Mechanism Of Harmful Gas Accumulation Near Fully Mechanized Mining Face And The Associated Safety Monitoring Techniques

Coal mine accidents occur frequently,many of which caused by harmful and toxic gases.In order to better understand the flow behavior of gas near the mechanized mining face,an "U" type working face was selected in the current study.By developing the geometric model and the associated governing equations,the wind flow and gas accumulation were studied by using numerical simulation method.The results for characterizing the wind flow pattern and the harmful gas diffusion and accumulation near working face were compared with the observations in actual mining sites.The reasons for the harmful and toxic gas accumulation near the working face were then explored in depth.In order to curb gas accidents,a new monitoring technique for the flow-system in an underground coal mine was also developed.The established understanding provides important guidance for the monitoring and control of the harmful and toxic gases near the working face in an underground coal mine.By using a steady flow model,the characteristics of wind near working face were studied.It has shown that airflow leaks into the goaf from the intake corner,and then returns to working surface from the return corner.Under the situation of the working surface without mining equipment,vortex just appears in the intake corner and return corner.The existence of equipment will cause the increase in wind speed near the corners;meanwhile,both windward and leeward sides of the equipment form vortex.It was also observed that the intensity of vortex weaken at an elevated height.All these results were in consistency with the observations at the actual mining sites.The model results also explained the reasons for higher concentration of gases in some particular locations.The distribution and accumulation of gases represented by CH4 and CO were traced at the underground mining site under normal ventilation.CH4 and CO sourced from the goaf and the mining seams enter in the mainstream by following the airflow and then accumulate in the return corner,with their concentrations gradually growing and eventually reaching the steady values.The process of gases accumulation near the equipment is similar to that observed in the return corner,but the accumulation process is even faster.Mainly influenced by the floating effect,the gases concentrations are lower at the windward side of the equipment.The process of gases accumulation at the leeward side is mainly influenced by the vortex,and the harmful gases accumulate in the upper part of the leeward side in principal.Under normal ventilation condition,CH4 concentration may reach the explosion limit and CO concentration can also reach the level of doing harm to human’s health in some particular locations.The study on the toxic gases accumulation in mechanized mining face not only can help locate the potential hazardous areas,but also provides guidance for ventilation and gases monitoring for coal mining.Because of the shortage of mine environmental monitoring technology,we propose a new method for monitoring the toxic gases in the flow-system in coal mine.The way of information display was introduced to help workers to identify the surrounding safety in real time,with the constant detection of the safety in the working environment including the areas near the mechanical equipment in motion.When danger occurs,alarm mode can start automatically according to the actual situation of the scene.Not only CH4 but also all common toxic gases existing in underground coal mine are required to be monitored.Combined with the self-developed portable gases monitoring device,specific implementation steps are given.The device invented has a broad application in the field of environmental safety monitoring in flowing environment including underground coal mines.