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

Chapter 2
Further potential cleaning steps after chlorine drying include [ 1, Ullmann's 2006 ], [ 3, Euro
Chlor 2011 ], [ 54, Euro Chlor 2010 ], [ 56, Euro Chlor 2008 ]:
adsorption on carbon beds to remove organic impurities;
absorption-desorption using a suitable solvent such as carbon tetrachloride to remove
nitrogen trichloride and organic impurities;
scrubbing with concentrated hydrochloric acid to remove nitrogen trichloride;
scrubbing with liquid chlorine to remove nitrogen trichloride, organic impurities,
carbon dioxide and bromine;
irradiation with UV to destroy nitrogen trichloride and hydrogen.
2.6.7 Compression
After drying and potential further cleaning, chlorine gas might be scrubbed with liquid chlorine
or treated with ultraviolet irradiation to reduce levels of nitrogen trichloride and then it may be
compressed in a variety of compressors, depending on the throughput and the desired pressure
[ 1, Ullmann's 2006 ], [ 3, Euro Chlor 2011 ]:
- Rotary compressors such as:
sulphuric acid liquid ring compressors for throughputs of 150 t/d per compressor and for
pressures of 4 bar or, in two stage compressors, 12 bar; at low pressures (~ 4 bar)
screw compressors for low throughputs and for pressures of up to 16 bar. (various
pressures)
- Reciprocating compressors such as:
dry-ring compressors for throughputs of 200 t/d per compressor and for pressures up to
16 bar. (>11 bar)
- Centrifugal compressors such as:
turbo compressors in mono- or multi-stage operation for throughputs of up to ~ 1800 t/d
per unit and for pressures of up to 16 bar; centrifugal compressors (5 bar or higher)
sundyne blowers for throughputs of 80 – 250 t/d per compressor and for pressures of up
to 3 bar.
Because of heat build-up from compression, multi-stage units with coolers between stages are
usually necessary. Compressor seals are generally fitted with a pressurised purge to inhibit the
leakage of chlorine to the atmosphere [ 39, HMSO 1993 ] [UK Guidance note, 1993].
To avoid noise, which is quite important even for low pressures, chlorine compressors should be
sound insulated.
WORKING DRAFT IN PROGRESS
Dry chlorine at high temperatures can react spontaneously and uncontrollably with iron.
Chlorine temperatures are therefore usually kept below 120 °C (see Section 2.6.2) [ 56, Euro
Chlor 2008 ].
2.6.8 Liquefaction
Liquefaction can be accomplished at different pressure and temperature levels, at ambient
temperature and high pressure (for example 18 ºC and 7 – 12 bar), at low temperature and low
pressure (for example -35 ºC and 1 bar) or any other intermediate combination of temperature
and pressure. Important factors for selecting appropriate liquefaction conditions include the
50 December 2011 TB/EIPPCB/CAK_Draft_1