Research On Dust Migration And Settlement Characteristics In The Return Airway Wind Flow Of Coal Mining Face

Coal mine dust is the general term of various fine solid particles produced in the coal mine production process.Dust is one of the top five disasters in coal mine.Dust brings a great threat not only to the safety production of coal mine but also to the health of underground workers.Underground workers inhale dust for a long time,which may lead to pneumoconiosis.What is more,dust will reduce the visibility of workplace and increase the incidence of accidents;Dust will explode under certain conditions and participate in gas explosion,which always lead to severely impair;Dust will accelerate the mechanical wear and shorten the life of instruments.With the mechanized,intensive and efficient development of coal mining technology,dust control has become an important part of coal mine safety production.There are two states of coal dust in general: floating state and sedimentary state.The two states will be converted under certain conditions.For example,a part of floating dust will settle to become sedimentary dust under its own gravity,and sedimentary dust will fly up to the floating state because of the high speed wind or shock wave.The upper limit of dust explosion is 1500~2000 g/m3,and the lower limit is 45g/m3.It will cause dust explosion when the dust concentration reach to the explosion limit caused by too much floating dust in the air.There are a lot of dust production sites in coal mining,and all the operations can produce dust.Coal mining face is the largest dust production workplace.In the absence of effective measures,dust concentration of the coal mining face can achieve 5000~10000mg/m3.As wind is blowed from the inlet lane into the return airway through the coal mining face,the dust from the coal mining face will be bring into the return airway inevitably.High concentration of floating dust in the return airway will subsidence gradually,which brings coal dust explosion risks.Wind speed,particle size distribution,dust concentration are the factors that affect the dust settlement,so it is necessary to give a comprehensive and systematic relationship between these factors.Therefore,the paper studies the migration and settlement law and theory of dust in the return airway of coal mining face.It has important reference value to study the dust collection and dust volume calculation,to determine and arrange the dust collecting point of coal mining face,to optimize the dust measurement method and scientific dust control and prevention of dust explosion.By reading a large number of domestic and foreign references,it is found that although many scholars have done a lot of research work around the theoretical research on migration and settlement of dust,many achievements have been made on mining and driving face.And there are few studies on the distribution of dust with different particle sizes under different wind speeds on the length and the height direction in return airway.In addition,many scholars often simplify the actual problems to one-dimensional or two-dimensional problems when they establish the mathematical model of dust migration and settlement process in tunnel airflow based on Eulerian coordinate system,and this is out of step with reality.If the mathematical model is not verified by experiments,it is impossible for us to know whether the model is correct or not and it cannot reveal the characteristics of dust migration and settlement correctly.Most domestic and foreign scholars do simulation research of dust migration and settlement with the help of FLUENT software at present.But the FLUENT software just can use its own mathematical models for calculation and the models are limited in number and cannot be covered and adapted to all situations.Therefore,sometimes the mathematical model cannot fit well with the actual situation at the scene,and the simulation results will be biased.Based on the shortcomings in researches,this paper studies the theory of dust migration and settlement in the special return airway of coal mining face.The three-dimensional mathematical model of dust migration and settlement in roadway is established according to the mass conservation law by analyzing the influencing factors.This paper proposes a new element control partitioning scheme in tetrahedral element on the basis of previous studies.According to the new element control partitioning scheme in finite volume,the mathematical model is discretized and write software to simulate the migration process of dust in the return airway.Based on the similarity principle,this paper designs the similar simulation experiment of dust migration and settlement in the return airway.Dust concentration and falling dust mass distribution and particle size distribution of different particle sizes and mixed dust under different wind speed were measured.Finally,the experimental and simulation results are compared to verify the correctness on migration and settlement theory of dust.Through the above researches,this paper achieves following conclusions:(1)The paper establishes the three-dimensional mathematical model of dust migration and settlement in return airway wind flow of coal mining face.And the characteristics and laws of dust migration and settlement in the airflow of return airway are revealedIn the coal mine lane,optional control body is selected.The control body mass is affected by airflow convection,gravity settlement and dust diffusion.Basing on the law of mass conservation,a universal theoretical mathematical model for dust movement and settlement is established.According to the actual situation of coal mining face return airway,the paper establishes the three-dimensional mathematical model of dust migration and settlement in return airway.And the characteristics and laws of dust migration and settlement in the airflow of return airway are revealed.(2)Discret the mathematical model based on the new element control partitioning scheme in tetrahedral element.The calculation area is deteremined and meshed with the tetrahedrion.At the same time,the new element control partitioning scheme in tetrahedral element is proposed through improving the formers' research.Namely,choose any vertex of the tetrahedral element,and connect the gravity center of the tetrahedral element,the gravity central of three faces and the midpoint of three edges linked with the vertex chosen,thus a tetrahedral element control body is established which is similar to the diamond.Based on the newly proposed tetrahedral element control method,the three-dimensional dust migration and settlement mathematical model in the return airway wind flow is discretized.And the node equations of the unknown variations are finally obtained,which lays the foundation for the computer program.(3)Design the program and develop softwareOn the basis of the above researches,the structure flow chart of the calculation program is designed,and the simulation software of dust migration and settlement in the return airway wind flow of coal mining face is developed by Visual Basic 6.0.(4)Solve the mathematical model according to the developed softwareSolve the mathematical model of the dust migration and settlement in the return airway by the use of the self-compiled simulation software.The dust concentration distribution on different heights of the different cross section along the roadway is obtained under different wind speed and dust particle size.The cloud charts of dust concentration distribution according with reality is graphically displayed by the use of post-processing software.(5)Design a similar laboratory simulation experiment to study the migration and settlement of dustBased on the similarity theory,the similar simulation experiment content and specific implementation steps of the migration and settlement of dust in return airway is determined.The dust concentration,the dusting quality of the mixed dust and the dust particle size distribution at different heights of the different sections along the different cross sections of the roadway are obtained under different wind speeds through the similar simulation experiments in the laboratory.(6)Compare experimental and numerical simulation results,and verify the correctness of dust migration and sedimentation theory.The dust concentration distribution of different particle sizes in the same wind speed is analyzed under the experimental and numerical simulations,as well as the dust concentration distribution of the same particle size at different wind speeds and the dust concentration distribution of the same wind speed in the same particle size.The results show that the experimental and numerical simulation results are consistent: the dust concentration always become more and more smaller along the direction of roadway.And the dust concentration increase in the height direction from the roof to the floor,but the growth rate is decreasing.As a whole,the floor dust concentration is greater than the roof dust concentration.Under the same wind speed and the same height of tunnel,the larger the particle size is,the lower dust concentration is.Under the same height of the same section in roadway,the greater the wind speed is,the smaller the dust concentration is.The same conclusion has been obtained in the dust quality and particle size distribution of the mixed dust laboratory experiments under different wind speeds.The theory of migration and settlement of flowing dust proved to be correct and reasonable ultimately through the above results.There are three innovation points in the paper:(1)The paper analyze the main influence factors of dust migration and settlement in return airway of coal mining face,and establish a three-dimensional mathematical model of dust migration and settlement,which includes diffusion,flow and gravity settlement.The mathematical model is calculated and simulated by software,and is verified by laboratory experiments.Finally,the characteristics and regularities of dust migration and settlement in return airway airflow are revealed.(2)In the paper,the coefficients of the finite volume discrete equation are different because of the different element control partitioning scheme,and the coefficients will directly influence the accuracy of the calculation.This paper proposes a new element control partitioning scheme in tetrahedral element by improving the old element control partitioning scheme in tetrahedral element which is proposed in our research group,and derives the theoretical formula of the tetrahedron finite volume algorithm of dust migration.(3)The paper uses Visual Basic 6.0 to develop the software based on the new element control partitioning scheme in tetrahedral element,which is named "Simulation Software of Dust Migration and Settlement in Return Airway Wind Flow".And then utilize the software to simulate the dust migration and settlement process in return airway.(4)The similarity principle is established through analysing of dust migration model.Then the simulation experiment platform is set up,and the similar simulation experiment of dust migration and settlement process in return airway of coal mining face is carried out.