Control of NOx Emissions
Burner design is critical in ensuring maximum efficiency
and low NOx.
Crucial to the consistent reduction of NOx is the
principle of Axial Air Flow which, when used in
conjunction with a correctly dimensioned Boiler, enables
Burners to be inherently low NOx emitters.
Axial Air Flow Burners with ultra low NOx heads when
fitted to a well designed Boiler will easily achieve NOx
emissions as follows :
• Gas - 70mg. per kW hour
• Oil - 165mg. per kW hour
The geometry of the Boiler or Furnace must be such that
hotspots are eliminated, eddying currents are created to
facilitate internal flue gas circulation & the design
provides for a low and smooth transfer of heat. In
addition, because NOx is a thermally produced gas, its
reduction is also dependent on the Calorific Value of
Air / Fuel Staging
It is one of the most effective methods of reducing NOx
and is achieved by seperating the air & fuel into areas
of sub stoichiometric and over stoichiometric
The main aim of this technique is to divide the air into
three distinct and seperate patterns - Primary,
Secondary and Tertiary. Each of these patterns is
controllable in its own right.
Flue Gas Recirculation ( FGR )
It is a popular and proven technique for reducing NOx
levels - particularly thermal NOx.
Reductions of NOx levels can be relatively modest and
installing FGR does create major restrictions in Boiler
design. This means that FGR cannot be easily
retrofitted without the Boilers being down - rated.
FGR also requires sophisticated control, extensive
and cumbersome external pipe work and in some
instances, Blowers - all of which have to operate at
exhaust gas temperatures. As a result, first costs and
maintenance costs increase and Boiler reliability diminishes.