Steam prime movers

Complete description of Steam prime movers like various turbines that produce electric energy

1. STEAM PRIME MOVERS
A device which convert any source of energy into
Mechanical work is defined prime movers.
Steam Engine.
Steam turbine.
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2.  Nozzle is duct of smoothly varying cross-sectional
area in which a steadily flowing fluid can be made to
accelerate by a pressure drop along the duct.

Applications:
steam and gas turbines
Jet engines
Rocket motors
Flow measurement
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3.  When a fluid is decelerated in a duct
causing a rise in pressure along the stream,
then the duct is called a diffuser.
 Two applications in practice in which a
diffuser is
used are :
The centrifugal compressor
Ramjet
Diffuser
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4. Steam Nozzle
Steam nozzle is an insulated
passage of varying cross-sectional area
through which heat energy (Enthalpy),
pressure of steam is converted into
kinetic energy.
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5. Functions of Nozzle :-
1) The main function of the steam nozzle is to
convert heat energy to kinetic energy.
2) To direct the steam at high velocity into
blades of turbine at required angle.
Applications :-
1) Steam & gas turbines are used to produces a
high velocity jet.
2) Jet engines and rockets to produce thrust
(propulsive force)
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6. Types of nozzles :-
1) Convergent nozzle
2) divergent nozzle
3) convergent - divergent nozzle
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7. 1) Convergent nozzle :-
It is a nozzle with large entrance and tapers gradually to a smallest section at
exit. It has no diverging portion.
2) Divergent nozzle :-
It is a nozzle with small entrance and tapers gradually to a large section at
exit. It has no converging portion at entry.
3) convergent - divergent nozzle :-
convergent - divergent nozzle is widely used in steam turbines. The nozzle
converges first to the smallest section and then diverges up to exit. The smallest
section of the nozzle is called throat. The divergent portion of nozzle allows higher
expansion ratio i.e., increases pressure drop. The taper of diverging sides of the nozzle
ranges from 6
0
to 15
0
. If the taper is above 15
0
turbulent is increased. However if it is
less than 6
0
, the length of the nozzle will increases.
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8. Nozzle Shape
Applying Steady flow energy equation:
…………………………… .. (1)
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9.  If the area at section X - X is A, and the specific volume is
v, then , using equation:
Substituting the valve of C in above equation,
Area per unit mass flow
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10. STEAM TURBINES
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11. “Steam Turbine is a prime-mover in which Pressure energy of
steam is transformed into Kinetic energy, and later in its turn
is transformed into the mechanical energy of rotation of
turbine shaft”
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12. WORK IN A TURBINE VISUALIZEDWORK IN A TURBINE VISUALIZED
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13. CLASSIFICATION OF STEAM TURBINE
Classification of steam turbines may be done
as following:
1.According to action of steam
(a) Impulse turbine
(b) Reaction turbine
(c) Combination of both
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14. 2. According to direction of flow:
(a)Axial flow turbine
(b)Radial flow turbine
3. According to number of stages
(a)Single stage turbine
(b)Multi stage turbine
(4). According to number of cylinders
(a)Single cylinder turbine
(b)Double cylinder turbine
(c)Three cylinder turbine
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15. (5)According to steam pressure at inlet of
Turbine:
(a) Low pressure turbine
(b) Medium pressure turbine.
(c) High pressure turbine
(d) Super critical pressure turbine.
(6)According to method of governing:
(a) Throttle governing turbine.
(b) Nozzle governing turbine.
(c) By pass governing turbine.
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16. (7) According to usage in industry:
(a) Stationary turbine with constant speed.
(b) Stationary turbine with variable speed.
(c) Non stationary turbines.
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17. Classification based on
Principle of Action
1.Impulse Turbine
Pressure energy of Steam is converted into Kinetic Energy.
Impulse action of high velocity jet of steam, due to change in its
direction is used to rotate the turbine shaft.
2.Reaction Turbine
Reaction force due to expansion of high pressure steam when it
passes through a set of moving and fixed blades is used to rotate
the turbine shaft.
Due to expansion of steam, pressure drop occurs continuously over
both fixed and moving blades.
This pressure difference exerts a thrust on the blades.
The resulting reaction force imparts rotary motion.
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18. Impulse Turbine
1.Casing
2.Nozzle – Pressure energy
of Steam is converted
into Kinetic Energy
3.Turbine Blade – Convert
kinetic energy into
mechanical work.
4.Rotor
5.Shaft
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NOZZLE
STEAM
CHEST
ROTOR

20. Impulse turbine - Working
High pressure steam from boiler is supplied to
fixed nozzles.
Nozzle – Pressure falls from boiler pressure to
condenser pressure
Reduction in pressure increases velocity.
High velocity steam impinges on moving curved
vanes
Causes change in momentum Impulsive force
on blades.
Pressure remains constant when steam flows
through blades.
Eg: De Lavel Turbine

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21. Impulse Turbine
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22. Disadvantages of Impulse Turbine
The velocity of Rotor is too high for practical purpose
The velocity of steam leaving the turbine considerably
high and hence there is a loss Kinetic Energy
These problems can be overcome by expanding the
steam in different stages.
This is known as Compounding.
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23. Reaction Turbine
1.Casing
2.Fixed Blades
•Performs the function
of Nozzle in Impulse
turbine.
•It directs steam to
adjacent moving blade.
3.Moving Blades
4.Shaft
5.Rotor
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STEAM CHEST
ROTOR

25. Working
High pressure steam directly supplied to turbine
blades with out nozzles.
Steam expands(diameter increases) as it flows
through fixed and moving blades Continuous drop
of pressure.
Produces reaction on blades
Reaction causes rotor to rotate.
Propulsive force causing rotation of turbine is the
reaction force. Hence called reaction turbine.
Eg: Parson’s Turbine
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26. Reaction Turbine
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28. IMPULSE TURBINE BLADEIMPULSE TURBINE BLADE
REACTION TURBINE BLADEREACTION TURBINE BLADE
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30. Problems in steam turbine:
Stress corrosion carking
Corrosion fatigue
Pitting
Oil lubrication
imbalance of the rotor can lead to vibration
 misalignment
Thermal fatigue
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31. Compounding of Impulse Turbine
The extreme high speed of Impulse Turbine of the order of
30,000rpm, cannot be directly used for practical purpose.
To reduce the speed more than one set of blades are used.
This is called compounding.
There are three types of compounding
Velocity Compounding
Pressure Compounding
Pressure – Velocity Compounding
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32. Velocity
Compounding .. 1
1.Nozzle
2.Moving Blades
3.Fixed Blades
4.Rotor
5.Shaft
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33. Velocity
Compounding .. 2
•Velocity of steam
absorbed in stages
•Moving and fixed
blades placed
alternatively.
•Entire pressure drop
takes place in nozzle.
•Kinetic energy of steam
converted into
mechanical work in 2
stages in figure
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34. Velocity Compounding ..
•Velocity reduced to
intermediate velocity in
the 1
st
row of moving
blades
•Fixed blade direct
steam to 2
nd
set of
moving blades.
•Velocity further
reduced in 2
nd
set of
moving blades
•Eg: Curtis Turbine
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35. Velocity Compounding ..
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36. Pressure
Compounding ..1
1.Nozzle
2.Moving Blades
3.Casing
4.Rotor
5.Shaft
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37. Pressure
Compounding ..2
•Pressure energy of steam
absorbed in stages.
•Expansion of steam takes
place in more than one
set of nozzles
•Nozzles followed by set
of moving blades
•Pressure energy of steam
converted into kinetic
energy in nozzles
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38. Pressure Compounding ..3
•Kinetic energy
transformed to
mechanical work in
moving blades.
•No change in pressure in
blades.
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39. Pressure
Compounding ..4
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40. Pressure Velocity Compounding..1
Combination of pressure compounding and velocity
compounding.
In a 2 stage pressure velocity compounded turbine –
total drop in steam pressure carried out in 2 stages.
Velocity obtained in each stage is compounded.
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41. Pressure Velocity Compounding..2
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42. Pressure Velocity Compounding..3
1
st
stage and 2
nd
stage taken separately are identical to
velocity compounded turbine.
Combines advantages of pressure and velocity
compounding.
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43. Pressure Velocity Compounding..4
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46. [email protected]
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Section 3.2 – Steam Turbine Design
Materials
•Blades
•Stainless Steel – 403 & 422 (+Cr)
•17-4 PH steel (+ Ti)
•Super Alloys
•Rotor
•High “Chrome – Moley” Steel – Cr-Mo-V
•Low “Ni Chrome Steel – Ni-Cr-Mo-V

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