A furnace which allows the continual production of molten iron. The furnace is charged with a mixture of coke, iron ore and limestone. At the bottom of the furnace, coke and oxygen from the air react to produce carbon dioxide. This an exothermic reaction, and the temperature rises to 1800*C. The formula is as follows:

            C(solid) + O2(gas)---> CO2(gas)

More coke then reacts with the carbon dioxide to produce carbon monoxide.

            C(solid) + CO2(gas)---> 2CO(gas)

The carbon monoxide reduces the iron oxides to iron. For example:

          Fe2O3(solid) + 3CO(gas) ---> 3CO(gas) + 2Fe(liquid)*
* remember the temperatures at which this is happening.

The molten iron flows to the bottom of the furnace where it is tapped off. The limestone in the charge is decomposed by the heat producing calcium oxide and carbon dioxide. The calcium oxide reacts with impurities from the iron ore (mainly silica(SiO2) and forms a molten slag.

            CaO(solid) + SiO2(s) ---> CaSiO2(liquid)

The slag also sinks to the bottom of the furnace where it floats on the molten iron. The iron produced by a blast furnace contains around 3% carbon and is very brittle. In iron and steel manufacturing, the amount of carbon and other impurities is reduced by blowing oxygen into the molten iron.

ASCII model of a blast furnace. Dotted lines mean a division between layers.

       | | 
      _| |_ >-- Through this intake, new fuel enters.
     / / \ \    (limestone, ore and coke)
  __/       \__                                     
  __         __ >-- waste gas(N2 + CO2)                                    
   /.........\      is burnt to heat the                              
   |         |        incoming air.                             
   /         \                                   
   |         |   >-- limestone, coke, 
  /           \         and iron ore                     
  \           /--- steel and                                   
   \         /     brick lining                               
 ___\       /___                                     
 ___  ...... ___ >-- hot air intake                                   
    || SLAG ||_
    ||......  _ >-- slag layer output                       
   _||      ||_                                       
   _  MOLTEN  _ >-- molten iron output
    || IRON ||                                     
Also known as a Pernot furnace.

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