Glycol dehydration is a process used in natural gas purification. It is designed to help remove excess water from raw natural gas to make it suitable for transport in natural gas pipelines and for use by consumers. In general, one of three types of glycol can be used, all of which have similar properties and typically function in similar systems.
When natural gas is piped up from underground wells, it often contains many substances in addition to the methane that is typically associated with commercial-grade natural gas. Such substances, often called contaminants, can include things such as ethane, propane, nitrogen and water. The majority of contaminants generally need to be removed before the natural gas can be transported away from the original wells and sold to consumers.
There are several different contaminant-removal methods, including several methods for removing water and water vapor. One of the most common methods for removing water vapor is glycol dehydration. The first stage of this process typically takes place in a contraction tower. Here, raw natural gas is generally piped upward through liquid glycol molecules, which latch on to the water vapor molecules and then sink to the bottom of the apparatus. The water-free natural gas generally then continues to rise up through the contractor tower and onto the next decontamination process.
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In general, the water-laden glycol molecules that sink to the bottom of the glycol dehydration contraction tower are not simply discarded. Instead, they are usually removed from the tower and recycled. To recycle the water-laden glycol, the solution is typically heated above 212 degrees Fahrenheit (100 degrees Celsius) to boil off the water, leaving only the glycol, which doesn’t boil until a much higher temperature, behind. This purified glycol is then often reused in the same contractor tower process described above.
Several types of glycol may be used in the glycol dehydration process. One of the most common forms is triethylene glycol, which has one of the highest boiling points, generally making it easier to remove the water vapor and reuse. Other forms that may be used in glycol dehydration include diethylene glycol and tetraethylene glycol. Diethylene glycol is generally cheaper than triethylene glycol, but it is typically used less often because more of it gets lost in the dehydration process. Conversely, the loss of tetraethylene glycol is typically less than that of triethylene glycol or diethylene glycol, but its higher initial cost generally makes it a less commonly used option.