Oxyfuel power plant design - Retrofit options for different fuels

Christian Steinmetz, Christian Bergins, Patrick Weckes, Klaus-Dieter Tigges

14th of September, 2011

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Aim of investigation

Retrofit of oxyfuel technology to existing coal fired power stations

Bituminous coal and raw lignite P.S.

Focus on the entire power plant

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The oxyfuel retrofit requires space

Air Separation Unit (in the vicinity of the power plant)

CO2-Processing-Unit

Flue gas recirculation system to adjust the furnace temperature

Auxiliaries, e. g. flue gas cooling

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Customers view

Customers require

Minimum changes on the existing plant

Coal range to remain unchanged

Minimum life cycle costs

operation

maintenance

investment

CO2-storage

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+107.200 m

+100.700 m

+ 7.700 m

+ 1.1375 m

820 MWel / 2106 t/h

Benson® Steam generator

Bituminous coal

Design parameter:

SH: 600 ºC / 280 bar a

RH: 620 ºC / 52 bar a

Bituminous coal - investigated steam generator

sealing air

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Bituminous coal – air operation

steam generator

Forced - draught fan

Primary

DeNOx catalyst

FGD

exhaust gas

preheater flue gas

ID fan

air preheater

over fire air

FD fan

primary air cooler

fuel

burner system

PA fan

mills

air

air

ESP

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Application of the oxyfuel process

How to achieve minimum changes?

Keep

heat transfer in furnace and convective path

furnace exit temperature

flame shape and length

momentum of burner flows

volumetric gas flow after mills

similar to air combustion.

How?

recirculate dry and clean flue gas (extraction after FGC)

a flow of about 75 % ensures the target

Result: No changes on existing components in the boiler house

sealing air

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Oxyfuel process – required measures

steam generator

Forced - draught fan

Primary

DeNOx catalyst

FGD O2

exhaust gas

preheater flue gas

CO2

ID fan

air preheater

over fire air

FD fan

primary air cooler

fuel

burner system

CO2

PA fan

mills

(retrofit components in red)

FGC

CO2- compression

ASU

ambient air

O2-preheater

CO2

vent gas

HP feed water preheater

steam preheater

flue gas bypass

air

air

ESP

Hot gas recirculation

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Flue Gas Temperature

Comparison air combustion / oxyfuel combustion

Water/Steam Temperature

SH 600 C

459 C 325 C

294 C

1306 C

381 C

SH1

SH2

RH2

RH1

SH3

Eco

SH 600 C

444 C 326 C

294 C

RH 620 C

385 C

Air Oxyfuel Air Oxyfuel

RH 620 C

1300 C

CO2-concentration downstream FGC

component

N2

O2

Ar

CO2

concentration [vol.-% dry]

95 vol.-% O2

11.3

4.3

80.2

3.9

99.5 vol.-% O2

10.7

4.4

84.1

0.3

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The reachable CO2-concentration downstream FGC depends on

oxygen excess for combustion

purity of applied oxygen

composition of the used coal

amount of air ingress

Example: • = 1.15

65

70

75

80

85

90

95

0 1 2 3 4 5

air ingress [%]

CO

2 co

nte

nt

aft

er F

GC

[v

ol.-

% d

ry]

O2-purity: 95 vol.-%

O2-purity: 99.5 vol.-%

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Retrofit for bituminous coal - conclusion

Oxyfuel retrofit can easily be done

No major changes on the existing boiler

Slight changes in the overall process

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500 MWel / 1330 t/h

Benson® Steam generator

Raw lignite

Design parameter:

SH: 603 ºC / 293 bar a

RH: 609 ºC / 51 bar a

Raw Lignite - Investigated steam generator

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Oxyfuel retrofit for raw lignite

Water content of used raw lignite is 48 wt.-%

Air mode: flue gas water content of 26.3 vol.-%

avoid further accumulation of water in oxyfuel mode

Recirculation downstream

ESP FGD FGC

40.2 68.1 31.4

H2O content at boiler outlet [vol.-%]

Recirculation after FGC

is mandatory

CO2-Storage

oxygen boiler

CO2-Processing-Unit SOX H2O

vent gas

gas-preheater

ESP FGD FGC raw lignite

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O2

Oxyfuel Operation – Raw Lignite

Forced - draught fan

FGC

CO2

vent gas

CPU

ASU

ambient air

draught

ESP

FGD

exhaust gas

steam generator

ID fan Forced -

draught fan

air preheater

FD fan

burner

flue gas preheater

air ingress

raw lignite

O2-preheater

HP feed water preheater

steam preheater

flue gas bypass

(retrofit components in red)

Hot gas recirculation

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Firing system for raw lignite

Coal is dried with hot flue gas from the end of the furnace

Various points of air ingress

between furnace and hot gas off take

at burners

at coal feeder

at coal mill itself

Typical amount of air ingress is 10 % of total combustion air

hot gas off take

suction shaft

burner

coal mill

air ingress

air ingress

air ingress

air ingress

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O2-purity: 95 vol.-%, • = 1.15

CO2-concentration after FGC depending on leak air ingress

N2 30.4

O2 3.1

CO2

Ar

65.1

1.4

O2-purity: 95 vol.-%, • = 1.15

concentration [vol.-% dry] component

N2 6.2

O2 3.4

CO2

Ar

88.6

1.8

concentration [vol.-% dry] component

10 % air ingress

0 % air ingress

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Retrofit for raw lignite - Conclusion

With a well sealed system the retrofit requires

no major changes on the existing boiler

slight changes on the overall process

The success of an oxyfuel retrofit for raw lignite depends on the amount of air ingress.

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Hitachi Power Europe GmbH 19

CPU, ASU, O2 preheater and respective ducts

flue gas cooler

cooling system

O2 / flue gas mixing

flue gas recirculation duct and connection to existing duct work

hot gas recirculation at GGH

fan modification

bypass heat exchanger for GGH

heat transfer system to feed water preheating

CO2 seal gas for mills to replace air

pure oxygen to FGD to replace air

CO2 for NH3 atomizing upstream of catalyst

I & C adaptation

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Retrofit of a hard coal unit – New components and modifications

Retrofit of a hard coal unit – Unchanged components

• boiler pressure part

• coal handling system (except seal gas)

• burners and p.f. lines

• duct work (except junction to flue gas recirculation and O2 supply)

• turbine and steam extraction lines

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Example: 820 MWel

CO2 Compression app. 2,000m²

Air Separation Unit

app. 26,000 m²

4 trains

Compressor Unit 1-4

ESP

Flue Gas Recycle

Heat Exchanger

FG Drier

FGD

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