EPA’s GHGRP Subpart W reports a triethylene glycol (TEG) dehydrator’s methane as one unit-level total, not broken out by individual component [1]. The Energy Emissions Modeling and Data Lab (EEMDL), a partnership of UT Austin, Colorado State, and Colorado School of Mines, published a 2026 dehydrator study [2]. Mdigo and colleagues found gas-assisted glycol pumps produced about 90% of uncontrolled dehydrator methane in the sites they modeled [2]. In those uncontrolled units, pump controls would capture most of the methane, leaving still-column and flash-tank controls a much smaller share. The GHGRP Subpart W emissions reporting framework governing US oil and gas dehydrator facilities is currently under EPA reconsideration.

Subpart W Reports Dehydrator Methane as One Number, Not by Component

EPA’s GHGRP Subpart W produces a single methane total for the entire TEG dehydration unit [1]. That total does not break out the glycol pump’s share from the regenerator still-column vent or the flash tank [1]. Operators submit one unit-level number. No component attribution comes with it.

Without component-level estimates, operators are guessing. A condenser on the still column reduces regenerator overhead [3]. A vapor recovery unit on the glycol pump captures exhaust gas with each stroke [3]. A single unit-level total does not indicate which one targets the larger emission share.

The Model Runs Component-Level Process Simulation Inside MAES

This component-level model runs inside MAES, the mechanistic emissions platform TetraSoft offers to the public by subscription through the MAES Platform [4]. It uses a physics-based polynomial surrogate of full process simulation, so per-component estimates respond to actual operating conditions [2]. The surrogate was trained on ProMax, a thermodynamic process simulator, running thousands of cases across a realistic range of field conditions [2]. Inputs spanned glycol circulation rates and contactor conditions typical of field dehydrators [2]. Inside MAES the surrogate runs at one-second resolution [2].

The surrogate preserves the thermodynamic relationships that govern emission variation across operating conditions [2]. When throughput or contactor pressure shifts seasonally, the MAES TEG module updates its emission distribution to reflect the new operating state. Conditions change through the year, but an annual reported estimate does not [1].

Contactor pressure is one of the most consequential variables. At lower contactor pressures, operators typically increase glycol circulation rate to maintain the outlet dew point specification [2]. Higher glycol circulation means more stroke cycles per unit time for a gas-assisted pump. As a result, reducing contactor pressure can increase pump methane emissions even while total gas throughput stays flat.

Gas-Assisted Glycol Pumps Produce About 90% of Uncontrolled Dehydrator Methane

Mdigo et al. attributed approximately 90% of total uncontrolled dehydrator methane to gas-assisted glycol pumps [2]. The study’s simulation distribution centered at 90.25%, with facility-specific estimates varying by glycol rate, contactor pressure, and inlet gas composition [2]. Still gas from the regenerator overhead and flash gas from the glycol flash tank made up the remainder [2]. The figure applies to dehydrators without emission controls on the glycol pump [2].

Nine-tenths from one component is not a marginal finding. Subpart W’s unit-level total reveals only the aggregate. Operators cannot see that the pump, not the still column, produces most of the methane.

For operators with methane intensity targets, pump controls are the highest-impact dehydrator investment.

Interested in building a Measurement-Informed Inventory for your operations? Contact us to learn about our MAES-based estimation services.

Component-Level Modeling Changes How Operators Allocate Control Investment

Operators relying on default factors for TEG dehydrators may spend on the wrong component first. A condenser on the regenerator still column addresses less than 10% of uncontrolled dehydrator methane [2]. The glycol pump accounts for the other 90% [2]. An operator who installs a still-column condenser first has spent capital on less than a tenth of the problem.

MAES is a mechanistic emissions model that generates probability distributions of expected emissions for each equipment component [5]. TetraSoft offers MAES to the public by subscription through the MAES Platform [4]. The TEG dehydrator module applies the same component-level methodology used across other MAES equipment categories. Colorado operators preparing facility-level inventories may find component-level attribution useful beyond federal reporting, particularly for ONGAEIR submissions.

Frequently Asked Questions

What is a gas-assisted glycol pump?

A gas-assisted glycol pump uses high-pressure natural gas to drive glycol circulation through the dehydration system [3]. After each stroke, the pump exhausts methane-rich driving gas at low pressure [3]. Without vapor recovery or combustion, the exhaust vents directly to atmosphere [3]. Electric pumps eliminate this emission pathway entirely [3].

Why do gas-assisted glycol pumps dominate TEG dehydrator methane?

Gas-assisted pumps vent methane-rich driving gas with every stroke cycle [3]. The venting is continuous during normal operation [3]. Still column and flash tank emissions depend on glycol rate, gas composition, and contactor conditions, and are typically smaller. A single reported dehydrator total hides the pump’s share, so this dominance stays invisible without component-level modeling.

Does the EEMDL TEG model apply to dehydrators with electric pumps?

The 90.25% glycol pump contribution applies only to gas-assisted pumps [2]. Facilities that have replaced gas-assisted pumps with electric pumps eliminate that emission pathway [3]. For those facilities, still gas and flash gas become the dominant dehydrator sources, and the MAES TEG module models those components separately.

How does component-level modeling complement GHGRP Subpart W dehydrator reporting?

A MAES-based dehydrator inventory complements Subpart W reporting by adding component-level attribution for control planning and voluntary programs like OGMP 2.0. Subpart W methods produce a single unit-level total with no component breakdown [1]. MAES attributes that total across the glycol pump, still column, and flash tank individually. EPA is reconsidering whether to suspend Subpart W reporting for RY2025 through RY2034; for context, see GHGRP Subpart W Deadline Moved to October 2026.

This post is for informational purposes only and does not constitute legal or compliance advice. Consult qualified legal counsel or a compliance professional for guidance specific to your operations and jurisdiction.

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References

  1. US EPA, 40 CFR Part 98, Subpart W (Petroleum and Natural Gas Systems), Greenhouse Gas Reporting Program.
  2. Mdigo et al., Mechanistic Modeling of TEG Dehydrator Emissions in Oil and Gas Industry, Fuels 7(2), 21, 2026, DOI:10.3390/fuels7020021, EEMDL (UT Austin, Colorado State University, Colorado School of Mines).
  3. US EPA Natural Gas STAR Program, Lessons Learned: Replacing Gas-Assisted Glycol Pumps with Electric Pumps.
  4. TetraSoft, MAES Platform, https://tetrasoftco.com/maes-platform/maes-landing.html.
  5. Santos et al., Using Measurement-Informed Inventory to Assess Emissions in the Denver-Julesburg Basin, ACS ES&T Air 2, 1598-1611, 2025, DOI:10.1021/acsestair.5c00089.