Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
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Control of wind energy conversion systems with permanent magnet synchronous generator for isolated green hydrogen production
Get PDFThis paper addresses the design and analysis of the control system for a Wind Energy Conversion System (WECS) with a Permanent Magnet Synchronous Generator (PMSG) and its application for isolated green hydrogen production. The designed control maximizes the wind turbine (WT) power generation by regulating the electrolyzer current consumption, where the electrolyzer operates as a controlled load, ensuring power balance in the system and enabling the generation of maximum power from the WECS without the use of any energy storage system. The system involves directly integrating a WECS with an alkaline electrolyzer (AEL), and its configuration includes a WT with a PMSG, an AC/DC voltage source converter (VSC) acting as the generator side converter (GSC), and a DC/DC converter acting as the electrolyzer side converter (ESC) with Maximum Power Point Tracking (MPPT) control for the WT. The proposed control system has been fully modeled and tested through simulations in Matlab/Simulink, demonstrating its reliable performance under variable wind speeds. Simulation results illustrate how, over rated wind speeds, the pitch control limits the rotational speed and power to their maximum values, and at under rated wind speeds, the ESC control regulates the AEL current following the MPPT of the WT, while the GSC control maintains the DC bus voltage at its designated nominal value. Overall, the proposed control system shows robust and effective performance across the entire range of possible operational points, ensuring no wind generation power losses by following the maximum power point
Periodic DFT Study of the Thermodynamic Properties and Stability of Schoepite and Metaschoepite Mineral Phases
Get PDFThe thermodynamic properties of schoepite and metaschoepite were obtained by means of theoretical solid-state methods as a function of temperature. Since the values of these properties for schoepite have not been measured experimentally, they were predicted. The computed thermodynamic functions of metaschoepite were in excellent agreement with the experimental information. These functions were used to obtain the thermodynamic properties of formation of these materials from the corresponding elements. The calculated Gibbs free energy of formation of metaschoepite was shown to be very reliable and differ from the experimental value at 800 K by only 2.0%. Besides, it extends the range of temperature in which this property is known to 0???1000 K. Then, these properties were combined with those of other important uranyl-containing materials to study the reactions of formation of schoepite and metaschoepite from uranium trioxide and the reactions of transformation of these materials into dehydrated schoepite, rutherfordine, and soddyite. Schoepite becomes unstable with respect to uranium trioxide for temperatures higher than 110 ??C (383 ?? 27 K) and its dehydration occurs at 64 ??C (337 ?? 44 K). The corresponding values of these temperatures for metaschoepite are 82 ??C (355 ?? 6 K) and 5 ??C (278 ?? 9 K), respectively. Under hydrogen peroxide free conditions, schoepite and metaschoepite were found to be less stable than rutherfordine and soddyite. The thermodynamic stability of schoepite with respect to metastudtite and studtite was then studied under different conditions of temperature and concentrations of hydrogen peroxide. Schoepite and metaschoepite have very similar thermodynamic stabilities, the first being slightly more stable than the second one. The availability of the thermodynamic properties of these minerals allowed to determine their relative thermodynamic stability with respect to a rich subset of the most relevant secondary phases resulting from corrosion of spent nuclear fuel. Schoepite and metaschoepite were found to be the first and second most stable phases under intermediate hydrogen peroxide concentrations and the second and third most stable phases under high concentrations of hydrogen peroxide, respectively
Measurement of the Gd-154(n,??) cross section and its astrophysical implications
Get PDFThe neutron capture cross section of Gd-154 was measured from 1 eV to 300 keV in the experimental area located 185 m from the CERN n_TOF neutron spallation source, using a metallic sample of gadolinium, enriched to 67% in Gd-154. The capture measurement, performed with four C6D6 scintillation detectors, has been complemented by a transmission measurement performed at the GELINA time-of-flight facility (JRC-Geel), thus minimising the uncertainty related to sample composition. An accurate Maxwellian averaged capture cross section (MACS) was deduced over the temperature range of interest for s process nucleosynthesis modelling. We report a value of 880(50) mb for the MACS at kT = 30 keV, significantly lower compared to values available in literature. The new adopted Gd-154(n,??) cross section reduces the discrepancy between observed and calculated solar s-only isotopic abundances predicted by s-process nucleosynthesis models
Thermo-hydro-chemical (THC) behaviour of a Spanish bentonite after dismantling of Heater#1 and Heater#2 of the FEBEX in situ test at the Grimsel Test Site
No full textFern??ndez, A.M., S??nchez-Ledesma, D.M., Mel??n, A., Robredo, L.M., Rey, J.J., Labajo, M., Clavero, M.A., Carretero, S.,Gonz??lez, A.M. 2018. Thermo-hydro-geochemical behaviour of a Spanish bentonite after dismantling of the FEBEX in situ test at Grimsel Test Site. FEBEX-Nagra Working Report NAB 16-25, 313 pp + AnnexesBentonites are an essential component of the multi-barrier system securing the long-term safety of the final disposal of nuclear wastes. The efficiency of such engineering clay barrier relies on its physical and chemical confinement properties: low permeability, low diffusivity, high retention and swelling capacity. Therefore, an important issue for performance assessment purposes is to have confidence and demonstrate the long-term preservation of these properties over the long term, i.e., hundreds of thousands of years under real conditions of a repository.
The challenging scientific approach used to tackle the problem of predicting long-term clay barrier behaviour is by analysing the results from experiments conducted in underground research laboratories (URL) at real scale and at real conditions. The FEBEX in situ test project provided the opportunity to understand and quantify the processes taking place in the near-field and to evaluate the behaviour of the compacted FEBEX bentonite after 18 years of experiment.
From the geochemical point of view, specific long-term requirements for the function of a bentonite to isolate the canisters from water and retard the migration of radionuclides is to maintain a suitable chemical environment for the canister integrity and radionuclide retention over time, buffering possible alteration/deterioration processes of the bentonite.
The dismantling of the second part of the FEBEX in situ test allowed to quantify the modifications of the bentonite after reacting due to changes in the initial physico-chemical conditions and different types of perturbations: a) interactions with granitic groundwater (saturation phase), b) heat (desaturation phase due to heating), c) perturbations linked to the interactions between the bentonite and the allochthonous engineered solid materials (concrete, iron, C-steels and other metals, organics, etc.), and d) interactions with different gases produced and consumed in the system (CO2, H2, CH4, etc.) due to mineral dissolution/precipitation, microbiological reactions and corrosion processes.
In this report the impact of different perturbations were described in terms of: 1) modifications in the pore water chemistry and redox conditions, which may affect the smectite structural stability and speciation of dissolved ions, 2) dissolution and redistribution of primary mineral phases and precipitation/neoformation of secondary minerals, 3) clay mineral alteration or modifications of the clay mineral properties (especially cation exchange capacity, cation exchange population, crystallochemical structure, layer charge and swelling ability), and 4) transport properties through modifications in porosity, permeability and tortuosity due to cementation processes.
Some specific reactions observed in laboratory and large scale experiments over time were also detected in the FEBEX in situ experiment. These reactions are: dissolution/precipitation, cation exchange, metal corrosion, gas production, hydrocarbons oxidation and Mg accumulation at the heater interface. However, specific results were obtained from this FEBEX in situ experiment, which is the longest real scale in situ experiment up to date.
Nevertheless, the global data analysed from samples obtained after the dismantling operations of the Heater #1 in 2002 and Heater#2 in 2015, indicated that no significant structural changes in the smectite were produced, the whole bentonite barrier preserving its main physico-chemical properties unaltered (CEC, layer charge, water adsorption capacity and total and external surface area). The alterations observed were restricted to localized zones, mainly at the bentonite/shotcrete (< 6.25-12.5 cm) and bentonite/heater (< 5-10 cm) interfaces
Effect of gas pulses on transport in NBI plasmas of the TJ-II stellarator
Get PDFThe experimental evolution of low-density (~1e19 m-3) NBI plasmas of the TJ-II Heliac-type stellarator in response to short gas-puff pulses is simulated with a transport model that includes elements for transport barrier formation, neoclassical radial electric field and the evolution of three carbon charge-states. Two typical phenomena following a gas pulse are described: the formation of pivot points in the emissivity profiles as a consequence of transport barrier formation processes, and the smooth confinement change due to changes in the neoclassical transport caused by the forced modification of plasma profiles
Power optimization modelling as a computational tool for power take off design in wave energy converters
Get PDFThis study presents a computational tool called Power Take-Off Optimisation Modelling (POM), a methodology for optimizing the design parameters of the Power Take-Off (PTO) in wave energy converters (WECs). POM uses a control optimization algorithm based on a differential evolution multi-objective approach to maximize the electrical power extracted by WECs while minimizing design costs. The methodology integrates a wave-to-wire (W2W) model in the time domain, including a PTO loss model. It also considers the sea states where WECs operate, and constraints related to the PTO rated force. These features allow a comprehensive evaluation of the electrical energy generated and the optimization of PTO design parameters. POM has been applied to a real case study involving a linear generator-based PTO operating under different sea states. The analysis includes four WEC technologies and two sea states to assess the tool???s effectiveness. Results show that PTO length influences not only CAPEX minimization but also optimal modular system design. Additionally, a sensitivity analysis indicates that the number of modules required to meet force requirements is not significantly affected by PTO efficiency. In conclusion, POM is a versatile support tool for technology developers and researchers, helping optimize PTO design to balance WEC manufacturing costs and generated power
Unlocking the potential of ionic liquid assisted fractionation of grapevine shoots for efficient fermentable sugar production and lignin recovery
No full textThe global transition from a fossil-based to a sustainable bio-based economy highlights the need for renewable
resources to obtain bioenergy and bioproducts. Vine shoots (VS), an abundant non-edible biomass from vine
pruning, have significant potential for biorefinery processes. This research investigates the use of ionic liquids
(ILs) like 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), 1-butyl-3-methylimidazolium hydrogen sulphate
([BMIM][HSO4]) and 1-ethyl-3-methylimidazolium ethyl sulphate ([EMIM][ESO4]) to pretreat VS, enhancing
enzymatic digestibility and lignin recovery. ILs can effectively fractionate lignocellulosic biomass. Experimental
conditions, including temperature, water addition to ILs and washing agents significantly influence the process.
High cellulose (86.0 %) and xylan (95.7 %) conversion rates were achieved using [EMIM][Ac]: H2O, and
delignification up to 42.5 % using [BMIM][HSO4]: H2O. The study also examines process intensification, with
favorable results at up to 20 % biomass loading. The recyclability of ILs suggests a sustainable circular process,
though efficiency decreases need to be addressed. Recycled ILs can depolymerize lignin into valuable phenolic
compounds, adding further value. Overall, IL-assisted fractionation presents a green and efficient method for
processing VS biomass, essential for sustainable biorefinery integration and commercial use. This research lays
the groundwork for future studies on ILs in VS biomass pretreatment, emphasizing the need for careful IL selection
and process conditions
Gene therapy could correct blood stem cells inside, rather than outside, the body
No full textExperiments in mice reveal
an early postnatal window of
opportunity for the effective
transfer of genes to blood-cellproducing
haematopoietic stem
cells by injecting mice with genecarrying
lentiviral vectors. This
approach showed therapeutic
benefit in three mouse models
of severe diseases, and could
expand the applicability of
haematopoietic stem-cell gene
therapy in the clinic
Stabilization of premixed flames in narrow channels by a highly conductive embedded wall segment: Application to hydrogen-air mixtures
No full textThis study uses numerical analysis to investigate the potential for stabilizing hydrogen-air flames within narrow channels by incorporating a wall segment of finite length with high thermal conductivity. The numerical model is based on the Navier???Stokes equations, coupled with energy and mass conservation equations for reacting gases, and incorporates detailed chemistry and transport models, including thermal diffusion (the Soret effect). For the gas???solid coupling, a novel computational method is used that avoids the expensive calculations associated with solving the unsteady conjugate gas???solid heat transfer.
For the first time, we demonstrate that this innovative thermal stabilization method provides stable operation for lean hydrogen-air combustion across a wide range of reactant flow rates. This offers significant flexibility in terms of power output variation, surpassing the performance of classical counterflow heat recirculating devices. Finally, this study emphasizes the importance of incorporating the Soret effect in the species transport model to accurately compute hydrogen-containing flames, especially in highly curved flame configurations
Assessing the Socioeconomic and Environmental Impact of Hybrid Renewable Energy Systems for Sustainable Power in Remote Cuba
Get PDFThis study evaluates the viability of a specific hybrid renewable energy system (HRES) in-
stallation designed for a remote community as a case study in Cuba. The system integrates
solar, wind, and biomass resources to address localised challenges of energy insecurity
and environmental degradation. Rather than offering a generalised evaluation of HRES
technologies, this work focuses on the performance, impacts, and viability of this particular
configuration within its unique geographical, social, and technical context. Using life cycle
assessment (LCA) and input???output modelling, the research assesses environmental and
socioeconomic impacts. The proposed HRES reduces greenhouse gas emissions by 60%
(from 1.14 to 0.47 kg CO2eq/kWh) and fossil energy consumption by 50% compared to
diesel-based systems. Socioeconomic analysis reveals that the system generates 40.3 full-
time equivalent (FTE) jobs, with significant employment opportunities in operation and
maintenance. However, initial investments primarily benefit foreign suppliers due to
Cuba???s reliance on imported components. The study highlights the potential for local
economic gains through workforce training and domestic manufacturing of renewable
energy technologies. These findings underscore the importance of integrating multiple
renewable sources to enhance energy resilience and sustainability in Cuba. Policymakers
should prioritise strategies to incentivise local production and capacity building to max-
imise long-term benefits. Future research should explore scalability across diverse regions
and investigate policy frameworks to support widespread adoption of HRES. This study
provides valuable insights for advancing sustainable energy solutions in Cuba and similar
contexts globally