Low Carbon Sinter Making: Use of Inert Gas to Improve Sinter RDI

Sinter making is an intermediate step in value-added chain for producing steel. Iron ore fines (−10 mm) is agglomerated to make it suitable blast furnace feed. In sintering process, iron-ore is partially reduced, and different fluxes are added to eliminate the undesirable elements in the slag. Solid fuel mainly coke breeze is used both as energy provider and reducing agent. During the sintering process, oxidised phase (Hematite) is converted to reduced phase (Magnetite). However, during post sintering process, the reduced phase again gets oxidised as it reacts with the atmosphere during cooling. Thus, higher the coke breeze input, higher is the generation of reduced phases and in turn higher % of reduced phases will be retained in the product sinter. With increase in low grade ores, consumption of fuel and fluxes will further increase. The challenge, therefore, is to produce sinter with good RDI without increasing the solid fuel. The knowledge on this domain is very limited and thus in this work an innovative approach on injecting an inert gas during cooling of sinter was suggested. The hypothesis is that the injection of inert gas reduces the availability of oxygen therefore inhibiting the re-oxidation of reduced phase to oxidised phase in sinter. Lab scale trials followed by a plant trial in TSL India sinter plant strengthened the hypothesis as the sinter RDI improved by 8 points. This technology has the potential to significantly decrease the coke breeze requirement and thereby reduce CO2 emissions, increased mine life, without affecting the sinter quality.