Mathematical&Physical Simulation Of COREX Pre-Reduction Shaft Furnace

COREX pre-reduction shaft furnace is a typical gas-solid countercurrent reactor. A reasonable gas distribution is of great importance for attaining a low gas pressure drop through the burden column, a high gas utilization and thereby a low gas consumption, as well as a high DRI metallization. In order to better understand the COREX process, particularly the prereduction furnace, a static model for the whole COREX process is developed and then the mathematical and physical simulations of pre-reduction shaft furnace are conducted in this thesis. The main works are as follows:(1) COREX process modelThe COREX process model is developed based on mass and heat balance equations and operation constraints. A raw material optimization module and a database modulel are also included in the process model. The relative error between the model calculation and typical production data is less than3%, showing that the process model is of high reliability. The material and heat balances for various operation conditions are calculated by using the process model, and the calculated results are used to determine the boundary conditions for physical and numerical simulations.(2) Cold physical similition of COREX shaft furnaceBased on the theory of similarity, the similarity criteria for physical simulation of COREX shaft furnace process are derived. A half-perimeter physical model with the scale1:20of COREX3000pre-reduction shaft furnace is constructed for physical simulation of the shaft furnace process. In the simulation experiments, the gas pressure distribution is measured under various gas flow rates, bed heights, bed moving speeds, bed structures and fine material additions. The gas flow distritution is also investigated.Visualization experiment of solid material movement is also conducted. The material movement in the furnace is investigated. The descriptions of axial and radial movements of solid materials in various regions of the furnace are determined.Visualization experiment of the gas-solid reactions is also carried out with silica gel, for that the colour of silica gel changes with moisture absorption. The gas-solid reaction process is ananyzed based on the simulation results.(3) Mathematical simulation of burden distribution effect on gas flow distributionA3-dimenssion mathematical model is developed to calculate the gas flow distribution in the COREX shaft furnace. The effect of burden distribution with various charging patterns on the distribution of gas flow in the furnace and the quantity of gas coming from the DRI discharge channels are investigated. The variations of pressure drop, gas quantity from DRI discharging channel and gas segregation with the increase of burden charging radius are determined. It is found that, when the burden charging radius is greater than2.0m, all the pressure drop, gas quantity from DRI discharging channel and gas segregation increase significantly. So, the charging radius should not exceed2.0m, and suitable charging radiusis1.6m.(4) Mathematical simulation of overall processes in COREX pre-reduction shaft furnaceA2-dimenssion mathematical model in cylindrical coordinates is developed to study all the processes of materials flow, heat transfer, mass transfer and chemical reactions in the COREX prereduction shaft furnace. The distributions of materials velocities, temperatures and compositions, as well as their variations with operation conditions are calculated and analyzed. The results show that the movement of solid materials in the upper part of the furnace follows the law of plug flow. In the lower part of the furnace, the solid material flow offset to the discharge exit and a deadman forms at the bottom of the furnace. Both of the temperatures of gas and solid material show an opposite radial distribution in the upper and lower shaft:the center temperature is higher in the upper shaft and the edge temperature is higher in the lower shaft. The distributions of reduction degree of iron oxide and reducing potential of gas from the results of materals composition calculation are similar to that of temperature. But the distribution of gas utilization is opposite to that of reducing potential of gas:the center gas utilization is higher in the lower shaft and the edge gas utilization is higher in the upper shaft.