1,720,966 research outputs found
NOVEL DIAGNOSTICS OF OXY-COAL COMBUSTION IN A SEMIINDUSTRIAL SCALE FURNACE
No full textIn oxy-coal combustion, a mixture of oxygen and recycled flue gases is used instead of air for fuel oxidation. Consequently, a gas consisting of CO2 and H2O is obtained, with a CO2 concentration ready for sequestration. Flue gases are recycled in order to make up the volume of the missing N2 and to ensure enough thermal capacity for the subsequent heat transfer operations.
Many studies in literature have been aimed at understanding solid fuel combustion in oxy-fuel conditions, by performing single-particle studies using conventional (e.g. thermogravimetry) analysis. A step further to the knowledge is provided by entrained flow reactors, which allow obtaining data under heating rates and temperatures typical of industrial boilers. However, in entrained flow reactors the burner fluid-dynamics is neglected, which means that the interaction of coal particle and flame with the turbulence cannot be investigated.
The present work aims at employing a relatively simple technique (Optical Diagnostics for Combustion – ODC) developed by ENEA (Giacomazzi et al., 2008), to derive information on coal combustion in air and oxy-fuel conditions by performing experiments in a semi-industrial (3 MW) furnace. The advantage of the proposed diagnostics is the very low intrusiveness which makes it suited for industrial applications.
The technique was found to be capable of monitoring the position of the flame in the furnace; for instance it was observed that the ignition delay is larger in oxy- than in air-fired conditions.
Variation of operating conditions or combustion characteristics were found to be easily detectable by the measuring probes, so that the technique can be potentially used to control and monitor the process.
The correlation of signals taken with more probes was used to evaluate the velocity distribution of coal particles. Such information is hard to be measured experimentally, but may be useful for the validation of numerical models.
The high acquisition rate of the technique allowed the identification of main frequencies for each experimental test. In addition the analysis of the frequency spectra could be used to shed light into the turbulence/flame interaction and thus arguing on the combustion regimes.
References
Giacomazzi, E.; Troiani, G.; Giulietti, E.; Bruschi, E. Exp. Fluids 2008, 44, 557-564
AIR-FIRED AND OXY-FIRED COMBUSTION: RATE OF CHAR OXIDATION BY O2, CO2 AND H2O
No full textChar conversion rates and mechanisms are investigated at oxy-fired and air-fired combustion
conditions. Experimental char conversion data was obtained from the IFRF Isothermal Plug
Flow Reactor within the RELCOM project. Char conversion rates were computed at the investigated conditions using a detailed single
particle model. The model takes into account development of internal surface area, diffusion
of gaseous species inside the particle, homogeneous chemistry outside the particle, the
Stefan-flow, temperature gradients and diffusion inside and outside the particle and
Langmuir-Hinshelwood type surface mechanisms. The modeled char burnout is in good
agreement to the experimental char burnout. The results show that char oxidation can be more
rapid at conventional combustion conditions than at oxy-combustion conditions, although the
oxygen concentration is that same in both cases. This is surprising, considering that a
significant part of the char is consumed by CO2 and H2O. This is mainly explained by
additional consumption of O2 in the boundary layer of the particle, by decreased diffusion
rates of O2 and by an increased coverage of occupied carbon sites in the oxy-combustion
case. The results suggests that more than 50% of the char is consumed by gasification
reactions both in conventional combustion and in oxy-combustion of pulverized coal
MODELING POSTED SPEED LIMITS FOR LOW-VOLUME ROADS
Full text linkHigh speed is a major problem in road safety (Benedetto et al., 2004; Capaldo and Nasti, 2012; Dell’Acqua, 2011a; De Luca et al., 2011). The main benefit of high speed traffic flow is that the cost attributed to travel time is reduced, despite higher running costs together with the associated higher environmental costs. The improvements of vehicle performance and road standards promote even higher speeds. Increased speeding will likely result in augmenting the number of traffic accidents, as well as the severity of the injuries, resulting from high-speed accidents. Many drivers are aware of the negative effects of speed, exceeding the speed limit is nevertheless one of the most frequent traffic violations. A feature of road safety is that inferences based on statistical information from individual studies are often imprecise. Designers need to take expert judgment and results from similar surveys into account when drawing conclusions. Traditional approaches have many points of weakness connected to the inadequacy of the accident database and to the low reliability of statistical methods for the diagnosis of the cause. Techniques based on artificial intelligence have been investigated (De Luca, 2015; Mauro et al., 2013). Hazard analysis approach has given important, very applicable and reliable results (Russo et al., 2014b; Russo et al., 2016a). The best point estimates for the link between speed and accidents suggest that the number of accidents could be substantially reduced; by either enforcing lower speed limits or at least reducing the spread of vehicle speeds. To determine the attitudes of drivers towards speed limits and understand their behavior, a survey (Figure 1) of Italian drivers was undertaken in two roadway environments
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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