| Daxing mine is located in the southwestern of Tiefa coalfield,where the igneous intrusions are extremely serious.The coal seams affected by igneous intrusions suffer serious risks of spontaneous combustion,restricting the safe exploitation and utilization of coals.Now,there are few literatures about the effects of igneous intrusions on spontaneous combustion characteristics of coal.Moreover,the existing theory about the relationship between igneous intrusions and coal spontaneous combustion still can not guarantee the safe and efficient production of coal seams.Hence,a study on the characteristics and prevention technologies of spontaneous combustion of coal under the condition of igneous intrusions is needed to be carried out urgently.The changes of physical and chemical structure of coal can directly affect the spontaneous combustion characteristics of coal.In this paper,a series of ana lysis technology were employed to investigate the influence of igneous intrusions on the structures of coal,including the coal quality,mineral composition,surface active functional groups,surface morphology,and pore structure of normal coals and thermally-altered coals.The results showed that igneous intrusions has obviously changed the composition of coal and improved the metamorphic degree of thermally-altered coals,which resulted in the decreased amount of functional groups and the content of oxygen-containing functional groups on the surface of thermally-altered coals.Moreover,due to the thermodynamic metamorphism of igneous intrusions,a large number of pyrolysis pores formed in the thermally-altered coals,which increased the average pore diameter and pore volume.Igneous intrusions significantly promoted the development of pores in the thermally-altered coals,especially the pores with the diameter>20 nm,which was more conducive to the diffusion of oxygen in coals and the reaction between oxygen and active groups.The oxidation kinetics exiperiments indicated that the thermally-altered coals showed higher oxygen consumption rate and lower crossing point temperature than normal coals.Moreover,the spontaneous combustion propensity index I of the thermally-altered coals was lower than that of the normal coals,which represented the higher incidence of spontaneous combustion for the thermally-altered coals.Compared with the normal coals,the thermally-altered coals shows higher ignition and burnout temperature,and lower comprehensive combustion parameter S,which indicated that the thermally-altered coals were difficult to ignite and exhibited worse combustion performance.The increase in the spontaneous combustion propensity for the thermally-altered coals was due to their higher porosity,larger pore volume,and average pore diameter,and the increasing pores?>20 nm?would improve the transport capacity of O2 in pores and increase the accessibility of O2 to the active sites on the pore surface,which promoted the spontaneous combustion of coal.The worse combustion performance for the thermally-altered coals was due to the reduction of volatiles and active functional groups affected by igneous intrusions.Numerical simulation about the air leakage and methane concentration of S2905 coalface was conducted using fluent software.The results show that the reasonable air volume should be selected according to the variation of oxidation zone and methane distribution in the goaf.The gas extraction of high-level entry for gas extraction and high drilling field can effectively reduce the methane content in the goaf,which is beneficial to alleviate the accumulation of gas in the top corner,but expanding the oxidation zone.Blocking the inlet and return airway of the goaf can effectively reduce the oxidation zone,which is conducive to preventing the coal fire in the goaf.Injecting the N2 to the goaf is beneficial to reduce the air leakage,dilute oxygen,and gas.The simulation results can be used as a reference to optimize air volume and gas extraction,which is also helpful to prevent spontaneous combustion of coal.The novel high water-retention foam with long-time stability and film forming characteristics was prepared to overcome the shortcomings of existing sandblasting and injection foam technology,such as poor water retention,water loss and so on.Moreover,combined with the existing technology in Daxing Mine,the comprehensive prevention and control technology of plugging-covering-cooling was proposed and applied in the S2905 coalface to prevent spontaneous combustion.The technology has controlled the hidden dangers in goaf and ensured the safety during coal mining,which provided a reference for other coalfaces in Daxing Mine. |
PDF Full Text Request