Triethylene glycol is a liquid desiccant system used for the removal of water from natural gas and NGLs. It is the most commonly used means of water removal. A TEG Unit uses absorption, which occurs when the water vapor is taken out by a dehydrating agent, or liquid desiccant.
A TEG uses dehydration to remove all the water vapor from the gas or liquids such as natural gas or oil. Water vapor in gas is like humidity in the air; it can only be removed through a dehydration process such as a liquid or solid desiccant or with refrigeration. Water vapor is the amount of water contained in gas at a given temperature and pressure. There are three main characteristics that affect the water vapor in gas; temperature, pressure and volume.
Here at CROFT, we like to first find out what the volume, temperature and pressure is, so we can determine how much water vapor needs to be removed and what size equipment will be needed to appropriately dehydrate the gas.
With higher temperatures, the more water vapor the gas can hold. For every 20°F, the water vapor capacity will double which means more desiccant will be needed to remove the water vapor. It is crucial that water vapor is removed from the natural gas stream because it can cause corrosion within the gas lines and equipment. Hydrates can also form, clogging pipelines, valves, and transport equipment.
There are different types of dehydration products, but this blog will focus specifically on glycol dehydration unit, which is a non-regenerative system utilizing liquid absorbents to hydrate the gas.
How the TEG system works:
Wet gas enters the inlet scrubber, which is placed before the contact tower to remove any free water, dust, condensed hydrocarbons, and other impurities
After going through the separator, the wet gas enters through the contact tower where it rises through the column. As its rises through the contact tower the gas meets the lean glycol solution flowing downward across either bubble trays, random packed or structured packed towers
Next, the rich TEG exchanges heat with the lean TEG and enters the still column. The TEG then flows downward through the still column to the reboiler where it is heated around 375°F and removes all but a small percentage of the water from the regenerator
The hot, dry glycol then flows through an overflow system to the surge section of the reboiler, where the glycol pump then pulls lean TEG and pumps the glycol back into the top of the contact tower, where the drying process is repeated
There are optional features you can have on a TEG. The BTEX unit is a heat exchanger condensing system used to capture and recycle BTEX and VOC from the regenerator still column. The liquids are collected and transferred to storage, while the residual VOC vapors are sent to the burner or to compression. They reduce operating costs by recovering sellable condensates and using VOC vapors for burner fuel.
If you are interested in a TEG unit, you can read more about it here.