of the intent Other than Complete substitution 4)

Conduct the study. Using the information collected, the unit is divided into study "nodes" and the sequence diagrammed in Figure , is followed for each node. Nodes are points in the process where process parameters (pressure, temperature, composition, etc.) have known and intended values. These values change between nodes as a result of the operation of various pieces of equipment' such as distillation columns, heat exchanges, or pumps. Various forms and work sheets have been developed to help organize the node process parameters and control logic information.

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When the nodes are identified and the parameters are identified, each node is studied by applying the specialized guide words to each parameter. These guide words and their meanings are key elements of the HAZOP procedure. They are listed in Table. Repeated cycling through this process, which considers how and why each parameter might vary from the intended and the consequence, is the substance of the HAZOP study. 5)

Write the report. As much detail about events and their consequence as is uncovered by the study should be recorded. Obviously, if the HAZOP identifies a not improbable sequence of events that would result in a disaster, appropriate follow-up action is needed. Thus, although risk reduction action is not a part of the HAZOP, the HAZOP may trigger the need for such action.

The HAZOP studies are time consuming and expensive. Just getting the P & ID's up to date on an older plant may be a major engineering effort. Still, for processes with significant risk, they are cost effective when balanced against the potential loss of life, property, business, and even the future of the enterprise that may result from a major release.

13.2 HAZOP Study of Storage Tank for Methyl Alcohol A HAZOP study is to be conducted on IPA storage tank, as presented by the piping and instrumentation diagram show in figure. In this scheme, IPA is unloaded from tank trucks into a storage tank maintained under a slight positive pressure until it is transferred to the process. Application of the guide words to the storage tank is shown in Table along with a listing of consequences that results from process deviation. Some of the consequences identified with these process deviations have raised additional questions that need resolution to determine whether or not hazards exist.

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Methyl Alcohol Storage Tank

Figure- Piping and instrumentation diagram

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Deviations from operating conditions Level: Less

What event could cause this deviation

182

Consequences of this deviation on Process item of equipment indications under consideration

Tank runs dry

Pump cavitates

Rupture of discharge line V-3 open or broken V-1 open or broken Tank rupture (busting of vessel)

Reagent released

More Unload too much from column Reverse flow from Temperature: process Less Temperature of inlet More is colder than normal Temperature of inlet is hotter than normal External fire

Reagent released Reagent released Reagent released

LIA-1 FICA-1 LIA-1, FICA-1 LIA-1 LIA-1 LIA-1

Tank overfills

LIA-1

Tank overfills

LIA-1

Possible vacuum Region released Tank fails

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13.1 CHEMICALS IN THE ENVIRONMENT: METHANOL Chemicals can be released to the environment as a result of their manufacture, processing, and use. EPA has developed information summaries on selected chemicals to describe how you might be exposed to these chemicals, how exposure to them might affect you and the environment, what happens to them in the environment, who regulates them,and whom to contact for additional information. EPA is committed to reducing environmental releases of chemicals through source reduction and other practices that reduce creation of pollutants.

WHAT HAPPENS TO METHANOL IN THE ENVIRONMENT? Methanol evaporates when exposed to air. It dissolves completely when mixed with water. Most direct releases of methanol to the environment are to air. Methanol also evaporates from water and soil exposed to air. Once in air, it breaks down to other chemicals. Microorganisms that live in water and in soil can also break down methanol. Because it is a liquid that does not bind well to soil, methanol that makes its way into the ground can move through the ground and enter groundwater. Plants and animals are not likely to store methanol. HOW DOES METHANOL AFFECT HUMAN HEALTH AND THE ENVIRONMENT? Effects of methanol on human health and the environment depend on how much methanol is present and the length and frequency of exposure. Effects also depend on the health of a person or the condition of the environment when exposure occurs. People have died as a result of drinking large amounts of methanol. Drinking smaller, non lethal amounts of methanol adversely affects the human nervous system. Effects range from headaches to incoordination similar to that associated with drunkenness. Delayed effects such as severe abdominal, leg, and back pain can follow the inebriation effects of methanol. Loss of vision and even blindness can also occur after exposure to amounts of methanol causing inebriation. These effects are not likely to occur at levels of methanol that are normally found in the environment. Human health effects associated with breathing or otherwise consuming smaller amounts of methanol over long periods of time are not known. Workers repeatedly exposed to methanol have experienced several adverse effects. Effects range from headaches to sleep disorders and gastrointestinal problems to optic nerve damage. Laboratory studies show that repeat exposure to large amounts of methanol in air or in drinking water cause similar adverse effects in animals.

13.2 Different Hazards TYPES OF HAZARD / EXPOSURE

FIRE

ACUTE HAZARDS / SYMPTOMS Highly flammable. See Notes.

PREVENTION NO open flames, NO sparks, and NO

FIRST AID / FIRE FIGHTING

Powder, alcohol-resistant foam, water in large amounts,

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carbon dioxide. In case of fire: keep drums, etc., cool by spraying with water.

EXPLOSION

Closed system, ventilation, explosionproof electrical equipment and lighting. Do NOT use compressed air for filling, discharging, or handling. Use nonsparking handtools.

EXPOSURE

AVOID EXPOSURE OF ADOLESCENTS AND CHILDREN!

Vapour/air mixtures are explosive.

Inhalation

Skin

Cough. Dizziness. Headache. Nausea. Weakness. Visual disturbance.

Ventilation. Local exhaust or breathing protection.

Fresh air, rest. Refer for medical attention.

MAY BE ABSORBED! Dry skin. Redness.

Protective gloves. Protective clothing.

Remove contaminated clothes. Rinse skin with plenty of water or shower. Refer for medical attention.

Redness. Pain.

Safety goggles or eye protection in combination with breathing protection.

First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then take to a doctor.

Abdominal pain. Shortness of breath. Vomiting. Convulsions. Unconsciousness. (Further see Inhalation).

Do not eat, drink, or smoke during work. Wash hands before eating.

Induce vomiting (ONLY IN CONSCIOUS PERSONS!). Refer for medical attention.

Eyes

Ingestion

SPILLAGE DISPOSAL

PACKAGING & LABELLING

Evacuate danger area! Ventilation. Collect leaking liquid in sealable containers. Wash away remainder with plenty of water. Remove vapour with fine water spray. Chemical protection suit including selfcontained breathing apparatus.

F Symbol T Symbol R: 11-23/24/2539/23/24/25 S: (1/2-)7-16-36/37-45 UN Hazard Class: 3 UN Subsidiary Risks: 6.1 UN Pack Group: II

Do not transport with food and feedstuffs.

IMPORTANT DATA Physical State; Appearance COLOURLESS LIQUID, WITH CHARACTERISTIC ODOUR.

Routes of exposure The substance can be absorbed into the body by inhalation and through the skin, and by ingestion.

Physical dangers The vapour mixes well with air, explosive

Inhalation risk A harmful contamination of the air can be reached rather quickly

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mixtures are easily formed.

on evaporation of this substance at 20°C.

Chemical dangers Reacts violently with oxidants causing fire and explosion hazard.

Effects of short-term exposure The substance irritates the eyes, the skin and the respiratory tract. The substance may cause effects on the central nervous system, resulting in loss of consciousness. Exposure may result in blindness and death. The effects may be delayed. Medical observation is indicated.

Occupational exposure limits TLV: 200 ppm; as TWA (skin) (ACGIH 1999). TLV (as STEL): 250 ppm; (skin) (ACGIH 1999).

Effects of long-term or repeated exposure Repeated or prolonged contact with skin may cause dermatitis. The substance may have effects on the central nervous system, resulting in persistent or recurring headaches and impaired vision.

13.3 Health & Safety Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria. As a result, there is a small fraction of methanol vapor in the atmosphere. Over the course of several days, atmospheric methanol is oxidized by oxygen by the help of sunlight to carbon dioxide and water. Methanol burns in air forming carbon dioxide and water: 2CH3OH + 3 O2 → 2CO2 + 4H2O A methanol flame is almost colorless. Care should be exercised around burning methanol to avoid burning oneself on the almost invisible fire. Methanol is toxic, as its metabolites formic acid and formaldehyde cause blindness and death. It enters the body by ingestion, inhalation, or absorption through the skin. Fetal tissue will not tolerate methanol. Dangerous doses will build up if a person is regularly exposed to fumes or handles liquid without skin protection. If methanol has been ingested, a doctor should be contacted immediately. The usual fatal dose: 100–125 mL (4 fl oz). Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. This is treated using ethanol or fomepizole[1]. Either of these drugs acts to slow down the action of alcohol dehydrogenase on methanol, so that it is excreted by the kidneys rather than being transformed into toxic metabolites. Though it is miscible with water, methanol is very hard to wash off the skin; it is best to treat methanol like gasoline. Symptoms of methanol ingestion are similar to those of intoxication: headache, dizziness, nausea, lack of coordination, confusion, drowsiness, followed by unconsciousness and death.The ester derivatives of methanol do not share this toxicity.Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of methanol. The result is known as methylated spirit or "meths" (UK use). (The latter should not be confused with meth, a common abbreviation for methamphetamine.) Pure methanol has been used in open wheel racing since the mid-1960's. Unlike petroleum fires, methanol fires can be extinguished with plain water (while methanol is lighter than water,

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they are miscible, and addition of water will cause the fire to use its heat boiling the water). The decision was made shortly after the death of two drivers

13.4 Dangers of Methanol Methanol is a clear, colorless liquid with a faint odor like alcohol. The smell is not very strong and is considered a poor indicator of vapor concentration. You might also know methanol as methyl alcohol, methyl hydrate, carbinol, wood alcohol or wood spirit. Methanol is used as a solvent for lacquers, paints, varnishes, cements, inks, dyes, plastics and various industrial coatings. It is also used in the production of pharmaceuticals, formaldehyde and other chemical products. Methanol appears as an ingredient in many products, from industrial solvents to windshield-washer fluid and nail-polish remover. It is also used as a fuel. Inhalation of methanol vapor is the most common route of occupational exposure. Poisonings have also resulted from absorption through the skin; although it is only a mild skin irritant, it can be absorbed through the skin in toxic amounts. Accidental swallowing is also possible. Methanol tastes and smells much like common alcohol (ethanol) and has been used as a substitute in illegal alcoholic beverages. In March 1997, three people died in northern Ontario as a result of methanol poisoning from a bad batch of moonshine.

13.5 Effects of Methanol Poisoning As little as four milliliters can cause blindness and 80 to 150 milliliters can be fatal; about half a milliliter per kilogram of weight is deadly. Drinking methanol causes effects similar to common alcohol, such as an upset stomach and dizziness, with the addition of pronounced vision problems. After these effects disappear, they reappear six to 30 hours later, only with much greater severity. severe symptoms tend to appear 18 to 24 hours after consumption. the relapse time makes it imperative to seek medical help as soon as possible. The most seriously poisoned lose consciousness and die of respiratory or heart failure. those who do not die may stay in a coma for as long as a week and may be left blinded. Accidental swallowing of methanol is not likely in the workplace. Should it happen, get medical help immediately. Never try to make the casualty throw up, but if that does happen hold the person leaning forward to reduce the risk of methanol being drawn into the lungs. you can give 240 to 300 milliliters of water to dilute the methanol in the stomach. Like common alcohol, methanol is broken down in the liver. Methanol breaks downs to produce formaldehyde and formic acid, which are responsible for many of the toxic effects. the body takes several days to eliminate the methanol. Short term exposure to methanol vapor can irritate the eyes, nose and throat and cause headache, nausea, throwing up, dizziness and trouble breathing. other common symptoms of drunkenness, such as lightheadedness, giddiness, blurred vision and dilated pupils, might also

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appear. the symptoms depend on the level and length of exposure and can vary from person to person. Industrial exposures to methanol vapors can cause death or blindness. many reported incidents have involved working in confined spaces without proper ventilation or respiratory protection. fortunately, increased awareness of the dangers of methanol, combined with safer work practices, have reduced the number of serious poisonings in recent years. Long term exposure to methanol has been linked to headaches, mood changes, eye and skin irritation, trouble sleeping, stomach problems and visual impairment. Repeated short term exposures can also lead to such symptoms. Methanol is a flammable liquid and can pose a serious fire risk. It burns with a pale blue flame not usually visible in normal light. Its flash point is 12 c. above this temperature enough vapor is produced to create a flammable mixture with air. The vapor is heavier than air and can travel along the ground to a distant source of ignition and flashback. Containers may explode in the heat of a fire. Although methanol is normally stable, contact with strong oxidizing agents increases the risk of a fire or explosion.

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1. Product Identification Synonyms: Wood alcohol; methanol; carbinol CAS No.: 67-56-1 Molecular Weight: 32.04 Chemical Formula: CH3OH

2. Composition/Information on Ingredients Ingredient CAS No Percent Hazardous --------------------------------------- ------------ ------------ --------Methyl Alcohol

67-56-1

100%

Yes

3. Hazards Identification Emergency Overview POISON! DANGER! VAPOR HARMFUL. MAY BE FATAL OR CAUSE BLINDNESS IF SWALLOWED. HARMFUL IF INHALED OR ABSORBED THROUGH SKIN. CANNOT BE MADE NONPOISONOUS. FLAMMABLE LIQUID AND VAPOR. CAUSES IRRITATION TO SKIN, EYES AND RESPIRATORY TRACT. AFFECTS CENTRAL NERVOUS SYSTEM AND LIVER. Health Rating: 3 - Severe (Poison) Flammability Rating: 3 - Severe (Flammable) Reactivity Rating: 1 - Slight Contact Rating: 3 - Severe (Life) Lab Protective Equip: GOGGLES & SHIELD; LAB COAT & APRON; VENT HOOD; PROPER GLOVES; CLASS B EXTINGUISHER Storage Color Code: Red (Flammable)

Potential Health Effects Inhalation: A slight irritant to the mucous membranes. Toxic effects exerted upon nervous system, particularly the optic nerve. Once absorbed into the body, it is very slowly eliminated. Symptoms of overexposure may include headache, drowsiness, nausea, vomiting, blurred vision, blindness, coma, and death. A person may get better but then worse again up to 30 hours later. Ingestion: Toxic. Symptoms parallel inhalation. Can intoxicate and cause blindness. Usual fatal dose: 100-125 milliliters. Skin Contact: Methyl alcohol is a defatting agent and may cause skin to become dry and cracked. Skin absorption can occur; symptoms may parallel inhalation exposure.

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Eye Contact: Irritant. Continued exposure may cause eye lesions. Chronic Exposure: Marked impairment of vision has been reported. Repeated or prolonged exposure may cause skin irritation. Aggravation of Pre-existing Conditions: Persons with pre-existing skin disorders or eye problems or impaired liver or kidney function may be more susceptible to the effects of the substance.

4. First Aid Measures Inhalation: Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately. Ingestion: Induce vomiting immediately as directed by medical personnel. Never give anything by mouth to an unconscious person. Get medical attention immediately. Skin Contact: Immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Get medical attention. Wash clothing before reuse. Thoroughly clean shoes before reuse. Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately.

5. Fire Fighting Measures Fire: Flash point: 12 oC (54 oF) Autoignition temperature: 464 oC (867 oF) Flammable limits in air % by volume: Flammable Liquid and Vapor! Explosion: Above flash point, vapor-air mixtures are explosive within flammable limits noted above. Moderate explosion hazard and dangerous fire hazard when exposed to heat, sparks or flames. Sensitive to static discharge. Fire Extinguishing Media: Use alcohol foam, dry chemical or carbon dioxide. (Water may be ineffective.)

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Special Information: In the event of a fire, wear full protective clothing and NIOSH-approved self-contained breathing apparatus with full facepiece operated in the pressure demand or other positive pressure mode. Use water spray to blanket fire, cool fire exposed containers, and to flush nonignited spills or vapors away from fire. Vapors can flow along surfaces to distant ignition source and flash back. Extinguishing media which must not be used for safety reasons: Do not use a solid water stream as it may scatter and spread fire. Specific hazards : Burns with colorless flame. Special protective equipment for firefighters: Wear self-contained breathing apparatus and protective suit. Specific methods: Standard procedure for chemical fires. Hazchem Code: 2WE

6. Accidental Release Measures Personal precautions: Evacuate personnel to safe areas. Remove all sources of ignition. Wear self-contained breathing apparatus and protective suit. Keep people away from and upwind of spill/leak. Environmental precautions: Contain or absorb leaking liquid with sand or earth. Consult an expert. Prevent liquid entering sewers, basements and work pits; If substance has entered a water course or sewer or contaminated soil or vegetation, advise police. Methods for cleaning up: Soak up with inert absorbent material (e.g. sand, silica gel, acid binder, universal binder, sawdust). Transfer to covered steel drums. Dispose of promptly.

7. Handling and Storage Handling: Use only in well-ventilated areas. Do not breathe vapors or spray mist. Avoid contact with skin, eyes and clothing. Take necessary action to avoid static electricity discharge (which might cause ignition of organic vapors.) Storage: Keep tightly closed in a dry, cool and well-ventilated place. Keep away from heat and sources of ignition. Store in original container. Electrical equipment should be protected to the appropriate standard.

8. Exposure Controls/Personal Protection Airborne Exposure Limits: For Methyl Alcohol: - OSHA Permissible Exposure Limit (PEL):

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200 ppm (TWA) - ACGIH Threshold Limit Value (TLV): 200 ppm (TWA), 250 ppm (STEL) skin Ventilation System: A system of local and/or general exhaust is recommended to keep employee exposures below the Airborne Exposure Limits. Local exhaust ventilation is generally preferred because it can control the emissions of the contaminant at its source, preventing dispersion of it into the general work area. Please refer to the ACGIH document, Industrial Ventilation, A Manual of Recommended Practices, most recent edition, for details. Use explosion-proof equipment. Personal Respirators (NIOSH Approved): If the exposure limit is exceeded and engineering controls are not feasible, wear a supplied air, full-facepiece respirator, airlined hood, or full-facepiece self-contained breathing apparatus. Breathing air quality must meet the requirements of the OSHA respiratory protection standard (29CFR1910.134). This substance has poor warning properties. Skin Protection: Rubber or neoprene gloves and additional protection including impervious boots, apron, or coveralls, as needed in areas of unusual exposure. Eye Protection: Use chemical safety goggles. Maintain eye wash fountain and quick-drench facilities in work area.

9. Toxicological Information Methyl Alcohol (Methanol) Oral rat LD50: 5628 mg/kg; inhalation rat LC50: 64000 ppm/4H; skin rabbit LD50: 15800 mg/kg; Irritation data-standard Draize test: skin, rabbit: 20mg/24 hr. Moderate; eye, rabbit: 100 mg/24 hr. Moderate. Investigated as a mutagen, reproductive effector. Acute toxicity: LD50/oral/rat = 6200 – 1300 mg/kg. LD50/inhalation/4h/rat = 48 mg/l. LD50/dermal/rabbit = 20000 mg/kg. Sensitization: Toxic by inhalation. Irritant effect on eyes. Long term toxicity: Repeated and prolonged exposure; May cause irreversible eye damage. Chronic toxicity: Chronic exposure may cause permanent damage of health.

10. Ecological Information Environmental Toxicity: This material is expected to be slightly toxic to aquatic life.

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Mobility: Completely miscible with water. Volatile / gaseous. Persistence / degradability: Readily biodegradable, according to appropriate OECD test. Biochemical oxygen demand (BOD) = 48-82% of theoretical oxygen demand (ThOD) Bio accumulation: Bio accumulation not significant. Estimated Bio concentration factor (BCF) = 0.2 Ecotoxicity: LC50/96h/bluegill sunfish = 15400 mg/l. NOEL/48h/daphnia = 1000 mg/l. Toxicity to algae = 8000 mg/l. Toxicity to bacteria = 530 mg/l.

11. Disposal Considerations Waste from residues / unused products: Can be incinerated, when in compliance with local regulations. Contact waste disposal services. Contaminated packaging: Empty containers can be land filled after cleaning, when in compliance with local regulation. Continued on next page

12. Transport Information Domestic (Land, D.O.T.) ----------------------Proper Shipping Name: METHANOL Hazard Class: 3 UN/NA: UN1230 Packing Group: II Information reported for product/size: 358LB International (Water, I.M.O.) ----------------------------Proper Shipping Name: METHANOL Hazard Class: 3, 6.1 UN/NA: UN1230 Packing Group: II Information reported for product/size: 358LB

13. Regulatory Information Classification according to European directive on classification of hazardous preparations 90/492/EEC Contains: METHYL ALCOHOL Symbol(s): F – Highly flammable,

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R – phrase(s): R11 – Highly flammable. R23/25 - Toxic by inhalation and if swallowed. S – phrase(s): S1/2 - Keep locked-up and out of reach of children. S7 - Keep container tightly closed. S16 - Keep away from sources of ignition – No smoking. S24 - Avoid contact with skin. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible.) Recommended restrictions: Take notice of labels and material safety data sheets for the working chemicals. Take necessary action to avoid static electricity discharge (which might cause ignition of organic vapors.) Recommended use: General purpose solvent.

14. Other Information NFPA Ratings: Health: 1 Flammability: 3 Reactivity: 0 Label Precautions: Avoid breathing vapor. Avoid contact with eyes, skin and clothing. Wash thoroughly after handling. Label First Aid: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. If swallowed, induce vomiting immediately as directed by medical personnel. Never give anything by mouth to an unconscious person. In case of contact, immediately flush eyes or skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. In all cases get medical attention immediately.

15- Personal protection equipment: Respiratory protection: Incase of insufficient ventilation wear suitable respiratory equipment.  Hand protection: Neoprene gloves / butylrubber gloves.  Eye protection: Goggles giving complete protection to eyes.  Skin and body protection: Rubber or plastic boots, Chemical resistant apron / complete suit protecting against chemicals.

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MATERIAL OF CONSTRUCTION Many facto rs h a v e to be c o n s i d e re d when s e l e c t i n g e n g i n e e r i n g m a t e r i a l , b u t f o r c h e m i c a l process p l a n t to o v e r r i d i n g c o n s i d e r a t i o n is u s u a l l y th e a b i l i t y to resist corrosion. The process designer w i l l he responsible for re comm en ding m a t e r i a l s t h a t w i l l be s u i t a b l e fo r t h e process c o n d i t i o n . He must also co nsi de r t h e r e q u i r e m e n t s of t h e m e c h a n i c a l d es ig n engineer; t h e m a t e r i a l selected must h a v e s u f f i c i e n t . s t r e n g t h a n d lie e a s i l y worked. The most economical m aterial t h a t salislles both process and mechanical requirements should be selected; t h i s w i l l be th e m a t e ri a l t h a t gives t h e lowest cost over the w o r k i n g l i f e of t h e p l a n t , a l l o w i n g for m a i n t e n a n c e a nd replacement. Other factors such as p ro d uct c o n t a m i n a t i o n a n d process safety, must also be considered.

STAIN LESS STEELS There are more t h a n 100 d i f f e r e n t types of s t a i n l e s s steels. These m a t e r i a l are h ig h c h r o m i u m or hi g h n i c k e l c h r o m i u m alloys of c o n t a i n i n g small amounts of o t h e r essential c o n s ti t u e n ts . They have e x c e l l e n t corrosion -resistance .and h e a l r e s i s t a n c e pr op er t i es . The most common s t a i n l e s s steels , s u c h as type 302 or t y p e 304, c o n t a i n a p p r o x i m a t e l y IS per c ent c h r o m i u m and 8 percent n i c k e l , and are designated as 1 <S-is stainless steels.

TYPES A wide range of st a inle ss steels is a va i l a b l e , w i t h co m p o sit io n t a i l o re d to give the properties required for sp e cif ic applications. Type 304 (the so-called I S/S stainless steels): the most generally used stainless steel. It contains the m i n i m u m (V and Ni t ha t give a .stable austenitic structure. The carbon co n t en t is low enough for heal treatment not to be normally needed w i t h t h i n section to p re ven t weld decay Type 304L: Low ca rbo n ve rsion of t yp e 304 ( - 0.03 per ce n t ( ' ) used for t h icke r welded section, where carbide p re c ip it a t io n wo u ld occur wi t h type 304. Type 32 I L: A stabilized version of 304, stabili zes w i t h t i t a n i u m to prevent carbide precipitation d u r in g welding. It has a s l i g h t l y higher strength than 304L,and more su itab le lor h igh temperature use. Type 347: Stabilized with niobium Type 316: In t h i s a llo y , molybdenum is added lo im p ro ve (he corrosion resistance in reducing condition , such as in d i l u t e s u l p h u r i c acid, and, in practical, to solutions containing chlorides. Type 3 I6L: A low carbon version of type 3 16, wh ich sh o u ld be specified if welding or heat treatment is lia ble lo cause carbide p re cip ita tion in type 3 16. Type 309/310: Alloy with a high chromium content, to give greater resistance to o xi d a t io n at h i g h temperatures above 500 'C. Sigma phase is an inlermetallic compound, FeCr.

Production Of Methanol From Natural Gas

198

.

MECHANICAL PROPERTIES The austenitic stainless steels have greater st r en gt h t h a n t h e p l a i n carbon steels, particularly at elevated temperatures

Resistance of Stainless Steel to Oxidation in Air Maximum tempera Stainless steel type ture,°C 650 416 700 " 800 403,405,410,414 430,431 850 430F 900 302,303,304,316,317 3 « , 21,347,348,1714CuMo 1000 30213,308,442 1100 309,310,314,329,446

Production Of Methanol From Natural Gas

199

SELECTION OF MATERIALS The chemical engineer responsible for (he sel ection of materials construction must have a thorough u n d e rs t an di n g of a l l t h e basic process information available. This knowledge of the process can t h e n be used to select materials of const ructi on in a logical manner. A b r i e f p l a n for st ud yi ng materials of construction is as follows .

1. Pr eli mi n ar y Selection Experience, manufacturer‘s data, special liter atur e, general literature, Availability, safely aspects, pr eliminar y laboratory tests.

2. Laboratory Testing Reevalualion of apparently suitable materials under process conditions 3. Interpretation of Laboratory Results and Other Data Effect of possible impurities, excess temperature, agitation, and presence of air in equipment.

Avoidance of electrolysis Fabrication method. 4. Economic Comparison of Apparently S u i t a b l e Materials Materials and maintenance cost, probable li f e, cost of product degradation, liability to special hazards.

SELECTION OF MATERIAL OF CONSTRUCTION

Production Of Methanol From Natural Gas

200

Sr. No

Equipment

Material

1

Reformer tubes

HK 40

2

Waste Heat Boiler

SS-304-shall,SS304-Tube

3

Air Cooler

SS

4

Condenser

CS-Shell,SS-304 Tube

5

Compressor

CS

6

Reactor

SS-316

7

Separator

SS-304

8

Distillation Column

SS-304

Production Of Methanol From Natural Gas

201

Production Of Methanol From Natural Gas

202

PURCHASED EQUIPMENT COST Cost in year “A”

= Cost in year “B” * (Cost index in year “A”/Cost index in year ”B”)

Marshall and Swift Equipment Cost Index Cost in 2002

=

924

Cost index in 2003

=

1062

Cost index in 2004

=

1092

Cost index in 2005

=

1132.1

$1

=

Rs. 60

1

=

Rs. 90

REACTOR (FIXED BED) Diameter

=

2.5 ft =

30 in

Length

=

Volume

= 57.56 ft3 =

Weight

=

w

Material of construction

=

Stainless Steel 316

Pressure

=

50 atm

12.5 ft

=

430.55 gallon 6491.16 lb

=

735 psi

From Peter and Timmerhaus ( Page No = 732 , 542 , Table No . 06) Cost of reactor column in 1990 =

8(W)-0.34 * W * Material factor * pressure factor

Range of W

=

800

Material factor

=

2.75

Pressure factor

=

3.8

Substituting the values, we get

100000 lb

Production Of Methanol From Natural Gas

Cost of Column in 1990

203

= 80(6491.16)-0.34 * (6491.16) * 2.75 * 3.8 = $ 274372 = 274372 * (1132.1/924) = $336165

Cost of column in 2005 Now Catalyst used Weight of catalyst

= =

Reference

=

Cu-Zn-Al 2331.181 lb internet

(http:// www.cere.energy.gov\hydrogenandfuel cell/pdfs/nn0123 aw.pdf) Cost of catalyst

= $ 7/lb

Total cost of catalyst = $16318

=

2331.18 *7

Cost of reactor

= =

336165 +16318 $ 352483

Cost of reactor in Rs.

= Rs 21148980

DISTILLATION COLUMN Diameter

= 5.427 ft

=

Length

=

50 ft

=

Plate type

=

sieve

No. of plates

=

31

Pressure

=

Material of construction

=

Stainless l Steel 304

Cost of distillation column

=

Cost of vertical column + Cost of sieve plates.

From Coulson Vol. 6 Page No.

255

1.654 m 15.24 m

1.1 atm

Third Edition Fig (b)

Cost of column in 2002

=

Cost from fig * material factor * pressure factor

Production Of Methanol From Natural Gas Material factor

=

Pressure factor

=

1

Cost of column in 2002

=

(22*1000) * 2* 1

=

$ 44000

=

(cost from fig) * material factor

Cost of plates in 2002

Cost of total plates in 2002

Cost of dist. column in 2002

2

=

500 * 1.7

=

$ 850

=

850 * 31

=

$ 26350

=

44000 + 26350

= $ 70350 Cost of dist. column in 2005

=

70350 * (1132.1/1062)

= $ 74994 Cost in Rs.

=

Rs. 4499618

HEAT EXCHANGER (W.H.B) Type

=

1-2 Exchanger

Area

=

307.2 ft2

Internal pressure

=

300 psi rating

Material of construction

=

SS-304 shell SS-304 tubes

Refrences: F.O.B Gulf Coast U.S.A. http://www.matche.com/equip.cost / reactor . htm purchased cost in 2002

=

$ 34200

purchased cost in 2005

=

34200 * 1132.1 / 1092 = $ 35456

CONDENSER

204

Production Of Methanol From Natural Gas

Type

=

1-2 Exchanger, Floating Head

Area

=

978.76 ft2

Internal pressure

=

150 psi rating

Material of construction

=

CS-shell-SS-304-tubes

Refrences : F.O.B. Gulf Coast U.S.A. http://www.matche.com /equip.cos / reactor , htm purchased cost in 2002

=

$59800

purchased cost in 2005

=

59800 * 1132.1 / 1092

= $ 61996 Purchased cost in Rs.

= Rs. 3719760

COMPRESSOR COMPRESSOR TYPE

=

Compressor power

= 1722.83 hp

Material of construction

= Carbon Steel

Purchased cost in 2002

= $530600

Cost in 2005

=

530600 * 1132.1 / 1092

=

$ 550084

Cost in Rs.

Centrifugal 1000 psi

= Rs. 33005040

PHASE SEPARATOR Diameter Height Pressure Material of construction

= 0.824 m = 6.11 m = 50atm = SS

205

Production Of Methanol From Natural Gas From coulson Vol. 6 Page No. Figure 6.5b

206

Third Edition

Purchased cost in 2002

=

Cost from fig * material factor * pressure factor

Cost from figure

=

$ 9.4 * 1000

Material factor Pressure factor

= =

2 1.8

Purchased cost in 2002 Cost in 2005 Cost in rupees

= = =

9.4*1000*2*1.8=$33840 33840*1132.1/1062 = Rs.2164440

$36074

FAN Type = centrifugal vein axial Capacity = 2125ft3/ min From Petter and Timmerhaus page # 35 Purchase cost in 1990 = $8010 Cost in 2005 = 800*1132.1/924 = 58800

AIR COOLER Exchanger type = air cooled bare tube area Area = 514ft2 Internal pressure = 300psi rating Material of construction = S.S Reference ; F.O.B GULF COAST USA Hhtp://www.matche.com/equipcost/reacter/htm Purchased cost in 2002` = $50000 Cost in 2005 = 50000*1132.1/1092 = $51836 Cost in Rs. = Rs3110160

STREAM REFORMER Number of tubes = 45 Length of one tube = 30 ft Surface area per unit length = 1.31ft2/ft Total surface area = 45*30*1.31 = 1768.5ft2 Reference: internet http://www.cheme/cornell.edu/courses/ cheme462/syllabus/costing/factmethod/pdf steam reformer (HK40) = $500/ft2 Firebox cost = $50000+$50/ft2 Cost of tubes = 500*1768.5 = $884250

Production Of Methanol From Natural Gas Firebox coct = Cost of steam reformer = Cost of steam reformer in Rs. =

207

50000+50*17683.5 884250+138425 Rs.61360500.

= =

$138425 $1022675

TOTAL PURCHASED EQUIPMENT COST “E” IN 2005 Equipment Reactor Distillation Column Heat Exchanger Condenser Compressor Phase Separator Fan Air Cooler Steam Reformer

Cost of one Equipment 352483 74994 35456 61996 550084 36074 980 51836 1022675

Number of Equipment 1 2 12 2 2 5 2 2 1

Cost of equipments 352483 149988 425472 123992 1100168 180370 1960 103672 1022675

Total purchased equipment cost, E =$3460780

CAPITAL INVESTMENT ESTIMATION (based on delivered equipment cost) (Table # 17: Page # 183/P&T)

DIRECT COST Item

Percent of Delivered Equipment purchased equipment delivered cost 100 Purchased equipment installation 47 Instrument and control 18 Piping 66 Electrical 11 Building 18 Yard improvements 10 Service facilities 70 Land 06 TOTAL DIRECT PLANT COST

Cost $ 3460780 1626567 722940 2284115 380686 622940 346078 2422546 207647 11974299

INIDRECT COST Engineering And Supervision 33 Construction expenses 41 TOTAL DIRECT AND INDERECT COST Contractor’s Fee 21 Contingency 42 FIXED CPITAL INVESTMENT, F

1142057 1418920 14535276 726764 1453528 16715568

Production Of Methanol From Natural Gas

Working Capital W.C

Total capital investment T.C.I.

= = = = = =

208

15%of total capital investment 86%of purchased equipment cost 0.86*3460780 $2976271 Fixed Capital Investment + Working Capital $19691839

RAW MATERIAL COST Natural gas required = 5094m3/hr Price of natural gas which is used for steam reformer in Pak-Arab fertilizer in june 2005 Natural gas price = 62.57Rs./106 Btu C.V. = 935 Btu/ ft3 Natural gas price = 10526 Rs./hr Cost of natural gas per year = Rs. 73843200 As, Raw Material cost = 10-50%of total product cost So, Taking raw material cost = 40%of total product cost Total product cost = Rs. 184608000 T = $3076800

MANUFACTURING COST Tbale # 27- Page 210/P&T Component of cost %age Raw material, R 40%T Operating labour, O 12%T Direct supervisory and clerical labour 18%T Utilities, U 10%T Maintenance and repair, M 3%F Operating supplies 0.75%F Laboratory charges 10%F Patents and royalties 3%T DIRECT PRODUCTION COST II. Fixed charges Fixed charges

= =

III. Plant overhead cost Plant overhead cost = = Manufacturing cost =

Cost $ 1230720 369216 553824 307680 501467 125367 36922 92304 3217500

015*T $461520

0.1*T $307680 direct production cost + fixed charges + plant

Production Of Methanol From Natural Gas

=

209

overhead cost. $3986700.

GGENERAL EXPENSES Components of cost Administration cost Distillation and selling cost Research and development Financing (Interest) GENERAL EXPENSES

%age 40%T 10%T 5%T 2%T.C.I

Cost $ 123072 307680 153840 393837 978429

TOTAL PRODUCT COST Total Product Cost

=

Manufacturing Cost + General Expenses

=

3986700 + 978429

=

$ 496512

PRODUCT COST PER LITER As capacity

=

150 tons/day

=

50271107 Lit/year

=

4949094/(5.271 * 107)

=

$ 0.0865

V

=

F.C.I – Land

V

=

16715568 – 207647

Vs

=

0

N

=

10 years

d

=

(V – Vs) / n

=

(16507921 – 0) /10

=

$ 1650792

=

Rs 99047520

Product cost per liter

=

Rs 5.2

DEPRECIATION

PROFIT In june 2005 Methanol price / LTR in Asia = Now

Rs 10

Production Of Methanol From Natural Gas Profit / year

= = =

210

50271 * 107 (10 – 5.2 ) – 99047520 Rs 17760480 $ 2926008

PAYOUT PERIOD Payout Period

=

fixed capital investment/(profit/year + depreciation/year)

Payout Period

=

16715568/(2926008+1650792)

=

3.65 year

TURNOVER RATIO Gross Annual Sales

=

5.721 * 107 * 10

=

TURNOVER RATIO

5.721 * 108 * Rs

=

$9535000

=

Gross Annual Sales/Fixed Capital Iinvestment

=

9535000/16715568

=

0.57

Production Of Methanol From Natural Gas

211

Production Of Methanol From Natural Gas

212

SITE SELECTION AND ECONOMIC ASPECTS Methanol is the product mainly used for the manufacturing of formaldehyde, acetic acid and MTBE. Currently there is no methanol plant in Pakistan and about 90 tons pe day is to be imported to occupy its consumption. In Pakistan it is used as raw material for urea formaldehyde, acetic acid, and also used as methalated spirit in pharmaceuticals, dyes etc. after comparing with the Asia and international markets rates, we can easily say that our product can capture 100% market of methanol in Pakistan. Our plant production capacity is 150 tons per day. The remaining 60 tons per day could be exported. We can compete Asia and international markets due to low product cost , also material (N.G) for the production of methanol is easily available in Pakistan at low rates. Keeping in mind the factors, we discuss now, what should be the plant site.

1) PLAND As mentioned earlier that we cover 100% methanol market in Pakistan and remaining is to be exported. Our main market is Karachi because two urea formaldehyde, pharmaceutical, and dying etc. plants are there. So a site near the Karachi and the seaport is preferred, where it could be exported from. The industrial zones are, KARACHI INDUSTRIAL ZONES: a) Site Karachi b) Site North Karachi c) Korangi Industrial Area d) Karachi Export processing Zone e) Qasim Industrial Zones HUB INDUSTRIAL AND TRADING ESTATE (BALOCHISTAN) There are number of projects in Karachi industrial zones so by now land has become costly and only (approximately) 30% of industrial area is available where in Hub and Industrial and Trading Estates (HITE) 95 % industrial area is available. Also environmental constraints are becoming strict in Karachi industrial zones. On the other hand HITE is nearest industrial area to port Qasim, it is newly being developed, land as relatively less costly and environmental constraints would be not strict as in Karachi zones. So from land point of view HITE is more suitable.

1) RAW MATERIAL The major raw material for manufacturing of methanol is “Natural Gas”. Raw material is easily available in HITE but it is not available in Karachi industrial zones except in Site North Karachi, the plots allotment has been frozen.

2) MANUFACTURING AREA Karachi is the nearest city to HITE and having a favorable market. On the other hand we can export easily using Port Qasim. The suitable markets for export are Korea, Japan, Russia, India, Europe, etc.

3) TRANSPORTATION Recently new plan for infrastructure is introduced by Govt. and implemented, in which it is planned to connect Hub Industrial and Trading Estate (HITE) with Punjab through national highway and with Karachi by coastal highway passes.

Production Of Methanol From Natural Gas

213

So there will be no problem for product transportation.

4) ENVIORNMENTAL IMPACT AND EFFLUENT DISPOSAL At Karachi industrial zones there are number of plants working, so environmental issues are arising day by day and in future environmental constraints would become more strict. On the other hand HITE is newly being developed so environmental constraints are less strict and sufficient land area is available for disposal.

5) UTILITIES In Hub and Trading Estate (HITE) water, Natural Gas, Electric Power, Telephone is available and seawater is used for cooling purposes so cooling tower is not required as used by HUBCO.

6) POLITICAL AND STRATEGIC CONSIDERATIONS Balochistan is relatively backward area as compare to the other provinces of Pakistan. So federal as well as provincial government is planning and keenly interested in developing this region and HITE is a part of this. Therefore in order to attract the investors and trades, government shall definitely be providing the incentives such as tax concessions and other inducements (HITE is a Tax Free Area).

7) LABOUR AND MANPOWER In HITE (Balochistan) cheaper labour is available for plant construction work and for operation. There is one limitation associated that HITE (Balochistan) as compare with Karachi Industrial Zones i.e., the availability from Karachi and others. Therefore this limitation is not overwhelming.

INFORMATION ABOUT INDUSTRIAL ZONES Hub Industrial and Trading Estate (HITE) Location

Hub, District Lasbela

Year of Establishment

1982

Total Number of plots

1440 plots

Size of plots

Variables

Uptake/number of plots allotted

150 plots

Industrial plots availability

Available, Occupaney-5%

Infra structure

Road, water, gas power, telephone

Type of industry

Power generation plastic industries

Nearest city

Karachi

Production Of Methanol From Natural Gas

PORT QASIM INDUSTRIAL ZONES Location

Port Qasim

Year of Establishment

1980

Total Area

2700 acres + 8300acres+1000 acres

Total Number of Plots

Not Fixed

Size of Plots

Variable

Uptake/Number of Plots Allotted

Large Tracts Available

Industrial Plots Availability

Available

Infra structure

Roads, Water, Power, Port

Type of Industry

Port Related Activities

Nearest City

Karachi

Karachi Export Processing Zones Location

Landi, Industrial Area, off Mehran Highway

Year of Establishment

1989

Total Area

500 acres

Total Number of Plots

Not Fixed

Size of Plots

Variable

Uptake/ No. of Plots allotted

103 Plots

Industrial Plots Availability

Available

Infrastructure

Roads, Water, Power

Type of Industry

Garments, Electronics, precision Machining, Light Chemical, Leather, food processing

214

Production Of Methanol From Natural Gas Nearest City

Karachi

Site Karachi Location

Mango Pir Road Karachi

Year of Establishment

1947

Tptal Area

4460 acres

Total Number of Plots

1956

Size of Plots

0.5-1 acres

Uptake/No. of Plots allotted

100%; Occupancy full

Industrial Plots Availability

Nil

Infrastructure

Roads, Sewerage, Electricity, Water Supply, Telephone Engineering, Textile, Consumer Goods, Telephone Karachi

Type of Industry Nearest City

Site North Karachi Location

Scheme No. 33 North Karachi

Year of Establishment

1983

Total Area

1029 acres

Total Number of Plots

280

Size of Plots

0.5 acres and to industry requirements

Uptake/No. of Plots allotted

98 Plots; occupancy full

Industrial Plots Availability

Plots are available but the allotment has been frozen Power, Water, Gas Telephone, Internet, Roads. Textile, Garments, hosiery, Light Engineering, soap, poultry, electronics, Cotton, Dyeing.

Infrastructure Type of Industry

215

Production Of Methanol From Natural Gas Nearest City

216

Karachi

Korangi Industrial Area Location Year of Establishment

South East of Karachi, about 20 km from the city centre 1961-69

Total Area

3500 acres

Total Number of Plots

2700Plots

Size of Plots

160 sq. yards-5000 sq. yards

Uptake /No. of Plots allotted

2571 operating units

Industrial Plots Availability

Available; Occupancy 60%

Infrastructure

Roads, Electricity, Water Supply, Sewerage, Telephone, Railway Siding available Textile, Garments, hosiery, Leather, Jute Thread, Pharmaceutical Products, Cosmetics, Soap, Sanitary Items, Basic Chemicals, Paints Karachi

Type of Industry

Nearest C ity

Production Of Methanol From Natural Gas

“NOMENCLATURE” as = Area of shell at = Flow area per tube B = Baffle Spacing C = Clearance b/w tubes Cp = Specific Heat Capacity D = Inside diameter of tubes De = Equivalent diameter of shell Ds = Inside diameter of shell F = Friction Factor Gt = Tube side mass velocity Gs = Shell side mass velocity hi , ho = Inside and Outside film coefficient hio = Value of hi when referred to the tube ,OD,Btu/hr.ft2.oF Hv = Heat of vaporization ID = Internal Diameter L = Tube Length,ft LMTD = Log Mean Temperature Difference M = Mass flow rate of vapors mm,mw,mDME = Mass Flow rate of vapors of methanol,water,DME n = Number of passes OD = Outer Diameter PT = Tube Pitch ∆P, ∆Pt, ∆Pr = Total,tube,return pressure drop ∆Ps = Pressure drop of shell Q = Heat Flow Rd = Combined dirt factor Re = Reynolds number, dimensionless s = Specific Gravity w = Mass Flow Rate of water = Viscosity = Viscosity ratio, ( / w) 0.14 ML = Mass flow of liquid entering vessel (kg/h) MV = Mass flow of vapor entering vessel (kg/h) K = Separator sizing factor (m/s) Vmax = Maximum allowable vapor velocity in separtor (m/s) A = Vessel cross sectional area (m2) r = Vessel radius (m) D = Vessel diameter (m) QL = Volumetric liquid flow entering vessel (m3/s) QV = Volumetric vapor flow entering vessel (m3/s)

217

Production Of Methanol From Natural Gas

Refernces Books  Shreve‘s Chemical Process Industries(5th Edition) by George T.Austin  Elementary Principle of Chemical Process(3rd Edition) by Richard M.Felder ,Ronald W. Rousseau.  Synthetic fuels by Ronald F. Probstein, R. Edwin Hicks.  Petrochemicals by Dr. B.K. Bhaskararo.  From Hydrocarbons to Petrochemicals by Lewis F. Hatch ,Sami Matar  Hand book of Petrochemical & Downstream Projects.  Encyclopedia of Chemical Processing & Design , Vol-29 by John J. Maketta  Encyclopedia of Chemical Technology, Vol-16 (4th Edition)  Chemical Process Principles by Olaf A. Hougen , Kenneth M. Watson  Coulson and Richardson‘s Chemical Engineering Vol-1 (5th edition), Vol-2 (4th edition), Vol-3 (3rd edition), Vol-6 (2nd & 3rd edition)  Unit Operation of Chemical Engineering (5th edition) by Warren L.McCabe , Julian C.Smith ,Peter Harriott.  Plant design and Economics for Chemical Engineers(4th edition) by Max. S. Peter, Klaus D. Timmerhaus.  Applied Process Design for Chemical Engineering , by Branan.  Equipment Design Handbook For Refineries and Chemical Plant Vol-2 (2nd Edition) by Frank L.evans.  Process Heat transfer by D.R Kern  Perry‘s Chemical Engineering Handbook by Robber H. Perry & Don Green  Chemical Process Equipment Selection & Design by Stanely M. Wales  Chemical and Catalytic Reaction Engineering by James J. Carberry.

218

Production Of Methanol From Natural Gas

219

 An introduction to Chemical Engineering Kinetics & Reactor design by Charles G. Hills . Jr.  Fundamentals of Heat Exchanger Design by Ramesh K. Shah  Methanol Synthesis Technology by Sunggyu Lee  Chemical Reactor Design by Peter Harriott  Chemical Process Engineering by Harry Silla  Basic Principles and Calculations in Chemical Engineering (6th Edition) by Himmelblau David M.

Web Sites: www.google.com www.methanol.org/methnaol/ www.drycoolers.com www.boilerdesign.com www.science.uwaterloo.ca www.ttmethanol.com