Transmission characteristics of exergy for novel compressed air energy storage systems-from compression and expansion sections to the whole system

Exergy flow characteristics of novel compressed air energy storage (CAES) is significant to evaluate CAES performance while few literatures have addressed this topic. The exergy flow characteristics of two cutting edge CAES systems, compressed air energy storage systems with thermal energy storage (TS-CAES) and supercritical compressed air energy storage (SC-CAES) systems are studied in this paper. All processes of the two systems are modeled (compression section, expansion section, air storage section for TS-CAES and cold storage/liquefaction section for SC-CAES) based on the commonness of the two systems. Exergy is decomposed into thermal and mechanical exergy for their different flow directions and characteristics. Thus, a general exergy flow model for the two systems was established. With the general model, the variations of the relevant proportional ratios and exergy transfer efficiencies with key parameters are revealed. Meanwhile, the energy coupling mechanism for the two systems are explored as well. For TS-CAES systems, except for the number of parts, the variation of each parameter only dominates the change of exergy transfer efficiency of a certain term or some two. All the variables except the pressure loss coefficient of the intercooler and the polytropic efficiency of the compressor, have large effect on the thermal exergy transfer efficiency of their respective flow section. For SC-CAES systems, with the increase of energy storage/release pressure, the system efficiency increases first and then decreases, which is due to change of liquefaction ratio. (C) 2019 Published by Elsevier Ltd.