What anti-corrosion measures are currently in use for atmospheric and vacuum distillation units?

Atmospheric and vacuum corrosion protection includes process corrosion protection and equipment corrosion protection. Different anti-corrosion measures are adopted based on the properties of the crude oil (sulfur content, naphthenic acid content). Process anti-corrosion: 1. Properly carry out electrodialysis ； 2. Corrosion inhibitors, anticorrosive agents, ammonia (amines), water, etc. are injected at the vapor lines at the top of each tower; these practices vary from plant to plant ； 3. Add high-temperature corrosion inhibitor ； 4. There is also the method of injecting alkali into crude oil; it is said that this technique is still in use in South Korea and Japan today. Equipment corrosion protection: 1. Upgrade the air-cooling tube bundles and cooler materials at the top of the tower (such as duplex steel, etc.). 2. Upgrade the materials used for the tower body and its internal components (different materials are required for high-acid and high-sulfur environments). 3. For moving equipment that operates within corrosive temperature ranges, upgrade its materials (especially in the case of high-acid crude oil). 4. Upgrade the materials of furnace tubes, transfer lines, and other process pipelines that are exposed to corrosive temperature conditions. For the others, you can look up relevant information and consult experts in equipment. Due to the differences in the properties of crude oil being processed, various plants adopt different measures. For different situations, consulting several companies will help you learn a lot.

The water content in the crude oil fed to the equipment may vary depending on the requirements of each company. Some requirements are ≯1%, while others are ≯0.5% ； This is related to the properties of the crude oil, the dehydration temperature in the tank area, the dehydration time, and the supply cycle of the crude oil; the main concern is to avoid affecting the operation of the electrical desalination unit as well as the subsequent processing steps. Generally, it is required that the salt content after desalination be below 3 mg, and the moisture content be ≤0.3% ； Generally, higher water content implies higher salt content. The initial attempts at electrodesalination did not yield satisfactory results. Now, in order to ensure long-term operation of atmospheric and vacuum distillation units as well as subsequent processing units, factories pay close attention to electrodesalination processes, and many companies have achieved fairly good results with this method. The heavy metal content in the raw materials for catalytic units can be found in relevant documentation; the amount of residue carbon varies depending on FCC/RFCC processes and design requirements (coking capacity), among other factors.

Anti-corrosion measures focus on two aspects: the production process and the equipment itself. In terms of the processing procedures, proper electrodesalination is essential; it is also necessary to regularly add corrosion inhibitors, desalting agents, and ammonia. Additionally, the operating temperature must be controlled to prevent corrosion caused by high temperatures. As for the equipment, the approach should be to upgrade its materials

Regarding the feed to the unit, high-sulfur oil can also be mixed with low-sulfur oil; the overhead gas is recovered and sent to a gas holder for desulfurization, thereby preventing the gas from being burned directly in the furnace.

Process anti-corrosion: 1. Properly carry out electrodialysis； 2. Inject corrosion inhibitors, preservatives, ammonia (amines), water, etc., at the vapor lines of each tower top. 3. Inject high-temperature corrosion inhibitors ； 4. Another approach is to use a process of one removal and four injections, which involves adding alkali after electrodialysis; however, many petrochemical plants now prohibit the addition of alkali due to the impact of sodium ions on subsequent processing steps! Actually, the most important thing is to set up electrodialysis properly, as this can help avoid many problems related to tower top corrosion later on!