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

Chapter 3
3.5 Emissions Emission and consumption levels and waste
generation from the mercury cell technique process
3.5.1 Overview
Emissions and consumption of mercury as well as the generation of mercury-contaminated
waste are specific to the mercury cell technique. At present some 12000 tonnes of mercury are
contained in mercury cells used for chlorine production in the EU. This is based on an average
of 1.8 kg of mercury per tonne of annual chlorine capacity and an EU mercury cell chlorine
capacity of 6.9 millions tonnes of chlorine per year [Lindley, 1997]. This mercury Mercury is
contained and recycled within the chemical process. Nevertheless, due to the process
characteristics, mercury emissions to air and water occur and some mercury leaves the process
via waste into air, water and also in wastes are generated. Products, mainly caustic soda, and to
a lesser extent hydrogen, contain certain amounts of mercury and are treated before being used
or sold. As regards the mercury level in chlorine, it is virtually zero and no mercury removal
processes are used for this product. Some emissions occur during the decommissioning of an
installation or its conversion to the membrane cell technique.
Any attempt to draw a balance generally results in a difference between inputs and outputs of
mercury, either positive or negative. This item issue is specifically addressed in Section 3.5.10.
3.5.2 Mercury in cells
At the end of 2010, the total chlorine production capacity in EU-27 and EFTA countries based
on the mercury cell technique amounted to 3.97 Mt/yr [ 55, Euro Chlor 2011 ]. A total of 6870 t
of metallic mercury were contained in cells and another 630 t were stored in facilities on site,
either as stock for further use or as waste after the respective mercury cell unit had ceased to
operate [ 82, Euro Chlor 2011 ]. Table 3.22 summarises the amount of mercury in cells.
Table 3.22: Amount of mercury in cells per annual chlorine production capacity in mercury
cell chlor-alkali plants in EU-27 countries in 2010
Amount of mercury in cells in kg per tonne of annual chlorine capacity ( 1 )
Min. 10th percentile 25th percentile Median 75th percentile 90th percentile Max.
0.795 1.20 1.39 1.54 2.04 2.54 4.36
( 1 ) 33 data from 33 plants.
Source: [ 55, Euro Chlor 2011 ], [ 82, Euro Chlor 2011 ]
3.5.3 Reporting of figures per chlorine capacity
As With regards to mercury outputs, figures are expressed and reported by the industry in terms
of chlorine capacity rather than real production. This is quite specific to the mercury cell chlor-
WORKING DRAFT IN PROGRESS
alkali sector. Because of the electrolytic process in itself, mercury emissions are not linked to
production in a linear way. The majority of the emissions are from the cell room where the
absolute amount mainly depends on small leaks or accidental losses and on historical
contamination of the building which are mostly independent from the production rate. The
emissions are is far more related to dependent on the equipment, plant design, maintenance
requirements, pressure and temperature of the cell and decomposer denuder [ 83, Euro Chlor
2010 ].
However, it could be assumed that if half of the cells are switched off, the reporting of figures
per chlorine capacity may be inappropriate this reasoning may be wrong. The industry gives two
main reasons to argue that this is usually not the case for reporting mercury emissions in terms
104 December 2011 TB/EIPPCB/CAK_Draft_1