Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Differential Expansion Sensitivity Studies During Steam Turbine Startup

[+] Author and Article Information
Monika Topel

Department of Energy Technology,
Royal Institute of Technology,
Stockholm SE-100 44, Sweden
e-mail: monika.topel@energy.kth.se

Markus Jöcker

Siemens Industrial Turbomachinery AB,
Finspång SE-612 83, Sweden
e-mail: markus.jocker@siemens.com

Sayantan Paul

Siemens Ltd.,
Gurgaon 122 015, India
e-mail: sayantan.paul@siemens.com

Björn Laumert

Department of Energy Technology,
Royal Institute of Technology,
Stockholm SE-100 44, Sweden
e-mail: bjorn.laumert@energy.kth.se

1Corresponding author.

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 24, 2015; final manuscript received September 17, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 062102 (Nov 17, 2015) (8 pages) Paper No: GTP-15-1419; doi: 10.1115/1.4031643 History: Received August 24, 2015; Revised September 17, 2015

In order to improve the startup flexibility of steam turbines, it becomes relevant to analyze their dynamic thermal behavior. In this work, the relative expansion between rotor and casing was studied during cold-start conditions. This is an important property to monitor during startup given that clearances between rotating and stationary components must be controlled in order to avoid rubbing. The investigation was performed using a turbine thermal simplified model from previous work by the authors. The first step during the investigation was to extend and refine the modeling tool in order to include thermomechanical properties. Then, the range of applicability of the model was validated by a twofold comparison with a higher order finite element (FE) numerical model and measured data of a cold start from an installed turbine. Finally, sensitivity studies were conducted with the aim of identifying the modeling assumptions that have the largest influence in capturing the correct thermal behavior of the turbine. It was found that the assumptions for the bearing oil and intercasing cavity temperatures have a large influence ranging between ±25% from the measured values. In addition, the sensitivity studies also involved increasing the initial temperature of the casing in order to reduce the peak of differential expansion. Improvements of up to 30% were accounted to this measure. The studies performed serve as a base toward further understanding the differential expansion during start and establishing future clearance control strategies during turbine transient operation.

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Fig. 1

Dynamic transient thermal modeling scheme

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Fig. 2

Geometric blocks in the heat transfer model superimposed over an axisymmetric view of the turbine (not to scale)

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Fig. 3

Turbine geometry as defined by the modular approach (not to scale)

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Fig. 4

Measured data of cold-start inlet conditions

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Fig. 5

Mid-casing temperature at axial location near the turbine inlet of thermal model and measured data

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Fig. 6

Differential expansion at exhaust axial location of turbine in thermal model and measured data

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Fig. 7

Theoretical cold-start inlet conditions

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Fig. 8

The 2D-WO version of turbine geometry (not to scale)

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Fig. 9

Inner and outer casing temperatures at axial location near the turbine inlet for three thermal models

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Fig. 10

Differential expansion at turbine exhaust for three thermal turbine models

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Fig. 11

Sensitivity of differential expansion to bearing oil and cavity steam heat transfer conditions

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Fig. 12

Measurement locations of axial displacement in turbine geometry (left). Individual differential expansion at measurement locations for time instants in the vicinity of the peak value of differential expansion during rolling up (right).

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Fig. 13

Reduction of the maximum differential expansion due to global and localized casing initial temperature increase




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