Rigorous simulation of geothermal power plants to evaluate environmental performance of alternative configurations

Different studies highlighted the environmental impacts of geothermal power plants (GPPs), especially in the operational phase. Primary data are essential for reliable environmental assessments, but these are not available when considering alternative configurations. Rigorous simulation can offer such a degree of information, representing also a tool for a digital twin technology transition. Considering a GPP in Tuscany, Italy, four alternatives configurations are simulated in UniSim Design (R), performing accurate refinements to the thermodynamic model to properly estimate the behavior of different pollutants (Hg, H2S, NH3, and SO2) among the various unit operations. The configurations alternate direct-contact and surface condensers as well as wet and dry towers as cooling systems, while a fifth one adopts an organic Rankine cycle. The actual plant model has been reconciliated with data collected during two different monitoring campaigns. Performance analysis shows a trade-off: the lowest pollutant emissions are obtained using the dry tower generating less net energy (20.17 MWe and 20.83 MWe), instead, adopting surface condenser and wet tower, 22.26 MWe are produced with NH3 emissions almost 3 times the measured ones. The CO2 and CH4 amount in the well fluid is not abated in any configurations and therefore their emissions are the same among them.