Carbon Dioxide Capture Using Dry Regenerable Sorbents

Presentation at GCEP Energy WorkshopCarbon Capture and Sequestration

Stanford UniversityBy

Raghubir Gupta

April 27, 2004

Research Triangle Park, North Carolina

2

Sorbent / Process Development at RTI

� Develop sorbents that have desired properties for various CO2-containing process streams:– Flue gas at low temperatures from fossil fuel combustion.– Flue gas at elevated temperatures from fossil fuel combustion.– Syngas (from carbonaceous fuel gasification) at moderate and

elevated temperatures and high pressures.

� Develop a simple, inexpensive process to separate CO2 as an essentially pure stream using a reversible reaction and dry chemical sorbents.

3

Carbonate-Bicarbonate Equilibrium

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0

2

4

6

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00(Absolute Temp., K)-1 x 103

Log[

P CO

2*P H

2O, a

tm2 ]

Na2CO3 + CO2(g) + H2O(g) = 2NaHCO3

K2CO3 + CO2(g) + H2O(g) = 2KHCO3

727 394 227 127 60 131727

Temperature, °C

PCO2 = 0.5 atmPH2O = 0.5 atm

PCO2 = 0.08 atmPH2O = 0.16 atm

Flue gas & Regen gas composition range.

Flue gas & Regen gas temperature range.

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Carbonate-Oxide Equilibrium

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0

1

2

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0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00(Absolute Temp., K)-1 x 103

Log[

P CO

2, at

m]

Li2O + CO2(g) = Li2CO3

CaO + CO2(g) = CaCO3

MgO + CO2(g) = MgCO3

727 394 227 1271727Temperature, °C

1470

0.15

14.7

1.47

147

PCO2,psia

60 13

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Integration of the “Dry Carbonate” Process in a Combustion Facility

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Key Aspects of Flue Gas Project

� Utilize the known CO2 removal potential of alkali carbonate materials.

� Overcome known reaction rate limitations with the use of a commercial fast fluidized-bed reactor (“entrained-bed” reactor).– Fast initial kinetics– Improved heat transfer

� Leverage RTI’s expertise in fluidized-bed sorbents to develop chemically reactive and attrition-resistant sorbent for CO2 removal.

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Reaction Chemistry� CO2 absorption (carbonation):

� Sorbent regeneration (decarbonation):

� Wegscheider’s Salt:

� Effect of HCl and SO2:

� No Effect of O2 and NOx

2NaHCO3(s) ↔ Na2CO3(s) + CO2(g) + H2O(g)

Na2CO3 (s) + CO2(g) + H2O(g) ↔ 2NaHCO3(s)

Na2CO3 (s) + 2HCl(g) → 2NaCl (s) + CO2 (g) + H2O (g) Na2CO3 (s) + SO2 (g) + ½O2 (g) → Na2SO4 (s) + CO2 (g)

5/3 Na2CO3 (s) + CO2(g) + H2O(g) ↔ 2/3 Na2CO3·3NaHCO3(s)

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Concept Evaluation

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Time (min)

Wei

ght F

ract

ion

0

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120

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Tem

pera

ture

(°C

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Temperature

Mass

Calcination/Regeneration:130 °C in HeCarbonation:11% CO27% H2O74%N27% O2

(Sodium Bicarbonate Sorbent – “Baking Soda”)

Inexpensive CO2sorbent identified

Sorbent is readily regenerated

Low temperature process

Convenient for flue gas treatment

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Material Testing/Material Development

� Pure chemicals– Sodium bicarbonate (SBC) – NaHCO3– Trona – Na2CO3•NaHCO3•2H2O– Potassium Carbonate – K2CO3– Soda Ash – dense ash, natural light low density

� “Supported” sorbent development– Carbonate compounds on inert, attrition-resistant metal oxide

support

� Advantages of supported sorbents– High surface area (10-200 m2/g)– High porosity and pore volume– Good attrition resistance– Thermally and chemically stable substrates

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Fundamental Kinetic andThermodynamic Studies (Carbonation)

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0 50 100 150 200 250 300 350 400

Time(min)

Dim

ensi

onle

ss W

eigh

t 60°C

70°C

80°C

8%CO2

16%H2O76%He

Na2CO3·3NaHCO3

NaHCO3

� First order reaction kinetics– CO2

– H2O

� Temperature sensitive kinetics: rate decrease with increased T suggests equilibrium hindrance.

� Sorbent operating temperature ranges

– Sodium carbonate (60 to 80°C)

– Potassium carbonate (60 to 120°C)

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Effect of Regeneration Temperature (in pure CO2 compared to He)

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Time (min)

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eigh

t

Calcination @170 o C# 80(CO 2 )

Calcination @150 o C# 81(CO 2 )

Calcination in 200 sccm pure CO2Base case: 414sccm He @120 oCCarbonation: 70 oCCO2 8% H2O 16%Balance He600 sccm

Calcination @200 o C# 84(CO 2 )

Calcination @120 o C# 85 (CO 2 )

Calcination @120 o C# 86 (He)

SBC#3

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Engineering Challenges

� Absorption of CO2 is highly exothermic∆H298 = -32.1 kcal/gmol CO2 (1314 Btu/lb)

� Absorption of CO2 is less favorable with increase in temperature.

� Large negative ∆H implies excellent heat removal required to prevent reaction from becoming self-extinguishing.

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Kinetic Modeling

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2.65 2.7 2.75 2.8 2.85 2.9 2.95 3 3.05

(Absolute Temp., K)-1 x 103

Ln[P

CO

2PH

2O, a

tm2 ]

PCO2 = 0.08 atmPH2O = 0.16 atm

Teq = 84.4°C

Na2CO3·3NaHCO3

Na2CO3

90 84 78 72 66 6097

Temperature, °C

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Conclusions from Kinetic Modeling Work� Initial reaction kinetics (relative to unconverted carbonate) appeared to be

first order.

� A “shrinking core” heat transfer model of the sorbent on the TGA pan was also consistent with the observed reaction rate.

� Heat transfer calculations based on bench-scale fluid-bed data showed that temperature difference between the gas and the solid is the driving force.

� The inferred heat transfer coefficient was applied to a conventional “shrinking core” model for a spherical particle (i.e., a sorbent particle in a dilute-phase entrained-bed reactor).

� Shrinking core model extrapolated to small particles and moderate solid loadings in transport gas suggests that:

– Substantial Na2CO3 conversion and CO2 removal is possible in moderate residence times with effective heat removal from reactor.

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Fixed-Bed Testing at LSU

N2

O2

CO2

Syringe Pump (H2O)

Vent

BPR : BackPressureRegulator

COND : CondenserCV : Check valveD : DryerF : FilterMFC : Mass Flow ControllerPI : Pressure

IndicatorPRV : Pressure

Relief valve

Furnace

BPR

To GCCOND

PRV MFC

CV F

D

MFC

CV F

D

D

MFC

CV FPI

PI

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0 50 100 150 200 250 300 350

Time (minutes)

Car

bon

Dio

xide

Rem

oval

(%) Cycle 1

Cycle 2Cycle 3Cycle 4Cycle 5

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arbo

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emov

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Calcination in CO2 at 160oC

Calcination in CO2 at 200oC

15-Cycle Fixed-Bed Testing at LSU

� High degree (>90%) of sorbent utilization is possible.

� Apparent improvement in reaction rate after 2nd regeneration.

� >90% CO2 removal from flue gas demonstrated.

� Rapid regeneration rate.

� No deactivation for 15 cycles.

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Fluid-Bed Testing at RTI

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(%) Cycle 1

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Carbonation in 7% Carbon Dioxide, 6% Water Vapor

Fluid-Bed Testing of 40% Supported Sodium Carbonate

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Highlights of Fluid-Bed Studies

� Very rapid initial carbonation rates.

� Rapid increase in bed temperature.

� Little or no decline in carbonation activity over 5 cycles in numerous multicycle tests.

� HCl and SO2 are irreversibly absorbed.

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Commercial Embodiment –Conceptual Reactor System

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Heat Duties – Comparative Flue Gas Processes

� Case 7A in EPRI, Evaluation of Innovative Fossil Fuel Power Plants with CO2 Removal, 2000.– Btu steam per pound of CO2: 1617.

� Case 7A recalculated using heat duties documented in AlstomPower, Engineering Feasibility and Economics of CO2 Capture on an Existing Coal-Fired Power Plant, 2002.– Btu steam per pound of CO2: 2350.

� Comparison: heat energy of bicarbonate regeneration to Wegscheider’s Salt.– Btu per pound of CO2: 1315

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RTI-5 Material: Scale-up at Süd-Chemie� Drum quantities have been

produced by commercial spray drying.

� Formulations and “recipes” developed at RTI, using lab-scale spray dryer.

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Ongoing Work– Flue Gas Process

� Process Modeling

� Exploration of innovative regeneration concepts to re-use heat of absorption

� Sorbent optimization

� Bench-scale/Pilot-scale entrained-bed reactor testing

� Slipstream field test

� Technical/Economic Assessment

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CO2 Separation from Syngas

Commercially Practiced Process

HotClean Syngas

Cold Hydrogen Rich Syngas

High Temperature Shift

Low Temperature Shift

CO2 Removal

CO2 Removal

Hot Raw Syngas

Hot Hydrogen Rich Syngas

Sour Gas Shift

Potential Elevated Temperature Process

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CO2 Separation from Syngas at Elevated Temperature

� Benefits– High CO2 concentration, smaller treatment volume at high pressure– High thermal efficiency of IGCC– Simpler process integration– Higher quality sequestration-ready stream

� Challenges– Complete CO conversion– Low sulfur tolerance of catalysts

• Equilibrium limited

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Research Objectives� Identify promising candidates for regenerable CO2 sorbent

– CO2 removal• Remove CO2 from synthesis gas• Temperatures 400ºF to 1000ºF

– CO2 release• Generate essentially pure, high-pressure CO2 product ready for

sequestration• CO2 release by temperature swing, inert purge, or pressure swing

� Possible candidates:– Magnesium Oxide– Calcium Oxide– Lithium Aluminate– Lithium Ferrite– Lithium Titanate

� Especially promising:– Lithium Zirconate– Lithium Silicate– Lithium Silicate – w/

Eutectic salt additions

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Screening Test Results

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Samples

% W

eigh

t Gai

n du

ring

CO

2 Exp

osur

e– Variables:

• Composition• Preparation (Dry mixing, coprecipitation,

calcination)• Promoters (Alkali carbonates, Li, Na, and

K)• Temperature (CO2 removal and CO2

release)• Test gas composition

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Time (min.)

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eigh

t Gai

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Tem

pera

ture

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from 0 to 2505 min. in 20%CO2 balance nitrogen

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1) Clean/Dry Texaco Syngas (15% CO2)2) Clean/Wet Texaco Syngas (15 % CO2)3) Raw/Wet Texaco Syngas (12.5% CO2)

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Multicycle Screening TestsSample 15

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20 % carbon dioxideclean/drysyngas

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Multicycle Screening TestsSample 16

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Effluent CO2 and Temperature Profiles

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2 C

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cent

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Temperature (ºF)

Gas Composition (vol%) CO 35.8 H2 26.8 H2O 18.1 H2S 0.5 N2 Bal

CO2 12.2 vol% CO2 1.8 vol%

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Accomplishments� Demonstrated:

– Sorbent CO2 loadings between 4 and 17 wt%

– Effective regeneration with temperature swings and inert purging

– CO2 removal actually improves in the presence of raw synthesis gas

� Initiated bench scale testing of sorbent formulations

� Sorbent development– Composition– Spray dried production– Highly active – Attrition resistant– Shift activity

� Bench scale testing– Regeneration modes– Multicycle testing

� Process development– Reactor design– Heat integration– Process integration– Economic evaluation

Research Priorities

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Acknowledgements

� U.S. DOE/NETL Support– Cooperative Agreement No. DE-FC26-00NT40923– DOE/NETL COR: Jose Figueroa– Sequestration Product Manager: Scott M. Klara

� Project Partners (Flue Gas)– Louisiana State University– Church & Dwight, Inc.