A Study on High-Grade Iron ore Beneficiation to Reduce Alumina for Enhanced Blast Furnace Productivity

Abstract

Iron ore pellets are largely characterized by inherent physical and chemical properties of the ore. Alumina and silica play important roles in determining the productivity of a Blast Furnace. On average, one percent increase in iron content improves productivity by 2% and reduces coke consumption by 1%. Therefore higher iron ore feed content to blast furnace is always preferred. Indian hematite, though rich in iron content has a higher content of alumina and lower silica content. Alumina to silica ratio is as high as 1.5–3%. Adverse alumina to silica ratio is detrimental for the blast furnace. This should be less than 1.5 and preferably below 1. High alumina content in the blast furnace burden irrespective of its composition (Lumps, Sinter and Pellet) generates slag with higher viscosity. This needs a higher amount of fluxes and coke, thereby producing large slag volumes and thus decreasing productivity of blast furnace. In general, 1% increase in alumina content in a blast furnace burden increases coke rate by 2.2%, decrease in the productivity by 4% and an increase in flux consumption by 30Kg /t of hot metal production. A typically high-grade iron ore assaying Fe 64%, SiO2 2.70%, Al2O3 2.50% is received at ArcelorMittal Nippon Steel India (Formerly known as Essar Steel India Ltd), Dabuna. The study with various beneficiation circuits was carried out to reduce alumina with least possible rejects. Subsequently, we were able to bring Al2O3 down by 0.15–0.30% in final concentrate. This resulted in productivity enhancement of Blast furnace by up to 3.69 T/cum/day. The 1905 cum working volume blast furnace has produced 7012 tons which was 140% of nameplate capacity. The study here highlights the optimization of beneficiation circuit for high-grade iron ore to attain higher productivity of both Pellet Plant and Blast Furnace with the least amount of rejections.