How to Retrofit a Packed Column When Old Tray Support Rings Must Remain

A column that once contained trays may later operate with packing while the original tray support rings remain welded to the shell.

Removing dozens of rings can require extensive hot work, inspection, and pressure-vessel repair.

In many brownfield projects, the plant prefers to leave them in place.

The retrofit must then determine how those unused rings influence packing, new supports, gas flow, and wall behavior.

Measure Every Retained Ring

Record:

• elevation;
• radial projection;
• width;
• thickness;
• condition.

Different tray elevations may contain different hardware.

Determine Whether Rings Are Structurally Usable

An old tray ring may look convenient for supporting a new internal.

However, its original load was different.

Before using it for a packed-bed support, verify:

• corrosion;
• attachment quality;
• allowable load.

Consider Local Hydraulic Obstruction

A tray ring reduces local tower area near the wall.

One ring may have little impact.

Many rings distributed through a packed bed can repeatedly disturb gas and liquid flow.

The significance increases in small-diameter or highly loaded towers.

Check Random Packing Behavior

Random packing will fill around protruding rings.

Local bed structure may differ near the wall.

If the ring projection is large relative to packing size, wall-channeling behavior can change.

Check Structured Packing Fit

Structured packing blocks may need shaped edges to clear the rings.

If too much clearance is left, a continuous annular bypass path can develop.

Wall sealing becomes important.

Coordinate Bed Elevations

Where practical, the retrofit may use selected existing rings as boundaries or support locations.

This can reduce new shell attachments.

However, process layout should not be forced into poor bed spacing merely because a ring exists.

Inspect Corrosion Even on Unused Rings

A non-load-bearing ring can still create loose metal if severely corroded.

It should not be ignored simply because it has no new structural role.

Avoid Unnecessary Cutting

Cutting old rings inside a lined or corrosion-sensitive vessel can create significant repair work.

If hydraulic impact is acceptable, retaining them can simplify the project.

Document Which Rings Carry New Load

After retrofit, drawings should clearly distinguish:

• reused structural rings;
• retained unused rings;
• new supports.

This prevents future crews from assuming all visible rings have the same function.

Inspect After Startup

If retained rings contribute to wall fouling or unusual flow behavior, future shutdown observations should be recorded.

Summary

Old tray support rings can often remain during a packed-column retrofit, but their geometry, corrosion, hydraulic obstruction, packing interaction, and possible structural reuse should be evaluated. The final as-built design should clearly identify which rings remain active and which are merely retained.

URL:https://www.pxdaier.com/retrofit-packed-column-when-old-tray-support-rings-remain/

---

R083 — How to Retrofit Tower Internals When the Top Head Cannot Be Opened

Some tower internals were installed before the vessel top head was permanently welded or before major external piping and structures were constructed.

Years later, the plant may need to replace those internals without opening the top of the vessel.

Everything must now pass through existing manways.

A direct copy of the original one-piece internal may therefore be impossible to install.

Identify the Real Entry Route

Measure:

• manway opening;
• nozzle neck;
• platform clearance;
• internal turning space.

The critical dimension may be the space available after the section enters the vessel.

Convert One-Piece Components into Modules

Large equipment may need to be redesigned as:

• bolted support panels;
• distributor sections;
• segmented frames;
• modular demisters.

The assembled internal should reproduce the required function of the original unit.

Check Section Weight

A module can fit dimensionally yet be too heavy to handle safely.

Available hoists and internal lifting methods should influence section size.

Design Field Joints

Connections must be practical to assemble inside the vessel.

Consider:

• tool access;
• worker position;
• connection sequence.

A joint that is simple in the workshop can be extremely difficult above a packed bed.

Preserve Structural Load Path

Segmenting a support grid changes how loads transfer between panels and beams.

Each joint should have a defined structural function.

Preserve Hydraulic Continuity

Segmented distributors and collectors should not develop leakage or bypass at joints.

Mist eliminator sections should not leave open gas paths.

Create an Installation Sequence

Some components must enter before others.

For example, long support beams may need to be inserted before panel sections.

Planning the sequence avoids discovering late in the shutdown that a required part can no longer pass the installed equipment.

Mark Every Module

Section numbers and orientation marks simplify assembly.

Factory trial assembly is particularly valuable.

Design for Future Removal

If the top head cannot be opened today, it probably will not be opened for the next shutdown either.

The replacement should therefore remain removable through the same manway route.

Do Not Over-Segment

Many tiny components increase:

• labor;
• hardware;
• error risk;
• potential leakage points.

Use the largest practical removable sections.