power - iea greenhouse gas r&d programme 1_b/paper-oxy sa.pdf · flue gas condenser for...

Flue Gas Condensers for Oxyfuel

Stefan Åhman*, Wuyin Wang, Jörgen Grubbström09/09/200909/09/2009

POWERPOWER

Flue Gas Condenser forOxyfiring

Flue gas desulfurization

NOx controlCO2 compressor

Air sepa-ration unit

Particulate t l

Flue gas CO2Air

Boiler controlg

condenser

Flue gas recirculation

A Flue Gas Condenser (FGC) plays an important role for drying & cooling of the flue gas prior to compression

Flue Gas Condensers previously used for recovery of low grade heat from flue gases when

Presentation title - 01/01/2007 - P 2

of low grade heat from flue gases when combusting waste, biofuel etc.

Latent & Sensible Heats when cooling flue gas


Tube condenserVertical, straight-tube HEX – one pass tube sidepass tube side

Tube Condensor Gas inTube Condensor− Gas passing

downwardsCooling

Gas in

CW Out

− Cooling water passing in multi stage multi-stage cross flow upwardsEssentially a CW In− Essentially a counter current device

Gas out

CW In


device− Tubes/Tube

sheet: Alloy Steel

Tube CondenserExample of Current Applications

Flue Gas Condenser at Flue Gas Condenser at an Incineration Plant

Heat delivered to the district heating net

Flue gas flows up to ~ 250,000 Nm3/h, /

Total plant efficiency = (El Power + Heat Power)/ Fuel Power may exceed Fuel Power may exceed 100 %, if based on Lower Heating Value (LHV) of fuel

Presentation title - 01/01/2007 - P 5Istalled at Waste- and Biofuelled plants

Condensing Scrubber

Condensing scrubberCondensing scrubber− Counter

current packed Gas out

tower− Gas passing

upwards Condensa

− Tower of FRP− Packing PP CW In

Gas in

− External HEX of Alloy Steel CW Out


Condensing ScrubberExamples of Current Applications

Flue gas Flue gas desulphurization by partial utilization of the alkalinity in of the alkalinity in sea water

As flue gas passes absorber absorber, condensation of water occurs parallell to the SO2 absorptionabsorption

Flue gas flow per absorber up to


3,500,000 Nm3/h

Cooling of Mixed Vapours with Noncondensing Gases

Similar calculation procedure for both types of condensercondenser

Heat transfer driven by

Sensible heat: ξAckhg0(Tg – Tc)ξAck g ( g c)

temperature difference

Latent heat ξStkg0λ(pv – pc) diffusion by

partial pressure differencedifference

Total heat (gas): ξ h 0 (T – T ) + ξ k 0λ(p – p )Total heat (gas): ξAckhg0 (Tg – Tc) + ξStkg

0λ(pv – pc)

Total heat (water): hi0 (Tc – tw) = U (Tg – tw) – Tube condenser


hl (Tc – TL) = U (Tg – TL) – Packed column

U is an over all heat transfer

Calculation procedureBasics

Mass transfer coefficients

k f(Re Sc packing & wetting properties)kl = f(Re, Sc, packing & wetting properties)

kg = f(Re, Sc, packing & wetting properties)Many correlations exist e g Onda Billet/Schultes etcMany correlations exist, e. g. Onda, Billet/Schultes, etc.

Packing constants matched to fit experimental data

By analogy between mass and heat transfer heat transfer coefficients are obtained:

h = k ( c K /D )hl = kl (ρl cp,l Kl/Dl)

hg = kg (ρg cp,g )2/3 (Kg/Dg)2/3

Total heat balance


Total heat balance

hg (Tg – Tc) + kg λ(pv – pc) = hl (Tc – TL)

Calculation Procedure – Packed ColumnFlow sheetFlow sheet

Input Input Tg,in; Tg,out; TL,in; L; G; Z=0

Calculate TL,out; Tg=Tg in

Tg,out TL,in

If ( Tg out -Tg ) < eYes

No

Z; TLdz

Calculate hl , hg , kg at Nth step

using appropriate correlations

Update Tg, TL

Tg,in TL,out

Calculate wet gas enthalpy change in

Solve heat balance for Tc

Choose appropriate dz

Z = Z + dz


enthalpy change in the Nth section, dH

appropriate dz

Calculation Procedure – Packed Column (Counter Current)Typical OutputTypical Output

90

100

70

80

rcen

t Gas temp

Gas saturation temp

Li id

50

60

e, d

eg C

; Per Liquid temp

% of total heat recovered

Gas water content, %

30

40

Tem

pera

ture

10

20

T


0

Column height

Calculation Procedure – Tube Condenser (Co Current) Typical OutputOutput

90

100

70

80

otal

pow

er t gas

t condensate

t watert gas

50

60

g C

; Par

t of t

osf

erre

d, %

% of total heat removed

30

40

pera

ture

, deg

tran

s

t condensate

10

20

Tem

p

Percent of total heat transferred per m

t cooling water


0

Condenser length, m

Cooling of Mixed Vapours with Noncondensing Gases

O a a a s560

Over all heat transfer coefficient U varies

primarily with350

420

490

560

cien

t, W

/m2,

deg

C

• Water content of gas• Temperature

Flows 70

140

210

280

Ove

r all

heat

tran

sfer

coe

ffic

• Flows

U varies in every point in the condenser Over all heat

0

70

0,00 2,00 4,00 6,00 8,00 10,00 12,00 14,00 16,00 18,00 20,00

Water content of gas, % vol

the condenser

Rigorous calculation procedure required to

transfer coefficientas function of water

content of gas Evaluation of full


procedure required to take into account very

varying gas conditions, due to phase change

Evaluation of full scale data

Tube condenser vs. Packed column

Packed column Tube condenserPacked column

Two pinch points

Tower: dT outlet gas

Tube condenser

One pinch point

HEX: dT cooling water / Tower: dT outlet gas / inlet

recirculating water

HEX: dT cooling water / condensate

HEX: dT cooling water / recirculating waterA detailed analysis show slightly less costs for

the tube condenser. However, cost is much influenced by actual prices for alloy steel, so analysis should be revisited for every project


Lab pilotPacked ColumnPurpose

Simulation of Oxyfuel conditions by addition of conditions by addition of CO2

Vary gas flow, composition, temperaturestemperatures

Secondary effects; SO2/SO3 removal etc.


Lab pilotPacked Column

Packed column - Water removal

100,00

80,00

90,00

Water removal as a

50 00

60,00

70,00

l effi

cien

cy, %

Increasing L/G

Water removal as a function of packing height

with L/G as parameter

30,00

40,00

50,00

Wat

er re

mov

al Increasing L/G

10,00

20,00


0,00

Column height

Lab pilotPacked Column

CO2 impact on water removal efficiency@ different L/G

Influence of CO2 content of gas 94

96

on water removal efficiency

90

92

l eff

icie

ncy

(%)

84

86

88

Wat

er re

mov

a

82

84

0 10 20 30 40 50 60 70

CO2 (%)


( )

Evaluation of dataModelling supplemented by evaluation of HTU valuesevaluation of HTU values

For heat transfer the NTU (number of transfer units) can be expressed as1units) can be expressed as

NTU =

Including correction for Stefan flow this

1

2)/( HHdH i Enthalpy used as driving force

Including correction for Stefan flow this expression transforms into ))/ln(/()()/(

1

2 giggigi ppPppHHdH

This is used for evaluation of experimantal data.

The height of a transfer unit is then

HTU = Z / NTU, where Z is the height of the columnCondensing scrubber, NOG

0,0300

0,0400

0,0500

0,0600

0,0700

0,0800

0,0900

1/(i-

i*) 1/(i-i*)Low limitHi limit NTU

Condensing scrubber

200,0

300,0

400,0

500,0

600,0

700,0

800,0

Enht

alpy

, kJ/

kg d

ry g

as

Sat curveOp line


0,0000

0,0100

0,0200

0,0 100,0 200,0 300,0 400,0 500,0 600,0 700,0 800,0

Enthalphy, kJ/kg dry gas

0,0

100,0

0,0 10,0 20,0 30,0 40,0 50,0 60,0 70,0 80,0

Temperature, deg C

Scale up

1,75Comparision of

1,40

Comparision of data from lab-and field pilot (~5 MW)

0,70

1,05

HTU

Lab Pilot

3 MW Pilot

Lab scale data correlates well with field pilot

0 00

0,35

and full scale data

As expected, only 0,000,00 3,00 6,00 9,00 12,00 15,00

Liquid to Gas RatioAs expected, only minor impact of Oxyfuel conditions on heat transfer


heat transfer

SO2 Removal

NaOH may be added for

control of SO2 emission &

corrosion protection

SO2 absorption is much

enhanced at high pH, but

CO2 absorption is alsoCO2 absorption is also

increasing …


SO2 Absorption/Neutralisation

4

4,5100,000 Nm3 dry gas/h0,4 l/Nm3 condensate50 deg C

3

3,5

tion,

kg/

h

Increase of CO2 content from 10 % to 40 % increases dissolved CO2 in the condensate

2

2,5

or C

O2

neu

tral

iza

10 % CO240 % CO2

40 % CO2NaOH consumption for neutralization will increase

1

1,5

NaO

H a

dded

fo

10 % CO2

0

0,5

4 00 4 20 4 40 4 60 4 80 5 00 5 20 5 40 5 60 5 80 6 00


4,00 4,20 4,40 4,60 4,80 5,00 5,20 5,40 5,60 5,80 6,00

pH

Condenser - Issues for Oxyfuel

Heat transferHeat transferTarget is moisture removal and cooling, rather than heat recovery

Oxyfuel conditions can be readily adjusted for

Mass transfer - SO2/SO3/HCl/HF/ash/aerosols2/ 3/ / / /- Alkali consumption will influence

range of application for SO2

removalremoval- Influence on mass transfer of other

species will be minor,


if any- SO2/SO3 removal tests in progress

Conclusion

Alstom has experience from condensing Alstom has experience from condensing scrubbers and heat exchangers that is relevant for Oxyfiring conditions

The unusually high water content requires rigorous sizing procedures

Supplementary studies in lab- and medium scale pilots confirm sizing methods and tools

The high CO2 content will have some (limited) impact on alkali consumption for adjustment of condensate pH


for adjustment of condensate pH

Performance of flue gas condenser will impact downstream process steps

www.alstom.com

POWER

Condenser Issues for Oxyfuel

Other

Integration with boiler cycle

Cooling water temperature

Size for seasonal variations

Optimize investment- and operating costs for complete systemsystem

Cooling water quality

Condensate treatment / re- use Condensate treatment / re- use

Leakage

Minimize impact of in-leakage of


Minimize impact of in leakage of ambient air

power - iea greenhouse gas r&d programme 1_b/paper-oxy sa.pdf · flue gas condenser for...

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