The biorefinery concept is attractive. Increasing international concerns over issuessuch as climate change have led to political as well as social pressures for a shift fromfossil fuels to renewable resources and biomass is one abundant renewable resource.Biomass has the potential of supplying many of the fuels and chemicals which arecurrently dependent on petroleum. Much development is still needed in the field ofbiorefineries and a systematic approach to evaluate and compare process technologiesand to suggest optimizations seems necessary.The objective of this thesis is to develop entropy analysis as a possible evaluation toolfor optimization of biorefinery processes. This is a new application of entropyanalysis which is rarely discussed in the literature. The scientific basis of the entropyanalysis is described and the proposed methodology is explained. The position ofentropy analysis among other system analysis tools such as exergy analysis and lifecycle assessment is discussed along with entropy analysis earlier applications.A case study is introduced which is the IBUS (Integrated Biomass Utilization System)project in Denmark. The idea in IBUS is to integrate the biomass plant with a powerplant to utilize the surplus steam from the power plant for the internal use of thebiorefinery. The suggested method of entropy analysis is applied to this case study tocompare different processes for production of ethanol along with solid biofuel andanimal feed from Danish wheat straw. The evaluation is a gate to gate analysis inwhich production of energy carriers are also included in addition to biorefining ofwheat straw. A parallel life cycle assessment study with equivalent system boundariesis also carried out to compare the results with a conventional environmental systemsanalysis method.The results from the entropy analysis of the IBUS case study show that fermentationof C5 and C6 sugars by yeast is the most efficient process thermodynamically whilefermentation of only C6 sugars by yeast is the least efficient among the three casesstudied. Integration of the biorefinery with a coal fired CHP plant is identified as awise choice by the results of the entropy analysis method.For the IBUS process alternatives investigated in this study, the entropy results andthe LCA results (aggregated environmental load) are in correlation; entropy results areconsistent with weighting results based on two different weighting methods namelyEco indicator 99 and EPS 2000. Entropy generation is also in correlation withproduction cost for the processes analyzed in this evaluation. Another observation isthat cooling in the biorefining process contributes highly in the generation of entropy.This potential improvement option is not surfaced by the LCA conducted.The potential for further investigation and development of the tool is recognizedreflecting on some interesting observations in the results. Improvement of the tool ishighly possible for example by supplementing other implications of entropy inprocess design such as "waste potential entropy" concept which is developed as aneco-toxicity measure. / Uppsatsnivå: D

Solid oxide fuel cells (SOFCs) are high temperature (600C-1000C) composite metallic/ceramic-cermet electrochemical devices. There is a need to effectively manage the heat transfer through the cell to mitigate material failure induced by thermal stresses while yet preserving performance. The present dissertation offers a novel thermodynamic optimization approach that utilizes dimensionless geometric parameters to design a SOFC. Through entropy generation minimization, the architecture of a planar SOFC has been redesigned to optimally balance thermal gradients and cell performance. Cell performance has been defined using the 2nd law metric of exergetic efficiency. One constrained optimization problem was solved. The optimization sought to maximize exergetic efficiency through minimizing total entropy production while constraining thermal gradients. Optimal designs were produced that had exergetic efficiency exceeding 92% while maximum thermal gradients were between 219 C/m and 1249 C/m. As the architecture was modified, the magnitude of sources of entropy generation changed. Ultimately, it was shown that the architecture of a SOFC can be modified through thermodynamic optimization to maximize performance while limiting thermal gradients. The present dissertation highlights a new design methodology and provides insights on the connection between thermal gradients, performance, sources of entropy generation, and cell architecture.

La diminution de l'impact environnemental de l'industrie des transports par l'allégement des structures des véhicules passe par une utilisation accrue de matériaux à base de magnésium. Ces matériaux peuvent bénéficier d'un développement accéléré par le biais de simulations numériques s'appuyant sur des bases de données thermodynamiques. En ce qui concerne le système Al-C-Mg, les bases de données thermodynamiques commerciales sont incomplètes à cause du nombre insuffisant de données disponibles. Cette lacune est notamment synonyme de l'absence de guide dans l'identification des mécanismes régissant l'affinement de microstructures d'alliages Mg-Al par inoculation de carbone débattus dans la littérature. Par conséquent, l'objectif de cette étude a été d'aboutir à une évaluation thermodynamique complète du système ternaire Al-C-Mg. Dans un premier temps, une étude critique de la littérature concernant le système Al-C-Mg et ses sous-systèmes a été menée. Cette revue a mis en lumière des désaccords et des manques à propos des données relatives aux systèmes Al-C et Al-C-Mg. Dans un second temps, une démarche expérimentale basée sur l'utilisation de creusets scellés en Ta a été développée. La méthodologie mise en place est prometteuse puisqu'elle a permis de travailler avec le magnésium jusqu'à 2094 K (1821°C) et 41 bars de pression. Dans un troisième temps, la détermination expérimentale ainsi que par le calcul DFT de données relatives aux systèmes Al-C et Al- C-Mg a été entreprise. La capacité thermique ainsi que l'enthalpie et l'entropie standard de formation des carbures Al4C3 et T2-Al2MgC2 ont été obtenues. De plus, la structure cristallographique de la phase T2-Al2MgC2 a été confirmée par DRX sur monocristal, et la nature et la température de la décomposition invariante du carbure ternaire ont été déterminées. Dans un dernier temps, une modélisation CALPHAD des systèmes Al-C et Al-C-Mg a été conduite sur la base des données de la littérature sélectionnée de façon critique et de celles nouvellement obtenues. Des descriptions thermodynamiques cohérentes de la phase Al2MgC2, de la solution de Mg dans Al4C3 ainsi que du liquide Al-C-Mg ont été obtenues. Ces descriptions vont alimenter les bases de données thermodynamiques et vont favoriser le développement des alliages Mg-Al et des composites à matrice Mg-Al renforcés par des matériaux carbonés. Cette étude apporte un argument fort supportant le fait que la phase Al2MgC2 est responsable de l'affinement de microstructures d'alliages Mg-Al par inoculation de carbone / To reduce its environmental footprint by lightweight vehicles design, the transportation sector relies on an increased use of magnesium based materials. Computational approaches relying on the use of thermodynamic databases can enable the accelerated development of such materials. Commercial thermodynamic databases regarding the Al-C-Mg are unreliable due to a lack of data. As a result, no guidance can be provided regarding the underlying mechanisms of the grain refinement of Mg-Al alloys by carbon inoculation which are debated in the literature. Therefore, the purpose of this study was to provide a reliable thermodynamic assessment of the Al-C-Mg system. First of all, the literature regarding the Al-C-Mg system and its subsystems was critically reviewed. This review highlighted disagreements and shortages regarding the data related to the Al-C and Al-C-Mg systems. Secondly, an experimental procedure based on the use of sealed Ta crucibles was developed. This procedure is promising as it allowed working with magnesium up to 2094 K (1821°C) and 41 bars of pressure. Thirdly, experimental investigation and ab-initio calculations of data related to the Al-C and Al-C-Mg systems were conducted. The heat capacity as well as the standard enthalpy and entropy of formation of Al4C3 and Al2MgC2 were obtained. Furthermore, the crystal structure of Al2MgC2 was confirmed on the basis of single-crystal X-ray diffraction data, and the thermal stability of the ternary carbide was determined. Lastly, CALPHAD optimization of the Al-C and Al-C-Mg systems was conducted on the basis of the critically assessed literature data as well as of those freshly obtained. Self-consistent thermodynamic descriptions of Al2MgC2, (Al,Mg)4C3 as well as the Al-C-Mg liquid phase were obtained. Those descriptions will fuel the thermodynamic databases and will enable the development of Mg-Al alloys and Mg-Al matrix carbon materials reinforced composites. This study provides a convincing argument supporting the fact that Al2MgC2 is responsible for the grain refinement of Mg-Al alloys by carbon inoculation

<p>The purpose of this research has been to reassess the Ag-Mg system using the CALPHAD technique. Compared with previous assessments, we carry out the optimization by fitting calculations to the original data instead of second-hand information. Moreover, we use a two sub-lattice model and a four sub-lattice model based on compound energy formalism to simulate both first-order and second-order transformations between the FCC phase and the L1₂ phase. Undoubtedly, the CALPHAD technique has achieved a degree of maturity, but its deficiencies are regularly ignored.</p> <p>In this thesis, we develop an interval method based on Kantorovich’s idea to overcome the shortcomings of the CALPHAD technique. Both advantages and disadvantages of the interval method are discussed. We also present an example of the interval approach on thermodynamic optimization of the Ag-Mg melt. The results suggest that this method would be helpful as a pre-optimization tool.</p> / Master of Applied Science (MASc)

This thesis presents work on a holistic approach for improving the overall design of solar cooling systems driven by solar thermal collectors. Newly developed methods for thermodynamic optimization of hydraulics and control were used to redesign an existing pilot plant. Measurements taken from the newly developed system show an 81% increase of the Solar Cooling Efficiency (SCEth) factor compared to the original pilot system. In addition to the improvements in system design, new efficiency factors for benchmarking solar cooling systems are presented. The Solar Supply Efficiency (SSEth) factor provides a means of quantifying the quality of solar thermal charging systems relative to the usable heat to drive the sorption process. The product of the SSEth with the already established COPth of the chiller, leads to the SCEth factor which, for the first time, provides a clear and concise benchmarking method for the overall design of solar cooling systems. Furthermore, the definition of a coefficient of performance, including irreversibilities from energy conversion (COPcon), enables a direct comparison of compression and sorption chiller technology. This new performance metric is applicable to all low-temperature heat-supply machines for direct comparison of different types or technologies. The achieved findings of this work led to an optimized generic design for solar cooling systems, which was successfully transferred to the market.