Study On Multiphysics Modeling And Thermal Energy Matching Of Preheating Section Of Pellet Chain Grate

With the rapid development of the steel industry,the quality requirements of iron-containing raw materials into the furnace has improved.The pellets are uniform in particle size,easy to transport and have good reducibility,and are widely used in the steel industry.The pellet chain grate is one of the main thermal equipment for drying and preheating pellets,and consists of drying section and preheating section.The temperature field in the preheating section of the chain grate is very important to the preheating quality of the pellets.During the preheating process,it is difficult to directly measure the space temperature inside the chain grate,the temperature of the pellet layer,the oxidation of the pellets and other key parameters describing the preheating effect.In this regard,this article starts from the multi-physics mathematical modeling of the preheating section of the chain grate,studies the distribution of the temperature field and the air velocity field of the preheating section over time and space,and analyzes the influence of multi-physics field on the oxidation reaction of pellets.The thermal energy matching model of pellet preheating process is established and the thermal parameters of the preheating section of the chain grate are optimized,which can increase the oxidation degree of pellets while reducing energy consumption and lay the foundation for the temperature field control of the preheating section of the chain grate.The main research contents and results of this paper are as follows:(1)Using a local-to-overall modeling method,a detailed analysis of the heat transfer process of single pellet oxidation and the overall heat transfer process of the pellet bed are conducted.Based on the theory of gas-solid coupling heat transfer,porous media theory and oxidation reaction kinetics theory,the model of the preheating section of the grate is obtained.The model includes a single pellet heat transfer model under local thermodynamic equilibrium,a mathematical model of the gas-solid heat transfer process of the preheating section under local non-thermodynamic equilibrium,and mathematical model of ordinary differential equation for distribution of pellet oxidation degree.(2)The physical models of the single pellet isothermal oxidation simulation reactor and the preheating section of the chain grate are established and meshed respectively.The isothermal oxidation process of single pellet is simulated by COMSOL Multiphysics,and the oxidation characteristics of single pellet are obtained.The partial simulation results of single pellet are used as the input parameters of multi physical field numerical simulation of preheating section of chain grate,and the numerical simulation results of temperature field,air velocity field and pellet bed oxidation degree of preheating section are obtained and analyzed.Finally,the different preheating conditions of single pellet are obtained.The change of temperature field,air velocity field and oxidation degree of pellet bed with time and space in the preheating section are investigated.(3)The mathematical model of heat energy matching in preheating section of chain grate is established,and the heat energy matching test was designed and carried out based on response surface analysis method.The influence of various factors on pellet oxidation degree and thermal efficiency of preheating section is analyzed,and the thermal parameters of preheating section of chain grate are optimized through multivariate regression analysis.The results showed that the optimal thermal parameters are set as the inlet air temperature of preheating section II 1332.2k,the inlet wind speed of preheating section 1.52m/s,the outlet pressure of bellows-786.6Pa,and the preheating time 662.9s.The results show that the oxidation degree of pellet is 81.0%,and the thermal efficiency of preheating section is 66.3%.(4)The laboratory scale experimental equipment is built,the experimental data acquisition and analysis system is designed and established,and the multi-physical field model verification experiment of the preheating section is carried out.The experimental results show that the maximum error between the simulation value and the experimental value is less than 8%,which verifies the correctness of the mathematical model of multi-physical field in the preheating section of chain grate.