Rasearch On Thermal Deviation At Furnace Exit In A 600MW Tangentially Fired Boiler

In recent years, the power station boiler is gradually moving towards the development of large capacity. In the development process of tangentially fired boiler gradually tends to large capacity, because there is airflow residual rotation at furnace exit and other factors, the left and right flue gas temperature and velocity are uneven distribution in the horizontal flue of furnace exit and carbon burnout rate decreased as well. These problems will certainly obstruct the process of large-scale development of the tangentially fired boiler. The particularly serious problem among which is the overtemperature tube explosion of superheater and reheater, which is caused by the left and right sides of the flue gas in the horizontal flue of furnace is not uniform.In this paper, the combustion process of lignite boiler is simulated by CFD software Fluent. In the simulation, the influence of moisture on the combustion process in the lignite boiler can not be ignored. Because of the widely used traditional coal definition method does not consider the effect of moisture, this paper uses the method which definited by empirical formula considering the effect of moisture in pulverized coal to simulate the combustion process in lignite boiler. Through the comparison of the numerical simulation results of the two methods, it can be found that the numerical simulation results whose method is definited by the empirical formula are more close to the industrial test value.Main causes of heat deviation of furnace outlet of tangentially fired boiler are flame of high temperature thermal radiation in the furnace and the uneven distribution of temperature distribution and velocity of flue gas., It can be seen from analysis that the heat absorption deviation of the radiation heating surface is mainly related with the location of flame center and the size of furnace, the heat absorption deviation of radiation-convection heating surface is related to the position of flame center in the furnace and the residual rotation at the furnace outlet and the heat absorption deviation of convection heating surface is related to the distribution of the left and right velocity in the horizontal flue of furnace outlet.The influence of OFA horizontal swing angle on the velocity deviation and temperature deviation of the furnace outlet is studied. Gas velocity deviation and gas temperature deviation can effectively be reduced at the furnace exit when the reverse tangent angle of OFA is proper. The best reverse tangent angle is 15° by the simulation results of this type of furnace. And the effect of different air distribution modes of three layer OFA on the thermal deviation of the furnace outlet is also studied in the case of the over fire air rate constant and the reverse tangent angle of OFA is 15°. The results show that when the reverse tangent angle of OFA is 15°, inverted pagoda-style air distribution mode is more conducive to reducing thermal deviation at furnace outlet comparing to the positive pagoda air distribution mode and the equal air distribution mode.