Coking problem in catalytic settlers

1. The steam temperature and flow rate for preventing scorching are insufficient； 2. Fluctuations in processing capacity ； 3. The properties of the crude oil have become more severe!

The pressure fluctuations in the settler are too large； Cutting too frequently ； The anti-scorching steam temperature is too low and the flow rate is too small ； Processing volume is too low ； Poor quality of raw materials ；

In the case of direct connection between the co-rotating and single-rotating units, extremely strict requirements are placed on operational flexibility, especially regarding pressure balance control. Fluctuations in differential pressure or a decrease in the linear speed of the feed to the centrifuge can lead to incomplete separation of oil and gas, which then enters the settler. This, in turn, reduces the efficiency of stripping and results in poor oil and gas recovery; as a consequence, coking in the settler connected directly to the centrifuge becomes severe.

Properties of the crude oil, preheating temperature. The shape of the nozzle, installation angle. Unstable pressure of the two devices, frequent cutting occurrences in accident conditions, and significant fluctuations in the amount of material processed. In short, to prevent coking in the settler, it is necessary to eliminate the causes of unvaporized oil

First, if the crude spin operation is carried out without stripping, and the discharge from this process occurs under positive pressure, then about 8% of the oil and gas will be carried into the settler. Together with the oil and gas stripped in the stripping section (which is heavy oil), the total amount of such oil and gas can reach 10 to 12% of the total oil and gas flow rate. Second, this oil and gas stays in the settler for a long time; my initial estimate for a catalytic unit with a capacity of 1.2 million tons was that the residence time would be around 120 seconds (depending on the specific steam flow rate). As a result, deposition and coking occur to a significant extent. Countermeasures: 1) Increase the amount of steam used for stripping, as well as the amount of steam used to prevent coking; it’s also advisable to estimate the linear velocity (i.e., residence time). 2) Raise the reaction temperature and increase the overall temperature in the stripping section to provide the necessary conditions for the conversion of heavy oil. Additionally, improving the activity of the catalyst can help convert the unconverted oil in the stripping section; this type of oil is even more problematic than slurry oil. These are just some suggestions; the previous colleagues have already covered everything in detail.

Another issue that everyone needs to pay attention to is the height of the gas lift pipe; if the height is not appropriate, the gas and oil mixture cannot enter the gas collection chamber, and coking often occurs at the top of the settler

Coking in settlers can be classified into two categories: 1. When the feedstock is heavy, especially catalytic cracking feedstocks with a high dry point, it cannot be completely vaporized upon contact with the hot catalyst from the regenerator; the unvaporized feedstock droplets moisten the catalyst, resulting in a \"wet\" catalyst. “The “wet” catalyst is the main cause of coking in the settler. 2 When the raw material comes into contact with the thermal catalyst, a cracking reaction occurs, producing heavier components with a higher dry point. These heavier components condense in areas of the settler where the temperature is lower (such as dead zones), forming droplets of heavier components; the catalyst becomes adhered to these components, resulting in a \"wet\" catalyst. In terms of operation, especially during the initial stages of startup, care must be taken to avoid operating at a low oil-to-fuel ratio, in order to suppress and reduce the formation of a large amount of \"wet\" catalyst.