Numerical Simulation On Characteristics Of Pneumatic Conveying Of Pulverized Coal In Horizontal Pipe

Coal plays an important role in the energy structure of our country,and the use of coal in the direct combustion mode brings serious environmental pollution and ecological damage.Therefore,the efficient use of energy and the development of clean energy is particularly important.Coal gasification is the core technology of clean and efficient use of coal,is the foundation and key in synthesizing bulk chemicals and liquid fuel which are coal-based,and developing advanced integrated gasification combined cycle power generation,poly-generation systems,hydrogen production,fuel cell,direct reduction iron-making process.The development of coal gasification technology as the core of poly-generation technology has become one of the most efficient and clean coal technologies.Large scale is the primary problem of coal gasification technology.The technical way in order to realize the large scale and high efficiency industrialization is improving the processing capacity and processing efficiency of unit time and unit volume under the certain conditions of high temperature,high pressure and enhanced mixing.So high pressure gasification requires pulverized coal must be transported under higher pressure than gasification,and must be transported as much as possible with less carrier gas(N2).In general,the coal powder concentration is as high as 300-600kg/m3 which belongs to typical dense phase conveying.In the dense gas-solid two-phase flow system,powder properties such as particle size,particle size distribution,particle shape,particle density,moisture content and so on is the important factor of Influencing powder Mechanics(repose angle,friction angle,compression),particle aggregation properties and the hopper type and pipeline flow.Particle dynamics theory was combined with modified particle friction stress model,based on Euler-Euler model and standard k-? turbulence model and less friction/all sliding boundary condition,taking into account the drag and lift simultaneously and taking full account of collision and friction between particles,to simulate gas-solid dense-phase pneumatic conveying under high pressure in a horizontal tube by using the software of CFD Fluent.In order to seize the problem of particle concentration distribution distortion near the wall,the Johnson and Jackson boundary parameters,specularity coefficient and particle recovery coefficient against the wall,were studied to reveal how they influence particle concentration distribution on dense phase pneumatic transport process;the results show that the specularity coefficient has great effect on particle concentration distribution near the wall.When the specularity coefficient is zero,the particle concentration distribution distortion did not occur.The recovery coefficient between the particles and the wall has little influence on the distribution of the particle concentration at the wall.Comparing the Johnson and Jackson and Jenkins wallboundary models on the particle concentration distribution,the results show that the two kinds of boundary conditions on the particle concentration in the vertical direction is not obvious,only a slight fluctuation in the transition zone.It provides a reference for the selection of the wall boundary conditions in the following research.Secondly,on the basis of verifying the correctness of the model,the numerical simulation of the vortex characteristics in the process of dense phase pneumatic conveying of pulverized coal is carried out.The model predicts the of pressure gradient variation that pressure gradient decrease first and then increase against the superficial gas velocity,which is in good agreement with the experimental data.The velocity distribution of gas-solid two-phase flow is obtained.The concentration distribution of particle phase is obtained which reveal the gradual process of the formation and development of the sedimentary layer.Simulation of the gas phase,particle velocity vortex phase diagram of the same speed under different sections of pipeline were obtained and the evolution process of the gas phase of the vortex was observed.the vortex scale increased along the pipeline direction and exacerbated the pressure loss;complex flow particle deposition or aggregation along the pipeline flow direction;comparing the same section velocity streamlines of the different superficial gas velocity shows that the higher superficial gas velocity was,the more complex and more intense the swirls were,which shows that the pressure loss is bigger.In summary,using the mathematical model of this paper to deal with high pressure dense phase pneumatic transport has good applicability,and provide valuable reference for the optimization of high pressure dense phase pneumatic transport design.To capture the movement mechanism of dunes and their cyclical changes is as the research direction in the future.