Glycol Contactor Demister Selection for TEG Dehydration

In a triethylene glycol (TEG) contactor, the demister is not just a commodity pad. Its job is to limit glycol carryover while avoiding flooding, foaming sensitivity and excessive pressure drop.

Separate free-glycol carryover from total glycol loss

A high glycol make-up rate does not prove that the top demister is the only cause. Loss can include free liquid carried with the gas, vaporized glycol, leaks, filter or maintenance losses and liquid sent to other parts of the regeneration system. Establish a unit mass balance and identify where glycol appears before changing the pad.

For the demister investigation, compare carryover or make-up trends with gas rate, contactor pressure and temperature, glycol circulation, foaming events, hydrocarbon contamination and differential pressure. A step change after throughput expansion suggests a different problem from a gradual increase with fouling.

Why this duty is sensitive

Gas dehydration towers may operate at elevated pressure, and gas density changes the allowable vapor velocity. A Souders-Brown K value is a service-specific engineering input, not a universal standard value. High pressure, foaming tendency, liquid load and pad construction can require a lower project value; use the applicable project design basis or a verified engineering source.

The demister also sits in a system where upstream liquid loading, tray or packing behavior, foaming, hydrocarbon contamination and level control can all affect carryover. Replacing the mesh alone may not solve a process upset.

The gas distributor, top tray or packing, disengagement height and outlet geometry determine the droplet field reaching the pad. Liquid thrown directly toward one area can overload a locally sound pad while the average vessel velocity remains acceptable.

Practical selection direction

For relatively clean service, a stainless steel knitted mesh pad is a common first choice. SS316L may be a candidate where the stated chemistry supports it, but uncertainty by itself is not a material-selection basis. Check chlorides, amine contamination and other relevant species before selecting the final grade.

Co-knit pads can improve fine mist capture, but they may increase pressure drop and fouling risk. Use them when fine glycol mist is the real issue and operating margin is available.

Ask the supplier to identify the actual composite construction and its design basis. A branded high-performance contactor medium may have field data behind it; an unnamed “high-efficiency pad” does not inherit those results. Where a proprietary system is required, procure it from the technology owner or under a clearly authorized performance basis rather than claiming equivalence.

A useful troubleshooting sequence

1. Verify the current gas rate and density at operating pressure and temperature.
2. Review glycol circulation, foaming tendency, contaminants and recent process changes.
3. Check liquid level, distributor or top-contacting device condition and disengagement space.
4. Inspect wall seals, section joints, support grids, deformation and deposit patterns.
5. Determine whether the remaining carryover is dominated by fine droplets before choosing co-knit.

If no droplet distribution is available, state what evidence supports the conclusion. Total glycol make-up alone is insufficient because it includes non-demister losses.

What to specify

Provide gas flow at operating pressure and temperature, gas and liquid densities if available, contactor ID, available demister height, manway size, glycol type, foaming history and old pad photos.

Also provide minimum, normal and maximum gas cases, glycol circulation rate, estimated liquid loading at the top, recent carryover or make-up trend, contaminant history, clean and current pressure drop where available, outlet geometry and the distance from the top contacting device to the pad. Identify any proposed throughput increase.

For replacement, define the scope in the RFQ so it is priced into the quotation and frozen in the PI: segmented construction and grid details, the material or batch traceability record you need, dimensional inspection against agreed measurement points and acceptance limits, and pre-shipment photos. Each shipment then carries those records as delivery evidence. EN 10204 Type 3.1 or Type 3.2 documentation, additional testing and third-party inspection are optional upgrades — request them before material procurement, production or inspection booking so traceability, cost and schedule are confirmed upfront.

Procurement risk check

A low-price quote that only says “SS demister pad” is incomplete. Buyers should lock material grade, mesh density, thickness, grid style, section size, material traceability requirement (per the PI) and packaging. Otherwise the delivered pad may fit the vessel but not the duty.

If the order is build-to-drawing, avoid writing a glycol-loss guarantee into the same line without a complete performance basis. If performance is required, freeze inlet droplet and liquid loading assumptions, operating envelope, outlet carryover criterion, pressure drop, test or field verification method and exclusions for foaming or upstream malfunction.

Use the co-knit guide to review the fine-mist option and the corrosion guide before treating SS316L as an automatic upgrade.

What authoritative case data can and cannot prove

Sulzer’s glycol contactor application note explains how inlet droplet distribution, liquid holdup and drainage were modeled for its proprietary KnitMesh 9797 construction. A separate retrofit case article shows that distributor, support and capacity changes can be part of the solution. These are useful evidence for the engineering method, not performance data that can be assigned to a generic co-knit pad.