1,720,958 research outputs found
Power-to-Gas: Process analysis and control strategies for dynamic catalytic methanation system
No full textThe methanation process, or Sabatier process, allows carbon dioxide and carbon monoxide to be hydrogenated into methane, which can be subsequently injected (once the gas grid specifications have been respected) into the gas network infrastructures already present in Europe. This process can be effectively adopted to convert captured CO2 streams from power plants or hard to abate plants by using green hydrogen from renewable-driven water electrolysis. The technical aspects of concern in the methanation process are certainly the strong exothermicity of the process, with consequent possible generation of hotspots along the entire catalyst bed and the management of reaction heat through thermal recovery. These peculiar aspects influence the choice of construction materials and geometry of the methanation reactor, operating parameters, cooling system, type of catalyst/support and the initial conditions of the feed. In particular, the generation of hotspots influences the local kinetic reaction in the methanation reactor, the diffusional limits of hydrogen and carbon dioxide inside the catalyst and the chemical-physical characteristics of the catalyst bed. The present work reports a first scale-up of the Sabatier process, developed in Aspen Plus simulation environment, with the following characteristics: reactor size to process 925 Nm3/h, (750 hydrogen and 175 carbon dioxide), at 15 bar and 250 degrees C. After the implementation in the steady state, a dynamic simulation is performed to carry out a transient study of the entire plant. In particular, the attention is focused on the variation in the hydrogen load, produced by electrolysis from the energy surplus from renewable sources. Considering the variable nature of the power flow supplied to the electrolyser and therefore any shutdown and cold start-up phases of this equipment, the following load variation scenarios for the Power to Gas (PtG) system are simulated: -5%, +5% and -30 % molar flow rate of incoming hydrogen, compared to steady conditions used in the preliminary design of the equipment. The study highlights how the cooled reactor configuration is more performing and characterized by a lower number of reactors in series (2 reactors) when compared to the adiabatic configuration (5 reactors). Furthermore, in the cooled reactor configuration the control system is able to respond more quickly to load variations compared to that designed for the adiabatic case, although the latter is mostly adopted from the industrial viewpoint due to temperature control issues. Moreover, the control system manages to respond to load variations by bringing the values of interest (gas grid residual concentration of hydrogen and carbon dioxide, Wobbe index) into the target intervals
Optimization of Power to Gas system with cooled reactor for CO2 methanation: Start-up and shut-down tests with Ru-based and Ni-based kinetics
No full textThe dynamic behavior of a methanation process is analyzed in the context of Power to Gas (PtG) technology, to
convert carbon dioxide from different sources and hydrogen produced via electrolysis with renewable energy to
synthetic methane. The process configuration consists of a single cooled plug flow reactor (PFR) where both
ruthenium and nickel-based kinetic models are tested in the Aspen Dynamics simulation environment. In
particular, dynamic analyses are performed to study the start-up and shut-down phases and respect injection
parameters in the existing gas network. The process consists of three main sections: conditioning, reaction and
separation. After the development and optimization of the control system, the start-up and shut-down tests are
carried out, to study the trend of composition for the injection in the gas network. The plant size is set according
to the following values: 700 Nm3
/h of hydrogen and 175 Nm3
/h of carbon dioxide, which correspond to the
methanation reaction stochiometric ratio. Different cases are considered in both the start-up and shut-down tests,
by changing the GHSV values and the catalyst adopted. Moreover, in the shut-down test two different rates are
considered to evaluate the behavior of the system
E-fuels, technical and economic analysis of the production of synthetic kerosene precursor as sustainable aviation fuel
No full textIn the context of European and national energy policies to pursue the energy transition process, the issue of alternative-renewable liquid fuels is clearly addressed, whose purpose is to support the growth of sustainable mobility towards the goal of net zero emissions. On the base of the goals to be achieved in the medium and long term in relation to the theme of decarbonization and the development of new sustainable technologies, the present work deals with the e-fuels, which are produced by hydrogen from water electrolysis driven by renewable energy and CO2 captured from air or industrial sources. In particular, the attention is focused on the production of synthetic kerosene with the purpose to decarbonize the aviation sector, which is one of the most difficult electrifiable sectors due to logistical problems. The main objective of this work is the techno-economic analysis of the production of synthetic kerosene starting from green H2 and CO2 from direct air capture. The study of two main process schemes is carried out for the production of a synthetic crude oil, also called syncrude, rich in the kerosene fraction of interest. In the first scheme, called two-stage or indirect process, the incoming carbon dioxide and hydrogen are transformed through the Reverse-Water-Gas-Shift (RWGS) reaction in a syngas which allows to produce, by means of the Fischer-Tropsch (FT) reaction, the product of interest. The second scheme, referred to as single-stage or direct process, involves the direct formation of syncrude (direct FT-CO2) starting from carbon dioxide and hydrogen. In both cases, kinetic models representative of the considered reactions are selected in order to carry out an accurate process analysis. Through sensitivity analysis and process evaluations, some process optimizations like material recycle and heat integration are performed in order to increasing the efficiency and carry out a cost comparison to evaluate economic feasibility. Regarding the indirect and direct processes, 66.18 bbl/d and 38.46 bbl/d are produced respectively. Considering all the results and scenarios with and without optimizations, the range of the product cost is from 460 to 1435 €/bbl for the indirect process and from 752 to 2364 €/bbl for the direct process. These values strongly depend on the considered prices of power energy and hydrogen used for the present work
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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