TABLE OF CONTENTS Dry gas seals are available in a variety of configurations, including single, tandem, tandem with intermediate labyrinth, triple, and double opposed. Triple gas seals were used in the past when tandem gas seals were incapable of meeting the demands of high pressure sealing applications. However, the state-of-the-art tandem gas seal designs have essentially rendered the triple gas seal configuration obsolete, so the triple seal is not discussed in this book. Explanations of the remaining gas seal configurations follow, and a gas seal application flowchart is included in Appendix D.
A single gas seal (fig. 3-1) consists of a single mating ring and primary ring assembly. Inboard of the dry gas seal is an inner labyrinth seal, which separates the process gas from the gas seal. A clean and dry sealing gas is injected between the inner labyrinth seal and the gas seal, providing the working fluid for the seal running gap. The vast majority of this injected gas flows across the inner labyrinth seal and into the compressor, or "process" side of the gas seal. A very small amount of the sealing gas (the seal leakage) passes through the primary seal and out the primary vent, which is normally connected to the user's flare system.
Outboard of the dry gas seal is a barrier seal, which separates the gas seal from the compressor shaft bearings. A separation gas (typically nitrogen or air) is injected into the barrier...
