Project Report On Liquid Nitrogen

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Project Report On

“MANUFACTURING OF LIQUID NITROGEN”

Submitted by TAMBE NINAD RUPCHAND KATARIWALA JAYMIN SANJAYKUMAR

-U07CH152 -U07CH123

B.Tech IV Chemical Engineering Year 2010-2011

Under the Guidance of MR. V.N.LAD Assistant Professor Chemical Engineering Department SVNIT

Chemical Engineering Department Sardar Vallabhbhai National Institute of Technology, Surat

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CERTIFICATE

This is to certify that the project report titled “MANUFACTURING OF LIQUID NITROGEN” submitted by Mr. TAMBE NINAD RUPCHAND Roll No. U07CH152 and Mr. KATARIWALA JAYMIN SANJAYKUMAR Roll No U07CH123 is a record of bonafide work carried out by them, in partial fulfillment of the requirement for the award of the Degree of Bachelor of Technology (Chemical Engineering).

Date: -

Examiner 1: ____________

GUIDE (Mr.V.N.Lad) Assistant Professor Chemical Engineering Department

Examiner 2: ____________

HOD (Dr. M. Chakraborty) Assistant Professor & Head Chemical Engineering Department

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ACKNOWLEDGMENT

I would like to express my deep sense of gratitude to my guide Mr.V.N.Lad (Assistant Professor, CHED, SVNIT, SURAT) for his valuable guidance and motivation and for his extreme cooperation to complete my seminar work successfully.

I would like to express my sincere respect and profound gratitude to Dr. M. Chakraborty (Assistant Professor & Head), of Chemical Engineering Department for supporting me and providing the facilities for my seminar work.

I appreciate all my colleagues whose direct and indirect contribution helped me a lot to accomplish this seminar work.

I would also like to thank all the teaching and non teaching staff for cooperating with me and providing valuable advice which helped me in the completion of this seminar.

TAMBE NINAD RUPCHAND KATARIWALA JAYMIN SANJAYKUMAR

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CONTENTS

Chapter

Page No

1.

Introduction

6

2.

Demand and Supply Of Product

7

3.

Process Selection And Description (MSDS Of Chemicals Involved)

8

4.

Material Balance and Energy Balance

16

5.

Thermodynamics

20

6.

References

22

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LIST OF MAIN FIGURES Figure No 1 Sales of Liquid gases

Title

Pg No 7

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Process flow diagram of Linde-Frankl process

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3

Entropy(S) Vs Temperature (T)

20

4

Pressure Vs Temperature (T)

21

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Chapter 1: Introduction Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colorless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4. Liquid nitrogen is often referred to by the abbreviation, LN2 or "LIN" Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at −195.8 °C. When insulated in proper containers such as Dewar flasks, it can be transported without much evaporative loss. At atmospheric pressure, liquid nitrogen boils at 77 K (−196 °C; −321 °F) and is a cryogenic fluid which can cause rapid freezing on contact with living tissue, which may lead to frostbite. When appropriately insulated from ambient heat, liquid nitrogen can be stored and transported, for example in vacuum flasks. Here, the very low temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks. Uses: Liquid nitrogen is a compact and readily transported source of nitrogen gas without pressurization. Further, its ability to maintain temperatures far below the freezing point of water makes it extremely useful in a wide range of applications, primarily as an opencycle refrigerant, including: 

as a coolant for CCD cameras in astronomy



to store cells at low temperature for laboratory work



in cryogenics



as a source of very dry nitrogen gas



for the immersion freezing and transportation of food products



for the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials



as a method of freezing water pipes in order to work on them in situations where a valve is not available to block water flow to the work area



in cryotherapy for removing unsightly or potentially malignant skin lesions such as warts and actinic keratosis



in the process of promession, a way to dispose of the dead



for cooling a high-temperature superconductor to a temperature sufficient to achieve superconductivity



For the cryonic preservation of humans and pets in the hope of future reanimation.



to preserve tissue samples from surgical excisions for future studies



to shrink-weld machinery parts together

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as a coolant for vacuum pump traps and in controlled-evaporation processes in chemistry.



as a coolant to increase the sensitivity of infrared homing seeker heads of missiles such as the Strela 3



as a coolant to temporarily shrink mechanical components during machine assembly and allow improved interference fits



as a coolant for computers



in food preparation, such as for making ultra-smooth ice cream.

Like dry ice, the main use of liquid nitrogen is as a refrigerant. Among other things, it is used in the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials. It is used medically in cryotherapy to remove cysts and warts on the skin. It is used in cold traps for certain laboratory equipment and to cool Xray detectors. It has also been used to cool central processing units and other devices in computers which are overclocked, and which produce more heat than during normal operation Liquid nitrogen production is an energy-intensive process. Currently practical refrigeration plants producing a few tons/day of liquid nitrogen operate at about 50% of Carnot efficiency

CHAPTER 2: DEMAND SUPPLY DATA FOR LIQUID NITROGEN COMMERCIAL ANALYSIS Beside liquid nitrogen ,whose application are described below ,industrial gases includeoxygen argon, acetylene ,hydrogen ,helium and others such as carbon monoxide,nitrous oxide and other noble gases. The global market share is given as below:-

Sales liquid oxygen ln2 argon carbon dioxide acetylene hydrogen helium other

Figure 1: sales of Liquid gases

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CHAPTER 3:PROCESS SELECTION AND DESCRIPTION





AIR SEPERATION TECHNOLOGY Though there are differences in process details displaying desired product mix and other factors, all air separation plants make use one of the following two types of process technology: Cryogenic plants: The air separation technique used in cryogenic plants produce gas and Liquid products (liquid oxygen, liquid nitrogen etc.) using very low temperature distillation which separates air components and produce desired product purities. Non-cryogenic plants: The air separation technique used in non cryogenic plants produce gaseous products with near-ambient temperature separation processes. They use differences in properties like molecular structure, size and mass to produce oxygen or nitrogen. As our area of interest is liquification ,this can be done by Low temp. rectification of liquid air. This process mainly comprises of two steps. One is the liquefaction & then the separation of liquid air into oxygen & nitrogen. Since the process mainly requires low temp., refrigeration is necessary. Different cycles are in use to have required refrigerating effect 1. Heylandt liquid nitrogen process 2. Claude process 3. Linde frankl process 4. Membrane separation technology Out of the above processes the Claude process and lindey frankl process are really important processes for the manufacture of liquid nitrogen. Briefly giving an overview of these two processes CLAUDE PROCESS: This process is characterized by the double expansion engine. After passing through the preliminary heat exchanger, at 60 atm pressure, part of the air traverses the liquefier from top to bottom & is admitted to the base of the dephlagmetar after expanded to 4 atm.The reset is expanded like wise to 4 atm,in the first stage of the expansion engine, after which it is again separated into two portions. One is added to the partially liquid air behind the valve; the other is warmed by passing up the upper part of the liquefier, & is then expanded to 1 atm. In the second stage of the engine, the expanded air there upon mixes with the cold nitrogen vapor emerging from the top of the column & returns through the lower part of the liquefier & through the preliminary heat exchanger. The oxygen in this air is wasted.

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The refrigerant between the tubes of the dephlagmator is liquid nitrogen from the column, part of which is withdrawn through tube.

LINDE-FRANKL PROCESS: This is the most important process for the commercial production of liquid nitrogen in this process at first air is filtered & compressed to 6.8 atm in turbo compressor. During the compression cooling is done to maintain the temp to 35 -400C. After compression the ,stream is passed through reciprocating compressor to increase the pressure to about 200atm.Here the air temp is maintained at 4-80C by intermediate cooling between stages using cold water obtained by heat exchanger. Then the air goes through high pressure heat exchanger where the temp of air is brought down to about-120 -1400C. Now the air undergoes expansion to about 6.5 atm in the expansion engine .The temperature of air is brought down to -170 to-1740Cby joule Thompson effect. Now the air will be in liquid.This saturation liquid is fed to Linde rectification column. This column may be single, double or compound depending on requirement. the liquid product coming out will have a purity of about 99.4 -99.99%.This liquid is partially vaporized in condenser, to liquefy the nitrogen vapor &the rest may be taken as liquid product or it may be obtained in gaseous state if it is used for cooling of incoming air, the other products that obtained are pure nitrogen of purity above 98% & waste nitrogen product of purity of about 92-96%.These cold streams are utilized for cooling air, this process is most economical for tonnage nitrogen plants &most widely used in the world

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Figure2: flow diagram of Linde-Frankl process Process Variables 1. Initial temperature:

The initial or the entrance temp for air is an independent variable.

Although it varies from 10 to 500C depending on the weather conditions and the type of after cooler, for most cases, it is assumed as 27-300C. 2. Initial pressure: This is an important variable; it is independent in the case of liquid oxygen process. The lowest allowable value of pressure is controlled by the saturation temp. Of air or nitrogen, this must be higher than the boiling point of oxygen at column pressure. In a double column, the air pressure must be such that the nitrogen will condense at the temp of boiling point of oxygen in order to produce reflux. This will be in the 46.5atm range, depending on the pressure in the lower pressure column, and on the necessary temperature difference in the condenser boiler. 3. Temperature approaches: An analysis of the process shows that it is necessary to establish the minimum temp approaches for heat exchangers. For the exchange of sensible heat, the minimum approach has to be 3-50C 4. Intake temperature to expander: this variable has the flexibility of being at almost any value between the room temp and one close to that of air liquefaction, without appreciable effect on the efficiency of expander. It is so chosen that the exhaust is saturated vapor. 5. Purity of product gases: this is fixed at some value less than 100%,with due regard to certain limitation that may set a definite upper limit with a single column.

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6. Heat leak: this is one of the most difficult variables to be selected since it depends on factors which cannot readily be evaluated in advance. For e.g. the size of the plant is of at most importance. Although the leak on an hourly basis increases when expressed the basis increases as plant size increases when expressed the basis of a unit of air treated or oxygen produced, it decreases and in large plants, is almost negligible. 7. Energy requirement: once the various quantities, temp, pressure are established the work done by the compressors and expanders, and hence the energy requirements can be easily calculated. 8. Sizes of equipment units: The thermodynamic analysis plays an important role in this variable, since it deals with the driving forces in the heat exchangers and in distillation columns. The type of column chosen also plays a big role in the operation of the unit. There are 3 types of columns that can be used for rectification namely simple, double and compound. Simple consists of only an exhausting column and liquid feed to it consists only the reflux. It has an adv of simplicity and economy of distribution and construction. The compound column has both exhausting and enriching sections, but it must be provided with a source of refrigeration at a very low temp, i.e. below the B.P.of nitrogen at the operating pressure of the column.

The double column has two rectification columns operated at two different pressures, so chosen that the nitrogen at high pressure column condenses at a temperature above the boiling point of oxygen of low pressure column. Usually the pressure in the high pressure column is 6-7 atm and in the other is 1.5-2 atm. This has the adv of high yield without auxiliary refrigeration, but it is expensive and complicated to manufacture. But on the tonnage scale, double column is preferred of high yield and high purity.

Selection of Process Prior to the selection of the process it should be emphasized that there are so many adjustable variables involved, it is very difficult to put all on a comparable basis. Usually on the smallest scale, the most important economic factors are capital and labor charges. Thermodynamic efficiency and hence power charges for compression are of less consequence. Charges for material such as compressor oil, chemicals for air purification are small in relation to the other costs. The labor charges also decreases when the scale increases and in this cases the capital costs and power costs dominate. When the plant produce a liquid product, as in this case the power requirement to provide necessary refrigeration is considerably increased and thermodynamic efficiency is of much importance.

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The essential requirement on a general scale is a cheap and simple plant, easy to operate for which a thermodynamic efficiency is not needed. But if the liquid is produced on a large scale, the thermodynamic efficiency becomes important. As the purpose of this project is to design large scale oxygen product plant the only process that seems economical is the LINDE FRANKL PROCESS. As the most important adv here is the high purity of liquid nitrogen (99.5) %, although the work of liquefaction of air is about 3.5kwh/gallon which is relatively higher than other process. Also the outgoing streams from the rectification column are used effectively in supplying the required refrigeration for cooling the incoming air. In view of all the above cited advantages the process. For this project is linde-frankl.

Material Data Safety Sheet 1. Chemical Product Product Name: Nitrogen, refrigerated liquid Trade Names: Liquid Nitrogen Chemical Name: Nitrogen Synonyms: Nitrogen (cryogenic liquid) Chemical Family: Cryogenic liquid 2. Hazards Identification Extremely cold liquid and gas under pressure. Can cause rapid suffocation. Can cause severe frostbite. May cause dizziness and drowsiness. Self-contained breathing apparatus and protective clothing may be required by rescue workers. Under ambient conditions, this is a colorless, odorless, cryogenic liquid. OSHA REGULATORY STATUS: This material is considered hazardous by the OSHA Hazard Communications Standard (29 CFR 1910.1200). POTENTIAL HEALTH EFFECTS:

Effects of a Single (Acute) Overexposure Inhalation. Asphyxiant. Effects are due to lack of oxygen. Moderate concentrations may cause headache, drowsiness, dizziness, excitation, excess salivation, vomiting, and unconsciousness. Lack of oxygen can kill. Skin Contact. No harm expected from vapor. Cold gas or liquid may cause severe frostbite. Swallowing. An unlikely route of exposure, but severe frostbite of the lips and mouth may

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result from contact with the liquid. Eye Contact. No harm expected from vapor. Cold gas or liquid may cause severe frostbite. Effects of Repeated (Chronic) Overexposure. No harm expected. Other Effects of Overexposure. Asphyxiant. Lack of oxygen can kill. Medical Conditions Aggravated by Overexposure. The toxicology and the physical and chemical properties of nitrogen suggest that overexposure is unlikely to aggravate existing medical conditions. 3. Composition COMPONENT CAS NUMBER CONCENTRATION Nitrogen 7727-37-9 >99% 4. First Aid Measures INHALATION: Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, qualified personnel may give oxygen. Call a physician. SKIN CONTACT: For exposure to liquid, immediately warm frostbite area with warm water not to exceed 105°F (41°C). In case of massive exposure, remove clothing while showering with warm water. Call a physician. SWALLOWING: An unlikely route of exposure. This product is a gas at normal temperature and pressure. EYE CONTACT: Immediately flush eyes thoroughly with warm water for at least 15 minutes. Hold the eyelids open and away from the eyeballs to ensure that all surfaces are flushed thoroughly. See a physician, preferably an ophthalmologist, immediately. 5. Fire Fighting Measures FLAMMABLE PROPERTIES: Nitrogen cannot catch fire. SUITABLE EXTINGUISHING MEDIA: Nitrogen cannot catch fire. Use media appropriate for surrounding fire PRODUCTS OF COMBUSTION: Not applicable.

Specific Physical and Chemical Hazards. Heat of fire can build pressure in cylinder and cause it to rupture. No part of cylinder should be subjected to a temperature higher than 125°F (52°C). Liquid nitrogen containers are equipped with pressure relief devices. Venting vapors may obscure visibility. Liquid causes severe frostbite, a burn-like injury 6. Accidental Release Measures Personal Precautions. Asphyxiant. Lack of oxygen can kill. Evacuate all personnel from danger area. Use self-contained breathing apparatus and protective clothing where needed. Liquid causes severe frostbite, a burn-like injury. (See section 2.) Shut off flow if you can do so without risk. Avoid contact with spilled liquid and allow it to evaporate. Ventilate area of leak or move container to a well-ventilated area. Test for sufficient oxygen, especially in confined spaces, before allowing reentry. Environmental Precautions. Prevent waste from contaminating the surrounding environment. Keep personnel away. Discard any product, residue, disposable container, or liner in an environmentally acceptable manner, in full compliance with federal, state, and local regulations. If necessary, call your local supplier for assistance.

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7. Handling and Storage PRECAUTIONS TO BE TAKEN IN HANDLING: Do not get liquid in eyes, on skin, or on clothing. Never allow any unprotected part of your body to touch uninsulated pipes or vessels containing cryogenic fluids. Flesh will stick to the extremely cold metal and will tear when you try to pull free. For liquid withdrawal, wear face shield and cryogenic gloves (see section 8). Use a suitable hand truck to move containers. Always handle and store cryogenic containers in an upright position. Do not drop or tip containers, or roll them on their sides. Open valve slowly. Close container valve after each use; keep closed even when empty. If valve is hard to open, discontinue use and contact your supplier. For other precautions in using nitrogen, see section 16. PRECAUTIONS TO BE TAKEN IN STORAGE: Store and use with adequate ventilation. Store only where temperatures will not exceed 125°F (52°C). Do not store in a confined space. Cryogenic containers are equipped with a pressure relief device and a pressure controlling valve. Under normal conditions, these containers will periodically vent product. Use adequate pressure relief devices in systems and piping to prevent pressure buildup; entrapped liquid can generate extremely high pressures when vaporized by warming 8. Exposure Controls/Personal Protection COMPONENT Nitrogen

OSHA PEL Not Established.

ACGIH TLV-TWA (2007) Simple asphyxiant

ENGINEERING CONTROLS: Local Exhaust. Use a local exhaust system, if necessary, to prevent oxygen deficiency. Mechanical (General). General exhaust ventilation may be acceptable if it can maintain an adequate supply of air. Special. None Other. None

PERSONAL PROTECTIVE EQUIPMENT: Skin Protection. Wear loose-fitting, cryogenic gloves, metatarsal shoes for container handling, and protective clothing where needed. Cuffless trousers should be worn outside the shoes. Select in accordance with OSHA 29 CFR 1910.132 and 1910.133. Regardless of protective equipment, never touch live electrical parts. Eye/Face Protection. Safety glasses and a full face shield are recommended. Select in accordance with OSHA 29 CFR 1910.133. Respiratory Protection. Use air-supplied respirators where local or general exhaust ventilation is inadequate. Air-supplied respirators must be used in confined spaces or in an oxygen- deficient atmosphere. Respiratory protection must conform to OSHA rules as specified in 29 CFR 1910.134. Select in accordance with 29 CFR 1910.134 and ANSI Z88.2.

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9. Physical and Chemical Properties APPEARANCE: ODOR: ODOR THRESHOLD: PHYSICAL STATE pH: MELTING POINT at 1 atm: BOILING POINT at 1 atm: FLASH POINT (test method):

Colorless liquid Odorless Not applicable Cryogenic liquid Not applicable. -346°F (-210°C) -320.44°F (-195.80°C Not applicable

EXPANSION RATIO for liquid at boiling

1 to 696.5

point to gas at 70°F (21.1°C): EVAPORATION RATE (Butyl Acetate = 1): FLAMMABILITY: FLAMMABLE LIMITS IN AIR, % by volume:

Not applicable Nonflammable LOWER: Not applicable. UPPER: Not applicable 50.7 lb/ft3 (808.5 kg/m3)

LIQUID DENSITY at boiling point and 1 atm: VAPOR PRESSURE at 68°F (20°C):

Not applicable 0.0724 lb/ft3 (1.160 kg/m3)

VAPOR DENSITY at 70°F (21.1°C) and 1 atm SPECIFIC GRAVITY (H2O = 1) at 19.4°F (-7°C): SPECIFIC GRAVITY (Air = 1) at 70°F (21.1°C) and 1 atm: SOLUBILITY IN WATER, vol/vol at 32°F (0°C): PARTITION COEFFICIENT: n-octanol/water: AUTOIGNITION TEMPERATURE: DECOMPOSITION TEMPERATURE: PERCENT VOLATILES BY VOLUME: MOLECULAR WEIGHT: MOLECULAR FORMULA: 6. Stability and Reactivity CHEMICAL STABILITY: CONDITIONS TO AVOID: neodymium, titanium and magnesium INCOMPATIBLE MATERIALS:

Not available. 0.967 0.023 Not available Not applicable. Not available 100 28.01 N2 Stable High temperatures, exposure to lithium, None known.

HAZARDOUS DECOMPOSITION PRODUCTS: None known. POSSIBILITY OF HAZARDOUS REACTIONS: May Occur Under certain conditions, nitrogen can react violently with lithium, neodymium, titanium [above1472°F (800°C)], and magnesium to form nitrides. At high temperature, it can also combine with oxygen and hydrogen. 7. Toxicological Information ACUTE DOSE EFFECTS: Nitrogen is a simple asphyxiant STUDY RESULTS:

None known

8. Ecological Information ECOTOXICITY: No adverse ecological effect expected.

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OTHER ADVERSE EFFECTS: Nitrogen does not contain any Class I or Class II ozonedepleting chemicals 9. Disposal Considerations WASTE DISPOSAL METHOD: Do not attempt to dispose of residual or unused quantities. Return cylinder to supplier.

CHAPTER 4. MASS AND HEAT BALANCE Basis: 10 tonnes/day ln2 , 10 tonnes/day gaseous nitrogen and 2 tonnes per day waste nitrogen gas So total nitrogen production = 22 T/day = (22*1000)/(24*14) = 65.476 kg moles/hr At standard temperature and pressure, 1kg.mole occupies 22.4m3 Nitrogen produced in volumetric units =65.476*22.4 =1466.66Nm3/hr Standard analysis of air: Component

volume%

Nitrogen

78.03

Oxygen

20.99

Argon

0.94

Hydrogen

0.01

Helium

0.0003

Krypton

0.00011

Xenon

0.00009

Carbon dioxide

0.03-0.06

Moisture

0.02-0.05

Quantity of intake air: = 1466.66m3/hr of nitrogen

 Capacity of the unit  Volume % of nitrogen in the air

=78%

 Quantity of air needed

=1466.66/0.78 =1880.34m3/hr

 Assuming about 15% less of air due to removal of moisture, CO2 and from possible leaks. The quantity needed

= 1880.34+1880.34 *.15 =2162.393m3/hr

Thus this much amount of air is required for production of 10 tonnes of liquid nitrogen

Heat balance: At turbo compressor

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Atmospheric conditions : Temperature =300C,

relative humidity =60%

Now the air passes through elements of the system  Enthalpy of air at 1 atm and 300C

=3701kcal/kgmol.

 Enthalpy of air at 6.8 atm and380C

=3766.23 kcal/kgmol

 Moles of air entering compressor  =2162.393Nm3 /22.414=96.475 kgmol/hr  Enthalpy of air entering compressor  =96.475*3701kcal/hr=357053.975kcal/hr  Enthalpy of air leaving the compressor  =96.475*3766.23=363347.0393kcal/hr. So change in enthalpy of air

= 363347.0393-357053.975

=6293.064kcal/hr Heat balance at reciprocating compressor  Amount of air passing = 96.475 kg moles/hr This air passes through compressor Compressor Before compression, air is at 6.5 atm and 38 0C And after it is at 800 atm & 6 0C Enthalpy of inlet air = 3766.23 kcal/kgmol Enthalpy of outlet air = 3251.119 kcal/kgmol

So net enthalpy of entrance = 3766.23*96.475 kcal/hr = 363347.0393 kcal/hr And for exit air 96.475*3251.119 kcal/hr=313651.7 Assuming no condensation of water vapor The net change in enthalpy of air = 49695.333kcal/hr  CO2 absorber: volume % ofCO2 in air =.045% Moles of V present = .045*96.475/100=.0434 kg moles/hr Moisture present volume% of moisture in air =0.05 Moles=0.05*96.475/100=0.0482 In the absorber most of the moisture and CO2 is removed Thus air=96.475-0.0434-0.0482 =96.3834kgmol/hr

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High pressure heat exchanger 96.3834 kgmol/hr is used to produce ln2, gaseous nitrogen and waste n2 Thus nitrogen entering HP heat exchanger is 0.78*96.834*10/22=34.20477kgmol/hr Considering the same data for oxygen entering (mole fraction is =0.21) Oxygen entering HP heat exchanger is 0.21*96.834*10/20=20.335kgmol/hr No change in mass. Now heat balance, from enthalpy chart in Perry’s handbook

Stream

Flow rate

Temp.

Pressure

Enthalpy

Kg

0

atm

Kcal/kg

-178

1.5

1500

4

1.5

2750

C

moles/hr Pure nitrogen

In34.2047 Out34.2047 In

Oxygen

-

20.335

-178.2

30

2161.6

2

30

3328.64

6

200

3251.119

T

200

H

Out20.335 Air

In

–

96.834 Out96.834

 Heat taken by pure nitrogen stream= 34.2047(2750-1500)= 42755.875 kcal/hr  Heat taken up by oxygen = 20.335 (3328.64-2161.6) = 23731.7584 kcal/hr  Heat lost by air = 96.834(3251.119-H) Now H=2428.91 kcal/kg mol Now the corresponding temp of air is -1500 C(T) So the air entering the expansion engine is at 200 atm and -1500 C Here air is expanded to 6.5 atm the temp. Of air after compression is -1740 C(liquid state) and fed to lower distillation column.

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Mass Balance at Columns: Let the liquid to vapor ratio at the top of both columns to be .58 So L1’/V1’=L2’/V2’=.58 Suffix 1 for upper column Now V2’=34.20472 L2’=.58*34.20472=19.8387kg moles /hr This L2’ comes out of condenser in vapor state and fed at the top of upper column as liquid after passing through expansion valve .58V1’+19.838=V1’ .42V1’=19.838 so V1’=4723.5 kg moles/hr The amount L1’ refluxed to the lower column after condensation occurs in the condenser =.58*4723.5 = 2739.63 kg moles/hr Let F=amount of feed =96.834kgmoles/hr W=bottom product from lower which is refluxed back to the top column ( rich liq) S=side stream from lower column, which is refluxed back to top column (impure liquid) Xf=mole fraction of N2 in feed = .79 Xw=mole fraction of N2 in rich liquid =.65 Xs= mole fraction of N2 in IPL=.96 X1= mole fraction of N2 in top product = .9999 Now, from overall& component balance F=W+S+L2

---- (1)

FXF =WXw +SXs + X1L2---- (2) From (1) 96.834 = W + S +19.8387

W +S = 76.99----- (3) From (2) (96.834*.079) = (W*.65)+(S*.96)+(19.8387*0.9999)----- (4)

56.67 = .65W + .96S Multiplying (3) by .65 Solving (3) and (4) we get S=21.377419 kg moles /hr & W = 76.67-21.377419 = 55.61258 kg moles/hr

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CHAPTER 5: THERMODYNAMICS The simplest liquefaction process is the Linde or Joule-Thompson expansion cycle Some of the steps in the process are 1. Gas is compressed at ambient pressure 2. Cooled in a heat exchanger 3. Passed through a throttle valve - isenthalpic Joule- Thompson expansion - producing liquid

Figure3: Entropy(S) Vs Temperature (T) The ideal work of liquefaction for nitrogen is only 0.207 kWh/kg (0.094kWh/lb)

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Figure 4: Pressure Vs Temperature

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References 

Department of mechanical and aerospace engineering-NASA hydrogen researchpdf



US Patent 4072023 - Air-rectification process and apparatus



Air liquefaction:distillation Encyclopedia of separation science 2007 science direct R.Agrawal, D.M. herron



MSDS worldwide library-praxair



Cryogenic air separation history and technological progress

www.linde-india.com  American Chemical society journal , some aspects of gas separation at low temperatures by W. H. Granville  Wikipedia  5pengineering –cro&eng srl -nitrogenhpn(pdf)

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