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

Chapter 3
brine purification
stack of caustic evaporators
hydrogen burnt or vented to atmosphere
mercury retorting
maintenance outside cell room
{The list of sources for mercury emissions from process exhausts was updated and moved to
Section 3.5.6.3.1.}
The reported overall emission factors of mercury to air from installations in EU-27 and EFTA
countries in 2010 range from 0.11 – 1.78 g/t annual chlorine capacity, the median being
0.52 g/t annual chlorine capacity (see Table 3.23).
3.5.6.2 Cell room ventilation
Ventilation air from the cell room is one of the main sources is usually the main source of
mercury emissions to air. Compared to process exhaust, It can be more than ten times as much
when compared to process exhaust. The cell room with the hot mercury cells (approx. 80 ºC) is
usually ventilated by means of natural ventilation. The heat produced during electrolysis
requires the air to be changed 10 – 25 times per hour, depending on the type of building [ 1,
Ullmann's 2006 ][Ullmann’s, 1996]. Ventilation airflows in the range of
20 000 – 120 000 m 3 /tonne annual chlorine capacity were found. This corresponds to total
ventilation airflows between 300 000 – 2 000 000 m 3 /h, depending on weather conditions,
season, design and size of the plant [ 17, Dutch Ministry 1998 ]. Due to this huge volume and
the fact that the ventilation flow escapes to the atmosphere from many points, mercury removal
techniques are not used [ 87, Euro Chlor 2006 ]. With good mercury housekeeping the
ventilation air contain mercury levels of 2 – 20 µg/Nm 3 . [Dutch report, 1998]
Some 2 – 8 µg/Nm 3 of mercury were reported, with an air flow of 300,000-600,000 Nm 3 /h. This
plant (chlorine capacity of 120,000 tonnes/year) was commissioned in the late 1960s and has
developed a very efficient mercury housekeeping since 1978. In 1997, the mercury emitted to
air from the cell room was estimated at 19.6 kg, corresponding to 0.17 – 0.21 g/tonne chlorine
capacity.
Reported emissions of mercury from the cell room are summarised in Table 3.25. The two
installations with the lowest emission factors in OSPAR countries report mercury
concentrations of 2 and 1.73 – 4.90 Zg/m 3 in cell room ventilation air and emission factors of
0.132 and 0.247 g/t annual chlorine capacity, respectively [ 57, EIPPCB 2011 ]. Directive
2009/161/EU sets an indicative occupational exposure limit value of 20 Zg/m 3 (at 20 °C and
101.3 kPa) measured or calculated in relation to a reference period of eight hours time-weighted
average [ 88, Directive 2009/161/EU 2009 ].
WORKING DRAFT IN PROGRESS
112 December 2011 TB/EIPPCB/CAK_Draft_1