Reaction kinetics of coal char in oxy-fuel combustion environment and characterization of reacted char

The work primarily focuses on combustion kinetics of devolatilized coal char fines (75-120 mu m), including the estimation of kinetic parameters and char morphological transformation in oxy-fuel environment (O-2-CO2 and O-2-N-2). Experimental work has been carried out to study the effect of higher CO2 concentration and elevated O-2 concentrations on the ignition, burnout behavior of pulverized coal char both non-isothermally and isothermally. The coal chars obtained from pyrolyzing three different types of coal are used in experiments; a high ash (HA) coal, a medium ash (MA) coal, and a low ash (LA) coal. Three different kinetic models, namely VM, GM and RPM, have been employed to determine the kinetic parameters. The kinetic parameters are observed to be a strong function of oxygen concentration for all the three models. The estimated activation energy employing non-isothermal analysis for LA coal char using VM lies in the range of 203-212 kJ/mol. In comparison, the activation energy predicted by GM for HA coal char lies in the range 137-144 kJ/mol. Moreover, the activation energy estimated for MA coal char by RPM varies in the range of 134-142 kJ/mol. It is also explored during the non-isothermal analysis that an increase in char particle size from 75-120 mu m to 250-300 mu m shows a small increase in the values of apparent activation energy and pre-exponential factor. The activation energy values calculated employing the isothermal method are 106-126 kJ mol(-1) (using RPM) for coal char MA and 96-135 kJ mol(-1) (using GM) for coal char HA. Both the isothermal and non-isothermal kinetic analysis reveals that the combustion of coal char LA follows VM while coal char MA and HA follows RPM and GM in order. SEM images and BET surface area analysis for partially converted coal chars are further analyzed to justify the suitability of different reaction mechanism followed by various coal chars.