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

Chapter 4
Environmental performance and operational data
Operational data provided by one equipment provider are shown in Table 4.23.
Table 4.23: Typical operational data from an on-site sulphuric acid reconcentration system
Stream Characteristics Flow
Spent acid
78 wt-% H2SO4
(~ 0.03 wt-% Cl2 , Salts Q 0.85 wt-%) ( 1 )
1500 kg/h
Reconcentrated acid 96 wt-% H2SO4 (including salts) 1214 kg/h
Condensate Q 1 wt-% H2SO4 450.5 kg/h
Exhaust gas
Heating steam
~ 38 wt-% air, ~ 56 wt-% Cl2
6 bar, 201 °C
0.8 kg/h
665 kg/h ( 2 )
Motive steam 6 bar, 201 °C 165 kg/h ( 3 )
Cooling water
4 bar, 25 °C supply temperature, 30 °C return
temperature
67 m 3 /h
Power 400 V, 50 Hz, 3 phase 7 kW ( 4 )
( 1 ) Depending on the salt concentration, a number of cleaning cycles per year are required.
( 2 ) The consumption of heating steam can be reduced by ~ 160 kg/h if an electrical heater is used (second
stage).
( 3 ) Motive steam is not required if an electrical heater is used (second stage).
( 4 ) The power consumption increases by 85 kW if an electrical heater is used (second stage).
Source: [ 47, De Dietrich 2011 ]
By using a reconcentration system, the consumption of sulphuric acid can be reduced to
Q 0.1 kg/t Cl2 produced [ 47, De Dietrich 2011 ].
Cross-media effects
Raw materials and energy are consumed for the installation and operation of the reconcentration
unit. Emissions to air may be generated depending on the presence of contaminants in the feed
acid. Waste water is generated in the condensers/vacuum generators. The concentration of
sulphuric acid requires energy. Depending on the energy source used, several types of air
emission may be generated (CO2 and NOx among others). Water is evaporated during the
concentration. A small bleed purge of the acid is usually will probably be necessary to avoid the
build-up of contaminants in the concentrated acid [ 47, De Dietrich 2011 ].
Technical considerations relevant to applicability
On-site reconcentration in closed loop evaporators can be applied at new and existing plants.
The required installation area depends on the capacity of the plant. If the acid is concentrated
only to 92%, investment cost as well as utility consumption may be reduced, as it may be
possible to concentrate in a single stage.
Economics
One supplier gives a price of around 360000 euros (700000 DEM, January 1999) for a new
installation designed for 1000 kg/h sulphuric acid. The price investment costs depends on the
customer’s requirements. In 2011, one equipment provider reported investment costs of
EUR 1 million for a two-stage unit capable of concentrating 1.5 tonnes of 78 wt-% H2SO4 per
WORKING DRAFT IN PROGRESS
hour to 96 wt-% H2SO4. The capacity is equivalent to 13.7 kt H2SO4 (78 wt-%)/yr and,
assuming a consumption of 20 kg H2SO4 (96 wt-%)/t chlorine produced, would be sufficient to
reconcentrate the spent acid of a plant with a chlorine capacity of 657 kt/yr. In the case of a final
concentration of 92 wt-%, the concentration can be carried out in one stage and the investment
costs would be reduced to EUR 0.75 million. The operating costs mainly depend on the energy
costs [ 47, De Dietrich 2011 ].
Savings result from the reduced consumption of sulphuric acid.
{Please TWG provide information on savings and payback times.}
252 December 2011 TB/EIPPCB/CAK_Draft_1