Q & A > Question Details
What are the implications of shell side fouling on the pulling of a VCFE/Texas Tower (Platformer) bundle for cleaning? Our client is looking to pull a VCFE which has been in-situ for 16 years and I would like to find out if others have carried out a similar exercise and any impacts fouling may have had on the activity.
17/03/2016 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
Platformer VCFE shellside (reactor effluent side) deposits typically include ammonium chloride, iron chloride, polycyclic aromatics (PCAs), catalyst dust and construction debris (gasket windings, welding rods, etc). The majority of the fouling deposits are likely to be found at the bottom end of the shell and may interfere with movement of the floating head in service. However there will also be an accumulation of coke and debris at the top of the shell in the annular gap between the OD of the fixed tubesheet and the ID of the shell. Consequently, a VCFE tube bundle which has remained in situ for 16 years is highly likely to be difficult to extract from the shell.
If VCFE tube bundle extraction is to be attempted, the lift crane needs to be properly rated with a large safety margin over the theoretical weight of the bundle to help break the bond between the tubesheets, the fouling deposits and the shell. Vibrators attached to the shell at the fixed (top) tubesheet elevation and hydraulic rams pushing on the underside of the floating (bottom) tubesheet can also help break that bond. If the bundle is to be laid down horizontally it will require proper support as it will sag under its own weight which may result in damage to some tube to tubesheet joints. A tailing crane and a relatively large laydown area will be required with this approach. An alternative approach is to keep the tube bundle suspended from the lift crane and clean the outer surfaces of the tubes by HP water jetting from multiple access platforms on a pre-constructed scaffold tower.
06/03/2010 A: Marcello Ferrara, ITW SrL, mferrara@itw.it
For sure you can expect having troubles in extracting such bundle.
Normally the fouling is of the polymeric type and this will "stick" the bundle.
We recently developed a new technology for polymers' modification, which can help both in eliminating or reducing the troubles for bundle extraction and in removing some fouling, without any mechanical cleaning.