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

Chapter 4
to an explosion. {This information was updated and moved to Technical considerations relevant
to applicability.}
Achieved environmental benefits
The achieved environmental benfits of this technique include:
prevention of asbestos emissions;
prevention of generation of asbestos-containing waste;
reduction of energy consumption.
Avoids consumption and emission of asbestos. Reduced energy use is also reported, depending
on operating conditions.
Environmental performance and operational data
PMX ® fibres have a diameter of 10 – 100 Zm and are 1000 – 7000 Zm long which render them
non-carcinogenic. Chrysotile asbestos fibres, for comparison, have a diameter of 0.1 – 0.3 Zm
and are 0.1 – 6.0 Zm long [ 216, O'Brien et al. 2005, Section 4.7.6 ].
Non-asbestos diaphragms have demonstrated a number of advantages over asbestos diaphragms
in chlor-alkali cell operation:
long lifetimes; at least 3 years can be considered as an average for an industrial cell room;
extreme stability concerning load variations and outages.
PMX diaphragm cells with three years on line show no increase in energy use, even after
repeated shutdowns at 95 °C. The operation of non-asbestos diaphragms may actually result in
net energy savings. Additional savings in material handling and waste disposal might be
realised, compared to asbestos diaphragms.
Non-asbestos diaphragms have demonstrated a number of advantages over asbestos diaphragms
in chlor-alkali cell operation with high current density. A lifetime of at least five years can be
considered average for an industrial cell room [ 31, Euro Chlor 2010 ] while the lifetime of
polymer modified asbestos diaphragms in usual diaphragm cells ranges from 200 – 500 days [ 1,
Ullmann's 2006 ], [ 10, Kirk-Othmer 2002 ]. Long life for PMX ® diaphragms has been
commercially demonstrated. The Vulcan-Geismar plant in Louisiana (USA) For example, the
OxyChem plant (formerly Vulcan Chemicals) in Geismar/Louisiana (US), fully converted since
1993, and the two Arkema plants in Fos-sur-mer and Lavera (France), fully converted since
2002, are is achieving average diaphragm lives of greater than 1000 3000 days, while operating
at an average current density of 2.55 – 2.65 kA/m 2 . Demonstration blocks of 10 to 20 PMX ®
diaphragm cells in Europe have lasted over 5 10 years and the oldest PMX ® diaphragm cell at
an Arkema plant operated for more than 13 years before it was replaced on the occasion of a
cathode leakage [ 31, Euro Chlor 2010 ]. the Occidental Chemical Deer Park plant in Texas
(USA) has been operating for over 8 years. [Florkiewicz, 1997]
On the other hand, for In the case of non-asbestos diaphragms the separator is therefore no
longer the most short-lived component of the diaphragm cell. As the non-asbestos diaphragm is
WORKING DRAFT IN PROGRESS
expected to last several years, the highest cause of failure of the diaphragm cell is the gaskets
(base covers and perimeter gaskets). It is These gaskets which now pose the biggest challenge to
overcome if a three to five 3 – 5 year cell life is to be achieved [ 212, Florkiewicz 1997 ]. For
this purpose, a company has developed a specific technique to change these gaskets without
damaging the diaphragm and to restart the cell with the same separator [ 31, Euro Chlor 2010 ].
In addition to the long lifetimes, asbestos-free diaphragms show extreme stability with respect
to load variations and outages. PMX ® diaphragm cells operated with pure brine do not show any
increase in energy consumption after a few years, even after repeated shutdowns. The operation
of non-asbestos diaphragms may actually result in net energy savings. They can be used with a
zero-gap cell design by using expandable anodes without the oxygen issue met with asbestos
174 December 2011 TB/EIPPCB/CAK_Draft_1