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

Chapter 3
3.7 Emissions Emission and consumption levels and waste
generation from the membrane cell technique process
3.7.1 Consumption and emission levels
Consumption and emission levels of membrane cell plants are fully described in Sections 3.3
and 3.4, respectively, which cover consumption and emission levels of relevance for all three
cell techniques.
Emissions from chlor-alkali plants using the membrane technology are, apart from chlorine,
linked to the brine purification needed to avoid undesirable impurities in the membrane cell and
solid wastes generated by the used membranes. Emissions coming from auxiliaries are
described in the relevant paragraphs.
3.1.2.3.1 Water emissions
Waste water from the membrane cell process originates from caustic evaporation, chlorine
drying and wash water from the ion-exchange resin used to purify the brine. Membrane plants
usually use a bleed from the brine circuit in order to prevent accumulation of contaminants. All
these emissions are described in the Section about auxiliary processes.
3.7.2 Generation of wastes
The generation of wastes specific to membrane cell plants relate to sludges generated during
secondary brine purification as well as to scrapped cell parts including gaskets and membranes.
Other types of waste generated are described in Section 3.4 on emissions and waste generation
of relevance for all three cell techniques.
Wastes are generated during the secondary brine purification and consist of used materials such
as pre-coat and body feed material made of cellulose. The pre-coat filter sludge from the brine
softener consists mainly of alpha-cellulose, contaminated with iron hydroxide and silica. In
2008/2009, reported figures from seven membrane cell plants amounted to 0.2 – 0.26, 0.23, 0.3,
0.26 – 0.39, 0.5, 0.5 and 0.56 kg/t annual chlorine capacity [ 57, EIPPCB 2011 ]. Membrane
plants report a figure of 600 g/t for sludges from brine softening. Ion-exchange resins for
secondary brine purification are very rarely changed. Resins are regenerated approximately
about 30 times per year. In 2008/2009, reported figures for ion-exchange resin wastes from two
membrane cell plants amounted to 4 and 5.6 – 6.7 g/t annual chlorine capacity [ 57, EIPPCB
2011 ].
Spent membranes and gaskets from membrane cells become waste after their service life. The
membranes have a lifetime of between three and five 2 and 4 years. The waste from cell gaskets
and membranes has been estimated at approximately about 60 g per tonne of chlorine produced
(data from one membrane plant) [ 75, COM 2001 ]. In [Dutch report, 1998] other values are
given: 3.3 g/t for gaskets and spent membranes respectively. Values reported for another plant
amount to 3 g/t for gaskets [ 57, EIPPCB 2011 ] and approximately 3.3 g/t for membranes [ 17,
Dutch Ministry 1998 ].
WORKING DRAFT IN PROGRESS
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