High temperature latent heat thermal energy storage integration in a co-gen plant

Kurzfassung

Within the framework of the project TESIN funded by the German Ministry of Economic Affairs and Energy, a high temperature latent heat thermal energy storage unit is being developed and will be designed, built, commissioned and tested in an operating cogeneration plant in Saarland, Germany. This plant provides superheated steam to industrial process customers from a gas turbine with a heat recovery steam generator. Currently, a secondary boiler is operated at minimal load, from which it can be heated to full load in 2 minutes. With the integration of the thermal energy storage into the plant, the secondary boiler will be reduced from minimal to warm load operation. In case of a failure of the gas turbine, the storage will produce steam for 15 min. while the secondary boiler is heated from a warm to a hot operating load. This standby load reduction in the secondary boiler will reduce the use of fossil fuels. The steam demand from the thermal storage is for 8 t/h at around 25 bar and a minimum temperature of 300 °C. This results in a high power level of about 6 MWth and a necessary storage capacity of 1.5 MWh. At this pressure level, the steam is superheated about at least 75 K. The combination of the superheating and the required power level has led to a smaller tube distance than in previous storage units as well as a new axial fin design. The basic storage as well as the fin design combined with nitrate salts as the storage material have been analyzed with simulation tools. Detailed design planning, permitting and build of the system are the coming steps in this part of the project. The design of these fins, storage unit design and planned integration in the cogeneration plant are presented here.