| The scarcity of coking coals and the high cost entailed in minimizing the emissions from the coke-making process as well as the relative inflexibility of large production capacity of the conventional blast-furnace ironmaking are the main reasons for the development of non-coke smelting reduction processes with the economical and ecological compatibility. The main objectives of the alternative processes development are to use ordinary coals directly, extend the range of usable raw materials, and allow the operation at a small scale. While most of smelting reduction processes are still in various stages of development, only the COREX ironmaking has successfully reached the industrial application with its first 300000 tpa plant operated in Pretoria, South Africa. The COREX process is composed of two main reactors: the vertical shaft furnace for the gaseous reduction of iron ore to sponge iron, and the melter-gasifier for the gasification of coal and smelting of iron. The gasification process generates the reducing gas mixture (CO and H{dollar}sb2){dollar} for use in the reduction furnace and also produces heat for smelting of the direct reduced iron.; In the present work, the operating data of the COREX process are studied and process material and energy balances are prepared. The coal consumption rate of the COREX process is found higher than the coke consumption rate of the conventional process; however, the total energy consumption for the COREX process compares well with that of the blast furnace. The COREX process also generates surplus gas of high heating value which is suitable for many applications.; A reduction model employing the diffusion-limited mass-transfer coupled with virtual equilibrium at core-interface is developed to determine the reduction of iron oxide pellets. The rate of oxygen-transfer between the solid and gas phases is computed by combining the Stefan-Maxwell multi-component diffusion formalism with the iterative equilibrium constant method. The computed results agree well with the observed data and the model is extended to simulate the reduction profiles in the reduction shaft of the COREX process. It is seen that the reduction process is mainly influenced by the pore-size and pore-structure of the reduced product layers. |
