Application

Why Gas Is Dehydrated

Gas extracted from a reservoir typically contains water vapour. The concentration depends on the temperature, pressure and conditions of the reservoir bed it comes from. Removing that water is known as dehydration.

The duty is driven by three requirements:

Meeting the water concentration target for sales gas
Preventing hydrate formation and water condensation during processing and transportation
Preventing corrosion

Triethylene glycol (TEG) is the glycol most widely used in contactor dehydration. Ethylene glycol (EG) is more often injected into the gas to prevent hydrates in chilling processes. The choice depends on the process and its operating temperature.

Process

How the TEG Unit Works

Water-saturated gas passes through an inlet scrubber to remove contaminants before contacting the glycol, which protects the performance and longevity of the solvent. The scrubbed wet gas enters the contactor tower and meets the down-flowing glycol.

Trays or structured packing inside the contactor provide the contact area for the glycol to absorb water. Dry gas leaves the top of the contactor; water-rich glycol leaves the bottom for regeneration.

System configuration

Major Equipment Within the System

System configuration varies with process duty, operating conditions and project requirements.

Inlet Scrubber

Removes contaminants from the wet gas before it meets the glycol; typically integrated with the contactor.
Contactor (Absorber)

Brings the wet gas into contact with down-flowing glycol over trays or structured packing, where the water is absorbed.
Glycol/Gas Heat Exchanger

Cools the lean glycol against the dry gas before the glycol enters the top of the contactor.
Flash Tank

Releases the gas entrained in the rich glycol.
Rich/Lean Glycol Exchanger

Preheats the rich glycol on its way to the reboiler and gives the lean glycol its first cooling.
Glycol Reboiler and Still Column

Regenerate the glycol: heat drives the absorbed water out, and lean glycol leaves the reboiler for reuse.

Also in the scope of supply

Vessels: surge tank
Rotating equipment: glycol pump
Filtration: glycol filters
Reboiler control: burner management system
Instrumentation and safety: analogue pressure and temperature indicators, pneumatic controllers, pneumatic control valves

Options

Process drain tank: collection of drained process liquids
Spare glycol pumps: installed spares to maintain circulation during maintenance

Final equipment arrangement and delivery format depend on process duty, transport constraints and site requirements. Design pressure, temperature and capacity envelope to be confirmed by SPEC engineering.

Advantages

Strengths and Limits

Lower capital cost

Lower initial investment than a comparable solid desiccant unit.

Straightforward regeneration

Glycol regeneration is simple and the process runs continuously rather than in cycles.

Where it does not apply

Glycol cannot reach the very low dew points that cryogenic processing requires, and contaminated glycol can become corrosive.

Evidence

Delivered

For BAPEX at the Shahbazpur gas field in Bangladesh, SPEC designed, engineered and supplied a 2 × 35 MMSCFD triethylene glycol dehydration plant, with commissioning support.

Detail

Contactor, Regeneration Skid and Fabrication

The contactor column and the regeneration skid are sized together from the inlet gas analysis and the required outlet water content. Vessels are fabricated and hydrotested in SPEC facilities before the unit is completed and shipped.