Organic Rankine Cycle Power Generation for Energy Recovery From Air Compressors

The organic Rankine cycle (ORC) is a power generating technology that can enable the utilization of waste heat to generate electric power from different sources, including geothermal hot springs, other power generating technologies, and industrial applications. There is a significant technical challenge in producing financially viable ORC plants, due to the high costs associated with custom heat exchange components and turbo-machinery. In the last few years, however, packaged systems have been developed from commercially available refrigeration systems, which significantly reduce cost. The goal of this project was to evaluate the feasibility of generating electricity using the waste heat from industrial air compression equipment. A simulation program was written to model the thermodynamics of the ORC. Several potential working fluids were surveyed and ranked based on their applicability to the industrial operating conditions. In particular, refrigerant R-236fa has been determined to be the most appropriate working fluid. The decision was made by weighing its thermal properties, as well as environmental and health considerations. Two types of heat rejection technology were considered, namely water-cooling and air-cooling, with emphasis on the effect of ambient conditions on ORC performance. It is concluded that water-cooling can be used for a plant located in Ontario, Canada, with the possibility of utilizing air-cooling during the cooler seasons of the year. An installation cost of U.S. $1,300/kW is feasible, yielding a simple payback period of 6.35 years. The results of this research project encourage further work to be done on this application of waste heat recovery.