Research On Key Technology Of Swirling Pneumatic Conveying In Bulk Grain Pipeline

Pneumatic conveying is widely used in bulk conveying in factories,workshops,ports and other places because of its advantages such as flexible pipeline configuration,high efficiency and completely closed system.In particular,swirling pneumatic conveying technology can effectively restrain particle settlement and pipe clogging,slow down pipe wear,reduce material conveying speed and reduce material crushing.However,the gas-solid multiphase flow field interphase action of swirling pneumatic conveying is complicated,and there is a lack of relevant flow field theory,swirling technology and equipment research,and there is no research and application in bulk grain conveying field.Therefore,this paper takes the swirling pneumatic conveying system of bulk grain in circular pipeline as the research object,based on gas-solid multiphase flow theory and computational fluid dynamics(CFD),adopts numerical simulation and experimental methods to study the key technologies in the conveying process.The main research work is as follows:(1)Based on the gas-solid two-phase flow coupling theory and Newton’s second law,the force of bulk grain particles in a horizontal straight pipe was analyzed,and the interaction mechanism between bulk grain particles and flow field,particles and wall surface was studied.The mass conservation equation and momentum conservation equation as well as the motion equation of particle phase were determined by the Eulerian-Lagrarian method with bilateral coupling,which provided a theoretical basis for the subsequent simulation and experimental research.(2)A vane type swirling device is designed,and 3D modeling and simulation analysis are carried out for the swirling conveying system.The number of blades,spiral angle and blade length of the swirling device were analyzed by single factor respectively,and the maximum rotation distance was taken as the objective.The optimal number of blades of the swirling device under single factor was obtained as 6～9,spiral angle as 17°,25°,33°,and length as 0.2m,0.3m,0.4m.Based on the single factor analysis results of the parameters of the swirling device,the orthogonal analysis of multi-factor interaction was carried out.The optimal parameters of the swirling device were determined as the number of blades was 6,the spiral angle was 25°,and the length of the spiral guide blade was 0.3m.(3)A swirling pneumatic conveying test platform for bulk grain particles was built and the experimental research was carried out.The picking speed is selected as the critical conveying speed of swirling pneumatic conveying in bulk grain pipeline,and the picking speed measurement test is carried out.It is determined that the picking time of swirling pneumatic conveying in bulk grain pipeline is 10 s and the picking speed is10.63m/s.The pure flow field and the gas-solid mixed flow field with bulk grain particles were tested on the swirling pipeline under different inlet velocities.By analyzing the static pressure value and the standard deviation of static pressure of the flow field,it was found that in the swirling pure flow field,when the inlet air speed was15-20m/s,the static pressure loss of the system was the minimum,and the swirling distance of the airflow was the furthest.In the flow field where bulk grain particles are added,when the inlet velocity is 20m/s,the particles in the swirl pipe are evenly distributed,the standard deviation of static pressure is minimum,and the conveying process is more stable.(4)The cyclone enhancement device is designed,and simulation and experimental research are carried out.Through numerical simulation,the same section arrangement of the air supplement port is determined as the air supplement mode of the cyclone device.It is found that when the angle between the cyclone auxiliary pipe and the cyclone main pipe is 45°,the inlet air speed of the cyclone main pipe is 20m/s,and the inlet air speed of the cyclone auxiliary pipe is 60m/s,the flow field conveying effect is better,and the system energy consumption is small.The hydrostatic pressure value and standard deviation of pure flow field and load flow field with different angle between main and auxiliary pipe of air device were analyzed.The rationality of the design of swirling device and the accuracy of numerical simulation were verified.