Corrosion Failure Analysis And Structure Optimization Of Heat Exchanger Under Multi-Physical Field

Heat exchanger is an important equipment for energy exchange,which is widely used in petrochemical industry.Corrosion of heat exchange wall is the main factor leading to equipment failure,which seriously affects industrial production and safety.Coating is a common protection method because of its good anti-corrosion performance,low cost and easy operation.However,the thermal conductivity of the anticorrosion coating is generally low,and the existence of the coating causes the change of the weak parts of the corrosion and the decrease of the heat transfer efficiency.Based on the above problems,it is of great significance to study corrosion protection of heat exchanger and structure optimization of heat exchanger.The main research contents and results are as follows:（1）Analysis of Dewpoint Corrosion Causes of Leakage Failure of Thermal Low Separation Air Cooler in Diesel Modification Unit by Multi-physical Field Numerical Simulation.The results show:That the heat transfer wall surfaces contact because of the expansion of the heat transfer tube.The contact area initiates the heat conduction phenomenon,which causes the temperature distribution of the heat transfer wall to change,and makes the low temperature point of the heat transfer wall migrate upstream,resulting in the condensation of water vapor.The condensate absorbs H₂S and HCl gas to construct the corrosive environment of HCl+H₂S+H₂O.At the same time,when the wall corrosion of the contact area of the heat exchange tube is thinned,the heat conduction at the contact area will be further promoted,and then the dew point corrosion at the contact area will be intensified.The continuous accumulation of local corrosion will eventually lead to the perforation of the heat exchange tube bundle.Based on the above corrosion causes,we give corrosion protection suggestions in material selection,structure and process.（2）There are three kinds of anticorrosive coatings:ordinary heat exchanger coating（DH22）coating,tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin（PFA）coating and DH22+PFA composite coating.Their anticorrosive and heat transfer properties are studied.Under the two extreme conditions of 20℃+1 wt.%and 140℃+80 wt.%H₂SO₄,the corrosion resistance was obtained by soaking experiment:DH22+PFA>PFA>DH22.The condensation heat transfer coefficient of wet air is PFA>DH22>DH22+PFA.Condensation heat transfer simulation was carried out for heat exchanger tubes coated with different thickness coatings,The simulation results show that with the increase of coating thickness,the heat transfer efficiency decreases and the steam condensation site moves backward,which leads to the corrosion weakness moves backward.In order to make up for the decrease of heat exchanger efficiency caused by the introduction of coating,the heat exchange tube arrangement and the shape of the heat exchange tube were optimized and simulated,and the optimized heat exchange efficiency was increased by 1 times.