Thermodynamic Analysis of Organic Flash Cycle (OFC) for Power Generation from Low to Medium Heat Sources

The low to medium temperature of renewable energy sources demands implementing other thermodynamic heat to power cycles other than the conventional power cycle. The existing Steam Rankine Cycle requires a lot of heat in order to ensure the working fluid used in the cycle does not condense during expansion process. Since 50% of the world’s renewable heat source is categorized as low to medium heat, Organic Rankine Cycle has always been the solution to this. However, temperature mismatching is always unavoidable. This project studied and compares the utilization efficiency of Organic Flash Cycle (OFC) with Organic Rankine Cycle and the parameters that might affect the performance of OFC by using three different working fluids: R113, R123 and N-Pentane. Result portrayed that the thermal efficiency of ORC is better than OFC. However, OFC appears to has a comparable utilization efficiency to ORC by generating only 1%-2.7% less efficiency. Although the OFC improved the heat addition efficiency, this advantage was negated by the irreversibility introduced during the flash evaporation. Some significant potential improvements to the OFC are proposed including the use of double flash evaporator or replacing the throttling valve with a two-phase expander to increase efficiency and fully utilize the finite heat source.