1,720,987 research outputs found
Attrition behavior analysis of four oxygen carriers in the in-situ redox jet attrition reactor
No full text11 figures, 5 tables.The anti-attrition properties of oxygen carriers (OCs) significantly impact the operation cost in chemical looping processes. A custom jet attrition reactor evaluates the attrition resistance of four OCs: ilmenite (Ilm-NO), Cusingle bondFe bi-ore OC via hydroforming (CuFe-Hy), and two perovskites via spray drying and hydroforming (Per-SD and Per-Hy), through cold, hot, and redox attrition tests. The anti-attrition performance order across all tests is Ilm-NO > Per-Hy > CuFe-Hy > Per-SD. Post-testing characterizations are conducted, including particle size distributions of consumed particles and captured powders, structure properties, and compositional evolution. Oxygen carrier lifetimes are quantified based on the particle size distributions. Multiple stresses affecting oxygen carrier attrition exhibit antagonistic interactions rather than linear superposition. Element migration, particle expansion, and strength evolution of the tested oxygen carriers are observed. Particle density and crushing strength are highly related to the anti-attrition properties of oxygen carriers. This study develops an efficient method for evaluating OCs under the in-situ redox condition with a high-velocity jet, offering guidance for designing OCs with high attrition resistance and advancing the study of attrition mechanisms.This work was supported by National Natural Science Foundation of China (52025063), and Hubei Province Key R&D Program (2022BCA087).Peer reviewe
Evaluation of ilmenite, manganese ore, LD slag and iron sand oxygen carriers for chemical looping gasification with microalgae
No full textMicroalgae could be a sustainable feedstock for production of liquid biofuels. However, as such fuels contain significant fractions of reactive ash species, it is necessary to deploy synthesis routes which can handle such “dirty” fuels. Chemical-looping gasification (CLG) has the potential to convert such feedstocks and generate a concentrated syngas stream, a common precursor for liquid fuel production. Suitable functional oxygen carriers are key for CLG, and herein we report our new work in fluidized-bed tests with four oxygen carriers, namely ilmenite, MnGBhne, LD slag and iron sand. These materials are economically viable natural ores or industrial by-products. The oxygen carrier is reduced to different oxidation degrees (0.2, 0.5, 1) at typical temperatures (850, 900, 950 °C) to define equal material states prior to the gasification. We found that the LD slag and iron sand had the highest gasification rate and fluidized well without agglomeration, thus they are selected as suitable oxygen carriers for the process. Several factors including catalysis, water splitting and water-gas shift are comprehensively discussed with regard to the outstanding performance of LD slag and iron sand. Calcium catalysis is deemed as a key reason for the fast gasification and a mechanism of this is proposed
Use of a high-entropy oxide as an oxygen carrier for chemical looping
No full text8 figures, 3 tables.-- Supplementary information available.One mixed oxide with 5 cations in equimolar proportions in the sublattice, to fulfil high-entropy oxide (HEO) criteria, has been developed and investigated as oxygen carrier for chemical looping combustion processes. As far as we know, nobody has explored this class of material for chemical looping combustion. Material is prepared by direct mixing of five metal oxides (CuO, Mn2O3, Fe2O3, TiO2, MgO), followed by calcination at 1000, 1100 and 1200 °C for 6 h in air. XRD characterization provides strong evidence that the synthesized oxygen carriers possess the hallmark properties of HEO, and SEM-EDX analysis shows an overall homogeneous metal distribution. Materials have one main cubic phase with the empirical formula MnCuMgFeTiO7, dominating under all conditions. One of the key objectives of this study is achieved, reduce chemical stress during redox cycles. Oxygen transfer capability is investigated by thermogravimetric analysis and batch fluidized bed reactor experiments for different fuels and atmospheres. Mass-based oxygen transport capacities for lattice oxygen and oxygen uncoupling are around 5.5 wt% and 1.1 wt%, respectively. This work opens up a new dimension for the future preparation of oxygen carriers for chemical looping processes, since the vast compositional space of HEO provides opportunities to tune both chemical and physical characteristics.This work was partiatially funded by the Swedish Research Council (2020–03487) and the Gobierno de Aragón – Dpto. de Ciencia, Universidad y Sociedad del Conocimiento - Project LMP166_21. I. Adánez-Rubio acknowledges for “Juan de la Cierva” Program (Grant IJC2019-038987-I funded by MCIN/AEI/10.13039/501100011033) and for the “José Castillejo” international mobility program for young researchers (CAS21/00200)Peer reviewe
Oxy-polishing of gas from chemical looping combustion: Fuel-nitrogen transformation and model-aided gas purity optimization
No full text17 figures, 7 tables.Chemical looping combustion (CLC) is a carbon capture technology for heat, power and hydrogen production. This work focuses on fuel-nitrogen transformation in fuel reactor and its further conversion in oxy-polishing step of CLC system. A 100 kW CLC pilot equipped with an oxy-polishing chamber (called POC) was used to perform experiment study and a zero-dimensional reactor model combining elementary reaction kinetics was developed and used for oxy-polishing simulation and reaction path analyses. An ilmenite and a manganese ore called Sinaus were used as oxygen carriers, and a coal and a coal-biomass mixture are the fuels in the CLC tests. It was found that in the fuel reactor, part of the fuel-nitrogen was converted to NO and the rest remained as NH3 which was then oxidized to NO in the POC. The concentrations of HCN and NO2 were negligible in the fuel reactor and POC. According to the simulation, when the oxygen excess is too low it is difficult to reach 1150–1200 °C which are temperatures needed for oxidizing the unconverted fuel gases. In a reference case, a high conversion was reached when the overall oxygen ratio was above 1.03 and temperature above 925 °C. With a fuel reactor temperature of 950 °C, the oxygen demand needed could be up to around 8 %. Based on the model, optimal geometrical designs of the POC were proposed. With a gas residence time of 3 s in the POC, it was possible to decrease the content of impurities (O2, H2, CO, NO, CH4) to 3.3 %.This work was supported by the Swedish Research Council, project Nitrogen Chemistry in Chemical-Looping Combustion and Oxygen-Carrier Aided Combustion (2016-05487) and the Swedish Energy Agency, as part of the projects OxyCar-FBC, conducted within the framework of ERA-NET Bioenergy, (P43936-1) and the project Kemcyklisk förbränning av biomassa och avfall (51585-1).Peer reviewe
Unveiling the pivotal role of Ni doping in ilmenite as oxygen carrier to realize simultaneous enhanced oxygen release and inhibited phase segregation in chemical looping process
No full textBiomass chemical looping gasification (BCLG) has demonstrated great potential in tackling global climate challenges through green energy transition. However, CH4 and tar generation are still significant obstacles for the commercialization of BCLG. In this study, we have developed a cost-effective Ni-modified ilmenite oxygen carrier (OC) for BCLG to greatly reduce the CH4 content and simultaneously increase the syngas generation. Several industrial wastes were investigated and screened based on their syngas and CH4 reactivity. Results show that ilmenite exhibits excellent syngas selectivity and potential reactivity with CH4. However, the reaction of ilmenite with CH4 proceeds slowly owing to the phase transformation process of TiFe2O5 - TiFeO3 - Fe being the rate-limiting step. Thus, various metallic dopants (i.e., Ni, Co, and Ca) were applied as promoters to reinforce its CH4 reactivity. Interestingly, Ni exhibited a higher promoting effect than Ca, whereas Co had little promotion on ilmenite reactivity. The superior performance of Ni doping could be attributed to the incorporation of Ni2+ element in Fe-O-Ti structure rather than Ni0, which was validated by pre-activation and cyclic experiments, and density functional theory calculations. Modulated electronic structure by Ni2+ in Fe-O-Ti lattice was responsible for significantly promoted oxygen release capacity and enhanced Fe/Ti interactions, thereby activating the reactivity of ilmenite with CH4 and suppressing Ti/Fe phase segregation. Therefore, this as-prepared 5Ni-ilmenite could be a promising cost-effective OC in BCLG for high quality syngas production.Peer reviewe
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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