1. Kinetics of Reactive Droplets in BOF Steelmaking
By: Glendon Brown
Supervisor: Dr. K. Coley
Jan 13th, 2012

2. Outline Purpose Introduction Elements of the model Results Future Work
Comprehensive model of BOF refining
Introduction
BOF Steelmaking
Importance of Droplets
Elements of the model
Droplet generation
Droplet residence time
Droplet swelling
Results
Cr Reduction Work
Future Work

3. Purpose Long Term: Current work:
To create a model that can accurately predict the complex process of BOF refining
The high degree of complexity
Current work:
Focus on specific reactions of interest

4. BOF Steelmaking
Blast furnace hot metal is charged into Oxygen converters to be made into Steel
Oxygen jet blows onto the hot metal, ejecting metal droplets into the slag
Image: T. Letcher, Chemical Thermodynamics for Industry, 2004

5. Importance of Droplets
Droplets offer a greatly increased SA/V ratio accelerating refining reactions
Desulphurization
Dephosphorization
Desiliconization
Decarburization
Wide range of opinions on importance of droplets. Some workers1 suggest up to 50% of metal in the slag at a given time.
1. Urquhart and Davenport, Canadian Metallurgical Quarterly, 1973, Vol.12, No.4

6. Phosphorous Phosphorous is refined to very low levels
Competition between decarb, and dephos (Limited Oxygen Supply)
C has stronger affinity for oxygen
P needs to be oxidized to PO2.5 no gas nucleation required
C oxidation requires CO nucleation

7. Droplet Generation Subagyo et al1
Created the blowing number (NB) which correlated to generation rate
Results were coincident with previous works2,3
Subagyo, et al1
Standish and He3,4
1. Subagyo, Brooks, Coley, Irons, ISIJ International, Vol 43, 2003
2. Koria and Lange: Met Trans. B, vol 15B, 1984
3. He and Standish, ISIJ International, Vol 30, 1990
4. Standish and He, ISIJ International, Vol 29, 1989

8. Droplet Residence Time
Subagyo et al1
Developed a model based of ballistic motion of metal droplets in slag, predicted residence times up to 60 times too small (order of 1 Second)
Brooks et al2
Recognized that swelling of droplet observed by Molloseau and Fruehan3 would affect predictions of Subagyo et al.
1. Subagyo, Brooks, Coley, Canadian Met. Quarterly , Vol 44, 2005
2. Brooks, Pan, Subagyo, Coley, Met Trans B, Aug 2005
3. Molloseau and Fruehan, Met Trans B, June 2002

9. Droplet Residence Time
Subagyo et al1
Developed a model based of ballistic motion of metal droplets in slag, predicted residence times up to 60 times too small (order of 1 Second)
Brooks et al2
Recognized that swelling of droplet observed by Molloseau and Fruehan3 would affect predictions of Subagyo et al.
1. Subagyo, Brooks, Coley, Canadian Met. Quarterly , Vol 44, 2005
2. Brooks, Pan, Subagyo, Coley, Met Trans B, Aug 2005
3. Molloseau and Fruehan, Met Trans B, June 2002

10. Droplet Swelling
Molloseau and Fruehan data inadequate for general prediction
Chen1 proposed a model for swelling by balancing internal gas generation with escape rate
Rate of gas generation controlled by internal nucleation
Pomeroy2 modelled the incubation time before the onset of swelling
1.Chen and Coley, Iron. and Steelamking, Vol 37, 2010
2. Pomeroy, MSc Thesis, McMaster university, 2011

11. 1. E. Chen, Ph.D. Thesis, McMaster University, 2011.

12. 1. Pomeroy, MSc Thesis, McMaster university, 2011

13. Cr Reduction Motivation Low oxygen potential
Explain previous work by Simukanga1; sulphur increased the rate of Chromium reduction from slag by Fe-C-S
Hypothesis: slag metal emulsification
1. S. Simukanga, Ph.D. Thesis, University of Strathclyde, 1990.

14. Cr Reduction Simukanga: slag metal emulsification
Pomeroy: x-ray showed no emulsification
Hypothesis: CO nucleation rate determining step
1. S. Simukanga, Ph.D. Thesis, University of Strathclyde, 1990.

15. Experimental Apparatus
Gas out/pressure transducer
Quench zone (optional)
Steel Research Centre, McMaster University, Dec 2011

16. 1. M. Pomeroy, G. Brown, Dr. K. Coley, AISTech 2011, Conference Proceeding, May 2010.

17. Results Increase as seen with Simukanga
Subsequent decrease in reaction rate as surface poisoning takes effect
The increased reaction rate is a result of lowered surface tension, as proposed by Chen, which causes enhanced CO evolution
Gas evolution peak was consistent with previous work by Chen, Pomeroy, and Fruehan
Droplet swelling was not observed (consistent with predictions of Pomeroy)

18. A gas halo was instead

20. Results
The linear correlation clearly indicates a volumetric dependency of gas evolution
Conclusion: a thin layer of internal nucleation exists, labelled δ, where sufficient oxygen has diffused to nucleate CO
Thickness δ

21. δ Analyzed Volume of this layer is: Expected rate of gas generation:
Numerical solutions (Pomeroy) of in relevant droplet size range show: δ ≈ 0.07R
Rate

22. Next Steps Dephosphorization High residence time desirable
High CO nucleation rate desirable
However, C in competition with P
High CO nucleation rate undesirable
Looking for a “sweet spot”

23. Next Steps
Fe-C-P-S droplets will be studied with C - ~4 wt%, P – 0.02 wt%, S – 0 to 0.02 wt%
2 different methods
CPVI and XRF to measure gas evolution and swelling
Quenching experiments to investigate the progress of dephos via ICP

24. Tying things together
Incorporation of the Cr reduction data and dephosphorization data into the model developed by Chen and Pomeroy
Expansion of the model to include more of the significant reactions of steelmaking will make this model useful and accurate in predicting BOF refining to increase yield and improve economics of the processes

25. Thanks
NSERC
McMaster SRC
Dr. K. Coley
Members of my research group

26. Questions?
Thank you for your attention

27. Appendix NB Surface Tension modification parameter of Chen:
When the Kelvin Helmholtz instability criterion is exceeded and the interface breaks down
Li and Harris1 found that splashing occurred at:
Surface Tension modification parameter of Chen:
1. Li and Harris, Pyrometallurgy 95 Conf. Proc., IMM, London, 1995

28. Molloseau also reported a peak at 0.011 wt% S with subsequent decrease