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

Chapter 2
amount of chlorine, and the gas is therefore normally led to the chlorine destruction/absorption
unit.
Production of hydrochloric acid
Instead of diluting the remaining gases after partial condensation of the chlorine gas, the
hydrogen can be removed from the system by means of a reaction with chlorine gas in a
column. This removes virtually all the hydrogen and yields gaseous hydrochloric acid, which
exists harmlessly with the chlorine gas and can be recovered in a hydrochloric acid unit. The
remaining chlorine gas can now safely be further condensed. The tail gases with some chlorine
gas and the remaining non-condensable gases (CO2, N2, O2) will be passed through a
hydrochloric acid unit. This solution can be chosen if HCl is a saleable product or if it can be
used as a feedstock for downstream production, such as ferric chloride.
{The contents of these paragraphs are covered by previous sections.}
2.6.12 The chlorine absorption unit
2.6.12.1 Purpose
Every chlor-alkali plant generates waste gases consisting of N2, O2, H2, CO2 and 1 – 8 % of the
original chlorine produced. Although the quality of these waste gases is usually insufficient for
the main chlorine uses, the chlorine therein still represents a certain market value and is often
used for the synthesis of bleach (sodium hypochlorite), hydrochloric acid, iron trichloride,
chlorinated hydrocarbons or sulphur monochloride. Most common is the production of bleach in
a chlorine absorption unit (Figure 2.18). Irrespective of the use of the residual chlorine,
absorption of chlorine in caustic solution usually represents the last step before waste gas is
released to the atmosphere [ 17, Dutch Ministry 1998 ].
WORKING DRAFT IN PROGRESS
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