Pump troubleshooting: Size up a tall order

An elevated vessel may provide a worthwhile alternative to a booster pump

By Andrew Sloley and Scott Schroeder for Chemical Processing

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Fixing pump suction head problems can cost a lot, as a recent experience illustrates. In this case, a site added a new unit to compress gas for sending via pipeline to a client. The specification stated the inlet gas would be liquid free. The initial assumption was that a small amount of liquid condensation would occur in the compressor inter-stage coolers. Inter-stage knockout drums would remove the condensate.

After startup, the knockout drums filled rapidly. The liquid rate exceeded the system’s handling capacity. Temporary measures included pumping the liquid into trucks for handling. The liquid pumps suffered short lives and high failure rates. The situation clearly was both unsatisfactory and unsustainable.

Lack of understanding composition variability in the feed gas to the compressors caused this problem. The gas came from multiple sources that each had highly variable compositions. About the only stable factor was the absence of free liquid. Sometimes, very little of the gas would condense in the inter-stages while, other times, large quantities condensed.

Investigation showed that composition variability was inherent in the system and wouldn’t change. Control systems move variability from where it has a large effect to where the effect is smaller. Here, all the variability ends up in that gas stream. This is the best option for the plant as a whole but poses a problem the engineers handling the gas stream must solve.

Read the full story at chemicalprocessing.com.

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