There is a lack of available technology to make small-scale power from biomass cost effectively. The proposed Hybrid Brayton cycle is an indirectly heated Brayton cycle with evaporative cooling for combined heat and power generation. It converts a direct fired microturbine to an indirectly heated power system. The Hybrid Brayton cycle offers a flexible biomass power generation platform in the 30 to 250 kWe range, achieving competitive efficiencies and advantages compared to other systems of similar power level. This cycle is designed to be implemented in remote and off-grids communities, small industries and net-zero communities, where local biomass feedstock is sustainably available. This proposed platform keeps operator qualifications to a minimum. In an effort to validate this new power cycle, a 30 kWe experimental facility was developed and initial commission phases performed. This facility purpose is to validate numerical model predictions and is used for optimization. The facility is described and results of the commissioning tests are reported with various problems encountered, solutions implemented and recommendations proposed. The thermodynamic model of the Hybrid Brayton cycle is also implemented in the MatLAB environment, incorporating experimental findings and new properties for humidified air at high temperatures. The MatLAB model confirms that an indirect fired Brayton cycle with evaporative cooling could be a viable approach for small scale distributed power generation using biomass. Additional experimental data of humidified air at elevated temperatures would provide more certainty in property predictions. The MatLAB model provides a modeling tool to allow resolving the issues identified during the commissioning of the test facility and offers alternatives to optimize various design configurations, implementing the most up to date property correlations for humidified air at elevated temperatures.

There is a lack of available technology to make small-scale power from biomass cost effectively. The proposed Hybrid Brayton cycle is an indirectly heated Brayton cycle with evaporative cooling for combined heat and power generation. It converts a direct fired microturbine to an indirectly heated power system. The Hybrid Brayton cycle offers a flexible biomass power generation platform in the 30 to 250 kWe range, achieving competitive efficiencies and advantages compared to other systems of similar power level. This cycle is designed to be implemented in remote and off-grids communities, small industries and net-zero communities, where local biomass feedstock is sustainably available. This proposed platform keeps operator qualifications to a minimum. In an effort to validate this new power cycle, a 30 kWe experimental facility was developed and initial commission phases performed. This facility purpose is to validate numerical model predictions and is used for optimization. The facility is described and results of the commissioning tests are reported with various problems encountered, solutions implemented and recommendations proposed. The thermodynamic model of the Hybrid Brayton cycle is also implemented in the MatLAB environment, incorporating experimental findings and new properties for humidified air at high temperatures. The MatLAB model confirms that an indirect fired Brayton cycle with evaporative cooling could be a viable approach for small scale distributed power generation using biomass. Additional experimental data of humidified air at elevated temperatures would provide more certainty in property predictions. The MatLAB model provides a modeling tool to allow resolving the issues identified during the commissioning of the test facility and offers alternatives to optimize various design configurations, implementing the most up to date property correlations for humidified air at elevated temperatures.

Submitted by Ricieri Fornazari Filho (ricieri.fornazari@gmail.com) on 2018-07-26T14:37:48Z No. of bitstreams: 1 Dissertação_Ricieri Fornazari Filho.pdf: 5238639 bytes, checksum: 37aec4ee567ed4046866f1a6f1be7a09 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-07-30T13:52:12Z (GMT) No. of bitstreams: 1 fornazarifilho_r_me_bauru.pdf: 4325526 bytes, checksum: 1bd8c929f67ded30499ed09950b7e38e (MD5) / Made available in DSpace on 2018-07-30T13:52:12Z (GMT). No. of bitstreams: 1 fornazarifilho_r_me_bauru.pdf: 4325526 bytes, checksum: 1bd8c929f67ded30499ed09950b7e38e (MD5) Previous issue date: 2018-07-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Desenvolver e projetar plantas de potência otimizadas é uma constante e antiga busca da engenharia de energia. Para tal, os modelos de ciclos foram constantemente aprimorados ao longo do tempo. Através de estudos que procuram incorporar funções que descrevam a realidade mais precisamente, o equacionamento de irreversibilidades presentes nos processos e dispositivos reais de interações de trabalho e calor é vasto na literatura. Uma modelagem matemática foi desenvolvida para um ciclo Brayton irreversível com inter-resfriamento, regeneração e reaquecimento. As irreversibilidades consideradas são provenientes das resistências térmicas nos trocadores de calor do ciclo, do comportamento não isentrópicos dos elementos de expansão e compressão, da perda de calor para o reservatório frio e das perdas de carga nas tubulações ao longo do escoamento do fluido de trabalho. O método de otimização escolhido foi uma função termoeconômica a qual relaciona potência líquida com diversos tipos de custos de uma planta de potência, tais como custos de investimentos, de combustíveis, ambientais e de operação e manutenção. A modelagem matemática consistiu em determinar todas as temperaturas e parâmetros de interesse do ciclo através do conhecimento de apenas uma temperatura, denominada temperatura de controle. A partir de variações nesta temperatura foi possível estabelecer o comportamento dos demais parâmetros do ciclo e relacioná-los com irreversibilidades e parâmetros construtivos. O presente trabalho apresentou um modelo de ciclo Brayton não encontrado na literatura, acopladas diversas fontes de irreversibilidades sob a ótica de uma função de custos de quatro termos. Os resultados obtidos demonstram que a faixa ótima para operação em máxima potência difere da faixa ótima para operação sob máxima eficiência, sendo que a operação termoeconômica maximizada se aproxima mais da última do que da primeira. Foi observado também que as perdas de carga e as resistências dos trocadores de calor são irreversibilidades significativas no ciclo de potência. / Developing and designing optimized power plants is a constant and ancient search for energy engineering. For this, cycles models have been constantly improved over time. Through studies that seek to incorporate functions that describe the reality more precisely, the equating of irreversibility present in real processes and devices of work and heat transfer interactions is vast in the literature. A mathematical modeling has been developed for an irreversible Brayton cycle with inter-cooling, regeneration and reheating. The irreversibility considered are due to thermal resistances in the heat exchangers of the cycle, to the non-isentropic behavior of the elements for expansion and compression, to the heat loss to the could reservoir and to the head loss on the pipes along the working fluid flow. The optimization method chosen was a thermoeconomic function that relates the net power to various types of costs of a power plant, such as investment costs, fuel costs, environmental costs and operation and maintenance costs. The mathematical modeling consisted on determining all the cycle temperatures and parameters of interest through the knowledge of only one temperature, called control temperature. From variations in this temperature, it was possible to establish the behavior of the other parameters of the cycle and relate them to irreversibility and constructive parameters. The present work presented a model of Brayton cycle not found in the literature, coupled several sources of irreversibility under the optics of a four terms cost function. The results obtained demonstrate that the optimal operational range under maximum power differs from the optimal operational range under maximum efficiency, and the maximized thermoeconomic operation is closer to the latter than the first. It has also been observed that the head losses and the resistances in the heat exchangers are significant irreversibility in the power cycle.

[pt] O presente trabalho trata da determinação experimental dos parâmetros de desempenho de um compressor rotativo de deslocamento positivo,que faz parte de um motor de refrigeração em desenvolvimento. Este opera segundo o ciclo de Brayton invertido utilizando o ar como fluido de trabalho. A vazão mássica real de ar em escoamento pelo compressor, eventuais vazamentos, potência de eixo entregue ao compressor e a potência desenvolvida pelo mesmo são obtidas com base em procedimentos experimentais. A vazão e a potência teóricas foram determinadas com base em uma simulação do funcionamento do compressor. A partir destes resultados, determinaram-se as eficiências isentrópica,mecânica e volumétrica, permitindo uma análise das condições de operação do compressor. Usando resultados experimentais, realizou-se uma análise termodinâmica convencional de disponibilidade associada ao processo real ocorrido no compressor para explicar a natureza das irreversibilidades envolvidas e indicar as condições ótimas de funcionamento. Com base na filosofia de análise utilizada, este novo tipo de máquina de refrigeração foi criteriosamente analisada. Sugestões de melhoria são apresentadas no sentido de melhor qualificar este novo tipo de compressor para trabalhar com sistemas que operem segundo o ciclo de Brayton invertido. Neste trabalho é apresentado uma proposta otimizada de um novo projeto de expansor. / [en] The present work describe tests of performance of a positive displacement rotary compressor which is part of a new type of refrigerating machine under development. The working fluid is air and the machine operates at the Brayton Cycle. The mass flow rate, eventual mass leakages, the power delivered to the compressor shaft and the actual power developed are obtained based upon experimental procedures. The theorectical mass flow rate and the isentropic power was calculed through a theorectical simulation, and, from these results, the isentropic mechanical and volumetric efficiencies have been evaluated allowing the determination of the favorable and critical conditions of operation. An uncertainty analysis is developed in order to control the experimental procedures and acuracy of the experiments conducted. Using experimental results as an input, a classical avaiability thermodynamics analysis of the process was developed in order to explain the nature of the associated irreversibilities and to indicate the optimum conditions of operation of the compressor. Based upon the described approach, this new type of refrigerating machine has been carefully analysed. Aiming better performance, design modifications are suggested as an attempt to better qualify this type of compressor for operation in systems which operate in the Brayton Cycle. Finalle, an improved design of an expander is discussed.

Ce travail de thèse a consisté à étudier les mécanismes réactionnels et les cinétiques d’interactions sodium-CO2, dans le cadre de l’évaluation d’un système de conversion d’énergie au CO2 supercritique pour les réacteurs à neutrons rapides à caloporteur sodium. La démarche suivie est la suivante. L’interaction entre le sodium et le CO2 a tout d’abord été mise en évidence par des expériences de laboratoire de type calorimétrie et expériences en four associées à l’analyse des produits formés. Celles-ci ont permis de proposer un mécanisme cohérent, en accord avec les données de la littérature, et ont donné des indications préliminaires sur la cinétique de réaction. Pour évaluer la cinétique de réaction de façon plus approfondie, nous avons cherché à nous rapprocher du phénomène observable dans le cas d’une fuite dans un échangeur de chaleur sodium-CO2. La géométrie de tels échangeurs n’est pas aujourd’hui fixée, même si le développement d’échangeurs compacts est envisagé. Par la suite, des jets libres de CO2 dans du sodium liquide ont été modélisés dans le but d’aboutir, par identification, aux paramètres cinétiques de la réaction. Ceux-ci, estimés à l’aide de ce type de géométrie, resteront valables avec une géométrie plus complexe, représentative de l’échangeur réel. Un banc expérimental a été défini et construit pour réaliser ces jets libres. Les premières études de laboratoire ont conclu à l’existence de mécanismes réactionnels différents selon les niveaux de température. Un seuil a été mis en évidence autour de 500 °C. En dessous de celui-ci, la réaction apparaît modérée, voire lente, d’exothermie moyenne et se produit après une période d’induction, fonction de la température, dont la durée pourrait atteindre plusieurs heures. Au contraire, au dessus de ce seuil, elle semble rapide et plus exothermique. En dessous de 500 °C, il se forme de l’oxalate de sodium, qui réagit ensuite avec le sodium de manière exothermique, suivant les réactions : CO2 + Na ! 1/4 Na2C2O4 + 1/ CO + 1/4 Na2CO3 (1) 4 Na + Na2C2O4 ! 3 Na2O + CO + C (2) Au dessus de 500 °C, il se forme du carbonate de sodium, susceptible de réagir ensuite avec le sodium avec une faible chaleur de réaction, de façon endothermique : 4 Na + 3 CO2 ! 2 Na2CO3 + C (3) 4 Na + Na2CO3 ! 3 Na2O + C (4) Cette dernière réaction a été observée en calorimétrie. La réaction a également été étudiée par l’élaboration d’un modèle de jet réactif de CO2 dans du sodium liquide. Ce modèle est fondé sur une hydrodynamique permettant de calculer les vitesses et les débits au sein du jet. Il ne prend pas en compte les phénomènes de glissement entre les phases gazeuse et liquide et repose sur une description homogène du jet. Ce modèle a été validé sur le couple eau-sodium dans les années 1980-1990. Les réactions chimiques et les cinétiques associées, de type Arrhenius, y ont ensuite été introduites. Les facteurs pré-exponentiels des constantes de vitesse et les énergies d’activation sont les paramètres à identifier. Les valeurs prises par les températures en chaque point du jet dépendent de ces paramètres cinétiques, et selon la valeur des constantes de vitesse, il est possible de définir trois domaines où la vitesse de la réaction est lente, modérée ou rapide. Un banc expérimental, appelé DISCO2 (Détermination des Interactions Sodium-CO2), permettant d’estimer les paramètres cinétiques, a été réalisé au CEA de Cadarache. DISCO2 permet de réaliser des jets réactifs de CO2 dans du sodium liquide et d’enregistrer les températures à différentes distances axiales et radiales dans le jet à l’aide d’un peigne de thermocouples. Des essais réalisés dans les deux gammes de température précitées, ont permis de retrouver le seuil de température mis en évidence en calorimétrie. Les campagnes expérimentales menées au cours de la thèse ont permis d’estimer les paramètres dans les deux domaines de température et de consolider le scénario réactionnel. Deux séries de paramètres ont été estimés, chacune dans une des zones délimitées par le seuil de température. Le mécanisme réactionnel introduit dans le modèle a été adapté à chaque zone de température. Les réactions (1) et (3) ont dans un premier temps été considérées comme prépondérantes dans chaque zone, puis le mécanisme a été amélioré en ajoutant les réactions (2) et (4), réactions successives et concurrentes, respectivement des réactions (1) et (3). La deuxième option s’est révélée meilleure dans les deux zones. Le système sodium-CO2 est exothermique et sa réaction est moins vigoureuse, mais plus complexe, que celle du sodium avec l’eau. En effet, elle dépend de la température et, en fonction du lieu où elle prend place dans un échangeur de chaleur, elle ne formera pas les mêmes produits de réaction. Les éléments de modélisation et de cinétique chimique issus de ce travail servent de données d’entrée à l’étude globale de l’interaction Na-CO2 dans les systèmes envisagés, qui permettra de déterminer les dispositifs de détection, sûreté et mitigation associés. / This PhD study consisted in studying reactive mechanisms and kinetics of sodium-CO2 interactions, in the frame of the assessment of an energy conversion system with supercritical CO2 for fast breeder reactors cooled by sodium. The approach was the following. First of all, the interactions between sodium and CO2 have been brought to light by laboratory experiments associated with products analysis. They have enabled the establishment of a coherent mechanism, in agreement with literature data, and gave preliminary indications on the reaction kinetics. In order to estimate a more detailed reaction kinetics, we tried to approach the phenomenon that appears in the case of a leak in a sodium-CO2 heat exchanger. Geometry of such heat exchangers is not fixed for the moment, even if the development of compact exchangers is foreseen. Then, free jets of CO2 in liquid sodium have been modeled in order to obtain, by identification, kinetics parameters of the reaction. Those parameters, estimated with such a geometry, will remain valid with a much complex geometry, that will better represent the real exchanger. An experimental bench has been defined and built to realize those jets. The first laboratory experiments have concluded in the existence of different reactive mechanisms according to the temperature level. A threshold has been brought to light around 500 °C. Below this one, reaction appears moderated, or even, slow, with a medium exothermicity, and appears after an induction period that depends on the temperature, and which duration could reach several hours. At contrary, above this threshold, it seems rapid and more exothermic. Below 500 °C, sodium oxalate is produced, and then reacts with sodium in an exothermic way, following the reactions : CO2 + Na ! 1/4 Na2C2O4 + 1/4 CO + 1/4 Na2CO3 (5) 4 Na + Na2C2O4 ! 3 Na2O + CO + C (6) Above 500 °C, sodium carbonate is produced, and can then possibly react with sodium in an endothermic way, following the reactions : 4 Na + 3 CO2 ! 2 Na2CO3 + C (7) 4 Na + Na2CO3 ! 3 Na2O + C (8) This last reaction has been observed in calorimetry. Reaction has also been studied with the development of a model of a reactive CO2 jet in liquid sodium. This model is based on an hydrodynamics that enables the calculation of speed and flow rates within the jet. It does not take into account sliding phenomenon between liquid and gaseous phases, and propose an homogeneous description of the jet. This model has been validated with sodium-water system during the years 1980-1990. Chemical reactions and associated kinetics, of an Arrhenius type, have been introduced. Pre-exponential factors and activation energies are the parameters to identify. Values taken by temperatures in every point of the jet depend on those parameters, and, according to their values, it is possible to define three areas where the reaction is slow, moderated or rapid. An experimental bench, called DISCO2 (Determination of Sodium-CO2 interactions), that enable the estimation of kinetics parameters, has been built in the CEA of Cadarache. DISCO2 enables to realize reactive jets of CO2 in liquid sodium and to record temperatures within the jet, thanks to a comb of thermocouples. Tests carried out in the two above mentionned ranges of temperature have enabled to find again the temperature threshold seen in calorimetric studies. Experimental campaigns have enabled to estimate parameters in both fields of temperature and to strengthen the reactive mechanism. Two series of parameters have been estimated, each one in both fields of temperature. The reactionnal mechanism introduced into the model was adapted to each area of temperature. The reactions (5) and (7) were initiallyregarded as dominating in each area. Then mechanism has been improved with the addition of reactions (6) and (8), successive and competitor to reactions (5) and (7). The second option appeared better in both areas. Sodium-CO2 system is exothermic and its reaction is less vigorous, but more complex than the one between sodium and water. In fact, it depends on temperature and, according to the place where it takes place, in a heat exchanger, it will not form the same products. Modeling and elements of chemical kinetics resulting from this study will be considered as entry data to the global study of sodium-CO2 interaction in foreseen systems. They will enable the determination of the associated detection, safety and mitigation devices.

Lately, car manufacturers have been put to a big challenge to reduce the CO2 emission of their entire fleets. Norms of pollutant emissions limit the ways to achieve the desired CO2 emission goals, as some of the solutions that would lead to lower CO2 emission also lead to higher pollutant emission. Waste Heat Recovery (WHR) could be a good solution to lower the CO2 emission of the Internal Combustion Engine (ICE) without increasing the pollutant emission. In the present thesis different WHR strategies are analysed and the results suggested it would be interesting to further study the Brayton cycle machine. Air Brayton Cycle (ABC) represents a way to recover a part of the heat energy of the ICE exhaust gases and transform it into mechanical energy. Recovered mechanical energy would then be returned to the crankshaft of the ICE, thereby reducing the amount of energy that has to be liberated by combustion of fuel which lowers the fuel consumption and CO2 emission. The study of ABC started with an analysis of the ideal cycle in order to obtain the theoretical maximum of the system. The study continued with an analysis of the semi ideal cycle where all losses are taken into account only by two efficiency coefficients. This analysis showed that for the diesel engine efficiency of the ABC is very low because of the low exhaust gas temperature. For the gasoline engine the cycle could be viable when the ICE is working under steady condition and higher load. These conditions could be fulfilled when the vehicle is driven on the highway. Detailed analysis was aimed at determining the cycle main losses. They were determined to be: pumping losses, losses caused by heat transfer and mechanical losses. Taking into account these main losses along with other direct and indirect losses it was concluded that the cycle is not viable for the types of the WHR machines that were considered in this study. In order for the cycle to be viable some other either existing or new machine type should be tested, that would lower the main losses and offer good isentropic and mechanical efficiency for desired conditions. / Últimamente los fabricantes de automóviles se han puesto el gran reto de reducir la emisión de CO2 en la totalidad de sus flotas. Las nuevas normativas para la reducción de las emisiones contaminantes limitan los medios para lograr los objetivos deseados en la emisión de CO2 porque algunas de las soluciones que llevan a la reducción en la emisión de CO2 también dan lugar a un incremento en la emisión de otros contaminantes. La recuperación de calor residual (WHR) podría ser una buena solución para reducir las emisiones de CO2 del motor de combustión interna (ICE) sin poner en peligro la emisión de contaminantes. En la presente Tesis se analizaron diferentes estrategias de WHR y se concluyó que sería interesante estudiar más a fondo la máquina de ciclo Brayton. El Ciclo Brayton de Aire (ABC) permite recuperar una parte del calor de los gases de escape del ICE y transformar este calor en energía mecánica. La energía mecánica recuperada se devuelve al cigüeñal del ICE, reduciendo de ese modo la cantidad de energía que tiene que ser liberada por la combustión del combustible, lo cual permite reducir el consumo de combustible y las emisiones de CO2. En esta Tesis se estudia el ABC mediante un análisis del ciclo ideal con el fin de obtener el máximo teórico del sistema. El modelo se mejora con un análisis del ciclo semi-ideal donde se tienen en cuenta todas las pérdidas mediante el uso de dos coeficientes generales. Este análisis muestra que para el motor diesel la eficiencia del ciclo ABC es muy baja debido a la baja temperatura del gas de escape. Para el motor de gasolina el ciclo podría ser viable cuando el ICE está trabajando bajo condiciones estacionarias y una carga mayor. Estas condiciones se podrían cumplir cuando el vehículo está circulando en autopista. El análisis detallado de este ciclo tiene como objetivo determinar las pérdidas principales de ciclo. Las pérdidas principales se identificaron como: las pérdidas de bombeo, las pérdidas causadas por la transferencia de calor y las pérdidas mecánicas. Teniendo en cuenta estas pérdidas principales junto con otras pérdidas directas e indirectas, se concluyó que el ciclo no es viable para los tipos de máquinas WHR que fueron considerados en este estudio. Para que el ciclo sea viable se tiene que buscar alguna otra máquina existente o un nuevo tipo de máquina que reduzca las principales pérdidas y ofrezca un buen rendimiento isentrópico y mecánico para las condiciones deseadas. / Últimament els fabricants d'automòbils s'han posat el gran repte de reduir l'emissió de CO2 de la totalitat de les seues flotes. Les noves normatives de reducció de les emissions contaminants limiten els mitjans per assolir els objectius desitjats d'emissió de CO2 perquè algunes de les solucions que porten a la reducció en l'emissió de CO2 també donen lloc a un increment a l'emissió de altres contaminants. La recuperació de calor residual (WHR) podria ser una bona solució per reduir les emissions de CO2 del motor de combustió interna (ICE) sense posar en perill l'emissió de contaminants. En la present Tesi s'han analitzat diferents estratègies WHR i es va concloure que seria interessant estudiar més a fons el cicle Brayton. El Cicle Brayton d'Aire (ABC) representa una manera de recuperar una part de la calor dels gasos d'escapament de l'ICE i transformar calor a l'energia mecànica. L'energia mecànica recuperada es retorna al cigonyal de l'ICE reduint d'aquesta manera la quantitat d'energia que ha de ser alliberada per la combustió del combustible permitint la reducció del consum de combustible i les emissions de CO2. En aquesta Tesi s'ha començat estudiant un ABC amb una anàlisi del cicle ideal per tal d'obtenir el màxim teòric del sistema. Este model es millora amb una anàlisi del cicle semiideal on es tenen en compte totes les pèrdues amb tan sols dos coeficients d'eficiència. Aquesta anàlisi va mostrar que per al motor dièsel l'eficiència del cicle ABC és molt baixa a causa de la baixa temperatura del gas d'escapament. Per al motor de gasolina el cicle podria ser viable quan l'ICE està treballant sota condicions estacionàries i una càrrega més gran. Aquestes condicions es podrien complir quan el vehicle està circulant en autopista. L'anàlisi detallada del cicle va tenir com a objectiu determinar les pèrdues principals de cicle. Les pèrdues principals es van identificar com: les pèrdues de bombament, les pèrdues causades per la transferència de calor i les pèrdues mecàniques. Tenint en compte aquestes pèrdues principals juntament amb altres pèrdues directes i indirectes, es va concloure que el cicle no és viable per als tipus de màquines WHR que van ser considerats en aquest estudi. Perquè el cicle puga ser viable s'ha de buscar alguna altra màquina existent o un nou tipus de màquina que puga reduir les principals pèrdues i puga oferir un bon rendiment isentròpic i mecànic per a les condicions desitjades. / Kleut, P. (2016). Recuperation of the exhaust gases energy using a Brayton cycle machine [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/76807

The aim of this study is to implement the model predictive control in order to optimally control the power output of a Brayton cycle based power plant. Other control strategies have been tried but there still exists the need for better performance. In real systems, a number of constraints exist. Incorporating these into the control design is no trivial task. Unlike in most control strategies, model predictive control allows the designer to explicitly incorporate constraints in its formulation. The original design of the PBMR power plant is considered. It uses helium gas as the working fluid. The power output of the system can be controlled by manipulating the helium inventory to the gas cycle. A linear model of the power plant, modelled in Simulink® is used. This linear model is used as an evaluation platform for the control strategy. The helium inventory is manipulated by means of actuators which use values generated by the controller. The controller computes these values by minimizing the cost of future outputs over a finite horizon in the presence of constraints. The dynamic response of the system is used to tune the controller. The power output performance at different configurations of the controller under perfect conditions and with disturbances is examined. The best configuration is used resulting in an optimal power control system for the Brayton cycle based power plant. Results showed that the method employed can be used to implement the control strategy. Furthermore, better performance can be realised with model predictive control. / Thesis (M.Ing. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2012

Gas turbines are the primary technology used for the purpose of power generation nearly everywhere. In this thesis, the Makkah Power Plant, running on a Brayton cycle, is considered for analysis. The peak demand for electric power in the City of Makkah occurs in the middle of the day during the summer and is almost double the off-peak demand. The plant employs turbines of two world renowned manufacturers. However, there are many mechanical and electrical issues related to the overall insufficient operation of the plant. From the balancing of mass, entropy, energy, exergy and cost equations, a greater understanding of the systems as well as their efficiencies is achieved. The parametric study and plant optimization are performed to investigate the effects of the variation of specific input parameters such as fuel mass flow rate, air volume flow rate and compressor inlet air temperature, on the overall operating efficiency of the system. Through this study, the overall plant energetic and exergetic efficiencies are increased by 20% and 12% respectively with cooling down the compressor inlet temperature to 10oC. Furthermore, exergy and exergoeconomic analyses are conducted to obtain that the largest exergy destruction occurs in the combustion chamber, followed by the turbine. The optimization results demonstrate that CO2 emissions can be reduced by increasing the exergetic efficiency and using a low fuel injection rate into the combustion chamber. Finally, this study will assist efforts to understand the thermodynamic losses in the cycle, and to improve efficiency as well as provide future recommendations for better performance, sustainability and lessen environmental impact. / UOIT

The aim of this study is to implement the model predictive control in order to optimally control the power output of a Brayton cycle based power plant. Other control strategies have been tried but there still exists the need for better performance. In real systems, a number of constraints exist. Incorporating these into the control design is no trivial task. Unlike in most control strategies, model predictive control allows the designer to explicitly incorporate constraints in its formulation. The original design of the PBMR power plant is considered. It uses helium gas as the working fluid. The power output of the system can be controlled by manipulating the helium inventory to the gas cycle. A linear model of the power plant, modelled in Simulink® is used. This linear model is used as an evaluation platform for the control strategy. The helium inventory is manipulated by means of actuators which use values generated by the controller. The controller computes these values by minimizing the cost of future outputs over a finite horizon in the presence of constraints. The dynamic response of the system is used to tune the controller. The power output performance at different configurations of the controller under perfect conditions and with disturbances is examined. The best configuration is used resulting in an optimal power control system for the Brayton cycle based power plant. Results showed that the method employed can be used to implement the control strategy. Furthermore, better performance can be realised with model predictive control. / Thesis (M.Ing. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2012

The geometry of the receiver and recuperator in a small-scale open and direct recuperative solar thermal Brayton cycle can be optimised in such a way that the system produces maximum net power output. The purpose of this work was to apply the second law of thermodynamics and entropy generation minimisation to optimise these geometries using an optimisation method. The dynamic trajectory optimisation method was used and off-the-shelf micro-turbines and a range of parabolic dish concentrator diameters were considered. A modified cavity receiver was used in the analysis with an assumed cavity wall construction method of either a circular tube or a rectangular channel. A maximum temperature constraint of 1 200 K was set for the receiver surface temperature. A counterflow plate-type recuperator was considered and the recuperator length was constrained to the length of the radius of the concentrator. Systems producing a steady-state net power output of 2 – 100 kW were analysed. The effect of various conditions, such as wind, receiver inclination and concentrator rim angle on the maximum net power output, and optimum geometry of the system were investigated. Forty-five different micro-turbines and seven concentrator diameters between 6 and 18 metres were considered. Results show the optimum geometries, optimum operating conditions and minimum entropy generation as a function of the system mass flow rate. The optimum receiver tube diameter was relatively large when compared with the receiver size. The optimum counterflow plate-type recuperator channel aspect ratio is a linear function of the optimum system mass flow rate for a constant recuperator height. The optimum recuperator length and optimum NTU are small at small system mass flow rates but increase as the system mass flow rate increases until the length constraint is reached. For the optimised systems with maximum net power output, the solar receiver is the main contributor to the total rate of minimum entropy generation. The contributions from the recuperator, compressor and turbine are next in line. Results show that the irreversibilities were spread throughout the system in such a way that the minimum internal irreversibility rate was almost three times the minimum external irreversibility rate for all optimum system geometries and for different concentrator diameters. For a specific environment and parameters, there exists an optimum receiver and recuperator geometry so that the system can produce maximum net power output. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted