Triethylene glycol (TEG) dehydration is the most commonly used method for removing water vapor from raw natural gas and natural gas liquid (NGL) streams. It is performed for a number of reasons, the two most important of which are to dehydrate raw gas so that it meets sales pipeline specifications and to prevent hydration formation and corrosion in downstream pipelines and processing equipment.
The process takes place in a glycol dehydration unit. It begins with raw natural gas entering a glycol contactor (i.e., the absorber tower). In the contactor, the wet gas rises and comes in contact with “lean” TEG, which absorbs any water vapor contained in it. The dry gas then exits the tower and enters the sales line where it can be transported to a gas processing facility.
The “rich” TEG (glycol saturated with water) descends to the bottom of the tower, where it is fed into a flash tank. The flash tank is at a lower pressure than the contactor and is used to remove any remaining hydrocarbons in the glycol. After it leaves the tank, rich TEG is fed into a thermal regenerator, which typically consists of a column, an overhead condenser, and a reboiler. The regenerator strips remaining water vapor from the TEG, thus returning it back to a high level of purity (often is in excess of 99%). This process generally takes place in a high-temperature, low-pressure environment in order to allow for minimum flow rate of stripping gas. Any inert gas or a portion of the natural gas undergoing dehydration can be used.
The regenerated glycol (now considered lean) then enters a sparger box, which removes any remaining water. It then flows into a storage tank and is pumped back to into the absorber tower where it once again comes in contact with raw natural gas and the process is repeated.