Feasibility study of a geothermal power plant with a double-pipe heat exchanger

The technologies currently in use for the power production in the geothermal field are sometimes affected by two crucial problems: the environmental impact and the drilling costs. The first issue is related to the techniques adopted to increase the heat exchange (as artificial subsoil fracturing) or to the use of aquifers which contain pollutants that are not properly disposed or confined. The drilling costs are high because two wells are generally necessary to operate properly the power plant. An interesting solution could be the adoption of a double-pipe heat exchanger that consists in two concentric pipes placed in a single well. This setup allows the operation of the plant in a closed loop configuration with no mass exchange between the subsoil and the surface. A coupled approach based on a 1D model for the pipe and a 2D axisymmetric model for the surrounding rocks was developed in this study to investigate the actual capability of a double-pipe system in different operating conditions.