CFD modeling and experimental validation of the TES system exploited in the Pollegio AA-CAES prototype

Zavattoni, Simone and Barbato, Maurizio and Geissbühler, Lukas and Haselbacher, Andreas and Zanganeh, Giw and Steinfeld, Aldo (2017) CFD modeling and experimental validation of the TES system exploited in the Pollegio AA-CAES prototype. In: SCCER Heat and Electricity Storage – 5° Symposium, 09.05.2017, PSI - Villigen.


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Currently, the worldwide installed storage capacity for electrical energy (EES) is dominated by pumped hydroelectric energy storage (PHES). With an installed capacity, at the end of 2015, of up to 145 GW, PHES represents about 97% of the global EES capacity. The power ratings of the existing PHES plants is in the range of 1 MW up to 3 GW with a round-trip efficiency of 70-85 %. Despite PHES is a well-known mature and efficient technology of electric energy storage, it has two main drawbacks: its applicability is limited to suitable sites and it has relatively low energy density that means large environmental impact. In the field of large-scale EES, a valid alternative to PHES is represented by compressed-air energy storage (CAES). As of today, two industrial-scale CAES plants are successfully in operation: the 321 MW Huntorf plant (first generation CAES), and the 110 MW McIntosh plant (second generation CAES with heat recuperator). The round-trip efficiency is 42% and 54% for the Huntorf and the McIntosh CAES plants respectively. However, an advancement in the technology is represented by the concept of adiabatic compressed air energy storage (AA-CAES). The difference with respect to conventional, or diabatic, CAES is that in AA-CAES a thermal energy storage (TES) is exploited to store the thermal energy produced during compression to be recovered prior to expansion. Although AA-CAES concept is still in the research and development stage, the expected round-trip efficiency is in the order of 70% comparable to PHES. Other advantages of AA-CAES such as limited environmental impact and lower estimated capital costs make this technology attractive as a potential alternative to PHES for achieving the long-term energy policy developed by the Swiss Federal Council. To evaluate the feasibility and applicability of the AA-CAES concept, ALACAES built a first prototype in Pollegio. A tunnel located north of Biasca (TI) and previously used by the AlpTransit project, was exploited as high-pressure air reservoir. The high temperature TES was realized with a packed bed of rocks installed inside the tunnel. Since the TES can be considered the key component of the AA-CAES technology, its thermo-fluid dynamics behaviour has been carefully evaluated by means of computational fluid dynamics (CFD) simulations. The comparison of simulation results against experimental data gathered from the Pollegio AA-CAES prototype showed fairly good agreement.

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