Study And Optimization Of 3D620 Acetic Acid Distillation Column

The main equipment and internal parts of 3D620 acetic acid rectification tower of a petrochemical unit in China are corrosion-resistant material TA2,but severe corrosion occurred during use.The corrosion thinning of the upper tower wall and the break of the tray not only reduce the service life of the equipment,but also affect the production efficiency,there are hidden safety hazards,and even have a greater impact on product quality and the normal operation of the entire vinyl acetate system.Therefore,it is urgent to solve the problem of corrosion of materials and propose reasonable maintenance programs to resume production as soon as possible.After researching and analyzing the corrosion morphology of titanium in 3D620 tower,it was found that erosion corrosion and hydrogen embrittlement are the two main failure modes,accompanied by a certain degree of crevice corrosion and pitting corrosion.Further research on the failure mode of titanium material can be concluded that the high-speed flow of acetic acid solution at high temperature will cause erosion and corrosion of titanium material,and the hydrogen embrittlement of the tray will be caused by reducing acetic acid environment.The influence factors of acetic acid environment on materials were clarified,which provided a theoretical basis for equipment selection.Corrosion-resistant materials C-276 and Zr-3 suitable for the environment were determined through field hanging test.Comparing the physical and mechanical properties of the two,the optimized equipment was selected as C-276.According to the results of the material selection,a partial transformation plan was formulated: Replace the TA2 tower body and its internal parts above the 42 # tray with severe corrosion with C-276 material.In order to meet the requirements of use and ease of manufacturing,the connection structure and internal structure of the two different material 3D620 towers are optimized.In view of the fact that C-276 and TA2 cannot be directly welded,a flange bolt connection structure is adopted to effectively and reliably connect the upper and lower sections of the tower with different materials.By establishing a mechanical model,the main pressure components(tower body,head,flange,etc.)were subjected to a force analysis.After accurate calculation and comprehensive consideration,the optimal thickness of each component that meets the requirements for use was determined.Welding is an important part of container manufacturing.In this paper,the welding performance of C-276 and TA2 was determined through reliable welding process evaluation.According to the welding process assessment results,a welding procedure specification was formulated.For different materials,structures and locations,various welding parameters were specified in detail: welding method,filling material,number of welding layers,current and voltage during welding,etc.The failure prevention of chemical equipment is not only guaranteed from the perspective of material selection and structural design,but also correct manufacturing processes and inspection methods can reduce or avoid possible failures during use.At the end of this article,technical requirements such as dimensional tolerances and flatness of the tower body and internal parts during manufacturing are proposed to the manufacturing unit to ensure the controllability of the manufacturing process and results;through the provisions of the equipment hydraulic test and air tightness test,and different types of welding with the proposed non-destructive testing method,the inspection department performs final quality control on the equipment.In this paper,taking the corrosion of titanium as an opportunity,the material selection of the 3D620 acetic acid distillation column was optimized after analyzing and analyzing the causes and factors of corrosion.And optimized it from the aspects of structural design,strength design,determination of welding parameters and manufacturing inspection,so that it completed the transformation in the shortest time and successfully installed and put into use.The smooth implementation of this project provides new ideas for the maintenance and renovation of large-scale equipment,and has certain reference significance in the industry.