Reaching the target in an innovative way
Keeping NGL (Natural Gas Liquid) pipeline components operating in optimal condition is an ongoing challenge for the oil and gas industry. Rising temperatures in the liquid pumps and the resulting issues for their seals represent one such challenge.
A facility in Houston, Texas separates mixed NGL streams into pure NGL products such as ethane, propane, butane, isobutene and gasoline. Critical components in this system include the ethane injection pumps operating at pressures from 28 bar (410 PSI) to 76 bar (1,100 PSI). The ethane temperature at the suction port must not exceed 16 °C (60 °F) to ensure that the specific vapor pressure never drops below the required values at the shaft seals.
Unfortunately, significant temperature rises are a frequent issue due to atmospheric conditions - then the ethane vaporizes, resulting in seal failure and loss of product. The solution for an increasingly failure-prone liquid ethane pump was to use an EagleBurgmann DF-DGS6. This is a mechanical seal with DiamondFace-bonded seal faces that was actually designed for purely gaseous media.
An unconventional approach: Dry gas seals for sealing liquids
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.
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, EagleBurgmann has developed and successfully applied dry gas seals with an innovative diamond technology on the seal faces.
The key is the DiamondFace Technology
EagleBurgmann DiamondFace is a microcrystalline diamond technology 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.
DF-(P)DGS6 – the 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 DiamondFace technology 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 EagleBurgmann 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 5 years are now feasible with the DF-(P)DGS6 solution.
Over 150 EagleBurgmann 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.