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

Chapter 4
All types of salt require energy for their extraction, purification and transport which depend on
the extraction techniques used as well as on the means of transport and the distance from the salt
source to the chlor-alkali plant.
Vacuum salt is the purest salt used in chlor-alkali plants which is favourable in terms of
consumption of ancillary materials, generation of brine filtration sludges, process stability and
energy consumption. However, the production of vacuum salt requires considerable amounts of
energy (see Section 3.3.4.2), ancillary materials for chemical purification might be needed and
wastes might be generated off-site [ 66, Ullmann's 2010 ]. Rock salt, salt from potash mining
wastes and solution-mined brine are less pure than vacuum salt and thus require higher amounts
of ancillary materials for brine purification and lead to higher amounts of brine filtration sludges
(see Table 3.17). When salt from potash mining wastes is used, no additional energy for mining
is required and raw materials are saved. Moreover, its consumption contributes to the restoration
of the original landscape [ 27, ANE 2010 ]. Solar salt uses the renewable energy from the sun
for the evaporative step but additional purification is usually required.
Several of the factors concerning the overall environmental impact of the different types of salt
are outside the scope of this BREF and depend on local conditions such as the means of
transport and the distance from the production of salt to the chlor-alkali plant. Therefore, no
proposals are made with respect to the use of a specific type of salt as a technique to consider in
the determination of BAT.
4.3.2.1.2 Techniques to reduce consumption of salt
In addition to the techniques described in the following Section 4.3.2.1.3, several of the
techniques to reduce consumption of water (see Section 4.3.2.2), to reduce emissions of chloride
(see Section 4.3.6.2) and to reduce emissions of chlorate (see Section 4.3.6.4) do also reduce
salt consumption.
4.3.2.1.3 Recycling of waste water from other production processes
Description
This technique consists in recycling salt-containing effluents from other production processes to
the brine system of the chlor-alkali plant.
Technical description
The treatment required for waste water recycling is plant-specific and depends on the impurities
contained in the waste water.
At the SABIC plant in Bergen op Zoom (Netherlands), waste water from the polycarbonate
production unit undergoes a series of purification steps before it is recycled to the brine circuit
[ 128, SABIC 2008 ]:
isolation of brine from the reaction product using special decanters at the resin plant;
removal of solvent via distillation at the resin plant (modified equipment);
removal of suspended solids via filtration at the central waste water treatment plant
(modified equipment);
adsorption of phenolic compounds via active carbon beds at the central waste water
treatment plant (modified equipment);
destruction of carbonates via acidification (newly designed unit for this purpose);
adsorption of nitrogen containing components via special active carbon beds (newly
designed unit for this purpose);
adsorption of metal ions on ion adsorption resins in the chlor-alkali plant (modified
equipment);
WORKING DRAFT IN PROGRESS
186 December 2011 TB/EIPPCB/CAK_Draft_1