Project data

Summary of the project

Due to the energy price increases and climate policy developments of recent months and years, industrial companies are increasingly endeavouring to increase their energy and resource efficiency and to exploit existing potential internally.

The electrical utilisation of waste gas heat from industrial production processes is seen as particularly promising. The Organic Rankine Cycle (ORC) represents one possibility for generating electricity. In contrast to the classic water vapour cycle (Rankine cycle), an ORC system uses an organic working medium instead of water. This enables the utilisation of fluctuating heat sources with low temperature levels of approx. 80-350 °C, which are characteristic of exhaust gases.

The use of turbines, such as those found in power plant processes, is problematic given the aforementioned boundary conditions and plant outputs of usually less than 200 kW. Microturbines are an option, but due to their speeds, which should not be underestimated, they also present a wide range of challenges, which is why scroll expanders have established themselves as an alternative displacement machine in the field of ORC technology. Their basic design is similar to that of scroll compressors, which in turn are installed in the refrigeration circuit of heat pumps, for example.

The basic design is characterised by two identical, but 180° out-of-phase spiral elements that are inserted into each other during assembly. One half is permanently installed and the other performs an orbital movement during operation, creating self-contained, crescent-shaped chambers that ensure controlled compression (scroll compressor) or expansion (scroll expander) of the working medium. Due to the design, the maximum temperature level of the working medium is limited by the thermal resistance of the bearing lubrication, so that the use of scroll expanders in the high-temperature range above 250 °C, which is of interest for ORC systems, is currently difficult or even impossible to realise.

This is precisely where the concept of the spherical scroll expander developed and investigated in the VASP project comes in. It pursues the approach of using a flexible corrugated tube to separate the storage space from the space pressurised with the working medium and thus improve thermal management. When a corrugated tube is used in combination with the planar design, the former is laterally deformed, making it difficult or even impossible to achieve fatigue strength. For this reason, the VASP scroll design utilises spherical segments as support plates for the spiral elements. The spherically curved carrier plates allow a modified orbital movement to be realised compared to the classic design, which reduces the structural-mechanical load on an assembled corrugated tube and therefore allows it to be integrated. With the successful realisation of the described design, it would be possible to extend the previously limited temperature range of the Scrolllexpander and use it in high-temperature ORC systems, for example. A design as a compressor for toxic or corrosive media is also conceivable due to the hermetic separation of the storage and working chamber.

In collaboration with our cooperation partner, Fella Maschinenbau GmbH, the mathematical modelling and design of the VASP scrolling machine, the simulation of the overall system and the practical implementation and testing of the developed VASP concept in the laboratory are being carried out as part of the project.

We would like to thank the Central Innovation Programme for SMEs (ZIM) for its support!