Stop the Domino Effect
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When a million dollar piece of turbomachinery shuts down at an LNG plant as the result of a cascading trip, it causes a domino effect of problems that go well beyond machine or process malfunction. Not only does a hard shutdown of a machine under full load decrease the lifespan and components of the machine due to the stress associated with the shutdown, the extra length of time required to get an LNG train back online causes considerable delays in production and significant profit loss. Avoiding the scenario altogether is the ideal solution.
Compressor Controls Corporation (CCC) was recently tasked with helping an LNG plant with interdependent compressor strings create a control system modification in which the compressors could operate with more independence, avoiding unnecessary machine trips caused by surge and excessive recycle that could overload the compressor drivers. The client’s LNG plant design included a four-stage sidestream Propane compressor, and a three-stage Mixed Refrigerant (MR) compressor, with the finalstage of the MR train — the HP stage — located on the same driver shaft as the propane compressor. Both compressor strings operate at near constant speed with an underspeed trip setting very close to normal operating speeds. This split-shaft design was created to better balance power between the two compressor strings.