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

Chapter 4
In general, the number of stages that will be installed for caustic concentration depends on the
available steam pressure, the temperature of the cooling water, and the costs of steam and
cooling water. Increasing the number of stages reduces energy and cooling water consumption
but increases investments costs. Relative investment costs for one-, two- and three-stage
evaporators amount to 100 %, 160 % and 230 %, respectively [ 63, Euro Chlor 2010 ].
The advantage of the one- and two-stage evaporation units is that low pressure steam at
approximately 3 bar can be used while three-stage evaporators require the use of middle
pressure steam at approximately 10 bar. The use of low pressure steam is favourable when a
heat and power cogeneration unit is present on the site. Cogenerated steam is normally less
expensive than the middle pressure steam required for a three-stage caustic evaporation because
it allows for more electricity production. Expanding one tonne of steam from 10 bar to 3 bar can
produce approximately 20 kWh of electricity [ 63, Euro Chlor 2010 ].
Driving force for implementation
The driving forces for implementation of this technique include:
installation of a new membrane cell unit or capacity increase of existing unit;
reduction of costs related to energy consumption.
Example plants
Approximately 35 chlor-alkali plants worldwide use plate evaporators with two stages and
approximately 15 plants with three stages including:
Akzo Nobel in Skoghall (Sweden), chlorine capacity 95 kt/yr (plant was shut down in
2010), two three-stage evaporators, put into operation in 2000 and 2004;
Electroquímica de Hernani in Hernani (Spain), chlorine capacity 15 kt/yr, two-stage
evaporator, put into operation in 2002;
Olin in St. Gabriel/Louisiana (US), chlorine capacity 246 kt/yr, caustic soda capacity
1100 t/d, three-stage evaporator, put into operation in 2009;
Solvay in Santo André (Brazil), chlorine capacity 155 kt/yr, caustic soda capacity
530 t/d, three-stage evaporator, put into operation in 2009.
Reference literature
[ 46, Ullmann's 2006 ], [ 63, Euro Chlor 2010 ], [ 144, Alfa Laval 2011 ]
4.3.2.3.9 Use of hydrogen as chemical reagent or fuel
Description
These techniques consist in using the co-produced hydrogen from the electrolysis as a chemical
reagent or fuel instead of emitting it.
WORKING DRAFT IN PROGRESS
210 December 2011 TB/EIPPCB/CAK_Draft_1