Binary Cycle Expander for Geothermal Power Generation

Abstract

A 50 megawatt hydrocarbon expander turbine was designed with an actual mechanical limit of approximately 80 Mwe. The design pressures of 34 bar (500 psia) inlet and 13 bar (200 psia) exhaust were based on a mixture of isobutane and isopentane. Inlet temperature is 149°C (300°F). The turbine is capable of being directly coupled with a two pole 3600 r/s (3600 RRM) AC generator. The expander casing is a single body, vertically split barrel. Internal access and rotor removal are through the end opposite the drive end. The double flow rotor configuration has three expansion stages in each of the two flow paths. The flexible shaft design operates between the first and second critical speeds. Mechanical contact seal contain the hydrocarbon under all operating and shutdown conditions. The turbine design incorporates already developed components with operating experience.