| Hydrocracking is a very important process in the petrochemical industry,through which liquefied gas,naphtha,diesel and other products can be obtained.However,due to the complex reaction,heat transfer,mass transfer and momentum transfer processes involved in the hydrocracking process,and many equipment are still carbon steel with poor corrosion resistance,there are serious erosion corrosion phenomena in the hydrocracking equipment,which is very easy to cause various production safety problems.The research object of this paper is the elbow of return tower pipeline of regenerator bottom reboiler and the tube bundle of headspace air cooler of fractionator tower in hydrogenation unit.Aiming at the elbow failure,based on the macro and micro perspectives and from the physical and chemical perspectives,to explore its corrosion mechanism,this paper not only summarizes and analyses the physical laws of the inner layer of the elbow,including the distribution of corrosion holes and wall thickness,but also characterizes the failure elbow by means of material and mechanical properties analysis,metallographic examination,X-ray diffraction analysis,scanning electron microscopy and energy spectrum analysis.It is found that the elbow itself has no defect in quality and all the requirements are in line with the national standards.Erosion corrosion is the main cause of elbow corrosion failure.Fluid erosion plays a dominant role in the failure process,and electrochemical corrosion plays a dominant role in the formation of corrosion holes.The fluid disturbance at elbow position aggravates the corrosion of inner wall of pipeline,and the shortcoming of insufficient evaporation space in horizontal siphon reboiler also causes serious corrosion of elbow outlet position and flange.Aiming at the headspace air cooler,CFD simulation results show that fluid scouring plays a dominant role in the whole erosion corrosion process,and electrochemical corrosion has less impact.The deviation is an important reason for the failure of air cooler tube bundles.Based on the simulation results,this paper simulates the flow of fluid under the actual working conditions.Through the steps of experimental scheme design,process simulation,equipment design and selection,a set of pipe flow erosion corrosion experimental device for air cooler is designed and built.Based on this device,the visualization experiment of air cooler tube bundle is designed and completed.The experimental results show that although the deflection angle at the entrance of each branch is different,there is no significant difference in the flow and distribution of fluid in the fourth and fifth section of the pipeline.The flow state of the experimental medium and the distribution and flow of droplets under gas-liquid two-phase flow can be clearly observed through a transparent glass tube.The results of visualization experiment and CFD simulation are compared,and they are consistent.Based on the experimental phenomena,the flow state of the fluid under the actual operating conditions was inferred,and the erosion and corrosion mechanism of the fractionator headspace cooler was preliminarily analyzed.In this paper,the erosion and corrosion mechanism of the elbow of the reboiler return tower pipeline and the tube bundle of the top air cooler of the fractionator tower in the hydrogenation unit is studied,which has a certain reference value for exploring the corrosion behavior and protection of the flow passage components in the petrochemical system. |
