Heat Transfer Equipment for a Compressed Air Energy Storage (CAES) Integrated with a Concentrated Solar System

Abstract The transition to sustainable electric grids requires advanced solutions to address the intermittency of renewable energy sources. The integration of a Compressed Air Energy Storage (CAES)with a Concentrated Solar Power Plant (CSPP) constitutes a promising solution to develop high-efficiency and zero-emission plants. In the proposed concept, the concentrated solar radiation is absorbed and stored in a High-Temperature Thermal Energy Storage (HTES) at 800 °C. During the CAES discharge phase, air at a nearly atmospheric pressure is used as thermal carrier to heat the stored compressed air before the expansion in a High-Pressure Turbine (HPT) and to reheat the HPT exhaust air before the expansion in a Low-Pressure Turbine (LPT). Medium/large CAES plants (20-100 MWe) are addressed. Therefore, to make the heat exchangers compact, conventional configurations like Shell&Tube (S&T) arrangements could be replaced by unconventional ones. One option is the adoption of the consolidated industrial Heat Recovery Steam Generator (HRSG) technology to design a Hot Air Generator (HAG). According to such a concept, the HAG is made of tube bundles placed into a rectangular duct. Such a configuration allows the installation of large heat exchange surfaces, making the HAG performance higher than S&T HT ones. In the present paper, preliminary design studies of a HAG for a 20 MWe CAES plant have been carried out. A computational code focused on HAG design has been developed in Visual Basic for Application (VBA). Different design layouts are presented and discussed. Finally, HAG off-design performance is shown in the entire expected operating range.