capture by solvents; co challenges and...

1

Talloires, July, 2010

J, 2008 U

Hallvard F. SvendsenNorwegian University of Science and Technology (NTNU)

Trondheim, NORWAY

CO2 capture by solvents; challenges and possibilities

Post-Combustion CO2 Capture WorkshopTalloires, July 11-13, 2010

2


IntroductionPost combustion CO2 capture by reactive absorption

• Energy requirements• Heat• Electricity

• Equipment size• Degradation• Environmental issues

Outline

3


Pathways to CO2 capture andSeparation technologies

CO�separation

CO� compression & conditioning

N�/O�

CO�

ShiftH�

CO�

Powerplant

Air Air seperation

O�N�

Air/O�

Raw materials Product: Gas, Ammonia, Steel

CO�

N�/O� CO� compression & conditioning

Powerplant

Gasification

Reforming

CO�separation

H�

CO�

CO/H�

Air separation

Process +CO� Sep.

CO/H�

Coa

l, O

il, N

atur

al G

as, B

iom

ass

PowerplantPost-combustion

Pre-combustion

Oxy-combustion

Other industries

Mem

bran

ete

chno

logi

es

Abs

orpt

ion

Abs

orp

tion

Ads

orpt

ion

Ads

orp

tion

4


Challenges

• High requirements of thermal and electrical energy

• Costly process and large space requirements

• Production of waste products

• Possible emissions of volatile amines and degradation products

5


Energy considerations

Amine reclaimer

Electrical energy

Reclaimerbottoms

Heat

6


Energy requirements

PQW G ��

)/( 3 smQG

( )P kPa�

Electricity requiredPressure drop in absorber: ~ 6 MWelRecompression: ~ 12 MWelMiscellaneous: ~ 1 MWel

400 MW NG fired power stationExhaust gas rate:

2000000 m3/h flue gas3,5 % CO21000000 tons CO2/year

Heat required for CO2 capture:90-140 MWsteam ~ 22,5-35 MWel

7


Energy requirements

PQW G ��

)/( 3 smQG

( )P kPa�

Coal example:

Electricity requiredPressure drop in absorber: ~ 3.5 MWelRecompression: ~ 27 MWelMiscellaneous: ~ 2 MWel

400 MW pulverized coal firedpower stationExhaust gas rate:

1000000 m3/h flue gas12 % CO22200000 tons CO2/year

Heat required for CO2 capture:200-310 MWsteam ~ 50-77.5 MWel

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• High requirements of thermal and electrical energyHeat of reactionEquilibrium temperature sensitivityEquilibrium approcahCyclic capacityWater solubility

Costly process and large space requirementsRate of reaction/Mass transfer ratesCyclic capacityFoaming propertiesCorrosion

Production of waste productsChemical stability

Possible emissions of volatile productsEcotoxicityBiodegradabilityVolatility

How can solvents influence these factors

9


Total heat required, (J/mol CO2 captured)

= Qsens + Q des + Q strip

2 2Tot CO H O AmP P P P� � �

Conc. CO2

Reboiler

Overhead condenser

Lean/Rich heat exch.

Lean solvent

Desorber

Reflux

Qsens+Qdes+Qstrip

Tlean,H=120C

Trich,H ~95-115C

Heat requirement(1)

Trich,C ~ 50C

�T = Tlean,H - Trich,H

( )sensrich lean Ab

Cp TQ

C

��

��

CO2 loading, molCO2/mol absorbentAbsorbent concentration mol/l

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� �

2

2

2

,

*,

,

,H O rich H rich vap

strip H O

CO rich H rich

P TQ H

P T

�

��

2 2( )Tot CO H O AmP P P P� � �

Conc. CO2

Reboiler

Overhead condenser

Lean/Rich heat exch.

Lean solvent

Desorber

Reflux

Qsens+Qdes+Qstrip

2des absC OQ H� �

Heat requirement(2)

Reversion of the reaction:

Water reflux(stripping steam):

Trich,H ~95-115C

Tlean,H=120C

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• High rich loading– Amine class– Polyamines– Fast amines

• Low lean loading– Close to intersection between steam and heat limited

regimes

( )sensrich lean Ab

Cp TQ

C

��

��

Increase cyclic capacity:2 2, ,( )rich lean Ab CO rich CO leanCC C C C� ��

Reduce cross flow heat exchanger temperature approach: T�

1) Sensible heat loss:How reduce the heat requirement?

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2) Stripping steam requirement(1):

� �

2

2

2

,

*,

,

,H O rich H rich vap

strip H O

CO rich H rich

P TQ H

P T

�

��

1

10

100

1000

10000

100000

1000000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Loading [mol CO2/mol solvent]

pCO

2 [

atm

]

40 C120 C

10-5

10-2

101

10-4

100

10-1

10-3

120°C

40°C

Beneficial with closeapproach to equilibrium at the absorber bottom: highloading gives high CO2pressure in desorber, and lower Qstrip

Fast absorbent

PCO2,1

PCO2,2

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System ASystem BSystem ASystem B

Component A

C1 at 40oCC2 at 40oCC1 at 120oCC2 at 120oC

Effect of amine system and concentration2) Stripping steam requirement(2):

Left side: Two systems with different temperature sensitivityRight side: Also amine concentration may affect temperature sensitivity

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How to take advantage of the increased CO2 pressure?

2) Stripping steam requirement(3):

a) Reduce reboiler temperature: Little or no saving in energy but in exergy

b) Increase pressure in stripper and maintain reboilertemperature: Improves CO2/H2O ratio in vapourleaving stripper, thereby reducing stripping steamrequirement

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3) Heat of desorption(1)

2des absCOQ H� �

10−2

10−1

100

10−6

10−4

10−2

100

102

Loading (mol CO2/mol Amine)

PC

O2 (

kPa)

Jou data at 25 40, 60, 80, 100 and 120 C

Measurements

Single isotherms

Dependent parameters

�2

ln1

CO absp H

T R

� ��

�

From Gibbs-Helmholtzequation:

High temperature sensitivityof pCO2 gives high heat ofreaction.

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baFrom equilibrium functionwith the Gibbs-Helmholtzequation:

�2

ln1

CO absp H

T R

� ��

�

Compared to calorimetric measurements

0

20

40

60

80

100

120

140

160

180

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

� , [mol-CO2/mol-Am]

�Hab

s, [k

J/m

ol-C

O2]

40ºC80ºC120ºC[Jou et al., 1994][Lee et al., 1974]


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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-20

0

20

40

60

80

100

120

H2O dissCO2 diss

HCO3- diss

MEAH+ diss

MEACOO- diss CO2 dissolution

overall �Habs

� /molCO2�molAm-1

- �H

abs/

kJ�m

olC

O2

-1

eNRTL*

eNRTL

�, Kim (2009); �, Mathonat (1995); �, Jou et al. (1994). Lines: —, eNRTL*; ---, eNRTL model (as in ASPEN)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-20

0

20

40

60

80

100

120

H2O diss

CO2 diss

HCO3- diss

MEAH+ diss

MEACOO- diss

CO2 dissolution

overall �Habs


- �H

abs/

kJ�m

olC

O2

-1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-20

0

20

40

60

80

100

120

140

160

H2O diss

CO2 diss

HCO3- diss

MEAH+ diss

MEACOO- diss

overall �Habs


- �H

abs/

kJ�m

olC

O2

-1

CO2 dissolution

• Heats of each of the key reaction and overall heat of absorption of CO2with 30 wt % MEA solution (different sets of correlations for K-values)

40 ºC 80 ºC 120 ºC


Effect of different reactions

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�Habs for CO2 with different amine systems at 40 and 120 oC (�~0.1/0.4)

0

20

40

60

80

100

120

140

MEAMDEA

AEEAAMP

DETADEEA

MAPA PZ

DEEA-MAPA

MDEA-MAPA

AMP-MAPA

MEA-AMP

MEA-PZ

PZ-K

-�H

abs/

kJ m

ol-C

O2

�/�, 40 oC, �=0.1/0.4 mol-CO2/mol-Am; �/� 120 oC, �=0.1/0.4 mol-CO2/mol-Am


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CO2 gradients

Mass Transfer

NLi

qVs

NVi

qLs

NiHLi NiHVi

qW

Vapor bulk

NAm

NH2O

NCO2

TL

TV

yi,b

xi,b

Liquid bulk

�V �L

Vapor film

Liquid film

acid gas transfer

total transfer

Heat of reaction

Latent heat of vaporization

Rx.Products

NLi

qVs

NVi

qLs

NiHLi NiHVi

qW

Vapor bulk

NAm

NH2O

NCO2

TL

TV

yi,b

xi,b

Liquid bulk

�V �L

Vapor film

Liquid film

acid gas transfer

total transfer

Heat of reaction

Latent heat of vaporization

Rx.Products

Reduce approach to equilibrium

• Kinetic rate constants• Solubility• Diffusivity

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1 2[ ]R R NH3

3 1 1

10 .

( . )

TDETAk

m kmol s

�

� � 2

3 1 1( . )

TH Ok

m kmol s� �

1 23

[ ]

( . )

R R NH

kmol m Source(s)

1.7 73.7 0.19 - 5.50 Aboudheir, et al., (2003) MEA

1.1 140.8 0.5-5.0 Hartono et al. (2009)

AEEA 2.35 161 1.19 - 3.46 Ma’mun, et al. (2007)

EDA 2.79* 17.72* 0.026-0.068 Li, et al. (2007)

DETA 17.5 179.7 1.0-2.9 Hartono et al. (2009)

Pz 70.1 550 0.45 - 1.5 Cullinane & Rochelle (2002)

Rate constants

Large variations, correlated with the water activity

� �

� � � ��

CO 2 32

22

r = ,obs

obs AmH H O OH

kmolk CO

m s

k k AmH k H O k OH AmH��

Termolecular mechanism

String of discs apparatus

Solubility of CO2 in amine solutions

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PQW G ��

)/( 3 smQG

( )P kPa�

Why not:

Reduce packing heightIncrease diameterMaintain area

Limitations as effective area can go down. Low liquid loadcan give partial wetting

Liquid

NG fired power stations are worst caseBecause of low CO2 content

Electrical energy requirementPressure drop in absorber

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K+ + Pz system� 6 m K+ + 1.2 m Pz; � 5 m K+ + 3.5 m Pz

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 110

20

30

40

50

60

70


- � H

abs/

kJ�m

olC

O2

-1

precipitation region

Phase change systemsPrecipitation/twoliquid phases Advantages

• High cyclic capacity• Improved equilibrium curves• High pressure desorption• Retain good liquid load in absorber

Disadvantages• Possibly higher heat of reaction

• Increased complexity

Desorption at elevated pressure:

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Phase change processes(liquid/liquid systems)

Amine reclaimer

Reclaimerbottoms

Separator

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Reddy S., ” Econamine FG PlusSG Technology for Post Combustion CO2 Capture”, 11th Meeting of IEA GHG International CO2 Capture Network Meeting, Vienna, May 2008

Absorber intercooling

Process modifications

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Reddy S., ” Econamine FG PlusSG Technology for Post Combustion CO2 Capture”, 11th Meeting of IEA GHG International CO2 Capture Network Meeting, Vienna, May 2008

Lean vapour recompression

•Lower steam consumption

•Lower cooling water requirement

•Increases electrical energyinput

•Effect depends on solvent

Desorber interheating

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Summing up on energy requirement:

Heat • High rich loading:

• Close to equilibrium in absorber• Fast absorbent, high heat of absorption

• High absorbent concentration• Low heat of reaction• High equilibrium temperature sensitivity

•High heat of reaction• Plant design modifications

• Intercooling• Interheating• Vapour recompression

Electricity• More effective packing materials • Solvents that desorb at high pressure

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Challenges





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Absorption tower

Example:

400 MW NG fired power station

Exhaust gas rate:2000000 m3/h flue gas

Typical gas velocity: 2 m/s

Tower cross sectional area:280 m2

Diameter: 19 mHeight: 35 m

Equipment size

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�Membrane not selective, only separates the phases

�CO2 affinity and selectivity provided by the alkanol-amine solution, e.g. 30 wt% Monoethanolamine (MEA)

�Diffusion through pores followed by reaction in liquid

�Membrane material must not be wetted by liquid (for liquid side controlled absorption)

Flue GasMicroporous Membrane

Absorption Liquid

CO2

CO2

An alternative: Membrane contactors

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Membrane properties

POLYMER SURFACE ENERGY

polytetrafluorethylene (PTFE) 19.1

polypropylene (PP) 30.0

polyethylene (PE) 33.2

polyvinylchloride (PVC) 36.7

High contact angle facilitated by low surface energy:

Fiber potting

Liquid flow

SpacerMembrane tube layer

Gas flow

Advantages compared to packed towers:� No foaming, channeling, entrainment or

flooding� Higher contact area, 500 - 1500 (m2/m3) � Insensitive to motion� Reduced solvent degradation problems� Reduced corrosion problems� Footprint requirement reduced by 40%� 60 - 75% reduction of size and weight for an

offshore application

Disadvantages:� Possible mass transfer resistance in

the membrane� Liquid is bound to laminar flow (can

be improved)

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Challenges





32


Process interaction with surroundings

Amine reclaimer

Reclaimerbottoms

Interactions

Degradation

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Absorbent degradation process conditions.

0

10

20

30

40

50

60

70

80

90

100

MDEA DMAE AMP MEA MAE DEA HEEDA

Degradationrate t %

other reactions

demethylation / dealkylation

addition compds

imidazolidinones

oxazolidinone

cyclic compds

methylation

All absorbent degrade. The degradation products vary with:Type of absorbent, Process conditions, temperature, O2and CO2 levels

Degradation products are•Volatile (Ammonia, aldehydes etc.

•Low volatility(Volatility lowerthan Ethanolamine(MEA))

•Non-volatile(Typically heat stable salts, organic acids, etc.)

34


Amine reclaimer

Reclaimerbottoms

Non-volatile degradation products

Reclaimer waste• Reduce as much as possible• Heat stable salts(e.g. neutralized acids)• Special waste• Safe deposit or storage

35


Challenges





36


Experimental activity coefficients of MEA and H2O at 40, 60, 80, and 100 oC

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

MEA (1) + H2O (2): 40 oC

x1

� i

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

MEA (1) + H2O (2): 60 oC

x1

� i

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

MEA (1) + H2O (2): 80 oC

x1

� i

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

MEA (1) + H2O (2): 100 oC

x1

� i

� /*, Kim(2009) at 40, 60, 80 and 100 ºC,

+/�, Nath and Bender (1983) at 60, 78 and 92 ºC;

�/�, Tochigi et al. (1999) at 90 ºC.

Lines: —, Wilson; ---, NRTL

Volatility

TT P

N2

P

P

1

2

45

6

3

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Amine reclaimer

Reclaimerbottoms

Water wash to reduce absorbent losses

Important features•Control the amount of water in inlet flue gas•Low temperature in the water wash section•Use of staged water wash•Non-azeotropic systems

ResultOutlet absorbent concentrations below0.01-0.03 ppm possible

38


Amine reclaimer

Reclaimerbottoms

Outlet for volatile degradation products

Possibilities• Bleed from upper wash stages• Acid wash• Biological waste treatment

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Norwegian offshore oil industry Categorization of chemicals

Testing not required

•Chemicals expected to have NO environmental effects•PLONOR list

Green

Accepted•Include compounds which based on their characteristics are not defined as RED or BLACK, and •NOT included in the PLONOR list

Yellow

Phased out or replaced

•Inorganic chemicals with high toxicity (EC50 or LC50 � 1 mg/L)•Organic chemicals with low biodegradability (BOD28 < 20 %)•Organic chemicals or mixtures which meet 2 of the 3 following criteria: Biodegradability < 60 %, bioaccumulation potential (Log POW � 5), or toxicity of EC50 or LC50 � 10 mg/L

Red

Not discharged

•Priority list (Stortingsmelding Nr. 25)•OSPAR List of Chemicals for Priority Action •Both low biodegradability and high bioaccumulation (BOD28 < 20 %, and Log POW � 5)•Low biodegradability and toxic (BOD28 < 20 %, and EC50 or LC50 � 10 mg/L)•Compounds expected to be carcinogenic/mutagenic or harmful to reproduction

Black

ActionsCriteria – Ecotoxicity testsCategory

Ecotoxicity and bio-degradability(1)

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Assessment of solvents

0 20 40 60 80 100Triethylam

TriethanolamTetra-N-methyl-propanediyldiamine

TetrahydrothiophenedioxideSpermine

SpermidineSarcosine

Pyrrolidine1.3-Propanediamine

Piperidine1-(2-Hydroxyethyl)-Piperazine

PiperazineN-tertbutylethanolamine

N-methyldiethanolamine(MDEA)Neopentandiamine

NN-dimethylethanolamineNN'-bis(2-hydroxyethyl)ethylenediamine

N-(2-hydroxyethyl)-ethylenediamineMorpholine

2-MethylaminoethanolGlycine

Ethylenediamine2-EthylaminoethanolEthanolamine(MEA)

DimethylpropanolaminDimethylaminopropylamin

DimethylaminDiisopropanolamineDiglycolamine(DGA)

DiethylenetriamineDiethylaminoethanol

Diethanolamine(DEA)4-Amino-1-butanol3-Aminopropanol

3-Amino-1-methylaminopropane3-Amino-1-cyclohexylaminopropan3-(2-Aminoetyl)aminopropylamine

2-Amino-2-methylpropanol(AMP)2-Amino-2-methyl-13-propanediol

2-Amino-2-ethyl-13-propanediol1-Amino-2-propanol

Alanine

BOD (% of ThOD)

100

101

102

103

104

TriethylamineTetra-N-methyl-propanediyldiamine

TetrahydrothiophenedioxideSpermine

SpermidineSarcosine

Pyrrolidine1.3-Propanediamine

Piperidine1-(2-Hydroxyethyl)-Piperazine

PiperazineN-tertbutylethanolamine

N-methyldiethanolamine(MDEA)Neopentandiamine

NN-dimethylethanolamineNN'-bis(2-hydroxyethyl)ethylenediamine

N-(2-hydroxyethyl)-ethylenediamineMorpholine

2-MethylaminoethanolGlycine

Ethylenediamine2-EthylaminoethanolEthanolamine(MEA)

DimethylpropanolaminDimethylaminopropylamin

DimethylaminDiisopropanolamineDiglycolamine(DGA)

DiethylenetriamineDiethylaminoethanol

Diethanolamine(DEA)4-Amino-1-butanol

3-Aminopropanol3-Amino-1-methylaminopropane

3-Amino-1-cyclohexylaminopropan3-(2-Aminoetyl)aminopropylamine

2-Amino-2-methylpropanol(AMP)2-Amino-2-methyl-13-propanediol

2-Amino-2-ethyl-13-propanediol1-Amino-2-propanol

Alanine

EC-50 (mg/L)

BiodegradabilityEcotoxicity

Ecotoxicity and bio-degradability(2)

41


Environmental status

• Environmentally benign solvents are available• Emissions of absorbent(amines) can be brought downto less than 0.01-0.03 ppm• Volatile degradation products can be handeled by acidwash and biological treatment• Methods for reducing degradation and corrosion rates are continuously being developed• The final special waste must be safely deposited• Alternative uses for this waste are being studied

42


Summing upEnergy considerations

• Significant variations in equilibrium• Close approach to equilibrium• High temperature sensitivity is positive• Phase change solvents promising• Run desorber at elevated pressure

Mass transferFast reactionsWatch solubility and viscosity

VolatilityCan be controlled at a cost

Degradation, biodegradation and ecotoxicityComplex mechanismsSome trends visibleSome similarities between process and bio-degradationToxicity normally not a problem

43


Thank you

capture by solvents; co challenges and...

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