Movement And Heat Transfer Characteristics Of High-temperature Slag Particles In Centrifugal Granulation Silo With Inclined Air Distribution And Compound Cooling

The energy consumption of steel industry accounts for 10%to 15%of the national total energy consumption,which is of great significance in the national energy conservation and emission reduction work.The blast furnace slag produced in the process of iron and steel smelting contains rich waste heat resources.The current treatment of blast furnace slag is mainly water quenching.However,the water quenching process consumes a lot of water resources,and harmful gases such as SO₂and H₂S are generated during the contact between the molten slag and the cooling water.In addition,the sensible heat of blast furnace slag has not been effectively recycled.In order to overcome the above shortcomings,scholars at home and abroad have proposed a variety of blast furnace slag dry treatment methods.Among them,centrifugal granulation waste heat recovery technology has become the most promising method due to its simple structure,convenient operation and good device stability.However,due to the reasons that the granulated slag particles are very easy to bond,the quality of waste heat recovery and the quality of materials are difficult to balance,the technology has not yet achieved industrial application.Based on the research and development ideas of strengthening the heat exchange of granulated slag particles,promoting particle movement,preventing particle adhesion,and achieving effective discharge of particles,this paper proposes an inclined air distribution compound cooling centrifugal granulation silo,which aims at the high temperature melting after centrifugal granulation.The movement and heat transfer characteristics of the slag droplets in the air cooling process of the granulation silo are studied,which provides theoretical guidance for the structural design and operating conditions of the efficient granulation silo,and promotes the industrial application of this technology.In view of the movement and heat transfer characteristics of high-temperature slag droplets in the inclined air distribution composite cooling centrifugal granulation silo.This paper firstly studied the dynamic behavior of the fluidization motion of solid particles under the inclined air distribution plate through cold experiments,and the effect of particle type,inclination angle and structure of the distribution plate on the fluidized motion behavior of the particles have been investigated.The optimal inclination angle of the distribution plate has been obtained.On this basis,an experimental system of a compound cooling centrifugal granulation silo based on inclined air distribution plates was built,and the movement and heat transfer characteristics of granulated slag droplets/particles in the granulation silo were experimentally studied,and the granulation was investigated.On this basis,an experimental system of a compound cooling centrifugal granulation silo based on inclined air distribution plates was built,and the movement and heat transfer characteristics of granulated slag droplets/particles in the granulation silo were experimentally studied.The effects of granulator speed,initial slag temperature,cooling air flow rate and cooling water flow rate on droplet/particle movement and heat transfer were investigated.Finally,a mathematical model of particle group movement and heat transfer in the granulation silo is established,and the movement and heat transfer process of high temperature particles in the granulation silo are numerically simulated,and the best working conditions for promoting gas-solid heat exchange are obtained.The main conclusions are as follows:(1)The cold experiment results show that as the inlet wind speed increases,the particles at the top of the inclined air distribution plate will first fluidize,which can promote the movement of the particles from the top of the air distribution plate to the bottom.The greater the apparent fluidizing wind speed,the lower the bed height,the more obvious this motion promotion effect.After the air supply is stopped,the shape of the solid particles on the inclined air distribution plate changes from the initial horizontal plane to the airfoil.That is,the bed layer near the top of the air distribution plate is the thinnest,and the bed height gradually increases along the direction in which the height of the air distribution plate decreases.The use of non-uniform air distribution plate can adjust the movement of bed material.When the inclination of the air distribution plate is 30°,it can effectively promote the movement of particles,and the energy consumption of the fan is minimum.(2)The movement process of particles in the whole granulation silo has three stages:flight stage,wall impact stage and fluidization stage.The particles in the flight stage are mainly in the state of droplets,the particles in the stage of impact on the wall are in the semi-molten state,and the particles in the stage of the air distribution plate are mainly in the solidified state.In the fluidization stage of particles,the heat absorption of air is the largest,Followed by the flight phase,when the particles impact the wall,the heat absorption of the cooling water is the smallest,but in terms of the heat transfer coefficients of these three stages,the smallest heat transfer coefficient is in the particle flight phase,which can reach 185 W·m^-2·K^-1,the maximum heat transfer coefficient in the fluidization stage can reach 717 W·m^-2·K^-1,and the heat transfer coefficient in the wall collision stage can reach 634 W·m^-2·K^-1.Reducing the speed of the granulator,increasing the initial temperature of the slag,and increasing the flow of cooling air into the granulation silo can increase the recovery rate of waste heat.Properly increasing the amount of cooling water can improve the heat transfer effect of the water-cooled wall surface,reduce the adhesion of particles in the granulation silo,and promote the overall increase in the recovery rate of waste heat.(3)By observing the simulation results of the movement and heat transfer of the particles in the granulation silo,it can be found that in the three stages of the particle movement in the granulation silo,the temperature of the particles in the stage of impacting the wall is the fastest,followed by the flight stage.The slag particles are mainly radiative heat transfer during the whole movement of the granulation silo,followed by convection heat transfer,and finally the heat conduction of the particles hitting the wall.The area with the highest air temperature in the granulation chamber is the area near the collision of the particles with the wall surface,and the air temperature in the granulation chamber gradually increases in the radial direction.Reducing the inlet air velocity of the air distribution plate and increasing the mass flow of the slag can increase the temperature of the outlet air of the granulation silo.A higher outlet air temperature means higher quality of waste heat recovery,and reducing the particle diameter is the best way to increase the recovery rate of waste heat means.In addition,when the inclined air distribution method is adopted,compared with the entrance wind direction perpendicular to the air distribution plate,when the entrance wind direction is vertically upward,it can promote the increase of the outlet air temperature.