A glycol dehydration unit removes water vapor from natural gas so the gas meets pipeline specification and will not form hydrates or corrode the line. It is one of the most common gas conditioning processes in the field. This guide explains how a TEG (triethylene glycol) unit absorbs water, how the glycol is regenerated and reused, and what an operator monitors.
Glycol Dehydration Unit (TEG) in one line: A glycol dehydration unit dries natural gas by contacting it with triethylene glycol (TEG), a liquid that strongly absorbs water. Wet gas rises through a contactor while lean glycol flows down and soaks up the water; the now-rich glycol is then boiled in a reboiler to drive off the water and regenerated back to lean glycol for reuse.
Raw natural gas leaves the reservoir saturated with water vapor. That water causes three problems downstream: it can freeze into solid gas hydrates that plug pipelines and equipment, it combines with acid gases like CO2 and H2S to corrode steel, and it fails the water-content limit that pipelines impose (commonly around 7 pounds of water per million standard cubic feet in the US). Removing water is therefore a required conditioning step before gas can be sold or transported.
Glycol absorption is the dominant method because it is continuous, reliable, and inexpensive to run. Triethylene glycol is used most because it has a strong affinity for water, low vapor loss, and can be regenerated to a high purity that achieves a deep water dew point. The result is measured as the water dew point of the outlet gas - see dew point control - which the unit must hold below the pipeline spec.
The heart of the unit is the contactor (absorber), a tall column. Wet gas enters the bottom and rises through trays or packing while lean (dry) glycol is pumped in at the top and flows down. As the two meet counter-currently, the glycol absorbs water from the gas. Dry gas leaves the top to sale, and the water-laden rich glycol leaves the bottom.
The rich glycol then goes to regeneration. It passes through a flash tank to release absorbed gas, is preheated by cross-exchange with the returning hot lean glycol, filtered, and fed to the reboiler and still column. The reboiler heats the glycol to around 200 degrees C (below TEG's degradation point of about 204 degrees C), boiling off the water as vapor that leaves through the still. Some units add stripping gas to reach an even higher glycol purity and a deeper dew point. The regenerated lean glycol is cooled and pumped back to the top of the contactor, closing the loop.
Key control points are the reboiler temperature (too low and the glycol will not dry out; too high and the TEG degrades), the glycol circulation rate, the lean glycol purity, the contactor pressure and level, and the outlet gas water dew point. Glycol losses, foaming, and a fouled or salted reboiler are common problems, and a BTEX/VOC-laden still vent must be managed for emissions.
These variables come from temperature, pressure, and level instruments feeding a PLC or unit controller, often with a moisture analyzer on the outlet gas. A cloud SCADA like Merobix reads those tags over Modbus, DNP3, or OPC UA and trends reboiler temperature, glycol circulation, contactor level, and outlet dew point across a fleet of unmanned dehy units, alarming when the reboiler drifts, glycol runs low, or the gas approaches its water spec - so operators act before off-spec gas reaches the pipeline.
Triethylene glycol (TEG) has a strong affinity for water, absorbing it readily from gas while itself vaporizing very little. It can also be regenerated by boiling off the absorbed water and reused continuously. That combination makes glycol absorption a reliable, low-cost, continuous way to dry gas to pipeline water specification.
A TEG reboiler is typically held around 190 to 200 degrees C. This is hot enough to boil the absorbed water out of the glycol, but kept below about 204 degrees C where triethylene glycol begins to thermally degrade. Holding this temperature window is critical to both drying the glycol and protecting it.
A glycol dehydration unit removes water vapor by absorbing it into TEG. A Joule-Thomson (JT) skid controls the hydrocarbon dew point (and drops water too) by expanding the gas to cool it and condense out liquids. Dehy targets water content for pipeline spec; a JT skid targets hydrocarbon dew point and NGL recovery. Some facilities use both.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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