深部地下大尺寸煤颗粒水力输运数值模拟

Numerical simulation of hydraulic transport of large size coal particles in deep underground

我国深部地下煤炭资源储量丰富且质量优良,具有巨大的商业开采价值,但需基于流体力学-离散元法(CFD-DEM)耦合方法对深部地下大尺寸煤颗粒水力运输进行数值模拟以研究开采输运方案。为解决网格尺寸受颗粒尺寸限制的问题,需改进统计内核法(SKM)对颗粒体积分数的计算方法,并采用三维高斯函数作为加权内核函数以更准确地描述颗粒体积分布,同时还采用特征点剖分法来取代传统的网格循环搜索方法以提高计算精准度和效率,重点研究水力输送管道中粗颗粒密集颗粒流的流动状态以及控制参数对流动特性的影响,并结合不同条件下输运管道内固-液两相流的流体动力学特性及其在实际工程中的高效性与经济性分析,得到最佳的初始参数。结果表明:不同进口液体相速度及颗粒体积分数条件下,模拟预测的颗粒局部体积分数、颗粒运动速度、管道压降等参数与实验误差均在10%以内,平均误差约为5.1%;颗粒运输速率(Q)与进口液体相速度、进口体积分数呈现明显正相关,随着颗粒直径的增加呈现先增加后减小的规律;而管道压降随着进口液体相速度、进口体积分数和颗粒直径的增加均呈现逐渐增大的趋势;综合考虑颗粒运输速率和压降的经济性指标,随进口液体相速度、进口体积分数的增加先减小后缓慢增长,随着颗粒直径的增加先减少后明显增长;在进口液体相速度为3 m/s,进口体积分数为0.08以及颗粒直径20 mm时,经济性指标P最低,其值为1640。

China boasts abundant deep underground coal resources with excellent quality and great commercial mining value.However,due to the huge engineering cost,it is difficult to study the deep coal mining and transportation technology through experiments.It is necessary to use the numerical simulation method based on the computational fluid dynamics-discrete element method(CFD-DEM)coupling scheme to study the hydraulic transport of large coal particles in deep underground to determine the mining and transport scheme.To overcome the drawback that the mesh size is restricted by the particle size in the CFD-DEM scheme,the calculation method of particle volume fraction is improved based on the statistical kernel method(SKM)algorithm,and the three-dimensional Gaussian function is used as the weighting kernel function to describe the particle volume distribution more accurately.Additionally,the characteristic point subdivision method is adopted to replace the traditional grid loop search method in order to improve calculation accuracy and efficiency.The flow state of coarse and dense particle flow in the hydraulic transmission pipeline and the influence of control parameters on the flow characteristics are mainly investigated in this paper.The optimal initial parameters are obtained by combining the hydrodynamic characteristics of solid-liquid two-phase flow in the transmission pipeline under different conditions and its efficiency and economy analysis in practical engineering.The results show that the prediction errors for local particle volume fraction,particle velocity,and pipe pressure drop at different inlet velocities and particle volume fractions are all within 10%,and the average error is about 5.1%.The particle transport rate Q is positively correlated with the inlet liquid phase velocity and inlet volume fraction,and increases first and then decreases with the increase of particle diameter.The pressure drop increases gradually with the increase of inlet liquid phase velocity,inlet volume fraction and particle diameter.Considering the economic indexes of particle transport rate and pressure drop comprehensively,with the increase of imported liquid phase velocity and imported volume fraction,it first decreases and then increases slowly,and with the increase of particle diameter,it first decreases and then increases obviously.When the inlet speed is 3 m/s,the particle diameter is 20 mm,and the inlet volume fraction is 0.08,the economic index P is at its lowest point,and its value amounts to 1640.