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The widespread use of gas turbines and cogeneration plants as a means of independent power generation have provided a considerable momentum for further study of cogeneration plant. Furthermore, in the design of new systems and an existing system improving their performance is a challenging task. This is largely achieved by studying the system performance as a whole or as an individual component. In order to do that, greater understanding of the behaviour of the plant during off-design operation and identifying the potential components that have wide margin of improvement are important. Thus, this thesis is concerned with a detailed investigation of how off-design conditions affect the cogeneration performance and the associated exergy destruction or loss. To carry out the investigation a new modeling procedure based on component matching is developed. The model is used to predict the design performance, offdesign performance, and the exergy destruction of the cogeneration plant. The cogeneration plant consists of gas turbine and heat recovery steam generator. The gas turbine compressor has variable stator vanes whose position may be set to control the inlet air flow to the compressor. During off-design the variable vanes are re-staggered to improve the overall cogeneration performance. Two modes of gas turbine operation are identified. The first mode is for part load less than 50% running to meet the part load demand. This is achieved by controlling the fuel flow and air bleeding at the downstream of the compressor to avoid surge formation. The second mode of operation is for part load greater than 50% and running to meet both the part load demand and the exhaust gas temperature set value by simultaneously regulating the fuel feeding and the variable vanes opening. To accommodate change of compressor parameters during variable vanes re-stagger correction coefficients are introduced. The unavailable information such as the compressor and turbine design point data are obtained using energy and mass conservation, and thermodynamic properties ratio relationships. The compressor and turbine maps are developed using scaling method from similar configuration known component maps. Both energy and exergy models of the components are developed. First, an energy based components model and their interactions using modified component matching concept are developed. To support the calculations required for off-design analysis, a computer program is developed in MATLAB software. The effect of variation of load on the cogeneration parameters such as fuel consumption, temperatures, pressure ratios, variable vanes opening, efficiencies, specific fuel consumption, and steam production rate are examined. The simulated results are compared with available actual data. Furthermore, statistical errors evaluation using Minitab program indicated that the error mean and standard deviations values were small and hence the developed model represents the real process. Once the model has been validated, based on the inlet and outlet properties of each component the exergy analysis is performed to find out the exergy destruction or loss in each component. Sensitivity analysis of the effect of ambient temperature on the cogeneration performance is carried out. It is found that the smaller the ambient temperature, the better is the gas turbine performance in the first mode of operation. In the second mode of operation the VV s is modulated to maintain the turbine exhaust gas temperature. Consequently, effect of ambient temperature on the thermal efficiency is not significant; but the higher the ambient temperature, the higher is the overall performance of the cogeneration plant at a given load. V111

Item Type: Thesis (PhD)
Academic Subject : Academic Department - Mechanical Engineering - Materials - Engineering materials - Metals alloys - Fabrication
Subject: T Technology > TJ Mechanical engineering and machinery
Divisions: Engineering > Mechanical
Depositing User: Users 2053 not found.
Date Deposited: 30 Sep 2013 16:55
Last Modified: 30 Sep 2013 16:55
URI: http://utpedia.utp.edu.my/id/eprint/8026

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