| The power industries, especially thermal power plants, have large energy consumptions, which play an important role in energy conversion. Thermal power plants not only consume enormous resources but also discharge SO2 and CO2 as representative pollutants.Therefor, the implementation of cleaner production technologies in thermal power plant is necessary, which can achieve energy conservation, consumption reduction, pollutants decreasing and synergy. Accurate and effective theories on energy conservation contribute to the implementation of energy-saving missions for thermal power plants, which help thermal power plants determine the main units of exergy loss. Thermal power plants are complex energy system, and exergy analysis of complex energy systems has plenty of computations by traditional means, and systems cannot be quickly analyzed with the changes of the environmental parameters. Based on the objective and the problem, the thermal power plant proposes a new mean of exergy analysis to analyse the system, which provide datas and measures to conserve energy and reduce environmental iMPactsThe objective of this paper is to perform exergy analysis for thermal power plants based on the simulation software Aspen Plus, which which helps the thermal power plant accurately determine real points of energy loss. The main contents of this dissertation include:(1)The main units of the thermal power plant are modeled using Aspen Plus via assumptions based on balances of mass, chemical reactions, energy. The main sections of a thermal power plant, including a boiler and steam turbine are simulated by Aspen Plus, and the modeled results are verified by industrial values. Both process flow diagrams for the boiler and the steam turbine are feasible and reliable, and the deviation of all parameters between the simulation results and actual data is below 5%.(2)Exergy analysis is performed for the modeled system based on the data from model simulations and exergy formulations, which reveal the energy loss distribution of the thermal power plant. Exergy balances of main units or equipments for the power plant are established, and input exergy streams and output exergy streams of main units or equipments can be obtained by Aspen Plus. Exergy loss,exergy efficiency and exergy loss coefficient can be calculated based on simulation results and exergy formulations. The results are shown that the main units of exergy loss in the thermal power plant are the boiler and the steam turbine. The combustion process has the highest exergy loss. Exergy efficiency of the high-pressure turbine is the lowest. However, the high-pressure turbine assumes the largest work output, accounting for 37.08%.(3)By applying the sensitivity analysis function of Aspen Plus, influencing factors related to exergy loss are discussed to determine how exergy efficiency of the system varies with these factors. The influences of various operating conditions on the exergy efficiency of the system are investigated including combustion temperature, excess air coefficient, steam temperature, and steam pressure. The results show that the exergy efficiency of the entire system increases with increasing combustion temperature, and steam temperature, steam pressure. The decrease of exergy efficiency is observed with the insufficient or excess supply of air.(4) In the text, we propose three clean production measures:alternative fuel, air staging combustion, fuel staging combustion, and we choose the best conditions of each clean production scheme by considering the exergy efficiency and pollutant emission. The results show that sludge is the best alternative fuel, which make exergy efficiency of whole system increase by 4.32%, and NOX and SO2 emission concentrations are lower than that of reference conditions. Both air staging combustion and fuel staging combustion can increase exergy efficiency of the whole system, and we choose appropriate operation parameters to reduce NOx and SO2 emission concentrations. |
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