Talk to enough field engineers about cutting emissions on a production site and two answers keep coming up: put in a vapor recovery unit, or put a BTEX condenser on the dehydrator. Both recover hydrocarbons, both help with air permits and both come up in the same conversations about compliance. That is exactly why they get confused so often.
In practice, they solve different problems at different points on the site. A vapor recovery unit, or VRU, captures low-pressure vapors from storage tanks. A BTEX condenser treats the vent stream coming off a glycol dehydrator’s still column. Choosing between them starts with a simple question: where are your emissions actually coming from?
Where the Vapors on Your Site Come From
Storage tanks are the first major source. When oil or condensate moves from a higher-pressure separator into an atmospheric tank, dissolved gas flashes out of the liquid, and more vapor escapes every time the tank fills or the temperature swings through the day. EPA describes these as flashing, working and standing losses, and it notes that methane typically makes up 40 to 60 percent of the vapor coming off a tank.
The glycol dehydrator is the second. Triethylene glycol is very good at absorbing water from natural gas, but it also picks up methane, volatile organic compounds and hazardous air pollutants, including benzene, toluene, ethylbenzene and xylenes, known together as BTEX. When the rich glycol is heated in the reboiler to drive off the water, those compounds leave through the still column vent along with the steam. EPA classifies benzene as a known human carcinogen, which is why regulators pay such close attention to that vent.
What a Vapor Recovery Unit Does
A VRU is essentially a compressor package that pulls vapor off the tanks before it can vent and sends it somewhere useful. According to EPA’s Natural Gas STAR program, VRUs can capture the vapors from low-pressure tanks about 95 percent of the time, and the captured gas is directed to a low-pressure sales line, the suction of a production compressor or the site’s fuel gas supply. Along the way, the unit also captures VOCs and HAPs.
The economics depend on the site. EPA points out that a VRU project needs a steady source and adequate volume of crude oil or condensate, along with an economic outlet for what it collects. Most units are driven by electric motors, so remote locations without reliable power may not be good candidates. A VRU also does nothing for the dehydrator still vent unless that stream is deliberately routed to it.
What a BTEX Condenser Does
A BTEX condenser sits on the dehydrator still column vent and cools the hot vapor stream until the water and heavier hydrocarbons, including most of the BTEX, condense into liquid. Instead of venting those compounds, the system collects them. On a JATCO system, condensed liquids are collected in the JATCO Environmental Tank and then automatically transferred to storage.
What remains after condensing is a much smaller stream of non-condensable gas. Depending on the site, that gas can be routed back to the reboiler for destruction through our Eliminator Package, or sent to a combustor, flare, VRU or thermal oxidizer. Our A-Frame BTEX system uses natural draft air cooling, the Shell and Tube system uses counter-flow glycol cooling, and our Vertical Panel systems are air-cooled units that can be expanded with add-on panels, so the cooling method can be matched to the location.
Why the Two Usually Work Together
Because they treat different sources, a VRU and a BTEX condenser are rarely true alternatives. A site with both tanks and a dehydrator may need both, with the VRU handling tank vapors and the condenser handling the still vent. In fact, sending the condenser’s non-condensable gas to an existing VRU is one of the standard ways to dispose of it.
The condenser also does the heavy lifting before anything else sees the stream. By knocking out the water and heavier hydrocarbons first, it leaves a far smaller volume of gas for a VRU, flare or combustor to handle. EPA’s guidance on glycol dehydrators notes that a condenser recovers natural gas liquids and HAPs more efficiently than flash tank separators alone, and the liquids it recovers can be kept instead of becoming emissions.
What the Regulations Expect
For glycol dehydrators, the federal air toxics rules for oil and natural gas production facilities, 40 CFR Part 63 Subpart HH, set the bar. The rule allows several types of control devices, and it lists a vapor recovery device such as a condenser as one option, provided it is designed and operated to reduce total organic compounds or total HAP in the vented gas by 95.0 percent by weight or more. In other words, the regulation itself treats a properly designed condenser as a form of vapor recovery.
Not every dehydrator is covered. At area sources, Subpart HH exempts a glycol dehydration unit from these requirements if its actual annual average gas flowrate is below 85 thousand standard cubic meters per day, roughly 3 million standard cubic feet per day, or its actual benzene emissions from the process vent are below 0.90 megagrams per year, just under one ton. That exemption does not apply to major sources, so check which category each site falls into. Storage tanks fall under separate federal and state rules with their own thresholds, and it is always worth confirming the requirements for each source with your environmental team before choosing equipment.
Questions That Point You to the Right Equipment
Start with the source. If the problem is the dehydrator still vent, a BTEX condenser is the direct solution, and if the problem is tank vapors, a VRU or a combustor is the usual answer. Next, look at the site itself. Is there reliable electric power, is there a sales line or fuel system that can take recovered gas, and is the vapor volume steady enough to keep a compressor running efficiently?
Then look at the gas. Hydrogen sulfide matters, because our Eliminator Package is not available for streams above 10 ppm H2S, so sour gas sites need a different route for the non-condensables. It is also worth reviewing your glycol circulation rate. EPA has found that many dehydrators circulate two to three times more glycol than they need, and every extra gallon picks up more methane and BTEX that has to be handled downstream.
Sizing a BTEX System for Your Dehydrator
A condenser only performs well when it is sized for the actual unit. Our system sizing form asks for the gas rate in MMSCFD, contactor pressure and temperature, reboiler rating, glycol pump rate in gallons per hour, ambient temperature, location and H2S content. With those numbers, we can recommend the right system and the right option for the non-condensable gas.
JATCO has been building emissions equipment in Oklahoma City since 1988, and we are glad to talk through a site even when the answer turns out to be a combination of equipment. If you are weighing a VRU against a condenser, contact our team with your dehydrator details and we will help you work out what the site actually needs.
Frequently Asked Questions
What is the difference between a vapor recovery unit and a BTEX condenser?
A vapor recovery unit uses a compressor to capture low-pressure vapors, usually from storage tanks, and send them to a sales line or fuel system. A BTEX condenser cools the vent stream from a glycol dehydrator’s still column so water and hydrocarbons, including BTEX, condense into liquid. They treat different emission sources and often work side by side.
Can a BTEX condenser send gas to a vapor recovery unit?
Yes. After condensing, the remaining non-condensable gas can be routed to a VRU, a combustor, a flare or a thermal oxidizer, or back to the reboiler for destruction. The right choice depends on the equipment already on site and the composition of the gas.
Does a condenser count as a control device under Subpart HH?
It can. Subpart HH lists a condenser as one type of vapor recovery device, as long as it is designed and operated to reduce total organic compounds or total HAP in the vented gas by at least 95.0 percent by weight. Your environmental team should confirm how the rule applies to each unit.
What happens to the liquids a BTEX condenser collects?
On a JATCO system, they go into the JATCO Environmental Tank first, and from there they are moved to storage automatically. Capturing those liquids, instead of venting them with the still column vapor, is what keeps most of the BTEX out of the atmosphere.
What information is needed to size a BTEX system?
Start with the dehydrator’s gas rate in MMSCFD and the contactor pressure and temperature. We also need the reboiler rating, glycol pump rate, ambient temperature, location and H2S content, because those details determine how much vapor the condenser must handle and which disposal option fits.