How to Retrofit an Existing Tower When Internal Support Rings Are at Unequal Elevations
Brownfield towers do not always match their original drawings.
Support rings may have been repaired, partially replaced, distorted, or installed with elevation differences around the circumference.
A new distributor, support grid, collector, or mist eliminator placed directly on an uneven ring can inherit that distortion.
For gravity liquid distribution especially, this can cause poor performance from the day of startup.
Survey the Ring Circumference
Measure elevation at multiple points.
Do not rely on one reference location.
A ring can be level in one direction and distorted locally in another.
Identify Why the Ring Is Uneven
Possible causes include:
- fabrication tolerance;
- shell deformation;
- previous repair;
- corrosion;
- weld distortion.
If the problem is active structural movement, simply shimming the new internal may not be sufficient.
Determine Whether Levelness Is Functionally Critical
A packing support can tolerate different conditions from a gravity distributor.
The required correction therefore depends on what the ring supports.
Use Secondary Leveling Structures
A new internal can sometimes sit on an adjustable frame or secondary support that creates a level working plane above the old ring.
This avoids modifying the pressure vessel shell.
Check Load Distribution
Shims or leveling devices can concentrate load if not designed properly.
A heavy packed-bed support should transfer load over suitable areas.
Preserve Gas Open Area
Additional leveling frames should not create unnecessary blockage.
Mechanical correction and hydraulic performance must be considered together.
Account for Corrosion
A severely corroded ring may not be suitable for reuse even if leveling can be corrected.
Thickness and attachment condition should be verified.
Consider Installation Tolerance
Field leveling needs practical adjustment range.
Too little adjustment may fail to correct the real condition.
Too much adjustable hardware can complicate installation.
Verify Final Elevation
After all bolts and connections are tightened, recheck levelness.
External piping or adjacent components can pull a new internal out of alignment.
Update Drawings
The final support elevation should be recorded so future replacement equipment does not repeat assumptions from the original drawing.