Oxidation And Heat Transfer Characteristics Of Fractured Coal Under Thermal-stress In Coal-fire Fields

China's coal resources are very rich,and the distribution is extremely unbalanced.Most of them are distributed in the Northeast,Northwest and North China.These areas are drought and less rain,and the coal seams are shallow.Because of the long-term contact with oxygen,the phenomenon of coal spontaneous combustion sometimes occurs.With the continuous expansion of the burning area,it will eventually cause a large area of coal-fire fields.The disaster caused by the coal-fire fields is very serious,which seriously threatens China's environment and energy security.In view of the fact that domestic and foreign researchers have little research on the combustion characteristics of fractured coal under thermal-stress,and aiming at the deficiencies of the existing experimental devices to test coal spontaneous combustion characteristic parameters under axial compression,the testing platform to test coal spontaneous combustion characteristic parameters(TP)was built,The oxidative heating and heat transfer characteristics of fractured coal under the thermal-stress in coal-fire fields were analyzed.In this paper,the long flame coal sample in Xinjiang Liuhuanggou mine was used to measure the parameters of the spontaneous combustion characteristics for coal.The coal newly collected was crushed and the particle size was respectively 0.6-2mm,2-6mm and 6-10mm,the coal was tested respectively under the air flow rate of 1200ml/min,1500ml/min and the flow of nitrogen(1200ml/min).The oxidative heating characteristics of different size coal at load were analyzed and studied.The influence of axial compression on coal spontaneous combustion characteristics under different air flow conditions was investigated.The effect of axial compressios on the heat transfer characteristics of the coal under nitrogen and oxygen was studied.The results shows that:the influence of axial compression on the oxidation heating characteristics of coal with different particle size and different air flow conditions(The particle size of coal is same)is different.When the gas flow rate is 1200 ml/min and the experimental coal sample particle size is 0.6-2mm,the applied axial compression reduces the self oxidation capacity of coal,reduces the heat generation rate of coal,and weakens the spontaneous combustion tendency of coal.When the particle size of coal is 2-6mm,when the axial compression is 2~8MPa,the self oxidation ability is reduced.When the axial compression is 2MPa,6MPa and 8MPa,the heat generation rate of coal is increased,and the axial compression is 2~4MPa,the coal has an increased tendency to spontaneous combustion.When the particle size of the coal sample is 6-10mm,in addition to 4MPa,the axial compression is applied,which increases the self oxidation ability of the coal.When the axial compression is 4MPa and 8MPa,the spontaneous combustion tendency of the coal increases.When the gas flow rate is 1500ml/min(The particle size of coal is 2-6mm),when the axial compression is 2MPa and 6MPa,the self oxidation ability is enhanced,and the axial compression is applied,the heat generation rate is lowered,and the spontaneous combustion tendency is increased.Under the condition of nitrogen gas(1200ml/min),the thermal conductivity of the coal increases firstly,then decreases,and then increases,decreases finally with the increase of temperature,when the axial compression is applied,the average thermal conductivity of the coal decreases.Under the condition of oxygen(1200ml/min),the thermal conductivity of the coal fluctuates with temperature:the thermal conductivity of the coal increases firstly,stable in the range of 50-120 ~0C,then it rises sharply with increasing temperature,at 230~250 ~0C(300 ~0C at 6MPa),it will drop slowly after reaching the extreme value.As the axial compression increases,the average thermal conductivity does not increase or decrease steadily.