Enerģijas un ekserģijas indikatori energosistēmu efektivitātes paaugstināšanā
Summary of the Doctoral Thesis
Edvīns Terehovičs, Riga Technical University, Latvia
The aim of the doctoral thesis is to analyze energy efficiency in different energy supply objects using both energy and exergy balance and to find their use ranges and interactions. The tasks of the doctoral thesis are two-dimensional, one dimension being the scope of the energy supply companies: 1. heat supply company; 2. fish processing company; 3. pellet production company; 4. solar power plant. The second dimension is the scope of the analysis of these companies: 1. energy analysis using energy balance method; 2. exergetic analysis with the use of exergy balance; 3. comparison of the results of the energy and exergy analysis and finding out the interaction. Structure of the thesis. Introduction part includes novelty and topicality of research. Aim and tasks of the work, as well as practical use of thesis are presented in the introduction The work consists of three chapters. In the first chapter, using different sources of literature, an understanding of exergy, the theoretical foundations of mathematical calculation of exergy and an overview of the peculiarities of exergy analysis of district heating systems in different European countries are formulated. Nowadays, the scientific notion of energy is made up of the sum of exergy and anergy, and it is the part of energy that characterizes the useful work of the thermodynamic system. Efficient management of energy saving is directed specifically at reducing anergy growth and increasing exergy. In the first chapter of the thesis, using the special and scientific literature, the basics of calculating the exergy calculations of the thermodynamic system were formulated, as well as the creation of the exergy balance of the thermodynamic system was studied. The following system thermodynamic parameters are used in the closed system for the exergy calculation of the substance: internal energy, entropy, temperature, pressure and volume. Calculation of heat flow exergy is related to the fact that the functioning of the technological system is conditioned by the energy exchange with the environment. By transferring from one body to another body and the environment energy in the form of heat flow (heat exchange), a certain amount of exergy moves along with the flow. The exergy balance is formed on the basis of the efficient operation of the thermodynamic system in determining exergy parameters. For any real system, such balance is the integration of all exergy flows at the entrance and exit from it, taking into account the loss of exergy consumption. The first chapter of the thesis also examines the exergy analysis of district heating systems in Denmark, Sweden, Turkey and Slovenia and the experience of using them in these countries. For example, the use of exergy analysis could determine the quality of the energy supplied, thus determining which fuel to use to reduce the loss of exergy. For exergy analysis it is useful to use several model calculation scenarios. Exergy of heat energy should be taken into account when determining the heat price. In the second chapter of the thesis, the model of calculation of exergy balance of the district heating system was created and certain exergy losses in each element of the heating system, i. a specific research methodology for the task solution is offered. The technical data of the operation of the heat production plant has been taken as output data. The output data block includes data on the capacity of the boiler house, the heat produced, the heat losses of the district heating network, the flow and return temperatures, the electricity consumed by the circulation pump, the heat supplied to the consumer and other data. The model of exergy balance of the district heating system is based on the second law of thermodynamics, which states that wherever and whatever changes in the material systems occur, they are always accompanied by: in isolated systems – energy conservation and entropy changes, but in open systems – energy changes and entropy changes. The mathematical calculations of exergy changes in the district heating system are based on the exergy balance. The exergy balance determines how the exergy of heat energy changes from the district heating system to the consumer, which allows us to estimate the stage at which the greatest losses occur. The third chapter of the thesis is a practical approbation of the exergy balance model on different power systems. The approbation of the exergy calculation model was carried out within the framework of the implementation of various scientifically practical research projects. The following data are taken as output data: amount of heat produced, heat carrier flow and return temperature, ambient (outdoor) temperature, boiler house capacity, heat losses, electricity consumed by the circulation pump, amount of heat supplied to the consumer and other process parameters of the process. The exergy balance model approbation data are summarized in tables and graphs and compared with European countries’ experience.
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