Study On The “Respiration Effect” Mechanism Of Gas Flow In Deep Coal Seam

The law of gas permeability gets more complicated due to the geological structure changes in coal with the increase of the depth,has become an important factor in coal mine safety production as gas got accumulated over a certain degree,which is easily happen when discontinuous mine ventilation happens caused by the complexity of the ventilation system,the diversity of ventilation resistance,the mine main fan switchover in deep mine.This paper,based on the discontinuous mine ventilation in deep coal seam,studied the “respiration effect” of gas flow in the coal face during the process of starting and stopping with different velocity and the influence of gas concentration distribution of that in the flow field of coal mining face and goaf.At the same time,the corresponding technical solutions were put forward to enable the continuous ventilation technology come into practical application in deep mine.Firstly,the causes of discontinuous ventilation in deep mine were analyzed and the three types of factors of mine ventilation are summarized systematically as seven factors.Then,the flow process of the “respiration effect”,taking the main fan for example,is analyzed under the condition of discontinuous ventilation.The “respiration effect” of gas-air mixed flow was build in the condition of the “respiration effect”,which was perfected by the pore and fracture model of coal.After this,the mixed flow governing equation of gas air two component gas is deduced,and the dynamic variation of coal matrix and coal fracture in coal matrix is described mathematically,and the concept of “respiration effect” of gas flow in deep coal seam is expounded.Secondly,this paper had laboratory analysis on the basic parameters and pore structure of the permeability of coal samples in deep coal seam,5 kinds of coal mining areas in Anhui coal field and Jinzhong coal field,Shanxi coal mine,are analyzed in this paper,using the coupling instrument to measure the stress and permeability of coal and rock in Safety Engineering School of China University of Mining and Technology,simulated and analysed the variation of permeability of coal structure under different stress conditions and obtained the mathematical relationship between axial strain and permeability by mathematical fitting method in the unloading process of coal samples with different initial confining pressures.The experimental analysis of the gas flow in the deep coal seam is carried out,too.In addition,the numerical simulation and experiment were carried out to simulate the gas flow in the coal mining area under the “respiration effect”.Taking the 1109 working face of Wan Feng coal mine in Shanxi as an engineering background,a numerical model was established.The "respiration effect" discontinuous ventilation conditions were set to unsteady entrance conditions according to the measured data and mathematical fitting,and using the method of characteristic line selection outside and inside the coal wall,to realize the numerical experiment analysis of gas air mixture flow “respiration effect” of the deep coal mining face in different ventilation velocity.In the process of numerical calculation,linear derivation of the N-S equation of fluid motion was used to simplify calculation of the partial differential equations,using the open source software developed a finite volume solver based on the newly derived fluid motion equation,improved the efficiency of the numerical simulation and optimized the algorithm for numerical calculation of gas seepage in porous media.Finally,this paper analyzes the distribution characteristics of gas concentration in the flow field,and puts forward the technical solution.The distribution of gas in goaf and upper corner angle were analysed by using numerical simulation,obtained the characteristics of gas concentration in the flow field under the condition of discontinuous ventilation “respiration effect”,summarized the underground gas accumulation and overrun flow field under the condition of deep coal seam intermittent ventilation.At the same time,the continuous ventilation technology based on “prevention of local coal mine gas short overrun and mine uninterrupted ventilation” were put forward and used in to Shanxi Jinhui Wan Feng coal mine 1109 coal face and that was verified its security and reliability through downhole measurement analysis.