Corrosion protection for the top of the fractionation tower in catalytic cracking units
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Current status of corrosion issues: The company currently has two catalytic cracking units, and corrosion problems are mainly concentrated in the top circulation system and the top condensation cooling system of the catalytic distillation tower, specifically in equipment such as the top circulation heat exchangers, tower top heat exchangers, and air coolers. Statistics on corrosion leaks that have occurred in recent years are shown in Table 3. Process anti-corrosion measures and management: Corrosion at the top of the catalytic distillation tower is mainly caused by ammonium salt hydrolysis corrosion. The anti-corrosion operations and management practices include: (1) controlling the chlorine content in the raw materials to reduce the formation of ammonium chloride salts at the source. (2) Calculate the ammonium chloride salt formation temperature at the top of the distillation column, and increase the temperature of the oil and gas outlet at the top of the column without affecting the normal operation of the distillation column. (3) Ensure that the temperature of the oil and gas at the top of the distillation tower is at least 14°C above the dew point temperature to prevent dew point corrosion. (4) Consider adding a corrosion inhibitor to the washing water during the online washing process. The extracted oil needs to be settled and dehydrated to prevent corrosion and salt formation during subsequent processing steps. (5) When process anti-corrosion measures are insufficient to control the formation of ammonium chloride salts, online desalination technology can be considered.
The anti-corrosion measures and management methods employed for the top of the fractionation tower in catalytic cracking units include the following: 1. Controlling the chlorine content in the feedstock: By reducing the chlorine content in the feedstock, the formation of ammonium chloride can be slowed down, which in turn helps to reduce corrosion issues. 2. Increase the temperature of the oil and gas outlet at the top of the tower: Calculate the salt formation temperature of ammonium chloride at the top of the distillation tower, and increase the temperature of the oil and gas outlet as much as possible to ensure it is at least 14°C above the dew point temperature of the oil and gas; this helps to prevent dew point corrosion. 3. Adding a corrosion inhibitor during the online water washing process: Adding a corrosion inhibitor to the washing water during this process can provide some level of corrosion protection. 4. Dehydration treatment of the extracted oil: The extracted oil needs to undergo sedimentation and dehydration treatment to prevent corrosion and salt formation during subsequent processing steps. 5. Online desalination technology: If the corrosion prevention measures outlined above are not sufficient to effectively control the problem of ammonium chloride salt formation, online desalination technology can be considered. This technique uses specialized desalination equipment to remove ammonium chloride from the gas at the top of the tower, thereby reducing the occurrence of corrosion issues. The above measures and methods can effectively prevent and control corrosion at the top of the catalytic fractionation tower, ensuring the normal operation of the plant. At the same time, regular inspections and maintenance are necessary to address any potential corrosion or leakage issues promptly, ensuring safe production. .
To address the corrosion issue at the top of the fractionation tower in catalytic cracking units, protection measures must be taken not only from a process perspective but also through equipment anti-corrosion techniques. A more mature approach is to apply anti-corrosion treatment to these heat exchange tube bundles to extend their service life. The reason is as follows: Since the system contains varying amounts of HCl, H2S, HCN, NH3, and H2O, which volatilize along with the light components, corrosion is generally minimal in their gaseous state. However, after condensation and heat exchange, the temperature drops by more than 100°C; once liquid water appears in the condensation zone, corrosion caused by the HCl-H2S-H2O and HCN-NH3-H2O systems occurs within the cooler shell. The severe corrosive damage to a single-processing unit is caused by cyclic corrosion resulting from the mutual promotion of HCl and H2S. Therefore, the heat exchange equipment in these areas can be protected against corrosion through coating applications and cathodic protection measures.