Choi_Japanese Combustion Symposium

7/27/2019 Choi_Japanese Combustion Symposium

1/55

Sangmin Choi

KAIST

Thermal Engineering Lab


2/55


3/55

Combustion of solid fuel bed

Combustion of the single particle + Interaction between the particles

Major phenomena

Material flow: Gas Solid Multi le Com onenets

Reactions : Solid-gas reaction, Gaseous reaction

Heat transfer : Conduction, Convection, Radiation

ys ca an geome r ca c anges

Generation of internal pore, Change of particle size

Bed structural change : Porosity, height

Melting, Sintering

Reactors containing solid bed Iron-making process

Coke oven, Sintering bed, Blast furnace



4/55

Bed combustion of mixed waste (solid fuel)

Waste heat boiler

y

Rotary kiln

Thermal Engineering LabTraditional stoker-type inc inerator Advanced incinerator : Stoker-type + Rotary ki ln type


5/55


6/55

Iron ore sintering process

~90% of inert : Physical changes of inert (iron ore) is important

Self-sustaining combustion (no external heat source) once ignited

No pyrolysis, very slow progress of coke combustion

+COKE, LIME etcPSEUDO-PARTICLES +WATER +COKE, LIME etc+COKE, LIME etcPSEUDO-PARTICLES +WATER

YARD

COG BURNERSTACK

ORE BINREROLLING MIXING YARDYARD

COG BURNERSTACK

ORE BINORE BINREROLLING MIXING

SINTERING BED

EP

HEARTH BED

WIND BOXESSINTERED ORE

SINTERING BED

EPEP

HEARTH BED

WIND BOXESSINTERED ORE

HOT CRUSHING

COOLINGCOLD CRUSHINGSCREENINGRETURN FINE

FAN HOT CRUSHING

COOLINGCOLD CRUSHINGSCREENINGRETURN FINE

FAN


BLAST FURNACEBLAST FURNACE


7/55


8/55

Each slice Batch type oven

Charge : 27.8 ton/oven

CHARGING

CAR

Coking t ime : about 20 hours

QUENCHING

COAL

CAR

16.0m

Charging

coal6m . . . .6.7m


0.45m fuel air0.70m More than100 slices


9/55

Blast Furnace

Iron ore+ Coke


10/55

Phenomena in Blast Furnace

Stack zone

Alternate coke/ore layers

Ore layer is heated up and partially reduced

Stack zone

wust te, e .

Cohesive zone

Ore layer is softened and agglomerates. Cohesive zone

Low permeability of ore layer coke slit Wustite is transferred to Fe.

Dripping zoneDripping

zone Ore starts to melt and fall down.

Raceway Reducing gas by coke combustion

-

Deadman



11/55

FINEX Process



12/55

Modeling Approach



13/55

Reactors with bed of solid material : Solid flow: batch or continuous

Common governing mechanism and physical/chemical phenomena but differ

in the dimension, the boundary conditions and additional physical changes

Solidmaterial Oxidizer

Solidmaterial

Solidmaterial Oxidizer

Solidmaterial

Solid

SolidmaterialSolidSolid

materialmaterialmaterial

Fixed bed combustor

Oxidizer

Co-current fixed

Oxidizer

Count-current fixed

Oxidizer

Grate-type incinerator

Fixed bed combustor

Oxidizer

Co-current fixed

Oxidizer

Count-current fixed

Oxidizer

Grate-type incinerator


Direct melting furnace

Coke oven

bed gasifier bed gasifier

Blast furnace

Iron ore sintering bed Direct melting furnace

Coke oven

bed gasifier bed gasifier

Blast furnace

Iron ore sintering bed


14/55


15/55

Flexibility in computation - In the model, user can define

Solid components and gaseous species

Combustion/reaction types and their rates

Boundary conditions

Physical and geometric properties

Numerical Scheme

Extension of 1-D, transient model to 2-D model

For moving bed, with constant traveling speed

yy


t=0 tmaxt+ttt=0 tmaxt+tt


16/55


17/55

Governing equations

Solid phase I : Mass, Energy, Component

( ) ( ), , , ,,

s I V I s I s I

solid gas reactions I Jphase J

f v

Mt y

+ = &

( )( ) ( ), , , , , , ,, , , , , , , , ,

1

V s I s I s I s I s I v I

V s I s I JI s I s J s I conv g I s I g s I rad

J

f h v h T f f k h A T T h A T T q

t y y y

+ = + + +

, , , , , ,s s

s s

I s I r r s I r p I s I

r r

( ) ( ), , , , , , , ,, , , s

s

s I V I s I k s I s I s I k

s I k r

r

f m v mM

t y

+ =

&

Gas phase : Mass, Energy, Species

g g gs I rv M + = &, , s

sI rt y

( ) ( )( ), , , , , , , , ,(1 ) s s s

s s

g g g g

g conv g I s I s I g I s I r r s I r p I s I

I r r

h v h Tk h A T T y M H M C T

t y y y

+ = + + +

& &


( ) ( ), ,, , , , ,s g

s g

g g k g g g k

s I k r g k r r I r

m v m

M Mt y

+ = + & &


18/55

-

Solid gas reactions & Gaseous reactions

Solid- as reactions

solid solid gas gas solid solid gas gas

solid gas solid gas

M M M M + +

Drying : Boling(>373K) and Diffusion(


19/55

Iron ore reduction : Fe2O3(s), Fe3O4, FewO, + CO

2

2

,,

,1,4

6 CO gg CO gi in n m m

mi i CO CO

f

R a Kd W M M

=

=

Solution loss : C+CO2->2CO

Com etitive reactions : Arrhenius rate + diffusion

( ) ( )2 2 2

11 1

, film, 5g CO g CO s COR M A k k = +

Melting ( )1 ,, inflow

j s face facej melt j

n

G AT T

RT M Vol

=



20/55

-

Heat Transfer

Conduction : Included in the energy equations

Convections : Wakao and Kaguei(1982)s equation

or Ranz-Marshall equation

Radiation : 2-flux model(Shin and Choi, 2000)

Among solid phases

( )

, , , ,

, ,,2

where

ss IJ IJ s I s J s I

V I s I s ps g g pgIV JI

IJ

V I s V I

f k C k Cf

hf t t f

+

= +

Geometrical changes

, ,

I

1/ 33 3

Generation of the internal pores , , , ,, , ,

V I ip I s ip I comb i

ip i ip loss I

i i

f v Mf

t y

+ = +

&

&

p u r


Bed structural changes : packing parameter, n

1 n o

V s Vf f f=


21/55

Waste

Incinerator

Iron Ore Sintering

Bed

Coke Oven Blast Furnace

Bed type Moving bed Moving bed Fixed bed Counter-current

Feeding Continuous Continuous Batch Continuous.

Solid

material

Solid waste Iron ore

+Limestone

Coking coal Sintered ore+Coke

+Coke

Mode of

gas/air flow

Blowing air Suction air Discharge of

pyrolized gas

Blowing of

preheated blast

Heat source Volatile/Char

combustion

Coke combustion External Wall

Heating, latent

Heat of Pyrolysis

Coke &

PC(pulverized coal)

combustionPhysical

change

Change of bed

height by

combustion

Melting/sintering

Negligible change

of bed height

Swelling,

shrinkage

Melting of iron ore,

coke diameter

change(combustion)



22/55

Waste Incinerator



23/55

Major phenomena within the bed in waste incinerators

Ignition by radiation from wall/hot gas

Drying Pyrolysis Char combustion

Combined closely with the gas flow in the incinerator

AIRAIR(1) Raw waste(2) Drying(3) Pyrolysis(4) Char reaction

AIRAIR(1) Raw waste(2) Drying(3) Pyrolysis(4) Char reaction

WASTE

WASTE BED

COMBUSTION GAS

WASTE

WASTE BED

COMBUSTION GAS

(1) (2) (3) (4)

(5) Ash

WASTE

WASTE BED

COMBUSTION GAS

WASTE

WASTE BED

COMBUSTION GAS

(1) (2) (3) (4)

(5) Ash

ASHHOPPER

PRIMARY AIR

GRATES ASHHOPPER

PRIMARY AIR

GRATES ASHHOPPER

PRIMARY AIR

GRATES ASHHOPPER

PRIMARY AIR

GRATES



24/55

Single solid phase

Bed height : 0.68 m

The particle size and porosity are not changed during the process

Calculation time : 6000 sec

Bed height (m) 0.68 Type Air

Waste incinerator (Moving bed, Continuous feeding)Ignition by radiation

from hot gas or wall (2)

Waste incinerator (Moving bed, Continuous feeding)Ignition by radiation

from hot gas or wall (2)

x zer o ce s

tmax (sec) 6000 vave 0.136m/st (sec) 1

IgnitionType Radiation

Size 30mm Value CFDresultsa

Solid waste(30~60%

combustible)

gas

Ash

Solid waste(30~60%

combustible)

gas

AshSolid

mat.

Moisture 45%Pyrolysis

A 1.5104

Volatile 39% E 30kcal/kmol

Char 6% A 2.3

Time = 0 Time = t1 Time = tmaxAirTime = 0 Time = t1 Time = tmaxAir

nc u ngmass-basecomposition)

Ash 10% E 22kcal/kmol

o 0.54

Gaseous

Volatile+O2CO+H2

LHVa 1790 CO+H2OCO2+H


reaction 2n 1 H2+0.5O2H2O

Shrinkage of grid YES


25/55

-

Model is well describing the physico-chemical process in the waste bed

Temperature distribution and gas composition

0.4

0.6

m)

3.73

130.6

m)

3.73

13

COMBUSTION GASCOMBUSTION GASCOMBUSTION GAS

0.3

n

O2

CO2

H2O CO

H2

CxH

yO

z

0.2

.

BedHeight

14

0.2

.

BedHeight

14

0.1

0.2

2

H2

CO2

2

MoleFracti

0 2 4 6 8 10 120.0

Location on the grate (m)

4681

013

0 2 4 6 8 10 120.0

Location on the grate (m)

4681

013

0 1000 2000 3000 4000 5000 6000

0.0

CO

Predicted temperature distribution (x100k) Predicted gas composition (x100k)

me sec



26/55

FURNACE ENCLOSURE

GAS FLOW FIELD :

Mass, Energy, Momentum and

Species Conservation Equations

Temperature, Heat Transfer

Velocity, Turbulent Mixing,

Chemical Species and Reaction

+Turbulence, Radiation, Reaction Models

MGAS, TGAS, VGAS

FUEL BED

QRAD

MODEL

Fuel Components and Temperature

Gas Species and Temperature

Bed Height, etc.

Combustion, Gas Reaction

Heat Transfers


( t = 0 )PRIMARY AIR(x)

x =

(tmax: Fuel Residence Time)

x =

(tmax: Fuel Residence Time)


27/55

12001300

TEMPERATURE

[ UNIT : K ]

1500 Tgas1100

[ UNIT : K ]

700

1100

emperature(K)

0.2

CO2

Mole

1500

Tgas

1400 300

G

asT

0.0

0.1

CxHyOz+CO+H2

Frac

tion

x=0.8m ( t=6.6 min )

1200

700

1100

0.2CO2

1500

1550

SECONDARY

AIR1300

0.35

0.70

Height(m)

0.35

0.70

Height(m)

0.35

0.70

Height(m)

0.35

0.70

Height(m)

0.35

0.70

Height(m)

300

0.0

.CxHyOz+CO+H2

1500 1500

1400

1400

500

0

0.00

4 8 12

Bed

Distance (m)

0

0.00

4 8 12

Bed

Distance (m)

0

0.00

4 8 12

Bed

Distance (m)

0.00

4 8 12

Bed

Distance (m)

4 8 12

Bed

Distance (m)0.70

(m)

0.70

(m)

0.70

(m)

0.70

(m)

0.70

(m)

0.70

(m)


700

1100

0

0.00

4 8 12

0.35

BedHeight

Distance (m)

13

13

12

11

0

0.00

4 8 12

0.35

BedHeight

Distance (m)

0

0.00

4 8 12

0.35

BedHeight

Distance (m)

0

0.00

4 8 12

0.35

BedHeight

Distance (m)

0.00

4 8 12

0.35

BedHeight

Distance (m)

4 8 12

0.35

BedHeight

Distance (m)

13

13

12

11


28/55

Iron Ore Sintering



29/55

Major Phenomena in the sintering bed

SINTERED

IGNITION

SINTERED

IGNITION

COMBUSTION

SINTERED

ZONE

SINTERINGCOMBUSTION

SINTERED

ZONE

SINTERING

RAW MIX ZONE

ZONE ZONEMIX

Hearth Bed

RAW MIX ZONE

ZONE ZONEMIX

Hearth BedRAW MIX

ZONE CHAR COMBUSTION

MOISTURE EVAPORATIONRAW MIX

ZONE CHAR COMBUSTION

MOISTURE EVAPORATION

x

y

COMBUSTION GASx

y

COMBUSTION GASHEARTH BED

MOISTURE CONDENSATIO

HEARTH BED

MOISTURE CONDENSATIO

COMBUSTION GASCOMBUSTION GAS



30/55

Iron ore sintering bed (Moving bed, ContinuousIron ore sintering bed (Moving bed, Continuous

Bed height (m) 0.57Oxidizer

Type Air

# of cells 57 T 300K

tmax(sec) 1500 vave 0.450m/s

Solidmateriala

AirIgnition by burner

Sinteredore

Solidmateriala

AirIgnition by burner

Sinteredore

t (sec) 1Ignition

Type Gas burner

Size(mm) 1.6/3.2 Value 4 m/s, 1400K

Time = 0 Time = t1 Time = tnaxCombustion as

Time = 0 Time = t1 Time = tnaxCombustion as

mat.

(includingmass-base

. Pyrol

ysis

-

Coke 3.8% E -Iron ore 83.2%

CharA 2.3

Limestona : Iron ore + Coke + Limestone (~4% combustible)a : Iron ore + Coke + Limestone (~4% combustible)on)

e .

o 0.4 Gaseousreact

ion

CO+0.5O2CO2n 0.6

Shrinka e of rid No



31/55


32/55

IRON ORE SINTERING BED COMPARISON WITH SINTERING POT TEST RESULTS

2000

Computed

25

O2-Computed

1200

1400

1600

1800y=0.11my=0.30m

y=0.49m

ture

(K)

Measured

15

20

ition

(Vol.%)

CO2-Computed

CO-Computed

O2-Measured

CO2-Measured

CO-Measured

600

800

1000

Tempera

5

10

Gascompos

0 200 400 600 800 1000 1200 1400

Time (sec)

0 200 400 600 800 1000 1200 1400

0

Time(sec)

Temperature profile flue gas composition in the sintering bed

4

5

ec

)

Extingushed

m/min) 1600

2000

Sintering timeFlame front speed (FFS) and

Sintering time for various air

velocities and particle

2

3

SinteringTime(s

eFrontSpeed(c

Coke diameter : 1.2mm

800

1200

FFSQuantification of the

Thermal Engineering Lab0.2 0.3 0.4 0.5 0.6 0.7 0.8

1

Fla

Averaged Air Velocity (m/s)



0

400

(Flame Front Speed,

Sintering Time)


33/55

Flame Front Speed (FFS)

Combustion Zone Thickness (CZT)

Melting Zone Thickness (MZT) : for an Iron Ore Sintering BedCZT : Combustion Zone Thickness

yy35

40MZT : Melting Zone Thickness

CZT(AirV=0.26m/s)

CZT(AirV=0.32m/s)

CZT(AirV=0.45m/s)

CZT(AirV=0.52m/s)

=

1800

2000

)

MaxT(AirV=0.26m/s)

MaxT(AirV=0.32m/s)

MaxT(AirV=0.45m/s)

MaxT AirV=0.52m/s

Sintered Zone

CZT

Sintered Zone

CZT

25

30

s(cm)

.

MZT(AirV=0.32m/s)

MZT(AirV=0.45m/s)MZT(AirV=0.52m/s) 1600

mperature(

.

Melt ing Zone

Combustion Zone

Melt ing Zone

Combustion Zone

10

15Thickne

1200

M

aximumT

Raw Mix

mperature

MZT

MaxT

Raw Mix

mperature

MZT

MaxT

0 400 800 1200 1600 2000

0

5

800

1000


1373K

1000K

T1373K

1000K

T

Time (sec)

Quanti fied resul ts : CZT, MZT, MaxT (for various air

supply)


34/55

Coke Oven



35/55

Plastic

(1) Wet Coal

(


36/55

Height (6m) is much longer than width(0.45m)

1D model

Bed width (m) 0.22

Oxidizer

Type

No oxidizer# of cells 44 T

tmax(sec) 54000 vave

t (sec) 10 Type -

blend but a single coal

Input data - Elemental/Proximate analysis

data

Solidmat.

(including

Size 3mm Value -

Moisture 7%Pyrolysis

A 1.5104

Volatile 24.2% E 30kcal/kmol

Char 60.5% A -

Homogeneous porous mediamass-basecomposition)

Ash 8.3% E -

o 0.4Gaseousreaction -

n 1

Shrinkage of grid No

Heat

GasCoke oven (Batch type fixed bed)

Heat

GasCoke oven (Batch type fixed bed)

fromhot wall Raw

cokingcoal

Coke

fromhot wall Raw

cokingcoal

Coke


Time = 0 Time = t1

Time = tmax

Time = 0 Time = t1

Time = tmax


37/55

-

Experimental data Temperature distribution within the oven

Time

700

800

900

1000

1100

e(oC)

300

350

400

450

re(mmH

2O)

#2 charging hole

#3 charging hole

1coke plant No. 2, No. 2 ovenMoisture : 5.8%

200

300

400

500

600

Temperatur

100

150

200

250

ternalgaspress

0 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 16 17 18 19Time (h)

0

100

0

50 In

Temperature change at the center Temperature change at the wall

1000

1200

1400

tu

re(K)

LV(0.15)

MV(0.25)

HV(0.35)1000

1200

tu

re(K)

LV(0.15)

MV(0.25)

HV(0.35)

400

600

800

Tempera

400

600

800

Tempera


0 5 10 15 20200

Time (hour)

0 5 10 15 20

200

Time (hour)


38/55

Blast Furnace



39/55

Modeling

-

Assumptions

2 phases - Gas and solid phases

Layer structure is obtained by Lo/Lc data & solid velocity ape o co es ve zone s e ne y range o so empera ure o ~ o

Shape of deadman(stagnant zone) is assumed

Layer properties (Dp, porosity) are function of locations

Raceway is treated as a boundary condition

# of cells 24x76 Reduction Rate

Size 20.0mma

50.0mmb3Fe2O3+CO

->2Fe3O4+CO2

Sold material : sintered ore + coke + flux(limestone)Blast furnace gas

... .

... .. .

Solidmat. [17]

.

0.45b

0.10c

3 4 ->FeO+CO2FeO+CO->Fe+CO2

Feeding

rate(kg/s)

180.8a

36.7

b

1/4Fe3O4+CO

...

. ... ... .. . . ...

... ...

..

. ... . .. .... .

.. ..

cokeore.

..... .

-> e+ 2

Blast air

T(oC) 1191

P(MPa) 0.42 Solution-loss Rate

V(Nm3/min) 6150 C+CO2->2CO [18]

...

. ..... ..

. .. .. .. . .

.. ... . ..

Solid flow


PCRd(kg/s) 15.9 -asGas

Liquid : pig i ron + slaga: Iron ore, b: Coke, c: Cohesive zone, d: Pulverized coal rate


40/55

29.5

30

30.5

28

28.5

29

Height(m) .

Coke+Ore

O.L

C.COKE

O.S

27

27.5

0 1 2 3 4

COKE

a us m

8

29

29.5

30

(m)

5

6

7Lo/Lc

smoothing of Lo/Lc

27.5

28

28.5

Heigh

1

2

3

4

Lo/Lc

COKE


0 1 2 3 4

Radius(m) 0 1 2 3 4

0

Radius(m)


41/55

7

Case A

5

6

Case C

c

2

3Lo/

0 1 2 3 4 5

0

1

Radius(m)

Lo/Lc data (Case A : Base)


Case A Case B Case C


42/55

-

Thermal Engineering LabCase A Case B Case C


43/55


Fe2O3 Fe3O4 FewO Fe


44/55

=

1.0

Fe O

0.35

0.40 CO2

CO

0.6

.

action

2 3

Fe3O

4

FewO

Fe0.20

0.25

0.30

action

0.2

0.4

Mas

sf

0.10

0.15

Mas

sF

10 15 20 25

0.0

5 10 15 20 25 30

0.00

0.05

Height(m) Height(m)

Mass Fraction of Ore Mass Fraction of Gas



45/55

Reactions of Indirect Reduction

2 3 3 4 23 ( ) ( ) 2 ( ) ( )Fe O s CO g Fe O s CO g+ +

Shrinking Core Model

3 4 2

3( ) ( ) ( ) ( )

4 3 4 3w

wFe O s CO g Fe O s CO g

w w+ +

2we s g w e s g+ +

3 4 21 3( ) ( ) ( ) ( ) ( 848 )4 4

sFe O s CO g Fe s CO g T K + +

Documents

Choi_Japanese Combustion Symposium