The overall efficiency of gas turbines is strongly affected by the performance of the sealing arrangement between the stationary and rotary components. Maintaining an accurate clearance during nominal and transient operation and providing effective damping is of key importance for seal designers. The implementation of brush seals as an alternative to labyrinth seals in a gas turbine engine is outlined in this article. A review of published literature is performed to analyze the leakage performance of brush seals and labyrinth seals. The emphasis lies on the importance of an accurate clearance control and the subsequent reduction in parasitic flows. Based on a discussion of the performance and integrity of brush seals in gas turbine applications their advantages over labyrinth seals are highlighted. Some attention is drawn into common drawbacks of brush seals and how these were improved over time to become more competitive and reliable. Finally, advanced concepts, technological aspects of the design of the brush seals influencing their leakage characteristics and future applications prospective are discussed. It was shown that one of the key advantages of brush seals over conventional labyrinth seals is their positive rotordynamic characteristic. The rotordynamic force coefficients demonstrate very low and generally negative cross-coupled stiffness thereby positively affecting the turbomachine operability in industrial gas turbine applications. The review concluded the need for further work on studying rotordynamic behaviour of brush seals operating at conditions more realistic to real engine operation environment in order to complete the understanding of the seal dynamics in real operation condition.

Although the use of dry gas seals (DGSs) in process centrifugal compressors has become an industry standard since the 1980s end users are still facing operational issues related to premature failures which incur significant maintenance and operational costs. It has been recognized that the majority of the failures are due to a lack of properly conditioned seal gas and this has driven more recent development of Gas Conditioning Units (GCUs) to deliver appropriate quantities of clean, superheated gas to the seal at the required pressure. However, there are a large number of operating units where retrofit of a GCU represents significant cost and engineering challenge. The aim of this paper is to share some recent experience of a DGS reliability improvement program that does not involve retrofitting a GCU. A basic introduction to DGS operating principles and an overview of DGS design and control issues is also included with a focus on tandem seals in high-pressure natural gas compression applications.

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