Research On Flow Field Characteristics Of Pneumatic Conveying System For Coal Particle

In order to change the method of raw coal transportation underground,cut down the construction budget of transportation,combat environment problems in conveying process,it is important to study an intensive and efficient method for sustainable development of coal resources.The pneumatic conveying technology is a kind of clean and recyclable transportation mode and an effective way to realize green coal logistics.Therefore,based on the pipe gas-solid flow theory,the discrete element method and coupled computational fluid dynamics(DEM-CFD)simulation and coal particles pneumatic conveying experiment,the proposes of the dissertation are reveal the interaction mechanism of coal particle between flow field and pipe-wall,conveying parameters and swirling flow pneumatic conveying,which provide theoretical and experimental basis for coal particle pneumatic conveying.According to gas-solid flow theory and Newton second law,based on the quantified description of coal particle size and morphology characteristics,kinetic analysis of coal particles in axial and swirling flow field and collision process between particles and pipe wall were analyzed.Then the force composition of coal particles in pneumatic conveying system is clearly defined,and the contact dynamics equations of particle collision process are deduced.And through the analysis of the movement form of material in the traditional pneumatic conveying system,the transport state of the coal particles in the pneumatic conveying is clarified.The research results provide a theoretical basis for the numerical simulation of the subsequent coal particle pneumatic conveying system.The DEM-CFD coupling simulation method was utilized to study injection process in gas-solid injector.The injection performance of different gas-solid injectors is analyzed by the particle distribution,particle teajectories and the number of particles.To study the relation between the structure parameters and injection performance,a gas-solid injector test-bed was produced.The results express that the convergent section angle is the critical factor affecting the injection performance when other parameters of gas-solid injectors are constant.As the convergent section angle increases,there are more particle-wall and particle-particle collisions in injectors,which indicates lower conveying velocity,longer invalid distance and more energy consumption;Particle conveying condition transit from suspension to deposition in conveying pipe,which leads to injection mass decrease and injection performance degrade.On this basis,the pneumatic conveying simulation of coal particles in horizontal straight pipe were conducted and the results shown that the coal particles mainly distributed in the bottom of the pipe and were symmetrical about the longitudinal section in the pneumatic conveying simulation of horizontal straight pipe.The bigger flow field velocity was,the more conducive to coal particles conveying in horizontal straight pipe.The swirling generator was designed on the basis of existing swirling generation technique and theory.DEM-CFD model was developed to study the swirling conveying process of coal particles.It is found that the coal particles distribution in swirling flow pipe is more uniform than horizontal straight pipe.The particle velocity in the swirling flow pipe was higher than that in horizontal straight pipe under the same air mass flow,and the smaller of included angle between auxiliary pipe and main pipe,the larger particle velocity was.The flow rate of swirling flow has a significant influence on the swirling intensity.Larger swirling intensity is helpful to the rotation of the coal particles in the initial stage of transportation.For the whole transportation system,there is a suitable flow ratio of swirling flow can make the particles fully swirling,reduce the collisions between and the energy consumption.On the above research,pneumatic conveying experimental platform for coal particle swirling pipeline was built and signal acquisition system was configured.Experimental research on pneumatic conveying of coal particles was completed.It is found that swirling generator is beneficial to the swirling pneumatic conveying system of coal particles,reasonable selection of the angle can reduce the energy consumption.In pure airflow,the static pressure of the system is higher and the static pressure drop is the least when the swirling flow ratio is 40%.In load-coal flow field,the hydrostatic holding capacity of the swirling flow field is weaker than that of the axial flow field.However,there is a suitable ratio of swirling flow to minimize the static pressure drop,and the optimal swirling flow ratio increases with the increase of size for coal particle.