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

Chapter 3
3.4.3 Emissions and waste generation from chlorine processing, gas
production, cooling, drying, liquefaction and storage and
handling
3.4.3.1 Overview
Air emissions consist of fugitive emissions of carbon dioxide and chlorine from the processing
steps, from storage and handling of chlorine as well as of channelled emissions from, the
chlorine destruction unit and the handling/storage of chlorine. The process of purifying and
liquefying impure chlorine gas involves the use of carbon tetrachloride at a few installations in
Europe, which is recovered to a large extent or incinerated. Small amounts of chlorine dioxide
could also be emitted from the chlorine destruction unit as well as small amounts of refrigerants
from the chlorine liquefaction system.
The condensed water formed after cooling is usually recycled as brine make-up although some
facilities combine this waste stream with other waste water streams prior to treatment. The
remaining water vapour is removed by scrubbing the chlorine gas with concentrated sulphuric
acid. The spent sulphuric acid waste is either used for other purposes, sent back to the vendor, is
recycled or released sent to the site's waste water system.
3.4.3.2 Emissions to air Air emissions
3.4.3.2.1 Carbon dioxide
Small amounts of carbon dioxide are released from the anode compartment and are collected
and treated together with the chlorine. During chlorine liquefaction, carbon dioxide and other
gases (and N2, O2, H2) remain in the gas phase and are finally purged from the system, together
with a small amount of chlorine. This waste gas stream is usually processed in the chlorine
destruction unit. The part of the Carbon dioxide that is not absorbed by the chlorine destruction
unit is emitted into the atmosphere.
3.4.3.2.2 Chlorine
Because chlorine is a hazardous gas, extreme precaution is taken to avoid prevent emissions of
chlorine from the process and from handling and storage. Therefore, emissions of chlorine gas
into the atmosphere are generally low and the sources of significant potential emissions are
normally connected with the chlorine destruction unit.
When measuring chlorine in the gas phase, other oxidising species are included due to the
analytical method employed. This holds true for both categories of measurement techniques.
The first is based on absorption of a gas stream in a liquid with subsequent wet chemical
analysis while the second is based on direct measurements in the gas phase with electrochemical
cells (see Section 4.3.4.4) [ 67, Euro Chlor 2010 ]. Other oxidising species are usually unlikely
to be present in relevant concentrations with the exception of chlorine dioxide (see
Section 3.4.3.2.3).
WORKING DRAFT IN PROGRESS
Emissions from non-condensable gases remaining from liquefaction
Chlorine is liquefied in several steps of cooling and compressing. Gases (H2, O2, N2, CO2) in the
process stream tend to concentrate in the gas phase. Therefore, chlorine gas liquefaction has an
outlet for non-condensable gases. The chlorine content of these non-condensable gases ranges
from 1-8% of the raw chlorine gas produced. The non-condensable gases are directed to a
system which is able to handle chlorine such as a chlorine absorption/destruction unit or the
manufacture of HCl, FeCl3 or ethylene dichloride, thus avoiding emissions into the atmosphere.
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