CONVERSION OF FUEL NITROGEN THROUGH HCN AND NH3 TO NITROGEN-OXIDES ATELEVATED PRESSURE

Reactions of fuel nitrogen during pyrolysis and combustion of pulveriz ed HVb coal, two peats and fir bark were studied experimentally in a p ressurized entrained flow reactor at T = 1123 and 1273 K, p = 0.2, 0.4 and 0.8 MPa. Mass loss of fuel, release of C, N, H and O, and formati on of NH3 and HCN were measured during pyrolysis (in N-2 containing O- 2 < 20 ppmv). Mass loss, and formation of NO, N2O and NO2 through HCN and NH3 were measured during combustion at 4-5 vol.% O-2 The rate of p yrolysis of high-volatile fuels (fir bark and peat) increased with pre ssure. The reverse trend was found with HVb coal. The order of release of the elements studied from the fuel (O > H > C > N) was found to be independent of pressure. The HCN/NH3 ratio in the flame was dependent on the fuel-O/fuel-N ratio and independent of pressure. Pressure did however increase the N2O/NO ratio, because the concentrations of the k ey radicals in NO formation are decreased by pressure. With peats, the formation of N2O increased slightly with pressure. The emission of N2 O however doubled with wood bark when the pressure increased from 0.2 to 0.8 MPa. Formation of NO2 increased distinctly with pressure, and w as fuel-dependent. One peat sample produced three times as much NO2 as the other under identical conditions. Copyright (C) 1996 Elsevier Sci ence Ltd.