CO2, NOx and SO2 emissions from the combustion of coal with high oxygen concentration gases

The emissions of CO2, NOx and SO2 from the combustion of a high-volatile coal with N-2- and CO2-based, high O-2 concentration (20, 50, 80, 100%) inlet gases were investigated in an electrically heated up-flow-tube furnace at elevated gas temperatures (1123-1573 K). The fuel equivalence ratio, phi, was varied in the range of 0.4-1.6. Results showed that CO2 concentrations in Rue gas were higher than 95% for the processes with O-2 and CO2-based inlet gases. NOx emissions increased with phi under fuel-lean conditions, then declined dramatically after phi = 0.8, and the peak values increased from about 1000 ppm for the air combustion process and 500 ppm for the O-2(20%) + CO2(80%) inlet gas process to about 4500 ppm for the oxygen combustion process. When phi > 1.4 the emissions decreased to the same level for different O-2 concentration inlet gas processes. On the other hand, NOx emission indexes decreased monotonically with phi under both fuel-lean and fuel-rich combustion. SO2 emissions increased with phi under fuel-lean conditions, then declined slightly after phi > 1.2. Temperature has a large effect on the NOx emission. Peak values of the NOx emission increased by 50-70% for the N-2-based inlet gas processes and by 30-50% for the CO2-based inlet gas process from 1133 to 1573 K. However, there was only a small effect of temperature on the SO2 emission. (C) 2000 Elsevier Science Ltd. All rights reserved.