Numerical Modeling-based Optimization And Application Of Flowing Resistance Reduction For Boilers’Flue Ducts

In order to meet the emission standards of pollutants in coal-fired power plants,such as no more thari 50mg/m3 of nitrogen oxides,no more than 35mg/m3 of sulfur dioxide and no more than 5mg/m3 of smoke and dust,many power plants have carried out ultra-low emission renovations,such as denitrification,desulfurlzation and dust removal.After renovation,the flue duct structure of boiler is more complicated,and the flow resistance of flue gas is further increased.Additionally,some units have the problems of insufficient output of induced draft fan,surge and limited load operation caused by insufficient output of induced draft fan.In order to solve these problems,according to the structural characteristics of flue of coal-fired boiler unit,the optimization research of flue structure resistance reduction is put forward.Based on the study of fluid flow resistance by domestic and foreign scholars and research institutes,the basic theory of flue flow resistance is discussed in detail,and the commonly used methods of obtaining resistance coefficient in engineering are introduced.The elbow and T-tube of flue were reconstructed and optimized.Through GAMBIT software modeling and meshing,the flow resistance in the elbow and T-tube of flue was simulated by FLUENT.According to the simulation results,the renovation scheme of flue elbow and T-shaped pipe fittings with minimum flow resistance loss,i.e.the arrangement scheme of equal spacing of guide plates with inner diversion,is determined.After the elbow and T-shaped pipe fittings of the flue are equipped with a guide plate at equal spacing,the flow resistance loss of the flue is reduced by 512.7 Pa under the condition of ftull load operation of the unit,and the drag reduction effect is obvious.The integrated reconstruction of induced draft fan and turbocharged fan is studied.Through ICEM software modeling and meshing,the flow resistance in existing flue and flue with different reconstruction schemes is simulated by FLUENT.According to the simulation results,the flow resistance of flue duct in different schemes is obtained,and according to the ratio of efficiency to cost,the most economical scheme of flue duct modification is determined,that is,the rectangular flue duct modification scheme of canceling bypass flue and booster fan.The simulation results show that the flow resistance loss of flue duct in this section is reduced by 333.9 Pa and the drag reduction effect is good after the unit is operated at full load.The test results show that the average flow resistance loss of flue from the inlet of air preheater to the outlet of absorption tower decreases by about 700 Pa,the current of induced draft fan decreases by 80 A,and the power consumption decreases by 706 kW.The retrofit not only has remarkable energy-saving effect but also eliminates the surge phenomenon of the induced draft fan,improves the safety of the operation of the induced draft fan,and enables the unit to run at full load,and achieves good comprehensive benefits.