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

differential pressure at inlet and outlet of packed columns;
liquid levels in storage and reaction tanks.
Chapter 4
If the sodium hypochlorite cannot be sold, it has to be treated before it is discharged. Several
technologies are available to destroy sodium hypochlorite without generating significant crossmedia
effects, in particular catalytic processes. {This is covered by the text under cross-media
effects.}
Achieved environmental benefits
The achieved environmental benefit of this technique is a reduction of emissions of chlorine and
other oxidants to air.
Environmental performance and operational data
Absorption units are generally designed to limit the chlorine content to below 5-10 mg/m 3 in the
emitted gas in the worst case scenario. Under normal operation the concentration of chlorine is
less than 1-3 mg/m 3 in the case of partial liquefaction and less than 3-6 mg/m 3 in the case of
total liquefaction.
Current emission levels of chlorine from the absorption unit are presented in Section 3.4.3.2.2.
{Please TWG provide more information on factors which influence the emission levels of
chlorine to air.}
The absorption unit at the AkzoNobel plant in Bitterfeld (Germany) is required to have the
capacity to absorb the full cell room chlorine production for eight minutes including during
power failure. During this period, the plant has to be shut down. The permit furthermore
requires the permanent availability of caustic soda in sufficient quantity and concentration as
well as redundant pumps for the scrubbing solution [ 69, Regierungspräsidium Dessau 1999 ].
Cross-media effects
Considerable quantities of raw materials and energy are consumed for the installation and
operation of the absorption unit. The main ancillary material consumed is the corrosive caustic
soda solution.
When the sodium hypochlorite (bleach) produced can be sold, no further emissions cross-media
effects occur, although it should be noted that the consumer might discharge free oxidants from
the bleach. When there is no demand for bleach and it cannot be recycled (see
Section 4.3.6.3.6), the bleach it has to be destroyed before it can be discharged. The effluent
from the bleach destruction may have an adverse effect on the recipient water, depending on the
technique technology used (see Section 4.3.6.3).
Technical considerations relevant to applicability
Generally, there are no technical restrictions to the applicability of this technique. The
achievement of lower residual chlorine concentrations may require a redesign of the absorption
unit and the replacement of some equipment.
Economics
{Please TWG provide information.}
WORKING DRAFT IN PROGRESS
Driving force for implementation
The driving force for implementation of this technique is environmental legislation.
Example plants
All existing plants are equipped with emergency chlorine absorption units systems.
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