Pumped heat energy storage with liquid media: Thermodynamic assessment by a Brayton-like model

D. Salomone-González, J. González-Ayala, A. Medina, J.M.M. Roco, P.L. Curto-Risso, A. Calvo Hernández
2020 Energy Conversion and Management  
A R T I C L E I N F O Keywords: Energy storage Molten salts Coupled Brayton model Round trip efficiency Internal and external irreversibilities A B S T R A C T A thermodynamic model for a steady state pumped heat energy storage in liquid media is presented: it comprises a coupled Brayton-like heat pump and heat engine cycles connected to a cryogenic liquid and a hot molten salt by counter-flow heat exchangers. The model considers non-isothermal heat transfers between the working fluid and the
more » ... quid media and explicitly includes a set of parameters accounting for the main internal and external losses, heat leak, and pinch point effects for both the heat pump (charge) and heat engine (discharge) modes. Specific expressions for the main magnitudes in the charge (as the input power and coefficient of performance) and discharge (as power output and efficiency) modes and the global round trip efficiency have been analytically derived in terms of isentropic efficiencies of the compressor and turbine, pressure losses in the heat exchange processes, effectivenesses of the external counter-flow heat exchangers, and coupling between the working fluid and the storage and cryogenic liquid media. Round trip efficiencies around of 35 − 40% have been obtained, internal losses being those with main negative influence on the calculated values. The strong constraints imposed by the pinch point effects and liquid media have been analyzed. The model provides a thermodynamic assessment of the main involved processes and their interplay for a selected arrangement (molten salts, cryogenic fluid, and the charge and discharge power blocks) in order to check parametric strategies for thermodynamic optimization and design. These strategies are based on a reduced set of parameters of the overall installation and without the high computational costs of dynamical models. .uy (P.L. Curto-Risso), anca@usal.es (A. Calvo Hernández). cycle [8] or an appropriate fluid operating a subcritical, transcritical or organic Rankine-like cycle [9] . Also research is emphasized on thermoeconomic design optimization [10] and integration of solar and eolic resources [11] . Most thermal energy storage (TES) media are based on sensible packed-bed materials due to its wide temperature range, high efficiency and small pressure losses [8] . This kind of TES has been studied for large scale electric applications [12] , using thermodynamic analysis [13] with main internal and external losses [14] , parametric optimization [15] , and response to cycle duration perturbations [16] . A detailed comparison in packed-bed materials using both Joule-Brayton and Rankine-like cycles was recently performed by Dietrich using exergoeconomic analyses [17] . For liquid media storage, conceptual design for cycles was first performed by Morandin et al. [9] and later applied to molten salts and synthetic oil as sensible heat storage with air as working fluid [18] .
doi:10.1016/j.enconman.2020.113540 fatcat:lx5xy2dbh5blppraf77xvgg2ny