RoTechBooster for pipeline compressors

The Alliance Pipeline is a 2,300 mile line delivering rich gas from North East British Columbia, Canada and the Williston Basin in North Dakota to the Chicago market, USA. The pipeline system’s success is based on low maintenance costs, high reliability, minimum fuel usage, application of best practices, direct access to manufacturers’ technology, and strategic alliances and partnerships to resolve technical issues.

All of these factors are critical for the pipeline to meet owners’ expectations and profitability. Reduced gas volumes due to poor compressor reliability result in losses for all parties involved.

Strategic alliances with key providers such as EagleBurgmann are contributing factors for Alliance Pipeline’s success. EagleBurgmann PDGS seals are installed in the pipelines’ 30 compressor stations across Canada (e.g. Windfall, Morinville) and the US (e.g. Tampico).

The pipeline was operated very successfully for more than 12 years until a new major gas stream with compositional differences in the NGL was brought on line. Dry gas seals are more susceptible to liquid contamination and failures when heavier hydrocarbons are present in the process or transported gas. As a result of the new gas stream composition, dry gas seal failures increased from a historic zero to one per year to 14 failures in one year.

Two failure modes were identified: liquid contamination from the seal gas supply during normal operation and contamination from the process (compressor casing) shortly after start-up. Together Alliance and EagleBurgmann identified causes for the increased seal failures, developed solutions and implemented the best technology to solve the problem.

Seal gas supply is taken from the discharge line in pipeline compressors, which is at a higher pressure than the internal casing pressure. During start up conditions the discharge line is at the same pressure as the internal casing pressure, so no clean seal gas is provided to the dry gas seal. This allows contamination to enter the seals reducing their reliability and leading to premature dry gas seal failures.

With the presence of heavy hydrocarbons the gas dew point also becomes an issue. When the discharge gas is at normal operating temperatures the components in the gas are gaseous. As the pressure and/or temperature of the gas are lowered some of these components will precipitate into liquids.

The discharge gas passing through lines to the seal gas panel also lowers the gas temperature, as the ambient temperature cools these lines. The gas pressure is regulated down to the sealing pressure, which is typically just above suction pressure.

This results in additional temperature and pressure reduction causing components in the gas to turn to liquid. Depending on the types of filtration in a seal gas system limitations can be present for the amount of liquids they can handle, which was the case for the Alliance filters.

The next piece in dealing with the heavy hydrocarbons is the seal itself. The pressure drops from the sealing pressure down to almost atmospheric pressure as it passes across the seal faces. As the pressure drops across the seal faces components in the gas can turn to liquid, which sooner or later results in seal failures.