Treatment of oil at the feed nozzle during shutdown purging of a catalytic cracking unit
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What is generally done with the oil at the feed nozzle after the catalytic cracking unit is shut down and feeding is stopped? This area is a dead zone; should steam be blown into the lift pipe before closing the nozzle hand valve? Should I use tape to let out the oil? How did everyone handle it? Specific steps?
This post was last edited by wyt1234 on 2010-10-23 at 11:40. There is usually a preheating return line at the nozzle feed point; during cleaning, the preheating line is activated to send the material back to the raw material tank.
We have installed a purging steam line behind the feed cut-off valve, specifically used for purging the pipeline between the cut-off valve and the feed nozzle after the feed is stopped.
Reply to 2# wyt1234: The nozzle pre-heating function is usually included in the design, but a dead zone still exists.
Reply to 3# Shuichangshou: I would like to ask the water team whether catalyst circulation is still necessary inside the lift pipe during pipeline purging It doesn’t really matter, right?
Reply to 5# chengkang: The entry of steam has little impact in this case, as the feed has already been stopped; at least safety is ensured. However, for catalysts that have been burned in a cyclic manner, it may cause damage such as fragmentation.
Reply to 4# chengkang: As long as the design is reasonable, there is basically no dead zone. The so-called dead zone is only a pipeline of about 20 cm in length, which has no impact on the overall situation. If perfectness is to be achieved, after completing the cleaning process with the nozzle, the wall valve of the lift pipe can be closed and the feed cut-off valve opened, allowing the steam used for cleaning with the special nozzle to flow back into the preheating line; this way, there will be no dead zones – not a single one at all.
There is purge steam between the two valves of the nozzle; the oil behind the second valve is blown into the lift pipe, and the amount of this oil is very small, so there is no risk. The oil in front of the second valve is blown into the feed oil system for purification.
I agree with what was said on floor 8. There are two manual valves before our nozzles; a purge steam line is installed between these two valves. After shutting off the feed, the first valve is closed, and the purge steam is used to push the remaining oil into the lift pipe. There is also a purge steam line in front of the first valve, which feeds the raw material system through a 2-inch preheating line.
Agree with what was said on the 2nd floor; that’s exactly how we do it