煤炭地下气化热-力耦合作用下条带开采数值模拟研究

Numerical simulation of strip mining under thermal-mechanical coupling of underground coal gasification

煤炭地下气化条带开采适应强,且有助于围岩稳定控制,应用前景良好。为研究地下气化热-力耦合作用下条带开采过程中燃空区围岩的温度场、应力场和位移场的演化规律,采用COMSOL Multiphysics对贵州盘江山脚树矿4号煤层地下气化条带开采进行了数值模拟,并对气化开采和常规开采后的围岩应力和变形特征进行了对比分析。结果表明:随着气化工作面推进,围岩体内部约2 m区域的温度先升高后降低,温度传导范围一直呈扩大趋势,最大影响范围为10~12 m,温度在顶板中的传导范围最大,两侧煤体次之,底板最小。地下气化高温会在燃空区围岩体中产生热应力,导致地下气化条带煤柱所受垂直应力要明显高于常规开采的,并使燃空区悬露面、煤柱与顶底板交界面均承受水平压应力。燃空区邻近区域的顶底板位移趋势与常规的相同,但顶底板深部的位移则出现相反情况,即顶板上移、底板下沉。燃空区围岩的水平位移量明显大于常规条带开采的,且开采区域的左侧围岩体向左水平移动,右侧围岩体向右水平移动。地下气化条带开采过程中直接顶变形的波动幅度明显大于常规开采的,并在有煤体支撑的区域出现上移现象,其模型顶部岩层出现了整体上移现象,且其变形量大于常规开采的,说明地下气化过程中形成的热应力能一定程度上阻止覆岩的下沉变形。数值模拟结果可为地下气化条带开采的工程设计提供理论指导。

Underground coal gasification(UCG) combined with the strip mining method has strong adaptability and is helpful to the stability control of surrounding rock, with a good application prospect. In order to study the evolution law of temperature field, stress field and displacement field of surrounding rock of the cavity during strip mining with thermo-mechanical coupling effects of UCG,COMSOL multiphysics was adopted to simulate the UCG combined with strip mining of No.4 coal seam in Shanjiaoshu Mine, Panjiang, Guizhou Province. The stress and deformation characteristics of the surrounding rock after gasification and conventional mining were compared and analyzed. The results show that, along with the UCG working face being advanced, the temperature in the area about two m inside the surrounding rock first increases and then decreases, and the temperature conduction range has been expanding, with the maximum influence range of 10-12 m. The conduction range of temperature in the roof is the largest, followed by the coal on both sides, and the smallest at the floor. The high temperature of UCG will produce thermal stress in the surrounding rock of cavity, which makes the vertical stress of strip pillars of UCG obviously higher than that of conventional mining, and makes the overhanging surface of the cavity and the interface between the pillar and roof and floor bear horizontal compressive stress. The displacement trend of the roof and floor near the cavity is the same as that of the conventional method, but the displacement of the deep part of the roof and floor is opposite, that is, the roof moves up and the floor sinks. The horizontal displacement of the surrounding rock of the UCG cavity is obviously larger than that of the conventional strip mining, and the left surrounding rock in the mining area moves horizontally to the left and the right part moves horizontally to the right. The fluctuation amplitude of the immediate roof deformation during the UCG strip mining process is obviously larger than that of the conventional mining, and it moves up in the area with coal support, and the top of the model moves upward as a whole, and its deformation is greater than that of the conventional mining, which indicates that the thermal stress formed in the UCG process can prevent the subsidence and deformation of overburden rock to a certain extent. The results of numerical simulation can provide theoretical guidance for the engineering design of the UCG strip mining.