Application of Dry Gas Seals in the Pumping of Liquid Hydrocarbons

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DÜPERTHAL Sicherheitstechnik GmbH & Co. KG

An Unconventional Approach: Dry Gas Seals

The team of experts from Eagle Burgmann hit upon a surprising and unconventional idea. Why not leverage the properties of a type of seal that is actually designed for sealing compressors, i.e. for gases?

Dry gas seals (DGS) have proved extremely reliable as shaft seals in compressor applications. They have broad sealing surfaces that incorporate structured (uni/bi-directional) gas grooves. These grooves allow lift-off of the seal faces and non-contacting operation. As with liquid-lubricated seals, where dry running can damage the seal faces, with dry gas seals it is the contact of the seal faces that leads to premature wear and ultimately to failure of the seal.

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This is because seals in compressors also have critical operating states. Coast-down (slow, controlled compressor run-out), turning (running at low speeds) and ratcheting (turning the shaft a further 90° at set intervals) all cause the seal faces, which are separated from one another under normal conditions, to come into contact. It is this contacting operation that can result in damage to the faces.

To overcome just these situations, Eagle Burgmann has developed and successfully applied dry gas seals with an innovative diamond bonding on the seal faces. The Diamond Face is a microcrystalline diamond bonding for mechanical seals. It is extremely hard and wear-resistant, offers excellent heat conductivity, maximum chemical resistance and low friction. The bonding adhesion also exceeds all known practical requirements. This demonstrably increases the service life of mechanical seals several times over; the maintenance intervals are extended accordingly and the life cycle costs greatly reduced.

Solution for Highly Volatile Media

The ethane pump in Houston was retrofitted with the DF-DGS6 and brought into service in July 2011. The solution sealed the medium reliably and safely in both the liquid and the gaseous state. In transient conditions that can result in dry running and contact of the seal faces, the Diamond Face bonding on the faces protects the seal against damage.

The mode of operation was also simplified: The seals require no flushing (API Plan 02). The previously-used filters can be omitted — so do not have to be maintained.

After a few months, the operator reported that ethane gas leaking to the flare system had dropped by 83 %, a value that improved even further to more than 90 %. After eight months, the pump was stopped and opened for remedial work on the impeller. The operator wanted the seal to undergo dynamic testing at the same time so the results could be compared with the original data. The seal was removed and tested at Eagle Burgmann Houston. The seal faces showed no signs of scoring whatsoever. They looked as good as new. The sealing components were cleaned and reassembled. The DF-DGS6 was then extensively tested on a dynamic test rig. The seal was in perfect condition and delivered excellent results (with a leakage rate below the value determined in the acceptance test), so the operator immediately reinstalled it in the pump with no further work.

The seals have been running without problems ever since. Operating periods in excess of five years are now feasible with the DF-(P)DGS6 solution. Over 150 Eagle Burgmann DF-(P)DGS6 seals (“P” stands for the high pressure version) are now being used successfully in many different NGL applications worldwide — more recently even in CO₂ applications.

* The author is Dep. Head of Group Marketing, Eagle Burgmann Germany GmbH & Co. KG, Wolfratshausen/Germany.

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