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.
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.
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.