Biomass combustion – current status and future developments€¦ · B L E E C O N M Y P Ca Mg K E N E R G Y B I O M A S S AS H BIOENERGIESYSTEME GmbH Inffeldgasse 21b, A-8010 Graz

BIOS BIOENERGIESYSTEME GmbHBIOS BIOENERGIESYSTEME GmbHInstitute for Process and Particle EngineeringInstitute for Process and Particle Engineering

Graz University of TechnologyGraz University of Technology

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E N E R G Y B I O M A S S

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Prof. Dr. Ingwald Obernberger

Biomass combustion Biomass combustion ––current status and future developmentscurrent status and future developments

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BIOENERGIESYSTEME GmbHInffeldgasse 21b, A-8010 Graz ContentsContents

Thermal biomass utilisation in Europe

Biomass combustion technologies

Relevant characteristics of biomass fuels andadvanced fuel characterisation

Ash related problems

Gaseous emissions under special consideration of NOx

CFD as an efficient tool to design and optimise biomass combustion systems

Intelligent process control systems

Relevant future R&D trends

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BIOENERGIESYSTEME GmbHInffeldgasse 21b, A-8010 Graz

Primary energy consumption and total Primary energy consumption and total turnover of biomass combustion plants turnover of biomass combustion plants in the EU for 2008 and outlook for 2020in the EU for 2008 and outlook for 2020

Explanations: small-, medium-, and large-scale plant considered; calculations based on present market and achievement of EU 2020 targets

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

prim

ary

ener

gy c

onsu

mpt

ion

[PJ/

a]tu

rnov

er [M

io. €

/a]

turnover medium- & large-scale plants [Mio. €/a]

turnover - small-scale plants [Mio. €/a]

primary energy consumption [PJ/a]

261%

203%

expected average annual market growth rate: 8.3% p.a.

2008 2020

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Biomass combustion technologies Biomass combustion technologies ––classification by capacityclassification by capacity

Small-scale biomass combustion systemscapacity range: <100 kWth

Medium-scale combustion systemscapacity range: 100 kWth to 20 MWth

Large-scale combustion systemscapacity range: >20 MWth

Co-firing of biomass in coal fired power stationscapacity range: some 100 MWth

Biomass Combustion• most advanced conversion technology• market proven applications for a broad range of fuels and plant

capacities

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Biomass combustion technologies Biomass combustion technologies ––overviewoverview

secondaryair

ash

fuel

ash

primary air

fixed bed combustion(grate furnace)

fuel

bubbling fluidisedbed combustion

circulating fluidisedbed combustion

fuel

fuel +

ash

bedmaterial

bedmaterial

ashash

pulverised fuelcombustion

bed materialfuel

primary air primary air

secondaryair

secondaryair

freeboard

secondaryair

primary air

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SmallSmall--scale biomassscale biomasscombustion systemscombustion systems

Application:residential heating

Technologies:wood stoves

wood chip boilerswood pellet boilerswood log boilersheat storing stovesfire-place inserts

Fuels used:log woodwood chipspellets

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MediumMedium--scale biomassscale biomasscombustion systemscombustion systems

Technologies:underfeed stokers

dust burnersgrate-fired systems

Fuels used:wood chipsbarkforest residueswaste woodstraw

flue gas

secondaryair

fuel

primary air

Application:district heatingprocess heating and coolingCHP production

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LargeLarge--scale biomassscale biomasscombustion systemscombustion systems

Application:CHP productionpower production

Technologies:

fluidised bedsgrate-fired systems

Fuels used:barkforest residueswaste woodstraw, cerealsfruit stones, kernels, husks, shells

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Biomass coBiomass co--firing in coal firing in coal fired power stationsfired power stations

Application:power productionCHP

Technologies:co-firing of finely milled biomass mingled with coal

Fuels used:forest residuessawdust, wood chipspelletsstrawfruit stones, kernels, husks, shells

biomass co-firing in fluidised bed combustion systemsco-firing in separate combustion units and junction of steambiomass gasification and utilisation of the product gas as fuel in acoal combustion system

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Chemical compositions ofChemical compositions ofdifferent different ““conventionalconventional”” solid biomass solid biomass

fuels fuels –– ash, S, Cl, Kash, S, Cl, K

mean values and standard deviations; d.b. … dry basis

ash content wt% (d.b.)

0

2

4

6

8

Woodchips

Bark Straw Wastewood

S mg/kg (d.b.)

0

400

800

1,200

1,600

Woodchips


Cl mg/kg (d.b.)

0

2,000

4,000

6,000

8,000

Woodchips


K mg/kg (d.b.)

0

4,000

8,000

12,000

Woodchips


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Chemical compositions ofChemical compositions ofdifferent different ““newnew”” solid biomass fuels solid biomass fuels ––

ash, S, Cl, Kash, S, Cl, K

mean values and standard deviations; d.b. … dry basis; SRC ... short rotation coppice

ash content wt% (d.b.)

0

1

2

3

4

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

S mg/kg (d.b.)

0100200300400500600

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

Cl mg/kg (d.b.)

0500

1,0001,5002,0002,500

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

K mg/kg (d.b.)

01,0002,0003,0004,0005,000

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

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Chemical compositions ofChemical compositions ofdifferent different ““conventionalconventional”” solid biomass solid biomass

fuels fuels –– relevant guiding parametersrelevant guiding parameters

Indicator for corrosion risk Indicator for embedding of S+Cl in the ashes and SO2/HCl emissions

Indicator for slagging behaviour Indicator for aerosol formation

2S/Cl mol/mol

05

10152025

Woodchips


(K+Na)/(2S+Cl) mol/mol

0

1

2

3

4

Woodchips


Si/(Ca+Mg) mol/mol

02468

10

Woodchips


mean values and standard deviations; d.b. … dry basis

K+Na+Zn+Pb mg/kg (d.b.)

02,0004,0006,0008,000

10,000

Woodchips


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Chemical compositions ofChemical compositions ofdifferent different ““newnew”” solid biomass fuels solid biomass fuels ––

relevant guiding parametersrelevant guiding parameters

Indicator for corrosion risk Indicator for embedding of S+Cl in the ashes and SO2/HCl emissions

Indicator for slagging behaviour Indicator for aerosol formation

mean values and standard deviations; d.b. … dry basis;SRC ... short rotation coppice

2S/Cl mol/mol

05

10152025

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

(K+Na)/(2S+Cl) mol/mol

0

1

2

3

4

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

Si/(Ca+Mg) mol/mol

012345

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

K+Na+Zn+Pb mg/kg (d.b.)

01,0002,0003,0004,0005,0006,000

Woodchips

Miscan-thus

Poplar(SRC)

Maizecobs

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Ash related problems in biomass Ash related problems in biomass combustion processescombustion processes

Fine particulate emissions

Ash melting / slagging and fouling

Corrosion

Additives to reduce ash related problems

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Influence of the fuel usedInfluence of the fuel usedon the mass of aerosols formedon the mass of aerosols formed

• Emissions at boiler outlet• Summary of the data gained during the test runs mentioned in the previous slides

grey regions: experiences from other projects• Particle emissions related to dry flue gas and 13 vol% O2

10

100

1.000

100 1.000 10.000 100.000concentration of aerosol forming elements in the fuel (K+Na+Zn+Pb)

[mg/kg (d.b.)]

parti

cles

<1

µm (a

e.d.

) [m

g/N

m³]

softwoodhardwoodbarkwaste woodstraw

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Average chemical compositions of aerosolsAverage chemical compositions of aerosolsfrom smallfrom small--scale biomass boilers and stoves scale biomass boilers and stoves

Appropriate fuel selection relevantPrimary measures of great relevance(complete combustion, reduction of the release of ash vapours)Aerosols with high non-carbonate carbon contents are of health relevance

0%

20%

40%

60%

80%

100%

full load 50%load

full load 50%load

full load 50%load

full load full load

modern pellet boilers modern wood chip boilers modern logwoodboilers

oldstoves

modernstoves

wt%

(d.b

.)

alkalimetal sulfate alkalimetal chloride alkalimetal carbonate oxides non-carbonate carbon

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0

5

10

15

20

25

30

35

40

0 200 400 600 800 1.000

organic gaseous carbon (OGC) content in the flue gas [mg/MJ (NCV)]

orga

nic

carb

on (O

C) c

onte

nt in

aer

osol

s [m

g/M

J (N

CV)

]

0

1

10

100

1.000

10.000

1 10 100 1.000 10.000

organic gaseous carbon content (OGC) in the flue gas [mg/MJ (NCV)]

PAH

con

tent

in a

eros

ols

[µg/

MJ]

(NC

V)

OC and PAH content in aerosols versus OC and PAH content in aerosols versus OGC content in the flue gas for small scale OGC content in the flue gas for small scale

combustion of wood fuelscombustion of wood fuels

Explanations: PAH … polycyclic aromatic hydrocarbons defined according to EU directive 2004/107/EC

r2=0.98statistically significant correlation (p<0.05)

r2=0.88statistic trend(p<0.10)

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Prediction of ash melting Prediction of ash melting ––results from TGAresults from TGA--DSC analyses and DSC analyses and

thermodynamic equilibrium analysesthermodynamic equilibrium analyses

Formation of molten phases – results from thermodynamic equilibrium analyses (left) and the influence of heavy metals on the melting temperatures of Cl-containing ash mixtures (right)

Appropriate fuel selective design and process control relevantUtilisation of new prediction tools importantFurnace cooling relevant (flue gas recirculation, grate, walls)

K2SO4

+ carbonate

+ chlorideK, Na, SO4, Cl

+ Pb

+ Zn196oC

609oC

1068oC

643oC

Tem

pera

ture

[o C]

K2SO4

+ carbonate

+ chlorideK, Na, SO4, Cl

+ Pb

+ Zn196oC

609oC

1068oC

643oC

Tem

pera

ture

[o C]

0%

20%

40%

60%

80%

100%

200 400 600 800 1,000 1,200 1,400 1,600temperature [°C]

mol

ten

phas

es [w

t%]

straw combustionbark combustion

15 wt% molten phase

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thickness of ash layer[mm]

Measurement and CFD modeling of ash Measurement and CFD modeling of ash deposit formationdeposit formation

Surface temperature[°C]

Ash deposit layer on a water-cooled deposition probe (left) compared with CFD simulations performed (middle) and influence of ash depositions on the surface temperatures (right); explanations: bulk flue gas temperature: 1,050 °C, clean probe surface temperature: 590 °C; figures at the top ... top view; figures at the bottom ... side view

4.03.83.63.43.23.02.82.62.42.22.01.81.61.41.21.00.80.60.40.20.0

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Ash related problems in biomass Ash related problems in biomass combustion processes combustion processes ––

corrosioncorrosionSolid phase reactions involving alkali metal and heavy metal chlorides2 KCl(s) + SO2(g) + 1/2 O2(g) + H2O(g) → K2SO4(s) + 2 HCl(g)

highly relevant (active oxidation)

Reactions involving molten alkali metal and other chloridesrelevant

Fuel selection relevantHighest allowable temperatures on boiler tube surfaces and inlet temperatures of flue gas in convective boiler section relevantBoiler cleaning relevantUtilisation of additives interestingDevelopment towards increased steam parameters as a driving force

straw: 540 °Cwood chips: higher than 540°C

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Ash related problems Ash related problems ––case study for appropriate case study for appropriate

technological solutionstechnological solutions

Source:

CHP plant MariboCHP plant Maribo--SakskSakskøøbing (Denmark)bing (Denmark)Main fuel: Wheat strawSteam pressure: 92 barSteam temperature: 542 °CPower output (gross): 10.6 MWThermal output: 20 MWElectric efficiency (gross): 31.7 %Thermal plant efficiency: 60 %Total plant efficiency: 91.7 %

Superheaters operated in slagging mode

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Gaseous emissions Gaseous emissions --NONOxx

Fuel selection relevant

Primary measures especially relevant

Combination of primary and secondary measures if needed

0

100

200

300

400

500

600

0.01 0.10 1.00 10.00

Fuel N [wt% (d.b.)]

NO

X em

issi

on

[mg/

Nm

³, dr

y flu

e ga

s, 1

3 vo

l% O

2 ] woodSRC (poplar, miscanthus)waste wood and chipboardnut shellswheat strawwhole crops (triticale)grasses (arundo, cynara)

0%

10%

20%

30%

40%

50%

60%

70%

80%

0.01 0.10 1.00 10.00

Fuel N [wt% (d.b.)]w

t% o

f fue

l-N c

onve

rted

to

N in

NO X

em

issi

on

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0

100

200

300

400

500

600

700

800

0.3 0.5 0.7 0.9 1.1 1.3 1.5 air ratio in the PCC

NO

x em

issi

ons

[mg/

Nm

3 (dry

flue

gas

; 13%

O2)

]

NONOxx emissions versus air ratio in the emissions versus air ratio in the primary combustion chamberprimary combustion chamber

Explanations: results of test runs performed at a 180 kW moving grate pilot plant; fuel used: chipboard (N content: 3.6 wt% d.b.); average boiler load: 150 kW; Rec. … flue gas recirculation; PCC … primary combustion chamber; T prim … temperature at outlet of the primary combustion chamber; d.b. … dry base; the air ratio in the PCC is calculated from fuel and oxidizing agents supplied (air, recirculated flue gas)

blue: Rec. above grate; T prim=1,000 °Cgreen: Rec. below grate; T prim=1,000 °C

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NO [ppmv] N2 net production rate [kg/m3s]

Measurement UnitCO 7.5 ± 10.2 4.5 ppmV d.b.NO 391.5 ± 68.0 417.4 ppmV d.b.NO2 - 8.4 ppmV d.b.NH3 - 1.6 E-07 ppmV d.b.HCN - 3.5 E-05 ppmV d.b.

Simulation Profiles of NO and N2 net production rate (indicator for NOx reduction) in a biomass grate furnace and comparison measurement/simulation Explanations: nominal thermal load 440 kWth; fuel fibre board, fuel nitrogen content 6.5 [wt.% d.b.]

CFD simulation of NOCFD simulation of NOxx formation formation ––grate furnacegrate furnace

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CFD simulation of CFD simulation of biomass combustion plants biomass combustion plants ––

model overviewmodel overview

Models for solid biomass conversionSingle particle conversion and volatiles releaseMultiphase modelling for particle-particle and particle-gas interactions in packed beds (and entrained flows)

Finite cell model for convective heat exchangers

For fire tube boilers, water tube and steam boilers, thermal oil boilersConsideration of flow, heat transfer, pressure distribution; calculation of tube surface temperaturesLink with ash deposit model (in progress)

Models for gas phase combustion and NOx formationTurbulence modelsTurbulence-chemistry interaction modelsReaction mechanisms

Models for ash deposit and aerosol formation

Direct wall condensation, deposition of fly ash particlesAerosol formation and depositionErosionDeposit growth and influence on heat transfer

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Intelligent process control systems for Intelligent process control systems for biomass combustion plantsbiomass combustion plants

Still a high potential for optimisation is given.

Currently applied control strategies• mostly a decentralised structure

(one input variable is coupled with one output and controlled separately)• they do not consider the coupled and non-linear nature of control

loops in biomass furnaces• do not utilise the full potential of well engineered plants

Most promising future approach: model based control strategies

+ consideration of essential physical characteristics of biomass furnaces

+ well established theory for the controller design

+ state-of-the-art control methods for nonlinear systems can be applied

- labour-intensive if no applicable mathematical model is available

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Comparison of conventional and model Comparison of conventional and model based control strategies based control strategies -- feed temperature feed temperature

at a stepwise increase of the set pointat a stepwise increase of the set point

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Ongoing research and Ongoing research and future R&D topicsfuture R&D topics

State of science Future R&D

conventional biomass fuels(wood fuels, straw)

new biomass fuelsshort rotation crops, agricultural residues, torrefied materials, hydrolytic lignin, pyrolysis char

modern biomass combustion technologies

next generation biomass combustion systemstowards zero emission technologiestowards new process control systems

conventional CHP technologies

advanced highly efficient systemstowards increased steam parameterstowards higher availability

single model development virtual biomass conversion plant

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Thank you for your attentionProf. Dr. Ingwald Obernberger

Inffeldgasse 21b, A-8010 Graz, AustriaTEL.: +43 (316) 481300; FAX: +43 (316) 4813004

Email: [email protected]: http://www.bios-bioenergy.at

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Documents

Biomass combustion – current status and future developments€¦ · B L E E C O N M Y P Ca Mg K E N E R G Y B I O M A S S AS H BIOENERGIESYSTEME GmbH Inffeldgasse 21b, A-8010 Graz