Dust Generation Mechanism And Suppression Method Of Spiral Hopper In Bulk Discharging Process Based On CFD-DEM

In the process of transshipment and discharging of bulk materials such as ore,coal and grain,especially in the discharging operation,fine particles in bulk materials easily diffuse into the air and cause dust pollution.Dust pollution is harmful to human health and work safety.At present,the methods of dust control for bulk materials discharge mainly include water spray dust suppression,spray suppression,ventilation dust removal,etc.However,all methods have their obvious limitations,so it is necessary to carry out dust suppression in bulk discharging process.Aiming at the problem of dust pollution in bulk materials discharging process,this paper uses CFD-DEM coupling method to simulate the dust generation mechanism and the dynamic distribution law of gas-solid two-phase flow field in bulk material discharging process.Based on this,a new type of spiral dust suppression hopper is proposed,and its dust suppression effect is simulated.The main contents and achievements of this paper are as follows:(1)Dust generation mechanism and its influencing factors in bulk materials discharging process.By establishing the theoretical model of particle force and suspension velocity in the air during the free falling process,the mechanism of primary and secondary dust raising in the discharging process of bulk materials is analyzed.It is known that the shearing,entrainment and dragging action of the airflow are the main causes of dust generation.Through the analysis of the impact law of the height of discharging and the angle of incidence of particle flow on dust production,it is known that changing discharge height and collision incidence angle in a reasonable way will help to reduce dust generation.(2)Numerical simulation of dynamic distribution of gas-solid two-phase flow field in bulk unloading process based on CFD-DEM.Taking the discharging process of bulk materials from grab to hopper as an object,through Fluent-EDEM coupling simulation,the movement of particle flow,the distribution of air flow field in hopper,the variation of flow field with time and space are analyzed,and the mechanism of dust generation in the discharging process of bulk materials is further elaborated.The simulation results show that the dust-laden airflow escapes from the hopper in all three stages of the discharging process,and the dust-laden airflow escapes from around the hopper in the free blanking stage and the material accumulation stage,while part of the dust-laden airflow forms eddy current in the hopper,which is gradually diluted and carried out during the weakening stage of the flow field.(3)A new dust suppression method of spiral hopper and its dust suppression effect were studied.Based on the mechanism of dust generation during bulk materials discharging,an innovative dust suppression method of screw hopper is proposed,and the optimum design of the structure size of screw guide plate is completed through theoretical and orthogonal simulation experiments.The results of CFD-DEM coupling simulation analysis show that by adding a spiral guide plate to reduce the free blanking height,increase the collision angle of the particles,and change the trajectory of the particles,so that the dust diffusion in the discharging process of the screw hopper mainly occurs in the free fall stage and the collision accumulation stage,greatly reducing the dust production during discharging process.(4)Study on the method of comprehensive dust suppression by negative pressure suction of screw hopper.In order to further improve the dust suppression effect of spiral hopper,a comprehensive dust suppression method of negative pressure suction of spiral hopper is proposed.The parameters of negative pressure suction are established based on flow ratio method.The numerical simulation by CFD-DEM shows that the dust suppression method of negative pressure suction can solve the dust diffusion problem of spiral hopper very well.In addition,by comparing the numerical simulation of the spiral hopper negative pressure suction comprehensive dust suppression method with the conventional hopper negative pressure suction comprehensive dust suppression method,it shows that the spiral hopper negative pressure suction comprehensive dust suppression method not only has better dust suppression effect,but also can significantly reduce the negative pressure suction volume and reduce energy consumption.