Experimental Isochoric Apparatus for Bubble Points Determination: Application to CO2 Binary Mixtures as Advanced Working Fluids

Experimental Isochoric Apparatus for Bubble Points Determination: Application to CO2 Binary Mixtures as Advanced Working Fluids

by | Jun 21, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

Carbon dioxide binarFIGy mixtures are increasingly considered as working fluids in transcritical power cycles, due to the capability to perform liquid-phase compression even at high environmental temperatures. However, a robust thermodynamic model is essential for optimal and reliable design conditions. It is widely recognized that fine-tuning the equation of state with experimental vapor-liquid equilibrium data of the mixture significantly enhances its reliability.

In this work, a new apparatus dedicated to vapour-liquid equilibrium measurements of mixtures is presented. The proposed method consists of a constant-volume system, where bubble points are identified from the divergence of slope of the isochoric lines between the two-phase and liquid regions, in the temperature-pressure plane. The temperature and pressure limits of the apparatus are 503 K and 25 MPa. Bubble points of CO2 binary mixtures with hexafluorobenzene (C6F6) and n-pentane (C5H12) have been measured and compared with previous literature data for validation purposes. Then, the CO2 mixture with octafluorocyclobutane (c-C4F8) is experimentally studied, addressing a literature gap in bubble point data.

The data are used to calibrate the thermodynamic model, leading to affordable design conditions of the power cycle compared to the non-optimized thermodynamics scenario, in a concentrated solar power tower plant.

 

https://doi.org/10.1016/j.ijft.2024.100742

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Authors:

  • M. Doninelli, G. Di Marcoberardino, C.M Invernizzi and P. Iora – Università degli Studi di Brescia, Dipartimento di Ingegneria Meccanica ed Industriale, via Branze, 38, 25123, Brescia, Italy
Silicon Tetrachloride as innovative working fluid for high temperature rankine cycles: Thermal Stability, material compatibility, and energy analysis

Silicon Tetrachloride as innovative working fluid for high temperature rankine cycles: Thermal Stability, material compatibility, and energy analysis

by | Apr 25, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

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

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Authors:

  • M. Doninelli, G. Di Marcoberardino, C.M Invernizzi, P. Iora, and M. Gelfi – Università degli Studi di Brescia, Dipartimento di Ingegneria Meccanica ed Industriale, via Branze, 38, 25123, Brescia, Italy
  • G. Manzolini – Politecnico di Milano, Dipartimento di Energia, Via Lambruschini 4A, 20156, Milano, Italy
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Experimental investigation of the CO2+SiCl4 mixture as innovative working fluid for power cycles: Bubble points and liquid density measurementsv- Energy Journal

Experimental investigation of the CO2+SiCl4 mixture as innovative working fluid for power cycles: Bubble points and liquid density measurementsv- Energy Journal

by | Apr 23, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

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

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Authors:

  • M. Doninelli, G. Di Marcoberardino, C.M Invernizzi, P. Iora – Università degli Studi di Brescia, Dipartimento di Ingegneria Meccanica ed Industriale, via Branze, 38, 25123, Brescia, Italy
  • G. Manzolini, E. Morosini – Politecnico di Milano, Dipartimento di Energia, Via Lambruschini 4A, 20156, Milano, Italy
  • M. Riva, P. Stringari – Mines Paris, PSL University, Centre of Thermodynamics of Processes (CTP), 77300, Fontainebleau, France
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Finalization of the thermophysical characterization of CO2 mixtures to power our desalination plant

Finalization of the thermophysical characterization of CO2 mixtures to power our desalination plant

by | Dec 26, 2023 | Milestones, Results - CO2 Mixtures in thermodynamic cycles

Our project has reached an important milestone: after an initial screening of promising dopants to be blended with CO2, thermal stability tests of the mixtures were carried out, and material compatibility test were performed for the most interesting blends. As an result, the most interesting CO2 mixtures for the pilot plant were determined.

The DESOLINATION project aims to develop an innovative CSP (Concentrated Solar Power) cycle using CO2 blends together with a heat recovery system to power a desalination plant. The working fluid becomes supercritical CO2-based and the turbomachinery is adapted to new ranges of temperatures and pressures, to be adapted to future CSP plants.

Thermo-chemical stability of the working fluid is one of the most important aspects to be considered for the working fluid selection, especially when dealing with high-grade sources such as concentrated solar power.

The thermodynamics of CO2 blends have been characterised based on experimental data available in the literature as well as with experimental campaign.

Relevant outcomes have been obtained from the test performed on the CO2 mixtures selected after an initial screening: three different dopants have successfully passed the thermal stability test above 550°C with the consolidated methodology developed in the Fluid Test Laboratory of our project partner, the University of Brescia.

However, it is crucial not only that the working fluid avoids chemical dissociation, but also that the interaction between the mixture and the equipment material is acceptable, particularly in the high-temperature sections of the power plant.

For this reason, the two most interesting fluid candidates have been tested in material compatibility test: a prolonged exposure of different material samples at the mixture atmosphere at 550°C, the maximum temperature of the pilot plant, provided interesting results.

The metal samples have been analysed with several methodologies, including mass weight change, optical microscope, and scanning electron microscope.

Our next step will be to test the compatibility of the new materials and coatings with the CO2 mixtures most suitable for the pilot plant. Stay tuned!

Contributors: Paolo Giulio IORA, Gioele Di Marcoberardino and Michele Doninelli (UNIBS)

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R&D Activities on supercritical CO2 in Europe

R&D Activities on supercritical CO2 in Europe

by | Jun 12, 2023 | Events, News, Results - CO2 Mixtures in thermodynamic cycles

4th episode of ETN webinar series – R&D Activities on sCO2 in Europe: Components challenge – Heat Exchangers
12 June 2023 | online ETN Global brings already the fourth episode of its successful free webinar series “R&D Activities on sCO2 in Europe”. Find out more information about speakers and agenda here, register & save the date!
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Study on the Operation of the LUTsCO2 Test Loop with Pure CO2 and CO2 + SO2 Mixture Through Dynamic Modeling

Study on the Operation of the LUTsCO2 Test Loop with Pure CO2 and CO2 + SO2 Mixture Through Dynamic Modeling

by | May 2, 2023 | Publications, Results - CO2 Mixtures in thermodynamic cycles

Within the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, CO2-based mixtures will be used as the working fluid of the power cycle coupled with the desalination plant. Desalination technologies require temperatures above 50℃, therefore a fluid with a critical temperature above 70 ℃ is required to perform the compression step in the liquid phase, minimizing compression work and increasing cycle efficiency. Blending CO2 with other fluids, such as SO2, leads to an increase in the critical temperature of the mixture and makes it suitable for transcritical cycles in concentrated solar power applications, while preserving the advantages of pure CO2 over steam cycles. Throughout the DESOLINATION project, CO2 blends will be tested in the LUTsCO2 test loop to provide validation data for the design of heat exchangers. In this work, the adaptation of the test loop to the CO2 blend is investigated. A dynamic model of the test loop is built in MATLAB-Simulink, which allows each component to be modeled independently and to realize a closed-loop cycle model coupled with a controller and real gas property tables. Steady-state simulations of the system are performed and the dynamic model of each component is verified with the design values. As a result, the study highlights the key performance and fluid dynamic differences which arise from the use of a CO2 blend instead of pure CO2.

Keywords:

  • CO2 mixtures
  • Transcritical refrigeration cycle
  • Dynamic model
  • Simulink
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Authors:

Giuseppe Petruccelli Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Teemu Turunen-Saaresti Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Aki Grönman Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

Afonso Lugo Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland

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