Process Description :
The oxygen steelmaking process converts the molten iron from the blast furnace - with up to 30% steel scrap - into refined steel. High purity oxygen is blown through the molten bath to lower carbon, silicon, manganese, and phosphorous content of the iron, while various fluxes are used to reduce the sulfur and phosphorous levels. The impurities and a small amount of oxidized iron are carried off in the molten slag that floats on the surface of the hot metal.

BOF Facility
The actual furnaces are a small part of the facility as the schematic drawing shows. Gas cleaning devices and materials handling equipment occupy most of the space.

Scrap Charging
The first step for making a heat of steel in a BOF is to tilt the furnace and charge it with scrap. The furnaces are mounted on trunnions and can be rotated through a full circle.

Molten Iron Charging
Hot metal from the blast furnace accounts for up to 80% of the metallic charge and is poured from a ladle into the top of the tilted furnace.

Furnace Operation
The charged furnace is returned to an upright position and a water cooled oxygen lance is lowered from the top; oxygen is blown into the bath at supersonic speeds causing rapid mixing and heat from the oxidation of iron and impurities. Fluxes (burnt lime, burnt dolomite, and fluorspar) are added to help carry off the impurities in the floating slag layer. This step requires only about 15 minutes of an overall 45 minute tap to tap cycle time.

Tapping
After the steel has been refined, the furnace is tilted (opposite to the charging side) and molten steel is poured out into a preheated ladle. Alloys are added to the ladle during the pour to give the steel the precise composition desired. In some steelmaking applications, further refining is conducted in the ladle to remove oxygen and sulfur from the molten steel.

Basic Oxygen Furnace

Equipments :
There are three principal categories of oxygen furnaces that are utilized.
Top Blown Process (BOP)
In the top blown process a water cooled oxygen lance is lowered from the top of the furnace and blows oxygen at supersonic speed into the melt.


Bottom Blown Furnace (Q-BOP)
In the bottom-blown processes, oxygen is introduced through a number of tuyeres in the bottom of the furnace. In the Q-BOP process, the oxygen tuyeres are cooled by injecting hydrocarbon gas through an outer pipe surrounding the oxygen pipe. Most bottom-blown processes use methane or propane as the hydrocarbon coolant, but fuel oil is also used. A principle advantage of the Q-BOP process is that it reduces the height requirements of the process allowing a lower profile building to be constructed.


Combination Processes
One class of combination blown process uses top-blown oxygen with inert gas (argon and Nitrogen) injection through the bottom by means of tuyeres or permeable elements. In the second class of combination furnaces, there are both top and bottom oxygen lances; the bottom lances can also be used for inert gas injection during stirring.






Combustion Technology :
Combustion Technology:- The natural gas injection in the Q-BOP design is shown. However, as previously indicated, this is not a combustion process per se, the fuel provides cooling by cracking into hydrogen and carbon monoxide. The carbon monoxide is carried through to the exhaust gases, while the hydrogen is absorbed in the melt.





Energy Consumption :
About 1.5 million Btu per ton of steel is required in BOP steelmaking. Slightly over half the energy is provided by the molten iron charge. The remaining energy is supplied by the oxidation reactions generated by the oxygen lance. Oxidation of carbon and silicon in the hot metal are the most important sources of oxidation energy for the process and levels of carbon and silicon in the hot metal are not only very important to the energy balance of the process but also determine the share of metal scrap that can be added. In the Q-BOP process where a hydrocarbon is injected as a coolant, this hydrocarbon does not add to the heat of the melt but provides cooling by the endothermic reaction. Carbon monoxide produced in the BOP is burned in the dust recovery and gas clean-up section.