Air gasification of peat, wood and brown coal in a pressurized fluidized-bed reactor. II. Formation of nitrogen compounds

Abstract

The formation of nitrogen compounds in the air gasification of peat, wood and brown coal was studied in a small fluidized bed reactor, which was operated under pressure (0.4 MPa to 1.0 MPa) and at temperatures ranging from 800°C to 995°C. The fuel nitrogen of all fuels studied was converted mainly into ammonia. Smaller amounts of HCN and nitrogen-containing tar compounds were formed too. The ammonia concentration of the product gas was in the range of 0.56–1.13 vol% in peat gasification, representing 55–95 wt% of the peat nitrogen. Raising the freeboard temperature from 800 to 950°C resulted only in a small reduction in the conversion of peat nitrogen into ammonia. Similar conversions were also observed in brown coal and wood gasification, but since the nitrogen content of these fuels is lower, the ammonia concentrations were correspondingly lower and ranged between 0.05 and 0.09 vol% for wood and between 0.21 and 0.28 vol% for brown coal. The HCN concentration of the product gas in peat gasification increased with the rising temperature and ranged between 50 ppmv at 820°C and 200 ppmv at 920°C. In brown coal gasification the HCN concentration was in the range of 60–100 ppm at gasification temperatures of 850–910°C.