(BAT) Reference Document for the Production of Chlor-alkali ...

Chapter 5
6. In order to reduce energy consumption in the electrolysis process, BAT is to use all of the
techniques given below.
a
Technique Description Applicability
Highperformance
membranes
b Asbestos-free
diaphragms
c
Highperformance
electrodes and
coatings
d High-purity
brine
e Nanofiltration
f
Iron(III) mesotartrate
as anticaking
agent
g Brine
acidification
High-performance membranes consist
of carbonate and sulphonate layers with
fluoropolymer grid, sacrificial fibres
and hydrophilic coatings. They show
low voltage drops while ensuring
mechanical and chemical stability.
Asbestos-free diaphragms consist of a
fluorocarbon polymer and fillers such as
zirconium dioxide. These diaphragms
show lower resistance overpotentials
than asbestos diaphragms.
Electrodes and coatings with improved
gas release (low bubble overpotential),
small gap between the electrodes
(diaphragm cell technique: Q 3 mm;
membrane cell technique: Q 0.1 mm)
and low electrode overpotentials.
The brine is purified to a level so that it
strictly complies with the
manufacturer's specifications of the
electrolysis unit, in order to avoid
contamination of electrodes and
diaphragms/membranes which may
increase energy consumption.
A specific type of membrane filtration
with membrane pore sizes of
approximately 1 nm, used to
concentrate sulphate in the brine purge,
thereby avoiding the use of barium salts
which may damage the membrane and
increase energy consumption.
Iron(III) meso-tartrate is used as an
anti-caking agent, thereby avoiding the
use of ferrocyanide whose
decomposition products may damage
the membrane and increase energy
consumption.
The brine is acidified prior to
electrolysis to reduce the formation of
chlorate and oxygen.
Applicable to
membrane cell plants
on the occasion of a
renewal of
membranes at the
end of their lifetime.
Applicable to
diaphragm cell
plants.
Applicable to
diaphragm and
membrane cell plants
on the occasion of a
renewal of coatings
at the end of their
lifetime.
[Section on
which BAT
conclusion is
based]
[4.3.2.3.3]
[4.2.2]
[4.3.2.3.4]
Generally applicable. [4.3.2.3.5]
Applicable to
membrane cell plants
with brine
recirculation.
Applicable to
membrane cell plants
using solid salt with
an anti-caking agent.
[4.3.6.2.2]
[4.3.2.3.6]
Generally applicable. [4.3.6.4.2]
WORKING DRAFT IN PROGRESS
7. In order to reduce energy consumption from the caustic concentration process, BAT is to
use plate evaporators.
Description
Plate evaporators use metal plates to transfer heat from steam to dilute caustic in order
to evaporate water.
Applicability
Applicable to new caustic concentrators in membrane cell plants.
TB/EIPPCB/CAK_Draft_1 December 2011 277