Numerical simulation of industrial scale RH degasser under different operational parameters

Abstract

With increasing stringent requirements, the requirement to produce ultra-clean steel is also increasing. The Ruhrstahl–Heraeus (RH) degasser plays an important role in ultra-clean steel production process by removing the dissolved gases from the molten steel by introducing a re-circulatory motion through a vacuum chamber. The de-gassing in RH vessel is a complex fluid dynamics-controlled process involving interaction between many process parameters. RH vessel performance during the campaign also gets affected due to nozzle blockages and refractory erosion. A detailed combined parametric study was required to understand the flow pattern of argon and molten steel and its effect on refractory wear with varying conditions during the campaign. In the present work, an Eulerian–Eulerian multiphase-based CFD model has been developed to simulate molten steel flow and argon gas distribution inside an industrial RH degasser. The model was validated and used to conduct the parametric study based on the plant operational conditions by varying the argon gas flow rate, snorkel diameter, snorkel immersion depth, nozzle blockage conditions and bottom purging in the ladle. The model indicated an increase in metal circulation rate with increasing argon flow rate but simultaneously leading to increased refractory wear in the upper snorkel area. Increasing snorkel diameter and immersion depth increases the circulation rate and shifts the erosion position towards the vacuum chamber. Maintaining a higher diameter for the up-snorkel improves process performance with lesser refractory wear. Different nozzle blockage conditions result in different circulating flow profiles where the re-circulation rate during treatment is more affected by unsymmetrical and lower nozzle blockage. Bottom purging in the ladle during the treatment leads to open eye formation affecting the steel quality. The developed model can be a valuable tool for optimising the process parameters, improving the RH degasser performance, and ensuring higher refractory life during RH treatment.