Effects of Pyrolysis on the Pore Structure of Four Chinese Coals

To study the influences of coal ash fusion on pore structure and surface morphology, four typical Chinese coals with different AFT (ash fusion temperature) were pyrolyzed in the range 950−1400 °C. The evolution of pore structure and surface morphology of chars prepared at different temperatures and heating rate were investigated by N2 adsorption/desorption at 77 K. The results of N2 gas adsorption/desorption isotherms indicate that different coals and chars showed different adsorption/desorption characteristics at relative pressures of 0−0.5 and 0.5−1. The pore shape inside coal and char particles was analyzed based on the N2 adsorption/desorption isotherms. Two fractal dimensions D1 and D2 (at relative pressures of 0−0.5 and 0.5−1, respectively) were calculated using the fractal FHH (Frenkel−Halsey−Hill) method. Specific surface area and average pore size of samples were also obtained through the BET model. Results show that the melting ash very probably caused the changes of pore structure inside the ch...