Experimental Study On Oxidation Spontaneous Combustion Characteristics Of Mining Unloading Coal

With the exhaustion of the shallow coal resources in China,deep mining has become an inevitable trend.The same depth of deep in different stress relative concentration areas and different depth of coal seam,the stress state of coal deposit is significant difference,has accumulated a large number of elastic deformation potential,the effect of loading or unloading or repeated loading and unloading during the mining process,the elastic deformation potential of coal storage can be released,the fracture of coal body hole will be grow,developed,deformation and through,coupled with the effect of deep mining face mining cracks air leakage and goaf air leakage,the oxygen absorption characteristics and heat storage environment of coal will change significantly,thereby increasing the risk of coal spontaneous combustion.To study the variation of oxidation characteristics of unloading coal,It firstly analyzed the relationship between the spontaneous combustion characteristics and the microscopic active structure of unloaded coal under different initial stress,repeated loading and different air leakage condition,meanwhile,the micropore fracture structure of unloading coal under different conditions is studied,revealing the inherent relationship between the oxidation spontaneous combustion characteristics of deep unloading coal and the variation of micropore fracture.It is significance for prevention and control of spontaneous combustion in deep mining seam.With Temperature-programmed oxidation and FTIR infrared experiments,the paper analyzed the variation of gas products and microscopic active groups with initial load,air leakage rate and repeated loading and unloading during deep unloading of coal oxidation,it is concluded that the oxidation spontaneous combustion tendency of the raw coal in Wang Tai mine increases first and then decreases with the increase of initial load and air leakage rate.We established the degree of oxidation of coal with coal seam occurrence stress environment and the strength of coal,this is:s₀?28?ks_st.We obtain that a critical threshold about the degree of oxidation coal withstress and coal strength,when0<k?1.136,with the increase of buried depth,ground stress increases,the degree of coal oxidation rising after mining;when k>1.136,after stress reaches a certain degree,the increasing of stress,the coal oxidation reduced after mining.Determined the best initial stress P=25MPa and the equivalent flow Q=150mL/min to promote the oxidation of the coal body.Under the above optimal conditions,the oxidation characteristic of coal is gradually increased with the time of loading and unloading,and the increment of coal oxidation characteristic parameters in adjacent working conditions gradually decreases.The loading and unloading of different stress conditions changed the contact ability of coal sample and oxygen,indirectly influenced the oxidation process of coal sample.With the oxidation process in-depth,the hydroxyl content is gradually less and the strength of aromatic nucleus polycondensation is enhanced,fatty hydrocarbons are attacked by oxygen,and a large number of acids,esters,and ethers are produced by the fracture of the side chain,the content of fatty hydrocarbons is gradually less,and the oxygen functional group decreases first and then increases.By using Atomic forcemicroscope,Porosimetry and Nitrogen adsorption experiment,the paper studied microscopic pore structure characteristics of the pore volume,the proportion of pore volume in each pore section and specific surface area in different conditions,analysised the intrinsic relationship between the oxidation characteristics of coal and microscopic pore cracks.It is indication that:the initial load increases the pore volume and pore size of the coal,micropores and pinholes are major contributors to O₂ oxidation zone with coal matrix.In the process of repeated loading and unloading,micropores and small pores increase,and the mesopores and larger pores collapse or crack and become cracked.In the repeated loading and unloading process,the existence of the best unloading times??3times?and the best BJH surface area??27.002 m²/g?makes the coal oxidation spontaneous combustion is the strongest.