Cette étude concerne la compréhension des mécanismes de transfert de chaleur et le développement d’un système de stockage pour la valorisation de la chaleur fatale industrielle. L’utilisation de Matériaux à Changement de Phase (MCP) permet d’atteindre une densité énergétique élevée et de restituer la chaleur à température constante. Cependant, leur faible conductivité thermique impose d’améliorer les transferts thermiques, notamment par l’utilisation d’échangeurs à surface augmentée. Le but est de comprendre le comportement de tels échangeurs en régime transitoire au contact de MCP. Une étude expérimentale à basse température, où quatre échangeurs de type tube-calandre ont été testés avec différentes orientations (horizontale/verticale) et injections (haut/bas), a mis en évidence des phénomènes de transfert thermique importants, comme la convection naturelle à la charge et la contraction volumique à la décharge. Ces observations ont été validées par un modèle CFD tridimensionnel. Une méthode de comparaison des performances basée sur un calcul d’énergie par le biais d’un maillage expérimental est proposée et permet de sélectionner un échangeur selon les critères de densités énergétiques, de temps caractéristique et de coût. Trois MCP, envisagés pour l’application, ont alors été testés à température réelle (100-200 °C) au contact d’un échangeur tube inox à ailettes transverses en aluminium pour évaluer leur cyclabilité et comparer leur comportement. Le mélange de sels, H105 (Tfusion = 122 °C), n’est pas retenu pour l’application à cause de sa faible densité énergétique (≈ 56 kWh/m3) et sa plage de fusion trop étalée. L’acide sébacique (Tfusion = 132 °C) a un comportement répétable au cours des cycles et une densité énergétique plus élevée (≈ 66 kWh/m3). L’alcool de sucre, l’érythritol (Tfusion = 118 °C), présente de bonnes thermo-physiques (128 kWh/m3) mais la maîtrise de sa cristallisation est un point clé pour l’utiliser en tant que MCP. / This PhD thesis deals with the understanding of the heat transfer mechanisms and with the development of thermal energy storage system for the industrial waste heat recovery application. The use of Phase Change Materials (PCM) is attractive for its high storage density and its possibility to deliver heat at constant temperature. However, the PCM low thermal conductivity leads to develop heat transfer improvement methods, such as heat exchangers with increased heat transfer surface. The goal is to characterize the behavior of such heat exchangers An experimental study, where four several heat exchangers have been tested with different orientations (horizontal/vertical) and injection types (upward/downward), highlighted the impact of natural convection during the melting process and the volume contraction one during the solidification. These results have been validated through a 3D numerical model. A performance comparison method based on an energy calculation through an experimental mesh is proposed and enables to select a heat exchanger on criteria such as the storage density, the characteristic time and the cost. Three PCM, adapted to our application, have been tested at the intended temperature (100-200 °C) by integrating them into a storage system made of a stainless steel tube with aluminum circular fins. Their ability to resist to repeated cycles has been assessed and their behavior has been compared. The salts mixture, H105 (Tmelting = 122 °C), is not selected for the application because of it low storage density (≈ 56 kWh/m3) and its large melting area. The sebacic acid (Tmelting = 132 °C) has a repeatable behavior with cycles and a higher storage density (≈ 66 kWh/m3) and is appropriate as storage material. The sugar alcohol, erythritol (Tmelting = 118 °C), has good thermo-physical properties (128 kWh/m3) but the crystallization control is a key point to use it as a PCM.

The focus of this thesis work was the development of an approachto couple a previosly existing Thermal Energy Storage (TES) modelwritten in C++ with a Simulink/Simscape plant model to simulate anAdvanced Adiabatic Compressed Air Energy Storage (AA-CAES) plant.After the creation and validation of such tool, the complete modelwas used to run simulations, with the aim of assessing the AA-CAESplant's performance under multiple patterns of charge anddischarge.Most of the works found in the literature only provide values ofstorage efficiency obtained from analytical approaches, whilethose that use simulation tools provide average values ofefficiencies when the plant is performing a series of identicalcycles of charge and discharge. During this thesis project,instead, simulations were performed for consecutive irregularcycles determined as the plant response to the electric grid powerrequest. The average efficiency values obtained provide thereforea better representation of how the plant would perform in realapplications.The results show that, under the assumptions made, the AA-CAESplant's overall storage efficiency is influenced very weakly byalterations of the charge-discharge patterns, and that goodperformances can be expected not only for identical chargedischargeconsucutive cycles, but for any pattern that observesthe cavern pressure limits, as long as the thermal energy storageis sized wisely.In addition, a sensitivity analysis was performed in order toassess the influence of turbomachinery efficiency on overallstorage efficiency, for a specified plant layout. The results showthat the turbine efficiency is the most affecting parameter to theplant's performance, while the impact of the main compressors'sinefficiency is mitigated by the thermal recovery that takes placein the TES.The present work confirms that AA-CAES is a promising technologyand that storage efficiencies above 70% can be achieved even inrealistic production scenarios.Finally, future steps for more accurate simulations of plants'performances and more detailed energy production scenarios areproposed.MSc ET 18007Examinator: Joakim WidénÄmnesgranskare: Ane HåkanssonHandledare:

Examining methods for controlling the electricity demand in Kuwait was the main objective and motivation of this researchp roject. The extensiveu se of air-conditioning for indoor cooling in office and large commercial buildings in Kuwait and the Gulf States represents a major part of the power and electricity consumption in such countries. The rising electricity generation cost and growing rates of consumption continuously demand the construction new power plants. Devising and enforcing Demand-SideM anagemen(t DSM) in the form of energye fficient operations trategies was the response of this research project to provide a means to rectify this situation using the demand-side management technique known as demand levelling or load shifting. State of the art demand-sidem anagementte chniquesh ave been examined through the developmenot f a model basedp redictive control optimisations trategyf or an integrateda ndm odulara pproachto the provisiono f ice thermals torage. To evaluate the potential of ice-storage assisted air-conditioning systems in flattening the demand curve at peak times during the summer months in Kuwait, a model of a Heating, Ventilation, and Air-conditioning (HVAC) plant was developed in Matlab. The model engaged the use of model based predictive control (MPQ) as an optimisation tool for the plant as a whole. The model with MPC was developed to chose and decide on which control strategy to operate the integrated ice-storage HVAC plant. The model succeeded in optimising the operation of the plant and introduced encouraging improvement of the performance of the system as a whole. The concept of the modular ice-storage system was introduced through a control zoning strategy based on zonal orientation. It is believed that such strategy could lead to the modularisation of ice-storage systems. Additionally, the model was examined and tested in relation to load flattening and demonstrated promising enhancement in the shape of the load curve and demonstrated flattened demand curves through the employed strategy. When compared with measured data from existing buildings, the model showed potential for the techniques utilised to improve the load factor for office buildings.

Made available in DSpace on 2014-12-17T14:58:19Z (GMT). No. of bitstreams: 1 PedroSGM_DISSERT.pdf: 2326508 bytes, checksum: 0470d41afc69c7b0199856916c484045 (MD5) Previous issue date: 2012-12-17 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Cada vez mais o mundo est? adotando uma matriz energ?tica limpa e sustent?vel, com o uso da agricultura para produ??o de agroenergia e combust?veis verdes, como bioetanol e biodiesel. A produ??o do biodiesel gera um coproduto, a glicerina, em que as usinas produtoras t?m dificuldades com o destino do seu excedente. V?rias pesquisas est?o sendo desenvolvidas para nortear diferentes usos do glicerol (glicerina pura). O glicerol possui total solubilidade com a ?gua e pode ser usado como aditivo anticongelante aplicado como fluido refrigerante secund?rio, em sistemas de refrigera??o indireta e com termoacumula??o. Tamb?m, o glicerol ? uma mat?ria-prima alternativa na produ??o de propilenoglicol, um ?lcool de grande aplicabilidade industrial inclusive como anticongelante. Por?m, o melhor ?lcool anticongelante ? o etilenoglicol, um ?lcool t?xico derivado do petr?leo. As solu??es ?gua-glicerol (AG) e ?gua-propilenoglicol (AP) possuem propriedades termof?sicas de qualidade inferior e desequilibradas se comparadas ?s solu??es ?gua-etilenoglicol (AE). Desta forma, esta pesquisa inovadora teve como prop?sito o desenvolvimento e a caracteriza??o de solu??es tern?rias ?gua-glicerol-propilenoglicol (AGP) como fluidos secund?rios, com propriedades termof?sicas desej?veis e competitivas com as solu??es ?gua-etilenoglicol. Equa??es preditivas simplificadas foram usadas para prever o comportamento das solu??es AGP, onde as seguintes propriedades termof?sicas foram avaliadas e estimadas teoricamente: ponto de congelamento, massa espec?fica, calor espec?fico e condutividade t?rmica. As concentra??es para definir o ponto de congelamento das solu??es AGP foram definidas a partir da Lei de Raoult das propriedades coligativas. A an?lise matem?tica inicial mostrou que as solu??es AGP possuem propriedades mais equilibradas que as solu??es AG e AP e competitiva com a solu??o AE. A comprova??o experimental das solu??es AGP foi feita a partir de ensaios para verificar suas propriedades (massa espec?fica, condutividade t?rmica e viscosidade din?mica), comparando com as solu??es de refer?ncia AG e AP. Os resultados experimentais comprovaram as expectativas iniciais e viabilidade t?cnica do novo fluido secund?rio tern?rio. A grande vantagem dos fluidos AGP ? que s?o at?xicos e derivam de fontes renov?veis

Atualmente é de complexa equalização o problema advindo da elevação da demanda energética e das ações antrópicas que corroboram para o aquecimento global e, neste sentido, apesar de o Brasil ser abundante em hidroeletricidade, há ainda um grande espaço para o uso de outras fontes renováveis de energia, como a biomassa residual. Na indústria, projetos de adoção de novos e eficientes processos para a redução da carga térmica, bem como o uso de biomassa e de biogás das estações de tratamentos de efluentes podem ser um diferencial no conjunto de soluções para o dilema energético-ambiental, uma vez vão ao encontro dos objetivos das políticas energéticas globais em vigência, as quais pregam a segurança e sustentabilidade. Porém, verifica-se que tais medidas ainda têm sido desprezadas por muitas empresas, pois os investimentos são ainda muito elevados, ressaltando-se ainda que, talvez por não se entender como esses projetos podem internalizar as externalidades positivas que os acompanham, essas empresas seguem alheias aos benefícios socioambientais e econômicos advindos dos créditos de carbono, que podem compensar os altos investimentos realizados em racionalização energética. Desta maneira, essa dissertação analisa a viabilidade econômica da implantação de projetos de substituição de combustíveis fósseis por biomassa renovável para geração de vapor de processos; de uso de biogás de ETEs para geração de eletricidade e de implementação de tecnologias para a redução do consumo de vapor industrial, com foco em cervejarias, considerando-se nas análises econômico-financeiras os créditos de carbono recebidos pelas reduções de emissões de gases de efeito estufa. Pelas análises de cenários, verificou-se que quando as medidas de eficiência energética reduzirem pelo menos 5% da demanda energética, com um custo de energia de pelo menos R$ 187,50/MWh, bem como reduções de consumo de energia acima de 10%, com custo energético mínimo de R$ 122,50/MWh, e preço de das RCE acima de 5,00, os projetos mencionados são viáveis, e as receitas dos créditos podem internalizar as externalidades positivas desses projetos, compensando os investimentos. / Nowadays it´s quite complex to solve the problem between energy demand growth and the human activities, which have negative, widespread effects on the global climate. In this sense, apart from the fact that Brazil adopts massivelythe hydropower, there is a large potential for the use of renewable energy sources, as biomass. In process industries, techologies for reducing thermal energy consumption associated with the use of the sustainable biomass and biogas from wastewater treatment systems can be one among other solutions for equalizing the energy-environment dilemma, also targeting the prorrogatives of the current global policies on safety and sustainable energy sypply. Anyway, such measures have still been left aside by many industries, because it´s still not properly understood regarding the way these projects can internilize their positive externalities, some enterprises keep distant from the social, economic and environmental beneffits that carbon credit projects can bring up to help them in succeeding and rationalizing energy consumption. This dissertation evaluates and assesses the economic viablitity of projects of fuel switch (from fossil fuels to renewable biomass); use of biogas from industrial wastewater treatment systems and also the implementation of technologies and processes for reducing steam comsumption, focusing on breweries. By means of economic sceneries, it´s shown that the revenues from carbon credits can significantly have positive impacts, while financial incentives, on the decision making process towards the carrying and dissemination of such projects. As demonstrated in this work, the RCE, if required in the sceneries analysed, can bring the cash flows whithin brewery IRR expectations. Hence, the model showed that when measures of energy afficiency achieve at least 5,0% with the price of energy saved is of at least R$187,50/MWh, and for measures above 10% and energy is bought at prices higher then R$ 122,50/MWh, all projects with CER prices above 5,00 viable, and can be conducted. Also, the revenues from carbon credits can make industries wake up for the fact that they can internalize the positive externalities of these projects, once the high investiments can be compensated by their carbon offsets.

Recently, the supercritical carbon dioxide (s-CO2) Brayton cycle has been identified as a promising candidate for solar-thermal energy conversion due to its potentially high thermal efficiency (50%, for turbine inlet temperatures of ~ 1000 K). Realization of such a system requires development of solar receivers which can raise the temperature of s-CO2 by over 200 K, to a receiver outlet temperature of 1000 K. Volumetric receivers are an attractive alternative to tubular receivers due to their geometry, functionality and reduced thermal losses. A concept of a ceramic pressurized volumetric receiver for s-CO2 has been developed in this work. Computational Fluid Dynamics (CFD) analysis along with a Discrete Ordinate method (DOM) radiation heat transfer model has been carried out, and the results for temperature distribution in the receiver and the resulting thermal efficiency are presented. Issues regarding material selection for the absorber structure, window, coating, receiver body and insulation are also addressed. A modular small scale prototype with 0.5 kWth solar heat input has been designed. The design of a small scale s-CO2 loop for testing this receiver module is also presented in this work. There is a lot of ongoing investigation for design and simulation of different configurations of heat exchangers and solar receivers using s-CO2 as the working fluid, in which wall temperatures up to 1000 K are encountered. While CO2 is considered to be transparent as far as solar radiation spectrum is concerned, there may be considerable absorption of radiation in the longer wavelength range associated with radiation emission from the heated cavity walls and tubes inside the receivers. An attempt has been made, in this study, to include radiation modelling to capture the effect of absorption bands of s-CO2 and the radiative heat transfer among the equipment surfaces. As a case study, a numerical study has been performed to evaluate the contribution of radiative heat transfer as compared to convection and conduction, for s-CO2 flow through a circular pipe. The intent is to provide a guideline for future research to determine the conditions for which radiation heat transfer modelling inside the pipe can be significant, and what errors can be expected otherwise. The effect of parameters such as Reynolds number, pipe diameter, length to diameter ratio, wall emissivity and total wall heat flux has been studied. The effect of radiation modelling on wall temperatures attained for certain amount of heat flux to be transferred to s-CO2 is also studied. The resulting temperature distribution, in turn, affects the estimation of heat loss to the environment

Comme les autres technologies liées aux énergies renouvelables, le solaire à concentration souffre des problèmes liés à l’intermittence de la ressource. La technologie thermocline est une solution prometteuse qui réduirait le coût du stockage thermique dans les centrales solaires de ce type. Cependant, aucune étude n’a jusqu’ici porté sur l’impact de la variation de la température en sortie du réservoir de stockage de type thermocline sur les autres composants de la centrale. Ce travail de thèse a pour but d’améliorer les connaissances sur ce sujet, grâce à l’utilisation d’une mini boucle solaire cylindro parabolique intégrant un stockage thermocline.En premier lieu, la compatibilité entre le fluide de transfert de la centrale (huile synthétique) et les potentiels matériaux de garnissage de la cuve de stockage (Cofalit, briques de cendres volantes, alumine) est vérifiée. Puis les performances de chacun des composants de la centrale (cuve de stockage, collecteurs solaires, générateur de vapeur) sont analysées expérimentalement et numériquement. Enfin, le comportement du système global est étudié, avec un accent porté sur l’impact de la variation de la température de sortie de la cuve thermocline sur les autres composants.Il a été montré qu’avec un dimensionnement et une stratégie de contrôle appropriés, la technologie thermocline diminue très peu les performances de la centrale solaire par rapport à la technologie conventionnelle à deux cuves (maximum 3 4 % de diminution de la production électrique). / Like other renewable energy technologies, concentrated solar power (CSP) suffers from resource intermittence. Thermocline technology is a promising solution to decrease cost of thermal energy storage in CSP plants. Thermocline behavior has thoroughly been studied in the past years and its behavior is considered well known. However no study treated of thermocline tanks integrated in CSP plants. Thus, the impact of the varying outlet temperature of the thermocline storage has not been assessed yet. This work aims to fill this lack of knowledge by studying a mini parabolic trough power plant integrating a thermocline tank as storage.First, the compatibility between the heat transfer fluid of the plant (synthetic oil) and various potential filler materials (Cofalit, coal fly ash bricks, alumina) of the storage tank is verified. Then, some performance studies are performed on the three main components of the power plant (energy storage tank, solar collectors, steam generator). Finally, the behavior of the whole system is assessed, with a focus on the impact of the varying fluid temperature at the outlet of the thermocline tank on the other components.It has been shown that, with a proper sizing and an appropriate control strategy, thermocline technology induces very low decrease of the solar power plant performance in comparison to the conventional two tank technology (maximum 3-4% of electrical power production difference).

Convaincu de l’intérêt et du potentiel des matériaux naturels et des déchets industriels, cette thèse a contribué à la mise au point de matériaux de stockage de la chaleur (TESM) pour les CSP en Afrique de l’Ouest. Plus spécifiquement, ce travail de recherche a porté sur la valorisation de la latérite du Burkina Faso, des cendres de foyer des centrales à charbon de la société SONICHAR au Niger, des résidus en carbonate de calcium (chaux) de l’industrie de production de l’acétylène au Burkina Faso et l’huile végétale de Jatropha curcas de la société Belwet au Burkina Faso. Les résultats de cette étude ont permis de montrer que l’huile de Jatropha curcas peut être considérée comme une alternative viable aux fluides de transfert et aux TESM conventionnels pour les CSP fonctionnant à 210 °C. Les matériaux élaborés à partir des cendres de foyer et de la latérite présentent un caractère réfractaire en raison de la présence de mullite et de spinelle. L’ajout de chaux permet de réduire le point de fusion tout en préservant le caractère réfractaire et conducteur des phases obtenues. En raison de leurs stabilités, et l’absence de conflit d'utilisation, les matériaux obtenus peuvent être utilisés comme TESM dans CSP à des températures allant jusqu’à 900 °C. / Convinced of the interest and potential of natural materials and industrial waste, this thesis has contributed to the development of heat storage materials (TESM) for CSPs in West Africa. More specifically, this research focused on the valorization of laterite from Burkina Faso, the bottom ashes from the coal-fired power plants of SONICHAR in Niger, residues of calcium carbonate (lime) from the acetylene in Burkina Faso and the vegetable oil of Jatropha curcas from the company Belwet in Burkina Faso. The results of this study showed that Jatropha curcas oil can be considered as a viable alternative to conventional HTF and TESM for CSP operating at 210 °C. The materials elaborated from bottom ashes and laterites present a refractory character due to the presence of mullite and spinel. The addition of lime makes it possible to reduce the melting temperature while preserving the refractory and conductive character of the obtained phases. Due to their stabilities, and the absence of conflict of use, the obtained materials can be used as TESM in CSP at temperatures up to 900 °C.

Continued emission of green house gases has energized research activity worldwide to develop efficient ways to harness renewal energy. The availability of large scale energy storage technologies is essential to make renewal energy a reliable source of energy. Redox flow batteries show potential in this direction. These batteries typically need expensive membranes which need replacement be-cause of fouling. The recently proposed soluble lead redox flow battery (SLRFB), in which lead ions deposit on electrodes in charge cycle and dissolve back in discharge cycle, can potentially cut down the cost of energy storage by eliminating membrane. A number of challenges need to be overcome though. Low cycleability, residue formation, and low efficiencies are foremost among these, all of which require an understanding of the underlying mechanisms. A model of laminar flow-through SLRFB is first developed to understand buildup of residue on electrodes with continued cycling. The model accounts for spatially and temporally growing concentration boundary layers on electrodes in a self consistent manner by permitting local deposition/dissolution rates to be controlled by local ion transport and reaction conditions. The model suggests controlling role for charge transfer reaction on electrodes (anode in particular) and movement of ions in the bulk and concentration boundary layers. The non-uniform current density on electrodes emerges as key to formation of bare patches, steep decrease in voltage marking the end of discharge cycle, and residue buildup with continuing cycles. The model captures the experimental observations very well, and points to improved operational efficiency and decreased residue build up with cylindrical electrodes and alternating flow direction of recirculation. The underlying mechanism for more than an order of magnitude increase in cycle life of a beaker cell battery with increase in stirrer speed is unraveled next. Our experiments show that charging with and without stirring occurs identically, which brings up the hitherto unknown but quite strong role of natural convection in SLRFB. The role of stirring is determined to be dislodgement/disintegration of residue building up on electrodes. The depletion of active material from electrolyte due to residue formation is offset by “internal regeneration mechanism”, unraveled in the present work. When the rate of residue formation, rate of dislodging/disintegration from electrode, and rate of regeneration of active material in bulk of the electrolyte becomes equal, perpetual operation of SLRFB is expected. The identification of strong role of free convection in battery is put to use to demonstrate a battery that requires stirring/mixing only intermittently, during open circuit stages between charge and discharge cycles when no current is drawn. Inspired by our experimental finding that the measured currents for apparently diffusion limited situations (no external flow) are far larger than the maxi-mum possible theoretical value, the earlier model is modified to account for natural convection driven by concentration gradient of lead ions in electrolyte. The model reveals the presence of strong natural convection in battery. The induced flow in the vicinity of the electrodes enhances mass transport rates substantially, to the extent that even in the absence of external flow, normal charge/discharge of battery is predicted. The model predicted electrochemical characteristics are verified quantitatively through voltage-time measurements. The formation of flow circulation loops driven by electrode processes is validated qualitatively through PIV measurements. Natural convection is predicted to play a significant role in the presence of external flow as well. The hitherto unexplained finding in the literature on insensitivity of charge-discharge characteristics to electrolyte flow rate is captured by the model when mixed mode of convection is invoked. Flow reversal and wavy flow are predicted when natural convection and forced convection act in opposite directions in the battery. The effect of the presence of non-conducting material (PbO on anode) on the performance of SLRFB is studied using a simplified approach in the model. The study reveals the presence of charge coup de fouet phenomenon in charge cycle. The phenomenon as well as the predicted effect of depth of discharge on the magnitude of charge coup de fouet are confirmed experimentally.

Par rapport aux ressources énergétiques fossiles combustibles, l’énergie solaire présente des caractéristiques inhérentes à la nature même de la ressource. Ce constat met en évidence la nécessité de système de stockage d’énergie. Ce travail de thèse consiste à étudier un stockage thermique pour une centrale solaire à concentration, ainsi que ses deux composants essentiels : le fluide de transfert et les matériaux de garnissage solides. La compréhension du système de stockage thermocline sur lit de roche est réalisée grâce à une approche expérimentale et numérique. Une alternative innovante sur le choix du fluide de transfert consiste à utiliser des huiles végétales. Concernant le garnissage, un matériau à géométrie contrôlée est développé à partir d’un coproduit issu de la sidérurgie. L’originalité de cette association pour le stockage thermique permet d’allier performance, disponibilité des matériaux en quantité industrielle tout en réduisant l’impact environnemental et financier. / Compare to fossil fuel energy resources, solar energy presents the inherent characteristic given by the very nature of the resource (intermittent availability). This observation highlights the need for thermal energy storage system. This doctoral thesis studies thermal energy storage for concentrating solar power plant, as well as its two essential components: the heat transfer fluid and the thermal energy storage materials. The analysis of the thermocline storage system with filler materials is achieved through experimental and numerical approaches. An innovative alternative for the heat transfer fluid consists to use vegetable oils, which offers comparable thermal properties and operating behavior to conventional thermal fluid. Regarding thermal energy storage materials, many natural and recycled materials can be used. A storage material with controlled geometry is developed from steel industry co-product. The originality of this combination for thermal energy storage combines performance, materials availability at industrial scale while reducing environmental and financial impact.