Silicon Tetrachloride (SiCl₄) is proposed as a new potential working fluid for high-temperature Rankine Cycles. The capability to overcome the actual thermal stability limit of fluids commercially employed in the state-of-the-art Organic Rankine Cycles (ORC) is demonstrated by static thermal stability and material compatibility tests. Experimental static test proves its thermo-chemical stability with a conventional stainless-steel alloy (AISI 316L) up to 650 °C. A preliminary material compatibility analysis performed with optical microscope on the AISI 316L cylinder, after exposure of 300 h to SiCl₄ at temperature higher than 550 °C, confirms the potentiality of this fluid when coupled with high-grade heat sources. A thermodynamic analysis has been carried out accounting for the effect of operating conditions on the axial turbine efficiency. A comparison with fluids adopted in medium–high temperature ORCs is performed, evidencing that the proposed fluid could achieve more than + 10 % points as thermal efficiency gain compared to any commercial solutions when coupled with high-temperature sources such as solar, biomass, waste heat from industrial processes and prime movers. A 2 MW SiCl₄ cycle operating full-electric at 550 °C reaches a thermal efficiency of 38 %, exceeding values attainable by any other working fluid under similar conditions and power size.

https://doi.org/10.1016/j.applthermaleng.2024.123239

Supercritical CO₂ is recognized as a promising working fluid for next-generation of high temperature power cycles. Nevertheless, the use of CO₂ mixtures with heavier dopants is emerging as a promising alternative to supercritical CO₂ cycles in the recent years for air-cooled systems in hot environments. Accordingly, this work presents an experimental campaign to assess the thermodynamic behaviour of the CO₂+SiCl₄ mixture to be used as working fluid for high-temperature applications, conducted in the laboratories of CTP Mines Paris PSL. At first, bubble conditions of the mixture are measured in a variable volume cell (PVT technique), then liquid densities are measured with a vibrating tube densimeter, for molar composition in the range between 70 % and 90 % of CO₂. The Peng Robinson EoS was fine-tuned on the bubble points obtained, resulting in a satisfactory accuracy level. Finally, a non-conventional methodology has been developed to measure bubble points with the vibrating tube densimeter, whose results are consistent with the VLE data obtained with the standard PVT technique. Thermodynamic analysis in next-generation concentrated solar power plant, at 700 °C turbine inlet, confirms the mixture overcomes 50 % thermal efficiency, providing +4.2 % net electrical output over pure supercritical CO₂ at equal thermal power from the solar field.

https://doi.org/10.1016/j.energy.2024.131197

Eine große Herausforderung war die Wahl der richtigen CO2-Mischung, um ein Gleichgewicht zwischen Effizienz und Zweckmäßigkeit zu finden. Durch die Zugabe eines “Dotierstoffs” zum CO2 konnten die Eigenschaften der Flüssigkeit angepasst werden, so dass das System eine Pumpe statt eines Kompressors verwenden kann. Dadurch wird der Wärmeaustausch effizienter, da die Flüssigkeit auf einer für die Solarwärmequelle geeigneten Temperatur gehalten wird. Es wurden mehrere Dotierstoffe getestet, um den besten für Effizienz und Kompatibilität zu finden.

Eine weitere Herausforderung war die Materialkompatibilität, da die Geräte Temperaturen von bis zu 550 °C standhalten müssen, die für die solarthermische Energietechnik typisch sind. Die endgültige Wahl des Dotierstoffs war ein Kompromiss zwischen der Verringerung der Korrosion und der Maximierung der Leistung.

Im Rahmen des DESOLINATION-Projekts soll 2025 die erste Pilotanlage in Betrieb genommen werden, die wettbewerbsfähige Lösungen mit einem solarthermischen Wirkungsgrad von über 42%, einer effizienten Süßwasserproduktion und bis zu 70% geringeren CO2-Emissionen pro Kubikmeter entsalztem Wasser im Vergleich zu den derzeitigen Systemen bietet.