Glycol Dehydrators

Dehydrators are used in the oil and gas industry to remove water from gas, to meet pipeline quality standards. The liquid desiccant most often utilized is triethylene glycol (TEG). During the dehydration process, TEG absorbs water along with methane, volatile organic compounds (VOCs), and hazardous air pollutants (HAPs) when contacted with the wet gas. TEG is then regenerated (i.e., water and impurities are removed) through heating in a reboiler, where absorbed methane, VOCs, and HAPs are vented to the atmosphere along with the water vapor. The TEG is often circulated with a gas-assist glycol circulation pump wherein produced gas is injected into the TEG to provide more power to the pump, resulting in additional methane emissions. 

Depending on operating and ambient conditions, water vapor in produced natural gas may condense and freeze, forming ice or methane hydrates (crystalline solids formed from water and methane molecules). The ice and methane hydrates can block pipelines, wellbores, and/or equipment. Inhibiting hydrate formation, especially during cold weather, is essential for producers to maintain a continuous flow of natural gas. Ice and hydrate formation can be prevented by removing water vapor from the natural gas (dehydration process). 

Most dehydrators in the industry use TEG to remove water from the natural gas stream. Figure 1 shows a typical TEG dehydrator system using a gas-assist glycol circulation pump. Gas-assist glycol circulation pumps, also referred to as energy exchange pumps, use gas as the source of power and are necessary to use at locations without reliable power. In this system, “lean” (dry) TEG is pumped to the gas contactor. In the contactor, the TEG absorbs water, methane, VOCs, and HAPs (including benzene, toluene, ethyl benzene, and xylenes [BTEX]), from the wet gas. With water removed from the natural gas stream, dry gas leaves the gas contactor and is sent to a sales pipeline and continues to downstream processes. The “rich” (wet) TEG leaves the contactor saturated with gas at sales pipeline pressure, typically between 250 and 800 psig. In a system using a gas-assist glycol circulation pump, the gas entrained in the rich glycol, plus additional wet gas that bypasses the contactor (“pneumatic gas” used to provide power to the circulation pump), expands through the glycol circulation pump driver. The rich TEG is then circulated through a reboiler where the absorbed water, methane, and VOCs are boiled off and vented to the atmosphere. Using a gas-assist glycol circulation pump results in more emissions from the reboiler, than from the TEG regeneration alone, due to the additional wet “pneumatic gas” used for the pump. The lean TEG is then sent through the glycol circulation pump back to the gas contactor, and the cycle repeats. 

Figure 1. Glycol Dehydrator with Gas-Assist Glycol Circulation Pump

Gas Research Institute and U.S. Environmental Protection Agency. (1996, June). Methane emissions from the natural gas industry. https://www.epa.gov/natural-gas-star-program/methane-emissions-natural-gas-industry

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