TABLE OF CONTENTS The compressor operator must provide a source for seal gas to be supplied to the compressor gas seal system. There are three areas of concern when evaluating potential sources of seal gas supply: gas pressure, quality, and composition.
The seal gas source must be available at a pressure slightly higher than the required sealing pressure across the entire operating range of the compressor, including transient conditions such as startup, shutdown, idle, and static (nonrotating). Although exactly how much higher depends on many specific factors, 50 psi above the required sealing pressure at the customer connection point on the gas seal system is usually sufficient to allow adequate regulation of the seal gas. For tandem gas seal applications, it is quite common to employ the compressor discharge as the sole source of seal gas. On the surface, this may appear to be a very sound practice, because compressor discharge pressure is obviously higher than compressor inlet pressure (normal sealing pressure). However, this design does not address transient conditions such as startup, shutdown, or idle. During these transient conditions, there is usually insufficient pressure rise across the compressor to allow for a continuous positive flow of seal gas into the seals. An alternate seal gas source or seal gas pressure boosting equipment is required in this case. The availability of the seal gas source at sufficient pressure is one concern for all types of dry gas seals, including double opposed and tandem with intermediate labyrinth.
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