Corex is a smelting reduction process combining a melter gasifier with a reduction shaft. The process takes lump iron ore or pellets, non-coking coal, and oxygen as main inputs. Similar to the blast furnace process, the reduction gas moves in counter flow to the descending burden in the reduction shaft. Then, the reduced iron is discharged from the reduction shaft by screw conveyors and transported via feed legs into the melter gasifier. The gas containing mainly of CO and H₂, which is produced by the gasification of coal with pure O₂ leaves the melter gasifier at temperatures between 1000 and 1050 °C. Undesirable products of the coal gasification such as tar, phenols, etc. are destroyed and not released to the atmosphere. The gas is cooled to 800-850C and cleaned from dust particles. After reduction of the iron ore in the reduction shaft, the top gas is cooled and cleaned to obtain high caloric export gas. The main product, the hot metal can be further treated in either EAF or BOF or can be cast and sold as pig iron (US DOE, 2003).

A modified version of the Corex process enables the recycling of off-gases back to the process and thereby reduces the energy consumption of the process further. It is also possible to use the off-gases in a combined cycle power plant to produce electricity.