Influence of high carbon monoxide concentration on the carbon dioxide gasification of a selected coal char

This study focuses on the effect of high CO concentration on CO2 gasification rates of chars of Illinois #6 coal, a bituminous coal that is industrially important because of its relatively high reactivity and low pollutant emissions. A pressurized thermogravimetric analyzer (PTGA) is used to obtain char gasification mass loss and surface area measurements. The mass loss profiles of Illinois #6 chars were measured at temperatures of 1200 and 1273K and pressures of 1.4, 10, and 25 atm in CO2-CO and CO2-N2 mixtures. CO concentrations between 10%--90% at 1.4 atm and 10%--85% at 25 atm were used. The surface areas of the chars are determined from room-temperature (298K) CO2 adsorption on chars after successive stages of partial gasification. A variable partial pressure gas adsorption technique was developed to effectively utilize the PTGA for CO2 surface area measurements.; Using experimental mass loss and surface area data combined with structural and kinetics modeling, an overall gasification curve description of kinetically-limited char-CO2 gasification reactivity is formulated for the life span of the char. The model consists of an intrinsic char reactivity expression with a conversion-dependent surface area modifier. First the surface area modifier is developed based on a random pore model and particle mode of burning relations. It is used with the unified gasification curve concept to interpret the isothermal gasification profiles and extrapolate the data to obtain the reactivity at the onset of char conversion. These isothermal initial char reactivities determined at selected gasification conditions are then used to calculate rate coefficients in the kinetics component of the model.; The proposed reaction mechanism contains paths for both gas phase and adsorbed CO to interfere with the gasification of Illinois #6 chars by CO 2. The main effect of adsorbed CO in the range of experimental conditions used in this study is to occupy carbon sites that could otherwise be attacked by CO2. This behavior persists even at 1273 K. The impact of CO inhibition, both gas phase and adsorbed CO, was found to decrease with temperature and increase with pressure. This model also reproduces reasonably well the overall rate variations measured in non-isothermal nonisothermal gasification environments.