Geothermal Binary Power Plants at Raft River, San Emidio, and Neal Hot Springs: Part 1 -Plant Descriptions and Design Performance Comparison

摘要

U.S. Geothermal Inc. built and operates the Raft River (Idaho), San Emidio (Nevada) and Neal Hot Springs (Oregon) geothermal organic Rankine cycle binary power plants. All of them use similar moderate-temperature geofluids pumped from wells and the same 280°F brine inlet design temperature. Raft River uses a recuperated subcritical isopentane cycle, while San Emidio and Neal Hot Springs employ R134a in cycles with supercritical turbine inlet pressures. Neal Hot Springs uses an air-cooled condenser, while the other two are water-cooled. The theoretical thermodynamic performance and net generation of these three power plants with very similar geothermal design conditions are compared. The comparison is made for the design conditions. We show that at the 280°F brine design temperature of the three plants, the supercritical cycle produces more power per pound of brine than the subcritical cycle does. However, while most of this difference is related to the inherent characteristics of the cycles, such as the amount of heat able to be extracted from the brine by the cycle, there are some differences related to economic choices made at the time the plants were built, such as the condenser approach temperature to the sink temperature (wet-bulb or dry-bulb design temperature).