The Corex Process is a smelting reduction process created by Primetals as a more environmentally friendly alternative to the blast furnace. Presently, the majority of steel production is through the blast furnace which has to rely on coking coal. That is coal which has been cooked in order to remove impurities so that it is superior to coal. The blast furnace requires a sinter plant in order to prepare the iron ore for reduction. Unlike the blast furnace, smelting reduction processes are typical smaller and use coal and oxygen directly to reduce iron ore into a usable product. Smelting reduction processes come in two basic varieties, two-stage or single-stage. In a single-stage system the iron ore is both reduced and melted in the same container. In a two-stage process, like Corex, the ore is reduced in one shaft and melted and purified in another. Plants using the Corex process have been put use in areas such as

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

, and China. First COREX process was installed in 1988 at South Africa.

Process

The Corex process consists of two main parts: a ''Reduction Shaft'' and a ''Melter-Gasifier''. The main reagents for the Corex process are iron ore, noncoking coal, and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. Unlike a blast furnace, the Corex process does not use a hot blast of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, thereby greatly reducing

NOx In atmospheric chemistry, is shorthand for nitric oxide () and nitrogen dioxide (), the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropo ...

gas emissions, but instead uses oxygen. In addition, the Corex process can use iron oxides containing up to 80% lump ore and uses non-coking coal directly as a reducing agent. In the reduction shaft the iron ore, along with

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

additives, is added and then reduced by reduction gas into 95% direct reduced iron, DRI. The DRI is then redirected via six discharge screws into the melter-gasifier. The melter-gasifier has three main sections, the gaseous free board zone, the char bed, and the hearth zone, and it has an effect on several stages in the process. First it serves to create the reduction gas by gasifying the coal with oxygen and then cooling it. After being reduced, the DRI is redirected to the char bed where the iron and slag are melted and then directed to the hearth zone. The heat inside the metal gasifier keeps the amount of phenols small, keeping them out of the atmosphere. Meanwhile,

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

gas from the original gasification of the coal exit the gasifier while other byproducts are captured in the metallic slag. The rest of the hot gas is then cooled and sent into the reduction shaft resulting in the Corex export gas which is used to control pressure in the plant. Many of the gases resulting from this process can then be recycled or used to produce electricity. Dust particles also appear in these gases and the melter-gasifier recycles them with four dust burners.

Advantages

There are many advantages to the Corex Process, for example

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

emissions are up to 20% lower than with the conventional blast furnace, and the Corex process produces far less SO2 and dust than the blast furnace. In addition Corex plants do not release as many phenols or sulfides limiting

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

contamination.

Disadvantages

There are drawbacks. For example, at the JSW Steel plant in India it was found that to be viable the Corex process still needed about 15% coke. Furthermore, it has also been found that Corex plants require large amounts of oxygen which can be expensive. Also the export gas can make the process highly inefficient. However, this particular problem can be mitigated by using the export gas in electricity production.

References

{{Reflist Smelting Siemens