Liquid carryover and demister pad support ring design

[thermmech]

We are having a number of vessels with demister pads consisting of 6 or more sections (nicely fitting through the manhole), where demister pad support ring welded to the vessel ID is split into 2 pieces. The gaps in the ring are approximately 12", and are filled in with removable ring pieces that are held in place with bolted clips and J-bolt clamps.

We have found out that these removable pieces tend to slide away from the vessel wall, during last shutdown we were able to stick our hand into the gaps between vessel wall and removable support piece / demister mesh.

This is likely creating a leak path causing liquid carry over. I'd like to weld in these removable pieces to ensure leak path is closed.

1. But, why do people split these support rings for multiple-section demister pads?

2. Any comments regarding possible liquid carryover causes and support ring configurations appreciated.

(P.S. These are Selexol removing vessels in De-Hy Unit where selexol is taken out of Fuel Gas stream and sent to Turbines).

 

[ash9144]

The demister pad should be snug against the wall and all the pieces snug into one another. So it shouldn't matter if the hold up ring has gaps or not. I have seen the support ring both ways fully welded out and gaps. I've never seen any performance issue due to one or the other.

 

[thermmech]

Thanks on the comment.

The demister pad drawings show that overall mesh OD matches vessel ID. I am unsure why would the mesh NOT be snug against the vessel wall in this case, barred vessel being obround or demister pads not being built to the drawings.

 

[ash9144]

Ok so your pad is loose. That is your problem not your support ring. Get some loose mesh material and fill in the gaps in your pad until it is all snug.