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

Chapter 3
Table 3.26: Fugitive mercury emissions from the cell room from three mercury cell chloralkali
plants in the United States in 2005/2006
Chlorine
production Fugitive mercury emissions from the cell room to air
Plant capacity
In kt/yr
In g/d
In g/t annual chlorine
capacity
Min. Average Max. Min. Average Max.
Olin, Charleston,
Tennessee (US) ( 1 )
OxyChem, Muscle
260 99 499 1256 0.14 0.70 1.76
Shoals, Alabama
(US) ( 2 )
OxyChem,
154 150 470 1300 0.36 1.11 3.08
Delaware City,
Delaware (US) ( 3 )
81 19 421 1100 0.09 1.90 4.96
( 1 ) Daily average values obtained during the period of August – October 2006.
( 2 ) Daily average values obtained during the period of August 2005 – January 2006.
( 3 ) Daily average values obtained during the period of April – November 2005.
Source: [ 104, US EPA 2008 ], [ 105, US EPA 2007 ]
The reported average emission factors for the Olin plant in Charleston and the OxyChem plant
in Muscle Shoals are higher than the median of the plants in OSPAR countries in 2009, but
lower than the maximum emission factor reported for the latter (see Table 3.25 and Table 3.26).
However, the emission factor of the OxyChem plant in Delaware City exceeds the maximum
emission factor reported for plants in OSPAR countries.
In 2011, the US EPA noted that mercury cell chlor-alkali plants with continuous monitoring
systems and methods to estimate the flowrates had reported lower diffuse mercury emissions
compared to the 2005/2006 study, averaging around 225 g/d in 2008 [ 103, US EPA 2011 ].
Mercury emissions losses are influenced by the basic design of the cell room, such as the
number and area of the cells, the leak tightness, the type of decomposers (horizontal or vertical)
(see Figure 2.4 and Figure 2.5), the accessibility of the cells and the construction materials.
Mercury emissions are also influenced by the use of operating and maintenance techniques
[ 87, Euro Chlor 2006 ] which minimise the possibility of mercury emission. Mercury spillage
can occur during essential operations involving cells or decomposers, such as opening the cells
for anode changing or cleaning, assembling or dismantling equipment, or replacing defective
pipes. Optimisation by keeping the cells closed as far much as possible reduces the emissions
due to maintenance operations [ 89, Euro Chlor 2004 ]. The existence of a maintenance plan has
been shown to increase the lifetime of cells six-fold and reduce the frequency of opening to only
once every two or three years. (see Chapter 4). The frequency of cell opening can be higher for
potassium chloride electrolysis, depending on the purity of the available salt.
Mercury emissions are also significantly reduced by good housekeeping practices which are
backed up by people employees with the motivation to work in such a way [ 89, Euro Chlor
2004 ]. The lowest values of mercury emissions have been observed in companies which have a
specific and stringent cleaning and housekeeping programme.
WORKING DRAFT IN PROGRESS
Another source of emissions into air is the evaporation of mercury deposited in the equipment
and in the building, for instance in cracks in the floor and in porous concrete and bricks
[ 87, Euro Chlor 2006 ].
The electrolysis of KCl is more sensitive to trace impurities and it is therefore necessary to open
the cells more frequently for maintenance and cleaning. As a consequence, mercury emissions
from a cell room in which KCl is used are higher than if NaCl were used in the same cell room
[ 42, Euro Chlor 2010 ]. On average, the emissions of mercury to air from installations using
114 December 2011 TB/EIPPCB/CAK_Draft_1