| The air cooler is the place where the fluid and the air are heat exchange.The air cooler structure mainly includes both sides of the tube box and finned tube.The flow and heat transfer and mass transfer of multiphase flow in the air cooler are very complex.The erosion-corrosion caused by multiphase flow and heat transfer in air cooler is extremely complex.At present,there are few reports about the flow and heat transfer law of air cooler to predict the erosion-corrosion of air cooler.In this paper,a multiphase flow erosion-corrosion problem in the actual production of the fractionator overhead condenser of a petrochemical plant hydrogenation unit is studied.The internal fluid medium of the air cooler is a mixture of naphtha and water.CFD is used to study the flow and heat transfer of the air cooler.HTRI simulation software is used to simulate the air cooler.The temperature distribution and the mass fraction of the gas phase in the air cooler tube bundle were obtained.All the naphtha steam become liquid when it locates at 8 meters away from the outlet of the second tube of the air cooler.The air cooler is modeled by FLUENT simulation software.The MIXTURE model,k-ε model and standard wall function are used to simulate the air cooler.The inlet boundary condition is mass flow inlet,and the outlet boundary condition is pressure-outlet.The coefficient of heat transfer is 816.3 w/(m2·k).The wall temperature is 307.15 K and the wall thickness is 0.0025 m of air cooler.The main findings of the simulation are as follows:the outlet temperature of the air cooler tube is 380 K,which is consistent with that of the HTRI simulation.The normal velocity distribution of each tube bundle in the air cooler is basically the same,and the normal velocity of the tube box changes largely.The normal velocity is relatively large which close to the inlet of air cooler.The normal velocity on both sides of the box is relatively small.The normal velocity of the tube box which close to the third pass tube bundle of air cooler is the largest.The normal velocity of the tube box which close to the second pass tube bundle of air cooler is the smallest.The distribution of the tangential velocity of each row of air cooler is very uneven,and the tangential velocity of the tube bundle near the inlet of the air cooler is large.The turbulent kinetic energy distribution of each row tube bundle of air cooler is extremely uneven,especially the turbulent kinetic energy of the inlet of tube bundle is large.The turbulent kinetic energy of the 5th,6th,7th,12th,13th,14th,17th,18th,19th,20th,21th,25th,26th,27th,33th,34th,35th tubes are large in the first row of tube bundles of the air cooler,so the erosion-corrosion is most serious.The turbulent kinetic energy of the 3rd,4th,5th,13th,14th,15th,16th,23th,24th,25th,26th,33th,34th,35th,36th tubes are large in the second row of tube bundles of the air cooler,so the erosion-corrosion is most serious.The turbulence kinetic energy of the third row of tube bundles of the air cooler changes relatively small,not prone to erosion corrosion.The maximum erosion rate of the tube bundle is concentrated at the inlet of the tube bundle,and there is no erosion phenomenon from the inlet to end.The maximum erosion rate is 4.76 mm/year.The maximum electrochemical corrosion rate of the air cooler tube bundle is mainly concentrated at the inlet end of the air cooler,and the maximum electrochemical corrosion rate is 0.00065 mm/year.Compared with the electrochemical rate,the erosion rate is dominant and the electrochemical corrosion rate is negligible.The simulation results are in agreement with the actual site erosion-corrosion analysis results.It is found that the main reason for the erosion-corrosion of the air cooler is that the fluid is uneven in the tube bundle of air cooler.Therefore,the air cooler is improved and the numerical simulation of the air cooler is carried out.The simulation results show that The turbulent kinetic energy distribution of each row tube bundle of air cooler is extremely uneven.The turbulent kinetic energy of the inlet of tube bundle changes greatly,but the turbulent kinetic energy distribution is more balanced than that before the air cooler.The turbulent kinetic energy of the 5th,6th,9th,11th,18th,19th,29th,30th,33th,34th tubes are large in the first row of tube bundles of the air cooler,so the erosion-corrosion is most serious.The turbulent kinetic energy of the 1st,2rd,3rd,4th,5th,12th,13th,25th,26th,35th,36th,37th tubes are large in the second row of tube bundles of the air cooler,so the erosion-corrosion is most serious.The turbulence kinetic energy of the third row of tube bundles of the air cooler changes relatively small,not prone to erosion corrosion.The erosion rate of the tube bundle of air cooler is the largest at the inlet of tube bundle,and the erosion rate does not change from the inlet to the end.The maximum erosion rate is 0.19 mm/year.The electrochemical corrosion rate of the inlet of the air cooler tube is the largest,and the maximum electrochemical corrosion rate is 0.00048 mm/year.The electrochemical corrosion rate can be neglected compared with the erosion rate.Compared with the previous air cooler,the erosion rate of the improved air cooler is greatly reduced. |
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