Lean TEG Filtration Guide: Prevent Reboiler Fouling

In natural gas glycol dehydration processes, engineers traditionally focus their filtration budget on the Rich TEG lines but neglect the lean TEG side. Drawing on a 25-year benchmark in manufacturing industrial filtration equipment, this comprehensive guide outlines how configuring your TEG regeneration filtration system slashes your facility’s monthly OPEX.

Table of Contents

What is TEG Regeneration Loop of TEG Dehydration System?

▶What is TEG in Oil & Gas Industry?

TEG (Triethylene Glycol) is a colorless, odorless, viscous liquid used in natural gas dehydration systems that possesses extremely strong hygroscopic properties.

During the extraction and transmission of oil and natural gas, moisture in the natural gas can cause pipeline corrosion or the formation of ice blockages. Therefore, TEG is widely used as a liquid desiccant to absorb moisture from natural gas, ensuring that natural gas pipelines meet the moisture content requirement of 7 lbs/mmcf or less.

▶Key Equipment Layout in TEG Regeneration Loop

Broadly speaking, you can consider the TEG regeneration side to begin when the rich solution flows out of the absorber and end when the regenerated lean TEG is pumped back into the absorber.

This process primarily includes the Stripping Still downstream of the absorption tower (TEG contactor), the Flash Tank, the Rich TEG Filter Train (Pre-Filtration—Activated Carbon Filtration—Fine Filtration), the Rich/Lean TEG Heat Exchanger, the Reboiler, the Surge Vessel, and the Lean TEG Filter.

What is TEG Filtration in TEG Dehydration System?

TEG filtration occurs throughout the entire TEG regeneration cycle, encompassing both rich TEG filtration and lean TEG filtration. During the dehydration cycle, TEG switches between two distinct states.

▶What are Rich TEG and Lean TEG?

Rich TEG (Wet Glycol): The water-loaded glycol leaving the bottom of the contactor tower after absorbing moisture from the gas stream. It typically contains dissolved hydrocarbons, mineral salts, and upstream impurities.

Lean TEG (Dry Glycol): The highly concentrated, pure glycol (typically 99.0% ~ 99.9% by weight) that has been boiled free of water in the regenerator column and reboiler, ready to be reused.

A complete TEG dehydration system is a closed-loop process consisting of “rich TEG → regeneration → lean TEG.”

Dry TEG (water-free TEG) is sprayed into the absorption tower to absorb water droplets from the gas, after which the dried gas is discharged; wet TEG (water-loaded TEG) flows out of the absorption tower and enters the regeneration loop.

After being processed in the reboiler, the dry TEG is regenerated and enters the next natural gas dehydration cycle.

Technical comparison table illustrating the distinct filtration parameters, micron ratings, operating pressures, and maintenance points between Rich TEG and Lean TEG filtration in a natural gas dehydration loop. — 5 Solid Particle Filters

▶Rich TEG Filtration VS Lean TEG Filtration

	Rich TEG Filtration	Lean TEG Filtration
Filtration Target	Remove solid debris Protect downstream reboiler or regenerator	Remove finer particles Final TEG liquid quality control before return to contactor/tower
Media Cleanliness	Dirty, contain a lot of solid and dissolved contaminants	Clean, but still contain contamination particles from the TEG regeneration process
Filtration Stage	Multiple stages (usually 3 stages in pre particle filter → active carbon filter bed → fine particle filter)	Single or dual stages
Micron Rating	Pre: 10 ~ 25 μm Fine: 5 ~ 10 μm	3 ~ 10 μm or 1 ~ 5 μm
Design Pressure	High pressure Equal to or close to the pipeline pressure	Low pressure Usually 72.5 psi or less
Design Temperature	High temperature (122 ~ 212 ˚F) Depends on the preheating degree after flash evaporation	Low temperature (86 ~ 140 ˚F) Already cooled by a heat exchanger
Maintenance Points	1. More frequent maintenance, pay close attention to the dP (Δp). 2. Activated carbon must be tested periodically for adsorption capacity and replaced in its entirety.	1. Maintenance cycle is relatively longer. 2. Pressure drop (Δp) is the only signal for changing out.

Why Does Lean TEG Still Need Filtration? Which Key Contaminants Are Included?

Because, after passing through the rich TEG filter group, the TEG must also flow through equipment such as the rich TEG heat exchanger, stripping still, reboiler, surge tank, and lean TEG heat exchanger, metal debris from these processes may be carried into the TEG stream.

Installing a lean TEG filter downstream of the lean TEG heat exchanger and upstream of the glycol pump can effectively trap these impurities, protect the pump and downstream heat exchangers from wear, and ensure that the cleanest possible TEG enters the next dehydration cycle.

And which key contamination particles are included in the TEG regeneration loop?

Thermal Carbon Sludge (Coke Fine Aggregates)

If the reboiler fire tube skin temperature spikes locally, the organic glycol solvent cracks. This molecular degradation creates micro-fine carbon soot particles. Over time, these particles aggregate into a sticky, abrasive black sludge.

Microscopic and cross-sectional view of a pipeline heavily fouled by black thermal carbon sludge and coke fine aggregates resulting from glycol solvent cracking. — Carbon scale / thermal degradation contaminants

Aqueous Salt Precipitates

Natural gas reservoirs carry trace formation waters rich in inorganic salts like sodium chloride (NaCl) and calcium chloride (CaCl₂). While water is vaporized and vented out of the stripping column top, these salts cannot evaporate. They lose solubility in the ultra-pure lean glycol and precipitate out as hard, crystalline scales.

Laboratory demonstration showing clear liquid blending into an opaque white precipitate, simulating how dissolved inorganic salts form crystalline scales in highly concentrated lean TEG. — Aqueous Salt Precipitates

Fine Iron Sulfides (FeS) and Oxides (Fe_xO_y)

Micro-corrosion occurring inside the hot stripping column continuously releases ultra-fine metallic debris into the stream. These particles average 1 to 5 microns in size and are highly abrasive to spinning machinery.

Macro view of fine, sandy metallic iron sulfide (FeS) and rust particles accumulated from high-temperature stripping column internal micro-corrosion. — Fine Iron Sulfides and Oxides

Polymerized Chemical Gels

Trace chemical carryovers from wellheads—such as corrosion inhibitors, scale inhibitors, and heavy compressor lubes—react under the high temperatures of the reboiler, forming compressible, gelatinous masses that quickly blind standard filters.

Close-up of compressible, viscous polymerized chemical gels and gelatinous masses formed by reactions of trace wellhead chemical carryovers under high reboiler temperatures. — Polymerized Chemical Gels

The Cost Impact: Leaving these contaminants to circulate results in Reboiler Fouling. Just 1 mm of carbon/metal scale on a reboiler tube reduces heat transfer efficiency by up to 30%. This forces the burner to run hotter, increasing fuel gas consumption and accelerating the risk of catastrophic reboiler tube rupture.

Filter Selection Criteria for Lean TEG Regeneration Side

So, what considerations must be included when designing an efficient, reliable filtration system for the lean TEG (regeneration) side?

Filter Type & Standard

Based on this fine micron rating design (1 ~ 10 μm), we commonly recommend cartridge type filter systems, and they should meet industrial standards such as ASME Section VIII / EN 13445.

Operating Pressure

The overall operating pressure in the TEG regeneration cycle is low, possibly only 15 ~ 45 psi (0.1 ~ 0.3 Mpa), so the filter vessel can be engineered at 87 psi (0.6 MPa), or as per your requirement.

Operating Temperature

After the heat exchanger upstream the lean TEG filter, TEG liquid has been cooled to less than 140 ˚F, making it more flexible on the selection of filter housing, filter element, and seal ring, gasket materials.

However, operational upsets can cause temperature spikes. Therefore, engineers prefer premium 316L stainless steel filter elements and high-fluorine Viton (FKM) seals, ensuring continuous structural integrity even during unexpected thermal fluctuations up to 350 °F+.

Flow Direction

For regeneration loops with heavy solid loading, an out-to-in (external-to-internal) flow maximizes the filtration surface area, optimizing cake formation and extending run times.

Maintenance & Operation Considerations

Maintaining an optimized low-pressure filtration system relies on proactive differential pressure (dP) tracking rather than simple calendar schedules:

Clean Differential Pressure (DP):A newly commissioned or freshly washed system should display a baseline clean drop of 2.1 ~ 3.6 psi (0.15 ~ 0.25 bar) under the design flow rate.
Terminal Change-Out Target:Filter elements must be cleaned or replaced when the DP gauge reads 17.4 ~ 21.8 psi (1.2 ~ 1.5 bar). Operating past 24.6 psi (1.7 bar) risks particle unloading—where structural pressure forces captured deformable gels through the media matrix, polluting downstream contactors.
Solvent Color Metric:Healthy lean glycol should maintain a stable straw-gold or light amber hue. A rapid transition to “black glycol” is a clear field indicator that either your reboiler is operating with localized hotspots or your filter housing is experiencing internal fluid bypass.
dP Tracking

Conclusion

Lean TEG filtration is not a “the icing on the cake” process, but a necessary action for long-term reliable gas dehydration. If you are planning a new TEG dehydration project, or you are worried about the existing filtration system, welcome to talk with us at anytime via sales@filsonfilters.com or +(86) 157-3695-8886.

We are not the standard answer supplier, we provide the most suitable customized solution for your specific working conditions.

FAQs

1.How can I tell if my unit has developed lean TEG contamination?

Observe the following three phenomena: 1. The color of the lean TEG becomes darker (brown or black); 2. Frequent leaks from the circulation pump’s mechanical seal; 3. The dew point of the dry gas begins to fluctuate, even with normal water replenishment.

If any of these conditions occur, please contact us for a filtration diagnosis.

Four glass jars containing glycol samples ranging from crystal clear and straw-gold to a degraded dark brown and completely fouled black glycol. — Solvent Color Metric

2.Is there a universal solution for both rich and lean TEG filtration?

Technically, yes, but we really don’t recommend this approach.

Rich TEG filtration and lean TEG filtration are based on entirely different working conditions. A universal filtration system would only result in additional costs (since it would be designed to meet the highest standard of the two) or filtration performance that is not 100% optimal. Independent designs are a safer and more maintainable solution.

Schematic diagram of a gas dehydration contactor tower illustrating the countercurrent flow where wet gas rises through bubble caps and dry glycol absorbs water vapor. — Rich/lean TEG circulation – simplified schematic

3.How often should the filter cartridge in a lean TEG filter be replaced? How do I know when it is time to change it?

This depends on your regeneration temperature and the stability of your operation. We generally recommend checking it once every 6 to 12 months.

The most obvious indicator is the pressure differential. We will equip you with a high-precision differential pressure gauge; when the pressure differential reaches approximately 1.2 ~ 1.5 bar (17.4 ~ 21.8 psi), this serves as a signal to replace the filter.

If your system experiences frequent fluctuations, we recommend shortening the replacement interval.

4.Is it necessary to install a lean TEG filter for our small TEG dehydration unit with only 1,000 m³ processing capacity?

Yes. The size of the unit does not affect the thermal degradation chemical reaction of TEG. Smaller TEG dehydration units often place greater emphasis on operating costs; however, if inadequate filtration leads to increased TEG loss or production shutdowns, the resulting losses can actually be even greater. For smaller units, we can design extremely compact, skid-mounted systems.