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Research Papers

Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation

[+] Author and Article Information
Ümit Mermertas

Siemens AG Power and Gas Division,
Rheinstr. 100,
Mülheim an der Ruhr 45478, Germany
e-mail: uemit.mermertas@siemens.com

Thomas Hagemann

Mem. ASME
Institute of Tribology and Energy
Conversion Machinery,
Clausthal University of Technology,
Leibnizstr. 32,
Clausthal-Zellerfeld 38678, Germany
e-mail: hagemann@itr.tu-clausthal.de

Clément Brichart

Engie Laborelec,
Rodestraat 125,
Linkebeek 1630, Belgium
e-mail: clement.brichart@engie.com

1Corresponding author.

Manuscript received July 3, 2018; final manuscript received July 17, 2018; published online October 29, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(2), 021033 (Oct 29, 2018) (10 pages) Paper No: GTP-18-1430; doi: 10.1115/1.4041116 History: Received July 03, 2018; Revised July 17, 2018

Modernization of steam turbine components can extend power plant lifetime, decrease maintenance costs, increase service intervals, and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the applied advanced modeling methods and performed validation for the optimization of a novel 900 mm three-pad tilting pad journal bearing that showed high temperature sensitivity to the fresh oil supply temperature. The bearing was developed to cope with increased rotor weights within the low pressure (LP) steam turbine modernization at two 1000 MW nuclear power plants. With a static load of 2.7 MN at a speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed considering the direct lubrication at the leading pad edge and pad deformation. The results of the entire analyses indicated modifications of bearing clearances, pad length, thickness, and pivot position. The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55 °C. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for turbomachinery.

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References

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Figures

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Fig. 1

Conventions for the 2D numerical implementation

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Fig. 2

Schematic view of steam turbine generator rotor train (1500 rpm, approximately 1000MW)

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Fig. 3

(a) and (b) Pad configuration of the existing (a) and new (b) bearing 3 (schematic)

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Fig. 4

Location of the thermocouples on the lower pads (schematic)

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Fig. 5

Location of the displacement sensors on the back of the lower pads (schematic)

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Fig. 6

Simplified bearing model

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Fig. 7

Measured displacement of the left pad during the fresh oil supply temperature test

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Fig. 8

Advanced bearing model

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Fig. 9

Impact of pad fresh oil flow rate on maximum temperature and minimum oil film thickness (initial design of new bearing 3)

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Fig. 10

Computation loop for co-simulation between THL code and structural mechanics software

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Fig. 11

Predicted oil film thickness of lower pads with and without deformation at the axial bearing center (initial design of new bearing 3)

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Fig. 12

Predicted oil film thickness of lower pads at the axial bearing center (initial design of new bearing 3)

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Fig. 13

Predicted oil film thickness of right pad at the circumferential position of minimum oil film thickness (initial design of new bearing 3)

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Fig. 14

Predicted oil film thickness of lower pads at the axial bearing center (optimized design of new bearing 3)

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Fig. 15

Predicted oil film thickness of right pad at the circumferential position of minimum oil film thickness (optimized design of new bearing 3)

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Fig. 16

Predicted pad temperature on the sliding surface at the axial bearing center (initial design of new bearing 3)

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Fig. 17

Predicted pad temperature on the sliding surface at the axial bearing center (optimized design of new bearing 3)

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Fig. 18

Measured displacement of the left pad of the optimized bearing during the fresh oil supply temperature test

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Fig. 19

(a) and (b) Photos of lower pads of the optimized bearing after 18 months of operation; left pad (a) and right pad (b)

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Fig. 20

Comparison of maximum measured and predicted pad temperature for the optimized bearing on both units

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Fig. 21

Measured and predicted pad temperature beneath the sliding surface (optimized bearing, Tsup = 42 °C)

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Fig. 22

Measured and predicted pad temperature beneath the sliding surface (optimized bearing, Tsup = 45 °C)

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Fig. 23

Measured and predicted pad temperature beneath the sliding surface (optimized bearing, Tsup = 50 °C)

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Fig. 24

Measured and predicted pad temperature beneath the sliding surface (optimized bearing, Tsup = 55 °C)

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