carbon dioxide capture using dry regenerable sorbents · pdf filecarbon dioxide capture using...
TRANSCRIPT
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
-10
-8
-6
-4
-2
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.
4
Carbonate-Oxide Equilibrium
-3
-2
-1
0
1
2
3
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
5
Integration of the “Dry Carbonate” Process in a Combustion Facility
6
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.
7
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)
8
Concept Evaluation
0.6
0.7
0.8
0.9
1
1.1
0 500 1000 1500 2000 2500 3000
Time (min)
Wei
ght F
ract
ion
0
20
40
60
80
100
120
140
Tem
pera
ture
(°C
)
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
9
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
10
Fundamental Kinetic andThermodynamic Studies (Carbonation)
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
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)
11
Effect of Regeneration Temperature (in pure CO2 compared to He)
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Time (min)
Dim
ensi
onle
ss W
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
12
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.
13
Kinetic Modeling
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
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
14
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.
15
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
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
Time (minutes)
Car
bon
Dio
xide
Rem
oval
(%) Cycle 1
Cycle 2Cycle 3Cycle 4Cycle 5
16
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14Cycle Number
Perc
ent C
arbo
n D
ioxi
de R
emov
al
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.
17
Fluid-Bed Testing at RTI
18
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10Time (minutes)
Rem
oval
(%) Cycle 1
Cycle 2
Cycle 3
50
55
60
65
70
75
80
85
90
0 2 4 6 8 10Time (minutes)
Ave
rage
Tem
pera
ture
(°C
)Cycle 1
Cycle 2
Cycle 3
Carbonation in 7% Carbon Dioxide, 6% Water Vapor
Fluid-Bed Testing of 40% Supported Sodium Carbonate
19
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.
20
Commercial Embodiment –Conceptual Reactor System
21
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
22
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.
23
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
24
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
25
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
26
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
27
Screening Test Results
0
2
4
6
8
10
12
14
16
18
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
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
28
-10
-5
0
5
10
15
20
0 500 1000 1500 2000 2500 3000 3500
Time (min.)
Perc
ent W
eigh
t Gai
n
0
100
200
300
400
500
600
Tem
pera
ture
(ºC
)
from 0 to 2505 min. in 20%CO2 balance nitrogen
1 2
1) Clean/Dry Texaco Syngas (15% CO2)2) Clean/Wet Texaco Syngas (15 % CO2)3) Raw/Wet Texaco Syngas (12.5% CO2)
3
Multicycle Screening TestsSample 15
29
-6
-4
-2
0
2
4
6
8
10
12
0 50 100 150 200 250 300 350 400 450
Time (min)
Wei
ght F
ract
ion
0
100
200
300
400
500
600
Tem
pera
ture
(ºC
)
20 % carbon dioxideclean/drysyngas
clean/wet syngas
raw/wetsyngas
Multicycle Screening TestsSample 16
30
Effluent CO2 and Temperature Profiles
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16 18 20
Time (minutes)
CO
2 C
once
ntra
tion
(per
cent
)
960
980
1000
1020
1040
1060
1080
1100
1120
1140
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%
31
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
32
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.