KINETICS AND MECHANISM OF REDUCTION OF IRON ORE PELLETS UNDER LOAD

摘要

Reduction of iron ore pellets under load is a crucial forward step towards simulating reduction operation in shaft furnaces. Therefore, an understanding of the kinetics and mechanism of reduction of iron ore pellets under different values of loads is the main aim of this work. A laboratory scale shaft furnace for testing the reduction of commercial iron ore pellets under load was constructed. A set of series of reduction experiments of iron ore pellets with a synthetic reformed natural gas similar to that used in Alexandria Iron and Steel Company (ANSDK), Egypt, was carried out under various operational conditions of varying temperature, type of ore pellets and applied load. The reducing gas mixture is composed of 55% H_2, 36% CO, 5%H_2O, 3%CO_2 and 1%N_2. The reduction tests were carried out at 750-1000°C under different values of loads namely, 0.2, 0.4 and 0.57 kg/cm~2. The reduction behavior of pellets was followed up by measuring the oxygen weight loss as a function of time. Experimental runs were performed to investigate the kinetics and mechanism under controlled conditions of temperature and applied load. Three procedures were applied to elucidate the kinetics and mechanisms of reduction of Samarco and LKAB pellets under load; the first depends on the calculation of activation energy values from Arrhenius plots whereas the second uses the heterogeneous gas-solid mathematical formulations and calculation. A third procedure was developed in the present work depending on the shrinking core modulus and the mixed control ratio to give a definite and quantified measure that allows for performing a good analysis about the actual effect of reduction temperature and applied load upon the controlling mechanism and furthermore it indicates the relative effect of the different mechanism in the mixed control regime. Results obtained by applying the three procedures were analyzed, compared and correlated.