Overview
Triethylene glycol (TEG) is the industry-standard solvent for continuous gas dehydration, used across natural gas processing plants, offshore platforms, LNG feed gas preparation units, and gas transmission pipelines. In a glycol dehydration unit, wet gas contacts lean TEG in an absorber (contactor) column. TEG selectively absorbs water vapor from the gas stream. The water-rich glycol is then regenerated in a reboiler at approximately 200°C, restoring it to lean TEG for recirculation.
TEG is preferred over monoethylene glycol (MEG) and diethylene glycol (DEG) for dehydration service because of its lower vapor pressure (minimising glycol losses with the gas), higher regeneration temperature (enabling deeper dehydration), and better thermal stability. A well-designed TEG unit can reduce the water dewpoint of natural gas to below −10°C, satisfying most pipeline gas specifications.
Typical Applications
- Natural gas dehydration prior to pipeline export, achieving water dewpoint specifications (typically −8°C to −20°C)
- Offshore platform gas treatment before export or gas-lift injection
- LNG feed gas preparation, removing bulk water before molecular sieve dryers
- Condensate stabiliser overhead gas dehydration
- Fuel gas conditioning to prevent hydrate formation in distribution piping
- Associated gas dehydration in upstream production facilities
Operational Considerations
- TEG circulation rate and lean TEG purity directly determine the outlet gas dewpoint; typical lean TEG concentration is 99.0–99.9 wt%.
- Reboiler temperature must be controlled carefully. Overheating above 204°C accelerates TEG degradation and increases losses.
- Entrained BTEX compounds (benzene, toluene, ethylbenzene, xylene) are co-absorbed with water and released during regeneration. Vent gas handling and BTEX control are important environmental considerations.
- Make-up TEG should match or exceed the purity of the lean glycol in the system to avoid accumulation of contaminants and degradation products.
- Regular sampling of circulating glycol and monitoring of pH, colour, and iron content are recommended to assess system health and schedule glycol replacement.
TEG vs. MEG Selection
| Criterion | TEG | MEG |
|---|---|---|
| Primary function | Gas dehydration (absorber) | Hydrate inhibition (injection) |
| Application method | Continuous circulation in contactor | Continuous injection & recovery |
| Regeneration temperature | ~200°C (atmospheric) | ~130°C (atmospheric) |
| Achievable dewpoint | −10°C to −25°C | Not applicable (hydrate control) |
| Vapour pressure | Very low, minimal gas-phase losses | Higher, more volatile |
| Thermal stability | Excellent up to ~200°C | Good up to ~130°C |