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Show PAPER NO.4 The Effects of Coal Particle Size on Reductions of NOx and Unburnt Carbon Kure Research Labora tory, Babcock -H i tach i K. K. Noriyuki Ohyatsu, Kunio Okiura, Iwao Akiyama Abstract For pulverized coal cOllbustion, it is well known that the particle size influences the combustion rate and a smaller particle size gives a higher combustion efficiency. However, the effect of particle size on NOx reduction is not always obvious. Then we evaluated the effects of particle size on reductions of NOx and unburnt carbon in fly ash using our low NOx burner. We measured the NOx behavior in a siigle-burner furnace and the cOMbustion characteristics in a multi-burner furnace. The main results we obtained are as follows. The variation of NOx reduction with particle size was greatly affected by the excess O2 concentration using this burner. That is, the NOx concentration becaMe lower f·o r fin e r par tic I e s i z e sat low e x c e s s 0 2 con c e n - trations whereas it became higher for finer particle sizes ' at high excess O2 concentrations. We also found froll the Ilulti-burner test with the two staged combustion that both NOx and unburnt carbon in fly ash decreased with decreasing the particle size. 1. Introduction It is well known that the particle size influences the combustion rate and a smaller particle size gives a higher combustion efficiency for pulverized coal combustion. t) However, the effect of particle size on NOx reduction is not always obvious. Chen et al. 2) have lIIeasured liO . conversions froM fuel-bound nitrogen using pulverized coals of three particle size distributions. The result they obtained was that the degree of NO conversion became larger for finer particle sizes when the fuel/air .ixed rapidly (premixed) whereas it becaMe smaller for finer particle sizes when the fuel/air mixed slowly (axial diffusion). Then we evaluated the effects of particle size on reductions of NOx and unburnt carbon in fly ash using our low NOx burner. We .easured the NOx behavior in a single-burner furnace and the co.bustion characteristics in a aulti-burner furnace. -1- |