Catalytic cracking riser
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For a single lift tube with two feed inlets, what kind of materials should be fed into the upper and lower inlets respectively? Please explain why. Thank you! !
Does a single lift tube have two inlets? We have four layers for feeding: material is fed from above and below ； Reprocessing of oil slurry, reprocessing of recycled oil. Among them, there are 4 nozzles per layer for the raw material feed, and 2 nozzles for the rest
If both of these feed nozzles are used for crude oil, the upper nozzle is used at low processing rates, while the lower nozzle is used at full capacity (the design allows for adjustments based on specific conditions during normal production). If there are two layers of nozzles, each handling different types of materials such as reduced-pressure wax oil, coker wax oil, atmospheric residue, or reprocessed oil and slurry oil, this is done to meet the requirements of selective cracking.
We have a total of three layers of feed nozzles: at the bottom are four nozzles for feeding the raw materials (to atomize the crude oil); in the middle (at the same elevation) are two slurry nozzles (used to recover fine catalyst particles from the slurry filter); and there are two recirculation nozzles (to reduce the amount of slurry that is discharged)； The upper layer is the heavy gasoline nozzle (which terminates the first reaction).
The feed from below is usually fresh raw material, while the feed from above is reprocessed oil; this allows the fresh raw material to react with the catalyst. It prevents the low-activity catalyst formed as a result of the reaction between the catalyst and the reprocessed oil from reacting further with the fresh raw material, thereby avoiding a decrease in yield.
Currently, feed from both the top and bottom is used very rarely; generally only bottom feed is utilized, with fresh feed entering through the bottom feed and reprocessed oil entering through the top feed. However, due to the shorter reaction time with top feed, poor cracking effects may occur, leading to the formation of soft coke, which in turn causes coking in the settler. Similar to the case with the middle-stage coker wax oil nozzles, top feed has not been used much in recent years, so we simply stopped using it – except in the MGD process.
We have two layers of feed nozzles; one layer consists of six nozzles for feeding the raw material oil (which is used to atomize the oil). Our reprocessed oil is fed into the raw material oil nozzles together with the raw material oil, at the feed valve assembly for raw material oil. In the middle (one layer higher) are two slurry nozzles; of course, at the very top of the riser is the heavy gasoline terminator nozzle. It hasn’t been in use for a long time. This post was last edited by jevy on 2009-4-10 20:39]
Generally, the lighter materials should be fed into the lower nozzle, while the heavier materials should be fed into the upper nozzle
It’s very simple – in one sentence, the upper and lower nozzles are designed to accommodate different reaction times required for various raw materials.
Feed enters from below as raw material; moving upward, there are reprocessed oil, slurry oil, and gasoline.
Depending on the required reaction depth, the raw material can be fed from either the top or the bottom, resulting in different reaction times. For raw materials of different properties, heavy raw materials can also be fed through the lower nozzle; this is determined by the product distribution.
When redesigning my unit, from bottom to top the nozzles are for fresh feedstock, reprocessed oil, slurry, and terminator. After 14 months of operation, the properties of the raw material gradually deteriorated. Disable the slurry nozzle and set the re-refining nozzle at minimum load. Some crude gasoline is injected at the bottom of the riser for reforming.