Influence of heating rate on structure of chars derived from pyrolysis of Shenmu coal

A series of char samples were derived from pyrolysis of Shenmu coal at low (3 and 5 ℃/min), medium (10 and 15 ℃/min) and fast (50, 100, 225, 350 and 750 ℃/min) heating rates, respectively, and at the same pyrolysis temperature of 750 ℃. Then these chars were characterized by means of X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and thermogravimetric analysis (TGA) with the aim to investigate the influence of heating rate in pyrolysis process on the microcrystallite structure, surface chemistry and gasification reactivity of the derived chars. The results show that with the increase of pyrolysis heating rate, the amount of oxygen-containing functional groups on the surface of the chars decreases, the dimension of microcrystallite lamella L_a and the graphitizing degree of the char increase obviously, the distance between lamella d₀₀₂ and mean height of lamella L_c decrease slightly, and the gasification reactivity R_T of chars reduces from 0.178 2 to 0.103 6. It can be concluded that the higher heating rate in the process of pyrolysis at 750 ℃ will result in higher graphitization of char with nonpolar surface and low gasification reactivity for Shenmu coal.