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Session: Poster Session and Sponsors Exhibition
Session starts: Thursday 22 September, 14:00

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Athanasios Papadopoulos (Centre for Research and Technology Hellas)
Mirko Stijepovic (Texas A&M University at Qatar)
Patrick Linke (Texas A&M University at Qatar )
Panos Seferlis (Centre for Research and Technology Hellas)
Spyros Voutetakis (Centre for Research and Technology Hellas)

Abstract:
Power generation from low enthalpy heat sources requires the use Organic Rankine Cycle systems (ORC), where organic fluids such as hydrocarbons or refrigerants are utilized to facilitate efficient heat extraction. The economic, operating and environmental performance of the ORC depends on the properties of the selected working fluids, the design and operating characteristics of the ORC process and the characteristics of the heat source (e.g. hot fluid temperature, flowrate etc.). This raises the challenge of selecting working fluids and ORC process features that will result in an integrated system of optimum performance for a particular heat source. Available works address the selection of ORC fluids based on fluid- and process-related properties by testing various available fluids in ORC simulation models, sometimes combined with optimization of process operating parameters. A common characteristic shared among all these approaches is the use of a data set containing several available working fluid options. Although useful, this approach limits the search for efficient working fluids that exhibit favourable properties to an often empirically compiled dataset containing ‘‘the usual suspects”. Such a small set is extremely limiting in view of the vast number of molecules that could be considered as candidate ORC working fluids. Instead, this work proposes a systematic approach combining computer-aided molecular design (CAMD) methods with process optimization to enable the design of working fluid options and ORC processes of optimum performance. CAMD tools utilize a database containing a few chemical groups that are used to generate and search a vast number of conventional or novel molecular structures to identify those working fluids that offer the best performance with respect to the properties of interest. The evaluation of the investigated working fluids is based on multi-objective optimization technology to identify a broad set of options with optimum physical, chemical, environmental and safety characteristics. The generated working fluids are subsequently introduced to ORC optimization in order to identify process and molecular features resulting in optimum economic performance [1]. Several ORC design stages are considered incorporating increasing modelling and design detail to enable fast and efficient screening of working fluid candidates in view of varying heat source conditions. The proposed developments are illustrated with applications in power or heat and power cogeneration from low enthalpy geothermal fields. Important working fluid properties are considered such as toxicity, flammability, ozone depletion and global warming potential, in conjunction to economic ORC performance. REFERENCES [1] A. I. Papadopoulos, M. Stijepovic, P. Linke. On the systematic design and selection of optimal working fluids for Organic Rankine Cycles, Applied Thermal Engineering, 30, 760-769 (2010)