Release of nitrogen and sulphur species from low-rank coal during entrained flow pyrolysis and gasification

Abstract

This paper investigated the emission of N and S species during pyrolysis and gasification of Maddingley and Yallourn coal in an entrained flow reactor. Nitrogen pollutants (HCN and NH3) and sulphur pollutants (H2S and COS) were investigated under different temperatures (1000–1400 °C) and CO2 concentrations (10–40%). The release of N and S species during the two gasification processes, direct and two-step gasification, were also studied. It was found that no NH3 and COS were detected during pyrolysis and gasification of coal. The N and S in coal were mainly converted to gas-N (>60%) and gas-S (>50%) during entrained flow pyrolysis. Coal-N and Coal-S were converted to nearly 100% gaseous nitrogen and sulphur species during entrained flow gasification. High temperature improved H2S and HCN emissions during coal pyrolysis. High temperature promoted the HCN release during entrained flow gasification, whereas elevated CO2 concentration inhibited H2S and HCN emission. The majority of H2S and HCN emissions came from the pyrolysis part during two-step gasification. Direct coal gasification released less H2S and HCN than two-step gasification. The results provide essential information for the gas cleaning process downstream of entrained flow gasifiers.