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2398 Luca Riboldi and Olav Bolland / Energy Procedia 114 (2017) 2390 – 2400 plants. PSA is already the benchmark for H2 purification but, within this framework, it can be used also for CO2 separation. Using PSA as the only gas separation technology demonstrated to be an attractive concept, as it can be argued by the system analysis outputs shown at the bottom of Table 7. For those sets of results, the performance is also reported in terms of cumulative energy efficiency, a term which takes into account the two different energy products of these plants. [52]. An issue related to the operability of PSA-based systems was noted. This has to do with the integration between the inherently dynamic PSA process and the other units of the system, especially the gas turbine. Even though proper scheduling of the PSA cycle is designed, some fluctuations of the PSA outlet gas streams characteristics (e.g. flow rate, composition, etc.) are unavoidable and potentially detrimental for some equipment (e.g. the gas turbine). Control strategies to smooth out those variations have to be carefully investigated [68]. 4. Conclusions A comprehensive analysis of PSA as CO2 capture technology in power plants is carried out in the paper. The different domains that have an influence on the technology viability are taken into account. The analysis encompasses post- and pre-combustion CO2 capture cases. The post-combustion analysis revealed that good maturity has been reached in the development of adsorbent materials and separation processes. Zeolites are the current adsorbent of choice in many instances, while MOF and amine- functionalized adsorbents displayed interesting potentials but are still under development. Many processes have been proposed and the challenge is now to achieve the desired CO2 separation performance with the minimum energy requirement. The integration of PSA into the plant is relatively straightforward and retrofitting of old plants is a viable option. The only system level analysis in the literature suggests that the energy and CO2 separation performance may be competitive with chemical absorption. However, the the footprint of the PSA unit demonstrated to be much larger than that related to absorption and unlikely acceptable, neither practically nor economically. Further work is suggested to investigate new options to deal with this issue. It would be interesting to assess the advantages coming along with the utilization of structured adsorbents and the feasibility of alternative process frameworks (e.g. moving bed reactors). The pre-combustion analysis revealed a margin for improvement in the adsorbent materials and in the separation processes. For cold PSA processes, activated carbons are feasible adsorbents, while MOFs are extremely interesting in prospect. Particularly, the possibility to tune their adsorbent properties on specific operating conditions could be critical in order to enhance the process performance. For hot PSA processes, potassium promoted hydrotalcites are the suggested adsorbents. However, the development of more effective adsorbents would be a key step forward. The gas separation process configurations should be developed in parallel to the advancements in the material science. The integration of PSA in the power plants is somewhat more challenging than in the post-combustion case. A higher complexity is involved and different degree of system integration are possible. The performance of cold PSA-based plants showed to be slightly lower than the absorption-based counterpart. However, if a hot gas separation process is demonstrated feasible, PSA may become advantageous in terms of energy efficiency. Sorption-enhanced processes are even more promising, as the available system analyses show a significant performance improvement in comparison with absorption-based systems. Further investigations of these systems are recommended. Additional assessments on the operability of the system need also to be undertaken, especially with regard to the integration between the inherently dynamic PSA process and the other process units. To complete the pre-combustion overview, an interesting concept could be a coproduction layout (i.e. power and H2 as energy product), which could guarantee a higher degree of flexibility of the plant. In such process framework, preliminary analyses show the utilization of PSA technology as, potentially, the most advantageous option. Acknowledgements The authors gratefully acknowledge the financial support provided through the Norwegian University of Science and Technology (NTNU).PDF Image | Pressure Swing Adsorption (PSA) as CO2 Capture Technology
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