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

Chapter 4
Techniques to reduce the concentration of chlorate in the brine are described in Section 4.3.6.4
while the addition of barium salts for sulphate removal can be avoided by using nanofiltration
(see Section 4.3.6.2.2).
Achieved environmental benefits
The achieved environmental benefit of this technique is a reduction of energy consumption.
Environmental performance and operational data
{Please TWG provide information.}
Cross-media effects
Additional brine purification steps may lead to additional consumption of energy and ancillary
materials and to generation of additional waste.
Technical considerations relevant to applicability
Generally, there are no technical restrictions to the applicability of this technique.
Economics
Additional brine treatment leads to increased costs which may exceed the savings due to
reduced energy consumption and reduced maintenance costs. Sometimes it is more economical
to select another salt source instead of modifying the brine purification.
Driving force for implementation
The driving forces for implementation of this technique include:
reduction of costs related to energy consumption;
reduction of costs related to equipment and maintenance.
Example plants
Primary brine purification is applied in all chlor-alkali plants. Secondary brine purification is
applied in all membrane cell plants.
Reference literature
[ 3, Euro Chlor 2011 ], [ 143, Healy 2011 ]
4.3.2.3.6 Iron(III) meso-tartrate as anti-caking agent
Description
This technique consists in using iron(III) meso-tartrate as anti-caking agent instead of
ferrocyanide whose decomposition products may damage the membrane and increase energy
consumption.
Technical description
Sodium chloride is hygroscopic above 75 % relative humidity (critical humidity). Therefore, salt
crystals can absorb enough moisture during storage to form a brine film on their surfaces.
WORKING DRAFT IN PROGRESS
Subsequent water evaporation due to changes in temperature or air humidity causes
recrystallisation of the brine film and the crystals bond together. The presence of small
quantities of brine included in the crystals can also contribute to caking. Evaporated salt that
exits the salt dryer at higher temperatures tends to undergo increased caking during cooling in
silos. Caking hampers the handling of salt in terms of loading/unloading and transport. To
prevent caking, an aqueous ferrocyanide solution is frequently sprayed onto the salt. A final
concentration of 2 – 20 ppmw of sodium ferrocyanide decahydrate (Na4[Fe(CN)6] · 10 H2O) is
generally sufficient to prevent caking [ 66, Ullmann's 2010 ]. Ferrocyanide prevents caking by
altering the crystallisation behaviour of sodium chloride [ 140, Giatti 2011 ].
204 December 2011 TB/EIPPCB/CAK_Draft_1