How to Retrofit a Packed Tower When Permanent Internal Ladders Cannot Be Removed
Older towers sometimes contain internal ladders, access structures, brackets, or braces that are welded permanently to the shell.
These structures may interfere with replacement supports, distributors, structured packing, or mist eliminators.
Removing them can require pressure-vessel work that the plant does not want to perform.
The new internal system must therefore be designed around a permanent obstacle.
Survey the Structure in Three Dimensions
Record:
- elevation;
- width;
- projection from the shell;
- orientation;
- support points.
A photograph alone is not enough for fabrication.
Confirm Whether Removal Is Truly Impossible
Some “permanent” obstacles are actually removable with limited work.
The decision should be confirmed before designing a complicated custom internal.
Check Hydraulic Obstruction
A ladder already occupies part of the tower cross-section.
Replacement equipment should avoid creating additional blockage around it.
Large solid cutouts or reinforcement near the ladder can further reduce open area.
Adapt Support Segmentation
Support panels can sometimes be divided so that joints fall around the ladder.
This is usually preferable to field-cutting a finished structural plate.
Consider Packing Around the Obstacle
Random packing can fill irregular spaces, but packing density near a ladder may differ.
Structured packing requires specially shaped segments.
Large continuous gaps should be avoided because they can create bypass.
Check Liquid Distribution Shadowing
A ladder directly below a distributor can intercept liquid.
This can create a dry region beneath the obstruction.
Outlet positions may need adjustment so liquid reaches the packing around the structure.
Preserve Personnel Function
If the ladder remains required for access, new internals should not make it unusable.
Future inspection routes matter.
Avoid Sharp Contact with Packing
Metal ladder edges or brackets can damage thin structured packing or plastic elements if vibration causes contact.
Controlled clearance is useful.
Consider Removal Sequence
Future maintenance crews may need to move demister or distributor sections around the ladder.
Module size and orientation should support that route.
Include the Obstacle on Fabrication Drawings
The worst approach is to send standard circular internals to site and expect installers to “make them fit.”
Permanent structures should appear explicitly on approved shop drawings.