2006 European Phoenics User Meeting, London Applied CFD in the Metallurgical Industry Jonas Alexis MEFOS AB

2006 European Phoenics User Meeting, London

Applied CFD in the Metallurgical IndustryApplied CFD in the

Metallurgical Industry

Jonas Alexis MEFOS ABJonas Alexis MEFOS AB


Outline

Why are MEFOS modelling Metallurgical processesWhat is applied CFD at MEFOSExample: Sulphur Refining of Steel— Transport description— Reaction model— Reaction Zone

* Scalar equation model* Empirical model

Validation— Transport Equation— Sulphur refining

Conclusions


Why are MEFOS modelling metallurgical processes?

The goal for the metallurgical industry is to achieve the material properties needed for production of a given product. This requires control of the amount of:

• Alloying elements (C, Si, Mn, Cr, Al ..)• Other elements (S, N, H, P, Cu, Zn ..)• Unwanted non-metallic particles (Inclusions). Also composition and size distribution

•Continuous measurement and sampling for process control is difficult in most process steps. The models are therefore needed for:

• Optimisation of the different process steps • Development of process control systems• Enhanced understanding • Education


What is applied CFD at MEFOS

When fundamental models are missing or impossible to realize because of the lack of data, which is often the case, other methods need to be utilised.

One example: Fundamental data needed to describe the slag/metal-interface in a stirred ladle during sulphur refining is missing. Instead, empirical models of that interface, based on sampling at the steel plant can be used. The use is necessary if sulphur-refining in a production ladle is to be simulated.


Sulphur RefiningTransport description (Gas

Stirring)

Ladle Radius = 1.25 mSteel Weight = 65 tSlag Weight = 1200 kgGas Flow Rate = 100 Nl/min

Open eyes


Slag Layer

Interface (Reaction zone)

Steel SurfaceGas Stirred Ladle

Sulphur RefiningTransport description (Gas

Stirring)


Sulphur RefiningReaction Model

2[Al] + 3 [O] =

Al2O3

[Fe] + [O] = FeO

[Mn] + [O] = MnO

2[Si] + [O] =

SiO2

[S] + (O2-) = [O] +

(S2-)

5 equations 6 unknowns (Al, Fe, Mn, Si, S and O)!!!


Sulphur RefiningReaction Model

Equation 1. Al is related to Al2O3

Equation 2. Fe is related to FeOEquation 3. Mn is related to MnOEquation 4. Si is related to SiO2

Equation 5. [S] is related to (S) O is related to:wt%O] = [wt%O]Al O + [wt%O]FeO +

[wt%O]MnO + [wt%O]SiO +[wt%O]S

2

2 3


Reaction Zone Scalar Equation model

Top part of a Plane in the in the ladle, through the open eyes

Gas flow Directed Upwards

Steel Phase

Slag Phase

Reaction Zone (Mixed Steel and Slag)


Reaction ZoneSampling (Empirical model)

Sampler

Sampling in the ladle

After sampling


Reaction ZoneSampling (Empirical model)

After sampling and quenching, each sample was mechanically opened. The metal bulk, slag bulk and slag-metal interface can be easily identified. Thereafter, the slag part was physically divided into a number of zones on the basis of the distance from the slag-metal interface. The width of each zone was not constant for all the samples. Small pieces of collected slag were analyzed using light optical microscope (LOM) and scanning electron microscope (SEM). The chemical compositions of the slag samples were analyzed and the sulphur contents were determined.


Reaction ZoneEmpirical Model

The figures shows schematically the contact of metal with the lowest layer of slag droplets and the flow of metal associated with slag droplets. The following assumptions are made:

1. After stabilization of the flow, the whole slag layer is in droplet form.2. All slag droplets are spherical and having the same size and shape.3. The linear velocity of the metal along the periphery of the slag droplet is equal to the

velocity of the bulk flow of the metal at the slag-metal interface.4. The contribution of the metal film covering each slag droplet to the rate of mass

exchange is negligible.


Reaction ZoneEmpirical Model

The metal volume associated with each slag droplet can be expressed by:

(1)

The mass of the metal associated with all slag droplets is given by:

(2)

The average time to travel a distance of 2 r can be evaluated by

(3)

The time required to flush out all the metal can be written as

(4)

The flush-out rate of the metal in a unit cell can be expressed by:

(5)

Eqs. (2) to (5) lead to

(6)

()⎥⎦⎤⎢⎣⎡π−=33r34r221v () mcelltotal rarrM ρπ⎟⎟⎠⎞⎜⎜⎝⎛⎥⎦⎤⎢⎣⎡−= 2233_ 434221

⎟⎟⎠⎞⎜⎜⎝⎛+π=metalmetalav Vr2Vr21t ⎟⎟⎠⎞⎜⎜⎝⎛+π== metalmetalavflushVr2Vr21tt

flushcell_totalmetaltMK=

2metalmmetalaV185.0Kρ=


Sulphur Refining and Reoxidation Model

0.0000.0020.0040.0070.0090.0110.0130.0150.0180.0200.0220.0240.0270.0290.031

0.0300.0330.0360.0390.0410.0440.0470.0500.0530.0560.0590.0610.0640.0670.070

1.1E-41.4E-41.6E-41.8E-42.2E-42.5E-42.7E-43.0E-43.3E-43.5E-43.8E-44.1E-44.4E-44.6E-44.9E-4

[%S] [%Al] [%O]

[%S] [%Al] [%O]

Steel/slag interface


ValidationTransport description

Velocity measurements with graphite rods


0.6 s efter start!

0,22

0,23

0,24

0,25

0,26

0,27

0,28

0,29

0,3

0,31

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 2

0,2 m/s0,3 m/s0,4 m/s0,5 m/s0,6 m/s1,0 m/s

0,2 m/s => = 0,2 H cm0,3 / => m s = 0,6 H cm0,4 / =>m s = 1,1 H cm0,5 / => m s = 2,0 H cm0,6 / =>m s = 3,1 H cm1,0 / => m s = 7,9H cm

ValidationWave Height Model

Simulated waveheight

Height above Fluid Surface

y = 1,4133x + 0,0002

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0 0,01 0,02 0,03 0,04 0,05 0,06

Height above fluid surface (m)

Total height (m)


ValidationValidation of Wave Height

Model

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10

Wave height (m)

Velocity (m/s)

Bernoulli CFD-model

Bernoulli’s equation for incompressible flow 101202 22tan2 ghvghvtConspghv =⇒=⇒=++ρ

Comparison between Bernoulli and simulation


ValidationTransport Description

1 2

3

Measuring positions in the ladle

Induction stirrer

1 2

Porous plugs for gas injection



Velocity measurements with graphite rods



0

0,2

0,4

0,6

0,8

1

1,2

0 0,5 1 1,5 2 2,5 3 3,5

Distance from stirrer (m)

Steel velocity (m/s)

Worn ladle

Measured

Steel velocities in ladle during induction stirring

Predicted


ValidationSulphur Refining and

ReoxidationFor a validation of the ”Sulphur refining and reoxidation predictions from the model a comparison between predicted results and data from the industry was performed. Slag and Steel was sampled before and after the sulphur refining process. The process took 850 seconds and was performed in vacuum making it impossible to sample during the process. The two sets of Slag and Steel samples were analysed and used as input data and resulting Steel analysis respectively.


ValidationSulphur Refining and

Reoxidation

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0 200 400 600 800Time [s]

wt% [Al], [O] and [S]

0,00

0,05

0,10

0,15

0,20

0,25

0,30

wt% [Mn] and

[Al]

[O]

[Mn]

[Si]

[S]

0,00

5,00

10,00

15,00

20,00

25,00

30,00

35,00

0 100 200 300 400 500 600 700 800 900

Time [s]

wt% (Al2O3), (MgO) and (SiO2)

0,00

0,40

0,80

1,20

1,60

2,00

2,40

wt% (FeO),(MnO) and (S)

(SiO2)

(Al2O3)

(MnO)

(FeO)(S)

(MgO)

Slag analysis Steel analysis

Meaured Predicted


Conclusions

• For a Qualitative description (Parametric studies) a simpler reaction zone model can be used.

• For a Quantitative description of Sulphur refining, the development of empirical models describing the reaction zone in a steel ladle must be utilised due to the lack of data prohibiting development of a fundamental model.

Documents

2006 European Phoenics User Meeting, London Applied CFD in the Metallurgical Industry Jonas Alexis MEFOS AB