Chlro-alkali Plant Project Work

1

Approval This is to endorse that three students of Chemical Engineering & Polymer Science Dept. of Shahjalal University of Science & Technology have completed their industrial project report on “Global Heavy Chemicals Ltd.” heading Industrial “Project on Chloro-Alkali process units of Global Heavy Chemicals Ltd.”

The report is about to the partial fulfillment of the requirements for the degree of B.Sc in Chemical Engineering & Polymer Science Dept. Their involvement was much appreciated and I wish for their stunning future. Name of the student

Registration no.

Md. Sumon Ali

2006332028

Ahmad-Ur Rob

2006332011

HM Bakhtiar Akib

2007332028

Supervisor

Sreejon Das, Lecturer, CEPS Shahjalal University of Science and Technology Sylhet.

2

Abstract

This paper is on a 20 days long project carried out from 7 March 2012 to 27 March 2102 for the accomplishment of the course CEP- 431 which is programmed for the industrial attachment as a curriculum of the Department of Chemical Engineering and Polymer Science of Shahjalal University of Science and Technology. The project was carried out at the Global Heavy Chemicals Ltd. whose valued collaboration is highly appreciated. Global Heavy Chemicals Ltd. is one of the renowned chlor-alkali Industries in Bangladesh that is completely integrated in producing caustic soda and also bleaching, NaOCl (clotech B), Cl2 as by products.

The topics covered, as team work, in this project were as follows: Feasibility survey, Plant layout, Process description, Material Balance, Energy Balance, Economic analysis by breakthrough curve, Equipment Design, Control Systems,, etc. The program had been finally completed successfully by the kind cooperation of many people.

3

Acknowledgement

I am grateful for the contributions from many individuals leading towards the successful completion of our program, especially those who gave the time to share their thoughtful criticisms & suggestions to improve it. I am deeply owing a favor to them for their personal encouragement and professional assistance. First, I would like to thank Global Heavy Chemicals Ltd. to give us the opportunity to do the project work in their industry. I convey my respectful gratitude to our Teacher and Project Supervisors, Department of Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology, for his valued co-operation in making this project paper. It is a great pleasure for us to acknowledge our Program Coach Md. Masudur Rahman, Process In charge, Global Heavy Chemicals Ltd. for his assistance and co-operation given to us throughout all the working time. Without his heartiest interest and support, it would be quite impossible for us to carry out our project work in such an industry and to complete this report with its full richness in information. I also want to say with great thanks to Mr. Jahangir Alom Mukul for the massive support of giving approach to the industry an also for whole contribution. Special thanks to Mahmudul Hasan and Bidyut Sarker, production engineers, for their constant support and heartiest effort to help us make this program come to a success. I also like to thank all the personnel of Global Heavy Chemicals Ltd. for their kind cooperation, throughout the period of the project work, with their sharing of the various engineering principles and techniques in the theoretical and practical grounds that made me realize and understand the real complexity of manufacturing processes and how to face them from the field of Chemical Engineering.

Author 25th July, 2012

4

Contents 1. Review of GHCL 2. Feasibility Studies 3. Process Description 4. Process Diagram 5. Material Balance 6. Sludge Calculation 7. Energy Balance 8. Equipment Design 9. Economic Evaluation 10. Industrial Safety 11. Plant Layout 12. Hazop Analysis 13. Reference

5 6 8 21 26 32 34 39 44 48 54 60 65

5

Review of Global Heavy Chemicals Ltd. In this modern age of competition, Chemical Engineers need to operate a Chemical plant in such way that it can compete in this business environment ensuring product quality. Global Heavy Chemicals Ltd. (GHCL) is a sister concern of OPSONIN group. In the beginning of 21st Century, GHCL starts its journey as the first private sector Chlor-Alkali Industry in Bangladesh. The industry is located on the southern part of Dhaka district in Hasnabad union under Keranigonj Thana. Significantly related to all the hopes and expectations of the new century, GHCL has energized the vision to open new horizon for industrial development in the country. The project site was a 20 feet deep low-lying land from the road level that has been filled and developed suitably for GHCL plant. It has incorporated most advanced state of the art technologies, machineries and equipments. Global Heavy Chemicals Ltd. believes in management excellence with commitment, honesty, sincerity, dedication and efficiency. With its well-educated, trained and skilled workforce, harmonious working atmosphere, good productivity record and strong environmental commitment, Global Heavy Chemicals Ltd. enjoys a good standing with government and local public. Some key points of Global Heavy Chemicals Ltd.: Company

: Global Heavy Chemicals Ltd. was incorporated on the 19

September 2000, Bangladesh.

th

6

Plant location

: Hasnabad union under Keranigonj Thana which is on the southern part of Dhaka district.

Plant occupied area : 8.5 acres. Plant type

: Chlor-alkali industry.

Plant capacity

: 70 TPD

FEASIBILITY SURVEY

7

Feasibility survey is the pre-pivotal task to establish a plant profitably. Some key factors are necessary to analyze for the feasibility survey of a plant. For Global Heavy Chemicals Limited, the important key factors are listed bellow:  Availability of raw materials: Raw material collection is one of the most predominant task. GHCL collects their raw materials from our neighbour country India. Though raw materials also available in Bangladesh it is collected from India because of higher quality than Bangladesh & river way transportation cost makes it attractive.  Availability of labour: Expert labours are available & there accomodation is also feasible by easy transportation cost as GHCL situated at Dhaka area.  Power: As our government can not provide electricity at low cost, So GHCL produce their electricity as they need. They 14.5 MW power generation capacity to fulfil their need. They use natural gas to produce electricity which collected from “Titas Gasfield” at low cost. They have also Disel power generation system.  GHCL uses surface water for their utility. Water is collected from river “Burigonga” and deep tubewel. So they can manage their necessary amount of water easily.  Transportation cost: Their transportation cost lower enough because of their industry situated at Dhaka. Buyer can easily collect product produced by GHCL.  Another important thing is that disposal treatment. After treatment they can easily through it to the river. They have good treatment system for their both effuent and disposal. So above discussion proved that GHCL is quiet feasible both economically & environmentally.

8

PROCESS DESCRIPTION

9

GHCL is mainly a chloro-alkali industry.Its main products are caustic Soda(NaOH), Sodium Hypochlorite(NaOCl), Clorine Gas(Cl2), hydrogen(H2), Bleaching(Ca(OCl)Cl). GHCL uses membrane cell technology. Sodium hydroxide is produced (along with chlorine and

hydrogen) via the Chloro-alkali process. This involves the electrolysis of an aqueous solution of sodium chloride. The sodium hydroxide builds up at the cathode, where water is reduced to hydrogen gas and hydroxide ion: Electrochemical and chemical reactions occurring in diaphragm and membrane cells [1]

2Cl- ==> Cl2+ 2e-

(anodic reaction)

[2]

2H2O + 2e- ==> 2OH- + H2

[3]

2Cl- + 2H2O ==> Cl2 + H2 + 2OH-

[4]

2NaCl + 2H2O ==> Cl2 +2NaOH + H2 (overall reaction)

(cathodic reaction) (overall ionic reaction)

10

Fig: Overall Process. In the process, three products are produced. It is vital that these are not allowed to mix. Thus, a requirement of a commercial cell for the electrolysis of brine is that it separates the three products effectively. Electrolysis in a simple vessel (described as a ‘one-pot’ vessel) leads to the reaction of chlorine with sodium hydroxide to give unwanted sodium hypochlorite (NaClO), sodium chlorate (NaClO3) and oxygen by the following reactions: Cl2 + OH- → Cl- + HOCl HOCl → H+ + OCl-

2HOCl + OCl- → ClO3 + 2Cl- + 2H+ 4OH- → O2 + 2H2O + 4e-

11

The main process units of GHCL are listed bellow:

I. II. III. IV. V.

VI.

VII. VIII. IX. X. XI.

14.6 MW power plant including diesel generator & boiler house. 2500 MT water storage tank including two-pump house & cooling tower. Bi-polar membrane cell house including rectifier, rectifier transformer, DCS control room, Anolyte & Catholyte tank, de-chlorination building as well as quality control department. Utility building including DM plant, Nitrogen plant, absorption chillers & compressors. This block has got HCl synthesis building including storage tank and delivery platform. Primary & Secondary brine purification area including Salt Saturator, Reactor, Chemical-dosing Tanks, Main Clarifier, Anthracite Filter, Candle Filter, Polished Brine Tank, Ion-Exchange Resin Column and Purified Brine Storage Tank. Automatic Salt Washer unit including separate storage area for raw & washed salt, conveyers, small clarifier etc. Chlorine Drying & Compression Building including Bottling area as well as four large storage tank and delivery platform. Caustic Evaporation and Flaking Building including bagging and storage facility. Hydrogen gas Compression and bottling building. Automatic Effluent treatment plant for industrial water treatment.

12

Process Procedure : GHCL works on the following step by step process. The main task of this industry is to purify the raw salt into two steps

 

Primary purification secondary purification

So total process procedure given sequencially:

Raw Material: The main raw material for this project the solid salt which is further processed to produce caustic soda. In this plant salts are imported from the neighboring country India. Because the composition of the salt comes from India is better from the local salt and also have less impurities than the local salt. We can say this by testing the composition.

Raw salt composition: Composition Ca2+ Mg2+ SO42Total Iron NaCl Moisture

Percentage 0.227% 0.049% 0.645% 13.2 ppm 95.43% 3.649%

Salt Saturator: For melting the solid salt, in the salt saturator there is a continuous process of pumping of return brine solution at about 75°c from the return brine tank which is executed from the cell and is not converted to the caustic soda.

13

After melting raw salt in the salt saturator the solution is passed through a plate filter to remove the floating substance and impurities that come from the salt feeding. Then the solution is fed to the dosing unit. Impurities or the mud which come from the salt decompose at the bottom of the salt saturator and decrease the efficiency of the salt saturator. For this reason after 3-4 months the salt saturator is washed to make it clean. Dosing: From analysis of the raw salt the dissolved impurities are the Ca2+ , Mg2+ ,SO42and the mud that can be said. To remove these impurities chemical dosing is required. BaCl2 is used to removed the S . C is used to remove Ca2+ and also NaOH for the Mg2+. After the dosing of these chemical the salt solution is send to the reactor for the proper mixing. In a chloro-alkali plant mainly five different dosing are performed and these are as follows: 1. 2. 3. 4. 5.

Soda Ash(Na2CO3) dosing Barium Chloride(BaCl2) dosing Sodium Sulphide(Na2SO3) dosing Caustic Soda(NaOH) dosing Flocculants dosing

Chemical dosing: .

Ca2+ in raw materials =

= 14.49 kg/hr For removing Ca2+ Na2CO3 needed: CaCl2 + Na2CO3 = CaCO3 + 2NaCl Na2CO3 needed =

∗

.

= 13.83 kg/hr

∗

.

14

Amount of

.

Mg2+ =

.

∗

= 3.129 kg/hr NaOH needed for removing Mg2+: MgCl2 + 2NaOH = 2NaCl + Mg(OH)2 NaOH needed =

∗ .

= 2.634 kg/hr .

Amount of SO42- =

∗

.

= 41.18 kg/hr BaCl2 needed for removing SO42-: Na2SO4 + BaCl2 = 2NaCl + BaSO4 BaCl2 needed =

∗

.

= 60.32 kg/hr Procedure of making Dosing: 1. Barium Chloride (BaCl2): Desired concentration- 0.15% by weight Required composition: 1. 475 kg BaCl2 2. 2000-2500 Liter H2O 3. 500 kg HCl Chemical Reaction:

15

BaCO3 + HCl = BaCl2 + CO2 + H2O In this reaction ph of HCl is 3.5 to 4 where ph should be maintained at level 6.This is done by adding 10 to 12 kg excess NaOH. 2. Soda Ash (Na2CO3): Desired concentration-0.14% Required composition: 1. Soda Ash (Na2CO3) 2. 1400 liter H2O 3. Flocculent: Required composition: 1. 500 gm floccal 2. 1000 liter H2O Chemical Reaction: 500gm floccal+1000L H2O Main function of flocculent is to hold up the moisture. 4. Sodium Sulphide(Na2SO3): Desired concentration- 7% by weight. Required composition: 1. 100L Na2SO3 2. 200L H2O

Reactor: Reactor which is used here mainly a CSTR. In this reactor the following reaction occurs:

16

Na2SO4 + BaCl2 → NaCl + BaSO4 ↓ Na2CO3 + Ca2+ → CaCO3 ↓ + 2 Na+ 2NaOH + Mg2+ → Mg (OH)2 ↓ After complete mixing of the brine and dosing solution a flocculent named Megna floc is added to the solution. Then the solution is send to the clarifier for the removing the precipitate of the solution and also increasing the turbidity of the solution. In reactor concentration range of brine is 295-305 gpl and is continuously monitored by a Hydrometer. Reactor temperature is 60-65oc and is continuously monitored by a Thermometer.

Clarifier: In the clarifier the mud, precipitated produced by the chemical dosing which are carried by the saturated brine solution is precipitated in the bottom of the clarifier. From the bottom of the clarifier the thick mud solution of the saturated brine is pumped to the decanter and mud is separated and collected for disposal as waste product. The brine solution driven from the clarifier is stored in clarified brine tank and then sends to anthracite filter for further removal of flock particles. Anthracite filter: Filter medium of the anthracite filter is mainly the anthracite. In anthracite filter solid-solid adsorption occurred. Three types of carbon: large, small and medium lies in the anthracite filter. When the brine solution is passed through the fine anthracite filter medium the flock particles cannot pass through the medium and get trapped in the anthracite medium. Then the solution is stored in the anthracite filter tank to make the process continuous. Candle filter: Candle filter is a special type of filter in which the filter medium is activated carbon and the filter coated with the alpha cellulose. This alpha cellulose blocks the micro level particles from the brine solution. To maintain the layer of the alpha cellulose which is externally exerted in the upper surface of the activated carbon filter 1-2 atm pressure is maintain continuously. If the pressure drops, there will no

17

more alpha cellulose layer upon the activated carbon filter. To maintain the efficiency the of the filter aid, alpha cellulose is continuously added in the candle filter. Brine solution is feed at the bottom of the filter and mud free solution is out at the top of the filter. After filtering in the candle filter the turbidity becomes -3 or -4 and brine solution is 3 to 4 times transparent than water. Regeneration: The candle of the alpha cellulose is washed away by using the back flow of the air. The new alpha cellulose is added from the pre-coat tank. Ion Exchanger: Multivalent ions are exchange with the Iminodiacetic acid of ion exchange resin in the ion-exchanger. But sodium is mono-valent ion so it is not exchanged with this resin. Na ion is replaced by Ca2+ and Mg2+. The resin used in ion-exchanger passed only Na+ and as it is a cation exchanger so Na+ and Cl- entered into cell house. The Iminodiacetic acid formula is as follows:

Regeneration of ion-exchange resin: Resin can work very well till its efficiency is high or moderate. But when concentration of Ca2+ is less than 10 ppm and concentration of Mg2+ is 2-3 ppb the bed is needed to regenerate. The regeneration process is as follows: Wash-1: At first the resin bed is washed away by demineralized water at constant flow 1600 L/h and it continue 1 hour as all ash and dust will washed. Back wash: Back wash is done by DM water at a flow rate of 1.6m3/h over 30 minute. DM water supplied at the bottom of the tower and resin was circulate with the tower. Water flow is maintained at a constant rate so that resin does not overflow. After ensuring that all brine washed away back wash was completed.

18

HCl regeneration: 18% concentrated HCl is then supplied in the at 600L/h flow rate over 30 to 50 minutes. By adding DM water at rate 1000L/h, 5% concentrated HCl made up. When the ph of HCl becomes 1 HCl supply will stop. During HCl regeneration Na of Iminodiacetic acid was replaced by Cl2 and the media become acidic. Wash-2: To remove the acidic media again DM water supplied at a flow rate 1600L/h over 1 hour. Consequently all Cl2 will replace by H+ ion of water. NaOH regeneration: Now 32% NaOH passed through the bed at a rate 200L/h with DM water of rate 1400L/h over 40 to 50 minutes. As a result COOH of iminodiacitic acid will converted to COONa and resin regeneration will completed. Wash-3: Again the bed will washed away by DM water at a flow rate of 1600L/h over 1 hour to maintain the ph 10. If ph 10 is obtained water supply should stopped. Brine filler: Now the resin bed will fill up by 30% NaCl at 1.8m3/h flow rate over 1 hour. Brine feed: At last feed brine is feed in the ion-exchange column as the bed is fully regenerated and ready to use with 100% efficiency.

19

Cell House: Membrane technology is the unique Single Element, which comprises an anode half shell, a cathode half shell and an individual sealing system with external flanges. The Single Elements are suspended in a frame and are pressed against each other by a clamping device to form a "Bipolar stack”. Each Single Element can be replaced quickly and easily. The elements are assembled in the Electrolyzer workshop, where tightness tests are also carried out.

Figure : Cell House

20

Important Feature of this Membrane  Perfluro Sulphonate Polymer act as a anode coating.  Perfluro Carboxylate Polymer act as a cathode coating.  High caustic flow is maintained as coating could not attach with the membrane body.  Hence chlorine is a heavy gas so it pulled from separator by a compressor.  This membrane is only permeable to Na+ ion.

21

DIAGRAMS

22

23

Figure: Block Diagram for Process

24

Fig: P & I Diagram Caustic Soda & Clorine Unit

25

Fig: Block Diagram for cpw unit

26

Fig: Block Diagram for Flaking Unit

27

Material Balance

28

Material balance for production 30% NaOH from 28% NaoH on the basis of 50 ton production per day.

Basis: 50 MT

Per day production of the plant is 50 MT. So capacity of the plant = 50 MT NaOH/day =

∗ ∗

kmol/hr

=52.083 kmol/hr = 2083.32 kg/hr

29

Basic reaction that takes place in the electrolyzer 2 NaCl + H2O = 2NaOH + H2 + Cl2 NaCl +1/2 H2O = NaOH + 1/2 H2 + 1/2Cl2 So equivalent amount of NaCl is needed for production of equivalent Caustic Soda (NaOH). We could write 1 kmol/h NaOH ≡ 1 kmol/h NaCl 52.083 kmol/h NaOH ≡ 52.083 kmol/h NaCl NaClin = 300 gpl = 300 g/l = 5.12 kmol/m3 soln NaClout = 220 gpl = 220 g/l = 3.76 kmol/m3 soln Amount of NaCl Consumption in the electrolyzer NaClconsumption= NaClin - NaClout =(5.12-3.76) kmol/m3 soln = 1.379 kmol/m3 soln Flow rate of brine in the anode side =

. .

/ /

= 37.91 m3/h Material balance at Anode side NaClin = 37.76 (m3/h)* 5.12 kmol/m3 soln = 193 kmol/h = 11309.805 kg/h NaClout = 37.76 (m3/h)* 3.76 kmol/m3 soln

30

= 141.247 kmol/h = 8262.9495 kg/h H2Oin = H2Oout = Production of Chlorine We know,

NaCl +1/2 H2O = NaOH + 1/2 H2 + 1/2Cl2

Cl2 produced = ½ * 52.083 kmol/h = 26.046 kmol/h = 1478.75 kg/h Flow rate at Cathod side Density of 28% NaOH at 600C , ρ = 1.284* 103 kg/m3 soln NaOHin=

.

∗

∗

.

∗

= 8.988 kmol/m3 soln Density of 30% NaOH at 850C , ρ = 1.296* 103 kg/m3 soln NaOHout=

.

∗

∗

.

∗

= 9.7263 kmol/m3 soln NaOHproduced = NaOHout − NaOHin = 9.7263 – 8.988 = 0.7383 kmol/m3 soln Flow rate at Cathod side =

.

∗

.

31

= 73.253 m3/hr Material balance at Cathode side: NaOHin = 8.988 (kmol/m3 soln)*73.253 (m3/hr) = 658.39 kmol/h = 26335.6 kg/h NaOHout = NaOHin + NaOHproduced = 658.39 + 52.083 = 28418.92 kg/h = 710.473 kmol/h H2Oin = 26335.6 * .72 =18961.632 kg/h =1053.424 kmol/h H2Oout = 28418.92 *0.70 = 19893.244 kg/h = 1105.1802 kmol/h

Hydrogen (H2) produced = ½ * NaOHout = ½ *710.473 =355.2365 kmol/h = 710.473 kg/h NaCl needed = (11309.805 – 8262.9495) kg/h = 3046.85 kg/h So for production of 50 MT NaOH, amount of Raw salt needed =

. .

= 3192.71 kg/h & for production of 1 kg NaOH, amount of Raw salt needed =

. .

kg

= 1.5325 kg raw salt

32

& amount of NaCl needed =

. .

kg =1.46 kg NaCl

Flow rate at both Anode & Cathode side is shown belowFlowrate (m3/h)

Anode in

Kmol/hr

Kg/hr

NaCl

193.37

11309.805

H2O

1478.75

26617.5

141.247

8262.9495

H2O

1478.75

26617.5

Cl2

26.0415

1848.94

NaOH

658.39

26335.6

18961.632

1053.424

28418.92

710.473

19893.244

1105.1802

710.473

355.2365

NaCl Anode out

Cathode in

H2O NaOH

Cathode out

37.76

H2O H2

73.253

33

Sludge Calculation From our material balance we found that 2083.32 kg NaOH is produced from 3192.75 kg raw material (raw salt). So 1 kg NaOH is produced from = (3192.75÷2083.31) kg raw salt = 1.5325 kg raw salt And we found from material balance that 1 kg NaOH is produced from 1.46 kg NaCl . Thus 1 kg raw salt produced some sludge due to unnecessary other component in raw salt. The amount of raw salt produced net amount sludge is found as Sludge (kg) = (1.5325—1.46) kg = 0.0725 kg The composition of raw salt is given bellow: Ca2+ Mg2+ SO42Total Iron NaCl Moisture

0.227% 0.049% 0.645% 13.2 ppm 95.43% 3.649%

Sludge is produced by the following chemical reactions: For Ca2+ removing we add NaCO3 which show the following reaction CaCl2 + Na2CO3 = CaCO3 + 2NaCl

34

So Ca2+ is present in 1.5325 kg raw salt = (1.5325 × 0.00227) kg =0.00347 kg For Mg2+ removing the chemical reaction is as follow MgCl2 + 2NaOH = 2NaCl + Mg(OH)2 So Mg2+ is present in raw salt = (1.5325× 0.00049) kg =0.0075 kg For SO42+ is present in 1.5325 kg raw salt= ( 1.5325 × 0.00645) kg = 0.00988 kg Moisture is present in 1.5325 kg raw salt = ( 1.5325 × 0.03469 ) kg =0.0531 kg Iron is present in 1.5325 kg raw salt = (1.5325 × 13.2 × 10-6) =0.00002022 kg Others component is present in 1.5325 kg raw salt = (1.5325 × 0.0053) kg = 0.00812 kg So total sludge is produced from 1.5325 kg raw salt = 0.0725 kg Our plant supervisor gave us the plant capacity is 50 ton per day. 50 ton = (50 × 1000) kg = 50000 kg per day. From above calculation we find 1 kg NaOH is produced when the amount of sludge is 0.0725 kg. So total sludge produced = (50000 × 0.0725) kg = 3625 kg So we can take a decision that Global Heavy Chemicals Ltd. Produce 3625 kg sludge per day.

35

Energy Balance

36

ENRGY BALANCE ON CELL HOUSE: Inflow energy balance: ∆ĤNaCl,in = ∆Hf + ∫ = (-411+ 0) = -411 ∆HNaCl,in = -44

* 193.37

= -79475070 ∆ĤH2O,in = ∆Hf + ∫ = -285.84 + 75.4[75-25] =3484.16 ∆HH2O in = 1222.16

* 20440.382

= 24981417265.12

37

∆Ĥ(NaOH in) = ∆Hf + ∫ = (-469.4 + 0) = -469.4

∆H(NaOH in) = -469.4

* 658.39

= -309048266 Total enthalpy at inlet ∆Hin = ∆HNaCl + ∆HH2O + ∆HNaOH = -79475070

+ 24981417265.12

= 24582893929.12 Outflow energy balance: ∆ĤNaCl,out = ∆Hf + ∫ = (-411 + 0) = -411 ∆HNaCl, out = -411

* 141.247

= -58052517 ∆ĤCl2 out = ∆Hf + ∫

- 309048266

38

= 0 + ∫ (33.60 + 1.367 ∗ 10 10

)dT = 1712.04

∆HCl2,out= 26.0415

* 1712.04

= 44584089.66 ∆ĤH2O,out = ∆Hf + ∫ = -285.84 + ∫

75.4

= -285.84 + 75.4[75-25] = 3484.16 ∆HH2O,out = 21371.994

* 3484.16

= 74463446615.04 ∆ĤH2,out = ∆Hf + ∫ = 0 +∫ = 1442.75 ∆HH2,out= 1442.75

* 710.473

= 1025612020.75 ∆ĤNaOH,out = ∆Hf + ∫

− 1.607 ∗ 10

+ 6.473 ∗

39

= (-469.9 + 0) = -469.9 ∆HNaOH,out= -469.9 = -13354050508 Total ∆Hout = ∆HNaCl + ∆HCl2 + ∆HNaOH+ ∆HH2 + ∆HH2O = -5802517

+ 44584089.66

+ 74463446615.04

-13354050508

1025612020.75 = 62100000000 =6.21*108

Overall Energy Balance: Total ∆Hout - Total ∆Hin = 37538695780 So, Reaction occurring in electrolyzer are exothermic.

+

40

Equipment Design Plate & Frame Heat Exchanger Design

Cold water, 55°C

30% brine, 25°C

20% brine, 55°C

Hot water, 95°C

At average temperature the fluid properties for each stream are listed belowPerry’s Chemical Engineering Handbook. Property

Brine at 450C

Water at 82.50C

41

Heat capacity, Cp (J/kg K) Thermal conductivity,( kW/mK) Viscosity, v (Pa.S) Density, ρ (kg/m3)

3320 0.470 1.4 * 10-3 1.2 * 103

Mass flow rate of brine =

.

∗

∗

. ∗

= 14.75 kg/s The total heat transfer rate is q= (mCpΔT)c = 14.75 * 3320 * (70 - 20) = 2448500 W The mass flow rate of water is, mh = q/(CpΔT)h =

∗(

)

= 23.31 kg/s Let’s assume Thickness of a plate, xw=7mm=0.007 m Length of a wall, L=1m Width of a plate, W=0.5 m Spacing between the plate, b=0.005 m The mean hydraulic diameter, De=2b=2*0.005=0.01m

4200 0.670 3.45*10-4 970

42

Log mean temperature difference LMTD= Where ∆

∆

∆ ∆ ∆

= hot fluid temperature difference

∆ = cold fluid temperature difference ∆

Hence LMTD (ΔTm)= =

(

∆ ∆ ∆

) ( ( (

) ) )

= 34.76 For single pass counter flow plate type heat exchanger, F=1 As the Plate is constructed by mild stainless steel, Thermal conductivity, kw=45.7 J/ms .K The heat transfer surface area of the exchanger in terms of plate, n A= (n-1)LW=(n-1)*1*0.5 = 0.5(n-1)m2 The flow area for each stream with S= Wb =

flow passage is given by,

* 0.5 *0.005

= 2.5*10-3n m2 Velocity of water, Vh=

= Velocity of brine, Vc=

.

=

=

∗ . ∗ .

m/s .

. ∗

∗ . ∗

43

=

.

m/s

Reynolds no. for hot fluid, Rh= .

=

∗ . ∗ .

∗ ∗ .

= Reynolds no. for cold fluid, Rh= =

.

∗ .

∗ . ∗

∗ . ∗

Prandlt number for hot fluid, Prh= (

.

=

)h ∗ .

=

∗

= 2.16

.

Prandlt number for cold fluid, Prc= (

)c ∗ . ∗

=

= 9.88

.

Heat transfer coefficient of hot fluid(water) *(Reh)0.8*(Pr)0.33

hh= 0.023* = 0.023* =

.

*(

.

.

)0.8 * 2.160.33

. .

Heat transfer coefficient of cold fluid(brine) *(Rec)0.8*(Pr)0.33

hc= 0.023* = 0.023*

. .

*(

.

)0.8 * 9.880.33

44 .

=

.

Overall heat transfer coefficient= U We know, =

+

+ .

=

.

+

.

.

+

.

. .

= 1.0945 ∗ 10

+ 1.53 ∗ 10

= 1.53 ∗ 10 (n0.8+.715)

Minimum Number of Transfer Unit for cold stream with a minimum mCp is define as, NTUmin=  

=

,

,

∆ . (

( . .

∗ ( .

)∗( )

.

) )∗(

.

∗

)

= 0.925

 0.0766( − 1)= 0.925(n0.8+1)  . − 0.0828n + 1.083 = 0 n = 67423

=

∗

.

45

Economics Analysis Using Breakthrough Curve

46

Total equipment cost { Pump (maximum pressure 42 psi) + Plate type heat exchanger + Reactors + Saturators + Clarifier + Tank + Membrane for cell house} = 21*10 TK Direct Cost = (Equipment Cost + Piping + Instrument and controlled installed + Electrical Cost + Equipment maintenance) = 21* 10 (1+0.4+0.7+0.2+0.1) = 50.4*10 tk. Investment which are not directly involved with material and labor of actual installation or complete facility. Indirect cost are cost of engineering & designing, contactors fee, contingency equals 20×106 tk. So fixed capital investment = 70.56×106 tk. Assume working capital investment is approximately 20% of fixed capital. Thus working capital is therefore 14.11×106 tk. So total capital investment = fixed capital + working capital. =84.67×106 tk. Sales value = (70×320×1000×75) tk. = 168×106 tk. We take unit production = production of 36 days =(36×70) ton = 2520 ton We know that breakeven point can be found by the following equation

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BEP = =

(

)

= 7702.957 We also found from breakeven curve breakeven unit is 45.9 The value of BEP unit in ton = (45.9×2520) ton =

days

=1652.4 days = 4.52 y

Determination of product price based on Break Even Point Variable cost/unit Fixed cost Price/unit BEP unit Break Even Point

14.11 7056 168.00 45.9 7702.957

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45000 40000 35000 30000 $

25000 20000 15000 10000 5000 0 0

50

100

150

200

250

Unit sales Fixed Cost

Total Cost

Revenue

Fig: Breakeven curve

Unit 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Fixed Variable Total Cost Cost Cost 7056 0 7056 7056 70.55 7126.55 7056 141.1 7197.1 7056 211.65 7267.65 7056 282.2 7338.2 7056 352.75 7408.75 7056 423.3 7479.3 7056 493.85 7549.85 7056 564.4 7620.4 7056 634.95 7690.95 7056 705.5 7761.5 7056 776.05 7832.05 7056 846.6 7902.6 7056 917.15 7973.15 7056 987.7 8043.7 7056 1058.25 8114.25 7056 1128.8 8184.8 7056 1199.35 8255.35

Revenue Profit 0 -7056.0 840 -6286.6 1680 -5517.1 2520 -4747.7 3360 -3978.2 4200 -3208.8 5040 -2439.3 5880 -1669.9 6720 -900.4 7560 -131.0 8400 638.5 9240 1408.0 10080 2177.4 10920 2946.9 11760 3716.3 12600 4485.8 13440 5255.2 14280 6024.7

49

Fig: Breakeven sequential data

SAFETY

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Industrial Safety: Industrial safety is the term consists of some precautionary measures that are observed by people at the time of performing a job inside the factory with the help of some machine or equipment design in such manner that can check the accident to be happened with ultimate view to achieve the possible higher productivity.

Importance of Safety: The ultimate aim of safety is the complete prevention of personal injury, loss of life and destruction of properties. Effective plant safety and fire protection are essential for every phase of operation and maintenance of equipment & machines. Calculated risks must be reduced as far as possible. Equipment & individual items must be examined time to time for normal service and also emergency demands. Some major principles and practice of plant safety are mentioned below. For safe plant operation, detailed safety instructions must always be established. All buildings, workshops, installation, machinery and equipment must be furnished and maintains so as to protect the workers against accidents and professional diseases. The instructions issued by the plant management for safe operation and for the conduct of personnel must be followed strictly.

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Responsibility of safety: The safety is of a preventive nature; the aim is to stop the risks and unsatisfactory conditions and their incorporation into better working conditions. This requires contributions from and above all, co-operation between both employees and employer.

General Safety Rules: The Bangladesh government established a general safety rule for industry called “Safety in the Factory Rules, 1979”. Every industrial personnel is to observe the following general safety rules: 

Use appropriate personal protective apparel and equipment for the operation.



Use alert to unsafe conditions and reactions. Call attention to hazards so the corrections can be made immediately.



Use laboratory equipment only for its designed purpose.



Know the location of emergency equipment in your area. Read and become familiar with emergency response procedures.



Label all chemicals clearly and correctly.



Avoid destructing or startling any co-worker in the laboratory. Practical jokes or any horseplay cannot be tolerated at any time in the laboratory.



Access to exits, emergency equipment, controls and such must never be blocked. Stairways and hallways must not be used as storage areas even temporarily.



Laboratory equipment must be inspected regularly and serviced accordingly to manufacturer’s suggested schedule.

Safety Sign: For the concern of the company’s personnel safety, different safety signs are used such as:

 Prohibition Sign Example: No smoking, Pedestrians prohibited, No drinking water etc.

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 Warning Sign Example: Risk of electrical shock, Laser beam, Risk of explosion, Risk of fire, Toxic hazard.

 Mandatory Sign Example: Eye protection, Hand, head and foot protection, Hearing and respiratory protection etc.

 Safe Condition Sign Example: First aid, Indication of direction.

Safety equipments: The following equipments are used for safety consideration

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Fig: Head protection gear

Fig: Hand protection equipment

Fig: Face protection equipment

Fig: Leg protection equipment

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Fig: Flame retardant cloth

Fig: high visibility wear

55

PLANT LAYOUT

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The laying out of a plant is still an art rather than a science. Plant Layout is the physical arrangement of equipment and facilities within a Plant. The Plant Layout can be indicated on a floor plan showing the distances between different features of the plant. Optimizing the Layout of a Plant can improve productivity, safety and quality of Products. Unnecessary efforts of materials handling can be avoided when the Plant Layout is optimized. It involves the placing of equipment so that the following are minimized: (1) Damage to persons and property in case of a tire or explosion; (2) Maintenance costs; (3) The number of people required to operate the plant; (4) Other operating costs; (5) Construction costs; (6) The cost of the planned future revision or expansion. All of these goals cannot be met. For example, to reduce potential losses in case of fire, the plant should be spread out, but this would also result in higher pumping costs, and might increase manpower needs. The engineer must decide within the guidelines set by his company which of the aforementioned items are most important. The first thing that should be done is to determine the direction of the prevailing wind. This can be done by consulting Weather Bureau records. In Bangladesh the prevailing winds are often from the north to south in the summer. Wind direction will determine the general location of many things. All equipment that may spill flammable materials should be located on the downwind side. Then if a spill occurs the prevailing winds are not apt to carry any vapors over the plant, where they could be ignited by an open flame or a hot surface. For a similar reason the powerhouse, boilers, water pumping, and air supply facilities should be located 250 ft (75 m) from the rest of the plant, and on the upwind side. This is to minimize the possibility that these facilities will be damaged in case of a major spill. This is especially important for the first two items, where there are usually open flames. Every precaution should be taken to prevent the disruption of utilities, since this could mean the failure of pumps, agitators, and instrumentation. For this reason, it may also be wise to separate the boilers and furnaces from the other utilities. Then, should the fired equipment explode, the other utilities will not be damaged. Other facilities that are generally placed upwind of operating units are plant offices, mechanical shops, and central laboratories. All of these involve a number of people who need to be protected. Also shops and laboratories frequently produce sparks and flames that would ignite flammable gases. Laboratories that are used primarily for quality control are sometimes located

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in the production area. A list of items that should be placed downwind of the processing facilities is given below Items That Should Be Located Upwind of the Plant  Plant offices  Central laboratories  Mechanical and other shops  Office building  Cafeteria  Storehouse  Medical building  Change house  Fire station  Boiler house  Electrical powerhouse  Electrical Substation  Water treatment plant  Cooling tower  Air compressors  Parking lot  Main water pumps  Warehouses that contain nonhazardous,  Non explosive, and  Non flammable materials  Fired heaters  All ignition sources

Items That Should Be Located Downwind of the Plant  Equipment that may spill inflammable materials  Blow down tanks  Burning flares  Settling ponds

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Storage Facilities Tank farms and warehouses that contain nonhazardous, nonflammable, and non explosive materials should be located upwind of the plant. Those that do not fit this category should not be located downwind of the plant, where they could be damaged and possibly destroyed by a major spill in the processing area. Nor should they be located upwind of the plant where, if they spilled some of their contents, the processing area might be damaged. They should be located at least 250 ft (75m) to the side of any processing area.2 Some authorities suggest this should be 500 ft. The same reasoning applies to hazardous shipping and receiving areas. Sometimes storage tanks are located on a hill, in order to allow the gravity feeding of tank cars. Care must be taken under these circumstances to see that any slop over cannot flow into the processing, utilities, or service areas in case of a tank fire. Spacing of Items The OSHA has standards for hazardous materials that give the minimum distances between containers and the distance between these items and the property line, public roads, and buildings. These depend on the characteristics of the material, the type and size of the container, whether the tank is above ground or buried, and what type of protection is provided. Specific details are provided for compressed gas equipment containing acetylene-air, hydrogen-oxygen, and nitrous oxide, as well as liquefied petroleum gases. They also prohibit the storage and location of vessels containing flammable and combustible materials inside buildings, unless special precautions are taken. Processing Area There are two ways of laying out a processing area. The grouped layout places all similar pieces of equipment adjacent. This provides for ease of operation and switching from one unit to another. For instance, if there are 10 batch reactors, these would all be placed in the same general area, and could be watched by a minimum of operators; if they were spread out over a wide area, more operators might be needed. This type of scheme is best for large plants. The flow line layout uses the train or line system, which locates all the equipment in the order in which it occurs on the flow sheet. This minimizes the length of transfer lines and, therefore, reduces the energy needed to transport materials. This system is used extensively in the pharmaceutical industry, where each batch of a drug that is produced must be kept separate from all other batches. In other industries it is used mainly for small-volume products. Often, instead of using the grouped or flow line layout exclusively, a combination that best suits the specific situation is used. Elevation If there is no special reason for elevating equipment, it should be placed on the ground level. The superstructure to support an elevated piece of equipment is expensive. It can also be a hazard should there be an earthquake, fire, or explosion. Then it might collapse and destroy the equipment it is supporting as well as that nearby. Some pieces of equipment will be elevated to simplify the plant operations. An example of this is the gravity feed of reactors from elevated

59

tanks. This eliminates the need for some materials-handling equipment. Other pieces may have to be elevated to enable the system to operate. A steam jet ejector with an inter condenser that is used to produce a vacuum must be located above a 34 ft (10 m) barometric leg. Condensate receivers and holding tanks frequently must be located high enough to provide an adequate net positive suction head (NPSH) for the pump below. For many pumps an NPSH of at least 14 ft (4.2 m) Hz0 is desirable. Others can operate when the NPSH is only 6 ft (2 m) H2O. The third reason for elevating equipment is safety. In making explosive materials, such as TNT, the reactor is located above a large tank of water. Then if the mixture in the reactor gets too hot and is in danger of exploding, a quick-opening valve below the reactor is opened and the whole batch is dumped into the water. An emergency water tank may need to be elevated so that, in case of a power failure, cooling water to the plant will continue to flow, and there will be water available should a tire occur. Sometimes this tank is located on a nearby hill. An elevation plan should be drawn to scale showing the vertical relationships of all elevated equipment. These drawings, as well as the plot plan, are usually sketched by the engineer and then redrawn to scale by a draftsman. Maintenance Maintenance costs are very large in the chemical industry. In some cases the cost of maintenance exceeds the company’s profit. Construction and Building Proper placing of equipment can result in large savings during the construction of the plant. For instance, large columns that are field-erected should be located at one end of the site so that they can be built, welded, and tested without interfering with the construction of the rest of the plant. Buildings Included with the layout of the plant is the decision as to what types of buildings are to be constructed, and the size of each. When laying out buildings, a standard size bay (area in which there is no structural supports) is 20 ft x 20 ft (6m x 6m). Under normal conditions a 20 ft (6 m) span does not need any center supports. The extension of the bay in one direction can be done inexpensively. This only increases the amount of steel in the long girders, and requires stronger supports. Lavatories, change rooms, cafeterias, and medical facilities are all located inside buildings. The minimum size of these facilities is dictated by OSHA. It depends on the number of men employed. Research laboratories and office buildings are usually not included in the preliminary cost estimate. However, if they are contemplated their location should be indicated on the plot plan. Processing Buildings Quality control laboratories are a necessary part of any plant, and must be included in all cost estimates. Adequate space must be provided in them for performing all tests, and for cleaning and storing laboratory sampling and testing containers. The processing units of most large chemical plants today are not located inside buildings. This is true as far north as Michigan. The only equipment enclosed in buildings is that which must be protected from the weather, or batch

60

equipment that requires constant attention from operators. Much of the batch equipment used today does not fit this category. It is highly automated and does not need to be enclosed. When buildings are used, the ceilings generally vary from 14 to 20 ft (4 to 6 m). Space must be allowed above process vessels for piping and for access to valves. One rule of thumb is to make the floortofloor heights 8- 10 ft (approximately 3m) higher than the sides of a dished-head vertical tank.6 Packaging equipment generally must be in an enclosed building, and is often located at one end of the warehouse. If the material being packaged is hazardous, either this operation will be performed in a separate building, or a firewall will separate it from any processing or storage areas Warehouse: The engineer must decide whether warehouses should be at ground level or at dock level. The latter facilitates loading trains and trucks, but costs 1520% more than one placed on the ground. It is usually difficult to justify the added expense of a dock-high warehouse. To size the amount of space needed for a warehouse, it must be determined how much is to be stored in what size containers. The container sizes that will be used are obtained from the scope. Liquids are generally stored in bulk containers. No more than a week’s supply of liquid stored in drums should be planned. Solids, on the other hand, are frequently stored in smaller containers or in a pile on the ground. Control Rooms The control center(s) and the electrical switching room are always located in an enclosed building. It is important that both of these services be maintained so that the plant can be shut down in an orderly manner in the case of an emergency. Therefore these buildings must be built so that should an external explosion occur the room will not collapse and destroy the control center and switching center. To avoid this, either the structure must have 3-4 ft (l-l.2 m) thick walls, or the roof must be supported independently of the walls. The Humble Oil and Refining Co. has specified that the building withstand a 400 psf (2,000 kg / m2) external explosive force. To keep any flammable or explosive vapors from entering the building, it is frequently slightly pressurized. This prevents the possibility of an internal explosion.

61

HAZOP STUDY

62

The hazard and operability study, commonly referred to as the HAZOP study is a systematic approach for identifying all plant or equipment hazards and operability problems. In this technique all segment are carefully examined and all possible deviation from normal operating conditions are identified. Hazard assessment is vital tool in loss prevention throughout the life of a facility. A through hazard and risk assessment of a new facility is essential during the final design stage. A hazard assessment during the prestart-up period should be a final check rather than an initial assessment. The major hazard usually include toxicity, fire, and explosions, however thermal radiation, nose, asphyxiation and various environmental concerns also need to be considered. Hazard in chlor-alkali industry: 1. Chlorine Hazard:  Hazards associated with breathing of Chlorine: Chlorine is a severe nose, throat and upper respiratory tract irritant. People exposed to chlorine, even for short periods of time, can develop a tolerance to its odour and irritating properties. Concentrations of 1 to 2 ppm produce significant irritation and coughing, minor difficulty breathing and headache. Concentrations of 1 to 4 ppm are considered unbearable. Severe respiratory tract damage including bronchitis and pulmonary edema (a potentially fatal accumulation of fluid in the lungs) has been observed after even relatively low, brief exposures (estimates range from 15 to 60 ppm). . However, long-term respiratory system and lung disorders have been observed following severe short-term exposures to chlorine. Reactive Airways Dysfunction Syndrome permanently reduced lung function  Hazard associated when Chlorine comes into contact with skin: Direct contact with the liquefied gas escaping from its pressurized cylinder can cause frostbite. Symptoms of mild frostbite include numbness, prickling and itching in the affected area. The skin may become waxy white or yellow.

63

Blistering, tissue death and gangrene may also develop in severe cases. In addition, the airborne gas may irritate and burn the skin

Hazard associated when Chlorine hurt eyes: Chlorine gas is a severe eye irritant. Stinging, a burning sensation, rapid blinking, redness and watering of the eyes have been observed at concentrations of 1 ppm and higher. Health effects to exposure of Chlorine:  INHALATION: Despite design limitations, the small number of human population studies conducted have not shown significant respiratory system effects in workers with long-term, low-level (typically less than 1 ppm) chlorine exposure and 1.42 ppm (0.15 ppm average) for an average exposure. Chlorine workers reported a higher incidence of tooth decay (based on medical history.  First Aid Measures : Inhalation: Remove to fresh air. Get medical attention for any breathing difficulty. Ingestion: If large amounts were swallowed, give water to drink and get medical advice. Skin Contact: Wash exposed area with soap and water. Get medical advice if irritation develops. Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes, lifting

64

upper and lower eyelids occasionally. Get medical attention if irritation persists. Bleaching Hazard: o

Chlorine bleach contains chlorine, a toxic gas, combined with sodium and oxygen as sodium hypochlorite. Hazards arise when the chlorine is released from this bond. The U.S. Food and Drug Administration reports that chlorine bleach is also a common food tampering adulterant.

Gastrointestinal Damage  Excluding deliberate beverage tampering, accidental ingestion is relatively unlikely because this strong-smelling, caustic liquid induces the gag reflex. However, when it is swallowed, bleach causes corrosive damage to the throat and stomach linings. At domestic concentrations, severe tissue damage or systemic poisoning are unlikely. Both toxicity levels and causticity are more hazardous in industrial-strength bleach products. Skin Damage  Undiluted bleach is corrosive. Even domestic bleach damages skin tissues and removes essential fats. During extended contact, small amounts of toxic chlorine may enter the body through the skin. Industrial bleach carries a much greater corrosive hazard, and protective clothing and eye protection are required. Lung Damage It is relatively easy accidentally to mix bleach, used in cleaning, with other cleaning products--for example in the toilet, sink or drain. Mixing bleach with ammonia is particularly hazardous, releasing chlorine gas, ammonia gas and chloramines. These gases are caustic and irritating, and inhalation damages the lungs and nasal passages. Exposure to high concentrations of ammonia gas for longer than 15 to 30 minutes can lead to irreversible

65

damage, even death. Because chlorine gas is water-soluble, it forms hydrochloric or hypochlorous acid upon meeting moisture in the mucus membranes, eyes and mouth. In the lungs, acid damage results in pulmonary edema (release of fluid into the tissues), causing breathing difficulties.Chloramines cause similar breathing difficulties and irritation to the eyes, nose, throat and skin. These are the compounds that cause irritation in swimming pools.

Explosion More likely to occur in an industrial than a domestic setting, ammonia mixed with bleach in higher proportion may form nitrogen trichloride or hydrazine, both of which are explosive. Exposure to hydrazine causes burning pain in the eyes, nose and throat, head.

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References: 1.

Kern D. Q. (1950) Process Heat Transfer, McGraw-Hill.

2.

Pletcher D., Walsh F. C. (1990) Industrial Electrochemistry. 2nd ed.

3.

Perry R. H (1997) Chemical Engineering Handbook. 7th ed., McGraw-Hill.

4.

Peters M. S., Timmerhaus K. D., West R. E. (2003) Plant Design & Economics for Chemical Engineers. 5th ed., McGraw-Hill, New York.

5.

Coulson J. M., Richardson, J. F. (1998) Chemical Engg. Vol.6, 3rd ed.

6.

Fogler H. S. (2007) Elements of Chemical Reaction Engineering. 4th ed., Dorling Kindersley (India) Pvt. Ltd.

7.

Douglas J. M. (1988) Conceptual design of chemical processes, McGraw-Hill.

8.

Website: www.opsoglobal.com