Thread Content
It is generally believed that if the sulfur content in crude oil is >0.5% and the acid value is >0.5mgKOH/g, it will cause severe corrosion of refinery equipment. Sulfur content and acid value constitute the basic corrosive environment in refineries. The ways to prevent corrosion in refinery processes include: One is "removal", that is, using special process methods to remove corrosive substances before corrosion occurs. ； The second is "prevention", that is, by adding chemical additives (corrosion inhibitors) to delay the corrosion of equipment by corrosive substances. Wuhan Petrochemical Plant has made breakthrough progress in process corrosion prevention through rational procurement and allocation of crude oil resources and the application of new technologies. 1 Process Measures 1.1 Desalination (1) Reasonable procurement and allocation of crude oil resources ensures the efficient operation of the desalting unit. Due to the reasonable procurement and allocation of crude oil resources, the salt and water content of the crude oil entering the plant is low. This not only ensures the efficient operation of the desalting unit and stabilizes the desalting qualification rate at a high level, but also ensures the stable and safe production of downstream units. (2) A reasonable atmospheric filtration desalting process has obvious advantages in treating heavier crude oil. The general electric desalting process can only desalt heavier intermediate base crude oil to less than 5 mg/L, which cannot meet the requirements of heavy oil catalytic cracking for crude oil desalination. After 10 years of industrial application, the filtration desalting process can now process intermediate-paraffin-based mixed crude oil. Due to its wide desalting range and strong processing capacity, it ensures that the desalting pass rate is always greater than 90%. (3) The application of YL-2010 crude oil demulsifier further improved the crude oil desalting qualification rate. (4) The role of WL-4 crude oil demetallizer. The use of WL-4 crude oil demetallizer significantly reduces the deactivation tendency of the catalyst. 1.2 "Three Notes" The neutralizing agent used in the distillation tower top and condensation cooling system of this plant is cheap inorganic ammonia, supplemented by HT01 oil-soluble corrosion inhibitor, and the dosage of corrosion inhibitor is 5μg/g ~8μg/g. The water injection process at the top of the distillation tower is a quenching water reinjection cycle process. On the surface, this recycling process seems to increase the content of corrosive ions in the condensate water at the top of the distillation tower, but it allows the reuse of inorganic ammonia and corrosion inhibitors. 1.3 Washing the hydrogen sulfide in the catalytic rich gas with demineralized water. Washing the hydrogen sulfide in the rich gas at the outlet of the catalytic cracking compressor is a traditional anti-corrosion process that has been used for many years. However, in recent years, this process method has been unable to meet practical requirements. Therefore, it is impossible to reduce the corrosion of equipment and pipelines by water washing alone, and new anti-corrosion methods must be developed. 1.4 Corrosion inhibitor injection at the top of the fractionation tower of the coking unit. The top of the fractionation tower and condensation cooling system of the coking plant have been using SH-2000 water-soluble corrosion inhibitor since March 2003. The loss of iron ions in the condensate water at the top of the tower has been reduced to less than 3 mg/L. 2 Process Anti-Corrosion Outlook The increasingly updated anti-corrosion technologies around the world are playing a greater role in various fields. Therefore, it is necessary to strengthen the application of anti-corrosion technology in refinery processes in the following aspects. (1) Use organic neutralizers to control corrosion at the top of the distillation tower and condensation system. Domestic oil refining companies often use ammonia as a neutralizer to adjust the pH value to control corrosion at the top of the three towers. Although this method reduces the uniform corrosion of the system, in actual use, due to the particular properties of ammonia water, the end point of the neutralization reaction jumps greatly, causing the pH value in the solution to suddenly rise to 9 and it is impossible to maintain it at around 7. At a pH of 9, the solubility of hydrogen sulfide increases, thereby increasing the corrosiveness of hydrogen sulfide. Chloride is also present in the system. In the initial condensation zone of the system, the dew point temperature of ammonium chloride makes ammonium ions very unstable. It quickly decomposes into ammonia gas and hydrogen ions, and immediately vaporizes out of the water. Stable chloride ions and hydrogen ions are left in the water to form hydrochloric acid, which is known as ammonium chloride and underscale corrosion. Therefore, in order to control the uniform corrosion of equipment and pipelines in the system without causing underscale corrosion, organic neutralizers should be used to control the pH of the system condensate water at 6.5~7.5. (2) Use oil-soluble corrosion inhibitors at the top of the catalytic fractionation tower and the top circulation system. Oil-soluble corrosion inhibitors can not only protect the top of the fractionation tower and the top circulation system, because the crude gasoline at the top of the tower serves as the absorbent of the absorption stabilization system, it can also protect the equipment and pipelines of the absorption stabilization system, extending further. It can also play a role in sweetening systems and oil tanks. If this technology is realized, it will directly solve the corrosion problem of absorption stabilization systems. (3) Add demetalling agent to control corrosion. The use of demetallizing agent in the atmospheric and vacuum unit not only reduces the metal content in the crude oil of the atmospheric and vacuum unit, but also reduces the metal content in the vacuum residue, which can benefit the catalytic unit, coking unit and even the hydrogenation unit. (4) Increase online corrosion monitoring methods. The current basis for showing the control effect of desalination operations is known through delayed indoor salt analysis results. This laboratory analysis method cannot quickly and timely feedback data to the operation site, so it can only be used as a tool for post-event evaluation and analysis. Therefore, it is necessary to install online monitoring instruments on site to quickly respond and strengthen on-site real-time control operations. At present, domestic scientific research institutions have applied a corrosion monitoring system to oil refineries, which will greatly improve comprehensive corrosion control capabilities. (5) Improve the corrosion resistance level of materials. The equipment corrosion control in refineries must not only rely on technological means, but also further improve the grade level of materials, including the reasonable selection of metal and non-metallic materials, and the use of various corrosion-resistant coatings and linings, which together shoulder the important task of protecting refinery equipment.