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

Chapter 5
5.7 Emissions to air
10. In order to reduce channelled emissions of chlorine and chlorine dioxide to air from the
processing of chlorine, BAT is to use a chlorine absorption unit.
Description
The chlorine absorption unit consists of a wet scrubber with caustic solution as
scrubbing liquid which can make use of packed columns or ejectors. Hydrogen peroxide
dosing equipment or a separate wet scrubber with hydrogen peroxide is used to reduce
emissions of chlorine dioxide.
The BAT-associated emission level for chlorine and chlorine dioxide (expressed as
Cl2) is < 0.10 – 1.0 mg/m 3 as hourly average value at the outlet of the chlorine
absorption unit based on absorption of the waste gas in sulphamic acid solution and
determination of total chlorine according to EN ISO 7393–1 or –2 (see BAT 9).
The lower end of the range is close to the typical limit of detection of the monitoring
method.
[This BAT conclusion is based on information given in Sections 4.3.5.1.2 and 4.3.5.2.]
11. In order to reduce channelled emissions of chlorine during incidents and accidents including
power failure, BAT is to use a chlorine absorption unit that absorbs the full cell room
production for a sufficient duration until the plant is shut down.
Description
See BAT 10.
[This BAT conclusion is based on information given in Section 4.3.5.1.2.]
12. The use of carbon tetrachloride for the elimination of nitrogen trichloride or the recovery of
chlorine from tail gas is not BAT. In order to prevent emissions of carbon tetrachloride to
air, BAT is to avoid the use of carbon tetrachloride by using a combination of the
techniques given below.
Technique Description Applicability
a
Direct use of
chlorine
Chlorine is compressed and used directly
without liquefaction, in order to prevent the
potential accumulation of nitrogen trichloride in
liquid chlorine.
Applicable to sites which
can directly use the
chlorine of this quality.
b
Reduction of
nitrogen intake
The nitrogen intake via the raw materials (salt,
water, ancillary materials) is reduced, in order
to reduce the formation of nitrogen trichloride.
Generally applicable.
c
Removal of
ammonia from the
brine
Ammonia is removed from the brine at alkaline
pH by stripping or by breakpoint chlorination,
in order to reduce the formation of nitrogen
trichloride.
Techniques to destroy NCl3 include:
Generally applicable.
Destruction of reaction with sodium hydroxide or
d nitrogen
hydrochloric acid;
Generally applicable.
trichloride
decomposition using heat, irradiation or
activated carbon.
e
Absorption of
chlorine in caustic
solution
Absorption leads to the recovery of chlorine
from the tail gas to produce bleach which can
be sold, recycled to the brine system or
destroyed.
Generally applicable.
f
Production of
other substances
The residual chlorine in the tail gas is used to
produce other substances such as hydrochloric
acid, iron(III) chloride and ethylene dichloride.
Applicable to sites with a
demand or market for the
produced substances.
WORKING DRAFT IN PROGRESS
280 December 2011 TB/EIPPCB/CAK_Draft_1