Evaluation of performance of various
alkanolamines for CO2 capture from a
pulverized coal-fired power plant
Sumedh Warudkar
PhD Candidate
Chemical and Biomolecular Engineering
Outline
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The CO2 problem
Current CO2 capture technology
Scope of Study
Amine Absorption Process
Comparison of absorbents properties
Comparison of Energy Consumption
Comparison of Absorber and Stripper Sizing
Comparison of Rich Amine Loading
Contribution of various processes and utilities to energy
consumption
• Conclusions
The CO2 problem
Fig 1. Worldwide energy consumption in TW
(2004)
Fig 2. Atmospheric CO2 variation (1860-2000)
Current CO2 Capture Technology
Figure 2.a. Membrane Separation
Figure 2.c. Gas Absorption
Figure 2.b. Gas Adsorption
Scope of Study
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With available technology, CCS will increase the cost of electricity from a
conventional power plant by 21% - 91%.7
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Current technology for CO2 separation was designed primarily for natural
gas sweetening – high pressure feed gas, large variance in acid gas (CO2,
H2S) content and generates value added product.
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Problem at hand involves power plant flue gas – near atmospheric, low
variance in CO2 content and will be a parasitic load for electricity generation
utilities.
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Due to the low variance in flue gas composition, it might be possible to
come up with a generic “best” absorbent for CO2 capture.
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Need to better optimize current technology by changing process
parameters.
Amine Absorption Flow-sheet
CO2 compression train
Simulation Parameters
Composition of coal-fired
power plant flue gas [1]
Parameter
Simulation Parameters
Value
Parameter
Value
Absorber – flooding
fraction
80%
Absorber tray spacing
2 feet
Volumetric Flow-rate
1100 MMSCFD
Water (mole %)
11.8
Absorber heir weight
3 inches
CO2 (mole %)
12.79
Stripper – flooding
fraction
80%
Oxygen (mole %)
5.6
Stripper – tray spacing
2 feet
Nitrogen (mole %)
69.8
Stripper – weir height
3 inches
Sulfur Dioxide (mole %)
0.01
Condenser
temperature
30 oC
Absorber/Stripper Specifications
Parameter
MEA
DGA
DEA
AMP
Absorber - # of Trays
2
2
10
10
Stripper - # of Trays
10
10
10
10
Amine Absorbents
Comparison
Monoethanolamine (MEA)
Diglycolamine (DGA)
Advantage
Advantage
• Primary amine with very high reaction rate with CO2
• Low amine circulation rate
• Low molecular weight
• High DGA concentrations around 50-70% (wt) can be
used due to low volatility
• High reaction rate with CO2
• Low amine circulation rate
Drawbacks
• High heat of reaction
• MEA concentrations above 30-35% (wt) are corrosive
• Highly corrosive at CO2 loadings above 0.35-0.4
• Highly volatile
Diethanolamine (DEA)
Drawbacks
• High heat of reaction
• Highly corrosive at CO2 loadings above 0.35-0.4
2-amino-2-methyl-1-propanol (AMP)
Advantage
Advantage
• Low volatility
• Low heat of reaction
• High theoretical CO2 loading capacity
• Low volatility and few corrosion problems
• Low heat of reaction
Drawbacks
• High amine circulation rate
• Secondary amine, low reaction rate
• DEA concentrations above 30-35% (wt) are corrosive
• Forms highly corrosive at CO2 loadings above 0.350.4. Reacts irreversibly with O2 in flue gas.
Drawbacks
• Very low reaction rate
• High amine circulation rate
• High steam consumption to heat amine solution in
stripper
Reaction Rate Constant & Heat of Reaction
Energy Required for CO2 capture
Effect of Amine Absorber Entry Temperature (MEA & DEA 40% wt)
Energy Required for CO2 capture
Comparison of Effect of Stripper Pressure on MEA & DGA
Energy Required for CO2 capture
Comparison of Effect of Stripper Pressure on DEA & AMP
Stripper Diameter
Comparison of Effect of Stripper Pressure on MEA & DGA
Stripper Diameter
Comparison of Effect of Stripper Pressure on DEA & AMP
CO2 loading of Rich Amine Loading
Comparison of DEA-AMP
CO2 loading of Rich Amine Loading
Comparison of DEA-AMP
Energy Consumption
Contribution of various processes and utilities
CO2 Compression
Effect of stripper pressure on specific volume of compressed
vapor and energy consumption
Conclusions
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4 amines – MEA, DEA, DGA and AMP were compared to evaluate their
performance for CO2 capture application.
3 absorber-stripper train configuration was investigated for 90% CO2
removal from 500 MW coal fired power plant flue gas. This permits
estimation of reasonable absorber and stripper sizes.
MEA and DGA require only 2 ideal (6 real) stages to achieve 90%+ CO2
capture.
DEA requires 10 ideal (30 real) stages to achieve 90% CO2 capture.
AMP requires a 10 absorber/stripper train to achieve 90% CO2 capture with
reasonable absorber/stripper sizes.
Increasing the stripper pressure from 1.5 atm to 3 atm results in a 40%
decrease in the energy consumption of CO2 capture (separation +
compression) on an average. Compression duty reduces by 25% on an
average.
Based on these considerations, DGA is the absorbent of choice across all
stripper pressures. It has a high reaction rate, it can be used in
concentrations up to 60-70% and is non-volatile.
Acknowledgements
• Prof. George Hirasaki Prof. Mike Wong and Prof. Ken
Cox.
• Dr. Brad Atkinson and Dr. Peter Krouskop from Bryan
Research and Engineering
• Loewenstern Graduate Fellowship
• Energy and Environmental Systems Institute (EESI) at
Rice University
• Rice Consortium on Processes in Porous Media
• Schlumberger
• Office of Dean of Engineering, Rice University
• Hirasaki Group & Wong Group members
References
1. ProMax Foundations, Bryan Research and Engineering.
2. Vaidya, CO2-Alkanolamine Reaction Kinetics: A review of recent studies,
Chem. Eng. Technol (2007), 30, No 11, 1467-1474.
3. Alper, Kinetics of Reactions of Carbon Dioxide with Diglycolamine and
Morpholine, Chem. Eng. J, (1990), 44, 107-111.
4. http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_017d/0901b8
038017d302.pdf?filepath=amines/pdfs/noreg/11101375.pdf&fromPage=GetDoc
5. http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_004e/0901b8
038004e5da.pdf?filepath=angus/pdfs/noreg/31900016.pdf&fromPage=GetDoc
6. http://www.bre.com/portals/0/technicalarticles/Selecting%20Amines%20for
%20Sweetening%20Units.pdf
7. D. Aaron and C. Tsouris. Separation of CO2 from flue gas: a review.
Separation Science and Technology, 40(1):321, 2005.
Questions