Q & A > Question Details
We are operating a hydrotreating reactor loaded with topsoe catalyst TK-562 Brim.We have 2 reactor in series guard bed and main reactor. Guard bed reactor is loaded with demat catalyst. During start of run the delta t across guard bed reactor was 28 Deg-C. But during six months we are observing that delta t of guard bed reactor is gradually reducing and had reached 6 Deg-C.Guard bed reactor delta p is normal and is around 1.5 bar. Also we observed that all guard bed rection had been shifted to main reactors and we are getting high delta taround 25 deg-C in 2nd and 3rd bed of reactor. We are operating our unit at 125 KBPSD. What is causing this?
 
Answers
05/01/2013 A: Amarjit Bakshi, Refining Hydrocarbon Technologies LLC, abakshi@rhtgulfcoast.com
I endorse the answers provided though proper monitor of metals after the guard bed might be best response. A more optimum guard bed option would be have a parallel so that one gets to this situation you have additional safeguard for the 2nd and 3rd reactor. Though same size reactor will be best but you could have a guard bed which is there to provide you time to change the demet catalyst in the main guard bed.
But monitoring of guard bed is a must and also after seeing any temperature changes one knows that guard bed is not its job. Might be another option is to look for higher capacity demat catalyst replacement so that you can enhance the operation.
31/10/2012 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
HDM catalyst in the guard reactor would have exhausted it's capacity to retain more metals. HDM catalysts are loaded above HDS cat. Breakthrough of metals after HDM bed will necessarily deactivate any HDS cat placed in guard reactor and subsequent reactors too. Pore dia. of HDM and HDS catalysts differ appreciably in addition to other important characteristics.
No increase in delta P is a good sign related to trash.
While loading fresh HDM cat in Guard Reactor the amount and type of the Guard catalyst needs to be kept in view.
24/10/2012 A: NS Murthy, Reliance Industries, ns.murthy@ril.com
I endorse the opinion given by earlier respondent. Typically Demet catalysts are supposed to hold about 30% of metals in spent catalyst. A good tracking of feed metals could show the metal loading and life of catalyst in guard bed.
20/10/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Without knowing the feedstock and the level of contaminants, I can still say that the progression of the data show a normal movement. The guard bed lost its activity as contaminants were trapped (metals, silicones, or whatever). Conversions were increased in the downstream catalyst, accounting for the increased delta T there. Low delta Ps indicate low trash in the feed, which is good. The guard bed catalyst needs to replaced before metals kill the downstream catalyst. Actually, metals are not trapped in a plug flow manner as originally thought by some; rather, the amount breaking through increases gradually, so, when to change the guard catalyst is not easy to define.