Super-high bed sintering for iron ores: mechanisms, causes, and countermeasures for reduction disintegration
摘要
Super-high bed sintering, with bed depths exceeding 800 mm, is widely adopted for reducing fuel consumption and emissions. However, it significantly decreases the reduction disintegration index (RDI+3.15 mm) of sinter from ~70% to 50%, impairing blast furnace permeability and efficiency. Through a combination of industrial sampling, in situ microscopic observation, thermodynamic analysis, and sintering pot experiments, the mechanisms behind reduction disintegration under super-high bed conditions were systematically revealed. The results demonstrated that crack initiation during reduction is primarily caused by crystallographic expansion associated with the transformation of hematite to magnetite, with the extent of damage strongly influenced by the content, morphology, and distribution of hematite. Chemical analysis showed that decreased CaO content in the liquid phase promotes hematite precipitation and the formation of less-resistant high-iron calcium ferrite, thereby reducing overall sinter strength. Furthermore, heat accumulation enhances liquid phase formation, which in turn increases hematite precipitation, while porosity plays a dual role in both weakening sinter mechanical strength and inhibiting crack propagation. By strategically concentrating 5–8 mm limonite in the middle and lower layers of the sintering bed, the thermal regime and pore structure are optimized, resulting in a notable improvement in RDI+3.15 mm from 69.35% to 82.51%.