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<p>Tar-rich coal is a valuable source of coal-derived oil and gas. Understanding its structural response and hydrogen-rich retention behavior during pyrolysis is essential for improving extraction efficiency. In this study, real-time acoustic emission (AE) monitoring combined with low-field nuclear magnetic resonance (LF-NMR) was employed to investigate the coupled evolution of pore–fracture structures and hydrogen-rich components in tar-rich coal during pyrolysis from 300 to 550&#xa0;℃. The results show that the AE ringing count can be divided into three distinct stages: incubation (&lt; 300&#xa0;℃, sparse signals, minor damage), active (&gt; 300&#xa0;℃, continuously enhanced signals), and extinction (late isothermal stage, signals gradually disappear). Porosity slightly decreases below 300&#xa0;℃ due to thermal expansion and tar blockage, then increases with temperature between 300 and 550&#xa0;℃, with the largest increment at 450&#xa0;℃ and the maximum value at 550&#xa0;℃. Transition pores and macropores increase significantly in this range. Hydrogen-rich components (water and tar) show retention signals appearing at 300&#xa0;℃, peaking at 450&#xa0;℃, and declining markedly at 550&#xa0;℃. Initial pore development provides space for retention, while subsequent fracture connectivity promotes product escape. A strong correlation is observed among AE signals, structural evolution, and product escape: The incubation stage corresponds to minor structural changes; the active stage corresponds to synergistic pore-fracture growth and enhanced hydrogen-rich retention; the extinction stage corresponds to well-developed fracture networks and substantial product escape. These findings demonstrate that AE responses are closely related to the structural evolution of tar-rich coal during pyrolysis. The combined interpretation of AE and NMR data provides theoretical support for evaluating macro- and micro-structural characteristics and offers insights into the pyrolysis reaction process.</p>

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Structural response and hydrogen-rich retention during pyrolysis of tar-rich coal: understanding based on acoustic emission (AE) and nuclear magnetic resonance (NMR)

  • 期刊论文

  • 发表日期：

    2026年5月29日

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  • Zetang Wang,
  • Jishi Geng,
  • Qiang Sun,
  • Shihao Yuan,
  • Xin Hu,
  • He Zhang

摘要

Tar-rich coal is a valuable source of coal-derived oil and gas. Understanding its structural response and hydrogen-rich retention behavior during pyrolysis is essential for improving extraction efficiency. In this study, real-time acoustic emission (AE) monitoring combined with low-field nuclear magnetic resonance (LF-NMR) was employed to investigate the coupled evolution of pore–fracture structures and hydrogen-rich components in tar-rich coal during pyrolysis from 300 to 550 ℃. The results show that the AE ringing count can be divided into three distinct stages: incubation (< 300 ℃, sparse signals, minor damage), active (> 300 ℃, continuously enhanced signals), and extinction (late isothermal stage, signals gradually disappear). Porosity slightly decreases below 300 ℃ due to thermal expansion and tar blockage, then increases with temperature between 300 and 550 ℃, with the largest increment at 450 ℃ and the maximum value at 550 ℃. Transition pores and macropores increase significantly in this range. Hydrogen-rich components (water and tar) show retention signals appearing at 300 ℃, peaking at 450 ℃, and declining markedly at 550 ℃. Initial pore development provides space for retention, while subsequent fracture connectivity promotes product escape. A strong correlation is observed among AE signals, structural evolution, and product escape: The incubation stage corresponds to minor structural changes; the active stage corresponds to synergistic pore-fracture growth and enhanced hydrogen-rich retention; the extinction stage corresponds to well-developed fracture networks and substantial product escape. These findings demonstrate that AE responses are closely related to the structural evolution of tar-rich coal during pyrolysis. The combined interpretation of AE and NMR data provides theoretical support for evaluating macro- and micro-structural characteristics and offers insights into the pyrolysis reaction process.