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Fluidized bed combustion wastes as a potential source of ettringite for recycling purposes - a hydration study
No full textThe fluidized bed combustion (FBC) technology is very effective in the conversion of solid fuels ensuring also a low environmental impact. A major problem related to the fluidized bed technology is the disposal and/or the utilization of solid wastes, owing to their remarkable quantity and poor quality. In order to find suitable applications fields of these residues, in this work it is explored the possibility of converting them, upon a controlled hydration treatment, into ettringite (6CaO•Al2O3•3SO3•32H2O), a compound having several useful properties. Three types of FBC wastes generated in industrial plants were investigated: 1) FA-Sul, a sulpho-calcic fly ash; 2) FA-Sil, a silico-aluminous fly ash; 3) BA, a sulpho-calcic bed ash. FA-Sul and two binary mixtures (83% FA-Sul/17% FA-Sil and 64% BA/36% FA-Sil) were the most promising, in terms of potential ettringite generation. Hydration tests were conducted at 70°C for 1, 2 and 4 days. Both ettringite and calcium hydroxide (Ca(OH)2) were detected within the hydrated systems, the former being the main reaction product. The kinetics of ettringite formation is related to the sample chemical composition and the conversion degree at 4 days of curing is equal to ~1 for FA-Sul, 0.74 for FA-Sul/FA-Sil and 0.42 for BA/FA-Sil
Hydration of coal combustion wastes aimed at obtaining ettringite-based materials
No full textCoal combustion wastes are often used as sources of raw materials, but their utilization degree is still relatively low. Therefore, a greater exploitation in the consolidated fields of use must be pursued and new applications have to be searched for. In view of the manufacture of preformed building elements based on ettringite (a calcium trisulphoaluminate hydrate characterized by good mechanical strength and low density), it has been investigated the hydration behaviour of a sulpho-calcic fly ash generated in an industrial coal combustor. Curing was performed at 70°C up to 4 aging days. X-ray diffraction and thermogravimetric analyses have assessed the fly ash ability to give ettringite as main reaction product within the hydrated system. Calcium hydroxide in the concentration range of about 15-18% was detected. The ettringite amount was comprised between about 43% (1d-curing) and 58% (4d-curing)
Fluidized bed combustion wastes as a potential source of ettringite for recycling purposes - a hydration study
No full textThe fluidized bed combustion (FBC) technology is very effective in the conversion of solid fuels ensuring also a low environmental impact. A major problem related to the fluidized bed technology is the disposal and/or the utilization of solid wastes, owing to their remarkable quantity and poor quality. In order to find suitable applications fields of these residues, in this work it is explored the possibility of converting them, upon a controlled hydration treatment, into ettringite (6CaO•Al2O3•3SO3•32H2O), a compound having several useful properties. Three types of FBC wastes generated in industrial plants were investigated: 1) FA-Sul, a sulpho-calcic fly ash; 2) FA-Sil, a silico-aluminous fly ash; 3) BA, a sulpho-calcic bed ash. FA-Sul and two binary mixtures (83% FA-Sul/17% FA-Sil and 64% BA/36% FA-Sil) were the most promising, in terms of potential ettringite generation. Hydration tests were conducted at 70°C for 1, 2 and 4 days. Both ettringite and calcium hydroxide (Ca(OH)2) were detected within the hydrated systems, the former being the main reaction product. The kinetics of ettringite formation is related to the sample chemical composition and the conversion degree at 4 days of curing is equal to ~1 for FA-Sul, 0.74 for FA-Sul/FA-Sil and 0.42 for BA/FA-Sil
Use of fluidized bed combustion wastes for the synthesis of low-energy cements
No full textAmong the low-energy binders, calcium sulphoaluminate cements are worthy of consideration also because a wide range of industrial solid wastes can be utilized in their manufacture. In this paper, it has been proposed the use of mixtures composed by fluidized bed combustion wastes as raw materials for the synthesis of calcium sulphoaluminate cements. Several systems based on two fluidized bed combustion-derived wastes (a sulpho-calcic fly ash and a silico-aluminous fly ash) and a solid waste generated within a traditional coal-fired power plant were heated in a laboratory electric oven for 2 hours at temperatures ranging from 1050°C to 1300°C. Calcium sulphoaluminate was often obtained and its formation was related to the waste nature and the burning temperature
Use of fluidized bed combustion wastes for the synthesis of low-energy cements
No full textAmong the low-energy binders, calcium sulphoaluminate cements are worthy of consideration also because a wide range of industrial solid wastes can be utilized in their manufacture. In this paper, it has been proposed the use of mixtures composed by fluidized bed combustion wastes as raw materials for the synthesis of calcium sulphoaluminate cements. Several systems based on two fluidized bed combustion-derived wastes (a sulpho-calcic fly ash and a silico-aluminous fly ash) and a solid waste generated within a traditional coal-fired power plant were heated in a laboratory electric oven for 2 hours at temperatures ranging from 1050°C to 1300°C. Calcium sulphoaluminate was often obtained and its formation was related to the waste nature and the burning temperature
Impiego di ettringite come materiale desolforante e sua generazione per idratazione di residui della combustione in letto fluido
No full textMediante prove di solfatazione eseguite in un reattore a letto fluido da laboratorio operante alla temperatura di 850°C si è riscontrato che l’ettringite sintetica possiede una capacità desolforante migliore di quella di un sorbente calcareo: l’indice di attività relativa, basato sulla determinazione in continuo della concentrazione di SO2 nel gas effluente dal reattore, è sempre favorevole all’ettringite e nel corso delle prove varia da 4.68 a 1.90. In prove d’idratazione su miscele a base di residui provenienti da impianti industriali a letto fluido, condotte alla temperatura di 70°C fino a 4 giorni di stagionatura, è stata rilevata la presenza di ettringite quale principale prodotto d’idratazione e si sono registrati gradi di conversione compresi fra 0.35 e ~1.00. I risultati ottenuti presentano interesse sotto il profilo del potenziamento dell’azione desolforante di residui della combustione in letto fluido idratati, che possono essere convenientemente riutilizzati come materiali sorbenti da reintrodurre nel combustore
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
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