Page 181 - New Trends In Coal Conversion

144 New Trends in Coal Conversion

Lower nitrogen
content

Higher volatile
Pre-combustion
content
Finer grinding

Low NO x
burners

Over fire air
NO removal In-combustion Flue gas
x
technologies recirculation
Burners out of
service

Low excess air

Selective
non-catalytic
reduction
Post-combustión
Selective
catalytic
reduction
Figure 6.1 Summary of NO x abatement techniques available at industrial scale.

Precombustion controls act on fuels before combustion.
The aim of the in-combustion control technique is to reduce the level of NO x emis-
sions, modifying or altering the firing conditions. The purpose of the postcombustion
control is to lower NO x emissions by transforming the NO x formed during combustion
to nitrogen gas by means of chemical reactions, applying these techniques after the
combustion zone (Bell and Buckingham, 2010). It is often necessary to combine
two or more primary and secondary control techniques to achieve the desired
level of NO x reduction and to obtain the most economical global system (Bell and
Buckingham, 2010).

6.2.1.3.1 Precombustion control techniques
Precombustion controls are based mainly on three methods: lower nitrogen content,
higher volatile content, and finer grinding. All of them involve an action on the raw
material, so these kinds of control techniques are not the most economical.