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Suggestions on the localization of ethylene "oxychlorination reactors" in large-scale ethylene plants Zhang Weituo, Hefei General Machinery Research Institute, Ministry of Machinery 1. Introduction to ethylene oxychlorination reactors Polyvinyl chloride is an important successor product of petroleum processing. The ethylene oxychlorination production process is the most advanced production process in the world. Major industrial countries in the world mostly use this process to produce polyvinyl chloride. The core equipment of the ethylene oxychlorination production unit is the oxychlorination reactor. The working principle of the oxychlorination reactor is as follows: Ethylene (C2H4), hydrogen chloride (HCL) and oxygen (O2) undergo an exothermic reaction under the action of coal contact copper chloride (CuCl2). The mixed gas passes through the gas distributor at the bottom of the reactor and the fluidized bed equipped with coal contact for fluidization reaction to generate dichloroethane. 0.3MPa circulating hot water flows into the cooling tube to take away the reaction heat in the reactor through endothermic vaporization. The three-stage cyclone separator at the top collects the coal-containing CuCl2 entrained in the reaction gas. Currently, there are only three process routes for producing PVC raw materials in my country, which are ethylene oxychlorination production processes, and the rest are calcium carbide production processes. Among these three oxychlorination production process devices, the oxychlorination reactors are all imported patented equipment, and the main material is 304L. During the production process of more than ten years, these imported oxychlorination reactors have suffered from quite serious corrosion, especially in the lower elbow and straight pipe weld areas of the cooling pipes, resulting in frequent emergency shutdowns for repairs. Some factories have to replace the entire cooler in the reactor every 1 to 2 years, causing economic losses of millions of yuan. In addition, a large number of stress corrosion cracks perpendicular to the direction of the weld have appeared in the weld area of the lower head and lower cylinder section of the reactor. Intergranular corrosion and pitting corrosion have appeared on the base metal side of the weld fusion line. Other parts of the reactor, such as the upper head of the cylinder, near the lifting lugs, near the top head weld, the inner wall of the cyclone separator, the gas distribution plate, the distribution cap, etc. are also corroded to varying degrees. The oxychlorination reactor imported from Japan has low corrosion resistance of structural materials and cannot meet the requirements of highly corrosive process media, which has seriously restricted the reaction function of the oxychlorination reactor. Therefore, before the equipment is localized, it is necessary to fully demonstrate key technologies such as material selection, material inspection and acceptance, equipment manufacturing process control, and equipment manufacturing quality inspection to ensure the smooth completion of the equipment's localization. 2. The key to the development of oxychlorination reactor equipment: 1. Selection of structural materials for the oxychlorination reactor. 304L has been proven to be non-corrosion resistant as the structural material for the oxychlorination reactor. Selecting appropriate corrosion-resistant materials based on the different corrosion forms and different corrosion levels of various parts of the oxychlorination reactor will determine the service life and safe operation period of the oxychlorination reactor. Since the corrosion forms of the oxychlorination reactor are mainly various local corrosions caused by hydrochloric acid, such as pitting corrosion, intergranular corrosion and stress corrosion, the structural materials of the oxychlorination reactor (including welds and heat-affected zones) should be able to withstand the corrosion of dew-point hydrochloric acid. At the same time, the degree of local corrosion generated in various parts of the reactor is not the same. Different corrosion-resistant materials can be selected according to different parts of the equipment to reduce the manufacturing cost of the equipment. 2. Comprehensive technical analysis of oxychlorination reactor structural materials and equipment manufacturing processes. In the petrochemical industry, there are nearly a hundred types of iron-based, iron-nickel-based, and nickel-based corrosion-resistant alloys available, and there are dozens of commonly used ones. This makes the choice of corrosion-resistant materials quite large. Therefore, more appropriate corrosion-resistant materials should be selected based on the equipment structural characteristics of the oxychlorination reactor and the corresponding equipment manufacturing requirements. Take the material selection of more than 800 elbows in the oxygen oxidation reactor as an example. These elbows are subject to corrosion by dew-point hydrochloric acid and require good resistance to hydrochloric acid corrosion. U-shaped elbows with thick walls, small diameters, and must be bent at 180° also have high requirements on the comprehensive mechanical properties of the materials. ； At the same time, two weldings must be performed on the elbow, which requires that the welded joint and heat-affected zone of the elbow can still maintain good material uniformity and local corrosion resistance after two welds. Therefore, the material selection of this batch of elbows should be very careful. 3. Inspection and acceptance of raw materials for the oxychlorination reactor. Whether the oxychlorination reactor uses domestic corrosion-resistant materials or imported corrosion-resistant materials, these materials are all high-alloy corrosion-resistant materials. Strict raw material inspection and acceptance should be carried out. This not only involves the inspection items specified in the relevant standards, but more importantly, the application of appropriate corrosion inspection methods to test its ability to resist local corrosion. ； In addition, additional technical conditions such as corrosion inspection methods and corrosion inspection assessment indicators are also involved. High-alloy corrosion-resistant materials have very strict requirements on alloy composition and impurity content. They also have strict requirements on cold and hot forming processes such as forging and rolling of raw materials, and final heat treatment of raw materials before leaving the factory. Various processing techniques in the raw material production process (such as the proportion of chemical components, improper control of hot processing processes such as forging and rolling) will reduce the ability of the raw materials to resist local corrosion, causing hidden dangers to future equipment manufacturing and equipment operation. The most important performance of an oxychlorination reactor is corrosion resistance. The corrosion resistance of the raw materials themselves, especially the resistance to various localized corrosions after welding, will directly affect the future performance of the equipment. However, the localized corrosion resistance of the raw materials itself cannot be improved through future equipment manufacturing processes. Therefore, the selection of materials for the oxychlorination reactor and the testing of the local corrosion resistance of the raw materials are one of the keys to determining the corrosion resistance of the oxychlorination reactor. 4. Control of the manufacturing process of oxychlorination reactor equipment and equipment manufacturing quality inspection. The structural material of the oxychlorination reactor is high-alloy corrosion-resistant material. High-alloy corrosion-resistant material has a very important feature in the equipment manufacturing process, namely: Welding of high-alloy materials after cold or hot deformation can easily cause intermetallic precipitation or phase change in the heat-affected zone of the weld, which not only deteriorates the mechanical properties of the material, but also * * The ability of the heat-affected zone of the weld to resist local corrosion is reduced. In addition, the welding process and heat treatment process will also directly affect the corrosion resistance of the oxychlorination reactor. Therefore, in the development process of oxychlorination reactor equipment, it is necessary to formulate correct manufacturing process technical documents such as cold and hot forming, welding and heat treatment, as well as related manufacturing process quality control and inspection technical documents, and establish a complete manufacturing supervision system to ensure the correct implementation of these technical documents. In short, the biggest difficulty in localizing oxychlorination reactors is the correct selection of materials and the full understanding and mastery of the material properties of the selected materials. The second is the optimization of equipment design structure, formulating correct equipment manufacturing processes and manufacturing quality control.