Development of Zhundong subbituminous coal char structure during hydrogasification under high pressure

In this study, the hydrogasification of Zhundong subbituminous coal char was performed in a pressurized fixed-bed reactor. The effects of hydrogen flow rate, char particle size, reaction temperature, hydrogen pressure, and char preparation temperature on hydrogasification reaction rate were investigated. Results showed hydrogasification was controlled by chemical reaction when hydrogen flow exceeded 1.5 L/min, particle size was less than 74 μm, and temperature was below 1123 K. The pore structural development of char during hydrogasification was studied using the nitrogen adsorption/desorption method. Two fractal dimensions were calculated based on fractal Frenkel-Halsey-Hill theory. Results indicated that the development of pore structure could be classified into three stages: the rapid formation of micropores in the initial stage, the increase in the amount of mesopores as a result of pore coalescence in the second stage, and the collapse of pores in the final stage. Fractal dimensions increased with carbon conversion in the beginning of hydrogasification, which indicated the well-developed pore structure and surface morphology of char. However, as reaction continued, the fractal dimensions decreased with carbon conversion due to the coalescence and collapse of pores, thereby reflecting a smoother surface of char. This finding was consistent with the result of scanning electron microscopy.