Simulation of CO capture with Solid sorbents using Aspen Plus … · Aspen Plus constructs J.W....
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Simulation of CO2 capture
with Solid sorbents using Aspen Plus constructs
J.W. Dijkstra
April 2016
ECN-L--16-016
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www.ecn.nl
Simulation of CO2 capture with
Solid sorbents using Aspen Plus
constructs Jan Wilco Dijkstra
Petten KOPSE Meeting
4th april 2016
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Post-combustion CO2 capture
for power stations
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Conventional technology for CO2
removal from flue gas
• Chemical solvents
• High regeneration heat – Reaction heat
– Sensible heat
– Water evaporation
• Significant solvent use/waste
• Nitrosamine emissions?
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Solid sorbents as an alternative
Potential benefits • Low Cp ~3.8 vs ~1.1 kJ/(mol.K) • Less water evaporation Only adsorbed water • Less degradation • Less emissions
Disadvantage • (Probably) no regenerative heat exchanger • Novel
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Supported polyamines
PEI = Polyethyleneimine
Polymer impregnation procedure on commercial porous silica material
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Objective and approach
Sorbent preparation & characterization
Systems model development
Development goals Optimum conditions Potential
isotherms
Objective: assessment of working conditions, energy savings potential and development goals
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Isotherms from break-through
experiments
CO2
CO2
k.p1
k.pΘ
H2Ok.pΘ
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 0.02 0.04 0.06 0.08 0.1 0.12
Wat
er
bre
akth
rou
gh C
apac
ity
[mm
ol/
g]
H2O pressure [bar]
60°C
70°C
80°C
90°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 0.05 0.1 0.15 0.2 0.25 0.3
CO
2b
reak
thro
ugh
Cap
acit
y (m
mo
l/g)
CO2 pressure (bar)
60°C
80°C
90°C
100°C
110°C
120°C
135°C
CO2: Langmuir H2O: Henry
Non-optimized sorbent: PEI on silica
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6
6.5
7
7.5
8
8.5
9
9.5
10
0.0027 0.00275 0.0028 0.00285 0.0029 0.00295 0.003 0.00305
-ln
(KH
2O)
1/T [K-1]
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.00255 0.0026 0.00265 0.0027 0.00275 0.0028 0.00285
-ln
(K
CO
2)
1/T (K-1)
Temperature dependency
RT
Δhexpkk abs
0van’t Hoff’s law:
CO2
dH=-91 kJ/mol Water dH=-60 kJ/mol
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Reactor concept
Multistage fluid bed adsorber Bubbling fluid be regenerator
Counter-current Cross-flow
BFB
Steam Cooling
CO2/H2O
Flue gas
Clean gas
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Modeling platform: Aspen Plus
+ Good in mass/heat balances
+ Useful thermodynamic properties
+ Staged development
- No isotherms Add iteration blocks
- No suitable models for reactors Use ‘constructs’ of HX, splitters, mixers etc.
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What are constructs?
Constructs are clever arrangements of simple blocks that allow you to model complex systems (Schad, 1998)
Example 1: Spray condenser
• No equilibrium achieved
- => flash vessel not possible
• Use rigorous distillation with low
stage efficiency
Ryan C. Schad, Make the most of process simulations, Chem. Eng. Prog., jan 1988. 21-27.
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Example 2: Membrane with sweep
Hydrogen
hydrogen Feed
Sweep
Retentate
Permeate
DESIGN SPEC e.g. TARGET : (X_FEED*P_FEED)-(X_PERM*PPERM) VALUE : xx bar VARY : P_PERM Optionally * Add also equations for membrane surface area * Add HX’s for heat exchange
SEP1
MIX1
FEED
RET
SWEEP PERM
MEMH2
Driving force= partial pressure difference pH2
Feed>pH2perm
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Modeling approach
Adsorber
Flue gas
CO2+ H2O
Regenerator
Clean gas
Rich solid sorbent
Lean solid sorbent
Assume equilibrium between gas and solid at outlet conditions
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Design strategy:
Adsorber
Flue gas
CO2+ H2O
Regenerator
Clean gas
Rich solid sorbent
Lean solid sorbent
2. Adapt solids flow rate to saturate rich sorbent
1. Target % CO2 in clean gas Dictates leanness of sorbent Dictates regenerator temperature
3. Optimize absorption temperature with sensitivity study
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Solids looping model
Adsorber section
Regenerator section
Flue gas
Cooling water
DCC SensibleSorbent/gas
DHCO2 DHWAT
SensibleSorbent/gas
DHCO2 DHWAT
Sensible water
Sensible water
Clean Flue gas
Total adsorption heat
Total regeneration
heat
Wet CO2 to compression
WaterLoaded sorbent
Lean sorbent
CO2
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Important blocks
• INISPEC – CALCULATOR block with isotherm PARAMETERS used throughout the model
– Executed FIRST
• LEANCAP – DESIGN SPEC with FORTRAN
– Calculate sorbent loading based on Temperature and PCO2 of regenerator outlet (SL1)
– Calculate sorbent loading based on Temperate and PCO2 of absorber outlet (SL2)
- Vary split fraction of SPLITTER in regenarator SEPARATOR unit SL1/SL2=1
• RICHCAP – Similar one for the absorber outlet
• CCR – VARY temperature of regenerator until x_co2_stackgas=10%
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When things get messy
• Adding water adsorption - Design on CO2, water follows
- ‘Pinch point’ in absorber can be on rich and lean side’ ==> IF/THEN needed
Use Excel (not recommended)
Install FORTAN compiler (not available)
Do something obscure with ROUND command
• Water, required as a separate stream, but condenses vapor only
• Convergence problems – 10 DESIGN SPEC, 9 CALCULATOR blocks makes that this requires some attention
– Assign CONVERGENCE blocks to loops to easily spot problems
– 2 DESIGN SPECS modified to NEWTON
– NESTING order specified for 4 CONVERGENCE blocks
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40
45
50
55
60
65
70
75
80
0
1
2
3
4
5
6
7
8
60 65 70 75 80 85 90 95 100
De
ltaT
[°C
]
He
at [
GJ/
ton
CO
2]
Absorber temperature [°C]
Total regeneration heat
CO2 sorption heat
Sensible heat
Water sorption heat
DeltaT
Regeneration heat
Optimum
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1.00
1.73
0.95
1.34 0.32
0.30
1.76
2.07
2.07
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
MEA reference Solid sorbent Solid sorbent 200% cap
Regeneration heat[GJ/ton CO2]
CO2 reaction heat
Water evaporation/desorption
Sensible heat reflux water
Sensible heat sorbent/solvent
Total 4.26 Total 4.13
Total 3.31
Comparison with MEA
CO2 reaction
Water evaporation /desorption
Sensible heat Q=cp T
Solid sorbent MEA
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Improved sorbent
4.96
5.28
4.68
3.69
4.00
3.51
4.17 4.184.07
3.243.37
3.16
0.0
1.0
2.0
3.0
4.0
5.0
6.0
CO2 100%H2O 100%Base Case
H2O 200% H2O 50% CO2 200% CO2 200%H2O 200%
CO2 200%H2O 50%
Re
gen
era
tio
n h
ea
t [G
J/to
n]
CO2 and H2O capacity relative to base case
NGCC case
PC Case
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Conclusions/evaluation Aspen Plus
• Constructs are very useful, use them in your simulations!
• Really complex constructs like the sorbent model Good if you are familiar with ASPEN PLUS, are not familiar with something else
• You benefit from – Thermodynamic data, or want to integrate with a flow sheet
– Staged development, you can start really easy
– Control over convergence
• If not you can consider: – Aspen Custom Modeler
– gPROMS
– Matlab (Simulink)
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Conclusions solid sorbents
• CO2 solid sorbents interesting as a 2nd generation post-combustion sorbent – Capacity required at least twice that of non-optimized sorbent
– Advantages low Cp and limited water sorption
• To arrive at these conclusions we need a combined modeling and experimental approach – Insight in optimal working conditions
– Insight in advantages, development goals and potential
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Thank you
ECN
Westerduinweg 3 P.O. Box 1
1755 LE Petten 1755 ZG Petten
The Netherlands The Netherlands
T +31 88 515 49 49 [email protected]
F +31 88 515 44 80 www.ecn.nl
Contributers: Stephane Walspurger, Gerard Elzinga, Rick Reijers, Miranda Heijink-Smit Özlem Pirgon-Galin, Jurriaan Boon, Wim Haije and others
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Graphical representation of
cyclic process
0
0.5
1
1.5
2
0 200 400 600 800 1000
Load
ing
CO
2,H
2O [
mm
ol/
g]
Partial pressure (CO2, H2O), [mbar]
H2O, des, 138°C
CO2, abs, 86°C
CO2, des,138°C
H2O, abs, 86°C
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8
ECN
Westerduinweg 3 P.O. Box 1
1755 LE Petten 1755 LG Petten
The Netherlands The Netherlands
T +31 88 515 4949
F +31 88 515 8338
info@ ecn.nl
www.ecn.nl