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.

Mathematical modelling

As a co-operation between Aalto University and University of Oulu, mathematical models were created for both the heat-up and reduction stages. Here, 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. As a co-author, my contribution is related primarily to the thermodynamic and kinetic treatment of chemical reactions.

Computational fluid dynamics modelling

During the reduction stage of the CAS-OB process, the argon-stirring of the bath induces detachment of slag droples from the top slag into the steel bath. Due to the complexity of this phenomenon, computational fluid dynamics (CFD) modelling was employed to provide valuable insight on the droplet generation rate and size distribution. Here, the magnitude of the interfacial area was tracked using the volume of fluid (VOD) method. My contribution as a co-author was related primarily to the interpretation of the results as well as their comparison to other studies.




  1. 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.
  2. 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. 35443556, 2016.
  3. 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.
  4. 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.
  5. V.-V. Visuri, M. Järvinen, K. Pääskylä, A. Kärnä, P. Sulasalmi, C. De Blasio, S. Ollila, and T. Fabritius, ”Preliminary Validation of a Numerical Model for the CAS-OB Process”, Proceedings of the 7th European Oxygen Steelmaking Conference, Czech Metallurgical Society, Třinec, Czech Republic, 2014.
  6. P. Sulasalmi, V.-V. Visuri and T. Fabritius, "Effect of Interfacial Tension on the Emulsification – Considerations on the CFD Modelling of Dispersion", in L. P. Karjalainen, D. A. Porter and S. A. Järvenpää (eds.), "Physical and Numerical Simulation of Materials Processing VII'', Materials Science Forum, vol. 762, pp. 242–247, 2013.

Theses instructed

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