Dry Gas Seals Application of Dry Gas Seals in the Pumping of Liquid Hydrocarbons

Author / Editor: Georg E. Probst / Dr. Jörg Kempf

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.Learn how you can profit from dry gas seals.

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Sulzer ethane pump in an NGL fractionation facility in Houston, Texas. The pump and seal have been running without interruption since conversion to the innovative Eagle Burgmann DF-DGS6 sealing solution in 2011.
Sulzer ethane pump in an NGL fractionation facility in Houston, Texas. The pump and seal have been running without interruption since conversion to the innovative Eagle Burgmann DF-DGS6 sealing solution in 2011.
(Picture: Eagle Burgmann)

One case experienced at an NGL fractionation facility in the US shows how seal failures when pumping hydrocarbons close to the specific vapor pressure can be analyzed, resulting in durable and sustainable design solutions. This 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.

Gallery

The solution for an increasingly failure-prone liquid ethane pump was to use an Eagle Burgmann DF-DGS6. This is a Diamond Face- bonded mechanical seal that was actually designed for purely gaseous media. This innovative sealing concept has since proved to be a reliable and durable solution for media with low vapor pressures. There are now many seals of this type in the field around the world. They replace liquid-lubricated seals which cannot handle critical operating conditions and phase transitions.

Why Liquid-lubricated Pump Seals Fail

The possibility of transient conditions in the pumped medium is frequently ignored when operating rotating equipment. But it is important to correctly assess the conditions for the sealing system in the start phase and in slow-roll or standby operation and to make sure that sufficient lubricating liquid is supplied to the shaft seal’s faces at all times.

Evaluation of the different phases illustrates the factors that affect a mechanical seal’s reliability — Please continue reading on the next page ...

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