Simultaneous design optimization of binary co2-mixture-based power cycles for concentrated solar power applications

Simultaneous design optimization of binary co2-mixture-based power cycles for concentrated solar power applications

by | Sep 11, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

In the push toward cleaner and more efficient energy, concentrated solar power (CSP) systems have emerged as a promising contender. But their potential has been limited by the need for innovative, cost-effective solutions to convert solar heat into electricity.

We’re thrilled to announce a groundbreaking publication by Teesside University, one of our partners, presented at the ASME (The American Society of Mechanical Engineers) Turbo Expo 2024 (Turbomachinery Technical Conference and Exposition).

This work unveils an innovative approach to optimizing power cycles for CSP systems, driving advancements in efficiency and sustainability.

A recent study introduces an innovative approach to improving power cycles for concentrated solar power (CSP) systems, a key technology in the renewable energy landscape. This research focuses on optimizing the performance of systems that use CO₂-based mixtures as working fluids, offering significant advancements in efficiency, cost-effectiveness, and adaptability to various operating conditions.

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Traditionally, CSP systems rely on converting solar heat into electricity through power cycles. This study enhances that process by developing a simultaneous optimization strategy. It considers the design of the power cycle, the selection of chemical additives (dopants), and the specific composition of the CO₂-based working fluids. By analyzing these factors together, the researchers aim to maximize system efficiency while reducing costs.

The study tests these innovations under realistic scenarios, including two operating temperature ranges: 550°C, typical of current CSP systems, and a higher 700°C for advanced designs. It also accounts for ambient temperatures of 30°C, 35°C, and 40°C, reflecting the diverse environments where CSP systems operate.

One of the key breakthroughs is the use of binary mixtures of CO₂ combined with chemical dopants like sulfur dioxide (SO₂) or acetonitrile (C₂H₃N). These additives enhance the thermodynamic properties of the working fluid, allowing the system to perform more effectively under varying conditions. The research team employed advanced modeling techniques to evaluate these mixtures, ensuring precise predictions of their performance.

Optimization in this context focuses on two main objectives: maximizing thermal efficiency (the amount of solar energy converted into electricity) and improving specific work (the energy produced per unit of working fluid). These improvements reduce the size and cost of system components, like power blocks and thermal energy storage (TES), making CSP systems more economically viable.

This innovative approach holds great promise for the future of renewable energy. By addressing technical and financial challenges, the study opens the door for CSP systems to play a larger role in the global transition to cleaner energy. With its flexible methodology, capable of incorporating new materials and designs, this research sets the stage for continued advancements in solar power technology.
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Authors: Balkan Mutlu, Kumar Patchigolla, Dhinesh Thanganadar

DOI: https://doi.org/10.1115/GT2024-124083

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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An Advanced Desalination System with an Innovative CO2 Power Cycle Integrated with Renewable Energy Sources

An Advanced Desalination System with an Innovative CO2 Power Cycle Integrated with Renewable Energy Sources

by | Oct 18, 2023 | Publications, Results - CO2 Mixtures in thermodynamic cycles

The rise in CO2 emissions is causing major problems like glaciers melting and sea levels rising. To help tackle these issues, the DESOLINATION project introduces a cutting-edge power cycle for desalination systems, using innovative CO2-based mixtures as the next generation of working fluids. This paper highlights the project’s benefits and the technical hurdles overcome in designing the necessary machinery.
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Key factors were considered when developing the thermal cycle and choosing the working fluid, including safety, environmental impact, material compatibility, and efficiency.

The system relies on turbomachinery—specifically a pump and an expander—to recover heat from a primary solar-powered cycle. This setup allows flexible heat production while simulating different solar conditions.

One major challenge was picking the right CO2 blend to balance efficiency and practicality. By adding a “dopant” to CO2, the fluid’s properties could be adjusted, allowing the system to use a pump instead of a compressor. This makes heat exchange more efficient by keeping the fluid at a temperature suitable for the solar heat source. Several dopants were tested to find the best one for efficiency and compatibility.

Material compatibility was another challenge, as the equipment needs to handle temperatures as high as 550°C, typical for solar-thermal power technology. The final dopant choice was a trade-off between reducing corrosion and maximizing performance.

The DESOLINATION project aims to launch its first pilot plant in 2025, offering competitive solutions with solar-thermal efficiency above 42%, efficient freshwater production, and up to 70% lower CO2 emissions per cubic meter of desalinated water compared to current systems.

Authors:

DOI: https://doi.org/10.2118/215993-MS