Comparison of two CO2 removal options in combined cycle power plants

In this paper, two concepts of CO₂ removal in CC are compared from the performance point of view. The first concept has been proposed in the framework of the European Joule II programme and is based on a semi-closed gas turbine cycle using CO₂ as the working fluid and a combustion with pure oxygen generated in an air separation unit. This is a zero emission system as the excess CO₂ produced in the combustion process is totally captured without the need of costly and energy consuming devices. The second concept calls for a partial recirculation of the flue gas at the exit of the heat recovery boiler of a CC. The remaining flow is sent to a CO₂ scrubber. Ninety percent of the CO₂ is removed in an absorber/stripper device. The two systems are compared to a state-of-the-art CC when the most advanced technology is used, namely a 9FA type gas turbine and a three pressure level and heat recovery boiler. Our results show also that the CO₂ semi-closed CC cycle performances are not very dependent on the configuration of the heat recovery boiler and that the recirculated gas CC performances are only slightly sensitive to the recirculation ratio. A high value of this latter mainly gives a significant reduction of the size and hence of the cost of the CO₂ scrubber. From the performance point of view, the results show that the system efficiency with partial recirculation and a CO₂ scrubber is always higher by 2–3% points than the CO₂-based CC efficiency in comparable conditions.