Siemens VAI is a licensee of Midrex Technology for the production of direct-reduced iron (DRI) from iron ores and primarily natural gas. With a cumulative production exceeding 500 million tons, which is approximately 70% of the total world output, Midrex is the leading DRI production process in the world.
Gas-based direct-reduction processes are particularly
suitable for installation in those areas where natural gas
is available in abundance and at economical prices. The
Midrex Process is a shaft-type direct-reduction process
where iron ore pellets, lump iron ore or a combination
thereof are reduced in a vertical shaft (or reduction
furnace) to metallic iron by means of a reduction gas. The
reducing gas is produced from a mixture of natural gas
(usually methane) and recycled gas from the reduction
furnace. The mixture flows through catalyst tubes where it
is chemically converted into a gas containing hydrogen and
carbon monoxide. The desired reducing-gas temperature is
typically in the range of 900 °C. The gas ascends through
the material column in the countercurrent direction and
removes oxygen from the iron carriers. The product,
direct-reduced iron, typically has a total iron content in
the range of 90–94% Fe. After the DRI exits from the bottom
of the shaft, it can be compressed in the hot condition to
hot-briquetted iron (HBI) for safe storage and
transportation. DRI or HBI are virgin iron sources free from
tramp elements and are increasingly being used in electric
arc furnaces to dilute the contaminants present in the
scrap.
The largest Midrex plant built to date was at the Hadeed Steel Works on the eastern seaboard of Saudi Arabia. The plant started up in July 2007 and has a nominal production capacity of 1.76 million tons of DRI per year. In addition to being the world's largest DR plant, another highlight of this facility is that the hot DRI is immediately transferred via the so-called hot-transport system directly to the EAF melt shop. With this solution, the sensible heat from the DR process is utilized for the melting of DRI in the electric arc furnace, significantly reducing energy costs and electrode consumption. This results in shorter tap-to-tap times and a corresponding increase in the output of liquid steel.
Combined Corex-Gas-Based Direct-Reduction Plant, ArcelorMittal South Africa/Saldanha Works
At the Saldanha Works of ArcelorMittal South Africa hot metal and direct-reduced iron are produced in a combined Corex and direct-reduction facility. Coal is used as the energy source for the generation of a reduction gas needed to reduce iron ore lumps or pellets to DRI, as well as the energy source for the melting of the DRI to approximately 750,000 tons of hot metal per year (see Corex webpage). The excess gas from the Corex process is used in an adjacent Midrex DR shaft to produce approximately 700,000 t/a DRI. Production already commenced in December 1998.
Siemens Metals Technologies
Ironmaking