The Particle Flow Theory And Experiment Research Based On The Screw-gas Mixing Condition

With the large proportion of bulk cargo in port trade,the research of equipment and technology has become an important branch of bulk cargo material handling,in which the process of material feeding is directly related to the efficiency of ship unloading.Thus,the performance of the feeding device is very important.Because of the non-linear characteristic of the screw-gas conveying process,it is influenced by common action of particle flowability and gas-solid separation.In addition,the flowability of different bulk materials is affected by multi-parameter interaction.Therefore,it is difficult for the classical continuum medium model to predict the internal mechanism of particle collision and separation.In this investigation,the theoretical numerical model is established based on particle flowability,and the key technologies and methods of screw-gas hadling device are researched by simulation and experiment in this article.The main research work and results are as follows:(1)The theoretical conditions for pneumatic lifting of particulate matter were determined,and then the effects of three important parameters on the free surface formed by particles in the screw lifting section,i.e.,the rotational speed of the screw,the filling rate of the material and the screw shaft size,were investigated in detail.After that,the critical separation particle diameter was deduced and the theoretical numerical model of screw-gas handling device was established.The disc experiment was used to study different working conditions and different particle materials.It was proved that the modified theoretical numerical model of free surface of particles had good applicability.The centrifugal separation process of particles was analyzed theoretically and numerically according to the particle group motion equation.(2)Based on the static and dynamic stacking angle in the field of particle transportation,a method of parameter calibration of discrete element method about particle flowability was proposed to solve the problem about inefficient parameter calibration of DEM in the process of particle DEM simulation.The BP neural network method was used in the data statistica and training,the mapping relationship between the DEM parameters and the macroscopic characteristics of particles was established.Moreover,an orthogonal search algorithm was proposed to optimize the range of prediction results,which can be used to predict the parameters of DEM simulation more quickly and accurately.Experiments and simulation results show that the proposed discrete element parameter calibration method has good applicability.(3)In view of the difficult in measuring the dynamic information of particle and air in the screw-gas device,and the complex distribution of air flow field and the severe collision of particle,the numerical simulation of the screw-gas device was carried out by CFD-DEM coupling method.The correctness and reliability of CFD-DEM coupling method were verified by comparing the simulation results of particle movement,air pressure distribution and bed height with fluidizition experiment.The effects of rotational speed of screw,air velocity and particle parameters on the conveying process were investigated.Then,the air flow field,particle distribution and movement characteristics were revealed.(4)The experimental platform of screw-gas device was designed,and the conveying process of different fluidity bulk materials was aslo investigated.The variation laws of screw rotational speed and separation efficiency,screw rotational speed and productivity of srew-gas device were analyzed,and the air pressure distribution in different working conditions was tested.The experimental results show that the conveying phenomenon of pulverized coal,sand and alumina powder issimilar,but the productivity of the three materials is not consistent due to the particle flowability.The best flowability material of sand has the best productivity,followed by the worst flowability material of pulverized coal.Comparing the experimental results with the theoretical results,it can be seen that the maximum error is within the effective range,which verifies the correctness of centrifugal separation theoretical model with screw-gas mixing condition.