Rome, February 22 2017
The application of a numerical code, validated by measurements on the ground, has made it possible to simulate the dispersion in the atmosphere of hydrogen sulphide, one of the main pollutants emitted by geothermal plants in Tuscany. The research results have been published in Science of the Total Environment
Monitoring the impact of polluting gaseous emissions from geothermal plants in Tuscany is the object of the study conducted by researchers from the National Institute of Geophysics and Volcanology (INGV), Naples and Pisa sections, in collaboration with the National Research Council ( CNR) and private Tuscan companies, within the SIMPAS project - Innovative Measurement Systems for the Protection of the Environment and Health. The results were published in Science of the Total Environment.
“Geothermal energy was born in the Tuscany Region,” explains Renato Somma, a researcher at the Vesuvius Observatory-INGV. Here the geothermal resource of the subsoil was used for the first time in the world for the production of electricity".
Begun more than a century ago (in 1913) the industrial production of geothermal energy is still very active today, thanks to the most modern technologies, supplying more than 25% of the electricity needs of the entire region.
“However”, continues Somma, “until now, a systematic study had never been conducted on the dispersion and effects of hydrogen sulphide (H2S), i.e. one of the main pollutants that is emitted into the environment by the process of exploiting the geothermal. The aim of the study was to evaluate, on a local scale, the potential impact of hydrogen sulphide on the quality of the air, water and soil, emitted by the 35 geothermal plants in Tuscany”.
The numerical code DISGAS - DISpersion of GAS developed by INGV, allows to investigate the iso-concentrations in the air of polluting gaseous elements, both from natural sources (volcanic soils, geothermal areas) and from anthropic sources (chimneys, vehicular traffic). In this case the Code was applied to the hydrogen sulphide emitted by the geothermal plants of the Tuscany Region.
“This numerical model”, adds Somma, “shows how the plumes emitted by geothermal power plants are concentrated around their emission point, with a dispersion trend that follows the direction of the wind. While conditions of atmospheric instability can favor the phenomenon of gas dilution, stagnant atmospheric conditions (such as a quiet summer night) can determine the persistence of the gas near the emission point".
The application of DISGAS, concludes the researcher, "can also be very useful in the design phase of new small or large experimental plants for the cultivation of geothermal resources, in order to predict any effects on the soil, water and air components".
Figure 1 - Map of the concentration of H2S in the atmosphere, in the wind conditions recorded by the mobile meteorological station located in Piancastagnaio (SI). The red star indicates the position of the station in the built-up area. The concentrated plumes that emerge from the three central ones of the area are evident (Piancastagnaio 3,4,5.
Extended
We applied the Eulerian code DISGAS (DISpersion of GAS) to investigate the dispersion of the hydrogen sulfide (H2S) from 32 geothermal power plants (out of 35 active) belonging to the geothermal districts of Larderello, Travale-Radicondoli and Monte Amiata, in Tuscany (Italy). An updated geographic database, for use in a GIS environment, was realized in order to process input data required by the code and to handle the outputs. The results suggest that H2S plumes emitted from geothermal power plants are mainly concentrated around the stacks of emission (H2S concentration up to 1100 μg/m3) and rapidly dilute along the dominant local wind direction. Although estimated values of air H2S concentrations are orders of magnitude higher than in unpolluted areas, they do not indicate an immediate health risk for nearby communities, under the more frequent local atmospheric conditions. Starting from the estimated values, validated by measurements in the field, we make some considerations about the environmental impact of the H2S emission in all the geothermal areas of the Tuscany region.