Research On Concealed Fire Dectection Of Coal Seam In NaLinMiao Mine Based On Magnetic Property Of Coal And Rock

The distribution and development status of underground coal fires are variable,and the detection of hidden coal fires is a world problem.Magnetic detection technology is an important method for detecting hidden fire sources in coal seams.However,the mechanism of magnetic detection of hidden fire sources is not well understood,which leads to deviations and errors in the interpretation of magnetic detection results.In this paper,the magnetic changes of NLM3-1 coal,coal roof sandstone samples and interlayer gangue were measured.The effects of temperature,particle size and magnetic field strength on the magnetic susceptibility were studied,and the high temperature using TG-DSC experiment and X-ray diffraction experiment The mechanism of coal and rock magnetic change before and after baking is studied in depth.The results show:At normal temperature,At normal temperature,NLM coal exhibits weak diamagnetism,and the top and bottom sandstones and gangues are paramagnetic;the mass susceptibility of the gangue and sandstone samples decreases with increasing particle size,and decreases significantly with increasing magnetic field strength;coal The mass susceptibility of the coal is in the particle size range of 3.0?5.0 mm,and decreases with the increase of the particle size,and it rebounds when the particle size exceeds 5.0 mm;the coal mass susceptibility is less affected by the magnetic field strength.After baking at high temperature,the burnt rock whose temperature drops to normal temperature,whether it is sandstone,gangue or coal,its mass susceptibility as a whole increases significantly with the increase of baking temperature.The mass susceptibility of coal began to increase sharply at 200?,while the susceptibility of sandstone and coal gangue began to increase rapidly at 300 ? and 400?,respectively.The smaller the particle size,the more easily the magnetic susceptibility of coal rock is affected by high temperature.Compared with normal temperature samples,the mass susceptibility of burnt coal samples is more susceptible to the influence of external magnetic induction,and the susceptibility of coal samples generally decreases with the increase of external magnetic induction.In a high-temperature environment,the mass susceptibility of the heated coal is around 350?,and the susceptibility decreases rapidly after the peak;the susceptibility of the heated rock follows Curie's law before 350?,reaching a peak around 550?,when the temperature exceeds 575?(Curie temperature),the magnetic susceptibility returns to the original condition.The magnetic susceptibility of the temperature-reduced rock shows a greater peak around 440?.When the temperature of the rock sample drops to normal temperature,its magnetic value is still dozens of times that of the original sample.The coal rock is more magnetic after baking at high temperature,mainly because the coal rock sample produces a stronger magnetic ferromagnetic substance as the temperature rises.The magnetic properties of coal rock samples obtained during cooling after heating are stronger than those obtained during the heating process.Based on the study of coal and rock magnetic properties in the fire area and the actual situation of the fire area,the magnetic detection work was carried out in the Nalinmiao fire area in Inner Mongolia,and three coal fire influence areas were delineated in the measurement area,and the delineation results are consistent with the site survey results.Consistent,further confirmed the reliability of the magnetic detection technology,and also improved the magnetic detection theory and field application technology.