Natural gas usually contains a large amount of water (typically water-saturated) which will undergo condensation and transforms into gas hydrates if the gas is cooled below its hydrate formation temperature. Gas hydrate solids can agglomerate and plug pipelines and equipment, interrupting operations and stopping gas production. To avoid these potential problems, the gas stream needs to be dried to lower its water dew point. Dehydration requires for pipe line transmission, NGL recovery units and off shore facilities. Sales gas plants must meet climate specific dew point requirements for pipeline. The use of generic glycols including MEG, DEG, TREG and most commonly used TEG to dehydrate gas streams is a method that has proven its functionality and versatility over many years in both onshore and offshore facilities. TEG is the most commonly used glycol in dehydration process.
In a gas dehydration package, wet natural gas is processed in an inlet filter separator to remove liquid hydrocarbons and free water. The separator gas is then contacted counter currently with glycol, typically in a packed column. Dry natural gas existing the absorber passes through a heat exchanger and then into the sales line. The rich glycol is preheated and enters the stripping column. The water vapor and desorbed natural gas are vented from the top of the stripper while the regenerated lean glycol flows out of the reboiler into the top of the absorber.
The design of dehydration system will vary to meet the specified moisture content of the gas at the process conditions, while a smart balance between packing height, glycol purity, and glycol amount allows you to benefit from minimized utility consumption levels and minimized energy consumption besides reboiler temperature control to prevent unwanted glycol degradation.