1,720,958 research outputs found
Thermodynamic Equilibrium Study of Ash Transformation during Entrained Flow Conversion of Agricultural Biomass Focusing on the Potential Extraction of Valuable Si and K-P Compounds via Condensation from the Gas Phase
No full textAgricultural biomass is today largely underutilized in combustion and gasification processes because of the abundant supply of other easier-to-process biomass fuels. These biomass types generally have a moderate to high ash content comprising valuable elements, such as Si, K, and P, which can lead to ash-related operational problems. The high share of Si, K, and P in agricultural biomass assortments also has a significant economic value. These elements are usually retained in the coarse or fly ash fractions. Extracting valuable Si- and K–P-containing compounds with high purity from these ash fractions often requires further postprocessing steps, which increases operational costs. Therefore, a potential novel design concept could be to control the combustion/gasification processes so that Si, K, and P can be extracted by condensation from the flue/hot gases at a quality that implies added value instead of extra costs. This work aims to identify the possibilities of extracting valuable Si and K–P compounds from the hot gases generated during entrained flow conditions via stepwise controlled condensation in the close-flame regions or heat exchanger zone. Thermodynamic equilibrium calculations were performed by employing the databases (GTOX and SGPS) in FactSage 8.0 software. The calculations were performed under varying conditions ,i.e., temperatures, atmospheres, and fuel compositions. The selected fuels were rice husks (Si-rich), brewer’s spent grains (P–Si-rich with moderate to minor amounts of Ca, Mg, and K), and grass (K–Si-rich with moderate amounts of Ca, Mg, and P). The results indicate that the high-temperature formation of the valuable Si compounds, such as SiC (s) and Si2N2O (s), would require an inert atmosphere during both the release and cooling stages. Moreover, a high Si/P molar ratio is needed to form valuable Si-containing compounds. The predicted K-bearing phosphates during the gas cooling near the burner zone were formed in the same temperature range as Ca-, Mg-, and Si-containing compounds with all of the fuels. The results obtained by this study can guide experimental research on the practical extraction of Si and K–P compounds from different types of agricultural biomass during thermochemical conversion in entrained flow conditions.Validerad;2025;Nivå 2;2025-05-12 (u5):Full text license: CC BY 4.0;Funder: Austrian Research Promotion Agency (892426);</p
Ash transformation during thermochemical conversion of agricultural biomass in entrained flow conditions
No full textAgricultural biomass is considered a prospective renewable feedstock in the energy conversion units. Despite its widespread availability, agricultural biomass is often underutilized in the thermochemical processes due to its high ash content. These types of biomass usually contain a relatively high share of potassium (K), silicon (Si), and phosphorus (P). The presence of these elements in the fuel can cause ash-related issues like slagging, deposit formation, fine particle emissions, etc. However, extracting these elements during thermochemical conversion processes can increase the economic viability of using agricultural biomassas a feedstock. There is still a lack of detailed understanding regarding ash-transformation reactions in entrained flow conversion of such biomassas sortments. Therefore, detailed knowledge regarding ash-transformation pathways during the thermochemical conversion of agricultural biomass can target the aim of reducing or eliminating ash-related issues together with recovering valuable Si- and K-P-rich compounds.The main objectives of this work were, therefore, to 1) investigate the ash transformation pathways of Si and P during entrained flow combustion of different types of Si- and P-rich agricultural biomass and 2) investigate the potential of extracting valuable Si- and K-P compounds with high purity from the gas phase and/or residual ashes formed during entrained flow conversion of different agricultural biomass. Experiments were conducted within a lab-scale laminar drop tube furnace (DTF) at 1200 and 1450 °C in combustion conditions (using air) and in pyrolysis conditions (using N2). Three different agricultural biomass types were used, namely, rice husks, grass, and draff (i.e., beer brewing residue). Rice husks represent Si-rich fuel with minor amounts of P, K, and Ca. The grass fuel represents K-Si-rich fuel with moderate amounts of P, Ca, and Mg. Draff, on the other hand, represents a P-rich fuel with a relatively high share of Si and a moderate to minor Ca, Mg, and K content. The produced residual materials, i.e., coarse ash (> 1 μm), fine particle (< 1μm) fractions, and chars after the experiments were morphologically and chemically characterized by SEM-EDS, XRD, ICP-AES, IC, and CHN-analysis. The interpretation of experimental findings and theoretical assessment of ash transformation were facilitated through TECs.The combustion experiments using a laminar drop tube furnace revealed distinctive ash transformations across the studied agricultural biomass. For all fuels, Si was entirely retained in the coarse ash (> 1 μm) fractions, whereas P was found mainly in coarse ash fractions and in a minor to moderate amount in the fine particle (< 1 μm) ash fractions.For the rice husks, most of the minor ash-forming elements (i.e., K, Ca, Mg, and P) present in the fuel were retained at the inner surface of the chars during the pyrolysis/devolatilization experiments conducted in the DTF, which were later incorporated into a melt found in the coarse ash fractions after combustion experiments. Consequently, Si-rich molten spheres were formed at the inner surface of the coarse ashes. The share of molten ash increased in the coarse ash fractions with the combustion temperature. Concerning grass, the retained P in the residual coarse ash fractions was found in a K-Ca-Mg-rich phosphosilicate melt and crystalline Ca9MgK(PO4)7(OH), Ca5(SiO4)0.3(PO4)2.7(OH)0.7, and Ca7(SiO4)2(PO4)2. The phosphosilicate melt was most likely formed through the initial formation of a K-rich silicate melt, with subsequent incorporation of Ca, Mg, and P. As for draff, the P retained in the coarse ash fractions was identified as Ca-Mg-rich phosphosilicate melt and crystalline Ca3Mg3(PO4)4. This phosphosilicate melt most likely originated from the phytate-derived Ca-Mg-phosphates that melt and interact with Si-rich particles/sites.TECs predicted that extracting pure Si-containing compounds (i.e., SiC(s)) from the gas phase during the entrained flow conversion of rice husks would require very high temperatures in the flame (i.e., around 2000 °C) to volatilize a moderate amount of Si present in the rice husks. Additionally, it would require a pyrolysis cooling atmosphere and relatively high surface temperatures (i.e., around 1500 °C) to form potentially valuable Si-containing compounds. These conditions are challenging to achieve in practice. However, the experimental investigations showed the possibility of extracting relatively pure silica from the residual coarse ash fractions collected after the entrained flow combustion of rice husks. TECs did not predict the probability of forming pure Si and/or K-P-containing compounds from the gas phase for grass fuel. Regarding draff fuel, both TECs and experimental investigations indicated that a surplus of P to Si and cations in the fuel can facilitate the formation of valuable K-phosphates and/or H3PO4 from the gas phase at lower surface temperatures (i.e., <400 °C). Moreover, the coarse ash fractions obtained after the combustion of grass and draff primarily contained different phosphosilicate melts. The plant availability of P in such melts needs to be evaluated.The findings derived from this work offer valuable insights into the ash transformation of phosphorus (P) and silicon (Si) during the thermochemical conversion of agricultural biomass with varying ash compositions under entrained flow conditions. The obtained knowledge could be used to propose efficient measures to mitigate the associated ash-related problems and to propose interesting pathways to extract valuable Si- and K-P-rich components during the thermal conversion of agricultural biomass in entrained flow reactors.</p
Ash Formation during Combustion of Rice Husks in Entrained Flow Conversion Conditions
No full textThis study investigates the detailed ash transformation process during the combustion of rice husks in entrained flow conditions. The experiments were conducted in a lab-scale drop tube furnace at 1200 and 1450 °C in pyrolysis/devolatilization (using N2) and combustion (using air) conditions. The detailed ash transformation process during the different fuel conversion stages in combustion (i.e., devolatilization and char combustion) was investigated by comparing the results obtained in the pyrolysis/devolatilization experiments with the combustion experiments. The resulting residual chars, ashes, and particulate matter (PM) were collected and characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM–EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), ion chromatography (IC), and CHN analyses. Furthermore, the obtained results were interpreted via thermodynamic equilibrium calculations (TECs). For all investigated conditions, Si, Ca, and Mg were retained entirely in the coarse ash and char fractions (>1 μm). Meanwhile, K and P were found in coarse ash/char fractions and fine particulate fractions (<1 μm). A moderate, at 1200 °C, to high share, at 1450 °C, of the detected K and P was found in the fine particle fractions after combustion. The majority (>95%) of the detected S and Cl were volatilized during the experiments. The study showed an accumulation of minor ash-forming elements (i.e., K, Ca, Mg, P) on the inner part of rice husk chars, initiating melt formation during the char combustion stage. The identified melt at 1200 °C after combustion was rich in Si with minor amounts of K, Ca, Mg, and P. The share of molten ashes was increased at 1450 °C compared to that at 1200 °C. Overall, the results presented in this work reveal detailed insights into the ash transformation processes taking place in different parts of the fuel during the combustion of rice husks in entrained flow conditions.Validerad;2024;Nivå 2;2024-08-15 (hanlid);Full text license: CC BY;This article has previously appeared as a manuscript in a thesis</p
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
Ash transformation during combustion of agricultural biomass in entrained flow conditions with a focus on phosphorus
No full textThe detailed ash transformation process during the combustion of agricultural biomass containing moderate to high amounts of P was studied in entrained flow conditions. The selected fuels were grass and brewer’s spent grain (BSG) containing a moderate and high amount of P in the fuel, respectively. The experiments were conducted in a lab-scale drop tube furnace at 1200 and 1450 °C. The residual chars, ashes, and particulate matter (PM) were collected and analyzed by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC), and CHN-analysis. Additionally, the obtained results were interpreted through thermodynamic equilibrium calculations (TECs). For both fuels, P was primarily identified in the residual coarse ash (>1 μm) fractions. In contrast, a minor to moderate amount of fuel inherent P was detected in the fine particulate (<1 μm) fraction at 1200 and 1450 °C, respectively. For grass, the retained P in the residual coarse ash fractions was mainly identified as amorphous K-Ca-Mg-rich phosphosilicate melt. These phosphosilicates were most likely formed through the initial formation of molten K-rich silicates, with subsequent incorporation of Ca, P, and Mg. For BSG, a P-Si-rich fuel with moderate to minor amounts of Ca, Mg, and K, most P was retained in a Ca-Mg-rich phosphosilicate melt, likely originating from phytate-derived Ca-Mg phosphates interacting with fuel-inherent Si-rich particles. The results obtained from this study could be used to address the ash-related challenges and potential P-recovery routes during pulverized fuel combustion of P-containing biomass
- …
