399149 Planning Early for Compressor Surge Avoidance

Wednesday, April 29, 2015: 1:30 PM
14 (Austin Convention Center)
Nicolas F. Ponchaut and Harri K. Kytomaa, Exponent, Inc., Natick, MA

Compressor stations are installed at regular interval to drive the flow of gas in a pipeline.  The principal component of the compressor station is the compressor itself and its drive.  The station is also equipped with recycle lines, recycle valves, check valves, isolation valves and coolers.  All of these need to be carefully selected or designed to ensure adequate compressor station operations, particularly in off-design conditions.  Pipeline compressors are typically centrifugal compressors since they allow the continuous compression of large volumes of gas.  These suffer from the drawback of their potential for surge, especially during emergency shut downs.

Surge occurs when the flow through the compressor drops below a critical level.  During surge, the flow of gas can reverse completely, large and rapid pressure fluctuations can occur, which can induce significant mechanical stresses and forces.  Repeated surge events are expected to cause cumulative damage to compressor systems and associated equipment such as check valves and ball valves, while surge with full flow reversal can cause immediate damage.  For these reasons, compressor stations are designed in such a way that surge events are either minimized or even completely avoided.

The success of a design will depend on the details of the control system (SCADA) and on the appropriate selection of a recycle valve, of the size and length of the recycle line(s), of the compressor and of its drive.  Successfully designing a compressor station to avoid surge can be challenging and in order to minimize design updates, surge has to be considered in the very early stages of the station design.  Although full transient analyses should always be performed to test the adequacy of a design, the current work presents a few rules of thumb that should be followed in the very early stages of the design process.  These simple considerations are able to identify design flaws that need to be addressed before further development.

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