Experimental Investigation on Metallic Droplet Behavior in Molten BOF Slag

Abstract

In order to better understand the metallic droplet behavior during a slag treatment process, a physical modeling based on the similarity principle was performed in a transparent scaled-down vessel at room temperature. Paraffin oil, 20 wt pct copper sulfate solution, and compressed air were used to simulate the molten slag, metallic droplet, and carrier gas, respectively. The droplets injected into paraffin oil during the experiment were captured by a high speed camera and were analyzed by Image Pro Plus software to obtain the droplet size distribution. The critical droplet size in the physical modeling and slag treatment process is quantitatively correlated. The results show that droplet breakage phenomenon is dominant over its coalescence in the current industrial practice, and droplet breakage is enhanced with increasing gas flow rate and/or lance depth. No significant effect of the nozzle configuration was found on the droplet breakage and coalescence. The droplet size distribution varies with the lance position. Gas flow rate and lance depth are the most important factors for droplet breakage, the extent of which can be reduced through a proper selection of the operational conditions. A linear relationship between the droplet size and the input energy flux is obtained.

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Abbreviations

a :

Cross-section area of lance (m2)

A :

Hamaker constant (around 10−20 J)

d :

Droplet diameter (mm)

\( d_{\text{c}} \) :

Critical droplet diameter (mm)

\( d_{\text{N}} \) :

Normalized droplet diameter

\( \bar{d}_{0} \) :

Average value of the initial droplet diameter (mm)

\( \bar{d}_{\text{i}} \) :

Average value of the resulting droplet diameter (mm)

\( E_{\text{In}} \) :

Input energy flux (kJ m−2 s−1)

\( Fr_{\text{m}} \) :

Modified Froude number

h :

Film thickness (mm)

\( h_{0} \) :

Initial film thickness (mm)

\( h_{c} \) :

Critical film thickness (mm)

H :

Submerged lance depth (m)

g :

Gravitational acceleration (m/s2)

\( L_{\text{X}} \) :

Lower limit of a given bin (mm)

\( L_{\text{Y}} \) :

Upper limit of a given bin (mm)

\( N_{\text{f}} \) :

Normalized frequency (mm−1)

\( N_{\text{XY}} \) :

Frequency in a given bin

\( P_{\text{a}} \) :

Atmosphere pressure (Pa)

\( Q_{\text{a}} \) :

Gas flowrate at pressure \( P_{\text{a}} \) (m3 s−1)

r :

Radius of droplet (mm)

\( r_{\text{eq}} ,\;r_{\text{i}} ,\;r_{\text{j}} \) :

Equivalent radius, radius of droplet i and j, respectively (mm)

R :

Top radius of the physical model (mm)

t :

Time (s)

\( t_{\text{i}} \) :

Interaction time (s)

u :

Gas velocity (m s−1)

V :

Approach velocity (m s−1)

We :

Weber number

\( We_{\text{c}} \) :

Critical Weber number

\( \eta \) :

Conversion efficiency of kinetic energy

\( \mu \) :

Viscosity, (Pa s)

\( \rho \) :

Density (kg m−3)

\( \sigma \) :

Interfacial tension between paraffin oil and droplet (N m−1)

d :

Droplet

g :

Gas phase

l :

Liquid phase

m :

Physical modeling

p :

Slag treatment process

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Acknowledgments

The financial support from an IWT project 140514 (Belgium) is highly acknowledged. Yannan Wang would like to give his thanks to the China Scholarship Council (CSC).

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Correspondence to Lingling Cao or Muxing Guo.

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Manuscript submitted April 16, 2019.

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Wang, Y., Cao, L., Vanierschot, M. et al. Experimental Investigation on Metallic Droplet Behavior in Molten BOF Slag. Metall Mater Trans B 50, 2354–2361 (2019). https://doi.org/10.1007/s11663-019-01635-8

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