Corrosion issues in hydrocracking units
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Regarding the hydrocracking unit, the top reflux drum of the distillation tower, and the issue of water removal from the top reflux drum of the distillation tower? Our company has been paying attention to the issue of pipeline corrosion since 2009, by measuring the pH value and iron ion content in the water drained from the reflux tank; the specified limit for iron ions is no more than 1.5 mg/l. We usually also add corrosion inhibitors and sodium polysulfide, but the iron ion level still doesn’t improve. Therefore, I would like to ask for your advice? Is it a problem with the additive or something else? This post was last edited by chengkang on 2009-4-9 06:53]
I wonder how much water and iron ions are in your oil? Generally, the control level is kept below 1 mg/l. Two aspects need attention: 1. What corrosion inhibitor to use? Film-forming or neutralizing? 2. What is the amount of corrosion inhibitor to add? For general film-forming corrosion inhibitors, a higher dosage should be used when they are first added in order to enable film formation; after the film is formed, the dosage can be gradually reduced depending on the iron ion concentration, but this must be done continuously to prevent the loss of the film. The neutralizing corrosion inhibitor can have its injection amount adjusted appropriately.
I agree with the opinion from the second floor, but it’s important to add the neutralizing agent before the film-forming corrosion inhibitor; it’s best to leave some distance between them, as this helps to better control corrosion. The injection of the neutralizing agent is preferably at a pH value of 6.8 to 7.6. If it is too low, corrosion may occur; if it is too high, emulsification may take place.
The retardants for the stripping tower and the butane removal tower are injected at the vaporization line at the top of the towers; there are no retardants in the oil at the bottom of these towers. No retardants are used in the distillation tower. The operation of the tower ahead should be properly controlled to prevent hydrogen sulfide from reaching the distillation tower and causing corrosion.