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

Chapter 3
3.6 Emissions Emission and consumption levels and waste
generation from the diaphragm cell technique process
3.6.1 Consumption levels
Over the past twenty years all diaphragm cell facilities in western European countries have
switched from the use of lead and graphite anodes with asbestos diaphragms to metal anodes
and treated diaphragms, which resist corrosion and degradation. The diaphragms used to
become clogged with graphite particles and had to be renewed after a few weeks. The use of
lead and graphite anodes and asbestos diaphragms generated lead, asbestos, and chlorinated
hydrocarbons in the caustic soda and chlorine processing waste. Lead salts and chlorinated
hydrocarbons were generated from corrosion of the anodes and asbestos particles formed by the
degradation of the diaphragm with use [USEPA, 1995]. Nowadays, Modified Diaphragms are
made of a mixture of chrysotile asbestos and PTFE fibres. They are fabricated at an average rate
of approximately 150 g asbestos per tonne of chlorine capacity.
The only ancillary material of concern consumed specifically by diaphragm cell plants relates to
asbestos in the case of plants using asbestos diaphragms. Other consumption levels are
described in Section 3.3 on consumption levels of relevance for all three cell techniques.
Consumption levels of asbestos have decreased significantly after the replacement of graphite
anodes by metal anodes and of pure asbestos diaphragms by diaphragms consisting of a mixture
of asbestos and fluorocarbon polymers. They range from 0.1 – 0.3 kg per tonne of chlorine
produced [ 75, COM 2001 ]. In 2011, half of the chlor-alkali plants in EU-27 countries use
asbestos-free diaphragms.
EC Directive 87/217 concerning the prevention and reduction of pollution of the environment
by asbestos has the aim of defining steps and complementing measures already in existence to
reduce and prevent pollution by asbestos, and to protect human health and the environment. The
Directive applies to discharges from all plants where more than 100 kg a year of raw asbestos is
used, which is the case in chlor-alkali plants using diaphragm technology. The provisions came
into effect on 31 December 1988 for all new plants and from 30 June 1991 for existing plants.
Limits have been set to ensure that the concentration of asbestos discharged into the air does not
exceed the limit of 0.1 mg/m 3 of released air. As far as the aquatic environment is concerned,
there is a general requirement to ensure that discharges of asbestos are, as far as reasonably
practicable, reduced at source and prevented. No specific provisions linked to the chlor-alkali
sector are given. {This information was shortened and moved to the following section.}
3.6.2 Emissions to air Air emissions
Air emissions consist of asbestos and fugitive emissions of chlorine from the cells and in the
process tail gases. Other emissions coming from auxiliaries are described in the relevant
paragraphs.
WORKING DRAFT IN PROGRESS
Emissions to air specific to diaphragm cell plants relate to asbestos in the case of plants using
asbestos diaphragms. Other emissions are described in Section 3.4 on emissions and waste
generation of relevance for all three cell techniques.
Asbestos
Air emissions can appear during production Emissions of asbestos to air can occur during the
preparation of the diaphragms and, excluding potential accidental releases during transportation,
unloading and storage, the major potential sources of air emission emissions to air are during
bag handling and opening and the disposal of spent asbestos.
TB/EIPPCB/CAK_Draft_1 December 2011 131