Effects of Pressure on the Characteristics of Bituminous Coal Pyrolysis Char Formed in a Pressurized Drop Tube Furnace

To investigate the pyrolysis characteristics of Shenhua bituminous coal under pressurized conditions, the effects of pressure (0-1.2 MPa) on the physicochemical structure and combustion reactivity of pyrolysis char samples prepared at 1073 and 1273 K were studied in a pressurized drop tube furnace. The low-temperature nitrogen adsorption test was used to characterize the physical structure of the char samples. The results showed that the increase of pyrolysis pressure is conducive to the formation of mesopores, and the specific surface area is larger at 1273 K. Raman and X-ray photoelectron spectroscopy analyses were used to characterize the chemical structure of the char samples. The results showed that the increase of pressure can promote the transformation of the smaller aromatic structure into a larger aromatic structure, and the graphitization degree is more obvious at 1273 K. With the increase of pressure, the proportion of the C=C/C-C bond in the char structure increases and the proportion of C-H bond decreases. It indicates that the unstable aliphatic side chains are more easily decomposed under pressurized conditions. Nitrogen in the char structure mainly exists in the form of N-5, N-6, and N-Q With the increase of pressure, unstable N-5 content decreases, while N-6 and N-Q content increase. In addition, the micro-fluidized bed reaction analyzer system was used to analyze the combustion reactivity of the char samples at 673 K. The results showed that with the increase of pyrolysis pressure and temperature, the combustion reactivity of the char samples decreases gradually.