Integrated Approach for the Design of Geothermal Binary Power Plants

Geothermal binary power plants are generally designed and optimized considering only the surface equipment of the plant. The optimization process consists of selecting the most suitable working fluid for the power cycle together with optimum operating parameters, namely the cycle pressures and temperatures. However, it would be desirable to adopt a more comprehensive approach, which includes also the subsurface part of the geothermal power plant: such an approach, though often invoked, is not commonly adopted. In this paper, an open-source software, aimed at the calculation of the performance of a geothermal doublet, is coupled to a commercial software, typically employed for power plant design. Particular attention is given to the combined subsurface/surface calculation, and plant performance will be optimized starting from the reservoir conditions. Ascertained that the reservoir temperature is the most important design parameter for the whole installation, the paper aims at investigating the effect of the other subsurface features on the design point of the surface installations, so as to attain a fully optimized power plant and the highest available conversion efficiency. The simulation model will feature a geothermal doublet coupled to an ORC plant for the power generation; several parametric calculations will be conducted, considering different reservoir conditions and a selection of appropriate working fluids for the ORC. Results of simulations will be discussed with the aid of Second Law analysis, with the scope of pointing out the key outcome of the integrated design procedure.