If increasing drawing interval , the movement and flow range of top coal will enlarge , and the velocity gradient on flow cross - section will diminish , so that it is good for controlling the flow rate of thin sand among loose top coal 研究表明,加大放煤步距,顶煤运移流动的范围变大,流动断面内速度梯度变小,有利于控制细砂的下窜速度。