Study of Multi Stage Steam Turbines

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Study of Multi Stage Steam Turbines

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Techno-economical Viable Solution forLow
Capacity Mechanical Power
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Blade Power at Maximum Efficiency COnditions
Ideal Impulse Stage
Ideal Parson Stage
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Moderate Capacity of Parson Same Blade Velocity
At optimum U/Va1, an impulse stage produces TWICE the power of a 50 reaction stage for same blade speed!
This means that an impulse turbine requires only half the number of stages as a 50 reaction turbine for a given application!
This fact has a major impact on the construction of the turbine
It is also responsible for some of the greatest miss understandings, since people assume that this means that impulse blading is cheaper overall - this is NOT true!
Impulse turbines have fewer stages, but they must use a different form of construction which is expensive
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Capacity of Parson Same Inlet Steam Velocity
So at optimum U/Va1, a 50 reaction stage produces TWICE the power of an impulse stage for same value of Highest Steam jet velocity.
This means that a 50 reaction turbine requires only half the number of stages as an impulse turbine for a given application!
This fact has a major impact on achieving lower fluid dynamic losses with improved capital cost.
Reaction turbines with fewer stages and less expensive cost are highly preferred in large power plants.
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Mechanical Arrangements of Steam Turbines

• Solutions to Turbo-machinery Issues.
• Tandem Reheat Steam Turbine
• Cross Compound Steam Turbine

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Tandem Reheat Steam Turbine
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Cross Compound Reheat Steam Turbine
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Tandem-compound four-flow steam turbine
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Large-Capacity Steam Turbines for Fossil Thermal
Power Plant
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Parsons concept of multi-stage had produced an
additional but marginal thermodynamic advantage.
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Enthalpy Entropy Diagram for Multistage Turbine
Turbine Inlet
Stage 1
h
Stage 2
Stage 3
Stage 4
Stage 5
Turbine Exit
s
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Internal Reheating due to Irreversibilities
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T
4s
s
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Behavior of Superheated Steam
h
T
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Well Behavior of Superheated Steam
T
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Steam Flow Path in a Multi Stage Impulse Turbine

• Global available enthalpy for Power

• Internally available enthalpy for Power

4IIss
4IIIss
4IVss

• Total actual stage work output per unit mass

4Vss
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Define Stage Efficiency
Global internal efficiency of turbine
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qi is always positive.
Therefore,

• Multistage turbines will increase the possibility
  of recovering lost availability!
• The larger the number of stages, the greater is
  the heat recovery.
• The difference is called heat recovery factor, a.
• General value of a is 0.04 to 0.06.

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Compounding of impulse turbine

• Compounding is done to reduce the rotational
  speed of the impulse turbine to practical limits.
  
• Compounding is achieved by using more than one
  set of nozzles, blades, rotors, in a series,
  keyed to a common shaft so that either the steam
  pressure or the jet velocity is absorbed by the
  turbine in stages.
• Three main types of compounded impulse turbines
  are
• a) Pressure compounded Steam Turbine The Rateau
  Design
• b) velocity compounded Steam Turbine The Curtis
  Design
• c) pressure and velocity compounded Impulse
  turbines The Rateau-curtis Design.

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Pressure compounded impulse turbine