Simulation Of Particles Mixing And Coalescence Behavior Of Sintering Raw Materialsin High-speed Granulator

The granulation process plays a vital role in the sintering process.The particle size and components can be reasonably controlled by granulation process,which guarantees the quality and yield of the subsequent sintering process.At present,the cylinder granulator is usually used to make granules in most sintering plants.With the usage of the amount of limonite increased,the problem of dirt growing on the inner wall of cylinder granulator is becoming increasingly serious.In addition,the size and compositions of quasi-particles produced by traditional cylinder granulator under high load are non-uniform.These serious problems will not only greatly reduce the efficiency and effectiveness of granulation,and also contaminates raw materials,accelerates the aging of the granulator,and increases the cost of sintering granulation.Although a variety of efficient granulation processes technologies have been developed and studied both at domestic and foreign to improve the efficiency and effect of granulation,no such advanced solutions have been proposed to improve the granulation equipment.For the above problems existing in granulation,a new horizontal high-speed granulator is proposed and designed in this paper.A suitable contact model for particle coalescence is established,and based on the contact model both the mixing behavior and granulation behavior of the raw material particles in the novel device were simulated and theoretical analyzed,as well as the influence of device parameters on granulation.The main conclusions are as follows:? The kinestate of the particles in cylinder granulator is cascade,which contains mainly two parts:sliding and drop.In high-speed granulator,the kinestate of the particles is cataracting with two parts:rolling and falling.The particle motion in high-speed granulator is more intense than it in the cylinder granulator.The motion of particles will become more intense as the stirring speed increases,but the number of stirring blade does not have much influence on the movement of the particles.? For a fixed particle size,the mass percentage distribution of small particles has the greatest influence on the fractal dimension of the particle group.The fractal dimension of particles increases with the increasing of the mass percentage of small particles.Increase the stirring speed will increase the fractal dimension of the particles.The fractal dimension of particles to go up and down violently with time under the action of more stirring blades,which will cause the spiral movement of the particles becomes more pronounced,so that the difference in distribution of the particles in the axial direction becomes greater.? The mixing effect of cylinder granulator is poor,and horizontal adjacent particles cannot mix well with each other,which causes a mixed dead zone.This phenomenon was not find in high-speed granulator,and the mixing effect of high-speed granulator is better than cylinder granulator.? Increase the stirring speed can reduce the coefficient of variation of the mass percentage of the particles and obtain a better mixing effect.However the number of stirring blades has little effect on the change of coefficient of variation.Compared with the initial coefficient of variation in mass percentage of particles in different granulators,the reduction of coefficient of variation in the 4blades and 125 rpm granulator is the highest,and the final coefficient of variation of these apparatu is the lowest,which is the closest to the desired particle composition thus indicates the mixing effect of it is the best.? The maximum speed and average speed of particles in various granulators fluctuate slightly with time.The maximum speed of particles in the cylinder granulator is similar to the maximum speed of particles in the 4 blades and 40 rpm and 4 blades and 60 rpm granulators.However it is much smaller than the maximum speed of the particles in the other high-speed granulators.For the average speeds:V 4-40rpm<??? 4-60rpm<??? cylinder<???3-100rpm<??? 4-80???_pnm<???4-1000rpm<???5-100rpmMost of the coalescence were type I coalescence in the 4 blades/40 rpm apparatus.The average speed of particles in all granulators were less than 2 m/s,which indicates that the liquid viscous force contributes the major kinetic energy dissipation during the particles coalescence.There is a good linear relationship between the stirring speed and the average particle speed,which the average particle speed increases linearly with the increasing of stirring speed.The regression formula is:???_p =-0.162 + 0.007vbIncrease the number of stirring blade will increase the average particle speed in the granulator.? The variation trend of the collision rate of particles in each granulator is relatively uniform.The collision rate increases continuously from Os,then begins to decline,and then gradually fluctuates and finally tends to be gentle with time.For the average collision rates:r_c^5-100rpm? r_c^3-100rpm? r_c^4-100rpm<r_c^cylinder<r_c^4-80rpm? r_c^4-60rpm? r_c^4-40rpm There is a good linear relationship between the stirring speed and the collision rate of particles.The average collision rate decreases linearly with the speed of the stirring blade.The regression formula is:???_p =3.37-0.01vbWhen the stirring speed is fixed at 100rpm,the collision rate of particles in the 4 blade granulator is the largest,followed by 3 blade and 5 blade in sequence;? When the material characteristics of particles is fixed,the relative coalescence function ?*of each granulator was obtained and the order is showed as follow:?B*??C*??D*??cylinder*??E*??A*??F*The value of coalescence core function is biggest in the 4 blades/40 rpm granulator,which indicates that it can achieve the best granulation effect in all test granulators.