Torsten Baumann

Moving Bed Heat Exchangers for Use With Heat Storage in Concentrating Solar Plants: A Multiphase Model

Heat storage based on particulate materials is a promising option to provide a demand-oriented electricity production with utility-scale solar power plants. For energy storage discharge, a moving bed heat exchanger is considered and its design is investigated. As a basis for a flexible design tool, a multiphase model based on the Eulerian continuum approach was set up to describe the bulk flow and the thermal performance. The model was applied to an example heat exchanger layout, and the simulation results were compared with an empirical model, confirming the validity of the approach. Initial parameter variations identify the key parameters and their effect on the thermal performance.

Theoretical and experimental investigation of a Moving Bed Heat Exchanger for Solar Central Receiver Power Plants

A Moving Bed Heat Exchanger for heat extraction from solar heated granular materials is investigated with respect to flow behaviour. To overcome limitations of existing empirical models, a numerical CFD model is established and parametrised with the help of experiments. Parametric studies are performed to quantify the effect of inlet velocities on the velocity field. A good agreement with an empirical model is found. Also, a comparison with PIV measurements confirms its validity, making it a solid basis for future design work.Sensible solid media storage based on particulate materials is a promising concept for solar central receiver systems. The bulk material can be used as heat transfer and storage medium at high temperatures. A new heat exchanger concept based on the principles of a moving bed has been developed deploying a compact design, a good part-load behaviour and low parasitic loads. Numerical investigations applying a multiphase CFD approach are conducted in order to identify the determining factors on heat transfer. In a subsequent design study, the tube shape as well as the tube arrangement is varied in order to identify a design improving the thermal performance of the device. A circular tube geometry is found to be the most economic one compared to rhombs or ovals. A narrow tube arrangement taking into account the flow properties of the bulk offers a potentially higher thermal efficiency and an even more compact design of the heat exchanger.

Jülich Solar Power Tower – System Behavior During Downtime

At the Julich Solar Power Tower, two new shut-off dampers have been installed in the hot air piping system in order to reduce thermal losses during downtime of the plant. The thermodynamic behavior of the thermal energy storage and the steam boiler has been investigated with respect to heat losses after shut-down of the plant. Also, the change of temperature and the pressure drop at both shut-off dampers during downtime has been analyzed. Results show that for the storage, a reduction of thermal losses can be achieved by closing the damper overnight. Regarding the steam boiler, no improvements on heat losses were observed. If only two of the four storage chambers have been charged during operation, heat transfer between the chambers is observed after shut-down. It is concluded that natural convection is not the main source of thermal overnight losses, however, it can be lowered thanks to the dampers. Heat conduction and convectional heat transfer at the surfaces also contribute to the decrease of thermal energy, which can be lowered by thicker insulation layers in the future.