超临界水与含瓦斯煤开闭孔结构的互反馈机制

The Supercritical water (T≥374 ℃,P ≥22.05 MPa) can achieve high efficiency gasification and liquefaction of coal at a lower temperature and a shorter time, thus, has been widely concerned. During the gasification and liquefaction process, the pore structure of gassy coal has been changed, and the variation of pore structure also has an effect on the diffusion of Supercritical water in gassy coal. To reveal the feedback mechanisms between diffusion of supercritical water and the pore structure evolution, This project adopts the high resolution scanning electron microscopy (SEM) and μmCT，combining with the image processing technique to analyze the quantitative characterization of pore structure variation before and after the adsorption, and to obtain the methane effect on pore structure of coal; Through the experimental analysis of opening- closing pore evolution in supercritical water, the impact of supercritical water on pore structures can be obtained; through experimental analysis of the Physicochemical reaction of gassy coals with different pore structures in supercritical water, the impact of pore structures on supercritical water diffusion can be obtained. Then, the interaction effect of diffusion of supercritical water and opening- closing pore variation can be obtained. Based on the theory of gasification dynamics, diffusion dynamics and pyrolysis kinetics, the mathematical model for describing the feedback mechanisms between diffusion of supercritical water and the pore structure evolution can be obtained, and this can provide theoretical basis for the underground coal gasification and liquefaction technology and the In situ Safety mining technology.

超临界水 (T≥374℃、P≥22.05MPa)可使煤无需干燥，即可在较低温度、较短时间内得到高效气液转化，从而受到广泛关注。超临界水对含瓦斯煤开闭孔结构有改造作用，孔隙结构的改变亦会影响超临界水在其中的反应扩散。为研究超临界水-含瓦斯煤开闭孔互反馈作用机制，本项目采用高分辨率扫描电镜、微米级CT扫描结合图像处理技术，研究煤吸附瓦斯前后定量化孔隙结构的变化特征，获得瓦斯对煤开闭孔结构的影响；通过超临界水-含瓦斯煤互反馈作用实验，研究反应过程中煤开闭孔结构的演化规律；分析不同变质程度煤定量化开闭孔结构演化特征，获得煤开闭孔结构对超临界水-含瓦斯煤气液转化反应的影响；采用气化动力学、扩散动力学及热解动力学等相关理论，得到描述超临界水-含瓦斯煤气液转化过程中反应扩散和孔隙结构演化的数学模型，揭示超临界水-含瓦斯煤开闭孔结构互反馈作用机制，为推进和发展煤炭地下气液化和原位安全开采提供理论基础。

煤炭原位气液化开采技术指以O2、CO2及水蒸气等为反应介质，以地下煤为原料生产CH4、H2等气体燃料及烯烃等气液化工原料，从而实现煤的安全、高效、清洁、综合利用的关键技术。以超临界水（T≥374℃、P≥22.05MPa）为反应介质，可使高水分含量煤无需干燥，即可在较低温度、较短时间内进行高效气液转化，从而受到国内外学者的广泛关注。由于煤是多孔介质，其孔隙是超临界水及中间或最终气化产物CH4、CO2等介质吸附运移的主要通道，故定量表述含瓦斯煤孔隙结构特征，对研究超临界水在煤炭地下原位气液化开采中的运移机理具有重要作用。为此，本项目对现有实验装置进行改造升级，通过理论分析与实验研究将煤的孔长与孔形相结合，实现了煤孔隙结构的定量化；通过测定不同粒径煤样的孔隙结构特征，获得了煤闭孔打开及开孔闭合的定量化结果。在此基础上开展了不同粒径煤吸附/解吸性能测试试验，并分析了煤的开闭孔结构对瓦斯吸附解吸性能的影响。利用自主研发的超临界水-瓦斯-煤相互作用实验装置，开展了给定温度、压力、反应时间、催化剂等条件下超临界水对瓦斯、煤单独作用时的转化实验，获得超临界水-瓦斯反应过程中气体成分、超临界水-煤反应过程中煤开闭孔孔隙结构特征。研究结果表明煤的孔隙结构与变质程度及破碎程度有关，且在破碎过程中，除微米级粒径煤样外，煤的比表面积及孔容整体呈增大趋势，比表面积的增量由微孔及过渡孔主导，而其孔容则由中大孔主导，且闭孔孔容为开孔孔容的数倍至数十倍，闭孔的打开有助于瓦斯在煤体内的吸附/解吸，在超临界水-煤反应过程中也存在大量闭孔打开情况，从而影响其化学反应动力学特性。研究结果对推进煤炭地下气液化和原位安全开采及煤炭资源的清洁化利用具有重要意义。