Large-Scale High Temperature and Power Latent Heat Storage Unit Development

A latent heat storage system for the production of superheated steam at >21 bar and 300 degrees C with a capacity of over 1.5 MWh has been developed, designed and is in build. The storage unit concept uses extended finned tubes with a high packing factor and sodium nitrate as the storage material, which changes phase from liquid to solid during charging. The storage unit is an upscaling from smaller designs, and the upper and lower headers were adapted for the operating conditions and upscaling. The storage contains 852 finned tubes, each ca. 6 m in tube length, so that a semi-automated assembly method was necessary for build. This large-scale storage system is being integrated into an operational process, from which real integration and operation experience can be gained. The integration is in a cogeneration plant in Saarland, Germany and the latent heat storage system serves as a backup to a gas turbine for steam generation. The storage design and build is discussed. Topics such as the manufacturing of finned-tubes, upscaling of headers as well as relevant permitting processes are critical for the development of large-scale latent heat storages for industrial as well as CSP and solar process heat applications.