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

Chapter 4
Cross-media effects
Cross-media effects of individual techniques are described in the Sections 4.3.2.2.2 to 4.3.2.2.7.
Technical considerations relevant to applicability
Technical considerations of individual techniques are described in the Sections 4.3.2.2.2 to
4.3.2.2.7.
Economics
Economics of individual techniques are described in the Sections 4.3.2.2.2 to 4.3.2.2.7.
{Please TWG provide more information on overall costs and potential savings.}
Driving force for implementation
The driving forces for implementation of these techniques include the following:
reduction of operating costs due to reduced consumption of water and often salt;
limited availability of water resources;
environmental legislation.
Example plants
{Please TWG provide information.}
Reference literature
[ 1, Ullmann's 2006 ], [ 73, Debelle 2011 ], [ 75, COM 2001 ], [ 131, Germany 2003 ]
4.3.2.3 Energy
4.3.2.3.1 Overview
In addition to the techniques described in the following Sections 4.3.2.3.2 to 4.3.2.3.9, the
acidification of brine also reduces energy consumption (see Section 4.3.6.4.2).
4.3.2.3.2 High-performance bipolar membrane cells
Description
This technique consists in using high-performance bipolar membrane cells which make use of
zero-gap structures with a serial electrical arrangement.
Technical description
At the stage of designing and building a new electrolysis unit, the electricity consumption of the
electrical equipment (transformers, rectifiers and busbars) and the electrolysers can be
optimised. The most important factors influencing electricity consumption are the cell technique
used and the nominal current density.
WORKING DRAFT IN PROGRESS
Membrane cells generally consume less electricity than diaphragm or mercury cells (see
Section 3.3.4.3). Within the membrane cell technique, bipolar electrolysers lead to lower ohmic
losses compared to monopolar electrolysers (see Section 2.4.3). Diaphragm cells may, however,
show lower consumption values than bipolar membrane cells if operated at low current densities
(see Figure 3.2). The caustic produced in diaphragm cells is of lower quality than that of
membrane cells and needs to be concentrated to 50 wt-% to be traded as commodity. Therefore,
all new electrolysis units are based on the bipolar membrane cell technique.
At the initial design of an electrolysis unit, a decision has to be made regarding the nominal
current density. Higher current densities lead to higher electricity consumption (see Figure 3.2)
and thus higher operating costs. On the other hand, production rates per cell increase with
194 December 2011 TB/EIPPCB/CAK_Draft_1