Inversion of the twin rotary screw compressor to an expander

Abstract

The screw compressor inversion is carried out in cooperation of the university UWB in Pilsen with the firm ATMOS Chrast and OTH Amberg-Weiden (Bavaria-Czech Cooperation Project). ATMOS produces screw compressors flooded with oil, which, unlike non-oiled, where only bearings and gears between screws are lubricated, have a more thorough oil machinery. Its importance rises with the expander. The oil must be thoroughly separated from the working medium behind the expander, where it has lower pressure and temperature than in the expander input. Since the oil must return to the expander inlet, both parameters need to be increased by the oil pump and in the heat exchanger to the inlet level in order to prevent cooling of the working medium and hence efficiency reduction. This creates an auxiliary oil cycle in addition to the main cycle with organic medium (ORC). The inversion of the compressor to the expander is not only about turning the rotation of the screws and the direction of flow, but also about optimizing the shape of the screwing to achieve acceptable efficiency. This problem is solved by numerical simulation, the results will be verified experimentally. From a structural point of view, it is necessary to solve a number of details that will prevent the unacceptable release of working organic media into the environment. This applies mainly to the expander and the circulation pump, where shaft seals cannot completely prevent leakage of liquid or gaseous phase of organic matter. An important design task is the perfect filtration of the lubricating oil from organic liquid substance. The cyclone commonly used here must be supplemented with another fine filter equipped with scavenge line. There is also a problem with the research facility how to manage electricity produced by the electrodynamic brake of the order of 100kW. It can either be returned to the power grid (expensive investment) or to the electric boiler of the organic cycle, or liquidated in resistive coils by heat conversion.