Simulation of sintering of iron ore packed Simulation of sintering of iron ore packed bed with variable porositybed with variable porosity

S. V. Komarov and E. Kasai

Institute of Multidisciplinary Research for Advanced Materials

Tohoku UniversityJapan

Phoenics User ConferenceMelbourne,2004

Flowchart of steel productionFlowchart of steel production

Sintering process conceptSintering process concept

region of interest

A schematic representation of sintering processA schematic representation of sintering process

Sintered part

Heat wave

Initial materials:1.Blend ore2.Coke3.Limestone

Preheated air

Exhaust gas: N2,O2,CO2

Principle of big pellet agingPrinciple of big pellet agingInduction bed

for combustion/sintering

Large pelletsfor aging

Objective of this studyObjective 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

Why simulation ?Why simulation ?

There are many parameters involved,which determine the system behavior. An experimental investigation would be too hard and costly.

Why Phoenics ?Why Phoenics ?Many thanks to friendly and highly skilled support team in Tokyo

Computational domain and its physical prototypeComputational domain and its physical prototype

z

r

O A

B CExhaust gas outlet

Air inlet

Wal

l

Axi

s

Spherical Spherical pellet:pellet:- 0= 0.25-R = 2.5 cm-dp=0.5 mm-Fe2O3

4.0 cm

8.0

cm

Preheated air

Inductionbed :-0=0.4~0.9-dp=2 mm-Fe2O3,C CaCO3

Packed bed 　

The sintering process chemistryThe sintering process chemistry

1. CaCO3=CaO+CO2 Q2 = –1.61106 J/kg

2. C+O2=CO2 Q1= 3.28107 J/kg

3. CaO+Fe2O3=(CaO·Fe2O3) Q3= –1.37106 J/kg

4. (CaO·Fe2O3)=CaFe2O4 Q4=5.07105 J/kg

Hematite (Fe2O3) – 0.82Carbon(C) – 0.03Limestone (CaCO3) – 0.15

Preheated airHematite (Fe2O3) – 1.0

The process related physical phenomenaThe process related physical phenomena

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)

Preheated air

ovcpOgc kAYr ,2

Kinetics of graphite combustionKinetics of graphite combustion

Diffusional control

Kinetic control

r

YO2

T

dc

C+O2= CO2

cc

cp Yd

A)1(6

,

mr

ov

kk

k11

1

s

asr RT

ETkk exp5.0

0

c

Om d

DShk 2

combustion rate

specific area

overall rate coefficient

chemical reaction rate coefficient

mass transfer rate coefficient

k0=6.532105 (m/s•K0.5)Ea= 1.839105 (J/mol•K)

Sherwood and Nusselt numbersSherwood and Nusselt numbers for sphere for sphere

32

Re Sc

Sh

31

2

21

2

6.00.2

O

g

g

c

O

cm

D

dU

D

dkSh

312

1

6.00.2

g

g

cc dUhdNu

5.022 11 WCVCU

Kinetics of the other reactionsKinetics of the other reactions

1. CaCO3=CaO+CO2

2. CaO+Fe2O3=(CaO·Fe2O3)3. (CaO·Fe2O3)=CaFe2O4

Assumptions1. The reaction rates are controlled by heat supply (1,2) or removal (3)2. The reactions proceed within a temperature interval T around the corresponding thermodynamic temperature Td

ccCaCOs

s

ll rQY

dt

dH

QTfr

3)1(

1)(1

T

TT d

e

Tf

1

11)(1

Example for reaction (1) T=10Td=1123 K

f1 – function of kinetic factor

rl – reaction rate

Ql – reaction heat

Qc – graphite combustion heat

rc- graphite combustion rateHeat supply rate

Initial porosityInitial porosity“Wall” effect

Mathematical formulation

ABB

A

A

B

rR

zoneTransition

AZone

BZone

,0,0

,0

,0

9.0

:

4.0:

25.0:

RB

B

A

rB

Transition zone

B A

Equation of motion　

gk

gggg

kgg S

xU

xt ,,

1,1;; , WCVCUU gggg

)1(75.1)1(150 2

2

2

2,

p

g

p

gg d

U

d

US

where

Ergunequation

dp - particle diameter - void fraction (porosity)g - gas viscosityg - gas density

;)(

,1 gg Sx

U

Equations of continuityEquations of continuity and mass conservationmass conservation

rc is the carbon combustion rate

rl is the lime decomposition rate

Mi is the molecular weight

3

22,2

CaCO

COl

c

COcgY M

Mr

M

MrS

CO

C+O2= CO2CaCO3=CaO+CO2

gYk

igig

kig i

Sx

YYU

xY

t ,,

(i = CO2,O2,N2)

;2,2

c

OcgY M

MrS

O 0,2

gYNS

gYgYg OCOSSS ,,,1 22

Equation of energy conservation (gas phase)Equation of energy conservation (gas phase)

Cexk

ggpgTggpg

kggpg SS

x

TCTCU

xTC

t)1(

)( ,,,,

hp d

A)1(6

gsph

gex TTA

d

NuS

Concept of C combustion

Gas-particle heat exchange rate

O2

C

Reaction front

C+O2=CO2

CO2+C=2CO

CO+O2=2CO2

)1( ccC rQS- part of C combustion heatgoing directly to solid phase( =0.5)

(fixed flux)

Equation of energy conservation (solid phase)Equation of energy conservation (solid phase)

),(

),(

,,

issp

iseffsH YTC

YT

Obstexk

ssH

kss SSSS

x

H

xH

t

,,

;)1(,, solds

sst HH

tS

CCaCOCaOOFeiY Radi

iieff ,,,; 332

Rad - radiative conductivity according to Rosseland diffusion model

;3

16 3ssRad T ;

)1(

2

3 h

s d

sp

ss C

HT

,

- Stephan-Boltzmann constant (=5.6710-8), s - scattering

coefficient

- the reflectivity coefficient (=0.5) , Ts – solid temperature

Equation of energy conservation (solid phase)Equation of energy conservation (solid phase)

sgph

gexH TTA

d

NuS

,

sfmmllo rQrQrQS

Obstexk

ssH

k

SSSSx

H

x

,,

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

Air (Ta)

Boundary and initial conditionsBoundary and initial conditions

B

AAir velocity at inlet

Initial chemical composition and porosity

Zone Fe2O3 C CaCO3 A 0.82 0.03 0.15 0.40 B 1.0 0.0 0.0 0.25

W1 is defined from condition gW1=const (1.2)

V1 = 0

Initial temperature

Tg=Ts=25OC

Air temperature at inlet

Setting of solver optionsSetting of solver options

Grid type : BFC 2048Time dependence: unsteady 1s 600 step = 600 s Flow : laminar One-phase mode (ONEPHS=T)Total number of iteration : 100Global convergence criteria : 0.5%Equation formulation : Elliptic GCVDifferencing schemes : Hybrid

Example of calculated results.Velocity vectorExample of calculated results.Velocity vectort = 90 s 180 s 330 s

Carbon mass fraction and heat generationCarbon mass fraction and heat generation

Carbon mass fraction Heat generationHeat generation

Solid temperature and limestone fractionSolid temperature and limestone fraction

Temperature of solid phase Limestone fraction

Solid temperature and melted phase fractionSolid temperature and melted phase fraction

Temperature of solid phase Melted phase fraction

Solid temperature and solid phase fractionSolid temperature and solid phase fraction

Temperature of solid phase Solidified phase fraction

Carbon mass fraction and void fractionCarbon mass fraction and void fraction

Carbon mass fraction Porosity

ConclusionsConclusions

Phoenics code has been applied to the problem of iron ore sinteringprocess 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