| Summary: | 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. === Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.
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