A furnace for smelting iron ores, such as haematite (Fe2O3) or magnetite (Fe3O4), to make pig iron. The furnace is a tall refractory-lined cylindrical structure that is charged at the top with the dressed ore (see beneficiation), coke, and a flux, usually limestone. The conversion of the iron oxides to metallic iron is a reduction process in which carbon monoxide and hydrogen are the reducing agents. The overall reaction can be summarized thus:Fe3O4+2CO+2H2 → 3Fe+2CO2+2H2O The CO is obtained within the furnace by blasting the coke with hot air from a ring of tuyeres about two-thirds of the way down the furnace. The reaction producing the CO is:2C+O2 → 2CO In most blast furnaces hydrocarbons (oil, gas, tar, etc.) are added to the blast to provide a source of hydrogen. In the modern direct-reduction process the CO and H2 may be produced separately so that the reduction process can proceed at a lower temperature. The pig iron produced by a blast furnace contains about 4% carbon and further refining is usually required to produce steel or cast iron.
Fe3O4+2CO+2H2 → 3Fe+2CO2+2H2O
2C+O2 → 2CO