Development of control techniques for mixing small coke at bell-less top blast furnace

Abstract

Increased gas utilization and improved permeability have been desired in order to achieve low RAR (Reducing Agent Rate) operation of blast furnace. Coke mixed charging in the ore layer is one effective measure for realizing these improvements. A burden distribution control technique for mixing small coke at a blast furnace with a parallel type and center feed type bell-less top were developed and investigated in an experiment with a scale model of an actual blast furnace at JFE Steel. The scale model consists of an ore bin, a coke bin, a surge hopper, belt conveyers, a bell-less top and a model furnace to simulate the charging system of the actual blast furnace. The mixed coke ratio at the furnace top was controlled by the discharge pattern of mixed small coke and ore, and mixing position. The optimum patterns were founded to discharge the small coke from the coke bin after the ore discharged from ore bin in center feed bell-less top, and to discharge the small coke on the ore at front of quarter part overlapped in parallel type bell-less top. These patterns were applied to the actual blast furnace, and the improvement of permeability in a furnace was confirmed by the effect of increase the mixed small coke yield into ore layer.