Innovative arrangements of multiple organic Rankine cycles to effectively generate power from the medium-to-low grade of heat source

Abstract Organic Rankine cycle (ORC) is an important method for waste heat recovery. However, there is a remarkable irreversible loss between ORC and heat source/sink, which reduces the performance in energy utilization. In this work, an innovative concept of multi-ORCs arrangement has been proposed for improving the energy utilization. The concept is something like playing the jigsaw puzzle. We have tried the best to fill the temperature gap between heat source and heat sink by multiple ORCs. According to the T-s diagram, the heating temperature of the working fluids paralleling to the temperature of heat source should be considered primarily. Based on the first and exergy laws, multi-ORCs arrangements and system thermo-economic analysis have been carried out for the given single-phase (hot air with 300℃) and two-phase (saturated steam with 185℃) heat source, respectively. For single-phase heat source, the net output/LCOE of three-ORCs and four-ORCs arrangements are 6789 kW/0.063 USD/kWh and 6627 kW/0.072 USD/kWh, respectively; for two-phase heat source, they are 5976 kW/0.069 USD/kWh and 6174 kW/0.068 USD/kWh respectively. This means that the performance improvement depends on the reasonable selection of working fluids and reasonable arrangement of the ORCs, and the thermodynamic and economic issues should be simultaneously considered. The research findings provide a new means for the ORC system optimization.