Research On The Experiment And Numerical Simulation Of Temperature And Fracture In Overlying Strata In UCG

Underground coal gasification technology is a kind of chemical technology which can convert coal into combustible gas,and is an advanced technology which is advocated by the state and can make effective use of coal resources.Underground coal gasification set built well,coal mining and ground gasification process as a whole,Changes the traditional physical mining for chemical mining,leaves out large coal mining,transportation,washing and gasification equipment.It has advantages such as good safety,less investment,high efficiency,less pollution,etc.And it is known as the second generation of the coal mining method.Compared with the traditional coal gasification and ground coal gasification technology has the following advantages: large reduce the miners' health and safety issues;reducing the solid waste emissions;reducing the impact on social economy.a huge empty area will be formed when coal underground gasification mining has been completed,Change of roof support conditions,the stress state of surrounding rock and the strength of the rock will be changed,thus producing fracture zones in the surrounding rock.Fissure zone have a directly effect on combustion zone of surrounding rock stability and permeability.After long-term soaking and leaching of groundwater,the harmful organisms and trace elements in the ash will dissolve in water,enters into the aquifer through the lead water fracture zones,causing pollution of groundwater quality.In recent years,despite a lot of theoretical researches were did on the overburden failure law in the empty area,but most is discussed in the perspective of stress and strain of gasification coal seam damage rule of overlying rock strata.But the researches on the relationship between combustion temperature and the overburden failure are very few.Therefore,there are important significances to set up the high temperature mechanics model in the process of gasification.This paper takes the Meiguiying mine of ENN in Wulanchabu as the study arear.Rock specimens of the study area were took the thermal physical test and mechanical test.The thermal physical properties different rocks is studied through tests under the condition of room temperature to 1000 ? temperature,Established the function relations between the thermal physical properties of different rocks(density,specific heat,coefficient of thermal conductivity,etc.)and the temperature changes.According to fitting the function relation between the thermal physical parameters change with temperature,COMSOL Multiphysics temperature field conceptual model was established,and according to various rock thermal physical parameters change with temperature curve equation and the temperature field control equation to simulate the temperature field in the gasification process.And studied the process of gasification temperature field changing with burning length distribution.The mechanical properties of the main strata(elastic modulus,poisson's ratio,compressive strength,shear strength,tensile strength,internal friction Angle,cohesive force)were studied through the tests at room temperature.Reference to the research achievements of mechanical parameters change with temperature,FLAC3 D numerical model was established,and according to the change of temperature field in the gasification process,the gasification coal strata fracture field simulation was studied.When the coal underground gasification has been completed,a huge empty area will be formed,the stress state of surrounding rock and the strength of the rock changes,and fissure zone in surrounding rock and fissure zone effect directly to the stability and permeability of surrounding rocks.After long-term soaking and leaching of groundwater,the harmful organisms and trace elements in the ash dissolve in water,causing pollution of groundwater quality.Against the phenomenon of pollution,the combustion zone grouting filling management advice is put forward.The following main conclusions are reached:1.Through the collection of data in the study area,the location and traffic conditions in the study area were determined,then a simple summary was made to regional geological survey in the study area.Formation in the study area: The archean erathem JiNing(rock)group,Mesozoic Jurassic epoch volcanic rocks,Cenozoic paleogene Oligocene huerjing group,Neogene Miocene Hanno dam group,Quaternary Holocene series.There are 7 faults in this mining area,DF1~DF7,all are normal fault,and these faults have little influence on the formation and coal seam.2 # coal seam is the target coal seam of the coal underground gasification.2.The thermal physical properties different rocks is studied through tests under the condition of room temperature to 1000 ? temperature,Established the function relations between the thermal physical properties of different rocks(density,specific heat,coefficient of thermal conductivity,etc.)and the temperature changes.According to fitting the function relation between the thermal physical parameters change with temperature,COMSOL Multiphysics temperature field conceptual model was established,and according to various rock thermal physical parameters change with temperature curve equation and the temperature field control equation to simulate the temperature field in the gasification process.In the initial stage of combustion,the combustion of coal seam zone range is small,the temperature of the coal seam roof and floor equal basic remained in a maximum of 1000 ?.When burning length L = 100 m,the left side of coal wall temperature of combustion zone close to the initial temperature of 20 ?.3.The(elastic modulus,poisson's ratio,compressive strength,shear strength,tensile strength,internal friction Angle,cohesive force)were studied through the tests at room temperature,and these mechanical properties of the main strata have great significances on the roof strata of combustion cavity damage law research.4.According to the law of the mechanical parameters of coal seam mudstone roof change with temperature,FLAC3 D mechanics model was set up.Simulating the gasification process by changing the mechanical parameters of mudstone roof based on four basic assumptions.Compare the simulation results of two cases(the end of the gasification and),There are different degrees of increase in the simulation results of the same position in the five years after the end of gasification.5.When the coal underground gasification has been completed,a huge empty area will be formed,the stress state of surrounding rock and the strength of the rock changes,and fissure zone in surrounding rock and fissure zone effect directly to the stability and permeability of surrounding rocks.After long-term soaking and leaching of groundwater,the harmful organisms and trace elements in the ash dissolve in water,causing pollution of groundwater quality.Against the phenomenon of pollution,the combustion zone grouting filling management advice is put forward.