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

Een grote uitdaging was het kiezen van het juiste CO2-mengsel om een balans te vinden tussen efficiëntie en bruikbaarheid. Door een “dopant” toe te voegen aan CO2 konden de eigenschappen van de vloeistof worden aangepast, waardoor het systeem een pomp kon gebruiken in plaats van een compressor. Dit maakt de warmte-uitwisseling efficiënter door de vloeistof op een temperatuur te houden die geschikt is voor de zonnewarmtebron. Er werden verschillende doteermiddelen getest om de beste te vinden voor efficiëntie en compatibiliteit.

Materiaalcompatibiliteit was een andere uitdaging, omdat de apparatuur temperaturen tot 550°C moet kunnen verwerken, wat typisch is voor zonne-energietechnologie. De uiteindelijke keuze van het doteringsmateriaal was een afweging tussen het verminderen van corrosie en het maximaliseren van de prestaties.

Het DESOLINATION-project wil in 2025 zijn eerste proeffabriek lanceren en concurrerende oplossingen bieden met een zonthermisch rendement van meer dan 42%, efficiënte zoetwaterproductie en tot 70% lagere CO2-uitstoot per kubieke meter ontzilt water in vergelijking met de huidige systemen.