Numerical Simulation Of Gas Solid Flow And Heat Transfer In Main Furnace Of Suspension Magnetization Roaster

The main furnace of suspension magnetization roasting furnace is one of the core components of suspension magnetization system,which has dual functions of particle heating and transportation.It involves complex physical and chemical coupling processes such as gas-solid two-phase flow,combustion reaction,mass transfer and heat transfer.Although the semi-industrial stable production of suspension magnetization roaster has been realized,there are still many theoretical and technical problems to be solved in process control and parameter control.The particle temperature distribution and gas-solid flow characteristics in the main furnace can directly or indirectly determine the quality of magnetic roasting products.High temperature and complex working conditions make it almost impossible to carry out the thermal experiment of suspension magnetization roaster.Therefore,in this paper,the computational fluid dynamics numerical simulation method is used to study the gassolid flow characteristics and heat transfer in the main furnace of suspension magnetization roasting.It is of great significance for the safe and stable production and accurate control of suspension magnetization roasting system to find out the influence of key operating parameters and material parameters on the gas-solid flow characteristics and heat transfer.According to above problems,the content of this thesis can be divided into three parts.The numerical simulation of temperature and thermal experiments of the empty bed in the main furnace are firstly carried out.The temperature at different axial heights was measured by the automatic multipoint temperature measurement system of the main furnace of suspension magnetization roasting.By comparing the experimental results with the numerical simulation results,it is found that the experimental results of temperature distribution in the main furnace are in good agreement with the numerical simulation results under multiple temperature conditions,which verifies the reliability of the flow model and combustion model in the numerical simulation,and verifies the accuracy of the established model.CFD-DPM method was used to carry out the three-dimensional numerical simulation of the main furnace of suspension magnetization roasting under stable conditions,and the temperature characteristics,gas-solid transport characteristics(gas velocity distribution,gas reactant concentration distribution,particle residence time,particle velocity,particle trajectory,particle velocity distribution,particle velocity distribution)and erosion and wear of the inner wall of the main furnace were studied.The distribution of gas phase temperature is characterized by high temperature at the bottom,high temperature at the top,high temperature at the center of the furnace,sharp temperature changes at the bottom and near the furnace wall,and uniform temperature distribution at the top.The gas velocity presents the distribution characteristics of "inverted bowl",that is,the distribution characteristics of high velocity in the furnace center and low velocity near the furnace wall.The residence time of particles presents the distribution characteristics of "early peak and long tail",which is closely related to the trajectory and velocity characteristics of particles.Within 0.2 s after the particles enter the main furnace,the temperature rises rapidly and reaches the maximum value,and then remains stable.Along the axial height direction of the main furnace,the standard deviation of particle temperature decreases gradually,and the width of particle temperature distribution decreases.Along the axial height direction,the temperature distribution of particles is similar to that of gas phase.According to the erosion model of the DPM model,the most serious wear is found at the particle inlet and the top of the main furnace.CFD-DPM method is used to investigate the effects of operation parameters(bottom air inlet velocity)and material physical parameters(feed particle size,feed density,feed rate)on gas-solid flow characteristics and heat transfer were studied.With the increase of the air inlet velocity,the gas temperature in the main furnace decreases gradually,but the cooling rate decreases gradually,which leads to the decrease of particle temperature.In the initial stage of particles entering the main furnace,the effect of air inlet velocity on gas-solid heat transfer rate is larger,but with the stability of gassolid flow,the effect of bottom air inlet velocity on gas-solid heat transfer rate is smaller.The particle time of high-speed state can be shortened,and the number of particles with longer stagnation time can be greatly reduced.High speed gas has a dilution effect on the particle concentration of the main furnace,which is beneficial to the transportation and discharge of particles,but the backmixing phenomenon in the main furnace is not improved by high speed gas.Small particles have faster movement speed in the main furnace,shorter residence time,and can leave the main furnace faster.Increasing the particle size can greatly increase the particle concentration in the main furnace.The higher the feed density can lead to the longer the residence time of the particles is and the higher the concentration near the particle inlet of the main furnace.The increase of feed rate are able to increase the particle concentration and backmixing strength in the main furnace,which is not conducive to the discharge of particles.The research of this thesis has proved the temperature and gas-solid flow law in the main furnace of suspension magnetization roasting,which provides theoretical support for the stable operation and accurate control of the main furnace of suspension magnetization roasting.