Due to better temperature matching of source and working fluid during heat addition, Organic Flash Cycles (OFCs) are suitable for geothermal power generation driven by medium-low temperature sources. In this paper, thermodynamic analysis of basic OFC (BOFC), and four modified systems with different internal heat recovery methods are presented. Internal heat exchange system (IHE) using a preheater to recover the heat of turbine exhaust. Regenerative organic flash cycle (ROFC) is a regenerative system that recover the part of heat of liquid after flashing. ROFC with an IHE system combines IHE with ROFC that achieves secondary internal heat recovery. Modified organic flash cycle (MOFC) directly mixes the hot liquid after flashing with cold working fluid. The flash temperatures for the five systems are optimized for maximum net power outputs at reinjection temperatures from 65-85 °C as well as source temperatures from 110-150 °C. Results show that internal heat recovery can greatly improve system performance. Exergy destruction of evaporators and throttling processes for ROFC, ROFC with an IHE, and MOFC systems are significantly decreased compared to BOFC. MOFC is superior to other systems in the power production and exergy efficiency. Furthermore, internal heat recovery could lead to change of positions of the pinch points.

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