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

3.3.4.3.6 Production of caustic potash
Chapter 3
The specific electrical energy consumption for the production of caustic potash does not differ
significantly from the production of caustic soda. In the mercury cell technique, the U0 term is
approximately 0.1 V higher. As compensation, the electrical conductivity of KCl is higher
(approximately 30 % at 70 °C). In practice, the cell characteristics such as the distance between
anode and cathode play a more important role than the U0 term and the electrical conductivity of
KCl [ 1, Ullmann's 2006 ], [ 42, Euro Chlor 2010 ].
3.3.4.4 Energy consumption for caustic soda concentration
The mercury cell technique allows for a direct production of 50 wt-% caustic soda (or potash),
but this is not the case for the two other cell techniques where a concentration step may be
necessary to bring the caustic to this commercial standard. The steam consumption for the
concentration of the caustic soda to 50 wt-% varies according to the number of evaporation
stages and the steam pressure used. For caustic from diaphragm cells, three to four evaporation
stages are usually used and the steam consumption ranges from 2.3 – 4.7 tonnes of steam per
tonne of caustic (100 %), the median being 2.6 tonnes per tonne of caustic (Table 3.7). For
caustic from membrane cells, one to three evaporation stages are used and the steam
consumption ranges from 0.4 – 1.5 tonnes of steam per tonne of caustic (100 % basis), the
median being 0.7 tonnes per tonne of caustic [ 63, Euro Chlor 2010 ].
Table 3.7: Caustic concentration at outlet cell and steam consumption for caustic
concentration in chlor-alkali installations in EU-27 and EFTA countries
Mercury cell technique ( 1 )
Parameter Unit
Min. Max. Average Median
Caustic concentration
at outlet cell
wt-% 49.0 51.0 49.9 50.0
Steam consumption t steam/t
for caustic evaporation caustic
NA NA NA NA
(50 %)
(100 %)
Diaphragm cell technique ( 2 )
Parameter Unit
Min. Max. Average Median
Caustic concentration
at outlet cell
wt-% 7.1 11.0 10.0 10.5
Steam consumption t steam/t
for caustic evaporation caustic
2.350 4.690 3.091 2.627
(50 %)
(100 %)
Temperature of steam °C 165 300 245 285
Pressure of steam bar 8.0 25.0 15.3 16.0
Membrane cell technique (monopolar and bipolar) ( 3 )
Parameter Unit
Min. Max. Average Median
Caustic concentration
at outlet cell
wt-% 24.0 33.0 31.8 32.0
Steam consumption t steam/t
for caustic evaporation caustic
0.460 1.500 0.736 0.703
(50 %)
(100 %)
Temperature of steam °C 145 285 199 190
Pressure of steam bar 3.0 30.0 10.4 10.0
( 1 ) Data from 34 mercury cell plants. Reference year 2008: 34 plants.
( 2 ) Data from 6 diaphragm cell plants. Reference year 2008: 6 plants.
( 3 ) Data from 40 membrane cell plants (monopolar and bipolar). Reference year 2008: 35 plants; reference year
2009: 4 plants; reference year 2010: 1 plant.
NB: NA = not applicable.
Source: [ 58, Euro Chlor 2010 ]
WORKING DRAFT IN PROGRESS
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