Numerical Study On The Abrasion And Ash Deposition Characteristics Of A New Type Economizer Tubes

Economizer is an important heat exchange equipment in boiler flue.Owning to the large amount of dust in the flue gas of industrial boilers,the ash accumulation and abrasion of the economizer pipe bundle will occur,which seriously affects the safety and economical efficiency of boiler.At present,there are a lot of research achievements about the ash accumulation and abrasion of economizer tubes,but the main limitations are concentrated on traditional tubes such as tubes,membrane tubes,H fin tubes and so on.Therefore,this paper proposes a new type of tube–pitted tube,studies the ash deposition and erosion characteristics of flue gas flowing across pitted tubes and provides theoretical guidance about reducing wear and ash deposition,which is of great importance to the application and popularization of pitted tubes.Firstly,this paper introduces the economizer structure and types,analyzes the factors that affect the abrasion of economizer tubes,and simulate the gas-solid two-phase flow about flue gas flowing across pitted tubes in-line by ANSYS FLUENT,which obtains the trajectory of the flying ash particles in the tube bundle,the tube erosion reprogram and the deposition rate and analyzes the influence of the smoke physical property parameters and the tube bundle structure parameters on the abrasion and deposition rate of the fly ash particles.The main work and achievements are as follows:?1?Compared and analyzed the erosion difference between pitted tubes and smooth tubes,the results show that pit structure on the surface of the tube has a good effect on the diversion of flue gas and particles,which effectively reduce the wall erosion.The abrasion of pitted tubes is reduced by about 15%than smooth tubes'under the same conditions.?2?Analyzed the effect on flue gas physical parameters on the abrasion characteristics of pitted tube.Abrasion exacerbates while the average particle size is increasing under the same gas velocity;abrasion increases greatly with the increasing of average particle size under the condition of larger smoke rate.?3?Studied the effects of structural parameters of tube bundles on the erosion characteristics of pitted tubes.Light tubes'and pitted tubes'wear rate decreases with the increase of transverse tube spacing.With the longitudinal tube distance increasing,the wear rate of the two tubes also increases,but the variable quantity is quite low.For the tubes with smaller transverse pipe spacing,the wear rate varies greatly with the change of longitudinal spacing.The wear rate of the pitted tube decreases with the increase of pit depth on the tube's surface.For large particles,the effect of wear reduction is more obvious with the increase of pit depth.?4?Investigated the effects of gas velocity and particle size on the deposition rate in the process of flue gas over rough tubes,and compared particle deposition on the surface of rough tubes and smooth tubes.When gas flows cross pitted tube bundle,pit structure on the surface of the tube has a good effect on the diversion of flue gas,and the particle deposition rate on the rough tube's surface is much lower than the light tube's.For the particles with average size of 25?m,when the inlet gas velocity v=8m/s,the pitted tube is more significant than the smooth tube in the effect of reducing particle deposition.?5?Explored the variation relationship between the structure parameters and the particle deposition rate in the rough tube bundles.The results show that flue gas flow area increases with the increase of transverse tube spacing between adjacent pipe,and more fly ash particles flowing through the middle area,which reduces ash deposition;As the longitudinal distance increases,the particle deposition rate decreases firstly and then increases.In all the analyses done,the case is determined when s₁/D=3.0 and s₂/D=1.8,the particle deposition rate is lowest,which is 20.72%.When the pit depth is increasing,the ash deposition rate on the surface of the pitted tube bundle is generally lower than the light tube's surface,but on the whole,For smaller particles of general size,the pitted tubes with e=0.75mm are much better than other kinds in the effect of reducing ash accumulation.