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

Further materials and/or further uses include:
Chapter 3
refrigerants such as ammonia, carbon dioxide, chlorine, HCFCs and HFCs for chlorine
liquefaction;
hydrogen peroxide for chemical dechlorination and to reduce emissions of chlorine
dioxide from the chlorine absorption unit;
ferric chloride and polyaluminium chloride as flocculants during waste water treatment;
hydrazine for the reduction of Hg(II) prior to filtration in the mercury cell technique;
sulphides for the precipitation of Hg(II) as mercury sulphide in the mercury cell
technique;
activated carbon for filtration of mercury-containing process streams in the mercury cell
technique;
sodium carbonate which can be used in mercury retorting to react with sulphur dioxide
(flue-gas desulphurisation) compounds as well as sodium hydrosulphide;
hydrochloric acid for the destruction of chlorate at high temperatures in the membrane
cell technique;
hydrogen for catalytic chlorate reduction in the membrane cell technique.
3.3.4 Energy
3.3.4.1 Overview
The energy consumption in chlor-alkali production originates from four main processes [ 63,
Euro Chlor 2010 ]:
energy to prepare and purify the raw materials, mainly the salt (sodium chloride or
potassium chloride) (see Section 3.3.4.2);
electrical energy used for the electrolysis process itself (see Section 3.3.4.3);
energy (steam) to obtain the caustic soda (or potash) at its commercial concentration (see
Section 3.3.4.4);
energy for auxiliary equipment such as heating devices, pumps, compressors, transformers,
rectifiers and lighting (see Section 3.3.4.5).
Energy is used both as electricity and as heat (steam). About half of the electricity consumed
energy expended is converted into the enthalpy of the products. The rest is converted into heat
transferred to the air in the building and the products, which have to be cooled. The heat is
partly recirculated through preheating of the brine. Surplus heat might also be used for heating
surrounding buildings or for the production of steam which could be used for the concentration
of caustic soda. Insulation of the salt dissolvers can be used to reduce the heat losses of the brine
system [ 3, Euro Chlor 2011 ] [ 62, UN/ECE 1985 ]. Insulation of the cells and salt dissolvers
reduces the need for ventilation of the cell room and increases the amount of heat transferable.
The hydrogen produced in chlor-alkali plants can be used as a raw material in the synthesis of
chemicals or as a fuel [UN/ECE, 1985].
WORKING DRAFT IN PROGRESS
Energy consumption depends on a number of factors such as [ 63, Euro Chlor 2010 ]:
the cell technique used;
the purity of the salt used as raw material;
the specific cell parameters such as nominal current density, anode/cathode gap, adherence
of developed gas bubbles on electrode structures, diaphragm/membrane type and thickness,
catalytic electrode coatings;
the age of the diaphragm, the membrane and the catalytic electrode coatings;
other technical characteristics of the installation such as the configuration of the
electrolysers (monopolar or bipolar), the number of evaporative stages in the caustic
concentration unit and the chlorine liquefaction conditions;
TB/EIPPCB/CAK_Draft_1 December 2011 71