Search

Este volumen reúne casi un centenar de contribuciones aportadas por especialistas de diversos ámbitos al 7th International Seminar on Organic Rankine Cycle Power Systems (ORC 2023), que se celebró en Sevilla entre el 4 y el 6 de septiembre de 2023 y fue organizado por la Universidad de Sevilla en colaboración con el Knowledge Centre on Organic Rankine Cycle Technology (KCORC). Se trata de un encuentro internacional de carácter bianual que se ha constituido en una cita fundamental para abordar los avances en tecnología ORC y, en un contexto más amplio, en la transición energética. En ella se coordinan fabricantes de equipos, asociaciones profesionales, usuarios, inversores, responsables políticos, académicos y científicos. Los trabajos englobados en este volumen cubren una amplia variedad temática: integración de sistemas, diseño de componentes, rendimiento termodinámico, eficiencia energética, entre otros. Como novedad, en esta edición de 2023 se aceptaron trabajos sobre la tecnología de las bombas de calor.

Past work by the authors has suggested that Solar micro Gas Turbines (SmGTs) can be used cost-effectively to produce electric power and heat for freshwater production through desalination, mainly in off-grid locations. This is further studied in this work, providing an exhaustive modelling procedure and methodology. Additionally, a comprehensive analysis of system performance under both design and part-load conditions is provided along with the complete set of characteristics of the components of the SmGT and the desalination unit. To this end, the SmGT is assessed first, incorporating innovative solutions that enable better off-design performance: Variable Inlet Guide Vanes (VIGVs) in the compressor and Variable Nozzle Guide Vanes (VNGVs) in the turbine. The implementation of these features brings significant advantages in part-load operation, leading to a considerable increase in solar-to-electric efficiency and rangeability, particularly under certain ambient conditions; in particular, using these features yields 5% higher efficiency at the minimum load of the original engine (without variable geometry) and, from this load setting downwards, 15% lower minimum stable load is enabled. Furthermore, a sensitivity analysis to control strategies and ambient conditions has been included, exploring their impact on system performance. The water treatment system is comprised of two elements. A Reverse Osmosis (RO) desalination unit is driven by the electric power produced by the SmGT. Considering the emphasis on flexibility and part-load operation enhancement addressed in this work, a moderate recovery rate is proposed for this unit. The RO unit produces brine with high salt concentration to be partially treated further in a Zero Liquid Discharge (ZLD) unit driven by the exhaust gases of the microturbine (at about 250–300 °C), where the sensible heat of this stream is harvested by the ZLD unit to “dry” and concentrate the effluent. Finally, the potential and the operationa

Past work by the authors has suggested that Solar micro Gas Turbines (SmGTs) can be used cost-effectively to produce electric power and heat for freshwater production through desalination, mainly in off-grid locations. This is further studied in this work, presenting a detailed description of system performance at design and part-load conditions, as well as the characteristics of the components of the SmGT and the desalination unit. To this end, the SmGT is assessed first, considering techniques that achieve a greater off-design performance such as incorporating Variable Inlet Guide Vanes (VIGVs) at the compressor inlet, and including the sensitivity to control strategies and ambient conditions, exploring their expectedly very negative impact on the SmGT performance. Water treatment system is comprised of two elements. A Reverse Osmosis desalination unit is driven by the electric power produced by the SmGT. This produces brine with high salt concentration to be partially treated further in a Zero Liquid Discharge (ZLD) unit driven by the exhaust gases of the microturbine (at about 250-300ºC), where the sensible heat of this stream is harvested by the ZLD unit to “dry” and concentrate the effluent. Finally, the potential and the operational limitations of the ZLD system are discussed, supplemented by an experimental proof of concept where its feasibility was verified.

Micro Gas Turbines are on-site generators with the potential to help the transition to a greener economy. However, their deployment into the market did not match the expectations. The Root Cause Analysis (RCA) is the methodology to uncover the highest-level causes before identifying possible solutions. This work applies the traditional approach to problem-solving, which originated as a methodology to find faults in processes. The methodology leads to an in-depth exploration of the problem and the cause–effect relationships within the microturbine and energy market. Specifically, the traditional RCA allowed for a creative and extensive approach. This study highlights the difficulty of targeting the problem from a general perspective with such tools. The process-based tools of the RCA make it challenging to represent such complex systems effectively. In this regard, the authors compare the present methodology with the Theory of Constraints, analysing benefits and obstacles. Eventually, the present methodology systematically isolated several root causes of the problem.

Micro gas turbines are an on-site power and heat generation technology with a small footprint, low gaseous (NOx) and acoustic emissions, low maintenance and high-grade heat. They entered the market at the dawn of the twentieth century; nevertheless, they achieved minimal success and a marginal role in the microgeneration market. Reciprocating internal combustion engines raised considerable barriers hindering their market deployment, and Fuel Cells are also set to compete in this segment. In this scenario, this work presents an analysis of competitiveness grounded in the Theory of Constraints. To this end, a specific Key Performance Indicator has been produced, which combines technical, economic, and operational factors according to the end-user requirement. This indicator is a function of several penalty factors representing technology and market barriers, which aims to yield a unique insight into the most competitive technology for a given application, accounting for the uncertainty deriving from technical and economic elements. This novel methodology is applied to a new potential niche market: Power-to-Hydrogen-to-Power for remote applications. The methodology is applied to an independent rural community in South Wales, for which a backup power system is assessed. Four technologies are considered in the analysis: reciprocating engines, fuel cells and two different microturbines layouts. Finally, this work provides an overview of the possible R&D&I paths necessary to increase the competitiveness of micro gas turbines in certain markets.

Power-to-Power is a process whereby the surplus of renewable power is stored as chemical energy in the formof hydrogen. Hydrogen can be used in situ or transported to the consumption node. When power is needed again, hydrogen can be consumed for power generation. Each of these processes incurs energy losses, leading to a certain round-trip efficiency (Energy Out/Energy In). Round-trip efficiency is calculated considering the following processes: water electrolysis for hydrogen production, compression, liquefaction or use of metal-hydride for hydrogen storage, fuel-cell-electric-truck for hydrogen distribution and micro-gas turbine for hydrogen power generation. From a first analysis of the commercial technologies available in the market, the achievable round-trip efficiency of the power-to-power energy storage system proposed is 29% when considering solid oxide electrolysis andmetal hydride storage. This number decreases sharply when using alkaline or proton exchange membrane electrolysers, 22.2% and 21.8% respectively. Round-trip efficiency is further reduced if considering other storage media, such as compressed- or liquefied-H2. Even if this is not positive, this thesis shows that there is a large margin to increase round-trip efficiency again, mostly through improvements in the hydrogen production process and the thermo-mechanical energy conversion step, which could lead to round-trip efficiencies of around 40%–42% in the next decade, for power-to-power energy storage systems based on micro gas turbines. By prioritising the development of a rapid techno-economic assessment tool, accuratemodels for the various components of the system have been successfully created and incorporated into a Python-based tool. The models encompass renewable energy sources such as PV Solar andWind Turbines, electrolyser technologies including proton-exchange membrane and solid oxide, a high-pressure storage system comprising volumetric compressors and high-pressure vessels, and the p, Power-to-Power es la denominación habitual para sistemas en los que el excedente de energía renovable se almacena como energía química en forma de hidrógeno. El hidrógeno se puede utilizar in situ o transportarse al punto de consumo. Cuando se necesita energía nuevamente, se puede consumir hidrógeno para generar energía eléctrica y térmica. Cada uno de estos procesos incurre en pérdidas de energía, lo que lleva a una cierta eficiencia de almacenamiento (Energía Eléctrica Salida / Energía Eléctrica Entrada). La eficiencia de almacenamiento se calcula teniendo en cuenta los siguientes procesos: electrólisis del agua para la producción de hidrógeno, almacenamiento de hidrógeno comprimido, licuado o en forma de hidruros metálicos, distribución de hidrógeno mediante camiones eléctricos con pila de combustible y generación de energía mediante microturbina de gas operando con hidrógeno. En un primer análisis de las tecnologías comerciales disponibles en elmercado, la eficiencia de almacenamiento alcanzable es del 29%, al considerar la electrólisis de óxido sólido y el almacenamiento en hidruros metálicos. Este número disminuye drásticamente al utilizar electrolizadores alcalinos o de membrana de intercambio de protones, 22.2% y 21.8% respectivamente. La eficiencia de almacenamiento se reduce aún más si se consideran otros medios de almacenamiento, como H2 comprimido o licuado. Sin embargo, el objetivo de la tesis es resaltar que todavía hay un margen amplio para aumentar la eficiencia de almacenamiento del sistema power-to-power, principalmente en los bloques de producción de hidrógeno y generación de energía, lo que podría llevar a eficiencias de almacenamiento de alrededor del 40% -42% en la próxima década, para sistemas de almacenamiento de energía power-to-power basados en microturbinas de gas. Al priorizar el desarrollo de una herramienta de evaluación tecnoeconómica rápida, se han creado con éxito modelos robustos para los diversos componentes del sistema y se han in

El cambio climático y calentamiento global son conceptos que nos competen a todos y con gran relevancia en el ámbito científico, puesto que cada vez más soluciones son propuestas a fin de mitigar sus efectos mediante el control las emisiones propias de las diferentes industrias. En este sentido, el sector energético no es la excepción, ya que es uno de los sectores que más acapara la atención de investigadores debido a su significativa contribución a las emisiones globales. Ante este escenario, los ciclos de potencia basados en dióxido de carbono (CO2) en condiciones supercríticas surgen como una alternativa de gran interés debido a diversos factores como su alta eficiencia térmica y la compacidad de los equipos. Dado el evidente potencial que tiene el desarrollo de esta tipología de ciclos, se ha abarcado su estudio desde diferentes frentes, fomentando la creación de eventos (tales como congresos y simposios) internacionales e incrementando el número de investigaciones y publicaciones al respecto. Producto de este constante intercambio de conocimiento, diversos autores han propuesto distintas configuraciones de ciclos que pretenden no solo primar la eficiencia, sino que también se busca propiciar la viabilidad tecnológica. Dentro de las fuentes de energía que se han considerado para su aplicación, la oxicombustión (combustión en un medio de oxígeno puro en lugar de aire) se perfila como una de las alternativas de mayor interés. Varias razones motivan la integración de estas tecnologías, una de ellas es que el fluido de trabajo (CO2) es uno de los productos de la reacción química, además, la posibilidad de alcanzar altas temperaturas que beneficien la eficiencia de los ciclos hace que esta fuente de energía capte la atención de la comunidad científica. Por otra parte, la necesidad de una corriente de oxígeno de alta pureza para llevar a cabo la oxicombustión surge como un desafío a abordar, puesto que el proceso de producción de oxígeno a partir de la separación de, Climate change and global warming are concepts that concern us all and hold significant relevance in the scientific field, as increasingly more solutions are being proposed to mitigate their effects by controlling the emissions from various industries. In this regard, the energy sector is no exception; it garners substantial attention from researchers owing to its substantial contribution to global emissions. Given this scenario, power cycles based on supercritical carbon dioxide (CO2) emerge as a highly interesting alternative due to various factors such as their high thermal efficiency and equipment compactness. Considering the evident potential of developing this type of cycle, its study has been approached from different perspectives, fostering the creation of international events (such as congresses and symposiums) and increasing the number of related research and publications. As a result of this ongoing knowledge exchange, various authors have proposed different cycle configurations aiming not only to prioritize efficiency but also to promote technological feasibility. Among the energy sources considered for their application, oxy-combustion (combustion in a medium of pure oxygen instead of air) stands out as one of the most interesting alternatives. Several reasons motivate the integration of these technologies, one being that the working fluid (CO2) is one of the products of the chemical reaction. Additionally, the potential to reach high temperatures that benefit cycle efficiency captures the attention of the scientific community. On the other hand, the need for a high-purity oxygen stream for carrying out oxy-combustion poses a challenge to be addressed, as the oxygen production process from air separation is highly energy-demanding, ultimately negatively impacting the cycle's performance. In this context, this present study aims to analyze some sCO2 power cycles proposed for oxy-combustion application. The objective is to conduct a thermodynamic comparis

This manuscript, developed in the framework of SCARABEUS project, presents an assessment of the part-load performance of a transcritical Recompression cycle running on a 80%CO2-20%SO2 mixture under different load-control schemes. The first part of the paper describes the computational platform of the integrated system, implemented in Thermoflex but with profuse use of in-house scripts, in order to accurately describe the off-design performance of key components when operating on CO2 mixtures with non-ideal gas behaviour. These off-design models make use of performance maps for turbomachinery -provided by the SCARABEUS partners- whereas the Conductance Ratio Method employed to model the counter-current heat exchangers is calibrated with in-house tools. The paper is specifically focused on the Heat Rejection Unit, for which a specific design tool accounting for accurate heat transfer between working fluid and cooling medium (air) and for auxiliary power consumption -both in off-design- has been developed by the authors. In the second part of the paper, different operating strategies of the power cycle are considered, based on keeping one of the following three parameters constant: turbine inlet temperature, turbine outlet temperature or return temperature of molten salts. Globally, plant operation is constrained by the need to keep the temperature of cold HTF returning to the storage system as close as possible to its rated (design) value and by the need to keep turbine outlet temperature below 450ºC to avoid the installation of an external cooling system in the low pressure section of this equipment. Therefore, the trade-off between these two parameters and system net efficiency are assessed in the paper. Regarding the Air-Cooled Condenser, the optimal operation strategy of this component found to be based on a combination of Single-speed and Variable Frequency Driver fans. The results show that the operation at constant turbine inlet temperature leads to the highest

This paper deals with the integration of a Power-to-Power Energy Storage System (P2P-ESS) based on a hydrogen driven micro gas turbine (mGT) for an off-grid application with a continuous demand of 30 kWe for three European cities: Palermo, Frankfurt, and Newcastle. In the first part of the analysis, the results show that the latitude of the location is a very strong driver in determining the size of the system (hence footprint) and the amount of seasonal storage. The rated capacity of the PV plant and electrolyzer are 37%/41% and 58%/64% higher in Frankfurt and Newcastle, respectively, as compared to the original design for Palermo. And not only this, but seasonal storage also increases largely from 3125 kg H2 to 5023 and 5920 kg H2. As a consequence of this, LCOE takes values of 0.86 €/kWh, 1.26 €/kWh, and 1.5 €/kWh for the three cities, respectively, whilst round-trip efficiency is approximately 15.7% for the three designs at the 3 cities. Finally, with the aim to reduce the footprint and rating of the different systems, a final assessment of the system hybridised with battery storage shows a 20% LCOE reduction and a 10% higher round-trip efficiency.

Micro gas turbines are an on-site power and heat generation technology with a small footprint, low gaseous (NOx) and acoustic emissions, low maintenance and high-grade heat. They entered the market at the dawn of the twentieth century; nevertheless, they achieved minimal success and a marginal role in the microgeneration market. Reciprocating internal combustion engines raised considerable barriers hindering their market deployment, and Fuel Cells are also set to compete in this segment. In this scenario, this work presents an analysis of competitiveness grounded in the Theory of Constraints. To this end, a specific Key Performance Indicator has been produced, which combines technical, economic, and operational factors according to the end-user requirement. This indicator is a function of several penalty factors representing technology and market barriers, which aims to yield a unique insight into the most competitive technology for a given application, accounting for the uncertainty deriving from technical and economic elements. This novel methodology is applied to a new potential niche market: Power-to-Hydrogen-to-Power for remote applications. The methodology is applied to an independent rural community in South Wales, for which a backup power system is assessed. Four technologies are considered in the analysis: reciprocating engines, fuel cells and two different microturbines layouts. Finally, this work provides an overview of the possible R&D&I paths necessary to increase the competitiveness of micro gas turbines in certain markets.

The SCARABEUS project investigates the use of CO₂–based mixtures as working fluid in power cycles for nextgeneration Concentrated Solar Power plants. These fluids exhibit a critical temperature higher than pure CO₂, enabling dry condensation of the working fluid even at the high ambient temperatures typical of sites with a high solar radiation. As a consequence, the SCARABEUS power cycle achieves higher thermal efficiency than standard sCO₂ cycles, whose performance deteriorates significantly with ambient temperature. In any case, the actual feasibility of this concept is still to be confirmed by a complete techno-economic assessment. To that purpose, it is critical to accurately estimate the power consumption of the Heat Rejection Unit (HRU), which is one of the most important parasitic loads of the system. Bearing all this in mind, this manuscript presents the design of a horizontal, direct air-cooled condenser (ACC). The bundle geometry proposed is comprised of seven tubes in three passes, with a staggered arrangement. The complete thermal model, developed in MatLab, has been already disclosed by the SCARABEUS consortium in a previous paper, and validated both experimentally in a dedicated test rig and against results obtained by the commercial software Xace®. The novelty in the present manuscript lies in the integration of this thermal model of the tubes with a complete design and integration tool of the whole heat rejection sub-system, including the design of a rotoronly axial fan and supporting frame. The impact of several design parameters (i.e., air temperature rise, acceptable hot pressure drops, tube length) is studied, taking into account auxiliary power consumption, footprint and cycle efficiency as main figures of merit. Two candidate mixtures are taken into account, identified in previous works by the same authors (85%CO₂-15%C6F6 and 80%CO₂-20%SO₂), and a pure sCO₂ case is also considered for the sake of comparison. The results show that, for a given g

The utilisation of certain blends based on supercritical CO2 (sCO2), namely CO2/TiCl4, CO2/C6F6 and CO2/SO2, have been found to be promising for enhancing the performance of power cycles for Concentrated Solar Power (CSP) applications; allowing for up to a 6% enhancement in cycle efficiency with respect to a simple recuperated CO2 cycle, depending upon the nature of the used blend and the cycle configuration of choice. This paper presents an investigation of the impact of adopting these sCO2-based blends on the flow path design for a multi-stage axial turbine whilst accounting for aerodynamic, mechanical and rotordynamic considerations. This includes assessing the sensitivity of the turbine design to selected working fluid and imposed optimal cycle conditions. Ultimately, this study aims to provide the first indication that a high-efficiency turbine can be achieved for a large-scale axial turbine operating with these non-conventional working fluids and producing power in excess of 120 MW. To achieve this aim, mean-line aerodynamic design is integrated with mechanical and rotordynamic constraints, specified based on industrial experience, to ensure technically feasible solutions with maximum aerodynamic efficiency. Different turbine flow path designs have been produced for three sCO2 blends under different cycle boundary conditions. Specifically, flow paths have been obtained for optimal cycle configurations at five different molar fractions and two different turbine inlet pressure and temperature levels of 250 & 350 bar and 550 & 700 °C respectively. A total-to-total turbine efficiency in excess of 92% was achieved, which is considered promising for the future of CO2 plants. The highest efficiencies are achieved for designs with a large number of stages, corresponding to reduced hub diameters due to the need for a fixed synchronous rotational speed. The large number of stages is contrary to existing sCO2 turbine designs, but it is found that an increase from 4 to 14

Micro Gas Turbines are small devices for on-site power and heat generation. Their high maintainability and fuel flexibility make them a suitable technology for transitioning to a greener economy. However, their commercialisation did not match the stakeholders’ expectations. The authors applied the Theory of Constraints – a methodology for the continuous improvement of systems – to the MGT industry introducing a structured and rigorous representation. The constraint – i.e. Root Cause – Analysis identified which entities sustain the cause–effect chain, eventually generating the Undesired Effects. The system constraints link to the specificity and effectiveness of commercialisation strategies and product innovation in agreement with evolutionary market theories. Moreover, the Theory of Constraints emphasises the presence of reinforcement loops that make targeting entities like high product costs ineffective. The missing piece to complete the puzzle is solving a logic block representing the product’s market competitiveness depending on economic and technical factors. This study suggests that combining market-driven innovation and commercialisation is likely the only long-term solution to the lack of commercial success of the technology. However, the work also highlights limitations in the proposed methodology and solutions. To tackle these, the authors suggest and introduce numerical frameworks based on the Theory of Constraint.

Micro Gas Turbines are small devices for on-site power and heat generation. Their high maintainability and fuel flexibility make them a suitable technology for transitioning to a greener economy. However, their commercialisation did not match the stakeholders’ expectations. The authors applied the Theory of Constraints – a methodology for the continuous improvement of systems – to the MGT industry introducing a structured and rigorous representation. The constraint – i.e. Root Cause – Analysis identified which entities sustain the cause–effect chain, eventually generating the Undesired Effects. The system constraints link to the specificity and effectiveness of commercialisation strategies and product innovation in agreement with evolutionary market theories. Moreover, the Theory of Constraints emphasises the presence of reinforcement loops that make targeting entities like high product costs ineffective. The missing piece to complete the puzzle is solving a logic block representing the product’s market competitiveness depending on economic and technical factors. This study suggests that combining market-driven innovation and commercialisation is likely the only long-term solution to the lack of commercial success of the technology. However, the work also highlights limitations in the proposed methodology and solutions. To tackle these, the authors suggest and introduce numerical frameworks based on the Theory of Constraint.

Las micro turbinas de gas son sistemas de producción de potencia eléctrica y térmica, de pequeño tamaño y con capacidad para emplear diferentes combustibles. El potencial de la tecnología para abordar el trilema energético ha sido reconocido por la comunidad científica desde hace décadas; no obstante, a pesar de estar presente en el mercado desde hace más de veinte años, todavía no han logrado una penetración significativa. Ciertamente, a pesar de que la industria y la comunidad científica reconocen la existencia de este problema, hasta el momento no se ha implementado ninguna acción correctora de manera efective. De hecho, la literatura científica no contiene ningún estudio que aborde este asunto de manera holística y científica. La presente tesis doctoral tiene como objetivo llenar este vacío mediante el diseño de una metodología que pueda definir el problema, identificar las causas fundamentales y proponer soluciones de manera científica. Al inicio del doctorado, el candidato investigó dos metodologías cualitativas que podrían sentar las bases para el propósito presentado, el Análisis de Causa Raíz basado en procesos tradicionales (Root Cause Analysis - RCA, por sus siglas en inglés) y la Teoría de Restricciones basada en sistemas (Theory of Constraints - TOC, por sus siglas en inglés), encontrando que esta última era más adecuada. Después de realizar la definición del problema mediante un análisis de deficiencias/debilidades y la identificación de la causa raíz mediante el el denominado Árbol de la Realidad Actual (Current Reality Tree -CRT, por sus siglas en inglés), el autor validó la causa raíz inicialmente a través de un estudio de patentes y tendencias de innovación y generación de conocimiento. Además, el autor desarrolló una herramienta numérica para medir el grado e impacto de la innovación; el estudio realizado en nichos de mercado existentes confirmó la conclusión del Árbol de la Realidad Actual y midió el posicionamiento de las micro turbinas de gas e, Micro gas Turbines are small fuel-flexible units for on-site power and heat generation. The scientific community has often recognised their potential as a technology to address the energy trilemma. However, despite being in the market for over two decades, they have yet to achieve significant market success. The industry and scientific community acknowledge the existence of this problem, but any remedial action so far proved unsuccessful. In fact, the scientific literature does not contain any study tackling this matter holistically and scientifically. This study aims to fill this gap by devising a methodology that could define the problem, identify the root causes, and propose solutions in a scientific manner. The author initially investigated two qualitative methodologies that could lay the foundations for such purpose - traditional process-based Root Cause Analysis and system-based Theory of Constraint - and found the latter to be more suitable. After performing the problem definition through gap analysis and the root cause identification through the Current Reality Tree, the author validated the identified root cause with a study in patent data and innovation trends. Further, the authors developed a numerical tool to measure innovation; the study performed in existing market niches confirmed the conclusion of the Current Reality Trend andmeasured the position of micro gas turbines in the market against competing technologies. Finally, the author defined competitiveness as a combination of an absolute and relative term. This final concept is applied to the methodology above to produce a simple tool. This ultimate tool aims to gauge the current position of technologies in the market and to differentiate feasible and unfeasible technology innovation paths. This study finally suggests some final work which involves implementing the proposed innovation paths and refining the utilised methodologies employing ongoing research resulting from the NextMGT project.

Closed supercritical and transcritical power cycles operating on Carbon Dioxide have proven to be a promising technology for power generation and, as such, they are being researched by numerous international projects today. Despite the advantageous features of these cycles enabling very high efficiencies in intermediate temperature applications, the major shortcoming of the technology is a strong dependence on ambient temperature; in order to perform compression near the CO2 critical point (31ºC), low ambient temperatures are needed. This is particularly challenging in Concentrated Solar Power applications, typically found in hot, semi-arid locations. To overcome this limitation, the SCARABEUS project explores the idea of blending raw carbon dioxide with small amounts of certain dopants in order to shift the critical temperature of the resulting working fluid to higher values, hence enabling gaseous compression near the critical point or even liquid compression regardless of a high ambient temperature. Different dopants have been studied within the project so far (i.e. C6F6, TiCl4 and SO2) but the final selection will have to account for trade-offs between thermodynamic performance, economic metrics and system reliability. Bearing all this in mind, the present paper deals with the development of a non-physics-based model using Artificial Neural Networks (ANN), developed using Matlab’s Deep Learning Toolbox, to enable SCARABEUS system optimisation without running the detailed – and extremely time consuming – thermal models, developed with Thermoflex and Matlab software. In the first part of the paper, the candidate dopants and cycle layouts are presented and discussed, and a thorough description of the ANN training methodology is provided, along with all the main assumptions and hypothesis made. In the second part of the manuscript, results confirms that the ANN is a reliable tool capable of successfully reproducing the detailed Thermoflex model, estimating the cycle

This manuscript investigates the supercritical carbon dioxide (sCO2) power cycle employed in the power block of concentrated solar power (CSP) plants—solar tower—as an alternative for solar desalination, developed with either distillation or reverse osmosis. This concept is investigated as a possible up-scaling of the SOLMIDEFF project, originally based on a hot-air micro gas turbine combined with a solar dish collector. For the upscaled concept, five different sCO2 cycles are considered, chosen amongst the best-performing configurations proposed in the literature for CSP applications, and modelled with Thermoflex software. The influence of ambient conditions is studied, considering two minimum cycle temperatures (35 °C and 50 °C), corresponding to Santa Cruz de Tenerife and Abu Dhabi, respectively. The results show that the low temperatures at the inlet of the heat rejection unit compromise the viability of distillation technologies. On the other hand, the high thermal efficiency achieved by these cycles, especially with the recompression and partial cooling layouts, reduces the specific energy consumption when combined with reverse osmosis (RO), below that of photovoltaic (PV)+RO. Feed-water preheating is explored as a solution to further reduce energy consumption, concluding that its actual interest is not clear and strongly depends on the location considered and the corresponding water quality standards.

This paper investigates the interest and potential of using working fluids based on Carbon and Sulphur Dioxide mixtures (CO2-SO2) in a transcritical Recompression cycle. In order to assess the actual thermodynamic potential of the concept proposed, the influence of dopant (SO2) content is assessed for two different turbine inlet temperatures (550 °C and 700 °C). The results obtained are compared with other CO2 mixtures already proposed in literature (CO2-C6F6 and CO2--TiCl4) and for two alternative cycle layouts (Recuperated Rankine and Precompression). The results pf the analysis reveal that, at high ambient temperature, the Recompression cycle operating on CO2-SO2, with Sulphur Dioxide content between 20% and 30%(v), is a very interesting option for Concentrated Solar Power plants, able to achieve thermal efficiencies of approx. 45% and 51% at 550 °C and 700 °C respectively. At a minimum cycle temperature of 50 °C, the proposed configuration leads to thermal efficiency gains of 6% and 2% with respect to the Brayton and Recompression cycles working on pure CO2. This performance enhancement of the Recompression cycle with CO2-SO2 is comparable to or higher than that enabled by other CO2 mixtures proposed in literature, but with significantly higher specific work (smaller footprint) and temperature rise across the solar receiver (lower installation costs).

Power-to-Power is a process whereby the surplus of renewable power is stored as chemical energy in the form of hydrogen. Hydrogen can be used in situ or transported to the consumption node. When power is needed again, hydrogen can be consumed for power generation. Each of these processes incurs energy losses, leading to a certain round-trip efficiency (Energy Out/Energy In). Round-trip efficiency is calculated considering the following processes; water electrolysis for hydrogen production, compressed, liquefied or metal-hydride for hydrogen storage, fuel-cell-electric-truck for hydrogen distribution and micro-gas turbine for hydrogen power generation. The maximum achievable round-trip efficiency is of 29% when considering solid oxide electrolysis along with metal hydride storage. This number goes sharply down when using either alkaline or proton exchange membrane electrolyzers, 22.2% and 21.8% respectively. Round-trip efficiency is further reduced if considering other storage media, such as compressed- or liquefied-H2. However, the aim of the paper is to highlight there is still a large margin to increase Power-to-Power round-trip efficiency, mainly from the hydrogen production and power generation blocks, which could lead to round-trip efficiencies of around 40%–42% in the next decade for Power-to-Power energy storage systems with micro-gas turbines.

The adoption of CO2-based mixtures as power block working fluid for CSP plant can turn supercritical CO2 cycles into efficient transcritical cycles even at high ambient temperature, with significant performance improvement and potential power block cost reduction. In this work, the use of CO2+C6F6 mixture as working fluid for a power cycle coupled with a solar tower is analyzed. Two different cycle maximum temperatures (550°C and 650°C) are considered and for both configurations the overall plant design is performed. The yearly energy yield is computed with hourly data and the LCOE is minimized varying storage and cycle recuperator sizes. Results show comparable results for the innovative working fluid and for the sCO2 cycles

Throughout the last decades the developments on desalination field have been focused on energy consumption and costs reduction. However, water recovery and brine disposal are becoming a matter of concern to desalination industry. In this work, a Zero Liquid Discharge (ZLD) unit coupled with a Solar Micro Gas Turbine (SMGT) system is presented to address, among others, the challenges of mining industry in remote areas, in particular, fossil fuel dependence, water availability and pollution derived from effluents disposal. As a way to assess the feasibility of the proposal, a techno-economic analysis of the application in two Southern American regions (Chile and Ecuador) of photovoltaic modules, wind turbines and Solar Micro Gas Turbines is performed. Afterwards, the main novel feature of the new system—i.e., the ZLD unit—is described and a sensitivity analysis on its functioning whilst coupled with the SMGT is carried out. The aim is to propose a preliminary design of the ZLD process. The selection of the optimal ratio between exhaust gases and brine mass flow rates is analyzed, as well as variation in inlet salinity and temperatures. Furthermore, the water which could be recovered from effluents, at the same time that the heat of exhaust gases from SMGT is harvested, is quantified. Lastly, according to the results obtained, a preliminary design of a 10 kWe rated power SMGT system, coupled to Reverse Osmosis (RO) and ZLD units, is proposed.

This paper investigates the interest and potential of using working fluids based on Carbon and Sulphur Dioxide mixtures (CO2-SO2) in a transcritical Recompression cycle. In order to assess the actual thermodynamic potential of the concept proposed, the influence of dopant (SO2) content is assessed for two different turbine inlet temperatures (550 °C and 700 °C). The results obtained are compared with other CO2 mixtures already proposed in literature (CO2-C6F6 and CO2--TiCl4) and for two alternative cycle layouts (Recuperated Rankine and Precompression). The results pf the analysis reveal that, at high ambient temperature, the Recompression cycle operating on CO2-SO2, with Sulphur Dioxide content between 20% and 30%(v), is a very interesting option for Concentrated Solar Power plants, able to achieve thermal efficiencies of approx. 45% and 51% at 550 °C and 700 °C respectively. At a minimum cycle temperature of 50 °C, the proposed configuration leads to thermal efficiency gains of 6% and 2% with respect to the Brayton and Recompression cycles working on pure CO2. This performance enhancement of the Recompression cycle with CO2-SO2 is comparable to or higher than that enabled by other CO2 mixtures proposed in literature, but with significantly higher specific work (smaller footprint) and temperature rise across the solar receiver (lower installation costs).

El diseño y análisis de una turbomáquina es un proceso complejo, existiendo diversos métodos para abordar el mismo problema. Este trabajo utiliza como base la herramienta de cálculo ya implementada por R. González [ 1], fundamentada a su vez en el modelo de Aungier [ 2], siguiendo un modelo de diseño unidimensional para el diseño y análisis de un turbocompresor centrífugo. En la herramienta de cálculo se han contemplado diferentes correlaciones de pérdidas que permiten diseñar y analizar un compresor centrífugo, con la posibilidad de elegir entre diferentes estimaciones existentes en la literatura. En efecto, al estudiar los diferentes modelos de pérdidas se observa que no existe una única vía para obtener un mismo diseño de compresor y que, en función de dichos modelos, se obtienen resultados de mayor o menor fiabilidad. Los resultados del trabajo muestran que cabe esperar diferencias entre estimaciones de hasta el 65 % para el mismo tipo de pérdidas, y respecto al cómputo global de las pérdidas estimadas por el modelo, lo que supone un impacto acumulado en el rendimiento de la máquina de hasta un 25 %. El trabajo incluye finalmente una valoración crítica de los resultados arrojados por el modelo propuesto con respecto al modelo más empleado en la literatura (Aungier [2])., The anaylisis and design of a turbomachine is a complex task, and there are several alternatives for evaluating the same case study. This work begins from the computational tool developed by González [1 ], based on the method proposed by Aungier [2], following a one-dimensional design criteria to design a centrigufal compressor and predict its performance. In this computational tool, different loss correlations have been implemented, designing and analysing the centrifugal compressor according to the sets of correlations used. By studying different design and performance models, it is observed that there are many options to achieve the same compressor design and, depending on the performance models, the results obtained are more or less reliable, being the deviation of the estimations obtained nearly 65 % in some cases, for the same loss mechanism, and with respect the sum of all the losses estimated by the model. This disparity in the loss estimations can cause an impact in the compressor efficiency which can diverge almost 25 % from the baseline. Therefore, the aim of this work is to study the impact of the different sets of correlations selected, compared to the baseline scenario, the Aungier’s method [2].

The SCARABEUS project, funded by the European Commission, is currently investigating the potential gains brought about by the utilization of carbon dioxide mixtures in supercritical power cycles of Concentrated Solar Power plants, in lieu of the common Rankine cycles based on steam turbines or even pure carbon dioxide cycles. The analysis has already confirmed that it is possible to attain thermal efficiencies higher than 51% when ambient temperatures exceed 40°C, which is unheard of when conventional technology or standard CO₂ technology is used. Additionally, this extraordinary performance is achieved with simpler cycle layouts, therefore with lower capital costs. The additives considered include organic and inorganic compounds which are added to the raw carbon dioxide in a variable proportion, depending on the composition of the additive and on ambient temperature. Regardless, it is important to assess whether or not there is an additional environmental advantage in terms of carbon dioxide and other potential hazards brought about by the new chemicals in the system. This is presented in this paper where the results obtained so far by the consortium for the carbon footprint from a Life Cycle perspective are discussed. Along with the assumptions and methodology, the results are compared for three reference plants: state-of-the-art CSP plant based on steam turbines, innovative CSP plant using pure supercritical CO₂ technology, and the SCARABEUS concept using supercritical CO₂ mixtures. The results are promising as they suggest that it is possible to reduce the carbon footprint of a 110 MWe CSP plant to be significantly less than 27kgCO₂/MWh from the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC AR5).

El enfoque general de este trabajo consiste en el desarrollo de una herramienta computacional, integrable en orta herramienta global de simulación de microturbinas de gas, que permita realizar tanto el prediseño de un turbocompresor centrífugo como la posterior evaluación de prestaciones en condiciones nominales y en operación fuera de diseño. Por ello, el modelado de la herramienta está desarrollado teniendo presente que el turbocompresor está ensamblado en un eje solidario con la turbina centrípeta y, por consiguiente, que las condiciones de diseño no son libres sino que están sujetas a los parámetros de diseño de la mencionada turbina así como del propio ciclo de trabajo del motor. En este trabajo se presentan diferentes mapas de comportamiento del turbocompresor centrífugo para diferentes diseños de la máquina, los cuales son analizados con el fin observar las diferentes tendencias tanto de los parámetros de diseño seleccionados para el compresor como de los elementos incorporados en el mismo. La principal innovación con respecto a otro trabajos previos realizados en el Grupo de Máquinas y Motores Térmicos de Sevilla es, además de la capacidad de integración en la herramienta completa de simulación de turbinas de gas, la incorporación de álabes guía de geometría variable a la entrada del compresor, provocando que en condiciones fuera de diseño, el rango de operación de la microturbina sea mayor. Este dispositivo también permite mejorar el rendimiento del compresor en operación fuera de diseño. El objetivo tanto del módulo de diseño y análisis de turbocompresores como de la herramienta de simulación completa no es otorgar un diseño definitivo de la máquina, sino un diseño preliminar, con su correspondiente análisis en condiciones de carga parcial, que permita facilitar y acotar la región de interés de diseño, reduciendo en la medida de lo posible tanto la fase experimental, que es sin duda la fase más costosa del proceso de diseño de una turbomáquina, como de la, The general aim and scope of this work is the development of a computational tool for the one-dimensional design and performance analysis of centrifugal compressors for the future integrationinto another global micro gas turbine simulation platform. Thus, the programming has been developed taking into account that the compressor is assembled on a single shaft along with the turbine and, furthermore, the design conditions are set by the mentioned turbine and by the working cycle requirements. In this work, many different compressor performance maps are shown for different designs of the centrifugal compressor, which are analysed in order to observe the different trends of the selected design parameters for the compressor as well as the components assembled in the compressor. The main innovation with respect to previous works carried out by the Thermal Power Group (GMTS) of University of Seville is, apart from the adaptation capacity into the global simulation platform, the integration of variable inlet guide vanes in the compressor. This enables an increase of the operating range of the micro gas turbine when the compressor operates in off-design conditions. This device also improves the compressor efficiency in off-design performance. The aim of both compressor design and analysis modules is not to provide a final and definitive compressor design but to provide a preliminary design along with the off-design performance maps.

The supercritical Carbon Dioxide power cycle technology has attracted growing interest from the scientific community, becoming one of the most important options currently considered for CSP applications. This is thanks to its high thermal efficiency, even at moderate turbine inlet temperatures, and small footprint. Nevertheless, sCO2 power cycles require a fairly low compressor inlet temperature to exploit their full thermodynamic potential. When this cannot be achieved, as it is usually the case for Concentrated Solar Power plants where ambient temperatures are high, the interest of the technology is compromised. To compensate for this effect, the SCARABEUS project is working on the development of certain chemical dopants that could be added to the raw CO2, obtaining new working fluids with the same or even better performance than pure CO2 even at higher minimum cycle temperatures. This paper studies the impact of using CO2 mixtures blended with Hexaflurorobenzene (C6F6) and Titanium Tetrachloride (TiCl4). It is found that these mixtures enable thermal efficiencies that are higher than if pure CO2 were used. The efficiency gain can be as high as 3 percentage points, depending on the dopant used and the operating conditions considered. In addition to this absolute performance gain, the paper reveals that there are additional degrees of freedom that enable more effective cycle optimisation. These are the dopant molar content, not only its composition, and the cycle layout used. When this is studied, it is found that the optimum molar content ranges from 10 to 20% and that the layouts of interest when using mixtures are simpler than if plain CO2 were used. These results open the way for a significant performance enhancement of Concentrated Solar Power plants.

The present paper explores the utilisation of dopants to increase the critical temperature of Carbon Dioxide (sCO2) as a solution towards maintaining the high thermal efficiencies of sCO2 cycles even when ambient temperatures compromise their feasibility. To this end, the impact of adopting CO2-based mixtures on the performance of power blocks representative of Concentrated Solar Power plants is explored, considering two possible dopants: hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4). The analysis is applied to a well-known cycle -Recuperated Rankine- and a less common layout -Precompression-. The latter is found capable of fully exploiting the interesting features of these non-conventional working fluids, enabling thermal efficiencies up to 2.3% higher than the simple recuperative configuration. Different scenarios for maximum cycle pressure (250–300 bar), turbine inlet temperature (550–700 °C) and working fluid composition (10–25% molar fraction of dopant) are considered. The results in this work show that CO2-blends with 15–25%(v) of the cited dopants enable efficiencies well in excess of 50% for minimum cycle temperatures as high as 50 °C. To verify this potential gain, the most representative pure sCO2 cycles have been optimised at two minimum cycle temperatures (32 °C and 50°C), proving the superiority of the proposed blended technology in high ambient temperature applications.

Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power (CSP) applications as a means to increase the performance and reduce the cost of state-of-the-art CSP systems. Nevertheless, the sensitivity of sCO2 systems to the usually hot ambient temperatures found in solar sites compromises the actual thermodynamic and economic gains that were originally anticipated by researchers of this innovative power cycle. In order to exploit the actual potential of sCO2 cycles, the utilization of dopants to shift the (pseudo)critical temperature of the working fluid to higher values is proposed here as a solution towards enabling exactly the same features of supercritical CO2 cycles even when ambient temperatures compromise the feasibility of the latter technology. To this end, this work explores the impact of adopting a CO2-based working mixture on the performance of a CSP power block, considering hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4) as possible dopants. Different cycle options and operating conditions are studied (250-300 bar and 550-700ºC) as well as molar fractions ranging between 10 and 25%. The results in this work confirm that CO2 blends with 15-25%(v) of the cited dopants enable efficiencies that are well in excess of 50% for minimum cycle temperatures as high as 50 or even 55ºC. It is also confirmed that, for these cycles, turbine inlet temperature and pressure hardly have any effect on the characteristics of the cycle that yields the best performance possible. In this regard, the last part of this work also shows that cycle layout should be an additional degree of freedom in the optimisation process inasmuch as the best performing layout changes depending on boundary conditions.

Actualmente son varios los esfuerzos que realizan las diferentes entidades internacionales para intentar solventar los efectos nocivos sobre el medio ambiente que ha producido el ser humano a lo largo de los últimos siglos. Ante estos avances, vemos una imposición de las diferentes tecnologías que aprovechan las energías renovables, no obstante, estas presentan ciertos picos de producción que quedan desaprovechados debido a que en ciertos periodos la demanda no coincide con la producción. A raíz de la necesidad de aprovechar los recursos al máximo surge la idea del almacenamiento energético, que en el caso de este estudio se enfocará en un almacenamiento de energía eléctrica mediante hidrógeno, que será posteriormente empleado en microturbinas de gas. Al conjunto de estos sistemas se les conoce como sistemas Power-to-Power, es decir, primero generamos energía eléctrica con las energías renovables, con ellas producimos hidrógeno mediante electrólisis, y posteriormente almacenamos y quemamos ese hidrógeno de forma que podamos volver a obtener energía eléctrica. En el estudio se compara el sistema Power-to-Power con los distintos sistemas de almacenamiento dentro de los cuales podemos ver grandes rendimientos como el de las baterías de litio llegando a rendimientos de entorno al 97% (siendo estas cada vez más utilizadas), o sistemas de almacenamiento con una gran madurez como son los de bombeo, los cuales presentan también un rendimiento razonablemente alto, situándose entorno al 70-82 %. Frente a ellos tendríamos los sistemas Power-to-Hydrogen que presentan unos rendimientos algo menores situándose en valores de entre el 43-64 %. No obstante, es importante destacar que no solo se deben tener en cuenta los rendimientos para justificar el uso o no de una tecnología de almacenamiento, sino que dependiendo del uso final que se le vaya a dar a la electricidad una podrá ser mejor que otra indistintamente del rendimiento. Para finalizar el estudio del sistema Power-to-Powers, There are currently several efforts being made by the different international entities to try to solve the harmful effects on the environment that human beings have produced over the last few centuries. Given these advances, we see a larger share of the different technologies that take advantage of renewable energies, however, these present certain peaks of production that are wasted because in certain periods the demand does not coincide with production. As a result of the need to make the most of resources, the idea of energy storage arises, which in the case of this study will focus on the storage of electrical energy through hydrogen, which will later be burnt in gas microturbines. This energy store system is known as Power-toPower Energy Storage System, that will first produce hydrogen via electrolysis whit power from renewable energy sources. Then, hydrogen is stored for its later used to generate power back. The study compares the Power-To-Power system with other energy storage systems. In the case of lithium batteries, it yields efficiencies of around 97% (being used more and more for enrgy storage purposes), or storage systems with a higher maturity such as pumping, which also have a reasonably high performance, standing around 70-82% round-trip efficiencies. In contrast, the Power-to-Hydrogen systems have somewhat lower round-trip efficiencies standing at values of between 43-64%. However, it is important to note that not only should efficiencies be considered to justify the use or not of a storage technology but depending on the end use that is going to be given to the electricity one may be better than another regardless of performance. To finish the study of the Power-to-Power Storage System, a practical case has been carried out. Three different types of microturbines are established, of 30, 65 and 200 kW, imposing an operating daily period on the system of 6h. As a result of the study, we have obtained several factors of interest such as the roundtrip

Se ha realizado un estudio del diseño de sistemas principales y una simulación de Ciclos de potencia Brayton de CO2 supercrítico para su aplicación en reactores nucleares de IV Generación. Se ha realizado el diseño y simulación de un ciclo Rankine de vapor para su aplicación en reactores nucleares de IV Generación. El entorno de simulación utilizado es MatLab ©. El proyecto, consta en la primera parte de un análisis de los fundamentos, la historia y las principales aplicaciones de los ciclos de sCO2. En la segunda parte de un análisis del estado del arte (en cuanto a ciclos de sCO2 y a reactores nucleares de IV Generación), un análisis de la oportunidad de aplicación de ciclos de sCO2 a reactores de IV Generación como los SFR, VHTR y GFR y finalmente una selección de un reactor nuclear de referencia SFR y dos ciclos de sCO2 con condiciones de contorno específicamente seleccionadas. En la tercera parte, se presenta el procedimiento de resolución de los ciclos de sCO2 así como sus resultados numéricos, gráficas y análisis de sensibilidad, también el diseño de un ciclo Rankine de vapor con condiciones de contorno que permitan la comparación de resultados entre esta y los ciclos de sCO2. La simulación y la representación de datos se llevan a cabo con el uso del software MatLab© y MiniRefProp©. Los códigos, disponibles en los anexos, son una imagen de los fundamentos teóricos y metodológicos que se desarrollan a lo largo del trabajo y que permiten cálculos iterativos necesarios para la determinación numérica de los ciclos. Se desarrollan aproximaciones más exactas mediante el uso de la metodología Nellis & Klein para el cálculo del punto de “pinch”. Los resultados obtenidos son lógicos y coherentes con investigaciones anteriores como la de Vaclav Dostal [1] o Yoonhan Ahn et al, [2]. Para una potencia de 600 MW, temperatura máxima de 500 ºC y temperatura mínima de 32 ºC el ciclo de sCO2 de recompresión resulta más eficiente que el simple con recuperación, 41,8 % frente a, A study of the design of main systems and a simulation of supercritical CO2 Brayton power cycles have been carried out for its application in Generation IV nuclear reactors. The design and simulation of a steam Rankine cycle has been performed for its application in Generation IV nuclear reactors. The simulation environment used is MatLab ©. The project consists in the first part of an analysis of the fundamentals, history, and main applications of the sCO2 cycles. In the second part, an analysis of the state of the art (in terms of sCO2 cycles and Generation IV nuclear reactors), an analysis of the opportunity to apply sCO2 cycles to Generation IV reactors such as SFR, VHTR and GFR and finally a selection of a reference SFR nuclear reactor and two representative cycles of sCO2 with specifically selected boundary conditions. In the third part, the resolution procedure of the sCO2 cycles is presented as well as its numerical results, graphs, and sensitivity analysis, also the design of a Rankine steam cycle with boundary conditions that allow the comparison of results between this and sCO2 cycles. Simulation and data representation are carried out with the use of MatLab © and MiniRefProp © software. The codes, available in the annexes, are an image of the theoretical and methodological foundations that are developed throughout the work and that allow iterative calculations necessary for the numerical determination of the cycles. More exact approximations are developed by using the Nellis & Klein methodology to calculate the pinch point. The results obtained are logical and consistent with previous research such as that of Vaclav Dostal [1] or Yoonhan Ahn et al, [2]. For a power of 600 MW, a maximum temperature of 500 ºC and a minimum temperature of 32 ºC, the recompression sCO2 cycle is more efficient than the simple recuperated, 41.8% versus 36,85%. However, the Rankine cycle with the same boundary conditions obtained a higher thermal efficiency of 43.32%. Generatio

En este trabajo se ha llevado a cabo una revisión literaria sobre el estado del arte de las plantas de carbón, seguidamente de los proyectos qué se están realizando para disminuir el consumo de carbón y, por tanto, las emisiones de CO2. También se ha realizado una simulación de una central de carbón de 350 MW en Thermoflex. Seguidamente se ha realizado un análisis de las posibles inyecciones de vapor que se podrían aplicar en una central de carbón con el objetivo de realizar una hibridación entre una planta convencional de carbón y una central de concentración solar, y así aprovechar los beneficios y las similitudes de ambas tecnologías en una planta hibridada. Posteriormente se presentan los resultados de las simulaciones realizadas y se analizan los resultados. Finalmente, se presenta una valoración global acerca de las hibridaciones, su potencial de descarbonización, las conclusiones y se incluyen los posibles trabajos a futuro.

This paper, developed in the context of the SCARABEUS project funded by the Horizon 2020 programme of the European Commission, focuses on the thermodynamic comparison between pure supercritical Carbon Dioxide and blended transcritical Carbon Dioxide power cycles by means of a thorough exergy analysis. A reference power plant based on a steam Rankine cycle and representative of the current state of the art of Concentrated Solar Power plants is selected as base-case. Afterwards, four cycles are added to the comparison. Two of these cycles employ pure CO2, with either a Recompression or a Partial Cooling layout, whereas two cycles employ CO2-based mixtures with either Hexafluorobenzene (CO2-C6F6) or Titanium Tetrachloride (CO2-TiCl4) with a Precompression and a Recuperated Rankine. The figures of merit used to carry out the second-law analysis are exergy efficiency and exergy destruction in the main components of the cycle. Two different cases are identified, corresponding to two temperatures of the energy (heat) source: 575oC and 725oC. The first one is representative of the peak temperatures achieved by the molten salts used in modern Concentrated Solar Power plants. 725oC will expectedly be achieved by next generation systems and it is hence assessed with the aim to unfold the true potential of the concept proposed. The results show that at 575oC pure sCO2 power cycles are clearly outperformed by steam Rankine cycles whilst, at 725oC, they are able to achieve higher thermal and exergy efficiencies, in the order of 49% and 72% respectively. When compared to state-of-the-art Rankine cycles using steam, blended-sCO2 power cycles enable thermal efficiency gains of up to 1.1 and 6 percentage points at 575oC and 725oC respectively, with exergy efficiencies of up to 75.2%.

El agua es un bien escaso, puesto que, a pesar de tratarse del elemento más abundante en el planeta, tan sólo un pequeño porcentaje es agua dulce. El aumento de la población, así como el cambio en sus hábitos de consumo junto con el desarrollo de la economía son factores que están provocando que el consumo de agua sea una función creciente, de hecho, con una tasa de un 1% anual. Este hecho hace que la desalación se convierta en la mejor opción para utilizar una fuente de agua, que de otra manera no podría aprovecharse. Tal y como ocurre con el agua, la energía también es recurso escaso en muchas zonas del planeta. Las fuentes de energía renovable se presentan como una opción a considerar con la creciente concienciación por la preservación del medioambiente, puesto que su utilización permite disminuir la dependencia de la importación de combustibles fósiles, así como la reducción de la emisión de gases de efecto invernadero procedentes de éstos, influyendo directamente de este modo en el calentamiento global y contaminación del aire. A pesar de esto, resulta de vital interés recordar que las fuentes de energía renovables no presentan sólo ventajas, sino que también acarrean desventajas como la intermitencia de su disponibilidad o los mayores costes asociados, inconvenientes que buscarán ser resueltos también en este trabajo. Son muchos los estudios y plantas piloto que han demostrado la viabilidad de las fuentes de energía renovables acopladas con plantas de ósmosis inversa; Thomson e Infield (2003) simularon e implementaron una planta de osmosis inversa accionada mediante fotovoltaica diseñada para Eritrea, el Instituto Tecnológico de Canarias ha desarrollado sistemas independientes que funcionan tanto con fotovoltaica (DESSOL) como con energía eólica (AEROGEDESA). La minería es de por sí, una actividad con alto impacto en el medioambiente, este proyecto pretende evaluar la viabilidad de diferentes diseños de plantas de ósmosis inversa para la producción de agua des

Sudamérica tiene un alto nivel de importancia en cuanto a la producción global de recursos naturales, en general, y de minerales metálicos en particular. Concretamente, Chile representa la mayor parte de las importaciones europeas de productos acabados de cobre desde el año 2012. Asimismo, Ecuador está emergiendo como un foco de inversión minera en Latinoamérica, impulsado por la combinación de un marco regulatorio favorable y unas extensas reservas de oro y cobre. Sin embargo, el sector minero sudamericano está ligado a una serie de retos, tales como la escasez de agua, la contaminación de los acuíferos y los riesgos sanitarios asociados. Por ello, este estudio se ha llevado a cabo con el objetivo de caracterizar los problemas que representa la minería en estos países para el recurso hídrico y analizar una posible solución que ayude a mitigar los mismos y la tecnología empleada para dicho fin. En lo referente a contaminación, en el presente trabajo se han recopilado los datos de composición del agua minera analizados en numerosas publicaciones científicas, de entre las cuales algunas estudian casos de Chile y Ecuador. Y si se comparan dichos valores con los límites que marcan la normativa de dichos países se puede observar como en varios casos son superados, algunos ampliamente. El resultado no es más que la contaminación por sólidos, tanto suspendidos como disueltos, y metales como el cobre, el hierro o el mercurio. Por último, dado que la composición del agua salobre se muestra semejante a la de las aguas mineras analizadas aquí, se estudia la tecnología de ósmosis inversa (RO, Reverse Osmosis en inglés) para su tratamiento. En primer lugar, se explica el cálculo energético y después se realizan cálculos de la permeabilidad de los elementos de membrana, todo esto apoyado con los reportes del software de simulación Q+ de LG Chem Water Solutions. El primero refleja un comportamiento lineal del consumo frente a la presión osmótica del concentrado. El segundo sirve p, South America has a high level of importance in terms of the global production of natural resources, in general, and of metallic minerals, in particular. Specifically, the Republic of Chile represents the major amount of European imports of final copper products since 2012. Likewise, the Republic of Ecuador is emerging as a focus of mining investment in Latin America, driven by the combination of a favorable regulatory framework and vast gold and copper reserves. Nevertheless, the South American mining sector is linked to a series of challenges, such as water scarcity, pollution of aquifers and associated sanitary risks. Therefore, this study has been carried out with the aim of characterizing the issues that mining industry represents in these countries for water resources and to analyze a possible solution that would help mitigate them as well as the technology involved for that purpose. Regarding contamination, this study compiles the composition data of mining water analyzed in numerous papers, amog which some research cases from Chile and Ecuador. Comparing these values with the limits set by the regulations of these countries, it can be observed repeatedly how they are exceeded, some of them widely. The consequences are nothing but contamination by solids, both suspended and dissolved, and by such as toxic metals as copper, iron or mercury. To conclude, since brackish water could be considered similar in terms of composition to the mining water compiled, treatment by reverse osmosis (RO) technology is studied herein. First, the energy consumption calculation is explained and then it is followed by a calculation of the permeability of the filtration membrane elements. The former reflects a linear behavior of the specific energy consumption (SEC) against the osmotic pressure of the concentrate. The latter can be used to obtain an initial estimation of the quality of the product, the amount of required membrane elements and some possible valid configurations. The

Los tubos receptores son elementos clave en las plantas termosolares de tecnología cilindro parabólica, puesto que en ellos tiene lugar la conversión de energía solar en energía térmica, y por tanto, cabe esperar que su rendimiento tenga un impacto directo sobre la producción de energía eléctrica. El rendimiento de los tubos receptores está determinado por las condiciones de contorno y por sus propiedades ópticas, térmicas y mecánicas. Sin embargo, estas propiedades sufren una serie de degradaciones a lo largo de la vida útil de los tubos debido a los procesos habituales de operación y al entorno físico en el que se ubican las planta termosolares, disminuyendo el rendimiento de los tubos receptores. Debido a la poca o nula información experimental existente en la literatura esta tesis se plantea con el objetivo de estudiar la evolución de las prestaciones de los tubos receptores instalados en campo solar tras varios años de operación. Posteriormente, se calcula el impacto que los resultados obtenidos ejercen sobre la producción eléctrica final de una planta comercial. Para conseguir estos objetivos, la tesis comienza con un análisis del estado del arte. En el capítulo 3 se exponen los equipos de medida que se utilizan para realizar la evaluación de los tubos receptores. Algunos de los equipos son desarrollos específicos con una participación personal directa. Posteriormente, en el capítulo 4, se aborda la caracterización del ensuciamiento que experimentan los tubos receptores en operación. Para ello se desarrolla una metodología que permite obtener valores de ensuciamiento representativos para una planta comercial de 50 MW. En el capítulo 5 se aborda el estudio de la degradación óptica irreversible que sufren tanto la cubierta de vidrio como el coating selectivo del tubo absorbedor. A continuación, en el capítulo 6, se caracteriza de forma experimental el estado de vacío que presentan los receptores instalados en campo solar. Por último, en el capítulo 7 se desarrol

El proyecto SOLMIDEFF (Solar micro gas turbine-driven desalination for environmental off-grid applications), financiado por el plan Nacional de Investigación del Gobierno de España tiene como objetivo el desarrollo de un sistema combinado de desalación de agua alimentado por energía solar, apto para instalaciones en en lugares aislados de la red eléctrica. En este trabajo se realiza un estudio teórico preliminar de un sistema de vertido cero o ZLD (Zero Liquid Discharge), instalado aguas debajo del escape de una microturbina de gas solar, el cual consiste en un proceso térmico para recuperar agua de la corriente de salmuera que, de otro modo, sería vertida al ambiente. Esta característica de SOLMIDEFF incorpora ventajas muy importantes respecto de los sistemas convencionales basados en tecnología fotovoltaica. El sistema ZLD consiste en un regenerador al cual entra un gas caliente en flujo horizontal y, tras pasar por un codo, asciende y se encuentra con la salmuera procedente del proceso de ósmosis, la cual se inyecta a contracorriente y por gravedad a cierta altura dentro del canal, evaporando el agua de la salmuera para separarla de la sal. En este estudio se incluye el análisis de la geometría del regenerador, el mallado empleado y unas condiciones de contorno suficientes para que el sistema alcance el objetivo de evaporar el agua de la salmuera introducida (caso base). Tras un estudio completo sobre el efecto de cada variable en el sistema se demuestra que el del tamaño de las gotas introducidas y su caudal toman un papel fundamental en la evaporación de las gotas. Finalmente, empleando la información recabada a lo largo del trabajo, se desarrollan mejoras para el caso base, consiguiendo duplicar la cantidad de salmuera evaporada en relación a un cierto caudal de gases de escape de la microturbina de gas., The SOLMIDEFF (Solar micro gas turbine-driven desalination for environmental off-grid applications) project, which is financed by the National plan of Investigation of the Government of Spain, persues the development of combined system that removes salt from seawater powered by solar energy, what makes it suitable to off-grid applications. This project consists on a preliminar theoretical study of the initial design of a ZLD (Zero Liquid Discharge) system, a thermal process in which water is recovered from bride, since it could not be recovered otherwise. Besides, this characteristic of SOLMIDEFF involves deep innovations regarding the conventional systems based on photovoltaic energy. The ZLD system consists on a regenerator where a hot gas enters horizontally and, after passing through an elbow, ascends and meets an introduced bride current coming from a previous osmosis process, which is counter current inyected and falls by gravity at a certain height into the canal, evaporating the water within the bride in order to separate it from the salt. This project involves the regenerator geometry, its mesh and preliminary boundary conditions that fulfil the goal of evaporating the water within the bride (reference frame). After a complete research about the effect that every variable has on the system, it is proved that bride’s drops size and flow rate are decisive aspects that determine the success of the process. Finally, the information gathered through the completion of this project is utilized to improve the reference frame, doubling the evaporated bride in relation with certain gas flow from the microgas turbine.

This paper provides an assessment of the expected Levelised Cost of Electricity enabled by Concentrated Solar Power plants based on Supercritical Carbon Dioxide (sCO2) technology. A global approach is presented, relying on previous results by the authors in order to ascertain whether these innovative power cycles have the potential to achieve the very low costs of electricity reported in the literature. From a previous thermodynamic analysis of sCO2 cycles, three layouts are shortlisted and their installation costs are compared prior to assessing the corresponding cost of electricity. Amongst them, the Transcritical layout is then discarded due to the virtually impossible implementation in locations with high ambient temperature. The remaining layouts, Allam and Partial Cooling are then modelled and their Levelised Cost of Electricity is calculated for a number of cases and two different locations in North America. Each case is characterised by a different dispatch control scheme and set of financial assumptions. A Concentrated Solar Power plant based on steam turbine technology is also added to the assessment for the sake of comparison. The analysis yields electricity costs varying in the range from 8 to over 11 g/kWh, which is near but definitely not below the 6 g/kWh target set forth by different administrations. Nevertheless, in spite of the results, a review of the conservative assumptions adopted in the analysis suggests that attaining costs substantially lower than this is very likely. In other words, the results presented in this paper can be taken as an upper limit of the economic performance attainable by Supercritical Carbon Dioxide in Concentrated Solar Power applications.

The aim of the present work is the parametric optimization of Organic Rankine Cycles (ORC) for its main application to medium-low temperature generic sources. For this purpose, a Matlab® [1] computational code has been developed, in which design parameters, mass flow ratios, cycle configuration and fluid selection (including mixtures) are simultaneously optimized to offer the best combination of variables for the maximization of the efficiency. Given its extraordinary reliability the reference thermodynamic database of the choice has been REFPROP® [2] v.9.1. The results accomplished por pure fluid configurations show great adaptability to previous validated optimization studies. Whereas, those for mixtures support the theoretical evidence that there is a significant efficiency growth to be accomplished when combining organic pure fluids into binary zeotropic mixtures. The main improvements of the present work with respect to previous ORC optimization studies are, in one hand the emphasis on looking for the most suitable mathematical method for optimization of variables, previous works lack more exhaustive considerations when choosing the theoretical nature of algorithm, for this purpose multiple algorithms had been put to test running the same model, concluding that heuristic and stochastic algorithms provide more accurate results in the job of converging to global optimal. In the other hand, regarding the specifics of ORC optimization, the goal of this work is to first develop a reliable computational tool for the analysis and optimization of ORC and then verificate it in orther to expand its performance to include the analysis of binary zeotropic mixtures, which is the ultimate objective of this study. It is a fact that the actual global situation calls for renewable and robust solutions for the energy production, these being one of the main reasons why there is a susbstantional increase of industries interest regarding the ORCtechnology. Aiming to represent a hum

En la actualidad, el sector energético ha tenido que buscar estrategias para una producción de energía más eficiente, centrando en las fuentes renovables esas medidas que permitan optimizar la generación de energía eléctrica para abastecer a la población. En el caso de las centrales termosolares optan por mejorar su capacidad de captación mediante la incorporación del CO2 en condiciones supercríticas como nuevo fluido de trabajo, el cual presenta características y propiedades de bastante interés para la sustitución de los actuales. El problema surge en el rediseño que hay que adoptar del ciclo de potencia y de las características de los componentes. Este trabajo se centra en el estudio de las turbomáquinas que compondrán los nuevos ciclos termodinámicos, realizando un análisis sobre el comportamiento de las mismas al operar con CO2 supercrítico. Se busca conocer las características del turbocompresor axial, estudiando el comportamiento ante cambios de fluido mediante simulaciones en la experimentación de una cascada de álabes de compresor. Para ello este proyecto se divide en dos grandes bloques. Se realiza como primer punto un análisis cualitativo de las actuaciones de la cascada mediante la resolución del problema directo, en el que, fijando condiciones geométricas de una hilera de álabes para un perfil NACA 65, se estudiarán tanto las prestaciones como las irreversibilidades que presenta la cascada al operar con tres fluidos distintos. Estos fluidos serán aire, CO2 y CO2 supercrítico, para poder establecer una comparativa entre gases de naturaleza ideal y no ideal. Los cálculos se realizarán mediante métodos numéricos computacionales de los que obtendremos resultados de la pérdida de presión total y del aumento de presión estática, representando así el rendimiento y las prestaciones del efecto difusor de la cascada de álabes de compresor. Y en un segundo bloque, con el objetivo de establecer una comparativa mayor entre las prestaciones de la máquina ante el cambi