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11
CO2
Capture From Air
David Keith
keith@ucalgary.ca
• www.ucalgary.ca/~keithDirector, Energy and Environmental Systems Group
Institute for Sustainable Energy, Environment and Economy
University of Calgary
MIT Carbon Sequestration Forum
16 September 2008
Cambridge MA
2
Thermodynamics of CO2
capture
Free energy of mixing:
To get 1 bar CO2
it takes:~ 5 kJ/mol starting at 14% CO2
in a power plant exhaust.~ 11 kJ/mol getting the last 10% of CO2
in a power plant exhaust.~ 20 kJ/mol starting at the 380 ppm
ambient atmospheric concentration
Compression from 1 to 100 bar ~13 kJ/mol
Carbon from fuels: Burning C & CH4
produces
394 & 890 kJ/mol‐C respectively.
Current amine technology: ~130 kJ/mol @ ~100 C (?)NaOH
thermodynamic limit: ~108 kJ/mol
At 400 ppm
& STP: 100 Pa= 5.6 kJ/mol= 13 m sec‐2
100 kJ/mol‐C = 2.27 GJ/t‐CO2
= 630 kWhr/t‐CO2
0ln pkT p⎛ ⎞⎜ ⎟⎝ ⎠
3
…but thermodynamics is irrelevant
Excerpt from response to reviews ofKeith, D. W., Ha‐Duong, M., & Stolaroff, J. K. (2006) Climate strategy with CO2
capture from the air Climatic Change
74:
17‐45.
4
50
40
30
20
10
Mt CO2
/yr
150 1000 2000 104 105
Source: Kurt Zenz House, Alliance Bernstein
Number of Point Sources
150 largest coal power plants emit ~10% of global CO2
The next 1000 largest point sources account for the next ~30%
The next 7000 account for the next ~ 15%
Distributed and mobile sources account for nearly half
of all emissions.
Air capture centralized control of diffuse emissions
5
Building air capture on conventional process technologies
66
AC Research at U‐Calgary and CMU 2002‐2008
2002‐2005: Technology assessment, negative emissions & optimal climate policy.
2003 (May): CMU‐LLNL‐Columbia meeting
2005: Spray tower experiment at UofC. Early cost estimation for Ca Cycle.
2007: Banff meeting
2007: Work on alternative methods of caustic recovery (B & Ti, Mg).
2007: Analysis of advanced spray systems. Costing. Coalescence modeling.
Charged particles.
2007‐08 (winter): Titanate conceptual process design (Provisional patent filed).
2008 (spring & summer): Experiments on simultaneous leaching & precipitation.
2008 (Feb‐July): Packed tower design and experiments.
2008 (September): First‐order process simulation model converged.
7
Contacting
8
A
A
2005 spray tower
9
But, this was with ~100 µm dropsand we now know we can make ~20 µm dropsat low capital and energy cost.
10
2008 packed tower
11
1212
Circuit Board
Electronics
Electrical
Fluid
Connections
RH and
Temperature
CO2 analyzer
intake
CO2 analyzer
Digital Sensors Analog Sensors
Differential
Pressure
Air Velocity
Liquid Flowrate
Liquid Pressure
Liquid Sample
Tall stack Short stack
Dimensions
Height 6m 4.8m
Diameter 1.2 m
Inlet 0.6 m
Packing Height 2.6 m 1.5 m
Operating Volume 350 – 450 L
Fluid Flow Range 1.9 ‐
6.3 L/s
Air Flow Range 0.5 – 3 m/s
Packing Sulzer 250X
1313
Intermittent operation
Steadystate
Cyclicoperation
15%
We get ~86% of peak performance with ~5% fluid pump duty cycle
14Time [s]
Time [s]
Intermittent operation 2: KOH and cyclic
1515
2008 packed tower results
At 1.25 m/sec
•
ΔP across full tower: 67 Pa•
ΔP packing 39 Pa•
Fan efficiency (shaft to air) 41% (It is ~70% at design point)
Typical CO2
concentrations: 375 ppm
at inlet 150 ppm
at outlet.
Typical fluid flow rate: 5 L/s
Longest continuous operating period ~8 hr.
Capture rate: 15 t‐CO2/m2‐year
Cyclic operation essentially eliminates caustic pumping work.
ΔP=60 Pa, ΔCO2=175 ppm and 60% pump efficiency 81 kWhr/t‐CO2
16
Packed tower packed pancake
17
Contactor design constraints
Low air velocity & Low pressure drop minimize energy cost
Low cost materials & High capture rate minimize capital cost
In practice, must hold velocity under about 10 m/sec2
to keep PV work under
~30 kWhr/tCO2
counting fan efficiency.
Contamination insensitive surfaces
•
Silicate dust
•
Organics (e.g., soaponification
of mosquitoes)
•
Sulfur
18
Conceptual design:
Intermittently‐wetted cross‐flow slabReversible fans
•
Follow ambient wind
Packing with vertically oriented plates.
•
Orthogonal liquid and gas flows
•
Optimized for intermitted liquid flow
•
Maximize hold up.
Sectionalized
•
Air flow can be stopped when fluid is flowing to minimize loss.
•
Sections operate asynchronously so pumps can operate continuously.
Compared to the horizontal slab:
•
Minimizes footprint and total structure size per unit of capacity to
reduce capital cost.
•
Reduces peak velocity, improving efficiency.
•
Enables the packing to be operated at higher peak velocities further
reducing capital costs.
air gap
fan wall
Basin
packing& fluid distribution
>100 m
10‐20 m
prevailing wind
air flow ~2‐5 m/sec
19
20
Contactor costing
Economic assumptions Base Better WorseCCF 15% 15% 15%O&M 5% 5% 5%Electricity cost ($/MWhr) 80 60 110 Cost of low-C electricity. Likley integate with recovery.
Contactor assumptionskWhr/t-CO2 100 80 150 Compare to "cross-flow contactor assumptions' below
Overall costingCost of packing + distributor ($/m^2) 1000 500 2000 500X is $5k/m2 at 1.5 m in small lots.Cost of structure ($/m^2) 500 300 1000 From Nexen and PCL for the spray structure scaled by 1:1 height:width ratioCost of pumps ($/m^2) 4 4 7 300 $/kW fluid pump costCost of fans ($/m^2) 206 165 309 500 $/kW blower cost (Kenton's correlation to listed costs Sept '08)Total ($/m^2) 1710 968 3316
Annual (tCO2/yr) 24 24 24
Capital cost ($/tCO2) 14.1 8.0 27.3Energy cost ($/tCO2) 8.0 4.8 16.5Total cost ($/tCO2) 22.1 12.8 43.8
Cross-flow contactor assumptionsCapture rate 200 ppm Our tests were 150-250 rangeAir velocity 2 m/sectCO2/m^2-yr 24Delta-P 75 Pa Our tests ~50 Pa at 1 m/sec. Will change with new design.Flow rate 0.4 mm/sec Cyclic operation at a 10% duty cycleFan eff 65%Pump eff 75%Fan power (W/m^2) 231 PV/fan-eff per unit of contactor slabPump power (W/m^2) 8 mgh/pump-eff assuming 1.5 head/height-ratiokWhr/t-CO2 86
21
Caustic recovery
22
ΔH = 65/90 kJ/mol‐C depending if you are below/above the Na2CO3 melting point, net about 90 kJ/mol‐C in either case.
Literature talks about solid‐solid reactions, but we think its solid TiO2 with carbonate melt.
Above 840°C, the conversion rate reported to be 100%.
Molar ratio (TiO2/Na2O) should be high enough (above 0.5) to prevent alkali in gas stream
Chemical Recovery: The titanate cycle
2 2 2 22(s) 3(s) (s) 2(g)5Na O 3TiO +7 Na CO 3(4Na O 5TiO ) +7CO→i i
s aq s2 2 2 2 23(4Na O 5TiO ) +7H O 14NaOH +5(Na O 3TiO )→i i
22
About 15.2 kJ/mol‐C at ~100 C.
Can produce NaOH concentrations > 4 M
23
Solubility of Na2
CO3
in water and NaOH(aq)
23
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50 60 70 80 90 100 110 120
Na2CO
3, mol/L
Temperature, °C
water
NaOH 1.5M
NaOH 3M
NaOH 5M
Na2
CO3
.10H2
O Na2
CO3
.7H2
O Na2
CO3
.H2
O Na2
CO3
Solubility swing anhydrous
Temp swing deca
24
Process design overview
Solubility swing anhydrousTemp swing deca
25
Simultaneous leaching and precipitation
25
Can we leach 4Na2
O•5TiO2
to make NaOH
& Na2
O•3 TiO2
while simultaneously
driving the Na2
CO3
out of solution?
There are other routes to isolating anhydrous Na2
CO3
, but simultaneous leaching
and precipitation greatly simplifies our process design.
26
Process model (1‐3)
VMG process simulator (www.virtualmaterials.com)
•
Custom titanate thermodynamics.
•
Custom Na2CO3 solubility model.
27
Process model (4‐5)
2828
29
Ti process enthalpy and exergy
summary
30
Economics
With 75% HX efficiency Ti process requires ~3 GJ/t‐CO2
@ 850 C •
50 to 75 C cooler than Ca process (a big deal for steel performance).•
~50% less thermal energy that the Ca process.•
Enthalpy requirements near the thermodynamic limit for NaOH.
At just under 100 kWhr/t‐CO2
the energy cost for contactor is similar to energy
cost for CO2
compression from 1 to 15 MPa.
Even with gas at 10 $/GJ the energy cost for the full process of
order 50 $/t‐CO2
.
Turning CaCO3
to
CaO
is a similar process to 5Ti 3Ti, except it uses half as much energy per mol carbon.Market prices of lime and limestone cost of calcination now1 ~65 $/t‐CO2.If energy was 50% of current prices (a guess) Ti should be ~ 50 $/t‐CO2.
Capital cost will be the driver.
1. 2004 prices.
31
Where next?
32
Next steps
1.
Refine and exercise process model.
2.
5Ti 3Ti kinetics as a function of T, pCO2 and particle size.
3.
Crystalactor
design and kinetics for Na2
CO3
• 10 H2
O.
4.
Continued testing of simultaneous leaching and crystallization.
5.
Contactor design study
•
CFD study of interaction with external winds.
•
Packing optimization study.
•
First‐order design and costing of a 1 Mt‐CO2
/yr unit.
6.
Kiln scoping study
•
Kiln designs for indirect heating with 0.1 mm particles.
•
Fueling options: NG, oxyfuel, coal indirect, nuclear.
7.
Contaminant chemistry.
8.
Titanate loss mechanisms and particle reactivity control
33
Air Capture: Implications for long‐term climate policy
Air capture can fundamentally alter the dynamics of climate mitigation:
its price caps the cost of mitigation across the economy.
It allows the removal of CO2
after emission
Permits reduction in concentrations more quickly than can be achieved by the natural carbon cycle. Net emissions can be negative.
It removes one of the central irreversibility's of the CO2‐climate problem. Leakage from reservoirs becomes simply a future cost.
It is (somewhat) decoupled from the rest of the energy system
returns‐to‐scale may be better than for conventional mitigation.
Keith, D. W., M. Ha‐Duong, J. K. Stolaroff
(2006). "Climate strategy with CO2 capture from the air.“
Climatic Change
74: 17‐45.
34
Concentrations
300
350
400
450
500
550
600
650
700
2000 2050 2100 2150 2200 2250
ppm
v C
O2
Year
Unlucky
Lucky
Reference
Air cap
Air cap
Keith, D. W., M. Ha‐Duong, J. K. Stolaroff
(2006). "Climate strategy with CO2 capture from the air.“
Climatic Change
74: 17‐45.
35
Carbon neutral hydrocarbons
Zeman, F. S. and D. W. Keith (2008) "Carbon Neutral Hydrocarbons." Philosophical Transactions of the Royal Society (A).
36
CNHC’s
VS Hydrogen
Zeman, F. S. and D. W. Keith (2008) "Carbon Neutral Hydrocarbons." Philosophical Transactions of the Royal Society (A).
37
People
Josh Stolaroff
(CMU): Spray tower, engineering, economics and management.Greg Lowry (CMU): Spray tower, engineering, economics and management.Kenton Heidel: 2005 & 2008 tower & process engineering.Leif Prebeau‐Menezes: 2005 tower.Brian Cox: Spray technology & Spray chargingMaryam Mahmoudkhani: Caustic recovery chemical engineering.Robert Cherry (INL): Process design, management and guidance.Frank Zeman (Columbia): Hot slaking, process design and economics.Baciocchi Renato (University of Rome, ETH): 2008 tower process design. Alessandro Biglioli: 2008 tower project management. Mike Foniok: 2008 tower.Brandon Hart: 2008 tower.Christelle Guillermier: 2008 towerCarolyn Ladd: Crystallization and leaching laboratory chemistry.Curtis Berlinguette: Crystallization and leaching laboratory chemistryMarco Satyro: UofC
& VMG, process simulation)Julian Ferreira: Process simulation
38
Air Capture Papers
Mahamoudkhani, M. and D. W. Keith (submitted) "Low‐energy sodium hydroxide
recovery for CO2
capture from air." International Journal of Greenhouse Gas
Control Technologies.
Zeman, F. S. and D. W. Keith (2008) "Carbon Neutral Hydrocarbons."
Philosophical Transactions of the Royal Society (A).
Stolaroff, J. K., D. W. Keith, et al. (2008). "Carbon dioxide capture from
atmospheric air using sodium hydroxide spray." Environmental Science &
Technology 42: 2728‐2735.
Keith, D. W., M. Ha‐Duong, J. K. Stolaroff
(2006). "Climate strategy with CO2
capture from the air." Climatic Change
74: 17‐45.
Stolaroff, J., D. Keith, et al. (2006). A pilot‐scale prototype contactor for CO2
capture from ambient air: cost and energy requirements. GHGT‐8, 8th
International Conference on Greenhouse gas Control Technologies
Trondheim, Norway.
Stolaroff, J. K., G. V. Lowry, D.W. Keith. (2005). "Using CaO‐
and MgO‐rich
Industrial Waste Streams for Carbon Sequestration." Energy Conversion and
Management
46: 687‐699.
3939
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