Iron which is the fourth most abundant element of earth crust. This is 5% of earth crust. Iron consists in the form of mineral compounds like, in the form of iron ore which is iron oxide mixed with other impurities. To get pure iron, ore is undergoing a process in furnace. In furnace ore, limestone, coke (as fuel) and air introduce in furnace which produce pig iron after breaking the iron oxide. Pig iron contains some other impurities in the form of other materials. Like carbon 3-4.5%, manganese 0.15-2.5%,phosphorus 0.1-2%,silicon 1-3%,sulfur 0.5-0.1%.this pig iron is further go through a process to give the final shape of it as cast iron and most of pig iron further proceed in to steel .
Iron making: Iron is produced by reducing iron oxide in to metallic iron. There are several step used to make iron in to metallic form. First pig iron (which consist of many other materials with iron like carbon , silicon, manganese, sulfur and some other impurities) is produced in Blast Furnace and then it’s further refine in different types or grades of iron in different other furnaces like cupola, Bessemer ,open-hearth and Linz-Donawitz-Verfahren ETC.
Blast furnace: Blast furnace is used to produce pig iron by reducing the iron ore. This process is called smelting of iron ore.It was invented in Germany in about 1400.It has about 30 meters high and 6meters diameter. The main benefit of blast furnace is that it can be used or operates continuously and no need to shut down for repair oftener than once every 5 to 7 years. Daily capacity of blast furnace is about 600 tons to 1000 tons of pig iron in 24 hours or in one day.
Iron making in blast furnace
Iron ore contain Hematite (Fe2O3).The lime stone (CaCO3)helps to reduce iron oxide with the help of coke and impurities in Ore form the slag, which melt near the bottom of the furnace. Coke is also used to heat the slag and iron. The slag is float on the top of the molten iron and it removed through the slag notch, just like cream remove from milk. The material and impurities are drawn separately. This form of material is called PIG IRON.
(pig iron is very impure form of iron which have manganese ,phosphorus ,silicon and carbon with iron)
Different Processes in Blast Furnace: There are different chemical and physical processes are happen in Blast Furnace.
The temperature In the blast furnace is between 2000C to 20000C.AT the top of the Blast Furnace, There are 2000C to 8000C temperature to remove the moisture from the raw material. All the volatile substance like hydrogen, nitrogen etc. are removed from the coke at the next high temperature zone. Carbonates or flux as limestone (Calcium Carbonate or CaCO3) for decomposition purpose. Sometime FeCO3 and MnCO3 also introduce in to blast furnace because FeCO3 has the lowest decomposition temperature of 5200C, whereas limestone the highest decomposition temperature of 9000C-9200C.First coke reacts with the oxygen(O2) and make the carbon mono-oxide(CO) , which further reacts with the iron ore(Fe2O3) to form the iron in molten form or some iron reacts with directly with coke to form the molten iron. The lime stone (CaCO3) decompose in to calcium- oxide(CaO)and carbon-dioxide(CO2).Then calcium- oxide(CaO) reacts with the silicon dioxide(SiO2) to form a liquid slag (CaSiO3).Slag which floated on the top of the iron remove at the bottom of the furnace. The final products of blast furnace PIG IRON and SLAG. The pig iron is further refine in to the several grades of the iron or steel , while the slag is actually the waste but it can be used as a material in road construction or to improve mineral-poor soils for agriculture.
Pig Iron formation chemical reactions: In which coke as carbon(C) reacts with the oxygen O2, Make carbon mono-oxide(CO) and then carbon mono-oxide reacts with iron ore component ( Fe2O3) to make pig iron.
2 C + O2 → 2 CO
Fe2O3+ 3 CO → 2 Fe + 3 CO2
Slag formation chemical reactions: Lime Stone which is use for decomposition process ,first convert in to calcium- oxide(CaO) and carbon-dioxide(CO2).Then calcium- oxide(CaO) reacts with the silicon dioxide(SiO2) to form a liquid slag (CaSiO3).Slag which floated on the top of the iron remove at the bottom of the furnace.
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3
