Dissertations / Theses on the topic 'Electric steam generator'

This master’s thesis is focused on the design of electric steam generator for superheated steam. Using heating cartridge is the easiest way how to make a saturated or superheated steam. This device is part of gasification reactor, which is used for experimental purposes. The thesis includes schematic involvement of technology. Technology contains evaporator and superheater. The evaporator is calculated as pool boiling. The superheater is design for steam flowing through heating cartridge bundle. At the end of the thesis are made projection drawings, which are based on the calculations.

Abstract This Bachelor thesis has been written at the Blekinge Institute of Technology. The thesis describes electricity production in Shoaiba Steam Power plant in Saudi Arabia. Shoaiba Power Plant is located 100 km South of Jeddah city in Saudi Arabia. Total power production ability reaches 4400 MW. Shoaiba Power Plant has two stages and is constructed with 11 units, each unit produces 400 MW at line voltage 24 kV and line current 16 kA. Main pieces of equipment and their function in the station are as follows: A Steam Generator (boiler), produces steam by burning natural gas or crude oil in the furnace. The steam is superheated and is passed into a steam turbine, which converts the thermal energy of the steam into mechanical power, in form of rotary motion. The turbine drives a generator, which converts the rotary energy of the turbine into electric power. Steam generator, steam turbine and electrical generator are components that are described in the thesis. When the flow of steam to the turbine is controlled, then the amount of thermal energy that changes to mechanical energy in the steam turbine is controlled. The electrical generator is where the final energy conversion takes place. The mechanical energy from the turbine is converted by the generator into electrical energy, which is transmitted to the service area by help of electrical transmission lines. The plant cycle is an essential part of the energy flow path. Without the plant cycle, the conversion of thermal energy into mechanical energy would not occur, The plant cycle is a closed loop that allows the same water to be used over and over again. Always, the power plants are situated far from residential areas and located outside cities and close to the sea, because the steam is produced from seawater. The advantages of the steam power stations are as follows: They can produce high amounts of electrical energy from small amounts of fuel. They have low initial costs, obstetrics and maintenance costs are not high, and the stations do not need much space to be built and they have usually high capacity. The disadvantages of steam stations are the following: They cause environmental pollution, they have low efficiency, and require very big quantities of cooling water, and the stations must be built away from populated areas.
Conclusion: Converting in steam power plant is one of many ways to produce electrical energy in the world. It can be done in any country because it can be done with different chemical sources. In Saudi Arabia we use oil, because it easier and cheaper than any other chemical source for us. As any country would use what is better for them. The thesis has described circulation system in Shoaiba power plant by converting chemical energy to thermal energy in the boiler, then the turbine converts thermal energy to mechanical energy. Then the mechanical energy is converted to electrical energy in the generator. The advantages of the steam stations are as follows: production of high amounts of electrical energy from small amounts of fuel, low cost of the initial costs, obstetrics and maintenance costs are not high, the station does not need much space to build and they are usually high capacity. The disadvantages of steam stations are the following: environmental pollution, low efficiency, requires very big amounts of cooling water, and these stations must be built away from population areas.
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In recent years, the trend for continuous down-scaling of CMOS device dimension has made analog design much more challenging. This trend has been a major driving force in trying to find new approaches for designing common analog building blocks. One such block is the bandgap voltage reference. This common circuit serves the purpose of generating a fixed DC voltage reference and has uses in a wide variety of applications.
This thesis introduces a new way of generating a programmable DC voltage reference with similar performance to the traditional means. This voltage reference generator is based on periodic bit-stream modulation and relies on simple digital logic combined with a low pass filter (LPF) to demodulate the DC reference level. The advantage of the proposed DC voltage reference lies in its immunity to technology scaling as it is mostly digital. The programmability of the proposed circuit also makes it usable as a digital to analog converter (DAC).
Through simulation and experimental results obtained using a set of integrated circuits implemented in 0.35 mum, 0.25 mum and 0.18 mum CMOS technologies a number of conclusions are reached. The tradeoffs between the two different bit-stream modulation scheme, pulse width modulation (PWM) and pulse density modulation (PDM), are compared yielding PDM as the best approach. The analysis and simulation of a new synthesis method will demonstrate that high-order passive RC filters yield the most attractive realization of the LPF. Experimental results will also demonstrate that performance due to temperature variations comparable to bandgap references can be achieved. A set of experiments will also demonstrate the excellent performance of this voltage reference when used as a DAC. Lastly, the use of asynchronous logic for generating periodic bit-streams will be shown to yield promising results.

Mitochondria are essential for the viability of mammalian cells and provide a compartment for specific chemical reactions. Cellular respiration -- the main mitochondrial function -- is tightly connected with ROS production: the mitochondrial electron transport chain complexes I and III are the main ROS sources in mammalian cells. It has been reported that complex I and complex III activities are essential for cell cycle, apoptosis and stem cell differentiation (Spitkovsky et al., 2004; Varum et al., 2009; Lee et al., 2011; Ma et al., 2011; Tormos et al., 2012). In our work, we aimed to investigate the role of mitochondrial electron transport chain activity in the regulation of the differentiation potential and to unravel signaling pathways that could participate in this regulation. As a model, we used the P19 pluripotent stem cell line that can be easily differentiated into trophoblasts, expressing intermediate filaments cytokeratin 8/18, and neurons, which express cytoskeleton protein beta-III-tubulin. We first showed that both trophoblast and neural differentiation of P19 cells were accompanied by activation of cellular respiration. The analysis of respiratory chain complexes and supercomplexes, however, showed that undifferentiated P19 cells, as well as their differentiated derivatives did not differ in their respiratory machinery, including functional respirasomes. While undifferentiated cells did not use respiration as the main energy source, cellular respiration was activated during differentiation, indicating that oxidative metabolism was important for efficient differentiation. To investigate the potential role of mitochondrial electron transport chain activity we monitored the influence of a disrupted electron flow on the differentiation of P19 cells. We found that the activity of complex I and complex III influenced the differentiation potential of the pluripotent P19 cell line: the presence of complex I and complex III inhibitors rotenone, antimycin A, or myxothiazol increased the amount of cytokeratin 8/18+ cells during trophoblast differentiation, but almost completely prevented the formation of neuron-like beta-III-tubulin+ cells during neuron differentiation. Moreover, a low oxygen level (1 % O2 vs 21 % O2 in atmosphere) - the final electron acceptor - had the same effect on differentiation. These data suggest that mitochondrial electron transport chain activity contributes to the regulation of differentiation. The presence of complex I and complex III inhibitors, as well as oxygen scarcity, increase ROS production. We suggested that increased ROS level could explain the observed effects. By visualizing mitochondrial superoxide production with a specific dye – MitoSox - we confirmed that rotenone, antimycin A, myxothiazol, as well as low oxygen conditions, increased the superoxide level. These results suggest that the observed changes of the differentiation potential of P19 cells are associated with ROS production. To prove this idea, we differentiated P19 cells in presence of paraquat – a known ROS inducer. In line with our hypothesis paraquat promoted trophoblast differentiation. The received results suggest that the mitochondrial electron transport chain activity regulates differentiation through the ROS level. ROS are secondary messengers that participate in numerous processes including cell proliferation and differentiation. We aimed to predict the signal pathway that connects ROS level in stem cells and their differentiation potential. For this purpose, we performed a microarray analysis and compared the gene expression profiles of cells grown under hypoxia or in the presence of the complex III inhibitor myxothiazol with untreated control cells. The expression analysis revealed p53 as a transcriptional factor that impacts the differentiation potential in treated cells. p53 is a known redox-sensing molecule (Bigarella et al., 2014) that influences the differentiation potential through cell cycle control (Maimets et al., 2008). This observation is in line with our results and suggests that p53 may regulate the differentiation potential of P19 cells. We are planning to investigate the role of p53 signaling in the regulation of cell cycle and differentiation potential of P19 cell line.

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As usinas siderúrgicas caracterizam-se, sob o ponto de vista energético, pela grande intensidade de energia empregada em processos de redução do minério de ferro, fusão das matérias-primas e refino do aço líquido obtido. Quanto aos processos utilizados para a produção de aço, destacam-se o emprego de duas rotas tecnológicas: usinas integradas e semi-integradas (mini-mills). As usinas integradas possibilitam a redução do minério de ferro até ferro-gusa e, a partir deste, a obtenção do aço. As mini-mills caracterizam-se pelo emprego de sucatas metálicas, ferro-gusa ou ferro esponja como matérias-primas e pela obtenção, como produtos, de diferentes tipos de aço. Na operação de refino do aço líquido produzido comumente é necessário o emprego de desgaseificadores a vácuo para remoção de contaminantes e, consequentemente, atendimento às especificações do produto acabado. Com isso, as mini-mills demandam potência elétrica para os processos de fusão do aço e vapor superaquecido para obtenção de vácuo nos ejetores do processo de desgaseificação. Para atendimento a legislações ambientais, sistemas de despoeiramento devem ser aplicados às aciarias, disponibilizando grandes vazões de gases quentes provenientes do forno elétrico. A operação do sistema de despoeiramento indica expressivo potencial para recuperação de calor em processos siderúrgicos. Na presente dissertação propõe-se a coleta e análise de dados de operação do sistema de despoeiramento de um forno elétrico a arco de uma mini-mill brasileira, visando concepção e análise técnica-econômica de uma central de cogeração associada à recuperação de calor destes gases do sistema de despoeiramento
The steel industry can be characterized by its high demand of energy in the process of reduction and production of pig iron and steel. For the production of steel the following routes can be highlighted: integrated plants and mini-mills. Integrated plants are used for production steel from iron ore, allowing the reduction of iron ore until pig iron, and pig iron to steel. Mini-mills are used for production of steel through metallic scraps and pig iron. In a mini-mill, the transformation of metallic scraps and pig iron to steel is reached in melting shop areas. The melting shop areas adopt vacuum degassers as a commonly equipment to remove contaminants of liquid steel and consequently reach requirements of finished products. As a consequence, in a melting shop, electricity is applied in electric arc furnaces and overheated steam is applied in vacuum degassers. According to environmental restrictions these melting shops are integrated with dust collectors. The dust collected in electric arc furnaces has great amount of energy and can express a high potential to heat recovering systems. The present dissertation has purpose in collect and analyzes data from an electric arc furnace with a dust collector in a Brazilian mini-mill for developing a thermal-economic analysis of a cogeneration plant integrated in this mini-mill.

The thesis discusses the use of biomass for electricity island operation. The first chapter explains the concept of biomass and its distribution. It also shows the potential and availability of biomass. The second chapter describes the transformation of biomass into a suitable fuel form. The third to fifth chapter describes the conversion of biomass as a fuel into electrical energy through combustion, Stirling and steam engine. In these chapters there are brought the following parameters and prices of these motors and single-phase and three-phase alternators that can be connected to these engines. Other chapters describe the production of electricity in line with consumption, where the cost per hour to run engines for the various types of fuel and price of the electricity produced in kilowatt hours is calculated. In the last chapter of the thesis there is described the possibility of accumulation of electrical energy.

The main content of this thesis is a suggestion of computing system for efficient energy manufacture. The introduction devotes to description of up-to-date waste-to-energy units (EVO), it concentrates on Incinerator of municipal wastes of TERMIZO a.s., specifically. In the main body of this work is the data analysis of factory journal that has been implemented, results have been used as mathematical model output value. These activities are necessary for computing system suggestion. Resulting optimization of batch wasting plan with maximum economic effect for entrepreneur is the main output of this work. Conclusion consists of environmental and economic evaluation of operation of up-to-date waste-to-energy units and offers another optimization posibility.

This diploma’s thesis discourses the cryptographic systems and ciphers, whose function, usage and practical implementation are analysed. In the first chapter basic cryptographic terms, symmetric and asymetric cryptographic algorithms and are mentioned. Also usage and reliability are analysed. Following chapters mention substitution, transposition, block and stream ciphers, which are elementary for most cryptographic algorithms. There are also mentioned the modes, which the ciphers work in. In the fourth chapter are described the principles of some chosen cryptographic algorithms. The objective is to make clear the essence of the algorithms’ behavior. When describing some more difficult algorithms the block scheme is added. At the end of each algorithm’s description the example of practical usage is written. The chapter no. five discusses the hardware implementation. Hardware and software implementation is compared from the practical point of view. Several design instruments are described and different hardware design programming languages with their progress, advantages and disadvantages are mentioned. Chapter six discourses the hardware implementation design of chosen ciphers. Concretely the design of stream cipher with pseudo-random sequence generator is designed in VHDL and also in Matlab. As the second design was chosen the block cipher GOST, which was designed in VHDL too. Both designs were tested and verified and then the results were summarized.

碩士
國立成功大學
電機工程學系碩博士班
91
To meet the criteria based on the designing viewpoints, it is often required to do some certain change of adding or extracting a substructures without reanalyzing the changed structure. For the reason of changing the partial structure, however, must be provide an effective methods to resolve mentioned problem. The purpose of this thesis is to investigate the natural frequency and damping ratio of a line structure. The measuring facilities contain an impact hammer, an accelerometer, an analogue/digital card, and an analysis software based on Fast Fourier Transformer. From the field tests, the characteristics of the structure body can be obtained in Hsin-Ta Power Station T.P.C. By utilizing the electrical- magnetic field equation, the existence of the reasonance force to damage the device from the line current was proved. The practical results changing parts of the structure to avoid of resonant frequency to damage the power device was verified in the thesis.

Mitochondria are essential for the viability of mammalian cells and provide a compartment for specific chemical reactions. Cellular respiration -- the main mitochondrial function -- is tightly connected with ROS production: the mitochondrial electron transport chain complexes I and III are the main ROS sources in mammalian cells. It has been reported that complex I and complex III activities are essential for cell cycle, apoptosis and stem cell differentiation (Spitkovsky et al., 2004; Varum et al., 2009; Lee et al., 2011; Ma et al., 2011; Tormos et al., 2012). In our work, we aimed to investigate the role of mitochondrial electron transport chain activity in the regulation of the differentiation potential and to unravel signaling pathways that could participate in this regulation. As a model, we used the P19 pluripotent stem cell line that can be easily differentiated into trophoblasts, expressing intermediate filaments cytokeratin 8/18, and neurons, which express cytoskeleton protein beta-III-tubulin. We first showed that both trophoblast and neural differentiation of P19 cells were accompanied by activation of cellular respiration. The analysis of respiratory chain complexes and supercomplexes, however, showed that undifferentiated P19 cells, as well as their differentiated derivatives did not differ in their respiratory machinery, including functional respirasomes. While undifferentiated cells did not use respiration as the main energy source, cellular respiration was activated during differentiation, indicating that oxidative metabolism was important for efficient differentiation. To investigate the potential role of mitochondrial electron transport chain activity we monitored the influence of a disrupted electron flow on the differentiation of P19 cells. We found that the activity of complex I and complex III influenced the differentiation potential of the pluripotent P19 cell line: the presence of complex I and complex III inhibitors rotenone, antimycin A, or myxothiazol increased the amount of cytokeratin 8/18+ cells during trophoblast differentiation, but almost completely prevented the formation of neuron-like beta-III-tubulin+ cells during neuron differentiation. Moreover, a low oxygen level (1 % O2 vs 21 % O2 in atmosphere) - the final electron acceptor - had the same effect on differentiation. These data suggest that mitochondrial electron transport chain activity contributes to the regulation of differentiation. The presence of complex I and complex III inhibitors, as well as oxygen scarcity, increase ROS production. We suggested that increased ROS level could explain the observed effects. By visualizing mitochondrial superoxide production with a specific dye – MitoSox - we confirmed that rotenone, antimycin A, myxothiazol, as well as low oxygen conditions, increased the superoxide level. These results suggest that the observed changes of the differentiation potential of P19 cells are associated with ROS production. To prove this idea, we differentiated P19 cells in presence of paraquat – a known ROS inducer. In line with our hypothesis paraquat promoted trophoblast differentiation. The received results suggest that the mitochondrial electron transport chain activity regulates differentiation through the ROS level. ROS are secondary messengers that participate in numerous processes including cell proliferation and differentiation. We aimed to predict the signal pathway that connects ROS level in stem cells and their differentiation potential. For this purpose, we performed a microarray analysis and compared the gene expression profiles of cells grown under hypoxia or in the presence of the complex III inhibitor myxothiazol with untreated control cells. The expression analysis revealed p53 as a transcriptional factor that impacts the differentiation potential in treated cells. p53 is a known redox-sensing molecule (Bigarella et al., 2014) that influences the differentiation potential through cell cycle control (Maimets et al., 2008). This observation is in line with our results and suggests that p53 may regulate the differentiation potential of P19 cells. We are planning to investigate the role of p53 signaling in the regulation of cell cycle and differentiation potential of P19 cell line.

This study centered on a novel thermoelectric generator (TEG) integrated into the built environment. Designed by Watts Thermoelectric LLC, the TEG is essentially a novel assembly of thermoelectric modules whose required temperature differential is supplied by hot and cold streams of water flowing through the TEG. Per its recommended operating conditions, the TEG nominally generates 83 Watts of electrical power. In its default configuration in the built environment, solar-thermal energy serves as the TEG’s hot stream source and geothermal energy serves as its cold stream source. Two systems-level, thermodynamic analyses were performed, which were based on the TEG’s upcoming characterization testing, scheduled to occur later in 2011 in Detroit, Michigan. The first analysis considered the TEG coupled with a solar collector system. A numerical model of the coupled system was constructed in order to estimate the system’s annual energetic performance. It was determined numerically that over the course of a sample year, the solar collector system could deliver 39.73 megawatt-hours (MWh) of thermal energy to the TEG. The TEG converted that thermal energy into a net of 266.5 kilowatt-hours of electricity in that year. The second analysis focused on the TEG itself during operation with the purpose of providing a preliminary thermodynamic characterization of the TEG. Using experimental data, this analysis found the TEG’s operating efficiency to be 1.72%. Next, the annual emissions that would be avoided by implementing the zero-emission TEG were considered. The emission factor of Michigan’s electric grid, RFCM, was calculated to be 0.830 tons of carbon dioxide-equivalent (CO2e) per MWh, and with the TEG’s annual energy output, it was concluded that 0.221 tons CO2e would be avoided each year with the TEG. It is important to note that the TEG can be linearly scaled up by including additional modules. Thus, these benefits can be multiplied through the incorporation of more TEG units. Finally, the levelized cost of electricity (LCOE) of the TEG integrated into the built environment with the solar-thermal hot source and passive ground-based cold source was considered. The LCOE of the system was estimated to be approximately $8,404/MWh, which is substantially greater than current generation technologies. Note that this calculation was based on one particular configuration with a particular and narrow set of assumptions, and is not intended to be a general conclusion about TEG systems overall. It was concluded that while solar-thermal energy systems can sustain the TEG, they are capital-intensive and therefore not economically suitable for the TEG given the assumptions of this analysis. In the end, because of the large costs associated with the solar-thermal system, waste heat recovery is proposed as a potentially more cost-effective provider of the TEG’s hot stream source.
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Σκοπός της παρούσας διπλωματικής εργασίας είναι η παρουσίαση των κυριότερων μεθόδων παραγωγής ηλεκτρικής ενέργειας και η ανάλυση όλων των οικονομικών παραμέτρων ώστε να επιτύχουμε τη σχεδίαση του βέλτιστου συστήματος. Στο πρώτο κεφάλαιο γίνεται μία παρουσίαση των κυριότερων μονάδων παραγωγής ενέργειας. Αναφέρονται οι αρχές λειτουργίας και το κύκλωμα πάνω στην οποία βασίζεται ο κάθε σταθμός, ο βαθμός απόδοσης του κάθε συστήματος και τα πλεονεκτήματα και μειονεκτήματα αυτών. Αρχικά παρουσιάζονται οι ατμοηλεκτρικές, οι αεριοστροβιλικές και οι συνδυασμένου κύκλου συμβατικές μονάδες. Εξηγείται ο θερμοδυναμικός κύκλος λειτουργίας του Rankine πάνω στον οποίο βασίζεται η λειτουργία τους και οι προϋποθέσεις βέλτιστης λειτουργίας. Περιγράφεται ο κύκλος λειτουργίας και οι μετατροπές ενέργειας που πραγματοποιούνται στους στροβίλους και τα πρόσθετα μηχανήματα. Στην συνέχεια γίνεται αναφορά στους υδροηλεκτρικούς σταθμούς ροής ποταμού και αποθήκευσης ενέργειας. Εξηγείται η μελέτη για την δημιουργία ενός τέτοιου σταθμού, αναλύονται οι υποδομές και οι κτιριακές εγκαταστάσεις που απαιτούνται. Κατόπιν, περιγράφονται οι πυρηνικοί σταθμοί. Αναλύεται η πυρηνική σχάση, παρουσιάζεται ο πυρηνικός αντιδραστήρας και τα είδη του. Εν συνέχεια, επισημαίνονται οι ανανεώσιμες πηγές ενέργειας. Για τα αιολικά συστήματα μελετάται η εγκατάστασή τους και τα κύρια χαρακτηριστικά τους. Αναφέρεται η δομή της ανεμογεννήτριας, η αρχή λειτουργίας και τα διάφορα είδη ανεμογεννητριών και αιολικών πάρκων που βρίσκουν εφαρμογή σήμερα. Για τα φωτοβολταϊκά συστήματα, περιγράφεται η βασική αρχή λειτουργίας τους, το φωτοβολταϊκό φαινόμενο καθώς και η δομή του συστήματος. Αναλύονται τα συστήματα επίπεδων και συγκεντρωτικών πλαισίων που υπάρχουν και οι διάφορες συσκευές που απαρτίζουν το φωτοβολταϊκό σύστημα. Επίσης, περιγράφονται τα συστήματα που είναι συνδεδεμένα στο δίκτυο, καθώς και τα απομονωμένα. Κλείνοντας το κεφάλαιο, αναφέρονται τα γεωθερμικά συστήματα, οι κυψέλες καυσίμου και τα συστήματα παραγωγής ηλεκτρισμού από ενέργεια βιομάζας και παλιρροϊκής. Στο δεύτερο κεφάλαιο παρουσιάζονται οι πηγές ενέργειας και συγκεκριμένα τα ορυκτά καύσιμα. Γίνεται μία κατηγοριοποίηση σύμφωνα με τον ενεργειακό πόρο, εξετάζοντας τα αποθέματα, τη ζήτηση και την παραγωγή τους. Δίνονται πληροφορίες για το πετρέλαιο, το φυσικό αέριο, τον άνθρακα και τα πυρηνικά καύσιμα. Ιδιαίτερη έμφαση δίνεται στον λιγνίτη, λόγω των αποθεμάτων που υπάρχουν στην χώρα μας, και παρατίθεται μία ανάλυση ενός λιγνιτικού θερμοηλεκτρικού συστήματος. Στο τρίτο κεφάλαιο παρουσιάζεται ο τρόπος σχεδιασμού ενός βέλτιστου συστήματος. Για την παραγωγή του βέλτιστου συστήματος πρέπει να ληφθούν υπόψη πολλοί παράμετροι που περιλαμβάνουν την πηγή ενέργειας, τον τύπου του ενεργειακού συστήματος, την εκτίμηση του κόστους παραγωγής και των εγκαταστάσεων καθώς και την επιλογή τοποθεσίας. Αυτές οι αποφάσεις βασίζονται σε έναν αριθμό από τεχνικούς, οικονομικούς και περιβαλλοντικούς παράγοντες που είναι σε μεγάλο βαθμό άσχετοι μεταξύ τους. Αναφέρονται οι μέθοδοι υπολογισμού του κόστους συντήρησης και λειτουργίας ενός ενεργειακού συστήματος. Γενικά ως συμπέρασμα δεν μπορούμε να καταλήξουμε σε έναν κανόνα, γιατί η βέλτιστη λύση είναι απόρροια αναγκών, προτεραιοτήτων και παραμέτρων που προκύπτουν σε κάθε περίπτωση Στο τέταρτο κεφάλαιο αναπτύσσεται μία μελέτη οικονομικής φύσεως. Για μια ενεργειακή επένδυση είναι απαραίτητη μία ανάλυση δαπανών του κύκλου ζωής της. Μέσω της ανάλυσης αυτής αξιολογούνται οι συνολικές κύριες και λειτουργικές δαπάνες, λαμβάνεται υπόψη η «χρονική αξία» των χρημάτων και ενσωματώνονται οι διακυμάνσεις στην τιμή των καυσίμων. Η ανάλυση δαπανών κύκλων ζωής εξετάζει το κόστος κατά τη διάρκεια της ζωής του συστήματος και όχι μόνο το αρχικό κόστος. Έτσι είναι ευκολότερη η συγκριτική μελέτη των συστημάτων που θέλουμε να εγκαταστήσουμε. Στο πέμπτο κεφάλαιο ως αποτέλεσμα ενός οικονομικότερου οπότε και βέλτιστου συστήματος αναφέρεται η συμπαραγωγή ηλεκτρισμού και θερμότητας. Τα συστήματα Συμπαραγωγής Ηλεκτρισμού και Θερμότητας παράγουν ταυτόχρονα αξιοποιήσιμη ηλεκτρική και θερμική ενέργεια μέσω ενός ενιαίου συστήματος. Η παραγόμενη θερμότητα μπορεί να χρησιμοποιηθεί τόσο για θερμική χρήση όσο και για ψύξη ή κλιματισμό. Βασικό πλεονέκτημα και κίνητρο εφαρμογής της αποτελεί η αυξημένη απόδοση του συστήματος, έναντι της χωριστής λειτουργίας συμβατικών συστημάτων ηλεκτροπαραγωγής και θερμικής ενέργειας. Η εξοικονόμηση αυτή προκύπτει από την ανάκτηση και αξιοποίηση της θερμότητας, που διαφορετικά θα απορριπτόταν στο περιβάλλον Στο έκτο και τελευταίο κεφάλαιο παρουσιάζεται το ελληνικό σύστημα παραγωγής ηλεκτρικής ενέργειας. Το Ελληνικό ενεργειακό σύστημα βρίσκεται την τελευταία δεκαετία σε φάση σημαντικών αλλαγών. Η διείσδυση του φυσικού αερίου, η κατασκευή των διευρωπαϊκών δικτύων, η προώθηση των ανανεώσιμων πηγών ενέργειας και εξοικονόμησης ενέργειας και τέλος η απελευθέρωση της αγοράς ηλεκτρικής ενέργειας αποτελούν τα νέα δεδομένα του. Σημαντικές είναι οι επιπτώσεις των νέων αυτών δεδομένων στην ασφάλεια του ενεργειακού εφοδιασμού της χώρας, στην μείωση της εξάρτησης της από το εισαγόμενο πετρέλαιο, με όλα τα συνεπαγόμενα οφέλη στην εθνική οικονομία, στην εξοικονόμηση μη ανανεωνόμενων ενεργειακών πόρων, στην αύξηση της αποδοτικότητας των διαδικασιών παραγωγής και κατανάλωσης ενέργειας, στην προστασία του περιβάλλοντος και τέλος στην βελτίωση των παρεχομένων υπηρεσιών στους καταναλωτές.
The subject of this diploma thesis is the study of the types of electric generation systems and their comparative study. Initially are presented summarizing the basic principles of operation and the particular characteristics of each station. The energy systems being analyzed are steam cycle, gas fired, combined cycle, hydroelectric, nuclear power, solar, wind, geothermal and biomass systems. A brief description of fuels takes place presenting oil, natural gas, coal and its derivatives and nuclear fuels. Accent is given in the lignite and a short description of a lignite thermoelectric station is given. Then, the criteria are mentioned which are suitable for the choice of optimal energy system such as operational and functional costs, prices of fuels, types of generation system and technical and environmental issues. Also an economic study is realized. A life cycle cost analysis that evaluates the total owning and operating cost and takes into account the “time value” of money. Furthermore, the co-production of energy and heat as emanation of the most optimal system is included. Finally, the energy situation that prevails in Greece is presented.

The performance of solid oxide fuel cells (SOFCs) at the cell and system levels is studied using computer simulation. At the cell level, a new model combining the cell micro and macro models is developed. Using this model, the microstructural variables of porous composite electrodes can be linked to the cell performance. In this approach, the electrochemical performance of porous composite electrodes is predicted using a micro-model. In the micro-model, the random-packing sphere method is used to estimate the microstructural properties of porous composite electrodes from the independent microstructural variables. These variables are the electrode porosity, thickness, particle size ratio, and size and volume fraction of electron-conducting particles. Then, the complex interdependency among the multi-component mass transport, electron and ion transports, and the electrochemical and chemical reactions in the microstructure of electrodes is taken into account to predict the electrochemical performance of electrodes. The temperature distribution in the solid structure of the cell and the temperature and species partial pressure distributions in the bulk fuel and air streams are predicted using the cell macro-model. In the macro-model, the energy transport is considered for the cell solid structure and the mass and energy transports are considered for the fuel and air streams. To demonstrate the application of the cell level model developed, entitled the combined micro- and micro-model, several anode-supported co-flow planar cells with a range of microstructures of porous composite electrodes are simulated. The mean total polarization resistance, the mean total power density, and the temperature distribution in the cells are predicted. The results of this study reveal that there is an optimum value for most of the microstructural variables of the electrodes at which the mean total polarization resistance of the cell is minimized. There is also an optimum value for most of the microstructural variables of the electrodes at which the mean total power density of the cell is maximized. The microstructure of porous composite electrodes also plays a significant role in the mean temperature, the temperature difference between the hottest and coldest spots, and the maximum temperature gradient in the solid structure of the cell. Overall, using the combined micro- and micro-model, an appropriate microstructure for porous composite electrodes to enhance the cell performance can be designed. At the system level, the full load operation of two SOFC systems is studied. To model these systems, the basic cell model is used for SOFCs at the cell level, the repeated-cell stack model is used for SOFCs at the stack level, and the thermodynamic model is used for the balance of plant components of the system. In addition to these models, a carbon deposition model based on the thermodynamic equilibrium assumption is employed. For the system level model, the first SOFC system considered is a combined heat and power (CHP) system that operates with biogas fuel. The performance of this system at three different configurations is evaluated. These configurations are different in the fuel processing method to prevent carbon deposition on the anode catalyst. The fuel processing methods considered in these configurations are the anode gas recirculation (AGR), steam reforming (SR), and partial oxidation reformer (POX) methods. The application of this system is studied for operation in a wastewater treatment plant (WWTP) and in single-family detached dwellings. The evaluation of this system for operation in a WWTP indicates that if the entire biogas produced in the WWTP is used in the system with AGR or SR fuel processors, the electric power and heat required to operate the plant can be completely supplied and the extra electric power generated can be sold to the electrical grid. The evaluation of this system for operation in single-family detached dwellings indicates that, depending on the size, location, and building type and design, this system with all configurations studied is suitable to provide the domestic hot water and electric power demands. The second SOFC system is a novel portable electric power generation system that operates with liquid ammonia fuel. Size, simplicity, and high electrical efficiency are the main advantages of this environmentally friendly system. Using a sensitivity analysis, the effects of the cell voltage at several fuel utilization ratios on the number of cells required for the SOFC stack, system efficiency and voltage, and excess air required for thermal management of the SOFC stack are studied.