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 pro- gramme and is based on a semi-closed gas turbine cycle using CO2 as the working fluid and a combus- tion 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 con- suming 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 per- formances 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 eAciency with partial recirculation and a CO2 scrubber is always higher by 2-3% points than the CO2-based CC eAciency in comparable conditions. # 1998 Published by Elsevier Science Ltd. All rights reserved CO2 removal CO2/O2 combustion CO2 semi-closed cycle Flue gas recirculation The objective of this study is to assess the impact of CO2 removal and transportation on de- sign and performance of a natural gas-fired gas turbine plant. Two diAerent concepts were ana- lysed; one including downstream removal of CO2 from combined cycle power plant flue gas and one with air separation prior to a CO2-based power cycle with near stoichiometric oxygen com- bustion. These alternatives are compared to a standard natural gas fired combined cycle where no measures are taken in order to reduce the CO2 emissions. The two mentioned options are considered here for a comparison because the Norwegian and Belgian research teams under the leaderships of O. Bollard and Ph. Mathieu, developed respect- ively a modelling of the CC with flue gas partial recirculation and of the semi-closed CO2-based power cycle. In the semi-closed cycle option, the big advantage is the 100% extraction of the excess CO2 produced in the combustion process from the CO2 working fluid with a simple valve, hence without an energy consuming and costly device like the MEA scrubber but on the other hand it requires an ASU. This is a zero CO2 emission concept.