Oxy-fuel combustion of selected solid fuels under atmospheric and elevated pressures

Oxy-fuel combustion is suggested as a clean technique for energy conversion with respect to the reduction of CO2 and NOx emissions. The positive effect of NOx reduction can be enhanced by an increase of the pressure inside the combustion chamber. The oxy-fuel combustion of bituminous and lignite coals was investigated. The influence of process parameters, such as the type of fuel, the type of oxidant and the pressure, on the emissions of NOx, N2O, and other exhaust gas compounds was investigated. The experiments were performed using a prototype, laboratory-scale (fuel input of up to 3 kg/h) pressurised fluidised-bed combustor (BFB). The main process parameters were a maximal pressure of 6 bar, a maximal temperature of 910 °C and an oxidant flow rate of 39 kg/h. The results of the experiment performed with the pressurised Flexi-Burn™ procedure are presented and discussed. In particular, the emissions of NO and N2O from air-fired and oxy-fuel processes were compared. The NO emission was significantly reduced under higher pressures. The maximal NO reduction (due to an increase in the pressure) was as high as 50%, which can be explained by the promotion of the char + NO reaction.