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Direct Air Capture E.J. Anthony Cranfield University
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
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
Direct CO2 Capture from Air
5
Forestry (CO2 Capture via Biomass) – BECS CO2 Capture (next presentation)
Gasification by Primary Feedstock
State of the Gasification Industry- the Updated Worldwide Gasification Database – C. Higman, Oct 16th, 2013
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
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
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?
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
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
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
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
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
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.
Direct CO2 Capture from Air
7
Wet Scrubbing Process
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
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
Direct CO2 Capture from Air
Dry Air Capture Systems
9
CO2 C
aptu
re
Rege
nera
tion
CO2 Free Stream
Inlet Air
Rich
CO
2 Fre
e St
ream
• Adsorption/Chemisorption process
• Regeneration needed • Degradation of sorbents
in cycles
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
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
78.5
7 m
m
7.48 mm Sorbent
Glass bead
Paper Filter
Experimental Set Up
12
Compressor Bubbler
Fixed Bed
Data Acquisition
System
RH-Transmitter
CO2 Analyzer
Air
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) + CO32- (aq) ↔ CaCO3 + H2O
Necessity For Moisture II
14
Ca2+ + CO32- ↔ CaCO3 + H2O
Ca(OH)2 Ca(OH)2
Ca(OH)2 CaCO3
Ca(OH)2
H2CO3
CO2
Necessity For Moisture III
15
CO2 (~400 ppm)
Relative Humidity ~ 0% No Reaction between CO2 and Ca(OH)2
Necessity For Moisture IV
16
CO2 (~400 ppm)
Water Blocks pores and CO2 cannot diffuse
Necessity For Moisture V
17
CO2 (~400 ppm)
Pores are covered by a water film CO2 reacts with Ca(OH)2
Necessity For Moisture VI
18
00.10.20.30.40.50.60.70.80.9
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 1000M
ASS%
Temperature (C)
RH~0
Hydration ~ 80% Carbonation ~ 10%
Necessity For Pre Hydration
19
Hydration ~ 27% Carbonation ~ 65%
Carbonation ~ 90%
0
2
4
6
8
10
12
0 200 400 600 800 1000
Mas
s (m
g)
Temperature (C)
Pellets-250-425µm-1L-Bottom
0
2
4
6
8
10
12
0 200 400 600 800 1000
Mas
s (m
g)
Temperature (C)
Pellets-250-425µm-1L-Top
00.10.20.30.40.50.60.70.80.9
11.1
0 500 1000 1500 2000 2500 3000
C/C
0
Time (min)
Pellets-250-425µm-1 Lit/min
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
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
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
Results III (carbonation of particles-TGA)
23
0
20
40
60
80
100
120
0 200 400 600 800 1000
Mas
s%
Temperature (C)
Natural Cadomin-425-600µm-1LPM-bottom
0
20
40
60
80
100
120
0 200 400 600 800 1000
Mas
s%
Temperature (C)
Natural Cadomin-425-600µm-1LPM-top
Carbonation ~ 93%
Carbonation ~ 95%
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
Results IV (Cycles)
26
Calcination (850 °C
75 minutes)
Carbonation (CO2 Capture) Hydration TGA BET
(Surface Area)
Number of Cycles: 9 (10 Calcinations)
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
%CO
2 Co
nver
sion
No.Cycle
Carbonation Conversion
Pellets-425-600 µm-1LPM
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
Noncatalytic Solid Gas Reaction
29
Time
T1 T2 T3
2R 2R 2R
2rc
2rc
Reacted Layer Reacted Layer
Unreacted Core Unreacted Core
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
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
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
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
