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

Chapter 3
Table 3.4: Consumption and use of main chemical auxiliaries in chlor-alkali plants using a
brine recirculation process
{The data in the table were updated according to the results of the survey. The TWG is asked to
provide more information.}
Substance Use
Sodium
(hydrogenbi)
carbonate
(NaHCO 3/Na 2CO 3)
Barium salts
(BaCl2, BaCO3) Calcium chloride
(CaCl2) Hydrochloric acid
(HCl)
Sodium (hydrogen)
bisulphite
(NaHSO3/Na2SO3) Sodium hydroxide
(NaOH)
Precipitation of calcium ions as calcium
carbonate (CaCO 3)
- essential if vacuum salt is not used
Precipitation of sulphate as barium sulphate
(BaSO4) in the case of high levels content in
brine
- not always used (high price and toxicity)
- alternatives include purging of the brine,
crystallisation of sodium sulphate as well
as nanofiltration combined with purging of
the brine or sulphate precipitation
Precipitation and elimination of sulphate as
calcium sulphate (CaSO4)- formation of
CaSO4 in the case of high levels in brine
- CaCl2 can be used in place of barium
salts or direct purge
used for pH adjustment of brine entering
cells
used for Dechlorination of brine in the
membrane process and on occasion in the
mercury cell technique process if there is no
hypochlorite production unit
used for Regeneration of ion-exchange
resins
Final stage of brine dechlorination in the
membrane cell technique used for
dechlorination of brine, final stage to
eliminate chlorine, in the membrane process
Treatment of waste water containing free
oxidants
- other reducing agents or filtration with
activated carbon can be used
removal Precipitation of magnesium and
heavy metals (iron mainly if an anti-caking
agent is used for salt transportation) as their
respective hydroxides, e.g. Mg(OH) 2
used for pH control in brine circuit
Regeneration of ion-exchange resins
Consumption in
kg/tonne chlorine produced
2 – 60 [ 57, EIPPCB 2011 ], [ 75, COM
2001 ] 3 – 20
This range can vary and reach 60 if the
brine contains a lot of impurities (mainly
rock salt). The value depends on the purity
of the salt. {Questionnaire: 2 plants: 1.9
and 7.7 kg/t.}
~ 3.5 [ 75, COM 2001 ]
- not always used (high price and toxicity)
- purging is an alternative
{A range should preferably be given.
Questionnaire: 1 plant: 5 kg/t.}
0.6 – 35
[ 75, COM 2001 ]
The value is higher for plants using the
membrane cell technique technology which
requires more sophisticated brine
purification.
CaCl2 can be used in place of barium salts
or direct purge
5 – 100 (data from 5 plants)
[ 57, EIPPCB 2011 ]
20 – 30
{Questionnaire: 5 plants: 5.8, 8, 34, 91 and
108 kg/t.}
~ 2 (data from 1 plant)
[ 57, EIPPCB 2011 ]
(no data about consumption)
This final chlorine elimination can also be
done with other reducing agents, or by
passing the brine through an activated
carbon bed
{Questionnaire: 1 plant: 1.77 kg/t.}
3 – 40 [ 75, COM 2001 ]
3 – 5 (mercury cells)
40 (membrane cells)
WORKING DRAFT IN PROGRESS
Sulphuric acid
(H 2SO 4, 92 –
98 wt-%)
Carbon
tetrachloride
Chlorine drying processes
Optional elimination of nitrogen chloride
Optional recovery of chlorine from tail gas
70 December 2011 TB/EIPPCB/CAK_Draft_1
2
{The distinction between mercury and
membrane cell plants does not seem
justified. Questionnaire: 2 mercury plants:
7.1 and 23 kg/t; 2 membrane plants: 9 and
16 kg/t. Since all values refer to total
consumption, it is also proposed to merge
the two rows.}
10 – 40 15 – 20 if not recycled
(data from 7 plants) [ 57, EIPPCB 2011 ]
{Questionnaire: 8 plants: 9, 12, 13, 14, 17,
23, 27 and 42 kg/t.}
0.013 – 0.63 (data from 4 plants)
[ 61, DG ENV 2009 ]