OXYCOAL-AC

1

Numerical Simulation of a 1200 MWth

Pulverised Fuel Oxy-firing Furnace

Jens Erfurth

Dobrin Toporov, Malte Förster, Reinhold Kneer

Institute of Heat

and Mass

Transfer

RWTH Aachen University

CCT2009, Dresden, 18-21 May 2009

OXYCOAL-AC

2

0,6

0,7

0,8

0,9

1

1,1

1,2

19 21 23 25 27 29 31 33O2, %

Q/Q

_AIR AIR

OXY21wetOXY21dryOXY27wetOXY30dry

Overview

23.8

% 28.6

%

ConclusionsResults

ModellingMotivation

0 1000 2000 3000 4000 5000 6000 7000 80000

0.5

1a) Transmissivities of Bands m

Wavenumber ν [1/cm]

0 1000 2000 3000 4000 5000 6000 7000 80000

0.5

1b) Total Absorptivities

Wavenumber ν [1/cm]

0 1000 2000 3000 4000 5000 6000 7000 80000

0.5

1c) Normalised Planck Distribution

Wavenumber ν [1/cm]

I ν/I ν

,max

Tgas = 1810 KT = 1000 K

CO2

H2OCO

OXYCOAL-AC

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Motivation: the

Case

for

CCS Retrofit

■

300 GW of capacity will have to be installed in the EU-25 until 2020.

■

Coal plants built before CCS is available (ca. 2020) pose risk of „carbon lock-in“.

■

Plants built between now and then could be retrofitted for CCS

Sources: VGB Powertech, EU Energy and Transport Outlook

OXYCOAL-AC

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Oxyfuel Retrofit

Can a boiler originally designed for air operation be operated in oxy-firing at the same thermal load?

■

Criteria:•

Burnout

•

Heat transfer

•

Furnace exit temperature

•

Corrosion in the furnace

■

Parameters available to meet these requirements:•

Oxygen concentration

•

Water content of oxidiser (wet or dry recycling)

•

…

OXYCOAL-AC

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Previous Experimental Work in Aachen■

Oxycoal test facility with 120 kWth

■

Oxycoal

swirl burners

•

Able to operate within wide range of oxygen O2

content and in air

•

Measures for oxycoal swirl flame stabilisation derived

•

Design of industrial burners based on these measures

Experiments CFD Simulations

OXYCOAL-AC

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■

Heterogeneous and homogeneous reactions are modelled as User Defined Functions (UDFs)

■

Changes in the CFD model for oxy-firing:•

Modelling of heterogeneous reactions:

Cs

+ 0.5 O2

→ CO

Oxidation, exothermal

Cs

+ CO2

→ 2 CO

BoudouardGasification, endothermal

Cs

+ H2

O → CO + H2

Water Gas Reaction

•

Adjustment of radiation model

CFD Models

OXYCOAL-AC

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Exponential Wide

Band Model (EWBM)*

EWBM

COp2H Op

2COpL tp0,mλBand locations T

mτ mλΔ

lk for

10 spectral

regions

l

Algorithm

11 single

Bands m (CO2

, H2

O, CO)

*Edwards D. K., Advances in Heat Transfer, vol.12, 1976

OXYCOAL-AC

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Results

of EWBM

Example:

L = 0.1 m

T = 1800 K

Spectral

absorptivities of flue

gas

0 1000 2000 3000 4000 5000 6000 7000 80000

0.5

1

Wavenumber [1/cm]

0 1000 2000 3000 4000 5000 6000 7000 80000

0.5

1

Wavenumber [1/cm]

Air combustion:

Oxyfuel combustion, wet

recycling:

α

α

OXYCOAL-AC

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Furnace designed for Air firing■

Thermal power: 1210 MW (RPP NRW)

■

18 burners → 70 MW each (λ

= 0.95)

•

Burner geometry designed based on criteria developed by the authors*

■

12 OFA nozzles (λtot

= 1.15)

■

Fired by South African hard coal

■

5 Cases:

•

AIR

•

Same oxygen: OXY21dry, OXY21wet

•

Same temperature:

OXY30dry,

OXY27wet

* Toporov et al, CCT 2007

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Temperature

Fields, dry

Recycling

T [K]

2300

300AIR OXY21dry OXY30dry

OXYCOAL-AC

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Temperature

Fields, wet

Recycling

T [K]

2300

300AIR OXY21wet OXY27wet

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CO Source

from

Particle

Oxidation, dry

Recycling

log SCO[kg/m3s]

3

1e-4AIR OXY21dry OXY30dry

Cs

+ 0.5 O2

→ CO

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CO Source

from

Particle

Oxidation, wet

Recycling

AIR OXY21wet OXY27wet

Cs

+ 0.5 O2

→ CO

log SCO[kg/m3s]

3

1e-4

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CO Source

from

Particle

Gasification, dry

Recycling

AIR OXY21dry OXY30dry

Cs

+ CO2

→ 2 CO

and Cs

+ H2

O → CO + H2

log SCO[kg/m3s]

0.5

1e-4

OXYCOAL-AC

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CO Source

from

Particle

Gasification, wet

Recycling

AIR OXY21wet OXY27wet

log SCO[kg/m3s]

0.5

1e-4

Cs

+ CO2

→ 2 CO

and Cs

+ H2

O → CO + H2

OXYCOAL-AC

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Surface

Incident

Radiation, dry

Recycling

Q´´[kW/m2]

500

0AIR OXY21dry OXY30dry

Locally

increased

wall temperature

OXYCOAL-AC

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Surface

Incident

Radiation, wet

Recycling

500

0AIR OXY21wet OXY27wet

Q´´[kW/m2]

OXYCOAL-AC

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Comparison: radiative

Heat

Transfer in Furnace

0,6

0,7

0,8

0,9

1

1,1

1,2

19 21 23 25 27 29 31 33O2, %

Q/Q

_AIR AIR

OXY21wetOXY21dryOXY27wetOXY30dry

1.2

1.1

0.9

0.8

0.7

0.628.6 %23.8 %

integrated

over

furnace

walls

OXYCOAL-AC

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0,85

0,9

0,95

1

1,05

0,9 0,95 1 1,05 1,1 1,15 1,2 1,25

H/H_AIR,exit

T/T_

AIR

,exi

tAIROXY21wetOXY21dryOXY27wetOXY30dry

1.0

5

0.9

5

0.

9

0.8

5

Comparison: Temperature* and Enthalpy

Flow

* averaged

at furnace

exit

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Heat

Transfer in the

convective

Section

■

Theoretical

considerations:

TubeAsh

Layer

Incident

Radiation

Emitted

Radiation

Tsurface

Tsteam Tsurface

Tgas

EWBM (Gas Radiation

only)

h

d

Leff

, αsurface

, εgas

εash

htotal

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Heat

Transfer: Differences

Air -

Oxy-firing

■

Energy balance

at pipe

surface:

800steamT K=

30 , 30

,

( )( )

OXY dry surface OXY dry steam

surface AIR steamAIR

Q T TT TQ

⋅

⋅

−Δ = =

−

261AIRWh

m K=

For OXY30dry

Leff

= 0.1 m Leff

= 1 m

Tgas

= 1000 K Δ

= 1.25 Δ

= 1.21

Tgas

= 1600 K Δ

= 1.25 Δ

= 1.23

30 266OXY dryWh

m K=

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Conclusions

■

CFD simulations

of a state

of the

art furnace

in air

and oxy-firing

of coal

were

conducted

using

a non-grey

implementation

of the

EWBM

■

Surface

incident

radiation

increases

relative to air…

•

…by

6 % for

dry

recycling

•

…by

14 % for

wet

recycling

■

In oxy-firing

gasification

gains

importance

•

Reason: abundance

of CO2

and water

vapour

OXYCOAL-AC

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Conclusions: Retrofit

Criteria:

■

Burnout

can

be

achieved

■

Furnace

exit

temperature

below

ash

melting

point

■

Overall heat

transfer:

•

Similar

in furnace

for

OXY30dry

•

In convective

section: increase

by

20-25 % for

OXY30dry, but

particles

will dampen

this

effect.

■

Wall temperatures: care

must

be

taken

to ensure

corrosion

does

not

unduly

increase

?

?

••

•

?

OXYCOAL-AC

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Acknowledgements

This work was conducted in the framework of the project OXYCOAL-AC and was funded by:

German Federal Ministry of Economics and

Technology

Ministry for Innovation, Science, Research and Technology of the State

of North Rhine-Westphalia

RWE Power

WS Wärmeprozesstechnik

Linde

MAN Turbo Hitachi Power Europe

E.ON Energie

OXYCOAL-AC

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Thank

you

for

your

attention

OXYCOAL-AC

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OXYCOAL-AC

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CFD Radiation

Modelling

in Coal Combustion

■

Radiation

Transport Equation

for

a given

wavelength

λ:

4

,4

''' 1( ) ( ) ( )4

PP s P i P

qdI Tk I k I I I dds π

σ σπ π π

⋅⎡ ⎤

= − + − − − Ω Φ Ω Ω⎢ ⎥⎣ ⎦

∫

Gas emission

and absorption

Particle

emission

and absorption

Particle

outscattering

and inscattering(Gas scattering

is

neglected)

OXYCOAL-AC

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CFD Radiation

Modelling

in Coal Combustion

■

Radiation

Transport Equation

for

a given

wavelength:

■

Particle

emission

in a given

control

volume:

■

Particle

absorption

in a given

control

volume

:

■

Particle

Scattering: (homogeneous, isotropic)

4

,4

''' 1( ) ( ) ( )4

PP s P i P

qdI Tk I k I I I dds π

σ σπ π π

⋅⎡ ⎤

= − + − − − Ω Φ Ω Ω⎢ ⎥⎣ ⎦

∫

, 4, ,

1'''

NP n

P P n P nn

Aq T

Vε σ

⋅

=

=∑

,,

1

NP n

P P nn

Ak

Vε

=

=∑

, 0,6s Pσ = ( ) 1PΦ Ω =

(Sum

over

particles)

(Sum

over

particles)

OXYCOAL-AC

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CFD Radiation

Modelling

in Coal Combustion

■

Radiation

Transport Equation

for

a given

wavelength:

■

Particle

emission:

■

Particle

absorption:

■

Particle

Scattering: (homogeneous, isotropic)

4

,4

''' 1( ) ( ) ( )4

PP s P i P

qdI Tk I k I I I dds π

σ σπ π π

⋅⎡ ⎤

= − + − − − Ω Φ Ω Ω⎢ ⎥⎣ ⎦

∫

, 4, ,

1'''

NP n

P P n P nn

Aq T

Vε σ

⋅

=

=∑

,,

1

NP n

P P nn

Ak

Vε

=

=∑

2 2( , , , , , ) ?CO H O CO tk k T p p p pλ= =

Absorption coefficient

k:

, 0,6s Pσ = ( ) 1PΦ Ω =

OXYCOAL-AC

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OXYCOAL-AC

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CO Source

from

Particle

Oxidation, dry Recycling

SCO[kg/m3s]

≥

0.05

0AIR OXY21dry OXY30dry

Cs

+ 0.5 O2

→ CO

Same thermal load

OXYCOAL-AC

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CO Source

from

Particle

Oxidation, wet Recycling

AIR OXY21wet OXY27wet

≥

0.05

0

Cs

+ 0.5 O2

→ CO

Same thermal load

SCO[kg/m3s]

OXYCOAL-AC

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CO Source

from

Particle

Gasification, dry

Recycling

≥

0.05

0AIR OXY21dry OXY30dry

Cs

+ CO2

→ 2 CO

and Cs

+ H2

O → CO + H2

Same thermal load

SCO[kg/m3s]

OXYCOAL-AC

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CO Source

from

Particle

Gasification, wet

Recycling

AIR OXY21wet OXY27wet

≥

0.05

0

Same thermal load

Cs

+ CO2

→ 2 CO

and Cs

+ H2

O → CO + H2

SCO[kg/m3s]

OXYCOAL-AC

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0,6

0,7

0,8

0,9

1

1,1

1,2

19 21 23 25 27 29 31 33O2, %

Q/Q

_AIR AIR

OXY21wetOXY21dryOXY27wetOXY30dryOXY238wetOXY286dry

Comparison: radiative

Heat

Transfer in Furnace

1.2

1.1

0.9

0.8

0.7

0.6