Development of Compound Steam Turbines for Industrial Applications

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Development of Compound Steam Turbines for
Industrial Applications

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Fluid Dynamic Solutions to Techno-economical
Viability
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Classification of Steam Turbines
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From Books of Sir Charles Parson

• In 1884 or four years previously, I dealt with
  the turbine problem in a different way.
• It seemed to me that moderate surface velocities
  and speeds of rotation were essential if the
  turbine motor was to receive general acceptance
  as a prime mover.
• I therefore decided to split up the fall in
  pressure of the steam into small fractional
  expansions over a large number of turbines in
  series, so that the velocity of the steam nowhere
  should be great.
• A moderate speed of turbine suffices for the
  highest economy.

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• This principle of compounding turbines in series
  is now universally used in all except very small
  engines, where economy in steam is of secondary
  importance.
• The arrangement of small falls in pressure at
  each turbine also appeared to me to be surer to
  give a high efficiency.
• The steam flowed practically in a non-expansive
  manner through each individual turbine, and
  consequently in an analogous way to water in
  hydraulic turbines whose high efficiency at that
  date had been proved by accurate tests.

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Impulse Vs Parson (50 Reaction)
Fixed blade row accelerates the steam
Fixed blade row accelerates the steam
Moving blade row changes both the speed and direction of the steam
Moving blade row changes only the direction of the steam
Force comes from rate of change of momentum
Force comes from rate of change of momentum
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The Reaction (Parsons) Stage
Va0Va2 Fixed blades expand steam from Va2 to Va1 using a blades whose angle vary from b1 to b2.
Assuming that the gap between stator and rotor
doesnt alter the flow conditions. ?!?....
Also in a 50 reaction stage, the moving blades
are a mirror image of the fixed blades,
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The thermodynamics of 50 Reaction SSSF
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The Fluid Dynamics of 50 Reaction
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Theory of Parsons Blading
Va1 Vr2 a1 ß2
approximately
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Strength of Blading
For an ideal Impulse Blade
For an ideal Parson Blade
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Blade Power
Ideal Impulse Stage
Ideal Parson Stage
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Blade Efficiency
Available power in Impulse Stage
Available power in 50 Reaction stage
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Stage Efficiency
Impulse Stage
50 Reaction stage
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Maximum Efficiency of Impulse Blade
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Maximum Efficiency of Parson Blade
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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
So 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