1 Energy consumption of alternative process technologies for CO 2 capture Magnus Glosli Jacobsen Trial Lecture November 18th, 2011

2 Outline Scope of presentation – what is CO 2 capture? Alternative technologies for CO 2 capture Minimum energy consumption Comparison of technologies Summary

3 Outline Scope of presentation – what is CO 2 capture? Alternative technologies for CO 2 capture Minimum energy consumption Comparison of technologies Summary

4 Scope of presentation CO2 capture has a big range of applications Small-scale: –Rebreathers for divers, mine workers etc –Air recirculation in spacecraft and submarines Industrial scale: –CO2 removal from feed gas (e.g. in gas treatment plants). Widely used today –CO2 removal from exhaust gas (e.g. in power plants, steel production etc)

5 CO2 capture in industry Removal of CO2 from feed gas –Avoid processing ”worthless” material – compression is costly! –Reduce corrosion on equipment –Keep specification on product gas (lower heating value) Removal of CO2 from exhaust gas –Reduce overall emissions of CO2 from power plants and refineries –Various approaches exist: –Pre-combustion CO2 removal –Post-combustion CO2 removal –Oxy-fuel combustion

6 Outline Scope of presentation – what is CO2 capture? Alternative technologies for CO2 capture Minimum energy consumption Comparison of technologies Summary

7 Alternative technologies for CO 2 capture Where is CO2 captured? –Post-combustion plants –Pre-combustion plants –Oxy-fuel plants How is CO2 captured? –Adsorption –Absorption –Membrane separation

8 Post-combustion capture This is the most conventional technology – fossil fuel is burned, and carbon dioxide is separated from the exhaust gas From coal: C + O 2  CO 2 From gas: CH 4 + 2O 2  CO 2 + 2H 2 O The CO 2 must be separated from the exhaust gas at low (partial) pressure

9 Post-combustion capture Illustration: Bellona (

10 Pre-combustion capture Fossil fuel is converted to CO 2 and H 2 by gasification and water-gas shift: 3C + O 2 + H 2 O  3CO + H 2 CO + H 2 O  CO 2 + H 2 Separation of CO 2 from H 2 is easier than separating it from N 2

11 Pre-combustion capture

12 Oxy-fuel processes Pure oxygen, rather than air, is used in the combustion The exhaust gas is either pure CO 2 or a mixture of CO 2 and H 2 O Main advantage: Easy separation of CO 2 from exhaust gas Main drawback: Requires separation of O 2 from air, which is costly

13 Oxy-fuel processes

14 Post-combustion: Separation of CO2 dominates energy consumption Pre-combustion: Lower separation cost for CO 2, requires water-gas shift Oxy-fuel: No separation cost for CO 2, high cost for air separation Efficiency loss for power plants Illustration: Davison (2007)

15 Examples of separation technologies Absorption –Amines –Chilled ammonia Adsorption –Pressure-swing adsorption (PSA) (physical) –Thermal swing adsorption (TSA) (physical) –Calcination/carbonation cycling (chemical) Membrane separation

16 Outline Scope of presentation – what is CO 2 capture? Alternative technologies for CO 2 capture Minimum energy consumption Comparison of technologies Summary

17 Minimum energy requirement All separation of gases requires energy. For an ideal gas mixture, the required energy at given T and P is ΔG separation = - T ΔS separation where, for total separation into pure components, ΔS separation = - ΔS mixing = nR Σ i (x i ln x i )

18 Example: CO 2 from exhaust Assume stoichiometric ratio between air and methane, and complete combustion: 8N 2 + 2O 2 + CH 4  8N 2 + CO 2 + 2H 2 O The composition of the exhaust is x N2 =0.73, x H2O =0.18 and x CO2 =0.09 At 298K, this gives a ΔG separation of 1.89 kJ/mol

19 Example, continued We don’t need to separate N 2 from H 2 O. Subtraction gives a ΔG separation of 0.76 kJ for separating the CO 2 from 1 mole of exhaust. This equals 190 kJ/kg CO 2 (or GJ/ton CO 2 ) removed from the exhaust stream, for 100% CO 2 recovery

20 Outline Scope of presentation – what is CO 2 capture? Alternative technologies for CO 2 capture Minimum energy consumption Comparison of technologies Summary

21 What do we compare? Papers report different measures of energy consumption, including: –Fraction of fuel heating value which is consumed by capture process –Energy consumed for a given amount of CO2 captured –Loss in overall plant efficiency Many papers are based on simulation models and pilot-scale plants Some include post-separation compression of CO 2, this is not considered here –This compression is independent of which separation technology is used, but can be integrated with separation

22 What do we compare? Papers report different measures of energy consumption, including: –Fraction of fuel heating value which is consumed by capture process –Energy consumed for a given amount of CO2 captured –Loss in overall plant efficiency Many papers are based on simulation models and pilot-scale plants Some include post-separation compression of CO 2, this is not considered here –This compression is independent of which separation technology is used, but can be integrated with separation

23 What do we compare? The CO 2 recovery varies, but 90% is a common goal: CO 2 recovery = (CO 2 captured)/(CO 2 captured + CO 2 emitted)*100%

24 Absorption processes CO 2 is absorbed in a liquid solvent in an absorber and driven off in a stripper –Amines (MEA, MDEA etc) –Ammonia The stripping stage is the most energy-intensive The only technology which has reached to the full- scale testing stage

25 Amine absorption processes

26 Amine absorption process Solvent is usually monoethanolamine (MEA), methyl- diethanolamine (MDEA) or a mixture of the two The process runs at pressures slightly above atmospheric and at moderate temperatures Well established process for CO 2 removal, only scale-up issues remain

27 Chilled ammonia absorption process

28 Chilled ammonia absorption process Uses less energy for regeneration than the amine process Uses more energy for compression Needs more process equipment than the amine process

29 Energy usage in absorption processes Pure MEA: 3,0 GJ/ton CO 2 at a CO 2 recovery rate of 90% (Abu-Zahra et.al, 2007) MEA/MDEA mixture: 2,8 GJ/ton CO 2 at 90% recovery (Rodriguez et.al., 2011) Chilled ammonia: About 1,5 GJ/ton CO 2, at >90% recovery (Valenti et.al., 2009)

30 Adsorption processes CO 2 is adsorbed in a porous material Uses the fact that adsorption properties change with temperature, pressure et cetera Thermal swing adsorption Pressure swing adsorption In physical adsorption, CO 2 selectivity is generally lower than for chemical absorption Chemical adsorption: CaO/CaCO 3 cycle

31 Energy usage in adsorption Thermal swing adsorption: 3.23 GJ/ton CO 2 at a recovery of 81% and a CO 2 purity of 95% (Clause et.al. (2011)) Pressure swing adsorption: GJ/ton CO 2 for a recovery of 91% and a CO 2 purity of 96% (Liu et.al (2011)) Calcination/carbonation: Not found. General remark: CaO degradation reduces efficiency quickly.

32 Membrane separation Two approaches: Membranes alone –Pre-combustion: Separate CO 2 from H 2 –Post-combustion: Separate CO 2 from N 2 Membranes in combination with absorption

33 Post-combustion separation with membranes (numbers are from Zhiao et.al. (2008))

34 Energy usage with membranes Post-combustion: 0.36 GJ/ton CO 2 at 80% recovery (Zhiao et.al. (2008)) Pre-combustion: 0.3 GJ/ton CO 2 at 85% recovery (Grainger & Hägg (2007))

35 Outline Scope of presentation – what is CO 2 capture? Alternative technologies for CO 2 capture Minimum energy consumption Comparison of technologies Summary

36 Summary Chemical absorption processes are more energy- intensive than membrane-based processes and pressure-swing adsorption However, the former are more mature and closer to realization The potential energy savings in CO 2 capture are huge!

37 Sources: Illustrations: Abu-Zahra, M.R.M.; Schneiders, L.H.J.; Niederer, J. P. M.; Feron, P. H. M.; Versteeg, G. F. (2007): CO 2 capture from power plants Part I. A parametric study of the technical performance based on monoethanolamine. International journal of greenhouse gas control, 1, 37–46 Clausse, M.; Merel, J.; Meunier, F. (2011): Numerical parametric study on CO2 capture by indirect thermal swing adsorption. International journal of greenhouse gas control, 5, Davison, John (2007): Performance and costs of power plants with capture and storage of CO2. Energy 32, 1163–1176 Hägg, M-B.; Grainger, D. (2008): Techno-economic evaluation of a PVAm CO2-selective membrane in an IGCC power plant with CO2 capture. Fuel, 87, Liu, Z.; Grande, C. A.; Li, P.; Yu, J.; Rodrigues, A.E. (2011): Multi-bed Vacuum Pressure Swing Adsorption for carbon dioxide capture from flue gas. Separation and Purification Technology, 81, Rodriguez, N.; Mussati, S.; Scenna, N. (2011): Optimization of post-combustion CO2 process using DEA-MDEA mixtures. Chemical engineering research and design, 89, 1763– 1773 Valenti, G.; Bonalumi, D.; Macchi, E. (2009): Energy and exergy analyses for the carbon capture with the Chilled Ammonia Process (CAP). Energy Procedia, 1, 1059–1066 Zhao, L.; Riensche, E.; Menzer, R.; Blum, L.; Stolten, D. (2008): A parametric study of CO2/N2 gas separation membrane processes for post-combustion capture. Journal of Membrane Science, 325,