Char gasification with O2, CO2, and H2O:: Effects of pressure on intrinsic reaction kinetics

Measurements of the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O-2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer (TGA). It was found that the reaction order in CO2 and H2O was not constant over the pressure range investigated-varying from 0.5 to 0.8 at atmospheric pressure and decreasing at pressures above approximately 10 atm. The apparent reaction order in oxygen was less affected by pressure over the range 1 to 16 atm. Char surface area after reaction at higher pressures was generally greater than that after reaction at lower pressures. This resulted in a reduced effect of pressure on the intrinsic rates at 10% conversion. Activation energies for all three reactions were not significantly affected by an increase in reaction pressure. The intrinsic rate data obtained in this work were used to estimate the high-temperature reactivity of the chars using a basic knowledge of the pore structure of the samples. This provided a framework within which coal behavior under high-temperature gasification conditions can be predicted using intrinsic rate data and a knowledge of the structure of the char.