International Review of Waste Management Policy - Department of ...

63.3.2 Air Quality Impacts of Incineration
Typical air pollution control (APC) technology installed in incinerators located in the UK
comprises of:
1002
� Bag filters, used to trap polluted dust (particulate matter) entrained with the
exhaust gases;
� Semi dry flue gas scrubbing involving the use of lime neutralizes acidic
pollutants (such as SOx) within the flue gas;
� Selective Non-Catalytic Reduction (SNCR) processes, used to thermally reduce
NOx by injection of a reducing agent (ammonia or urea) into the post
combustion flue gas;
� Activated carbon to deal with dioxin (and furan) formation.
Whilst SNCR processes typically allows the incinerator to meet WID with respect to
NOx emissions, use of Selective Catalytic Reduction (SCR) techniques results in
significant further reduction in NOx. SCR involves the addition of ammonia and the
use of a catalyst (usually made of titanium oxide) to convert the NOx and ammonia
into steam and nitrogen. 1244 The reduction in NOx is typically achieved at the expense
of additional energy expenditure, as has been previously discussed in Section
63.3.1.1. 1245
NOx emissions have a significant influence on the damage costs attributed to the air
pollution from waste incineration facilities. Reductions in NOx emissions results in a
considerable improvement in the performance of the facility with respect to external
costs attributed to the non greenhouse gas air pollution impacts.
A significant proportion of the NOx emission from waste incineration is generated by
the thermal process itself, and is not therefore directly linked to the nitrogen content
of waste entering the facility. Data on the chemical constituents of waste varies
considerably between different literature sources with the nitrogen content being
particularly variable, largely reflecting the natural variation in the nitrogen content of
organic material (likely to be the main source of nitrogen within residual waste). We
have therefore based our assessment of the air pollution impacts of incinerators
upon emissions data, rather than linking to specific chemical elements within the
composition.
Our analysis considers emissions from two types of incinerator:
1. A facility that meets the Waste Incineration Directive (WID), typical of those
that have installed SNCR to reduce NOx emissions;
2. A facility that significantly out-performs the requirements of the WID through
the installation of SCR and wet scrubbing techniques. Emissions are based on
1244 The ammonia is added to support the reduction reaction.
1245 To ensure the catalyst is not contaminated by other elements within the flue gas the SCR system is
typically located just prior to the emissions stack. This requires the flue gas to be reheated using
additional electrical energy.
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