PHASING OUT FOSSIL GAS STEAM GENERATORS: Demand-based generation of process steam from thermally stored renewable energy with the Rotating Drum Heat Exchanger

Kurzfassung

By utilizing the phase change enthalpy as well as the thermal energy that can be stored during a temperature change, the storage density of typically used nitrate salts can be raised up to 330 KWh*m-3, which is an increase of 60 % compared to state-of-the-art two-tank molten salt storages. The Rotating Drum Heat Exchanger recently developed by the authors is predestined for the evaporation of water while transferring thermal energy from a nitrate salt. Thereby, a horizontally mounted rotating drum is partially immersed in liquid nitrate salt. While water evaporates inside the drum, the liquid nitrate salt solidifies at the outer surface, transferring both sensible heat and latent heat of the nitrate salt. The solidified nitrate salt is removed from the surface of the drum by a stationary scraper, which enables the separation of the liquid and solid phase of the storage material. This results in a complete separation of the thermal power and thermal capacity of a storage system based on the Rotating Drum Heat Exchanger. Numerical simulations indicate a surface-specific heat transfer density of up to 200 KW*m-2 when sodium nitrate is used as storage material and saturated stream is generated at a pressure of 20 bar. While the technology of the Rotating Drum Heat Exchanger has been experimentally proved for low-temperature application, a high-temperature prototype for high-pressure steam generation is currently under development. In addition to the current progress on the prototype, the presentation will describe and discuss a freely scalable design of the Rotating Drum Heat Exchanger for steam generation in the megawatt range. The heat exchanger is thereby integrated into an entire thermal energy storage system, which also enables the cogeneration of electricity and the flexibilization of current steam supply systems. The use of a phase change material also allows the integration of high-temperature heat pumps.