Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Experimental and Numerical Investigation Into the Aerodynamics of a Novel Steam Turbine Valve and Its Field Application

[+] Author and Article Information
Giorgio Zanazzi

Alstom Power,
Brown Boveri Str. 7,
Baden 5400,Switzerland
e-mail: giorgio.zanazzi@power.alstom.com

Timothy Rice

Alstom Power,
Newbold Road,
Rugby CV21 2NH, UK
e-mail: tim.rice@power.alstom.com

Michael Sell

Alstom Power,
Brown Boveri Str. 7,
Baden 5400, Switzerland
e-mail: michael.sell@power.alstom.com

Colin Ridoutt

Alstom Power
Brown Boveri Str. 7,
Baden 5400, Switzerland
e-mail: colin.ridoutt@power.alstom.com

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 6, 2014; final manuscript received January 18, 2014; published online March 21, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(9), 091601 (Mar 21, 2014) (11 pages) Paper No: GTP-14-1002; doi: 10.1115/1.4026860 History: Received January 06, 2014; Revised January 18, 2014

Control valves are one of the key steam turbine components that guarantee operational safety in a power plant. There are two aerodynamic aspects, which are the current focus for the development of Alstom's valves. One is the reduction of the aerodynamic loss to increase the efficiency of the power plant. The other is operational flexibility, which is increasingly required to react faster to load requirements from the electric grid. This is becoming more important as power generation becomes increasingly decentralized, with a growing contribution from renewable energy sources. For this reason, a fast control loop is required for valve operation, which depends on an accurate linearization of the valve characteristic. In this paper the flow fields in an existing steam control valve have been analyzed and subsequently optimized using CFD techniques. The approach specifically designed for drilled strainers is further illustrated. Following the validation of the baseline design with model testing, an improved diffuser has been designed using CFD analysis and the resulting performance benefit has been confirmed with further testing. The grid frequency support requires control valve throttling. For this reason, an accurate prediction of the linearization table is extremely important to support the required response time limits. Further numerical work has been carried out with various opening positions of the valve, leading to an improved valve linearization characteristic. It is demonstrated that the numerical prediction of the linearization curve agrees very well with data obtained from operating power plants.

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Fig. 1

Schematic view of the turbine inlet valve used in this study. Top half shown shut, bottom half shown open.

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Fig. 2

Test facility for valves at Alstom

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Fig. 3

Structure and measurement locations of the test rig

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Fig. 4

Typical strainer model and pattern of holes

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Fig. 5

Test model at FHNW Windisch

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Fig. 6

Computational model of a direct calculation of a single strainer hole

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Fig. 7

Computational mesh of single hole

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Fig. 8

Grid independency study

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Fig. 9

Computational domain for the porous model validation

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Fig. 10

Comparison between loss coefficient of a directly modeled bore and porous modeling

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Fig. 11

Computational 3D domain of turbine inlet valve

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Fig. 12

Computational meshes for turbine inlet valves

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Fig. 13

Diffuser location inside the valve (a) and diffuser casing (red line) to be optimized (b)

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Fig. 14

Comparison of the diffuser shapes

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Fig. 15

Comparison of the relative diffuser area ratios

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Fig. 16

Loss coefficient parameter for different diffuser designs at different operating points

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Fig. 17

Comparison of relative changes in loss coefficient of different valve diffusers

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Fig. 18

Location of visualization planes in the 3D CFD calculation

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Fig. 19

Comparison of flow Mach number in diffuser and outlet ring chamber between baseline and design 1

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Fig. 20

Schematic of the loss breakdown along the flow path

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Fig. 21

Analysis of loss creation along the flow path

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Fig. 22

Experimental data of valve characteristics and turbine operating conditions with a typical steam turbine valve

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Fig. 23

Example of a CFD result with 20% relative lift stroke

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Fig. 24

Procedure of the CFD-based valve linearization

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Fig. 25

Comparison between on-site data and CFD prediction of valve lift over mass flow




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