2012-03-02T11:39:00.000-08:00

Iron making by Linz-Donawitz-Verfahren process

It is also known as the Basic oxygen processes or Oxygen converter method. It is usually denoted by BOS process. And commonly, It is also known as LD converter method. It is the moderate form or type of Bessemer converter, the main different is that in Bessemer converter air is used and in this method oxygen I used instead of air. Today most of the steel or iron is produced by this process due to the low cost, less time consuming and better quality.

The basic oxygen steel-making process is as follows:

Molten pig iron from a blast furnace is poured into a large refractory-lined container called a ladle. The metal in the ladle is sent directly for basic oxygen steelmaking or to a pretreatment stage. Pretreatment of the blast furnace metal is used to reduce the refining load of sulfur, silicon, and phosphorus. In desulfurizing pretreatment, a lance is lowered into the molten iron in the ladle and several hundred kilograms of powdered magnesium are added. Sulfur impurities are reduced to magnesium sulfide in a violent exothermic reaction. The sulfide is then raked off. Similar pretreatment is possible for desiliconisation and dephosphorisation using iron oxide and lime stone as reducing agent. The decision to pretreat depends on the quality of the blast furnace metal and the required final quality of the Basic Oxygen Steel making process (BOS). Filling the furnace with the ingredients is called charging. The BOS process is autogenously (the required thermal energy is produced during the process). Maintaining the proper charge balance, the ratio of hot metal to scrap, is therefore very important. The BOS vessel is one-fifth filled with steel scrap. Molten iron from the ladle is added as required by the charge balance. A typical chemistry of hot metal charged into the BOS vessel is 4% C, 0.2–0.8% Si, 0.08%–0.18% P, and 0.01–0.04% S. The vessel is then set upright and a water-cooled lance is lowered down into it. The lance blows 99% pure oxygen onto the steel and iron, igniting the carbon dissolved in the steel and burning it to form carbon monoxide and carbon dioxide, causing the temperature to rise to about 1700°C. This melts the scrap, lowers the carbon content of the molten iron and helps remove unwanted chemical elements. It is this use of oxygen instead of air that improves upon the Bessemer process, for the nitrogen (and other gases) in air does not react with the charge as oxygen does. High purity oxygen is blown into the furnace or BOS vessel through a vertically oriented water-cooled lance with velocities faster than Mach 1. Fluxes (which burnt lime stone or dolomite) are fed into the vessel to form slag, which absorbs impurities of the steelmaking process. During blowing the metal in the vessel forms an emulsion with the slag, facilitating the refining process. Near the end of the blowing cycle, which takes about 20 minutes, the temperature is measured and samples are taken. The samples are tested and a computer analysis of the steel given within six minutes. A typical chemistry of the blown metal is 0.3–0.6% C, 0.05–0.1% Mn, 0.01–0.03% Si, 0.01–0.03% S and P. The BOS vessel is tilted again and the steel is poured into a giant ladle. This process is called tapping the steel.

The steel is further refined in the ladle furnace, by adding alloying materials to give the steel special properties required by the customer. Sometimes argon or nitrogen gas is bubbled into the ladle to make sure the alloys mix correctly. The steel now contains 0.1–1% carbon. The more carbon in the steel, the harder it is, but it is also more brittle and less flexible. After the steel is removed from the BOS vessel, the slag, filled with impurities, is poured off and cooled.

IRON MAKING

2012-02-04T10:47:00.005-08:00

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

First Raw Material such as iron ore (which consists naturally and contain iron oxide. There are different classification of iron ore, such as Fe₂O₃,Fe₃O₄and FeO etc.), Coke (used as fuel) and Lime Stone (used for decomposition of materials) are introduce from the top of the 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 between200⁰C 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 FeCO₃and 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 O_2, 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