Effect of particle size on the pyrolysis process of low‐rank coal: Assessment of structural evolution by N₂ adsorption, Raman, X‐ray diffraction, and Fourier transform infrared

Abstract

It is of great theoretical significance and application value to study the influence of particle size difference of low-rank coal on the structure of char and establish a relationship to regulate the pyrolysis process and performance of char. The structure changes of char prepared from raw coal with different particle sizes were analyzed by N 2 adsorption, Raman, X-ray diffraction (XRD), and Fourier transform infrared (FTIR). The results show that with the increase of pyrolysis temperature (500 C-700 C), the specific surface area of char first increases and then decreases and reaches the maximum value at 650 C. When the particle size of raw coal increases gradually, the process of volatile matter removal is limited by mass transfer, and the diffusion pore expansion makes the specific surface area and pore volume of char increase rapidly, and the char degree of ordering increases. The central sample of char prepared from raw coal with the same particle size has a larger specific surface area than the edge sample, which may be due to the restriction of mass transfer resistance in the release process of volatiles, resulting in a larger specific surface area of the central sample and a lower ordering degree of the central sample. The sample with pyrolysis temperature of 550 C was selected for comparison, and its structural parameters were inconsistent, because the volatiles were not removed at this temperature, which had a great impact on the structural evolution.