Is there any harm adding cracked stocks too quickly after break-in following hydrotreating catalyst activation? What is typical introduction rate?
The fresh or newly sulfided catalyst is very active and introducing cracked stocks too early after sulfiding will cause noticeable activity loss in hydrotreating catalysts. Heavy coke precursor molecules in the cracked feeds have more tendency to form coke over the fresh and highly active sites of the catalyst.
Delaying the introduction of cracked stocks for at least 3 days after sulfiding will allow the catalyst activity to be passivated with the normal straight run feed stock.
After running for three days on straight run the cracked material should be added to the feed stream gradually. Further the cracked feed should be added in small increments making sure the reactor exotherm remains under control and within acceptable limits before increasing the cracked feed amount any further.
Further about sulfiding and its troubleshooting please see the blog.