Dry Gas Seals – Seal gas back-up supply for compressor discharge seal gas during idling

At slow roll speeds or even when stopped, there may be enough gas force to provide lift-off of the primary seal faces. Current gas seal designs are pressure balanced to provide hydrostatic lift-off at a target pressure without rotation, in order to minimize rub damage on start-up. Without sufficient discharge pressure to provide seal gas flow, compressor gas stream particulates can enter the seal faces during idle time and cause damage once rotating speeds are sufficient. In order to prevent this contamination, an external seal gas supply can be used, again with proper attention to liquid removal requirements. As an alternative, packaged pressure boosting systems can be used to raise the seal gas pressure when compressor discharge pressure is inadequate. Either alternative should be designed for automatic cut-in, as discharge pressure falls. Note that a back-up seal gas supply may not be necessary if the compressor is not capable of slow roll, sealing pressure is below the hydrostatic lift-off pressure, and the process gas is relatively clean.

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