vtt processesash chemistry, deposits, corrosion optimization of multi-fuel operation power plant...

VTT TECHNICAL RESEARCH CENTRE OF FINLANDVTT PROCESSES

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Optimisation of Optimisation of multimulti--fuel fuel operation in operation in fluidized fluidized bed bed

boilersboilersJouni Hämäläinen, Markku Orjala, Martti Aho

VTT ProcessesContent:- Background - Biomass fuel properties for power availability, methods forfuel characterisation

- R&D needs- Conclusion


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Fluidized Bed Combustion: R&D Fields

Fluidized Bed Processes

Know-how and understanding of CFB combustion process

Multifuel operation

Fuel combustion profile andbehaviour

Fuel reactivity

Material behaviour

Emissions: performance, directives, etc.

Plant availavility

Ash chemistry, deposits, corrosion

Optimization of multi-fueloperation

Power plant operation economyTechnical support

Maintenance and construction of pilotplants

Field measurements and pilot tests


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Future challenges at deregulated energy markets

• Plant performance• Investment costs, operation (operational and fuel)and maintenance costs

• Fuel flexibility

• Fuel saving (plant efficiency)

• Environmental performance• Emissions, CO, NOx, SOx and particularly CO2emissions


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Background for multifuel operation

(1) Common in industrial boilers (2) uses various with different fuel properties(3) each fuel has slightly own combustion behaviour(4) optimization of multifuel operation is needed

REFPuru ja puujäte


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Ash elements in fuel ashesAshed 550 oC

Element Peat BarkLogging

residue bales Coal

Si 24.0 8.79 9.86 27.3

Al 5.98 2.62 0.98 12.1

Fe 9.79 4.44 0.529 2.97

Mn 0.124 0.937 1.53 0.024

Mg 1.21 2.68 2.94 1.13

Ca 5.35 21.4 21.9 3.14

Na 1.72 1.14 0.430 1.13

K 1.77 5.36 8.80 2.15

P 1.31 2.17 2.66 0.374

S 1.78 2.13 0.893 1.50

Cl 0.165 0.15 0.131 0.004

Fuel characteristics for plant availability: Ash properties

Fuel characteristics for plant availability: Ash properties

� Fossil fuel ash; SiO2, Al2O3, CaOand Fe2O3. Alkalines in silicate matrix(non-soluble)

� Biomass ash; main ash components:CaO, K2O, MgO ja Na2O� exists as salts or in fuel organic

matrix (release during combustioninto gas phase)

� Ash behaviour very different comparedto fossil fuel ash

The use of more demanding biofuels - straw - short rotation biomassash behaviour will be even more challenging


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Chloride vapours Alkali aerosol particles &coarse mode particles

Turbulent flow instaggered tube array

Boundarylayer

Condensation onaerosol particles

Condensationon deposit

layer

SulphationThermophoresis

Corrosion

Sintering &removability by

sootblowing

Diffusionin porousdeposits

Heattransfer

SO2 HCl

Coarse particlesticking

DepositionDeposition

Ash behaviour in biomass combustion

By Jouni Pyykönen /VTTPRO

Alkaline rich deposits

K 2SO 4 HClConditions

S / Cl ratio increases

Cocombustion of biomass withfossil fuels or peat

Wood-based fuels →→→→KCl-salt (deposits)

Tuhkan koostumus

Alkuaine Turve Kuori Metsähake

K 1.77 5.36 8.80

P 1.31 2.17 2.66

S 1.78 2.13 0.893

Cl 0.165 0.15 0.131

Tyypillisiä polttoaineen pitoisuuksiaTuhka (850C) 4.77 2.51 2.57S 0.2 - 0.3 ~ 0.1 ~ 0.05Cl 0.04 - 0.08 0.01 - 0.03 0.01 - 0.03


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� Boiler fouling →→→→ increase in flue gas temperature→→→→ decrease in boiler efficiency

� Increased need for boiler soot-blowing and cleaning� Increase in plant power own-use (increase in flue gas flow,

deposition)� Use of more expensive superheater materials (high

temperature risk)� Ash end-use. Due to ash quality increased costs for ash

utilization� Investments for fuel storaging systems

Operational economy at power plants

• substitution of fossil fuels with biomass increase plant operational costs:

Operational economy at power plants

• substitution of fossil fuels with biomass increase plant operational costs:


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Probe for deposit / corrosion monitoringSpecimens: * superheater materials* adjusted for steam temperature by air /

water cooling

Optimization of fuel mixture: power plant monitoring OptimizationOptimization ofof fuel mixturefuel mixture: : power plant monitoring power plant monitoring


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Probe temperature behavior during monitoring periodProbe temperature behavior during monitoring period

Monitoring period 672 h. Strong increase in leeward and side temperatures → on-line information of deposit formation rate = deposition onto windward side of the probe

4 viikon sondimittaukset CFB -kattilassa

300

400

500

600

pvm

Sond

in p

inta

läm

pötil

a er

i pin

noill

a [d

eg C

]

Four week monitoring at CFB boiler

Prob

e te

mpe

r atu

r es


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Co-combustion of recovered fuels (REF) with peat and wood based fuels. The share of REF 10 to 15 % as energy basis

Co-combustion of recovered fuels (REF) with peat and wood based fuels. The share of REF 10 to 15 % as energy basis

Test period I: Combustion of REF IIIwith peat and wood based fuels:One week probing

Test period II: Combustion of REF Iwith peat and wood based fuels:One and half week probing


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PROBE TEMPERATURE BEHAVIOUR IN COCOMBUSTIONTEST OF REF WITH PEAT AND WOOD

PROBE TEMPERATURE BEHAVIOUR IN COCOMBUSTIONTEST OF REF WITH PEAT AND WOOD

December 2001: Exposure time c. 190 hour

Note: sootblowing interval. Longer as in the testof spring 2000

Spring 2000: Exposure time c. 140 hour

Severe increase of probe side and leeward temperatures during the test →→→→ deposition ontoprobe surface

420

440

460

480

500

520

540

560

580

9:36

13:5

818

:19

22:4

03:

067:

2711

:48

16:0

920

:31

0:58

5:20

9:41

14:0

218

:24

22:4

53:

137:

3411

:56

16:1

720

:38

1:06

5:27

9:49

14:1

018

:32

22:5

33:

217:

4212

:03

16:2

520

:46

1:14

5:35

9:57

Time; 16th and 22th of February

Tem

pera

ture

(o C)

TIA 3; tulopuolen lämpötila, käytetty säätävänä lämpötilana

TIA 1; jättöpinnan lämpötila

TIA 7; sivupinnan lämpötila

420

440

460

480

500

520

540

560

580

10:10

18:10 2:1

110

:1118

:11 2:11

10:11

18:11 2:1

110

:1118

:11 2:11

10:11

18:11 2:1

110

:1118

:11 2:11

10:11

18:12 2:1

210

:1218

:12 2:12

10:12

Aika, 190 h

Läm

pötil

a C

TIA 1; T, jättöpinta

TIA 2; T, sivupinta

TIA 3; T tulopuoli, säätävä

LIITE 3


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How to improve plant availability and controllability?

How to improve plant availability and How to improve plant availability and controllability?controllability?

� Fuel quality and treatment - handling, feeding etc. - even fuel quality

– new measurements for fuel quality and feeding to guarantee stable combustion process

– attention to fuel handling at power plants: new solutions are neededLogging residue (risutukki)

0

1000

2000

3000

4000

5000

6000

7000

Si Al Fe Ti Mn Ca Mg P Na K S Cl

mg/

(kg

dry

solid

s)

Rest fraction, analysedLeached in HClLeached in AcetateLeached in H2OUntreated Fuel

Fuel analysis- basic fuel analysis- ash composition- ash melting behaviour- ash solubility (by Åbo Akademi)


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ConclusionConclusion

� Use of biomass based fuel may decrease plant availability and performance if the fuel characteristics are not taken into account.

� At deregulated markets the need for optimisation of multi-fuel operation will increase in the future to achieve the most economical operation and profit.

� New monitoring methods and measurements are needed to achieve the most flexible operation

vtt processesash chemistry, deposits, corrosion optimization of multi-fuel operation power plant...

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