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

4.1 Mercury cell plants
4.1.1 Overview of mercury emission abatement
4.1.1.1 Reduction of mercury emissions to air, including hydrogen gas
4.1.1.2 Reduction of mercury emissions to water
4.1.1.3 Removal of mercury from caustic soda
4.1.1.4 Treatment of mercury-containing wastes, including recovery of
mercury
Chapter 4
{These Sections are proposed to be deleted completely. Rationale: The original chlor-alkali
BREF concluded that the mercury cell technique is not BAT and that BAT for mercury cell
plants is to convert to the membrane cell technique. From 1997 to 2010, the share of the
mercury cell technique to the total chlorine production capacity in EU-27 and EFTA countries
has roughly halfed from more than 60 % to a bit more than 30 % while the total production
capacity has remained on the same level. This indicates that conversion of mercury cell
chlor-alkali plants to the membrane cell technique is technically and economically viable for
the chlor-alkali sector as a whole. Given that techniques to prevent mercury emissions are
available, it is therefore not necessary to describe techniques which reduce mercury emissions
during normal plant operation. Nevertheless, techniques to reduce mercury emissions and to
reduce the generation of mercury-containing wastes are relevant for decommissioning. There
description including performance levels is therefore covered by Section 4.1.3.}
4.1.2 Conversion of mercury cell plants to membrane cell plants
technology
{Please note that the paragraphs of the original text were reordered to be compatible with the
current standard 10-heading structure.}
Description
This technique consists in converting mercury cell plants to membrane cell plants. A conversion
to the membrane cell technique includes change of electrolysers, additional brine purification,
additional brine dechlorination, inclusion of a cell room caustic soda recirculation system and a
change of transformers and rectifiers.
Technical description
The conversion of mercury cell plants to membrane technology has the advantage of avoiding
any future losses of mercury to the environment and reduces the energy consumption. To realise
the conversion, technical changes are required depending on the existing situation. Most
membrane cell operators have either built a new 'green field' plant or expanded production
capacity with a new plant alongside their mercury facilities. Some plants have been completely
WORKING DRAFT IN PROGRESS
converted their existing plant, but there are also examples of partial conversion. Figure 4.1
below shows the main changes that need to be carried out to an existing plant when converting
from the mercury cell to the membrane cell technique technology.
Conversion is technically applicable at all existing mercury cell chlor-alkali plants. Economic
feasibility may vary from site to site (see Table 4.8, page 94).
TB/EIPPCB/CAK_Draft_1 December 2011 147