Metallurgical coal

Martin

Almost but not quite.

1. Ore, carbon (coke or charcoal) and limestone are loaded into the top of the furnace. Sometime limestone is not included (as at Corby) since the ore contains a lot of it. The limestone is the flux
2. Hot air is blown in at the bottom of the furnace (the air is heated by the exhaust gas from the furnace). Now days the air pressure can be 4 or more atmospheres.
3. Some of the carbon burns to provide heat. There then follows a number of chemical reactions between the carbon, ore, air and limestone resulting in the removal of the oxygen from the iron ore by most of the remaining carbon.
4. The products from the furnace are: Raw cast iron (containing an uncontrolled amount of carbon and other impurities such as sulphur), slag (the remains of the limestone) which was, at Corby, tipped and then quarried for road stone, and blast furnace gas. The gas, nitrogen and carbon monoxide, is washed with water and used as a low calorific value fuel. The more efficient the furnace the lower the carbon monoxide content. The water, after washing, contains nasties such as zinc and cyanides.

This is different from a cupola which is used for remelting iron and steel for casting.

Scrap steel is used in the steel making process where the remaining carbon is burnt out of the raw iron using a jet of oxygen in a separate furnace. This is highly exothermic and scrap is added, usually half way through a blow, to cool everything down. The resulting metal is essentially pure iron. The correct amount of carbon, may be as coke, is then added to give steel of the required composition.

High alloy steels are produced from steel scrap of known provenance (not scrap cars) in specialist furnaces.

JA