The CAS-OB (Composition
Adjustment by Sealed argon bubbling – Oxygen Blowing)
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.
As a co-operation between Aalto University and University of
Oulu, mathematical models were created for both the heat-up
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
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
detachment of slag droplets in ladle metallurgy was studied using CFD
simulations. 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
mathematical models were derived and validated for chemical reactions
during the heat-up and reduction stages. The models are well-suited
for studying the rate limiting mechanisms and heat losses in
- 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.
"A Mathematical Model for the Reduction Stage of the CAS-OB
and Materials Transactions B: Process Metallurgy and Materials
Processing Science, vol. 47, no. 6, pp. 3544–3556, 2016.
- P. Sulasalmi, V.-V.
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,
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.
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.
- 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.
- K. Pääskylä, "Experimental validation of a CAS-OB model",
Master's thesis, University of Oulu, 2014.