furnace

The blast furnace is used to extract iron from a mixture of iron ore, coke, and limestone. The less dense impurities float above the molten iron and are tapped off as slag. The molten iron sinks to the bottom of the furnace and is tapped off into moulds referred to as pigs. The iron extracted this way is also known as pig iron.

Structure in which fuel such as coal, coke, gas, or oil is burned to produce heat for various purposes. Furnaces are used in conjunction with boilers for heating, to produce hot water, or steam for driving turbines - in ships for propulsion and in power stations for generating electricity. The largest furnaces are those used for smelting and refining metals, such as the blast furnace, electric furnace, and open-hearth furnace.