Improving the Performance of an Existing Air-Cooled Binary Geothermal Power Plant: A Case Study

An existing air-cooled binary geothermal power plant in northern Nevada is studied. The current performance of the plant is analyzed with an emphasis on the effects of seasonal climate changes. Two potential sites have been identified to improve the performance of the plant. Northern Nevada has a dry climate, particularly in hot summer months, and the temperature of cooling air can be decreased considerably by evaporative cooling. When the air temperature is decreased to the wet-bulb temperature, the decrease in the condenser temperature is determined to increase the power output by up to 29 percent. The required amount of water for this case is calculated to be about 200,000 tons per yr. Several parametric studies are performed by simulating the operation of the plant with an equation solver with built-in thermophysical property functions. It is determined that the net power output of the plant can be increased by 2.8 percent by optimizing the maximum pressure in the cycle. Also, replacing the existing working fluid isobutane by other commonly used binary fluids such as butane, R-114, isopentane, and pentane do not produce as much of an improvement in the plant performance as operating with isobutane at the optimum maximum pressure. Therefore, isobutane appears to be the best choice for this power plant.