煤炭地下气化多场耦合数值模拟程序开发及多场演化规律

Development of a multi-field coupled numerical simulation program for underground coal gasification and multi-field evolution laws

开发了一种多场耦合作用下煤炭地下气化的数值模拟程序和方法,基于ABAQUS软件中DFLUX、HETVAL、USDFLD三个子程序同时进行了热-力-化学-位移的多场耦合计算。以贵州省盘州市山脚树煤矿12号煤层第1气化工作面为工程背景,通过该数值模拟方法实现了煤炭地下气化初期点火装置对煤体加热的模拟;实现了注入点不断后退移动下,煤体自燃引发的化学热变化的模拟;实现了煤气化反应后空腔形成的模拟。最后分析了山脚树煤12号煤层气化反应后温度场-应力场-位移场的演化规律。结果表明,温度场演化趋势整体先增后减,随气化点的后退移动依次达到温度峰值,上覆岩层在热传导影响下温度传导范围逐渐扩大,气化120 d后,温度整体传导范围近似泪滴形状,且随着高度的增加,上覆岩层的温度变化略微延迟,温度也逐渐降低;上覆岩层在高温环境下应力重分布,气化120 d后,上覆岩层的拉应力区近似呈现为“凹”形,下伏岩层的拉应力区近似呈现为“T”形,不同高度处岩层的应力演化规律差异较大,燃空区与直接顶交界面处岩层受空腔形成的影响,应力集中现象随着气化工作面的推移逐步发生;上覆岩层整体下沉,沉降量先增再减后趋向稳定,岩层的变形程度随高度的增加而减小,同时上覆岩层在高温影响下受热膨胀产生的热应力支撑岩层上移,沉降量减少,可以推论,在大型煤炭地下气化实际项目运行中,高温环境产生的热应力可在一定程度上阻碍上覆岩层的下沉垮落。本研究以期更接近煤炭气化实际工况,研究成果为模拟煤炭地下气化提供更加实际的新方法。

A numerical simulation procedure and method for underground coal gasification under the action of multi-field coupling has been developed, and the multi-field coupled thermal-force-chemical-displacement calculations are carried out simultaneously based on three subroutines DFLUX, HETVAL and USDFLD in ABAQUS software. Taking the first gasi-fication working face of No.12 coal seam of the Shanjiaoshu coal mine in Panzhou, Guizhou Province as the engineering background, through this numerical simulation method, the simulation of heating the coal body by the ignition device at the initial stage of underground coal gasification is realized. The simulation of chemical heat change triggered by the spon-taneous combustion of coal body under the continuous backward movement of the injection point is achieved. Also, the simulation of cavity formation after the coal gasification reaction is accomplished. Finally, the evolution law of temperat-ure field-stress field-displacement field after the gasification reaction of No.12 coal seam of the Shanjiaoshu coal is ana-lyzed. The results show that the overall trend of temperature field evolution increases first and then decreases, reaching the peak temperature in turn with the backward movement of the gasification point. The temperature conduction range of the overlying rock layer gradually expands under the influence of heat conduction. After 120 days of gasification, the overall temperature conduction range is similar to the teardrop shape, and there is a slight delay in the temperature change of the overlying rock layer and a gradual decrease in temperature as the height increases. After 120 days of gasification, the tensile stress area of the overlying rock layer is approximately “concave” in shape while that of the underlying rock layer is approximately “T” in shape. The stress evolution pattern of rock layers at different heights varies greatly, whereby the rock layers at the intersection of the combustion void area and the direct top are affected by the formation of cavity, and the stress concentration phenomenon occurs gradually as the gasification working face progresses. The overlying rock lay-er sinks as a whole, with the settlement amount increasing and then decreasing before stabilizing. The deformation of the rock layer decreases with the increase of height, while the overlying rock layer is thermally expanded under the influence of high temperature, which generates thermal stress to support the upward movement of the rock layer so that the settle-ment amount decreases. It can be inferred that the thermal stress generated by the high temperature environment can hinder the sinking of the overlying rock layer to a certain extent in the actual operation of large coal underground gasification projects. The present study aims to be closer to the actual working conditions of coal gasification, and the research results provide a new method to simulate coal underground gasification more practically.