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Modeling CO2 Capture Using Concentrated PZ
Jorge M. Plaza, David H. Van Wagener, Peter Frailie, Eric Chen, Gary T. RochelleLuminant Carbon Management Program
Department of Chemical EngineeringThe University of Texas at Austin
1st Post Combustion Capture ConferenceAbu Dhabi, United Arab Emirates , May 18, 2011
Outline
Concentrated PZ
Model Framework
5deMayo and Guy Fawkes
Pilot Plant Campaigns
Intercooling & Interheating
Conclusions and Future Work
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8m Piperazine
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Benefits of 8 m PZ
Double MEA CO2 absorption rate & capacity
Thermally stable to 150 °C
Negligible oxidative degradation
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NN HH
NN+
HH
HNNH
O-
OPZ
PZH+ PZCOO-
Model Framework
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Model Characteristics
Rigurous independent absorber/ stripper models Built in Aspen Plus® RateSepTM
Model integration matching loadings and solvent rate
Thermodynamics Regressions in Aspen Plus® for Cp, VLE, PZ volatility Guy Fawkes model – Absorber 5deMayo – Stripper
Activity – based kinetics WWC data by Dugas (2009) Fitted by adjusting k2 and diffusivity of CO2 and amine species
Transport properties Density and viscosity using FORTRAN subroutines Diffusivity implemented using Dugas (2009) and FORTRAN subroutine
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Pilot Plant Campaigns
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CO2 Capture Pilot Plant
Column ID = 0.43 m (16.8 in)
Packed height – 6.1 m in 2
beds (3.05 m each)
12mol% CO2 Synthetic flue
gas
Equiv to 0.1-0.2 MW
3-6 tons CO2/day
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8 m PZ Pilot Plant Flowsheet
Gas Acc
Condenser
Liq Acc
Feed Tank
Blower
Stripper
CrossExchanger
Trim Cooler
Air
CO2 Makeup
GasOut
Recycled CO2
Lean AmineRich Amine
20-60 psia
Intercooling
12% CO2
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Absorber Intercooling Process Flowsheet
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Campaign Conditions
Campaign November ‘08 September ‘10
PZ (m) 5, 8, 9 8
Gas rate (ACFM) 350 350 -750
Liquid Rate (gpm) 12, 15, 18 8 – 26
Absorber Packing Mellapak 2X RSP 250
Stripper Packing Mellapak 2X Mellapak 2X
Intercooling No Yes/No
Runs 14 13
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Pilot Plant Modeling
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PP Absorber model
1 packing section (30 segments) Mellapak 2X
3 packing sections:
1st & 3rd : 3.05 m RSP-250 (15 segments)
2nd reduced to min. mass transfer
Intercooling using pump around 2nd section
Fortran subroutines for:
Interfacial area (Wang) based on Tsai (2010)
kL & kG (Wang) for RSP-250
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CO2 lean flue gas
Rich solvent
Lean solvent
CO2
H2O
N2O2
CO2
H2OPZ
Inlet Gas
Liquid intercooling
PP Absorber model validation
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LoadingFlow
T, P
TemperatureFlow
yCO2, yH2OFlow
Match removal by changing lean loading
Loading
T, P
0.E+00
2.E-08
4.E-08
6.E-08
8.E-08
1.E-07
30
40
50
60
70
0 0.5 1
CO
2M
ass
Tran
sfer
(km
ol/s
)
T (o
C)
Z/ZTotal
T and mass transfer for L/G= 2.9350 ACFM
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RSP- 250Removal = 91%• Lean=0.21/0.22• Rich=0.37/0.38yCO2-out =0.011/0.010
0.E+00
2.E-08
4.E-08
6.E-08
8.E-08
1.E-07
30
40
50
60
70
0.0 0.2 0.4 0.6 0.8 1.0
CO
2M
ass
Tran
sfer
(km
ol/s
)
T (o
C)
Z/ZTotal
T and mass transfer for L/G= 2.9350 ACFM -Intercooled
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RSP- 250Removal = 90%• Lean=0.22/0.25• Rich=0.38/0.41yCO2-out =0.013/0.012
PP Absorber Simulations
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Variable Average Adjustment
Campaign 2008 (Mellapak 2X) 2010 (RSP-250)
Removal Matched (NTU)
LLDG 0.01 (±0.01) 0.02 (±0.01)
MLDG ----- -0.01 (±0.04)
RLDG 0.02 (±0.01) 0.02 (±0.01)
TG-out -1.0 oC (±0.3) -1.0 oC (±0.5)
TL-out 0.2 oC (±0.3) 0.2 oC (±0.3)
Stripper Calculations Rate-based calculations for 5 m packed columns RadFrac with rate-based calculation of H&M transfer Reactions assumed to reach equilibrium - high T In-house correlation for packing area (Tsai, 2010)
Equilibrium calculations for other units Flash tanks Heaters/cross exchangers Pumps
Equivalent work: electric capacity used for capture
comppumprebeq WWWW ++=
+−+
=KT
KKTQW
reb
rebreb 5
3135750.
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8 m PZ Pilot Plant Example
Condensate
CO2
Lean
Rich48.0 °C0.365 ldg1.23 kg/s
52.0 °C0.287 ldg / 0.286 ldg1.21 kg/s / 1.18 kg/s
106.8 °C / 111.7 °C0.033 kg/s / 0.035 kg/s
131.9 kW
27.1 kW
272.3 kPa
122.3 °C / 122.2 °C
2010 - Run 1
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PP Stripper Simulations
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Variable Average Adjustment
Campaign 2008 (Mellapak 2X) 2010 (Mellapak 2X)
Lean flow -0.5% (±0.5%) 0.7% (±3.9%)
LLDG 2.8 % (±1.8%) -1.2% (±3.5%)
Overhead T -9.0oC(±4.7) -3.2oC (±2.5)
CO2 rate -7.8% (±7.1%) -2.6% (±3.9%)
Reboiler T 2.1 oC (±1.9) 0.2oC (±1.1)
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1E+1
1E+2
1E+3
1E+4
1E+5
1E+6
1E+7
0.2 0.3 0.4 0.5
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
Solid lines: Aspen Plus®
Dashed lines: Empirical model Fawkes Model, 8m PZ
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1E+1
1E+2
1E+3
1E+4
0.2 0.3
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
Solid lines: Aspen Plus®
Dashed lines: Empirical model Fawkes Model, 8m PZ
40oC
60oC
80oC
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1E+1
1E+2
1E+3
1E+4
1E+5
1E+6
1E+7
0.2 0.3 0.4 0.5
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
Solid lines: Aspen Plus®
Dashed lines: Empirical model Fawkes Model, 8m PZ
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1E+3
1E+4
1E+5
0.35 0.4 0.45 0.5
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
Solid lines: Aspen Plus®
Dashed lines: Empirical model Fawkes Model, 8m PZ
40oC
60oC
80oC
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1E+1
1E+2
1E+3
1E+4
1E+5
1E+6
1E+7
0.2 0.3 0.4 0.5
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
Solid lines: Aspen Plus®
Dashed lines: Empirical model Fawkes Model, 8m PZ
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1E+5
1E+6
1E+7
0.35 0.4 0.45
PC
O2 (P
a)
CO2 Loading (moles/equiv. PZ)
CO2 Solubility in 0.9-12 m PZ
120oC
140oC
160oC
Process Configurations
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Water for reflux
CO2 Multistage compressor
Lean
Rich
Stripper
Water knockout
Simple Stripper (SS)150 bar
Pumping for gravity and P drop
5 m IMTP#40 packing
5°C approach
Isothermal (variable P) at maximum allowable T
150°C
Rich loading assumed constant:
5 kPa CO2 @ 40°C
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2-Stage Flash (2SF)
Water for reflux
CO2 Multistage compressor
Lean
Rich
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Equal vapor production per stage
Interheated Column (IH)
Water for reflux
CO2 Multistage compressor
Lean
Rich
Stripper
Liquid drawoff
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Benefit of interheated column
30
32
34
36
38
40
42
44
0.20 0.25 0.30 0.35
Equi
vale
nt W
ork
(kJ/
mol
CO
2)
Lean Loading (mol CO2/equiv. PZ)
8 m PZ0.40 rich loading
150°C in reboiler(s)
0.31 lean
loading
2-Stage Flash
Simple Stripper
Interheated Column
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Intercooling +
Interheating
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Case Conditions
1100 MW plant – 90% Removal (1/3 gas flow)
Absorber and stripper modeled separately Solvent flow rate based on 1.1 Lmin for absorber
Stripper optimum based on Minimum Weq
Complete system model: Optimum stripper loadings fed to absorber
Absorber loadings adjusted based PP results
Resulting ldgs fedback to stripper and Weq recalculated
Compared to 9m MEA using Plaza et al. 2010
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8 m PZ Flowsheet
Stripper
CrossExchanger
Trim Cooler
GasOut
Lean AmineRich Amine
CO2 to Compression
Intercooling
Flue Gas
Interheating
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Optimum - Absorber
Variable Units Value
Solvent ------ 8m PZ 9m MEA
yCO2 mol frac 0.15
Gas flow m3/s (actual) 286
Gas T °C 40
L/G mol/mol 6.2 9.2 (48%)
Lean ldg mol CO2/mol alk 0.300 0.390
Rich ldg mol CO2/mol alk 0.391 0.492
Packing Type ----- RSP-250
Packing per kmolCO2 removed/hr
Characteristic m2 83 145 (74%)
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Optimum - Stripper
Variable Units Value
Solvent 8m PZ 9m MEA
Stripper P bar 8.71 5.1
Stripper T °C 150 120
Packing type -------- IMTP - 40
Pump work kJ/mol CO2 1.5 2.2
Compression work to 15MPa
kJ/mol CO2 9.3 11.5
Heat work kJ/mol CO2 21.2 21.5
Equivalent work kJ/mol CO2 32.0 36.2 (13.1%)18/05/2011 The University of Texas at Austin 36
Conclusions
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Conclusions
38
PP absorber performance can be adequately matched using PZ model and correlations by Wang (2010).
Temperature profiles require revision Location of the thermocouples in the absorber Effect of kL and kG in water transfer Thermal inertia
Ldgs required adjustments possibly due to VLE fit. Larger deviation for intercooled cases and lean ldg Minimum adjustment in the stripper (high T fit)
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Conclusions
39
An absorber/stripper system for 90% for 1/3 gas flow of a 1100 Mw unit has been designed.
Interheating and intercooling can improve capture performance (6% reduction of Weq)
It is possible to integrate separate rigorous absorber and stripper to generate an optimized capture unit
8 m PZ optimum system requires: 74% more packing (83 m2 per kmol CO2/hr removed)
48% less solvent ( L/G = 6.2 mol/mol)
13% less work requirement (32 kJ/mol CO2)
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Luminant Carbon Management ProgramPSTC staff
Thank you!18/05/2011 The University of Texas at Austin 40
Questions?
Jorge M. Plazajmplaza@che.utexas.edu
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