This paper presents a design and off-design study of a geothermal field consisting of a number of wells, a steam network which collects the geothermal fluid, and a power plant to generate electricity. The geothermal field considered is located in Italy and the fluid is a mixture of steam and non-condensable gases. The power plant is a conventional type for vapor dominated fields and has a compressor-extractor to remove non-condensable gases from the condenser. The condenser has wet cooling towers to remove heat. In this study, computer codes developed at the University of Perugia were used to simulate the behavior of geothermal field as a whole. The wells are modeled with second order functions in order to describe pressure-flow rate and temperature-flow rate correlations. The geothermal fluid network is calculated by setting pressures and thermal losses in all the branches. The power plant is simulated with all its components: steam turbine, condenser, gas extractor, cooling towers and auxiliaries. All the components of the geothermal field are simulated at both design and off-design conditions. The fluid network is solved with an algorithm developed by the authors, which allows the definition of boundary conditions by means of curves based on experimental data. The advantage in comparison with conventional techniques, requiring a fixed pressure or flow rate as boundary condition, is that the solution of the network and the power plant is always a real solution. The results show how changes in ambient conditions or in the characteristic curve of one or more plant components may influence power production and the exploitation of the geothermal source.
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