Research On Determination Of Coal Spontaneous Combustion Danger Zone In Regenerated Roof And Grouting Prevention

Spontaneous combustion of coal caused by air leakage from regenerated roof cracks is one of the main disasters in the process of coal seam remining and layered mining.In this paper,considering the inhomogeneous distribution of porosity in the fracture space of the regenerated roof,the mathematical model of coal spontaneous combustion is established.FLUENT is used to numerically solve the problem,and the flow field distribution law in the crack space of the regenerated roof is obtained.Based on the criteria for the three-zone coal spontaneous combustion division,combined with the structural characteristics of the regenerated roof,a judgment method suitable for the danger zone of coal spontaneous combustion of regenerated roof is proposed.According to the distribution characteristics of the spontaneous combustion danger zone of the regenerated roof,a micro-particle stabilized foam slurry was prepared from the perspective of material modification for the prevention of spontaneous combustion of regenerated roof coal.Based on the rheological properties of the micro-particle stabilized foam slurry,a numerical model for grouting in the limited crack space of the regenerated roof was established,and the diffusion law and pressure field distribution law of the micro-particle stabilized foam slurry grouting process were explored.Based on the numerical simulation results of grouting,considering the shunt effect of the crack network and the accumulation effect of the limited crack space,a simplified three-dimensional mathematical model of the grouting diffusion in the crack network space was established,in order to provide a certain theoretical basis for the construction design of the grouting and fire prevention of the regenerated roof.The main research results of this article are as follows:(1)The porosity of the overlying coal rock in the regenerated roof is distributed in a shovel shape,and the flow field is highly heterogeneous in the vertical direction;(2)According to the projection superposition method based on traditional indicators,it is concluded that the coal spontaneous combustion danger area is distributed in a triangle shape in the inner area of the intake and return air lane,and the area of the dangerous area at the return air lane is larger than that of the intake air lane;(3)The cell diameter of the microparticle-stabilized foam slurry is between 350 and 400 microns,indicating that the microparticle-stabilized foam slurry can better penetrate into the micro-cracks,reducing the filtration phenomenon during the flow of the cracks;(4)The diffusion process of micro-particle-stabilized foam slurry in a finite crack network space is divided into three stages.The diffusion front of the slurry in different stages changes from an initial semi-circular arc to a plane.At the same time,with the increase of the diffusion range,the pressure decays nonlinearly.The greater the inclination of the fracture,the greater the pressure decay;(5)The mathematical model of grouting slurry flow in the crack space of the regenerated roof is derived,and the factors affecting the diffusion distance of the micro-particle stable foam slurry are construction factors(grouting flow rate,grouting pressure,grouting hole radius),slurry factors(viscosity,Yield stress,density)and fracture factors(fracture occurrence,fracture density,fracture opening).