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

En af de store udfordringer var at vælge den rigtige CO2-blanding for at skabe balance mellem effektivitet og praktisk anvendelighed. Ved at tilsætte et “dopingmiddel” til CO2 kan væskens egenskaber justeres, så systemet kan bruge en pumpe i stedet for en kompressor. Det gør varmeudvekslingen mere effektiv ved at holde væsken på en temperatur, der passer til solvarmekilden. Flere dopingstoffer blev testet for at finde det bedste i forhold til effektivitet og kompatibilitet.

Materialekompatibilitet var en anden udfordring, da udstyret skal kunne håndtere temperaturer helt op til 550 °C, hvilket er typisk for solvarmeteknologi. Det endelige valg af dopingstof var en afvejning mellem at reducere korrosion og maksimere ydeevnen.

DESOLINATION-projektet sigter mod at lancere sit første pilotanlæg i 2025 og tilbyde konkurrencedygtige løsninger med en solvarmeeffektivitet på over 42%, effektiv ferskvandsproduktion og op til 70% lavere CO2-emissioner pr. kubikmeter afsaltet vand sammenlignet med de nuværende systemer.