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Vijay Mandayam
Gary K. Rice
Scott A. Drennan
Residual oil continues to be the fuel of choice for many industrial steam
users while environmental regulations allow its use. However, new emissions
regulations on NOx and SOx are requiring substantial improvements in emissions
performance or it will be regulated out of existence. This paper discusses
the results and effectiveness of low NOx design modifications to residual
oil firing industrial boilers. Industrial package boilers have specific
performance criteria that impede the effectiveness of such low NOx techniques.
Factors such as smaller furnaces, higher firing densities, lack of air
preheat, widened operating envelope, simple controls, and variable fuel
quality make the industrial package boiler a more challenging low NOx
environment than a field erected or utility boiler. This paper summarizes
the results of this NOx reduction program on several industrial water
tube boilers, both package and field erected. The results indicate that
significant NOx reduction can be obtained through spray pattern modification
to produce a staged spray flame with rich and lean zones. The resulting
spray flame reduces both thermal and fuel NOx production in cases where
the furnace possessed sufficient volume to allow the increases in flame
length and width resulting from the flame staging. These results indicate
the effectiveness of NOx reduction techniques is directly linked to the
size and residence time in the furnace and the quality of the fuel. Reductions
in NOx of up to 25% can be obtained simply through judicious use of spray
staging. The greatest NOx reductions are obtained in field erected boilers
with low firing densities as a result of the ability to stage the combustion.
The variability in fuel characteristics such as viscosity, distillation
curve, carbon residue, and ash composition limits the potential emissions
reduction and maintaining stable combustion.
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