Selection of amine solvents for CO2 capture from natural gas power plant

Jiafei Zhang, Paul Fennell, Martin Trusler

Cardiff, 11th September 2014

Gas-FACTS project: Gas - Future Advanced Capture Technology Systems

UKCCSRC Biannual Meeting Natural Gas CCS Technical Session

Outline

Introduction • Project overview • Solvents selection

Process Evaluation • Conventional • Phase change

Properties and Influence • VLE & CO2 capacity • Viscosity & Density • Heat capacity & Energy requirement • Surface tension

Summary

2

Absorption Desorption

Image Source: Siemens

Gas-specific solvents for CO2 capture

Thermophysical properties

VLE: Vapour-Liquid Equilibrium

Project overview

2.1 Gas-Specific Solvents

2.2 Flexible

Capture Systems

2.3 Advanced

Testing

Wor

k pa

ckag

es

3

Consortium Members:

Natural Gas Combined Cycle + CO2 Capture & Storage NGCC-CCS

PCC for gas-fired power plants

4

CO2 Emissions (kg/MWh) w/o w/ CCS

Coal-fired 800-1000 ~100 Gas-fired 350-400 ~40

After Combustion: CO2 H2O O2 N2 Ar

Coal-fired 13.53 15.17 2.40 68.08 0.82

Gas-fired 4.04 8.67 12.09 74.32 0.89

Natural gas becomes the new ‘coal’ for power generation… burns much cleaner than coal but...

Lower CO2 partial pressure Reduce αCO2 Seeking specific solvents

reduce: solvent flow column size CapEx & OpEx

Higher O2 concentration Enhanced solvent degradation Seeking solvents resisting oxidation

Exhaust Gas Recycle (EGR) CO2 ↑ & O2 ↓ w/o EGR: ~4% CO2, ~12% O2

w/ EGR: 6-8% CO2, 8-10% O2

Ideal solvent

The ideal chemical solvent for PCC

Fast reaction kinetics and mass transfer – reduce height requirements for the absorber and/or solvent circulation flow rates High absorption capacity – directly influences solvent circulation flow

rate requirements and equipment size Good regenerability and reaction enthalpy – reduce energy

consumption High thermal stability and low solvent degradation – reduce solvent

waste due to thermal and chemical degradations Low solvent costs – easy and cheap to produce No negative environmental impact Technical feasibility

5

Process economic evaluation

Strategy for solvent selection

6

Gas-specific solvents

• Monoethanlamine (MEA) as benchmark primary amine

• 2-Amino-2-methyl-1-propanol (AMP) sterically hindered • Dimethylaminoethanol (DMAE) tertiary • Diethylaminoethanol (DEAE) tertiary • Piperazine (PZ) as activator diamine • Piperazinyl ethylamine (PZEA) triamine

• Blended amines – recommended • Solvent formulations

• DEAE+PZ • AMP+PZ • etc.

N

OH

HONH2

HN NH

N

OH

NH2HO

High net CO2 loadings

Chemically stable

N NH

H2N Rapid reaction

kinetics Low energy

consumption

Challenges High O2 Low CO2

Processes

Conventional absorption • 30wt% MEA solution • Activated MDEA • Other alkanolamines Liquid-Liquid phase change • DEAE+MAPA (NTNU) • Lipophilic amine, e.g. • DMX (IFP) Liquid-Solid phase change • KHCO3 solution • Concentrated AMP

7

NH2

N

Before regeneration

During regeneration

After regeneration

N

OH

NH

NH2

HONH2

NH2HO

OHN

OH

Conventional post-combustion capture process

8 Image Source: Sasol

Flue gas cooling & desulfurization

CO2 absorption Solvent regeneration

DCC = Direct Contact Cooler

Phase change capture process

9

Measurement & conditions

Density • 25-80 °C • 0.01% (uncertainty)

Viscosity • 30-80 °C • 1%

Heat capacity • 30-120 °C, 1-40 bar • 1.5%

Surface tension • 25-60 °C • 2%

VLE & composition analysis with GC

10

T2

Peltier Device

Pump Bath

T1

P

BPR

Feed flow

Column packings

Energy consumption

Packing wettability

(Sensible heat)

VLE + GC

Gap in the literature: few with CO2 loading

VLE: Experimental set-up

11

Process flow sheet GSV

LSV

Validation with 30wt% MEA 30wt% DMAE, DMAE+PZ 30wt% DEAE

12

VLE: Results

1

10

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

p CO

2 / k

Pa

α

This workTong 2012Jou 1995

1

10

100

0 0.2 0.4 0.6 0.8 1 1.2

p CO

2 / k

Pa

α

30wt% DMAE25wt% DMAE + 5wt% PZ20wt% DMAE + 10wt% PZ30wt% DEAE

MEA DEAE

40oC 120oC

120oC

40oC

NH2HO

N

OH

N

OH

Solvent circulation

Net CO2 capacity

Δα for T between 40 and 120 oC at low pCO2

Higher Δα than for benchmarks

13

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

30% MEA 30% MDEA 30% AMP 25% AMP +5% PZ

20% AMP +10% PZ

30% DMAE 25% DMAE+ 5% PZ

20% DMAE+ 10% PZ

30% DEAE

Net

CO

2 loa

ding

4 kPa 12 kPa

NH2

HO

OH

NO

H

HONH2

N

OH N

OHHN NH

Benchmarks New solvents

Viscosity: Influence on absorption

Solvent viscosity (↑)

Electrical energy (↑) : e.g. pump power Pressure drop (↑) in absorption column

Porosity of column packing (↑)

14

e.g.: 20%AMP+10%PZ

2.3 cP

4.1 cP

Viscosity: Validation

30wt% MEA solution Our studies on influences of • Concentration • Temperature • CO2 loading

15

NH2HO

0.5

1

1.5

2

2.5

3

3.5

4

0 0.1 0.2 0.3 0.4 0.5

η / m

Pa∙s

α

at 25 °C at 30 °Cat 40 °C at 50 °Cat 60 °C at 70 °Cat 80 °C

tK ⋅=ν

ρνη ⋅=

Kinematic viscosity

Dynamic viscosity

Compared to Weiland’s (1998) correlation

Pump & Packing

Viscosity: Amine solutions

Correlations

Influence of T:

Influence of Cam:

16

TCaCa am2

am1w

amln ⋅+⋅=

ηη

(General Equation)

0

1

2

3

4

5

6

300 310 320 330 340 350 360

η / m

Pa∙s

T / K

Mod.15%wtMod.30%wtMod.45%wtExp.15%wtExp.30%wtExp.45%wt

0

1

2

3

4

5

6

300 310 320 330 340 350 360

η / m

Pa∙s

T / K

Exp.15%wtExp.30%wtExp.45%wtMod.15%wtMod.30%wtMod.45%wt

DMAE DEAE

N

OH

N

OH

AAD=2.4%

TBA+=

w

lnηη

Cam mol/kg T K

Viscosity: Effect of CO2 loading

Correlations Influence of α:

17

TCCcCbCaCCcCbCa amCO2CO2am2

amCO1CO1am1w

am 2222ln ⋅⋅+⋅+⋅

+⋅⋅+⋅+⋅=

ηη

1

2

3

4

5

6

7

8

9

0 0.4 0.8 1.2 1.6 2 2.4

η / m

Pa∙s

CCO2 / (mol/kg)

303.15 K 313.15 K323.15 K 333.15 KCorrelation

0

2

4

6

8

10

12

14

0 0.8 1.6 2.4 3.2

η / m

Pa∙s

CCO2 / (mol/kg)

303.15 K 313.15 K323.15 K 333.15 KCorrelation

45% DEAE 45% DMAE

AAD=3%

Cam mol/kg CCO2 mol/kg T K

Density

Amine solutions MEA DMAE DEAE AMP PZEA Xam + PZ Influences • Concentration • Temperature • CO2 loading

Plot: presented as ρ/ρw suppress the T dependence

18

0.97

0.98

0.99

1

1.01

1.02

1.03

1.04

1.05

1.06

290 300 310 320 330 340 350 360

ρ/ρ w

T / K

30% DMAE

w. α=0.26

w. α=0.43

w. 5%PZ

w. 10%PZ

Linear fits

+CO2

+PZ

N

OH

Feed flow

Heat capacity: Influence on desorption

Energy consumption CO2 capture, transport, storage Solvent thermal regeneration: >50%; + blow + compression Sensible heat, reaction enthalpy, stripping energy, heat loss A lower Cp is preferred

19

TCF psol ∆⋅⋅

Sensible heat Reaction enthalpy Stripping energy Heat loss Total

(∆T=15)

30% MEA

0.9 (∆α=1.5 mol-CO2/kg-sol)

1.8 (∆rH=80 kJ/mol-CO2)

1.1 (Reflux ratio ~2)

0.2 (∆T=90 °C)

4.0

Unit: MJ/kgCO2

~25%

Heat capacity: MEA

30wt% MEA solution Temperature CO2 loading Influence: T ↑ Cp ↑ α ↑ Cp ↓ (J/g/K) α ↑ ρCp ↑ (J/ml/K)

NH2HO

20 3.2

3.4

3.6

3.8

4

30% MEA α=0.12 α=0.26 α=0.38

Cp /

(J/g

/K)

3.4

3.5

3.6

3.7

3.8

3.9

4

40 50 60 70 80 90 100 110 120

Cp /

(J/g

/K)

T / oC

α=0 α=0.12 α=0.26 α=0.38 Hilliard 2008, α=0 ρC

p / (J

/ml/K

)

4.164.184.2

4.224.244.26

40 50 60 70 80 90 100 110 120 130

Cp /

(J/g

/K)

T / oC

This workManya 2011IAPWS

AAD=0.2%

H2O

30% MEA

Sensible heat

Heat capacity: Other amines

Our studies: DMAE, PZAE, DMAE+PZ, AMP+PZ …

21

3.7

3.8

3.9

4

4.1

4.2

4.3

40 50 60 70 80 90 100 110 120 130

Cp /

(J/g

/K)

T / oC

25% DMAE + 5% PZ20% DMAE + 10% PZ30% DMAE30% DMAE (α=0.43)

4.06

4.08

4.1

4.12

4.14

4.16

4.18

4.2

40 50 60 70 80 90 100 110 120 130

Cp /

(J/g

/K)

T / oC

30% PZEA20% AMP + 10% PZ20% AMP + 10% PZ (α=0.33)

N NH

H2N

N

OH

HN NH

HONH2

+CO2

+PZ

Energy requirement

Estimation of energy consumption • Sensible heat Qsen

• Heat of reaction Qr • Stripping energy Qstr

• Heat loss Qlos

How to reduce?

22

Qsen Qr Qstr Qlos Qsum

MEA 0.9 1.8 1.1 0.2 4.0

DMAE+PZ 0.6 1.4 1.0 0.2 3.2

Target 0.5 1.2 0.6 0.1 2.4

TCFQ psolsen ∆⋅⋅=

HFQ rCOr ∆⋅=2

vsteamstr LFQ ⋅=

ATQlos ⋅∆⋅=φ

Surface tension

Our tests: 30wt% MEA AMP, AMP+PZ Varying: T, Cam, α Influences: T ↑ γ ↓ Cam ↑ γ ↓ α ↑ γ ↑ Lower γ: better wettability

23

Wilhelmy plate

35

40

45

50

55

20 30 40 50 60 70

γ / (

mN

/m)

T / oC

15% AMP

30% AMP

45% AMP

20% AMP + 10% PZ

25% AMP + 5% PZ

62646668707274

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

γ / (

mN

/m)

α

This workJayarathna 2013

30% MEA

AAD=0.6%

HONH2

HN NH

NH2HO

Packing wettability

Summary

Highlight Measuring thermophysical properties of CO2 loaded amine solvents VLE High Δα reduce solvent circulation Viscosity AMP > PZEA > DEAE > DMAE > MEA > H2O

• Cam increase • T decrease • αCO2 increase • w. PZ increase

Heat capacity H2O > PZAE > AMP > DMAE > MEA αCO2 decrease CP but increase ρCP

Surface Tension T ↑ or αCO2 ↓ γ ↓ (better wettability)

24

Correlations

Summary

Evaluation Cyclic loading ∆abH Reaction rate / Base strength (pKb) Amine/Da Cost & availability Viscosity / Volatility / Thermal degradation Oxidative degradation Corrosivity HSE

25

Comments

• Recommendation of blended solvents

• Viscosity ↑ porosity of packing ↑

• Volatility preferable to degradation

Thank you for your attention!

26

Consortium Members: Financial support

27

Viscosity

Availability in literature Amine + Water Varying Concentrations Many Varying Temperatures Many (25-80 oC) Varying CO2 loadings Few

Influence of CO2 loading Weiland et al. MEA, DEA, MDEA, MEA+MDEA Fu et al. MDEA+DEA Svendsen et al. MEA Rochelle et al. PZ This work Single amine & blended solvent Influence of T, αCO2 and Cam. Correlations 28

U-Tube capillary viscometer

tK ⋅=ν

ρνµ ⋅=

kinematic viscosity

dynamic viscosity

Heat capacity

Flow calorimeter

29

Calorimeter cell

TmQC net

p ∆⋅=

)( measuredbasenet QQbaQ −⋅+=

)( 21 TTT −=∆ρ⋅=Vm

T2

Peltier Device

Pump Bath

T1

P

BPR

Isocratic pump

Vacuum degasser

Power supplier

Data Acqu. Unit

Multimeter

Water or Oil Bath

4.16

4.18

4.2

4.22

4.24

4.26

40 50 60 70 80 90 100 110 120 130

Cp

/ (J/

g/K

)

T / oC

This workManya 2011

Water AAD=0.2%