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

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

Sintering process concept region of interest

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

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

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

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

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

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)

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

Sherwood and Nusselt numbers for sphere

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

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

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

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

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)

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

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

Boundary and initial conditions Initial chemical composition and porosity Air (Ta) Zone Fe2O3 C CaCO3  A 0.82 0.03 0.15 0.40 B 1.0 0.0 0.0 0.25 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

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

Example of calculated results.Velocity vector

Carbon mass fraction and heat generation

Solid temperature and limestone fraction Temperature of solid phase Limestone fraction

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

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

Carbon mass fraction and void fraction Porosity

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