CFD analysis of the flow in the reheater shroud of the boiler spine

1
CFD analysis of the flow in the reheater shroud
of the boiler spine

• E Romero
• British Energy

2
Introduction

• A description of the problem
• A discussion of the functionality of FEAT used in
  the analysis of the problem

3
Boiler support spine at HRA/HYA

• There are a number of critical welds vulnerable
  to reheat cracking, see 12.3, 12.8 and12.4

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Flow in the reheater shroud

• The gas flow in the reheater shroud is critical
  in maintaining the temperature of weld 12.3 at
  reasonable levels.
• 6kg/s of pressurised CO2 flowing through a 18mm
  annular gap
• Outer walls heated by the main boiler gas flow
• Inner wall cooled by the feed pipes in the centre
  of the spine.

5
CFD Models

• A 2D axisymmetric model of the passage including
  the spine body and the shroud
• A 3D model of one azimuthal segment containing a
  bleed hole also comprising the walls.

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2D Model - Reheater shroud

• Axisymmetric representation of the reheater
  shroud passage and solid walls
• Bleed holes represented by smaller convergent
  passages with the same area.

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3D Model - Bleed Holes

• One octant of the reheater shroud passage
• PATRAN generated mesh

8
Boundary conditions (2D Model)

• Internal wall exposed to a natural convection
  flow. Modelled through a temperature dependent
  Nusselt number calculated with the help of CO2
  material database.
• External wall exposed to a gas flow with an axial
  thermal gradient and radiation to reheater tubes.

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Results (2D Model)

• After judicious use of upwinding in the dead
  space and length scale limiting (LSCUTFAC)
  reasonable results obtained with ?-?.
• Bleed holes modelled as convergent passages

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Results (2D Model) 2

• The key result was to justify a small gas
  temperature rise
• In addition it supported reasonable heat transfer
  in the dead space

11
Results (3D Model)

• Not an ideal solution in CFD terms
• However it showed significant stirring of gas in
  the dead space
• Showed the small variation in temperature around
  the weld

12
Conclusions

• CFD analysis of the flow in the reheater shroud
  has shown that rise in gas temperature is small
  and has helped to support weld temperature
  predictions.
• Much of FEATs functionality has been brought to
  bear Turbulence modelling, axi-symmetric ray
  tracing, variable properties, multifrontal
  solution, FE mesh handling, TURCYC.