A Comprehensive Review of Organic Rankine Cycles

Climate change is one of the main issues that humanity is currently facing due to carbon dioxide emissions caused by the use of fossil fuels. Organic Rankine cycles may play an important role in reducing these emissions since they can be operated by using industrial waste heat of renewable energies. The present study presents a comprehensive bibliographic review of organic Rankine cycles. The study not only actualizes previous reviews that mainly focused on basic cycles operating on subcritical or supercritical conditions but also includes the analysis of novel cycles such as two-stage and hybrid cycles and the used fluids. Recuperative and regenerative cycles are more efficient than reheated and basic single-stage cycles. The use of two-stage cycles makes it possible to achieve higher thermal efficiencies and net power outputs of up to 20% and 44%, respectively, compared with those obtained with single-stage cycles. Theoretical studies show that hybrid systems, including Brayton and organic Rankine cycles, are the most efficient; however, they require very high temperatures to operate. Most organic Rankine cycle plants produce net power outputs from 1 kW up to several tens of kW, mainly using microturbines and plate heat exchangers.