- Blast furnace
- External hot metal treatment station
- Steelmaking vessel
- Steel ladle treatment station
Where the sulphur is best removed depends on a number of processing options such as thermochemical factors, steel product mix, available facilities, process variability, level of operation and local economics. In practice the sulphur is removed to some extent at all of these locations but the extent at each will depend on the above.
In the blast furnace, desulphurisation is effected at the expense of iron productivity and fuel (coke). When hot metal is desulphurised outside the blast furnace, iron output increases and coke consumption decreases as less limestone is added. Thermochemical considerations show that the tendency of sulphur o react is about 5 times as high in hot metal as in steel. This makes the hot metal ladle the most effective location to remove sulphur.
The are many hot metal ladle desulphurising processes. Historically, they have been classified by reagent and include soda ash, lime base reagents, magnesium and magnesium mixtures, calcium carbide and combinations of all of these. Which one to use will depend on many factors related to the existing facilities, technological justification and economic considerations. Injection is the most widely accepted. Materials use tends to concentrate on co-injection of magnesium and lime-based or calcium carbide combinations which yield fluid, thin easily removable slags with little of no iron holding potential. Multi-silo injection installations will have the capability to store and supply a variety of reagents so that hot metal desulphurisation can be more accurately tailored to the compositional and quality demands of the final steel.
To assist with the process of iron desulphurisation Foseco Steel offers FOSCAST Iron injection lances and SLAX 35 slag coagulant for the efficient removal of the fluid slag before transfer to the steelmaking vessel.
