1

Prof. Dr. techn. G. Scheffknecht

Institute of Combustion and Power Plant Technology

Pilot scalePilot scale combustion testing

Installation and Operation of R&D test facilities under oxy-fuel

conditions

4th APP OFWG Capacity Building Course, Tokyo, Japan 2012

Joerg Maierjoerg.maier@ifk.uni-stuttgart.de

University Stuttgart

Prof. Dr. techn. G. Scheffknecht

Institute of Combustion and Power Plant Technology

Institute of Combustion and PowerInstitute of Combustion and Power Plant Technology - IFK (former IVD)

Universität Stuttgart

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Outline

• 0.5 MWth Unit Retrofit

• Oxy-fuel Burner DevelopmentOxy fuel Burner Development

• Test Results and Experiences• NO formation and reduction• S behaviour• Corrosion, slagging and foulinggg g g• Modelling

• Ongoing/Future R&D topics

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Example of Emission Reduction (Reunion of Germany)

1982 - 1999: old federal states1990 - 1999: new federal statesDust

in millon tons0.25

Sulphur dioxidein millon tons2.0

Nitrogen oxidein millon tons0.8

4

1982 84 86 88 90 92 94 96 1999

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IFK 0.5 MWth Unit Retrofit for Oxy-Fuel operation

under the requirement to keep availability for air firingunder the requirement to keep availability for air firing

0.5MWth Unit Modifications for Oxyfuel Combustion Conditions

Coal feeding

FD fan

Oxygen supply

Flue gas recycle duct

Condensers

6

Bottomash

APH

g

ID fan

ESPSCR stack

Bypass

4

Pf-fired 0.5 MWth Test Facility(15 years operation)

additional fuel +conveyor air

coal + primary air

secondary air, flue gas recirculation

ti l

burner

to stack

verticalfurnace

SP 1 SP 2 SP 3 SP 4 SP 5

7

ESP

fabricfilter

slag and ash

Φ > 100 µm

SCR Catalyst

fly ash(1 fraction)

fly ash(3 fraction)

fly ash(1 fraction)

SP 6

O2/ CO2 Supply Infrastructure

Preparation:

Oxy-fuel Mode IntegrationInfrastructure

• Negotiations with providers:commissioning of tanks, lines, product prices, installations, maintenance, …

• Permission procedures:City of Stuttgart and

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City of Stuttgart and University authorities

• Engineering:work safety aspects, construction and ground works,climatic constraints, …

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O2/ CO2 Supply Infrastructure

Consumption (planned):

Infrastructure

• Oxygen: 72,000 m3N

• Carbon dioxide: 48 tons

Tank capacities:

• Oxygen: 6,000 m3N

• Carbon dioxide: 5 tons

Modifications for Oxyfuel Combustion

CO2O2

gas distribution

storage tanks consumers20kWth

0.5MWth

others

6

level no.

123

Concerned area of the major changes for the adaptation for the new burner design

COCO

Infrastructure

Air-Oxyfuel Test Facility (500kWth)

345

6789

10

1112131415

1617181920

21

22

StoragetanksFD/ RG fan

O2

CO2

AiO2 CO2

Gasdistribution

Coal feeding

Burnerwindbox

Air

StoragetanksFD/ RG fan

O2

CO2

AiO2 CO2

Gasdistribution

Coal feeding

Burnerwindbox

Air

Inflame Measurements•Gas emissions•Gas temperature•Heat Flux•Radiation etc.

Air/Flue gas

11

23

24

25

26

27

28

29

30

31

Continuous gas emission measurements

Bottomash

ID fanESPSCR

Stack

Air

APH

By-passes

Bottomash

ID fanESPSCR

Stack

Air

APH

By-passes

Sampling•Ash, HCL, SO3

re-circulationventilator

O2/recyled flue gas 0.5MWth Unit Modifications for Oxyfuel Combustion Conditions

duct for re-cycled flue-gas

O2 injection system(MFC, injector)

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Venturi orifice to furnace

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Topics of first Oxyfuel-Tests

• Start-up/shut-down procedure

• Identification of air inleakage• Identification of air-inleakage

• Max. CO2 concentration

• Switch from air to oxyfuel operation

• Parameter optimisation (variation of O2-injection,

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Parameter optimisation (variation of O2 injection,

recycle rate, …)

• Definition reference flame definition (air/oxyfuel)

• Start of test programmes

Switch from once-through to re-circulation mode (I)Lausitz lignite

80

100

80

100O2 in vol.-%dry

CO2 in vol.-%dry

flap open

air combustion

start of O2 injection and

CO2 as carrier gas

flap for flue-gas re-circulation (FGR) opened

40

60

40

60FGR flapposition in %

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air combustion

0

20

18:09 18:29 18:49 19:09Time

0

20

LA_OXY_1_20980-21450

flap closed

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Shift from Air to Oxyfuel of the 30MW Pilot Plant

Approx. 60 min

Behaviour of flue gas concentrations

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Source: Vattenfall, Alstom Cottbus 2009

• Switching from air to oxy-fuel combustion, achievable in short time interval (~30 minutes).

• High CO2 concentration achievable (~95% dry).

Conclusions from 0.5 MW Retrofit Test Facility

High CO2 concentration achievable ( 95% dry).• Operation under oxy-coal combustion with different

ranks of coals achieved successfully.• Burner adjustments required and successful

implemented• O2-concentrations at the burner inlet ducts up to 100%

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• High flexibility of recycle rate (40-90%)• Additional safety measures required

More than 1500h successful Oxyfuel operation

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Burner adjustments and further burner developments

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Development of Low NOx Oxyfuel burner

Performed Investigations at the electrically heated 20 kW test facility:

•Determination of optimum oxygen injection method (pure or premixed

•Determination of optimum burner operation mode; swirl,

O2 concentrations in the different gas streams

Total combustion gas

Carrier stream Primary stream Secondary stream

21% 21% / 5% / 5% 21% / 23% / 100% 21% / 23% / 5%

27% 27% / 5% / 5% 27% / 30% / 100% 27% / 30% / 5%

39% 39% / 5% / 5% 39% / 43% / 100% 39% / 43% / 5%

momentum, velocity•Determination of optimum parameters for oxy-fuel operation using high volatile Brown Coals (Stoichiometric ratio, oxygen excess, oxygen content in combustion gas)•Staging at the oxyfuel combustion

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Development of Low NOx Oxyfuel burner

Investigations at the 500 kW semi-technical test facility:

Comparison of two different burner designs• Flame characterisation and ignition optimisation under recycled

diti

Inflame Measurements•Gas emssions

•Gas temperature

conditions• Optimum O2 injection method• Impact of recycle rate on flue gas momentum,

flame stabilisation, internal recirculation• Staging at the oxyfuel combustion• Emission behavior

New burner designActual burner

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secondary gas stream(optionally swirled)

primary gas streamand fuel

gas probe with nine drillings

secondary gas stream(optionally swirled)

primary gas streamand fuel

gas probe with nine drillings

Continuous gas emssion

measurements

Integration of the new burner design

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Implementation of:• new primary line for the new burner• 4 new secondary lines for the new burner

• oxy-fuel staging• Second source of oxygen injektion

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Integration of the new burner design

Previous burner installation (previous burner) with one primary and one secondary lines.

Current burner installation (new burner) with:• one primary • four different measured and controlled secondary lines • one oxygen line

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Example of O2-Injection Modes

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Pre-mixing (total) Individual Pre-mixing Direct injection

Source: Alstom Cottbus 2009

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Test Results and ExperiencesTest Results and Experiences

• NO formation and reduction• S behaviour• Slagging and fouling

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• Corrosion• Modelling

Electrically heated test reactor (20kW)

Experiment Conditions Air & 27% O2/73% CO2

Coals Klein Kopje, Lausitz

Oxidant flow through burner

Constant for all cases [6.7 m³/h]

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λoverall 1.15λ1 (burner stoichiometry) 0.75, 0.85, 0.95

T1 1, 2 and 3 seconds

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NOx reduction potential during staged combustion

300

350

400Air_3 sec

Air_2 sec

Klein Kopje Coal

0

50

100

150

200

250

0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

Burner Stoichiometry

NO

x [m

g/M

J] 27% Oxy_3 sec

27% Oxy_2 sec

Un-staged

Com

bustion

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Parameters Optimum EffectBurner Stoichiometry 0.75-0.85 Oxygen deficiency, encouraging

formation of N2

Residence time in reduction zone 2-3 seconds Longer time available for conversion of NOx precursors to N2

Temperature Shift of coal-N towards gas phase

Fate of recycled NO - Summary

99

8596

8895

81

9810091

72

92

798391

80

100

120

led

NO

[%]

Air_KK 27% O2_KK Air_LA 27% O2_LA Air_NG Oxy_NG

595049

3847

13

5339

0

20

40

60

80

0.75 0.85 0.95 Unstaged

Stoichiometric Ratio

Red

uctio

n of

recy

cl

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• Reduction dependent on combustion mode (burner stoichiometry and residence time in reduction zone).

• Generally higher reduction for oxy-coal combustion.

• For the coals investigated: for a particular combustion condition, percentage reduction during oxy-coal combustion is almost similar.

• Combustion modification can take care of recycled NOx accumulation.

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Conclusions from 20 kW furnaceNOx emission rate is lower during oxy-coal combustion with oxygen partial pressure between 21-27% (un-staged combustion). Oxidant staging is applicable for oxy-coal combustion.Recycled NOx can be reduced by combustion modification, with ~60% reduction during un-staged combustion and ~100% during staged combustion (λ1=0.75 and T1=3 sec) for all coals tested.CO in the near burner region is higher during oxy-coal

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CO in the near burner region is higher during oxy coal combustion indicating enhancement of water-shift and CO2shift reactions.

Test Results and ExperiencesTest Results and Experiences

• NO formation and reduction• S behaviour• Slagging and fouling

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• Corrosion• Modelling

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Set-up and description of 20 kW once through furnace

• SO2 Injection: up to 6000 ppm via the secondary stream of the burnerof the burner

• In-flame measurements H2S/SO2, staged/unstaged

• SO2 measurements outlet rediative section T=1150°C

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• SO2/SO3 measurements outlet of convective section T= 350°C

SO2 and H2S formation concentrations in an Air and Oxyfuel environment

6000

24

30SO2 H2S SO2+H2S O2

6000

24

30SO2 H2S SO2+H2S O2

SO2+H2S]max

SO2+H2S]-mass balance

0

2000

4000

0 0.5 1 1.5 2 2.5

SO

2 , H

2 S [p

pm]

0

6

12

18

O2

[vol

%]

SO2+H2S]max

0

2000

4000

0 0 5 1 1 5 2 2 5

SO

2 , H

2 S [p

pm]

0

6

12

18

24

O2 [

vol%

]

30

Distance from Burner [m]0 0.5 1 1.5 2 2.5

Distance from Burner [m]

Air- Blown Combustion, λ1=0.75

OF27 Combustion, λ1=0.75

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Measuring SO3 - Methods

• Controlled condensation method (CCM): discontinuous sampling; selective

condensation of H2SO4 in a tempered (85-95°C) glass coil

in out

H2SO4 condenser

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• Continuous SO3 monitor working on a wet-chemical principle1: The analyser should be further tested under oxy-fuel conditions (tested by EOn in the UK2)

1 Jackson, P. J.; Hilton, D. A.; Buddery, J. H. Continuous measurement of sulphuric acid vapour in combustion gases using a portable automatic monitor. J. Inst. Energy 1981, 54, 124–135. 2 Couling, D. Impact of Oxyfuel Operation on Emissions and Ash Properties based on E.ON’s 1MW CTF. Presented at the IEAGHG Special Workshop on Oxyfuel Combustion, London, January 2526, 2011.

Correlation of SO3-Moisture and Acid dew point

• Considerable increase of acid dewpoint due to high SO3 and H2O concentrations• Increase by 20-40°C will influence operation of low temperature units

)

air

wpo

int

tem

pera

ture

(°C

)

32(Scheffknecht et al 2009)

Moisture content of flue gas (%Vol)

Acid

dew

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Correlation of SO3-Moisture and Acid dew point

Similar increase of SO3 concentration at a SCR catalyst, but much less effect on dew point temperature under oxy-fuel conditions.

)w

poin

ttem

pera

ture

(°C

)

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SO3 content (mg/Nm3)

Acid

dew

(Spörl et al 2011)

Measuring SO3

• Measuring SO3 is difficult, due to high reactivity

• SO3/H2SO4 can be absorbed by3 2 4 y

• filter materials

• fly ash on sample filter

• Carefull choice of construction materials for sampling system

• Sampling system must be carefully heated above sulfuric

acid dewpoint

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Test Results and ExperiencesTest Results and Experiences

• NO formation and reduction• S behaviour• Corrosion, slagging and

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fouling• Modelling

Corrosion under oxy-fuel

• Corrosion risk• Tests at IFK• Results

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Identification of corrosion risk

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Source: Takashi Kiga, Experimental study Results on corrosion issues in oxy-fuel combustion process, Special Workshop on Oxyfuel Combustion, Addressing SO2/SO3/Hg and Corrosion Issues, London, Jan. 25th – 26th, 2011

Tests at IFK

CO2

GC lAir

CO2

GC lAir

short-term testsup to 100 h

long-term tests

StoragetanksFD/ RG fan

O2

Stack

AirO2 CO2

Gasdistribution

Coal feeding

Burnerwindbox

By-passes

StoragetanksFD/ RG fan

O2

Stack

AirO2 CO2

Gasdistribution

Coal feeding

Burnerwindbox

By-passes

Bottomash

ID fanESPSCRAPHBottom

ash

ID fanESPSCRAPH

Real fly ashGas composition: SO2,

CO2, H2O, O2, NOx

source: Stein-Brzozowska et al, [GSB6]

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Lignite fly ash deposit, end of radiative zone

air oxy-fuel

conc

entra

tion

S S

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In both cases Fe-rich molten phasesMore S in oxyfuel and bigger fraction of smaller particles noticedEnrichment at the particles surface

SEM-MAP – Ca + S + O / Ca + C + O

Ca+S+O Ca+C+O

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- Close relation between sulfates and carbon on the particle surface- Carbon content increased by exposure time

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Alloy N1 after 350h at 750°C

0C_7

50h_

3

case

BSE MAE and O S

conc

entra

tion

N1-

A_3

550

C_7

50h_

1

air-c

y-fu

el

BSE MAE and O S

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N1-

O_3

5

oxy

• higher growth of oxide-scale under oxy-fuel conditions;• internal oxidation was noticed already in the pre-exposed state;• no sulphur-front recognized

Results of the 500kW facility- SO3 and Deposits

• Clear tendencies that under Oxyfuel conditions the SO3concentration are higher

• Impact of Oxyfuel conditions on SO2/SO3 conversion rateneeds further clarification

• Verification of data according to pilot scale measurements (30MW plant Schwarze Pumpe)

• Indications that beside sulfatization carbonization on the particle

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• Indications that beside sulfatization carbonization on the particle surface of deposits occurs under Oxyfuel conditions

• Carbonatisation of sulfates can enhance the release of SulphurComponents which promotes sulphur corrosion mechanism

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Test Results and ExperiencesTest Results and Experiences

• NO formation and reduction• S behaviour• Corrosion, slagging and

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fouling• Modelling

Numerical Modeling and Simulation, combined Simulation (Furnace and Steam Side)

Program Code AIOLOS

Burner level 3

Burnout air

PulverizedCoal

Combustion

HomogeneReaktionen

Radiation

TurbulenceTwo Phase

Flow

Homo-geneous

Reactions

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Burner level 1

Burner level 2ChemicalReactions

HeatTransfer

HeterogeneReaktionen

OpticalProperties

Hetero-geneous

Reactions

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Detailed Coupled Simulation

Measurement data 3D geometry Heat3D geometry

AIOLOS DYNAMIK

Measurement dataProcess data

Tubewall

Heat fluxesTemperatures

3D geometry Heat exchanger

Water/SteamProcess

Simulation

Iterations

g yboiler

Furnace Simulation

Iterations

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Results forthe whole system

with high spatial resolution

Temperaturepressure

material stressTemperature velocity

concentrations

Current Model Developments for Oxy-Fuel

• Model developments for Oxy-fuel combustion• Development of mathematical models for heterogeneous char

conversion under Oxy-Fuel conditions including enhanced gasificationconversion under Oxy Fuel conditions, including enhanced gasification reactions

• Mathematical models for turbulent gas phase reactions:

• gas phase combustion, NOx formation and destruction

• Development of mathematical models for radiative heat transfer in CO2-enriched atmospheres

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• Validation of new modelling approaches with experimental results

• Combined coupled approach to furnace and steam generation simulation

• Simulation and optimization of oxyfuel-combustion (0.5MWth, 30MWth,….

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Extended chemical reaction models

» Gas phase reactions:

(1) CnHm + n/2 O2 → n CO + m/2 H2n m 2 2

(2) CnHm + n H2O → n CO + (m/2 +n) H2

(3) H2 + ½ O2 ↔ H2O(4) CO + H2O ↔ CO2 + H2

» implementation of additional reactions and considering equilibrium reactions enables accounting for chemical effects of specifically high O2and CO levels in the oxidizing atmosphere during oxy fuel combustionand CO2 levels in the oxidizing atmosphere during oxy-fuel combustion

» including reverse reaction of (3) is particularly required for correct prediction of local flame temperatures since equilibrium is shifted towards educts in high temperature flames

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Extended chemical reaction models

» Char burnout reactions:

(1) C + ½ O2 → CO (char oxidation)2

(2) C + CO2 → 2 CO (Boudouard reaction)(3) C + H2O → CO + H2 (water-gas-shift reaction)

» gasification reactions (2) and (3) may have major impact in O2-lean regions due to higher partial pressures of CO2 and H2O compared to conventional air-firing

» at ambient pressure and typical combustion temperatures the reactions (2) and (3) may be considered irreversible since the equilibrium is shifted towards the product side

48

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Simulation results / Validation

» Test case: 500 kWth reactor, Lausitz lignite, O2 direct injection @ burner, total [O2] = 21%

Axial plots showing:Axial plots showing:

• very good agreement after ~ 0.5 m

• improved CO prediction

• deviations at near burner region

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regiondelayed ignition late O2 consumption

• overall good accuracy

Ongoing/Future R&D Topics at IFK

• Experimental Oxy-fuel combustion topics: • Rank of coal (bituminous, lignite, hard coals…)• Slagging, Fouling, (impact of higher SO2, H2S, CO2, HCl etc.)Slagging, Fouling, (impact of higher SO2, H2S, CO2, HCl etc.)• Corrosion high-low temperature (Deposits, HCl, SO2, SO3, H2O…)• Fly ash quality and utilisation (EN 450 …)• Component development and test (burner, …)• Emissions (Hg, fine dust, etc)• Flue gas cleaning (SCR, Additives…)• Particle removal and impact to particle removal systems ( ESP and Bag

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• Particle removal and impact to particle removal systems ( ESP and Bag-filter performance)

• Biomass (co-)combustion• Oxy-fuel: CFB • Improvement and validation of CFD models

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Biomass (co)-firing under oxy-fuel Bio-CCS

In order to keep• Global temperature rise• Safe CO2 levels Below 450 ppm

Below 2°C

2

Given • Growing population• Increasing energy demand• Energy mix

Atmosphericcarbon

51

measures beyond CCSneed to be considered

Organiccarbon

Geological Storage

Bio-CCS

Bio-CCS (or BECCS)

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(Koornneef, ECOFYS, 2010 in Dixon et al, IEA, 2012)

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Bio-CCS technologies

• Biochemical production of biofuels• Biomethane• Bioethanol

• Thermochemical production of biofuels• Hydrogen• SNG• BtL

• Biomass combustion for electricity and/or heat production• Biomass co-firing (direct/indirect)g ( / )• 100% Biomass combustion (CHP plants and CFB boilers)• Biomethane/Bio-SNG• Biomass-based IGCC (BIGCC)

• Industrial applications (Fuel substitution, pulp and paper, etc.)

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(EBTP/ZEP, 2012)

Vattenfall Oxy-fuel Pilot Plant

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Road Map Vattenfall

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Source: Vattenfall IEA Cottbus 2009