Gas Dehydration is a widely used application in Gas Processing Plants. This process is carried out to remove moisture from natural gas to achieve the required water dew point for pipeline specification or for downstream processing like NGL extraction.

This process is required to prevent hydrates formation at low temperatures and reduce corrosion problems due to the presence of carbon dioxide or hydrogen sulfide present in natural gas.

Based on the required outlet gas specification, the Gas Dehydration process is classified into the following processes:

• Glycol Based Gas Dehydration Process
• Molecular Sieve Gas Dehydration Process

Process Description

1. Glycol Based Gas Dehydration Process:

Tri-Ethylene Glycol (TEG) is the most widely used chemical for Gas Dehydration Units (GDU). This process can achieve 3–7 lb/MMSCF of gas which is suitable for most Pipeline transportation specification. CAPEX and OPEX of this process is significantly lower than Molecular Sieve based Dehydration.

The wet gas from the well or compressor station is brought into contact with lean glycol in the Contactor column. The column is normally provided with structured packing which provides mass transfer surface.

Moisture present in the gas is absorbed in the lean glycol in a countercurrent absorption process resulting in reduction of water dew point. The rich glycol then flows from the absorber to TEG regeneration system in which the entrained gas and moisture is fractionated in a Column and Reboiler. The heating allows boiling off the absorbed water vapor. The lean glycol is cooled and pumped back into the absorber.

To achieve a higher degree of water removal from amine, fuel gas is used for stripping in the regenerator to achieve a higher glycol concentration.

2. Molecular Sieve Based Gas Dehydration Process:

To avoid any hydrate formation during cryogenic process like LPG or NGL recovery, Molecular Sieve based gas dehydration Process is employed.

The molecular sieve-based dehydration utilizes an adsorption process where moisture present in the gas is adsorbed on the surface of zeolite beds. The zeolite particles are available in various pore sizes (3–5 Å). Selection of media is critical for efficient operation of the system. CECO Peerless offers design with an optimized operation cycle resulting in extended life and higher efficiency.

In a standard process a two or three vessel design is used where one or two vessels is under drying cycle and the remaining vessel will be under regeneration mode. Rising Steam Switching Valves are used for switching from dehydration to regeneration mode.

A slip-up gas stream from the GDU outlet is compressed, superheated, and then introduced to the vessel which is in regeneration mode. The principle of heating the molecular sieve removes the adsorbed water and the regeneration gas flows back to inlet of the unit gas.