International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
Single Stage Brine Filtration System in Chlor-Alkali
Industries
Unnikrishnan H 1 , Rakesh A2
1
M Tech Student , 2Assistant Professor
Production and Industrial Engineering, SCMS School of Engineering & Technology, Kerala, India
Abstract— The Conventional Brine Filtration in Chlor-Alkali
industries is done using clarifier and precoat systems which is
time consuming and requires huge amount of electricity .It also
generates large amount of sludge causing environmental
pollution .The maintenance cost is also high these problems are
overcome by single stage brine filtration system. This report
compares the present and conventional filtration systems and its
benefits. The use of new system like PTFE membrane for brine
filtration is also included. This report is based on the study
conducted on one of the Chlor - Alkali plant in Kerala.
Keywords— Clarifier, PTFE membrane, Saturator.
I. INTRODUCTION
The main raw material of chlor-alkali plant is the salt. The
salt is purified only after making it into brine after which it is
filtered using the clarifier and other secondary filters. The
purified brine is fed towards electrolyser where it is converted
into different by products like chlorine, hydrogen and caustic
soda. The caustic soda which is one the main product in the
chlor-alkali industry used in the manufacture of soaps and
detergents, the quality of the caustic soda depends on the
quality of brine used. The traditional filtration of brine is done
through two stages. The first stage is the primary filtration
stage in which the majority of impurities are removed in the
form of sludge and the second stage helps in ultra-high
purification and ionization of brine before being fed to the
electrolyser.
maintenance and service of the clarifier. The disposal of the
sludge within the limited space is also a main concern. The
process of single stage filtration tackles most of problems in
primary filtration and maintaining the quality of the
brine .Maintenance cost was reduced to much extend and the
sludge disposal cost was reduced up to 55%.The process flow
diagram is shown in fig 1.
II. METHODOLOGY
A study was conducted one of the chlor-alkali industry during
which it was found that most of the problems occurred in
primary stage of brine filtration and the company has incurred
more expenditure on the maintenance of the current system. A
cause and effect diagram could reveal reasons behind. Fig 2
shows the cause and effect diagram.
Fig 2 Cause and Effect Diagram
A. The main problems associated with the present brine
filtration where the following:
Fig 1 Process Flow Diagram
During the study majority of the problems encountered was
on the first stage which includes frequent maintenance of
clarifier, large energy consumption and sludge disposal
problems. Companies spend large amount of money on
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Frequent maintenance of machines
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Large energy consumption
Sludge disposal cost
Safety problems
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
The equipment’s were undergoing frequent maintenance
which increased the overall maintenance cost. The main
equipment’s undergoing the brine filtration was clarifier, precoat system and anthracite filters. Most of the brine was
filtered by the clarifier. Wearing of the rubber lining inside the
clarifier was a common problem. Since the clarifier is the only
filter removing more than 70 % sludge in the brine therefore it
is considered as the primary source of filtration. The energy
consumption was high due the use of turbines running
continuously there were other pumps and motors for
maintaining the flow in the line. The sludge generated from
the clarifier was nearly 1.5 TPD (tonnes per day) effective
disposal mechanism was one of the main issue resulting in
environmental pollution due to which the company has to
spend more expenditure for the sludge handling and disposal.
Adequate safety measure has to be taken by the workers while
repairing the Clarifier when it is at full capacity. The fig 3
shows the yearly maintenance done on the primary brine
filtration systems.
Fig 3 Number of Maintenance done on Brine Filtration Plant
B. Economic Life of the Clarifier
The clarifier has an economic life of 12 years after which
the total cost of the equipment start rising as shown in Fig 4.
.
Fig 4 Economic Life of Clarifier
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Fig 5 Process Flow Diagram for Brine Filtration (Traditional Systems)
III. SUGGESTION OF NEW SYSTEM
Expert discussion was undergone to resolve the present
issue after which we reached at a conclusion of replacing the
present stem with light weight PTFE (polytetrafluoroethylene)
membrane. The PTFE membrane has many advantages
compared to the present system. It can filter up to submicron
level. The PTFE membrane is applied at many of the recent
technologies where filtration is an essential part. The
conventional filtration is done through multiple steps before
reaching to the electrolyser but the PTFE membrane does not
require clarifier and precoat systems which reduces much of
the operation and maintenance cost. A bundle of tube inserted
with PTFE membrane will be placed inside a dome like
structure will be used for the brine filtration. The brine enters
the bottom part of the vessel and passes through the tube
during which much of the suspended solids gets absorbed and
crystal clear brine will reach at the top surface. The solid
sludge is removed by back wash process. It is also seen that
economic life of the PTFE membrane is high compared to the
traditional systems.
A. Analysis of suggested system
The analysis of suggested system includes its cost and
economic life which will be compared to the present systems.
The single stage filtration removes much of the problems
present in the conventional filtration the main advantage is the
energy consumption is less and also the sludge generate from
the suggested system is very less compared to the present
system since the sludge quantity is directly proportional to the
cost of handling and disposal they also tend get reduced.
Skilled operators were required for operation of the clarifier
and precoat systems as they have to undergo periodic
maintenance inside the clarifier which was mainly an accident
prone area. The operators were subjected to serious health
issues due to the direct exposure of brine. Since the suggested
is a closed container there will be no direct exposure of the
operator which will reduce much of the health related issues.
B. Cost Analysis of the suggested system
The cost analyses include cost of purchase of the new
system replacement of present system its scrap value and
demolishing cost etc. payback period has been estimated as
shown in Table 1.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
Table 1 Cost Analysis of the Suggested System
IV.
MODIFICATION PRESENT LAYOUT WITH
SUGGESTED SYSTEM
Fig 6 Process Layout with Suggested System
The modification of the present system with suggested as
shown in Fig 6 removes Clarifier, Precoat systems and
anthracite filters etc.
The payback period is estimated to about 5.8 years.
C. Economic analysis of the suggested system
Table 2 Economic Life of the Suggested System
V. CONCLUSIONS
The replacement of conventional brine filter with one step
brine filtration process which will reduce the operation and
maintenance cost, sludge disposal cost and safety problems. It
is understood that 55% of the maintenance and the operation
cost can be saved per year. The sludge disposal cost has been
reduced to 45 % and the annual sludge generate is reduced to
0.25 TPD. The proposed system has an economic life of 25
years compared to the present system of 12 years. The average
total cost of the conventional system can be saved when it is
replaced by proposed system .The payback period for the
proposed system is 5.8 years
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The economic life of the suggested system is estimated to
be about 25 years .
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