1,720,959 research outputs found
High-temperature electrolysis integrated with advanced power cycles for the combined production of green hydrogen, heat and power
No full textEvaluating the Energy Recovery Potential in Industrial Gas Pipeline Networks: A Preliminary Analysis of Gas Expander Applications for Nitrogen, Oxygen and Hydrogen
No full textTechno-economic analysis for the design of membrane reactors in a small-scale biogas-to-hydrogen plant
Full text linkPd-based membranes are a key-component to obtain high-purity hydrogen from gaseous mixtures. They can be integrated in reactors called Membrane Reactors (MR), where the selective removal of reaction products allows to circumvent equilibrium limitations of traditional reactors. MRs for hydrogen production from methane reforming have been already investigated in literature, where they showed potentialities in small-scale biogas plants. However, analyses have typically been performed fixing many operating conditions and geometrical parameters, while only investigating few of them. It is therefore difficult to generalize the conclusions and to have a clear overview of the process behaviour. This article proves that MR performance can be summarized in generalized performance charts, where it is possible to characterize the reactor and the overall MR-based system only based on the membrane area it contains, for each set of temperatures, pressures, feed composition, catalyst amount and steam-carbon-ratio. From techno-economic analysis, it turned out that LCOH is 6.81 €/kg for a system with 100 kg/day of hydrogen production at 20 bar, reaching 7.49 €/kg if compressed up to 700 bar. System performance have been compared with a traditional reactor followed by a PSA (LCOH = 7.31 €/kg), showing that MR-based solution outperforms benchmark for its higher capacity to separate hydrogen. A sensitivity analysis assessed the influence of major uncertain costs.</p
Optimization of Small-Scale Hydrogen Production with Membrane Reactors
Full text linkIn the pathway towards decarbonization, hydrogen can provide valid support in different sectors, such as transportation, iron and steel industries, and domestic heating, concurrently reducing air pollution. Thanks to its versatility, hydrogen can be produced in different ways, among which steam reforming of natural gas is still the most commonly used method. Today, less than 0.7% of global hydrogen production can be considered low-carbon-emission. Among the various solutions under investigation for low-carbon hydrogen production, membrane reactor technology has the potential, especially at a small scale, to efficiently convert biogas into green hydrogen, leading to a substantial process intensification. Fluidized bed membrane reactors for autothermal reforming of biogas have reached industrial maturity. Reliable modelling support is thus necessary to develop their full potential. In this work, a mathematical model of the reactor is used to provide guidelines for their design and operations in off-design conditions. The analysis shows the influence of temperature, pressures, catalyst and steam amounts, and inlet temperature. Moreover, the influence of different membrane lengths, numbers, and pitches is investigated. From the results, guidelines are provided to properly design the geometry to obtain a set recovery factor value and hydrogen production. For a given reactor geometry and fluidization velocity, operating the reactor at 12 bar and the permeate-side pressure of 0.1 bar while increasing reactor temperature from 450 to 500 °C leads to an increase of 33% in hydrogen production and about 40% in HRF. At a reactor temperature of 500 °C, going from 8 to 20 bar inside the reactor doubled hydrogen production with a loss in recovery factor of about 16%. With the reactor at 12 bar, a vacuum pressure of 0.5 bar reduces hydrogen production by 43% and HRF by 45%. With the given catalyst, it is sufficient to have only 20% of solids filled into the reactor being catalytic particles. With the fixed operating conditions, it is worth mentioning that by adding membranes and maintaining the same spacing, it is possible to increase hydrogen production proportionally to the membrane area, maintaining the same HRF
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
Small scale CO2 based trigeneration plants in heat recovery applications: A case study for residential sector in northern Italy
Full text linkThis study investigates the potential of trigeneration systems utilizing CO2-based power cycles to harness hightemperature excess heat. Various CO2-based cycles are proposed, comprising pure CO2 and CO2-mixture, emphasizing integration into district heating and cooling networks. Given the non-isothermal heat rejection of CO2-based cycles, performance maps for absorption chillers at different thermal levels and temperature drop of the heat source are generated. These maps are beneficial not only for the current study but also for generic applications. Various cycle layouts are studied, employing strategies to maximize overall electrical efficiency, electrical power output, or thermal production, starting from available high-grade heat above 500 degrees C. Depending on the specific cycle layout and strategy, the optimal cycle-thermal user coupling is evaluated. The economic and environmental viability of the proposed solution is evaluated in comparison to an existing case-study in northern Italy where the exhaust gases of 10 MWel gas turbines are currently exploited for district heating purposes and centralized vapour-compression chillers meet the residential cooling demand. Compared to the case-study, the adoption of a simple recuperative CO2-mixture bottoming cycle, at a minimum cycle temperature of 70 degrees C, allows not only a primary energy saving of 16 % but also an 8 % reduction of levelized cost of electricity
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
POTENTIAL OF TRIGENERATIVE WASTE HEAT RECOVERY CO2- MIXTURE TRANSCRITICAL POWER PLANTS FOR INCREASING THE SUSTAINABILITY OF DISTRICT HEATING AND COOLING NETWORKS
No full textThe waste heat released by high-temperature processes can be exploited by power cycle designed for full electric or combined heat and power applications, with the potential to cover even the cooling demand in a trigenerative perspective. The use of CO2-based mixtures as working fluids for power cycles can be a promising solution for power production. These systems present a rejected heat in a temperature range (50–180 °C) that allows, depending on the needs, an effective coupling with a district heating and cooling network. This work investigates the potential of trigenerative system adopting CO2based power cycles which exploit the residual thermal power of the exhaust gases of a small-scale gas turbine. First, the performances of lithium bromide absorption chiller are investigated for various heat source levels, adopting different configuration. Then, various designs of CO2-based power cycles are simulated focusing on the coupling with both the district heating and the chiller. A sensitivity analysis on the cycle minimum temperature is presented, evidencing that CO2 mixtures can achieve remarkable net electric efficiency values even at high cycle minimum temperatures, marking a significant difference with respect to CO2 cycles. Considering the yearly demand of district heating and cooling, keeping the electric output at design value, the economic profitability of the investment is characterized presenting the LCOE of the retrofitted solution, considered comparable with actual selling prices
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