Influence of the mineral gangue on pellets softening melting properties in blast furnace. Experimental study of phase equilibria during the melting of pre-reduced pellets.

The progressive decarbonization of the steel industry is being undertaken through the transformation of blast furnace operations, notably through the reduction of coke consumption. Lower coke rates may affect gas permeability in the cohesive zone, a viscous and impermeable layer formed by the softening and melting of iron-bearing materials. Controlling the cohesive zone, its shape, thickness, and permeability, is essential for efficient blast furnace performance. The choice of adapted raw materials, i.e. their softening and melting properties, is a straightforward way to control the cohesive zone and to increase permeability. This study investigates the melting behavior of iron ore pellets with varying chemical compositions (acidic vs. fluxed) under conditions representative of the cohesive zone. Pellets were pre-reduced using the BORIS® counter-current pilot up to 1000 °C under representative conditions of the blast furnace. Reduced pellets were then subjected to melting tests via differential thermal analysis (DTA) and quenching furnace experiments. These analyses make it possible to better understand the softening and melting behavior of pellets in a blast furnace and results show that basic pellets generate less liquid phase at high temperatures, improving mechanical properties and improved reductive gas distribution. This result also implies a deeper and thinner cohesive zone inside the blast furnace. Attention was paid to the microstructure of the iron ores as the deformation of reduced materials is triggered by the partial melting of pellets and the formation of primary slag. Results also indicate that thermodynamic modelling could be a suitable and rapid tool to anticipate the behavior of different pellets at the cohesive zone level of blast furnaces, though existing databases must be refined to better reflect real phase equilibria in commercial iron ores. [ABSTRACT FROM AUTHOR]