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

Chapter 3
3.4 Emissions and waste generation from all cell plants
Emissions from auxiliary processes
3.4.1 Emissions from the storage and handling of solids salt
unloading and storage
The salt is normally stored in sealed areas, sometimes equipped with a roof, to prevent it from
blowing off site. Protective systems are installed to prevent contamination of the brine, in
particular in case of rain or if the storage is located near to surface waters or ground waters.
{This is covered in Chapter 2.}
Emissions from the storage and handling of solids include minor dust emissions to air
originating from salt and ancillary materials as well as emissions to water caused by the seeping
of rainwater and discharge with run-off water. Usually, there is no percolation into the soil
because of an impermeable layer (sometimes with hardened salt) under the salt [ 3, Euro Chlor
2011 ].
3.4.2 Emissions and waste generation from the brine circuit
3.4.2.1 Overview
Table 3.3, page 38, shows the different chemical agents which are employed to purify the brine
before electrolysis. The consumption of chemicals varies from plant to plant depending on the
impurities of the brine and the type and sensitivity of the local environment into which the purge
is discharged.
As explained in Chapter 2, brine purification by pH adjustment, precipitation, flocculation and
filtration is required, on a full flow or sidestream basis, to keep impurities at acceptable levels.
Membrane and mercury cells may use recycled brine requiring dechlorination. Specifically for
membrane technology, brine purification is of critical importance to long membrane life and
high efficiency. Thus, impurities need to be removed by ion-exchange resin units which then
require regeneration with caustic soda and acid washing. Some plants use vacuum crystallised
salt, which is the most pure salt form (but also the most expensive) and for this reason have a
simplified brine purification step. {This paragraph contains too many details for an
introduction. Some issues are described in Chapter 2.}
Emissions from the brine circuit to air include fugitive emissions of chlorine and carbon
dioxide. Emissions to water occur via the brine purge. Releases The emission levels depend on
the purity of the incoming salt used, the cell technique technology used (mercury amalgam,
diaphragm or membrane), the techniques used for brine purification trade-off (use of chemical
agents or direct purge in the media) and whether the brine is recirculated or wasted. Brine
sludges which are generated during brine purification are one of the largest waste streams of the
chlor-alkali industry.
WORKING DRAFT IN PROGRESS
3.4.2.2 Emissions to air Air emissions
Emissions to air from the brine circuit include mainly emissions of carbon dioxide and chlorine.
The fugitive emission of carbon dioxide is possible from all three chlor-alkali technologies.
Carbon dioxide is emitted from the brine acidification tanks due to the decomposition of
carbonate and hydrogen bicarbonate ions into water and carbon dioxide. The carbonate and
hydrogen bicarbonate stem are from the auxiliary chemicals used in the brine purification step
(see Table 3.4). The carbon dioxide either escapes from the brine and is emitted to the
atmosphere or is led to the chlorine destruction unit, depending on the presence of chlorine in
the brine. The concentration of (hydrogenbi) carbonate is expected to be lower when the
82 December 2011 TB/EIPPCB/CAK_Draft_1