TOTAL SYSTEM ANALYSIS OF SMELTING REDUCTION SYSTEM WITH A CIRCULATING FLUIDIZED BED

摘要

In the smelting reduction ironmaking process that combines an iron bath smelting reduction furnace and a fluidized bed prereduction furnace: Study by total system simulation was made on the feasible range of combination of post combustion and prereduction degrees with a one-way gas flow-type system configuration that dispenses with the costly recirculating gas treatment loop. The upper limit of the prereduction degree is achieved when the gas utilization in the prereduction furnace reaches the limit governed by the equilibrium of gas reduction. The upper limit of the post combustion degree depends on the heat transfer efficiency. A reduction model was developed from the results of reduction experiments made with a circulating fluidized bed. Using this model, the gas utilization degree and coal consumption rate were estimated for the case of the circulating fluidized bed being used in a prereduction furnace. With the one-way gas flow-type system configuration, a coal consumption rate comparable to that in the blast furnace ironmaking process can be achieved by increasing the post combustion degree when the prereduction degree is 30 percent or lower. In this case, the heat transfer efficiency of post combustion must be kept high. When the prereduction degree is 30 percent or higher, a prereduction furnace composed of two circulating fluidized bed stages in series and a gas reforming furnace are necessary to attain a coal consumption rate comparable to that in the blast furnace ironmaking process.