Effect of pressure on char combustion in a pressurized circulating fluidized bed boiler

The combustion of coal char under simulated pressurized circulating fluidized bed conditions was studied at furnace temperatures between 700 and 850 degrees C. Kinetic rates of char combustion were measured at 1, 3, 5, and 7 atmospheres, at oxygen concentrations of 10 and 21%. The surface reaction rates increased with pressure up to a pressure of 5 atm. A further increase in the pressure led to a decrease in the reaction rate. Derived kinetic parameters showed a strong influence of pressure. The chars burned primarily under kinetically controlled conditions. Results indicate that traditional char oxidation models cannot adequately predict the variation of reaction rates with pressures. Mass transfer rates were measured for comparison with those obtained from previous studies. These results show a marked difference in comparison with calculated values. (C) 1998 Elsevier Science Ltd. All rights reserved.