CO2 removal from power plant flue gas: comparison of different membrane gas separation configurations
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Poster Session (EPIC - Poster) - P2
Keywords: GHGs, membrane gas separation, pressures ratio, process intensification.
The production of greenhouse gases (GHGs), particularly carbon dioxide affecting the global climate, is increasingly causing undesired warming worldwide. As well as the recourse to less pollutant energy sources using alternative technologies, CO2 sequestration from flue gas is an approach in GHG emissions reduction. In particular, it can be successfully applied to large existing power plants that can meet, for instance, policy specifications on CO2 emission.
Current processes for CO2 removal from flue gas are too expensive (e.g., chemical absorption requires large scale equipment and energy consumption). Therefore, new and less expensive processes are necessary: membrane technology (membrane gas separation, membrane contactors) might contribute to solving this problem.
In this work the performance of gas separation membrane systems for carbon dioxide removal from flue gas have been theoretically analysed using a 1-D model for steady-state permeation. The membrane stage-cut, CO2 recovery and permeate stream composition were analysed as a function of feed flow rate and composition. Moreover, the effect of the feed to permeate pressures ratio, phi, on membrane modules performance was investigated, considering, in particular, the variation of permeate composition versus CO2 recovery.
Two different membrane system configurations, (a) flue gas stream compression and (b) the vacuum on the permeate stream, were compared for a permeate stream with the same CO2 concentration and recovery. In particular, the vacuum provides a valuable alternative to the more expensive compression. This happens specifically for applications in which the species to be recovered is at a low concentration (the CO2 content in flue gas ranges around 10%) and low recoveries could be enough to meet process specifications (the Kyoto protocol indicate a CO2 emission reduction of 5.2% with respect to those of 1990).
At a fixed phi the configuration (a) requires a lower installed membrane area but a higher investment and operating compression cost (the whole stream must be processed). On the contrary, in the configuration (b), even if the total installed membrane area increases considerably, the compression cost greatly reduces (only the permeate stream must be sucked). The large compressor in the (a) configuration is substituted by a high number of modular, easily controlled, low investment and operating cost membrane modules. For a 20% recovery from a flue gas stream with 13% CO2 and phi=15 the vacuum system (b) reduces the compression cost to less that 5% with respect to the pressured system (a); in the meantime, the required membrane area in (b) increases up to more than 10 times.
Acknowledgments
The Italian Ministry for Foreign affairs, Direzione generale per la promozione e la Cooperazione Culturale, Rome, Italy is gratefully acknowledged for co-funding this research.
Presented Thursday 20, 13:30 to 14:40, in session EPIC-1: Poster Session (EPIC - Poster) - P2.
