The MIDREX® Process
The success of the MIDREX® Process is due to the soundness of the basic technology plus continuous technology development. There are three major stages: reduction, reforming and heat recovery.
Reduction
Iron oxide, in pellet or lump form, is introduced through a proportioning hopper at the top of the shaft furnace. As the iron ore descends through the furnace by gravity flow, it is heated and the oxygen is removed from the iron ore (reduction) by counterflowing gases that have a high H2 and CO content. These gases react with the Fe2O3 in the iron ore and convert it to metallic iron, leaving H2O and CO2. For production of CDRI, the reduced iron is cooled and carburized by counterflowing cooling gases in the lower portion of the shaft furnace. The DRI can also be discharged hot and fed to a briquetting machine for production of HBI, or fed hot, as HDRI to an EAF.
To maximize the efficiency of reforming, offgas from the shaft furnace is recycled and blended with fresh natural gas. This gas is fed to the reformer, a refractory-lined chamber containing alloy tubes filled with catalyst. The gas is heated and reformed as it passes through the tubes. The newly reformed gas, containing 90-92 percent H2 and CO (dry basis), is then fed hot directly to the shaft furnace as reducing gas.
Heat Recovery
The thermal efficiency of the MIDREX® Reformer is greatly enhanced by the heat recovery system. Sensible heat is recovered from the reformer flue gas to preheat the feed gas mixture, the burner combustion air and the natural gas feed. In addition, depending on the economics, the reformer fuel gas may also be preheated.
Reduction
Iron oxide, in pellet or lump form, is introduced through a proportioning hopper at the top of the shaft furnace. As the iron ore descends through the furnace by gravity flow, it is heated and the oxygen is removed from the iron ore (reduction) by counterflowing gases that have a high H2 and CO content. These gases react with the Fe2O3 in the iron ore and convert it to metallic iron, leaving H2O and CO2. For production of CDRI, the reduced iron is cooled and carburized by counterflowing cooling gases in the lower portion of the shaft furnace. The DRI can also be discharged hot and fed to a briquetting machine for production of HBI, or fed hot, as HDRI to an EAF.
Heat Recovery
The thermal efficiency of the MIDREX® Reformer is greatly enhanced by the heat recovery system. Sensible heat is recovered from the reformer flue gas to preheat the feed gas mixture, the burner combustion air and the natural gas feed. In addition, depending on the economics, the reformer fuel gas may also be preheated.
