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

Preliminary Characterization of the Desolination Project Demo Plant: Design and Off-Design Operability

Preliminary Characterization of the Desolination Project Demo Plant: Design and Off-Design Operability

by | Sep 5, 2024 | Milestones, Publications, Results - Pilot plant preparation

The DESOLINATION project, a beacon of innovation in renewable energy, has taken a major step forward with the preliminary performance analysis of its demonstration plant.

Recently unveiled at the ASME Turbo Expo 2024, this work brings together the expertise of TEMISth, UNIBS (University of Brescia), and Politecnico di Milano (POLIMI) to explore the potential of a novel power cycle built for sustainability and efficiency.

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What makes this Demo Plant unique?

This demo plant operates a simple recuperative transcritical power cycle, a system that sets new standards in energy conversion. Here’s what makes it stand out:

  • Innovative Working Fluid: Instead of conventional fluids, the plant uses a mixture of CO₂ and SO₂, selected for its unique thermodynamic properties.
  • Adapted to Harsh Conditions: Designed to thrive in environments with high solar radiation and elevated ambient temperatures, this air-cooled system mirrors real-world challenges faced by Concentrated Solar Power (CSP) plants.
Key features of the cycle
  • Powerful yet Compact: At the heart of the system is an axial turbine handling a flow rate of 0.2 m³/s, enabling a power output of 1.8 MWel.
  • Next-Gen Heat Exchangers: Equipped with gyroid-structured recuperators and heat exchangers, these components maximize thermal transfer while minimizing material use.
  • Modeling Precision: Advanced simulations in MATLAB, enhanced by Computational Fluid Dynamics (CFD) results, ensure the system is optimized for both design and off-design conditions.
How efficient is it?

Efficiency is key for renewable energy systems, and the DESOLINATION demo plant doesn’t disappoint. By operating in a sliding pressure mode, the cycle achieves impressive efficiencies of over 30%, even when running at partial load.

Adapting to changing temperatures

One of the standout features of this system is its ability to handle varying ambient conditions:

  • At high ambient temperatures (above 30°C), the cycle functions seamlessly, thanks to fixed-speed condenser fans.
  • At lower temperatures (around 10°C), the air velocity can be adjusted to ensure optimal operation.
Handling the system’s inventory

The study also delves into the plant’s piping system, revealing that the total fluid inventory is heavily influenced by the condenser’s operation. Adjustments in fluid storage of up to 300 kg are required to maintain stability when switching between different temperature conditions.

This research represents a significant milestone in the DESOLINATION project’s mission to develop renewable energy systems that are not only efficient but also adaptable to a variety of real-world conditions. By bridging the gap between innovative design and practical application, the demo plant is a glimpse into the future of clean, sustainable power generation.
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Authors: Ettore Morosini, Marco Astolfi, Michele Doninelli, Paolo Iora, Damien Serret, Jean-Michel Hugo and Giampaolo Manzolini.

DOI: https://doi.org/10.1115/GT2024-127246

Experimental study on coalescer efficiency for liquid-liquid separation

Experimental study on coalescer efficiency for liquid-liquid separation

by | Jul 8, 2024 | Publications, Results - Draw solution

The global community acknowledges water demand and accessibility as major challenges impacting human well-being. Forward Osmosis (FO) desalination coupled with concentrate solar power might represent a promising solution to combine water production with renewable sources. This work assesses the performance of a liquid-liquid separator (coalescer), an important component of the FO process, when using a polymeric thermo-responsive draw agent (PAGB2000). Experimental characterization of the coalescer is carried out for different regeneration temperatures (from 50 to 80 °C), residence time, draw concentration (from 0.30 to 0.60) and metal meshes. The separation efficiency of the coalescer can be as high as 95% for high residence time and regeneration temperatures (> 70 °C). Eventually, an analytical expression of the coalescer efficiency as function of the main operating parameters is proposed both to support desalination plant design and to enable understanding its applicability beyond its original context.

https://doi.org/10.1016/j.desal.2024.117840

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Authors:

Igor Matteo Carraretto, Davide Scapinello, Riccardo Bellini, Riccardo Simonetti, Luca Molinaroli, Luigi Pietro Maria Colombo, Giampaolo Manzolini – Dipartimento di Energia, Politecnico di Milano, Via Lambruschini 4, Milano 20156, Italy

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

Commercial thermo-responsive polyalkylene glycols as draw agents in forward osmosis

Commercial thermo-responsive polyalkylene glycols as draw agents in forward osmosis

by | May 24, 2024 | Publications, Results - Draw solution

Forward osmosis (FO) is a promising technology for efficient water reclamation at low operating costs. It has shown potential in producing fresh water from seawater; however, the regeneration of the diluted draw solution (DS) still holds back further development. Thermo-responsive polymers, especially polyalkylene glycol (PAG) based copolymers with hydrophilic ethylene oxide and hydrophobic propylene oxide units, have shown suitability as DSs in FO using low-temperature waste heat to regenerate the DS. In this study, we explored five commercially available copolymers: Pluronic® PE 6400, Pluronic® L-35, Pluronic® RPE 1740, Unilube® 50 MB-26, and Polycerin® 55GI-2601 as DSs in a laboratory FO setup, with DI water as the feed solution (FS). The water
flux and reverse solute flux varied from 1.5 to 2.0 L⋅m􀀀 2⋅h􀀀 1 and from 0.04 to 0.4 g⋅m􀀀 2⋅h􀀀 1, respectively.

Furthermore, all polymer solutions showed the ability to be recovered and reused using temperatures below 100◦C. Therefore, the tested PAGs turned out to be promising as draw solutions for FO systems that utilize low-grade waste heat. The re-usage in FO was shown for regenerated Pluronic® L-35 through a three-step experiment where its recovery was 91.1 %, 93.1 %, and 91.9 % for each FO cycle, respectively.

Keywords: Forward osmosis, Draw solution, Osmotic pressure, Polyalkylene glycols, Lower critical, solution temperature, Reuse of polymer.

Authors: Irena Petrinic, Natalija Jancic, Ross D. Jansen van Vuuren, and Hermina Buksek.

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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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