Geothermal power plants in Italy: increasing the technological performance

Abstract

The need of increasing the efficiency of geothermal power plants has brought in last years to several evolutions in the technology of plants and in operational practices. We describe in detail the technological solutions put in place in order to expand the characteristics of the fluids that can be used, reduce maintenance need, increase efficiency and reliability of machinery, improve operational control techniques. With the increasing of wells depth, we find fluids that are more and more corrosive. For this reason we have developed various techniques, changing with different steam superheating degree, and that make possible the economic utilization of the new fluid found. Different technical solutions are applied, depending on where the dew point is formed according to thermodynamic conditions. Very hot fluids do not bring corrosion problems in the casing and pipes, but only in certain stages of the turbine according to the expansion curve. To avoid this problem we have tested new materials able to resist corrosion. In this way it is also possible to remove the treatment of steam just before the turbine, which reduces the efficiency of cycle. The new machine designed with the concepts of modularity has increased the efficiency of transformation and allowed to operate changes in a fast and flexible way, in order to follow the evolution of the reservoir. We have also developed our monitoring capability with the development of sensors and signals transfer network. In this way we have increased our capacity of events prediction and elimination of false alarms, with an increase in the availability of the machinery. The evolution of our ability to process signals has allowed to discriminate each small variation indicating a deterioration in operation (plant signature), in order to promptly operate both to reset the operation parameters on the values of maximum efficiency or to plan any maintenance action.