Ash Deposition and Shedding in Straw and Wood Suspension … · Fly Ash Elemental Composition (AMV2) 22. Background Experiments Results and Discussion Conclusions Acknowledgment

Ash Deposition and Shedding in Straw and Wood

Suspension-Fired Boilers :

Full-scale Measurements

Student: Muhammad S. BashirSupervisors: Professor Kim Dam-Johansen

Asso. Prof. Peter A. JensenAsso. Prof. Flemming FrandsenAsso. Prof. Stig Wedel

CHEC Research Centre, Technical University of Denmark

DTU Chemical Engineering Technical University of Denmark

2

•Background

•Experiments• Experimental Objectives

• Materials and Methods

•Results and Discussion• Experimental Set Up

• Quantification of Deposit Buildup

• Deposit Shedding using Artificial Sootblowing

• Elemental Release of Major Ash Components

•Conclusions/Experimental Findings

22

Presentation Outline


Ash Deposition during Biomass Combustion

L. Tobiasen et al; Fuel Processing Technology, 88 (2007) 1108-1117.

Biomass (straw) K, Cl, S

Increased risk of fouling/slagging on heat exchange surfaces.

AMV2Superheater Region

Background Experiments Results and Discussion Conclusions Acknowledgment

3


4

Boiler Configuration : AMV1

4

Parameter AMV1

Capacity(wood, straw)

350, 320 MWth

Wood, Straw pellets

(full load)

20 kg/s

Steam DataSuperheater (oC) 540



5

Boiler Configuration : AMV2

5

Parameter AMV2

Capacity(wood, straw) 250 MWth

Wood, Straw pellets(full load) 60 t/h

Steam DataSuperheater (oC) 480



Experiments

• Measurement of extent of boiler fouling/slagging by meansof an ash deposition/shedding probe.

• Influence of fuel type, boiler load, probe metaltemperature and probe exposure time on deposition rate,heat uptake and deposit characteristics.

• Investigation of PIP needed to remove the deposits ofdifferent exposure time and probe surface temperature.

• Investigation of residual ash and deposits chemistry.

6



7

Deposition/Shedding Probe

7

600



8

Experimental Setup Description (AMV 1)

8



Experimental Resume : AMV2

9

Test No. 1 3 2 4 5

Straw (%) 35 65 80 100 0

Ash (%) 4.21 4.99 5.38 5.85 3.3

Probe Temp. (oC) 500 500 500 500 500

Exposure Time(h)

90 72 124 76 24

Boiler Load (%) 46 63 50 53 52



Experimental Resume : AMV1

10

Test No. 1 2 3 5 4

Straw (%) 80 65 35 50 50

App. Ash (%) 5.2 4.0 2.4 3.4 3.4

Probe Temp. (oC) 500 600 500500

(600)500

Exp. Time (h) 56 45 185 168 73

Boiler Load 66 57 62 64 86

Oil Share (%) 12.9 13.5 2.4 7.1 4.8


7 6 8

0-10 0-10 0-10

1.0 1.0 1.0

550 550 550

335 434 212

62 60 60

2.7 5.3 6.9


11

AMV1: Primary Data (120 s): 50 % Straw (flue gas: 843 oC)

1111

0 20 40 60 80 100 120 140 160 180600

800

1000

Time [h]

Gas

Tem

p.(o C)

Thermocouple

0 20 40 60 80 100 120 140 160 1800

5000

10000

Time [h]

(g/m

2 )

Weight Uptake

0 20 40 60 80 100 120 140 160 1800

50

100

Time [h]

(kW

/m2 )

Heat Uptake0 20 40 60 80 100 120 140 160 180

80100120

Soot

blow

er

0 -185 h (500)


Actual flue gas temp. (suction pyrometer, Qualitative trend is same as of thermocouple)


12

AMV1: Primary Data (120s): 50 % Straw (avg. flue gas: 880 oC)

1212

0 20 40 60 80 100 120 140 160600

800

1000

Time [h]

Gas

Tem

p.(o C)

Thermocouple

0 20 40 60 80 100 120 140 1600

1

2 x 104

Time [h]

(g/m

2 )

Weight Uptake

0 20 40 60 80 100 120 140 1600

40

80

Time [h]

(kW

/m2 )

Heat Uptake0 20 40 60 80 100 120 140 160

80100120

Soot

blow

er

0 -30 h (500) 30 -94 h (600) 94-145 h (500) 145 -168 h ( 600)


Actual flue gas temp. (suction pyrometer, Qualitative trend is same as of thermocouple)


13

Flue Gas Temperature and Heat Uptake

13

500 550 600 650 700 750 800 850 900 9500

10

20

30

40

50

60

70

80

90

100

Gas Temp.(oC)

(kW

/m2 )

y = 0.1247*x - 55.35

Heat Uptake linear

500 550 600 650 700 750 800 850 900 9500

10

20

30

40

50

60

70

80

90

100

Gas Temp.(oC)

(kW

/m2 )

y = 0.1427*x - 70.12

Heat Uptake linear

500 550 600 650 700 750 800 850 900 9500

10

20

30

40

50

60

70

80

90

100

Gas Temp.(oC)

(kW

/m2 )

y = 0.06928*x - 29.89

Heat Uptake linear

13



14

Brief Results of Tests

14

Test No. 1 2 3 5 4

Straw (%) 80 70 50 50 30

Ash (%) 5.0 4.3 3.4 3.4 3.0

Probe Temp. (oC) 500 600 500500

(600)500

Exp. Time (h) 56 45 185 168 73

Boiler Load 66 57 62 64 86

Oil Share (%) 12.9 13.5 2.4 7.1 4.8

Flue Gas Temp.Mean (oC)

852 821 843 880 918

Weight Uptake Final (kg/m2)

3.78 4.95 3.07 16.26 7.34

Heat Uptake Mean(kW/m2)

34 21.1 35.0 23.3 41.1 14


7 6 8

10 5 0

1.0 0.8 0.7

550 550 550

335 434 212

62 60 60

2.7 5.3 6.9

774 724 788

1.95 1.82 --

-- 24.0 --


Overall Comparison of Weight Uptake of Different Full Scale Measurements (45 h)

15

Boiler Fuel AnalysisProbe

Temp.

Flue gas

Temp.

Final WeightSignal

Ref.

Tests Ash K Cl oC oC kg/m2

Avedøre Test 1 5.5 0.69 0.32 500 1020 9.50 [11]

Avedøre Test 2 4.7 0.92 0.35 500 784 1.50 [6]

Amager Unit 2 (Test 4)

5.9 0.83 0.40 500 830 1.70


5.0 -- -- 500 852 2.20


3.4 -- 0.25 500 843 0.45


3.0 -- -- 500 918 4.90



4.3 -- -- 600 821 4.95


3.4 -- -- 600 880 9.60


Overall Comparison of Weight Uptake of Different Full Scale Measurements (72-77 h)

16

Boiler Fuel AnalysisProbe

Temp.

Flue gas

Temp.

Final WeightSignal

Ref.

Tests Ash K Cl oC oC kg/m2

Avedøre Test 1 5.5 0.69 0.32 500 1022 15.0 [11]

Avedøre Test 2 4.7 0.92 0.35 500 784 2.40 [6]


5.9 0.83 0.40 500 830 1.67


3.4 -- 0.25 500 843 1.01


3.0 -- -- 500 918 7.34



3.4 -- -- 600 880 10.0


17

Ash Deposit Removal using Artificial Sootblowing Probe (Example: Test 3 (500))

1717

60 70 80 90 100 110 120600

800

1000

Time [h]

Gas

Tem

p.(o C

)

Thermocouple60 70 80 90 100 110 120

600

800

1000

(o C)

Suction Pyrometer

60 70 80 90 100 110 1200

5000

10000

Time [h]

(g/m

2 )

Weight Uptake

60 70 80 90 100 110 1200

40

80

Time [h]

(kW

/m2 )

Heat Uptake60 70 80 90 100 110 120

80100120

Soo

tblo

wer

Shedding through artificial sootblowingShedding through plant sootblowing



18

Artificial Deposit Removal: Image Analysis

18

Weight Signal : 8747.18 g/m2 Weight Signal : 1584.83 g/m2

Probe Exposure Time : 91.2 hFlue gas temperature : 825 CTarget Probe Temperature : 500 oC

Straw Share : 50 %Boiler Load : 65 %


Image Before Deposit Removal

Image After Deposit Removal


Air Pressure and PIP

19


0

50

100

150

200

250

300

0 50 100 150 200 250 300 350 400 450 500

PIP

(kPa

)

Air Pressure (kPa)

20 cm 15 cm 13 cm 11 cm 9 cm 7 cm 5 cm


Impact of Probe Exposure Time and Temperature on Deposit Removal

20


0,1

1,0

10,0

100,0

0 50 100 150 200 250

% D

epos

it R

emov

ed

PIP (kPa)

500 oC (Probe Temperature)

30 h (1695 g/m2) 72 h (7100 g/m2) 91 h (9090 g/m2)

120 h (12750 g/m2) 144 h (15006 g/m2)


Impact of Probe Exposure Time and Temperature on Deposit Removal

21


0,1

1,0

10,0

100,0

0 50 100 150 200 250

% D

epos

it Re

mov

ed

PIP (kPa)

600 oC (Probe Temperature)

46 h (4494 g/m2) 76 h (500 C for initial 30 h) ( 11123 g/m2)

95 h (14024 g/m2) 167 h (17850 g/m2)


Fly Ash Elemental Composition (AMV2)

22


0

10

20

30

40

50

60

10*Al2O3 10*Fe2O3 10*MgO 10*Na2O K2O P2O3 CaO SiO2 SO3 Cl

Com

posit

ion (

wt.

%)

Grate boiler (Fuel ash) Grate boiler (Fly ash) Suspension boiler (Fuel ash) Suspension boiler (Fly ash)


Deposit Elemental Composition (AMV2)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

Al Ca Fe K Mg Na P Si S Cl

wt %

Elements

35% Straw (Front Upper Layer)

100 % Straw (Upper Front Layer)

23



24

Preliminary Conclusions

24

Deposits are more sintered in the windward directionduring pure straw-firing.

Deposits and fly ashes obtained during suspension-firingcontain significant amounts of Ca and Si.

The final deposit weight uptake is not higher compared tobiomass grate-firing at almost similar conditions.



25

Preliminary Conclusions

25

Image analysis reveal that deposit shedding is primarilythrough debonding.

Deposits of less than 91 h exposure time are easy toremove and PIP needed is less than 55 kPa at 500oC temp.

With increase in probe surface temperature from 500 to600 oC, PIP needed to remove the deposits increases.

Natural shedding is possible at higher flue gastemperatures (> 940 oC), but temperature needs toremain higher as lower temperature fluctuations are nothelpful.



26

Acknowledgment

2626

• Dr. Johan Wadenbäck/Søren Thaaning., Vattenfall A/S

• Energinet.dk for PSO project funding


Questions?

Many Thanks!

27

Documents

Ash Deposition and Shedding in Straw and Wood Suspension … · Fly Ash Elemental Composition (AMV2) 22. Background Experiments Results and Discussion Conclusions Acknowledgment