Dry gas seal


Dry gas seal

Dry gas seals are non-contacting, dry-running mechanical face seals consist of a mating (rotating) ring and a primary (stationary) ring. When operating, grooves in the rotating ring generate a fluid-dynamic force causing the stationary ring to separate and create a gap between the two rings. Dry gas seals are mechanical seals but use other chemicals and functions so that they do not contaminate a process. These seals are typically used in a harsh working environment such as oil exploration, extraction and refining, petrochemical industries, gas transmission and chemical processing.

The dry gas seal has spiral grooves, with provides for lifting and maintaining separation of seal faces during operation. Grooves on one side of the seal face direct gas inward toward a non-grooved portion of the face. The gas that is flowing across the face generates a pressure that maintains a minute gap between the faces, optimizing fluid film stiffness and providing the highest possible degree of protection against face contact. The seal's film stiffness compensates for varying operations by adjusting gap and pressure to maintain stability.

Contents

Design and use

Grooves on the seal direct gas inward toward the non-grooved portion. The action of the gas flowing across the seal generates pressure that keeps a minute gap, therefore optimizing fluid film stiffness and providing protection against face contact.[1][2]

The use of these seals in centrifugal compressors has increased significantly in the last two decades because they eliminate contamination and do not use lubricating oil. Non-contacting dry gas seals are often used on compressors for pipelines, off-shore applications, oil refineries, petrochemical and gas processing plants.[3] Dry Gas Seal configurations: there are many dry gas seal configurations base on their application. 1- Single gas seal 2- Tandem gas seal 3- Tandem gas seal with intermediate labyrinth 4- Double opposed gas seal

Also the dry gas seal can be unidirectional or bidirectional.

History

John Crane Inc. issued the first patent for dry gas seals in 1968 with field applications beginning in 1975. When the technology was introduced, it was aimed at correcting the problems with dry gas film environments by eliminating friction. Soon, the technology became a common replacement for other lubricated seals. The patented spiral-groove technology of the dry gas seal allows for easy lifting and separation of seal faces during operation. There are three common types of lubrication for these seals: full liquid film, which contains oil and requires light-duty conditions; partial liquid/gas film, which requires a 50 percent balance of liquid to preserve the seal; and dry gas film, which has an absence of liquid that creates hot localized areas that may lead to cracking or damage to the seal. Seal failure results from a flooded compressor with oil or liquid, foreign contaminants and alignment problems.[4][5]

See also

  • Hydrogen turboexpander-generator

References


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