Optimization of Pellet Plant Straight Grate Induration Furnace Firing Cycle for High Alumina and High LOI Iron Ore Pellet

Indian iron ores are suffering from high amounts of alumina and loss on ignition (LOI), which are deleterious constituents in both the pelletizing as well as iron making processes. Iron ore fines utilized in pellet making consist of alumina in the range of 3.20–3.35% and LOI in the range of 3.50–3.70%. Detailed palletization studies have been carried out on high alumina as well as high LOI pellets to improve the properties of the pellet for direct reduced iron making plant (DRI) by optimizing the straight grate induration furnace firing cycle. Preheated and fired pellets were tested for physical and metallurgical properties. Mineralogical studies were carried out using an optical microscope. From the laboratory studies, it was found that under optimum conditions, such as preheating temperature of 1000 °C and preheating time of 2.7 min, roasting temperature of 1300–1310 °C and roasting time of 14.5 min, the roasted pellet properties like tumbler index (T.I) of 94.2%, cold crushing strength (CCS) of 275 kg/p and reduction degradation index (RDI) of 8.5% were achieved due to better coating of slag phase around the hematite grains by improving the fluidity of the melt phase, This led to an increase in the pore density of the pellet by decreasing the bigger size pores. For high alumina and high LOI pellets, the residence time of the existing firing cycle should be increased by 3.7 min (from 39.9 to 43.2 min) and machine speed should be decreased by 0.23 m/min (from 2.91 to 2.68 m/min) to achieve better pellet properties which are suitable for DRI making.