Steam gasification of low-rank coal chars: Insights into the kinetic compensation effects and physical significance of kinetic parameters

Abstract

Study aims to experimentally investigate the physical significance of continuously evolved kinetic parameters i.e.lnAapp and Eapp including the importance of parameters, i.e., m and c, in the kinetic compensation effect (KCE) lnAapp = mEapp + c during steam gasification of char. To gain further insights into the char gasification mechanism in the steam atmosphere, an understanding of KCE is desirable. Two low-rank coals, viz., Loy Yang brown coal and Collie sub-bituminous coal samples of particle sizes 106150 µm and 180212 µm, are selected for fluidized bed gasification. The high-sensitive, quadrupole mass spectrometer (QMS) is used to measure the product gas composition for determining the instantaneous rate of char-H₂O reactions. Results suggest that the difference in Eapp with the change in coal sample at fixed conversion level, signifies the relative condensation of residual char, whereas the respective differences in lnAapp reflects the difference in the relative proportion of active sites consumed during char gasification under the reaction controlled by the chemical reactivity of char. However, the continuous variation in Eapp with conversion in the event of char gasification of any coal sample, displays the change in the rate of surface reaction following surface desorption with conversion and the variation of lnAapp potentially presents the change in the rate of adsorption of gasifying agents with conversion. In the subsequent KCE, the slope ‘m’ shows the reactiveness of char by displaying the impact of change in the rate of surface reaction with the desorption on the rate of surface adsorption during char gasification. The degree of deviation in char reactivity due to the evolution of KCE from a foreseeable condition of having non-KCE is indicated by intercept ‘c’.