Numerical Simulation Of The Effect Of Magmatic Heat Effect On The Degree Of Metamorphism Of Low Rank Coal In Daxing Coal Mine

The Daxing Minefield in the Tiefa Mining Area was invaded by severe magma.This is the main research background.Through the interdisciplinary research methods of minefield geological structure,coal geochemistry,coal petrography,etc.,the regional thermal evolution of magmatic intrusion into water-bearing coal seams is studied.On this basis,theoretical analysis,numerical simulation and laboratory physical property parameters were used to further study the effects of magmatic rock intrusion on coal characteristics and metamorphism of water-bearing coal seams.The conclusions are as follows:1)The magmatic movement in the Tiefa mining area is intrusion and eruption.The high-temperature magma has an effect on the coal metamorphism and the coal-sedimentary structure.There are abundant coal types in the mine field,including long-flame coal,gas coal,non-stick coal,weakly coal,lean coal and natural coke.Non-stick coal and natural coke are concentrated in the magma intrusion area.coal seams in the mine field are high water content and high volatile.The moisture content is 3.70% on average and the volatile content is generally 37%.2)In the process of establishing the heat transfer model,the main influencing factors of coal seam temperature change are: initial magma temperature,thickness,length,thermal conductivity of coal,cooling time and distance from magma.The difference in water content will result in different thermal conductivity of coal,affecting the highest temperature that the coal seam can reach.3)The thermal conductivity of coal is closely related to the water content.As the water content increases,the thermal conductivity of coal also increases.However,there is no simple linear relationship between them.Through the formula 3-18,the thermal conductivity of coal under different water content conditions can be obtained by the thermal conductivity of coal in the dry state.The calculation shows that the thermal conductivity of the coal is 0.291,0.358,0.887,2.024 at 3%,8%,30%,and 50%.4)The simulation of the magma cooling process was carried out using COMSOL software.It was found that the maximum temperature reached by the underlying coal seam decreased significantly with the increase of water content.When there is no water,the maximum temperature reached by the coal seam is about 120 °C.When the moisture content of the coal seam is 3%,the highest temperature reached by the coal seam is 113 °C.When the moisture content of the coal seam is 8%,the highest temperature reached by the coal seam is 94 °C.When the moisture content of the coal seam is 30 %,the maximum temperature reached by the coal seam is about 75 °C.When the moisture content of the coal seam is 50%,the maximum temperature reached by the coal seam is only 35 °C.5)Combined with the coal seam evolution diagram of Daxing Minefield,it is found that the maximum effective temperature of coal contact metamorphism is 100 a,200a,500 a when the water content is 3%,8% and 30%.It can be seen that If the coal seam moisture content is high,the rapid evolution period of the coal seam subjected to thermal action becomes longer,and the thermal effect is weaker.