1,720,970 research outputs found
Performances of a micro-CHP system fed with bio-ethanol based on fluidized bed membrane reactor and PEM fuel cells
No full textA micro-CHP system, rated at 5 kWel, based on membrane reactor and PEM fuel cells is simulated in the present work. Bio-ethanol is used as feedstock and converted into hydrogen inside the innovative fuel processor: a membrane-assisted fluidized-bed auto-thermal reforming reactor. The pure hydrogen separated by the Pd-based membranes inside the reactor is fed to a low-temperature PEM fuel cells stack. Heat is recovered to produce low temperature water. Two different reactor configurations are investigated: the first one adopts a sweep-gas stream, the second one a vacuum pump. Parametric analysis is performed for both cases evaluating the impact of feed composition (water-to-ethanol ratio) and operative conditions of the membrane reactor (temperature and feed/permeate pressures) on performances and design parameters. Optimal conditions are defined as a trade-off between efficiency and Pd-membranes area. For the sweep-gas layout, net electric efficiency higher than 40% can be achieved for a wide range of operative conditions, but large Pd-membranes area is required (≈0.4 m2); for the vacuum pump layout efficiency is lower (down to 39%), but Pd-membranes area is lower too (≈0.2 m2). Future work is the economic evaluation of the system for off-grid installations
PEM fuel cell stack protection from CO poisoning in a m-CHP system with membrane reformer
No full textOff-design operation of a PEM fuel cell stack integrated into a m-CHP system with membrane reformer
No full textA micro-CHP system, rated at 5 kWel, based on a membrane reformer and a PEMFC is studied. The identification of the operative conditions of the PEMFC is crucial for a good integration with the membrane reformer: the hydrogen separated in the membrane reactor, after cooling, directly feeds the FC [1]. In principle, Pd-based membranes can produce high-purity hydrogen (target= 99.99%, i.e. selectivity=104). However, the selectivity may decrease, in particular when thin Pd-membranes on ceramic support are adopted, and determine low-purity hydrogen (e.g. 99.9% with 100ppm CO, i.e. selectivity=102). A methanator is therefore added along the hydrogen cooling line to prevent CO-poisoning of the FC anodes. The quality of hydrogen affects the cell voltage and the overall system performances, therefore FC control strategies must be investigated. Build-up of inert and poisoning species in the hydrogen recirculation loop can be limited by venting a fraction of the anodic off-gas, whose amount can be optimized. Efficiency losses are estimated around one percentage point for each decrement of the order of magnitude of the selectivity. Deviations from the nominal operation occur during transients, at part-load or in case of faults of the Pd-membranes. These circumstances are investigated by simulating the FCs subsystem that includes the stack, the air and hydrogen blowers and the air humidifier. A dynamic, 1D (along the channels) model of PEMFC has been developed to simulate mixed co/counter flow between anode and cathode streams, which characterize the flow field of large-surface cells. The poisoning effect of CO on Pt-Ru catalyst is also modeled [2]. An experimental campaign on an 8-cells stack (cell area 220 cm2) was performed to characterize the FC operation with reformate gas. The impact of fuel composition, containing up to 20% of inert gases (N2, CO2, CH4) and CO up to 40 ppm, and operative conditions (pressure and humidity) was analyzed on the overall stack performance as well as on the current density distribution along the cell surface. Experimental data constituted a valuable source for the validation of the model
Experimental investigation of PEM fuel cells for a m-CHP system with membrane reformer
No full textAn innovative small-scale cogeneration system based on membrane reformer and PEM fuel cells is under development within the FluidCELL project. An experimental campaign has been carried out to characterize the PEM fuel cell and to define the operative conditions when integrated within the system. The hydrogen feeding the PEM is produced by a membrane reactor which in principle can separate pure hydrogen; however, in general, hydrogen purity is around 99.9%â99.99%. The focus of this work is the assessment of the PEM performance under different hydrogen purities featuring actual membrane selectivity and gases build-up by anode off-gas recirculation. Their effects on the cells voltage and local current distribution are measured at different conditions (pressure, humidity, stoichiometry, with and without air bleeding, in flow-through and dead-end operation). In flow-through mode, the cell voltage is relatively insensitive to the presence of inert gases (e.g. â20 mV with inerts/H2 from 0 to 20·10â2 at 0.3 A/cm2), and resistant also to CO (e.g. â35 mV with inerts/H2 = 20·10â2 and CO/H2 from 0 to 20·10â6 at 0.3 A/cm2), thanks to the Ru presence in the anode catalyst. Looking at the current density distribution on the cell surface, the most critical areas are the cathode inlet, likely due to insufficient air humidification, and the anode outlet, because of low hydrogen concentration and CO poisoning of the catalyst. Dead-end operation is also investigated using humid or impure hydrogen. In this case relatively small amount of impurities in the hydrogen feed rapidly reduces the cell voltage, requiring frequent purges (e.g. every 30 s with inerts/H2 = 0.5·10â2 at 0.3 A/cm2). These experiments set the basis for the management of the PEMFC stack integrated into the m-CHP system based on the FluidCELL concept
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
Potentiality of a biogas membrane reformer for decentralized hydrogen production
Full text linkThis paper investigates the potentiality of membrane reactor for green hydrogen production from raw biogas. The assessment is carried out both from thermodynamic and economic point of view to outline the advantages of the innovative technology with respect to the conventional one based on reforming, water gas shift and pressure swing adsorption unit. Both biogas produced by landfill and anaerobic digestion are considered to evaluate the impact of biogas composition on system design. BIONICO system model is implemented in Aspen Plus and Aspen Custom Modeler to perform respectively the balance of plant with thermal integration and a detailed fluidized bed membrane reactor design. Two permeate side configurations, sweep gas and vacuum pump, were modelled and compared. The adoption of membrane reactor increases the system efficiency by more than 20% points with respect to reference cases. Focusing on the economic results, hydrogen production cost show lower value respect to the reference cases (4 €/kgH2vs 4.2 €/kgH2) at the same hydrogen delivery pressure of 20 bar. Between the landfill and anaerobic digestion cases, the latter has the lower costs as consequence of the higher methane content
Modeling of 2-MW co-generative PEM fuel cell for hydrogen recovering from Chlorine industry
No full textThe chlorine industrial production process is energy-intensive in terms of heat and electricity and generates a relevant amount of hydrogen as byproduct; consequently, it is particularly interesting for cogeneration and energy integration by means of fuel cells. The DEMCOPEM-2MW European Project is meant to design and build a demonstrative 2MW PEM fuel cell power plant coupled with a chlor-alkali process in China, aiming at covering about 20% of the industrial process consumptions based on the use of waste hydrogen. Scale-up of stationary fuel cell plants is an ongoing process with many open challenges. Therefore, in the framework of the project, a model is developed in order to evaluate the plant expected performances and optimize operational strategies on plant lifetime.
The simulation is built in Aspen PLUS® environment, using available thermodynamics libraries and standard process components and developing customized components for electrochemical and electronic devices. The general modeling approach was described in a previous work, while here the model is refined and applied to the 2 MW plant in view of operational optimization and lifetime performances evaluation. Calibration and validation of the model are performed against data from (i) a 70 kW PEM stack installation operating in AkzoNobel’s plant in Delfzijl, where Nedstack PEM fuel cell stacks of the same class used in the projected plant are being tested; and from (ii) a 1 MW PEM plant operated in Lillo (Belgium), developed by Nedstack and MTSA with a layout similar to the design of DEMCOPEM-2MW plant
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