Thermoeconomic Analysis And Optimization Of Complex Energy Systems

In China, energy resources are very scarce, the average efficiency of energy conversion is very low and natural environment is damaged heavily by the production of energy industries. The problems in energy and environment restrict the development of national economy. The potential energy savings in many energy systems are very high, especially for the coal-fired power plants. A better approach to the energy savings will be not only able to save natural resources but to improve the qualities of natural environment, which is very important to the development of energy economy. Hence, in this thesis, the main research objects is oriented to the coal-fired power plants, the main aim is to attain the sustainable development in energy, economy and environment. The thermodynamic simulation of the analyzed plant is developed based on the modeling and analysis methods in process system engineering. A complete approach to evaluating , diagnosing and optimizing the energy systems is developed based on the structural theory of thermoeconomics, which can be used for the energy savings and system optimization in all kinds of complex energy systems, especially for the coal-fired power plants.In this thesis, the main methods in the modeling and evaluation of energy systems are reviewed, the problems and drawbacks in the conventional methods are discussed. The process system engineering and the thermoeconomic methods are used to model and evaluate the system. The main methods in thermoeconomics developed up to now are reviewed and discussed. Structural theory of thermoeconomics is used as the research base of this thesis. Lots of efforts has been made to improve and refine the structural theory of thermoeconomics by combining the advantages in other thermoeconomic methods.The thermodynamic modeling and simulation are the premise for the system evaluation and optimization. A simulator is developed based on the modeling and simulation principle of process system engineering, which is oriented to a N300-16.7/537/537-1 pulverized coal-fired power plant located in Hunan Province. By varying the operating parameters, loads and system environment conditions, this simulator can reproduce the cycle behavior for different operating conditions with relative errors less than 2% compared with those obtained from the performance tests.The exergy and thermoeconomic analysis of complex energy systems including the coal-fired power plants are constructed based on the second law of thermodynamics and the structural theory of thermoeconomics, which are beyond the first law modeling of thermodynamics. The 300MW coal-fired power plant is used to illustrate the whole process of converting the thermodynamic model into the thermoeconomic model. The thermoeconomic model, exergy cost model and thermoeconomic cost model based on the Fuel-Product definition are used to quantify the productive interactions among different components of the plant. The thermodynamic process of cost formation and the distribution of the resources throughout the plant can be analyzed.The unit cost of each component can be obtained by using the structural theory of thermoeconomics. But the real causes of the variations in the performance of the system or components still can not be identified by only using these costs. The exergy and thermoeconomic cost equations in the structural theory of thermoeconomics are improved to identify and quantify the composition of the unit exergy/ thermoeconomic cost of the product in each component. A performance index, i.e. specific irreversibility cost, is obtained from this improvement. This index can quantify the system performance from a global point of view, and can be used to compare the production performance of each component in a same system or between different systems under the same benchmark.The"inverse problem", i.e. identifying the induced malfunctions, in the thermoeconomic diagnosis has not been solved until now. This problem impedes the development of the thermoeconomic diagnosis. An improved method for approaching the induced malfunctions is presented based on a simulation technique and differential method. By combining the conventional thermoeconomic diagnosis procedure with the improved method, a progressive separation method of the induced effects for energy system diagnosis is constructed in this thesis. This method is applied to diagnose the malfunctions in the 300MW coal-fired power plant.An improved Local-Global decomposition optimization (LGDO) method is proposed to make up the insufficient in conventional global and local optimization methods, which is base on the structural theory of thermoeconomics and the thermoeconomic isolation principle. The aim is not to achieve the thermoeconomic isolation, but to construct a decomposition strategy. With this strategy the more coupled components are integrated into a subsystem. The subsystem is de-coupled (i.e. thermoeconomically isolated) from the rest of the system, thus this subsystem can be optimized by itself without considering the optimization in the rest of the system. When the components can not be de-coupled, they will be optimized by using the global optimization directly. Thus the local optimization can approach the thermoeconomic isolation as much as possible. When comparing the results obtained from the LGDO method and a conventional local optimization method with those obtained from a global optimization, the LGDO method can get more exact results than the conventional local optimization method. The convergence speed of the LGDO method is very fast.