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Metallurgical and Materials Transactions B

, Volume 48, Issue 3, pp 1868–1884 | Cite as

A Mathematical Model for Reactions During Top-Blowing in the AOD Process: Validation and Results

  • Ville-Valtteri VisuriEmail author
  • Mika Järvinen
  • Aki Kärnä
  • Petri Sulasalmi
  • Eetu-Pekka Heikkinen
  • Pentti Kupari
  • Timo Fabritius
Article

Abstract

In earlier work, a fundamental mathematical model was proposed for side-blowing operation in the argon oxygen decarburization (AOD) process. In the preceding part “Derivation of the Model,” a new mathematical model was proposed for reactions during top-blowing in the AOD process. In this model it was assumed that reactions occur simultaneously at the surface of the cavity caused by the gas jet and at the surface of the metal droplets ejected from the metal bath. This paper presents validation and preliminary results with twelve industrial heats. In the studied heats, the last combined-blowing stage was altered so that oxygen was introduced from the top lance only. Four heats were conducted using an oxygen–nitrogen mixture (1:1), while eight heats were conducted with pure oxygen. Simultaneously, nitrogen or argon gas was blown via tuyères in order to provide mixing that is comparable to regular practice. The measured carbon content varied from 0.4 to 0.5 wt pct before the studied stage to 0.1 to 0.2 wt pct after the studied stage. The results suggest that the model is capable of predicting changes in metal bath composition and temperature with a reasonably high degree of accuracy. The calculations indicate that the top slag may supply oxygen for decarburization during top-blowing. Furthermore, it is postulated that the metal droplets generated by the shear stress of top-blowing create a large mass exchange area, which plays an important role in enabling the high decarburization rates observed during top-blowing in the AOD process. The overall rate of decarburization attributable to top-blowing in the last combined-blowing stage was found to be limited by the mass transfer of dissolved carbon.

Keywords

Decarburization Slag Sample Metal Droplet Metal Bath Decarburization Rate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

\( c_{{{\text{p}},{\text{L}}}} \)

Specific heat capacity of liquid metal (J/(kg K))

\( d_{\text{t}} \)

Nozzle throat diameter (m)

\( d_{\text{p}} \)

Diameter of the particle (m)

\( C_{i,\omega } \)

Control factor of species i at the reaction interface ω

\( J_{\text{eff}} \)

Multiplication factor of the metal droplet generation rate

\( h_{\text{lance}} \)

Distance of the top lance from the surface of the metal bath (m)

\( {{\Delta }}h_{\text{dis}} \)

Specific enthalpy of dissolution into liquid iron (J/kg)

\( l_{\text{m}} \)

Latent heat of melting (J/kg)

\( m_{\text{a}} \)

Mass of the added material (kg)

\( m_{\text{bath}} \)

Mass of the metal bath (kg)

\( \dot{m}_{\text{md}} \)

Metal droplet generation rate (kg/s)

\( \dot{m}_{{{\text{md}},{\text{eff}}}} \)

Effective metal droplet generation rate (kg/s)

MAE

Mean absolute error

\( n_{\text{lance}} \)

Number of exit ports in a nozzle

\( N_{\text{B}}^{\prime } \)

Modified blowing number

\( p_{0} \)

Stagnation pressure at upstream part of the top lance (Pa)

Re

Reynolds number

RMSE

Root-mean-square error

\( R^{2} \)

Correlation coefficient (square of the Pearson product-moment correlation coefficient)

Sc

Schmidt number

Sh

Sherwood number

\( T_{\text{a}} \)

Temperature of the added material (K)

\( T_{\text{bath}} \)

Temperature of the metal bath (K)

\( T_{\text{bath}}^{\text{new}} \)

Updated temperature of the metal bath (K)

\( T_{\text{m}} \)

Melting temperature of the particle (K)

\( \dot{V}_{{{\text{G}},{\text{lance}}}}^{\prime } \)

Volumetric gas flow rate through top lance (Nm3/s)

\( y_{i} \)

Mass fraction of species i in the bulk phase

\( y_{i}^{*} \)

Mass fraction of species i at the reaction interface

\( \theta \)

Inclination angle of each nozzle relative to lance axis (deg)

\( \rho_{\text{p}} \)

Density of the particle (kg/m3)

\( \lambda_{\text{e}} \)

Effective heat conductivity (W/(m K))

\( \tau_{\text{m}} \)

Melting time of additions (seconds)

Notes

Acknowledgments

This research has been conducted within the framework of the DIMECC SIMP research program. Outokumpu Stainless Oy, the Finnish Funding Agency for Technology and Innovation (TEKES), the Graduate School in Chemical Engineering (GSCE), the Academy of Finland (Projects 258,319 and 26,495), the Finnish Foundation for Technology Promotion, the Finnish Science Foundation for Economics and Technology, and the Tauno Tönning Foundation are gratefully acknowledged for funding this work. The first author thanks Professor Herbert Pfeifer for the possibility to conduct part of the research at RWTH Aachen University. Tommi Kokkonen is acknowledged for preparation of the slag microsections. In addition, Professor Rauf Hürman Eriç, Kevin Christmann, and Tim Haas are acknowledged for their valuable comments on this manuscript.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2017

Authors and Affiliations

  • Ville-Valtteri Visuri
    • 1
    Email author
  • Mika Järvinen
    • 2
  • Aki Kärnä
    • 1
  • Petri Sulasalmi
    • 1
  • Eetu-Pekka Heikkinen
    • 1
  • Pentti Kupari
    • 3
  • Timo Fabritius
    • 1
  1. 1.Process Metallurgy Research UnitUniversity of OuluOuluFinland
  2. 2.Department of Mechanical EngineeringAalto UniversityAaltoFinland
  3. 3.Outokumpu Stainless OyTorneFinland

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