1,720,960 research outputs found
Techno-Economic Analysis and Optimal Supercritical Carbon Dioxide Power Cycle Configuration for Novel Concentrating Solar Power Plants Adopting Tubular Fluidized Particles Central Receivers
Full text linkTechno-economic analysis of a solar-driven biomass pyrolysis plant for bio-oil and biochar production
No full textPyrolysis has become one of the most attractive options for converting carbonaceous biomass into bio-oil or biochar. This study explores a novel solar pyrolysis process intended to produce both bio-oil and biochar, thereby improving carbon efficiency. Aspen Plus and SolarPILOT were used to model a 10 MW biomass pyrolysis plant thermally sustained by hot particles from a falling-particle solar tower receiver. A yearly analysis was carried out for three configurations to estimate the annual production of oil and biochar. The results showed that the hybrid plant, combining solar receiver and biochar backup combustor, leads to the lowest cost of bio-oil (18.7 per GJ, or 0.29 per kg) and a carbon efficiency of 83%. Whereas, the plant fully sustained by solar power achieves a carbon efficiency of 90%; however, it results in a significantly higher cost of bio-oil (21.8 per GJ, or 0.34 per kg) due to the larger size of particle storage and a lower capacity factor of the pyrolysis plant. In comparison, a conventional pyrolysis plant with no biochar production yielded the most expensive option in terms of the cost of produced bio-oil (27.5 per GJ) and features the lowest carbon efficiency (74%). Sensitivity analysis shows that the pyrolyzer Capex, operational cost, biochar market price, plant availability and discount rate significantly affect bio-oil production cost.Transforming conventional biomass pyrolysis through solar-driven pyrolysis with a falling particle receiver and intermediate hybrid solution reduces costs by 21% and 32% and emissions by 27.5 and 22.3 kgCO2 GJoil-1, respectively
A falling particle receiver thermal model for system-level analysis of solar tower plants
Full text linkFalling particle receivers are one of the most promising new generation solar tower technologies. They have the advantage of being directly heated, thus relaxing flux limitations associated with conventional receivers, and being able to achieve very high temperatures (>1000 °C) without degradation. The goal of this work is the development of a thermal model able to describe the behaviour of a falling particle receiver under different operating conditions, to provide the value of its thermal efficiency within reasonable computational time so that the model can be applied for optimization of solar tower plants at system-level. The thermal model was developed starting from models described in literature, upgrading them with various features (e.g., 2D/3D discretization, drag force effect, etc.) to describe more in detail the heat transfer phenomena occurring during receiver operation. The obtained model results were verified against CFD showing better agreement than the original model. Furthermore, the thermal model was employed in a case study with the goal of optimizing the receiver size for a given solar field and performing off-design and annual performance analyses. Results showed that the adoption of multiple stages increases performance compared to a free-falling particle receiver both under nominal and off-design conditions, and the higher the number of stages the better is the performance. A free-falling particle receiver showed a yearly thermal efficiency of 72.0 %, while the five stages one achieved 75.3 %. In addition, recirculation was investigated as part load strategy for improving performance of the free-falling receiver, but the benefits in terms of performance were limited
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Preliminary analysis on tubular fluidized particles receivers for Solar Tower applications
No full textLAUREA MAGISTRALECon l’avanzare della transizione energetica, emergono con rilevanza i sistemi a concentrazione solare, in quanto rappresentano al contempo una fonte di energia rinnovabile e dispacciabile. Tuttavia, i costi sono ancora troppo elevati, il che richiede ulteriori miglioramenti. Un innovativo modo di concepire il fluido termovettore, basato sulla tecnologia della fluidizzazione di particelle solide, emerge come una soluzione promettente per superare lo stato dell’arte di questa tecnologia. Le particelle solide vengono quindi fluidificate e le loro proprietà termofisiche permettono di aumentare la temperatura massima del ciclo, offrendo quindi la possibilità di sfruttare cicli supercritici e quindi di migliorare l’efficienza. Inoltre, il costo di queste particelle può essere molto basso rispetto ai fluidi termovettori attualmente utilizzati. Il presente lavoro di tesi ha l’obiettivo di sviluppare un’analisi preliminare di questo nuovo fluido termovettore per l’applicazione in torri solari, che comprende: la valutazione sulla tipologia di particelle, l’analisi di modelli per stimare il
coefficiente di scambio convettivo interno e le prestazioni termiche. Tale metodologia è poi
applicata al caso studio, con l’obiettivo di trovare una correlazione adeguata e di valutarne
prestazioni e limiti. I risultati mostrano che è possibile raggiungere un’efficienza termica massima di circa l’80% ed una temperatura di uscita dal ricevitore delle particelle fino a 750°C, dimostrando che questa tecnologia può essere combinata con cicli termodinamici altamente efficienti. Tuttavia, esistono alcuni limiti che devono essere rispettati, dettati dalla tollerabilità alle alte temperature del materiale dei tubi e dal fenomeno del choking, che ristringono il campo di applicabilità di questa tecnologia a impianti di piccola e media taglia.As the energy transition advances, CSP can play a major role as it is a renewable and dispatchable energy source. However, costs are still too high, thus requiring engineering improvements. An innovative way of conceiving the heat transfer fluid for solar towers, based on the fluidization technology of solid particles, emerges as a promising solution to overcome the state of the art of this technology. Solid particles are fluidized and their thermophysical properties allow to enhance the maximum cycle temperature, enabling the possibility to drive supercritical cycles and thus, improve the power generation efficiency. Moreover, solid particles’ cost can be very low compared to the heat transfer fluid currently used. This thesis focuses on the development of a preliminary analysis for the novel heat transfer fluid in solar tower application, including: particles assessment, analysis of models to estimate the internal heat transfer coefficient and thermal performances evaluation. The methodology is then applied to the case study, aiming to find a proper correlation for the heat transfer coefficient and assess its performances. Results show that a maximum thermal efficiency of ~ 80% can be reached, together with a particle outlet temperature up to 750 °C, proving that this technology can be combined with highly efficient thermodynamic cycles. However, some limits must be respected, dictated by the tolerability of the tube material and choking phenomenon, restricting the applicability range of this technology to small-middle scale plants
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A bi-level optimization approach for the management of energy communities
No full textLAUREA MAGISTRALELe comunità energetiche sono destinate ad assumere un ruolo di particolare importanza nella transizione energetica facilitando la diffusione di risorse derivanti da fonti rinnovabili. Il massimo potenziale può essere ottenuto attraverso l'ottimizzazione del loro funzionamento attuando un coordinamento centralizzato da parte dall'aggregatore.
Tuttavia, questo approccio presenta alcuni limiti; a titolo esemplificativo il conflitto di interessi tra membri e aggregatore e problemi di privacy e memoria. Nel tentativo di affrontarli, seppur parzialmente, questo lavoro presenta un approccio bilivello per l'ottimizzazione del funzionamento della comunità energetica in cui l'aggregatore assume il ruolo di leader mentre i membri quello di followers. In questo contesto entrambe le parti hanno come obiettivo quello di minimizzare il proprio costo operativo. Si propone l'applicazione del modello di gioco di Stackelberg "one-leader-multi-followers" in cui il leader fornisce gli stessi segnali di prezzo a tutti i followers, che risolvono così il loro problema. Il livello superiore è ottimizzato con l'algoritmo evolutivo PGS-COM, mentre il problema dei membri è formulato attraverso un LP o un MILP. Nella risoluzione vengono ottimizzati sia i prezzi di acquisto che di vendita per ciascun intervallo temporale all'interno dell'orizzonte considerato. Il metodo è testato su comunità energetiche caratterizzate da diversi tipi di membri (con/senza PV, veicolo elettrico, sistema di accumulo, DSM) per il funzionamento invernale ed estivo, utlizzando profili di domanda elettrica reali acquisiti specificatamente per questo lavoro. I risultati vengono confrontati con quelli che si otterrebbero con un approccio centralizzato e nel caso in cui i membri agissero in modo indipendente.
In termini di benefit per la comunità, l'approccio si è rivelato efficace quando sono presenti componenti di tipologie diverse caratterizzati da una grande flessibilità nella gestione delle loro risorse. I risultati mostrano che, in questi casi, il risparmio totale ottenuto con la formulazione bilivello, rispetto all'ipotesi in cui i membri agiscano in modo indipendente, è paragonabile con quello che si ottiene con l'approccio centralizzato. Infine, il metodo proposto per ridurre il costo computazionale si è rivelato efficiente poiché raggiunge risparmi simili in un tempo ridotto.Energy communities (ECs) are expected to play an essential role in the energy transition by facilitating the diffusion of renewable-based energy resources. The full potential of ECs can be exploited by optimizing their operation through a centralized coordination handled by an aggregator. However, this approach comes with many drawbacks (e.g., conflict of interests between members and the aggregator, and privacy and memory concerns). In the attempt to partially address these issues, this work presents a bi-level approach for optimizing the operation of the ECs, with the aggregator acting as the leader and the community members as the followers, with the objective of both parties being the minimization of operational costs. The one-leader-multiple-followers Stackelberg game model is established, where the leader gives the same price-based signals to all the followers that proceed to solve their problem. The upper level is optimized with the evolutionary algorithm PGS-COM, while the followers' problems are formulated as either LP or MILP. The problem is solved by optimizing both buying and selling prices for each time step within the optimization horizon. The approach is tested on ECs characterized by various types of prosumers (with/without PV, EV, BESS and DSM) for both a summer and winter day, using real electricity demand profiles specifically collected for this work. The results are compared to those obtained by a centralized approach and by the case when members are given the exact grid prices for the internal trade. The approach is proven to be effective when a wide range of diverse members with great flexibility is present. The results show that, in these cases, the total savings achieved by the proposed bi-level approach, compared to the costs incurred by independent members, are comparable to those of the centralized approach. Additionally, the proposed method for reducing the computational burden has been verified as efficient, as it achieves similar cost savings within a limited time
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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