Compound Hybrid Geothermal-Fossil Power Plants

Abstract

The principles governing the design of geothermal preheat and fossil superheat hybrid plants are reviewed. Limitations of these designs are pointed out and compound hybrid systems are proposed. Compound hybrid plants are well matched to geothermal resources which produce mixtures of liquid and vapor at the wellhead. One state an two stage compound plants are analyzed using a computer code incorporating realistic assumptions on various losses throughout the systems. Results of analysis are quoted for wellhead temperatures of 150, 200, and 250°C, an for wellhead qualities of 10, 20, 30, and 40% for one stage systems. The analyses for two stage systems are reported for the same temperatures, for 20% quality, and for hot water flash percentages of 25, 50, 75, and 100%. Examples are cited for typical geothermal resources, including the Roosevelt Hot Springs KGRA in Utah, which show what compound hybrid plant at that site would utilize the geothermal energy at an efficient of greater than 80% compared to current geothermal plants with 40-50% based on the Second Law.