黄淄博，刘倩如，刘红，等. H2O气氛下富油煤热解过程的反应分子动力学模拟[J]. 煤田地质与勘探，2024，52(7)：189−199. DOI: 10.12363/issn.1001-1986.24.01.0076
引用本文: 黄淄博，刘倩如，刘红，等. H2O气氛下富油煤热解过程的反应分子动力学模拟[J]. 煤田地质与勘探，2024，52(7)：189−199. DOI: 10.12363/issn.1001-1986.24.01.0076
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HUANG Zibo，LIU Qianru，LIU Hong，et al. Simulation of the pyrolysis process of tar-rich coals in an H2O atmosphere based on the reactive force field molecular dynamics[J]. Coal Geology & Exploration，2024，52(7)：189−199. DOI: 10.12363/issn.1001-1986.24.01.0076
Citation: HUANG Zibo，LIU Qianru，LIU Hong，et al. Simulation of the pyrolysis process of tar-rich coals in an H2O atmosphere based on the reactive force field molecular dynamics[J]. Coal Geology & Exploration，2024，52(7)：189−199. DOI: 10.12363/issn.1001-1986.24.01.0076
shu

H2O气氛下富油煤热解过程的反应分子动力学模拟

Simulation of the pyrolysis process of tar-rich coals in an H2O atmosphere based on the reactive force field molecular dynamics

    摘要
  • 摘要:
    目的 我国富油煤资源丰富，通过热解技术可将其转化为能源产品(化学品、气体或液体燃料等)，缓解我国油气资源的对外依存程度。深入认识热解过程中的产物变化规律和反应机理，对于煤炭清洁高效转化工艺的研究至关重要。
    方法 采用反应分子动力学(ReaxFF MD)模拟探究富油煤(长焰煤)热解过程以及H2O气氛对热解产物分布的影响和作用机制。
    结果和结论 结果表明，富油煤(长焰煤)热解的温度范围为1 200~2 800 K，热解过程主要分为热解(1 200~2 000 K)和缩聚(2 000~2 800 K)两个阶段。在热解阶段，随着温度的升高，煤分子快速裂解，焦炭产物不断减少，焦油和气体产物不断增加；在缩聚阶段，焦油产物之间发生缩聚反应生成焦炭，同时释放小分子气体，导致焦油产物减少，焦炭和气体产物增加。因此，提高热解温度、延长热解时间可得到更多的气体产物，而提升焦油产量的关键则是抑制缩聚反应发生。在高温缩聚阶段引入H2O气氛热解，结果表明，H2O能够有效地促进煤分子的裂解，随着H2O占比的增加，煤热解体系中C―C键减少，C―H和C―O键增加。分析二者之间的交互作用发现，煤热解产生的自由基与H2O反应，促进H2O分子分解，H2O分解产生的H•和OH•又进一步促进煤裂解，并与煤热解产物反应，生成更多的焦油和气体。研究加深了对富油煤热解过程的理解，对煤炭资源的清洁高效利用具有一定指导意义。

     

    Abstract:
    Objective Tar-rich coal resources, abundant in China, can be converted into energy products (e.g., chemicals and gas/liquid fuels) through pyrolysis, thus alleviating the country’s dependence on oil and gas imports. A thorough understanding of the product evolution and reaction mechanisms of the pyrolysis of tar-rich coals is crucial to research into the clean and efficient conversion processes of coals.
    Methods Based on the reactive force field molecular dynamics (ReaxFF MD), this study simulated the pyrolysis process of tar-rich coals (long-flame coals) and explored the impacts of the H2O atmosphere on the distribution of pyrolytic products, along with the mechanism behind the impacts.
    Results and Conclusions  The results indicate that tar-rich coals (long flame coals) are pyrolyzed at temperatures ranging from 1200 K to 2800 K, involving two stages: pyrolysis (1200 K to 2000 K) and polycondensation (2000 K to 2800 K). In the pyrolysis stage, coal molecules decompose rapidly as the temperature rises, accompanied by gradually decreasing coke products and constantly increasing tar and gas products. The polycondensation stage witnesses the polycondensation among tar products, which generates coke and releases low-molecular-weight gas, leading to decreased tar products but increased coke and gas products. Therefore, more gas products can be obtained by increasing the pyrolysis temperature and prolonging the pyrolysis time, while the key to improving the tar yield is to inhibit the polycondensation. The introduction of the H2O atmosphere into the pyrolysis during high-temperature polycondensation demonstrates that H2O can effectively accelerate the cracking of coal molecules. Specifically, with an increase in the proportion of H2O, the coal pyrolysis system exhibits decreasing C―C bonds but increasing C―H and C―O bonds. As revealed by the analysis of the interactions between coals and H2O, the free radicals generated during coal pyrolysis react with H2O, promoting the decomposition of H2O molecules. In turn, the H• and OH• generated from H2O decomposition further expedite coal cracking and react with the products of coal pyrolysis to produce more tar and gas. This study, contributing to a deeper understanding of the pyrolysis process of tar-rich coals, can serve as a guide for the clean and efficient utilization of coal resources.

     

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