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Distributed power generation and cogeneration of heat and power is an attractive way toward a more rational conversion of fossil and bio fuels. Solid oxide fuel cell (SOFC) – gas turbine (GT) hybrid systems are emerging as the most promising candidates enabling the achievement of a cleaner and more efficient conversion of a large variety of resources across a broad power range covering from small to medium scale applications. This thesis introduces an innovative concept of SOFC-GT hybrid system that allows reaching efficiencies higher than the state of the art while enabling the carbon dioxide separation and avoiding fuel cell pressurisation technical issues. Several hybrid system design alternatives based on this concept are analysed through a thermodynamic optimisation approach combining process modelling, advanced process integration techniques and multi-objective optimisation. A number of optimal hybrid system configurations are determined for different design targets. The results consistently demonstrate the higher energy conversion performance and flexibility enabled with respect to the state of the art. The innovative concept analysis is extended to two applications for which SOFC-GT hybrid cycles are expected to provide the most significant impact toward sustainability: the small scale distributed generation and the conversion of renewable resources. A simplified version of the new hybrid system layout is especially developed for small scale distributed generation, typical of residential building applications (5-10 kWel). Experimental data are used to prove the technical feasibility of the system and to assess the performance potentially achievable with currently feasible technologies. The results of the analysis underline that energy conversion efficiencies higher than traditional centralised power generation can be achieved even at such a small scale. A systematic process integration and optimisation approach is used to assess the energy conversion performance of the original SOFC-GT hybrid cycle fuelled with hydrothermally gasified wet waste biomass. The analysis highlights the considerable potential of the integrated system that allows for converting wet waste biomass into electricity with First Law efficiency higher than 60% while simultaneously enabling the separation of the biogenic carbon dioxide.

The constituent countries of the MENA region---defined in this thesis in conformity with the regional definition of the International Energy Agency and encompassing 17 Muslim countries in North Africa, in the Levant, on the Arabian Peninsula, and Iran---have developed very rapidly over the past decade. Two figures best exemplify the region's tremendous transformation: Total population has expanded by more than 20% and its aggregate economic output has more than doubled. As much as this development is desirable, said development trends have also dramatically reshaped the energy policy environment in the MENA region and began causing problems of their own---affecting the region's large oil exporters and its energy importers alike. Having traditionally enjoyed high energy security and handsome resource rents by virtue of their abundant and cheap fossil fuels, new realities in the domestic energy systems demand a new policy focus on domestic energy issues. Energy challenges have emerged which threaten security of supply, fiscal stability, and environmental integrity. The challenges differ in magnitude from country-to-country and reflect the specific national conditions and circumstances. However, given the similarity in the underlying drivers and the governing energy policies, the energy challenges resemble each other across borders. More specifically, ballooning domestic energy demand consumes a rising share of national energy production and thus increasingly imperils the constant flow of the much needed proceeds from oil and gas exports. In the MENA countries with less abundant hydrocarbon resources, domestic demand growth has heightened energy dependence and, to make matters worse, the tighter supply situation in the energy exporting neighbors may eventually also lead to a discontinuation of the preferential supply agreements which they have benefitted from in the past. As a further corollary of demand growth, massive capital-intensive infrastructure investments are necessary to keep pace with the growth on the demand side. The regional tradition to sell energy commodities domestically at prices non-competitive prices or even below cost, however, limits the national energy sectors' own capability of mustering the required capital. Finally, the universally observable heavily fossil fuel-dominated national energy mixes in the region render the study countries vulnerable to supply shocks. The virtually complete reliance on the regionally available hydrocarbons for meeting energy demand is also a principal contributor to environmental degradation and at the core of the large carbon footprint of energy consumption in MENA countries. Given current policies in combination with the emerging demographic and economic trends, these challenges must be expected to become more severe in the years to come. Rising living standards, especially in the region's expanding urban population, are likely to boost per capita energy consumption. The projected, continued demographic and economic growth will further drive commodity demand. And the supply side cannot be counted on to mitigate the challenges under given policies. On the contrary. Although no reliable production projections are available, it stands to reason that production from the region's most prolific oil and gas fields---some of which have been producing for several decades now---will increasingly require the use of costly secondary and tertiary recovery methods and that some will eventually [...]

Natural gas is defined as a combustible mixture of hydrocarbons coming from ground deposits and it is mainly used as a source of energy for burners and motors. Its consumption is increasing worldwide, as this represents a cheap and abundant source of energy, while releasing less CO2 emissions than other fossil fuels, in addition to low emissions of particulates. The diversification of the supply sources of gas and the increase of international trading through pipelines and liquefied natural gas (LNG) shipments makes the gas quality vary more than before, which is a rising challenge for the natural gas industry, as currently the vast majority of gas appliances and motors are unable to adapt to changes in gas quality. This will even worsen in the upcoming years with the multiplication of biogas sources and power-to-gas systems that will be added to the pipeline networks. In order to accomodate the appliances to changes in gas quality, compact and low cost natural gas quality transducers have to be developped for the natural gas industry. The present Thesis aimed at investigating the existing methods to determine natural gas quality for combustion, focusing on the determination of the Wobbe Index (WI), which is a key parameter to set up the air-fuel ratio of the combustion in burners and motors, and to qualify a new type of dynamic viscosity transducer developped at Laboratoire de Production Microtechnique (LPM) of EPFL for the determination of the combustion properties. Inference transducers are a new kind of transducers that allow determining the combustion parameters of the gas by relating to fundamental thermo-physical parameters, and not through the determination of the concentration of the gas constituents, as in gas chromatographs and spectrometers. Here, the dynamic viscosity is chosen as the most promising thermo-physical property of a natural gas to relate to the WI and the Higher Heating Value (HHV). The viscometer takes measurements proportional to the resistance to flow of a gas through a capillary under the action of pulses of heat, and it can be therefore be described as a thermal pumping gas viscometer. A mathematical model and a finite element model (FEM) are used to predict the behavior of the system and for thermal optimization, which are combined by a thermal characterization of the system. The miniature heater used to generate the heat pulses inside the viscometer is a key element of the transducer, and after reviewing potential technologies, the design choices are reported and the fabrication process is exposed, followed by a mechanical and thermal characterization. In order to determine and validate the conversion of the WI from the dynamic viscosity, theoretical relations are analyzed and empirical characterizations are done with a test and calibration setup allowing to create given mixes of gases. Finally, the degradation of the transducer to contaminants of natural gas is investigated, and the analysis is focused to the characterization of the corrosion by the sulfur compounds of natural gas. Test vehicles are developed to study the effect of sulfur corrosion on metallic parts, electronic substrates, silicone adhesives and wirebonds materials, and experiments are held with the dedicated test setups developed at LPM of EPFL.

This paper provides a synthesis and comparison of methodologies and results obtained in several studies devoted to the impact of climate change on hydropower. By putting into perspective various case studies, we provide a broader context and improved understanding of climate changes on energy production. We also underline the strengths and weaknesses of the approaches used as far as technical, physical and economical aspects are concerned. Although the catchments under investigation are located close to each other in geographic terms (Swiss and Italian Alps), they represent a wide variety of situations which may be affected by differing evolutions for instance in terms of annual runoff. In this study, we also differentiate between run-of-river, storage and pumping-storage power plants. By integrating and comparing various analyses carried out in the framework of the EU-FP7 ACQWA project, this paper discusses the complexity as well as current and future issues of hydropower management in the entire Alpine region.

This thesis presents a methodology for energy management in large companies and its implementation through a web application and through a prototype of a simulation platform. By combining existing tools in an innovative manner and by making use of recent web technology developments, the methodology adopted provides engineers and managers with tools capable of guaranteeing an efficient and sustainable energy management. Although the methodology presented in this work is based on the experience acquired in the food industry, it can be easily applied in other industrial sectors. The methodology is based on two fundamental approaches commonly used to analyse energy consumption in industrial contexts: the top-down approach and the bottom-up approach. The top-down approach is used in the first place to identify the factories and the specific areas within the factories in which the largest improvement potentials can be achieved. In turn, the bottom-up approach builds on the results from the top-down approach to identify and quantify the energy saving potentials. The top-down approach is implemented through a web application in collaboration with an industrial partner. This application encompasses a modular factory model –accessible to engineers in factories through a user-friendly interface– which enables each factory to define its energy usage, allocate energy costs among the different energy consumers and compute key performance indicators. For a rational cost allocation in multi-service energy conversion units, an exergy-based methodology is presented. The efficiency of energy conversion units defined in the factory model, such as the boilerhouse or the air heaters, is assessed using thermodynamic models. The latter are simplified parametric models derived from accurate thermodynamic models developed in a general flow-sheeting and simulation software to comply with computation time and reliability requirements of the web application. The different factory models defined in the web application can be browsed as part of the proposed top-down approach: starting from a high level overview of the factory –targeted mainly at managers– users can then focus on a specific area of the factory. Strategies are developed to guide users in identifying factories or specific areas within the factories with the largest improvement potentials. They include the use of mechanism to rate the quality of a performance indicator as well as a benchmarking module that allows to compare performance indicators across factories worldwide. In sum, the modular and adaptive aspects of the web application guarantee its long-lasting use. In order to quantify energy saving potentials in the energy conversion units defined in a factory model, "what if?" scenarios are performed in a web-based simulation platform prototype developed in this thesis. This platform acts as a decision-support tool by providing graphical representations of profitability and risk analysis. The platform can be accessed by human users through a web browser while other applications, such as the web application described above, may use the simulation functions through a web service. Statistical tools that can help engineers in defining the factory model described above are also presented. They are used to correlate energy consumption with factors such as production volumes or the climate. Tests to validate the developed correlations are also described. The application of this technique in a factory shows that more than 50% of the energy consumption does not have a direct correlation with production factors and allows to identify improvement potentials. Finally, the concept of a bottom-up approach to identify and quantify energy saving potentials in the different production processes of a factory is presented. A triple representation of the requirements of a process is introduced and applied to process integration in a concrete example. The 80/20 rule is also applied to reduce the complexity of the problem. The optimal integration of cogeneration engines and heat pumps using multi-objective optimisation is also presented.

This thesis is motivated from the fundamental decision problem in today's manufacturing industry which could be summarized as one simple question: how is it possible to achieve economic growth by taking advantage of the latest technologies while protecting the environment? The machine tool has undergone a remarkable change in recent years and the classical concept of an independent, manually operated machine tool, specially dedicated to a particular machining process no longer belongs to the production environment. The increasing usage of computer control and measuring equipment as well as workpiece and tool handling devices has transformed the machine tool into a sophisticated hybrid production system having a lower demand for human supervision of the process. All these efforts are gathered together in order to achieve a high productivity system able to machine different parts respecting quality requirements at the lowest cost. In addition, increasing attention to the environmental and health impacts by governmental regulations and by growing awareness in society is forcing manufacturers to find environmentally friendly designs and machining strategies. The objective of this research is to propose a multicriteria decision aid methodology (MCDA) for evaluation of the use phase of a machine tool system by jointly considering economical, technical and environmental criteria which allows the decision maker to be in a better position to make sustainable decisions. The evaluation is carried out at two levels by addressing the process level with its local cutting area effects and the main activities of the machine tool system by giving full consideration to reduction/elimination of the cutting fluid and reduction of the overall energy consumption. After carefully reviewing previous research, a consistent hierarchical evaluation criteria structure and an entity relationship diagram characterizing the organizational scheme of a database, which stores the data to be used in the evaluation process, is proposed for each level. As a second step, this thesis proposes a model for estimation of the mechanical energy requirements of the cutting subsystem of a machine tool based on the cutter location data, the cutting parameters and the technical specifications of the spindle and feed axes. The MCDA methodology and the energy consumption model were implemented in a software tool using the VBA (Visual Basic for Applications) language and was validated through various tests consisting in the machining of different milling and drilling features of a prismatic part by employing different cutting parameters and cooling/lubrication alternatives. In addition to the cutting tests, an extensive monitoring of the power share amongst the main subsystems of a modern machining center was carried out and a power data collection framework was proposed. The acquisition, interpretation and storage of the experimental data were supported by a measurement platform developed in the LabVIEW environment.

Storage capacity is a key aspect when validating potential CO2 sequestration sites. Most CO2 storage projects, for obvious reasons, target conventional aquifers (e.g., saline aquifers, depleted hydrocarbon fields) with good reservoir properties and ample subsurface data. However, non-geological factors, such as proximity to the CO2 source, may require storing CO2 in geologically “less-than-ideal” sites. We here present a first-order CO2 storage resource estimate of such an unconventional storage unit, a naturally fractured, compartmentalized and underpressured siliciclastic aquifer located at 670–1,000 m below Longyearbyen, Arctic Norway. Water injection tests confirm the injectivity of the reservoir. Capacity calculations, based on the US DOE guidelines for CO2 storage resource estimation, were implemented in a stochastic volumetric workflow. All available data were used to specify input parameters and their probability distributions. The areal extent of the compartmentalized reservoir is poorly constrained, encouraging a scenario-based approach. Other high-impact parameters influencing storage resource estimates include CO2 saturation, CO2 density and the storage efficiency factor. The hydrodynamic effects of storing CO2 in a compartmentalized aquifer are accounted for by calculating probable storage efficiency factors (0.04–0.79 %) in a fully closed system. The results are ultimately linked to the chosen scenario, with two orders of magnitude difference between scenarios. The fracture network contributes with up to 2 % to the final volumes. The derived workflow validates CO2 storage sites based on initial feasibility assessments, and may be applied to aid decision making at other unconventional CO2 storage sites with significant data uncertainty.

The recycling of homogeneous acids imposes great challenges to the feasibility of lignocellulose hydrolysis processes. Although heterogeneous catalysts would offer a perspective to circumvent these challenges, conventional solid acids are instable under the hydrothermal conditions typical of hydrolysis processes. In this regard, acid functionalized carbons appear as auspicious alternatives due to the higher perseverance of carbon frameworks. The strong Brønsted acid sites in sulfonated carbons would be particularly well suited to catalyze the hydrolysis of cellulosic biomass. The utilization of these materials has so far been impeded by the controversy regarding the stability of sulfonic acid groups in carbons. Furthermore, it remains uncertain how the constraints imposed on the reaction system by the insolubility of lignocellulose influence the ability of solid acids to function as hydrolysis catalysts. This thesis shows that hydrothermally stable sulfonated carbons can be prepared by utilizing the structure-stability dependence of sulfonic acid groups in carbonaceous materials. The sulfonation of materials featuring a low degree of graphitization resulted in active solid Brønsted acid catalysts that however deactivated through the leaching of sulfonic acid groups. An in-depth physicochemical characterization of the catalysts paired with a systematic study of the stability of model sulfonic acids, revealed that the leaching-tendency is defined by substituent effects. Activating/deactivating substituents control the hydrothermal stability of aryl sulfonic acids by decreasing/increasing the tendency of the carbon-sulfur bond to undergo solvolysis. The presence of stabilizing and destabilizing substituents was found to be tunable by the temperature dependent decomposition of oxygen containing surface groups. Sulfonation of cellulose carbonized at 350°C resulted in a catalyst with 850 µmol g-1 hydrothermally (180 °C) stable sulfonic acid groups. Additionally, a hitherto unknown mode of deactivation was identified that proceeds by the ion-exchange of cationic impurities with protons of the active sites. This mode of deactivation can be fully overcome by implementing countermeasures to reverse or suppress ion-exchange processes. To tackle the limitations of homogeneous acids, the stable sulfonated carbons were used as catalysts in a semi-batch based lignocellulose hydrolysis process. It was found that the chemical recalcitrance and the insolubility of the substrate imposed strong limitations on the reaction with the catalyst and that soluble product formation occurred predominantly via auto-hydrolysis. The propensity of cellulose to undergo auto-hydrolysis could be enhanced by amorphizing its crystal structure through mechanical pretreatment in ball-mill. A heterogeneously catalyzed hydrolysis was achieved through mechanocatalytic processes facilitated by the concerted ball-milling (CBM) of the sulfonated carbon with the substrate. Sulfonic acid groups were pinpointed as active sites during the mechanocatalytic formation of soluble oligosaccharides. The secondary hydrolysis to monosaccharides in the semi-batch reactor was no longer constrained by the insolubility of the substrate. The combination of CBM pretreatment and hydrolysis in the semi-batch reactor was successfully extrapolated to the conversion of spruce fir wood to achieve yields in C5 and C6 derived products that are competitive with state-of-the-art diluted acid processes.

AbstractGlobal biodiversity is eroding due to anthropogenic causes, such as climate change, habitat loss, and trophic simplification of biological communities. Most studies address only isolated causes within a single group of organisms; however, biological groups of different trophic levels may respond in particular ways to different environmental impacts. Our study used natural microcosms to investigate the predicted individual and interactive effects of warming, changes in top predator diversity, and habitat size on the alpha and beta diversity of macrofauna, microfauna, and bacteria. Alpha diversity (i.e., richness within each bromeliad) generally explained a larger proportion of the gamma diversity (partitioned in alpha and beta diversity). Overall, dissimilarity between communities occurred due to species turnover and not species loss (nestedness). Nevertheless, the three biological groups responded differently to each environmental stressor. Microfauna were the most sensitive group, with alpha and beta diversity being affected by environmental changes (warming and habitat size) and trophic structure (diversity of top predators). Macrofauna alpha and beta diversity was sensitive to changes in predator diversity and habitat size, but not warming. In contrast, the bacterial community was not influenced by the treatments. The community of each biological group was not mutually concordant with the environmental and trophic changes. Our results demonstrate that distinct anthropogenic impacts differentially affect the components of macro and microorganism diversity through direct and indirect effects (i.e., bottom‐up and top‐down effects). Therefore, a multitrophic and multispecies approach is necessary to assess the effects of different anthropogenic impacts on biodiversity.