HEAT AND MASS-TRANSFER LIMITATIONS IN GASIFICATION OF CARBON BY CARBON-DIOXIDE

Rates of gasification of carbon by carbon dioxide were measured in the laboratory using a thermogravimetry apparatus. The experiments were conducted at various temperatures and sample bed depths using powders of graphite and coconut char as sources of carbon, under flowing gas of CO2. Various CO-CO2 mixtures were also employed for the study of coconut char. The measured rate data were subjected to a heat and mass transfer analysis to find out the values of isothermal and non-isothermal effectiveness factors. These values were utilized to predict the intrinsic chemical reactivities of graphite and coconut char samples, free from heat and mass-transfer limitations. Extrapolation of experimental data to hypothetical zero bed depth showed good agreements with the above at various temperatures, thus providing valuable cross-checks. The activation energies were found to be 260 and 250 kJ/mol for graphite and coconut char, respectively, under CO2. Carbon monoxide was found to decrease the rate of gasification but not as drastically as some literature reports predict.