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

Chapter 3
Substance Emission in kg/tonne chlorine capacity
Sulphate
0.3-0.7
15
(Vacuum salt)
(rock salt)
Strictly depends on the purity of
the incoming salt
Chloride 4–25
Free oxidants 0.001–1.5 (1)
Chlorate 0.14-4 (2)
Metals Depends on the purity of the incoming salt
Chlorinated hydrocarbons
0.03-1.16 (3) g/tonne Cl2 capacity
(measured as EOX)
Generally treated before discharging
1) Higher figure from a plant that destroy the produced bleach in a chlorine destruction unit and
releases the remaining liquid. In this case, a value of 1.5 kg/tonne chlorine capacity is reported.
2) Values will depend on the presence or not of a chlorate decomposer.
3) Higher figure from a plant that destroy the produced bleach in a chlorine destruction unit andreleases the
remaining liquid. In this case, a value of 1.16 g/tonne chlorine capacity is reported
Table 3.6: Releases into water from the brine circuit using a recirculation process
{This table is completely contained in the summary Table 3.1 and therefore is proposed to be
deleted.}
3.4.2.3.2 Sulphate
{For each of the following pollutants, it is proposed to describe in the following order (if
appropriate): source, relevance for the process, definition in the case of sum parameters,
current emission levels, factors which influence the emission levels including a brief mentioning
of techniques to reduce emission levels, and a brief mentioning of the relevance for the
environment.}
Brine is generally purged from cells to reduce the levels of sodium sulphate and/or sodium
chlorate in the cells. The source of sulphate in brine is the salt used. Sulphate has a negative
effect on the electrolysis process (damages the anode coating) and its level is carefully
controlled. This is normally done by a bleed purge from the brine treatment system for mercury
amalgam and membrane cell plants processes and by purge from in the caustic evaporator for
from diaphragm cell chlor-alkali plants. Sulphate emissions may also be due to the
neutralisation and discharge of spent sulphuric acid from chlorine drying. In addition,
(hydrogen) sulphite is frequently used for complete dechlorination of the brine in the membrane
cell technique as well as for the treatment of waste water containing free oxidants. In both cases,
(hydrogen) sulphite is converted to sulphate. Reported emission concentrations and factors are
summarised in Table 3.10.
WORKING DRAFT IN PROGRESS
84 December 2011 TB/EIPPCB/CAK_Draft_1