Numerical investigation of 700 °C boiler flue gas thermal deviation based on orthogonal experiment

Abstract

In the present work, computational fluid dynamic (CFD) models have been established to investigate a newly presented flue gas temperature deviation solution on the basis of ANSYS FLUENT16.0 considering a 700 °C tangentially fired pulverized-coal boiler, which confronts with severe flue gas temperature deviation. Orthogonal test method was used to complete the optimization parameters with deflected secondary air swing angle (A), separated over-fire air reverse tangent angle (B), burner upward swing angle (C); and the thermal deviation at the outlet of the furnace as the performance index. The orthogonal test table L9(34) with three levels for each factor was designed. Using the range analysis method and the weight-based matrix analysis method respectively, the significance degree of the influence of different factors and levels on the deviation of the flue gas temperature at the furnace outlet was discussed, the optimal factor and level combination was determined, and the corresponding influence weights were given. It is found (1) Residual swirling flow in the upper furnace causes the flue gas velocity and temperature deviations in crossover pass. (2) The influence degree of various factors on the deviation of the flue gas at the furnace outlet is as follows: separated over-fire air reverse tangent angle > deflected secondary air swing angle > burner upward swing angle, the influence weights of different factors are A = 0.2184, B = 0.5962, C = 0.1560, and the best factor and level combination is A1B3C2. (3) In this test, when the deflection secondary air angle is 0°, separated over-fire air reverse tangent angle is 25°, and the burner upward swing angle is 11°, the flue gas temperature deviation of the furnace outlet section is the minimum, which is 29.297 K, compared with the maximum, the decrease is up to 86.22 K.