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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%