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

Chapter 4
Cross-media effects
Plants which use solution-mined brine need to evaporate water from the depleted brine for its
recirculation. This requires significant additional energy (see Section 4.3.2.3.7). Alternatively,
the depleted brine can be reused for solution mining (see Section 4.3.2.2.6).
Technical considerations relevant to applicability
Due to their inherent design, diaphragm cell plants do not use brine recirculation.
Economics
The reduction of operating costs due to reduced consumption of salt and water renders brine
recirculation in most cases economically favourable.
Driving force for implementation
The driving forces for implementation of this technique include the following:
reduction of operating costs due to reduced consumption of water and salt;
limited availability of water resources;
environmental legislation.
Example plants
Almost all membrane cell chlor-alkali plants in EU-27 and EFTA countries use a brine
recirculation system.
Reference literature
[ 1, Ullmann's 2006 ], [ 10, Kirk-Othmer 2002 ], [ 17, Dutch Ministry 1998 ], [ 37, Euro Chlor
2010 ], [ 73, Debelle 2011 ]
4.3.2.2.3 Recycling of other process streams
Description
This technique consists in feeding back process streams from the chlor-alkali plant to various
steps of the process. Process streams which are usually recycled include the condensates from
chlorine, caustic and hydrogen processing.
Technical description
A number of process streams originating in the chlor-alkali plant can be recycled [ 33, Euro
Chlor 2011 ]:
The condensates from chlorine processing are usually recycled in the brine.
The condensates from hydrogen processing can be used to produce caustic.
The condensates from caustic evaporation are usually recycled in the catholyte circuit of
the membrane electrolysis unit, in the brine loop or to dilute caustic if necessary.
Diluted sulphuric acid from the chlorine drying unit can often be used (at least partially)
to adjust the pH of the liquid effluents to be discharged. Alternatively, the acid may be
re-concentrated and reused.
The off-specifications caustic can be used for pH adjustment and to feed the caustic
production circuit.
The chlorinated caustic effluent from the chlorine safety absorption unit can be recycled
in the brine or for the production of saleable hypochlorite.
WORKING DRAFT IN PROGRESS
Achieved environmental benefits
The achieved environmental benefits of this technique include the following:
reduction of water consumption;
reduction of salt consumption (for some of the streams);
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