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Category: Scientific Articles

2021, Scientific Articles

Thermodynamic cycles for solar thermal power plants: A review

Thermodynamic cycles for solar thermal power plants: A review, M. Muñoz, A. Rovira, M. J. Montes, WIREs Energy and Environment, e420, 2021, Online version, https://doi.org/10.1002/wene.420

Abstract

Solar thermal power plants for electricity production include, at least, twomain systems: the solar field and the power block. Regarding this last one, theparticular thermodynamic cycle layout and the working fluid employed, havea decisive influence in the plant performance. In turn, this selection dependson the solar technology employed. Currently, the steam Rankine cycle is themost widespread and commercially available option, usually coupled to a para-bolic trough solar field. However, other configurations have been implementedin solar thermal plants worldwide. Most of them are based on other solar tech-nologies also coupled to a steam Rankine cycle, although integrated solar com-bined cycles have a significant level of implementation. In the first place, powerblock configurations based on conventional thermodynamic cycles—Rankine,Brayton, and combined Brayton–Rankine—are described. The achievementsand challenges of each proposal are highlighted, for example, the benefitsinvolved in hybrid solar source/fossil fuel plants. In the second place, proposalsof advanced power block configurations are analyzed, standing out: supercriticalCO2Brayton cycles, advanced organic Rankine cycles, and innovative integratedsolar combined cycles. Each of these proposals shows some advantagescompared to the conventional layouts in certain power or source temperatureranges and hence they could be considered attractive options in the mediumterm. At last, a brief review of proposals of solar thermal integration with otherrenewable heat sources is also included.

2021, Scientific Articles

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1−xFex)3O4 Spinels

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1−xFex)3O4 Spinels, A. J. Carrillo, L. E. Chinchilla, A. Iglesias‐Juez, S. Gutiérrez‐Rubio, D. Sastre, P. Pizarro, A. B. Hungría, J. M. Coronado, Small Methods, 5 (10), 2100550, 2021, Online version, https://doi.org/10.1002/smtd.202100550

Abstract

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn3O4 to Mn2O3 limits efficiency. In contrast, (Mn1−xFex)3O4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe-doped Mn oxides is performed to elucidate how Fe incorporation influences solid-state transformations. X-ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high-resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe-enriched crystallites likely correspond to jacobsite. In situ X-ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn2+ in the spinel phase to Mn3+ in bixbyite. Extended X-ray absorption fine structure shows that Fe-O length is larger than Mn-O, but both electron energy loss spectroscopy and X-ray absorption near edge structure indicate that iron is always present as Fe3+ in octahedral sites. These structural modifications may facilitate ionic diffusion during bixbyite formation.

2021, Scientific Articles

Thermal Spray processes in Concentrating Solar Power technology

Thermal Spray processes in Concentrating Solar Power technology, F. Rubino, P. Poza, G. Pasquino, P. Carlone, Entropy, Metals, 11 (9), 1377, 2021, Online version, https://doi.org/10.3390/met11091377

Abstract

Solar power is a sustainable and affordable source of energy, and has gained interest from academies, companies, and government institutions as a potential and efficient alternative for next-generation energy production. To promote the penetration of solar power in the energy market, solar-generated electricity needs to be cost-competitive with fossil fuels and other renewables. Development of new materials for solar absorbers able to collect a higher fraction of solar radiation and work at higher temperatures, together with improved design of thermal energy storage systems and components, have been addressed as strategies for increasing the efficiency of solar power plants, offering dispatchable energy and adapting the electricity production to the curve demand. Manufacturing of concentrating solar power components greatly affects their performance and durability and, thus, the global efficiency of solar power plants. The development of viable, sustainable, and efficient manufacturing procedures and processes became key aspects within the breakthrough strategies of solar power technologies. This paper provides an outlook on the application of thermal spray processes to produce selective solar absorbing coatings in solar tower receivers and high-temperature protective barriers as strategies to mitigate the corrosion of concentrating solar power and thermal energy storage components when exposed to aggressive media during service life.

2021, Scientific Articles

Bibliometric analysis on supercritical CO2 power cycles for Concentrating Solar Power applications

Bibliometric analysis on supercritical CO2 power cycles for Concentrating Solar Power applications, M. A. Reyes-Belmonte, R. Guedez, M. J. Montes, Entropy, 23 (10), 1289, 2021, Online version, https://doi.org/10.3390/e23101289

Abstract

In recent years, supercritical CO2 power cycles have received a large amount of interest due to their exceptional theoretical conversion efficiency above 50%, which is leading a revolution in power cycle research. Furthermore, this high efficiency can be achieved at a moderate temperature level, thus suiting concentrating solar power (CSP) applications, which are seen as a core business within supercritical technologies. In this context, numerous studies have been published, creating the need for a thorough analysis to identify research areas of interest and the main researchers in the field. In this work, a bibliometric analysis of supercritical CO2 for CSP applications was undertaken considering all indexed publications within the Web of Science between 1990 and 2020. The main researchers and areas of interest were identified through network mapping and text mining techniques, thus providing the reader with an unbiased overview of sCO2 research activities. The results of the review were compared with the most recent research projects and programs on sCO2 for CSP applications. It was found that popular research areas in this topic are related to optimization and thermodynamics analysis, which reflects the significance of power cycle configuration and working conditions. Growing interest in medium temperature applications and the design of sCO2 heat exchangers was also identified through density visualization maps and confirmed by a review of research projects.

2021, Scientific Articles

Thermodynamic Analysis and Systematic Comparison of Solar-Heated Trigeneration Systems Based on ORC and Absorption Heat Pump

Thermodynamic Analysis and Systematic Comparison of Solar-Heated Trigeneration Systems Based on ORC and Absorption Heat Pump, J. García-Domínguez, J. D. Marcos, Energies, 14 (16), 4770, 2021, Online version, https://doi.org/10.3390/en14164770

Abstract

Modular and scalable distributed generation solutions as combined cooling, heating and power (CCHP) systems are currently a promising solution for the simultaneous generation of electricity and useful heating and cooling for large buildings or industries. In the present work, a solar-heated trigeneration approach based on different organic Rankine cycle (ORC) layouts and a single-effect H₂O/LiBr absorption heat pump integrated as a bottoming cycle is analysed from the thermodynamic viewpoint. The main objective of the study is to provide a comprehensive guide for selecting the most suitable CCHP configuration for a solar-heated CCHP system, following a systematic investigation approach. Six alternative CCHP configurations based on single-pressure and dual-pressure ORC layouts, such as simple, recuperated and superheated cycles, and their combinations, and seven organic fluids as working medium are proposed and compared systematically. A field of solar parabolic trough collectors (SPTCs) used as a heat source of the ORC layouts and the absorption heat pump are kept invariant. A comprehensive parametric analysis of the different proposed configurations is carried out for different design operating conditions. Several output parameters, such as energy and exergy efficiency, net electrical power and electrical to heating and cooling ratios are examined. The study reveals that the most efficient CCHP configuration is the single-pressure ORC regenerative recuperated superheated cycle with toluene as a working fluid, which is on average 25% and 8% more efficient than the variants with single-pressure simple cycle and the dual-pressure recuperated superheated cycle, respectively. At nominal design conditions, the best performing CCHP variant presents 163.7% energy efficiency and 12.3% exergy efficiency, while the electricity, cooling and heating productions are 56.2 kW, 223.0 kW and 530.1 kW, respectively.

2021, Scientific Articles

Supercritical CO2 Binary Mixtures for Recompression Brayton s-CO2 Power Cycles Coupled to Solar Thermal Energy Plants

Supercritical CO₂ Binary Mixtures for Recompression Brayton s-CO₂ Power Cycles Coupled to Solar Thermal Energy Plants, P. Tafur-Escanta, R. Valencia-Chapi, I. López-Paniagua, L. Coco-Enríquez, J. Muñoz-Antón, Energies, 14 (13), 4050, 2021, Online version, https://doi.org/10.3390/en14134050

Abstract

In this work, an evaluation and quantification of the impact of using mixtures based on supercritical carbon dioxide “s-CO₂” (s-CO₂/COS, s-CO2/H₂S, s-CO₂/NH3, s-CO₂/SO₂) are made as a working fluid in simple and complex recompression Brayton s-CO₂ power cycle configurations that have pressure drops in their components. These cycles are coupled with a solar thermal plant with parabolic-trough collector (PTC) technology. The methodology used in the calculation performance is to establish values of the heat recuperator total conductance (UAtotal) between 5 and 25 MW/K. The main conclusion of this work is that the cycle’s efficiency has improved due to using s-CO₂ mixtures as working fluid; this is significant compared to the results obtained using the standard fluid (pure s-CO₂). Furthermore, a techno-economic analysis is carried out that compares each configuration’s costs using pure s-CO₂ and a mixture of s-CO₂/COS with a molar fraction (70/30), respectively, as working fluid where relevant results are obtained. These results show that the best configuration in terms of thermal efficiency and cost is the RCC-RH for pure sCO₂ with values of 41.25% and 2811 $/kWe, while for the mixture sCO₂/COS, the RCC-2RH configuration with values of 45.05% and 2621 $/kWe is optimal. Using the mixture costs 6.75% less than if it is used the standard fluid (s-CO₂).

2021, Scientific Articles

Design and off-design performance comparison of supercritical carbon dioxide Brayton cycles for particle-based high temperature concentrating solar power plants

Design and off-design performance comparison of supercritical carbon dioxide Brayton cycles for particle-based high temperature concentrating solar power plants, R. Chen, M. Romero, J. González-Aguilar, F. Rovense, Z. Rao, S. Liao, Energy Conversion and Management, 232, 113870, 2021, Online version, https://www.sciencedirect.com/science/article/pii/S0196890421000479

Abstract

Concentrated solar power (CSP) plants using dense particle suspension as heat transfer fluid and particles as the storage medium are considered as a promising solution to provide the high temperature required for the supercritical carbon dioxide (S-CO₂) Brayton cycle. During plant operation, variations in the heat transfer fluid temperature and ambient temperature would significantly affect system performance. Determining the suitable S-CO₂ Brayton cycle configuration for this particle-based CSP plant requires accurate prediction and comprehensive comparison on the system performance both at design and off-design conditions. This study presents a common methodology to homogeneously assess the plant performance for six 10 MW S-CO₂ Brayton cycles (i.e. simple regeneration, recompression, precompression, intercooling, partial cooling and split expansion) integrated with a hot particles thermal energy storage and a dry cooling system. This methodology includes both design and off-design detailed models based on the characteristic curves of all components. The optimal design for each thermodynamic cycle has been determined under the same boundary design constrains by a genetic algorithm. Then, their off-design performances have been quantitatively compared under varying particle inlet temperature and ambient temperature, in terms of cycle efficiency, net power output and specific work. Results show that the variation in ambient temperature contributes to a greater influence on the cycle off-design performance than typical variations of the heat transfer fluid temperature. Cycles with higher complexity have larger performance deterioration when the ambient temperature increases, though they could present higher peak efficiency and specific work at design-point. In particular, the cycle with maximum efficiency or specific work presents significant changes in different ranges of ambient temperature. This means that for the selection of the best configuration, the typical off-design operation conditions should be considered as well. For integrating with high-temperature CSP plants and dry cooling systems, the simple regeneration and the recompression cycles are the most suitable S-CO₂ Brayton cycle configurations due to their fewer performance degradations at ambient temperatures above 30 °C, which is a frequent environmental condition in sunny areas of the world.

2021, Scientific Articles

Assessing Cr incorporation in Mn2O3/Mn3O4 redox materials for thermochemical heat storage applications

Assessing Cr incorporation in Mn2O3/Mn3O4 redox materials for thermochemical heat storage applications, A. J. Carrillo, P. Pizarro, J. M. Coronado, Journal of Energy Storage, 33, 102028, 2021, Online version, https://doi.org/10.1016/j.est.2020.102028

Abstract

Widening the use of renewable sources requires more efficient energy storage systems to overcome the inherent intermittence of solar energy. In this respect, thermal energy storage coupled to concentrated solar power represents an inexpensive technology to achieve that goal. In particular, the use of reversible thermochemical reactions is promising due to a higher energy storage density if compared with commercial sensible heat storage on molten salts. However, some of these systems that rely on gas-solid reactions can suffer a cycle-to-cycle loss of activity due to slow kinetics and materials degradation, which is detrimental for its potential future commercialization. In this work, we have assessed the incorporation of Cr cations in the redox couple Mn₂O₃/Mn₃O₄, as a way to stabilize the multi-cyclic activity over prolonged operation at high temperatures (650-1000 °C). Reduction has been studied with in situ XRD and kinetic analyses, which confirm that Cr incorporation shifts the reaction towards high temperatures. Long term redox cycling tests confirm that 5% Cr incorporation helps to stabilize the redox activity of Mn₂O₃/Mn₃O₄.

2020, Scientific Articles

Synthesis, Structural Features, and Hydrogen Adsorption Properties of Three New Flexible Sulfur-Containing Metal-Organic Frameworks

Synthesis, Structural Features, and Hydrogen Adsorption Properties of Three New Flexible Sulfur-Containing Metal-Organic Frameworks, H. Montes-Andrés, P. Leo, G. Orcajo, A. Rodríguez-Diéguez, D. Choquesillo-Lazarte, C. Martos, J. A. Botas, G. Calleja, Crystal Growth & Design, 20, 6707-6714, 2020, Online version, https://doi.org/10.1021/acs.cgd.0c00857

Abstract

Three novel flexible sulfur-containing MOF materials named Co-URJC-5, Cu-URJC-6 and Zn-URJC-7, based on the 5,5′-thiodiisophthalic acid linker have been synthesized through solvothermal methods and characterized by different physicochemical techniques. Hydrogen adsorption analysis at room temperature reveals that these compounds display a gate-opening type adsorption mechanism at low pressures, attributed to the flexible nature of the H4TBTC ligand. This behavior is even more noticeable for Cu-URJC-6, since the layer arrangement by π–π stacking interactions between the aromatic layers could contribute to the flexibility of the structure. These results can be considered as a representative example to elucidate how MOF structures are built using flexible ligands and more significantly as a promising route for designing materials with selective gas sorption properties.

2020, Scientific Articles

Two Isostructural URJC-4 Materials: From Hydrogen Physisorption to Heterogeneous Reductive Amination through Hydrogen Molecule Activation at Low Pressure

Two Isostructural URJC-4 Materials: From Hydrogen Physisorption to Heterogeneous Reductive Amination through Hydrogen Molecule Activation at Low Pressure, H. Montes-Andrés, P. Leo, A. Muñoz, A. Rodríguez-Diéguez, G. Orcajo, D. Choquesillo-Lazarte, C. Martos, F. Martínez, J. A. Botas, G. Calleja, Inorg. Chem., 59, 21, 15733–15740, 2020, Online version, https://doi.org/10.1021/acs.inorgchem.0c02127

Abstract

Herein, two novel isostructural metal–organic frameworks (MOFs) M-URJC-4 (M = Co, Ni; URJC = “Universidad Rey Juan Carlos”) with open metal sites, permanent microposity, and large surface areas and pore volumes have been developed. These novel MOFs, with polyhedral morphology, crystallize in the monoclinic P21/c space group, exhibiting a three-dimensional structure with microporous channels along the c axis. Initially, they were fully characterized and tested in hydrogen (H₂) adsorption at different conditions of temperature and pressure. The physisorption capacities of both materials surpassed the gravimetric H₂ uptake shown by most MOF materials under the same conditions. On the basis of the outstanding adsorption properties, the Ni-URJC-4 material was used as a catalyst in a one-pot reductive amination reaction using various carbonyl compounds and primary amines. A possible chemical pathway to obtain secondary amines was proposed via imine formation, and remarkable performances were accomplished. This work evidences the dual ability of M-URJC-4 materials to be used as a H₂ adsorbent and a catalyst in reductive amination reactions, activating molecular H₂ at low pressures for the reduction of C═N double bonds and providing reference structural features for the design of new versatile heterogeneous materials for industrial application.

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Thermodynamic cycles for solar thermal power plants: A review

Abstract

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1−xFex)3O4 Spinels

Abstract

Thermal Spray processes in Concentrating Solar Power technology

Abstract

Bibliometric analysis on supercritical CO2 power cycles for Concentrating Solar Power applications

Abstract

Thermodynamic Analysis and Systematic Comparison of Solar-Heated Trigeneration Systems Based on ORC and Absorption Heat Pump

Abstract

Supercritical CO2 Binary Mixtures for Recompression Brayton s-CO2 Power Cycles Coupled to Solar Thermal Energy Plants

Abstract

Design and off-design performance comparison of supercritical carbon dioxide Brayton cycles for particle-based high temperature concentrating solar power plants

Abstract

Assessing Cr incorporation in Mn2O3/Mn3O4 redox materials for thermochemical heat storage applications

Abstract

Synthesis, Structural Features, and Hydrogen Adsorption Properties of Three New Flexible Sulfur-Containing Metal-Organic Frameworks

Abstract

Two Isostructural URJC-4 Materials: From Hydrogen Physisorption to Heterogeneous Reductive Amination through Hydrogen Molecule Activation at Low Pressure

Abstract

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