Modular Geothermal Plants in Italy: Technical Characteristics and Operation Results

Abstract

The paper presents the experience of supplying 6 geothermal power plants in Italy.
The article shows the complete plant philosophy, a description of the equipment supplied and some comments to the main issues that the supplier faced up during the development of the job.
All the plants were specified on a modular basis, in order to reduce the number of differences among the 6 plants. Three size of plant, 10, 20, and 40 MW were standardized, and the proposed steam turbines were of two sizes only. A minimum number of capital spare parts are required to ensure the strategic maintenance of the plants.
In details, the paper places a particular focus on the technical issues that have been faced to find suitable solution for this geothermal scenario.
Starting from the well-proven design criteria, used for standard turbo-generators, new solutions were investigated to this specific application. The aggressive environment led to use special materials for casing, rotor and blading like High Alloy Steel, Stellite coatings and Inconell inlays.
Direct contact steam condensers were designed in order to match the highest performance with the specific operating conditions and are fully integrated with the Non-Condensable Gas extraction system. The NCG extraction system is composed of an integrally geared compressor with several impellers and intercooling phases; the compressor is driven by the shaft of the generator. The compressors are sized in compliance to the gas percentage present in each geothermal well.
All the turbo-compressors units have been tested by performance test on site and are actually in operation.
The 6 plants, some of which were supplied on turn-key basis, were successfully completed in a short period thanks to the creation of a dedicated team of job management and to the synergistic co-operation between the supplier and the operating company.