An investigation into a lower temperature and low cost direct reduction process for iron-making.
The blast furnace process for the reduction of iron ore to pig iron faces problems such as emission of air pollutants, high investment cost and the current major problem of decreasing supplies of coke. Coke is used in large quantities to promote a combination of direct and indirect reduction within the furnace. Due to the lack of good coking coal within South Africa, and dwindling supplies worldwide, new iron-making processes, are being developed using coal and/or natural gas to replace coke as the reductant. The new processes allow efficient use of carbon, fed in the form of coal pellets (coalbased processes) or natural gas (gas-based processes), as the reducing agent. Presently, most coal-based processes Use an excess of coal, up to 500% stoichoimetric addition, and are run at temperatures up to ±1200°C, although reduction tends to proceed at ±850°C. This project developed a low temperature process using mixed pellets of fine waste iron oxide and fine domestic coal with a natural carbonaceous binder (a by-product from local pulping industry). Reduction tests performed on composite pellets in a tube furnace and thermobalance indicated, upon analysis by X-Ray Diffraction and Scanning Electron Microscope, that reduction occurred gradually at 900°C. Implementing induction heating of bulk pellets reduced heating times substantially. Induction heating also resulted in direct reduced iron [DRI] containing 75 - 80% metallic iron. Energy consumption based on coal usage amounted to 23.71 GJ/ton DRI, which compares with the calorific consumption of most coal-based processes, i.e. coal consumption range between 15 and 25 GJ/ton DRI. Energy consumed during induction heating amounted to 9.94 GJ/ton DRI, as electricity. This energy consumption value does not take into account the efficiency of the primary energy required to generate electricity.