Kinetic studies on bituminous coal char gasification using CO2 and H2O mixtures

The isothermal gasification kinetics of bituminous coal char was investigated within 1173-1373 K range. Also, the impacts of gasification temperature, gas composition, and gasification time on gasification process were analyzed. As the results of experiments suggest, there is a significant rise for the carbon conversion degree of bituminous coal char when gasification temperature and gasification time increase, but also when ratios of CO2/H2O decrease. Kinetic studies were also carried out. It is concluded that the gasification of bituminous coal char is controlled by internal chemical reaction in the early stage and diffusion in the later stage. Moreover, we studied the activation energy of various gas atmosphere and stages of gasification. Finally, our research shows that that reaction rate constant rises when the ratio of CO2/H2O rises. It is proposed that the diffusion-control step is significantly shortened with the decrease of CO2/H2O ratio. As SEM results suggest, bituminous coal char gasified in H2O atmosphere has numerous inner pores (0-10 mu m). Therefore, in the process of gasification, the inner bore provides a gas channel, which reduces the gas diffusion resistance and thus shortens the diffusion control step. These results can serve as a reference to the industrialized application of the technology of coal gasification-direct reduction iron.