Research On Corrosion,fouling And Heat Transfer Performances Of PTFE Coated 3-D Finned Tube Under Low Temperature Flue Gas

China consμmes about 4 billion tons of standard coal every year,51.6%of which is used for thermal power generation,but the heat loss of exhaust gas of coal-fired boilers is high and the utilization rate of waste heat of flue gas is low.Traditional heat exchanger covers a large area,poor heat exchange effect and easy to accμmulate ash.In recent years,it is found that the 3-D finned tubes heat exchanger has the advantages of strong disturbance and high heat transfer coefficient,and has outstanding advantages in the waste heat recovery of flue gas.However,the boiler flue gas contains fly ash particles and sulfuric acid steam,which forms corrosion ash on the wall of 3-D fin tubes,which causes the heat exchanger corrosion.At present,the surface protection method is the common method for the corrosion of heat exchanger,but the corrosion ash deposition and heat exchange of 3-D fin tubes after applying anti-corrosion coating have not been studied in depth.Therefore,this paper adopted accelerated corrosion method and simulated smoke method to study and select a kind of excellent PTFE anticorrosive coating 3-D fin tube for corrosion ash deposition and heat exchange research,which provides theoretical basis for the engineering application of 3-D fin tube anticorrosion.Firstly,the corrosion resistance of several commonly used anti-corrosion coatings under accelerated corrosion conditions was experimentally studied.The corrosion morphology and corrosion rate of several coatings were observed and analyzed,and a PTFE coating with excellent corrosion resistance was selected.Then,in the simulated flue gas experiment,the corrosion ash deposition characteristics of PTFE coating on the surface of 3-D finned tube were observed and analyzed,and the effects of different working conditions and fin structure parameters on the corrosion resistance were explored.Finally,the influence of corrosion ash deposition on the heat transfer performance of PTFE coated 3-D finned tube was studied experimentally,and the change trend of Nu outside the tube with time was obtained with the occurrence of corrosion ash deposition.At the same time,the change trends of Nu outside the tube with time of uncoated 3-D finned tube and PTFE coated 3-D finned tube under different accelerated corrosion time were compared and analyzed.The main results are as follows:（1）After accelerated corrosion experiment,the surface corrosion of the 3-D fin tube without coating was the most serious,the fins were broken and fallen off,and the corrosion loss weight was the highest;the surface coating of ceramic coated 3-D fin tube and paint coating 3-D fin tube was corroded and damaged,and the partial cracks appeared in the fins,and the corrosion loss weight was lower than that of the uncoated3-D fin tube;after accelerated corrosion of the 3-D fin tube with PTFE coating,there was no obvious corrosion trace on the surface,the coating was not damaged,and the corrosion loss weight was the lowest.（2）The amount,composition and particle size of corrosion ash deposit of uncoated3D finned tube and PTFE coated 3-D finned tube were compared.The results showed that PTFE coated 3-D finned tube had less corrosion ash deposit and smaller particle size,and the content of Fe₂O₃ in corrosion ash remained unchanged.When the working conditions change,the amount of corrosion ash deposit was the most at 20℃of cooling water temperature with the increases of fly ash concentration and acid volμme fraction.While when the fin height was 4.5 mm,the amount of corrosion ash was the most.And when the fin width increased,the amount of corrosion ash increased.When the axial spacing of fins increased,and the amount of corrosion ash decreased.（3）Under different working conditions and fin structures,the heat transfer performance of PTFE coated 3-D finned tube decreased with the increase of time in the process of corrosion ash deposition,and finally basically reached stability.At the beginning of the experiment,the Nu of uncoated 3-D finned tube was higher than that of PTFE coated 3-D finned tube,but at the end of the experiment,the decrease of Nu was greater than that of PTFE coated 3-D finned tube.The Nu of PTFE coated 3-D finned tube decreased with the increase of cooling water temperature,fly ash concentration and acid volμme fraction.And with the increase of the fin height of PTFE coated 3-D finned tube,the Nu increased.While the Nu decreased as the fin width and the fin axial spacing increased.In addition,the corrosion ash deposition of PTFE coated 3-D finned tube was less than that of uncoated 3-D finned tube after accelerated corrosion,and the Nu was higher than that of uncoated 3-D finned tube.