A glycol dehydration unit can only dry gas as well as its glycol is dry to begin with, and boiling water out of the glycol in the reboiler runs into a limit - past a certain point, heat alone cannot drive the last of the water out without cooking the glycol. Stripping gas is the technique that pushes past that limit: a small stream of dry gas bubbled through the hot lean glycol carries away residual water and pulls the glycol far drier than boiling can achieve on its own. This guide explains how stripping gas works, why it lets a unit reach much lower dew points, and what the regeneration side's flows and temperatures look like in SCADA.
Stripping Gas (Glycol Still) in one line: Stripping gas is a small stream of dry gas injected into the glycol regeneration system - into the reboiler or a stripping column below it - to drive residual water out of the hot lean glycol beyond what boiling alone can achieve. The dry gas lowers the effective water content in contact with the glycol, so more water evaporates from it, producing a much drier lean glycol. That drier glycol absorbs more water from the wet gas in the contactor, letting the unit reach lower dew points than it could without stripping gas.
In a glycol dehydration unit, wet gas gives up its water to lean triethylene glycol in the contactor, and the resulting rich glycol is then regenerated by boiling the absorbed water off in a reboiler so the lean glycol can go back and do it again. The dryness of that regenerated lean glycol sets how dry the unit can make the gas - drier lean glycol pulls more water out of the gas and delivers a lower dew point. So the whole performance of the unit hinges on how completely the reboiler can strip water back out of the glycol.
The trouble is that heat alone cannot fully dry the glycol. TEG has a maximum practical regeneration temperature above which it begins to break down, so the reboiler is held below that limit, and at that temperature a small but stubborn fraction of water remains in equilibrium with the glycol. No matter how carefully the reboiler is run, that residual water caps how lean the glycol can get, and therefore caps how low a dew point the unit can deliver. Pushing the temperature higher to drive out more water simply degrades the glycol.
Stripping gas breaks this deadlock by changing the equilibrium rather than the temperature. When dry gas is bubbled through the hot lean glycol, it sweeps away water vapor from the surface of the liquid, lowering the partial pressure of water the glycol is in contact with. Because the glycol is now exposed to a much drier environment, more water evaporates out of it to re-establish equilibrium, and the glycol ends up substantially leaner - all without raising the temperature past the point that would harm it.
Stripping gas can be introduced in a few ways, and where it enters affects how effective it is. In the simplest arrangement the dry gas is sparged directly into the reboiler, bubbling up through the pool of hot lean glycol and carrying water vapor with it out the still vent. More effective is a dedicated stripping column - often called a Stahl column - installed below the reboiler, through which the lean glycol flows downward while stripping gas rises against it. This countercurrent contact in a packed column exposes the glycol to progressively drier gas as it descends, driving it much leaner than sparging into the reboiler pool alone.
The stripping gas itself is typically a slipstream of dry gas, sometimes taken from the unit's own product or from fuel gas, and only a modest rate is needed. There is a balance to strike: more stripping gas produces drier glycol and a lower dew point, but the gas leaves with the still vapors and represents a small loss, so the rate is set to reach the required lean glycol dryness without overshooting. The stripping gas that exits with the water vapor at the still top can, in some units, be routed to recovery rather than simply vented, depending on the facility.
The payoff is a meaningful step in performance. A glycol unit relying on boiling alone is limited in how low a water dew point it can hit, while adding stripping gas can push the lean glycol dryness - and therefore the treated-gas dew point - well beyond that, which is what lets a unit meet a tight dew-point specification it could not otherwise reach. Where the destination pipeline or process demands very dry gas, stripping gas is often what makes the difference between meeting the spec and falling short.
The regeneration side of a glycol unit is where the key indicators of dehydration performance live, and the stripping-gas system adds a few more to watch. The central one is reboiler temperature, which must be held in the band that maximizes water removal while staying safely below the point where TEG degrades - too low and the glycol is not lean enough, too high and the glycol is damaged. Alongside it, the still-column overhead temperature indicates how well water is being separated from glycol vapor at the top, and the stripping-gas rate is the lever that sets how far below the boiling limit the lean glycol dryness can be pushed.
A cloud SCADA such as Merobix reads these regeneration-side signals - reboiler temperature, still overhead temperature, stripping-gas flow, glycol circulation, and the contactor conditions - and presents them together so an operator can see the whole dehydration loop rather than isolated readings. That matters because the variables interact: the reboiler temperature, the stripping-gas rate, and the glycol circulation rate together determine the lean glycol dryness, which in turn sets the treated-gas dew point. Seeing them on one screen lets the operator tune the unit as a system to hold the dew-point target.
For an operator running dehydration units across a field, remote monitoring of the regeneration side is also an early-warning tool. A reboiler temperature drifting low, a stripping-gas rate that has fallen off, or a circulation rate out of range all point toward glycol that is not being regenerated dry enough, which shows up downstream as gas that risks missing its dew-point spec or forming hydrates. Catching these on the regeneration side, before the treated gas goes off-spec, is exactly the kind of remote oversight that keeps unmanned dehydration units running reliably with a lean crew.
TEG has a maximum regeneration temperature above which it begins to break down, so the reboiler is held below that limit - and at that temperature a stubborn fraction of water stays in equilibrium with the glycol, capping how lean it can get. Stripping gas gets around this by sweeping water vapor away from the hot glycol, lowering the partial pressure of water it is exposed to so more water evaporates out. It drives the glycol drier by changing the equilibrium rather than by raising the temperature to a level that would damage the glycol.
A Stahl column is a stripping column installed below the reboiler through which lean glycol flows downward while stripping gas rises against it in countercurrent contact. This exposes the glycol to progressively drier gas as it descends, driving it much leaner than simply bubbling stripping gas into the reboiler pool. It is a common way to get the extra dryness needed to meet a tight water dew-point specification.
By producing a much drier lean glycol, stripping gas lets the unit absorb more water from the wet gas in the contactor, which lowers the water dew point of the treated gas. A unit relying on boiling alone is limited in how low a dew point it can reach, while adding stripping gas can push it well beyond that limit. Where a pipeline or process demands very dry gas, stripping gas is often what allows the unit to meet the specification.
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