Design and modelling of a small-scale reversible high temperature heat pump – organic Rankine cycle system for industrial waste heat recovery

Abstract

Organic Rankine cycle (ORC) and heat pump (HP) are two well-established technologies for industrial waste heat recovery. Given the similarity between ORC and HP configurations, a system that can switch between HP and ORC modes with minimal modification is feasible. The reversible system according to the requirement of the industry can exploit waste heat in lower temperature bands operating as a high-temperature heat pump (HTHP) to provide useful process heat or as an organic Rankine cycle system generating power and thus increasing the efficiency of waste heat exploitation. This study discusses the design aspects of a small-scale reversible HTHP - ORC system, including the system layout, component selection, selection of an appropriate working fluid, the operating conditions for both modes, and equipment sizing. R1233zd(E) was selected as the refrigerant for the reversible system and an automotive open drive scroll compressor was found to be suitable which can also be employed as an expander for ORC with minimum modifications. The study also presents the modelling of the reversible system in ORC and HTHP modes including performance analysis of scroll machine in expander and compressor roles attaining isentropic efficiency values up to 62.4% and 75.4% respectively. The modelling results show a cycle efficiency of 5.9% (Tev = 102 °C, ṁr = 0.064 kg/s) in ORC mode and a COP of 4.19 in HTHP mode (for a temperature lift of 49 K with Tsource: 85 °C, Ncomp: 2000 RPM).