internship report at scil

Internship Report

Caustic Soda Plant

Sitara Chemical Industries Limited (SCIL)

Training Period (8th June 2010 - 5th July, 2010) (Duration: 4 weeks)

By:

Sajjad Rasool Chaudhry (M08-PG12)

Ahtisham Arshad (M08-PG16) 6th Semester

B.Sc. Chemical Engineering

Institute of Chemical Engineering & Technology,

University of the Punjab

Lahore

Internship Report (SCIL)

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Institute of Chemical Engineering & Technology, Punjab University, Lahore

Acknowledgments

We are thankful to the Institute of Chemical Engineering & Technology, University

of the Punjab, and Sitara Chemical Industries Limited for providing us such a marvelous and

informative professional training program.

After that we are very thankful to Mr. Saeed Akhter (DGM Prod. Area-I)Mr.

Muhammad Yousaf (DM Prod. Area-I), Mr. Muhammad Saleem (DPM Prod Area-I), Mr.

Faheem Ahmed (Senior Manager ISO) for their kindness and complete guidance throughout

our training period.

Then we will be glad to say thanks to Mr. Sheikh Imran (Tr. Engineer), Mr. Ahmed Waqas

(Tr. Engineer), Mr. Zaman Ahmed (Tr. Engineer), Mr. Sharjeel (Tr. Engineer), and Mr.

Ahsan Mushtaq (Tr. Engineer) for their friendly behavior and time to time guidance.

And at the end, special thanks to Mr. Ramzan (Senior Superindent) and all plant operators

for their help and cooperation.


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TABLE OF CONTENTS PAGE NO.

Ch. 1 Company Profile 4

1.1 Introduction 4

1.2 Company’s Mission statement 4

1.3 Achievements 4

1.4 Safety & Environment Management 5

1.5 Corporate social responsibilities 5

Ch. 2 Caustic soda plant 7

2.1 Primary brine section 8

PFD of Primary brine section 12

2.2 Secondary brine section 18

PFD of secondary brine section 23

2.3 Cell room 24

PFD of cell room 28

2.4 Dechlorination 29

2.5 Evaporation unit 32

PFD of evaporation 34(b)

2.6 Caustic solidification plant (CSP) 35

Block diagram of CSP 39

Ch. 3 Utilities and protective equipments 40

3.1 Utilities 40

3.2 Personal protective equipments (PPEs) 41

Ch. 4 Product Details 42

4.1 Ammonium chloride 42

4.2 Carbon dioxide gas 42

4.3 Bleaching powder 43

4.4 Calcium chloride 44

4.5 Liquid Caustic soda (33%) 45

4.6 Liquid Caustic soda (50%) 46

4.7 Caustic soda flakes 47

Summary 48


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Chapter # 1

Company Profile

1.1 Introduction:-

Sitara Group of Industries is one of the renowned industrial groups of Pakistan.

This group started its industrial activity with textile weaving sector in 1956. Sitara Group by now

is in textile cloth finishing and processing, textile spinning, chlor alkali industries and power

plant.

The chemical production unit of Sitara Group of Industries is known as Sitara Chemical

Industries Limited (SCIL). It is situated at 32 km, sheikhupura road, Faisalabad. It was

incorporated in 1981 and began producing caustic soda in 1985, initially at a rate of 30 metric

tons per day. The plant’s capacity was gradually increased over years to current level of 545

metric tons per day. In addition, various by-product facilities have been added and expanded

from time to time to cope with growing demand. Its specialty chemicals and export division was

established in 2001 and agri chemicals division in 2003.

Besides manufacturing Caustic Soda and various allied chemicals, the company has been

able to set up independent plants of some more gases i.e. Oxygen (O2), Nitrogen (N2), Carbon

Dioxide (CO2), Nitrous Oxide (N2O) in the same premises, during last one and half year.

1.2 Company’s Mission Statement:-

“We believe in stimulating and challenging team oriented work environment that

encourages, develops and rewards excellence and diligently serve communities, maintaining high

standards of moral and ethical values. We strive to develop and employ innovative technological

solutions to add value to business with progressive and proactive approach. As well as work hard

for continuing growth and diversification for bottom line results with risks well contained”

1.3 Achievements:-

Three times winner-Top 25 Companies Corporate Excellence Award by Karachi Stock

Exchange.

Winner of Corporate Excellence Award of Management Association of Pakistan year

2000

Sitara Chemicals stand amongst top 10 plants of the world based on Denora, Italy,

mercury free, membrane technology. Also acquired state of art technology from M / s.

Asahi Kasei Japan.

Certified ISO-9001: 2008

Certified EN14001:2004


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1.4 Safety & Environment Management:-

SCIL is a very much responsible organization. It cares greatly for the environment as

well satisfaction of its customers. For this reason they have adapted almost all national and

international quality and environment safety policies.

QUALITY POLICY :

“Sitara Chemical Industries Ltd. is committed to remain alert and advance, to

continuously grow as a Quality Symbol for its products and in meeting industrial and consumer

requirements, through training, team work, and procedures, on time, every time.”

ENVIRONMENTAL POLICY:

“Sitara Chemical Industries Ltd. is committed to continual improvement of its

Environmental Management System (EMS) by adoption of appropriate pollution

prevention measures and complying with all relevant training, teamwork and procedures

as implemented from time to time.

In actual words, SCIL has well developed and recognized Quality Management Systems

as well as Environmental Management Systems. SCIL has following certifications in QMS and

EMS from SGS under the authority of UKAS Quality Management.

ISO 9001:2008

ISO 14001:2004

1.5 Corporate Social Responsibilities (CSR):-

For Professional & Industrial growth, training plays an imperative & optimistic role in

today’s competitive and rapidly changing work environment. Employee’s development &

grooming become more critical & essential for which importance of training & development

cannot be denied, as it is a proactive process leading towards building the competencies and

capabilities of employees.

SCIL is a socially responsible organization. They are investing in healthcare and skills

development of their people and peoples of the area as well as education of best of the brains.

This industry is well acknowledged for its contribution to socio-economic uplift of the region

and strengthening social safety nets. They value their workforce as the most integral part of the

organization. A brief discussion on different projects of social welfare run by SCIL is given in

the following lines.

1.5.1 Human Development Center:-

SCIL has introduced numerous tools to train, re-train/upgrade their people. In this context, a

Human Development Center has been established at Sitara Chemical Industries Ltd where


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internal training sessions are held regularly. The renowned trainers are also called at the center to

impart training in the fields of technical, supervisory and management skills.

In continuation to its existing training & development activities, the management of SCIL

has broadened its internal training activities for fresh graduates and plant workforce in order to

make them ready to face the challenges of future and for their career growth. In this perspective,

the Senior Executive’s lectures and discussion sessions are being arranged for the fresh graduates

& middle management employees. Academic & on job training (OJT) of plant operators and

supervisors is being conducted by Senior Manager Training of the company.

1.5.2 Aziz Fatimah Hospital:-

Aziz Fatimah Hospital is the brain child of SCIL and is a welfare wing of sitara group for

the people of Faisalabad. The hospital was established in 1979 by the group elders and was

inaugurated by, the then, president of Pakistan General Muhammad Zia-ul-Haq.

1.5.3 Sitara Institute of Management & Technology:-

SCIL is not only remaining alert and advance as symbol of its products, but is also very

much conscious to the rising need of keeping pace with Technology and Management Sciences.

To achieve this potential of Technical & Managerial skills as a key contributor to socio-

economic and educational development, Hence Sitara Group of Industries has established its

own institute, which would not only take hold requirement of industries in Faisalabad but will

contribute in other nation building projects as well.

Thus with this vision, SIMT came into being under Aziz Fatima Trust (Education Wing)

as one of the welfare projects.

1.5.4 Aziz Fatimah Girls High School

SCIL has also established a girl’s school for quality education. This school is situated in

Gulshan-e-Iqbal to provide quality education at doorstep to the girls residing in this area. It has

highly qualified and trained teachers. School has just started its first educational year.


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Chapter # 2

Caustic Soda Plant

Although SCIL is manufacturing many important chemicals such as Ammonium

Chloride (NH4Cl), Bleaching Powder (Ca(OCl)2), Chelated Iron, Clorinated Parafin Oil,

Hydrochloric acid (HCl), Ferric Chloride (FeCl3), Ferric Sulphate (Fe2(SO4)3) etc. But their main

product is Caustic Soda (NaOH) chemically known as Sodium Hydroxide. SCIL is selling

caustic Soda in three forms: (1) 33% liquid Caustic Soda, (2) 50 % liquid Caustic Soda and

(3) 98.5 % caustic flakes

Sitara Chemical Industries is manufacturing caustic soda (NaOH) by electrolysis of brine

solution. Process is carried out in membrane cells equipped with latest technology. At time,

SCIL has three caustic manufacturing plants in working, named as BMR, M-I and M-III.

Another plant M-II is being established and is almost in final stages. Overall caustic production

of SCIL is 545 MTD with 210 MTD contributed by BMR. Since, our internship program was

conducted at BMR; therefore in the following lines we will have detailed discussion of all unit

operations and unit processes taking place in the cycle of production of Caustic Soda.

Very first step in the production of caustic is the preparation of brine solution from Rock

Salt. Rock salt is obtained from Khushab. Since this saturated brine solution contains impurities

which can scale within pipelines and other equipment and also damage the electrolyzer

membrane, therefore various techniques are employed to filter and purify this brine solution.

After necessary preliminary treatments, ultra pure brine solution is sent to the cell room where

electrolysis is carried out. Two by products Hydrogen and Chlorine are formed along with

caustic soda.

The production cycle of NaOH goes through the following series of steps.

Primary Brine Section

This section involves saturation of brine solution, its purification by settling after

treatment with certain regents and primary filtration by pressure filters.

Secondary Brine Section

In this section, brine coming from primary brine section is filtered by resins to

remove any remaining impurities which may cause damage to membranes of the

electrolyzer.

De-chlorination Unit

Here de-chlorination and other preliminary treatments of depleted brine coming

from cell room are carried out before sending it to primary brine section.


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Evaporation Unit

Caustic soda obtained from cell room has a concentration of 32 % w/w. in

evaporation unit; this concentration is raised to 50 %.

Caustic Solidification Plant( CSP)

In this section, caustic soda from evaporation unit is concentrated upto 98.5% and

solidified for packing in bags and drums.

In next lines is the detailed discussion on each section along with complete description of

all unit operations and unit processes involved.

2.1 PRIMARY BRINE SECTION

2.1.1 INTRODUCTION

Primary brine section involves three types of activities

Brine saturation

Brine purification and settling

Brine filtration

Main purpose of the brine processing is to resaturate the depleted brine coming

from the electrolyzer, by adding the quantity of salt which has been electrolyzed. The impurities

which has been introduced in the brine together with the salt are to be removed first by settling

and then by chemical treatment and settling. The suspended impurities are removed by filtration

2.1.2 Process Description:-

In this section de-chlorinated depleted brine coming from cell room after

electrolysis is concentrated and purified by sedimentation and filtration. After electrolysis,

concentration of brine decreases to 180-200 g/l. so it is sent to saturators (DS-5010 A/B) where it

is concentrated to 300-310 g/l. The flow rate of the depleted brine is 80m3/hr. Two saturators are

present at BMR one in process and one at standby. Saturators are made of concrete, reinforced

with steel and internally epoxy lined. Depleted brine is introduced with the help of five nozzles

installed at the bottom of each saturator. Saturator is filled with lumps of Rock Salt with the help

of tractor blades from salt yard. Water percolates through the salt lumps dissolving the salt in it

and over flows in separate overflow line. Makeup de-mineralized water is also fed through a

pipeline to cover water losses and maintain the required flow rate.

The level of the salt in the brine saturator is kept as constant as possible by

feeding salt in the saturator at required rate. The raw salt impurities such as Ca and magnesium

salt are dissolved in the depleted brine faster as compared to sodium chloride, so that if

excessive amount of salt is loaded into the saturator, the impurities content in the saturated brine

would be higher than the normal.


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Follow rate is maintained so that the desired concentration is obtained. If concentration is

much higher, salt may crystallize in pipelines, reactors or tanks in cold seasons. When saturator

is exhausted (filled with sludge), flow is shifted to second saturator and first one is subjected to

cleaning. After concentration brine many suspended and dissolved impurities which are

necessary to be remove. Approximate composition of Rock Salt and impurities associated with it

are as given below:

NaCl ---------------------------------------------------------- 97% w/w

Ca+2

-------------------------------------------------------------021%w/w

Mg+2

------------------------------------------------------------0.06% w/w

SO4--------------------------------------------------------------0.9% w/w

K+---------------------------------------------------------------0.17% w/w

Sr----------------------------------------------------------------1.0 ppm

SiO2-------------------------------------------------------------5.0 ppm

Al ---------------------------------------------------------------0.2 ppm

Fe ---------------------------------------------------------------1.0 ppm

Mn --------------------------------------------------------------0.5 ppm

Ni----------------------------------------------------------------0.05 ppm

I -----------------------------------------------------------------0.5 ppm

F ----------------------------------------------------------------1.0 ppm

Cr, Mo, V------------------------------------------------------0.5 ppm

Insolubles -----------------------------------------------------0.69% w/w

Moisture-------------------------------------------------------0.97% w/w

So in order to remove these impurities, brine is treated with Calcium Chloride CaCl2. For this

purpose brine coming out of saturator is collected in Brine Collecting Tank (D-510) from

where almost 40% of it is sent to CaCl2 pits while 60% overflows from tank to the Settling Pits

(D-5610 A/B). Settling pits are working alternatively i.e. one in process and one at standby.

Insoluble and suspended impurities are settled down settling pits and brine overflows to the next

pit known as Common Pit (D5620). In CaCl2 pits, CaCl2 in the form of solution is infused to

maintain 3000-4500 ppm of Ca++ in excess. The CaCl2 pit is made ready twice in a day and

transferred in the common pit D-5620. CaCl2 pit is made ready to transfer in 6-8 hrs .CaCl2

which is infused has sp. Gravity 1.1-1.2 and pH in range of 6-9. From the settling pit, the brine

over flows into the common pit D-5620 where it is mixed with the brine coming from the CaCl2

pit.

From common pit brine is pumped to the first Reactor (R-5020 A). The flow rate is 105-

110m3/hr. In this reactor brine is treated with 8% Barium Carbonate solution to remove any left


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over sulphates. After reactor, brine flows to the first Settler (TH- 5010 A). This settler has a

capacity of 1800 m3 and its material of construction (MOC) is RLS (rubber lined steel).

Suspended impurities settle down at the conical bottom of settler and are removed through a

drain valve and screw pump by a slow moving rack. Rack rotates at a speed of 0.1 RPH. Nalco

solution prepared in tank D-5310A/B is dosed at controlled rate. The amount of flocculants,

Nalco, is maintained at 1-2 ppm.

Brine over flows from the settler and is collected in a Tank D-515. From D-515, brine is

pumped to the second Reactor (R-5020 B) where it is treated with 8% solution of Soda Ash

(Na2CO3) and Caustic Soda in order to remove Ca+2

and Mg+2

. Both reactors are equipped with

agitators for intimate mixing to facilitate reaction and to avoid settling of insoluble compounds

formed, within the reactor instead of settler. After second reactor, brine solution flows by gravity

to the second Settler (TH-5010 B). This settler has a capacity of 2630 m3. Flocculent (Nalco) is

also added in the settler. This settler is also equipped with a slow moving rake at the bottom to

drain settled sludge through a drain valve. This sludge is collected in two Brine Recovery Pits

(D-5710 A/B) where any brine which was drained previously with sludge and is sent to Common

Pit.

From second settler brine overflows to the Pre-filtered storage tanks (D-5060 A/B). From

tanks D-5060 A/B, brine solution is fed to six Pressure Leaf Filters (F-5070 A-F) in parallel

manner. Brine filters are required to remove the suspended solids overflowing with the brine

from the settler TH-5010B. There are six leaf filters F5070A-F operating in parallel, five

normally in operation and one in standby. Brine from tank D-5060 A/B is pumped and

distributed to each filter through individual manual valves, before proceeding to the filtration the

filters must be pre-coated. For pre-coating, the pre-coat slurry is prepared in the tank D-5100.

The pre-coat material Arbocel is thoroughly dispersed in the filtered brine.

The end of the filtering cycle is indicated by the pressure drop in the filter .When the

filter reaches the maximum operating pressure, the filter must be cleaned. The pressure across

the filter should not exceed 3 bars. Filters contain 17 leaves each and total filtering surface of

each filter is 38.2 m2. Casings of all filters are made HRLS (hard rubber lined steel) and filtering

cloth is of FRP (fiber reinforced plastic).

Filtered brine comes out of each filter at a flow rate of 18-20 m3/hr and is fed to two

Guard Filters (F-5080 A/B) which stops the Arbocel fibers eventually released by pressure leaf

filters. These guard filters are of basket type with a total filtering of 2.78 m2 for each filter.

Casing of the filters is made of HRLS (hard rubber lined steel) and filtering cloth is of PP

(Polypropylene). Sequence is so that one filters in process and one is at standby. From these

guard filters, brine is sent to two Storage Tanks (D-5070 A/B).

From storage tanks, brine is pumped to Secondary Brine section after raising its

temperature to 55 C by using a plate type Heat Exchanger (E-5070). Material of construction of


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the heat exchanger is titanium and its heat duty is 905.0 k Cal/hr. Here low pressure steam and

cooling water connections are provided to allow the brine heating or cooling in order to control

the temperature of the brine at 50-60 oC.

At the end of Primary section, brine has following proportion of impurities in it.

Ca+2

----------------------------- 8 ppm (maximum)

Mg+2

----------------------------- 1.92-2 ppm (maximum)

Sulphates (SO4) -------------- 10 g/l

2.1.3 Reactions Involved in Primary Section:-

Sulphates

These are precipitated as barium sulphate by reaction with barium carbonate in 1st

reactor R-5020 A.

Na2SO4 + BaCO3 BaSO4 + Na2CO3

Calcium

This is precipitated as calcium carbonate by reaction with sodium carbonate in 2nd

reactor R-5020 B.

CaCl2 + Na2CO3 CaCO3 + 2NaCl

Magnesium

This is precipitated as magnesium hydroxide by reaction with caustic soda in 2nd

reactor R-5020 B.

MgCl2 + 2NaOH Mg(OH)2 + 2NaCl

Strontium,

This is precipitated mainly as strontium carbonate

Sr++

+ CO3-- SrCO3

Most of the sulphates in the brine are being removed by treating with calcium chloride.

Hence the consumption of barium carbonate is controlled. BaCO3 is an imported commodity and

is very costly, where as calcium chloride is a waste produced in HCl neutralization pits. Another

advantage is that Calcium sulphate, which is precipitated out, is a good fertilizer where as barium

sulphate is dangerous to water bodies and soil.


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2.1.4 Equipment Details:-

Tanks, Mixers and Reactors:-

SATURATOR DS-5010A/B

Capacity 312 m3

Dimension 6000*8000*2000

M.O.C Concrete Epoxy Lined

SETTLING PITS D-5610A/B

Capacity 280 m3

Dimension 7000 * 20000 * 2000


COMMON PIT D5620

Capacity 138 m3

Dimension 6000 * 11500 * 2000


CALCIUM CHLORIDE PITSA/B/C

Capacity 700 m3

Dimension 7000 * 40000 * 2500


BRINE RECOVERY PIT D-5710A/B

Capacity 256 m3

Dimension 8000 * 16000 * 2000


REACTOR R-5020

Capacity 50 m3

Diameter 3800mm

Height/Depth 4400mm

M.O.C RLS (Rubber lined Steel)


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TANK D-515

Capacity 15 m3

Diameter 2000mm

Height/Depth 4500mm

M.O.C RLS

SETTLER TH 5010A

Capacity 50m3

Diameter 22000mm

Height/Depth 4500mm

M.O.C RLS

SETTLER TH 5010B

Capacity 2630m3

Diameter 26000mm

Height/Depth 4500mm

M.O.C RLS

TANK D-5060A/B (STORAGE)

Capacity 75m3

Diameter 3000mm

Height/Depth 11170mm

M.O.C FRP (Fiber Reinforced Plastic)

TANK D-5070 A/B (STORAGE)

Capacity 75m3

Diameter 3000mm

Height/Depth 11170mm

M.O.C FRP


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TANK D-5200A/B (Sodium Carbonate)

Capacity 10m3

Diameter 2000mm

Height/Depth 3440mm

M.O.C FRP

TANK D-5210A/B (Barium Carbonate)

Capacity 20m3

Diameter 2800mm

Height/Depth 3200mm

M.O.C FRP

TANK D-5310A/B (Nalco)

Capacity 10m3

Diameter 2000mm

Height/Depth 3050mm

M.O.C FRP

TANK D-5100(Pre-coat)

Capacity 4 m3

Diameter 1500 mm

Height/Depth 2390mm

M.O.C RLS

Pumps and Related Motors:-

P-5610A/B (common Pit Pump)

Type Cent MOTOR

Volute size 5*4

Flow rate 120 m3/hr RPM 2900

TDH 20 m R.kw 15

MOC Titanium R.Amp 26


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P-5060A/B (Pre-filtered Brine)

Type Cent MOTOR

Volute size 4*3


TDH 50 m R.kw 37

MOC SS R.Amp 68

P-5070A/B (Filtered Brine)

Type Cent MOTOR

Volute size 4*3


TDH 50 m R.kw 37

MOC SS R.Amp 68

P-5080/B (Resin Regeneration)

Type Cent MOTOR

Volute size 4*3


TDH 25 m R.kw 15

MOC SS R.Amp 26

P-5100A/B (Precoat)

Type Cent MOTOR

Volute size 3*1.5


TDH 25 m R.kw 5.5

MOC SS R.Amp 11


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P-5200A/B (Sod. Carbonate)

Type Cent MOTOR

Volute size 1.5*1


TDH 20 m R.kw 3.7

MOC SS R.Amp 6.5

P-5210A/B (Barium Carbonate)

Type Cent MOTOR

Volute size 1.5*1


MOC SS R.Amp 6.5

P-5310A/B (Nalco)

`Type Cent MOTOR

Volute size 2*1.5

Flow rate 0.7 m3/hr RPM 2900

TDH 20m R.kw 3

MOC SI R.Amp 5.2

P-515A/B (Reactor 5020 B Supply)

Type Cent MOTOR

Volute size 5*4


TDH 20 m R.kw 3.6

MOC SS R.Amp 6.5


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P-5710A/B (Brine Recovery)

Type Cent MOTOR

Volute size 2*1.5


TDH 20m R.kw 3.7

MOC SS R.Amp 6.5

Calcium Chloride Pits (Transfer Pump)

Type Cent MOTOR

Volute size 5*4


TDH 20m R.kw 18.6

MOC SS R.Amp 33

Calcium Chloride pits ( Circulation Pump)A/B

Type Cent MOTOR

Volute size 5*4


TDH 20m R.kw 18.5A/15B

MOC SS R.Amp 33A/29B

2.2 SECONDARY BRINE

2.2.1 Nature of Ion Exchange Resin:-

Ion exchange resins are based on solid insoluble polymers supplied in the form of beads,

which have fixed active ionic groups. Mobile ions of opposite charge can be exchanged

reversibly and stoichiometercally for ions of the same charge present in the solution.

The resin being used TP-260 has Na ions as mobile ions and exchange with Ca++

& Mg++

present in the brine. When most of the Na+ has been exchanged with Ca++

&Mg++

, the bed is

exhausted and needs to be regenerated. The exhausted column is taken out of the stream and the

other two are remained in operation. TP-260 has weak acidic chelating amino methyl phosphonic


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acid groups which form stable complexes with a number of transition metals and main group

elements.


Before feeding brine to electolyzers it is passed through ion exchange resin towers C-

5040 A/B/C placed in series in order to absorb Ca++,

Mg++

and Sr++

contained in brine.

The brine feeding to the resin tower has following typical specifications

NaCl 290-310g/l

Na2SO4 7-8g/l

NaClO3 15g/l

Ca++ 4-6ppm

Mg++ 1-2ppm

Sr++ 1 ppm max

SiO2 5 ppm max

Cl2 Nil

Suspended solids 0.5ppm

Temperature 50-6 oC

PH 9-10

The resin bed in the tower stayed on a grid plate. The spargers are fitted on this plate. The

purified brine from tank D-5070 is fed in the tower through P-5070A/B at a flow rate of 105-110

m3/hr. As the towers are connected in series, so the brine is fed in the first tower in the series and

ultra purified brine is collected from the discharge of the third tower and collected in Ultra Pure

Brine Tank (D-5160). From D-5160 brine is pumped to Brine Head Tank (06D-001). Then it is

sent to the cell room after controlling its temperature through two Heat Exchangers (06E-001)

and (06E-002).

2.2.3 Regeneration of the Resin Bed:-

The chemical nature of the resin functional group is suitable to form complex compounds

with a lot of metal ions. The resin at the beginning of the operating cycle is in the sodic form.

During the operation it fixes Ca++ & Mg++ to which it has a high affinity, and releases Na+.

When the resin is exhausted, means when it has absorb max. Ca & Mg ions, it must be

reconverted in the sodic form. This process is referred to as “resin regeneration”.


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The regeneration process requires a sequence of different operations. The most

significant of which are a treatment with diluted HCl which displaces the metal ions previously

fixed by the resin functional groups followed by a treatment with diluted NaOH solution which

makes the resin to change form the acidic form to the sodic form i-e H+ replaced with Na+

STEPS INVOLVE IN THE REGENERATION PROCESS

1. Brine drainage (half empty)

2. Washing with demi water

3. Counter washing with demi water

4. Drainage

5. Washing with 4% HCl solution

6. Drainage


8. Drainage

9. Counter washing with 5% NaOH solution

10. Drainage


12. Drainage

13. Water replacement with brine

14. Filling with brine

After regeneration resetting is done almost in 60 minutes and brine is circulated between

resin towers and brine tanks D-5070. The circulation of brine remains on till the required

results of Ca & Mg are achieved. Then the column is taken in operation and placed in the last

in series.

Some Important points:-

Resin washing with water has the purpose of removing the brine from the tower and

counter washing is done to remove the brine trapped in the resin bed.

Brine must be removed completely because the chlorates possibly present in the brine

could decompose during the acid washing and give free chlorine, which oxidizes the resin

with an increase in resin consumption.

During washing with HCl real regeneration of the resin bed is occurred. The metal ions

attached by the resin are displaced and the resin is converted into the acidic form.

After washing with HCl, the bed is again washed with water in order to reduce the

consumption of the caustic soda and to fully remove HCl in the column. The more

important is to avoid the possible damage of the resin particles due to heat evolved in the

reaction between acid and caustic soda.

During the washing with caustic soda, the resin is converted from the acidic form to the

sodic form. i.e. H+ replaced with Na

+

Before filling brine in the regenerated column it is emptied so that the conc. of the brine

remained within the range, otherwise it may be lowered.


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2.2.4 Chemical Reaction Involved:-

Chemical reactions involved in secondary purification and regeneration of resin towers

are as given below.

BRINE PURIFICATION

Na2(Resin) + Ca++

Ca(Resin) + 2 Na+

Na2(Resin) + Mg++

Mg(Resin) + 2 Na+

RESIN REGENERATION

Ca(Resin) + HCl H2(Resin) + Ca++

(Washing by HCl)

Mg(Resin) + HCl H2(Resin) + Mg++

(Washing by HCl)

H2(Resin) + NaOH Na2(Resin) + H2O (Washing by NaOH)


RESIN TOWERS

TOWER RESIN BED

Capacity 13m3 Volume 4m

3

Diameter 1900mm Diameter 1900mm

Height 4600mm Height 1410mm

MOC HRLS No. Of Sparger 249

MOC Haste Alloy Openings 0.2mm

TANKS

TANK D-5130 (5% NaOH) Capacity 40 m

3

Dia 3000 mm Heights 6190 mm MOC PP-R

TANK D-5140 (4% HCl) Capacity 30 m

3

Dia 3000 mm Height 4770 mm MOC FRP

TANK D-5150A/B (Effluents)

Capacity 75 m3

Dia 3000 mm

Height 11170 mm

MOC FRP


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TANK D-5160(ULTRA PURE BRINE) Capacity 75 m

3

Dia 3000 mm

Height 11170 mm

MOC FRP

PUMPS AND RELATED MOTORS

P-5130A/B(5%. NaOH) PUMP MOTOR Type Centrifugal Capacity 5.0 kW F.Rate 20 m

3/hr Rated Amp. 9.8 A

TDH 25 m RPM 2900 MOC SS Volute 1.5*1.0 Impeller 5

P-5140A/B(4%. HCl) PUMP MOTOR Type Centrifugal Capacity 5.5 kW F.Rate 30 m


TDH 25 m RPM 2900 MOC FRP Volute 2*1.5 Impeller 5

P-5150A (Effluents) PUMP MOTOR Type Centrifugal Capacity 5.0kW F.Rate 15 m


TDH 25 m RPM 2900 MOC FRP Volute 1.5*1.0 Impeller 8

P-5150B (Effluents) PUMP MOTOR Type Centrifugal Capacity 5.0 kW F.Rate 20 m


TDH 25 m RPM 2900 MOC SS Volute 1.5*1.0 Impeller 5

P-5160A/B PUMP MOTOR Type Centrifugal Capacity 15.0 kW F.Rate 90 m


TDH 35 m RPM 2900 MOC Titanium


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2.3 CELL ROOM

2.3.1 Electrolyzer:-

The equipment used to carry the process of electrolysis is called electrolyzer. The cell

room comprises of three electrolyzers A/B/C placed in parallel fashion. Each electrolyzer has

capacity of 164 cells. At present electrolyzer A has 162, electrolyzer B has 161 and electrolyzer

C has 162 elements. Each element acts as an electrolyzer individually. Each element consists of

anode and cathode compartments separated by a membrane. Anodic side is made of titanium

while cathodic side is made of nickel. The ion exchange membrane is clamped between the half

shells with interposed PTFE gaskets. The half shells are bolted together at the flange, thus

constituting a cell element.

The ion exchange membrane is made by an organic polymeric matrix incorporating fixed

ionic groups neutralized by mobile ions of opposite charge. Fixed group are sulphonic type or

carboxylic type, while mobile counter ion is sodium ion. Only the cation exchange selectivity of

the membrane can prevent migration of OH-. The flow of Cl- across the membrane is about

negligible, because membrane selectivity and electric field across the membrane opposes the

chloride ions transport.

The raw material feeding to the electrolyzer is brine. The brine nearly saturated, is

introduced into the anode compartment of the cell. The aqueous solution in this compartment is

called anolyte. The membrane separates the anolyte from the catholyte compartment.

32% caustic soda from catholyte tank plus Demineralized water to make a 29-30%

caustic solution is admitted to catholyte compartment where sodium hydroxide is formed by the

combination of hydroxyl ions and sodium ions, which migrate through the membrane to the

cathode. Chlorine gas, usually called cell gas, is formed at the anode while Hydrogen gas and

sodium hydroxide are formed at the cathode.


Ultra pure brine is stored in tank D-5160 and pumped via P-5160A/B into over head feed

brine tank. 06D001. Brine enters in the overhead tank from the top and over flows by gravity

from the top side back in D-5160. The outlet is from the bottom of the tank and leads to cell

room by gravity. The brine is heated in the way before entering cell room through heat

exchanger 06E001 to raise its temperature up to 65-75 C. It is a plate type heat exchanger. Heat

exchanger is provided with steam as well as cooling water connections. There is also a stand by

heat exchanger 06E002 which is either used to fill a single electrolyzer or in case of emergency.

In the cell room main feed brine line has three connections to feed each of the three electrolyzers.

These supply lines are underneath of each electrolyzer. Brine is fed in the anodic compartment of

each cell.


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Catholyte (33% NaOH) is stored in the storage tank 31D002. Its temperature is about 80-

85 C. It is cooled in 31E001 before transferred in overhead tank 31D001.A temperature of 70-

75C is usually required to feed in cells.

31E001is a plate type heat exchanger which is provided steam as well as cooling water

connections. There is also a stand by heat exchanger/cooler 31E003 which is used in case of

emergency or for single electrolyzer filling. This heat exchanger can be used only for cooling

purpose as there is no steam connections associated with it. Catholyte enters into catholyte

overhead tank 31D001 from the top and over flows from top side. Outlet is from the bottom and

leads to cell room by gravity.

In the cell room three electrolyzers are arranged in parallel. In each electrolyzer 164

elements are placed in series. At present Electrolyzer A has 162 ELZ-B has 161 and ELZ-C

has162 elements. Brine is introduced in the anodic compartment of the cell while caustic soda is

introduced in cathodic compartment of the cell. When current is introduced, electrolysis takes

place. As a result of it caustic soda is produced in the cathodic compartment together with

hydrogen gas where as chlorine gas is produced in the anodic compartment.

2.3.3 Electric Supply Circuit:-

11KV power is supplied from grid station. It is passed through transformer to step it

down to 440 V. Then it is passed through rectifiers to convert it into DC which is then supplied

to electrolyzers via bus bars and flexibles. There are 2 bus bars and 9 flexibles associated with

each electrolyzer.

2.3.4 Reactions:-

Following reactions takes place in the cells

Sodium chloride and water are dissociated in the brine solution according to the equations

NaCl Na+ + Cl

-

H2O H+

+ OH-

The principal anode reaction involves the oxidation of the anion Cl- to produce chlorine gas

2Cl- Cl2

+ 2e

-

The primary cathode reaction is the reduction of the cation H+ to produce hydrogen gas

2H+ + 2e

- H2

The sodium cation Na+ then combines with the OH- ions to form third overall product NaOH

Na+

+ OH- NaOH

The overall cell reaction is

2NaCl + 2H2O 2NaOH + Cl2 + H2


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2.3.5 Side Reactions:-

The predominant side reactions in the anodic compartment of the cell are

4OH- O2 + 2H2O + 4e

-

2OH- + Cl2 ClO

- + Cl- + H2O

6ClO- + 3H2O 2ClO3

- + 4Cl

- + 3/2 O2 + 6H+ + 6e

-

3ClO- ClO3

- + 2Cl

-

The source of the OH- ions in these reactions is the migration of OH

- ions through the

membrane from the catholyte solution, caused by attraction to the positively charged anode.

2.3.6 Products Handling:-

31.5-32.5% caustic soda is produced in cathodic compartment of the cell and is collected

in the catholyte header along with hydrogen gas. It leaves the catholyte header by gravity in the

main caustic soda header and passes through hydrogen gas separator 31F002.Then it is stored in

the catholyte storage tank 31D002 to maintain its level about 50% for circulation through the

cells. The excess caustic is transferred in the caustic buffer tank D2000 from where it is fed to

evaporators for concentration. It is also transferred to storage tanks as such 32% caustic soda as

finished product.

The stream leaving the cells, composed of depleted brine and chlorine gas, is discharged

in the anolyte header and termed as anolyte. The depleted brine leaves the anolyte header by

gravity in the depleted brine header and chlorine gas is separated in the vertical gas header which

is connected to main chlorine gas header. The depleted brine is passed through the chlorine gas

separator in order to remove maximum chlorine gas contents carried with it. The depleted brine

is acidified in the acidification pot 07D005 and then stored in the depleted brine storage tank

07D001U.

In the anodic compartment of the cell chlorine gas is produced as a result of electrolysis.

It is separated from depleted brine in the vertical gas header as well as in the gas separator

07F001 and is collected in the main chlorine gas header.

Hydrogen gas is produced together with caustic soda in the cathodic compartment of the

cells and discharged in the catholyte header. It is disengaged from caustic soda in the vertical gas

header as well as in the hydrogen gas separator 31F002 and is collected in the main hydrogen gas

header Hydrogen gas is also cooled before it is transferred to furnaces for HCl production

through heat exchanger E2310Aand B.


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2.3.7 Equipment Details

BRINE OVERHEAD TANK 06D001 Capacity 28m

3

ID 3000mm Height/length 3450mm MOC PP+FRP

CAUSTIC O/H TANK 31D00 Capacity 8m

3

ID 1800mm Height/length 3248mm MOC Ni

CATHOLYTE TANK31D002 Capacity 31m

3

ID 24mm Height/length 5228mm MOC Ni

HYDROGEN SEPARATOR31F002 Capacity 1.6m

3

ID 700mm Height/length 4175mm MOC Ni Allowable pressure 0.5bar

CHLORINE SEPARATOR07F001 Capacity 1.2m

3

ID 600mm Height/length 4150mm MOC Ti

ACIDIFICATION POT07D005 Capacity 0.54m

3

ID 800mm Height/length 1200mm MOC FRP

DEPLETED BRINE TANK07D001 Capacity 42m

3

ID 2600mm Height/length 8300mm MOC FRP

PUMPS

ANOLYTE PUMP07P001A/B Type Centrifugal Flow rate 140 m

3/h

TDH 30m MOC Tit

CATHOLYTE PUMP31P001A/B Type Centrifugal Flow rate 100m

3/h

TDH 30m MOC Ni


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2.4 DECHLORINATION

2.4.1 Introduction:-

Depleted brine from electrolyzer usually contains 0.3 g/lit dissolved chlorine at a pH

about 3.5-4.0 and 1.0 g/lit as available chlorine in the form of hypochlorite ions. Depleted brine

also carries 2000-2500 ppm of free chlorine. The process of removal of chlorine from the

depleted brine is termed as “Dechlorination”

Chlorine must be removed from brine because of the following facts.

The removal of impurities in the primary brine purification becomes difficult.

In the presence of high contents of chlorine, the impurities in the rock salt are more easily

dissolved during brine saturation.

Chlorine oxidizes ion exchange resins, hence increasing its consumption.

The chlorates are necessary to remove because

It decreases the sodium chloride solubility resulting in decreased efficiency, possible salt

precipitation and potentially adverse chlorate conc. in the caustic soda product.

Chlorates have a strong oxidizing effect which is more evident at high concentrations.

Chlorates are formed in the anodic compartment of the cell of electrolyzer via chemical or

electrochemical reactions as mentioned before. Chlorates removal rate is a function of the

chlorate concentration so that it is convenient to operate at a relatively high chlorate

concentration in the feed brine. High temperature also favors the chlorates removal, so a

temperature of 85- 90C is recommended. The third parameter affecting chlorates removal is pH.

A low pH less than 2.0 is favorable.


Dechlorination is carried out in three successive steps

By vacuum stripping

By Sodium Sulphite treatment

With activated carbon

Depleted brine leaving the electrolyzers flows into the acidification pot 07D005 where it is

mixed with acidified stream of brine from reactor R-5050. Then it is collected in depleted brine


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storage tank 07D001, from here the brine is pumped through 07P001A/B. The discharge of the

pump is divided into two streams, one leads to vacuum stripper C-5010 and second leads to acid

mixing drum DM-5050. Normally 70 to 75% material goes to C-5010 and 25-30% in DM-5050

for decomposition of chlorates. In DM-5050, 33% HCl is added to lower down its pH almost

zero, after acidification the brine flows down by gravity into the reactor R-5050 where it is

mixed with chlorinated steam coming from the vacuum stripper C-5010. In R-5050 at low pH

and high temperature, chlorates are decomposed, producing free chlorine which is vented in the

chlorine sniff line. The over flow of R-5050 entered in the acidification pot and lower the pH of

the depleted brine ranging 1.5-2.0

NaClO3 + 6HCl NaCl + 3Cl2 + 3H2O

a) By Vacuum Striping

Brine containing absorbed chlorine enters from the upper part of the packed tower C-

5010 where vacuum is generated by means of steam ejector J-5600. In such condition brine

leaving the tower has 20-50ppm of chlorine. The wet chlorine stripped from the brine leaves the

tower and is cooled in the shell and tube type heat exchanger E-5010. The condensed chlorinated

water is returned in the depleted brine tank 07D001 while the chlorinated steam is sent to reactor

R-5050. The brine flows down by gravity in the dechlorinated brine tank D-5020. The tank is

vented to chlorine sniff line.

b) By Sodium Sulphite Treatment:

Sodium sulphite is added to the depleted brine leaving the tank D-5020 by means of an in

line injection on suction of the pump P-5020A/B.

Sodium sulphite solution is prepared in the tank D-5250B by absorbing of SO2 in sodium

carbonate solution and sent in D-5300 by means of pump P-5250A/B. Sulphur dioxide (SO2) is

prepared by burning sulphur mud in the sulphur furnace which is sucked through an absorber by

a suction fan. The gas is entered from the bottom of the absorber and left from the top. The

sodium carbonate solution is fed from the upper side of the absorber and flows down back to the

same tank. When the solution is ready it is transferred in tank 5250A.

During chlorates decomposition following reaction takes place

Na2SO3 + Cl2 + H2O Na2SO4 + 2HCl

c) With Activated Carbon

After treatment with sodium sulphite, brine is passed through an activated carbon bed in

tower C-5020. Care must be taken that the carbon should work with acidic brine pH less than 2

and chlorine less than 50ppm. High chlorine contents in brine feeding the tower causes to violent


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reaction with the carbon, relatively high pH in the feed brine to tower causes carbon degradation

in the form of fine particles which can plug the tower. The brine passing out of the tower is made

alkaline by the addition of dilute caustic effluent from tank D-5150B. The pH is raised up to 6.0-

9.0 before it is transferred in primary brine section.

When the carbon is packed down it is necessary to counter wash the carbon bed tower.

When the pressure drop across the carbon bed became more frequent, then it is packed with fresh

activated carbon. Normally this situation occurs after 40-45 days.


DEPLETED BRINE TANK-07D001

Capacity 42 m3

ID 2600 mm

Length/Height 8300 mm

MOC FRP

07P001 (DEP. BRINE PUMP)

Type Cent

F.R 100 m3/hr

TDH 20 m

MOC Titanium

ACIDIFICATION POT (07D005)

Capacity 0.54 m3

ID 800 mm


MOC FRP

DM-5050

Capacity 0.5 m3

ID 800 mm


MOC FRP

D-5020

Capacity 15 m3

ID 2000 mm


MOC FRP

P-5020A/B

Type Cent

F.R 120 m3/hr

TDH 34 m

MOC Titanium

D-5250A/B

Capacity 5 m3

ID 1800 mm


MOC FRP


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P-5250A/B

Type Cent

F.R 5 m3/hr

TDH 20 m

MOC AISI 316

D-5300

Capacity 5 m3

ID 2000 mm


MOC FRP

R-5050 (REACTOR)

Capacity 20 m3

ID 2500 mm


MOC FRP

C-5010 (VACUUM STRIPPER)

ID 1300 mm


Packing height 1200 mm

Packing material ceramic saddles

MOC Titanium

C-5020 (ACTIVATED CARBON)

ID 2200 mm


Packing length 1600 mm

Packing material Activated carbon

2.5 EVAPORATION UNIT


The plant is designed for continuous concentration of caustic soda 31-32% to 50%. The

concentration is improved by evaporation in a triple effect counter flow falling film evaporator.

The plant consists of three falling film evaporators. At first there was only one unit of capacity

120mt/day, with the passage of time capacity of caustic soda plant was enhanced so another

evaporation unit of capacity 250 MT/day was designed to meet industrial and consumer’s needs.

Falling film evaporator is a tube bundle heat exchanger with a separator at the bottom. In the

separator vapors and thick liquor are separated. The feed liquor is uniformly distributed in the

tubes by a distribution device, thus the liquid moves down forming a thin film along inside wall

of the tube. That is why it is called a falling film evaporator.


The caustic is fed to the first evaporator EV-201 by a pump P-2000A/B installed at the

discharge of caustic buffer tank D-2000. On product side the first evaporator is operated under a

vacuum. the caustic leaves the first evaporator effect Ev-201at a concentration of 36-37%. The

first evaporator is heated with vapors formed in the second evaporator EV202. The shell of the


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evaporator EV-201 is also under vacuum about 250-270mmHg. The condensate of the EV-201

collected in the same tank. This vacuum is produced by connecting the condenser 201,duct D-

201and shell condensate lines of EV-201 to TK-201. The vapors of EV-201 are condensed in E-

201. The cooling water is fed in the shell and the vapors are condensed in the tubes. The

condensate is collected in the tank TK-201.The vacuum in E-201 is produced through steam

ejectors.

After the EV201, pump 201A/B pumped the caustic soda to the second evaporator EV-

202 via heat exchangers E-202 & E-203. The discharge of the pump P- 201 is divided into two

streams; one admitted to the shell of E-202 and second is admitted in the tubes of the E-203.

These two streams rejoined before entering the EV-202. This evaporator effect is heated with the

vapors from EV-203.the pressure in the shell of EV-202is about 1.9-2.0.The caustic soda enters

EV-202 at conc. range 36-37%, and temp. range110 -115C and leaves at conc. 42-43% and

temp.120-125C.This caustic soda is fed to the third evaporator EV-203 through pump P-202 via

E-204 & E205. The condensate is collected in condensate tank TK-202 and then transferred in

TK-201 from where it is transferred in D-5150B.

The discharge of pump P-202 is again divided into two streams; one admitted to the shell

of E-204 and second is admitted in the tubes of the E-205. These two streams rejoined before

entering the EV-203. This evaporator effect is heated with the steam at a pressure of about

14bars.The caustic side is under a pressure of 2 bars. The vapors produced here are used to heat

the second evaporator and the condensate is collected in the tank TK-203.The caustic leaves this

evaporator at 50% conc. at temp. of 175-185C.

Now it is to be cooled before storage. For this purpose it is first passed through tube side

of E-204. Here it’s temp. is reduced to 155-160C. Then it is pumped via P-203 through the tube

side of the E-202 and E-206, the final temp is about 55-65C. The condensate of the evaporator

EV-203 also bears a sufficient amount of heat, which is recovered by passing it through the shells

of E-205 & E-203.The steam condensate at a temp about 97-98C is returned to boiler section.

2.5.3 Equipment Detail:-

EVAPORATION PLANT

Equipment No. of

tubes

Length

(mm) Diameter

(mm) Thickness

(mm) Material of

Construction

EV-201 139 6000 48.3 1.65 SS.904L

EV-202 116 6000 48.3 1.65 Ni-201

EV-203 81 6000 48.3 1.65 Ni-201

E-201 405 6000 25.0 1.00 SS.904L

E-202 48*3=144 6000 26.7 1.65 Ni-201

E-203 20*2=40 6000 26.7 1.65 Ni-201

E-204 48*3=144 6000 26.7 1.65 Ni-201

E-205 24*3=72 6000 26.7 1.65 Ni-201

E-206 26*3=78 6000 26.7 1.65 Ni-201


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CONDENSATE TANKS

TK-201 Capacity 2.8 m

3

Diameter 1400 mm Height 2000 mm


3



3


2.5.4 Normal Operating Data:-

Plant capacity 250 ton/day Feed flow rate 15-25 m

3/h

Steam pressure 14-15 bar Pressure in duct 203 1.9-2.0 bar (safety blows at 2.1bar) Vacuum in E-201 600-650 mm Hg Vacuum in D-201 550-570 mm Hg Vacuum in EV-201 260-280 mm Hg Vacuum in TK-201 0.70-0.75 bar

Evaporator 201 Feed inlet temperature 75-80

oC

Feed concentration 30-32 % Product concentration 35-36 % Product temperature 75-80

oC

Evaporator 202 Feed temperature 90-100

oC

Product temperature 120-125 oC

Feed concentration 35-36 % Product concentration 41-42 %

Evaporator 203 Feed temperature 150-160

oC

Product temperature 150-160 oC

Feed concentration 41-42 % Product concentration 50-51 %

HEAT EXCHANGERS E-201(surface condenser)

Vacuum 600-650 mmHg Condensate temp. 58-60

oC

Cooling water flow rate 250-280 m3/h

Cooling water temp. 28-32 oC

Cooling water pressure 1.2 bar Parameter Tubes Shell Material flow 35-36 % Caustic cooling water Inlet temperature 75-80

oC 28-32

oC

Outlet temperature 55-60 oC 35-40

oC


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E-202

Parameter Tubes Shell

Material flow 50 % Caustic 35-36 % Caustic

Inlet temperature 130-135 oC 75-85

oC


oC

E-203


Material flow 35-36 % caustic steam condensate


oC


oC

E-204


Material flow 50% caustic 41-42% caustic


oC


oC

E-205


Material flow 41-42 % caustic steam condensate


oC


oC

E-206


Material flow 50% caustic cooling water


oC


oC

2.6 CAUSTIC SOLIDIFICATION PLANT


Caustic solidification plant is designed in order to concentrate 50 % caustic soda to 97-

98% caustic soda in solid form. For this purpose a single effete tube bundle falling film

evaporator is used as pre-concentrator. 50% NaOH is concentrated up to 60% NaOH using

vapors produced in the final concentrator for heating in this equipment. In the final concentrator

the concentration is improved up to 97-98% using outside heating media.

Due to increasing demand of the solidified caustic soda three CSP units are designed on

same pattern named as CSP-I capacity, CSP-II and CSP-III. Another plant named as CSP-IV is

under construction yet.


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2.6.2 Process Description

a) Pre-Concentrator:-

50% caustic soda stored in caustic buffer tank is pumped via PBT-1&2 to feed into

pre-concentrator. The flow of the feed is controlled by LCV-9.11. There are temperature and

pressure gauges to indicate the feed temperature and pressure respectively. Pre-concentrator is

heated with vapors formed in final concentrator. The pre-concentrator is designed as tube bundle

falling film evaporator. Above the tubes there are vertical slits through which caustic soda feed

flows evenly into the tubes and form an unbroken film along the inner wall of the tube.

The pre-concentrator works at 0.93 bar vacuum on the product side. This vacuum is

created in the system by steam ejector. A two stage ejector, 14 bar steam, is used for this

purpose. The vapors produced in the pre-concentrator are removed by steam ejector and are

condensed in a condenser. Vapors are introduced in the shell side of the condenser while cooling

water is introduced in the tubes.

Vapors condensed in the condenser are collected in the condensate tank. The condensate

of the pre-concentrator also goes into condensate tank by gravity. From condensate tank it may

transfer in M-II plant under level control where it is stored it the D-5150B. The condensate may

be overflow into the drain. This condensate is also used for sugar solution preparation and for

heating the seal of 60% caustic pump A/B.

b) Final Concentrator:-

60% caustic soda obtained from pre concentrator is pumped via P8.11A/B to feed it into

final concentrator. The feed rate is controlled by FIC-9.09. The final concentrator is basically

consisting of 6 individual concentrator tubes and the vapor separator. The caustic soda feed is

evaporated in the falling film concentrator at atmospheric pressure by means of heat applied by

salt heating medium. The feed liquor is uniformly distributed to each concentrator element. It

flows evenly with the inner wall of the tubes from top to bottom. The heat transfer medium

moves counter currently from bottom to top inside the heating jackets surrounding the

concentrator tubes. The vapor produced in the course of the concentration process reached the

horizontal collecting channel together with concentrated caustic side. The collecting channel is

provided with conic baffle which separate vapors and molten caustic side. The vapors leads to

the separator which retains caustic droplets contained in the vapor. These vapors leave the

separator from the top and are used to heat the pre concentrator. The molten caustic soda leaves

the separator through its lower part and is directed by the distributing device to the flaker and/or

drum filling device.

The heating medium is a mixture of following salts in a particular composition.

KNO3 53%

NaNO2 40%

NaNO3 7%


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c) Sucrose System:-

All the equipment and piping in contact with caustic melt is made of pure nickel are low

carbon nickel because of corrosive resistant of nickel. Oxygen acts corrosively, particularly when

combines with high temperature and form nickel oxide which would contaminate the product i.e.

caustic melt, so it is very important to prevent the penetration of atmospheric oxygen into the

equipment. For this purpose system is blanketed with nitrogen or steam. In addition by adding

0.15 Kg sugar solution into the system just after the feeding valve to pre concentrator, the nickel

pickup of the caustic soda melt is reduced to 2 ppm approximately.

5% aqueous solution of sugar is prepared by using food grade sugar in the water/vapor

condensate in the sugar tanks and dosed into the caustic system by pumping via sugar pump at a

rate of 3 - 5 lit/hr. Flow rate of sugar dose is very important, low flow may cause increasing

nickel ppm and excessive flow may leads to blackish particles in the caustic melt.

d) Flaker:-

The flaker consists of a rotating drum/cylinder which dips in the vat containing caustic

melt. The cylinder is cooled to 60-55 oC by showering cooling water on its inner walls thus a thin

film of caustic melt is formed over the drum surface which is scrapped by a sharp blade/scrapper.

The flakes thus formed are directly made to fall into the duct which conveys them to the filling

hopper where it is provided with an automated weighing and then filling in PPW bags lined with

polyethylene bags which is tied with cable ties and then stacked inserting tag cards in the

stitching.

e) Dust Collector:-

For purpose of operational safety and to facilitate the operator working at filling station, a

dust collection system is provided. The system consists of a suction fan .It sucks dry air from the

flaker, passed through the duct, weighing system and also from the bags. The suction pipe is

dipped into a water tank where the caustic soda is precipitated in water in seal pot when its

concentration is about 5 to 10%, it is replaced by another water filling.

2.6.3 Normal Operating Conditions:-

PRECONCENTRATOR

Caustic feed concentration 50%

Caustic feed flow rate 1.0-1.25 m3/hr

Caustic feed temperature 60-65 oC

Caustic feed pressure 6.4-6.5 bar

Temperature in the separator 90-110 oC

Vapor inlet temperature 350-360 oC shell side

Vapor outlet temperature 160-165 oC product side


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Vacuum 0.9-0.95 bar

Caustic outlet temperature 68-72 oC

Caustic outlet concentration 60-61 %

Sugar dose flow rate 3-5 lit/hr

CONDENSOR

Cooling water inlet temperature 30-32 oC

Cooling water outlet temperature 35-40 oC

Cooling water flow rate 150-200 m3/hr

STEAM EJECTOR

Steam pressure 13-14 bar

Water flow rate 900-1000 lit/h

BURNER

Fuel gas flow rate 190-210 Nm3/hr

Salt inlet temperature 390-405 oC

Salt outlet temperature 420-430 oC

Salt coil temperature 420-435 oC

Flue gas temperature 475-500 oC

FINAL CONCENTRATOTR

Caustic feed concentration 60-61 %

Caustic feed flow rate 1.0-1.25 m3/hr

Caustic feed temperature 68-70 oC

Caustic temperature in distributor 360-380 oC

Caustic temperature in vat 325-330 oC

Salt inlet temperature 420-430 oC

Salt outlet temperature 390-405 oC

Vapor outlet temperature 360-370 oC

FLAKER DRUM

Cooling water inlet temperature 30-32 oC

Cooling water outlet temperature 35-40 oC

Cooling water flow rate 50 m3/hr

Cooling water pressure 1.3-1.5 bar

Air pressure 1 bar


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Chapter # 3

Utilities and Protective Equipments

3.1 Utilities

Different utilities used during process along with their use and required amounts are

given in the following lines

3.1.1 Water:-

Uses:

Electrolysis feeding, Resin regeneration, Preparation of Brine, Caustic soda and HCl dilution, Flocculent preparation

Amount :

15 ms/h

Source:

Tube well water

Types:-

Demineralized water, R.O. water

Specifications :-

pH 6-7

Conductivity 10 micron siemen/cm (max)

Fe 100 pbb (max)

SiO2 100pbb (max

Suspended Solids Nil

3.1.2 Instrument Air :-

Uses:

For controlling Auto valves etc.

Specifications:-

Design pressure 7 ATA

Temp. 40 oC

Dew point at 7 ATA -25 oC

Oil and dust free


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3.1.3 Nitrogen:-

Uses:

For purging Hydrogen and Nitrogen lines

Types:

Industrial nitrogen in cylinders

N2 (99.5% v/v) O2 (0.5% v/v)

3.2 Personal Protective Equipments (PPEs):-

Following personal protective equipments are exclusively used at SCIL by workers, operators, engineers and all other related persons.

Face sheet Goggles Rubber gloves Safety boots Gas masks/ Filter masks Air mask OBA Safety helmets

Besides these PPEs many other safety devices are used such as fire extinguishers, anti firing gas cylinders etc.


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Chapter # 4

Product Details

Besides producing Caustic Soda, SCIL manufactures many important chemicals. A brief

detail on quality and specifications of some of the products is given in the following lines.

4.1 Ammonium Chloride:-

Installed Annual Production Capacity 3,000 MT

Technology Developed by Mannesmann (Germany)

Specifications

Physical Appearance White Crystals

Quality 99.7 ± 0.2%

Moisture 0.1 % max.

General Product Information

Evolves ammonia when reacting with alkali. Exhibits endothermic nature in aqueous

media. Absorbs water & moisture when exposed to atmosphere. Shelf Life: Long life is

expected in airtight bags.

Product Handling and Safety Instruction

It is supplied in the packing of 25 kg Polypropylene bags, having polyethylene liner in

bags. Must be stored in well-ventilated and covered area. Do not store it along with caustic

soda and other alkaline materials If ammonium chloride contacts the eyes, then eyes must

be irrigated immediately with plenty of water for at least 15 minutes.

4.2 Carbon dioxide Gas:-

Specifications

Appearance/ Colour Normal/Colorless gas.

Purity 99.9 % min

Taste None

Odor None/Characteristics

Uses

Large quantities of solid carbon dioxide (i.e. in the form of dry ice) are used in processes

requiring large scale refrigeration.

Carbon dioxide is also used in fire extinguishers as a desirable alternative to water for most

fires.

It is a constituent of medical gases as it promotes exhalation. It is also used in carbonated

drinks.

http://www.sitara.com.pk/scil/node/72


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Product Handling & Safety Instructions

Dry carbon dioxide can be handled in most common structural materials.

Moist carbon dioxide is generally corrosive by its formation of carbonic acid.

Ferrous Nickel alloys are slightly susceptible to corrosion. At normal temperatures carbon

dioxide is compatible with most plastics and elastomers.

Use local exhaust to prevent accumulation of high concentrations so as to reduce the oxygen

level in the air to less than 19.5% and the carbon dioxide concentration below the exposure

limit.

Protective gloves of any material appropriate for the job.

Positive pressure air line with full-face mask and escape bottle or self-contained breathing

apparatus should be available for emergency use.

4.3 Bleaching Powder:-

Installed annual production capacity 4,500 MT

Technology Developed by Davy mc-kee (Germany)

Specifications

Physical Appearance White fine Powder

Available Chlorine 30 % ± 1

Moisture 0.50 % max.

Stability On heating at 100 ± 2 ºC it does not lose more than

1/15th of the available chlorine.


Stable below 0.5 % moisture contents.

Produces chlorine odor or HOCl in case of high moisture contents and start decomposing.

Decomposes by absorption of CO2 from air.

Decomposition by oxygen separation with low water contents, which is accelerated in the

presence of heavy metals (Fe+3, Ni and Co etc).

Shelf Life: One year in airtight drums; 03 months in airtight bags, if stored at room temperature

and dry place


It is supplied in 25 kg Polypropylene bags having polyethylene liner in bags. Airtight packing

protects decomposition of bleaching powder due to carbon dioxide from air. Must be stored

separately in well-ventilated and covered area. Avoid contact with other chemicals especially

from all acids. It catches fire on exposure to naked flame and high temperature.



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4.4 Calcium Chloride

Purity Minimum 77%w/w

Physical Appearance White granules /powder

Specifications

Calcium Chloride 77% Min

Magnesium Chloride 2.0% Max

Calcium Hydroxide 0.3% Max

Calcium Sulfate 0.3% Max

Alkali Chloride 0.5% Max

Water Insoluble 0.5% Max

pH (5% w/v solution) 4.5-9.2

Arsenic As 3.0 ppm (max)

Lead Pb 10.0 ppm(max)

Iron Fe 20.0 ppm(max)

Barium Ba 10.0 ppm(max)

Sodium Na 20000.00 ppm(max)

Principal Application

Additive to oil well completion. Drying petroleum fractions. Beverages for removing Sodium

ion. Mining as dust proofing and freezing resisting ore & coal. Drying air and gases, remove

moisture by Hygroscopicity. Fungicides as oxidizing agent. Pharmaceutical as drying and

desiccating agent. Water Treatment.

Material Handling

Must be store in well-ventilated, covered and dry area.

Long life is expected in airtight bags.

If calcium chloride contacts the eyes, then eyes must be irrigated immediately with plenty of

water for at least 15 minutes.

Packing

Supplied in packing of 25 kg PP Laminated bags having polyethylene line



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4.5 Caustic Soda Liquid (33%)


Technology Developed by Denora(Italy),AKCC(Japan)

Grade Commercial

Specifications

NaOH 50 + 0.5 %

Na2CO3 0.5 % max

NaCl 0.02 % max

NaClO3 0.01 % max

Na2SO4 0.01 % max

Iron 10 ppm max

Silica 10 ppm max

Hg free


Caustic attacks body tissue upon contact. The degree of injury depends upon the extent and

duration of contact, temperature and concentration of the caustic.

Its corrosive action on tissues causes burns and frequently deep ulcerations.

Its contact with the eyes rapidly causes severe damage.

Caustic solution is detectable by a slippery feeling like soapy water.

Toxic limits are TLV = 2 mg. / cubic meter of air.

Shelf Life: Long life if protected from air & contamination.


Immediately remove all contaminated clothing and equipment effected by the Caustic, Flush the

exposed area thoroughly with a lot of water, followed by washing with a solution of 5 %

ammonium chloride in water. If caustic contacts the eyes, they should be irrigated immediately

with plenty of water for at least 15 minutes. Hold the eyelids opened during irrigation. The eyes

should be then washed with a dilute boric acid solution and wash the eye with water for an

additional 15 minutes. A physician should be seen immediately after the eye is thoroughly

washed.

For personal protection, use face shields, gloves, gum-boots and protective suites. Use safety

shower and wash with plenty of water for at least 15 minutes. Caustic soda (liquid) is transported

in Mild Steel tanks.



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4.6 Caustic Soda Liquid (50%)

Installed annual production capacity 129,500 MT


Grade Commercial

Specifications

NaOH 50 + 0.5 %

Na2CO3 0.5 % max.

NaCl 0.02 % max.

NaClO3 0.01 % max.

Na2SO4 0.01 % max.

Iron 10 ppm max.

Silica 20 ppm max.


Caustic attacks body tissue upon contact. The degree of injury depends upon the extent and

duration of contact, temperature and concentration of the caustic. Its corrosive action on tissues

causes burns and frequently deep ulcerations. Its contact with the eyes rapidly causes severe

damage. Caustic solution is detectable by a slippery feeling like soapy water. Toxic limits are

TLV = 2 mg. / cubic meter of air. Shelf Life: Long life if protected from air & contamination.


Immediately remove all contaminated clothing and equipment effected by the Caustic, Flush the



with plenty of water for at least 15 minutes.

Hold the eyelids opened during irrigation. The eyes should be then washed with a dilute boric

acid solution and wash the eye with water for an additional 15 minutes. A physician should be

seen immediately after the eye is thoroughly washed.

For personal protection, use face shields, gloves, gum-boots and protective suites. Use safety

shower and wash with plenty of water for at least 15 minutes. Caustic soda (liquid) is transported

in Mild Steel tanks



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4.7 Caustic Soda Flakes



Grade Commercial

Specifications

NaOH 97.0 ± 1 %

Na2CO3 1.0 % max.

NaCl 0.04 % max.

NaClO3 0.02 % max.

Na2SO4 0.01 % max.

Iron 20 ppm

Silica 20 ppm


Caustic attacks any body tissue upon contact. The degree of injury depends upon the extent and

duration of contact and the temperature and concentration of the caustic. Its corrosive action on

tissues causes burns and deep ulcerations. Its contact with the eyes rapidly causes severe damage.

Caustic solution is detectable by a slippery feeling like soapy water Toxic limits are TLV = 2

mg. / cubic meter of air.

Shelf Life: Long life if protected from air & moisture.


Immediately remove all contaminated clothing and equipment effected by the Caustic. Flush the



with plenty of water for at least 15 minutes. Hold the eyelids opened during irrigation. The eyes

should then be washed with a dilute boric acid solution and wash the eye with water for an

additional 15 minutes. A physician should be seen immediately after the eye is thoroughly

washed. For personal protection, use face shields, gloves, gum-boots and protective suites.

Caustic soda (Flakes) is packed in 25 kg polypropylene bag having polyethylene liner in it.



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Summary

Sitara chemical industries is a well known and famous chemicals manufacturer of

Pakistan. It is an organization of very responsible and well trained professionals. At the same

time SCIL has well developed and well managed Environment Management System and Quality

Management System which have been certified and audited by SGS under the authority of

UKAS. They produced Caustic Soda along with many other chemicals. SCIL produces Caustic

Soda in form of either 33% Caustic solution or as 50% Caustic solution or Caustic flakes of

98.5% purity. Four Caustic Soda manufacturing plants are working at SCIL. The Caustic

production cycle goes through many steps. These sections include primary brine section, where

depleted brine is saturated and purified by settling, chemical treatment and filtration through

pressure leaf filters. After primary treatment brine is ultra purified in secondary section by

passing through ion exchange resin beds. When brine meets the required degree of purification

and concentration, it is fed to electrolyzers in cell room. In cell room, a current of almost 12.5kA

is passed through the brine solution in special type of cells called as membrane cells. Chlorine

and Hydrogen are also produced as by products along with Caustic in cell room. They are

separated from Caustic and depleted brine and are sent to HCl furnace after necessary treatments.

Caustic, thus produced is 33%. It is concentrated up to 50% in three effect, backward feed,

falling film, evaporation unit. This 50% caustic is then sent to Caustic Solidification Plant (CSP)

to convert it into 98.5% Caustic which is then packed in drums or as flakes in PP bags. Some

side reactions also occur in cell room resulting, the formation of chlorates. Therefore brine

coming out of cell room contains chlorine and chlorates in it. This brine is sent to the

dechlorination section where these contaminates are removed by stripping, treatment with HCl

and sodium sulphite and by passing through carbon tower. This dechlorinated brine is then

recycled in primary section for saturation. Different utilities such as water, electricity, instrument

air and nitrogen for purging H2 and Cl2 lines are also used.

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