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Description
The burden materials in the blast furnace are traditionally charged to build distinct layers of ore and coke, which makes it possible to control the conditions in the shaft. Since ore and coke have fundamentally different density, the mass flow rates of solids at different radial locations will vary, which affects the heating of the burden upon its descent. Further, as the materials show different gas permeability, the burden distribution affects the gas flow distribution in the shaft, which, in turn, affects the thermal state and chemical reactions in the lumpy zone. The conditions close to the burden surface are complex due to the intermittent charging. Even though traditional (probe) measurements of the gas temperature in or above the bed surface seldom consider the rapid changes caused by charging, new acoustic gas temperature measurements may be able to do so in the future. In order to gain a better understanding of the effect of charging on the thermal and flow conditions in the upper shaft, an analysis based on Computational Fluid Dynamics combined with the Discrete Element Method (CFD-DEM) was undertaken. The model, which studies the counter-current flow of gas and solids and the temperature evolution of the two phases in a simplified setup, simulates the intermittent charging and descent of burden, consisting of pellets and coke, and the simultaneous ascent of gas through the particle bed. The results demonstrate the complex interaction between the solid and gas flows, which affects the radial temperature distribution of the due to both heat transfer and gas redistribution. These dynamic changes are analysed and illustrated for different parts of the simple charging cycle, and implications of the observed behaviour are analysed and discussed in the paper.