Glycol dehydrators are one of the largest sources of benzene, toluene, ethylbenzene, and xylene (BTEX) emissions at natural gas production, gathering, and processing facilities. When triethylene glycol (TEG) or diethylene glycol (DEG) contacts raw natural gas in the contactor column, it absorbs water vapor along with BTEX compounds which are then stripped out during regeneration and vented or combusted. EPA regulations under NSPS Subpart OOOO, OOOOa, OOOOb, and NESHAP Subpart HH impose BTEX control requirements on glycol dehydrators above specified throughput thresholds. This guide covers what those requirements are, what control options exist, and how to select the right equipment for your facility.

Why Glycol Dehydrators Generate BTEX Emissions

The BTEX problem in glycol dehydration is a mass transfer issue: the same thermodynamic properties that make glycol an effective water absorber also cause it to absorb aromatic hydrocarbons from the gas stream. At typical contactor conditions (700 to 1,200 psi, 70 to 110°F), BTEX compounds partition from the gas phase into the lean glycol at rates that depend on gas composition, operating pressure, and contactor temperature. The contaminated rich glycol is then heated in the regenerator to strip water, which simultaneously vaporizes and releases the absorbed BTEX into the regenerator overhead vapor stream. This overhead stream called the “still overhead” or “reboiler vent” is the primary source of BTEX emissions from glycol dehydrators.

At most production and gathering sites, benzene is the primary regulatory driver. EPA’s NESHAP Subpart HH establishes a 900 kg/year benzene emissions threshold above which major source MACT controls apply. For dehydrators below the major source threshold, NSPS OOOOb (for facilities constructed after December 6, 2022) imposes control requirements at lower throughput levels than previous subparts.

EPA BTEX Control Requirements for Glycol Dehydrators

The regulatory framework for glycol dehydrator BTEX control is layered across multiple subparts. NSPS Subpart OOOO and OOOOa (for facilities constructed between 2012 and 2022) require combustion control for dehydrators with natural gas throughput above 85,000 scfd at facilities with a potential BTEX emission rate above specified limits. NESHAP Subpart HH applies to glycol dehydrators at major HAP sources (facilities emitting 10 tons per year of any single HAP or 25 tons per year of combined HAPs) and imposes benzene-specific control requirements either a condenser control system or combustion control that achieves 95% reduction of HAP emissions. OOOOb (for facilities with construction, modification, or reconstruction after December 6, 2022) includes glycol dehydrators in its scope and imposes control requirements at lower throughput thresholds with continuous parameter monitoring requirements similar to those applied to storage vessels.

State air quality regulations in BTEX-sensitive states including New Mexico, Colorado, Wyoming, and parts of Texas may impose more stringent BTEX control requirements than the federal floor, with lower throughput thresholds and higher minimum DRE requirements. Operators should confirm which federal and state rules apply to each specific dehydrator based on throughput, facility construction date, and state permit conditions.

BTEX Control Options for Glycol Dehydrators

Option 1: Combustion Control (Flare or Combustor)

Routing the glycol reboiler still overhead to a flare or enclosed combustor is the most common BTEX control approach for production and gathering site dehydrators. The still overhead stream a mixture of water vapor, BTEX, and residual methane is piped from the regenerator overhead to the combustion device, where the BTEX compounds are oxidized to CO2 and water at 98%+ DRE. Combustion control is operationally straightforward, does not require chemical regeneration or product recovery systems, and is compatible with the variable BTEX loadings typical of dehydrators serving wells with changing composition over their production life.

The key equipment considerations for combustion control of glycol reboiler vents are: the still overhead flow rate (typically 2 to 50 scfh for small dehydrators), the BTU content of the still overhead (which varies with glycol temperature and BTEX loading), and the requirement for a continuously burning pilot to meet 40 CFR 60.18 parameters. A dedicated low-flow combustor sized for the still overhead flow rate is typically the most cost-effective combustion control option for individual dehydrator units at production sites.

Option 2: BTEX Condenser Recovery

A BTEX condenser system cools the glycol regenerator overhead vapor stream to condense and recover the BTEX compounds as a liquid product before the uncondensed vapor is vented or combusted. The recovered BTEX liquid can be sold as a condensate byproduct or pumped into the tank battery for co-mingling with produced condensate. BTEX condenser systems are most cost-effective at higher-throughput dehydrators where BTEX recovery has commercial value that offsets equipment costs, and at facilities where combustion control of the condenser overhead vent is also required for residual HAP control after condensation.

Option 3: Glycol Throughput Optimization

For dehydrators near the regulatory throughput threshold, reducing glycol circulation rate to the minimum needed for product specification dew point control can lower BTEX absorption and keep the dehydrator below the applicable regulatory threshold. This is not a control option for dehydrators clearly above the threshold, but it is a legitimate operational optimization for facilities near the threshold where minor reductions in glycol rate would achieve sub-threshold status without requiring capital equipment investment.

Equipment Selection for Combustion Control of BTEX Emissions

Selecting a combustion control device for a glycol reboiler still overhead requires matching the device to the specific characteristics of the dehydrator’s vent stream. Critical parameters include the still overhead flow rate (scfh), the BTU content of the stream (which determines combustion stability at minimum flow), the H2S content (which affects material selection), the BTEX concentration (which determines the DRE needed to meet mass emission limits), and whether the regulatory requirement specifies combustion at 98% DRE, 95% DRE, or a specific mass emission rate.

For most small to mid-size production site dehydrators, a low-flow combustor or enclosed combustor provides the most cost-effective and reliable BTEX control. These units are designed for the low flow rates and variable BTU content typical of glycol reboiler vents, include continuously burning pilot systems that satisfy 40 CFR 60.18, and can be configured with OOOOb-compatible monitoring packages for facilities subject to continuous parameter monitoring requirements.

Hero Process Solutions engineers combustion control systems for glycol dehydrator BTEX applications from its Kellyville, Oklahoma facility, with equipment in service across Oklahoma, Texas, and New Mexico production basins. Contact HPS at (918) 941-2166 or through the contact page to discuss BTEX control equipment sizing and specifications for your glycol dehydrator application.