Analysis of pore-fracture structure evolution and permeability in tar-rich coal under high-temperature pyrolysis using μCT technology

Abstract To study the internal evolution characteristics of tar-rich coal under high-temperature pyrolysis and improve pyrolysis efficiency, three-dimensional reconstruction and analysis of tar-rich coal from northern Shaanxi after high-temperature pyrolysis were conducted using μCT technology. The evolutionary development of pore and fracture structure at different temperatures and the relationship between pore-fractures and permeability was studied and discussed. The results show that when tar-rich coal from 300 to 600 °C, it mainly undergoes two stages: in the first stage, the internal substance structure of the coal mainly undergoes thermal cracking, forming large fracture bands; in the second stage, the coal undergoes intense pyrolysis reactions, resulting in primarily circular or elliptical large pore structures within the coal, with a reduction in the number of fractures. Furthermore, a strong exponential relationship is exhibited between the porosity and permeability of tar-rich coal, and a predictive equation is provided. When the temperature exceeds 500 °C, the coupled effect of pores and fractures contributes more than 20% to permeability, and its impact cannot be ignored.