Improvement of Conventional Seals for Stator-Rotor Cavities of Heavy-Duty Gas Turbines by Application of Interstage Brush-Seals

Abstract

In order to achieve significant secondary air savings in heavy duty gas turbines, a remarkable item of improvement is the reduction of seal flows for turbine stator-rotor cavities. The optimization of such flows allows to avoid waste of air, obligatory with standard labyrinth seals, to ensure the minimum sealing flow rate in all operating conditions. Based on the experience gained in the design of sealing system of stator-rotor cavities with standard seals, the project of installation of inter-stage brush-seals was undertaken incorporating such devices into the vane seal rings of 2nd and 3rd turbine stages of a AE94.3A Gas Turbine (GT). The paper offers a detailed description of the installation project. The following describes in detail the design flow process and the calculation methodologies used, step by step, to define the geometry of brush-seals in order to ensure mechanical integrity and durability, needed in the commercial operation, without thereby affecting the performance. The first prototype of brush-seal devices has been installed on a AE94.3A4 unit of the Ansaldo fleet. In order to verify the behavior of stator-rotor sealing system, in particular in terms of temperature and pressure variations, vane seal rings have been equipped with special instrumentation. A series of tests to optimize the set points of bleed control valves was carried out.

Brush seal design and secondary air system modification of a heavy-duty gas turbine to improve the output power

“…For instance, brush seals are applied in the second and third inter-stages of a four-stage gas turbine. 29 The published data show that leakage flow is lessened by about 30% for each inter-stage. Two locations for brush seal installation are examined: upstream and downstream of the diaphragm.…”