Τα τελευταία χρόνια έχει δημιουργηθεί επιτακτική ανάγκη ανάπτυξης νέων μεθόδων για την παραγωγή ανανεώσιμων μορφών ενέργειας. Οι ενεργειακές απαιτήσεις που καλύπτονται από τα ορυκτά καύσιμα, τα οποία περιέχουν άνθρακα, έχει σαν αποτέλεσμα την αυξανόμενη απελευθέρωση CO2, γεγονός που ευνοεί το φαινόμενο του θερμοκηπίου και την όξινη βροχή. Η εξάρτηση λοιπόν από τις εξαντλήσιμες πηγές ενέργειας, αφού οι ποσότητες των ορυκτών καυσίμων είναι περιορισμένες, και η ρύπανση του περιβάλλοντος, αποτελούν κινητήριες δυνάμεις για την ανάπτυξη και εκμετάλλευση νέων εναλλακτικών μορφών ενέργειας. Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη, κατασκευή και υλοποίηση ενός αυτόνομου υβριδικού συστήματος παραγωγής υδρογόνου, ως μια ανανεώσιμη μορφή ενέργειας (ΑΠΕ), εκμεταλλευόμενο την πλεονάζουσα ενέργεια από ΑΠΕ. Το σύστημα περιλαμβάνει μια ανεμογεννήτρια και μια φωτοβολταϊκή γεννήτρια, οι οποίες αποτελούν τις κύριες ενεργειακές πηγές, ενώ μια υδρογονογεννήτρια (ηλεκτρόλυσης) χρησιμοποιείται για τη πλήρωση με υδρογόνο των φιαλών που περιέχουν μεταλλικά υδρίδια. Το αποθηκευμένο υδρογόνο των φιαλών τροφοδοτεί την κυψέλη καυσίμου τύπου PEM. Η παραγόμενη ηλεκτρική ενέργεια από το αποθηκευμένο υδρογόνο καλύπτει τις ανάγκες φορτίου τις ώρες αιχμής. Ως εξομοιωτής φορτίου χρησιμοποιήθηκε ρυθμιζόμενη ωμική αντίσταση ισχύος. Συγκεκριμένα στο 1° κεφάλαιο, «Τεχνολογία ΑΠΕ», γίνεται μία γενική αναφορά γύρω από τη διεσπαρμένη παραγωγή, τις ανανεώσιμες πηγές ενέργειας (ΑΠΕ) και το έντονο ενδιαφέρον που έχει παρατηρηθεί τα τελευταία χρόνια παγκοσμίως σε αυτόν τον τομέα. Εξετάζονται οι χρήσεις τους, τα πλεονεκτήματα - μειονεκτήματά τους και η κατάσταση που επικρατεί. Επίσης, παρουσιάζονται οι αρνητικές επιπτώσεις από τη καύση των υδρογονανθράκων, που αποτελούν κύρια πηγή ενέργειας τη σημερινή εποχή. Στο 2ο κεφάλαιο, «Ενέργεια υδρογόνου», γίνεται αρχικά μια σύντομη αναφορά στις ιδιότητες του υδρογόνου όσο και στις τεχνολογίες για την παραγωγή του, δίνοντας έμφαση στην παρασκευή μέσω της ηλεκτρόλυσης του νερού, αφού αυτή η μέθοδος θα χρησιμοποιηθεί. Στη συνέχεια γίνεται παρουσίαση των τρόπων μεταφοράς-διανομής και σύγκριση του υδρογόνου έναντι άλλων συμβατικών πηγών ενέργειας. Τέλος εξετάζονται οι κίνδυνοι που ενέχει ως καύσιμο και τα πλεονεκτήματα του έναντι των μπαταριών ως μέσο αποθήκευσης ενέργειας. Στο 3ο κεφάλαιο, «Αποθήκευση του υδρογόνου», γίνεται αναφορά σε όλες τις τεχνολογίες αποθήκευσης και δέσμευσης του υδρογόνου, όπως υγροποίηση σε πολύ χαμηλές θερμοκρασίες, αποθήκευση σε δοχεία υπό υψηλή πίεση και με εισχώρηση σε μεταλλικά υδρίδια. Συγκεκριμένα αναλύεται η χρήση προηγμένων υλικών (μεταλλικά υδρίδια) που είναι το αντικείμενο της παρούσας διπλωματικής εργασίας. Στο 4ο κεφάλαιο, «Κυψέλες καυσίμου», παρουσιάζεται η αρχή λειτουργίας των κυψελών καυσίμου. Ακολουθεί η διάκριση ανάλογα με τον τύπο του ηλεκτρολύτη που διαθέτουν καθώς και σύγκριση όλων των τύπων. Στη συνέχεια γίνεται αναφορά στην εμπορευματοποίησή τους ανάλογα τον τύπο τους και τέλος παρουσιάζονται οι εφαρμογές τους στη βιομηχανία. Στο 5ο κεφάλαιο, «Αυτόνομο υβριδικό υπό μελέτη σύστημα», γίνεται μια εισαγωγή στα υβριδικά συστήματα παραγωγής ενέργειας και στη συνέχεια ακολουθεί μια πιο λεπτομερής περιγραφή στα κύρια στοιχεία του συστήματος (γεννήτρια υδρογόνου, κυψέλη καυσίμου, αντίσταση φορτίου, φιάλες αποθήκευσης υδρογόνου και εναλλάκτης θερμότητας) που χρησιμοποιήθηκαν για τις ανάγκες της εργασίας. Παρακάτω περιγράφεται συνοπτικά η αρχή λειτουργίας ενός τέτοιου υβριδικού συστήματος. Εάν τα φωτοβολταϊκά και η ανεμογεννήτρια παράγουν αρκετή ισχύ, το σύστημα υποστηρίζεται εξολοκλήρου από αυτά. Στην περίπτωση που η ισχύς εξόδου τους ξεπερνάει την επιθυμητή, η πλεονάζουσα ισχύς μπορεί να χρησιμοποιηθεί για την παραγωγή Υδρογόνου, το οποίο μπορεί να αποθηκευτεί και να χρησιμοποιηθεί όταν υπάρξει ανάγκη, στις κυψελίδες καυσίμου. Σε περίπτωση χαμηλού ανέμου και ηλιοφάνειας, ένα μέρος της ισχύος μπορεί να συμπληρωθεί από την ενέργεια που προέρχεται από τις κυψελίδες καυσίμου. Προφανώς, σε τέτοια υβριδικά συστήματα ανεμογεννητριών φωτοβολταϊκών - κυψελίδων καυσίμου, σαν αυτά που μελετώνται στην παρούσα εργασία, οι κυψελίδες καυσίμου λειτουργούν με μεταβλητό ρεύμα. Τέτοιες κυψελίδες καυσίμου, ακόμα δεν διατίθενται στο εμπόριο. Στο τελικό στάδιο της Διπλωματικής εργασίας και συγκεκριμένα στο 6ο κεφάλαιο, «Επεξεργασία πειραματικών μετρήσεων», υπάρχουν τα αποτελέσματα των μετρήσεων με σχηματικές απεικονίσεις και ερμηνεία των διαγραμμάτων που προέκυψαν από τις πειραματικές μετρήσεις, καθώς και τα τελικά συμπεράσματα που προκύπτουν. Κατά την διάρκεια των πειραμάτων παρατηρήθηκε ότι το μεταλλικό υδρίδιο κατά την πλήρωση του με υδρογόνου αντιδρά εξώθερμα με συνέπεια να έχουμε αύξηση θερμοκρασίας στη φιάλη (μέγιστο 43 οC). Κατά την απελευθέρωση του υδρογόνου από τη φιάλη υπάρχει ενδόθερμη αντίδραση και ελάττωση της θερμοκρασίας της φιάλης (ελάχιστο -13.2 οC). Τα κυριότερα λοιπόν προβλήματα του συστήματος που παρατηρήθηκαν είναι τα παρακάτω: α) μεγάλες αυξομειώσεις θερμοκρασίας είχαν αρνητικές συνέπειες στην απόδοση του συστήματος β) η μέγιστη και ελάχιστη θερμοκρασία λειτουργίας υπερβαίνουν τα όρια θερμοκρασιών ομαλής λειτουργίας. Συνεπώς κρίθηκε απαραίτητο (συστήνεται από τον κατασκευαστή) να κατασκευαστεί ένα σύστημα ψύξης (εναλλάκτης θερμότητας) των φιαλών, ώστε να έχουμε όσο το δυνατόν πιο σταθερό εύρος θερμοκρασιών λειτουργίας του συστήματος και να αποφευχθούν τα παραπάνω μειονεκτήματα. Το εύρος θερμοκρασιών που επιτεύχθηκε με το σύστημα ψύξης είναι: ελάχιστο 10.3 οC - μέγιστο 29 οC. Επιπλέον διαπιστώθηκε πως με ίδιες αρχικές συνθήκες (φορτίο, πίεση φιάλης, κλπ.) κατά την λειτουργία με τον εναλλάκτη, η κυψέλη καυσίμου παρήγαγε την ίδια ισχύ άλλα για περισσότερη ώρα. Αυτό δεν σημαίνει πως έχουμε μεγαλύτερη ποσότητα υδρογόνου στην φιάλη, άλλα σταθεροποιώντας την θερμοκρασία, επιτυγχάνεται μια πιο ομαλή λειτουργία του συστήματος και κυρίως πιο σταθερή παροχή υδρογόνου στην κυψέλη καυσίμου, με αποτέλεσμα να αυξάνεται η απόδοση της. Με αυτό τον τρόπο βελτιώνεται η ταχύτητα απορρόφησης άλλα όχι και η ποσότητα του υδρογόνου που απορροφάται. / During the last years an urgent need to develop new methods for the production of renewable energy was created. The energy requirements covered by the fossil fuels, which contain carbon, result in the increase of the CO2 releases in the atmosphere, a fact that favors the greenhouse effect and acid rain. So the dependence on depletable energy sources like fossil fuels that are limited as well as the pollution of the environment, are driving forces for the development and exploitation of new alternative energies. This thesis deals with the design, construction and implementation of an autonomous hybrid system producing hydrogen as a renewable energy source (RES), exploiting the excess energy from RES. The system includes a wind turbine and a photovoltaic generator, which are the main energy sources, while a hydrogen generator (electrolysis) is used to fill the bottles with hydrogen containing metal hydrides. The bottles of stored hydrogen feeds fuel cell type PEM. The electricity generated from the stored hydrogen meets the needs of the load during peak hours. Simulator was used as load power adjustable resistor. Specifically, in chapter 1, "Technology RES" is a general discussion around the dispersed production, renewable energy sources (RES) and the strong interest that has been observed during the recent years worldwide in this field. As well this chapter considers the uses, advantages - and disadvantages of the situation. It also shows the negative impact from the combustion of hydrocarbons, which are the main source of energy today. In chapter 2, "Hydrogen Energy", as a start, a short report on the properties of hydrogen and technologies for its production, and it emphasizes on the production by electrolysis of water, since this method will be used. Then we present a modal distribution of hydrogen compared to other conventional energy sources. Finally we consider the risks of fuel and its advantages over batteries as energy storage is medium. In chapter 3, "Hydrogen Storage" we refer to all storage technologies and hydrogen binding as liquefaction at very low temperatures, storage containers under high pressure and penetration in metal hydrides. It specifically analyzes the use of advanced materials (metal hydrides) which is the subject of this thesis. In chapter 4, "Fuel Cells" the principle for the operation of fuel cells is presented. Here a distinction is made according to the type of electrolyte and features as well as comparison of all types. Then we refer to the commercialization according to their type and finally present their applications in industry. In chapter 5, "Autonomous hybrid system under study" we introduce to hybrid power systems, followed by a more detailed description of the main elements of the system (hydrogen generator, fuel cell, load resistance, hydrogen storage cylinders and heat exchangers) used for the needs of the job. After that, it summarizes the operating principle of such a hybrid system. If the solar panels and wind turbines generate enough power, the system is supported entirely by them. If the output power exceeds the desired, the excess power can be used to produce hydrogen, which can be stored and used when there is need, in fuel cells. In case of low wind and sunshine, a place of power may be supplemented by the energy from the fuel cells. Obviously, in such hybrid systems, solar wind - fuel cells, such as those studied in this paper, fuel cells operate at variable current. Such fuel cells, is not yet commercially available. In the final stage of the thesis and specifically in Chapter 6, "Processing experimental measurements", we present the results of measurements with the maps and interpretation of charts derived from experimental measurements, and the final conclusions drawn. During the experiments it was observed that the metal hydride during the filling with hydrogen reacts exothermically with the result to have an increase in temperature in the flask (43 ° C maximum). The release of hydrogen from the bottle is an endothermic reaction and it reduces the temperature of the bottle (minimum -13.2 ° C). So the main problems of the system observed are: a) The large temperature fluctuations had a negative impact on system performance b) The maximum and minimum operating temperatures exceed the temperature limits of normal operation. It was therefore necessary (recommended by manufacturer) to construct a cooling system (heat exchanger) for the bottles in order to have as far as possible stable operating range of the system and to avoid the above disadvantages. The temperature ranges that were achieved with the cooling system are: minimum 10.3 ° C and maximum 29 ° C. Furthermore it was found that with the same initial conditions (load, pressure bottle, etc.) during operation with the alternator, the fuel cell produced the same effect but for longer. This does not mean that we have a greater amount of hydrogen in the bottle, but by stabilizing the temperature, a more smooth operation of the system and especially more stable supply of hydrogen in the fuel cell is achieved, thereby increasing the performance. In this way, we improve the rate of absorption but not the amount of hydrogen absorbed.

Made available in DSpace on 2016-05-17T16:51:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-10-20. Added 1 bitstream(s) on 2016-05-17T16:55:28Z : No. of bitstreams: 1 000864141.pdf: 2474920 bytes, checksum: 0df8cf23c83271ed498848b27a4c4cdc (MD5) / Com a motivação existente pela necessidade de crescimento das novas fontes de energia alternativas, bem como pelos avanços das tecnologias para os sistemas de conversão de energia, o presente estudo propõe a utilização do conversor integrado três estados Buck-Boost monofásico para o aproveitamento da energia proveniente dos sistemas solares fotovoltaicos. Os sistemas de painéis fotovoltaicos fornecem tensões contínuas, contudo, a grande maioria de aparelhos ou cargas de uso domiciliar necessita de tensões alternadas, com valores eficazes nominais de 127 V ou 220 V, no Brasil. Isso leva à necessidade do estudo de estruturas conversoras CC-CA, conhecidas como inversores. Considerando que as tensões alternadas fornecidas pelos inversores encontram-se dependentes do valor máximo da tensão de entrada, é indispensável a inclusão de um estágio elevador no sistema geral, antes de fornecer energia para as cargas, resultando, assim, em uma redução no rendimento, devido à quantidade de componentes, ao aumento de peso e ao volume. Nesta dissertação, o inversor estudado realiza, em uma única estrutura, a função do estágio elevador ou redutor, garantindo níveis reduzidos de distorção harmônica na corrente injetada e tensão de saída no modo ilhado, com um bom rendimento, fornecendo energia para cargas conectadas em modo de operação ilhado ou conectado à rede. Neste conversor, o sistema de chaveamento de três estados proporciona uma melhora das características dinâmicas. A adição do terceiro estado simplifica o controle por modo tensão, na medida em que elimina o zero presente no semiplano direito da função de transferência do conversor Buck-Boost convencional. Para o desenvolvimento das estratégias de controle, adotou-se o modelo matemático por valores médios instantâneos, em espaço de estados. Adicionalmente, foi realizada uma revisão e avaliação de alguns dos algoritmos de MPPT (Maximum Power Point... / The current motivation of growing need for new alternative energy sources, as well as by improvements in technologies for energy conversion systems, this study proposes the use of the single-phase tri-states Buck-Boost integrated converter for the use of energy from solar photovoltaic systems. Photovoltaic systems provide DC voltages and, on the other hand, the large majority of machines or domestic use loads require alternating voltage with RMS values of 127 V or 220 V in Brazil. This points out to the need to study of DC-AC converter structures, known as inverters. Due to the limitation that the alternating voltage supplied by the inverters are dependent on the maximum value of the input voltage, the inclusion of an elevator stage in the general system is necessary, before providing power to the load, thus resulting in a reduction in the performance by the number of components, increased weight and volume. In this dissertation, the studied inverter performs, in a single structure, the functions of the elevator stage or reducer stage, also performs the continues in alternating voltage conversion function, ensuring reduced levels of harmonic distortion in the current injected to the main grid and the output voltage in islanding mode, with an increase performance in the output voltage, and that should provide power to loads connected in both modes islanding or grid connected. In the presented converter, the switching system of three states has improved the behavior of dynamic characteristics due to the addition of the third estate, simplifying the control by eliminating the zero present in the right half-plane of the transfer function of Buck-Boost inverter, controlled in voltage mode. For the development of control strategies is adopted the mathematical model for instantaneous average values. The modeling of the structure is made by the mean values method in the state spaces. Additionally, is carried out a review and assessment of some ...

This thesis describes the research undertaken to formulate a systematic chemical kinetic mechanism reduction scheme to generate compact yet comprehensive chemical kinetic models for diesel and biodiesel fuels, for multi-dimensional Computational Fluid Dynamics (CFD) applications. The integrated mechanism reduction scheme was formulated based on the appraisal of various existing mechanism reduction techniques. It consists of five stages including Directed Relation Graph (DRG) with Error Propagation method using Dijkstra’s algorithm, isomer lumping, reaction path analysis, DRG method and adjustment of reaction rate constants. Consequently, a single-component diesel surrogate fuel model with only 79 species (i.e. n-hexadecane (HXNv2)) and a multi-component biodiesel surrogate fuel model (i.e. methyl decanoate/methyl-9-decenoate/n-heptane (MCBSv2)) with only 80 species were successfully derived from their respective detailed mechanisms, which contain thousands of species and elementary reactions. Here, both auto-ignition and jet-stirred reactor (JSR) conditions were applied as the data source for mechanism reduction. An overall 97 % reduction in mechanism size in terms of total number of species as well as an average 97 % reduction in computational runtime in zero-dimensional (0-D) chemical kinetic simulations was achieved. Both HXNv2 and MCBSv2 were also comprehensively validated in 0-D simulations in terms of ignition delay (ID) timings and species concentration profiles. Good agreement between the predictions and measurements was obtained throughout the test conditions. Subsequently, HXNv2 and MCBSv2 were integrated into the OpenFOAM-2.0.x solver to simulate spray combustion in a constant volume combustion chamber. The simulation results were validated against the experimental data of no.2 Diesel Fuel (D2) for diesel combustion and Soy Methyl Ester for biodiesel combustion. It was found that MCBSv2 was able to capture the combustion and soot formation events reasonably well. However, further refinement on HXNv2 was essential to improve the complex soot formation predictions. Fuel blending was then suggested to match the diesel fuel kinetics and compositions. As a result, two different versions of multi-component diesel surrogate fuel models were produced in the form of MCDS1 (HXNv2 + 2,2,4,4,6,8,8-heptamethylnonane (HMN)) and MCDS2 (HXNv2 + HMN + toluene + cyclohexane). All the fuel constituent reduced mechanisms and the integrated mechanisms were extensively validated in 0-D simulations under a wide range of shock tube and JSR conditions. Successively, the fidelity of the multi-component diesel surrogate fuel models was evaluated in two-dimensional spray combustion simulations. The computations were compared with the experimental data of D2 fuel. MCDS1 was found to be useful for simulations with less aromatic chemistry effects. In contrast, MCDS2 was a more appropriate surrogate model for fuels with aromatics and cyclo-paraffinic contents. Following that, fidelity of MCDS2 and MCBSv2 was further assessed in three-dimensional internal combustion engine simulations. The performance of the surrogate models was compared under the same operating conditions in a light-duty, direct injection diesel engine. The computed peak pressure and heat-release rate for biodiesel combustion were lower than diesel owing to the advanced ignition timing. The soot formation of biodiesel was also found to be 1.4 times lower than diesel due to oxygenated effects. Overall, the integrated reduction scheme proves to be an attractive approach for large-scale mechanism reduction to reduce the computational time-cost as well as to expedite multi-dimensional CFD computations.

The depletion of fossil fuels and the increasing energy demand for energy has led to the search for better and improved technologies with special focus renewable energy, especially solar cells. The first generation solar cells based on silicon are expensive, hence dye sensitized solar cells come in as a better alternative as these solar cells are environmental friendly, they have moderately good conversion efficiency and they are relatively cheap to produce. Dithiocarbamate ligands have been widely used in many research fields, as these are versatile ligands. Coordination of dithiocarbamates with metals such as ruthenium has produced high conversion efficiency and have the ability to extend the MLCT absorptions, and this can further extend their wavelength. In this study five dithiocarbamate sodium salt ligands were prepared and were coded as FL1= Aniline, FL2= p- toluidine, FL3= p- anisidine, FL4=dibenzyl, FL5=diphenyl. These ligands were used to synthesize Ru(II) metal complexes which were formulated as [Ru(FLx)(dcbpy)(NCS)] and [Ru(FLx)2(dcbpy)] where FLx is the dithiocarbamate ligand and dcbpy is 2,2-bipyridine-4,4’-dicarboxylic acid and the complexes were coded as FCx. The synthesized compounds were characterized using techniques such as the melting point, molar conductivity, FT-IR and NMR spectroscopy. For spectroelectrochemical studies of the metal complexes, techniques such as UV-Vis and photoluminescence spectroscopy were carried out. Furthermore, redox properties of the complexes were analyzed using cyclic and square wave voltammetry. The FT-IR displayed all the expected peaks of interest both in the dithiocarbamate ligands and in the metal complexes. The electronic spectra confirmed the successful coordination of ligand to the metal centre, the electronic spectra of the complexes also confirmed the six coordinate octahedral geometry of the complexes. The complexes exhibited some photoluminescence properties that are suitable for dye sensitization. The cyclic voltammogram of the complexes displayed more reduction potentials that could be attributed to the π-conjugation in the ligands incorporated during synthesis. The square wave voltammogram of the complexes is in agreement with the results obtained in cyclic voltammetry.

Título original: Remoção de lignina e hemicelulose influencia na acessibilidade à celulose e digestibilidade enzimática / Orientador: Michel Brienzo / Banca: Fernanda Perpetua Casciatori / Banca: Jonas Contiero / Resumo: A biomassa lignocelulósica, como a proveniente da cana-de-açúcar, é uma fonte abundante de resíduo que pode ser usado como matéria-prima na produção de energia. Para melhor aproveitar essa biomassa, moagem e pré-tratamentos podem ser usados para alterar a estrutura do material lignocelulósico, remover lignina e hemicelulose, expondo a celulose e assim aumentando sua acessibilidade. A acessibilidade à celulose tem sido indicada como uma das propriedades mais importantes para uma boa digestibilidade enzimática. Entretanto, as biomassas geradas da cana-de-açúcar possuem características físico-químicas diferentes, respondendo de modo diferente aos pré-tratamentos. Neste contexto, este estudo teve como objetivo verificar os efeitos da remoção de lignina e hemicelulose das biomassas da cana-de-açúcar (fração externa, entrenó, nó e folha) na acessibilidade à celulose. A cana-de-açúcar foi fracionada em fração externa, nó, entrenó e folha. Cada fração passou pelos pré-tratamentos ácido (5, 10, 20 %, m/m massa de ácido por massa de material, a 121°C/30 min), alcalino (5, 10, 20 e 30 % NaOH m/m) e oxidativo (0,5, 1, 2 e 3 horas com clorito de sódio 30 %). As amostras foram caracterizadas quanto ao seu conteúdo de celulose, hemicelulose e lignina. A determinação de acessibilidade foi realizada com corantes Direct, Orange (superfície específica externa), Direct Blue (superfície específica interna) e Vermelho Congo (superfície total). A hidrólise enzimática (15 FPU/g de material, Cellic C... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The lignocellulosic biomass, such as the provided by the sugarcane, is an abundant source of raw materials for energy production. In order to better use this biomass, milling and pretreatments can be employed to alter the structure of the materials, remove lignin and hemicellulose. This effect exposes the cellulose and raises its accessibility, which is is one of the most important property to ensure enzymatic digestibility. However, the biomass generated from the sugarcane have different physicochemical characteristics, giving different responses to the pretreatments. In this context, this study aimed to verify the effects of lignin and hemicellulose removal from the sugarcane biomass (external fraction, node, internode and leaf) on cellulose accessibility. The sugarcane was fractioned in external fraction, node, internode and leaf. Each fraction was pretreated with acid (5, 10, 20 % m/m acid mass per material mass, at 121°C/30 min), alkaline (5, 10, 20, 30 % NaOH m/m) oxidative (0,5, 1, 2,3 h charged with 30 % sodium chlorite). The chemical composition of the samples was determined based on cellulose, hemicellulose and lignin contents. Accessibility was determined by dye adsorption of Direct Orange (external specific surface), Direct Blue (internal specific surface) and Congo Red (total surface). Enzymatic hydrolysis (15 FPU/g of biomass, Cellic Ctec 2 - Novozymes) was used to verify the effects of pretreatments and cellulose accessibility on the glucose yield. All studied... (Complete abstract click electronic access below) / Mestre

This research was established due to an increase of interest in renewable energy sources and utilisation of various wastes and biomass. Gasification is currently one of the most promising thermal-chemical conversion techniques for recovering energy from waste, and the pyrolytic behaviour of secondary refuse fuel (SRF) briquettes and biomass-derived fuels is the starting point for the process. The purpose of this study was to evaluate the pyrolytic characteristics of SRF briquettes and biomass materials, suggest a kinetic model for simulating the pyrolytic process and obtaining the kinetic parameters, and then predict the yield of volatile products in pyrolysis. Knowledge of the chemical composition, the thermal behaviour and the reactivity of SRF briquettes and their blends with other materials, such as biomass and plastic during pyrolysis is very important for the effective design operation of gasification units. The kinetics of the pyrolysis of simulated SRF briquettes, SRF briquettes and pulverised biomass samples was successfully modelled by a scheme consisting of two independent general order parallel reactions of the main components which were hemicellulose, cellulose, lignin and plastic. The kinetic parameters estimated through the model were comparable with those reported in the literature. In this research, activation energy values varied between 30 – 70 kJ/mol for lignin pyrolysis, 96 – 137 kJ/mol for hemicellulose and cellulose pyrolysis, and about 260 kJ/mol for plastic pyrolysis. Biomass has a very high volatile content. Adding biomass into SRF briquettes could increase the volatile yield. Increasing the plastic content of SRF briquettes could increase the volatile yield, the derivative thermogravimetric (DTG) peak height and the repeatability of pyrolysis. Inorganic component could shift the cellulose pyrolysis to a lower temperature and cause the hemicellulose pyrolysis and the cellulose pyrolysis highly overlapped, but it could have a positive effect by acting as catalysts and lower the activation energy in the pyrolysis of hemicellulose and cellulose. Molasses used as a binder could improve the DTG peak height and restrain the curve shifting effect of inorganic component on the hemicellulose and cellulose pyrolysis, but couldn’t restrain the lignin pyrolysis at low temperatures during the hemicellulose and cellulose pyrolysis. Molasses could restrain the effect of the lignin pyrolysis at high temperatures on the plastic pyrolysis. Mechanical biological treatment (MBT) process could highly improve the volatile yield and improve the DTG peak height of SRF briquettes.

An air source heat pump (ASHP) water heater is a renewable and energy efficient hot water heating technology. ASHP water heaters are fast gaining maturity in the South African market and in Africa at large due to their low energy consumption (about 67 percent lower than conventional geysers), relatively low installation and operation cost, their environmental friendly nature and possibly the ease to retrofit with the old inefficient technologies. Furthermore, ASHP water heaters make use of some of the most recent advancement in refrigeration technologies enhancing their performance through a wide range of weather conditions. However, residential ASHP water heaters which come at the tail of a series of highly sophisticated models still harbour primitive control designs. One of such control system is the intermittent (on/off) control whereby the ASHP unit responds to a temperature differential threshold rather than instantaneous temperature fluctuations. Unfortunately, this control method contributes to a rapid deterioration of the compressor and other actuators due to high starting current during transient states and partial loading. Capacity control is a better alterative as it offers a more reliable system’s performance as well as a better protection for the system components. However, the drawbacks of implementing such a technology on residential ASHP water heaters is the initial purchasing cost. We use a systematic approach in this research to circumvent the purchasing cost and complete redesign hysteresis. The first step was centered around a hypothetical analysis of the performance of the heat exchangers in a bid to uncover the weakness during the operation of a residential ASHP water heater. It was observed that at ambient temperatures above 22°C notably during summer and winter afternoons, water only harnesses about 75 percent of the total heat rejected. Furthermore, the actuators keep doing work for about 15-20 minutes even after the heat transfer process has ceased completely. Following these observations, a sequential flow algorithm was developed aimed at matching the consumption point to weather variables like ambient temperature and secondly to most efficiently synchronize actuator components for a better energy management. This novel control method can save up to 58 percent of energy compared to the conventional on/off method during summer afternoons and averagely 20 percent during the rest of the day. It also has the merit to be cost effective as it barely requires no component retrofitting.

This study shows a detailed report on the morphological, structural and optical properties of CdSe QDs synthesised by the hot injection method. Cadmium acetate dihydrate and Se powder were used as cadmium and selenide precursors, respectively. Various QD sizes were achieved by synthesizing in temperature range of 150ºC, 175ºC, 200ºC, 225ºC, 250ºC, 275ºC and 300ºC, respectively. The as synthesized QDs by the hot injection method were cross-examined for their morphological, structural and optical using HRTEM, FTIR, XRD, RS, and UV-Vis spectroscopy techniques respectively. FTIR analysis has revealed vibrations at 738, 738, 738, 738, 735, 735 and 733 cm-1 for the QDs synthesized at various temperatures of 150, 175, 200, 225, 250, 275, and 300℃, respectively. The presence of the above mentioned peaks confirms the presence of Cd-Se bond in our samples. XRD analysis of CdSe QDs revealed diffraction peaks at 2 angles of 16.66 , 25.20 , 34.77 , 40.9 , 45.39 and 49.1 for 150 17.4 , 25.22 , 34.85 , 41.7 , 44.45 and 47.5 for the QDs synthesized at various temperatures of 175 17.07 , 25.19 , 34.85 , 41.34 , 44.41 and 48.86 for 200 ; 16.34 , 25.20 , 34.76 , 40.6 , 44.74 and 49.48 for 225 ; 17.44 , 25.17 , 34.19 , 41.7 , 44.45 , 49.24 for 250 ; 16.70 , 25.16 , 34.85 , 40.32 , 45.1 and 49.1 7 for 275 ;and 17.35 , 25.18 , 35.13 , 41.63 , 45.7 , 49.48 for 300 . These XRD peaks relate to crystal planes of (100), (002), (102), (220), (103) and (112) which belong to hexagonal Wurtzite CdSe crystal structure. Additionally XRD analysis has revealed a general peak shift to higher 2 values was observed for CdSe QDs. HRTEM analysis showed that the synthesised CdSe QDs have a spherical shape and are monodispersed. Moreover, HRTEM analysis has revealed CdSe QDs modal crystallite size of 1.79 nm, 1.81 nm, 2.06 nm, 2.08 nm, 2.11 nm, 3.10 nm and 3.12 nm for the QDs synthesized at various temperatures of 150ºC, 175ºC, 200ºC, 225ºC, 250ºC, 275ºC and 300ºC, respectively. HRTEM results were in mutual agreement with XRD results. Additionally, the SAED images showed intense electron diffraction rings, which confirmed that the as-synthesised CdSe QDs have a Wurtzite crystal structure. RS analysis showed that CdSe QDs have LO and 2LO vibrational modes which are characteristic peaks for CdSe. The presence of these peaks in Raman spectra further supports our previous observation from XRD analysis and HRTEM analysis that the synthesized CdSe QDs have a Wurtzite crystal structure. The effect of synthesis temperature Raman peak shift, FHWH and peak intensity has been cross examined in this work, Moreover, the effect of increasing temperature on the peak shift, FWHM and peak intensity is discussed in detail below. UV-Vis analysis revealed an absorbance of CdSe QDs in higher wavelengths as temperature was increased. Furthermore, the Yu et al 2003 relation was used to calculate QD size and band gap energy of CdSe QDs. The results showed that QD size increases with increasing synthesis temperature, which is in agreement with HRTEM and XRD results.

Little is known about the impact of marine renewable energy installations upon the marine environment and those who use it. Harnessing marine energy will involve the offshore siting of energy extraction devices and their associated infrastructure. This will alter the local environment and substantially modify use and access for a variety of marine stakeholders, potentially leading to conflict. Using the Ecosystem Approach (EA) as a conceptual framework, this thesis aimed to answer the question: What is the potential for conflict between the marine renewable energy industry and marine stakeholders, and how can this be mitigated? The research consisted of three components which used a variety of methods: i) stakeholder identification through a review of the literature and use of a novel interactive mapping method; ii) an investigation of the potential consequences for the priority stakeholder which used a mail survey and in-depth interviews; and iii) an exploration of potential mitigation which used ecosystem modelling. The stakeholder most likely to be affected by marine renewable energy device (MRED) deployment was the fishing industry. Potential consequences included: navigation and safety hazards, loss of access and alternative employment. Further exploration revealed that a loss of livelihood was the all-encompassing concern for fishers, and that skills shortages (transferable skills) may mean that should a loss of livelihood occur there may not be acceptable alternative employment. The modelling exercise indicated that it is not currently possible to definitively predict whether any opportunities which may be created by MRED installation will mitigate any negative effects, and that exclusion zones may actually decrease catches for most fleets. The findings of this study have implications for ‘conflict-free’ development of the marine renewable energy industry. To address this, several policy recommendations were offered as regards to operationalising the EA in terms of marine renewable energy.

Beach‐cast kelp (principally Laminaria spp.), known as macroalgal wrack, has been suggested as a feedstock for biofuel. However, to be extracted sustainably it is necessary to understand its ecological role and predict the impacts of its removal. Field‐based observations combined with food web modelling were used to predict the ecosystem effects of removing wrack from beaches of the Uists, western Scotland. Beaches with wrack were associated with enriched benthic infauna (polychaetes) on the lower shore, and wrack mounds supported abundant macroinvertebrates (mainly Diptera larvae and oligochaetes); with some of the highest biomasses reported globally for beaches. These fauna are valuable prey to shorebirds, as demonstrated by a strong positive relationship (R2 = 0.82) between wader abundances and the percentage cover of wrack on beaches. Inshore, drifting macroalgae was associated with elevated abundances of detritivorous hyperbenthic fauna (mysids, isopods and gammarid amphipods). In addition, the volume of drifting macroalgae inshore was a significant predictor (along with physical beach characteristics) for the abundance of decapods and fish. Food web models and network analysis indicated that beaches which accumulate wrack had a greater diversity of trophic links and more functional redundancy, making their food webs more resilient to perturbations. Such perturbations may include stressors induced by climate change, such as increased erosion of sediments during storms, elevated atmospheric and sea surface temperatures and elevated CO2 concentrations. Model simulations of wrack harvesting predicted an immediate decline in primary consumers in direct proportion to the quantity of wrack removed, and a slow decline in shorebirds in response to reduced prey. Primary consumers were predicted to recover to their pre‐harvest biomasses within 1 to 2 years regardless of harvesting intensity, but recovery times for shorebirds were an order of magnitude longer, and increased with harvesting intensity. Harvesting more than 50% wrack predicted a ‘collapse’ in wader populations within 25 years, and recovery times of 45‐60 years were estimated if >70% wrack was removed. The findings of this thesis suggest wrack provides essential food and shelter to coastal fauna, and its large‐scale removal would have significant negative impacts to the ecosystem functioning.