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Differences of Pyrolysis Products and Controlling Factors of Oil-Rich Coal with Different Grain Sizes under Fully-Mechanized Mining Conditions

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Abstract

China’s need for energy resources is growing every day. Future energy demands will be partly met by low-temperature pyrolysis of oil-rich coal, which is a form of coal-to-oil technology. Under the existing fully-mechanized coal mining technology, oil-rich coal is mechanically broken into different particle sizes by a shearer and used in different industrial utilization directions. However, due to differences in particle size and material composition, the pyrolysis products of oil-rich coal with different natural particle sizes are different, which affect the pyrolysis efficiency of oil-rich coal with different particle sizes. In order to explore the differences and influencing factors of pyrolysis products of oil-rich coal with different particle sizes, and taking Jurassic oil-rich coal in northern Shaanxi as the research object, the differences and causes of pyrolysis production of oil and gas from nine kinds of oil-rich coal with different natural particle sizes under existing coal mining conditions are discussed according to particle size characteristics, pore structure, heat transfer velocity and molecular structure. The findings demonstrate that the pyrolysis characteristics of coal do not show a single trend with change in particle size. With decrease in particle size, the ash and sulfur contents were relatively high, and the tar yield increased first and then decreased. In contrast, the light fraction decreased overall, and the heavy fraction decreased. The tar yield of 0.125–0.25 mm was the highest, and the tar content was 1.996 g. For the gas components produced by pyrolysis, the contents of CH4, CO and H2 first increased and then decreased with decrease in particle size, while the contents of CO2 and CnHm showed the opposite trend. Larger particles (about 30 mm) affect the escape efficiency of pyrolysis products and the amount of carbon deposition due to the difference in porosity (interparticle resistance) of the inner surface and pyrolysis bed, resulting in secondary reactions of the products escaped from a primary reaction, thus affecting the differences in pyrolysis products. The heat transfer process of coal was affected by particle size, and the thermal conductivity increased gradually with decrease in particle size, which is consistent with the change of tar yield with particle size. The maceral components and molecular structure functional groups in coal with different particle sizes were also different, which resulted in the differences in tar yield. Studies have shown that smaller particle sizes have longer alkyl side chains, and pyrolysis accompanied by rising temperature causes different changes in the aliphatic hydrocarbon content in coal coke after pyrolysis. The aliphatic hydrocarbon content decreased the most when the particle size was 0.125 mm, which is more beneficial to the improvement of tar yield. In addition, vitrinite is a good carrier of tar yield, and the granular coal vitrinite after crushing is enriched to smaller particles.

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Acknowledgments

The author would like to thank Shaanxi Coal Caojiatan Mining Company for providing important information and the experimental platform provided by the Shaanxi Provincial Key Laboratory of Coal Green Geology Support. The study was supported by National Natural Science Funds of China (Grant No. 42002194, Grant No. 42330808). Science and Technology Research Program of Shaanxi Coal and Chemical Industry Group Co., Ltd. (No. 2021SMHKJ-A-J-07-02).Natural Science Basic Research Program of Shaanxi (2021JLM-12).

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Authors and Affiliations

  1. College of Geology and Environment, Xi’an University of Science and Technology, Xi’an, 710054, China

    Junwei Qiao, Xiangyang Liang, Changjian Wang, Qingmin Shi, Lei Zhang & Yabin Lin

  2. Geological Research Institute for Coal Green Mining, Xi’an University of Science and Technology, Xi’an, 710054, China

    Junwei Qiao, Qingmin Shi, Lei Zhang & Yabin Lin

  3. Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation, Xi’an, 710054, China

    Junwei Qiao, Qingmin Shi, Lei Zhang & Yabin Lin

  4. Shaanxi Shanmei Caojiatan Mining Co., Ltd, Yulin, 719000, China

    Longxiang Jiao & Gang Su

  5. Shaanxi Coal Chemical Industry Technology Research Institute Co., Ltd., Xian, 710100, China

    Weifeng Xue

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  1. Junwei Qiao
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Correspondence to Junwei Qiao.

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Author Gang Su and Longxiang Jiao are employed by Shaanxi Shanmei Caojiatan Mining Co., Ltd. Weifeng Xue is employed by Shaanxi Coal Chem Ind Technol Res Inst Co Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Qiao, J., Liang, X., Wang, C. et al. Differences of Pyrolysis Products and Controlling Factors of Oil-Rich Coal with Different Grain Sizes under Fully-Mechanized Mining Conditions. Nat Resour Res 33, 867–886 (2024). https://doi.org/10.1007/s11053-024-10315-7

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