热力耦合作用下气化炉顶板下沉规律与相关参数

Roof subsidence law and related parameters study of gasifier under thermodynamic coupling action

为对煤炭地下气化开采过程中顶板下沉规律及其相关参数进行定性化及定量化的研究,根据地下气化后燃空区、上覆岩层和两侧煤层的空间位置形态,建立了关键层的热力耦合固支梁模型,在对模型进行简化和模型受力进行分析计算的基础上,利用复合岩梁理论,推导出热力耦合作用下关键层岩梁中性层位置随温变化方程;利用静力平衡理论,推导出岩梁挠曲线微分方程,对其求解得到关键层挠曲线方程。对该方程的参数进行赋值,理论分析岩梁挠度随时间变化规律,定量分析中性轴位置、温度力和热抗弯刚度随时间变化规律及其对关键层下沉的影响规律。结果表明,地下气化过程中,关键层的变形是一个连续的下沉过程,与常温下岩梁的变形程度相比,其变形程度取决于岩梁弹性模量随温度变化特性,当弹性模量随温度升高而降低时,其变形程度要大于常温岩梁的变形,反之则小于常温岩梁的变形;岩梁中性轴位置主要受弹性模型随温特性的影响,当岩梁弹性模量随着温度的升高而降低时,中性轴位置先上升,而后下降,反之,先降后升,中性轴位置的上升会减小热抗弯刚度,下降则会增大热抗弯刚度;热抗弯刚度对岩梁下沉起决定性作用,热抗弯刚度增大,关键层变形程度减小,反之,则变形程度增大;温度场传播在岩梁内部引起的附加温度力呈现“增大—减小—增大”的变化趋势,但其对岩梁下沉过程的影响很小,影响程度可以忽略;影响热抗弯刚度变化规律的岩梁热物性参数是弹性模量,其随温度变化特性会对热抗弯刚度产生一个叠加的影响。利用所建立的模型对华亭地下气化项目地表沉陷进行了预测,预测值与实测值相差仅有6.2 mm,表明建立的模型能够准确的对地表下沉的最终形态进行预测。

In order to qualitatively and quantitatively study the subsidence law of seam roof and its related parameters in the process of underground coal gasification,a thermally coupled solid support beam model of key layer was estab⁃lished according to the spatial position morphology of combustion air zone,overlying rock layer and coal seam on both sides after underground gasification.On the basis of simplifying the model,and analyzing and calculating the force of the model,the equation of the temperature change of the position of the neutral layer of the critical layer rock beam under the action of thermodynamic coupling was derived by using the composite rock beam theory.Using the static equilibrium theory,the differential equation of the rock beam torsion curve was derived.After solving this equation,the equation of critical layer deflection curve was obtained.After assigning the equation's parameters,the rock beam's de⁃flection law with time was theoretically analyzed.The changes in the neutral shaft position,temperature force,and ther⁃mal bending stiffness with time and their influence on the subsidence of essential layers were quantitatively analyzed.The results show that the deformation of the critical layer is a continuous subsidence process during the under⁃ground gasification process.Compared with the deformation degree of the rock beam at room temperature,the degree of deformation depends on the elastic modulus of the rock beam with temperature.When the elastic modulus decreases with the increase of temperature,the deformation degree is greater than the deformation of the rock beam at room tem⁃perature;otherwise,it is smaller than the deformation of the rock beam at room temperature.The neutral axis position of the rock beam is mainly affected by the temperature characteristics of the elastic model.When the elastic modulus of the rock beam decreases with the increase in temperature,the neutral axis position rises first and then falls.Con⁃versely,if it falls first and then rises,the rise of the neutral shaft position will reduce the thermal bending stiffness.De⁃scending will increase the thermal bending stiffness.Thermal bending stiffness plays a decisive role in the sinking of rock beams.The thermal bending stiffness increases,the deformation degree of the critical layer decreases,and con⁃versely,the deformation degree increases.The additional temperature force caused by the temperature field propagation inside the rock beam shows a trend of“increase⁃decrease⁃increase”.However,its influence on the subsidence process of rock beams is too tiny that the degree of influence is negligible.The thermal physical property parameter of rock beams that affects the change law of thermal bending stiffness is the elastic modulus.Its temperature⁃dependent prop⁃erties have a superimposed effect on thermal flexural stiffness.The established model was used to predict the surface subsidence in the Huating underground gasification project.The difference between the predicted and measured values is only 6.2 mm,indicating that the model established in this paper can accurately predict the final shape of the surface subsidence.