Study On Adaptability Comprehensive Evaluation And Overlying Strata Movement Of Narrow Band Gasification Technology

Underground coal gasification is a new technology for the fluidized mining of solid coal,which proceeds through physical and chemical reactions under a certain temperature and pressure.During the process,the underground in-situ coal resources are taken as raw materials,and oxygen(air,oxygen-rich/pure oxygen)and vapor are used as gasification agents.In this article,field investigation,literature review,theoretical research,numerical simulation,and engineering application are combined as the technical route.The adaptability of resource geological conditions of using narrow strip underground gasification process and the rules of the movement and deformation of overlying strata are detailed investigated,with a goal of solving the mining area selection and the stable control of overlying strata while this technology is applied.The innovative achievements are shown as follows:(1)On basis of deeply analyzing the effects and mechanism of geological conditions on underground gasification,utilizing the basic theory of cloud model,a comprehensive evaluation method based on cloud model was proposed.Firstly,this method combined referring relevant publications and experts' investigations to screen out the geological factor which has effects on coal gasification.The geological factor was used as an evaluation factor to build evaluation index system,and the weight was determined.Next,expert grading method was used to build the cloud model of secondary evaluation factors.Then the comprehensive evaluation cloud was obtained from aggregating secondary evaluation cloud and primary evaluation cloud by floating cloud and comprehensive cloud algorithms,respectively.At last,the comprehensive evaluation cloud and the evaluation standard concept cloud were compared in a manner of cloud picture,and the evaluation results were obtained.During the process of building secondary evaluation factor cloud model,in order to reduce the blindness of expert grading,the scoring procedure was optimized through specifying the scoring rubrics and scoring standard of part of secondary evaluation factors.(2)The one dimensional equation of heat conduction was built under the boundary conditions of the first category where the temperature fields were distributed at the surrounding rocks of roof and floor,the surrounding coal seams,and the gasification coal seams.The corresponding solution function of mathematical analysis was obtained by using Laplace transformation and its inverse transformation equations.After the parameter assignment it could be found that: In the unstable state,the temperature spread gradually from the flame working faces into the gasification coal seams.But the spreading speed decreased gradually and eventually tended to be stable.The time spent in the temperature transition from unstable state to stable state in gasification coal seams was inversely proportional with the advance rate of the flame working faces.The faster the advance rate was,the shorter the time spent,vice versa.In the stable state,the spreading range of temperature fields in gasification layers exhibited a decreasing tendency with the increasing of the advance rate of the flame working faces.During the increasing and decreasing states,the temperature fields in the surrounding rocks of roof and floor and the surrounding coal seams spread towards the inside as time went on.However,because of the existence of the cooling stage,the temperatures of each point in the surrounding rocks of roof and floor and the surrounding coal seams exhibited a tendency which increased first and then decreased.The peak positions of the temperature field at different time moved towards the inside from boundary positions,and the peak value decreased gradually.(3)Under the mining conditions of single strip,two-strip,and three-strip gasifiers,the clamped beam model of thermal mechanical coupling in key layer was built.Besides,the effects of the existence of temperature field on the thermophysical parameter of overlying strata and the elastic foundation coefficient of surrounding coal seams were taken into consideration in the model.After the parameter assignment it could be found that: For any number of mining strips,there was an extremum of deflection in each range of combustion space area.Affected by the temperature fields,the extremum of deflection exhibited the same changing rule as the time changed.That is,the extremum of deflection increased first and then decreased with the time went on.In each range of combustion space area,there was an extremum of sagging moment.In the range of both ends of each establishing pillar,an extremum of hogging moment could be found.Under different mining conditions,the extremum of bending moment showed the same changing rule as the time changed.That is,with the time went on,increased first and then decreased.(4)For the subsidence rule of vertical surrounding rock in key layer,the results from software simulation were as same as the results from theoretical calculation.As time went on,the displacement value gradually increased.Comparing the maximum subsidence values obtained from software simulation and theoretical calculation,the difference was small.Therefore,the theoretically derived results could be used to predict the roof subsidence rule in key layer during the gasification mining process.