1,720,979 research outputs found
A systems perspective analysis of an increased use of forest bioenergy in Canada: Potential carbon impacts and policy recommendations
No full textThe Government of Canada aims at reducing overall greenhouse gas emissions by 30% by 2030 (compared to 2005) and reaching net-zero GHG emissions by 2050. Several of the climate actions under development would incentivize an increased use of forest biomass for energy. However, lessons learned from bioenergy policies worldwide have shown that increasing the use of bioenergy can impact the forest sector as a whole and that the carbon impacts of bioenergy should be assessed holistically to limit unintended negative consequences. This study aims to summarize and present existing data in a manner that enables the Canadian government and stakeholders to identify bioenergy pathways that can contribute to Canada's decarbonization targets. Firstly, we synthetize existing statistical datasets on wood removals and uses into a holistic picture of wood flows across Canada's economy. We find that, in 2017, a minimum of 77.7 Mm3 of wood were used for energy in Canada, and that reported quantities of wood used exceeded the amount of wood removals by 14–33 Mm3 annually. Thus, while 72% of wood used for energy in 2017 derived from secondary industry residues, the origin of 26% of wood for energy cannot be identified, seriously hindering any consideration on the sustainability of the current forest bioenergy use in Canada. Secondly, we assess that the amount of wood used for energy might increase by 5.5–20.4 Mm3 by 2030. In order to identify the potential impacts of this extra bioenergy demand on GHG emissions, we reviewed relevant literature based on our qualitative analysis of the system dynamics of the forest sector in response to such an increased demand. Our results show that unless targeted measures are defined to stimulate the use of residues, it is possible that direct and indirect biogenic GHG emissions from increased use of forest bioenergy will undermine Canada's decarbonization goals. We recommend several measures to avoid this, including: discouraging the dedicated harvest of logs for bioenergy, prioritizing the collection and use of logging residues which are usually burned at roadside, and favoring the recovery and use of post-consumer wood. In addition, we recommend improving the consistency among statistical datasets on Canada's forestry sector
Flaws in the interpretation phase of bioenergy LCA fuel the debate and mislead policymakers
No full textPurpose: We hypothesize that the current heated scientific debate on bioenergy sustainability is fuelled by flaws in the interpretation phase of bioenergy LCA studies rather than by the lack of studies or shared methodologies. The interpretation phase is the key step in LCA studies, which guarantees their quality and consistency and gives meaning to the work carried out by delivering results that are consistent with the defined goal and scope, which reach conclusions, and explain limitations. Methods: To test our hypothesis, we selected the 100 most cited articles found in Scopus utilizing a query to include most of the relevant works on LCA of bioenergy. The rationale underpinning the choice of the most cited articles is that these are presumably the most influential. A further screening identified off-topic articles, reviews, and methodological papers, which were discarded. We have also checked whether the articles analysed referred to the ISO standards. The study is organized as a reasoned and parametrized review in which we assess the methodological approach of the studies, rather than the results obtained. Results and discussion: We find that overlooking some of the fundamental steps in the interpretation phase in bioenergy LCA is a rather common practice. Although most of the studies referred to the ISO standards, the identification of issues, their framing with sensitivity analyses, and the identification and reporting of limitations, which are all needed to comply with ISO14044 standards, are often neglected by practitioners. The most problematic part of the interpretation phase is the consistency check. In most cases, the assessment framework built is not apt at answering the question set in the goal. Limitations are properly identified and reported only in few studies. Conclusions: We conclude that in many studies either the conclusions and recommendations drawn are not robust because the inventory and the impact assessment phases are not consistent with the goal of the study, or the conclusions and recommendations go well beyond what the limitations of the study would allow. In our opinion, these flaws in the interpretation phase of influential LCA studies are among the responsible factors that continue to fuel the debate around the sustainability of bioenergy. We report a set of recommendations both for LCA practitioners and for users to guide the LCA practitioners in properly organizing and reporting their work, and to facilitate the readers in understanding and evaluating the significance and applicability of the results presented
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Exploring new visions for a sustainable bioeconomy
Full text linkThe Bioeconomy is both an enabler and an end for the European Green Deal transformation: achieving the EGD
transformation entails transforming the very meaning of sustainable bioeconomy.
Among the deepest and most effective leverage points to transform a system are the worldviews driving our
behaviours: they yield an enormous power to influence the framings which determine the solution space we
explore. Transforming the bioeconomy, thus, requiresreflecting on the stories we tell about ourselves, our place in nature, and our relationship with others.
Scholars have highlighted how narratives surrounding the EU Bioeconomy have predominantly embraced a “Green Growth” perspective, centred around economic growth, technological innovation, and anthropocentric values, largely ignoring the social and justice dimensions, as well as not questioning the role, relations, and responsibilities of humans in the web of life. These dominant framings are increasingly contested, though, because they have failed to produce the social and ecological outcomes desired.
This report introduces perspectives which have been under-represented in the Bioeconomy discourse and integrates them into an alternative vision for a “green, just and sufficient bioeconomy”. This vision places environmental sustainability and social equity at its core, regardless of economic growth; has an inclusive and participatory perspective; care, respect, and reciprocity for and with other humans and non-humans are core values; technology is important to deliver on the green and just objectives, but ethical considerations for new technologies are openly debated
Characterization of second generation biomass under thermal conversion and the fate of nitrogen
No full textThis dissertation deals with the characterization of several biomass materials under thermal conversion conditions using small--scale equipment. The fuels are tested under the conditions of slow and fast heating rate pyrolysis and combustion, with the main goal of investigating the chemistry of fuel--bound nitrogen. New energy policies put forward in almost every country in the world, and especially in the European Union, are strongly promoting the use of renewable energy sources. Decreasing the use of imported fossil fuels in favour of locally available renewables is the answer to many energy--related problems of the 21st century: global warming, security of supply and high energy prices among some. Among renewable sources, biomass materials hold a special position because they can, in the short term, substitute or integrate fossil fuels in all of their applications applying comparatively few changes to the existing equipment. Biomass wastes, from agriculture or other processes, are convenient in more respects since their use would not only substitute fossil fuels but it would also valorize waste streams. These materials, however, present several issues that are highly delaying their deployment on a large scale. Three of the most important problems are dealt with in this thesis: the heterogeneous nature of the materials, high amount of ash forming matter containing troublesome compounds such as K, Cl and P, and finally, high content of nitrogen. First of all, many biomass residues contain a higher amount of nitrogen compared with woody biomass or even coal. This high content of fuel--N could directly translate into high NOx emissions in combustion conditions or into a high content of nitrogen containing gases such as NH3 and HCN in the syngas from gasification. Primary measures, such as air staging, can be applied directly in the reactor in order to promote the reduction of NOx and NOx--precursors to molecular nitrogen. However, in order to apply such measures and optimize the syngas composition or minimize emissions without relying on expensive catalysts, a detailed knowledge of the mechanisms of fuel--N conversion is required. This thesis has as its main purpose to study the release of volatile nitrogen compounds under pyrolysis conditions and the analysis of the emissions of NO under combustion conditions from high--N fuels. Secondly, as explained in the first two chapters of this dissertation, the definition of biomass is very broad and it includes materials with extremely different composition and characteristics. Additionally, the interest in exploiting some of these materials, such as manures, for energy conversion has never been high enough to trigger substantial research. As a consequence, fundamental data such as reactivity and products distribution are almost completely lacking for many biowastes. One of the purposes of this thesis is, therefore, to gather extensive fundamental data for potential fuels, which have not yet fully characterized. Finally, some elements such as K, Cl, P and S, contained in biomass materials, are known to cause several problems during boiler operation. At high temperatures alkali silicates with melting temperatures lower than the operating one are formed; these partly molten particles can then create issues like slagging, fouling, loss of fluidization and, when Cl is present, corrosion of the boiler surfaces. Together with specific research on boiler materials and optimization of operating conditions, possible pre--treatments used to remove these compounds from the fuel before entering the reactor could greatly enhance the overall process. In this thesis, the effects of a water--leaching pre--treatment on the fuels' reactivity and product yields during pyrolysis are explored. After a general introduction, Chapter 2 has the purpose of providing the reader with an overview of definitions and concepts that are used in the rest of the dissertation. The main components of biomass are listed as well as their behavior under thermal conversion conditions. A special focus is given to nitrogen structures, such as proteins and heterocyclic compounds, and the mechanisms of their decomposition under pyrolysis conditions as reported in available literature studies. Finally, an overview of NOx formation mechanisms is given. The materials studied in this work and the setups used are introduced in Chapter 3. The materials are divided into two main categories: agricultural residues, including wheat straw, olive residues and peach stones, and biomass waste streams, including dry distiller's grains, palm kernel cake and chicken manure. All these materials have a high nitrogen content and are not yet fully exploited because of the issues mentioned above. Several different small--scale setups have been used in this work depending on the conditions that needed to be study. Chapter 4, then, presents the results of measurements performed on agricultural residues under slow pyrolysis conditions. The measurements were carried out using a thermogravimetric analyzer (TGA) connected with a Fourier Transform InfraRed spectrometer (FTIR). All the fuels presented peaks of reactivity at approximately 330 - 360°C associated with the decomposition of cellulose. A shoulder was also found at lower temperatures, approximately 290 - 310°C, and was associated with the pyrolysis of hemicellulose. The main volatile species released resulted to be CO2 for all the fuels followed by CO and methane. No nitrogen compounds were detected because of too little concentrations in the pyrolysis gases which could not be accurately detected by the FTIR. The kinetic parameters for the pyrolysis reactions were found using a Distributed Activation Energy Model (DAEM). This analysis revealed a common reaction path for the main structures (cellulose and hemicellulose) among the various fuels. The water--leaching pre--treatment seemed very effective in removing the troublesome inorganic elements from these fuels. The removed elements, furthermore, had a catalytic effect on the pyrolysis of the fuels; once removed, the samples reacted at higher temperatures and with less reaction paths. Only the peach stones sample, which already had a very low ash content, did not seem to be affected by the treatment. Chapter 5 reports the results of a similar analysis to the previous one, that was performed on different biomass residues: dry distiller's grains with solubles (DDGS) and chicken manure. Also these fuels were found to react with two main peaks at about 280°C and 330°C. Accordingly, also the kinetic parameters resulted very similar to the ones of the agricultural residues, clearly indicating a similar decomposition path for common structures. For DDGS and chicken manure, an additional component was found to react at approximately 400 - 430°C and it was assigned to proteinic structures decomposing. The main volatile nitrogen compounds were found to be NH3 and HCN for DDGS with traces of HNCO. The manure released more of its fuel--bound nitrogen in volatile form and the main compound was found to be HNCO, followed by HCN and ammonia. The water leaching pre--treatment, similarly to what was found for the peach stones sample, did not seem to affect substantially the reactivity of the fuels nor their ash composition. The share of fuel--N released as light volatiles, however, increased for the washed fuels. Building up on the results of the previous two chapters, Chapter 6 describes the results of fast pyrolysis measurements of DDGS and palm kernel cake. These tests were carried out on a heated foil reactor integrated with an FTIR using much higher heating rates, closer to industrial applications. A numerical model of the reactor has been developed in order to have a better insight into the temperature and velocity profiles in the reactor chamber. The simulations, in combination with non--contact temperature measurements, have indicated a significant difference between the expected foil temperature and the actual one. This has been corrected in the experimental campaign, granting a more precise knowledge of the actual conditions. The fast pyrolysis measurements have shown an increased weight loss compared to slow heating rates. CO2 resulted to be still the main light volatile at temperatures below 900°C while CO became more relevant at high temperatures due to tar cracking in the hot area around the foil. Compared to low heating rates measurements of the DDGS sample, HCN was the main volatile nitrogen compound while the yield of NH3 was much lower. The palm kernel cake sample only released detectable yields of HCN, nor ammonia nor HNCO were found. Even at high temperatures, approximately 10% of the initial N was retained in the char of DDGS. The water leaching pre--treatment again did not affect the weight loss behaviour neither the main gaseous product distribution but the yields of light volatile nitrogen compounds increased for the washed samples. After the pyrolysis behaviour of different nitrogen compounds has been analyzed, Chapter 7 presents the results of measurements under combustion conditions for several biomass residues. It is shown that the devolatilization profiles for carbon to CO + CO2 and fuel--N to NO are very similar among very different fuels, implying that a common approach could be taken for their modeling and it could very well be acceptable as a first approximation. Moreover, the conversion of fuel--N to NO appeared to follow a decaying trend where the fuels with lower initial N content presented a higher conversion than fuels with higher nitrogen content. Fuels with high nitrogen content, in fact, are likely to release a larger amount of it in volatile form with a consequent larger amount of NHi radicals available for thermal De--NOx reactions. Finally, the release of carbon as CO2 and nitrogen as NO during devolatilization was found to be proportional for temperatures around 800°C while at 1000°C almost all of the NO was released during devolatilization. Finally, in Chapter 8 the main conclusions of the work described in thesis are drawn and recommendations for future research are expressed.Process and EnergyMechanical, Maritime and Materials Engineerin
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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