Characterization of nitrogen and sulfur migration during pressurized coal pyrolysis and oxy-fuel combustion

In the present work, pressurized coal pyrolysis and oxy-fuel combustion experiments were carried out in a pressurized drop tube furnace to investigate the migration and transformation characteristics of nitrogen and sulfur. The pyrolysis experiments showed that high pyrolysis pressure inhibited the release of nitrogen and sulfur. The content of oxidized nitrogen (N-X), pyrite, sulfide, sulfoxide and sulfate in char decreased, while the content of pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q), thiophene and sulfone in char increased with the increase of pyrolysis pressure. The elevated pyrolysis temperature was conducive to the decomposition of nitrogen and sulfur-containing functional groups, and it also promoted the conversion of nitrogen and sulfur to functional groups with high stability such as N-Q and thiophene. The release of volatiles and the decomposition of nitrogen and sulfur-containing functional groups in coal were promoted by CO2 gasification. The increase of the total CO2 gasification pressure led to more nitrogen and sulfur remaining in char. During pressurized oxy-fuel combustion in O-2/CO2 atmosphere, the emissions of NO, NO2 and SO2 were lower than those in air combustion. The emissions of NO, NO2 and SO2 gradually decreased with the increase of pressure at air and oxy-fuel atmospheres. The increase of temperature increased the emissions of NO and SO2 at different pressures, but the NO2 emission decreased at elevated temperature. In addition, the emissions of NO and NO2 increased, but the emission of SO2 decreased with the increase of oxygen concentration.