Q & A > Question Details
In Hydrocracker unit, after revamp, quench pipe is routed below the catalyst support grid. The gap between support grid and quench pipe is filled with ceramic rope. The quench pipe is supported with C type support. With this arrangement unit has run two cycles without any problem. But at present cycle, one of the bed DP started rising. After shutdown and reactor opening, it was observed that catalyst migrated through the gap as ceramic rope damaged. Also the quench pipe rested below the support grid was observed to be lifted up from C support.
During one month of unit run after catalyst loading, there were no emergency or sudden shock to the system so that quench pipe should lift.
How has this Ceramic rope become damaged and Quench pipe lifted up?
 
Answers
02/03/2018 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
From your description, it sounds like vibration of the quench pipe due to inadequate support is the most likely cause of damage to the ceramic rope packing. This also creates the risk of erosion damage to the OD of the quench pipe if it comes into contact with the catalyst support grid and of an internal leak developing at the joint between the internal quench pipe in the reactor quench nozzle. A leak at the joint could potentially cause localised fluidisation of the catalyst and erosion of the reactor wall.
02/03/2018 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Couple of points to consider. AS such it is tough to visualize without design information along with modifications done, if any. You have stated that there had been damage to both ceramic ropes and quench pipe support. Was there anytime stoppage of quench flow to reactor which could have resulted in back flow? A liquid filled line can give rise to substantial shear stress when vapour flow is suddenly restored. Further, was there any change with respect to loading of catalyst as well as the drying of catalyst prior to pre-sulphiding stage. We have seen bed collapse (leading to catalyst passing thru grid and moving the bed below) when drying is done at faster rate than recommended. As regards damage to ceramic ropes it could be resultant of other two.