COREX

The COREX^® Process

Corex is an industrially and commercially proven smelting-reduction process developed by Siemens VAI for the cost-efficient and environmentally friendly production of hot metal from iron ore and coal. The process differs from the conventional blast furnace route in that non-coking coal can be directly used for ore reduction and melting work, eliminating the need for coking plants. The use of lump ore or pellets also dispenses with the need for sinter plants.

Process History
The Corex process was developed in the late 1970s and its feasibility was confirmed during the 1980s. Following the first industrial application of a Corex C-1000 plant (nominal production of 1,000 tons of hot metal per day) at Iscor Pretoria, South Africa, four C-2000 plants (nominal production of 2,000 tons of hot metal per day) were subsequently put into operation at Posco/Korea, Mittal Steel/South Africa and at JSW Limited/India. In early November 2007, the first Corex C-3000 plant was started up at Baosteel, China. It has a nominal production capacity of 1.5 million tons of hot metal per year.

Corex C-2000 Plant, Saldanha Steel, RSA

Process Description
In the Corex Process all metallurgical work is carried out in two separate process reactors – the reduction shaft and the melter gasifier. Lump ore, sinter, pellets or a mixture thereof are first charged into a reduction shaft via a lock-hopper system where they are reduced to direct-reduced iron (DRI) by a reduction gas moving in the counter-flow direction. Discharge screws convey the DRI from the reduction shaft into the melter gasifier where final reduction and melting takes place in addition to all other metallurgical and slag reactions. Hot metal and slag tapping are carried out as in conventional blast furnace practice. The quality of the hot metal is equivalent to that produced in a blast furnace.

Main Plant Sections of Corex Plant

Viewing the process from the coal-route perspective, non-metallurgical coal is directly charged into the melter gasifier via a lock-hopper system. Due to the high temperatures predominating in the dome of the melter gasifier (in excess of 1000 °C), a portion of the hydrocarbons released from the coal during devolatilization are immediately dissociated to carbon monoxide and hydrogen. Undesirable by-products such as tars and phenols, etc. are destroyed and therefore cannot be released to the atmosphere. Combustion with oxygen injected into the melter gasifier results in the generation of a highly efficient reduction gas.

The reduction gas exiting from the melter gasifier consists mainly of CO and H2 laden with fine coal, ash and iron dust. This dust is largely removed from the gas stream in a hot-gas cyclone and is then recycled to the process. Through the addition of a cooling gas, the reduction-gas temperature is adjusted to its optimum working range. After leaving the hot-gas cyclone, the reduction gas is then blown into the reduction shaft via a bustle, reducing the iron ores in counter flow.

The top gas is subsequently cooled and cleaned in a scrubber, after which it is available as a highly valuable export gas with a net calorific value of approximately 7,500–8000 kJ/m³ (STP). This gas is suitable for use for a wide range of applications.

Process Flow Sheet

Process Economy
Because coking and sintering plants are not required for the Corex Process, substantial cost savings are achieved in the production of hot metal. The extent of such savings depends, of course, on the local site conditions, however, can be in the range of up to 20% as proven under actual operating conditions.

Environmental Aspects
Corex plant emissions contain only insignificant amounts of NOx, SO2, dust, phenols, sulphides and ammonium. Emission values already exceed by far future European standards. Also, waste-water emissions from the Corex Process are far lower than those in the conventional blast-furnace route. These environmental features are additional key reasons for the attractiveness of the Corex Process.

Use of Export Gas
After the cleaning and cooling of the top gas which exits the reduction shaft, it is then available for use in numerous industrial applications. These include electrical power generation, production of DRI (direct-reduced iron) and for heating purposes throughout the iron and steel works. In the chemical industry the Corex export gas can also serve as a feed stock for many other applications.

Additional Considerations
The latest generation of Corex plants, the C-3000, is ideally suited for integration into green- or brown-field steel works projects. It can replace the blast furnace, or can be used as a source of virgin iron for minimills. The economics of the Corex plant already provide an answer to future scrap and coke shortages, and the continually increasing demands placed on steel quality. Another alternative is the installation of a Corex C-3000 plant as a stand-alone merchant plant for the production of hot metal and/or pig iron.