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

Chapter 2
composition of the chlorine gas, the desired purity of the liquid chlorine and the desired yield.
Increasing the liquefaction pressure increases the energy consumption of compression, although
the necessary energy for cooling decreases, resulting in an overall reduction in energy
consumption.
The chosen liquefaction pressure and temperature influence the choice of cooling media and the
safety precautions necessary to operate safely. However, the efficiency of The liquefaction yield
is typically limited to 90 – 95 % in a single-stage installation because hydrogen is concentrated
in the residual gas and its concentration needs to be kept below the explosive limits (see
Section 2.6.11.3).
Higher yields of up to 99.8 % can be achieved by multi-stage liquefaction. Typically, small
volume liquefiers which are protected against explosions are used after primary liquefaction,
and inert gas is added to keep the mixture below the explosive limit [ 1, Ullmann's 2006 ].
Another possibility is to remove hydrogen from the system by reaction with chlorine gas in a
column, yielding gaseous hydrochloric acid which can be recovered in a hydrochloric acid unit.
The remaining chlorine gas can then safely be further condensed. 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 choice of the refrigerant cooling media in a certain stage of the liquefaction depends on the
pressure temperature of the chlorine. When the pressure temperature is sufficiently high, water
can be used as an indirect refrigerant cooling media. When the pressure temperature is relatively
low, other refrigerants cooling media such as HCFCs or HFCs, typically chlorodifluoromethane
(R-22) and 1,1,1,2-tetrafluoroethane (R-134a) (indirect cooling), ammonia (indirect cooling) or
liquid chlorine (direct cooling) are used.
The temperature of the chlorine gas in a certain stage depends mainly on the pressure after
compression. initial temperature and on the pressure increase during compression. A large
pressure increase A pressure > 8 bar generally enables water cooling, but implies an increased
hazard [ 3, Euro Chlor 2011 ]. risk. Chlorine temperature has to be kept well below the point
where it reacts spontaneously and uncontrollably with iron. (approx. 120 °C). {This information
was moved to the previous section.}
Construction materials must be chosen to suit the conditions under which chlorine is being
handled:
Wet or dry
Gas or liquid
Temperature
Pressure
In terms of safety, it is very important to avoid, during compression and liquefaction, any
possibility of mixing chlorine with oils or greases which are reactive as regards chlorine.
{This information was moved to Section 2.6.2 because it applies to all stages of chlorine
processing.}
WORKING DRAFT IN PROGRESS
Table 2.5 shows the possible trade-offs between different types of chlorine gas liquefaction
systems and refrigerants used. cooling methods applied and safety aspects.
TB/EIPPCB/CAK_Draft_1 December 2011 51