The shift towards renewable energy has steered the focus of power plant operation towards flexibility and fast response which are more attainable through the use of combined-cycle power plants. These aspects are required to account for the fluctuation of the supply as well as the demand of power that is associated with renewable energy. Combined-cycle power plants consist of a gas turbine as the topping cycle, forming the core of the plant, and a Rankine cycle with a steam turbine as the bottoming cycle. A component called the Heat Recovery Steam Generator (HRSG) forms a connection point between the two cycles. It uses the heat released from the gas turbine to produce high pressure and temperature steam to be sent to the steam turbine. The objective of this project is to develop a model of a combined-cycle power plant in Flownex which can be solved in off-design conditions in order to compare it to plant data. The verification of this model will show that Flownex can be used to effectively and efficiently model a combined-cycle power plant. The process of development of the final Flownex model was achieved using various additional software. Initially, an analytical model was developed in Mathcad (software used for engineering calculations). This software provides a tool for understanding knowns, unknowns and what is being calculated in the system. Manual calculations of the Heat Recovery Steam Generator (HRSG) were done using heat balance equations. A temperature profile of the gas and water/steam in the HRSG was developed so that the duties of each component (economiser, evaporator, superheater) could be calculated. The overall conductance (UA) of each component was calculated in the design mode for the system to be evaluated in off-design mode. The development of an analytical model provided detailed understanding of the process of mathematical modelling used in commercial tools. Thereafter, a model was built in Virtual Plant, a thermodynamic modelling software for assessing plant performance. Virtual Plant uses plant design information and first engineering principles to predict plant performance. Finally, the Flownex model was designed. Flownex uses endpoint values (initial pressure and temperature and outgoing mass flow) and the UA of each component to calculate the characteristics of the flow at each intermediate point. For the single-, double-, and triple-pressure combined-cycle power plant systems, the analytical, Virtual Plant and Flownex models were compared. The results of all the models agreed closely with one another. The triple-pressure design and off-design Virtual Plant and Flownex models were also compared to plant data and it was concluded that Flownex was successful in modelling the design and off-design conditions of a combined-cycle power plant.

Recuperated Brayton Cycle (RBC) has attracted the attention of research scientists not only as a possible replacement for the steam cycle at nuclear power plants but also as an efficient bottoming cycle for waste heat recovery and for concentrated solar power. RBC’s compactness and the ease at which it can be integrated into existent power plants for waste heat recovery require few modifications. Methane, carbon dioxide and trifluoromethane are analyzed as possible working fluids. This work shows that it is possible to achieve higher efficiencies using methane under some operating conditions. However, as it turns out, the performance of Recuperated Brayton Cycle should be evaluated based on net output work. When the performance is assessed on the net output work criteria carbon dioxide still proves to be superior to other gases. This work also suggests that piston engines as compressors and expanders may be used instead of rotating turbines since reciprocating pistons have higher isentropic efficiencies.

This thesis discusses the thermoeconomic modeling and simulation of micro-CHP systems powered by various prime movers. Micro Cooling, Heating, and Power (micro-CHP) is becoming an increasingly important energy option as the demand for electrical power as well as heating and cooling for buildings increases worldwide. Micro-CHP has the potential to increase the total energy efficiency for cooling, heating, and powering residences, offices, and other relatively small buildings by using waste thermal energy from electricity production to deliver heating and cooling. Calculation methodologies are presented for the different components of micro CHP systems using thermodynamic cycles and mass and energy balances. System performance characteristics are calculated and compared for different prime movers using various fuels. Performance characteristics that are compared include fuel consumption, monthly energy savings, and system energy efficiencies.

No description available.

Le marché du gaz naturel liquéfié (GNL) est en plein essor et présente l'avantage de diversifier les approvisionnements. Le GNL est acheminé à une température de -162 °C et à pression atmosphérique. L'objet principal de la thèse vise à valoriser l'exergie contenue dans le GNL lors de sa gazéification et de son réchauffage avant d'être distribué sur le réseau. La thèse étudie un nouveau concept de gazéification qui se différentie des développements en cours par l'usage de l'air ambiant comme seule source de chaleur et par la valorisation d'une partie de l'exergie du GNL en énergie mécanique.Une analyse énergétique et exergétique a permis de définir des architectures de cycles moteurs utilisant l'énergie calorifique de l'air comme source chaude (récupérée par un fluide intermédiaire qui est le propane) et le GNL comme puits froid.L'usage de l'air ambiant conduit à gérer les cycles de givrage et dégivrage sur les évaporateurs du fluide intermédiaire récupérant les calories de l'air. Ceci nécessite la compréhension des phénomènes couplés de transferts de chaleur et de masse. Pour cela un banc d'essai a été construit afin de caractériser des échangeurs à ailettes rondes discontinues en condition de givrage et de valider un modèle numérique simulant le comportement de ces échangeurs en présence de givre. Cette modélisation a permis de proposer une logique de dimensionnement et d'exploitation des évaporateurs à air en prenant en compte l'effet du givre. Une étude saisonnière a montré que le procédé proposé est énergétiquement excédentaire tout au long de l'année. / The market of liquefied natural gas (LNG) is growing and presents the advantage of diversifying supplies. The LNG is fed at a temperature of -162°C and at atmospheric pressure. The main objective of the thesis aims at the valorization of the LNG exergy during its gasification and heating before being delivered through the network. The thesis investigates a new concept of gasification that differs from the current developments by the use of ambient air as the only heat source and by partial valorization of the LNG exergy in mechanical energy.An energy and exergy analysis helped to the definition of engine-cycle architectures using the air heating capacity as a heat source (recovered by an intermediate fluid, here propane) and LNG as a cold sink.The use of ambient air led to manage frosting and defrosting cycles on the evaporators of intermediate fluid recovering heat from the air. This requires understanding the coupled heat and mass-transfer phenomena. A test bench was built to characterize Circular Finned-Tube Heat Exchangers in frosting conditions and to validate a numerical model simulating the behavior of such heat exchangers in presence of frost. As a result, a logic for the design and operation of air heat exchangers is proposed taking into account the frosting effect. A seasonal study showed that the output power generated by the new concept of gasification is superior to its energy consumption throughout the year.

L'amélioration des systèmes énergétiques est considérée comme un levier technologique pour répondre aux défis liés à la croissance de la demande d’électricité et des émissions des gaz à effet de serre. Les futures centrales devraient présenter une intégration thermique plus flexible et des sources de chaleur mixtes possibles. Une des solutions fiables consiste à utiliser un cycle de Brayton au CO2 supercritique (CO2-SC), un tel cycle à haut rendement est théoriquement prometteur pour les applications nucléaires, fossiles et solaires thermiques. Un des principaux obstacles au déploiement du cycle de Brayton au CO2-SC est de justifier sa faisabilité, sa viabilité et son potentiel à l’échelle industrielle. Dans ce contexte deux axes de recherche ont été identifiées : • Une sélection rigoureuse de l’équation d’état qui permet de représenter les propriétés d’intérêt du CO2-SC. • Une nouvelle méthodologie pour l’optimisation des centrales électriques, permettant de sélectionner automatiquement le procédé optimal parmi une grande quantité de configurations possibles (dénomme superstructure). Les résultats de la première partie de cette thèse mettent en lumière que l’équation de SW est pertinente pour limiter l’impact de l’imprécision de l’équation d’état sur le dimensionnement du procédé. Dans cette thèse, un simulateur de procédé commercial, ProSimPlus a été combiné avec un solveur type évolutionnaire (MIDACO) afin d’effectuer des optimisations superstructure. Premièrement, le critère d’optimisation est de maximiser le rendement énergétique du procédé. Dans un deuxième temps, on cherche simultanément à minimiser les coûts du procédé. Pour ce faire, des fonctions de coût internes à EDF ont été utilisées afin de permettre l’estimation des coûts d'investissement (CAPEX), des dépenses opérationnelles (OPEX) et du coût actualisé de l'électricité (LCOE) / Efficiency enhancement in power plant can be seen as a key lever in front of increasing energy demand. Nowadays, both the attention and the emphasis are directed to reliable alternatives, i.e., enhancing the energy conversion systems. The supercritical CO2 (SC-CO2) Brayton cycle has recently emerged as a promising solution for high efficiency power production in nuclear, fossil-thermal and solar-thermal applications. Currently, studies on such a thermodynamic power cycle are directed towards the demonstration of its reliability and viability before the possible building of an industrial-scale unit. The objectives of this PhD can be divided in two main parts: • A rigorous selection procedure of an equation of state (EoS) for SC-CO2 which permits to assess influences of thermodynamic model on the performance and design of a SC-CO2 Brayton cycle. • A framework of optimization-based synthesis of energy systems which enables optimizing both system structure and the process parameters. The performed investigations demonstrate that the Span-Wagner EoS is recommended for evaluating the performances of a SC-CO2 Brayton cycle in order to avoid inaccurate predictions in terms of equipment sizing and optimization. By combining a commercial process simulator and an evolutionary algorithm (MIDACO), this dissertation has identified a global feasible optimum design –or at least competitive solutions– for a given process superstructure under different industrial constraints. The carried out optimization firstly base on cycle energy aspects, but the decision making for practical systems necessitates techno-economic optimizations. The establishment of associated techno-economic cost functions in the last part of this dissertation enables to assess the levelized cost of electricity (LCOE). The carried out multi-objective optimization reflects the trade-off between economic and energy criteria, but also reveal the potential of this technology in economic performance.

No atual período de incertezas na geração e transmissão de energia elétrica no Brasil, a utilização dos sistemas de cogeração com uso de gás natural, tornou-se uma grande oportunidade econômica, estratégica e tecnológica, para as pequenas e médias empresas, considerando a extensão e perspectivas de expansão da rede de distribuição de gás natural. Uma empresa farmacêutica para se manter competitiva e reduzir o impacto dos custos indiretos em seus produtos, necessitava aumentar sua linha de injetáveis, produzindo no Brasil alguns medicamentos que até então eram importados de filiais em outros países e para que isto fosse possível, teria de investir na construção de novos laboratórios, compra de equipamentos, aumento de utilidades para sua fabricação como vapor de água para injetáveis, sistema de HVAC para salas limpas, o que levaria a um aumento de consumo de energia, vapor, água de refrigeração. Este investimento inviabilizaria a produção desta nova linha de produtos, pois tanto o custo do investimento em novas centrais de utilidades, quanto mais o custo desta geração e sua manutenção, decretariam um fim para a esta empreita. Neste trabalho, apresentou-se uma alternativa como solução para viabilizar esta instalação, trocando-se os chillers convencionais por um chiller de absorção, que alem de consumir pouca energia elétrica utilizando a troca térmica entre brometo de lítio e vapor para gerar água de resfriamento para o sistema de ar condicionado, o sistema proposto proporcionou um aumento de fornecimento de vapor não só para alimentar o sistema de HVAC como para a produção da fabrica, anexo a esta caldeira de recuperação é proposto a instalação de uma turbina á gás com condições suficientes de gerar energia elétrica para todo o site e ainda ter condições de negociar o excedente de energia para ser vendido para a concessionária. O resultado deste sistema proposto demonstrou uma excelente eficiência, frente ao sistema convencional, o que tecnicamente se apresentou como muito viável. / In the current period of uncertainty in the generation and transmission of electric energy in Brazil, the use of cogeneration systems using natural gas, has become a great economic opportunity, strategic and technology for small and medium enterprises, considering the extent and prospects for expansion of the distribution of natural gas. A pharmaceutical company to remain competitive and reduce the impact of indirect costs in their products, needed to increase its line of injectables, producing here in Brazil some drugs that were previously imported from subsidiaries in other countries and to make this possible, would invest in building new laboratories, purchase equipment, increase of utilities for its manufacture steam as water for injection, the HVAC system for clean rooms, leading to an increased consumption of energy, steam, cooling water. This investment would make impracticable the production of this new line of products, therefore not only the cost of the investment in new central offices of utilities, the more the cost of this generation of utilities and its maintenance, would decree an end for the this take over on a contract basis. In this work, presented as an alternative solution to enable this facility, exchanging conventional chillers for an absorption chiller, which besides consume little electricity using the heat exchange between lithium bromide to generate steam and cooling water for the air conditioning system, the proposed system provided an increased supply of steam to feed not only the HVAC system for the production of manufactures, attached to this recovery boiler is proposed to install a gas turbine with sufficient conditions generate electricity for the entire site and still be able to trade the surplus energy to be sold to the utility. The result of this proposed system showed an excellent efficiency, compared to the conventional system, which technically is presented as very viable.

Recently, attention has been drawn to the viability of using S-CO(2) as a working fluid in modern reactor designs. Near the critical point, CO2 has a rapid rise in density allowing a significant reduction in the compressor work of a closed Brayton Cycle. Therefore, 45% efficiency can be achieved at much more moderate temperatures than is optimal for the helium Brayton cycles. An additional benefit of the S-CO2 system is its universal applicability as an indirect secondary Power Conversion System (PCS) coupled to most GEN-IV concept reactors, as well as fusion reactors. The United States DOE's GNEP is now focusing on the liquid Na cooled primary as an alternative to conventional Rankine steam cycles. This primary would also benefit from being coupled to an S-CO2 PCS. Despite current progress on designing the S-CO2 PCS, little work has focused on the principal supporting systems required. Many of the required auxiliary systems are similar to those used in other nuclear or fossil-fired units; others have specialized requirements when CO2 is used as the working fluid, and are therefore given attention in this thesis. Auxiliary systems analyzed within this thesis are restricted to those specific to using CO2 as the working fluid. Particular systems discussed include Coolant Make-up and Storage, Coolant Purification, and Coolant Leak Detection. / Contract number: N62271-97-G-0026. / US Navy (USN) author

There has been an ever-increasing demand for power generation, which is predicted to grow as society becomes more advanced. However, tradition fossil fuels are beginning to deplete, and there is a great necessity for alternative fuel sources that will bridge the gap between energy production and consumption. To decrease the high demand alternative fuel sources are gaining in popularity. The supercritical carbon dioxide Brayton power cycle has been proposed as a possible cycle for nuclear and concentrated solar power generation. Two main advantages of having supercritical carbon dioxide are the large property variations and component size associated with power cycle. Forced convection heat transfer of supercritical carbon dioxide in printed circuit heat exchanger geometries were investigated in the following study using a finite volume framework and the FLUENT 12.1 code. The geometries of interest were: non- chamfered zig-zag, chamfered zig-zag, and air foil. Flow through the three geometries was in the horizontal orientation and subject to a heating mode operation. A range of testing conditions were explored, including operating pressures between 7.5 to 10.2 MPa with the mass flux ranging from 326 to 762 kg/m2-s. Due to the turbulent nature of this problem, the k−E with enhanced wall treatment and shear stress transport k−ω turbulence models were considered. With this addition a total of 54 simulations were performed. Results indicated that there was an increase in the heat transfer coefficient as the supercritical carbon dioxide reached the pseudocritical temperature, conversely as there was an increase in operating pressure, the heat transfer coefficient decreased. Nevertheless, this increase near the pseudocritical temperature was due to a sharp increase in the specific heat. Mass flux effects indicated that there was an increase in heat transfer as the mass flux was increased. This was due to the increase in Reynolds number near the pseudocritical temperature. Next, pressure losses were investigated for the three geometries. The non-chamfered zig-zag channel had the greatest pressure loss associated with it, while the air foil channel had the least. Based on the results, the ratio of the friction factor to heat transfer for the non-chamfered and chamfered zig-zag geometries were approximately 2.65 and 1.57 times higher than for the air foil, thus leading to the idea that the air foil channel may be best suited for practical applications. Finally, the simulation results were compared to experimental data and existing correlations. Many existing correlations failed to accurately predict the magnitude of heat transfer, although they exhibited a similar trend. A new correlation was developed for the zig-zag geometries based on the numerical data obtained during this investigation and published experimental data. The new correlation is able to predict the maximum heat transfer coefficient within 12.4%.

Thesis (M. App. Sc.)--Carleton University, 2005. / Includes bibliographical references. Also available in electronic format on the Internet.