What is the difference between catalytic reaction re-refined slurry and re-refined oil?

In heavy oil catalytic cracking, if production is carried out with a focus on maximizing the yield of liquid hydrocarbons, it is necessary to maintain a greater degree of reaction depth. In such cases, it may be possible to stop the re-refining process, increase the flow rate to the secondary tower, and send more slurry out of the unit, thereby achieving operational balance. But if diesel is produced in excess, the degree of reaction is relatively mild; reprocessing of oil is necessary. After all, there are still some components in the reprocessed oil that can be cracked again, and by feeding them back into the reaction settler for reprocessing, the yield can be improved to some extent. So whether to send it back to refining depends mainly on the degree of reaction. As for oil slurry, I personally am not in favor of reprocessing it. Once reprocessed, it not only increases the coke yield but also raises the tendency for coking at the bottom of the distillation tower, without any significant increase in yield. Therefore, I have always advocated for discharging the oil slurry entirely.

First, analyzing the properties and components of oil slurry and reprocessed oil: oil slurry is heavier than reprocessed oil, and it contains more gums and asphaltenes. Therefore, as the person above mentioned, reprocessed oil slurry does not have a significant impact on increasing yield; however, it does cause considerable coking, which has a big effect on coking within the plant. Here, we generally reprocess the oil, and if the resulting reprocessed oil is not reused, it can only be sent to the distillation tower and discharged from the plant as oil slurry, which significantly affects the plant’s yield

The difference between reprocessed oil slurry and reprocessed oil lies in their composition; the oil slurry has a heavier composition and contains more non-metallic elements. After reprocessing, there are significant changes in the composition of the products produced: the slurry component becomes heavier, with higher levels of both metallic and non-metallic substances. More gas is generated as a result of reprocessing, the amount of coke formed increases, and the properties of the slurry deteriorate, requiring increased discharge of waste materials. Reprocessing is generally undesirable; the more oil that is reprocessed, the lower the conversion efficiency per cycle, which in turn affects the processing capacity of the entire plant. Typically, the amount of oil to be reprocessed is determined based on the thermal balance between the two reactors. When there is insufficient heat, oil needs to be reprocessed. If the composition of the oil is heavy and the amount of coke produced is high, more oil must be reprocessed to achieve the desired results, and such reprocessing reduces the plant’s processing capacity. I suggest avoiding reprocessing altogether; if it’s really unavoidable due to the low quality of the crude oil, then a smaller amount of reprocessed slurry can be used to increase the amount of coke produced.

What changes have taken place in the distribution of reprocessed oil, reprocessed oil slurry products?

What changes have taken place in the distribution of reprocessed oil, reprocessed oil slurry products?

Just look at the definition of one-way conversion rate to understand

My skills are limited, and I find it difficult to answer this question. In my opinion, the impact of reprocessing slurry on the product is relatively simple; the slurry contains some light components, and some plants are equipped with flash towers that allow the slurry to be flashed, thereby enabling the recovery of a small amount of components similar to light diesel. If the oil slurry is reprocessed directly, part of the diesel components in it will undergo further cracking; as a result, the amounts of gases, liquid hydrocarbons, gasoline, and diesel in the product will increase theoretically. Of course, what increases the most after reprocessing the oil slurry is coke. As for the reprocessing of recycled oil, the situation is more complex, because the amount of recycled oil to be reprocessed cannot be determined arbitrarily; it is first determined by the degree of reaction – the greater the degree of reaction, the less recycled oil is needed, while a lesser degree of reaction requires more recycled oil. There is another scenario: for example, when summer arrives, the factory adjusts the diesel production parameters through its quality control department. In order to produce more diesel, the distillation temperature of 90% of the product is increased by 5°C as part of a distillation adjustment process; as a result, the level in the re-refining tank drops, forcing the reactor to reduce the amount of oil being re-refined. However, the degree of reaction itself does not change at this point. If we simply analyze the product distribution after changing the amount of reprocessed oil, it is clear that reprocessed oil contains more components that can be cracked again compared to slurry, while its coking tendency is much lower; there is a noticeable increase in gasoline and diesel production.

It depends on the actual conditions of each plant. In our case, we basically recycle all of the refinery sludge, as our raw materials are relatively light; the gasoline yield can reach around 52%. Some plants, on the other hand, do not recycle any refinery sludge, as they have further coking processes. From a reaction perspective, the greater the degree of reaction, the less sludge needs to be recycled, and the amount of sludge to be recycled can be determined based on its density. My personal understanding!

In my opinion, ignoring other factors, it is better to send oil slurry to the coking unit rather than recycle it, as when oil slurry is recycled, 50% becomes raw coke, 20% becomes dry gas, and around 30% is obtained as liquid product; whereas in a coking unit, the value of the raw coke is higher.