Working in smelting can be a very dangerous profession; if something goes wrong it can have serious consequences. In 2001, an accident happened at a blast furnace in Wales because of a problem with the cooling system.

Blast furnace accident

Iron is not found as a pure metal in the ground as it is too reactive. Instead, it is found as a compound such as iron oxide. The ore haematite contains iron(III) oxide.

How is the pure iron metal extracted from iron oxide?

If you look at the reactivity series, carbon is higher than iron. This means that carbon can displace iron from its compounds.

iron oxide + carbon à iron + carbon dioxide

To extract iron a blast furnace is used. This is a large steel structure, about 30 m high. Blast furnaces are used day and night continuously. The largest one in the UK can produce around 8,000 tonnes of iron a day. This is enough to make five cars every minute!

Iron oxide and carbon in the form of coke, a material like coal, are added to the top of the blast furnace. Hot air at around 1,000 °C is blasted into the bottom and temperatures inside can reach up to 2,000 °C. These temperatures are needed for the reaction to take place. The iron produced is molten and is removed from the bottom of the furnace.

Because temperatures inside the blast furnace are so high it is important that the walls are cooled to stop them melting. A cooling system is normally used where cold water is pumped in-between the inner and outer walls of the furnace.

In an accident in Wales in 2001, around 60 tonnes of water leaked into the inside of the furnace. When the cold water touched the molten iron huge quantities of steam were produced inside the furnace. It caused the walls of the furnace to explode outwards and many people were hurt.

 

Your students can read Smart Scientist: Pioneering metal scientist Constance Tipper to learn how a life-threatening engineering problem was solved.