CCC Annual Report. UIUC, August 20, Modeling SEN Preheating. Yonghui Li. Department of Mechanical Science & Engineering

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1 CCC Annual Report UIUC, August 20, 2014 Modeling SEN Preheating Yonghui Li Department of Mechanical Science & Engineering University of Illinois at Urbana-Champaign 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). University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 2

2 Preheating experiment setup [1] Premixed natural gas(mainly CH 4 )/ O 2 Burner tip Two-port SEN Infra-red photo of SEN outside wall 324 o C Standoff Gas distance temperature TC 1 SEN o C 174 o C TC 3 TC 4 Wall temperature TC 5 TC 6 91 o C 23 o C Unit: mm University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 3 Measurements [2] (for model validation) 1. Gas temperature 197mm below SEN top 3. The shape of flame 2. Wall temperature (transient are not listed here. ) Thermocoupl e 4. SEN outside wall temperature 324 o C 249 o C TC3 TC4 TC5 TC 6 X* (mm) Y* (mm) Temp. ( o C) X: Distance from top air inlet; Y: Distance from SEN centerline. 174 o C 91 o C 23 o C University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 4

3 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. Rosebud tip surface 24*1.6mm diameter Mixture inlet Simplified as 1*0.8mm diameter 17.4mm diameter of outer ring of holes University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 5 Model geometry and mesh 97mm Validation Case 147mm Case Insulation Case Stand-off distance mm coating layer with 4 cells through thickness quadrilateral cells total University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 6

4 Material Properties Flow SEN [1,4,5] Species thermodynamic properties: thermo.db Gas average [3] thermal conductivity W/mK viscosity kg/m Thermal Conductivity (W/m-K) Specific Heat (J/kg-K) Glaze 16% Porosity Doloma-Graphite Temperature ( C) 16% Porosity DG Glaze Temperature ( C) University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 7 Key features--combustion Non-premixed species model. Fuel inlet: perfectly mixed CH 4 and O 2 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. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 8 8

5 Model validation University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 9 9 Temperature across SEN: 97mm Validation Case University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 10

6 Temperature across SEN: High-k Refractory Case SEN refractory wall SEN outer wall Nozzle inner bore with gas SEN inner wall Inner glaze Measured TC3 Outer glaze TC 3-5& 4-6 line at SS TC4 TC5 TC6 TC 3-5line at 10min TC 3-5line at 5min University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 11 Temperature across SEN: Insulation Case University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 12

7 Transient temperature validation SEN wall temperature ( C) TC3 MEASURE 300 TC4 MEASURE TC5 MEASURE 200 TC6 MEASURE TC3 FLUENT TC4 FLUENT 100 TC5 FLUENT TC6 FLUENT Time (min) TC 3 error= 25 o C TC 4 error= 45 o C TC 5 error= 32 o C TC 6 error= 83 o C 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 tip University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 13 Flame shape & Outer wall temperature contour validation Flame shape comparisons of predicted temperature contours and close-up photograph SEN outer wall temperature comparison University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 14

8 Model Parametric study University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li Inputs of 4 cases Model Inputs 97mm Validation Case 147mm Case Thermal conductivity DG, Glaze DG, Glaze Specific heat Stand-off distance Insulation layer DG, Glaze DG, Glaze Insulated Case DG, Glaze, Insulation DG, Glaze, Insulation High-k Case DG, Glaze DG, Glaze 97mm 147mm 97mm 97mm No No Yes No University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 16

9 Flow distribution 5 m/s Velocity (m/s) ሶଵ ሶଶ (c) Zoom-in vector near SEN top 97mm Case 147mm Case Air entrainment 154% 135% Stand-off distance Flame spreads Air entrainment 97mm Validation Case 147mm Case (a) Direction arrows in the whole domain University of Illinois at Urbana-Champaign 60 m/s Flame temperature (b) Velocity vector inside SEN Metals Processing Simulation Lab Yonghui Li Temperature distribution Temperature (oc) (a) (b) (c) (a) 97mm Validation Case (b) 147mm Case University of Illinois at Urbana-Champaign (d) (c) Insulation Case (d) High-k Refractory Case Metals Processing Simulation Lab Yonghui Li

10 1200 Transient temperature comparisons among 4 cases SEN wall temperature ( C) Measure TC3 97mm Case TC3 147mm Case TC3 High-k Refractory Case TC3 High-k Refractory Case TC5 Insulation Case TC3 Insulation Case TC Time (min) Measure TC5 97mm Case TC5 147mm Case TC5 University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 19 Flame Temperature Model in Excel VBA University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 20 20

11 Flame Temperature Model(VBA) Inputs Fuel type Oxygen source Oxygen source fraction Air entrainment Reactants temperature Reactants pressure Gaseq[7] Outputs Flame/Products temperature Products pressure Species component Products properties Force convection coefficient Free convection coefficient Gaseq [7] : a chemical equilibrium program which can predict adiabatic temperature and composition at constant pressure. mole of oxygen input Oxygen Source Fraction = mole of oxygen required for stoichiometric reaction mole of entrained air Air Entrainment = mole of air needed for stoichimetric reaction University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 21 Flame Temperature Model Results Combustion Model Air entrainment Oxygen source fraction Measurement Reactants Temp. Result Flame Temp. Simple spread-sheet model can predict flame temperature approximately without sophisticated chemical reactions and thermal hydraulic models. Comb. Model Flame temp. 97mm Validation Case 154% 100% 19 o C 1328 o C 1343 o C 147mm Case 135% 100% 19 o C 1451 o C 1587 o C Reactants, products pressure is 1atm. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 22

12 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 23 Acknowledgements The authors are grateful to R. Nunnington and 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. University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 24

13 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 Aluminium and Zirconia fiber insulators at high temperature. Yogyo Kyokai Shi 1983;91: [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 [7] Gaseq, Chemical equilibrium program, available at [8] Y. Li, MS Thesis, Transient Model of Preheating a Submerged Entry Nozzle, 2014 University of Illinois at Urbana-Champaign Metals Processing Simulation Lab Yonghui Li 25