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

Chapter 3
produced per year has been reported for one amalgam chlor-alkali plant (chlorine production
capacity of 115000 tonnes).
3.4.5 Emissions from hydrogen processing
The hydrogen produced in all of the electrolytic processes contains small amounts of water
vapour, sodium hydroxide and salt, which is are removed through cooling and are recycled or
treated with other waste water streams. However, in the mercury cell plants amalgam cells the
hydrogen leaving the decomposer is nearly saturated with mercury which may lead to emissions
to air, the emission levels depending on the treatment techniques used (see Section 3.5.6.3.4).,
which must be recovered prior to compression. Some facilities further purify the hydrogen of
mercury using sulphurised carbon which may be treated to recover mercury or disposed of in an
approved landfill.
On average, approximately 10 % of the hydrogen produced by chlor-alkali installations in
EU-27 and EFTA countries is emitted to the atmosphere [ 8, Euro Chlor 2011 ]. For individual
installations, the share of emitted hydrogen ranges from 0 % to approximately 53 % (Table
3.20). High shares of emitted hydrogen often concern isolated mercury cell plants because of
lack of opportunities for hydrogen use (no customers and only limited need for steam) [ 3, Euro
Chlor 2011 ].
Table 3.20: Share of hydrogen emitted by chlor-alkali plants in EU-27 and EFTA countries in
2010
Share of hydrogen emitted ( 1 )
Min.
10th
percentile
25th
percentile Median
75th
percentile
90th
percentile
Max.
0 % 0 % 2 % 9 % 18 % 36 % 53 %
( 1 ) Data from 64 plants.
Source: [ 186, Euro Chlor 2011 ]
3.4.6 Emissions during other than normal operating conditions
3.4.6.1 Emissions during start-up and shutdown operations
Start-up and shutdown operations generally lead to increased hydrogen emissions. This is due to
the fact that during plant shutdowns the relevant parts of the hydrogen network are flushed with
nitrogen to prevent the formation of explosive gas mixtures. Therefore, the produced hydrogen
during start-up usually does not have the required purity for its intended use [ 196, Solvay
2011 ].
Similarly, the chlorine produced during plant start-up is usually of insufficient quality for its
intended use and therefore transferred completely to the chlorine absorption unit. Some plants
report slightly increased emissions of chlorine from the absorption unit during these start-up
phases [ 196, Solvay 2011 ].
WORKING DRAFT IN PROGRESS
Chlor-alkali plants are typically shut down once per year during a period of one week to carry
out maintenance activities. The start-up phase typically lasts one hour.
3.4.6.2 Emissions during malfunctions
Fugitive emissions of chlorine and mercury are described in Sections 3.4.2.2 and 3.5.6,
respectively. {Please TWG provide more information.}
TB/EIPPCB/CAK_Draft_1 December 2011 101