块度级配对散体顶煤流动特性影响的试验研究

Experimental investigation on the effect of size distribution on the flow characteristics of loose top coal

掌握破碎后散体顶煤的流动特性和放出规律是综放开采优化放煤工艺参数、提高顶煤采出率、降低含矸率的重要基础。不同块度的顶煤在松散煤块集合体中所占的比例称之为块度级配,块度级配是松散煤体流动特性的重要影响因素之一。为了研究块度级配对散体顶煤流动特性的影响,基于自主研制的放煤试验台,采用物理模拟试验和理论分析相结合的方法探究了块度级配对初始放煤量、颗粒运移轨迹以及煤岩分界面演化特征的影响。不同块度级配条件下的放煤试验结果表明,初始放煤量随顶煤平均块度的增大而增大;放出顶煤的块度级配变化显著,小块度顶煤占比高时,大块顶煤更易被放出;反之,大块顶煤因成拱频繁而放出量少;初始煤岩分界面演化过程中其最低点由放煤口中心线逐渐偏向采空区侧,且顶煤平均块度越大越显著,其运动轨迹基本符合横向抛物线形式。支架上方顶煤颗粒运动速度明显快于采空区侧顶煤颗粒;顶煤平均块度较小时,顶煤颗粒运动速度较快,成拱次数较少;顶煤通过放煤口以后,顶煤流动扩散角随顶煤平均块度的增大而增大。基于散体介质力学理论推导了支架侧和采空区侧初始煤岩分界面动态演化方程,结合放煤试验结果确定了不同顶煤块度级配条件下煤岩分界面理论方程的修正系数取值:支架侧初始煤岩分界面理论方程的修正系数k_R的取值为0.30～0. 35,采空区侧分界面理论方程的修正系数|k_L|的取值为0.25～0.28;讨论了顶煤块度级配对方程修正系数的影响规律,发现随着顶煤平均块度的增大,k_R和|k_L|的取值范围呈增大趋势。

A good understanding of flow characteristics and drawing mechanism of loose top coal is an important foundation for optimizing the drawing parameters,increasing the top coal recovery and reducing the rock mixed ratio in longwall top coal caving.The proportion of top coal in different sizes is called size distribution,and size distribution is one of important factors affecting the flow characteristics of loose top coal.In order to study the effect of size distribution on the flow characteristics of loose top coal,both physical simulation experiments and theoretical analysis were conducted based on a self-developed experimental device.The initial drawing volume,the flowing path of top coal and the evolution characteristics of initial boundary of top coal were investigated in depth.The results show that under the different size distribution of top coal,the initial drawing volume increases with the increase of average size of top coal.The size distribution of top coal draw out changes significantly,and when the proportion of small top coal is higher,the large top coal is easier to be drawn.In contrast,the large top coal is more difficult to be drawn due to the frequent formation of arch structures.The lowest point of the initial boundary of top coal is gradually moved toward the gob side other than the center line of the shield opening during the top coal drawing process.The moving path of the lowest point is basically consistent with the horizontal parabolic form,and the larger the average top coal size is,the more obvious the characteristic is.The speed of top coal particles above the caving support is obviously faster than that of top coal particles near the gob side.When the average size of top coal is small,the speed is faster and the number of arching frequency is relatively low.After the top coal passes through the shield opening,the diffusion angle of top coal flow increases with the increase of average size of top coal.The dynamic evolution equations of the initial boundary of top coal on the support side and gob side are proposed based on granular medium mechanics and the correction coefficients of the equations are determined according to the physical experimental data.The correction coefficient of the equation on the support side(k R)is in the range of 0.30-0.35 while the correction coefficient of the equation on the gob side(|k L|)is between 0.25 and 0.28.The effect of size distribution on the correction coefficients is also discussed.The value of k R and|k L|increases with the increase of average size of top coal.