| 1. |
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| 2. |
- Gómez-Barea, Alberto, et al.
(author)
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Improving the performance of fluidized bed biomass/waste gasifiers for distributed electricity: A new three-stage gasification system
- 2013
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 50:2, s. 1453-1462
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Journal article (peer-reviewed)abstract
- Methods to increase the conversion of char and tar in fluidized bed gasifiers (FBG) are discussed, with thefocus on small to medium-size biomass/waste gasifiers for power production (from 0.5 to 10 MWe).Optimization of such systems aims at (i) maximizing energy utilization of the fuel (maximizing charconversion), (ii) minimizing secondary treatment of the gas (by avoiding complex tar cleaning), and(iii) application in small biomass-to-electricity gasification plants. The efficiency of various measures toincrease tar and char conversion within a gasification reactor (primary methods) is discussed. The optimizationof FBG by using in-bed catalysts, by addition of steam and enriched air as gasification agent, andby secondary-air injection, although improving the process, is shown to be insufficient to attain the gaspurity required for burning the gas in an engine to produce electricity. Staged gasification is identified asthe only method capable of reaching the targets mentioned above with reasonable simplicity and cost, so itis ideal for power production. A promising new stage gasification process is presented. It is based on threestages: FB devolatilization, non-catalytic air/steam reforming of the gas coming from the devolatilizer, andchemical filtering of the gas and gasification of the char in a moving bed supplied with the char generatedin the devolatilizer. Design considerations and comparison with one-stage FBG are discussed.
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| 3. |
- Householder, John Ethan, et al.
(author)
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One sixth of Amazonian tree diversity is dependent on river floodplains
- 2024
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In: NATURE ECOLOGY & EVOLUTION. - 2397-334X.
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Journal article (peer-reviewed)abstract
- Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.
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| 4. |
- Luize, Bruno Garcia, et al.
(author)
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Geography and ecology shape the phylogenetic composition of Amazonian tree communities
- 2024
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In: JOURNAL OF BIOGEOGRAPHY. - 0305-0270 .- 1365-2699.
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Journal article (peer-reviewed)abstract
- Aim: Amazonia hosts more tree species from numerous evolutionary lineages, both young and ancient, than any other biogeographic region. Previous studies have shown that tree lineages colonized multiple edaphic environments and dispersed widely across Amazonia, leading to a hypothesis, which we test, that lineages should not be strongly associated with either geographic regions or edaphic forest types. Location: Amazonia. Taxon: Angiosperms (Magnoliids; Monocots; Eudicots). Methods: Data for the abundance of 5082 tree species in 1989 plots were combined with a mega-phylogeny. We applied evolutionary ordination to assess how phylogenetic composition varies across Amazonia. We used variation partitioning and Moran's eigenvector maps (MEM) to test and quantify the separate and joint contributions of spatial and environmental variables to explain the phylogenetic composition of plots. We tested the indicator value of lineages for geographic regions and edaphic forest types and mapped associations onto the phylogeny. Results: In the terra firme and v & aacute;rzea forest types, the phylogenetic composition varies by geographic region, but the igap & oacute; and white-sand forest types retain a unique evolutionary signature regardless of region. Overall, we find that soil chemistry, climate and topography explain 24% of the variation in phylogenetic composition, with 79% of that variation being spatially structured (R-2 = 19% overall for combined spatial/environmental effects). The phylogenetic composition also shows substantial spatial patterns not related to the environmental variables we quantified (R-2 = 28%). A greater number of lineages were significant indicators of geographic regions than forest types. Main Conclusion: Numerous tree lineages, including some ancient ones (>66 Ma), show strong associations with geographic regions and edaphic forest types of Amazonia. This shows that specialization in specific edaphic environments has played a long-standing role in the evolutionary assembly of Amazonian forests. Furthermore, many lineages, even those that have dispersed across Amazonia, dominate within a specific region, likely because of phylogenetically conserved niches for environmental conditions that are prevalent within regions.
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| 5. |
- Salinero, Jesús, et al.
(author)
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Impact of using thermocouples to measure char particle temperature in a fluidized bed combustor
- 2017
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In: 12th International Conference on Fluidized Bed Technology, CFB 2017. ; 12, s. 655-662
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Conference paper (peer-reviewed)abstract
- Circulating fluidized bed can be applied in several methods of CO2 capture. In oxy-combustion the fuel particle temperature can peak in the regions near the entrance with high oxygen concentration, being a critical factor. To study this aspect, techniques to measure fuel particle temperature have been developed mainly based of thermocouples, where it is usually assumed that the thermocouple does not affect the movement of the fuel particle, although there is no rigorous evidence. In the present paper this aspect is studied by comparing the temperature of char particles with and without an embedded thermocouple (with 0.25 and 0.5 mm sheath diameters). Char particles (10 mm) are burnt in a laboratory fluidized bed made in quartz, allowing visual observation of the particles. The surface temperature is measured by pyrometry coupled to a digital camera at the same time as the particle’s temperature is recorded by a thermocouple. The temperature of a char particle fluidized with an embedded thermocouple is shown to be higher than that of a freely fluidized char particle, and its burnout time is shorter. This is because the fluidization with a thermocouple makes the char particle sink in the bed, increasing its residence time in the bubble phase compared to the freely fluidized particle. Besides, this work shows how the pyrometry technique is able to track the size and movement of a particle and its surface temperature gradients during conversion, improving the data collected with this method as compared to other measurement techniques.
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| 6. |
- Salinero, Jesús, et al.
(author)
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Measurement and theoretical prediction of char temperature oscillation during fluidized bed combustion
- 2018
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In: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 192, s. 190-204
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Journal article (peer-reviewed)abstract
- There is experimental evidence of oscillations of the char particle temperature during combustion in a fluidized bed (FB), resulting from the movement of the char throughout the bed. However, in most theoretical FB combustion studies the char particle is assumed to always stay in the emulsion phase, and existing models do not take into account the movement of the char particle explicitly. Moreover, it is difficult to quantify the magnitude and frequency of these temperature oscillations with the common measurement techniques employed in FB (thermocouple and pyrometry with optical probe). In this work, the combustion of single char particles (8 mm) from beech wood and sub-bituminous coal is carried out in a 2-dimensional FB made of quartz, using two O2 concentrations (11 and 21%v) in N2. The time-evolution of the temperature and the size of the char in the different phases are estimated by the analysis of images resulting from a new method combining pyrometry with readings from a digital camera. It is found that the combustion temperature oscillates in hundredths of seconds with an amplitude varying from 10 to 100 °C, resulting from the movement of a particle between the emulsion, bubble and splash phases. The amplitude increases with higher O2 concentration and smaller char-particle size. A combustion model is developed using the experimental characterization of the movement of the char particle through the bed as input. The temperature and burnout time predicted by the model compare well (within 15 %) with measurements obtained from this work and from literature.
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| 7. |
- Salinero, Jesús, et al.
(author)
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The effect of using thermocouples on the char particle combustion in a fluidized bed reactor
- 2017
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 207, s. 615-624
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Journal article (peer-reviewed)abstract
- The char temperature during combustion in a fluidized bed (FB) is often measured by thermocouples due to simplicity, and because it is assumed that the thermocouple effect on the movement of the char is negligible. It is also accepted that the combustion temperature of a char particle fluidized with an embedded thermocouple is similar to a freely fluidized particle. However, few publications have given evidence of this fact. In the present article this question is dealt with by comparing the evolution of conversion andtemperature of fluidized char particles with and without an embedded thermocouple. Char from beech wood, sub-bituminous and bituminous coal of an initial diameter of 10 mm is burnt in two laboratory FBs; one 2-dimensional made of quartz with rectangular cross-section allowing visual observation andtemperature tracking of the particles, and the other being 3-dimensional with 50 mm internal diameter. The surface temperature of the char particles is followed by a recently developed visual technique, based on pyrometry coupled with a digital camera. The consumption of char is evaluated by sampling particles from the bed at different stages of conversion, analyzing the density and size of the particle. It is found that, due to the greater resistance of the particle-thermocouple to the drag of the bed, the time that the char particle is in the bubble phase is 40% longer when the thermocouple is used, leading to higher combustionrate and temperature, and consequently, shorter burnout time. Moreover, the rotation of the char particle is restricted, provoking a non-homogeneous consumption of char, which enhances the size reduction of the particle along the direction perpendicular to the insertion of the hermocouple.Overall, these findings suggest that conclusions about char conversion by temperature measurements using thermocouples should be made with caution, since significant error might be committed under some operating conditions.
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| 8. |
- Salinero, Jesús, et al.
(author)
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The influence of CO2 gas concentration on the char temperature and conversion during oxy-fuel combustion in a fluidized bed
- 2018
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In: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 215, s. 116-130
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Journal article (peer-reviewed)abstract
- In spite of the extensive theoretical and experimental work carried out on coal/char oxy-combustion in a fluidized bed (FB), the effect of changing the atmosphere from O2/N2 to O2/CO2 for a high O2 concentrations is not entirely understood. In this work, experiments with single char particles are conducted in a bi-dimensional FB at 800 and 850 °C, varying the O2 concentration from 11 to 50%v/v in N2 or CO2. The FB reactor has a quartz window for visual observation, allowing the measurement of temperature and tracking the char conversion process by pyrometry with a digital camera. The method is shown to overcome the inherent limitations of other methods used in FB, such as thermocouples or pyrometry with an optical probe. Results indicate that the transfer of O2 from the bulk gas of the bed to the surface of a char particle controls the overall rate of char conversion in O2/N2 and in O2/CO2. In the latter gas mixture, the carbon consumption by gasification is significant even at a relatively low char temperature (850 °C). This additional carbon consumption makes the apparent char consumption rate in both atmospheres roughly equal (at the same O2 concentration) for char temperatures below 925 °C, and higher in O2/CO2 than in O2/N2 for char temperatures above 925 °C. Moreover, during the time in which the char stays in the emulsion phase, its temperature is roughly the same in both atmospheres, but when the char is in the bubble or splash zone its temperature is much higher than that in the emulsion phase. As a result, the difference in char conversion rate, observed in both atmospheres, is mainly controlled by the time in which the char particle is out of the emulsion phase. These results underline the importance of paying attention to the movement of a char particle through the different phases of the bed in order to improve the understanding of the oxy-fuel behavior in FB.
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| 9. |
- ter Steege, Hans, et al.
(author)
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Mapping density, diversity and species-richness of the Amazon tree flora
- 2023
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In: COMMUNICATIONS BIOLOGY. - 2399-3642. ; 6:1
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Journal article (peer-reviewed)abstract
- Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution. A study mapping the tree species richness in Amazonian forests shows that soil type exerts a strong effect on species richness, probably caused by the areas of these forest types. Cumulative water deficit, tree density and temperature seasonality affect species richness at a regional scale.
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