College of Mining Engineering, Taiyuan University of Technology

In order to study the influence of micro pore fissure structure on permeability under the thermal-fluid-solidcoupling during lignite pyrolysis, real-time CT scanning of lignite during low-temperature pyrolysis was carried out by usingthe μCT225kVFCB high-precision micro-CT test system of Taiyuan University of Technology, combined with the selfdevelopedhigh-temperature atmosphere furnace. The micro-structure of lignite was studied and analyzed with AVIZOsoftware. Through the extraction and analysis of the effective pore and fissure of lignite, the evolution process of the permeabilityof lignite under non-stress condition with temperature was studied from the perspectives of Kozeny-Carman permeabilityestimation equation and Darcy’s law. The results show that: ① From room temperature to 600 ℃, the evolutionprocess can be divided into three stages: the first stage, at room temperature to 300 ℃, thermal cracking occurs in the coalbody, resulting in the generation of a large number of pores and fissures, and the permeability increases by orders of magnitude.The second stage is at 300 to 500 ℃, the coal matrix is pyrolysed and the new pyrolysis products change the fluid channels, causing a slow decrease in permeability. The third stage is at 500 to 600 ℃, permeability begins to increaseagain, permeability enters the next rapid increase stage. ② At 300 ℃, the permeability of lignite reaches 15.5×10−12 m2,and the coal body is basically completely penetrated. ③ Under the thermal-fluid-solid coupling, the pyrolysis permeabilityof lignite depends not only on the micro-structure of pores and fissures, but also on the flow characteristics of fluid inthe coal matrix. With the increase of temperature, the influence of heat and mass transfer characteristics of fluid on the permeabilitybecomes more and more obvious. ④ The permeability estimated by Kozeny-Carman equation based on pore fissurestructure parameters is similar to the absolute permeability, which can basically reflect the relationship between permeabilityand temperature. The permeability estimation based on the real pore fissure structure can greatly reduce the difficultyof seepage experiment at high temperature and pressure, and provide a method for simplifying and verifying theseepage experiment of rock mass.

国家自然科学基金面上资助项目(51974191)；山西省省筹资助回国留学人员资助项目(2021-059)

李亚军，孟巧荣，陈涛，等. 热解褐煤的渗透性与微细观结构[J]. 煤炭学报，2023，48(4)：1707−1714

LI Yajun，MENG Qiaorong，CHEN Tao，et al. Permeability and microstructure of pyrolysis lignite[J]. Journal of China Coal Society，2023，48(4)：1707−1714