What is the primary environmental concern related to glycol dehydration units, and how is it typically mitigated?

The primary environmental concern related to glycol dehydration units is the emission of volatile organic compounds (VOCs), particularly benzene, toluene, ethylbenzene, and xylenes (BTEX), which are hazardous air pollutants (HAPs). Glycol dehydration units use glycol solvents, such as triethylene glycol (TEG), to remove water from natural gas. During the dehydration process, the glycol solvent absorbs not only water but also some VOCs present in the natural gas stream. When the glycol is regenerated by heating to remove the absorbed water, the VOCs are released along with the water vapor in the regenerator still vent. These VOC emissions contribute to air pollution and can have adverse health effects. The most common method for mitigating VOC emissions from glycol dehydration units is to install a vapor recovery unit (VRU) or a condenser on the regenerator still vent. A VRU captures the VOCs and returns them to the process stream, while a condenser cools the vent stream to condense the VOCs, which can then be collected and disposed of properly. Other mitigation methods include using a BTEX removal system to remove BTEX from the glycol solvent before regeneration, optimizing the glycol circulation rate to minimize VOC absorption, and using a less volatile glycol solvent. Regulatory requirements often mandate the use of specific control technologies to reduce VOC emissions from glycol dehydration units. Careful monitoring of VOC emissions is essential for ensuring compliance with environmental regulations.