| 1. |
- Carvalho, Lara, et al.
(author)
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Alkali enhanced biomass gasification with in situ S capture and a novel syngas cleaning : Part 2: Techno-economic analysis
- 2018
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In: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 165:Part B, s. 471-482
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Journal article (peer-reviewed)abstract
- Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning systemcomprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reductionwith zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol productionallowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantagederived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.
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| 2. |
- Carvalho, Lara, et al.
(author)
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Challenges in small-scale combustion of agricultural biomass fuels
- 2007
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In: 9th Conference on Energy for a Clean Environment.
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Conference paper (peer-reviewed)abstract
- In the present work, several agricultural biomass fuels, namely straw, Miscanthus,maize whole crop and horse manure mixed with two bedding materials, woodshavings and straw, were reviewed in terms of fuel characteristics. Furthermore,these fuels were tested in several existing boiler technologies and the particulateand gaseous emissions were monitored. The ash was analysed visually in terms ofpresence of sintered material. As expected, all the fuels showed problems withash lumping and slag formation, especially straw and horse manure. Differentboiler technologies showed different operational performance regarding ash andslag management. Miscanthus was the best fuel tested regarding emissions. Maizeand horse manure are problematic fuels regarding NOx and particulate emissions.Due to the big variation of the fuel properties and therefore combustion behaviourof agricultural biomass, further R&D is required to adapt the existing small-scalecombustion systems for these new fuels. Improvements in the combustionchamber design, controlling technology and ash removal systems of small-scalecombustion systems are therefore essential.
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| 3. |
- Carvalho, Lara, et al.
(author)
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Challenges in small-scale combustion of agricultural biomass fuels
- 2008
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In: International Journal of Energy for a Clean Environment. - 2150-3621 .- 2150-363X. ; 9:1-3, s. 127-142
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Journal article (peer-reviewed)abstract
- Straw, Miscanthus, maize, and horse manure were reviewed in terms of fuel characteristics. They were tested in existing boilers, and the particulate and gaseous emissions were monitored. The ash was analyzed for the presence of sintered material. All the fuels showed problems with ash lumping and slag formation. Different boiler technologies showed different operational performances. Maize and horse manure are problematic fuels regarding NOx and particulate emissions. Miscanthus was the best fuel tested. Due to the big variation of fuel properties and therefore combustion behavior of agricultural biomass, further R&D is required to adapt the existing boilers for these fuels.
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| 4. |
- Carvalho, Lara, et al.
(author)
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Methanol production via black liquor co-gasification with expanded raw material base : Techno-economic assessment
- 2018
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In: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 225, s. 570-584
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Journal article (peer-reviewed)abstract
- Entrained flow gasification of black liquor combined with downstream-gas-derived synthesis of biofuels in Kraft pulp mills has shown advantages regarding energy efficiency and economic performance when compared to combustion in a recovery boiler. To further increase the operation flexibility and the profitability of the biofuel plant while at the same time increase biofuel production, black liquor can be co-gasified with a secondary feedstock (blend-in feedstock). This work has evaluated the prospects of producing biofuels via co-gasification of black liquor and different blend-in feedstocks (crude glycerol, fermentation residues, pyrolysis liquids) at different blend ratios. Process modelling tools were used, in combination with techno-economic assessment methods. Two methanol grades, crude and grade AA methanol, were investigated. The results showed that the co-gasification concepts resulted in significant increases in methanol production volumes, as well as in improved conversion efficiencies, when compared with black liquor gasification; 5-11 and 4-10 percentage point in terms of cold gas efficiency and methanol conversion efficiency, respectively. The economic analysis showed that required methanol selling prices ranging from 55-101 €/MWh for crude methanol and 58-104 €/MWh for grade AA methanol were obtained for an IRR of 15%. Blend-in led to positive economies-of-scale effects and subsequently decreased required methanol selling prices, in particular for low cost blend-in feedstocks (prices below approximately 20 €/MWh). The co-gasification concepts showed economic competitiveness to other biofuel production routes. When compared with fossil fuels, the resulting crude methanol selling prices were above maritime gas oil prices. Nonetheless, for fossil derived methanol prices higher than 80 €/MWh, crude methanol from co-gasification could be an economically competitive option. Grade AA methanol could also compete with taxed gasoline. Crude glycerol turned out as the most attractive blend-in feedstock, from an economic perspective. When mixed with black liquor in a ratio of 50/50, grade AA methanol could even be cost competitive with untaxed gasoline.
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| 5. |
- Carvalho, Lara, 1978-
(author)
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Opportunities to broaden biomass feedstocks in thermochemical conversion technologies
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Global environmental concerns are motivating a growing interest in broadening the biomass feedstock base in several energy sectors, including (i) the domestic heating sector, presently dominated by stem wood combustion, and (ii) biofuel production, presently dominated by edible crops. The objective of this thesis is to investigate new opportunities to broaden the biomass feedstock in thermochemical conversion technologies. The performance of different feedstocks was therefore investigated for (i) heat production in small-scale combustion systems and (ii) biofuel production in large-scale gasification-based plants. The selected feedstocks were agricultural residues, forest wood, pyrolysis liquid and industrial by-products, such as lignin, black liquor, crude glycerol and fermentation residues.The alkali metals content in biomass has an important role in combustion and gasification. Alkali metals can cause ash-related problems in small-scale combustion systems, while they can catalyse gasification reactions thus increasing conversion efficiency. Keeping this effect in mind, the present investigation was based on combustion tests with pelletised agricultural residues (non-woody feedstocks with ash contents of 3-8 wt% on a dry basis) to evaluate their combustion feasibility in several small-scale appliances. Moreover, the potential techno-economic benefits of alkali addition in gasification-based biofuel plants were investigated in two different systems: (i) stand-alone biofuel plant operated with wet-alkali-impregnated forest residues and alkali-rich lignin as well as (ii) biofuel plant integrated with a Kraft pulp mill operated with black liquor (an inherently alkali-rich feedstock) mixed with different blend ratios of pyrolysis liquid, crude glycerol or fermentation residues (co-gasification concept). The techno-economic analysis in large-scale entrained-flow-gasification-based biofuel plants was made with the help of simulation tools.The combustion tests have shown that high alkali feedstocks lead to problems with ash accumulation and slag formation in small-scale appliances. The results indicated that non-woody feedstocks can only be burned in appliances adapted to manage high ash content feedstocks. Effective ash cleaning and enhanced combustion controlling mechanisms are relevant characteristics to have in appliances when using these feedstocks. It has been shown that four out of the seven selected feedstocks can be burned in small-scale appliances, while fulfilling the legal European requirements (EN 303-5:2012) in terms of combustion efficiency and emissions. The nitrogen content and ash composition were shown to be important parameters to evaluate whether a feedstock can be utilised in small-scale combustion appliances.The techno-economic investigations of the gasification-based biofuel plants have shown that alkali impregnation is an attractive option to increase energy performance and downstream biofuel production. The economic assessment has indicated that alkali impregnation does not significantly increase biofuel production costs, while it allows the application of a new syngas cleaning system that can significantly reduce biofuel production costs. The present study has shown that the vi co-gasification concept has also techno-economic benefits as a result of the (i) alkali content in black liquor and (ii) economy-of-scale effects. These benefits can be enhanced by choosing energy-rich and low-cost blend-in feedstocks. The gasification-based biofuel production routes hereby investigated exhibit a good economic performance since biofuel required selling prices were economically competitive with other biofuel production routes as well as with taxed gasoline.
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| 6. |
- Carvalho, Lara, et al.
(author)
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Performance of a pellet boiler fired with agricultural fuels
- 2013
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In: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 104, s. 286-296
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Journal article (peer-reviewed)abstract
- The increasing demand for woody biomass increases the price of this limited resource, motivating the growing interest in using woody materials of lower quality as well as non-woody biomass fuels for heat production in Europe. The challenges in using non-woody biomass as fuels are related to the variability of the chemical composition and in certain fuel properties that may induce problems during combustion. The objective of this work has been to evaluate the technical and environmental performance of a 15 kW pellet boiler when operated with different pelletized biomass fuels, namely straw (Triticum aestivum), Miscanthus (Miscanthus × giganteus), maize (Zea mays), wheat bran, vineyard pruning (from Vitis vinifera), hay, Sorghum (Sorghum bicolor) and wood (from Picea abies) with 5% rye flour. The gaseous and dust emissions as well as the boiler efficiency were investigated and compared with the legal requirements defined in the FprEN 303-5 (final draft of the European standard 303-5). It was found that the boiler control should be improved to better adapt the combustion conditions to the different properties of the agricultural fuels. Additionally, there is a need for a frequent cleaning of the heat exchangers in boilers operated with agricultural fuels to avoid efficiency drops after short term operation. All the agricultural fuels satisfied the legal requirements defined in the FprEN 303-5, with the exception of dust emissions during combustion of straw and Sorghum. Miscanthus and vineyard pruning were the best fuels tested showing comparable emission values to wood combustion.
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| 7. |
- Carvalho, Lara
(author)
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Small-scale combustion of agricultural biomass fuels
- 2012
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Licentiate thesis (other academic/artistic)abstract
- The ambitious targets of the European Union in increasing the use of renewable energies to 20% of Europe’s energy needs, call for urgent changes, including in the biomass sector. The share of solid biomass for heating purposes could be further increased by replacing oil- and gas-fired furnaces with biomass boilers and by expanding the spectrum of biomass raw materials for small-scale combustion systems. The interest in using non-woody biomass fuels for heat production has been increasing in Europe due to two main factors. First, the market for fossil fuels is unstable and their prices are continuously rising. Second, the increase competition for woody biomass between the heating sector and other industries, have increased the price of wood. As a result, the interest for alternative biomass fuels is growing rapidly, covering woody materials of low quality, energy crops and forest residues.The present work aims at investigating the technical feasibility of using non-woody biomass fuels in existing small-scale combustion appliances developed for burning wood. Therefore, combustion tests with different non-woody biomass fuels and in different combustion appliances were performed in standard laboratory conditions and in households under real life conditions (field tests). The laboratory tests were performed using eight different fuels (straw, Miscanthus, maize, vineyard pruning, hay, wheat bran and Sorghum) while in the field tests straw, Miscanthus and maize were burned. The gaseous and particle emissions, the slag tendency and the efficiency of the combustion systems operated with non-woody biomass fuels were analysed and when possible compared with the legal requirements defined in FPrEN 303-5. The limitations of the investigated combustion appliances when operated with non-woody biomass fuels were analysed and discussed.Non-woody biomass fuels could be used for heat production in existing combustion appliances as long as the systems are adapted for burning high ash content fuels. Among the investigated fuels, Miscanthus, vineyard pruning and hay could be burnt in most of the tested combustion appliances while fulfilling the legal European requirements (defined in FprEN303-5) in terms of emissions and efficiency. The non-woody biomass fuels showed problems with ash accumulation and slag formation and could only be burned without unwanted shutdowns in combustion appliances adapted to manage high ash content fuels. Straw, wheat bran and maize were the most problematic fuels regarding slagging. The combustion appliances require appropriate technological developments to manage the strong variability in terms of chemical and thermal properties of the non-woody biomass fuels. The results of the laboratory tests were generally in agreement with the field test results.
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| 8. |
- Carvalho, Lara, et al.
(author)
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Techno-economic assessment of catalytic gasification of biomass powders for methanol production
- 2017
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In: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 237, s. 167-177
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Journal article (peer-reviewed)abstract
- This study evaluated the techno-economic performance and potential benefits of methanol production through catalytic gasification of forest residues and lignin. The results showed that while catalytic gasification enables increased cold gas efficiencies and methanol yields compared to non-catalytic gasification, the additional pre-treatment energy and loss of electricity production result in small or no system efficiency improvements. The resulting required methanol selling prices (90–130 €/MWh) are comparable with production costs for other biofuels. It is concluded that catalytic gasification of forest residues can be an attractive option as it provides operational advantages at production costs comparable to non-catalytic gasification. The addition of lignin would require lignin costs below 25 €/MWh to be economically beneficial.
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| 9. |
- Carvalho, Sérgio A., et al.
(author)
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Self-as-context and depressive symptoms in the general population : A further analysis of the self experiences questionnaire
- 2022
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In: Current Psychology. - : Springer. - 1046-1310 .- 1936-4733. ; 41:12, s. 8897-8907
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Journal article (peer-reviewed)abstract
- The current study aims to contribute to the psychometric validation of the Self Experiences Questionnaire (SEQ), a measure of self-as-context as conceptualized by Acceptance and Commitment Therapy, and to contribute to a better understanding of the relationship between self-as-context, other psychological flexibility processes, and depressive symptoms. The sample (N = 266; 72.6% women) was obtained through paper-pencil and online collection methods in the general Portuguese population. Confirmatory factor analysis, reliability analyses, and convergent and divergent analyses were conducted. A mediation analysis of the effects of self-as-distinction and self-as-observer on depression symptoms through openness to experience, behavioral awareness, and valued action (while controlling for brooding) was performed using PROCESS. Items 8, 12 and 15 were removed to achieve the best model fit, which resulted in a 12-item final version of the SEQ. This version appears to be a psychometrically valid two-dimensional measure of self-as-distinction and self-as-observer, as well as a one global measure of self-as-context. Results from mediation analyses suggested that the relationship of self-as-observer and self-as-distinction with depressive symptoms is mediated by the ability to be behaviorally aware and to act according to personal values, but not by the ability to be open to experience. The behaviorally-oriented aspects of psychological flexibility seem to have particular importance on the presentation of depressive symptoms. More studies are nonetheless needed to analyze SEQ's structure and validity in order to attain a consensual version of the questionnaire.
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| 10. |
- Clark, Andrew G., et al.
(author)
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Evolution of genes and genomes on the Drosophila phylogeny
- 2007
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 450:7167, s. 203-218
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Journal article (peer-reviewed)abstract
- Comparative analysis of multiple genomes in a phylogenetic framework dramatically improves the precision and sensitivity of evolutionary inference, producing more robust results than single-genome analyses can provide. The genomes of 12 Drosophila species, ten of which are presented here for the first time (sechellia, simulans, yakuba, erecta, ananassae, persimilis, willistoni, mojavensis, virilis and grimshawi), illustrate how rates and patterns of sequence divergence across taxa can illuminate evolutionary processes on a genomic scale. These genome sequences augment the formidable genetic tools that have made Drosophila melanogaster a pre-eminent model for animal genetics, and will further catalyse fundamental research on mechanisms of development, cell biology, genetics, disease, neurobiology, behaviour, physiology and evolution. Despite remarkable similarities among these Drosophila species, we identified many putatively non-neutral changes in protein-coding genes, non-coding RNA genes, and cis-regulatory regions. These may prove to underlie differences in the ecology and behaviour of these diverse species.
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