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Research Papers: Gas Turbines: Structures and Dynamics

Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

[+] Author and Article Information
Rahul A. Bidkar

General Electric Global Research,
Niskayuna, NY 12309
e-mail: bidkar@ge.com

Edip Sevincer, Jifeng Wang, Azam M. Thatte, Andrew Mann, Maxwell Peter

General Electric Global Research,
Niskayuna, NY 12309

Grant Musgrove, Timothy Allison, Jeffrey Moore

Southwest Research Institute,
San Antonio, TX 78238

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 19, 2016; final manuscript received July 3, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022503 (Sep 13, 2016) (8 pages) Paper No: GTP-16-1234; doi: 10.1115/1.4034258 History: Received June 19, 2016; Revised July 03, 2016

Supercritical carbon dioxide (sCO2) power cycles could be a more efficient alternative to steam Rankine cycles for power generation from coal. Using existing labyrinth seal technology, shaft-end-seal leakage can result in a 0.55–0.65% points efficiency loss for a nominally 500 MWe sCO2 power cycle plant. Low-leakage hydrodynamic face seals are capable of reducing this leakage loss and are considered a key enabling component technology for achieving 50–52% thermodynamic cycle efficiencies with indirect coal-fired sCO2 power cycles. In this paper, a hydrodynamic face seal concept is presented for utility-scale sCO2 turbines. A 3D computational fluid dynamics (CFD) model with real gas CO2 properties is developed for studying the thin-film physics. These CFD results are also compared with the predictions of a Reynolds-equation-based solver. The 3D CFD model results show large viscous shear and the associated windage heating challenge in sCO2 face seals. Following the CFD model, an axisymmetric finite-element analysis (FEA) model is developed for parametric optimization of the face seal cross section with the goal of minimizing the coning of the stationary ring. A preliminary thermal analysis of the seal is also presented. The fluid, structural, and thermal results show that large-diameter (about 24 in.) face seals with small coning (of the order of 0.0005 in.) are possible. The fluid, structural, and thermal results are used to highlight the design challenges in developing face seals for utility-scale sCO2 turbines.

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Figures

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Fig. 1

Schematic diagram of a typical hydrodynamic face seal

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Fig. 2

Schematic of one end of a turbine with end seal, buffer seal, and bearing

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Fig. 3

Thermodynamic differences in recovery of turbine end-seal leakage for (a) sCO2 and (b) steam turbines

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Fig. 4

Cycle efficiency impact of two labyrinth end seals for a utility-scale sCO2 turbine

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Fig. 5

Cross section of a utility-scale sCO2 turbine-face seal. Note that all the dimensions are normalized by the bearing face radial height.

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Fig. 6

CFD domain: A periodic sector of the fluid film between the stationary ring and the rotor

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Fig. 7

Average bearing pressure (normalized by Phigh) as a function of film thickness

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Fig. 8

(a) Radial velocity profiles and (b) tangential velocity profiles through the film thickness for different operating film thickness of 0.0001 in., 0.0003 in., and 0.0006 in

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Fig. 9

Coning (1/1000 in.) for different combinations of b/a and c/(a-b) for a fixed value of d = 0, a = 4, and e = 1.21. Note that positive coning indicates a radially converging film shape, and a small positive coning value is desirable.

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Fig. 10

Coning (1/1000 in.) for different combinations of b/a and c/(a-b) for fixed value of d = 2.54, a = 4, and e = 1.21. Note that positive coning indicates a radially converging film shape, and a small positive coning value is desirable.

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Fig. 11

Temperature contours for the seal stationary ring and the rotor

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