Multi-Bed Ion-Exchange Column: Design of internal screens for installation/removal

[JohnyO]

A three-level, packed bed, ion exchange column, approx. 7’ OD x 20’ tall, ambient water, 100 psi MWP is the subject, link to sketch attached. It will have three IX resin beds, each separated from the other by a disk of wedge-wire screen with 0.009” slots. The disks will be segmented for removal through the access flanges and will be supported by some sort of structural framework. Two access flanges, one in upper head, one in the shell of the bottom compartment. Height of each bed compartment is approx. 6’ and the disks would probably be transversely sliced into four strips, with the longer pair in the center sliced in half; something like that so they could be tilted and maneuvered for installation/removal.

The question: If you were specifying how the three screen plates would be installed or removed, which affects the design details, would you recommend working from top to bottom, or bottom to top.

1) Work from bottom to top on scaffolding; enter @ bottom, remove floor screen, erect first level of scaffolding, remove screen 6’ above, add scaffolding, raise/lower material via pulley, etc., or
2) Work from top to bottom on ladder; enter @ top, slip ladder in, remove most of the upper screen about 6’ below entry point, extend the ladder downwards, remove the next and work your way down.

This is not my area of expertise but I don’t gravitate towards the top down approach. I doubt there will be any sort of work platform on the column (is that legal?), slipping a ladder into the upper access flange seems tricky, climbing each section up and out on the ladder isn’t something I’d want to do, and if someone gets injured before there is any access to the lower access flange it would be pretty difficult to get them out.

Working from below is counter intuitive to my colleagues but I see it as pretty straightforward, particularly with the relatively small size of the screened segments. Small jacks could be used if necessary to initially dislodge the screens and once into the upper reaches, a pulley system off of the scaffolding could be used to raise/lower material. I’d rather work from a scaffold, the lower access flange would always be available for injured person extraction.

What do you all think?

Thanks for any assistance.

 

[Duwe6]

Like a lot of things, reinventing something that has been proven to work is a terrible idea, *unless* you have a brilliant insight. Lacking that, stay with 'Tried & True'.

Segmented trays that fit through the manway work. Building and filling a column from the bottom up, and cleaning one from the top down works. For safety, there are wire-rope retractable lanyards up to 100-ft long. [maybe more]. The workers would be thankful for a welded tie-off lug just above the manway(s), on the inside so that placing these 'yo-yo' retractable lanyards is easy, fast and safe.

My other thought is to contact one of the firms that specializes in catalyst change-out and exchange resin bed cleaning. They can tell you what is the quickest designs to work on, and their safety preferences. My googling got "Clean Harbors" and "Envirosystems"