Presentation given by Dr Maria Chiara Ferrari from University of Edinburgh on "Capturing CO2 from air: Research at the University of Edinburgh" at the UKCCSRC Direct Air Capture/Negative Emissions Workshop held in London on 18 March 2014

1. University of Edinburgh , School of Engineering, Edinburgh
SCCS – Scottish Carbon Capture and Storage Centre
Capturing CO2 from air: Research at
the University of Edinburgh
Maria-Chiara Ferrari
UKCCSRC workshop
18th March 2014
m.ferrari@ed.ac.uk
www.eng.ed.ac.uk/carboncapture

2. What people who are developing it claim:
• It is technically feasible.
• It addresses the direct cause of climate change.
• It does not require high recovery – this reduces the energy
requirement compared to CC from power plant. Can be as low as
25% recovery.
• It can tackle emissions from transport and other small sources
(approx 50% of total emissions).
• It can be located near storage sites – eliminating transportation
costs (approx 10% of total).
Direct air capture

3. Air Capture
It is not difficult to produce air with very low CO2 content:
Military tanks; Nuclear submarines; Space shuttle;
Pre-treat (PTSA) of a cryogenic air separation unit
The difficult part is to concentrate the CO2
It is technically feasible, but:
• Not cheap: likely to cost ten times more than “conventional” CC.
• It needs 2 to 3 times more energy than “conventional” CC which
should come from renewable sources.
• In short to medium term can only develop at small scale.
• It will need “conventional” CCS to provide the CO2 transport and
storage infrastructure, but who will pay to store the CO2 produced?
• Requires incentives and legislation.

4. Solar Air Capture CaO-CaCO3:
Nikulshina et al. Chem. Eng. J. (2009) 146: 244.
Aqueous NaOH:
Zeman AIChE J. (2008) 54: 1396
350 kJ/mole CO2 (down to 200 in the future)
Baciocchi et al. Chemical Engineering and
Processing (2006) 45:1047
530-750 kJ/mole CO2
Air capture: proposed flow sheets

5. GRT/Lackner’s Solid Adsorbent
• Lackner Scientific American 01/06/2010. Washing Carbon Out of the Air.
1 ton CO2/day: 60 filters (2.5 m x 1 m x 0.4
m) with a wind of 1 m/s.
With a single stage, CO2 is produced as a
pure component at 5 kPa.
The unit would capture 5 times the CO2
generated to produce the electricity to run
the system.
Energy consumptions: 50 kJ/mol
First prototype: 200$/ton CO2
Goal 30$/ton CO2
10 millions units to impact on world’s
emissions: 5ppm less per year.
Ion–exchange resin
Humidity swing: sorption in dry air and
desorption in water vapour under vacuum.

6. IMechE, Geoengineering Report, 2009
“A North Sea location would be advantageous
as renewable energy could power the trees
and empty oil wells could be used to store
captured CO2.”
GRT/Lackner’s Solid Adsorbent

7. Amine capture should be comparable to NaOH route (i.e. aqueous solutions)
It uses approx 30-40% of the energy in coal to capture the CO2.
Assuming 400 kJ/mole CO2 for a high rank coal: 120-160 kJ/mole CO2
Zenz House et al. Energy & Environmental Science (2009) 2: 193
Compression 1-100 bar: 9.6 kJ/mole CO2 from NIST webbook.
Air Capture vs CC from Power plants
Air CC Ratio (including compression
in energy calculation)
Energy (kJ/mole CO2)
and cost ($/tCO2)
solvent based separation
200-750
50-5001
120-160
501
1.6 – 4.3
1 – 10
Energy (kJ/mole CO2)
and cost ($/tCO2)
adsorption separation
50
30-100
60-902
252
0.9 – 0.6
1.2 – 4
1 Values from Herzog MIT LFEE 2003-002 WP
2 Guessing 50% reduction in energy and costs compared to amines
Compression = 20 kJ/mole CO2 assuming ≈ 50% efficiency.

8. For NaOH route full flowsheet is available but other routes are not
fully defined.
VERY SIMPLE comparison based on:
• No compression before the separation.
• Same thermodynamic separation efficiency.
Air CC coal
y0 0.0004 0.12
Purity 0.95 0.95
Recovery Variable 0.9-0.99
y1 Variable > 0.0012
Comparison with CC from concentrated sources
25 °C and 1 bar
n0, y0
n1, y1
n2 = 1/X
y2 = X
CO2 rich stream
Separation
Process
Gas to vent
n0, y0
n1, y1
n2 = 1/X
y2 = X
CO2 rich stream
Separation
Process
Gas to vent

9. Comparison with CC from concentrated sources
HOW can something 1000 times larger cost less?
Clearly even in a VERY optimistic scenario air capture will cost
more than 10X conventional capture.
Brandani S., Carbon Dioxide Capture form Air: a Simple Analysis. Energy &
Environment 2012, 23, 319-328

10. CO2 capture unit Energy supply
One unit should capture the same amount of CO2 of 10 trees
Air capture: domestic system

11. Compression and concentration of CO2 with fixed beds
Air capture: domestic system
......Capture
Compression Stages
Storage
EPSRC grant EP/I016686/1 - Nanotubes for Carbon Capture

12. Air capture domestic system
12
CO2 stored in the final vessel as a
function of number of compression
stages and compression ratio
Effect of the volume of the 1st
compressor on the amount of CO2
captured

13. Air capture domestic system
13
Effect of the regeneration temperature
on the amount of CO2 and CO2 purity in
the storage vessel.
Effect of vacuum stages and number of
compression stages on the amount of
CO2 and CO2 purity in the storage
vessel

14. Air capture domestic system
14
It is in principle possible to capture and concentrate
the CO2 with the proposed system.
Current research: Dr. Giulio Santori
EU Marie Curie Career Integration Grant (Atmospheric
Carbon CApture).
Objectives:
- Development of more sophisticated models
- Development of a proof-of-concept experimental
apparatus for demonstrating the feasibility of the
solution.
The concept can be scaled-up to use low grade waste
heat.

15. Biomass electricity generation accounts for nearly 1.5% of the
total worldwide production.
Biomass is considered to be a nearly carbon neutral fuel. Carbon
capture applied to biomass would lead to negative emissions.
The introduction of bioCCS may reduce the cost by 40% in order
to reach the 450 ppm CO2 concentration (14 Gt CO2 emitted in
the energy sector in 2050).
Clearly, though, availability of biomass would become a
potential issue unless vast areas of land are reassigned to energy
crops.
Bio-CCS as an air capture option
Azar et al., Climatic Change (2006) 74: 47–79

16. A gasifier has the compositions that
give a lower separation energy
penalty.
Güssing CHP plant
Güssing CHP plant:
electrical capacity of approx. 1.8 MWe
and generates approx. 4MWt to provide
district heating.
Biomass is processed in an indirect
heating 2 zone FCIFB gasifier.
http://www.guessingrenewable.com/htcms/en/wer-was-wie-wo-
wann/wie/thermische-vergasungficfb-reaktor.html

17. Electrical efficiency 18.4 %
Thermal efficiency 44.3%
Overall efficiency 62.7 %
Introduction of VPSA in biomass plant
Schuster G. et al.,. Biomass steam gasification –an extensive parametric modelling
study. Bioresource Techno.2001; 77: 71-79.

18. A two step 2 bed VPSA unit has been designed and optimised to treat the effluent
upstream the gas turbine (after WGSR system)
Feed temperature close to 60 °C and purge pressure ~0.2-0.3 bar
VPSA upstream gas turbine

19. Cysim - Dynamic Process Simulation
Process optimisation using Particle Swarm Optimisation
Non-isothermal, non-equilibrium dynamic process simulation.

20. Amines plant upstream gas turbine

21. Amines plant downstream gas turbine

22. Levelised Cost of Electricity- LCOE:
)1(
)1(
1
1
∑
∑
=
=
+
+
+++++
= n
t
t
t
n
t
t
storagetCCtCCttt
r
E
r
IMIFMI
LCOE
• It: capital costs (CAPEX),
• Mt: operation and maintenance costs
(O&M)
• Ft: fuel costs
• Istorage: storage costs
• r : discount rate (assumed 10 %).
• CC suffix: contribution for carbon capture
• CAPEX includes equipment and installation costs. Equipment cost are
function of design parameters (area or power)
• Maintenance cost are calculated as a yearly fraction of CAPEX and also
utilities and salaries have been added
• Fuel cost is 0.016 Euros/kW (agreement with farmers)
• Profit obtained by heat sale is considered a negative cost . 0.041£/kWh
was assumed
Economic comparison
DECC. UK Electricity Generation Costs Update. 2010.
IEA. Biomass with CCS study. 2009
DECC. Renewable Heat Incentive. 2013.

23. 82.44 97.52 99.91 107.30
The CHP plant with the
VPSA unit presents the
highest overall efficiency
(thermal + electrical)
And the lowest LCOE
18.4
44.3 35.5
14.7
20.8
15.5
31.0
13.6
Comparison

24. • Direct air capture is technically feasible but requires a large
amount of energy for the concentration of the CO2.
• The integration of renewables into air capture scheme can
ensure net capture of the process.
• It is in principle possible to capture and concentrate CO2 with a
small domestic system based on adsorption and thermal swing.
• More research is required to develop more accurate models and
build a test system.
Conclusions - 1

25. • The use of bioCCS may lead to negative emission power and
heat generation.
• An optimised 2 stages 2 bed VPSA unit has been designed and
optimised in order to recover 90% of the CO2 fed to the capture
unit with at least 95% CO2 purity.
• Possible issue: biomass supply. In the longer term it will have to
be sourced locally as it is likely that major international
producers would not be able to supply enough worldwide.
• In the UK, large bio-CCS plants (i.e. plants of 100 MWe or more)
would lose the advantages of small to medium CHPs in terms of
overall energy efficiency.
Conclusions - 2

26. Acknowledgements
26
Prof. S. Brandani, Dr H. Ahn, Dr G. Santori and Mr G. Oreggioni.
Carbon capture group at the University of Edinburgh
www.eng.ed.ac.uk/carboncapture
• EP/F034520/1 - Carbon Capture from
Power Plant and Atmosphere
• EP/I016686/1 - Nanotubes for Carbon
Capture.
• EU Marie Curie Career Integration Grant
Agreement No PCIG14-GA-2013-630863
(Atmospheric Carbon CApture)

27. In PSA processes gas mixtures are separated by cyclic adsorption and desorption steps
driven by cyclic pressure swings.
4 basic steps: pressurisation, adsorption, blowdown and purge plus pressure
equalisations are added in order to reduce the energy penalty.
Coal Post Combustion amines = 130-150 kJt/ mol of captured CO2
Coal Post combustion VPSA = between 70 and 90 kJt/ mol of captured CO2
Biomass Pre Combustion VPSA = approx. 50 kJt/mol of captured CO2
(CO2 capture unit recovery= 90% ; CO2 purity=95%)
VPSA cycle