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Study On The Spontaneous Combustion Of Resutal Coal In Fully Mechanized Caving Face Goaf And Efficent Control Technology

Posted on:2014-10-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:K CaoFull Text:PDF
GTID:1261330392965075Subject:Safety Technology and Engineering
Abstract/Summary:PDF Full Text Request
Coal is the major sources of energy in our country, but the spontaneouscombustion of coal seriously threaten the mining safety. The fully mechanized cavingtechnology and gas discharge which are widely used in recent years caused moreresidual coal and air leaking in goaf. The fully mechanized caving face goaf is themain area of coal spontaneous combustion which is characterized by high goaf space,widely distributed residual coal and stereoscopic distribution of spontaneouscombustion risk area. The inadequate research related to the regularity of spontaneouscombustion in the stereoscopic goaf results in a lot of blindness in controlling it, evenleads to extraordinarily serious spontaneous combustion accidents. Regarding thespontaneous combustion environment in goaf as the starting point, this dissertationanalyzed the space characteristics of spontaneous combustion environment in the goaf,studied the spontaneous combustion oxidation characteristics of residual coal underlean oxygen conditions, revealed the regularity of spontaneous combustion of residualcoal in goaf that more consistent with the actual conditions, at the same time,proposed targeted prevention measures to improve the overall technical level of thecaving face.As a hemi-closure space, the oxidation process of coal spontaneous combustionin fully mechanized caving face goaf occurred in the oxygen-poor conditions. In orderto get characteristic parameters and oxidation law that was more in line with theactual situation of coal spontaneous combustion and so as to lay the experimentalfoundation for the systematic study the law of spontaneous combustion of coal, thepaper carried out the experimental study of the characteristic parameters of thespontaneous combustion of coal in oxygen-poor conditions. In order to ensure thereliability and accuracy of the experiment, the study for the first time used thecomputer intelligence dynamic volumetric device, to achieve high accuracy anddynamic stability preparation of the different oxygen concentration in the gas mixtureof N2-O2. On this basis, using Differential Scanning Calorimetry (C80microcalorimeter) and multivariate testing device used to test characteristics parameters ofoxidation process of coal, the paper accurately and quantitatively analyzed the oxygenconsumption, the law of heat release and the generating law of gas product underdifferent oxygen concentration conditions. Research derived that the effect degree of the oxygen-poor conditions on oxygen consumption and heat release is less thangaseous products of the coal sample, and the process of spontaneous combustionexists the slow and accelerated exothermic stages before300℃, moreover, theapparent activation energy of coal samples linearly and slowly increases with thereduction of the oxygen concentration. When analyzed from the metamorphic gradeof coal samples, it was discovered that the effect degree of the oxygen-poorconditions on oxygen consumption, heat release and gaseous products of coal that islow degree of metamorphism is more than coal that is high degree of metamorphism.Overall, the effect of the oxygen-poor conditions on coal spontaneous combustioncharacteristics in fully mechanized caving face goaf.The distribution model of fracture field in goaf and overlying strata is theair-leaking and oxygen supply channel of spontaneous combustion of residual coal,fugitive channel of flue gases and heat, and it is the important factor of the process ofcombined effects of coal and oxygen and heat storage, and determines the distributionof concentration field, flow field, as well as the temperature field, so researching thedistribution law of porosity in goaf and overlying strata is particularly important tomaster the transfer law of heat and mass in the process of spontaneous combustion.On the basis of field observations and theoretical analysis, the paper established themathematical model of the three-dimensional void field of goaf and overlying strata.The paper put forward the proportional coupling model of tendency and trend bend ofoverlying strata on the basis of flexure equation of critical layer. Trough this model,the "double hump" proportional coupling space model of the fractured field wasraised. Meanwhile, based on the sinking curved surface of basic top and the changecoefficient of porosity in goaf tendency, and considering the effect of gravity on theporosity of broken rock, the paper deduced the continuously varying surface equationof porosity in caving zone. In addition, the checking results of this model wereconsistent with field data. It provides important parameters to reveal the spontaneouscombustion law of residual coal and quantitatively simulate characteristics of thesource of fire in goaf.On the basis of the above theoretical analysis and experimental studies, fieldobservation and numerical simulation of the spontaneous combustion risk area in goafwere conducted, and the spontaneous combustion regularity in fully mechanizedcaving face goaf was obtained, i.e. there was "Stereoscopic Three Zone" exist in goaf,the area of high concentration oxygen constantly reduced with the increase of the distance to the floor. Therefore, near the face, the upper residual coal in the goaf waslikely to have higher possibility of spontaneous combustion than that of the floorresidual coal; with the gradual entering into the goaf, the spontaneous combustion riskof the floor residual coal gradually increased, the rate of the upper residual coal’sentering the choking area was accelerated, and this reduced the spontaneouscombustion risk of the upper residual coal.On the basis of revealing the regularity of spontaneous combustion of coal infully mechanized caving face goaf, according to the stereoscopic distribution of thespontaneous combustion risk area, the hydroxy-type inhibitive foam technology wasproposed for the first time and has been applied in Dafosi mine successfully. Theinhibition effect of the hydroxy-type inhibitor was investigated in the laboratory fromboth macroscopic and microscopic characterization. A new efficient foam generatorwith large flow that suitable for small space underground was developed. The macrostereoscopic coverage and microscopic efficient inhibition of the goaf with largespace were realized, and the risk of spontaneous combustion in goaf was effectivelyreduced. Thereby, the conundrum of the prevention of hidden fire source in goaf withlarge space was successfully resolved.
Keywords/Search Tags:fully mechanized caving face goaf, oxygen-poor, spontaneouscombustion, numerical simulation, inhibitive foam
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