Kinetics and mechanism of iron ore coal composite pellets reduction

Composite pellet contains mixture of fines of iron bearing oxide and carbonaceous material (coal, coke etc), which has been imparted sufficient green strength for subsequent handling by cold bonding technique. The composite pellets offer the advantage of reduction rate, utilization of fines and pollution control. During non-isothermal reduction of composite pellets, it is found that degree of reduction varies from 46 to 99 pct, depending upon pellets composition and heating rate. It is also observed that devolatilization of coal generates reducing gases (such as H-2, CO etc). A significant quantity (approximately 10 to 20 pct of pellet weight) of extraneous H2O and CO2 are retained by oven-dried pellets as chemically combined or strongly adsorbed species. These gases, liberate during heating to high temperature, react with carbon and hydrocarbon to generate additional quantities of CO and H-2. The paper analyses the non-isothermal kinetics data and discusses the mechanism of iron ore - coal composite pellets reduction. Activation energy values obtained for final stage reduction, vary from 183 to 268 KJ/mol. Hence, it can be concluded that the overall rate of reduction of composite pellets is controlled by the rate of gasification reactions.