Session: 21-07 Mechanical Integrity and Materials for Steam Turbines

Paper Number: 103823

103823 - Preliminary Wear Investigations With Pressure Actuated Leaf Seals for Superheated Steam Turbine Application 

The change in the operation of classic steam power plants caused by renewable energies away from long-term full load to partial load and load changes requires changes to turbine components such as seals. Inflexible sealing systems, e. g. the classic labyrinth, reach their limits in terms of efficiency and leakage reduction and must be replaced by adaptive seals in the future.

Pressure-actuated leaf seals, which are based on sealing by means of pressure-deflected leaves, can provide a remedy here by leaving a comparatively large radial gap during low-load operation, especially when starting up or shutting down a turbine, while they are deflected to the maximum under full load and are intended to ensure minimum leakage. It is even possible to design them with a slight overlap of leaves and shaft at the beginning, which then grinds in during operation.

The first objective is a basic understanding of the operating behaviour of the seal as a function of the rotational speed and the applied pressure difference. Additionally, it is absolutely necessary to investigate the wear behaviour both on the shaft and on the seal if an overlapping design is given. A clear distinction must be made between centric wear and wear caused by a slightly eccentric shaft position, which also occurs in practice during load changes.

The question was investigated by means of tests on a compressed air seal test bench which will serve as preparation for later superheated steam tests. Two different shaft diameters (299.60 and 299.88 mm) were tested at up to 3,000 rpm and 7.0 bar pressure difference. In this way, the tests on general operating behaviour and wear behaviour could be strictly separated. The wear tests with the larger shaft were then first carried out concentrically and with a gradual increase in pressure, i.e. also wear-in. This was followed by tests with abrupt pressurisation in a concentric set-up. For the eccentric wear tests, the shaft position was radially shifted by 0.1/0.2/0.3 mm relative to the seal. During the tests, in addition to the leakage, the frictional torque and the temperature of certain leaves in the shaft contact were measured. Finally, the depth of the resulting grooves in the shaft and the change in length of the leaves were measured.

Firstly, it can be seen that the rotational speed has no relevant effect on the leakage in the examined range. Secondly, it could be shown that with gradual pressurisation, as with moderate start-up of a turbine, the sealing system behaves robustly and does not generate high frictional torques or temperature peaks while the material is gradually removed. Only in the case of pressure surges can stronger effects be demonstrated. Overall, the overlap of leaves and shaft is worked off, but no further clear gap is generated under full load, with wear being divided approximately 3:1 between leaves and shaft. This finding is similar in the eccentric tests, where the seal wears further on the corresponding side and the shaft running track deepens further.

Presenting Author: Andreas Wittenberg TU Braunschweig - Institute of Jet Propulsion and Turbomachinery

Presenting Author Biography: 2010: graduated from high school
2010/11: military service at Bundeswehr
2011: internship at ThyssenKrupp Steel Europe (steel production and practical work at workshop)
2013/14: president of a Germany-wide catholic fraternity association
2016/17: Internship and Bachelor thesis at MAN Energy Solutions (development of diesel engines for trucks)
2017: graduated as Bachelor of Science in Mechanical Engineering at RWTH Aachen University
2017/18: exchange semester at University of Linköping, Sweden
2019: graduated as Master of Science in Energy Engineering (Turbomachines and Jet Propulsion) at RWTH Aachen University
since 2019: Research Assistant at TU Braunschweig, Institute of Jet Propulsion and Turbomachinery
Current topics: research project in sealing technology for hot steam turbines, experimental and numerical analysis of radially adaptive seals for load-follow operation of power plants and turbines; teaching and examination of Master students in Aircraft Engines
2022: first scientific publication at International Symposium of Unsteady Aerodynamics, Aeroacustics and Aeroelastics in Turbomachines (ISUAAAT) at Toledo, Spain (topic: leaf oscillations at Pressure Actuated Leaf Seals)

Authors:

Andreas Wittenberg TU Braunschweig - Institute of Jet Propulsion and Turbomachinery
Tobias Rühle Siemens Energy AG
Johannes Greving MAN Energy Solutions SE
Florian Wichern TU Braunschweig - Institute of Jet Propulsion and Turbomachinery
Jens Friedrichs TU Braunschweig - Institute of Jet Propulsion and Turbomachinery