Dissertations / Theses on the topic 'Power to Fuels'

With the issue of the rise of anthropogenic CO2, global warming and rise of the primary energy demand, strong measures for the energy transition and the diversification with renewables and existing fossil-based infrastructure are required. Also, carbon capture and utilization of CO2 would also be needed. In that sense, thermochemical redox cycles gain particular interest to produce synthetic fuels, which can be used for energy generation and production of chemicals. In a two-step redox cycles, metal oxides acts as oxygen carriers and undergo looping between two reactors. In the reduction reactor, metal oxide is reduced with release of oxygen (solar-thermal) or produces syngas (for fuel reduction) whereas, in oxidation, CO2/H2O splits for form syngas when in contact with the metal oxide. Ceria being readily available at large scale and due to its nature of undergoing reduction non-stoichiometrically at low temperature makes it a good candidate. In the present thesis, a detailed investigation of thermochemical dissociation of CO2 and H2O considering solar thermal and fuel reduction with a focus on non-structured reactors is carried out. For the solar-driven cycle, an assessment of counter-current flow moving bed reactors for reduction and oxidation is performed and a chemical looping (CL) unit is added to a 100 MW power plant. With an operating temperature of 1600oC and 10-7 bar pressure, a maximum power output of 12.9 MW with solar to electricity efficiency of 25.4% is calculated. This additional power would bring down the efficiency loss due to carbon capture from 11.3 to 6%. Even though a considerable efficiency is obtained on very optimistic operating conditions, it still requires a huge solar field. Economics revealed that with a carbon tax of $40/tone of CO2 the levelized cost of electricity (LCOE) achieved is 17.8 times higher than the existing market price (without carbon capture). If a higher carbon tax of 80$/MWh is considered that it would still be 6.28 times higher for a plant with a carbon tax. As an alternative, methane-driven CL unit is integrated into a power plant to access the overall system efficiency and amount of efficiency regain after carbon capture. Since there exists no solid-state kinetic model in the literature for methane driven CO2/H2O splitting cycle, an experimental investigation was performed which revealed that an Avrami-Erofe’ev (AE3) model fit best to both oxidation and reduction, with activation energies of 283 kJ/mol and 59.7 kJ/mol, respectively. A comparative assessment was performed to investigate the influence of kinetics. A CL unit based on thermodynamics and kinetics (with moving bed reactors) were tested in a power plant. A drop of 20% in the efficiency of the CL unit was observed when the kinetic-based CL unit is considered. However, due to thermal balance within the system, a similar thermal efficiency of the overall plant was achieved as 50.9%. However, when the thermodynamic-based CL unit layout is considered there exists an excess heat which predicts the possibility of improving the efficiency. An economic assessment revealed a specific overnight capital cost of 2455$/kW, a levelized cost of CO2 savings of 96.25 $/tonneCO2, and a LCOE of 128.01 $/MWh. However, with a carbon tax of 6 $/tonneCO2, the LCOE would drop below 50 $/MWh. The methane-driven CL unit is later integrated as an add-on unit to a polygeneration plant that produces electricity and dimethyl ether. The results showed that the plant can produce 103 MWe and 2.15 kg/s of DME with energy and exergy efficiency of 50% and 44%, respectively. The capital investment required for the plantis about $534 million. With the carbon tax of $40/tonne of CO2, a current DME price of $18/GJ and an electricity price of $50/MWh would be achieved. Overall, the integration of the CL unit as an add-on unit to the power plant is more suitable than polygeneration with respect to the existing market price.
El aumento del CO2 antropogénico y el calentamiento global y el aumento de la demanda de energía primaria hace que se requieran medidas para la transición energética y la diversificación con energías renovables e infraestructuras existentes basadas en combustibles fósiles. Además de implementar medidas para la captura y el secuestro de carbono, también se necesita desarrollar métodos para la utilización de CO2. En ese sentido, los ciclos redox termoquímicos son particularmente interesantes para producir combustible sintético que, a su vez, pueden utilizarse para la producción de otras substancias químicas. La rotura de CO2 / H2O (CL) mediante una vía termoquímica de dos pasos está compuesta por dos reacciones redox con un óxido metálico. El primer paso es la reducción de los óxidos metálicos al perder oxígeno y crear vacantes en la red a una temperatura más alta y convertirse en óxido de metal de valencia más baja. Durante la etapa de oxidación, los gases reactivos CO2 / H2O reaccionan con el óxido metálico reducido formando CO y H2. Se ha investigado el uso de diferentes óxidos metálicos en función de su capacidad de transporte de oxígeno y sus propiedades para realizar ciclos redox continuos a distintos valores de temperatura y presión. Después de un examen cuidadoso, se ha seleccionado a la ceria para la división de CO2 / H2O a gran escala. En el presente trabajo, se investigan las divisiones termoquímicas de CO2 / H2O impulsadas por energía solar y la reducción de metano para la producción de gas de síntesis, con especial atención a su aplicación en reactores no estructurados. Se evalúa el uso de reactores de lecho móvil basado en flujo contracorriente y reactores de lecho fluidizado que funcionan en diferentes regímenes de fluidización. Es un reactor de lecho móvil tanto para la etapa de reducción como para la etapa de oxidación se obtienen altas selectividades de CO y H2 con volúmenes óptimos del reactor, mientras que en un reactor de lecho fluidizado el volumen requerido es mucho más alto, lo que lo hace inviable. Los modelos de reactor se han desarrollado en Aspen plus y se validan a partir de la literatura. Un análisis de sensibilidad ha revelado que la unidad CL depende en gran medida de la temperatura y la presión. El análisis se ha ampliado integrando la unidad desarrollada de CL como una unidad adicional a una central eléctrica de 100 MW con captura de carbono. La eficiencia de la planta se ha investigado considerando sólo la división de CO2, sólo la del H2O y la mezcla de CO2 y H2O como alimentación al reactor de oxidación de la unidad CL. El resultado es de una potencia máxima de 12.9 MW con una eficiencia de energía solar a eléctrica de 25.4%. Esta potencia adicional reduciría la pérdida de eficiencia debido a la captura de carbono de 11.3 a 6%. Para lograr esto, el reactor de reducción de la unidad CL debe funcionar a 1600 ° C y 10-7 bar de presión. Estas condiciones necesitarían un enorme campo solar y la operación, en ausencia de almacenamiento térmico, se limitaría a unas pocas horas durante el día. El análisis técnico-económico ha revelado que el coste nivelado de la electricidad es de 1321 $/MWh sin incluir incentivos ni impuestos sobre el carbono. Posteriormente, se ha considerado la reducción del metano como una alternativa a la reducción térmica. Al principio, se realizaron análisis termodinámicos de la unidad de CL impulsada por metano. A partir del análisis, se ha demostrado que la temperatura mínima requerida es de 900°C con 50% de exceso de metano para la reducción, lo que supone una eficiencia de la unidad CL de 62% con un rendimiento óptimo de CO y H2. La división de CO2/H2O en el reactor de oxidación a una mayor temperatura de salida beneficiaría considerablemente la eficiencia energética del ciclo redox CL completo. La variación de la relación H2/CO en la salida con respecto a los parámetros de entrada variables que incluyen la composición del gas al reactor de oxidación se ha estudiado con el fin de especificar las condiciones operativas idóneas. Posteriormente, la unidad CL impulsada por metano se ha integrado como una unidad adicional a una central eléctrica de 500 MW alimentada por oxígeno. Se ha investigado el rendimiento de un sistema con un ciclo combinado de gas natural convencional con o sin captura de carbono. Se ha obtenido una eficiencia de sistema y eficiencia energética de 50.7 y 47.4%, respectivamente. La eficiencia del sistema podría mejorarse a 61.5%, sujeto a la optimización del sistema. La evaluación tecno-económica ha revelado un coste de capital durante la noche de 2455 $/kW con un coste de ahorro de CO2 de 96.25 $/tonelada CO2 y un LCOE de 128.01 $/MWh. Sin embargo, con créditos de carbono de 6 $/tonelada CO2, el LCOE caería por debajo de 50 $/MWh.
Con l'aumento delle emissioni di CO2 antropogenica che contribuiscono al riscaldamento globale e l'incremento della domanda mondiale di energia primaria, sono richieste significative misure per favorire la diversificazione delle fonti e la transizione energetica tramite fonti rinnovabili a partire dalle infrastrutture esistenti basate su combustibili fossili. Prima ancora degli interventi per la cattura e il sequestro dell’anidride carbonica, anche l’utilizzo della CO2 rappresenta una misura necessaria al raggiungimento degli obiettivi di decarbonizzazione. In questo senso, i cicli redox termochimici hanno acquisito particolare interesse per la produzione di combustibile sintetico da utilizzare come intermedio nella produzione di altri prodotti chimici. La separazione chimica di CO2/H2O attraverso un ciclo termochimico – chemical looping splitting (CL) – in due fasi è composta da due reazioni redox con un ossido di metallo. La prima fase del ciclo avviene alla temperatura più elevata e consiste nella riduzione dell’ossido di metallo, che cede ossigeno creando vacanze nel reticolo e diventando ossido di metallo a bassa valenza. Durante la fase di ossidazione, i gas reagenti CO2/H2O reagiscono con l'ossido di metallo ridotto che forma CO e H2. Una mappatura dettagliata dei diversi ossidi di metallo è stata effettuata in base alla loro capacità di trasporto dell’ossigeno e alle proprietà nei cicli di ossido-riduzione a funzionamento continuo in condizioni di variazione di temperatura e pressione. Dopo un attento esame, l’ossido di Cerio - ceria - è stato selezionato per l'applicazione che può essere disponibile per la scissione CO2 / H2O su larga scala. In questo lavoro, sia la separazione termochimica di CO2/H2O alimentata tramite energia solare, sia i cicli con riduzione tramite metano, entrambi finalizzati all produzione di syngas sono stati studiati con particolare attenzione ai reattori non strutturati. Per il ciclo termochimico basato su energia solare, è stata effettuata la valutazione dei reattori a letto mobile a flusso in controcorrente e a letto fluido che operano in diversi regimi di fluidizzazione. Il reattore a letto mobile è stato individuato come il più performante sia per la riduzione che l’ossidazione, con elevate selettività verso CO e H2 e volumi ottimali del reattore, mentre una resa analoga con reattori a letto fluidizzato potrebbe essere ottenuta solo con volumi di reattore molto alti, rendendo questa scelta irrealizzabile nella pratica. I modelli di reattore sono stati sviluppati in Aspen plus e sono stati validati dalla letteratura. Un'analisi di sensitività ha rivelato che la performance dell'unità CL è in larga misura dipendente dalla temperatura e dalla pressione di riduzione. L'analisi è stata estesa integrando l'unità CL sviluppata come unità aggiuntiva di una centrale elettrica a ossicombustione da 100 MW con cattura di carbonio. L'efficienza dell'impianto è stata studiata considerando di alimentare il reattore di ossidazione dell'unità CL sia con CO2, sia con H2O, sia con una miscela di CO2 e H2O. I risultati indicano una potenza massima di 12,9 MW con un rendimento da solare a elettricità del 25,4% generabile grazie all’unità di CL. Questa potenza aggiuntiva ridurrebbe la perdita di efficienza dovuta alla cattura di carbonio dall'11,3 al 6%. Per ottenere ciò, il reattore di riduzione dell'unità CL deve operare a 1600 ° C con una pressione di 10-7 bar. Queste condizioni avrebbero bisogno di un enorme campo solare e l'operazione sarebbe limitata a poche ore durante il giorno senza l’integrazione di un accumulo termico. L'analisi tecno-economica ha rivelato che il costo livellato (levelizad cost) dell'elettricità era di 1321 $ / MWh, senza includere incentivi o tassazione sul carbonio. Successivamente, è stata considerata la riduzione della ceria con metano come alternativa alla riduzione termica. Inizialmente, sono state condotte analisi termodinamiche dell'unità CL con riduzione a metano. Dall'analisi è emerso che la temperatura minima richiesta era 900 °C per la riduzione con un eccesso di metano del 50%, che ha prodotto un'efficienza dell'unità CL del 62% con una resa ottimale di CO e H2. In questo caso, la scissione di CO2/H2O nel reattore di ossidazione consisteva nell'ossidazione completa esotermica della ceria, per cui una temperatura di uscita più elevata avrebbe notevolmente migliorato l'efficienza energetica del ciclo CL redox completo. La variazione del rapporto H2 / CO all'uscita rispetto ai vari parametri di input, compresa la composizione del gas inviato al reattore di ossidazione, è stata studiata per specificare le condizioni operative necessarie. Successivamente, l'unità CL a metano è stata integrata come unità aggiuntiva in una centrale elettrica a ossicombustione da 500 MW. Sono state studiate le prestazioni del sistema in una valutazione comparativa con un ciclo combinato convenzionale a gas naturale, un ciclo a ossicombustione con cattura di carbonio e l'impianto proposto. Sono stati ottenuti per l’impianto rispettivamente un rendimento del sistema e un'efficienza energetica del 50,7% e del 47,4%. L'efficienza del sistema potrebbe essere migliorata fino al 61,5% tramite l'ottimizzazione del recupero termico del sistema, valutata attraverso la pinch analysis del sistema. Una dettagliata valutazione tecno-economica ha rivelato un costo specifico del capitale di 2455 $ / kW (overnight cost), un costo livellato delle emissioni di CO2 evitate 96,25 $ / tonnellata di CO2, e un costo dell’elettricità (LCOE) di 128,01 $ / MWh. Tuttavia, considerando un incentivo di 6 $ / tonnellata di CO2 evitata, il LCOE scenderebbe sotto i 50 $ / MWh. L'unità CL a metano viene successivamente integrata come unità aggiuntiva in un impianto di poligenerazione che produce elettricità e dimetil-etere. I risultati hanno mostrato che l'impianto può produrre 103 MWe e 2,15 kg/s di DME con un’efficienza energetica ed exergetica del 50% e del 44% rispettivamente. L'investimento di capitale richiesto per l'impianto ammonta a 534 M$. Con un valoré per la carbon tax di $ 40 / tonnellata di CO2, il DME e l’elettricità raggiungerebbero la parità con gli attuali prezzi di mercato, pari a $18/GJ per il DME e $50/MWh per l’elettricità. I costi risultanti sono dovuti all'unità di separazione dell'aria richiesta per la centrale elettrica a ossicombustione e può essere ridotta sostituendo l'unità di separazione dell'aria con una tecnologia a membrana per la separazione dell'ossigeno. Poiché in letteratura non esiste un modello completo per cinetica dello stato solido che descriva la riduzione con metano della ceria, esso è stato ricavato per via sperimentale. Sono stati condotti esperimenti in un reattore tubolare orizzontale a letto fisso in un intervallo di temperatura di 900-1100 °C. E’ stata studiata la cinetica della scissione della CO2, essendo una reazione più complessa rispetto alla scissione dell'acqua, la cui cinetica è stata invece ottenuta dalla letteratura. In base all’analisi sperimentale condotta, il modello cinetico Avrami-Erofe'ev (AE3) è risultato essere il migliore per entrambe le reazioni, con le rispettive energie di attivazione ottenute rispettivamente come 283 kJ/mol e 59,68 kJ/mol. L'ordine della reazione è stato ricavato come relazione tra temperatura e concertazione dei reagenti. L'analisi è stata effettuata seguendo un approccio termodinamico, ma la reazione eterogenea dell'ossido di metallo e dei gas reagenti limita il raggiungimento dell'equilibrio durante la reazione e dipende sempre dal tipo di reattore scelto per x l'applicazione. Pertanto, un modello di reattore a letto mobile è stato sviluppato considerando la riduzione del metano ottenuta sperimentalmente e la cinetica di splitting della CO2 è stata incorporata per valutare i due impianti proposti: la centrale elettrica e l'impianto di poligenerazione. È stata osservata una riduzione del 20% nell'efficienza dell'unità CL. Tuttavia, grazie all’integrazione termica interna al sistema, l’efficienza termica dell'impianto complessivo è molto simile a quella raggiunta nell’analisi termodinamica, con un valore del 50,9%. Tuttavia, a differenza del layout termodinamico, non è disponibile calore in eccesso per migliorare ulteriormente l'efficienza del sistema. Oltre al riciclo e all'utilizzo della CO2, come criteri di valutazione della sostenibilità per il layout proposto sono stati analizzati anche l’occupazione del suolo terreno e il fabbisogno idrico. Sia il fabbisogno di terra che di acqua aumentano di 2,5 volte rispetto ad una centrale convenzionale a ciclo combinato a gas naturale. Inoltre, anche l’impianto di poligenerazione con produzione di energia elettrica e dimetil etere (DME) è stato studiato considerando un modello dell’unità CL basato sulla cinetica e ha rilevato che la produzione di DME scenderebbe da 2,15 kg/s a 1,48 kg/s e la potenza elettrica prodotta da 103 a 72 MW. Pertanto, la cinetica ha una forte influenza sulla prestazione complessiva del sistema, e considerarla nell’analisi porta a ridurre la produzione di energia e DME di circa il 30% con un aumento di costo del 30%. Complessivamente, l'integrazione dell'unità CL come unità aggiuntiva ad una centrale elettrica a ossicombustione risulta più adatta rispetto alla poligenerazione, considerando il prezzo di mercato attuale per le commodities prodotte.

Thesis (M.S. in Operations Research)--Naval Postgraduate School, March 2007.
Thesis Advisor(s): Daniel A. Nussbaum. "March 2007." Includes bibliographical references (p. 95-99). Also available in print.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The main objective of this thesis is to investigate the fundamental combustion process of ammonia-based fuels and the application on swirl-stabilised flames in the context of engineering type gas turbine combustion. The present study begins with a fundamental validation and mechanism reduction for chemical kinetics of ammonia/methane combustion. Different-sized reduced mechanisms of the well-known Konnov’s mechanism were compared at high-pressure conditions relevant to gas turbine devices. The reduced models can benefit the future simulation work with considerably less computational cost. Then characteristics of ignition delay time, laminar flame speed and emissions were obtained over a wide range of equivalence ratios and ammonia fractions. Prediction results showed a good potential of ammonia/methane to be used in gas turbine engines with relatively low emission. In the second part of this dissertation, in order to identify reaction mechanisms that can accurately represent ammonia/hydrogen kinetics at industrial conditions, various mechanisms were tested in terms of flame speed, combustion products and ignition delay against experimental data. It was preliminarily found that the Mathieu mechanism and Tian mechanism are the best suited for ammonia/hydrogen combustion chemistry under practical industrial conditions. Based on the Mathieu mechanism, an improved chemical mechanism was developed. Verification of the established model was quite satisfying, focusing particularly on elevated conditions which are encountered during gas turbine operation. Finally, a first assessment of the suitability of a chosen 70%NH3-30%H2 (%vol) blend was performed for utilisation within a gas turbine environment. It was found that stable flames can be produced with low NOx emissions at high equivalence ratios. Also, results showed that high inlet temperature conditions representative of real gas turbine conditions can significantly improve the combustion efficiency and reduce NOx emissions. A numerical gas turbine cycle calculation was performed indicating more research are required to enable higher efficiencies using ammonia/hydrogen.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-63).
The thesis is divided into two parts - 1) assessing the energy return on investment for alternative jet fuels, and 2) quantifying the tradeoffs associated with the aviation and non-aviation use of agricultural residues. We quantify energy return on energy investment (EROI) as one metric for the sustainability of alternative jet fuel production. Lifecycle energy requirements are calculated and subsequently used for calculating three EROI variants. EROI₁ is defined as the ratio of the lower heating value (LHV) of the liquid fuel produced, to lifecycle (direct and indirect) process fossil fuel energy inputs and fossil feedstock losses during conversion. EROI₂ is defined as the ratio of fuel LHV to total fossil fuel energy input, inclusive of the fossil energy embedded in the fuel. EROI₃ is defined as the ratio of fuel LHV to the sum of renewable and non-renewable process fuel energy required and feedstock energy losses during conversion. We also define an approximation for EROI₁ using lifecycle CO₂ emissions. This approach agrees to within 20% of the actual EROI₁ and can be used as an alternative when necessary. Feedstock-to-fuel pathways considered include jet fuel from conventional crude oil; jet fuel production from Fischer-Tropsch (FT) processes using natural gas, coal and/or switchgrass; HEFA (hydroprocessed esters and fatty acids) jet fuel from soybean, palm, rapeseed and jatropha; and advanced fermentation jet (AF-J) fuel from sugarcane, corn grain and switchgrass. We find that ERO₁ 1 for conventional jet fuel from conventional crude oil ranges between 4.9-14.0. Among the alternative fuel pathways considered, FT-J fuel from switchgrass has the highest baseline EROI₁ of 9.8, followed by AF-J fuel from sugarcane at 6.7. Jet fuel from oily feedstocks has an EROI₁ between 1.6 (rapeseed) and 2.9 (palm). EROI₂ differs from EROI₁ only in the case of fossil-based jet fuels. Conventional jet from crude oil has a baseline EROI₂ of 0.9, and FT-J fuel from NG and coal have values of 0.6 and 0.5, respectively. EROI 3 values are on average 36% less than EROI₁ for HEFA pathways. EROI₃ for AF-J and FT-J fuels considered is 50% less than EROI₁ on average. All alternative fuels considered have a lower baseline EROI₃ than conventional jet fuel. Using corn stover, an abundant agricultural residue, as a feedstock for liquid fuel or power production has the potential to offset anthropogenic climate impacts associated with conventional utilities and transportation fuels. We quantify the environmental and economic opportunity costs associated with the usage of corn stover for different applications, of which we consider combined heat and power, ethanol, Fischer-Tropsch (FT) middle distillate (MD) fuels, and advanced fermentation (AF) MD. Societal costs comprise of the monetized attributional lifecycle greenhouse gas (GHG) footprint and supply costs valued at the shadow price of resources. The sum of supply costs and monetized GHG footprint then provides the societal cost of production and use of corn stover for a certain application. The societal costs of conventional commodities, assumed to be displaced by renewable alternatives, are also calculated. We calculate the net societal cost or benefit of different corn stover usages by taking the difference in societal costs between corn stover derived fuels and their conventional counterparts, and normalize the results on a feedstock mass basis. Uncertainty associated with the analysis is captured using Monte-Carlo simulation. We find that corn stover derived electricity and fuels reduce GHG emissions compared to conventional fuels by 21-92%. The mean reduction is 89% for electricity in a CHP plant, displacing the U.S. grid-average, 70% for corn stover ethanol displacing U.S. gasoline and 85% and 55% for FT MD and AF MD displacing conventional U.S. MD, respectively. Using corn stover for power and CHP generation yields a net mean societal benefit of $48.79/t and $131.23/t of corn stover, respectively, while FT MD production presents a mean societal benefit of $27.70/t of corn stover. Ethanol and AF MD production from corn stover result in a mean societal cost of $24.86/t and $121.81/t of corn stover use, respectively, driven by higher supply costs than their conventional fuel counterparts. Finally, we note that for ethanol production, the societal cost of CO₂ that would need to be assumed to achieve a 50% likelihood of net zero societal cost of corn stover usage amounts to approximately -$100/tCO₂, and for AF MD production to ~$600/tCO₂.
by Parthsarathi Trivedi.
S.M.

Nuclear power is in focus of attention due to several factors these days and the expression “nuclear renaissance” is getting well known. However, concerned voices are raised saying that the fuel availability will phase out nuclear power faster. The Swedish Royal Academy of Sciences declared in 2006 a wish for scientific focus on nuclear power in years to come. The Academy identified six areas of interest regarding nuclear power and fuel availability was one. In this thesis an attempt is made to give an overview of the circumstances regarding fuel availability in nuclear power by gathering information from relevant scientific articles, the industry and international authorities. The results presented in this thesis show that in the coming 20 years it is likely that the construction rate of new power plants is a bigger challenge than fuel availability. The rate of new constructions must within a few years reach the peak levels that were reached during a few years in the 1980´s on over 30 new reactors per year. This is a challenge since only the amount of new nuclear reactors have been less than four on average the last 15  years and it needs to increase 5 folds at least.

Biomass is classed as a renewable resource. Depending on the means of production, it can be sustainable and can provide net benefits regarding CO2 emissions by displacing fossil fuels as an energy source. A significant biomass energy conversion technology is combustion in conventional thermal power stations. This can be implemented in large scale plants such as those which dominated electricity generation throughout the 20th century. While these power stations were generally fuelled by the erstwhile ‘King Coal’, the technology is not exclusive to it. Coal consumption can be displaced in these types of plants by either co-firing biomass with coal or full conversion to biomass. Currently, in the UK, the vast majority of the biomass fuel consumed for power generation is imported pelletized forestry wood. However, sustainability and domestic energy security concerns have created interest in using other resources including energy crops such as short rotation coppice willow and miscanthus, agricultural by-products such as wheat straw and olive residue. The variation in the properties of these fuels presents a number of technical challenges which conventional power plant must overcome to achieve ‘fuel flexibility’. Along with other technical challenges regarding the operation of conventional thermal power plant, these formed the basis of the Research Councils UK funded consortium grant (EPSRC, 2012) entitled Future Conventional Power. As a consortium partner in this project, the University of Leeds led research tasks associated with fuel flexibility. Much of the research presented in this thesis was based on the objectives set out in the Future Conventional Power project and was financially supported though this grant. Two particular challenges provide the incentive for the investigations presented in this thesis and can be summarised as: • assessing the variability in fuel combustion behaviour and control of burn-out efficiency for different fuels • understanding the behaviour of potassium during the combustion of biomass fuels to aid in the prediction of ash behaviour, emissions and associated operational problems Both these points were addressed with a series of experimental studies. In addition, a model of the combustion of single particles was developed for validating and interpreting the results. A range of fourteen solid biomass fuels, typical of those likely to be used in large scale power plant, were selected for the experimental studies. The composition and fundamental characteristics of these fuels, obtained by standard analytical techniques, are presented. In the first experimental study, single particles were exposed to a methane flame, simulating biomass combustion in a furnace. Measurements of ignition delay, volatile burning time and char burn-out time were undertaken using high speed image capture. Particle surface temperatures were measured by infra-red thermal imaging. Analysis of the data identified correlations between the biomass fundamental characteristics, particle size, and the observed combustion profiles. Empirical expressions for the duration of each combustion stage are obtained from the data. From these, a “burn-out” index is derived which provides a useful indication of the relative milling requirements of different fuels for achieving effective burn-out efficiency. A similar experimental method was used in the second study in which the gas-phase potassium release patterns from single particles of various biomass fuels were measured by use of flame emission spectroscopy. The observed potassium release patterns for the various fuel samples are presented. The release patterns revealed qualitative differences between different fuel types. Relationships between the initial potassium content, peak rate of release and the fractions of potassium released at each stage of combustion were identified. These were subsequently used for comparing with results of modelled potassium release. A third experimental study investigated the variation in thermal conductivity between different types of solid biomass using a technique and apparatus developed specifically for the study. The results showed variation of thermal conductivity between different types of biomass which had been similarly homogenised and densified. The thermal conductivity of small particles of each fuel was derived. The resulting data provides useful values for thermal modelling of biomass particles and is used subsequently in a combustion model. Elements of each of the experimental studies were used in a detailed model of single particle combustion. In this, the particle was modelled as a series of concentric spherical layers which enabled calculation of internal mass diffusion and heat transfer. Devolatilisation and char oxidation were approximated with single step reaction kinetics. A volatilisation and diffusion mechanism was adopted to simulate the release of gas-phase potassium from the particle. The output from the model was compared and validated using data from the experimental studies. The modelling produced confirming evidence that the assumed mechanisms for gas-phase potassium release were valid and provided a tool for future investigation of the subject.

This dissertation analyzes the case of organized climate change denial in the United States as a manifestation of the power of the policy planning and opinion shaping networks in the US. It uses a variety of power structure research techniques to put together a topographical study of a fossil fuels network sitting at the core of a wider conservative network which sits at the core of the policy planning and opinion shaping processes. The connections between the core fossil fuels network and wider conservative policy network are examined at length. Using climate change denial as the case allows for the study of how a distinct industry— fossil fuels—can organize a faction which can help set the ideological agenda of the wider corporate and conservative networks. A power elite theoretical approach outlined by Domhoff is used, and the conclusions that may be drawn from this case study support the usefulness of that approach. I also find that the case at hand illustrates how Domhoff’s model may be extended and augmented in light of the strategic and tactical innovations employed by those in the climate change denial faction. Although elites have often tried—with varying levels of success—to employ at least a veneer of populist support in formulating policy, climate change denial employs a new level of sophistication in then fossil fuels’ faction’s long-term strategic planning and investment. This faction’s ability to wrest ideological control of much of the tea party movement and bring that party's policy aims into lie with its own allowed for the addition of a powerful populist element to the climate change denial tactical repertoire. Similarly, new secrecy techniques go far beyond those used by elites in the past, reflecting a new set of needs on the part of the individuals and groups involved in the policy network and necessitating the augmentation of the existing network with specialized entities.

The study shows conclusively that brine composition and concentration is highly variable at these South African power utilities and processes such as RO, contact with ash and CO2 ingress can have an impact upon the overall brine quality. Aq.QA was found to be a more accurate tool for classifying waters according to dominant ions than Stiff diagrams but Stiff diagrams still have the superior advantage of being a mapping tool to easily identify samples of similar composition as well as quickly identify what has been added or what has been removed from a water stream. Chemical speciation could identify effluent streams where CO2 dissolution had taken place.

Les procédés thermochimiques solaires étudiés concernent la conversion de charges hydrocarbonées solides ou gazeuses en syngas, ainsi que la réduction d’oxydes en métaux en utilisant l’énergie solaire concentrée pour effectuer les réactions endothermiques, permettant ainsi le stockage de l’énergie solaire intermittente en carburants sans émissions de CO2. Ce travail a pour objectif l’étude expérimentale de trois procédés solaires incluant la gazéification de biomasse, le reformage de méthane en boucle chimique, et la carboréduction de ZnO et MgO. La gazéification et le reformage permettent la valorisation de biomasse bois et de méthane en syngas, tandis que la carboréduction permet de produire Zn et Mg à partir de ZnO et MgO. Ces procédés ont été étudiés dans des réacteurs solaires de 1.5 kWth, en utilisant le rayonnement concentré fourni par des systèmes à concentration du laboratoire PROMES, Odeillo, France. L’impact des paramètres opératoires de chaque procédé sur les mécanismes réactionnels, conversion, rendement, et performances énergétiques a été évalué en détail. Ces procédés ont permis d’améliorer la conversion chimique, les rendements en syngas, les efficacités énergétiques tout en permettant un stockage de l’énergie solaire en combustibles transportables, avec des performances globales supérieures aux procédés conventionnels. De plus, leur faisabilité, fiabilité et robustesse pour la conversion de méthane et biomasse en syngas et la production de Mg et Zn en fonctionnement batch ou continu sous pression réduite ou atmosphérique en conditions solaires réelles ont été démontrés
The investigated solar thermochemical processes consist of the thermochemical conversion of solid and gaseous carbonaceous feedstocks into syngas as well as metal oxides reduction into metal commodities utilizing concentrated solar energy to drive endothermic chemical reactions, thereby enabling intermittent solar energy storage into solar fuels and avoiding CO2 emissions. This work aims to experimentally investigate three key solar thermochemical conversion approaches regarding biomass gasification, chemical looping reforming of methane, and carbothermal reduction of ZnO and MgO. Solar gasification and solar chemical looping reforming allowed valorizing wood biomass and methane into syngas, while solar carbothermal reduction was applied to produce Zn and Mg from ZnO and MgO. Such solar thermochemical processes were performed in 1.5 kWth prototype solar chemical reactors, utilizing highly concentrated sunlight provided by a solar concentrator at PROMES laboratory, Odeillo, France. The impact of controlling parameters of each process on the reaction mechanism, conversion, yields, and process performance, during on-sun testing was investigated and evaluated thoroughly. Such processes were proved to significantly improve the chemical conversion, syngas yields, energy efficiency, with solar energy storage into transportable fuels, thereby outperforming the conventional processes. Moreover, their feasibility, reliability, and robustness in converting both methane and biomass feedstocks to syngas as well as producing Mg and Zn metals in batch and continuous operation under vacuum and atmospheric conditions during on-sun operation were successfully demonstrated

Cette étude se focalise sur le développement de procédés de dissociation de H2O et CO2 par voie thermochimique utilisant des oxides métalliques non-stœchiométriques et l’énergie solaire concentrée pour la production de carburants solaires. Les procédés redox se décomposent en deux réactions distinctes : tout d’abord, une réduction thermique à haute température de l’oxyde métallique avec la création de lacunes en oxygène dans la structure cristallographique, entrainant une production d’oxygène ; puis, une réoxydation de l’oxyde métallique par H2O et/ou CO2, conduisant à la production de H2 et/ou CO. La cérine et les pérovskites ont été étudiées comme matériaux réactifs pour les cycles thermochimiques. Pour augmenter l’efficacité des cycles thermochimiques, différents paramètres ont été étudiés, comme la composition chimique et la morphologie de l’oxyde réactif, les conditions opératoires, ainsi que la configuration du réacteur solaire. Dans un premier temps, les activités redox, la cinétique et la thermodynamique de différentes pérovskites ont été étudiées expérimentalement pour les cycles redox. Par la suite, les performances thermochimiques de différents matériaux réactifs sous forme de structures poreuses ou de particules ont été étudiées dans des réacteurs solaires (configuration monolithique ou lit fixe) permettant de réaliser des cycles thermochimiques en deux étapes. Une étude paramétrique détaillée a été effectuée pour déterminer les taux et vitesses de production. La vitesse de production de CO la plus élevée (9.9 mL/min/g) a été obtenue avec des mousses réticulées en cérine. Enfin, un réacteur solaire membranaire a été développé pour produire en isotherme et en continu du CO (ou H2) par dissociation de CO2 (ou H2O) avec une membrane réactive et perméable à l’oxygène. La vitesse de production la plus élevée atteint 0.133 µmol/cm2/s à 1550 °C en utilisant une membrane en cérine avec un revêtement en pérovskite
This study is focused on the development of thermochemical H2O and CO2 splitting processes using non-stoichiometric metal oxides and concentrated solar energy to produce solar fuels. The redox process is composed of two distinct reactions: first, a thermal reduction at high temperature of the metal oxide with creation of oxygen vacancies in the crystallographic structure, resulting in released oxygen; second, the re-oxidation of the metal oxide by H2O and/or CO2, leading to H2 and/or CO production. Ceria and perovskite materials have been investigated as reactive oxides for thermochemical cycles. To increase the thermochemical process efficiency, different aspects were investigated, such as chemical composition and morphology of the metal oxide, operating parameters, and solar reactor configuration. The redox activities, kinetics and thermodynamics of different perovskite materials were first experimentally investigated for two-step thermochemical cycles. Then, the thermochemical performances of various reactive materials shaped as porous structures or particulate media were investigated in solar reactors (monolithic or packed-bed configurations) able to perform two-step thermochemical cycles. A detailed parametric study was performed to determine fuel production rates and yields. The highest CO production rate (9.9 mL/min/g) was achieved with ceria reticulated foams. Finally, a solar membrane reactor was developed for isothermal and continuous production of CO (or H2) by CO2 (or H2O) splitting with a reactive and oxygen-permeable membrane. The highest CO production rate reached 0.133 µmol/cm2/s at 1550 °C using a perovskite-coated ceria membrane

The modern concept of "biorefinery" is dominantly based on chemical pulp mills to create more value than cellulose pulp fibres, and energy from the dissolved lignins and hemicelluloses. This concept is characterized by the conversion of biomass into various biobased products. It includes thermochemical processes such as gasification and fast pyrolysis. In mechanical pulp mills, the feedstock available to the gasification-based biorefinery is significant, including logging residues, bark, fibre material rejects, biosludges and other available fuels such as peat, recycled wood, and paper products. This work is to study co-production of bio-automotive fuels, biopower, and steam via gasification in the context of the mechanical pulp industry.   Biomass gasification with steam in a dual-fluidized bed gasifier (DFBG) was simulated with ASPEN Plus. From the model, the yield and composition of the syngas and the contents of tar and char can be calculated. The model has been evaluated against the experimental results measured on a 150 KWth Mid Sweden University (MIUN) DFBG. The model predicts that the content of char transferred from the gasifier to the combustor decreases from 22.5 wt.% of the dry and ash-free biomass at gasification temperature 750 ℃ to 11.5 wt.% at 950 ℃, but is insensitive to the mass ratio of steam to biomass (S/B). The H2 concentration is higher than that of CO under normal DFBG operating conditions, but they will change positions when the gasification temperature is too high above about 950 ℃, or the S/B ratio is too far below about 0.15. The biomass moisture content is a key parameter for a DFBG to be operated and maintained at a high gasification temperature. The model suggests that it is difficult to keep the gasification temperature above 850 ℃ when the biomass moisture content is higher than 15.0 wt.%. Thus, a certain amount of biomass needs to be added in the combustor to provide sufficient heat for biomass devolatilization and steam reforming. Tar content in the syngas can also be predicted from the model, which shows a decreasing trend of the tar with the gasification temperature and the S/B ratio. The tar content in the syngas decreases significantly with gasification residence time which is a key parameter.   Mechanical pulping processes, as Thermomechanical pulp (TMP), Groundwood (SGW and PGW), and Chemithermomechanical pulp (CTMP) processes have very high wood-to-pulp yields. Producing pulp products by means of these processes is a prerequisite for the production of printing paper and paperboard products due especially to their important functional properties such as printability and stiffness. However, mechanical pulping processes consume a great amount of electricity, which may account for up to 40% of the total pulp production cost. In mechanical pulping mills, wood (biomass) residues are commonly utilized for electricity production through an associated combined heat and power (CHP) plant. This techno-economic evaluation deals with the possibility of utilizing a biomass integrated gasification combined cycle (BIGCC) plant in place of the CHP plant. Integration of a BIGCC plant into a mechanical pulp production line might greatly improve the overall energy efficiency and cost-effectiveness, especially when the flow of biomass (such as branches and tree tops) from the forest is increased. When the fibre material that negatively affects pulp properties is utilized as a bioenergy resource, the overall efficiency of the system is further improved. A TMP+BIGCC mathematic model is developed based on ASPEN Plus. By means of this model, three cases are studied:   1) adding more forest biomass logging residues in the gasifier, 2) adding a reject fraction of low quality pulp fibers to the gasifier, and 3) decreasing the TMP-specific electricity consumption (SEC) by up to 50%.   For the TMP+BIGCC mill, the energy supply and consumption are analyzed in comparison with a TMP+CHP mill. The production profit and the internal rate of return (IRR) are calculated. The results quantify the economic benefit from the TMP+BIGCC mill.   Bio-ethanol has received considerable attention as a basic chemical and fuel additive. It is currently produced from sugar/starch materials, but can also be produced from lignocellulosic biomass via a hydrolysis--fermentation or thermo-chemical route. In terms of the thermo-chemical route, a few pilot plants ranging from 0.3 to 67 MW have been built and operated for alcohols synthesis. However, commercial success has not been achieved. In order to realize cost-competitive commercial ethanol production from lignocellulosic biomass through a thermo-chemical pathway, a techno-economic analysis needs to be done.   In this work, a thermo-chemical process is designed, simulated, and optimized mainly with ASPEN Plus. The techno-economic assessment is made in terms of ethanol yield, synthesis selectivity, carbon and CO conversion efficiencies, and ethanol production cost.   Calculated results show that major contributions to the production cost are from biomass feedstock and syngas cleaning. A biomass-to-ethanol plant should be built at around 200 MW. Cost-competitive ethanol production can be realized with efficient equipments, optimized operation, cost-effective syngas cleaning technology, inexpensive raw material with low pretreatment cost, high-performance catalysts, off-gas and methanol recycling, optimal systematic configuration and heat integration, and a high-value byproduct.

The demand for fossil fuels by Ontario's conventional steam power generation sector is examined. It is hypothesised that the enactment of a carbon fee policy will induce a change in the relative prices of the three fuels used in this sector (coal, natural gas and heavy fuel oil). This would lead to substantial interfuel substitution and greenhouse gas abatement. The demand share equations for the three fuels are derived from the translog functional form and set in a simulation model to estimate the value of a carbon fee necessary, to reduce carbon dioxide emissions in compliance with the Kyoto Protocol. Results suggest that a fuel specific carbon fee policy would be successful in achieving the desired emissions reduction at a negligible net cost to society.

Mestrado em Finanças
Este projeto consiste num relatório de avaliação da empresa GALP Energia S.G.P.S., S.A., com especial foco na unidade de negócio de eletricidade e a contribuição dos seus projetos solares mais recentes para o preço-alvo de 2020YE. O relatório segue o formato recomendado pelo CFA Institute, uma vez que, grande parte do mesmo, foi submetido para o CFA Institute Research Challenge de 2020. A GALP é a principal Empresa Integrada de Petróleo em Portugal. Opera em toda a cadeia de valor do combustível fóssil, desde a extração do mesmo, o seu transporte e refinação, e por fim a comercialização dos diferentes subprodutos. Foi aplicada a abordagem de Soma das Partes para avaliar a GALP, aplicando o FCFF DCF a cada unidade de negócio, de forma a refletir todas as idiossincrasias de cada unidade. O resultado gerou um preço-alvo de 12,1€/sh. Foram também utilizados outros métodos para complementar a avaliação, como o FCFF DCF para a empresa como um todo, o FCFE DCF, o APV e o DDM. Foi ainda realizada uma análise complementar à contribuição dos projetos mais recentes da GALP em energia solar, para o preço-alvo inicial de 12,1€/sh, uma vez que o nosso relatório inicial não considerou esses projetos porque apenas foram anunciados após a conclusão do relatório inicial. Ao adicionar os investimentos mais recentes da GALP em projetos de energia solar, a minha recomendação de investimento fornece informações mais precisas e atualizadas aos investidores e às suas decisões de investimento. Este capítulo reforça a nossa recomendação de compra.
This project is an Equity Research of GALP Energia S.G.P.S., S.A., with a special focus on the value added by the power business unit's most recent solar projects to the initial 2020YE price target. The report follows the CFA Institute format, as a significant portion of it was submitted for the 2020 CFA Institute Research Challenge. Only public information released until January, 2nd 2020 was considered. GALP is the leading Portuguese Integrated Oil Company. It operates throughout the whole fossil fuel value chain, from extracting fossil fuel, to transporting and refining it, and then commercializing the different by-products. It was applied a Sum-of-the-Parts approach to value GALP, where a FCFF DCF was applied to each business unit, reflecting all the idiosyncrasies of each unit. The result yielded a final price target of 12.1€/sh. Other methods were also used to support the valuation, such as a FCFF DCF for the company as a whole, FCFE DCF, the APV and the DDM. A complementary analysis to the contribution of GALP's most recent projects in solar energy to the initial price target of 12.1€/sh was carried out, since our initial report didn't incorporate these projects, as they were announced after the initial report was concluded. By adding GALP's most recent investments in solar energy projects, I believe our investment recommendation provides more accurate and updated information to investors and to their investment decision. It is also of importance to highlight that this chapter further supports our buy recommendation.
info:eu-repo/semantics/publishedVersion

In recent years, Renewable Power to Fuels technology is becoming a vitally important pathway from the value-added products point of view. This electricity-to-fuel transformation is regarded as an efficient way not only to preserve renewable energy (i.e. wind and solar) and to offset the fluctuating nature of these sources but also to generate synthesis fuels with respect to the demand for, the capacity limitation and the existing infrastructure of the targeted products. In this sense, many E.U. countries are transforming CO2 into clean and the carbon-free products to achieve the targets of greenhouse gas (GHG) emissions. With regards to the renewable energy action plan, each E.U. country has a contribution target to reach by 2020: Italy’s overall target is to reach 17% of contribution, and it has already surpassed this (it reached 17.5% by the end of 2015). Germany is aiming for 35%, whereas Austria has a targeted of 34% [1]. In this study, two main scenarios through Power to Fuels conversion are considered: 1) Power to Gas (PtG) technology (methanation process); 2) Power to Liquid (PtL) technology based on Dimethyl ether (DME), a direct one-step process, and Low Temperature Fischer Tropsch (LTFT) process. Therefore, the conceptual design of all three processes based on a Solid Oxide Electrolysis Cell (SOEC) is analyzed. In the optimized configuration of methanation, a methane fraction of 95% at the outlet is achieved, which is compatible with the existing pipeline network. The main challenge of this technology is the lack of accurate and explicit kinetic data for its catalyst. Also, the heat released from methantion and its utilization for providing the heat required for electrolysis is another issue in the latest configuration of methanation. In DME synthesis, four explicit Langmuir Hinshelwood Hougen Watson (LHHW) kinetics were implemented in Software Aspen plus. The main challenge in one-step direct DME synthesis (based on renewable energy) is the low value of yield and selectivity of the DME product (15% and 78% in the once-through process, respectively). However, the separation process and recycling of unreacted syngas in order to achieve high purity of the DME product is quite complex due to the presence of the unreacted syngas and the CO2 produced in the one-step synthesis process. Above all, it leads to higher operational costs. In the optimized configuration of LTFT based on renewable energy, a comprehensive simulation was conducted. To model an FT reactor, an external subroutine within an Excel spreadsheet through USER2 MODEL on the simulator was implemented. It was found that total efficiency of the system was achieved at 76.6 %. However, the main challenge of this configuration is the low value of liquid products due to the low capacity of the SOEC. Having considered the challenges and limitations of each process, it is concluded that FT synthesis is more interesting to model due to the complexity of the products and the more highly developed catalyst and reactor used. As a consequence, this dissertation mainly focuses on the dynamic modeling of a Fischer-Tropsch Slurry Bubble Column Reactor (FT-SBCR), which is considered as the best candidate for Fischer-Tropsch synthesis. In the dynamic modeling of FT-SBCR, a comprehensive computer model was developed to investigate flexible reactor operation. This flexibility was performed by a step-change of syngas flow rate load (3.5, 5, 7.5 m3/h) in a low-temperature Fischer–Tropsch synthesis. It was found that the dynamic simulation is not only able to predict all Fischer–Tropsch components over the reactor bed but can also describe the behavior of superficial gas velocity as a sub-model using the overall gas mass balance. The effects of a step-change volumetric syngas flow on the performance of the FT slurry reactor, CO conversion and α-value, as well as information about the inside of reactor were investigated. The results show that the temperature distribution of the slurry reactor remains constant under base load and change load conditions. It is concluded that load change conditions do not have a negative influence on the temperature distribution inside the reactor and the dynamic model of the slurry reactor presented responds quite well to the load change conditions.

The human effort to continuously improve their standard of living in conjunction with the rapid growth of world‟s population, the reckless and the wasteful misuse of energy reserves threaten to lead mankind in an energy deadlock. In an effort to realize the size of the waste of our planet‟s available energy resources, we only need to point out that people have spent the last century stocks of raw materials and energy, which were saved and produced during the lifetime of our planet. The management of the energy systems in a proper and best way is considered to be essential worldwide. In this project the energy system of Greece is studied. The power production systems used in different sectors of life were analyzed. The study emphasized in the electricity production from different sources. Lignite electricity power plants were first introduced in the country followed by the gas power plants and Renewable Energy Sources (RES) installations. The deregulation of electricity market formed the new energy scenery of the country. Electricity grid reinforcements with smart metering and energy storage proved to be necessary in order the RES to be fully penetrated to the national grid, so as Greenhouse Gas (GHG) emissions to be reduced as much as possible. The further expansion of RES could help to cope with the barriers of the country‟s electrification due to singularity of hundred islands that are not yet interconnected to the mainland. Analytical theory methods and numerical skills used to derive the appropriate data and results. Installed capacity of the power sources was verified as well as costs and polluted emissions per unit and type of sources involved. Weaknesses and abnormalities of the electric system were pointed out. Proved gains from the RES use were verified for ensuring the sustainability of the country‟s energy system

A sociotechnical energy transition requires both a shift to new technologies and attention to social issues like political movements, policy and human behavior. This dissertation investigates social elements of the renewable energy transition occurring at different scales. The core research questions are: How are universities creating and responding to the shifting language of fossil fuel investments? How and for whom do behavioral interventions work? And finally, do in-home displays (IHDs) change behaviors and attitudes of millennial energy users? The three studies covered here occurred within higher education and reflect the importance of colleges and universities as dynamic players in energy transitions. These spaces encourage learning and organizational change on the inside while also pushing outward, challenging social norms. Using a coding approach and text analysis software, this research identifies common frames of language used by colleges and universities who have released formal statements rejecting or adopting divestment policies. This study provides a quantitative assessment of themes and an early overview of this dynamic movement. The second and third study describe the outcomes of a behavioral energy experiment with off-campus students at the University of Vermont testing real-time feedback and financial incentives on individuals' behavior. The second study analyzes the results of a survey conducted with participants in the experiment, investigating changes in attitudes and self-reported behaviors and correlations with actual energy usage. Applying Wilcoxon-signed rank tests and a repeated measures marginal model, showed a minimal effect from the behavioral interventions in survey responses. The results also raise questions about surveys as a reliable predictor for behavior-based outcomes. In the third study, interview data from participants sheds light on questions of how and for whom behavioral interventions work. A within-households split-incentive is discovered, describing one factor contributing to the limited effect of in-home displays on household energy usage. Other factors affecting household energy use are also discussed. This dissertation concludes with recommendations for utilities and policy makers.

Dissertation (DTech(Electrical Engineering))--Cape Peninsula University of Technology, 2012
The confluence of the limited resources of fossil fuels (e.g. coal, oil and natural gas), environmental degradations leading to climate change, security of supplies and fossil fuels high costs have demanded a tremendous efforts on humanity to seek for a sustainable and unlimited natural energy sources. Amongst these renewable energy sources stands out solar energy because of its ubiquitousness. Solar energy is converted to DC electricity by the photovoltaic effect. Photovoltaic (PV) power systems installed in commercial and industrial buildings are a good example of distributed power generation. Here the energy consumption and production match and thus electricity taken from the grid during daytime peak hours can be reduced. This is beneficial as the transmission losses in the grid are avoided and also transmission need is reduced. The cost effectiveness of a solar energy system has hindered its wide adoption and deployment in terms of the initial capital cost even though it has a zero energy cost and very minimal operating and maintenance costs. Different governments have instituted many financial incentives for fast adoption of PV systems for both residential and commercial applications. However, all these incentives are not sustainable in the longer term forecast. For PV system to attain grid parity requires more than unsustainable approach of many governments providing time limited subsidies. The technical solution to the problem is to reduce the overall system cost through technical innovations. One such method is the adoption of transformerless inverter technology as the grid interface system. Transformerless inverter topology provides galvanic isolation through innovative inverter topology and switching strategies that eliminates problems created by not employing the service of transformer.

A new generation of compact and highly efficient power production and propulsion technologies are critically needed in enabling NASAs long-term goals. Nuclear fission power technologies as part of project Prometheus are in development to meet this need. Proposed reactor concepts utilize a combination of refractory metals and stainless steels. One such refractory alloy, Niobium 1% Zirconium (Nb-1Zr), will be used because of its strength at high temperatures, neutron absorption properties, and resistance to corrosion by liquid alkali metals. One potential problem in using Nb-1Zr is that it undergoes rapid high temperature oxidation, even in low oxygen concentrations. Long-term oxidation of the niobium matrix can significantly deteriorate the mechanical properties of the alloy. This thesis reports on experimental studies of the high temperature interaction of 316 stainless steel (316 SS) and Nb-1Zr under prototypic space fission reactor operating conditions. Specifically, how the high temperature oxidation rate of Nb-1Zr changes when in contact with 316 SS at low external oxygen concentrations. The objective of the project is to determine if transport of gaseous contaminants, such as oxygen, will occur when Nb-1Zr is in contact with 316 SS, thereby increasing the oxidation rate and degrading material properties. Experiments were preformed in a realistic non-nuclear environment at the appropriate operating conditions. Thermal Gravimetric Analysis techniques were used to quantify results. Coupons of Nb-1Zr and Nb-1Zr in contact with 316 SS foil are subjected to flowing argon with oxygen concentrations between 4-15ppm and heated to a temperature of 500, 750, and 1000oC for 2 to 10 hours. Experiments were conducted at the Early Flight Fission Test Facility at NASA Marshall Space Flight Center. The experimental results indicate that a complex oxidation process, which depends greatly on temperature and oxygen concentration, occurs at the expected operating conditions. Non-linear regression techniques were applied to experimental data in order to derive correlations for the approximate oxidation rate of Nb-1Zr and Nb-1Zr in contact with 316 SS as a function of time, temperature, and oxygen concentration.

Sistemas híbridos consistem de duas ou mais fontes geradoras de eletricidade, normalmente uma ou mais fontes convencionais e uma ou mais fontes renováveis e, objetivam promover a economia de combustível e obter uma fonte confiável de suprimento de energia, podendo estar ou não conectados a rede de distribuição. Este trabalho objetiva avaliar através do software HOMER, a viabilidade técnica, econômica e ambiental de implantação de um sistema híbrido de geração de eletricidade. Este sistema é composto por gerador movido a biogás, gerador movido a biodiesel e captação de energia solar. Todo o sistema está localizado no município de Serafina Corrêa onde há elevada concentração de suinocultores que, através do tratamento dos resíduos suinícolas poderá levar a produção de biogás para ser aproveitado como combustível para geração de energia elétrica. Diversas configurações foram avaliadas sob aspecto econômico e ambiental. A configuração ótima da estrutura do sistema híbrido foi a composta por geração elétrica a partir de painéis fotovoltaicos com 172,4 kW, gerador a biogás 55 kW e inversor de frequência de 110 kW. Neste cenário, o capital inicial soma R$ 1.150.055,00, valor presente líquido de R$ 1.150.004,00 e o custo da energia (COE) é de R$ 0,22/kW. O payback definido pelo software é de 7,1 anos, mostrando-se economicamente viável. Neste contexto, o software HOMER apresenta-se como importante ferramenta a tomada de decisões configurando-se como método de avaliação quanto ao melhor cenário para instalação de sistemas híbridos.
Hybrid systems consist of two or more electricity generating sources, usually one or more conventional sources and one or more renewable sources, and aim to promote fuel economy and obtain a reliable source of energy supply, off-grid or grid-connected to the distribution network. This work aims to evaluate through the HOMER software the technical, economic and environmental feasibility of implementing a hybrid electricity generation system. This system consists of a biogas generator, biodiesel generator and solar energy capture. The entire system is located in the municipality of Serafina Corrêa where there is a high concentration of swine farmers that, through the treatment of pig waste, can lead to the production of biogas to be used as fuel for electric power generation. Several configurations were evaluated under economic and environmental aspect. The optimum configuration of the hybrid system structure is composed of electric generation from photovoltaic panels with 172,4 kW, 55 kW biogas generator and 110 kW inverter. In this scenario, the initial capital amounts to R$ 1.150.055,00, net present value of R$ 1.150.004,00 and the cost of energy (COE) is R$ 0.22. The payback defined by the software is 7.1 years, proving to be economically viable. In this context, the HOMER software presents itself as an important decision-making tool, being configured as an evaluation method for the best scenario for the installation of hybrid systems.

Historically, the most frequently used energy sources have been those nearest and easiest to consume. Unfortunately, society’s reliance on fossil fuel for power generation has occurred at the expense of the environment, coal being a major contribution to carbon dioxide (CO2) emission. Carbon dioxide is classified as a greenhouse gas (GHG); it contributes to the phenomenon of climate change (Haw & Hughes, 2007, p.1). According to Worrell (2011), industry uses nearly 40 percent of worldwide energy on economic activities. Value chain activities alone contribute almost 37 percent to global GHG. Organisations are socially and ethically required to minimise the carbon footprint of their operations. Reducing energy use makes perfect business sense; it saves money, enhances corporate reputations and helps everyone participate the fight against climate change (Carbon Trust, 2011). Gielen, Newman, and Patel (2008) strongly believe the overall energy and emissions trends can be mitigated through additional energy efficiency measures. However, implementing EnMS will enable organisations to establish systematic approaches and the processes necessary to improve energy performance, including energy efficiency, use and consumption (SANS 50001, 2011). The objective of this paper was to evaluate the current energy management strategy adopted by selected automotive manufacture in Eastern Cape. The research was motivated by the fact that previous researchers have focused more on technological aspects and less of management functions. The research paradigm followed in this paper was qualitative because a case study is used to gain an insight and understanding about more and less successful energy management strategies. In this report, background about the global energy outlook and its significant to economic development, factors behind energy demands, the link to climate change and providing effective energy management principles are covered. The energy management principles covered key elements for delivering successful energy management. Literature highlighted that, senior management commitment is the foundation of good energy management, which is delivered through a formal energy policy and a supporting energy strategy with action plan. High level commitment will provide: Advocacy from senior managers; Visibility of the issues across your organization; Impetus for the organisation to implement energy management; Resources, both human and financial. It will also demonstrate that good energy management is part of your organisation’s mission and as relevant as other management aspects. The empirical study is focused on the characteristics of the current management system and organisational structure employed with its relevant functions. Based on these reference points the paper concludes with recommendations for the case study organisation.

This thesis estimates the impacts of rooftop photovoltaic (PV) capacity on electricity generation and CO2 emissions in America's Pacific Northwest. The region's demand for electricity is increasing at the same time that it is attempting to reduce its greenhouse gas emissions. The electricity generated by rooftop PV capacity is expected to displace electricity from fossil fueled electricity generators and reduce CO2 emissions, but when and how much? And how can this region maximize and focus the impacts of additional rooftop PV capacity on CO2 emissions? To answer these questions, an hourly urban rooftop PV generation profile for 2009 was created from estimates of regional rooftop PV capacity and solar resource data. That profile was compared with the region's hourly fossil fuel generation profile for 2009 to determine how much urban rooftop PV generation reduced annual fossil fuel electricity generation and CO2 emissions. Those reductions were then projected for a range of additional multiples of rooftop PV capacity. The conclusions indicate that additional rooftop PV capacity in the region primarily displaces electricity from natural gas generators, and shows that the timing of rooftop PV generation corresponds with the use of fossil fuel generators. Each additional Wp/ capita of rooftop PV capacity reduces CO2 emissions by 9,600 to 7,300 tons/ year. The final discussion proposes some methods to maximize and focus rooftop PV impacts on CO2 emissions, and also suggests some questions for further research.

CAPES
Neste trabalho é descrito um sensor de índice de refração baseado em redes de Bragg em fibra multimodo para o setor de combustíveis líquidos. A utilização dos dispositivos propostos visa superar as desvantagens associadas com a monitoração de amostras de índice de refração elevados. A sensibilidade do transdutor pode ser adaptada, ajustando o diâmetro final da fibra na qual a rede de Bragg é gravada. Devido à relação entre a razão sinal-ruído e a sensibilidade, os parâmetros do sensor devem ser otimizados para obter uma faixa dinâmica de índice de refração adequada para aplicações específicas. A características metrológicas do sensor são determinadas, resultando em resoluções entre 5,6% v/v e 0,4% v/v para os índices de refração variando entre 1,4562 e 1,4729. Os resultados mostram o potencial do dispositivo em aplicações específicas relativas à avaliação da qualidade do biodiesel e análise de conformidade de misturas diesel-biodiesel.
In this work, a multimode fiber Bragg refractive sensor for the liquid fuel sector is described. The use of etched devices is proposed to overcome the drawbacks associated with sensing high refractive index samples employing fiber transducers. The transducer sensitivity can be tailored by adjusting the final diameter of the etched Bragg grating. Due to a trade between the signal-to-noise ratio and the sensitivity, operational parameters of the sensor must be designed to match the expected refractive index dynamic range for specific applications. Metrological properties of the sensor are determined, resulting in resolution from 5.6% v/v to 0.4% v/v for refractive indexes ranging from 1.4562 to 1.4729. Specific applications regarding the quality assessment of biodiesel and conformity analysis of diesel- biodiesel blends are discussed.

Fossil fuels are the major sources of electrical power generation in the world. Among all fossil fuels, oil is considered as the most sought-after fuel. The burden on countries that provide subsidized electricity produced from oil-fired power plants is noteworthy. Kuwait is a notable example of these countries. Electricity in Kuwait is heavily consumed by residential air conditioning, which comprises 60% of the total electricity generated at peak times on a hot summer day. From this perspective, residential air conditioning in Kuwait was selected to undergo further investigation regarding low energy air conditioning choices. Three solutions to control the rapid growth of demand for electricity by residential air conditioning are examined. The first solution investigated assesses the orientation and grouping of houses in Kuwait in order to examine their effect on cooling load and electrical energy consumption for future houses. Four residential cases were developed; each case comprises six typical houses. The cases identified are: (1) single block facing east-west, (2) single block facing north-south, (3) double block facing east-west and (4) double block facing north-south. Cooling loads are calculated using the DesignBuilder building thermal simulation software. Case (2) is found to have the smallest cooling load, and case (1) the largest. The estimated savings from applying case (2) compared to the average of the four cases for the future houses planned to be built by the government by the year 2016 (i.e. approximately 20,000 houses) are found to be approximately .US 33 million of power system capital costs, 15 GWh per year of electrical energy consumption and 11 kilotons per year of CO2 emissions. In the second solution, a lifecycle cost analysis is performed to evaluate the economic feasibilities of electricity driven chilled water system compared to predominant air conditioning system in Kuwaiti houses which is Packaged- Direct Expansion. The study considers the total cash paid by the consumer and the total cash paid by the government, since electricity is subsidized in Kuwait. The study finds that the chilled water system is not cost-effective for consumers due to high installation cost. However, a chilled water system would be cost-effective for the government because it consumes 40%less electrical energy than Packaged-DX. So, the study suggests subsidising the installation of chilled water systems so that the installation cost to the consumer is the same as for Packaged-DX systems. In the third solution, the study examines the viability of a single-effect LiBr absorption chiller driven by steam extracted from the steam turbine in the configuration of a combined cycle power plant (CCPP). The analysis shows that CCPP with absorption chiller yields less net electrical power available to utility grid compared to similar CCPP giving electricity to the grid and to Direct-Expansion air conditioning systems for the same cooling requirements. The reasons for that are the reduction in steam turbine power output resulted from steam extraction, and the amount of electrical energy required to operate the configuration of CCPP with absorption chiller.

Although concentrated solar power can be used to produce power using traditional electricity generation, energy storage has become a problem due to the intermittent supply of solar energy. By using solar energy in chemical production processes, the solar energy can be stored in a useful chemical product. The purpose of this thesis will be to examine the possibilities of a new solar chemical cycle the produces iron and ethylene from hematite (a form of iron oxide) and ethane using concentrated solar power. These two products are important stepping stones in the production of steel and polymers. This process could allow for the current process of steel production to move away from processes using coal and towards a more sustainable process using the hydrogen formed from the ethane cracking process and solar energy. The thesis will include: (1) the development of a new solar powered iron and ethylene combined cycle, (2) a feasibility study of a Concentrated Solar Heat Supply System (CSHSS) being developed at Georgia Tech, and (3) an assessment of the proposed cycle. The assessment will include an estimate of production including a thermodynamic ASPEN model, assessment of research to realize actualization of the theoretical cycle, an exergy analysis, and a heat exchanger analysis for the exchange of heat between the CSHSS and the chemical process.

Distributed generation (DG) systems as local power sources have great potential to contribute toward energy sustainability, energy efficiency and supply reliability. This thesis deals with DGs that use solar as primary energy input, hydrogen energy storage and conversion technologies (fuel cells and water electrolyzers) as long term backup and energy storage batteries and supercapacitors as short term backup. Standalone power systems isolated from the grid such as those used to power remote area off-grid loads and grid connected systems running in parallel with the main utility grid or a microgrid for local grid support are treated. As cost is the key challenge to the implementation of PV-hydrogen DGs, the main focus is developing sound control methods and operating strategies to help expedite their viability in the near future. The first part of the thesis deals with modeling of system components such as PV generator, fuel cell, lead acid/Li-ion storage batteries, electrolyzer, supercapacitor, power electronic converters and auxiliaries such as hydrogen storage tank and gas compressor. The subsystems are modeled as masked blocks with connectable terminals in Matlab®/Simulink® enabling easy interconnection with other subsystems. The models of main subsystems are fully/partially validated using measurement data or data obtained from data sheets and literature. The second part deals with control and operating strategies in PV hybrid standalone power systems. The models developed in the first part are used to simulate integrated systems. An attempt is made to provide some answers on how the different power sources and energy storages can be integrated and controlled using power electronics and feedback control to enhance improved performance, longer life time, increased supply reliability and minimize fuel use. To this end, new control methods and operating strategies are proposed to mediate near optimal intersubsystem power flows. The third part of the thesis concerns grid connected PV-Fuel cell power systems. Control schemes and operating strategies for integrating PV and fuel cell hybrids into the grid to serve both local demand and weak grids are investigated. How hydrogen energy storage and conversion technologies can be controlled to suppress PV fluctuations in future utility grids are also explored. A smoothing algorithm enhanced by a stepwise constant forecast is developed to enable more smooth and subhourly dispatchable power to be fed to the grid. The proposed methods were verified through longtime simulation based on realistic irradiance data over a number of typical days/weeks using suitably defined performance indices. It was learned that using power electronics and sound control methods, PV-hydrogen DGs can be flexibly controlled to solve lifetime and performance issues which are generally considered economic bottle necks. For example, conventionally in PV-hydrogen hybrids, to improve performance and life time, more battery capacity is added to operate fuel cell and electrolyzer under more stable power conditions in the face of highly fluctuating PV generation to prevent low state of charge (SOC) operation of the battery. Contrarily, in this thesis a sound control method is proposed to achieve the same objectives without oversizing the battery. It is shown that the proposed method can give up to 20% higher battery mean state of charge than conventional operation while PV fluctuation suppression rates up to 40% for the fuel cell and 85% for the electrolyzer are found for three typical days. It is also established that by predictively controlling battery SOC instead of conventional SOC setpoint control, substantial improvements can be obtained (up to 20-30% increase in PV energy utilization and ca. 25% reduction in fuel usage for considered days). Concerning use of hydrogen storage and conversion technologies in PV fluctuation suppression, results obtained from the developed smoothing mechanism and performance indices show that a trade-off should be made between smoothing performance and dispatchability. It was concluded that the right size of fuel cell and electrolyzer needs to be selected to optimize the dispatch interval and smoothing performance. Finally, a PV-hydrogen test facility which can act as show case for standalone, grid-connected and UPS applications was designed and built. The test facility was used to characterize key subsystems from which component models developed were experimentally validated. The facility also acted as a reference system for most of the investigations made in this thesis.

Monitoring parameters characterizing water quality, such as temperature, pH and concentrations of heavy metals in natural waters, is often followed by transmitting the data to remote receivers using telemetry systems. Such systems are commonly powered by batteries, which can be inconvenient at times because batteries have a limited lifetime and have to be recharged or replaced periodically to ensure that sufficient energy is available to power the electronics. To avoid these inconveniences, we have designed and tested a self-renewable power source, a microbial fuel cell, which has the potential to eliminate the need for batteries to power electrochemical sensors used to monitor water quality and small telemetry systems used to transmit the data acquired by these sensors. To demonstrate the utility of the microbial fuel cell, we have combined it with low-power, high-efficiency electronic circuitry providing a stable power source for wireless data transmission. To generate enough power for the telemetry system, energy produced by the microbial fuel cell was stored in an ultracapacitor and used in short bursts when needed. Since powering commercial components of electronic circuits requires 5 Volts, and our cell was able to deliver a maximum of 2.1 V, we used a DC-DC converter to increase the potential. The DC-DC converter powered the transmitter, which gathered the data from the sensor and transmitted them to a receiver. To demonstrate the utility of the system, we initially measured temporal variations in temperature followed by the implementation of a chemical sensor to measure copper and lead concentrations in water; this data was then wirelessly transmitted to a remote receiver.

Les Piles à Combustible Microbiennes (PCMs) mettent en oeuvre le métabolisme de micro-organismes et utilisent de la matière organique pour générer de l'énergie électrique. Les applications potentielles incluent le traitement d'eau usée autonome en énergie, les bio-batteries, et le grappillage d'énergie ambiante. Les PCMs sont des équipements basse-tension et basse-puissance dont le comportement est influencé par la vitesse à laquelle l'énergie électrique est récupérée. Dans cette thèse, on étudie des méthodes pour récupérer l'énergie électrique de façon efficace. La tension à laquelle l'énergie est récupérée des PCMs influence leur fonctionnement et leurs performances électriques. La puissance délivrée est maximum pour une tension spécifique (environ 1/3 de la tension en circuit-ouvert). Les PCMs ont été testées à ce point en utilisant une charge contrôlée automatiquement qui inclut un algorithme de recherche de puissance maximale. Un tel outil a été utilisé pour évaluer la puissance maximum, la vitesse de consommation du combustible, le rendement Coulombic et le rendement de conversion de 10 PCMs à chambre unique de 1.3 L, construites de façon similaire. Bien que d'autres choix structurels et opératoires peuvent permettre d'améliorer ces performances, ces résultats ont étudié pour la première fois les performances des PCMs en condition de production d'énergie de point de puissance maximal et les PCMs ont été testées avec des conditions de récupération d'énergie réalistes. Récupérer un maximum d'énergie des PCMs est la ligne directrice de ce rapport. Cela est rendu possible par des circuits dédiés de gestion de l'énergie qui embarquent un contrôle contre-réactif pour réguler la tension des PCMs à une valeur de référence qui est égale à une fraction de leur tension en circuit ouvert. Deux scénarios typiques sont développés dans la suite. Une application critique des PCMs concerne le grappillage autonome de petites énergies, pour alimenter des équipements électroniques basse-puissance (e.g. capteurs sans fil). Dans ce cas, les contraintes basse-puissance et basse-tension imposées par les PCMs nécessitent des fonctionnalités de démarrage autonomes. L'oscillateur d'Armstrong, composé d'inductances couplées à fort rapport d'enroulement et d'un interrupteur normalement-fermé permet d'élever des tensions de façon autonome à partir de sources basse-tension continues comme les PCMs. Ce circuit a été associé à des convertisseurs d'électronique de puissance AC/DC et DC/DC pour réaliser respectivement un élévateur-de-tension et une unité de gestion de l'énergie (UGE) auto-démarrante basée sur une architecture flyback. La première est adaptée pour les puissances inférieures à 1 mW, alors que la seconde peut être dimensionnée pour des niveaux de puissance de quelques mW et permet de mettre en oeuvre une commande qui recherche le point de puissance maximal du générateur. Une seconde application d'intérêt concerne le cas où de l'énergie est récupérée depuis plusieurs PCMs. L'association série peut être utilisée pour élever la tension de sortie mais elle peut avoir des conséquences négatives en terme de performances à cause des non-uniformités entre cellules. Cet aspect peut être résolu avec des circuits d'équilibrage de tension. Trois de ces circuits ont été analysés et évalués. Le circuit " complete disconnection " déconnecte une cellule défectueuse de l'association pour s'assurer qu'elle ne diminue pas le rendement global. Le circuit " switched-capacitor " transfère de l'énergie depuis les MFCs fortes vers les faibles pour équilibrer les tensions de toutes les cellules de l'association. Le circuit " switched-MFCs " connecte les PCMs en parallèle et en série de façon alternée. Chacune des trois méthodes peut être mise en oeuvre à bas prix et à haut rendement, la plus efficace étant la " switched-capacitor " qui permet de récupérer plus de 85 % de la puissance maximum idéale d'une association très largement non uniforme

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 83-92).
In this thesis, a literature review of hybrid solar-fossil fuel power generation is first given with an emphasis on system integration and evaluation. Hybrid systems are defined as those which use solar energy and fuel simultaneously, thus excluding the viable alternative of solar thermal plants which use fossil fuels as backup. The review is divided into three main sections: performance metrics, the different concentrated solar receiver technologies and their operating conditions, and the different hybridization schemes. In addition, a new linear combination metric for analysis of hybrid systems, which considers trade-off of different metrics at the fleet level, is presented. This metric is also compared to alternative metrics from multi-objective optimization. Some previous work only evaluates the hybrid cycle at a certain point in time, which can be misleading as this evaluation would not take into account certain aspects of hybrid cycle such as fluctuating solar supply. Furthermore, almost all previous work designs the hybrid solar-fossil fuel systems for a certain point in time and then evaluates the performance of the system for an entire year. By not taking into account fluctuating solar supply and selling price of electricity in the design of the system, the best possible annual performance of the hybrid cycle may not be reached. Second, an analysis of solar reforming as the integration method for the hybrid cycle is presented, in particular steam reforming of methane. Two solar reforming systems are analyzed: one with a parabolic trough and the other with a solar tower. From the analysis, it is determined that parabolic troughs are not suitable for steam reforming due to the relatively low operating temperatures. The tower reformer system is integrated with a standard combined cycle, and the design and operation of the hybrid cycle is optimized for highest work output for a fixed fuel input and solar collector area (essentially optimizing for maximum cycle efficiency). A heuristic two step procedure is used for the optimization due to the limitation of the optimizer which cannot simultaneously optimize both design and operation. From the optimization, it is determined that the tower reforming integration method is a promising integration option in that this type of hybrid cycle yields high incremental solar efficiencies and also satisfies the linear combination metric for efficiency and CO₂ emissions (i.e., the analyzed hybrid cycle has a higher efficiency for a fixed CO₂ emissions compared to a linear combination of solar only and fossil fuel only cycles).
by Elysia J. Sheu.
S.M.

PEMFCs are the most popular type of Fuel Cells (FCs) and traditionally use hydrogen as the fuel. One FC problem is its relative slow dynamics caused by the time constant of the hydrogen and oxygen supply systems that can be in the range of several seconds. In this sense, supercapacitors (SCs) respond faster than FC to a fast increase or decrease in power demand. Thus, using SCs together with FCs improves FC life and performance by absorbing faster load changes and preventing fuel starvation of the FC. Therefore, it becomes necessary to study structures of power conditioners with their respective control systems that can mitigate the disadvantages mentioned of the FC itself. Several researches have studied the different topologies with their respective control proposals to operate FC and SC. This thesis proposes a digital control scheme to operate a PEMFC module of 1.2 kW and a SC through a DC/DC hybrid converter. A FC has been proposed as a primary source of energy and a SC has been proposed as an auxiliary source of energy. An experimental validation of the system implemented in the laboratory is provided. Several tests have been performed to verify that the system achieves an excellent output voltage (V0) regulation and SC Voltage (VSC) control, under disturbances from FC power (PFC) and output power (P0) as well as other perturbations described in analysis results.

Despite increasing fuel cost volatility, regulatory uncertainty, and imminent shifts to industry dynamics, utility managers are forced to make tough decisions in regards to installing long-life generation assets. This study seeks to identify and quantify determinants of fuel choice in new electric power plants given vast uncertainties in the electricity generation sector. Using a probit functional form to estimate marginal effects on the likelihood of choosing wind versus natural gas powered generation, I find positive effects of natural gas prices in the period three years prior to initial operation of the new facility, positive effects of static-level standard score of mix, and positive effects of wind-power density. Additional feedstock choice sets and parameters are considered. All models suggest that (a) feedstock costs are significant predictors of fuel choice, (b) state-level regulatory learning enhances likelihood of choosing relatively young technologies, (c) Renewable Portfolio Standards result in artificial substitution between wind and solar technologies, and (d) population density, more so than political influence, predicts choices to install wind-powered capacity. Public policy and managerial implications are discussed.

This thesis concerns system studies of power plants wheredifferent types of fuel cells accomplish most of the energyconversion.

Ever since William Grove observed the fuel cell effect inthe late 1830s fuel cells have been the subject or more or lessintense research and development. Especially in the USA theseactivities intensified during the second part of the 1950s,resulting in the development of the fuel cells used in theApollo-program. Swedish fuel cell activities started in themid-1960s, when ASEA (now ABB) ran a fuel cell projectdeveloping fuel cells to power submarines.

When the then project manager, Olle Lindström, wasappointed professor of Chemical Technology at KTH, the fuelcell activities at KTH were initiated, these activities havesince then been pursued at varying levels of intensity.

The fuel cell development experienced a recession during thelatter part of the 1970s and early 1980s, only to bere-vitalised during the 1990s as the full potential of theadvantages of environmental benefits and efficiency wereidentified.

System studies and process simulation utilising differentcomputer software programs may be used to study the behaviourand characteristics of fuel cells and their supportsystems.

Paper I describes the characteristics of a naturalgas-fuelled fuel cell power plant using alkaline fuel cells,both regarding efficiency and economics.

In paper II, a benchmark study of three different types ofsimulation software is presented. Theintention was to clarifyhow the selection of software might influence the resultsobtained, and some of the associated possible pitfalls.

Paper III presents a study of a fuel cell power plant wherethe primary source of energy is biomass (wood chips), which viahigh-pressure gasification and subsequent gas cleaning is madeavailable for conversion into electricity and heat by moltencarbonate fuel cells.

The last paper, paper IV, presents a s system study of ahigh-temperature fuel cell system, where the primary fuel iscoal, which through gasification is converted into a gaseousform. This study was a vital part of an EU-project studying thetechnical and economical feasibility of such systems.

Keywords: fuel cells, fuel cell systems, system studies,process simulation, system analysis, alkaline fuel cells,high-temperature fuel cells.

Microfabricated fuel cells have been designed and constructed on silicon integrated circuit wafers using many processes common in integrated circuit fabrication, including sputtering, polymer spin coating, reactive ion etching, and photolithography. Fuel delivery microchannels were made through the use of sacrificial polymers. The characteristics of different sacrificial polymers were studied to find the most suitable for this work. A polypropylene carbonate solution containing a photo-acid generator could be directly patterned with ultraviolet exposure and thermal decomposition. The material that would serve as the fuel cells proton exchange membrane (PEM) encapsulated the microchannels. Silicon dioxide deposited by plasma enhanced chemical vapor deposition (PECVD) at relatively low temperatures exhibited material properties that made it suitable as a thin-film PEM in these devices. By adding phosphorous to the silicon dioxide recipe during deposition, a phosphosilicate glass was formed that had an increased ionic conductivity. Various polymers were tested for use as the PEM or in combination with oxide to form a composite PEM. While it did not work well alone, using Nafion on top of the glass layer to form a dual-layer PEM greatly enhanced the fuel cell performance, including yield and long-term reliability. Platinum and platinum/ruthenium catalyst layers were sputter deposited. Experiments were performed to find a range of thicknesses that resulted in porous layers allowing contact between reactants, catalyst, and the PEM. When using the deposited glasses, multiple layers of catalyst could be deposited between thin layers of the electrolyte, resulting in higher catalyst loading while maintaining porosity. The current and power output were greatly improved with these additional catalyst layers.

La creciente complejidad de los dispositivos electrónicos portátiles demanda fuentes de energía que cumplan con los requerimientos de entregar una alta densidad de potencia en un tamaño reducido y en muchos casos la posibilidad de lograr una completa integración. En este sentido, un intenso trabajo de investigación se ha enfocado hacia la miniaturización de las fuentes de alimentación en una amplia variedad de tecnologías. Una tendencia similar se ha seguido en el campo de los sistemas micro electromecánicos (MEMS), donde el concepto de sistema inteligente o Smart System ha impulsado el desarrollo de una nueva generación de dispositivos de alimentación, tales como baterías, pilas de combustible o generadores de energía, que en conjunto se conocen como powerMEMS. Entre los diferentes sistemas de generación de energía, las micro pilas de combustible han recibido una especial atención debido a sus particulares características, como son la alta densidad de energía, emisiones no-tóxicas y la posibilidad de eliminar partes móviles simplificando el proceso de fabricación y reduciendo la probabilidad de fallo. Las pilas de combustible de electrolito polimérico (PEMFC) son particularmente atractivas debido a su capacidad de trabajar a temperatura ambiente usando hidrógeno o combustibles líquidos. La posibilidad de funcionar con combustibles líquidos, tales como metanol o compuestos orgánicos, representa una ventaja importante para las aplicaciones portátiles debido a la simplicidad de almacenamiento y manipulación del combustible. En esta tesis se presentan los primeros desarrollos y contribuciones tecnológicas al campo de micro pilas de combustible llevados a cabo en el IMB-CNM (CSIC). En particular, este trabajo está dedicado al estudio de pilas de combustible microfabricadas como fuentes de energía para microsistemas. Esta tesis se compone de siete capítulos: el capítulo de introducción y seis capítulos experimentales divididos en tres secciones. La primera sección describe el desarrollo de una micro pila de combustible de metanol directo utilizando un enfoque híbrido, el cual fue utilizado para identificar y medir los efectos que más influyen en el rendimiento del dispositivo en la microescala. La segunda sección presenta las estrategias realizadas respecto a la integración de todos los componentes de la micro pila hacia un dispositivo más compacto utilizando tecnologías de microfabricación compatibles. Estos métodos incluyeron el uso de diferentes técnicas de microestructuración de polímeros como una manera de optimizar las dimensiones del dispositivo, así como la reducción de costes de los materiales y producción. Por último, la tercera sección presenta dos aplicaciones específicas de las micro pilas de combustible desarrolladas, una bio pila de combustible microfabricada utilizando microorganismos como biocatalizadores de compuestos orgánicos y una plataforma microfluídica alimentada por una micro pila de combustible que puede ser de gran interés para aplicaciones Lab-on-a-Chip o micro Total Analysis Systems (µTAS).
The increasing complexity of portable electronic devices demands energy sources that meet the requirement of delivering a high power density within a reduced size, and in many cases the possibility of achieving complete integration. In this sense, an intense research effort has been focused towards the miniaturization of powering devices in a wide variety of technologies. A similar trend has been followed in the micro electromechanical systems (MEMS) technology field, where the smart-system concept has impelled the development of a new generation of powering devices, such as batteries, fuel cells or energy harvesters, which altogether are known as powerMEMS. Among the different energy generation systems, micro fuel cells have received special attention due to their particular features, i.e. high energy density, non-toxic emissions and the possibility of avoiding movable parts simplifying the fabrication process and reducing the risk of failure. Polymer electrolyte membrane fuel cells (PEMFCs) are particularly attractive due to their capability of working at room temperature using both hydrogen and liquid fuels. The possibility to operate using liquid fuels, such as methanol or organic compounds, represent an important advantage for portable applications due to the great simplification of fuel storage and handling processes. This thesis presents the first developments and technological contributions to the micro fuel cell field performed at IMB-CNM (CSIC). Particularly, this work is dedicated to the design and fabrication of microfabricated fuel cells as power sources to be integrated within the microsystems to be powered. The work is organized in seven chapters: one introductory chapter and six experimental chapters that have been divided in three sections. The first section describes the development of a micro direct methanol fuel cell using a hybrid approach, which was used to identify and measure the effects that influence the most on the device performance at a microscale. The second section presents different strategies regarding the integration of all micro fuel cell components into a more compact device by taking advantage of microfabrication compatible technologies. These approaches involved the use of different polymer micropatterning techniques as a way to optimize the device dimensions and reduce materials and production cost. Finally, the third section presents two particular applications of the developed micro fuel cells, a microfabricated bio fuel cell using microorganisms as biocatalysts of organic compounds and a fuel cell powered microfluidic platform that can be of great interest for Lab-on-a-Chip or micro Total Analysis Systems (µTAS).

The topic of this thesis is the generation of electricity from hydrocarbon fuels via polymer electrolyte fuel cells (PEFC). The aim has been to develop methods and hardware for experimental evaluation of process parameters and design variables in PEFC reformate cells and stacks. Reformate fuel cell systems have the potential to offer a way for utilizing fuels efficiently with low global and local emissions. Reforming of hydrocarbon fuels may also provide a way around the famous “chicken or egg” dilemma of hydrogen vehicles and infrastructure. In this thesis current distribution measurements are introduced as a tool for investigating the current distribution in a PEFC with Pt/C or PtRu/C anode catalyst as function of reformate fuel gas composition. It is shown that CO may induce a strong transient behavior, with respect to current density, on both Pt/C and PtRu/C catalysts, depending on mode of operation. Analysis of the exhaust fuel gas showed that the oxygen in the air bleed most likely reacts close to the anode inlet, but this is not visible in the measured current density plots.  The time dependence of the CO poisoning reactions is studied more closely in a commercial fuel cell stack. The development of a test fuel cell system, called multisinglecell, that can multiply the capacity of a conventional test station is reported. The setup is successfully demonstrated with initial screening of the corrosion resistance of different stainless steel grades and coatings. Most of the iron originating from a stainless steel sample accumulates in the MEA and GDLs. These results were validated with a similar measurement in a commercial fuel cell stack. The experimental validation of a 3D FEM computer endplate model, which can accurately predict pressure distribution within any type of fuel cell at any temperature, is described. The model could reliably predict trends in changes in the compression pressure distribution. The PBI fuel cell competes with the PEFC in small-scale power applications. A high temperature break-in procedure for PBI fuel cells is developed, which can rapidly and reproducibly ensure stable cell behavior.
QC 20101130

To mitigate the global greenhouse gases (GHGs) emissions, carbon dioxide (CO2) capture and storage (CCS) has the potential to play a significant role for reaching mitigation target. Oxy-fuel combustion is a promising technology for CO2 capture in power plants. Advantages compared to CCS with the conventional combustion technology are: high combustion efficiency, flue gas volume reduction, low fuel consumption, near zero CO2 emission, and less nitrogen oxides (NOx) formation can be reached simultaneously by using the oxy-fuel combustion technology. However, knowledge gaps relating to large scale coal based and natural gas based power plants with CO2 capture still exist, such as combustors and boilers operating at higher temperatures and design of CO2 turbines and compressors. To apply the oxy-fuel combustion technology on power plants, much work is focused on the fundamental and feasibility study regarding combustion characterization, process and system analysis, and economic evaluation etc. Further studies from system perspective point of view are highlighted, such as the impact of operating conditions on system performance and on advanced cycle integrated with oxy-fuel combustion for CO2 capture. In this thesis, the characterization for flue gas recycle (FGR) was theoretically derived based on mass balance of combustion reactions, and system modeling was conducted by using a process simulator, Aspen Plus. Important parameters such as FGR rate and ratio, flue gas composition, and electrical efficiency etc. were analyzed and discussed based on different operational conditions. An advanced evaporative gas turbine (EvGT) cycle with oxy-fuel combustion for CO2 capture was also studied. Based on economic indicators such as specific investment cost (SIC), cost of electricity (COE), and cost of CO2avoidance (COA), economic performance was evaluated and compared among various system configurations. The system configurations include an EvGT cycle power plant without CO2 capture, an EvGT cycle power plant with chemical absorption for CO2 capture, and a combined cycle power plant. The study shows that FGR ratio is of importance, which has impact not only on heat transfer but also on mass transfer in the oxy-coal combustion process. Significant reduction in the amount of flue gas can be achieved due to the flue gas recycling, particularly for the system with more prior upstream recycle options. Although the recycle options have almost no effect on FGR ratio, flue gas flow rate, and system electrical efficiency, FGR options have significant effects on flue gas compositions, especially the concentrations of CO2 and H2O, and heat exchanger duties. In addition, oxygen purity and water/gas ratio, respectively, have an optimum value for an EvGT cycle power plant with oxy-fuel combustion. Oxygen purity of 97 mol% and water/gas ratio of 0.133 can be considered as the optimum values for the studied system. For optional operating conditions of flue gas recycling, the exhaust gas recycled after condensing (dry recycle) results in about 5 percentage points higher electrical efficiency and about 45 % more cooling water consumption comparing with the exhaust gas recycled before condensing (wet recycle). The direct costs of EvGT cycle with oxy-fuel combustion are a little higher than the direct costs of EvGT cycle with chemical absorption. However, as plant size is larger than 60 MW, even though the EvGT cycle with oxy-fuel combustion has a higher COE than the EvGT cycle with chemical absorption, the EvGT cycle with oxy-fuel combustion has a lower COA. Further, compared with others studies of natural gas combined cycle (NGCC), the EvGT system has a lower COE and COA than the NGCC system no matter which CO2 capture technology is integrated.
QC 20111123

This dissertation consists of two studies, both related to the impacts of economic and political factors on fuel choice in electric power generation. The primary purpose of the first study is to estimate the degree of price-induced interfuel substitution between three fossil fuels in West European power generation. The problem is studied within two restricted flexible cost functions, a translog model and a Generalized Leontief model. The results show that both models generate reasonable short-run responses to changes in relative fossil fuel prices. In general the degree of short-run interfuel substitution is found to be substantial, a result that is partly explained by the large share of multi-fuel plants in West European power generation. In addition, by deriving the shadow price of capital from the Generalized Leontief cost function the long-run own- and cross-price elasticities of fossil fuel demand are presented. Overall, however, this approach is not able to produce empirically reliable long-run estimates. Finally, the empirical investigation also indicates that public policies and changes in system load factors have had significant impacts on fossil fuel choices in West European power generation. The main purpose of the second study is to explore what factors have been the most important in determining the choices between different electricity supply alternatives in Zimbabwe since 1980. In a first step the economic costs of the available electricity supply options are estimated and secondly these costs are contrasted with the actual choices made by the electricity authorities. It is shown that in the early 1980s the electricity supply choices in Zimbabwe were dictated by a self-sufficiency policy, and accordingly least-cost alternatives were rejected. Due to a new political environment, financial problems and pressures from the World Bank, the step towards least-cost choices was substantial in the 1980s and the 1990s, although not complete. This and the ongoing trend towards higher discount rates imply that thermal power, be it coal- or gas-fired power, probably will dominate future electric power investments in Zimbabwe.
Godkänd; 1997; 20061128 (haneit)