Two Dimensional Cold Model Study on Unstable Solid Descending Motion and Control in Blast Furnace Operation with Low Reducing Agents Rate

Abstract

Unsteady behavior with bridging/slipping of solid bed in low reducing agents operation of blast furnace was simulated using a two dimensional cold model. Alumina sphere was used as representative particle of coke/ore packed bed. Two kinds of deadman particles different in gas permeability was examined. To simulate the effect of cohesive zone on unsteady behavior, a sand layer of lower gas-permeability was charged with a certain thickness at the top of the bed, which descended with a form of cohesive zone when it reached at the lower part. Further, a fine coke layer was set at the shaft bottom with a certain size assuming accumulation of fines. Unsteady phenomenon with the fine coke accumulation was also observed with another thin sand layers, charged in the shaft assuming increase of gas-permeability resistance in reducing coke supply operation. It was revealed that the ratio of peripherally flowing rate of tuyere gas had a considerable effect on the discontinuous behavior of both solid descending motion and gas static pressure. The ratio increased with decline in deadman gas-permeability, approach of the simulated cohesive zone to deadman surface and inflow of small particles into raceway. There was a lowest critical position of the simulated cohesive zone for the rapid increase of discontinuity. The bridging/slipping behavior with fines accumulation was significantly affected by the low gas-permeability layers charged in shaft. Setting up the chimney zone of high gas-permeability at the central part was effective to decrease the discontinuous motion.