| Air preheater is an important equipment in the power plant. It can reduce the exhaust gas temperature and improve the combustion efficiency. It is meaningful to study the thermal performance of air preheater. The air preheater include tube air preheater and rotary air preheater. The operating performance of rotary air preheater is studied in this thesis.The rotary air preheater, a significant heating surface at the end of boiler, is widely used in utility boilers. Distributed Control System (DCS) has been equipped in most power plants, the function of which are centralized monitoring, trouble retrospect, data collection and saving. DCS can be used to show data, alarm accident, emergency protect and so on. But the present DCS can only show some simple data, which can not assess the performance of some equipment according to the monitored data. Workers in the power plant make use of their experience and field data showed by DCS to judge about the inside trouble. Therefore, to develop monitoring model is the imminent requirement of the power plant.The trisection rotary air preheater which is widely used is taken as investigated subject in the paper. Based on the design calculating model of rotary air preheater and field data of DCS, the paper sets up the physical model and mathematics model about the thermal performance of the rotary air preheater. Besides, a program used to monitor the thermal performance is programmed by Visual Basic language. The program include the following calculating modules: theoretical exchanging heat, actual exchanging heat, resistance, the gas dew-point temperature, average ash thickness. Through the program, not only the thermal performance of rotary air preheater can be analyzed according to the field data, but also how some parameter affects the air preheater can be studied, and the abnormal condition can be predicted.To validate the program, the paper takes a trisection rotary air preheater of 300MW unit in Shandong Province as an example. A time in which the load is stable is chosen as monitor time. Record the field data every one hour and see these data as different operation condition. The theoretical exchanging heat and actual exchanging heat are calculated. For the coal and load are both stable, the theoretical exchanging heat in all the operation condition were nearly invariable, but the actual exchanging heat, affected by operation parameters and ash deposit, largely changed. Through the program, the resistance are calculated, the trend of which is consistent with that of pressure differential between flue inlet and outlet. The variation of pollution coefficient is studied and the average ash thickness is also analyzed. After the soot blowing, both the pollution coefficient and average ash thickness decrease. How the variation of coal and over-air coefficient affect the exchanging heat quantity is studied.The exhaust gas temperature, which is also named the outlet gas temperature of air preheater, is analyzed about its influential factors. Primary-air flow rate, kind of coal, feed water temperature, furnace over-air coefficient and trouble of air preheater are the most factors. Through calculating and analyzing, affecting laws how the above influential factors affect the exhaust gas temperature are given in the paper. The air leakage and ash deposit give more effect on the exhaust gas temperature.Conclusively, the study results of this thesis provide the theoretical basis for the stable and reliable running of air preheater and enhancing the boiler efficiency. |
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