Reaction Behaviors of Mixed Burdens Consisting of Pellets and Sintered Ores in an Experimental Blast Furnace

Low-MgO sintered ores have developed into dominant burden materials for large blast furnaces operating under high pulverized coal injection in Japan, because of their low gangue content and high strength. Mixing MgO-bearing burdens with low-MgO sintered ores is an effective approach to satisfy the MgO requirement of blast furnaces. Therefore, a basket-evaluation test was performed in an experimental blast furnace (EBF) to investigate the reduction behavior of olivine pellets mixed with low-MgO sintered ores. The reduction behavior with lime-fluxed pellets was also evaluated as a reference. Softening-melting tests were also conducted under the same mixing conditions as those in the EBF tests. Olivine pellets exhibited smaller pores and contained finer hematite grains before reduction. These microstructural features influenced their reduction behavior, with low size disintegration observed in the lumpy zone in the EBF. Numerous cohesive masses with slag formed at the interface between sintered ores and lime-fluxed pellets in the EBF, facilitating their melting. In contrast, a small amount of slag was found at the interface between sintered ores and olivine pellets. The results of the softening-melting tests also revealed the superiority of olivine pellets during melting. Despite the low temperature of the initial melt formation during reduction, olivine pellets exhibited lower liquid ratios at high temperatures, resulting in a decrease in exuded slag when mixed with low-MgO sintered ores. This work proposes a general mechanism for the melting behaviors of mixed burden materials for blast furnaces.