Co 2 capture by aqueous absorption stripping
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CO 2 Capture by Aqueous 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 [email protected] Outline. Absorption/Stripping: THE technology

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CO 2 Capture by Aqueous Absorption/Stripping

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Co 2 capture by aqueous absorption stripping

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

[email protected]


Outline

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


Capture by aqueous absorption the critical technology

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


Txu an extreme example

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


Absorption stripping the technology

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


System for co 2 sequestration

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


Co 2 capture by aqueous absorption stripping

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


Aqueous abs str near commercial

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


Tail end technology ideal for development demonstration deployment

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


Other solutions for existing coal plants

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


Practical problems

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


Analogy to caco 3 slurry scrubbing

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


Aqueous solvent alternatives mea is hard to beat

Aqueous Solvent AlternativesMEA is hard to beat

  • Stripper Energy Requirement

  • Mass Transfer Rates

  • Makeup and Corrosion


Carbonate tertiary hindered amines

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(?))


Primary and secondary amines 60 85 kj gmol fast

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)


Components of stripper heat duty mol stm mol co 2

Components of Stripper Heat Duty (mol stm/mol CO2)

Srxn = HCO2/HH2O


Total equivalent work

Total Equivalent Work

W = Weq + Wcomp

Wcomp= RT ln (100 atm/(PCO2+PH2O)


Mass transfer with fast reaction co 2 2mea meacoo meah

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


Mass transfer with fast reaction

Mass Transfer with Fast Reaction


Co 2 capture by aqueous absorption stripping

Mass Transfer with Reaction in Wetted Wall Column


Reagent energy properties

Reagent Energy Properties


Mea makeup corrosion

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


Reagent properties affecting makeup

Reagent Properties Affecting Makeup


Flowsheet enhancements

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


Needs for capture deployment

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


Opportunities for capture r d

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


Deployment schedule

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


Conclusions

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


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