Centrifugal Compressor Labyrinth Seal Systems

Abstract

For years, labyrinth shaft-end seals have been used for centrifugal compressors handling air and nonhazardous gases, and for low suction pressure compressors in hydrocarbon service. To prevent gas leakage from the hydrocarbon machines, either injection of inert gas or jet ejector systems have been applied with the seals. The ejectors were normally arranged to exhaust back to the compressor suction. Early application of labyrinth/ejector seal systems were generally on compressors with suction pressures in the 0-8psig range, and the seal system operation was generally satisfactory. Many of the older machines have been uprated to higher suction pressures. The labyrinth/ejector seal systems have been applied to newer compressors with suction pressures as high as 15 psig. Many of the systems do not perform satisfactorily, and operators complain of leakage of hydrocarbons and contamination of the lube oil. This may be the result of noncritical-flow ejectors operating with critical pressure ratios. Labyrinth/ejector seal systems can be designed to perform satisfactorily with the higher compressor suction pressures, but these systems often require critical-flow ejectors. Despite their relatively low initial cost, the economics of labyrinth/ejector seal systems for high compressor suction pressures may not compare favorably with oil-type seal systems because of the energy required to recycle motive gas.