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TransTech Fabrication News

Liquids Carry Over Elimination for High Liquid Loads

[fa icon="calendar"] Apr 9, 2017 2:00:00 PM / by Greg Ezzell

Advanced Methods for Maximum Returns

How Mist Elimination Failure Erodes Business Performance

Failure to remove entrained liquids from a gas stream during natural gas processing is among the most common causes behind an array of related business performance issues, from deficient processes and product losses to costly shutdowns—all of which can lead to higher operational costs and lost profits.

Indeed, carried over liquid can not only result in off-spec products, but can also inflict grave damage to downstream equipment—from steady erosion to catastrophic destruction—wreaking havoc on, and even halting, downstream operations.

It’s no surprise that mist elimination, the process of removing free entrained liquid from the gas stream, is among the most commonly encountered priorities in gas processing, regardless of the unit operations.

And yet, despite devoted efforts, liquid carryover challenges are pervasive to refineries, petrochemical plants, gas plants, and similar facilities where mist elimination equipment fails to perform adequately.

Why Do Mist Elimination Efforts Fail?

Natural gas processing is a multi-stage process by which hydrocarbons, liquids and various impurities are separated from raw natural gas to produce pure pipeline quality dry natural gas (methane), which can ultimately be fed into natural gas pipelines for use.

Water in the raw natural gas stream is common and can be abundant— particularly in aging wells— and more than one stage of separation is generally required for its complete removal.

Slug catchers and inlet separators, which are designed to handle considerable amounts of liquid over very short time intervals, are often a first line of defense against the presence of upstream liquids, addressing both naturally occurring large liquid slugs and those created by pigging operations.

From a simple two phase knock out vessel to more sophisticated harp type designs, slug catchers are extremely effective in the bulk separation of gas-liquid process streams, utilizing a combination of momentum change, coalescing, and gravity settling to separate high density fluids from lighter gas phases.

However, the amount of liquid entrained in mist form is significant during slug flow conditions and regardless of overall bulk separation success, often microscopic droplets of liquid in the form of liquid aerosols remain within gas streams.

Slug catchers are often fitted with a vane inlet device and mist eliminator to combat these entrained liquids. However, mist extractors often have innate limitations on the amount of entrained liquid they can effectively remove from the gas stream.

To make matters worse, mist eliminators are often treated as commodity items and are specified without consideration of all available technologies and sometimes ignoring advanced design approaches more capable of addressing the unique and changing characteristics of a given operation.

Problems may include:

•  Selecting a wholly inadequate mist eliminator for the job at hand
•  High mist loading within the gas stream
•  Liquid slugs in feed
•  Uneven velocity profiles (gas mal-distribution)
•  Incorrectly executed installations
•  Capacity range too high
•  Incorrectly sized equipment for given parameters

Depending upon the plant configuration, a gas stream with unaddressed entrained liquid will typically make its way to compression or to a dehydration unit:

Compression: If mist elimination device in the Suction Scrubber is not adequately sized to accommodate the liquid rate, it will create high compressor maintenance issues in the long run. This can become costly.

Dehydration: If the Inlet Separator (and Filter Separator) is not sized adequately to accommodate the high liquid rate, this will lead to increased operational cost due to the additional amount of glycol required to meet the outlet water content requirements.

Better Solutions. Better Results.

Rather than trying to address or treat symptoms, taking a diagnostic approach and determining the root cause for entrained liquids will lead to a far more effective and long-term solution.

Operating conditions (pressure & temperature), physical properties of gas and liquid, flow regime in the inlet piping, type & amount of liquid (water or HC), slug rate and frequency are among the chief parameters that should be taken into consideration.

Employing a specialized 'Polishing Vessel' with high performance internals downstream of the slug catcher will ensure liquid carryover issues are addressed properly; both protecting downstream equipment and ensuring pipeline specs are met—without adding to operational cost.

Said Sandy Morris, Director of Business Development, “TransTech Energy pairs its state of the art, high performance horizontal and harp type slug catchers with a downstream Polishing Vessel featuring a high performance inlet diffuser and agglomerator along with AMACS MAXSWIRL™ Cyclone for unmatched liquid carryover elimination. The results speak for themselves."
MAXSWIRL™ Cyclone, High Capacity, High Efficiency Mist Eliminator-2.pngTransTech Energy's Advanced Polishing Vessels deliver outstanding performance due to:

  • Higher capacity than Mesh and Vane Mist Eliminator and hence smaller vessel size.
  • Vertical orientation configuration offers footprint advantages
  • No rotating parts and easy for maintenance (typically through a manway)
  • Higher operating ranges can be accommodated without affecting efficiencies.

TransTech Energy’s innovative Polishing Vessel mist eliminator designs are effective in both low- and high-pressure operations and are available in both horizontal and vertical orientation for upstream and downstream applications.

Due to its high capacity and efficiency, this device can provide optimized solutions for new built vessel designs as well as for troubleshooting and solving existing operational problems and retrofit projects.

Other applications and equipment ideally suited to benefit from TransTech's Polishing Vessel include: 

  • Liquids Carryover Solution - 1.pngAll High Pressure Scrubber/Separator Applications.
  • Places wherein incoming liquid flow is high and high quantitative liquid separation (gross separation) efficiency is required
  • Inlet Separator
  • Gas Plant
  • Before and After Dehy units (associated with high pressure)
  • Before and After Amine units (associated with high pressure)
  • Compression stations.Liquids Carryover elimination.png
  • LNG Plant
  • FPSO
  • Chemical Plants (before dryer beds)
  • Cold Separators
  • NGL Plants
  • Compressor Suction Scrubbers (high pressure)
  • FPSO
  • Compressor Stations.
  • Gas Lift Suction Scrubbers
  • High Pressure Discharge Scrubbers

Gas processing plants that do not address entrained liquids risk the compound negative impact of potentially high operational costs, low reliability and frequent shutdowns. To ensure plants run with higher reliability—and maximum returns—removing unwanted water in the gas feed prior to processing is critical. TransTech Energy can help!

Contact us today to learn more about our liquid carry over solutions at: (+1) 888.206.4563

Learn about our Horizontal Slug Catchers here. 

Learn about our Harp-Type Slug Catchers here.

Learn about our high performance mist eliminator Polishing Vessels here. 





Topics: High Efficiency Demisting, Liquids carryover, High Capacity Demisting Device, Liquid Slugs, Gas Liquid Separation, Demister

Greg Ezzell

Written by Greg Ezzell