Pore Structure and Fractal Characteristic Analysis of Gasification-Coke Prepared at Different High-Temperature Residence Times

An accurate and quantitative description of the pore structure of gasification-coke using fractal geometry could be of great significance to its industrial utilization. In this study, gasification-coke was prepared with low-quality coal blending at different high-temperature residence times to investigate the variation in the pore structure, fractal dimensions, reactivities, and their relationship. The pore structure parameters (e.g., specific surface area, pore volume, and average pore diameter) of gasification-coke were investigated by low-temperature N-2 adsorption/desorption and mercury intrusion porosimetry. Fractal dimensions D-1 and D-2 (at relative pressures of 0-0.5 and 0.5-1, respectively) were calculated using the fractal Frenkel-Halsey-Hill model, and the fractal dimension D-3 was obtained using the Menger sponge model. The results show that the pore structure systems of gasification-coke prepared at different high-temperature residence times are continuous and complete, which contributes to the gasification reaction. The variation trend of the macropore structure parameters is more complex than that of micropore and mesopore with the extension of the high-temperature residence time. It is found that D-1 is linearly correlated with the micropore specific surface area, indicating that D-1 is more suitable for reflecting the roughness of the micropore surface; D-2 is linearly correlated with the mesopore volume and can describe the volumetric roughness of the mesopore; and D-3 reflects the irregularities and surface roughness of the macropores. Gasification reactivity is closely related to the D-2 value, and the reactivity of the gasification-coke may be improved if the number of mesopores is increased by controlling the high-temperature residence time or other pyrolysis conditions. The research results will provide theoretical reference for controlling the gasification reaction of gasification-coke and gasifier design.