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

Chapter 3
{The following text was significantly extended and updated in the preceding sections.}
A comparison of typical energy use for the three technologies is given in Table 3.2.
Amalgam
Technology
Asbestos
Diaphragm
Membrane
Technology
Theoretical voltage (V) 3.15
Technology
2.19 2.19
Current density (kA/ m 2 ) 8 - 13 0.9 - 2.6 3 - 5 1
Cell voltage (V) 3.9 - 4.2 2.9 - 3.5 3 - 3.6
Caustic strength (% by weight) 50 12 33
Electrical energy use (alternating 3360
current) (ACkWh/t Cl2)
at 10 kA/m 2
2720
at 1.7 kA/m 2
2650 2
at 5 kA/m 2
Electrical energy use by other
electrical equipment (pumps, 200 250 140
compressors, etc) (ACkWh/t Cl2)
Total energy use (ACkWh/t Cl2) 3560 2970 2790
Energy use by steam to concentrate
caustic to 50% (ACkWh/t Cl2) 3 0 610 180
Adjusted total energy use
(ACkWh/t Cl2)
3560 3580 2970
1) There is a tendency towards membrane cells operating at a higher current density, allowing higher production
per m 2 but causing a higher electrical energy use per tonne Cl2. A higher current density causes more
resistance heat which results in less steam being required for brine preheating.
2) According to the main suppliers the best values at 5 kA/m 2 are 2575 ACkWh/tonne Cl2 at start-up and 2650
ACkWh/tonne Cl2 after two years in production.
3) 1 tonne steam = 250 kWh at 19 bar (figure based on the electricity that would be generated by passing 1 tonne
of steam through a condensing steam turbine. Provided by EdF, French energy supplier).
Table 3.2: Comparison of typical energy use by the mercury, diaphragm and membrane cell
chlor-alkali technologies, assuming production of 50% caustic soda and before liquefaction of
chlorine
[Dutch Report, 1998], [Euro Chlor report, 1997], [Lindley, 1997]
The energy required to liquefy chlorine is not included in the table above. It should be noted,
however, that chlorine from membrane cells might need to be liquefied and evaporated to
remove oxygen (O2) and carbon dioxide (CO2). The energy required to liquefy and evaporate 1
tonne of chlorine is about 200 kWh (AC).
Electrical energy use is lower in the membrane technology. The power costs are lower, even
allowing for the steam requirements and brine purification.
Increased current density reduces the capital costs of an installation because the production per
unit cell capacity is higher. However, there is a trade-off in that higher current densities mean
higher power consumption, and the unit cost of electricity can be a factor when determining the
appropriate trade-off between capital cost and power consumption. [Lindley, 1997].
3.1.1.4 Ancillary materials
{The information on ancillary materials was moved before the section on energy consumption.}
WORKING DRAFT IN PROGRESS
3.1.2 Outputs in the production line
Main products
The products are obtained more or less in a fixed ratio, independent of the technique used:
Per 1000 kg of chlorine produced,
1128 kg of NaOH (100 %) is produced if NaCl is used as a raw material
1577 kg of KOH (100%) is produced if KCl is used as a raw material (the molecular
weight of KOH is higher than that of NaOH)
80 December 2011 TB/EIPPCB/CAK_Draft_1