The potential of halogenated olefins as working fluids for organic Rankine cycle technology

The phase-out of hydrofluorocarbons triggered by the enforcement of new environmental regulations forces the search for new substances that comply with the stricter environmental requirements, while offering similar thermodynamic performance and safety features. Olefins containing fluorine and/or chlorine have the potential to be used as replacement fluids with sufficient performance.

Currently, only a few halogenated olefins are available on the market for their use as refrigerants or working fluids, but the potential of all other possible olefinic molecules has not yet been studied. In this work we present a comprehensive evaluation of halogenated olefins of up to five carbon atoms, containing fluorine and/or chlorine, as potential working fluids for use in organic Rankine cycle power systems.

To this end, tailored predictive models for the thermophysical properties of the considered olefins are used to explore the potential use of halogenated olefins having low global warming potential and low ozone depletion potential as working fluids for organic Rankine cycle power systems. The results indicate that options with good thermodynamic performance exist for both low and high temperature applications, each of them implying the use of more fluorinated or more chlorinated olefins, respectively.

Preliminary estimates indicate reasonable environmental and safety features for these options, however, a deeper study to confirm their compliance with regulations on ozone protection or global warming should be carried out for their future use. Furthermore, these options may be considered as future replacements for current flammable working fluids for high temperature applications, where they may even outperform them in terms of net power output.