MADHAV INSTITUTE OF

TECHNOLOGYAND SCIENCE
Gwalior (M.P.)

(Affliated to RGPV, Bhopal)

INTERNSHIP REPORT

Prepared at
Gacl Nalco Alkalies and Chemicals Pvt
Ltd Dahej-Gujarat

Submitted by
Jitesh Jaiswal

B. Tech Chemical
0901CM181025
 MADHAV INSTITUTE OF TECHNOLOGY ANDSCIENCE GWALIOR (M.P.) -
474002
Department of Chemical Engineering

2 CERTIFICATE

This is to certify that major project work entitled

“Caustic soda production and working of polish filter”
by Jitesh Jaiswal (0901CM181025) is a record of work
carried out under my supervision and guidance in partial
fulfilment of the requirements for the Major Project of the
degree of Bachelor of Technology in Chemical
Engineering.

Prof Anish P Jacob

Major-project Coordinator
 Acknowledgement

I would like to express my sincere thanks to Prof. Anish P Jacob his/her valuable
guidance and support in completing my project.

I would also like to express my gratitude towards planthead Mr Ashish Govil giving
me this great opportunity to do internship in Gacl Nalco alkalies and chemicals pvt
Ltd dahej -Gujrat
 PREFACE

As per the curriculum of Madhav Institute of Technology (MITS), Gwalior (M.P), Students are
recommended to undergo Training cum Internship to gain some practical knowledge of how
the work (Production, Experiment, and Maintenance) is supposed to be done in the real world
with all the extraordinary cases that a personal (student) is not familiar to. Hence, the training
provides the bridge between theoretical and practical knowledge. It also provides an
opportunity to learn various aspects and facts of real life and teaches us the difference between
books and reality. Other than the practical knowledge, one gets a chance to observe aspects of
industrial management, discipline, and safety precautions which are an important part of the
industry of any kind. I feel fortunate enough to get trained in such an esteemed company
GaclNaco alkalies and chemicals pvt ltd
Table of contents

1 Introduction of Plant

2 Brine saturation and purification

2.1 Saturator
2.2 Primary purification
2.3 Secondry purification

3 Chlor alkali electrolysis process

1.1 General description

1.2 Membrane cell chemical reactions

4 anolyte Dechlorination

5 Cautic system

6 Chlorine system

7 Hydrogen system

8 Waste Air Dechlorination 9 HCL synthesis unit 10 Caustic evaporation amd falling unit 11
Effulent system 12 Project
Introduction to plant

GACL-NALCO Alkalies and Chemicals Private Limited (GNAL) is a joint venture company of
Gujarat Alkalies and Chemicals Limited GACL ,.

The equity holding of GACL and NALCO for the joint venture company is in the ratio of 60: 40

Building a strong bond between these two companies, GNAL aims at consolidating GACL’s
supremacy in chlor-alkali and other integrated downstream products and ensuring a steady
supply to Nalco for and future expansions. GNAL is setting up a green field 266670 TPA caustic
soda plant and, to cater to its power requirements, a 130 MW coal based captive power plant
at Dahej, Gujarat

Sodium hydroxide (NaOH), commonly known as Caustic Soda, is a strong base and is
one of the most widely used chemicals in the industry either as a raw material or as an
auxiliary chemical. Caustic soda is produced by the electrolysis of brine. In the
electrolytic cell, brine (sodium chloride solution) is decomposed to chlorine at the
anode and to a sodium hydroxide solution and hydrogen at the cathode. About 200 TPD
of caustic soda will be purchase by NALCO; the rest can be supplied as 48% lye (liquid)
or as flakes (solid).
Hydrogen is coproduct of cautic soda . It is used in HCL synthesis and supplied in
bottling

Hydrogen chloride (HCl) is a colorless gas. Its aqueous solution is known as Hydrochloric Acid.
Hydrogen chloride or hydrochloric acid is produced by burning hydrogen and chlorine together.
Hydrogen chloride is supplied as gas through pipelines and as acid/30% solution in bulk
containers as well as 25, 50 Kg containers.

Sodium hypochlorite (NaOCl) commonly known as soda bleach is produced by adding chlorine
into caustic soda solution. It is an excellent steriliser, oxidiser and decolouring agent, and also
acts as a germicide, fungicide and deodorant. The chemical is used as a bleaching agent for
rayon pulp, paper and fabrics and for industrial water treatment and pool chlorination. It also
finds application as a food additive

Plant capacities
Caustic Soda (100% w/w) 266667 MTPA
Chlorine 236267 MTPA
Hydrogen 76800000 Nm3 PA
Hydrochloric Acid (100% w/w) 86667 MTPA
Power 130MW (2 x 65 MW)
Steam 100 TPH

Brine saturation and purification

Solid salt is the raw material, Salt is charged in saturator by conveyors or pay loaders . The
water and/or depleted brine introduced at the base of the saturator for progressive
saturation .
There are two no of truck tripplers and trucks emptied in feed hoppers . Motorized
diverter is also provided in conveyors , one shall make stockpile In storage area and the
other one distribute the salt in horizontal saturators .
There are three no of saturators one is in operation second is standby and the third one is
for manual cleaning mode .
220 gpl brine comes from lean brine pump to distribution pipes submerged under the salt
bed where it is saturated to 305-310 gpl .
Saturator brine overflows to saturator pumping pit .
Brine is pumped from saturator pumping pit to precipitation tanks.
Precipitation Tank

Raw salt contains calsium magnisium and sulphate impurities for removal of this
impurities brine is treated with Ba2CO3 , Na2CO3
And NaOH

Precipitation tanks are operated in series . First tank overflows to second and second
overflows to mixing pot

The precipitation reactions taking place are as follows:

Na2SO4 + BaCO3  BaSO4 + Na2CO3

CaCl2 + Na2CO3  CaCO3 + 2 NaCl

MgCl2 + 2 NaOH। Mg(OH)2 + 2 NaCl

7-10% Ba2CO3 added in first precipitation Tank and 7-10% Na2CO3

And 18% NaOH added in second precipitation Tank chemical preparation tanks .

Brine Clarification

The raw brine is fed by gravity from the precipitation tanks to the conical bottom clarifier.
Before entering the clarifier, the raw brine is mixed with Flocculants in a Mixing Pot.

Flocculant added to form larger flocks out of very fine particles like mg(oh)2 and promotes
the settling of fine particles
In the Clarifier most of the impurities settle form and scrapped by the Clarifier raker arm.

Sludge from Clarifier underflow and pumped to sludge filters. Cake

from sludge filters falls in trolly and used in land filling.

The supernatant brine from Clarifier overflows to Clarifier brine tank .

 From the clarified brine tank, brine is pumped to the Anthracite Filters by the Clarified
Brine Pumps

Brine filtration

The biggest threat to sustain good performance of membranes in electrolyser cells comes From
impurities in salt especially sea salt. These impurities can be removed by ion Exchange unit if it
is in dissolved state. The suspended solids cannot be removed by the Ion exchange unit and
therefore has to be completely removed prior to feeding the brine to Secondary brine
treatment. In view of above, a two-stage filtration system is provided:

First stage – anthracite filters

Second stage – brine polishing filters for removal of the suspended solids like mg(oh)2 which
Escapes in the first stage.

The two-stage filtration system ensures that the brine going to secondary brine purification Is
virtually free of all suspended solids. Typical suspended solid concentration at polishing Filter
outlet is less than 0.2 ntu
Brine Anthracite Filtration
Brine from the clarifier still contains approx. 50 ppm of suspended solids. In order to Achieve a
reasonable performance from the polishing filters, these solids must be removed Beforehand.
The removal of these suspended solids is done in the anthracite filters . Clarified brine with
approx. 50 ppm suspended solids is passed through the Anthracite filters .During normal
operation six filters are in operation, while One is in backwashing mode.

The brine filters are packed with anthracite of three different grain sizes. The top layer consists
of fine particles and act as the filter media. The lower layers are Meant for supporting the top
layer. Distribution headers are provided with perforations for Uniform distribution of brine.
Brine enters the filter from the top. By means of the Clarified brine pump , brine is passed
through the filters and the solids are Retained on the surface of the filter media. The filtrate
passes through the filter nozzles to the lower part of filter housing and from there to filtered
brine tank .To remove the sludge collected over the filter media, periodic backwashing of filters
is Necessary.

Backwashing is done in Every 3.5 hour , one filter is in Bout 24 hour operation .Backwash also
depends on quality of clarified brine .

Backwashing is done by filtered brine using backwash pump

And the backwash is from backwash recovey again taken in system .

For backwashing of anthracite filter have 4 steps

1 Isolation
2 Backwash
3 Recycle
4 Normal operation

Backwashing can be done in auto or manual mode .

Filtered brine from anthracite filter flows to filtered brine tank
Polish filter

The purpose of Brine polishing unit is to remove the final traces of suspended solids from The
brine prior to removal of dissolved impurities in ion exchanger. The polishing unit Consists of
three identical Brine polishing ffilters, two operating and one Standby.

Brine polishing system consists of three filter housings containing PP cloth filter candles.
The candles are hung from a register to the shell. By means of the filtered brine pump
pressure, the brine passes through the candles and the Solids are retained on the outer surface.
A discharge channel is installed in the upper part of the filters. The polished brine is discharged
via this channel to the polished brine tank .
Due to the retention of solids on the candles, a filter cake builds up on the outer surface of The
candles in the course of operation. Since the brine throughput is maintained constant, The
pressure drop across the filter increases with increasing thickness of the filter cake. The
Pressure drop across the filter is constantly monitored. The pressure drop across the filter Must
not exceed 2.0 kg/cm2 g. As soon as the pressure drop approaches this value, the Filter must be
taken out of operation for cleaning. Normally one filter is backwashed after 48 hours of
operation depending on quality of brine.

This filter operation is by sequence –the main steps are the following:

1. Filling of filter
2. Back washing (hose cleaning) with air
3. Refilling of filter and homogenizing
4. Precoating
5. Filtration with body feed
6. Draining of filter and heel draining
7. Cake drying with air [shock method]
8. Pressure release
9. Cake discharge
After polishing filtration, hcl is added in the brine stream via 18% hcl pump To dissolve
precipitated fine mg(oh)2. Further, 18% naoh is added to this acidic brine by 18% naoh pump
[26p004a-c], before sending it to ion-exchange column for secondary Brine purification.The
candle filters operate with precoat. Precoat [0.5% alfa cellulose] is prepared in the Precoat cum
bodyfeed tank [05d003]. Precoat solution is pump to the filter by precoat Pump [05p005]
during the precoating stage. Body feed solution [0.5% alfa cellulose] as Prepared in the precoat
cum bodyfeed tank is mixed with the filtered brine and Send to the polishing filter during
filtration stage by the body feed metering pump . The candle filters are cleaned with air
pressure. For the steps no. 6, 7 & 9

Adequate amount of air is required so a separate air buffer vessel is provided for This purpose.

From the polished brine tank ,the brine is pumped by polished brine pump to chlorine
recuperators where the brine is heated by moist chlorine Gas coming from cell room. From
chlorine recuperator it goes to the ion exchange columns at a temperature of approx. 63-65oC.

Secondry brine purification

In order to warrant trouble-free operation of the membrane cells and a long service life of

The membranes, the cells must be supplied with extremely pure brine. The calcium and
Magnesium content in the brine is not allowed to exceed 20 ppb as the deposition of these
Ions in the membrane affects its function and leads to an increased power consumption.
Such low contents can be achieved using proven technology in special ion exchange Columns.
The columns are filled with a chelating cation – exchange resin (with the help of resin Transfer

device -ejector & charging pot), with a high selectivity for calcium, magnesium and

Strontium ions. The ion exchange reaction as an example for Ca2+ ion can be written as follows:
Ca++ + Na2[Resin] Ca[Resin] + 2Na+

This reaction continues until equilibrium is achieved and the breakthrough point is
Reached. Then the resin must be regenerated to its original state by another ionexchange
reaction using consecutively approx. 7% Hydrochloric acid and approx. 4% caustic soda
solution.

Chlor alkali electrolysis proces

There is total 8 no of electrolyser each electrolyser contains 214 elements and can increase
upto 222.
The single elements are supplied with ultra-Pure brine and with catholyte. Ultra-pure brine
enters the anode compartment where Chlorine is generated at the anodes. The anode and
cathode compartments are separated By a membrane. This membrane only allows Na+-ions
and a certain quantity of water to

Diffuse into the cathode chamber. The brine leaving the cells is depleted. The chlorine gas is
generated at the anode. The two-phase mixture of chlorine and anolyte Is discharged via a
collecting channel to the discharge pipe into the anolyte cell header Where the major part of
the chlorine gas is separated from the anolyte.

Gross reaction
The gross reaction for the formation of chlorine, caustic soda, and hydrogen from a sodium
Chloride solution can be expressed as follows:
NaCI + H2O =>NaOH + ½ Cl2 + ½ H2

This reaction is taking part as two separated single element electrode reactions: the anode And
the cathode reaction.

Anolyte Dechlorination and chlorate distruction unit

The system is design to completely dechlorinate depleted brine (anolyte) saturated with
chlorine. For this two-stage dechlorination system is used i.e. vacuum dechlorination followed
by chemical dechlorination.

The depleted brine from cells flows to anolyte tank .

The anolyte coming from the cells is chlorine saturated. Before the brine is resaturated and

Purified, the brine must be totally dechlorinated. For this a two-stage dechlorination system is

Foreseen.

First Stage : Vacuum Dechlorination

In the first stage chlorine is desorbed by means of vacuum, the remaining concentration of
Chlorine being about 10 – 30 mg/l.

Second Stage : Chemical Dechlorination

The free chlorine is chemically destroyed by means of Sodium Bisulphite [NaHSO3]. The

NaHSO3 solution is added in a slight excess of approx. 10 – 15 ppm to ensure no chlorine is

Passing to the process steps downstream. In case of presence of free Cl2 in brine, the resin in
Ion exchanger will be damaged. The anolyte leaving the cells at a pH value of approx. 2.5 – 3.5
is monitored by pH-analyser . For dechlorination and chlorate destruction, the pH must be
reduced to approx. 2.0. The solubility of chlorine also reduces by the addition of the acid. This is
achieved by Adding 18% HCl with the aid of control valve. The addition is also controlled by pH
analyser. Acidified anolyte flows into the anolyte tanks .Anolyte Tanks are provided with an
overflow seal line to Anolyte Drain Tank which Mainly serves for draining of electrolysers. The
anolyte from the anolyte drain tanks can be Returned to the anolyte header by means of
anolyte recovery pump .The acidified anolyte is pumped to the dechlorination tanks by anolyte
pumps . Vacuum is induced in the dechlorination tank by the help of vacuum pumps. These
vacuum pumps are equipped with vapour condensers and Condensate separators . Under
reduced pressure, the acidified anolyte is allowed to Boil in the dechlorination tank. This
reduces the solubility of Cl2 in brine and thereby causes Desorption of Chlorine gas. The water
content in the Chlorine gas is reduced in the vapour Condensers and separated out in
condensate separators & the condensate Is returned back to the inlet of dechlorination
tank.The wet chlorine gas from the Condensate Separator are sucked by vacuum pump and
then Sent to the chlorine header.

Catholyte system

The Catholyte system comprises of Catholyte (Caustic) circulation system of the electrolysers.
The Catholyte system supplies approximately 30% Catholyte feed to the cell room or to single
Electrolysers at temperatures between 40oC and 85oC to enable start up, shutdown and
Operation at different cell room loads. The Catholyte Head Tank provides a reservoir of
Catholyte to automatically fill the electrolysers In the case of power failure.

Catholyte mixture of caustic and hydrogen coming from cell is seperated in header itself and
further is separated by hydrogen seperator

Catholyte from catholyte pump have two possible flows one from catholyte heat exchanger for
heating and another for cooling , from this two heat exchanger catholyte tempreture adjusted
in catholyte system.

Level of catholyte tank controlled by level controller and some part of cautic withdrawan in
intermediate tank for internal consumption and as product .
Catholyte head tank is always in line In overflow in condition for the emergency supply of
catholyte to cell .
Chlorine system
The Chlorine gas saturated with water leaves the electrolysis cells at an overpressure of 3500
mmWC[g] and a temperature of 88°C. The chlorine gas exchanges heat with polished brine in

the chlorine recuperator [21E001]. The chlorine is cooled down whereas the polished brine is
heated.

Chlorine gas from the chlorine recuperator enters the Chlorine cooler ], where it is cooled
to 40°C by circulating cooling water. Cooled chlorine gas enters Chlorine Chiller where it is
cooled to approx. 15°C by chilled water. From the chlorine chiller the chlorine gas enters

the Wet Chlorine Filter ]. The function of this filter is to separate brine mist
[aerosol] carried along with the gas. The filter is equipped with candles of glass fibre .
Demineralised water is sprayed into the Cl2 stream at the filter inlet to prevent any
crystallisation of NaCl on filter surface and consequent increase in pressure drop. The NaCl
from the brine mist would form Na2SO4 and crystallise in the drying tower, if not

effectively separated in the filter.

An under pressure safety vesselis provided between the chlorine recuperator and the chlorine
cooler to protect membranes against too low chlorine pressure.

The chlorine condensate from the recuperator, Chlorine cooler, Chlorine Chiller, Wet Chlorine
Filter and under pressure safety vessel flows to a condensate collection header from where it is

Fed to inlet of dechlorination tank. Wet chlorine gas from wet chlorine filter goes to Cl2 Drying
unit
And part stream to HCl synthesis unit as per requirement. At the outlet of chlorine cooler, cell
Pressure control valve is provided with a back flow protection to protect electrolyser.
Hydrogen system

Hydrogen gas leaving the cells is at a pressure of about 3700 mmWC and a temperature of
88°C. The gas is saturated with water vapour at these conditions and is cooled to remove water
in Hydrogen Cooler to approx. 40°C using cooling water. The gas is further cooled down to 20°C
in the Hydrogen Chiller using the chilled water. The cooled gas is passed through a Hydrogen
Filter to remove the NaOH aerosols at filter candles
]. Hydrogen gas out from is connected to the stack via control valve

. This is provided to control the cell differential pressure and to ensure minimum fluctuation in
electrolyser when downstream section is upset. In case of high differential pressure across cell
the excess hydrogen is vented through stack. The stack is equipped with
flame arrestor and provided with a steam and Nitrogen connection for safety.Hydrogen buffer
Vessel-I is provided at the outlet of the hydrogen filter to ensure
Minimum pressure fluctuation at Electrolyzers. The flow of hydrogen gas to Hydrogen buffer
Vessel-II is controlled by the cell differential pressure PDIC1159. Hydrogen buffer
Vessel-II is provided at the outlet of the Hydrogen buffer vessel-I to ensure minimum pressure
Fluctuation at HCl synthesis unit. Hydrogen to HCl unit is supplied from the hydrogen buffer
Vessel-II , the required pressure at the inlet of the HCl synthesis unit is controlled by

The control valve provided at the inlet of unit. The flow of hydrogen gas to Hydrogen Gas
Holder Is controlled by the pressure PIC4108A. The pressure in the Hydrogen buffer vessel-II
Is controlled by PV4108B. In case of high pressure in the hydrogen gas holder, the excess

Hydrogen is vented through stack. The stack is equipped with flame arrestor and provided with
a steam sniffing connection for safety. Provision has been given for supply of hydrogen from
Buffer vessel-II to flaking unit.

Waste air Dechlorination

The waste gas dechlorination system acts as a safety system of the plant and cleans up the
Chlorine and traces of HCl contained in the waste gases generated at various points in the
Chlorine plant. The dechlorination of the waste gas stream is accomplished by scrubbing with
18% NaOH solution in two stages Jet scrubbers connected in series followed by a final
Absorber. The resultant product is bleaching lye (sodium hypochlorite) solution.emergency
situation the system is designed to absorb total chlorine production of current density of
6.0 kA/m2 operation (960TPD caustic (100%) for 10 minutes.
During normal operation of the plant, it is estimated that approximate 106.4 kg/hr of chlorine is
To be absorbed in the waste air dechlorination system. However, the quantity will vary
Depending on vent gas release from liquid chlorine storage, tonner filling etcDuring normal
operation very small quantity of waste air is generated and capacity of waste air System is too
large for this service. Therefore, some quantity of air must be bypassed from
Discharge to inlet of Jet Scrubber to maintain constant pressure in waste air header through

PIC2605 at inlet of 1st Jet Scrubber. With this internal bypass, ingress of atmospheric air and

Consequently reaction of atmospheric CO2 with NaOH (i.e. formation of Na2CO3 by reaction of

Atmospheric CO2 with NaOH) is avoided.

HCl synthesis unit

The package unit consists of Two HCI Synthesis Units [51U001A/B] each with a capacity of 120

MTPD 32% HCl (100% Basis) comprising of Furnace, Absorber, Tail Gas Scrubber, steam
generation skid and startup air Blower.

Both HCl units are designed for production of 32% HCl liquid along with steam generation. 32%
HCl liquid is used for internal consumption of caustic soda plant and sale.

The synthesis of HCl gas is formed by combusting H2 coming from H2 buffer vessel & wet
chlorine from outlet of wet chlorine filter, dry chlorine from compressor discharge and sniff Cl2
from chlorine liquefier. Further the HCl gas is absorbed in DM water to produce 32% acid is
accomplished in a furnace / absorber.

The air blower is used for start-up of the synthesis unit

The demineralised water, which is used for the absorption of the HCl gas, is fed to top of the
Tail
Gas Scrubber from where it flows by gravity through the packing to the falling film absorber of
The synthesis. This quantity is controlled according to the concentration of the produced

Hydrochloric acid. The HCl produced is collected in 32% HCl Product storage tank [52T001A-F].

The hydrogen gas sent to the synthesis come from the H2 Buffer Vessel 41D003, at a
Temperature of about 15-20 °C. Before entering the burner, it passes through the H2 flame
Arrestor to avoid occasional flame backflow into the H2 pipeline. The wet chlorine from wet
chlorine filter outlet and dry chlorine comes from the liquefaction unit Used for synthesis.

Cautic evaporation and flaking unit

The Caustic evaporation unit is designed for 600 TPD NaOH 100% to concentrate caustic soda

from 32% NaOH to 49% NaOH and Caustic Flaking unit is design to produce either 200 TPD
NaOH 100% flakes from 32% NaOH or 200 TPD 49% Caustic Lye from 32% NaOH.

The 32% NaOH coming from Cell is sent to the Evaporation unit [32U001] & Flaking unit
[32U002] by Intermediate Caustic Transfer pumps [31P002A/B] from intermediate caustic
Storage tank ]. In Caustic Evaporation Unit 32U001, NaOH is concentrated from 32% to

49% in triple effect evaporation unit, 600 MTPD NaOH 100% NaOH capacity. The 49% solution is
Drawn out to 48% Caustic Soda Storage Tanks]. In Caustic Flaking Unit

32U002 of 200 TPD capacity, 98% NaOH flakes are produced from 32% NaOH
The 32% membrane cell NaOH liquor at 80°C is fed to the first stage evaporator, a falling

Film evaporator 32E001 operating on the product side under vacuum.

During a single pass through the evaporator, the caustic solution is concentrated to

Approximately 37% wt. The generated vapour is fed via duct 32D001 (D-1101) to the surface
condenser
32E010 , where they are indirectly condensed by cooling water.
Inert gases are extracted by the vacuum pump 32P004A/B (P-7102A/B) and areDischarged to
the atmosphere.
The 37% caustic solution is discharged from the bottom of the first effect evaporator by

Means of a pump 32P001A/B (P-1101A/B) and passed through the gasketted plate type Heat
exchangers 32E004 ) and 32E005 (1). On passing these heat

Exchangers, the NaOH solution is heated up before being fed to the second stage of
Evaporation. During a single pass through the second stage evaporator, a falling film evaporator

32E002 1), operating on the product side under vacuum, the caustic solution is
Concentrated to approximately 42% wt. The vapour generated hereby is used to heat the
First stage evaporator 32E001 .

The 42% caustic solution is discharged from the bottom of the second effect evaporator By
means of a pump 32P002A/B) and passed through the heat exchangers

32E006 , 32E007 ( 32E008 ). On passing these heat

Exchangers, the NaOH solution is heated up before being fed to the third stage of Evaporation.
During a single pass through the third stage evaporator, a falling film evaporator
32E003 , operating on the product side under pressure, the caustic solution is Concentrated to
49% wt. The vapour generated hereby is used to heat the second stage
Evaporator 32E002 . The falling film evaporator 32E003 is heated by Live steam at
approximately 185 °C and 10 kg/cm2 g.

The 49% NaOH solution is discharged from the bottom of 32E003 by means of A pump
32P003A/B and consecutively passed through the heat exchangers
Exchange), 32E006 , and 32E004 in order to preheat the

Intermediate NaOH solution. On finally passing the water cooled plate type heat Exchanger
32E009 , the product is cooled down to 45°C and fed to the battery Limit of the plant.

The steam condensate from 32E003 (iis collected in the steam condensate tank

32D006 (). It is then used to consecutively preheat the intermediate NaOH solution

In the heat exchangers 32E008 and 32E005 before being

Discharged to the battery limit at pressure.

The vapour condensate coming from 32E002 is fed to the condensate

Flash duct 32D002 ). In the condensate flash duct, a part of the condensate

Flashes because of the pressure difference between condensate outlet (overpressure)

From 32E002 ) and the vacuum in 32D002 ). The vapours created by the Flash effect are led to
the vapour duct 32D003 ) and are used to heat the shell
Side of 32E001 1). The remaining condensate together with the vapour

Condensates coming from 32E001 and 32E010 are then collected

In the condensate tank 32D005 (1). The condensate in the tank 32D005 ) is discharged by the
extraction pumps 32P005A/B for further use in other sections of the process plant.

Effulent system

Effluent pits [81X001A-K] are provided in various units in the plant to collect the effluents
Generated due to floor washings, drains from various plant sections, Pumps seal flushing etc.
Effluents from these pits are pumped to effluent neutralization tanks [81T001A/B] with the help

Of effluent pit pumps [81P002A-K]. Additionally, effluents like acidic effluent from ion
Exchange unit are taken in Neutralization tank [81T001A/B] via above ground pipe line. To

carry out the neutralization of the above mentioned effluents provisions for addition of 18%
HCl, 18% NaOH & Bisulphite solution is made available to Neutralization tanks [81D001A/B].

Adequate and quick mixing of 18% HCl, 18% NaOH and bisulphite (if required) with effluent is
Ensured by Tank Jet mixer [81F001A/B]. The resulting neutralized treated water is then pumped
to common effluent treatment plant
Located at nearby power plant with the help of treated water tank pump [81P001A/B].

Project on polishing filter

The purpose of Brine polishing unit is to remove the final traces of suspended solids from the
brine prior to removal of dissolved impurities in ion exchanger. The polishing unit consists of
three identical Brine polishing filters [05F002A-C], two operating and one standby.

Brine polishing system consists of three filter housings containing PP cloth filter candles.

The candles are hung from a register to the shell. By means of the filtered brine pump
[05P001A/B] pressure, the brine passes through the candles [05F002A-C Z01] and the
solids are retained on the outer surface. A discharge channel is installed in the upper part of
the filters. The polished brine is discharged via this channel to the polished brine tank
[05D002] at downstream of the filtration stage.
Due to the retention of solids on the candles, a filter cake builds up on the outer surface of

The candles in the course of operation. Since the brine throughput is maintained constant,
The pressure drop across the filter increases with increasing thickness of the filter cake. The

Pressure drop across the filter is constantly monitored. The pressure drop across the filter
Must not exceed 2.0 Kg/cm2 g. As soon as the pressure drop approaches this value, the
Filter must be taken out of operation for cleaning. Normally one filter is backwashed after 48
hours of operation depending on quality of brine.

This filter operation is by sequence –the main steps are the following:

1. Filling of Filter
2. Back washing (hose cleaning) with Air
3. Refilling of Filter and Homogenizing
4. Precoating
5. Filtration with Body feed
6. Draining of filter and Heel draining

7. Cake Drying with Air [shock method]

8. Pressure release
9. Cake discharge

After polishing filtration, HCl is added in the brine stream via 18% HCl pump [06P001A-C]

To dissolve precipitated fine Mg(OH)2. Further, 18% NaOH is added to this acidic brine by

18% NaOH Pump [26P004A-C], before sending it to Ion-exchange column for secondary Brine
purification.
The candle filters operate with precoat. Precoat [0.5% alfa cellulose] is prepared in the
Precoat Cum Bodyfeed tank [05D003]. Precoat solution is pump to the filter by precoat
Pump [05P005] during the precoating stage. Body feed solution [0.5% alfa cellulose] as
Prepared in the Precoat Cum Bodyfeed tank [05D003] is mixed with the filtered brine and

Send to the polishing filter during filtration stage by the body feed metering pump
[05P008A/B]. The candle filters are cleaned with air pressure. For the steps no. 6, 7 & 9

0.5 % alpha cellulose mixture is used in precoating baceause it or its highly selective
quality
• Organic in nature
• Harmless to human and environment
• Biodegradable
• High permeability
• Non abrasive in nature
• Great adsorption quality
• Form a permeable, stable and incompressible filter cake
• Remove fine solids at high flow rates

Polishing filter vessle Shell dia 2208mm

Height 6015mm
Polishing filter internals filter element - Flow 230 M3/h
candles

Precoat Tank Volume 50 m3

Air Buffer Vessel Volume 50 m3
Precoat Pump Capacity 270 M3/h
Bodyfeed Metering Pump 2.6 M3/h
Troubleshooting
Troble Indication Effect Action

High turbidity in Visual indication Presence of Isolate the brine

polished brine and sampling suspended solid in polishing filter ,
outlet of the polish brine drain and check in
polishing filter case the Filter
candles and cloth
are damaged

High pressure Pdi across Reduced brine Check

drop across ion the ion exchanger flow performance of
exchanger
polishing filters.

The precoating pumps almost always are centrifugal pumps because they produce no
pulsations to disturb precoat formation.

If the Filteration time going shorter then

• If the cake is not discharged properly the new batch have residue suspended particles
in। Filter resulting into lower capacity
Action – increase precoat height and increase drying time may help cake discharge
• If the precoat not cover the cloth filter then the suspended solids blind the medium
Action – increase precoat time and weight percent of alpha cellulose
• If low PDI in larger Filteration times and high turbidity in polished brine Action – check
tha cloth and candles may be damgaed