Impact of organic Rankine cycle working fluid selection on heat exchanger design and cost

Abstract

The Organic Rankine Cycle (ORC) is used to convert low temperature heat into useable energy. Each ORC is a specifically tailored system and its design must take into account each aspect of the project, such as the resource available, size of the power plant, and the economics of the project. The working fluid selection is a critical design decision for an ORC as it influences the design of each of the components. There are several different working fluids used in commissioned ORCs, the most common being N-Pentane. Non-flammable refrigerants such as R134a and R245fa are also used in small automated ORCs because of their reduced risk of explosion. R134a and R245fa are both HFC refrigerants with high global warming potentials that could potentially be phased out in the near future. This paper uses thermodynamic models to investigate the impact of the working fluid on an ORC and further investigate the choice of working fluid on the design of the heat exchangers. The heat exchangers are a critical component for ORCs as they can contribute to at least 20% of the capital cost[1].