Okolinski i termodinamički prihvatljivi radni fluidi u organskom Rankinovom ciklusu za upotrebu biomase
Fully halogenated chlorofluorocarbons (CFCs) are, despite their good thermodynamic properties, stability and non-toxicity, eliminated from use. Due to the content of one chlorine atom in the molecule, the use of hydrochlorofluorocarbons (HCFCs) has been reduced in many European countries. The use of partially halogenated hydrofluorocarbons (HFCs) in which the molecules have no chlorine atoms, due to increased inflammability, is also to a large extent limited. This paper presents a methodology for selecting working fluids or mixtures for use in cogeneration ORCs on biomass, which will, in addition to thermodynamics, also take into account the safety and environmental requirements of working fluid acceptability. The effects of thermodynamic properties of preselected working fluids on the performance of the cogeneration ORC plant have been analyzed and the thermodynamic properties of the working fluid are optimized by the exergy efficiency of the ORC as a function of the target, using a genetic algorithm. Optimal values of the exergy efficiency, component size and exergy losses of the cogeneration ORC for the use of biomass energy are compared and analyzed under the same heat source conditions and pre-defined boundary conditions. The experimental analysis of the cogeneration ORC shows that the most preferred working fluid is p-xylene because in comparison to undekan, MDM (OMTS) and D4 (OMCTS) it has the highest value of exergy efficiency but also requires the least dimension of ORC components (turbines and capacitors).