A Mathematical Model of Desulphurization Kinetics for Ultra-low-sulfur Steels Refining by Powder Injection during RH Processing

A mathematical model about the variation of sulphur content in liquid steel during a 300 t RH refining process was established based on the consideration of thermodynamics, kinetics of desulphurization and conditions of practical production. The effect of initial sulphur content in the top slag on the ration of contribution of transitory desulphurization reaction in total desulphurization was included. The effects of initial sulphur content in the liquid steel, powder injection rate, particle size of powder, flow rate of RH driving gas and initial temperature of the bath on the temperature drop were taken into account. Sulphur content in the steel bath during desulphurization process and the final sulphur content in the liquid steel were analyzed. The lowest sulphur content can decrease to 10 ppm from 30 ppm by taking reasonable injection operating conditions to treat 10 min. The simulated results of sulfur removal rate and final sulphur content in liquid steel agree well with that of plant production under the same conditions, which indicates that the present model can be used to predict desulphurization process. The simulated results also show that powder injection desulphurization has better desulphurization efficiency compared with adding desulphurization agent simply onto the top of molten steel in the vacuum vessel in the practical production process.