The purpose of a blast furnace is to reduce and convert iron oxides into liquid iron called "hot metal".
The blast furnace is a huge, steel stack lined with refractory brick.
Iron ore, coke and limestone are put into the top, and preheated air is blown into the bottom.
IRONE ORE:
Iron ore is a rock that contains iron combined with oxygen.
Some of the world's highest quality iron ore comes from Australia.
COKE:
• Coke is made from coal. Once mined, the coal is crushed and washed.
• Coal is then baked in coke ovens for about 18 hours.
• During this process, by-products are removed and coke is produced.
FLUX:
• Flux is a term for minerals used to collect impurities during iron and steelmaking.
• Limestone and dolomite are fluxes.
• The flux causes a chemical reaction and elements not needed for steelmaking join together to form slag.
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METHOD:
Three substances are needed to enable to extraction of iron from its ore. The combined mixture is called the charge:
Iron ore, haematite - often contains sand with iron oxide, Fe2O3.
Limestone (calcium carbonate).
Coke - mainly carbon
The charge is placed a giant chimney called a blast furnace. The blast furnace is around 30 metres high and lined with fireproof bricks. Hot air is blasted through the bottom.
BLAST OPERATION:
• The Charge is fed in at the top,
• Bell Doors open (One at a time)
• Coke burns & makes Carbon Monoxide,
• The Carbon Monoxide mixes with the Oxygen in the Iron Ore (leaving Iron),
The Molten Iron falls to the bottom of the Furnace,
The limestone joins with the impurities to make Slag and floats on top of the Molten Iron. The slag and the Molten Iron are tapped off regularly.
Special rail cars bring the Molten Iron away, The liquid iron typically flows into a channel and indentations in a bed of sand.
Once it cools, this metal is known as pig iron.
REATIONS:
Oxygen in the air reacts with coke to give carbon dioxide:
C(s) + O 2(g) CO2(g)
The limestone breaks down to form carbon dioxide:
CaCO3(s) CO2 (g) + CaO(s)
Carbon dioxide produced in 1 + 2 react with more coke to produce carbon monoxide:
CO2(g) + C(s) 2CO(g)
The carbon monoxide reduces the iron in the ore to give molten iron:
3CO(g) + Fe2O3(s) 2Fe(l) + 3CO2(g)
The limestone from 2, reacts with the sand to form slag (calcium silicate):
CaO(s) + SiO(s) CaSiO3(l)
WHY PIG IRON IS PIG IRON:
• PIG IRON is raw iron in an ingot form.
• It is the result of smelting Iron Ore, Coke and Limestone in a blast furnace.
• It is a hard but brittle mix of iron (90% or more) and carbon (typically 4-5%), manganese, sulfur, phosphorus, and silicon (roughly 3% in total).
• The name is derived from the time when the iron ran into moulds. A row of moulds was said to resemble a litter of suckling pigs, so the single ingots were referred to as pigs.
• To create a ton of pig Iron
• We start with 2 tons of ore,
• 1 ton of coke and
• ½ ton of limestone.
• The fire consumes 5 tons of air.
• The temperature reaches almost 3000 deg F (about 1600 degrees C) at the core of the blast furnace!
BLAST WASTE:
• Slag, Ammonia, Light Oils and Coal Tars are waste from the Furnace,
• They make raw materials for cements, plastics and fertilisers.
• Pig iron contains 4 percent to 5 percent carbon and is so hard and brittle that it is almost useless.
We do one of two things with pig iron:
• You melt it, mix it with slag and hammer it to eliminate most of the carbon (down to 0.3 percent) and create wrought iron.
Wrought iron is the stuff a blacksmith works with to create tools, horseshoes and so on. When you heat wrought iron, it is malleable, bendable, weldable and very easy to work with. Or we can create steel.
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