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Research Papers: Gas Turbines: Turbomachinery

Natural Cooling and Startup of Steam Turbines: Validity of the Over-Conductivity Function

[+] Author and Article Information
Gabriel Marinescu

Alstom Power,
Baden 5401, Switzerland
e-mail: gabriel.marinescu@power.alstom.com

Peter Stein

Alstom Power,
Baden 5401, Switzerland
e-mail: peter.stein@power.alstom.com

Michael Sell

Alstom Power,
Baden 5401, Switzerland
e-mail: michael.sell@power.alstom.com

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2014; final manuscript received April 18, 2015; published online May 12, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(11), 112601 (Nov 01, 2015) (9 pages) Paper No: GTP-14-1384; doi: 10.1115/1.4030411 History: Received July 14, 2014; Revised April 18, 2015; Online May 12, 2015

The temperature drop during natural cooling and the way in which the steam turbine restarts have a major impact on the cyclic lifetime of critical parts and on the cyclic life of the whole machine. In order to ensure the fastest startup without reducing the lifetime of the turbine critical parts, the natural cooling must be captured accurately in calculation and the startup procedure optimized. During the cool down and restart, all turbine components interact both thermally and mechanically. For this reason, the thermal analyst has to include, in his numerical model, all turbine significant parts—rotor, casings together with their internal fluid cavities, valves, and pipes. This condition connected with the real phenomenon lead-time—more than 100 hours for natural cooling—makes the analysis time-consuming and not applicable for routine projects. During the past years, a concept called “over-conductivity” was introduced by Marinescu et al. (2013, “Experimental Investigation Into Thermal Behavior of Steam Turbine Components—Temperature Measurements With Optical Probes and Natural Cooling Analysis,” ASME J. Eng. Gas Turbines Power, 136(2), p. 021602) and Marinescu and Ehrsam (2012, “Experimental Investigation on Thermal Behavior of Steam Turbine Components: Part 2—Natural Cooling of Steam Turbines and the Impact on LCF Life,” ASME Paper No. GT2012-68759). According to this concept, the effect of the fluid convectivity and radiation is replaced by a scalar function K(T) called over-conductivity, which has the same heat transfer effect as the real convection and radiation. K(T) is calibrated against the measured temperature on a Alstom KA26-1 steam turbine (Ruffino and Mohr, 2012, “Experimental Investigation on Thermal Behavior of Steam Turbine Components: Part 1—Temperature Measurements With Optical Probes,” ASME Paper No. GT2012-68703). This concept allows a significant reduction of the calculation time, which makes the method applicable for routine transient analyses. The paper below shows the theoretical background of the over-conductivity concept and proves that when applied on other machines than KA26-1, the accuracy of the calculated temperatures remains within 15–18 °C versus measured data. A detailed analysis of the link between the over-conductivity and the energy equation is presented as well.

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References

Marinescu, G., Mohr, W., Ehrsam, A., Ruffino, P., and Sell, M., 2013, “Experimental Investigation Into Thermal Behavior of Steam Turbine Components—Temperature Measurements With Optical Probes and Natural Cooling Analysis,” ASME J. Eng. Gas Turbines Power, 136(2), p. 021602. [CrossRef]
Marinescu, G., and Ehrsam, A., 2012, “Experimental Investigation on Thermal Behavior of Steam Turbine Components: Part 2—Natural Cooling of Steam Turbines and the Impact on LCF Life,” ASME Paper No. GT2012-68759. [CrossRef]
Spelling, J., Joecker, M., and Martin, A., 2011, “Thermal Modeling of a Solar Steam Turbine With a Focus on Start-Up Time Reduction,” ASME Paper No. GT2011-45686. [CrossRef]
Mukhopadhyay, D., Brilliant, H., M., and Zheng, X., 2014, “Development of a Conjugate Heat Transfer Simulation Methodology for Prediction of Steam Turbine Cool-Down Phenomena and Shell Deflection,” ASME Paper No. GT2014-25874. [CrossRef]
Ruffino, P., and Mohr, W., 2012, “Experimental Investigation Into Thermal Behaviour of Steam Turbine Components: Part 1—Temperature Measurements With Optical Probes,” ASME Paper No. GT2012-68703. [CrossRef]
Marinescu, G., Sell, M., Ehrsam, A., and Brunner, P., 2013, “Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 3—Startup and Impact on LCF Life,” ASME Paper No. GT2013-94356. [CrossRef]
Marinescu, G., Stein, P., and Sell, M., 2014, “Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 4—Natural Cooling and Robustness of the Over-Conductivity Function,” ASME Paper No. GT2014-25247. [CrossRef]

Figures

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Fig. 1

Alstom KA26-1 IP steam turbine during instrumentation (source: Ref. [1])

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Fig. 2

Alstom KA26-1 IP steam turbine instrumentation

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Fig. 3

The over-conductivity function (source: Ref. [1])

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Fig. 4

The mesh of the finite element model

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Fig. 5

Position of points A, B, C, D, and E

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Fig. 6

Variation of the temperature gradient module |∇T|

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Fig. 7

Time variation of the Laplacian function ΔT

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Fig. 8

Time variation of the function f(p,T)

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Fig. 9

Time variation of the velocity module and its components at point A

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Fig. 10

Temperature variation at thermocouples T11.1, T24.1, Tm33, and Tm42 (source: Ref. [6])

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Fig. 11

Startup and natural cooling on over-conductivity diagram

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Fig. 12

Gland steam flow from time t1 to t5

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Fig. 13

Temperature distribution at 30 min after the glands system is switched ON

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Fig. 14

Measured and calculated temperature at T24.1

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Fig. 15

Alstom HP 460 MW turbine. Temperature distribution at base load regime.

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Fig. 16

Alstom HP 1100 MW turbine. Temperature distribution at base load regime.

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Fig. 17

Alstom IP 1100 MW turbine. Temperature distribution at base load regime.

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Fig. 18

Alstom 460 MW HP turbine. Temperature distribution at 8 hr after natural cooling start.

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Fig. 19

Alstom 460 MW HP turbine. Temperature distribution at 60 hr after natural cooling start.

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Fig. 20

Alstom 460 MW HP turbine. Temperature variation at Th22. Calculated versus measured data.

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Fig. 21

Alstom KA26-1 HP turbine. Temperature variation at Th32. Calculated versus measured data.

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Fig. 22

Alstom 1100 MW HP turbine. Temperature distribution at 8 hr after natural cooling start.

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Fig. 23

Alstom 1100 MW HP turbine. Temperature distribution at 60 hr after natural cooling start.

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Fig. 24

Alstom 1100 MW HP turbine. Temperature variation at Turbomax location. Calculated versus measured data.

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Fig. 25

Alstom 1100 MW IP turbine. Temperature distribution at 8 hr after natural cooling start.

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Fig. 26

Alstom 1100 MW IP turbine. Temperature distribution at 60 hr after natural cooling start.

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Fig. 27

Alstom 1100 MW IP turbine. Temperature variation at turbomax location. Calculated versus measured data.

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