Irreversibilities : Turbine to Condenser-II

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Irreversibilities Turbine to Condenser-II

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

Loss in Capacity of Turbine Increase in
Capacity of Condenser.
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Irreversible Adiabatic Flow Through Turbine SSSF
Ideal work wiso h0in h0exitiso Actual work
wact h0in h0exitact Internal Efficiency of a
turbine
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Losses in Turbine Stage

• Losses in Regulating valves The magnitude of
  loss of pressure due to throttling with the
  regulating valves fully open is
• Dpv 3 to 5 of pmax.
• Loss in nozzle blades.
• pressure loss in moving blades.
• Loss due to exit velocity.
• Loss due to friction of the disc and blade
  banding
• Loss associated with partial admission.
• Loss due to steam leakages through clearances.
• Loss due to flow of wet steam.
• Loss due to exhaust piping.
• Loss due to steam leakage in seals.

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Losses in Nozzles

• Losses of kinetic energy of steam while flowing
  through nozzles or guide blade passages are
  caused because of
• Energy losses of steam before entering the
  nozzles,
• Frictional resistance of the nozzles walls,
• Viscous friction between steam molecules,
• Deflection of the flow,
• Growth of boundary layer,
• Turbulence in the Wake and
• Losses at the roof and floor of the nozzles.
• These losses are accounted by the velocity
  coefficient, f.

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500 MW
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Nozzle Moving Blade Losses for HP Stages 500
MW
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Nozzle Moving Blade Losses for IP Stages 500
MW
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Nozzle Moving Blade Losses for LP Stages 500
MW
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H-s Diagram of Turbine Exhaust Steam
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Irreversible Flow Turbine Exit to Condenser

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

Irreversibilities due to Closed Cycle Policy ..
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The Last Stage of LP Turbine
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LP Turbine Exhaust System

• In a condensing steam turbine, the low-pressure
  exhaust hood, consisting of a diffuser and a
  collector or volute!, connects the last stage
  turbine and the condenser.
• The function of the hood is to transfer the
  turbine leaving kinetic energy to potential
  energy while guiding the flow from the turbine
  exit plane to the condenser.
• Most of exhaust hoods discharge towards the
  downward condenser.
• Flow inside the hood therefore must turn about 90
  deg from the axial direction to the radial
  direction before exhausting into the condenser.
• The 90-deg turning results in vortical flow in
  the upper half part of the collector and also
  high losses.
• The exhaust hood is one of the few steam turbine
  components that has the considerable aerodynamic
  losses.
• It is a challenge for engineers to operate a hood
  with high pressure recovery and low total
  pressure loss in a compact axial length.

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H-s Diagram of Turbine Exhaust Steam
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Exhaust Hood
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Exhaust Diffuser For L P Turbine
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Steam Turbine Exhaust Size Selection

• The steam leaving the last stage of a condensing
  steam turbine can carry considerably useful power
  to the condenser as kinetic energy.
• The turbine performance analysis needs to
  identify an exhaust area for a particular load
  that provides a balance between exhaust loss and
  capital investment in turbine equipment.

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Path Lines in Exhaust Hood
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• Residual velocity loss
• Steam leaving the last stage of the turbine has
  certain velocity, which represent the amount of
  kinetic energy that cannot be imparted to the
  turbine shaft and thus it is wasted
• Exhaust end loss
• Exhaust end loss occur between the last stage of
  low pressure turbine and condenser inlet.
• 2. Exhaust loss depends on the absolute
  steam velocity.
• Turbine Exhaust end loss
• Expansion-line -end point - Used energy at end
  point.

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Typical exhaust loss curve showing distribution
of component loss
50
40
Exhaust Loss, kJ/kg of dry flow
30
20
10
0
120
240
180
240
300
360
Annulus Velocity (m/s)
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Optimal Design of Exhaust Hood
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H-s Diagram of Turbine Exhaust Steam