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Simulation of sintering of iron ore packed bed with variable porosity

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Presentation on theme: "Simulation of sintering of iron ore packed bed with variable porosity"— Presentation transcript:

1 Simulation of sintering of iron ore packed bed with variable porosity
S. V. Komarov and E. Kasai Institute of Multidisciplinary Research for Advanced Materials Tohoku University Japan Phoenics User Conference Melbourne,2004

2 Flowchart of steel production
First of all let me briefly introduce the objects we are dealing with in our research.

3 Sintering process concept
region of interest

4 A schematic representation of sintering process
Preheated air Sintered part Heat wave Initial materials: 1.Blend ore 2.Coke 3.Limestone Exhaust gas: N2,O2,CO2

5 for combustion/sintering
Principle of big pellet aging Induction bed for combustion/sintering Large pellets for aging

6 Objective of this study
There are many parameters involved, which determine the system behavior. An experimental investigation would be too hard and costly. Why simulation ? Why Phoenics ? Many thanks to friendly and highly skilled support team in Tokyo Objective of this study Development of a Phoenics-code based model which could predict influences of such parameter as - void fraction - pellet size initial temperature and flow rate of gas coke and limestone content ignition time on heat propagation over induction bed to large pellets

7 Computational domain and its physical prototype
Packed bed  Preheated air Air inlet O A Spherical pellet: - 0= 0.25 R = 2.5 cm dp=0.5 mm Fe2O3 Wall Axis 8.0 cm Induction bed : -0=0.4~0.9 dp=2 mm Fe2O3,C CaCO3 z 4.0 cm r B C Exhaust gas outlet

8 The sintering process chemistry
Hematite (Fe2O3) – 1.0 Preheated air CaCO3=CaO+CO2 Q2 = –1.61106 J/kg C+O2=CO2 Q1= 3.28107 J/kg CaO+Fe2O3=(CaO·Fe2O3) Q3= –1.37106 J/kg (CaO·Fe2O3)=CaFe2O4 Q4=5.07105 J/kg Hematite (Fe2O3) – 0.82 Carbon(C) – 0.03 Limestone (CaCO3) – 0.15

9 The process related physical phenomena
Preheated air 1.Momentum transfer 2.Two phase heat transfer - convection (gas) - diffusion (gas,solid) - radiation (interparticle space) - heat exchange (gas-solid interface) - heat generation (C combustion) - heat absorption (CaCO3 decomposition, CaO•Fe2O3 melting) 3. Mass transfer (only gas phase) - convection (O2,N2,CO2) - diffusion (O2,N2,CO2) - gas sourcing (CO2) and sinking (O2)

10 Kinetics of graphite combustion
C+O2= CO2 Diffusional control Kinetic control r YO2 T dc combustion rate specific area overall rate coefficient k0=6.532105 (m/s•K0.5) Ea= 1.839105 (J/mol•K) chemical reaction rate coefficient mass transfer rate coefficient

11 Sherwood and Nusselt numbers for sphere

12 Kinetics of the other reactions
Assumptions The reaction rates are controlled by heat supply (1,2) or removal (3) The reactions proceed within a temperature interval T around the corresponding thermodynamic temperature Td CaCO3=CaO+CO2 2. CaO+Fe2O3=(CaO·Fe2O3) 3. (CaO·Fe2O3)=CaFe2O4 Example for reaction (1) T=10 Td=1123 K f1 – function of kinetic factor rl – reaction rate Ql – reaction heat Qc – graphite combustion heat rc- graphite combustion rate Heat supply rate

13 Initial porosity  “Wall” effect Mathematical formulation rB B A A B
Transition zone B A

14 Equation of motion where Ergun equation dp - particle diameter
- void fraction (porosity) g - gas viscosity g - gas density

15 Equations of continuity and mass conservation
(i = CO2,O2,N2) C+O2= CO2 CaCO3=CaO+CO2 rc is the carbon combustion rate rl is the lime decomposition rate Mi is the molecular weight

16 Equation of energy conservation (gas phase)
Gas-particle heat exchange rate Concept of C combustion O2 C+O2=CO2 CO2+C=2CO CO+O2=2CO2 C Reaction front (fixed flux) - part of C combustion heat going directly to solid phase ( =0.5)

17 Equation of energy conservation (solid phase)
Rad - radiative conductivity according to Rosseland diffusion model - Stephan-Boltzmann constant (=5.6710-8), s - scattering coefficient - the reflectivity coefficient (=0.5) , Ts – solid temperature

18 Equation of energy conservation (solid phase)
Qi and ri are heat effect and rate of appropriate reactions l - CaCO3=CaO+CO2 m - CaO+Fe2O3=(CaO·Fe2O3) f,s - (CaO·Fe2O3)=CaFe2O4

19 Boundary and initial conditions
Initial chemical composition and porosity Air (Ta) Zone Fe2O3 C CaCO3  A B A Air velocity at inlet B W1 is defined from condition gW1=const (1.2) V1 = 0 Initial temperature Air temperature at inlet Tg=Ts=25OC

20 Setting of solver options
Grid type : BFC 2048 Time dependence: unsteady 1s  600 step = 600 s Flow : laminar One-phase mode (ONEPHS=T) Total number of iteration : 100 Global convergence criteria : 0.5% Equation formulation : Elliptic GCV Differencing schemes : Hybrid

21 Example of calculated results.Velocity vector

22 Carbon mass fraction and heat generation

23 Solid temperature and limestone fraction
Temperature of solid phase Limestone fraction

24 Solid temperature and melted phase fraction
Temperature of solid phase Melted phase fraction

25 Solid temperature and solid phase fraction
Temperature of solid phase Solidified phase fraction

26 Carbon mass fraction and void fraction

27 Conclusions Phoenics code has been applied to the problem of iron ore sintering process which includes coke ignition and flame front propagation through the sintering bed It is shown that Phoenics can be used to simulate transient two-phase problems under one-phase setting option Ground coding allows to simulate gas flow, heat and mass transfer through bed of variable porosity The predicted results seem to be realistic but the model needs to be validated against experimental data

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