A kinetic study on lignite char gasification with CO2 and H2O in a fluidized bed reactor

Lignite char gasification experiments in CO2, H2O and their mixture were performed in a fluidized bed reactor over the temperatures range of 1060-1210 K. The active sites occupied by different gasifying agents in CO2/H2O mixture were separated and the kinetics was analyzed. Results show that the reactivity of gasification increases rapidly as the temperature rises. The average reaction rate in 50%CO2/50%H2O mixture is slower than the reaction rate in 50%N-2/50%H2O atmosphere, which indicates that CO2 and H2O compete for the same active reaction sites on the char surface. Furthermore, with an increase of temperature, the competition capacity of CO2 gasification over H2O gradually increases, as a result, CO2 gasification occupies more active sites than H2O when the temperature is higher than 1160 K. Calculations of the activation energy in the kinetically controlled region based on the shrinking core model reveal that the activation energies follow the trend: N-2/CO2 > N-2/H2O > CO2/H2O.