1,720,965 research outputs found
Ultrapure hydrogen from biomass syngas by PD/AG membrane reactor
No full textThe work dealt with the enrichment of hydrogen by Water Gas Shift (WGS) reaction in a catalytic Membrane Reactor (MR) starting from a syngas having the typical composition obtained in updraft gasification of lignocellulosics. The used MRs were externally made of Pd-Ag membranes, which exhibit high hydrogen selectivity, and contain a Pt on ZrO2 catalyst. The permeate flow of hydrogen is of ultrapure quality and positively affected the WGS yields that, in optimized conditions, overcame the theoretically expected values in closed system. The experiments were performed in a recently built rig designed to treat up to 0.25 Nm3/h of syngas and explored the operative ranges 300-350°C, 2 -8 bar; H2O/CO molar ratio 2-4. © 2018 ETA-Florence Renewable Energies
Life cycle assessment of hydrogen production from biorefinery residues
No full textGasification of biomass can be used for obtaining hydrogen so reducing the greenhouse gases emissions due the fixation of CO2 during photosynthetic processes. The hydrolytic lignin residue is an appropriate raw material since it does not compete directly with the food chain and can be exploited for producing additional chemicals, power, combined heat and power. Indeed, the optimal use of this residue is a key factor for the economic and environmental sustainability of a bio-refinery, not only disposal costs can be avoided but also additional incomes can be provided. The work dealt the environmental potentials impacts of the production of hydrogen through gasification of this residue and to identify the hotspots of the process. An LCA study was developed for a 200 kWth gasification pilot plant using experimental data. Model was constructed using GaBi software in accordance with LCA leading Standards and ILCD Handbook recommendations. A gate-to-gate analysis of the gasification process was carried out and compared to a reference scenario consisting of hydrogen production by steam reforming of methane. LCA methodology was applied using global warming potential, acidification, eutrophication and the gross energy necessary for the production of 1 kg of hydrogen as impact categories
Pilot plant air-steam gasification of nut shells for syngas production
No full textAutothermal gasification of hazelnut and almond was carried out and the performances of a pilot plant with a feeding rate of 20-30 kg/h were evaluated. Air, mixes of air with steam and oxygen with steam were used as gasification medium; the gas flows corresponded to different equivalence ratios of combustion, ER(O2), and water reaction, ER(H2O). The recording of the thermal profile inside the reactive bed during the runs made it possible to highlight a sequence of exothermic and endothermic reactions. In the plant tests, the residues were completely converted in gaseous and liquid energy carriers with a cold gas efficiency (CGE) ranging from 61% to 75% while the production of biooil ranged from 90-250 g/kg of fed nutshell (dry basis). The molar ratio H2/CO in syngas increased by using steam as co-gasification agent. Steam was necessary to stabilize the process in the case of using oxygen as main gasification agent. Oxy-steam gasification also provided the best results in terms of syngas heating value and thermal power output of the plant. The tar yield was inversely correlated to the residence time of the gas in the bed, in according with a zero order reaction for tar cracking into incondensable hydrocarbons. © 2017, ETA-Florence Renewable Energies. All rights reserved
Production of hydrogen-rich syngas from biomass gasification by double step steam catalytic tar reforming
No full textThis study focused on the catalytic steam reforming of tar produced from updraft gasification of hazelnut shells. Two streams of syngas were extracted from different heights in the reaction bed of a gasifier able to treat 20–30 kg/h of biomass. The syngas was then conveyed to the new built catalytic section for further processing. A two-bed in series approach was tested. This design enables the use of dolomite as a cheap catalyst and as chemical trap for sulphur and chlorine, mitigating potential damage to the more performant and complex catalyst Ni/CeO2/Al2O3. The latter catalysts underwent comprehensive characterization to evaluate its efficiency. The reforming of tar in both streams achieved a remarkable >98.5% yield. The study highlights the diverse roles of dolomite in the gasification process and the positive effects of CO2 pre-adsorption, enhancing H2 content, cleanliness and heating value of the upgraded syngas
Experimental investigation of syngas composition variation along updraft fixed bed gasifier
No full textFixed bed gasification represents a convenient pathway for exploiting lignocellulose since it can be carried out on a small scale, while current technology is robust and fairly simple. Updraft gasifier is characterized by higher efficiency and is flexible towards feedstock, compared to the downdraft gasifier. The hydrogen to carbon monoxide ratio is the decisive parameter for determining syngas quality. Present contribution for the first time reports the evolution of the syngas composition at different heights of the reactive biomass bed in a pilot plant operating in a continuous mode, i.e. 20–30 kg/h of biomass feed. This was achieved by probing syngas streams directly from the core and analysing it onsite to measure the content of hydrogen, carbon monoxide, carbon dioxide, light hydrocarbons, nitrogen and oxygen, whilst the tar content was analysed offline. The addition of steam deeply affected the evolution of the chemical species and thermal profile. The syngas chemical composition was related to the thermal profile provided by in bed measurements of six thermocouples at the same locations. In the tests, almond shells were gasified with air or air and superheated steam mixture at equivalence ratio of 0.20 ± 0.01 and various steam to biomass ratios between 0 and 0.16 kg/kg. Addition of steam stabilized thermal profile inside the gasifier below 900 °C, improved the production of hydrogen up to 37.5 g/kg of biomass and the cold gas efficiency up to 72.5%. The use of steam positively affected the molar ratio of hydrogen to carbon monoxide that reached a steady value of 0.77 during the gasification operated at steam to biomass ratio of 0.11 kg/kg, versus the value of 0.46 measured in the corresponding test operated only with air. On the other hand, steam addition increased tar production up to 163 g/kg in air/steam gasification compared to the 137 g/kg with air gasification. Obtained data of the syngas composition along the bed height provide insight into the underlying physical and chemical phenomena and can be further used for the improvement and validation of gasification mathematical models
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
Gasification of lignocellulosic residues at pilot scale: Evidence of the catalytic effect of its ash
No full textThe updraft gasifications of the two residues of biorefinery having different inert content were carried out at the very close operating conditions, namely at almost the same equivalence ratio of air and steam. The temperature inside the autothermal gasifier was monitored and a detailed profile was obtained. The H2/CO ratio and condensable organics produced from the two feedstock were different. The average temperatures in the reactor differed in the two cases of 89°C. Being the process carried out in authothermal mode, it was correlated the different exothermicity and with the reaction kinetics, in particular to a different degree of advancement of the water gas reaction (WGS) that in the case of high ash content feedstock was more favoured. Metals content affected also the content of organic condensable molecules in the producer gas and it was 50% higher in the case of low ash content feedstock
Updraft gasification at pilot scale of hydrolytic lignin residue
No full textAutothermal gasification of lignin-rich residues was carried out to evaluate the performances of a pilot plant with a feeding rate of 20-30 kg h-1 of feedstock. The facility was based on an updraft gasifier and a gas cleaning train composed of a biodiesel scrubber and coalescence filters. The tests were performed with solid residues of ethanol production starting from straws or canes. Air at a low equivalence ratio was used as gasification medium. The autothermal processing and the lignin-rich feedstock made it possible to highlight a sequence of exothermic and endothermic reactions by measuring the heating rates along the reactive bed. The CO2 production was proportional to the ash content. The average production of raw syngas was 1.94 kg per kg of dry residue, of which H2 and CO were 27.2 and 696 g, respectively. The efficiency of energy conversion from solid to cold gas was 64% and reached about 81% including the contribution of the condensable organic fraction. © 2014 American Chemical Society
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
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