1,720,962 research outputs found
Simulation tools for design and analysis of CO2-based innovative energy plants
No full textIn an energy scenario where climate change and geopolitical concerns drive the energy production and utilisation towards decarbonisation strategies, the need to exploit energy sources in efficient ways as well as to manage electrification of processes, is paramount.
In this context, power plants evolving supercritical carbon dioxide (sCO2) can be an efficient, cost-effective, and fast-response solution. Being firstly studied for nuclear applications, these cycles offer a variety of design choices and possible application that need to be analysed and evaluated to identify the best performances and the most profitable applications.
Some of the tools that can be used to assess the performances of such variety of designs of these plants can be the heat and mass balances and the cost analyses to be performed upon them.
Starting from the logical structure of a software tool pre-existing at the Thermochemical Power Group at the University of Genova, the TEMP-EVO tool has been developed and it is illustrated in the present dissertation. This is a tool enabling modular simulation of equipment to be assembled to obtain the desired process configuration. Once the desired layout is chosen, thermodynamic design and optimisation analyses can be performed, to evaluate performances and profitability.
The tool is structured in blocks, separating the process definition, its thermodynamic resolution, and its economical evaluation. The modules developed are presented, together with the integration methods and the possible solvers that have been chosen and developed. Some applications of the tool to cycles evolving sCO2 are presented thermoeconomic results to evaluate different cycle layouts and compare solutions
Techno-Economic Comparison of Supercritical CO2, Steam, and Organic Rankine Cycles for Waste Heat Recovery Applications
No full textSupercritical CO2 (sCO(2)) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to concentrating solar power and waste heat recovery (WHR). To evaluate the competitiveness of sCO(2) cycles relative to other competing technologies, mainly steam and organic fluid Rankine cycles (ORC), a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO(2) plants, compared to the existing steam and ORC solutions. In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO(2) cycle configuration shows competitive performance, while in the second case, the simpler sCO(2) cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately -130 Euro/kW compared to the steam cycle). In general, while traditional technologies confirmed a good tradeoff between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation
Performance analysis of PTES layouts evolving sCO2 for industrial WHR integration
No full textA consistent amount of renewable energy (RES) from nonpredictable sources in the energy mix brings an increasing need of energy storage technologies to support grid stability. At the same time, electrification of industrial processes as well as the more and more common habit of industries to self-produce power via RES or CHP, can make industries a partner in disrupting grid stability. Thermo-mechanical storages can contribute through the use of traditional technologies (rotating machinery) employed in power plants, which are currently used to manage peak demand and grid services, and typically classify as hours-size storages, also capable of providing spinning reserve services to the electrical grid. Among such type of storages, Pumped Thermal Energy Storages (PTES) are a promising technology that enhance the concept of power-toheat-to-power and long duration energy storage, and presents also different layouts and applications. This paper analyse the thermal performance of Pumped Thermal Electricity Storage (PTES) evolving supercritical CO2 (sCO2), comparing different layouts, while valorising waste heat (WH) sources, which are typically in temperature ranges of 100-400°C. WH temperature in this range are difficult to be exploited for traditional energy generation, but they are currently under investigation for the possibility to be valorised via High Temperature Heat Pump. In this sense this quality of Waste Heat could be valorised via PTES. In fact, the use of additional heat, otherwise dumped to ambient, may make the system capable of an apparent round-trip efficiency (RTE) higher than 100%. The use of sCO2 could enhance the techno-economic features of these systems, if compared to similar plants evolving steam or air. Starting from an identified reference case (a cement production plant with WH temperature to be valorized around 350°C), a sCO2-based PTES cycle is presented and analysed in this paper. The waste heat integration to the PTES system has been found to add an undeniable value in terms of RTE. The use of sCO2 enhances the techno-economic features of these systems, the independent charging and discharging system proposed in this study can also provide a keen sense of flexibility. At the same time, the valorisation of low temperature waste heat enables industries to enhance their energy efficiency, limit their operational costs and environmental impact, whilst becoming an active part in the regulation of the grid. Nevertheless, CAPEX of the proposed systems are still quite relevant and only a robust exploitation of the PTES in ancillary service market could attract industrial customers interest on sCO2 PTES
A prototype recuperated supercritical CO<sub>2</sub> cycle : Part-load and dynamic assessment
No full textHigh efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and by a few projects in the EU Horizon 2020 (H2020) program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures. The H2020 SOLARSCO2OL project, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. After a detailed explanation of the modelling approach for steady and unsteady cycle simulations, this paper presents the off-design and dynamic analysis of such plant layout, which is based on a simply recuperated sCO2 cycle. The entire system model has been developed in TRANSEO environment. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet. The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely molten salt mass flow rate, CO2 mass flow rate, total CO2 mass in the loop, and shaft line speed. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected. Finally, the dynamic characterization of the closed loop shows the relatively fast responsiveness of the plant to compressor speed variations, causing quick changes in CO2 mass flow rate, together with longer time scale phenomena related to the plant heat exchangers. In this respect, sCO2 plants demonstrate to have the potential to provide primary reserve for the electrical grid, as far as thermal stresses on main plant components are kept under acceptable limits.</p
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
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
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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