Research On Air Infiltration For Oxygen Supply And Spontaneous Combustion Hazard Assessment In Dry And Windy Mining Coal Gangue Hills

Spontaneous combustion coal gangue hills in China are mainly distributed in dry and windy mining areas in the middle and upper reaches of the Yellow River.Spontaneous combustion not only leads to the loss of coal gangue resources and accidents,but also poses a serious threat to the surrounding environment and human health.Therefore,it is particularly important to accurately and effectively prevent the problem of spontaneous combustion of coal gangue piles.In response to the above situation,this paper takes the self ignition coal gangue hills in the dry and windy Wuhai and Shendong mining areas as the research background,and uses theoretical analysis,on-site measurement,indoor experiments,and numerical simulation methods to study the air infiltration oxidation law and self ignition risk zone determination of coal gangue hills in the dry and windy mining area.The research results can provide theoretical basis and practical reference for the safety prevention and control of coal gangue hills in the dry and windy mining area.The main research conclusions are as follows:(1)The phase composition and microstructure of coal gangue in dry and windy mining areas were clarified.Based on thermodynamic parameters,its characteristics of high ash content,low moisture content,low carbon content,and low tendency to spontaneous combustion were obtained;Based on the thermogravimetric experiment,the temperature determination conditions for the spontaneous combustion danger zone of coal gangue hills were determined;A fitting formula between oxygen consumption rate,temperature,and oxygen concentration was established through the oxidation and heating experiment of coal gangue,providing a theoretical basis for numerical simulation of coal gangue spontaneous combustion.(2)Based on the conclusion of characterizing the structure of coal gangue,a simplified model of coal gangue structure was established;By using molecular dynamics and grand canonical Monte Carlo simulation,the effects of temperature and pressure environment,coal gangue pore size,water content,and gas composition on the adsorption diffusion effect of oxygen on the surface of coal gangue were analyzed;The four stage characteristics of the internal seepage process of coal gangue cracks with increasing pressure were revealed,and the trend of maximum displacement deformation,stress distribution,and maximum flow velocity with increasing pressure was obtained.The influence of the seepage channel structure,gas diffusion rate,and oxygen consumption rate of coal gangue cracks on the internal oxygen diffusion was clarified.(3)Through on-site measurement and indoor screening,it has been determined that the inclined slope surface of the coal gangue mountain is mainly composed of coarse gangue particles.The relative height of the slope surface increases,and the fractal dimension and non-uniformity coefficient both increase accordingly,showing a change pattern from steep to gentle;Based on the theory of geotechnical mechanics,seepage theory,and permeability experiments,a calculation model for porosity and permeability under the influence of slope compression pressure of coal gangue loose bodies on the slope surface of the coal gangue mountain was established,as well as the internal seepage velocity equation on the slope surface;The internal permeability of coal gangue hills can be divided into two stages: rapid decrease and slow decrease.Based on the distribution of air infiltration,the interior of coal gangue hills can be divided into three regions: surface cooling,heat accumulation and flammability,and internal low temperature.(4)Through theoretical analysis and numerical simulation,the risk ranking of spontaneous combustion of coal gangue hill slope shapes was obtained: arc type>plane type>corner type>arch type;Under the condition of oblique airflow,the maximum and average temperatures inside the coal gangue hill decrease to varying degrees,showing a lower risk of spontaneous combustion compared to direct airflow;The evolution law of the area of coal gangue spontaneous combustion danger zone with changes in external wind speed,initial porosity,environmental temperature,and internal carbon content was obtained,and a formula for calculating the area of coal gangue spontaneous combustion danger zone was further established;Revealed the increasing patterns of the overall temperature,average wind speed,and low oxygen concentration area inside the coal gangue hill with the accumulation time;Through the dynamic simulation of the temperature field of the coal gangue heap,the specific hazard zone of spontaneous combustion in the coal gangue heap is determined to primarily exist within the overall height range of 3/10 to 9/10 along the slope surface.The outer side is at depths ranging from 1.8 m to 6.4 m from the slope surface,while the inner side extends from depths of 3.4m to 11 m.The distances exhibit a decreasing trend followed by stabilization as the height increases.The natural combustion period of coal gangue was determined to be 143 days,and a calculation formula for the minimum safe stacking speed of coal gangue hills with stacking time was established,providing theoretical support for the safety technology of gangue discharge.