Energy and Exergy Analyses of Geothermal Power Plants with and without Re-Injection

Abstract

Growing energy demands and the desire to reduce pollution have increased interest in research on unconventional power plant technologies. Geothermal power plant technology is an important area being explored as a renewable and environmentally benign alternative to fossil fuel technologies. Geothermal power plants have sources of emissions associated with use, including the use of evaporation ponds. An example of a geothermal power generation unit that utilized an evaporation pond to manage spent geothermal fluids during its operation is the Cerro Prieto I plant in Mexico. A theoretical model is developed to retrofit the plant with geothermal fluid re-injection. Energy and exergy analyses are performed for the standard plant, using the evaporation pond, as well as a hypothetical system utilizing fluid re-injection. The plant without re-injection is found to have an energy efficiency of 12.6% and an exergy efficiency of 47.5%. With re-injection the energy efficiency is 16.5% and the exergy efficiency is 51.5%. The greatest loss in the standard system is through direct discharge of the geothermal fluids to the evaporation pond.