Basic Oxygen Furnace

Basic Oxygen Furnace is the device which is used for changing molten iron into liquid steel. Due to its effectiveness and precise operation, it is preferred by the most of the steel manufacturer of the world.

How it Works?
In basic oxygen furnace, oxygen is blown into the furnace or BOS vessel through a water cooled oxygen lance, like the LD converter. This helps in the oxidation of carbon and the other unwanted elements in the hot metal. After oxidation carbon is transformed into carbon monoxide gas, which passes from the converter to a cleaning plant. After cleaning, carbon can be again used as a fuel gas. The rest of the elements in the metal are converted to acidic oxides. They combine with the lime and other fluxes that are added during the blow. This produces a slag that floats on the surface of the metal. From the surface the steel is tapped when it is at the correct temperature and composition.

The molten metal is run out via the tap hole into a ladle, when the furnace is tilted. After the removal of the steel, the furnace is turned upside down and the slag that is left inside runs into another ladle.

Types
There are three types of oxygen blown furnace that are categorized on the basis of functions:

Top blown process (Furnace)
In the top blown furnace oxygen lance that is water cooled lance is lowered from the top of the furnace and blows oxygen at supersonic speed into the melt.

Bottom Blown Furnace
In the bottom blown furnace the oxygen is introduced through a number of tuyeres in the bottom of the furnace. The injected hydrocarbon gas through an outer pipe surrounding the oxygen pipe helps in the cooling of the oxygen tuyeres. Apart from fuel oil, methane or propane are also used as hydrocarbon coolant. Bottom blown furnace reduces the height requirements of the process allowing a lower profile building to be constructed.

Combination Furnace
These types of furnaces are generally of two types. The first type of furnace uses top-blown oxygen with inert gas (argon and nitrogen) injection through the bottom by means of tuyeres or permeable elements. Whereas the second type uses both top and bottom oxygen lances. The bottom lances can also be used for inert gas injection during stirring.