Research On Particle Coalescence Of Granulated Raw Material In High Shear Movement

The granulation effect of the sinter mixture determines the air permeability and sintering uniformity of the sintering material layer,and it can reasonably control the composition and particle size range of the sinter mixture,so as to have a significant impact on the improvement of the quality and output of the sinter.The proportion of the fine-grained fine ore powder and porous limonite powder in the sinter mixture of iron and steel enterprises is higher and higher.The traditional pelletizing process is difficult to adapt to such a situation of material use.In addition,the sintering of thick material layer also puts forward higher requirements on the homogeneity and strength of particles.In view of the above problems,the development of new pelletizing equipment and process has important theoretical significance and practical value for sintering production.In this paper,a new high speed shear granulator is used to study the process of granulator mixing.DEM software is used to simulate the coalescence behavior of granulator and the experimental research on granulator is carried out by the new equipment.The main conclusions are as follows:(1)Under the rotating action of blade,the contact force network structure and the surface characteristics of particle bed are different when dry particles and wet particles are tossed and dropped in the cylinder.The normal contact force network of dry particles is very uniform and the surface of the particle bed is smooth;while the wet particles are in contact with each other,their contact force network structure is more complex and heterogeneous,and the particle bed surface is rough.(2)With the rotation of the blade,the range of the drop space for the coalescence of the particles is the entire granulator barrel;while the particle motion in the cylinder mixer has a rapid flow layer,the particles cannot reach the space above the cylinder drop movement.Therefore,the range of the moving space of the coalescence particles in the high shear granulator is larger than the flow space of the particles in the cylinder.The mixing effect of the coalesced particles in the high shear granulator is better than that in the cylinder.(3)At the same blade speed,the average speed of wet particles is less than the average speed of dry particles.This shows that the liquid bridge between the wet particles limits the vertical and radial movement of the particles.The presence of the liquid bridge increases the size of the agglomerates,which requires more energy to break the liquid bridge between the particles.The greater the obstacles encountered during the rotation,the smaller the energy transmitted to the wet particles by the rotation of the blades,which affects the coalescence behavior of the particles.(4)In a high shear granulator,the number of particles in contact with each other increases as the rotational speed increases.The increase of the rotation speed is beneficial to the increase of the number of agglomerated particles at the same height,that is,the size of the agglomerates is increased,and the vertical height that the agglomerated particles agglomerates can reach also shows an increasing trend.(5)When the blade speed is 70 rpm,the effect of increasing the granulation time on the mixture particle size and the air permeability of the material layer is known.The change trend of the material particle size and the air permeability of the material layer is to increase first and then maintain a stable fluctuation.This shows that at a certain blade speed,the material reaches the "equilibrium" of the granulation process under the stirring and shearing action of the high shear granulator.(6)With the increase of granulation time,when the blade speed is 50 rpm,the particle size,fractal dimension and air permeability of the mixture are increasing,and the change of the drop strength of the material is opposite.When the blade speed is 70 rpm and 90 rpm,the particle size of the mixture and the permeability of the material layer increase,while the change of the fractal dimension of the material increases first and then decreases,and the change of the falling strength of the particles decreases.(7)Under the same granulation time,the particle size of the mixture and the permeability of the material layer show an increasing trend with the increase of the rotation speed.This shows that at high speeds,the crushing of particles does have no effect on their growth,the increase in speed is beneficial to improve the granulation effect of the material.