Dry gas seals are used in process gas centrifugal compressors. It is necessary to have shaft sealing to prevent the process gas from escaping to the atmosphere. Dry gas seals can be applied to accomplish the required shaft sealing and although available in a variety of configurations, a tandem style seal is typically applied within a process gas service.
Tandem seals consist of a primary seal and a secondary seal. During normal operation the primary seal absorbs the total pressure drop to a vent system and the secondary seal acts as a back-up should the primary seal fail. Dry seals are basically mechanical face seals, consisting of a mating (rotating) ring and a primary (stationary) ring. During operation, grooves in the mating ring generate a fluid-dynamic force causing the primary ring to separate from the mating ring and create a running gap between the two rings. A sealing gas is injected into the seal, providing the working fluid for the running gap and the seal between the atmosphere or flare system and the compressor internal process gas.
It is necessary for the high pressure seal gas to be heated to ensure the removal of moisture and prevent condensation within the seal. EXHEAT heaters are typically used within this generally high pressure application