The evolution characteristics of bituminous coal in the process of pyrolysis at elevated pressure

In the present study, we report the formation rules of gas products (CO, CO2, CH4, HCN, NH3) and the evolution characteristics of the physicochemical structure during the pyrolysis of Shenhua bituminous coal under evaluated pressure using pressurized drop tube furnace (PDTF). The operating pressure, temperature, and residence time were in the range of 1073 - 1273 K, 0.3 - 1.2 MPa, and 0.3 - 3.0 s, respectively. During the experiments, the outlet flue gas was analyzed with an online Fourier Transform Infrared Spectroscopy (FTIR) gas analyzer, and the physicochemical structure of pyrolysis char were sampled and characterized with FTIR, X-ray Photoelectron Spectrometer (XPS), and nitrogen adsorption-desorption methods. The results show that the increasing pyrolysis pressure, temperature and residence time would all promote the release of carbon and nitrogen-containing light gases. The increasing pyrolysis pressure and temperature would promote the decomposition of aliphatic hydrogen content and oxygen-containing functional group. When the pyrolysis residence time is less than 0.6 s, the decomposition of the active structure would be promoted as the residence time increases. While, when the pyrolysis residence time is in the range of 0.6-3.0 s, the active structure of the char products tends to be stabilized. As the pyrolysis residence time increases, the carbon content in the char products first shows a rapidly increase from 69.89% to 87.78%, and then slowly up to 91.25%; however, the oxygen content in the char products first decrease from 28.38% to 10.08% rapidly, and then slowly down to 6.98%; the nitrogen content has an overall downward trend. The specific surface area of the pyrolysis char reached its peak at the pyrolysis residence time of 0.6 s. When the pulverized coal particles were pyrolyzed for 0.6 s under high temperature (1273 K), high pressure (0.9 MPa) and high heating rates, most of the volatiles in the pulverized coal particles have been released.

Automated summary

The study reports the formation rules of gas products and evolution characteristics of physicochemical structure during the pyrolysis of Shenhua bituminous coal under different pressures, temperatures, and residence times. Increasing pressure, temperature, and residence time promote the release of carbon and nitrogen-containing gases, affecting the physicochemical structure of the char products.