CO 2 Capture by Aqueous Absorption/Stripping

1. CO2 Capture byAqueous Absorption/Stripping Presented at MIT Carbon Sequestration Forum VII By Gary T. Rochelle Department of Chemical Engineering The University of Texas at Austin October 31, 2006 rochelle@che.utexas.edu

2. Outline • Absorption/Stripping: THE technology • MEA: not a bad solvent alternative • Stripper Energy favored by greater DHabs • Mass Transfer Requires Fast Kinetics • MEA Makeup and Corrosion Manageable • Optimized systems approach 1.5 x ideal W • Critical Opportunities & Needs for R, D, D, & D • Now the time to plan Demo and Deployment

3. Capture by Aqueous AbsorptionThe Critical Technology • For Coal Combustion • in “existing” power plants • that are an important, growing source of CO2. • Aqueous Absorption/Stripping is preferred • because it is tail-end technology

5. TXU: an extreme example • Current TXU CO2 emissions • 60 MM ton/y from 16 plants • 11 x 800 MW fossil plants in the next 5 years • 100 million ton CO2/y • Good for Texas and TXU • Capacity for growth • Replace expensive gas-fired capacity • TXU capital from deregulation • Inconceivable in the next 5 years • IGCC, Oxycombustion • CO2 Capture by absorption/stripping • The prime market for retrofit CO2 capture

6. Absorption/stripping = The technology • Near Commercial • Tail End Technology for Existing Plants • Oxycombustion and gasification are not. • Expensive in $$ and energy • By analogy to limestone slurry scrubbing • Expect significant evolutionary improvements • Do not expect major cost & energy reductions • Do not waste resources on step change R&D

7. 150 atm CO 2 Disposal Well System for CO2Sequestration 10 atm stm Net Power 3 atm stm CaCO 3 Turbines Coal Boiler ESP FGD Abs/Str CaSO Flyash 4

8. MEA Absorption/Simple Stripping Steam 3 atm CO2 DT=5oC H2O Rich Lean Absorb Strip 40°C 117°C 1 atm 2 atm 12% CO2 5% O2 7% H2O 40oC Purge to 30% MEA (Monoethanolamine) Reclaim SO2, HCl, NO

9. Aqueous Abs/Str: Near commercial • 100’s of plants for treating H2 & natural gas • MEA and other amine solvents • No oxygen • 10’s of plants with combustion of natural gas • Variable oxygen, little SO2 • Fluor, 30% MEA, 80 MW gas, 15% O2 • MHI, KS-1, 30 MW, <2% O2 • A few plants with coal combustion • Abb-Lummus, 20% MEA, 40 MW • Fluor, 30% MEA, 3 small pilots • CASTOR, 30% MEA, 2.5 MW pilot • MHI, KS-1, <1 MW pilot

10. Tail End Technology Ideal for Development, Demonstration, & Deployment • Low risk • Independent, separable, add-on systems • Allows reliable operation of the existing plant • Failures impact only Capture and Sequestration • Low cost & less calendar time • Develop and demonstrate with add-on systems • Not integrated power systems as with IGCC • Reduced capital cost and time • Resolve problems in small pilots with real gas • Demo Full-scale absorbers with 100 MW gas • Ultimately 500 MW absorbers

11. Other Solutions for Existing Coal Plants • Oxy-Combustion • O2 plant gives equivalent energy consumption • Gas recycle, boiler modification for high CO2 • Gas cleanup, compression including air leaks • Coal Gasification • Remove CO2 and burn H2 in existing boiler • O2 plant, complex gasifier, cleanup, CO2 removal • H2 more valuable in new combined cycle • Neither is Tail end • Require higher development cost, time, and risk

12. Practical Problems • Energy = 25-35% of power plant output • 22.5%, Low P stm, 30-50% of stm flow • 7%, CO2 Compression • 3.5%, Gas pressure drop • $42/tonne CO2 (0.7 MWh/CO2 x $60/MWhr) • Capital Cost $500/kw • Absorbers same diameter as FGD, 50 ft packing • Strippers somewhat smaller • Compressors • $20/tonne CO2 for capital charges & maint • Amine degradation/environmental impact • $1-5/tonne CO2

13. Analogy to CaCO3 slurry scrubbing • 1970 “Commercial” starting point • Only process “immediately” available • “Inappropriate” for government support • Starting point was “too expensive” • Environmentally messy, solid waste unattractive • Initial applications even more expensive • Cost decreased with experience • Alternative developments heavily funded • Regenerable FGD processes – too complex • Coal gasif/combined cycle – not tail end • Fluidized bed combustion – not tail end • 2006 Commercial Generic Process

14. Aqueous Solvent AlternativesMEA is hard to beat • Stripper Energy Requirement • Mass Transfer Rates • Makeup and Corrosion

15. Carbonate & Tertiary/Hindered Amines CO3= + CO2 + H2O↔ 2 HCO-3 20 kJ/gmol Carbonate Bicarbonatevery slow HO-CH2-CH2-N-CH2-CH2-OH ↔ MDEAH+ + HCO-3 ׀ CH3 60 kJ/gmol, slow Methyldiethanolamine (MDEA) CH3 ׀׀ HO-CH2-CH2-NH2 + CO2 ↔ AMPH+ + HCO-3 ׀ CH3 60 kJ/gmol, slow 2-Aminomethylpropanolamine (AMP, KS-1(?))

16. CH2-CH2 HNNH CH2-CH2 Primary and Secondary Amines60-85 kJ/gmol, fast 2 HO-CH2-CH2-NH2 + CO2 ↔ HO-CH2-CH2-NH-COO- + MEAH+ Monoethanolamine (MEA) MEA Carbamate (MEACOO-) 2 NH3 + CO2 ↔ NH2-COO- + NH4+ Ammonia + CO2 ↔ +HPZ-COO- Piperazine (PZ)

17. Components of Stripper Heat Duty (mol stm/mol CO2) Srxn = HCO2/HH2O

18. Total Equivalent Work W = Weq + Wcomp Wcomp= RT ln (100 atm/(PCO2+PH2O)

20. Mass Transfer with Fast Reaction CO2 + 2MEA = MEACOO- + MEAH+ [MEACOO-]i [MEA]b PG [MEA]i [MEACOO-]b Pi=H[CO2]i P*i P*b [CO2]*i [CO2]b Rxn Film Gas Film Liquid Film

21. Mass Transfer with Fast Reaction

22. Mass Transfer with Reaction in Wetted Wall Column

23. Reagent Energy Properties

24. MEA Makeup & Corrosion • Degradation • MEA Oxidizes to NH3, aldehydes, etc • MEA Polymerizes at Stripper T • Optimize operating conditions, add inhibitors • Reclaim by evaporation to remove SO4=, NO3-, Cl-, etc. • Volatility • Use Absorber Wash Section • Corrosion • Minimize Degradation • Add Corrosion inhibitors such as Cu++ • Use Stainless Steel, FRP

25. Reagent Properties Affecting Makeup

26. Flowsheet Enhancements • Absorber • Direct Contact Cooling & Intercooling • To get lower T • Split feed – to enhance reversibility • Stripper • Minimum exchanger approach T • Internal Exchange • Multistage Flash, Multieffect Stripper • Multipressure, Matrix, • Vapor Recompression

29. Needs for Capture Deployment • Large Absorbers: different from FGD • Countercurrent Gas/liquid Distribution • 35 gal/mcf • Pressure drop • Capital cost of internals • Test and demonstrate at 100+MW • Steam integration • Control systems for load following • Test at 100+MW • Environmental impact & losses of solvent • Long term test at 1 MW

30. Opportunities for Capture R&D • Better Solvents • Faster CO2 Transfer: Blends with PZ, etc. • Greater Capacity – MEA/PZ, MDEA/PZ • Oxygen scavengers/Oxidation inhibitors • Better Processes • Matrix, split feed • Reclaiming by CaSO4/K2SO4 Precipitation • Better contacting • Packing to get G/L area

31. Deployment Schedule • 2007 - 0.5 MW pilot plant on real flue gas Demonstrate solvent stability & materials • 2008 - 5 MW integrated pilot plant Compressor/stripper concepts • 2010 – 100 MW Integrated module Energy integration and absorber design • 2012 – 800 MW full-scale on CaCO3 Energy, multitrain, operation • 2015 – Deployment on all plants

32. Conclusions • Absorption/stripping is THE technology for existing coal-fired power plants • Expect 15-30% reduction in cost and energy • The solvent should evolve from MEA • High DH, fast rate, high capacity, cheap reagent • Process & contactor enhancements expected • Now time to plan technology demonstrations