Reducing Slag Volume at Cohesive Zone of Blast Furnace by using Low-slag Sintered Ore with Reducible Magnetite

摘要

Lowering the reducing agent rate (RAR) of blast furnaces (BFs) is an effective way to mitigate CO2 emissions in the steel industry. It is well known that low-slag sintered ores can be effective at lowering the RAR. Therefore, in this study, we focused on the manufacturing technologies of low-slag high-FeO sintered ores. High-temperature sintering was used to maintain enough strength before and during the reduction, resulting in the chemical composition of sintered ores with a T.Fe above 60 mass% and an FeO content above 8 mass%. Improvement in the permeability of the sintering bed and the melt properties were the main challenges. Stand- support sintering, selective granulation, and binder use are essential for improving the permeability. The use of brucite and reducing the Al2O3 content of ores while designing their penetration length are essential for improving the melt properties as well. We implemented all of these measures in plant trials, and low- slag high-FeO sintered ores were successfully manufactured. The sintered ores exhibited a low slag volume in the cohesive zone, resulting in a lower RAR of the BF both in the offline simulator and actual plant operation. The sintered ores differed from other low-slag sintered ores manufactured previously in two aspects; large numbers of both small-sized magnetite grains and voids between grains. The reducibility of magnetite was superior to that of hematite with CaO doping, whereas MgO doping had the opposite effect. These behaviors of magnetite may explain the high reducibility of the manufactured low-slag high-FeO sintered ores.