Numerical Simulation And Experimental Research On Cohesive Fouling Of Ammonium Bisulfate In Air Preheater

After the ultra-low emission transformation of power plant boilers,the ammonia escape of SCR caused ammonium bisulfate(ABS)fouling on the surface of the regenerative plate of the downstream air preheater.This type of fouling is different from loose fouling,and its viscosity is very strong.The traditional ash deposition model is not suitable for ABS cohesive fouling.In addition,the experimental research on ABS cohesive fouling mostly focused on the mechanism of ABS’s influence on ash particles.Therefore,this paper has studied the ash accumulation characteristics on the surface of the regenerative plate through numerical simulation and experiment respectively.The purpose is to predict the position and strength of ABS cohesive ash deposits when the air preheater is running.It is of great significance to instruct the air preheater to blow soot efficiently and reduce the ABS clogging of the air preheater.This paper firstly constructed a deposition model that can predict the growth process of ABS adhesive fouling on the surface of the regenerative plate.Combined with the characteristics of ABS formation and deposition,the temperature range of the ABS deposition zone on the surface of the regenerative plate is determined.Established the flow and heat transfer model of flue gas and ash particles,as well as the collision and deposition model of ash particles on the surface of the regenerative plate.The dynamic grid model is used to describe the growth process of ash on the surface of the regenerative plate.At the same time,the simulation results are compared with the literature results to verify the accuracy and reliability of the fouling model.Secondly,this paper takes the CU-type regenerative plate as the research object,and applies the built ash accumulation model for numerical simulation calculations.After the air preheater rotates one circle(80 s),the characteristic quantities such as the flow field,temperature field,ash accumulation intensity,and ash accumulation probability between the regenerative plates are analyzed.And the influence of inlet flue gas parameters and inlet ash particle parameters on ash accumulation characteristics is studied.The results show that along the flue gas flow direction,the regenerative plate z=1.25～2.05 m is the ABS cohesive ash accumulation area,and the ash accumulation probability is about 90%;z=0～1.25 m and z=2.05～2.30 m are loose ash accumulation areas,and the ash accumulation probability is about25%.The ABS cohesive fouling strength of A board and B board are 4.98 times and 3.68 times of the loose fouling strength respectively.The inlet flue gas parameters affect the location of the ABS cohesive fouling area,where every 10 K increase in temperature,the ABS cohesive fouling area will move back by 0.1 m.Every time the flow velocity increases by 1 m/s,the ABS cohesive fouling area will move back by 0.03 m.The inlet fly ash particle flow has a significant influence on the strength of loose fouling and ABS cohesive fouling.The inlet fly ash particle size directly determines the ash particle size distribution on the surface of the regenerative plate.Thirdly,this paper built a small-scale simulated air preheater experimental platform,prepared different experimental gray samples.The influence of factors such as gas temperature,gas flow rate,ABS-ash mass ratio and particle size on the ash characteristics of the regenerative plate surface area was studied.The experimental results are compared with the numerical simulation results.The results show that when the gas temperature is 420～493 K,as the temperature increases,the ABS ash accumulation strength,ABS adhesion rate and the average particle size of ash particles gradually increase.When T=493 K,the ABS adhesion rate of A board and B board reached the maximum,which were 31.7% and 27.9% respectively.With the decrease of gas flow rate,the growth rate of total ash accumulation strength,ABS ash accumulation strength,ABS adhesion rate and ABS adhesion rate all increase,and the total ash accumulation strength on the surface of the regenerative plate promotes the ABS adhesion rate.With the increase of R value,ABS ash accumulation strength and ABS adhesion rate increase significantly.As the particle size increases,the ash accumulation strength of ABS decreases,and the adhesion rate of ABS decreases significantly.When the ash particle size is less than30.8 μm,the ABS adhesion rate is close to 60%.Through the comparison of the dimensionless values of the ash accumulation strength,the accuracy of the numerical simulation is further verified.Finally,this paper analyzes the reasons for the blockage of the air preheater in a certain factory,and proposes the countermeasures against the blockage of ABS.The results show that the ABS cohesive fouling of the air preheater mainly occurs in the middle temperature section and the cold end of the regenerative plate,and at the same time causes serious corrosion to the regenerative plate,which affects the safe and efficient operation of the air preheater.It can control the ABS blockage of the air preheater from the two aspects of controlling the generation of ABS and reducing the adhesion of ABS.