Glycol Dehydration System
Most natural gas producers use Triethylene glycol (TEG) to remove water from the natural gas stream in order to meet the pipeline quality standards. This process is required to prevent hydrates formation at low temperatures or corrosion problems due to the presence of carbon dioxide or hydrogen sulfide (regularly found in natural gas).
Dehydration, or water vapor removal, is accomplished by reducing the inlet water dew point (temperature at which vapor begins to condense into a liquid) to the outlet dew point temperature which will contain a specified amount of water.
Absorption of water vapor in the TEG is the common method. The wet gas is brought into contact with dry glycol in an absorber. Water vapor is absorbed in the glycol and consequently, its dew point reduces. The wet rich glycol then flows from the absorber to a regeneration system in which the entrained gas is separated and fractionated in a column and reboiler. The heating allows boiling off the absorbed water vapor and the water dry lean glycol is cooled (via heat exchange) and pumped back to the absorber.
Mol Sieve Dehydration System
Mol sieve dehydration units provide an effective means to remove water vapor from a natural gas stream. Achieving cryogenic temperatures (-50°F and less) in natural gas processing requires the inlet gas to be free of water vapor. High water vapor can freeze at low temperature forming hydrates, and these hydrates can be problematic in a cryogenic process. Use of a mol sieve is an effective method to combat this issue.
The mol sieve design usually consists of a silicate compound containing very small pores of precise uniform size. The space between the silicate molecules act as a “trap” for the water vapor as it passes through the silicate.
Basic design consists of two or more identical molecular sieve units. In a simple two-unit design, one unit operates in dehydration mode while the other in regeneration mode. Switching from dehydration to regeneration is done by use of automatic switching valves. As the dehydrated unit becomes saturated with water vapor, it is automatically switched to regeneration mode while the regeneration unit becomes active in dehydration mode.
