Analysis and application of low-temperature economizer erosion induced by two-phase flow
Objective To enhance the dust removal efficiency of electrostatic precipitators,especially for the removal of fine particulate mat-ter like PM2.5,a low-temperature economizer is often integrated into a sub-low-temperature electrostatic precipitator.It's worth noting that the sub-low-temperature electrostatic precipitator is often subjected to wear,ash accumulation,and corrosion during operation,leading to blockages and leaks in the heat exchange tubes.To address the wear problem of low temperature economizer within the low-temperature electrostatic precipitator induced by gas-particle two-phase flow,we diagnosed the causes and proposed optimization measures that can serve as a reference for the design and optimization of similar engineering projects.Methods Computational fluid dynamics and discrete phase model(CFD-DPM)method were employed to capture multi-phase flow details,and an erosion prediction model(EPM)was utilized for wear prediction.The realizable k-e turbulence model was applied to solve the continuous phase,employing the Lagrange method to track the dust particle trajectories and the rebound model for particle-wall collision.The reliability of the numerical model was verified by comparing the wear rates.The sensitivity of the grid was assessed by examining the uniformity of velocity distribution at the inlet section of low-temperature economizer.Results and Discussion In the benchmark model study,it was observed that lower flue gas velocities corresponded to reduced wear rates of the heat exchange tubes,indicating the necessity of a sufficiently large flue section area in the design of a low-temperature economizer.Furthermore,a decrease in dust concentration upstream of the low-temperature economizer correlated with a slower wear rate of the heat exchange tubes,suggesting the importance of implementing pre-collection measures to miti-gate high dust concentrations entering the economizer.The impact of dust particles on the heat exchange tubes and its fins led to decreased velocity and changed direction,resulting in wear conditions in the low-temperature economizer that did not fully corre-spond to the gas distribution.In the engineering application study,flow field distributions before and after reconstruction were compared and analyzed from the following aspects:1)The optimized design of the flue structure and baffles eliminated the eddy zone on the leeward side of individual baffles that existed before the renovation.2)Before the renovation,the flue gas produced a high-velocity jet downstream after passing through the guide plate in the inlet horn of the low-temperature economizer.The maximum flue gas velocities of the first row of the left and right sides of the pseudo-pipe were 21.94 and 21.12 m/s,respec-tively,which were reduced to 12.97 and 12.81 m/s,respectively,after the renovation,effectively reducing the local maximum wear rate of the low-temperature economizer.3)Flow field optimization significantly decreased the relative standard deviation of the first column of the pseudo-pipe section on the left and right sides,with reductions from 0.322 to 0.201 on the left side and from 0.310 to 0.210 on the right side.4)The flow distribution deviation of the low-temperature economizer on the left and right sides was reduced from±2.03% to±1.23% ,showing an improvement.5)The system pressure drop decreased from 791 Pa before renovation to 603 Pa after renovation,indicating that reasonable deflector measures can reduce system resistance.Conclusion 1)The inlet flue gas velocity,velocity distribution uniformity,and dust concentration of low-temperature econo-mizer significantly affected its wear.Higher gas velocity increased dust concentration,and poorer velocity distribution unifor-mity led to more severe wear of a low-temperature economizer.2)Optimization and renovation of a low-temperature economizer in a coal-fired power plant were carried out.This involved replacing the shell and tube type low-temperature economizer with a vacuum heat pipe type,transforming the streamlined flue design and setting streamlined baffles to reduce eddies in the flue and enhance gas velocity.These modifications significantly improved the velocity distribution uniformity at the inlet section of the economizer,which was beneficial for reducing ash accumulation in the flue and lowering the system pressure drop.Compared to pre-renovation,the maximum wear rates of the low-temperature economizer decreased by 75.2% and 87.8% on the left and right sides,respectively,effectively reducing the risk of leakage.3)Performance test results showed that,after the renovation,the flue gas temperature at the outlet of the low-temperature economizer,the side pressure drop of the flue gas,and the particu-late matter concentration of dry flue gas in the standard state at the outlet of the dust collector all met the corresponding design requirements.
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