NO(X) EMISSIONS AND BURNOUT FROM A SWIRL-STABILIZED BURNER FIRING PULVERIZED COAL - THE EFFECTS OF FIRING COAL BLENDS

Results are reported of the effects on NO(x) emissions and burnout of firing coal blends in a 2.5 MW semi-industrial-scale test furnace. An experimental swirl-stabilised pulverised-coal burner was used and oper ated under baseline, unstaged and aerodynamically air-staged condition s. The components of the various blends were a semi-anthracite, a medi um-volatile bituminous and two high-volatile bituminous coals. Results showed that for unstaged firing, NO(x) emissions rose almost linearly with the fraction of higher-volatile coal in the blends. Results corr elated strongly with high-temperature volatile nitrogen yields determi ned for the component coals when weighted by the mass fraction of each coal in a blend. These results confirmed the importance of volatile n itrogen in determining NO(x) emissions for unstaged firing. For aerody namically air-staged operation, the NO(x) emissions were observed to f all marginally as the fraction of the higher-volatile coal in the blen ds increased, and were relatively insensitive to the high-temperature volatile nitrogen yields. This illustrated the greater importance of t he oxidation of char nitrogen in staged combustion. Burnout did not sh ow a clear relationship in either staged or unstaged firing. However, the results presented indicate that blending a high-volatile coal with a lower-volatile coal to improve the burnout of the latter does not a lways have the desired effect, and in many cases it results in lower b urnout.