Previous
studies have found that the nitric oxide (NO) trend above the fuel
seam of a chain boiler is opposite that of a reciprocating grate boiler.
We have researched the factors that influence fuel NO emissions during
the char grate-fired process by changing the char/oxygen (O2) ratio in a small-scale one-dimensional fixed-bed system. With an
increase in the char/O2 ratio compared to the mass loss
of char, the advent of excess O2 is delayed and carbon
monoxide (CO) is generated. As a result, oxidation–reduction
layering of char occurs. Char grate firing leads to an increase in
char mass of the complete oxidation layer, and a thicker ash layer
covers the char surface. The reduction layer and low-O2 region of the oxidation layer favor NO reduction; therefore, NO
emission is delayed or shows a double-peak trend. The ash layer covering
and a long residence time at a high temperature increase the NO generation
rate of the oxidation layer. However, the overall NO generation rate
is controlled by the reduction and oxidation layer, and an optimal
char/O2 ratio exists, which makes the overall NO generation
rate the lowest. A difference in the NO trend between the chain boiler
and reciprocating grate boiler in and after the O2-deficient
zone is because of the influence of the reciprocating disturbance
on the reduction layer, ash layer, and char N release.