Conversion of fuel nitrogen through HCN and NH 3 to nitrogen oxides at elevated pressure

Abstract

Reactions of fuel nitrogen during pyrolysis and combustion of pulverized HVb coal, two peats and fir back were studied experimentally in a pressurized 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 formation of NH 3 and HCN were measured during pyrolysis (in N 2 containing O 2 < 20 ppmv). Mass loss, and formation of NO, N 2O and NO 2 through HCN and NH 3 were measured during combustion at 4–5 vol.% O 2. The rate of pyrolysis of high-volatile fuels (fir bark and peat) increased with pressure. 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 NH 3 ratio in the flame was dependent on the fuel-O fuel-N ratio and independent of pressure. Pressure did however increase the N 2O NO ratio, because the concentrations of the key radicals in NO formation are decreased by pressure. With peats, the formation of N 2O increased slightly with pressure. The emission of N 2O however doubled with wood bark when the pressure increased from 0.2 to 0.8 MPa. Formation of NO 2 increased distinctly with pressure, and was fuel-dependent. One peat sample produced three times as much NO 2 as the other under identical conditions.