Introduction :
Iron produced in the blast furnace is known as pig iron or cast iron. Pig iron is the iron which contains 4% of carbon and some other impurities.
Carbon contents present in pig iron are reduced by burning off carbon as carbon monoxide and carbon dioxide. Impurities present as sulphur, manganese etc are oxidised as their oxides. There are three methods of burning carbon for production of steel.
(i) Bessemer Process
(ii) Open Hearth Process
(iii) Electric Furnace Process
This was the first process for the mass-production of steel from molten iron. Henry Bessemer invented this process in 1855.
Principle: Removal of impurities from iron by oxidation is the key principle of this process. The oxidation also raises the temperature and hence melts the iron.
Process: In this process, burning takes place in a pear shaped furnace called Bessemer Converter. This furnace is coated with basic mixture of calcium oxide or magnesium oxide (CaO / MgO). Hot air is introduced through holes. The temperature of furnace is maintained at 1873K. Manganese in the iron is removed as manganese silicate, (which is called as slag).
This process can be used for rapid manufacture of large quantities of steel. The steel producd by this process can be used for the construction of the high buildings. This process complemented the Bessemer process to produce steel. It is easier to control because it is a slow process.
In this process, cast iron, iron scrap, haematite and lime is taken in open hearth furnace. This furnace is heated at temperature of 1873 K. This furnace is heated with (CO+N2). (CO+N2) is called producer gas. Impurities are removed by oxidation with haematite.
Energy Consumption: An electric arc furnace consumes an energy of 350 - 700 kWh/ton of steel produced. We can reduce the energy consumption to 425 kWh/ton by using oxy-fuel burners.
This process is used for the electric production of steel. It is used for remelting of steel scrap. This process is useful for those markets where the quality of steel is not critical.
Iron produced in the blast furnace is known as pig iron or cast iron. Pig iron is the iron which contains 4% of carbon and some other impurities.
Carbon contents present in pig iron are reduced by burning off carbon as carbon monoxide and carbon dioxide. Impurities present as sulphur, manganese etc are oxidised as their oxides. There are three methods of burning carbon for production of steel.
(i) Bessemer Process
(ii) Open Hearth Process
(iii) Electric Furnace Process
Bessemer Process of Manufacturing:
This was the first process for the mass-production of steel from molten iron. Henry Bessemer invented this process in 1855.
Principle: Removal of impurities from iron by oxidation is the key principle of this process. The oxidation also raises the temperature and hence melts the iron.
Process: In this process, burning takes place in a pear shaped furnace called Bessemer Converter. This furnace is coated with basic mixture of calcium oxide or magnesium oxide (CaO / MgO). Hot air is introduced through holes. The temperature of furnace is maintained at 1873K. Manganese in the iron is removed as manganese silicate, (which is called as slag).
2Mn + O2 ----------> 2MnO
Si + O2 -----------> SiO2
MnO + SiO2 -----------> MnSiO2
Phosphorus
present as impurity is removed by formation of slag. This slag is
called Thomas slag. Thomas slag is very useful fertilizer.
4P + 5O2 -----------> 2P2O5
3CaO + P2O5 -----------> (Ca)3(PO4)2 Thomas Slag
Open hearth process of manufacturing:
This process can be used for rapid manufacture of large quantities of steel. The steel producd by this process can be used for the construction of the high buildings. This process complemented the Bessemer process to produce steel. It is easier to control because it is a slow process.
In this process, cast iron, iron scrap, haematite and lime is taken in open hearth furnace. This furnace is heated at temperature of 1873 K. This furnace is heated with (CO+N2). (CO+N2) is called producer gas. Impurities are removed by oxidation with haematite.
Fe2CO3 + 3C ----------> 2Fe + 3CO
2Fe2O3 + 3S -----------> 4Fe + 3SO2
5Fe2O3 + 6P ------------> 10Fe + 3P2O5
2Fe2O3 + 3Si ------------> 4Fe + 3SiO2
3CaO + P2O5 ------------> Ca3(PO4)2 (Slag)
Electric Arc Furnace
In this method, iron is heated electrically. Normally thesedays, steel is prepared by open hearth process. About 39% of the steel manufactured in US is produced from the electric furnace. The stel produced by this process is not very pure or of high quality.Energy Consumption: An electric arc furnace consumes an energy of 350 - 700 kWh/ton of steel produced. We can reduce the energy consumption to 425 kWh/ton by using oxy-fuel burners.
This process is used for the electric production of steel. It is used for remelting of steel scrap. This process is useful for those markets where the quality of steel is not critical.
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