Development of a waste heat recovery orc prototype using an oil-free scroll expander

The world is facing a historical increase in energy demand and energy consumption. As consequence the conventional fossil fuels are deple ting faster with an inherent pollution causing severe damages to our environment. Renewabl energy sources are considered as a solution to both environmental issue and energy dem and. At the same time a lot of waste heat is witnessed in processes in industries. Our objec tive is to contribute to the development of ORC systems, that appear to us as a good solution t o recover this wasted heat. In such waste heat applications, depending on the h eat source flow rate and temperature, electrical power output can be as low as a few kilo watts. In this power range, there is no cost effective expansion machine available on the market . On existing prototypes, expansion devices are usually retrofitted volumetric compress or originally designed for refrigeration or air compression applications. Air compressors have the advantage to handle higher inlet temperature but tightness is often an issue in ORC application since the fluids used have a non negligible environmental impact. This paper presents the development of a small-scal e WHR ORC unit at the Thermodynamic Laboratory of the University of Liège: the prototyp e uses a scroll expander, plate heat exchangers, a diaphragm piston pump and a liquid re ceiv r. This system was tested with different working fluids (R123, R245fa and HFE7000) and a thermal efficiency close to 8% was obtained for a net output power of about 2 kWe. The specificity of the proposed prototype is the ab sence of lubrication: in order to avoid oil circulation in the ORC loop, an oil-free scroll exp ander is developed. This expander is originally an air scroll compressor that was modifi ed using a magnetic coupling to ensure tightness. The experimental results highlight the good efficiency of the device, despite a relatively high internal leakage due to absence of lubrication. The necessity of using magnetic coupling is also justified by comparing the experim ental results with previous ones obtained using mechanical sealing. REFERENCES B. Aoun, D. Clodic, Theoretical and experimental st udy of an oil-free scroll type vapor expander, in: Proceedings of the Compressor Engineering Conferenc , Purdue, 2008 (Paper 1188) Declaye, S., Quoilin, S., & Lemort, V. (2010). Desi gn and Experimental investigation of a Small scale organic Rankine using a scroll expander . Proceeding of the 13th International Refrigeration and Air Conditioning Conference at Pu rd e. V. Lemort, S. Quoilin and C. Cuevas et al., Testing a d modeling a scroll expander integrated into an organic Rankine cycle, Applied Thermal Engineering 29 (14–15) (2009) , pp. 3094– 3102 Quoilin, S., Lemort, V., & Lebrun, J. (2010). Exper imental study and modeling of an Organic Rankine Cycle using scroll expander. Applied Energy, 87 (4), 1260-1268. Saleh, Bahaa, G. Koglbauer, M. Wendland and J. Fisc her, Working fluids for low temperature organic Rankine cycles, Energy 32 (2007) , pp. 1210–1221 T. Yanagisawa, M. Fukuta, Y. Ogi, T. Hikichi, Perfo rmance of an oil-free scroll-type air expander in: Proceedings of the IMechE Conference on Compressors and their Systems , 2001, pp. 167–174