A case study of working fluid selection for a small-scale waste heat recovery ORC system

AUTHORS: PIOTR KLIMASZEWSKI, DAWID ZANIEWSKI, ŁUKASZ WITANOWSKI, TOMASZ SUCHOCKI, PIOTR KLONOWICZ, PIOTR LAMPART

The paper illustrates a case study of fluid selection for an internal combustion engine heat recovery organic Rankine c ycle (ORC) sys- tem having the net power of about 30 kW. Various criteria of flu id selection are discussed. Particular attention is paid to thermodynam ic performance of the system and human safety. The selection of working fluid for the ORC system has a large impact on the next steps of the design pr ocess, i.e., the working substance affects the turbine design and th e size and type of heat exchangers. The final choice is usually a compromise b etween ther- modynamic performance, safety and impact on natural enviro nment. The most important parameters in thermodynamic analysis inclu de calculations of net generated power and ORC cycle efficiency. Some level of t oxicity and flammability can be accepted only if the leakages are very low. The fluid thermal stability level has to be taken into account too . The econ- omy is a key aspect from the commercial point of view and that i ncludes not only the fluid cost but also other costs which are the conse quence of particular fluid selection. The paper discusses various con figurations of the ORC system - with and without a regenerator and with direct or indirect evaporation. The selected working fluids for the considered particular power plant include toluene, DMC (dimethyl carbonate) and MM (hex amethyld- isiloxane). Their advantages and disadvantages are outlined.

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