Evaluation of performance of various alkanolamines for CO 2 capture from a pulverized coal-fired power plant Sumedh Warudkar PhD Candidate Chemical and Biomolecular Engineering

Outline The CO 2 problem Current CO 2 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 CO 2 problem Fig 1. Worldwide energy consumption in TW (2004) Fig 2. Atmospheric CO 2 variation ( )

Current CO 2 Capture Technology Figure 2.a. Membrane Separation Figure 2.b. Gas Adsorption Figure 2.c. Gas Absorption

Scope of Study With available technology, CCS will increase the cost of electricity from a conventional power plant by 21% - 91%. 7 Current technology for CO 2 separation was designed primarily for natural gas sweetening – high pressure feed gas, large variance in acid gas (CO 2, H 2 S) content and generates value added product. Problem at hand involves power plant flue gas – near atmospheric, low variance in CO 2 content and will be a parasitic load for electricity generation utilities. Due to the low variance in flue gas composition, it might be possible to come up with a generic “best” absorbent for CO 2 capture. Need to better optimize current technology by changing process parameters.

Amine Absorption Flow-sheet

CO 2 compression train

Simulation Parameters Composition of coal-fired power plant flue gas [1] ParameterValue Volumetric Flow-rate1100 MMSCFD Water (mole %)11.8 CO 2 (mole %)12.79 Oxygen (mole %)5.6 Nitrogen (mole %)69.8 Sulfur Dioxide (mole %)0.01 Simulation Parameters ParameterValue Absorber – flooding fraction 80% Absorber tray spacing2 feet Absorber heir weight3 inches Stripper – flooding fraction 80% Stripper – tray spacing2 feet Stripper – weir height3 inches Condenser temperature 30 o C Absorber/Stripper Specifications ParameterMEADGADEAAMP Absorber - # of Trays2210 Stripper - # of Trays10

Amine Absorbents Comparison Monoethanolamine (MEA) Advantage Primary amine with very high reaction rate with CO 2 Low amine circulation rate Low molecular weight Drawbacks High heat of reaction MEA concentrations above 30-35% (wt) are corrosive Highly corrosive at CO 2 loadings above Highly volatile Diglycolamine (DGA) Advantage High DGA concentrations around 50-70% (wt) can be used due to low volatility High reaction rate with CO 2 Low amine circulation rate Drawbacks High heat of reaction Highly corrosive at CO 2 loadings above Diethanolamine (DEA) Advantage Low volatility 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 CO 2 loadings above Reacts irreversibly with O 2 in flue gas. 2-amino-2-methyl-1-propanol (AMP) Advantage High theoretical CO2 loading capacity Low volatility and few corrosion problems Low heat of reaction 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 CO 2 capture Effect of Amine Absorber Entry Temperature (MEA & DEA 40% wt)

Energy Required for CO 2 capture Comparison of Effect of Stripper Pressure on MEA & DGA

Energy Required for CO 2 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

CO 2 loading of Rich Amine Loading Comparison of DEA-AMP

Energy Consumption Contribution of various processes and utilities

CO 2 Compression Effect of stripper pressure on specific volume of compressed vapor and energy consumption

Conclusions 4 amines – MEA, DEA, DGA and AMP were compared to evaluate their performance for CO 2 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%+ CO 2 capture. DEA requires 10 ideal (30 real) stages to achieve 90% CO 2 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 CO 2 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, CO 2 -Alkanolamine Reaction Kinetics: A review of recent studies, Chem. Eng. Technol (2007), 30, No 11, Alper, Kinetics of Reactions of Carbon Dioxide with Diglycolamine and Morpholine, Chem. Eng. J, (1990), 44, d302.pdf?filepath=amines/pdfs/noreg/ pdf&fromPage=GetDoc e5da.pdf?filepath=angus/pdfs/noreg/ pdf&fromPage=GetDoc 6. %20Sweetening%20Units.pdf 7.D. Aaron and C. Tsouris. Separation of CO 2 from flue gas: a review. Separation Science and Technology, 40(1):321, 2005.

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