A Janus Orn Research

7/30/2019 A Janus Orn Research

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Numerical and Experimental Studies onHeat Transfer in Circulating Fluidized BedBoilers

6thsemester

Asian Institute of Technology Energy

Anusorn Chinsuwan

Examination Committee: Prof. Sivanappan Kumar (Chairman)

Dr. Animesh Dutta (Co-chairman)

Dr. Hemantha P Jayasuriya


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3/37


Hydrodynamics in CFB furnace

Most combustion take place in fast fluidized bed zone

The majority of bed particle move upwards through core, but they flowdownwards along the wall.

Turbulent or Bubbling

Fluidized Bed

F

astFluidized

Bed

Swirl

Flow

Moving

PackBed


4/37


Heat Transfer in CFB Boilers

fraction of wall receiving

heat from clusters

fraction of wall receiving

heat from clusters

Heat transfer surface

Cluster moving

upward

Cluster moving

downward

Cluster moving

downward

Convection from

dilute phase

Conduction from

particles

Radiation of dense

and dilute phase

CFB water walls

Particles flow down

along

the wall in

form of

clusters

Particle Convection plays most important role in heat transfer.


5/37


Advantages of CFB boilers

Fuel Flexibility

The special

hydrodynamics

condition inCFB furnace

Excellent gas-solid

andsolid-solid mixing

Fuel particles are

rapidly heated aboveignition temp.

CFB furnace

can burnany fuel

High Combustion Efficiency

Better gas-solid mixing

A majority of unburned fuel

particles are recycled backto the furnace

High combustionefficiency

Efficient Sulfur Removal

More residence time

for sulfur

dioxide to contact withsorbents

Smaller particle size ofsorbents

Efficient

sulfurremoval

Low NO2 Emission

Fuel

Nitrogen does not find O2 in

the immediate vicinity forproduce oxides

Fuel nitrogen transfer tomolecular nitrogen

Sub-

stoichiometri

c air supplied

as primary

air

Reducingzone

Secondary air

Limited opportunity forformation of NO2


6/37


Heat Transfer Coefficient

Summary of empirical correlations of heat transfer in large scale CFBboilers (Dutta and Basu, 2003)

The heat transfercoefficient is a function of

cross section averagesuspension density.

b

h a


7/37


Model for Predicting Suspension Density

I t seems to b e more practical but it can not exp lain the inf luence of bed diameter and it have been

yet validated with o ther commercial CFB boilers


8/37


Statement of Question 1

Are there models for

predicting the suspension

density along the height ofcommercial CFB boilers?

What are the

limitations of eachavailable model?

Could the suspension density along

the height of commercial CFB boilersbe developed in more practical?

Yes, there are Kunii and

Levenspiel Model(1991),

Johnsson and Leckner

Model(1995) and Teplitskiy andRyabov Model(1999)

The models need some measured

values which are not available anddifficult to measure.

?



Is there

information of

heat transfer

behavior in

membrane water

wall along the

height of

commercial CFB

boilers ?

No, there is not.

Is there any way to increase the heat

absorption from CFB furnace with less costlyand less risk of material erosion ?

Is it easy to manufacture and revamp from anexisting boiler ?

Yes, by weldinglongitudinal fins on tube.

?

Does longitudinal fin

orientation have any effecton heat transfer behavior?

Is there literature reporting heat transfer

behavior in membrane water wall with two fins at45 deg on both sides of the tube crest ? No


9/37


Rational

Heat transfer coefficientHeat transfer coefficient correlation:

b c

h a T

Model for predicting cross sectional

average suspension density alongCFB furnace height

Temperature

distribution alongthe height of

CFB furnaceswall

Heat flux along

the height of CFBfurnaces wall

Opt imum designofCFB boilers

Numerical investigation of heat

transfer behavior in membrane

water wall tube along the height ofCFB boilers

Heat generation bycombustion

Water wall of CFBfurnace

Small heat absorbedby wall

Large heat absorbedby wall

High furnacetemp

Low furnacetemp

To mainta in the combust ion temp at an

opt imum level , i t is required for the wal l of

CFB furnace to absorb a certain fraction o f

the heat input

Enhancement of heatabsorption in CFB furnace

Additional heat transferequipments

Additional heating surface areaon membrane water wall

Wing wall, omega tubes,external heat exchangers

Cost ly and may enhance the

r isk of tube sur face erosion

Simple to manufacture and

less cost ly and i t may be

used to revamp an exist ingboiler


10/37

Objective

1. Develop an empirical model for predicting the cross sectional averagesuspension density in commercial circulating fluidized bed boilers.

2. Numerical simulations on heat transfer behavior along the height ofmembrane water wall of CFB boilers. The specific objectives are:

a) Numerical simulations on temperature distribution in membrane waterwall tubes of commercial CFB boilers

b) Numerical simulations on heat flux distribution on membrane water walltubes of commercial CFB boilers

3. Experimental study and numerical analysis on the effect oflongitudinal fin orientation on heat transfer in membrane water walls.The specific objectives are:

a) Experimental investigation of the effect of longitudinal fin orientation onheat transfer in membrane water wall tubes in a circulating fluidizedbed.

b) Investigation of the heat transfer behavior of longitudinal finnedmembrane water wall tubes in CFB boilers.



11/37


Scope and Limitations

Objective 1

The empirical model is developed and

validated based on measured data ofcommercial CFB boilers reported inliterature.

The model is developed as a function:

Fr , ,p

t

s

d zf

D H

z

Airdistributor

Secondary air

injectors

Center of

furnace exit

Fuel feed Return

D

z

Z H

Objective 2

Numerical simulations are performed in3D under normal operating conditions ofCFB boilers:

Tb =850CFrt = 0.0007, 0.125 and 0.250

dp/D= 15,125 and 250 mm/m

Membrane tube configurations

25.4 , 6w mm t mm 50.8 30.8mmOD mmID

Objective 3

Experiments are performed on 3 tube types in acold model CFB riser.

Tb =75C,


12/37


Research Methodology

Experimental data from

Andersson (1996)

Grouping based on

Proposed model based on dimensionless

groups:

Error analysis based on

RMS differences


RMS

differences for the model

of Johnsson and Leckner

(1995)


RMS

differences for the model

of Teplitskiy and Ryabov

(1999)

Model

assessment

Available measured data of

large scale CFB boilers from

literature

Development of m odel

Comparison

of error

Error analysis based

on RMS differences

for the obtained

model


on RMS differences

for model of

Johnsson and

Leckner(1995)


on RMS differences

for model of

Teplitskiy and

Ryabov (1999)

Conclusions

Comparisonof error

Model val idat ion

3 3

3

3

c d

pb

t

s

d za Fr

D H

pd

Objective 1

A i I tit t f T h l


13/37



Objective 2

GAMBIT

Geometry setup Grid generation Boundary setup

Develop User Defined (UDF)

Function using C language

FLUENT Material definition Boundary definition Calculation Postprocessing

Problems

Solution

Available data from literaturesModel validationNo

Grid dependence studyNo

Yes

Yes

Computational model

Geometry

Operating and geometric conditions of

CFB boilereported in literature:

Fr , / , /t p

d D z H andZ

Physicalmodel

Obtained model from Study #1

3 3

3

3

c d

pb

t

s

d za Fr

D H

Available model for predicting localheat transfer coefficient in literature

(Dutta and Basu, 2002)

Development of

computational model

Simulation

Perform the simulation

Fr , / , /t p

d D z H andHin therange of simulation

Model of Dutta and Basu (2002)

Obtained model from Study #1

3 3

3

3

c d

pb

t

s

d za Fr

D H

Results

Temperature profiles

Fr , / , /o t pf d D z H

Material limit based

on allowable stress

Material limit based

on oxidation

A i I tit t f T h l


14/37



Objective 3

Experimental study

Study #3

Compare the obtained

data with data in

literature

Conclusion

H drod namics

Heat transfer study

Compare the obtained

data with data in

literature

Heat transfer coefficient

Ratio of heat transfer in

longitudinal fin to the combination

of tube and membrane fins portion

Ratio of heat transfer coefficient at

longitudinal fin to the combination of

tube and membrane fins portion

Membrane water

wall with a

longitudinal fin at

the tube crest

Membrane water

wallMembrane water wall

with two longitudinal

fins at 45 on both sides

of the tube crest

Ratio of heat transfer of membrane

tube with longitudinal fin(s) to

without longitudinal fin

Ratio of heat transfer coefficient of

membrane tube with longitudinal

fin(s) to without longitudinal fin

Available

heat transfer

coefficientin

commercial

CFB boilers

in literature

Hin

m

a

tu

Cfl

m

a

tuAgree

Disagree DisagreePre are a aratus

A i I tit t f T h l


15/37



Objective 3, Experimental setup

EL. 00

Distributor

plate

300

300

300

300

300

400

400

400

400

400

400

400

To bag filter

From bag filterFrom air

compressor

Water manometer

Temperature

indicator

Pressure gauge

Pressure gauge

Pressure regulator

Pitot tube

Rotameter

Storage

column

EL. 1800

EL. 3000

EL. 4200

EL. 4800

Particle

measuring valve

Particle control valve

Test section

Bypass

Air heater box

Blower

T

Circulating

pump

Bypass

Drain

Water storage

tank

Rotameter

Flow control

valve

T

To

test

tube

type

B

To

test

tube

type

A

To water manometer

To

test

tube

type

C

Test

tube

400Particle measuring

column

Bed material sand

Mean diameter,p

d 231 mm

Density,s

31515kg m Bed properties

Bulk density 32774kg m

Superficial velocity, U 18ms

Suspension density, 325 75kg m

Bed inventory, I 15kg

Solid circulation rate, sG 2 122 110kgm s

Operating conditions

Bed temperature, bT 70 75 C

Experimental conditions

Asian Institute of Technology


16/37



Objective 3, Experimental setup

Plywood

6mm thk

Tube type A

2 inch thick Glass Wool

Pressure tap

Temperature

probe

Tube type B

Tube type C

SECTION C-C

Temperature

measuring point400

400

EL. 1800

EL. 3000

E E

E E

C C

Pressure tapping

2 inch

Glass Wool

For clarity, one test tube is shown.

Plywood

6mm thk

Tube type A

Pressure tap

Tube type B

Tube type C

SECTION E-E

Temperature

measuring point

2 inch thick Glass Wool

(a) (b) (c)

InsulationInsulation Insulation

Membrane

fin Longitudinal

finTube type A Tube type B Tube type C

3 3 3

14 14

14

14 14

14 14

3

3 3

7 7

45o

31.8 OD x 6.5 thk.31.8 OD x 6.5 thk.

31.8 OD x 6.5 thk.

Asian Institute of Technology E


17/37


Schedule

Tentative Schedule

http://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tentative%20Schedule.dochttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tentative%20Schedule.doc


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Results

Objective 1

Air distributor

Secondary air injectors

Center of furnace

exit

Fuel

feed

Return

DZ H

z

z/H

.001 .01 .1 1

(

/s)/[Frt

0.4193(d

p/D)-

0.998]

.01

.1

1

10

100

dp=224mm, U=1.83m s-1, U

t=1.25m s

-1

dp=224mm, U=2.65m s-1, U

t=1.32m s

-1

dp=329mm, U=3.58m s-1, U

t=2.26m s

-1

dp=329mm, U=2.68m s-1, U

t=2.39m s

-1

dp=432mm, U=4.53m s-1, U

t=3.33m s

-1

dp=432mm, U=6.39m s-1, U

t=3.45m s

-1

0.4326

0.9980.4193

/2.5513 /

Fr /

s

t p

z H

d D

Boiler No.Equation (Equation no.)RMS

1 2 3 4 5

overallRMS 8.890.998 0.4326

0.41932.5513Fr (4.6)p

t

s

d z

D H

Present work RMS 5.60 11.50 14.51 1.77 1.94

overallRMS 24.900.45

0.620.053Fr (4.3)t

s

z

H

Teplitskiy and Ryabov (1999) RMS 21.93 30.45 15.58 2.49 7.84

overallRMS na( ) ( )

2,( ) (4.2)x

x

a z H b H z

x H exit ge e

Johnsson and Leckner(1995) RMS 14.6 na na na na

RMS is the Root Mean Squared Deviations and 2

/predicted measuredRMS N , where N is number of data.

na: not applicable

The numbers in italic show the lowestRMS .

Boiler specification Operating conditionsBoilerNo.

AuthorsCapacity

Furnace size

( W L Z )[ 3m ]bT [ C] pd [ mm ]

U

[ 1ms ]tU

[ 1ms ]

1 Andersson(1996) 12 thMW 1.5 1.7 13.5 865 288 3.68 1.90

2 Johnsson and Leckner (1995) 12 thMW 1.5 1.7 13.5 850 320 2.7,4.7 2.2

3 Yang et al. (2005) 135 eMW 6.6 13.1 38 885,896,892 332,318,300 3.5 3.02,2.89,2.73

4 Kavidass et al. (1997) 35 thMW 3.1 3.66 24.4 870 350 5.0-6.0 3.2

5 Kavidass et al. (1997) 81 thMW 4.32 4.57 30.5 870 350 5.0-6.0 3.64

0.998 0.4326

0.41932.5513Frp

t

s

d z

D H



19/37


Suspension density [ kg m-3

]

0 10 20 30 40 50 60

0

2

4

6

8

10

12

14

16

18Data from boiler no. 4 (Kavidass, 1997)

Present predicted curve eq. (4.6)

Teplitskiy and Ryabov (1999) model eq. (4.3)


]

0 10 20 30 40

Heightaboveinflectionpoint[m]

0

5

10

15

20

25

30

Data from boiler no. 3 (Yang et al.,2005)




]

0 10 20 30 40 50 60

Heightabovesecondaryairports[m]

0

5

10

15

20

25

Data from boiler no. 5 (Kavidass et al., 1997)




]

0 20 40 60

Heightaboveairdistributor[m]

0

2

4

6

8

10

12

Data from boiler no. 1 (Andersson, 1996)

dp=288 mm, U=3.68m s-1, U

t=1.90m s

-1


Johnsson and Leckner (1995) model eq.(4.2)predicted by Andersson (1996)

Teplitskiy and Ryabov (1999) model eq.(4.3)



20/37


Results

Objective 2

Parameters Symbol Unit Values

Water tube diametero

d mm 60 Tube thickness t mm 6 Tube pitch P mm 78 Membrane fin thickness

ft mm 6

The height from secondary air ports to furnace exit H m 10,20,30

Thermal conductivity k 1 1Wm K 20 Inner heat transfer coefficient of the water tube

ih 2 1Wm K 5500

External heat transfer coefficient of the water tubeo

h 2 1Wm K As Dutta and Basus Model

Cross sectional average suspension density 3kg m As result from Study #1

Inner fluid temperaturefT C 342.25 15MPa

Bed temperatureb

T C 850 Froude number Frt - 0.0007,0.125,0.25

Particle to furnace diameter ratio /pd D

1mmm 15,125,250

Adiabatic surface

External surface

Internal convection

surface

Symmetric surface

Symmetric surface

Symmetric surface

Insulation

CFB or PC furnace



21/37


Temperature distribution at the top of water wall

Temperature distribution at the bottom of

water wall

Heat flux distribution at the top ofwater wall

Grid Scheme



22/37


Height along furnace, z[m]

0 5 10 15 20 25 30

Heatflux[k

W/m2]

0

200

400

600

800

1000

Steam

quality[-]

0.00

.05

.10

.15

.20

.25

.30

72MWth, Chatham unit

109MWth, Flensburg unit

Predicted steam quality165MW

th, Orebro unit

Heat flux absorbed of 165MWth, Orebro unit

Design heat flux of 158MWth PC boiler,(Payan-Rodriguez et al., 2005)

Design steam quality of 158MWth PC boiler,

(Payan-Rodriguez et al., 2005)

Temperature Distribution

0.324

0.1414

,0.8976Fr

p

o m t

d

D

0.13985

0.3240.1414

0.8147Fr /

o

t p

z

Hd D

Frt= (U-Ut)2/gH

.01 .1

o,m/(d

p/D)-

0.324

.01

.1

1

10

100

, 0.1414

0.3240.8976Fro m

t

pd

D

Numerical predicted curve

Chalmers, 12MWth (Andersson, 1996)

Chatham, 72MWth (Couturier et al., 1993)

Flensburg, 109MWth (Werdermann and Werther, 1994)

Orebro, 165MWth

(Andersson et al., 1997)

0.13984

0.324

0.1414

5.2244

Fr

o

p

t

z

Hd

D

Heat Flux Distribution

0.86016

xx F z

0.324

0.1414

0.13984

Fr /26.0738

b f t p

x

fg

T T d DF k

Gdh d H

Steam Quality

Material Limits

,

, 0.3240.1414

0.8976Fr /

max stress

stress

t p

Fd D

,

, 0.3240.1414

0.8976

Fr /

max ox

ox

t p

F

d D

Common steel tubes used

in boiler industrial can be

used to as evaporator tube

in CFB boilers.

Tube Burnout

Parameters

for DesigningCFB Furnaces

Next page



23/37


z[m]

0 5 10 15 20 25 30

Heatflux[k

W/m

2]

0

200

400

600

800

1000

1200

1400

1600

1800

Frt=0.125, d

p/D=15mm/m, 15MPa

Frt=0.125, d

p/D=15mm/m, 20MPa

Frt=0.250, d

p/D=15mm/m, 20MPa

Frt=0.250, d

p/D=15mm/m, 15MPa

Frt=0.125, d

p/D=15mm/m, 15MPa

Frt=0.250, d

p/D=15mm/m, 15MPa

Frt=0.125, d

p/D=15mm/m, 20MPa

Frt=0.250, d

p/D=15mm/m, 20MPa

H= 30m

Heat flux absorbed

Critical heat flux

Height along CFB furnace, z[m]

0 5 10 15 20 25 30

Heatflux[k

W/m

2]

0

1000

2000

3000

4000



165MWth, Orebro unit



165MWth, Orebro unit

Critical heat flux

Heat flux absorbed

z[m]

0 5 10 15 20

Heatflux[kW

/m2]

0

200

400

600

800

1000

1200

1400

1600

1800

Frt=0.125, d

p/D=15mm/m, 15MPa Fr

t=0.125, d

p/D=15mm/m, 20MPa

Frt=0.250, d

p/D=15mm/m, 20MPaFrt=0.250, dp/D=15mm/m, 15MPa

Frt=0.125, d

p/D=15mm/m, 15MPa

Frt=0.250, d

p/D=15mm/m, 15MPa

Frt=0.125, d

p/D=15mm/m, 20MPa

Frt=0.250, d

p/D=15mm/m, 20MPa

H= 20m

Heat flux absorbedCritical heat flux

Parameters for

Designing CFB

Furnaces

Tube Burnout

0.0007 Fr 0.250, 10 ,20 ,30t H m m m

15 / / 250 /pm m d D m mm m

max

300 20

6 8

pd m D m

D m m

m

Fr 0.12520

Fr 0.250

Fr 0.12530

Fr 0.25

20

/ 15 /

0

t

t

t

t

p

H

MPa

d

H

m

m

D

m

mm

Real situation

4 cases of tube burnoutare found.



24/37


Height above secondary air ports, z(m)

0 2 4 6 8 10

0.0

.5

1.0

1.5

2.0

2.5

3.0

Frt=0.0007, dp/D=15mm/m

Frt=0.0007, dp/D=125mm/mFrt=0.0007, dp/D=250mm/m

Frt=0.125, dp/D=15mm/m

Frt=0.125, dp/D=125mm/m

Frt=0.125, dp/D=250mm/m

Frt=0.250, dp/D=125mm/m

Frt=0.250, dp/D=250mm/m


H=10m


0 5 10 15 20

0

1

2

3

4

5

6

Frt=0.0007, dp/D=15mm/m



Frt=0.125, dp/D=125mm/m

Frt=0.125, dp/D=250mm/m


Frt=0.250, dp/D=125mm/m

Frt=0.250, dp/D=250mm/m

H=20m


0 5 10 15 20 25 30

0

2

4

6

8

10

Frt=0.0007, d

p/D=15mm/m



Frt=0.125, dp/D=250mm/m


Frt=0.250, dp/D=125mm/m

Frt=0.250, dp/D=250mm/m

Frt=0.125, dp/D=125mm/m

H=30m

Hot water CFBboilers

/ 125 /

/ 15010 Fr 0. 0

/00 7

p

t

p

Hd D m m

d Dm

m m

m

m



25/37


Results

Objective 3

Suspension density, (kg m-3)20 40 60 80

Heattransfercoefficient,

h(Wm

- 2o C-1)

20

40

60

80

100

Test tube type A

Test tube type B

Test tube type C

Suspension density, (kg m-3)10 20 30 40 50 60 70 80

Heattransferratio(-)

0.0

.2

.4

.6

.8

1.0

Qt-mf,lf/QT,lf

Qt-mf,2lf/QT,2lf

Suspension density, (kg m-3)20 40 60 80

Heattransfercoefficient,

h(W

m-2oC-1)

20

40

60

80

100

120

hlf

ht-mf,lf

h2lf

ht-mf,2lf

havg,mf hlf

ht-mf,lf

ht-mf,2lf

h2lf

havg,mf



26/37


Suspension density, (kg m-3)0 20 40 60 80

Heattransferrateandheattransfer

coefficientratio

.2

.4

.6

.8

1.0

1.2

1.4

1.6

QB / QA

QC / QA

hB / hA

hC/ hA

1.25CB

A A

QQ

Q Q

0.8CB

A A

hh

h h

Measured heat transfer coefficient, h(W m-2 oC-1

)

80 100 120 140 160

Predictedheattransfercoefficient,

h(W

m-2oC-1)

80

100

120

140

160

+10%

-10%

Angle from the tube crest, [degree]0 45 90 135 180

Innerwallheatflu

x,

qi(kWm

-2)

0

50

100

150

200

250

300

Tube type A

Tube type B

Tube type C

Angle from the tube crest, [degree]0 45 90 135 180

Temperatu

re[oC]

200

250

300

350

400

450

500

550

Tube type A

Tube type B

Tube type C

Membrane fin tip of tube type A

Membrane fin tip of tube type B

Membrane fin tip of tube type C

Longitudinal fin tip of tube type B

Longitudinal fin tip of tube type C

Membrane fin base

Membrane fin base

Longitudinal fin base

Longitudinal fin base



27/37

Chinsuwan, A. and Dutta, A. (2008). An empirical model for predicting thecross sectional averaged suspension density in commercialcirculating fluidized bed boilers, Journal of the Energy Institute,81(2).

Chinsuwan, A. and Dutta, A. An experimental investigation on the effectof longitudinal fin orientation on heat transfer in membrane water

wall tubes in a circulating fluidized bed. Submitted to InternationalJournal of Heat and Mass Transfer, 2008.

gy EnergyWorks Published

Paper in Refereed International Journal

Papers in Refereed International Conference

Chinsuwan, A. and Dutta, A. (2006). A Developing of EmpiricalCorrelation for Predicting the Axial Suspension Density Distribution

in Circulating Fluidized Bed Boiler. Proceeding of Sustainable

Energy and Environment: Technology and Policy Innovations.

November, Bangkok, 761-765.



28/37

Chinsuwan, A. and Dutta, A. Investigation of the heat transfer behaviorof longitudinal finned membrane water wall tubes in circulatingfluidized bed boilers. Submitted to Powder TechnologysinceJanuary, 2008.

Chinsuwan, A. and Dutta, A. Investigation of the temperature distributionand material limits of membrane water wall tubes of circulatingfluidized bed boilers. Submitted to Canadian Journal of ChemicalEngineeringin April, 2008.

gy EnergyWorks under Review

Under Review in Refereed International Journals(2 papers)



29/37

Summary of Present Studygy Energy

Experimental

Literature review; Chapter 2

Summary of thestudy

Numericalsimulations

Membrane waterwall tube

Chapter 7

Membrane water wall tube

with a longitudinal finChapter 7

Membrane water walltube with two

longitudinal finsChapter 7

Develop model for predicting

suspension densityChapter 4

Temperature

distribution in

membrane wallChapter 5

Heat flux

distribution on

membrane wallChapter 6

Heat behavior

in membrane

water wall with

and without

longitudinal finChapter 8

The

empiricalmodels

Total heat transfer

Heat transfer on fin portion

Heat transfer on the combination of tube

and fin portion

Heat transfer and heat transfer coefficientratio

Average heat transfer

coefficient

Heat transfer coefficient on

fin portion

Heat transfer coefficient onthe combination of tube andmembrane fins portion

Temperature profile

Material limits base on

strengthMaterial limits base onoxidation

Temperature and heat flux distribution on inner tube wall of membrane

tubes with and without longitudinal fin under normal operating conditions ofCFB boilers

Heat flux profile

Steam qualityCHF and DNB

Critical height of hotwater CFB boilers

Theoretical



30/37

Summary of the Resultsgy Energy

Descriptions Equation Operating/Test ConditionsError

(%)

Reference/

Nature of

investigation

Model for predicting average suspension

density

Section 4.3/

Theoretical

Model for predicting temperature profile at the

membrane tube crest.

Section 5.5.1/

Numerical

Model for predicting mean temperature profile

at the membrane tube crest.ditto

Section 5.5.1/

Numerical

Model for predicting temperature limits of tubes

based on allowable stressditto

Section 5.5.2/

Numerical

Model for predicting temperature limits of tubes

based on oxidationditto

Section 5.5.2/

Numerical

Model for predicting heat flux profile at the

membrane tube crest of steam CFB boilersditto

Section 6.3.1/

Numerical

Model for predicting heat flux profile at the

membrane tube crest of hot water CFB boilersditto

Section 6.3.1/

Numerical

Model for predicting steam quality in

membrane water wall tubeditto

Section 6.3.2/

Numerical

Heat transfer ratio

Section 8.4/

Theoretical

0.998 0.43260.41932.5513Fr

p

t

s

d z

D H

0.00092 Fr 0.075t 1 134.17 / 200.75

pmm d D mmm m

25%

0.13985

0.3240.1414

0.8147Fr /

o

t p

z

Hd D

0.0007 Fr 0.250t 1 115 / 250

pmm d D mmm m

24.80%

12.08%

0.324

0.1414

, 0.8976Frp

o m t

d

D

24.80%

12.08%

, 0.8976stressF

, 0.8976oxF

0.13984

0.324

0.1414

5.2244

Fr pt

z

HdD

0.1181

0.2722

0.1227

3.3747

Frp

t

z

Hd

D

0.86016xx F z

/ / 0.8B A C A

h h h h

35.61 6.62kg m

858 918bT C 10%



31/37

Summary of the ResultsEnergy

Descriptions Table/Figure Operating/Test Conditions

Reference/

Nature of

investigation

Limits of water wall

tube material based on

allowable stress

Table 5.5Section 5.4.4/

Theoretical

Limits of water wall

tube material based on

oxidation

Table 5.6Section 5.4.4/

Theoretical

Steam quality factor Table 6.1 and Table 6.2Section 6.3.3/

Numerical

Tendency of water wall

tubes burnoutFigure 6.8-6.10

Section 6.3.3/

Numerical

Critical height of hotwater CFB boilers

Figure 6.14-6.16 Section 6.3.3/Numerical

Comparison of heat

flux on inner tube wall

among tubes type A, B

and C

Figure 8.4Section 8.4/

Numerical

Comparison of

temperature on outer

tube wall among tubes

type A, B and C

Figure 8.5-8.8Section 8.4/

Numerical

0.0007 Fr 0.250t

1 115 / 250pmm d D mmm m

0.0007 Fr 0.250t 1 115 / 250

pmm d D mmm m

15MPa

20MPa

15MPa

20MPa

0.0007 Fr 0.250t

1 115 / 250pmm d D mmm m

10 30H m

0.0007 Fr 0.250t

1 115 / 250p

mm d D mmm m

10 30H m

850bT C315kg m

15p MPa

850bT C315kg m

15p MPa

http://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Limits%20of%20Water%20Wall%20Tubes.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Limits%20of%20Water%20Wall%20Tubes.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Steam%20Quality%20Factors.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tube%20Burnout.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Critical%20Height.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux%20and%20Temp..ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux%20and%20Temp..ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux%20and%20Temp..ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux%20and%20Temp..ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Comparison%20of%20inner%20heat%20flux.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Critical%20Height.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Critical%20Height.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Critical%20Height.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tube%20Burnout.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tube%20Burnout.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Tube%20Burnout.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Steam%20Quality%20Factors.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Limits%20of%20Water%20Wall%20Tubes.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Limits%20of%20Water%20Wall%20Tubes.ppt


32/37

Summary of the ResultsEnergy

0.8CB

A A

hh

h h

,,,,

riserdimension:

Descriptions Equation/Figure Operating/Test Conditions

Reference/

Nature of

investigation

Ratio of heat transfer

through the tube and

membrane fins portion

of the tubes type B and

C

Figure 7.9Section 7.4/

Experimental

Heat transfer

coefficient of the

longitudinal fin and the

combination of tube

and membrane

portions of the tube

type B and C

Figure 7.10 dittoSection 7.4/

Experimental

Average heat transfer

capacity, heat capacity

of the longitudinal fin

portions of the tubes

type A, B and C

Figure 7.11 dittoSection 7.4/

Experimental

Heat transfer ratio of

membrane tube withlongitudinal fin to

membrane tube

ditto Section 8.4/Experimental

Heat transfer

coefficient ratio of

membrane tube with

longitudinal fin to

membrane tube

dittoSection 8.4/

Experimental

18U m s 231pd mm

325 75kg m 2 122 110sG kg m s

70 75bT C

100 100 4.8mm mm m

Test tube: 31.8 1000mmOD mm

1.25CBA A

QQQ Q

http://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppthttp://e-learning.kku.ac.th/file.php/467/6th%20semester%20progress%20Backup/Fig7.9-7.11.ppt


33/37

Contribution of Present StudyEnergy

Heat transfer

There is no literature thatreported:

temperature and heat

flux profile along the

height of CFB boilers

limit of tube materials

base on stress and

oxidation

steam quality in

membrane water wall

tubes

tendency of tube burnout in CFB boilers

critical height of hotwater CFB boilers

There is no

practical model

for predicting

averagesuspension

which includesthe effect of

The average heat transfercoefficient is not available

Present study

Modify the model which was

developed as a function of

dimensionless parameters

based on operating

conditions by taking intoaccount of the effect of

First reported the study on temperature and heat

flux profile on CFB water wall tubes, limits of tube

based on stress and oxidation, steam quality in

tube along the height of CFB boilers, tendency of

tube burn out in CFB boilers and critical height ofhot water CFB boilers.

First reported the study on heat transfer

behavior in membrane water wall tube

with two longitudinal fins at on both sides

of the tube crest and comparison of inner

wall heat flux of membrane tube with andwithout longitudinal fins

C

O

N

T

R

I

B

U

TI

ON

B

A

C

K

G

RO

U

ND

Hydrodynamics

Membrane wall tube Membrane water walltube with a

longitudinal fin

The comparison of heat transfer rate

and heat transfer coefficients between

membrane tube with longitudinal finand without the fin is not available

The heat transfer from

longitudinal fin portion is not

available

The heat transfer from the

combination portion of tube

and membrane fins is notavailable

The heat transfer coefficient of

longitudinal fin portion is notavailable

The heat transfer

coefficient of the

combination portion of

tube and membrane finsare not available Heat flux profile on inner

wall tube is not available

Membrane water walltube with twolongitudinal fins

/pd D

/pd D



34/37

Contribution of Study #1Energy

Hydrodynamics in CFB boilers

There is no practical model forpredicting cross sectional average

suspension density in commercialCFB boilers

Back ground

Modify the model which was developed as a function of

dimensionless parameters based on operatingconditions by taking into account of the effect ofContribution

/pd D



35/37


Numerical Analysis

TemperatureProfile

Heat FluxProfileModel for predictingTemp. and heat flux profiles

along the CFBfurnace height

Steam Quality

Critical Heat Flux

Tube Burnout

Materials

limits

Material Limits

Based onStress

Material Limits Based

onOxidation

The model for predicting

steam quality

Critical heat flux

Critical height of H/W CFB boilers

Contribution

Result fromStudy #1

Steam BoilersH/W Boilers

Critical Height

Tendency of tube burnout



36/37


Experimental

Heat Transfer Heat TransferCoefficients

First reported the heat

transfer behavior in

membrane tubes with a

longitudinal fin at thetube crest and two

longitudinal fins at 45o

on both sides of thetube crest

First reported the

comparison of the heat

transfer behavior among

the 3 tube types under

normal operating

conditions of CFB boilers

ContributionHeat Transfer

Capacity

B

A

Q

Q

,

,

t mf lf

T lf

Q

Q

,2

,2

t mf lf

T lf

Q

Q

C

A

Q

Q

B

A

h

h

C

A

h

hlfh 2lfh ,t mf lfh ,2t mf lf h

,avg mfhA ,avg lfhA ,2avg lfhA lfhA 2lfhA

Numerical simulations on heat transfer behavior of 3

tube types under normal operating conditions of CFB

boilers

Temperature distribution Heat Flux distribution



37/37

THANK YOU

Energy

Documents

A Janus Orn Research