Parametric optimization and comparative study of an organic Rankine cycle power plant for two-phase geothermal sources

Abstract

For two-phase geothermal sources, Organic Rankine Cycle (ORC) based binary plant is often applied for power production. In this work, a network topology is designed with the open-source Thermal Engineering Systems in Python (TESPy) software to simulate the stationary operation of the ORC plant. With this topology, the performance of six different working fluids are compared. From the thermodynamic perspective, the gross and net power output are optimized respectively. Results show that R600 has the highest gross power output of 17.55 MW, while R245fa has the highest net power output of 12.93 MW. However, the turbine inlet temperatures for these two working fluids need to be designed at the upper theoretical limit. R245ca and R601a require the heat exchange rates of internal heat exchanger to be larger than 1.51 MW and 0.99 MW to satisfy the re-injection temperature limit, which are smaller than the R600 (6.7 MW) and R245fa (6.0 MW) cases. Besides, the working fluid with lower critical state is preferred for a geothermal source with smaller steam fraction to establish a stable ORC plant. The workflow for the ORC design and optimization in this work is generic, and can be further applied to thermo-economic investigation.