CAS-OB

The CAS-OB (Composition Adjustment by Sealed argon bubbling – Oxygen Blowing) is a unit process designed for controlling the steel composition and temperature in secondary metallurgy. The process can be divided into heat-up, alloying and reduction of slag. The objective of the heat-up stage is to increase the temperature of the steel bath by chemical heating with aluminium particles. Typically, heating rates up to 10 °C/min can be obtained in industrial practice. The reduction stage aims to improve the yield of the alloying elements.

Highlights

• The detachment of slag droplets in ladle metallurgy was studied using CFD simulations. The magnitude of the interfacial area was tracked using the volume of fluid (VOD) method. The volume of the droplets generated was found to be in close agreement with that calculated analytically on the basis of energy balance at the interface. Furthermore, it was found that the size distribution of slag droplets can be characterised well with the Rosin-Rammler-Sperling distribution function. 
• Two mathematical models were derived and validated for chemical reactions during the heat-up and reduction stages. The employed approach is somewhat similar as in the AOD models developed in our earlier work. The developed models can be used for accurate prediction of the changes in bath composition and temperature and are ideal tools for studying the energy efficiency and yield of the process.

Selected publications

• A. Kärnä, M. Järvinen, P. Sulasalmi, V.-V. Visuri, and T. Fabritius, "An Improved Model for the Heat-up Stage of the CAS-OB Process: Development and Validation", Steel Research International, vol. 89, no. 10, article 1800141, 2018.
• P. Sulasalmi, V.-V. Visuri, A. Kärnä, M. Järvinen, S. Ollila, and T. Fabritius, "A Mathematical Model for the Reduction Stage of the CAS-OB Process", Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, vol. 47, no. 6, pp. 3544–3556, 2016.
• P. Sulasalmi, V.-V. Visuri, A. Kärnä, and T. Fabritius, ”Simulation of the effect of steel flow velocity on slag droplet distribution and interfacial area between steel and slag”, Steel Research International, vol. 86, no. 3, pp. 212–222, 2015.
• M. Järvinen, A. Kärnä, V.-V. Visuri, P. Sulasalmi, E.-P. Heikkinen, K. Pääskylä, C. De Blasio, S. Ollila, and T. Fabritius, ”A Novel Approach for Numerical Modeling of the CAS-OB Process: Process Model for the Heat-Up Stage”, ISIJ International, vol. 54, no. 10, pp. 2263–2272, 2014.

Theses instructed

• K. Pääskylä, "Experimental validation of a CAS-OB model", Master's thesis, University of Oulu, 2014.