Interaction between CO2 and H2O on char structure evolution during coal char gasification

Alternating gasifying agents is an effective way to study the interaction between CO2 and H2O and is helpful to reveal competitive, independent and synergistic effect between CO2 and H2O in the co-gasification process. A bituminous coal was used in this study. And the alternate process is as follows: demineralized coal was first gasified in the presence of H2O (CO2) at 900 °C in a thermal gravimetric analyzer (TGA) to prepare coal char with 25% carbon conversion level. After 20 min Ar purging, CO2 (H2O) was switched to prepare residual char with 50% conversion. The pore structure and surface morphology were investigated by N2 adsorption and scanning electron microscopy (SEM), respectively. The results indicate that CO2 gasification occurs on the char surface and creates micropores. H2O molecule is more prone to diffuse into the pore structure to react with the char matrix, it is helpful to the enlargement of the pore size and the formation of micropores. In the co-gasification, the reaction could occur both on the char surface and in the matrix simultaneously, H2O more easily enters into the char matrix in the presence of CO2. A positive interaction develops between H2O/CO2 in developing the coal char pore structures during gasification.