Midrex is direct reduction process using a shaft-reactor and is developed by Midrex/Kobe Steel. Iron ore pellets, lump iron ore or a combination of pellets and ore 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 and recycled gas from the reduction furnace. The mixture flows through catalyst tubes where it is chemically converted into a gas containing H2 and carbon monoxide (CO). The desired reducing gas temperature is typically in the range of 900°C. As the iron ore descends through the furnace by gravity flow,the gas ascends through the material column and removes oxygen from the iron carriers. The product, DRI, is typically 90% to 94% iron. After the DRI exits from the bottom of the shaft, it can be compressed to hot briquetted iron (HBI) for safe storage and transportation. A derivative of the Midrex process can use coal through gasification (MXCOL©Technology).
The process offers the following benefits:
Using natural gas and agglomerated iron ore makes the process simple;
The packed reactor with the counter-current flow of reactants provides a high efficiency;
As the doubling of capacity requires only a 40% increase in the reactor diameter, the technology offers good economies of scale;
The process is highly flexible with regards to iron ore reducing gas sources. Plants can operate at a wide spectrum of hydrogen to carbonmonoxide ratios (0.5 to 3.5) (Eliot and Kopfle, undated)
This DRI production process is highly energy efficient and further energy gains are realized if the hot DRI is immediately transferred to the EAF melt shop. This way, the heat from the direct reduction process lowers the cost of melting the DRI in the EAF, significantly cutting energy costs and electrode consumption (IEA, 2009. p.68).
The MIDREX process represents 70% of the installed DRI capacity worldwide. The largest plant in operation has a capacity of 1.76 Mt per year, about half the capacity of a standard-size blast furnace (IEA, 2009. p.68).