modeling sen preheatingccc.illinois.edu/s/2014_presentations/16_li-y... · 2014. 8. 18. ·...
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CCC Annual ReportUIUC, August 20, 2014
Yonghui Li
Department of Mechanical Science & EngineeringUniversity of Illinois at Urbana-Champaign
Modeling SEN Preheating
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 2
Objectives
• Develop an accurate preheating model to optimize preheating process:– Fuel composition;– Preheating time;– Torch configuration;– Insulation;– Refractory conductivity.
• Obtain air entrainment, flow and temperature distributions from combustion model.
• Evaluate Flame Temperature Model (in spread-sheet).
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 3
Burner tip
TC 1 SEN
TC 5TC 3
TC 4 TC 6
Gas temperature
Wall temperature
Premixed natural gas(mainly CH4)/ O2
Two-port SEN
Preheating experiment setup[1]
Stand-off distance
97
197
341
Unit: mm
324oC
249oC
174oC
23oC
91oC
Infra-red photo of SEN outside wall
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 4
Measurements[2] (for model validation)2. Wall temperature (transient are not listed here. )
1. Gas temperature 197mm below SEN top
3. The shape of flame
4. SEN outside wall temperature
324oC
249oC
174oC
23oC
91oC
Thermocouple
TC3 TC4 TC5 TC6
X* (mm) 394 538 394 538
Y* (mm) 48 48 69 69
Temp. (oC) 584 554 453 397
X: Distance from top air inlet;Y: Distance from SEN centerline.
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 5
Thermal – Flow Model
• FLUENT simulation is 2D axisymmetric. – The two-port SEN is simplified as a ring shaped port with the
same exit area.• The burner tip is assumed as annular shape with 3× bigger area.
– To avoid supersonic and mesh refinement at burner tip, accounting for gas expansion.
24*1.6mm diameter
1*0.8mmdiameter
Simplified as
Mixture inlet
17.4mm diameter of outer ring of holes
Rosebud tip surface
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 6
Model geometry and mesh97mm Validation Case 147mm Case
1-mm coating layer with 4 cells through thickness
Stand-off distance
88843 quadrilateral cells total
14797
Insulation Case
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 7
Material Properties
• Flow • SEN [1,4,5]
0
5
10
0 200 400 600 800 1000 1200
Ther
mal
Con
duct
ivity
(W
/m-K
)
Temperature (°C)
50010001500200025003000
0 200 400 600 800 1000 1200Spe
cific
Hea
t (J/
kg-K
)
Temperature (°C)
16% Porosity Doloma-Graphite
Glaze
Glaze
16% Porosity DG
Gas average [3]thermal conductivity2.7006 W/mK viscosity 9.32×10-5 kg/m
Species thermodynamic properties: thermo.db
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 8
Key features--combustion
• Non-premixed species model. • Fuel inlet: perfectly mixed CH4 and O2 in
1:2 mole ratio in a total mass flow rate of 3.8 g/s[2].
• Ambient air entrainment.• Non-adiabatic energy treatment.• GRI-Mech 3.0[6] natural gas combustion
mechanism, contains 325 reactions and 53 species.
8
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 9
Model validation
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 10
Temperature across SEN: 97mm Validation Case
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 11
Temperature across SEN: High-k Refractory Case
Outer glaze
SEN outer wall
SEN refractory wall
Nozzle inner bore with gasInner glaze
SEN inner wall
Measured TC3
TC 3-5line at 5min
TC5TC6TC4
TC 3-5line at 10min
TC 3-5& 4-6 line at SS
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 12
Temperature across SEN: Insulation Case
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 13
Transient temperature validation
TC 3 error= 25oCTC 4 error= 45oC
TC 5 error= 32oC
TC 6 error= 83oC
Error causes:
• Excessive thermal conductivity/diffusivity due to uncertain refractory properties
• Neglect of Zirconia sleeve at lower part of SEN
• Neglect of contact resistance at TC tip0 10 20 30 40 50 60 70 80 90 100 110
0
100
200
300
400
500
600
700
S
EN
wal
l tem
pera
ture
(°C
)
Time (min)
TC3 MEASURE TC4 MEASURE TC5 MEASURE TC6 MEASURE TC3 FLUENT TC4 FLUENT TC5 FLUENT TC6 FLUENT
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 14
Flame shape & Outer wall temperature contour validation
Flame shape comparisons of predicted temperature contours and close-up
photographSEN outer wall temperature comparison
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 15
Model Parametric study
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 16
Inputs of 4 cases
Model Inputs97mm
Validation Case
147mm Case
Insulated Case
High-kCase
Thermal conductivity DG, Glaze DG, Glaze
DG, Glaze, Insulation DG, Glaze
Specific heat DG, Glaze DG, Glaze DG, Glaze, Insulation DG, Glaze
Stand-off distance 97mm 147mm 97mm 97mm
Insulation layer No No Yes No
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 17
Flow distribution
Velocity (m/s)
(a) Direction arrows in the whole domain (b) Velocity vector inside SEN
(c) Zoom-in vector near SEN top
60 m/s
5 m/s
147mm Case
97mm Case 147mm Case
Air entrainment154% 135%
Stand-off distance
Flame spreads
Air entrainment
Flame temperature97mm Validation Case
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 18
Temperature distribution
(d)
(a) 97mm Validation Case(b) 147mm Case
(c) Insulation Case(d) High-k Refractory Case
(c)(b)(a)
Temperature (oC)
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 19
Transient temperature comparisons among 4 cases
0 10 20 30 40 50 60 70 80 90 100 1100
200
400
600
800
1000
1200
SE
N w
all t
empe
ratu
re (°
C)
Time (min)
Measure TC3 Measure TC5 97mm Case TC3 97mm Case TC5 147mm Case TC3 147mm Case TC5 High-k Refractory Case TC3 High-k Refractory Case TC5 Insulation Case TC3Insulation Case TC5
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 20
Flame Temperature Modelin Excel VBA
20
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 21
Flame Temperature Model(VBA)
InputsFuel typeOxygen sourceOxygen source fractionAir entrainmentReactants temperatureReactants pressure
OutputsFlame/Products temperatureProducts pressureSpecies componentProducts propertiesForce convection coefficient Free convection coefficient
Gaseq[7]
• Gaseq[7]: a chemical equilibrium program which can predict adiabatic temperature and composition at constant pressure.
• Oxygen Source Fraction = mole of oxygen inputmole of oxygen required for stoichiometric reaction
• Air Entrainment = mole of entrained airmole of air needed for stoichimetric reaction
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 22
Flame Temperature Model Results
Simple spread-sheet model can predict flame temperature approximately without sophisticated chemical reactions and thermal hydraulic models.
Air entrainment
Oxygen sourcefraction
Reactants Temp.
Flame Temp.
Flametemp.
97mm Validation Case 154% 100% 19 oC 1328 oC 1343oC
147mm Case 135% 100% 19 oC 1451 oC 1587oC
MeasurementCombustion
Model ResultComb.Model
Reactants, products pressure is 1atm.
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 23
Conclusions• A 2D axisymmetric model of nozzle preheating is developed, including
325 chemical reactions with 53 species of methane combustion.• Steady-state fluid flow, heat transfer and gas combustion, and transient
heat conduction in the SEN walls are simulated. • The model predictions were validated with a preheating experiment,
including the gas temperature across the flame, SEN wall temperature histories, flame shape, and SEN outer wall temperature distribution.
• Moving the burner further away from the SEN top leads to higher SEN temperature, due to flame expansion causing less air entrainment.
• Adding an insulation layer causes higher SEN wall temperatures and milder temperature gradients.
• Increasing refractory conductivity causes milder temperature gradient at SEN.
• To optimize preheating, a proper stand-off distance, stoichiometric fuel composition, proper refractory thermal properties , and insulation layers are recommended.
• A simple spread-sheet model of the adiabatic flame temperature predicts gas temperature approximately, based on knowing the air entrainment.
University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 24
Acknowledgements
• The authors are grateful to R. Nunningtonand other personnel at Magnesita Refractories for providing the measurement data.
• The authors appreciate the support from the Continuous Casting Consortium at the University of Illinois.
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University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Yonghui Li • 25
References[1] R. Nunnington, Magnesita Refractories, private communication, Jun, Aug 2012 [2] Magnesita Refractories, PB10 SEN Temperature Data for CCC Heat Flow Model, Report, York, March 31st, 2010[3] FLUENT 13.0[3] Charles E. Heat Transfer in Industrial combustion, p469[4] T. Shimizu, Thermal conductivity of high porosity alumina refractory bricks made by a slurry gelation and foaming method, Journal of the European Ceramic Society, 2013[5] Hayashi K, Fujino Y, Nishikawa T. Thermal conductivity of Aluminiumand Zirconia fiber insulators at high temperature. Yogyo Kyokai Shi 1983;91:450–6.[6] Gregory P. Smith, David M. Golden, Michael Frenklach, Nigel W. Moriarty, Boris Eiteneer, Mikhail Goldenberg, C. Thomas Bowman, Ronald K. Hanson, Soonho Song, William C. Gardiner, Jr., Vitali V. Lissianski, and Zhiwei Qin http://www.me.berkeley.edu/gri_mech/[7] Gaseq, Chemical equilibrium program, available at http://www.gaseq.co.uk/[8] Y. Li, MS Thesis, Transient Model of Preheating a Submerged Entry Nozzle, 2014
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