1,721,128 research outputs found
COMBINING WASTE-TO-ENERGY STEAM CYCLE WITH GAS TURBINE UNITS
No full textIn recent years, interest has been growing in developing new possibilities to maximize the conversion of waste into energy. Technologies allowing for efficient Waste-To-Energy (WTE) conversion are supported in the EU, by the European Waste Framework Directive, suggesting an efficiency criteria aimed at introducing a reference quality standard. Nevertheless, current state-of-the-art WTE plants are typically characterized by low efficiency values, compared to conventional steam power plants using fossil fuels. This is mainly due to limitations in the WTE steam cycle design parameters, in comparison with large fossil fuelled power plants.
This paper focuses on an innovative and promising strategy to improve waste conversion through integration of a conventional WTE power plant with a Gas Turbine (GT). The resulting WTE-GT integrated plant requires to conceive a redesign and an optimization of the steam-gas cycle. In particular, this study investigates the feasibility of utilizing the hot gases leaving the GT to superheat the steam leaving the WTE steam generator, as well as heating the feed water returning to the steam generator of the WTE condenser. Parametric analysis of the effect of the GT discharged heat on the steam mass flow production is carried out and the optimum plant match condition in terms of plants capacity ratio is identified. Detailed modifications to the WTE cycle and the resulting enhancement of its performance are presented.
Numerical results of a representative WTE plant integrated with different GT commercial units are shown and discussed. Results of the study suggest issues and useful guidelines to: (i) create new advanced WTE-GT integrated power plants or to (ii) repower existing low-performing WTE power plant, in order to increase waste conversion into energy
Performance analysis of a micro gas turbine and solar dish integrated system under different solar-only and hybrid operating conditions
No full textA hybrid energy system comprising a parabolic dish solar energy concentrator (Solar Dish) and a micro gas turbine is investigated in the study. A thermodynamic model of the system is presented, able to simulate both on-design and off-design performance of the system and accounting for the main technical aspects of the concentrator, receiver and gas turbine engine. Then, simulations are performed for various system sizes and operating strategies, with and without supplementary firing and for a reference location (Seville, Spain), yielding solar-to-electric power conversion efficiencies between 16.78% and 18.35% (rated conditions), depending on size. Annual performances result in a capacity factor of about 29% (2540 full operating hours) in solar only operation and annual average efficiency at 95% of the nominal value.The main results indicate that moderate supplementary firing is interesting for it increases the average efficiency of the system and the annual yield, whilst still keeping the carbon footprint within reasonable values. Nevertheless, as heavy fossil fuel firing is adopted, the system becomes less competitive against conventional, standard distributed generation power systems either for natural gas or diesel fuel. Whilst these trends were somehow to be expected, the interest of this paper is to provide the reader with a fundamental analysis from which a technical and economic analysis can be performed, aimed at identifying the most leveraged solar share (i.e., fuel utilisation)
Application of environmental performance assessment of CHP systems with local and global approaches
No full textThis paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario. Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the "Avoided Heat Generator" is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact. Numerical evaluations of the CHP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for several CHP systems with different technologies and electric power sizes, in order to provide a comprehensive overview of current CHP prime mover environmental performance and to serve as an application reference example of the two methods potential use, in the framework of the CHP units authorization procedure. The significant effect of the reference comparative scenario is also highlighted
Performance Indexes and Output Allocation for Multi-fuel Energy Systems
No full textAbstractIn this paper we take into account the concept of conversion efficiency by exploring Multi-Fuel (MF) energy systems. A MF system can be defined as a system with various fuel energy input and useful product output. The difficult task in defining a performance index for MF systems consists in quantifying the contribution of each input fuel to the total output energy.This paper intends to make few proposals and start a discussion that would be helpful to assess the MF system performance.The conventional first law efficiency, normally used to assess performance of Single-Fuel (SF) system, can be applied but it provides incomplete information for a MF system. The electric equivalent efficiency, the relative and overall MF synergy index concepts are introduced as most significant performance indexes; these new performance indexes are presented with the aim to evaluate the MF performance compared to reference SF scenarios. Proposed performance indexes are analyzed, discussed and compared from a general point of view, identifying aspects of relation and main differences. The introduced conversion efficiency indexes are applied and discussed to a specific co-combustion power plant case. The influence of the reference scenarios, as it is highlighted in the paper, results of key importance. The evaluation of the proposed indexes is of relevant interest with the goal of formulating a specific and unified theory about MF power energy systems
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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