Presentation given by Dr EJ Anthony from Cranfield University about Direct Air Capture at the UKCCSRC Direct Air Capture/Negative Emissions Workshop held in London on 18 March 2014

1. Direct Air Capture
E.J. Anthony
Cranfield University

2. Global Warming
“By the influence of the increasing percentage of
carbonic acid in the atmosphere, we may hope to
enjoy ages with more equable and better climates,
especially as regards the colder regions of the earth,
ages when the earth will bring forth much more
abundant crops than at present, for the benefit of
rapidly propagating mankind” [Savante Arrhenius,
“Worlds in the Making” 1906]
Nonetheless there is a conviction that we need to
have CCS ready within the next few decades if we
are not to exceed 450 ppm CO2
There are still some modern adherents of the view that
global warming will be good for parts of the world, plus
endless armies of global warming contrarians

3. CCS as conceived today is not climate control and
cannot prevent climate change, it can only prevent
worse climate change!
However, it is probably essential for technologies
like Direct Air Capture
Alternatives include mineralization, bio-CCS,
biochar, or use!
Direct Air Capture

4. Direct CO2 Capture
from Air
5
Forestry (CO2 Capture via Biomass) – BECS CO2 Capture (next presentation)

5. Gasification by Primary Feedstock
State of the Gasification Industry- the Updated Worldwide
Gasification Database – C. Higman, Oct 16th, 2013

6. What if we don’t
succeed or partially
succeed with CCS?
Possible strategies might be to decarbonize
thermal power, but leave transportation “privileged”,
in which case we need a route to compensate for
CO2 from vehicles, planes and other mobile carbon
sources
• Could this be air capture?
Another question is, whether there is any history of
attempting to influence the climate

7. Originator Technology Success
John Espy (the storm
king) US 1849
Burning large tracts of forest
to make rain
None
General Daniel Ruggles
and Robert Dryenforth,
1891
Concussion Theory –make
rain by creating large
explosions in the
atmosphere
None
Various (Recent used in
China in 2007)
Seed clouds to make rain Moderate
John von Neumann
1950’s
Develop computer models
of climate, with the ultimate
goal of weather control!
None, but unintended
consequences
USSR 1950’s Stalin’s great plan to
transform the nature, e.g.
dam the Bering Straits to
melt arctic ice!
None, but some
environmental
disasters
Various Geo-engineering (seeding
oceans with Fe, reflective
mirrors in space, air capture)
Too soon to say

8. Here we present a new index of the year when the projected mean climate of
a given location moves to a state continuously outside the bounds of
historical variability under alternative greenhouse gas emissions scenarios.
Using 1860 to 2005 as the historical period, this index has a global mean of
2069 (±18 years s.d.) for near-surface air temperature under an emissions
stabilization scenario and 2047 (±14 years s.d.) under a ‘business-as-usual’
scenario. Unprecedented climates will occur earliest in
the tropics and among low-income countries,
highlighting the vulnerability of global biodiversity
and the limited governmental capacity to respond to
the impacts of climate change.
Our findings shed light on the urgency of mitigating greenhouse gas
emissions if climates potentially harmful to biodiversity and society are to be
prevented.
The Projected Timing of Climate Departure from Recent Variability
C. Mora et al., 2013 - Nature 502, 183, 2013.
Are there scenarios under which Direct
Air Capture might be essential?

9. Direct Air Capture
Pros
• Air is ubiquitous
• Air contains relatively
few contaminants
• Could be used for
niche markets
Cons
• Water and energy to
drive such schemes
and CCS sites are not
ubiquitous
• CO2 concentrations
are 400 ppm, implying
a high cost for CO2
removal

10. Who Pays for
Direct Air Capture?
Air Capture is something done for the public good,
unless there is a value for the CO2
Carbon Price?
Carbon Use – (How much)?
Unlike other forms of pollution (SO2, NOx, Heavy
metals etc.), CO2 is truly global, and would require
international agreements to pay for removing it from
the atmosphere for the global good

11. American Physical Society,
2008-2011
Direct Air Capture of CO2
with Chemicals
Report Committee
Robert Socolow (Princeton), Co-Chair
Michael Desmond (BP), Co-Chair
Roger Aines (LLNL)
Jason Blackstock (IIASA)
Olav Bolland (NTNU Trondheim, N)
Tina Kaarsberg (DOE)
Nate Lewis (Cal Tech)
Marco Mazzotti (ETH Zurich, CH)
Allen Pfeffer (Alstom)
Karma Sawyer (UC Berkeley)
Jeffrey J. Siirola (Eastman)
Berend Smit (UC Berkeley)
Jennifer Wilcox (Stanford)
Green: We are here.
Earlier co-chairs:
Bill Brinkman, then Arun Majumdar

12. 400 PPM: Can Artificial Trees Help Pull CO2
from the Air? Klaus Lackner
American Physical Society suggests such air
capture might cost $600/tonne
Scientific America, May 16th, 2013
* Direct Air Capture of CO2 with Chemicals: A
Technology Assessment for APS Panel on
Public Affairs, June 1st, 2011
Direct Air Capture

13. High Level Messages
“First things first: Virtually all large-scale industrial CO2
sources should be decarbonized before DAC is deployed.
Not only is DAC much more expensive, but DAC requires
low-C power to be carbon-negative.”
“I cannot persuade myself that DAC is a relevant climate
change strategy for this half century.”
“It is obligatory, therefore, for experts (including those here
today) not to create false hopes – in this case, not to allow
our audiences to infer that humanity can “solve” climate
change while being relaxed about fossil fuels.”
Robert Socolow speaking at Direct Air Capture Summit,
University of Calgary, March 7th, 2012

14. Direct Air Capture
• If natural gas/hydraulic fracturing represent a bridge
to the future, can capture from low CO2 sources
represent a bridge for the development of air
capture?
• Obvious examples include producing CO2 for
Enhanced Oil Recovery, removing CO2 from natural
gas etc.

15. Direct CO2 Capture
from Air
7
Wet Scrubbing Process

16. Objective
Comparing Performance of Pelletized and Natural
Limestone for CO2 Capture from Air in a Fixed Bed
• Effect of Particle Type, Particle Size, Gas
Flow Rate and Relative Humidity on CO2
Capture (breakthrough time, breakthrough
curve,…) and its global reaction rate
• Study Carbonation Decay in Series of Cycles
(Capture and regeneration) for:
- Pellets
- Limestone (Natural Cadomin)2

17. Wet Scrubbing Process
8
Disadvantages
• Energy consumption
• Complexity of the process
• Large water consumption
• Use of Na or K will present problems in any
high temperature regeneration step

18. Direct CO2 Capture
from Air
Dry Air Capture Systems
9
CO2Capture
Regeneration
CO2 Free Stream
Inlet Air
RichCO2Free
Stream
• Adsorption/Chemisorpti
on process
• Regeneration needed
• Degradation of sorbents
in cycles

19. CaO Sorbent Properties
10
Pellets(250-425 µm) Pellets(425-600 µm)
Natural Limestone
(250-425 µm)
Natural Limestone
(425-600 µm)
Bulk Density (g/cm3) 0.87 0.84 0.98 0.96
Surface Area (m2/g) 14.6085 12.0098 13.6017 11.5432
Components (wt%)
Calcium Oxide (81%), Calcium Aluminate
Cement (10%), Impurities (9%)
Calcium Oxide (90%), impurities (10%)
 Particles are pre-hydrated for 3 h

20. Conditions
• Particle Size
(a) 250-425 µm
(b) 425-600 µm
• Flow Rate
(a) 0.5 Lit/min (25 °C and 1 barg)
(b) 1 Lit/min (25 °C and 1 barg)
• Bed Length
 60 mm
• Bed Diameter
 7.48 mm
• Relative Humidity
(a) 55%
(b) 70%
11
78.57mm
7.48 mm
Sorbent
Glass bead
Paper Filter

21. Experimental Set Up
12
Compressor
Bubbler
Fixed Bed
Data
Acquisition
System
RH-Transmitter
CO2 Analyzer
Air

22. Necessity For Moisture I
13
H2O
Ca(OH)2
Ca(OH)2 ↔ Ca2+ (aq)+ 2OH- (aq)
CO2 + H2O ↔ H2CO3 (aq)
H2CO3 ↔ HCO3
- (aq)+ H+ (aq)
HCO3
- (aq) ↔ CO3
2- (aq)+ H+ (aq)
Ca2+ (aq) + CO3
2- (aq) ↔ CaCO3 + H2O

23. Necessity For Moisture II
14
Ca2+ + CO3
2- ↔ CaCO3 + H2O
Ca(OH)2Ca(OH)2
Ca(OH)2 CaCO3
Ca(OH)2
H2CO3
C
O
2

24. Necessity For Moisture III
15
CO2 (~400 ppm)
Relative Humidity ~ 0%
No Reaction between CO2 and Ca(OH)2

25. Necessity For Moisture IV
16
CO2 (~400 ppm)
Water Blocks pores and CO2 cannot
diffuse

26. Necessity For Moisture V
17
CO2 (~400 ppm)
Pores are covered by a water film
CO2 reacts with Ca(OH)2

27. Necessity For Moisture VI
18
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100
C/C0
Time (min)
Natural Cadomin-250-425µm-
1LPM-RH~0
0
20
40
60
80
100
120
0 200 400 600 800 1000MASS%
Temperature (C)
RH~0
Hydration ~ 80% Carbonation
~ 10%

28. Necessity For Pre
Hydration
19
Hydration ~ 27%
Carbonation ~ 65%
Carbonation ~ 90%
0
2
4
6
8
10
12
0 200 400 600 800 1000
Mass(mg)
Temperature (C)
Pellets-250-425µm-1L-Bottom
0
2
4
6
8
10
12
0 200 400 600 800 1000
Mass(mg)
Temperature (C)
Pellets-250-425µm-1L-Top
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 500 1000 1500 2000 2500 3000
C/C0
Time (min)
Pellets-250-425µm-
1 Lit/min

29. Results I (Effect of
flowrate & particle size)
20
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 1000 2000 3000 4000 5000 6000
C/C0
Time (min)
Breakthrough Curves (Pellets)
Pellets-250-
425µm-0.5
Lit/min
Pellets-425-
600µm-
0.5Lit/min
Pellets-425-
600µm-1
Lit/min
Pellets-250-
425µm-1
Lit/min

30. Results I (Effect of
flowrate & particle size)
21
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 1000 2000 3000 4000 5000 6000
C/C0
Time (min)
Breakthrough Curves (Natural Cadomin)
Natural
Cadomin-250-
425µm-0.5
Lit/min
Natural
Cadomin-250-
425µm-1
Lit/min

31. Results II (effect of
particle type)
22
Natural
Cadomin-250-
425 µm-1
Lit/min
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 1000 2000 3000 4000 5000 6000
C/C0
Time (min)
Natural Cadomin vs. Pellets
Natural
Cadomin-250-
425 µm-0.5
Lit/min
Pellets-250-
425 µm-0.5
Lit/min
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 500 1000 1500 2000 2500
C/C0
Time (min)
Natural Cadomin vs. Pellets
Pellets-250-
425 µm-1
Lit/min

32. Results III (carbonation
of particles-TGA)
23
0
20
40
60
80
100
120
0 200 400 600 800 1000
Mass%
Temperature (C)
Natural Cadomin-425-600µm-
1LPM-bottom
0
20
40
60
80
100
120
0 200 400 600 800 1000
Mass%
Temperature (C)
Natural Cadomin-425-600µm-
1LPM-top
Carbonation
~ 93%
Carbonation
~ 95%

33. Results III (carbonation
of particles-Mass
Balance vs. TGA)
Conversion
(Mass Balance)
Conversion
(TGA-average)
Difference
%
Pellets 250-425 µm
0.5 lit/min
0.93 0.87 6.89%
Pellets 250-425 µm
1lit/min
0.80 0.87 8.05%
Pellets 425-600 µm
0.5 lit/min
0.85 0.88 3.41%
Natural Cadomin
250-425 µm 0.5
lit/min
0.90 0.92 2.17%
Natural Cadomin
250-425 µm 0.5
lit/min
0.80 0.89 10.11%
Natural Cadomin
425-600 µm 0.5
lit/min
0.86 0.90 4.44%
25

34. Results IV (Cycles)
26
Calcination
(850 °C
75 minutes)
Carbonation
(CO2 Capture)
Hydration TGA
BET
(Surface Area)
Number of Cycles: 9 (10 Calcinations)

35. Results IV (effect of
cycles on surface area &
carbonation conversion-
Pellets)
27
4
5
6
7
8
9
10
11
12
13
0 1 2 3 4 5 6 7 8 9 10
m2/g
No. Cycle
Surface Area
70
72
74
76
78
80
82
0 1 2 3 4 5 6 7 8 9 10
%CO2Conversion
No.Cycle
Carbonation Conversion
Pellets-425-600 µm-1LPM

36. Future Experiments
• Carbonation decay in series of cycles for Natural
Cadomin (BET, BJH, SEM, Conversion)
• Carbonation decay in series of cycles at realistic
conditions (920 °C and pure CO2 stream)
• Study the effect of relative humidity on CO2 capture
from air
• Fitting data with a solid-gas reaction model for
quantitative comparison
28

37. Noncatalytic Solid Gas
Reaction
29
Time
T1 T2 T3
2R 2R
2R
2rc
2rc
Reacted Layer Reacted Layer
Unreacted CoreUnreacted Core

38. Noncatalytic Solid Gas
Reaction
31
Unreacted Shrinking Core Model
t = τDP [1-3(1-X)2/3+2(1-X)]+ τMT[X]+ τR,CS[1-(1-X)1/3] X= 1- (rc/R)3
τDP = ( )( ) Diffusion through product layer
τMT = ( )( ) External mass transfer from bulk to the surface
τR,CS = ( )( ) Chemical reaction

39. Summary
• Existence of humidity is crucial for CO2 capture from air (air
capture) at low temperature
• Pre-hydration will improve carbonation conversion along the
bed
• Effect of chosen flow rates on global reaction rate is
negligible
• Since smaller particles provide greater surface area, in
similar conditions (temperature, flowrate) their breakthrough
curves were sharper
• Due to high porosity, pellets have better global reaction rate
31

40. Conclusions
• Air Capture remains an interesting concept which
should be pursued
• It cannot substitute and depends on CCS, which must
remain the priority while large quantities of fossil fuels
are used globally
• Like mineralization which remains a possible solution it
requires dramatic improvements in cost
• The alternative to both is increasingly expensive
mitigation steps, and/or geoengineering, which has
profound implications for the global environment and
human wellbeing

41. Acknowledgements
• Mr Mohammad Samari, who is currently carrying out
his MASc on “CO2 Capture from Dilute Sources via
lime based processes” under the joint supervision of
Professor Arturo Macchi (University of Ottawa) and
Dr. E.J. Anthony (Cranfield University)
• Professor Robert Socolow, Princeton University for
some of the material used in this presentation
• Professor Vasilije Manovic (Cranfield University) for
useful discussions