Effective utilisation of waste fines in preparation of high-basicity double-layer DRI pellets for minimisation of sticking

Abstract

Sinter of high basicity is well known for affecting the permeability of the burden in the lower portion of the blast furnace due to the formation of more viscous slag. The high-basicity pellets possess less weather resistance if hardened below 1200°C due to the presence of free lime particles. When hardened above 1200°C, the weather resistance increases with increasing sticking tendency among the pellets due to the formation of low-melting eutectics. In the present investigation, efforts were made to make composite-coated iron ore-fluxed pellets to minimise the problems mentioned above. Lime addition to the core of pellets varied from 5 to 100%. The composite pellets subsequently were fired at 1150, 1200 and 1250°C for 30 min. Increasing lime content in the pellets resulted in increasing crushing and drop strength of the green pellets. The percent of reduction and cold crushing strength were found comparable to the conventional pellets with varying lime content up to 30% (core basicity 4.68). Weathering resistance was also found increasing trends with increasing firing temperature. XRD analysis revealed the presence of free lime particles inside the core of composite pellets with increasing lime content. From the present work, it could be concluded that the composite-fluxed pellet made with 20% lime in the core (core basicity 3.0) has enough physical strength (187 kg), a high percentage of reduction (96%) and excellent weather resistance properties.