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Research Papers: Gas Turbines: Turbomachinery

Aerodynamic Analysis of Steam Turbine Feed-Heating Steam Extractions

[+] Author and Article Information
Budimir Rosic

Mem. ASME
Osney Thermo-Fluids Laboratory,
Department of Engineering Science,
Oxford University,
Southwell Building,
Osney Mead,
Oxford OX2 0DP, UK
e-mail: budimir.rosic@eng.ox.ac.uk

Cosimo Maria Mazzoni

Mem. ASME
Osney Thermo-Fluids Laboratory,
Department of Engineering Science,
Oxford University,Southwell Building,
Osney Mead,
Oxford OX2 0DP, UK
e-mail: cosimo.mazzoni@eng.ox.ac.uk

Zoe Bignell

Beaumont Leys School,
Anstey Lane,
Leicester LE4 0FL, UK
e-mail: czrimmer@gmail.com

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 27, 2014; final manuscript received April 22, 2014; published online May 16, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(11), 112602 (May 16, 2014) (10 pages) Paper No: GTP-14-1170; doi: 10.1115/1.4027569 History: Received March 27, 2014; Revised April 22, 2014

Feed-heating in steam turbines, the use of steam extracted from the turbine to heat the feed-water, is known to raise the plant efficiency and so is included in most steam turbine power plant designs. The steam is extracted through an extraction slot that runs around the casing downstream of a rotor blade row. The slot is connected to a plenum, which runs around the outside of the turbine annulus. Steam flows to the feed-heaters through a pipe connected usually to the bottom of the plenum. The steam extraction is driven by a circumferentially nonuniform pressure gradient in the plenum. This causes the mass flow rate of steam extracted to vary circumferentially, which affects the main passage flow downstream of the extraction point. The flow in the extraction plenum and the influence of the steam extraction on the mainstream aerodynamics is analyzed numerically in this paper. A complete annulus with the extraction slot and plenum together with the downstream stator and rotor blade rows is modeled in this study. The results reveal a highly nonuniform steam extraction around the annulus with the highest extraction rates from the bottom nearest the extraction pipe and the lowest at the top of the annulus. This difference in extraction rates modifies the flow angle and loss circumferential distribution downstream of the stator blade row. This study finds out that the distribution of steam extraction around the annulus and its influence on the main passage flow could be greatly improved by changing the shape and increasing the volume of the extraction slot and plenum.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

A block diagram of a typical steam turbine power plant with seven regenerative heaters for feed-heating and a typical expansion turbine line in the h-s diagram [2]

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Fig. 2

Relative gain in specific heat consumption for steam turbine power plant with a different number of regenerative heaters

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Fig. 3

Axial cross section of AD700 Siemens IP steam turbine showing steam extraction points (left) [4]. A schematic of steam extraction geometry (right).

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Fig. 4

Sketches of different plenum chamber shapes that can be found in modern steam turbines

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Fig. 5

TBLOCK computational flow domain

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Fig. 6

TBLOCK block decomposition and grid details

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Fig. 7

Measured and predicted pitchwise averaged (a) axial velocity and (b) absolute yaw angle downstream of stator

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Fig. 8

Measured and predicted total pressure coefficient Cp0T contours downstream stator

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Fig. 9

Radial velocity distribution in the extraction slot and plenum

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Fig. 10

Flow field in the extraction plenum at the top part for the annulus

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Fig. 11

Flow field in the extraction plenum at the bottom part of the annulus

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Fig. 12

Total pressure loss coefficient contours around the annulus downstream of stator blade row: (a) with clean end walls, (b) with uniform extraction, and (c) with real extraction geometry with plenum end extraction pipe at the bottom of the annulus

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Fig. 13

Streamlines at the casing end wall in the case with clean end walls (a) and with extraction (b) in passages at the bottom of the annulus close to the extraction pipe

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Fig. 14

Predicted yaw angle distribution downstream of the stator blade row for the case with clean end walls (a) and for the case with the real extraction geometry (b) for three different circumferential locations

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Fig. 15

Pitchwise averaged yaw angle distribution for four different passages downstream of the stator trailing edge

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Fig. 16

Fluid extraction around the annulus for three different extraction plenum volumes

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Fig. 17

Fluid extraction around the annulus for a geometry with a variable extraction slot width

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Fig. 18

Fluid extraction around the annulus for the improved extraction geometry

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Fig. 19

Total pressure loss coefficient contours around the annulus downstream of stator blade row for the case with the improved extraction geometry

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