Истражување на можности за подобрување на енергетската ефикасност и намалување на емисиите на енергетски парогенератор на јаглен

Abstract

Despite the rapid development of renewable energy systems, fossil fuels dominate the global energy supply. Improving the efficiency of solid fuel power plants is necessary for many reasons, including environmental impact and economic performance. The thesis aims to contribute to the identification of sources and magnitude of energy losses in coal steam power generators, as well as to prepare and demonstrate a methodology for analyzing the possibilities and measures to improve their efficiency. The methodology is based on the integration of the modified method of zone thermal calculation, the exergy method, the numerical fluid dynamics (CFD) technique and the adapted calculation method for determining the concentration of nitrogen oxides (NOx). Using the methodology, the impact of some measures on the efficiency and emission of NOx is analyzed. The work conducts a parallel analysis of energy and exergy balances of the coal-fired steam generator belonging to a thermal power unit of 315 MW. The steam generator is designed to work on low quality coal - lignite with calorific value between 6280 and 9211 kJ/kg, in Rankin cycle at 545 ºC / 177.4 bar, with feed-water temperature of 251 ºC, combustion air heated to 272 ºC and exhaust gas temperature of 160 ºC. The improved zone thermal calculation method is used as a basis for exergetic analysis and application of the method for calculation of NOx formation. The exergy method is included in the analysis in order to distinguish between quality and quantity of energy, because the actual loss of useful energy can not be fully seen with the first law of thermodynamics. The methodological approach establishes a model for optimization of the operation of energy steam generators on solid fuel, in order to determine the energy distribution, temperature profiles along the gas tract of the steam generator, the dissipation of the exergy and a number of other parameters. The results indicate that the greatest dissipation of exergy in the thermal power plant cycle occurs in the steam generator due to the irreversibility of the combustion process and heat transfer between the combustion products and the working fluid water / steam. The combustion process is responsible for about 30% of the total exergy loss in the steam generator. Based on the analysis, the optimization of combustion processes, heat transfer and reduction of NOx emissions can be achieved through a set of measures, including the option of redistribution of air and fuel intake by the height of the storage space, installation of OFA (over-fire-air) openings, drying of lignite with gases and heating of the air with exhaust gases. The effects of air and fuel redistribution, excess air optimization and gas recirculation rate on the temperature profile, and thus on the NOx concentration in the gases are presented. At the end, directions for further research in the subject matter are given.