Steel Desulphurisation Unit – Principle, Process, Application and Advantages
PRINCIPLE
The Principle of the desulphurisation process is as follows:
A ladle of liquid steel is transferred by car turntable to the desulphurisation station. In this Position, the ladle is covered by a hood which is designed to capture and extract the fume generated during the process, and , at the same time, minimize contact between the surface of steel and the atmosphere.
For effective desulphurisation, the amount of slag carry- over from the furnace or convertor is minimized, and a basic synthetic slag is added to the ladle surface.
Desulphurisation is achieved by the deep injection of a mixture of elements including lime-fluorspar and calcium bearing compounds such as calcium silicide or calcium itself. These materials are injected through an immersed lance as fine powder, using argon as a carrier gas.
Sulphur dissolved in the liquid steel combines with calcium in the injected materials to form calcium sulphide, which floats up into the top slag.
The combination of the reaction between sulphur in the liquid steel and both the injected materials and the top slag is effective in producing extremely low residual sulphur levels of less than 10 ppm.
To achieve good results, the steel must be fully killed, with very low residual oxygen levels. The top slag must be within a fairly narrow compositional range, with very low levels of reducible oxides such as FeO, MnO and P2O5.
