Post-combustion capture
In post-combustion capture, fuel is burned as usual in a (more-or-less) unmodified power plant. Currently the commercialised technology for post combustion capture is chemical absorption. It is the most advanced method due to considerable industrial experience with similar processes. CO2 is absorbed from the flue gas in a separation tower using a solvent and regenerated by heating in a recovery column at temperatures over 100˚C. Post combustion is advantageous because it can be applied to already constructed plants (retrofit), where components can be replaced, developed and upgraded without fundamental impacts on the power plant.
In post-combustion capture, fuel is burned as usual in a (more-or-less) unmodified power plant. Currently the commercialised technology for post combustion capture is chemical absorption. It is the most advanced method due to considerable industrial experience with similar processes. CO2 is absorbed from the flue gas in a separation tower using a solvent and regenerated by heating in a recovery column at temperatures over 100˚C. Post combustion is advantageous because it can be applied to already constructed plants (retrofit), where components can be replaced, developed and upgraded without fundamental impacts on the power plant. This also allows for staged introduction of carbon capture onto a plant, which reduces disruption to the plant as well as investment risk. The fact that post-combustion can be retrofitted to existing power plants means that such demonstration projects have thus far been more common than for other capture technologies. The major disadvantage of chemical absorption for post combustion capture is the large energy penalty associated with thermal solvent regeneration. Other research challenges include large equipment requirements due to high volumes of flue gas, corrosion of equipment in the presence of oxygen and other impurities, solvent degradation due to reaction with oxygenated impurities, potential releases of harmful solvent degradation products and disposal requirements of expired solvent. Future development of second and third generation capture technologies to improve efficiency and reduce cost may include better liquid solvents and novel membranes or microporus solids.
Pre-combustion capture
Pre-combustion capture, typically operated with Integrated Gasification Combined Cycles (IGCC), involves gasification and partial oxidisation of the fuel to produce CO2 and hydrogen which are then separated, commonly using physical absorption processes.
Pre-combustion capture, typically operated with Integrated Gasification Combined Cycles (IGCC), involves gasification and partial oxidisation of the fuel to produce CO2 and hydrogen which are then separated, commonly using physical absorption processes. The hydrogen is then combusted in a modified gas turbine or fuel cell producing power and water. This method has been demonstrated at the megaton-per-year scale but it has not been fitted to an operational power plant. Advantages for pre-combustion are that multiple fuels can be used and the hydrogen produced can be utilised as a transportable fuel or product. There are potential increased efficiency gains from improved integration of the technology into power plants. Disadvantages include high construction costs, reliability of all components for efficient integration and decreased short-term flexibility. Further development of high-temperature membranes may allow syngas to be reformed into CO2 as hydrogen is separated. The FutureGen project is looking to build and demonstrate this capture technology in Illinois, USA, using a 275-MW capacity power plant.
Oxyfuel combustion
Oxyfuel combustion separates oxygen from air using established cryogenic methods and then burns the coal or gas fuel in a mixture of that oxygen, often combined with recycled flue gas to regulate the temperature of combustion.
Oxyfuel combustion separates oxygen from air using established cryogenic methods and then burns the coal or gas fuel in a mixture of that oxygen, often combined with recycled flue gas to regulate the temperature of combustion.
Advantages of oxyfuel are the comparative ease with which CO2 can be separated (no solvent is required) which allows for very high capture levels, small physical size of the unit, and the possibility of retrofit to an existing plant with some alterations. Drawbacks include , inflexibility due to the use of multiple burners and air separation requirements, large energy penalty of the air separation unit, high combustion temperatures requiring expensive materials, very low SOx require on leaving burners, possible need for an extra purification stage for the CO2 and the challenges of operation at sub-atmospheric pressure to prevent leakage leading to ingress of air and reduced purity. Future gains may come from improved high temperature operation, reduction of energy costs of oxygen separation from the air and minimizing air leak.
The UK Carbon Capture and Storage Research Community (UKCCSRC) is supported by the Engineering and Physical Sciences Research Council (EPSRC) as part of the UK Research and Innovation (UKRI) Energy Programme.
The mission of the UKCCSRC is to ensure that carbon capture and storage (CCS) plays an effective role in helping the UK achieve net-zero greenhouse gas emissions by 2050.
Location
D03 Ella Armitage Building
University of Sheffield
40 Leavygreave Road
Sheffield
S3 7RD
UK
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