Experimental Study On Smoldering Process Of Coal Packed Bed Based On Spatial Features Of Actual Underground Coal Fires

Underground coal fires not only waste coal resources,pollute the atmospheric environment,but also threaten the health of nearby residents.The main mode of transmission of underground coal fires is smoldering.Therefore,understanding and mastering the basic characteristics of the smoldering of underground coal fires has certain significance for the prevention and control of coal fires.In this paper,an experimental scale reaction tank for smoldering of coal particle packed bed is designed and built based on the spatial features of three actual underground coal fires.The effects of sidewall ventilation and ignition position on coal smoldering process were mainly studied.The results of the ignition process show that the coarse coal sample(0.5-1 mm)cannot be ignited successfully,while the fine coal sample(0-0.5 mm)can carry out selfsustaining propagation of smoldering after ceasefire.The results of repeatability test show that the formation of surface cracks in the ignition process is random,which leads to the unrepeatable ignition stage,while the repeatability of the smoldering selfsustaining stage is better.The experimental results show that when there is no air passing through the side wall,the smoldering process exhibits an approximate "layerby-layer" propagation mode.During smoldering,the peak temperatures of shallow and middle coal samples far away from the boundary and heating rod are stable at about590℃ and 540℃ respectively,and propagate at an approximately uniform speed.The deep coal sample is in the condition of extreme oxygen deficiency,and its temperature rise mainly depends on the thermal conductivity of the upper layer.When air enters the coal seam through the side wall,the smoldering intensity at the boundary of the side wall increases significantly,and its influence on each layer increases with the increase of the distance from the coal seam surface.At the same time,it also changes the propagation direction of the coal fire in the middle layer.The influence of the ignition position on the smoldering process of the coal packed bed is as follows: Comparing right-side ignition and intermediate ignition,when smoldering propagation occurs in the shallow layers of the coal packed bed,the mass loss rate during intermediate ignition is about twice that of right-side ignition.While propagating to the middle and deep layers,the mass loss velocity is similar to that when air enters the coal seam through the side wall,and is about twice as fast as that when there is no air passing through the side wall.