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 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

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.

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

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

Made available in DSpace on 2014-10-09T12:46:36Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:41Z (GMT). No. of bitstreams: 1 08350.pdf: 7511291 bytes, checksum: 18b3142f54961c0556b2d92490449a3a (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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.