PRIMARY HEADING: ARIAL NARROW BOLD 22PT
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Transcript PRIMARY HEADING: ARIAL NARROW BOLD 22PT
Options for Capturing
Carbon Dioxide from the Air
Klaus S. Lackner
Columbia University
May, 2008
The Challenge:
Holding the Stock of CO2 constant
Extension of
Historic Growth
Rates
Constant emissions
at 2010 rate
560 ppm
33% of 2010 rate
10% of 2010 rate
0% of 2010 rate
280 ppm
Comparison With Keeling’s Data
Carbon as a Low-Cost Source of Energy
US1990$ per barrel of oil equivalent
Lifting Cost
Cumulative
Carbon
Consumption
as of1997
Cumulative Gt of Carbon Consumed
H.H. Rogner, 1997
A Triad of Large Scale Options
• Solar
– Cost reduction and mass-manufacture
• Nuclear
– Cost, waste, safety and security
• Fossil Energy
– Zero emission, carbon storage and
interconvertibility
Efficiency, conservation and alternative energy will help,
but not solve the problem
Net Zero Carbon Economy
• Closing the carbon cycle
CO2
extraction
from air
CO2 emissions
power
consumption
refining
energy
carrier
CO2 collection
FOSSIL FUEL CYCLE
fossil carbon
extraction
oxidized
carbon
disposal
CO2
handling
Net Zero Carbon Economy
CO2 from
concentrated
sources
CO2
extraction
from air
Permanent &
safe
disposal
Initially Air Capture is tied to Carbon Dioxide Storage
Schematic diagram of possible CCS systems
SRCCS Figure TS-1
Mg3Si2O5(OH)4 + 3CO2(g)
3MgCO3 + 2SiO2 +2H2O(l)
+63kJ/mol CO2
Air Capture
• Takes CO2 from the atmosphere to offset
CO2 emissions
• Can compensate for all and any emissions
• Aims at distributed, small and mobile
sources
• Preserves access to hydrocarbon fuels
The Substitution Principle
• All CO2 is equal
• Combustion and capture cancel out
– No need to co-locate
• Air is a perfect transport system
– Mixing times are fast, weeks to months
• Air is an excellent storage buffer
– Annual emissions are 1% of stored CO2
Air Capture: A Different Paradigm
• Leave existing infrastructure intact
• Retain quality transportation fuels
• Eliminate shipping of CO2
• Open remote sites for CO2 disposal
• Enable fuel recycling with low cost electricity
Separate sources from sinks in space and time
Air Capture
Is it Geo-Engineering?
• Con
– Air capture simply separates sources and sinks in space and time
– Air capture matches emissions one for one
– Air capture provides a source of CO2
• Pro
– Air capture makes it possible to control the CO2 level in the
atmosphere
Air capture directly counters an emission,
it does not fight one change with another
Natural Air Extraction
• Ocean Uptake
– 30% of anthropogenic CO2 emission
• Trees
– Biomass absorbs 100 GtC annually
– Capture cost ~ $27/ton of CO2
– Land demand too large
– Leaves are underutilized for CO2 extraction
Air Capture: Many Options
• Growing biomass
– Terrestrial biomass: Biofuels
• Carbon is delivered as bio-based fuel
• Combustion at a power plant with CCS leads to a net carbon
reduction
– Marine biomass: Ocean fertilization
• Carbon is never collected but some is removed from the
surface carbon cycle
• Raising the alkalinity of the ocean
– Adding base
• E.g. dissolving CaCO3 into the ocean
– Removing acid from ocean water
• Removing HCl via electro-dialysis and disposing of it through
neutralization
Air Capture: Collection & Regeneration
Synthetic Tree
Courtesy GRT
Challenge: CO2 in air is dilute
• Energetics limits options
– Work done on air must be small
• compared to heat content of carbon
• 10,000 J/m3 of air
• No heating, no compression, no cooling
• Low velocity 10m/s (60 J/m3)
Solution: Sorbents remove CO2
from air flow
CO2 Capture from Air
1 m3of Air
40 moles of gas, 1.16 kg
wind speed 6 m/s
mv 2
20 J
2
CO2
0.015 moles of CO2
produced by 10,000 J of
gasoline
Volumes are drawn to scale
How much wind?
(6m/sec)
0.2
m2
for CO2
Wind area that
carries 22 tons
of CO2 per year
50 cents/ton of CO2
for contacting
Wind area that
carries 10 kW
of wind power
80 m 2
for Wind Energy
Ca(OH)2 as an absorbent
Air Flow
CO2 diffusion
Ca(OH)2 solution
CaCO3 precipitate
CO2 mass transfer is limited by diffusion in air boundary layer
A First Attempt
Ion exchanger:
Na2CO3 + Ca(OH)2
2Na(OH) + CaCO3
Calciner:
CaCO3CaO+CO2
Air contactor:
2Na(OH) + CO2 Na2 CO3
Process
Reactions
Hydroxylation
Reactor
(4)
(1)
(2)
(6)
Fluidized
Bed
CO2
(3)
Membrane
Capture
Device
Trona
Process
Limestone
Precipitate
Dryer
Air
(5)
Membrane
Device
(1) 2NaOH + CO2 Na2CO3 + H2O
(2) Na2CO3 + Ca(OH)2 2NaOH + CaCO3
Ho = - 171.8 kJ/mol
Ho =
57.1 kJ/mol
(3) CaCO3 CaO + CO2
Ho = 179.2 kJ/mol
(4) CaO + H2O Ca(OH)2
Ho = - 64.5 kJ/mol
(5) CH4 + 2O2 CO2 + 2H2O
Ho = -890.5 kJ/mol
(6) H2O (l) H2O
Ho =
(g)
Source: Frank Zeman
41. kJ/mol
Depleted
Air
Lime Based Air Capture
• Is feasible
• Carbon Neutral
• < 250 kJ/mole of CO2
Need Better Sorbents
• Fast Reaction Kinetics
– Limited by air side transport
• Low binding energy
– Comparable to flue gas capture
• Small environmental footprint
• Failsafe designs
Sorbents designed for flue gas scrubbing are strong
enough to capture CO2 from air
Sorbent Choices
Binding Energy (kJ/mole)
0
-5
-10
-15
350K
Air
300K
Power plant
-20
-25
-30
100
1000
10000
CO2 Partial Pressure (ppm)
100000
Cost of Contacting the Air
Unit
Cost
1/
Cost of CO2 from Air
Unit
Cost
1/
Cost of CO2 from Air
(rescaled)
Unit
Cost
Fixed Cost
1/
Comparison to Flue Stack Scrubbing
• Much larger collector
• Similar sorbent recovery
• Cost is in the sorbent recovery
Sketching out a design
• Compare to windmills in 1960
• Cost goal
– $30/ton of CO2
– Motivated by cost of fuel, oxygen, electricity,
raw materials
15
km3/day
of air
115m
15 km3/day of air
300m
9,500t of CO2
pass through
the tower
daily.
As
electricity
producer
the tower
generates
3-4MWe
Water sprayed into the air at
the top of the tower cools
the air and generates a
downdraft.
Cross section
10,000 m2
air fall velocity
~15m/s
Half of it
could be
collected
450 MWe
NGCC plant
60m by 50m
3kg of CO2 per second
90,000 tons per year
4,000 people or
15,000 cars
Would feed EOR for 800
barrels a day.
250,000 units for
worldwide CO2 emissions
Air Extraction can
compensate for CO2
emissions anywhere
2NaOH + CO2 Na2CO3
Art Courtesy Stonehaven CCS, Montreal
GRT’s approach
to air capture
• GRT in Tucson has developed a sorbent
process that is energetically efficient,
always carbon positive
• GRT plans to provide small factory
produced units
• Begin with the physical CO2 market
Together with Allen Wright & Gary Comer, I helped
found a company to develop air capture technology.
I am now a member
Small factory produced units can be
packed into a standard 40 foot
shipping container
GRT’s Vision
The first
of a kind
Collection and Regeneration
Collection
• Natural wind carries CO2 to
collector
• CO2 binds to surface on ion
exchange sorbent materials
Regeneration
• CO2 is recovered with:
○
○
○
○
liquid water wash
or carbonate solution wash
or low-temperature water vapor
plus optional low grade heat
• Regenerated sorbent is reused many
times over
Courtesy GRT
Options for Regeneration
• Pressure Swing
• Thermal Swing
• Water Swing
– Liquid water – wet water swing
– Water vapor – humidity swing
• Carbonate wash is a water swing
– With CO2 transfer
– Salt splitter for CO2 recovery
Electrodialysis
Bipolar
membrane
salt
Na+
Bipolar
membrane
salt
H+ OH-
Cl-
Na+
acid base
anionic
membrane
salt
H+ OH-
Cl-
Na+
acid base
cationic anionic
membrane
H+ OH-
Cl-
acid
cationic anionic
membrane
Air Capture: Collection & Regeneration
Courtesy GRT
GRT’s Carbon, Energy and Water Balance
• Production costs are negligible compared to lifetime capture
• Energy consumption is small
– Low grade heat
– Electric power
– Ambient energy
• Water consumption can substitute for energy
– Water consumption can be 5 to 15 times CO2 collection
– Water can be salty or dirty
– Some fresh water can be produced
• Indirect emissions depend on energy sources
– Worst case is still carbon positive
Four Stages of Air Capture
• Industrial and commercial CO2
• CO2 capture compensating for emissions
• CO2 capture for reducing CO2
concentrations in the air
• CO2 capture for fuel recycling
Hydrogen or Air Extraction?
Coal,Gas
Fossil Fuel
Hydrogen
Distribution
Oil
Gasoline
Cost comparisons
Consumption
Distribution
Consumption
CO2 Transport
Air Extraction
CO2 Disposal
Carbon Capture and Storage
for
Carbon Neutral World
• CCS simplifies Carbon Accounting
– Ultimate Cap is Zero
– Finite amount of carbon left
Air Capture Supports
Underground Injection
• Safety Valve
– Unpredicted changes in the underground
reservoir should trigger a safe release of CO2
– Compensated for by air capture
• Carbon Accounting
– Losses can be made up by air capture
– Air capture can introduce C-14 tracking
Stabilizing CO2 in the atmosphere
• CO2 capture can exceed emissions
• CO2 capture can aim for design point
Materially Closed Energy Cycles
O2
CO2
CO2
O2
Energy
Source
H2
H2 CH2
H2O
H2O
Energy
Consumer
O
Oxygen
Free O2
CO2
Free C- H
Increasing Oxidation State
Oxidizer
CO
Coal
C
Carbon
H2 O
Combustion
products
Town Gas
Methanol
Fischer Tropsch Synthesis Gas
Biomass
Ethanol
Petroleum
Benzene
Gasoline
Natural Gas
Methane
Increasing Hydrogen Content
Hydrogen
Fuels
H
O
Oxygen
Free O2
CO2
Free C- H
Increasing Oxidation State
Oxidizer
CO
Coal
C
Carbon
H2 O
Combustion
products
Town Gas
Methanol
Fischer Tropsch Synthesis Gas
Biomass
Ethanol
Petroleum
Benzene
Gasoline
Natural Gas
Methane
Increasing Hydrogen Content
Hydrogen
Fuels
H
O
Oxygen
Free O2
CO2
Free C- H
Increasing Oxidation State
Oxidizer
CO
Coal
C
Carbon
H2 O
Combustion
products
Town Gas
Methanol
Fischer Tropsch Synthesis Gas
Biomass
Ethanol
Petroleum
Benzene
Gasoline
Natural Gas
Methane
Increasing Hydrogen Content
Hydrogen
Fuels
H
Public Institutions
and Government
guidance
Carbon Board
certification
Private Sector
Carbon
Extraction
Farming, Manufacturing, Service,
etc.
Certified Carbon Accounting
certificates
Carbon
Sequestration