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Category: Scientific Articles

2022, Scientific Articles

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH, A. Pérez, M. Orfila, M. Linares, R. Sanz, J. Marugán, R. Molina, J. A. Botas, Catalysis Today, 390, 22-33, 2022, Online version, https://doi.org/10.1016/j.cattod.2021.12.014

Abstract

Aluminum based perovskites, La0.8Al0.2MeO3-δ (Me = Co, Ni, Fe, Cu), were synthesized following the Pechini method at different pHs and evaluated for hydrogen production by water splitting in a two-step thermochemical cycle. The pH of the synthesis medium showed a critical influence in the redox properties of the aluminum-based perovskites during the thermochemical cycle. Both the thermal reduction and the hydrolysis step produce irreversible changes in the crystalline structure of La0.8Al0.2MeO3-δ perovskites prepared at acid pH, avoiding the cyclability of the material and a stable production of hydrogen during consecutive cycles. However, these changes are not observed when the perovskites were synthesized at basic pH and operated at isothermal conditions at 800 ºC. In this case, the materials keep the crystalline structure leading to stable hydrogen production during consecutive cycles. Among all the studied materials, the nickel-based La0.8Al0.2NiO3-δ perovskites exhibited the best hydrogen productivity per cycle, 4.4 cm3 STP /gmaterial·cycle (Standard Temperature and Pressure conditions), which is a remarkable result considering that the thermochemical water splitting is conducted under isothermal conditions at just 800 ºC. Moreover, this result is accompanied with a good performance of the perovskite in terms of solar to fuel efficiency (being 0.46 the ratio between the potential energy recovery from the produced hydrogen and the solar heat required for its production), comparable or even higher than values reported in the literature for other metal oxides. These results confirm the La0.8Al0.2NiO3-δ perovskite as an auspicious material for a full-scale H2 production from water splitting by solar-driven thermochemical cycles at low temperatures.

2022, Scientific Articles

A new design of multi-tube receiver for Fresnel technology to increase the thermal performance

A new design of multi-tube receiver for Fresnel technology to increase the thermal performance, M. J. Montes, R. Abbas, R. Barbero, A. Rovira, Applied Thermal Engineering, 204, 117970, 2022, Online version, https://doi.org/10.1016/j.applthermaleng.2021.117970

Abstract

Solar heat for industrial processes is a promising way to meet the high thermal demand required by the industry, while this application becomes an important niche market for solar technology. In this research line, it is proposed a novelty concept based on a rotary Fresnel solar collector to supply heat above 150 °C. This work is focused on the multi-tube receiver for this Fresnel collector, proposing a thermal design based on three criteria that can be generalized for any multi-tube receiver: the fluid flow layout is arranged to meet the symmetry of the solar flux map; the fluid circulates from the lower to the higher flux density zone; and the fluid velocity is modified by modifying the tube diameter, to optimize the heat transfer. Following these criteria, the final configuration of the receiver is chosen based on an exergy optimization, in which both heat loss and pressure drop must be quantified. It has been also accomplished a generalization of the optimization methodology for Fresnel collectors providing heat at different temperatures, showing that, in these cases, the configuration that maximizes the exergy efficiency does not correspond to the one with the highest energy efficiency. This thermal design method can be applied to multi-tube receivers working at higher temperatures in longer Fresnel loops, in which case the optimization will result in more marked differences between the optimal values and the standard ones.

2022, Scientific Articles

Thermo-economic analysis of a particle-based multi-tower solar power plant using unfired combined cycle for evening peak power generation

ES Thermo-economic analysis of a particle-based multi-tower solar power plant using unfired combined cycle for evening peak power generation, F. Rovense, M. Á. Reyes-Belmonte, M. Romero, J. González-Aguilar, Energy, 240, 122798, 2022, Online version, https://doi.org/10.1016/j.energy.2021.122798

Abstract

This work analyses a 150 MWe multi-tower solar-only combined cycle power plant (nominal efficiency ∼50%) for evening peak operation. Olivine particles are used as heat transfer fluid and thermal energy storage medium based on their suitable thermo-physical properties for high temperature operation. Technical constraints to handle hot particles lead to an integration of the power block and thermal storage system with an array of heliostat fields (with a solar receiver per field). Unitary 53.0 MWth solar tower was designed to satisfy these constrains. Two electricity dispatch strategies covering the evening peak power have been analyzed. Number of solar fields and storage capacity have been optimized from thermo-economic optimization. It is concluded that the best layouts have seven solar towers and storage capacities of 2.0 GWh for the first dispatch scenario (with an electricity generation from 17:00 to 22:00) and eight solar towers with 2.5 GWh for the second one (from 17:00 to 24:00). Solar multiple is between 1.1 and 1.25. These two configurations cover 56.2% and 55.8% of the total energy demand at full power with LCOE of 14.6 c€ kWh−1 and 13.2 c€ kWh−1. A sensitivity analysis on the components costs indicates that 11.0 c€ kWh−1 could be achieved.

2022, Scientific Articles

Enhanced performance of CH4 dry reforming over La0.9Sr0.1FeO3/YSZ under chemical looping conditions

Enhanced performance of CH₄ dry reforming over La_0.9Sr_0.1FeO₃/YSZ under chemical looping conditions, D. Sastre, C. Á. Galván, P. Pizarro, J. M. Coronado, Fuel, 309, 122122, 2022, Online version, https://doi.org/10.1016/j.fuel.2021.122122

Abstract

Catalytic dry reforming of methane is an attractive route for CO2 valorization that yields syngas (CO + H₂) for subsequent synthesis of chemical and fuels. Alternatively, chemical looping approaches based on discontinuous cyclic operation are lately gaining relevance because, among other advantages, these processes are less prone to deactivation, and they are amenable to be used for thermosolar fuel production. With this background, here we investigate the isothermal activity of CO₂ and CH₄ over La_0.9Sr_0.1FeO₃ perovskite modified with yttria-stabilized zirconia (YSZ), comparing conventional catalytic activity, tested by continuous feeding an equimolar blend of these two gases, with the chemical looping process, where the inlet composition swings between CH₄ and CO₂ in 20 min intervals. Two preparation methods were used to obtain these composites: direct synthesis by Pechini method of the perovskite in the presence of YSZ support and mechanical mixing by ball-milling of the two pre-synthetized oxides. Catalytic activity feeding a CH₄ and CO₂ blend showed a moderate but rather stable activity (226 µmols.min⁻¹.g⁻¹ of H₂ and 206 µmols.min⁻¹.g⁻¹ of CO) at 850 °C for 24 h, with little difference between catalysts. Chemical looping operation at the same temperature, resulted in enhanced production of syngas, with the sample with perovskite synthetized on the support showing significantly higher peak performance (476 µmols.min⁻¹.g⁻¹ of H2 and 432 µmols.min⁻¹.g⁻¹ of CO). The observed high H₂/CO ratio in the methane stage (up to 6.5) indicates the relevant contribution of methane cracking. Characterization of the fresh materials confirmed the formation of the expected phases in both cases, while after CH₄ treatment at high temperature the perovskite decomposed mainly into La₂O₃ and reduced Fe phases. In addition, carbon is also deposited, mainly as multiwall nanotubes. However, the initial perovskite composition is recovered after re-oxidation with CO₂, allowing a stable operation of the La_0.9Sr_0.1FeO₃/YSZ system for at least five cycles.

2022, Scientific Articles

Cold-sprayed coatings: microstructure, mechanical properties, and wear behaviour

Cold-sprayed coatings: microstructure, mechanical properties, and wear behaviour, P. Poza, M.A. Garrido-Maneiro, Progress in Materials Science, 123, 100839, 2022, Online version, https://doi.org/10.1016/j.pmatsci.2021.100839

Abstract

Deposition of coatings on the surface of a bulk material is a versatile, economical, and effective strategy to provide additional features to the bulk material, mainly to improve its functionality and extend its service life. Among all the thermal deposition techniques, cold spray (CS) is the only technique in which particles are deposited below their melting point, and therefore, it is a solid-state processing technique. Coatings generated via CS exhibit different characteristics from those of the coatings produced by other methods; this may make CS a competitive technique for the repair and even for the manufacture of self-standing components.
This study presents a basic description of CS and a review of its applications in the deposition of metallic coatings, specifically those based on materials such as Al- and Ti-based alloys, used in aeronautical components. CS is a thermal spray technique that enables the production of coatings with properties and behaviours similar to those of bulk materials with similar compositions.

2021, Scientific Articles

Thermochemical Energy Storage using the phase transitions Brownmillerite-2H perovskite – Cubic perovskite in the CaxSr1-xCoO3-δ (x = 0 and 0.5) system

Thermochemical Energy Storage using the phase transitions Brownmillerite-2H perovskite – Cubic perovskite in the Ca_xSr_1-xCoO_3-δ (x = 0 and 0.5) system, M. T. Azcondo, M. Orfila, M. Linares, R. Molina, J. Marugán, U. Amador, K. Boulahya, J. A. Botas, R. Sanz, ACS Applied Energy Materials, 4 (8), 7870-7881, 2021, Online version, https://doi.org/10.1021/acsaem.1c01235

Abstract

The oxides Ca_0.5Sr_0.5CoO_3−δ and SrCoO_3−δ, which present perovskite or perovskite-related phases in different temperature domains, have been tested as materials for thermochemical energy storage. The first one, Ca_0.5Sr_0.5CoO_3−δ, experiences a reversible phase transition upon consecutive cycles under an airflow at a maximum operating temperature of 1196 K. Unfortunately, the heat stored in this process, associated with an oxygen loss/gain and a structural phase transition, is very small, hindering its use for thermochemical heat storage. The as-prepared oxide SrCoO_3−δ, which displays a brownmillerite structure like the Ca-containing compound, in the first heating step irreversibly segregates some Co₃O₄ at 823 K to yield a 2H hexagonal perovskite. This phase reversibly transforms at 1073 K into a cubic perovskite. These 2H ⇄ C transitions occur from the 2nd to, at least, 30th cycle. The average absorbed and released heat is ∼104.1 ± 0.06 and ∼68.8 ± 1.8 J/g, respectively, and therefore, SrCoO_3−δ presents a high exo/endo ratio. The exergy efficiency is, on average for the 30 cycles performed, as high as 63.9 ± 1.2%. The mechanism of the phase 2H ⇄ C transition of SrCoO_3−δ explains the good performance of this material for thermochemical energy storage.

2021, Scientific Articles

H2 production by thermochemical water splitting with reticulated porous structures of ceria-based mixed oxide materials

H2 production by thermochemical water splitting with reticulated porous structures of ceria-based mixed oxide materials, M. Orfila, D. Sanz, M. Linares, R. Molina, R. Sanz, J. Marugán, J. A. Botas, International Journal of Hydrogen Energy, 46 (13), 17458-17471, 2021, Online version, https://doi.org/10.1016/j.ijhydene.2020.04.222

Abstract

In this work, we present for the first time the preparation and evaluation of Ceria-based mixed oxides reticulated porous ceramic (RPC) structures for H₂ production by thermochemical water splitting. After appropriate screening of the powder materials, ceria-based materials modified with Co, Mn and Zr were discarded due to their low cyclability and/or hydrogen productivity, derived from segregation of active phases or sintering during the thermal reduction and reoxidation. Sponge replica method has been optimized to allow obtaining a Ce_0.9Fe_0.1O_y RPC sponge structure with an outstanding hydrogen production of 15 STPcm³/gmaterial·cycle at a maximum temperature of 1300 °C. This better performance, comparing to the powder, can be attributed to the open macroporosity of the reticulated porous structure which enhances both heat and mass transfer. The H2 production is maintained along several consecutive cycles without loss of activity, reinforcing the favorable prospects for large-scale hydrogen production.

2021, Scientific Articles

Thermo-mechanical study of a novel rotating disk volumetric receiver

Thermo-mechanical study of a novel rotating disk volumetric receiver, X. Rández, F. Zaversky, D. Astrain, M. A. Garrido-Maneiro, S. Tortuero, A. Rico, P. Poza, Solar Energy, 223, 302-317, 2021, Online version, https://doi.org/10.1016/j.solener.2021.05.066

Abstract

This study evaluates the mechanical behaviour of a ceramic disk which makes up an innovative volumetric absorber design. The new receiver design is formed by a group of disks which are rotating inside a cavity, distributing the radiation absorbed in the aperture to the whole cavity. This research studies the stress fields due to thermal gradients and its effect in the crack propagation in the disks. The complete analysis has been carried out in three steps: the mechanical characterization of the material, in order to know its fracture properties, the computational fluid dynamics (CFD) analysis of the disk, in order to know the temperature distribution in the disk and the finite element model (FEM), which uses as inputs the results of the two previous steps and solves the stress fields in the disk and the fracture behaviour. Fracture and crack growing in the disk have been modelled by using a cohesive element, which, from the fracture properties of the material, allows simulating the crack growing in the disk. This investigation, by means of stress fields and crack propagation analysis, demonstrates the mechanical viability of the disks concept.

2021, Scientific Articles

Solar and biomass hybridization through hydrothermal carbonization

Solar and biomass hybridization through hydrothermal carbonization, J. V. Briongos, S. Taramona, J. Gómez-Hernández, V. Mulone, D. Santana, Renewable Energy, 177, 268-279, 2021, Online version, https://doi.org/10.1016/j.renene.2021.05.146

Abstract

Hydrothermal carbonization process can transform wet bio-wastes into value-added products. This work aims to hybridize a concentrating solar technology and a biomass reactor for the continuous and sustainable valorization of biomass. The novel technology proposed integrates a linear beam-down solar field with a twin-screw reactor for continuous HTC process. The solar field consists of two reflections that concentrate linearly the sun energy on the ground, where the twin-screw reactor is placed. A mathematical model is proposed to solve both the heat transfer and HTC kinetics for a co-rotating twin-screw reactor. The incoming heat flux from the solar field (8–20 kW/m2), the reactor length (L/D = 30–60 where D is the diameter) and the rotating velocity of the screw (25–100 rpm) are the main variables used to process the biomass up to the desired severity factor. The simulation results of different lignocellulosic biomasses (loblolly pine, sugarcane bagasse, corn stover and rice husk) are validated against literature data. The developed model shows good agreement with experimental results shown in the literature. The proposed technology foresees hydrochar yields of 64–78% for severity factors of 4.2 and 5.3, respectively, in agreement to the experimental results of 63–70% shown in literature.

2021, Scientific Articles

The influence of the elemental and structural chemical composition on the ash fusibility of sugarcane bagasse and sugarcane straw

The influence of the elemental and structural chemical composition on the ash fusibility of sugarcane bagasse and sugarcane straw, K.R.D. Palma, E. Tomaz, A. Soria-Verdugo, M.A. Silva, Fuel, 304, 121404, 2021, Online version, https://doi.org/10.1016/j.fuel.2021.121404

Abstract

Agricultural residues have been pointed out as an important source to energy conversion by direct burning. Nevertheless, their use still faces operational problems, such as slagging and fouling, mainly related to the inorganic fraction of their composition. The objectives of this work were to understand the fusion behavior of sugarcane biomass ash formed during thermal conversion and the tendency of slag and fouling to occur, in addition to propose possible solutions to minimize these problems using a mixture of biomass species and/or additive minerals. To that end, experimental measurements and thermodynamic simulations were employed to relate the chemical composition to the fusibility. The ashes chemical composition was characterized by EDS and XRD, while the ash fusion temperatures AFT́s (DT, ST, HT and FT) were measured by AF700 equipment and estimated using FactSage modeling. Statistical analysis helped to derive the relationship between chemical composition and AFT́s. The ashes were rich in SiO2, Al2O3 and Fe2O3 and revealed that for bagasse the element that most contributes to increase DT is Si, whereas for straw the presence of Al has a stronger effect to increase DT. Fe was found to act as flux element. XRD results showed the phases differences, finding more amorphous components in straw ash than in bagasse, which may lead to a different ash fusion behavior. Straw 2015 ash presented a DT of 733 °C while for bagasse 2015 and 2016 ashes the values of DT were 777 and 917 °C, respectively. In contrast, the DT of straw ash increased when mixed with bagasse 2015 and 2016 to values of 841 and 885 °C, respectively, and also when 1% of Al2O3 was added, obtaining a DT of 930 °C. For bagasse samples, the additives showed a minor effect on ash melting behavior.

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Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH

Abstract

A new design of multi-tube receiver for Fresnel technology to increase the thermal performance

Abstract

Thermo-economic analysis of a particle-based multi-tower solar power plant using unfired combined cycle for evening peak power generation

Abstract

Enhanced performance of CH4 dry reforming over La0.9Sr0.1FeO3/YSZ under chemical looping conditions

Abstract

Cold-sprayed coatings: microstructure, mechanical properties, and wear behaviour

Abstract

Thermochemical Energy Storage using the phase transitions Brownmillerite-2H perovskite – Cubic perovskite in the CaxSr1-xCoO3-δ (x = 0 and 0.5) system

H2 production by thermochemical water splitting with reticulated porous structures of ceria-based mixed oxide materials

Abstract

Thermo-mechanical study of a novel rotating disk volumetric receiver

Abstract

Solar and biomass hybridization through hydrothermal carbonization

Abstract

The influence of the elemental and structural chemical composition on the ash fusibility of sugarcane bagasse and sugarcane straw

Abstract

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