Potential of zeotropic mixtures as working fluids in organic Rankine cycles

The effect of using mixtures as working fluids in organic Rankine cycles (ORCs) is examined with a simulation model of the cycle that includes all elements of an actual installation. We consider several of the commonly used pure ORC fluids as potential components, discuss a mixture selection method, and suggest optimal concentrations. For heat sources at 150 °C and 250 °C, a potential increase of 16% and 6% in cycle efficiency is found. The electricity production at optimal thermal power recuperation can be increased by 20% for the low temperature heat source.

► The performance of zeotropic mixtures of several ORC working fluids is compared.
► An actual ORC installation with two heat source types is simulated.
► An increase in cycle efficiency is observed for both heat source types.
► The improvement is higher for lower temperature heat sources.
► Optimal thermal power recuperation can lead to a 20% increase in electricity output.