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
Porosity

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