Decarburisation rates in RH–KTB degasser of CST steel plant through physical modelling study

Abstract

A physical model based on similarity principles was constructed to simulate the RH (Ruhrstahl–Heraeus) degasser of CST (Companhia Siderúrgica Tubarão, Vitória, Brazil) to evaluate the influence of metal circulation rate, which essentially defines the degree of exposure of the metal to the vacuum in the chamber, on the decarburisation rate. The circulation rate in addition influences the removal of dissolved gases such as nitrogen, and hence it is essential to optimise this parameter to achieve maximum refining efficiency with minimum refining time, thus improving the productivity of the secondary refining process. In the present work, simulation experiments investigating the kinetics of decarburisation have been carried out using the CO₂ adsorption–desorption process in sodium hydroxide solution as the circulating fluid. The effect of bottom gas flowrate and snorkel diameter in this case was also evaluated. Bottom gas injection practice, under the upleg, improves the circulation rate. Increasing the circulation rate by bottom injection leads to an increased degassing rate. However, degasification efficiency does not remain at the same level. The circulation and degasification rates can be improved by an increase in diameter of the downleg snorkel. The relative gain in degasification seems to be higher at the higher flowrate range. The results have been translated to a prototype, to optimise the process.