How to Verify Whether a Packed Tower Retrofit Actually Improved Performance

A retrofit is not complete when the manway is closed.

The real question is whether the modified tower achieves the performance objective that justified the project.

Without a defined post-startup verification plan, a plant may know that new internals were installed but not whether they delivered the expected improvement.

Define Success Before the Retrofit

Performance targets should be established before shutdown.

Possible targets include:

• lower pressure drop;
• higher throughput;
• improved outlet concentration;
• lower carryover;
• reduced energy consumption;
• longer operating cycle.

A retrofit cannot be evaluated objectively if success was never defined.

Preserve Pre-Retrofit Baseline Data

Collect representative operating data before modification.

Useful information includes:

• gas flow;
• liquid flow;
• feed composition;
• temperature;
• pressure;
• tower differential pressure;
• outlet quality.

The comparison should be made at similar operating conditions.

Comparing the old tower at low throughput with the new tower at high throughput can give a misleading impression.

Check Mechanical Installation Before Startup

Before closing the tower, verify:

• packing level;
• distributor levelness;
• correct support installation;
• hold-down position;
• structured-packing orientation where applicable;
• mist-eliminator sealing.

Many apparent “design failures” are actually installation problems.

Monitor Differential Pressure

Tower differential pressure is one of the most useful startup indicators.

Compare pressure drop at:

• low load;
• normal load;
• high load.

The trend is often more informative than one measurement.

Unexpectedly high pressure drop may indicate:

• incorrect packing installation;
• blocked internals;
• excessive liquid load;
• hydraulic restriction.

Verify Process Performance

The tower must still meet its primary duty.

Depending on service, this may include:

• outlet pollutant concentration;
• product purity;
• removal efficiency;
• absorption efficiency.

Hydraulic improvement alone is not sufficient if process efficiency deteriorates.

Check Liquid Distribution Indirectly

Direct observation during operation is often impossible.

Possible indicators of distribution quality include:

• temperature profile;
• sampling results;
• pressure behavior;
• outlet performance;
• localized fouling observed later.

If performance is below expectation despite adequate packing capacity, distribution should be investigated.

Monitor Carryover

If gas throughput was increased, check downstream liquid entrainment.

Indicators may include:

• separator drainage;
• downstream contamination;
• visible droplets;
• process measurements.

A retrofit that increases capacity while creating severe carryover has simply moved the bottleneck upward.

Test Across the Operating Range

Do not verify only one production rate.

Where practical, assess:

• low load;
• normal load;
• maximum intended load.

This confirms both capacity and turndown behavior.

Allow for Stabilization

Some process systems require time to reach stable:

• temperature;
• composition;
• liquid inventory;
• surface wetting.

Do not judge final tower performance immediately after startup unless the process is already stable.

Compare Against the Correct Baseline

Changes elsewhere in the plant can affect performance.

When comparing pre- and post-retrofit results, account for differences in:

• feed rate;
• composition;
• temperature;
• solvent rate;
• pressure.

The more similar the operating conditions, the more meaningful the comparison.

Investigate Underperformance Systematically

If the tower fails to meet expectations, avoid immediately blaming the packing.

Check in sequence:

• actual operating conditions;
• liquid distribution;
• internal installation;
• fouling;
• support restriction;
• mist eliminator;
• process assumptions.

A systematic review is faster than replacing components by trial and error.

Create a New Operating Baseline

Once the retrofitted tower reaches stable operation, record its normal performance.

This becomes the reference for future monitoring.

Gradual increases in pressure drop or declining efficiency can then be identified earlier.