Coal gasification and combustion of LCV gas

Experiments were performed on the gasification of bituminous coal with air and steam in a 2·5 kW atmospheric fluidized bed. Thermal conversion efficiencies, the retention of sulphur and the conversion of fuel nitrogen to NH3 were determined for various oxygen-to-carbon ratios (equivalence ratios between 0·58 and 0·82), with and without limestone in the bed. The conversion efficiency increased with increasing equivalence ratio, while the conversion of fuel-nitrogen to NH3 decreased with increasing equivalence ratio. The sulphur conversion without the addition of limestone increased with increasing equivalence ratio. As expected, the presence of limestone in the bed led to increased sulphur retention, more so at the high and low ends than at intermediate values of the range of equivalence ratios. In addition, limestone adversely affected thermal conversion efficiency and increased the conversion of fuel-nitrogen. The low calorific value (LCV) fuel gas, produced by the AFBG, was combusted in a cyclone combustor at atmospheric pressure. Stable combustion of the LCV fuel gas was possible down to a calorific value of 1·57 MJ/m3n. The combustion efficiency in the atmospheric topping combustor varied between 98·72 and 99·96%. Nearly 60% of the NH3 in the fuel gas was converted to NO in the combustor.