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

Chapter 3
in process and waste water streams or to destroy surplus hypochlorite, or it can be sold to an
user who can accept this quality of acid. Otherwise, the spent acid becomes waste. Reported
figures on the generation of spent sulphuric acid are summarised in Table 3.19.
Table 3.19: Generation of spent sulphuric acid in chlor-alkali plants in EU-27 and EFTA
countries in 2008/2009
Generation of spent sulphuric acid in kg per tonne of annual chlorine capacity ( 1 )
Value
reported ( 2 10th 25th
Min.
)
percentile percentile Median
75th 90th
Max.
percentile percentile
Min. ( 3 ) 0 ND 0.96 6.3 18 ND 20
Max. ( 3 ) 1.5 ND 7.4 11 23 ND 32
Average ( 4 ) 0 2.1 3.3 14 24 34 67
( 1 ) 7 plants out of a total of 22 reported to which concentration the amount of generated spent sulphuric acid
referred to: 1 plant reported a concentration of 50 wt-%, 2 plants a concentration of 78 wt-% and 4 plants a
concentration of 100 wt-%.
( 2 ) Some plants reported ranges with minimum and maximum values and some reported average values.
( 3 ) 8 data from 8 plants.
( 4 ) 17 data from 16 plants. 1 of these plants provided separate data for different electrolysis units.
NB: ND = not enough data.
Source: [ 57, EIPPCB 2011 ]
The consumption of sulphuric acid depends on the water concentration in the feed gas, the
absorption temperature and the original sulphuric acid concentration. Where it is possible to
reconcentrate it sulphuric acid in a closed loop, consumption is very low, close to 0.1 kg
sulphuric acid per tonne of chlorine produced [ 47, De Dietrich 2011 ]. Acid consumption can
also be reduced by optimising the time contact between chlorine and acid, keeping the fresh acid
concentration as high and the spent acid concentration as low as possible.
3.4.3.4.2 Carbon tetrachloride
When carbon tetrachloride is used to absorb NCl3 or to recover chlorine from tail gas, it from
the liquid chlorine, the carbon tetrachloride needs to be replaced periodically because of the
build-up of pollutants (bromine, FeCl3, and chlorinated hydrocarbons, for example). The
removed carbon tetrachloride is recycled, reclaimed or destroyed in line with the provisions of
the regulation on substances that deplete the ozone layer [ 78, Regulation EC/1005/2009 2009 ].
either incinerated or sent as hazardous waste. It must, however, be destroyed according to
approved destruction processes, as mentioned in Annex VI of the report of the fourth meeting of
the parties to the Montreal Protocol. A plant with a capacity of 300000 tonnes chlorine per year
uses carbon tetrachloride for NCl3 destruction and consumes approximately 12 tonnes of CCl4
per year, corresponding to 40 g CCl4/tonne of chlorine capacity (this figure includes fugitive
emissions from the CCl4 system of 0-4 g CCl4/tonne of chlorine capacity) [Dutch report, 1998].
The quantities of waste generated can be calculated from the reported consumption and
emission figures (see Sections 3.3.3 and 3.4.3.2.4) and range from 12 – 630 g/t annual chlorine
capacity [ 61, DG ENV 2009 ].
WORKING DRAFT IN PROGRESS
3.4.3.4.3 Bleach
During normal operation of a chlor-alkali plant, the bleach produced can be sold or used on site.
When the bleach production unit must handle a large amount of chlorine in a short period of
time (in the event of release of chlorine due to a malfunctioning of equipment), the bleach
produced usually does not usually comply with the product specifications. In that case the
‘off-spec’ bleach is either destroyed on site and discharged with the waste water, or is removed
TB/EIPPCB/CAK_Draft_1 December 2011 99