Steam Turbine and Condenser of Steam Power Plant

1. CHAPTER-6:
6. Steam Turbines

2. History of turbines
• 150 BC – Hero, Aeolipile
• 1232 - Chinese began to use rockets as weapons
(battle of Kai Keng)
• 1629 - Giovanni Branca developed a stamping mill

3. 6.1 Introduction
Steam turbine is one of the most important prime
mover component of steam power plant for
generating electricity and is falls under the
category of power producing turbo-machines.
The purpose of turbine technology is to extract the
maximum quantity of energy from the working
fluid, to convert it into useful work with maximum
efficiency, by means of a plant having maximum
reliability, minimum cost, minimum supervision
and minimum starting time.

4. Principle of Operation of
Steam Turbine• Steam turbine depends completely upon the dynamic action of the
steam flowing over turbine blade.
• According to Newton’s Second Law of Motion, the force is proportional
to the rate of change of momentum.
• If the rate of change of momentum is caused in the steam by allowing a
high velocity jet of steam to pass over curved blade, the steam will
impart a force to the blade.
• If the blade is free, it will move off (rotate) in the direction of force which
created by change of momentum.
• In other words, the motive power in a steam turbine is obtained by the
rate of change in moment of momentum of a high velocity jet of steam
impinging on a curved blade which is free to rotate.
• The steam from the boiler is expanded in a passage or nozzle where due
to fall in pressure of steam, thermal energy of steam is converted into
kinetic energy of steam, resulting in the emission of a high velocity jet of
steam.

5. Steam Turbine Classification
Steam turbines can be
classified in several different
ways:
1. By details of stage design
Impulse or reaction
2. By steam supply and exhaust
conditions
• Condensing or non-condensing
• Automatic or controlled extraction
• Mixed pressure
• Reheat
4. By number of exhaust stages in
parallel
• Two flow, four flow or six flow
5. By direction of steam flow
Axial flow, radial flow or
tangential flow
6. Single or multi-stage
7. In taking Condition
• Superheated or saturated

9. Cont…
• Depending up on the types of blades
used and the method of energy
transfer from the fluid to the rotor
wheel, the turbines may be two types:
i. Reaction turbine
ii. Impulse turbine

10. i. Reaction turbine.`
• In Reaction turbines, addition to the pressure drop occurs in
the nozzle there will also be pressure drop occur when the
fluid passes over the rotor blades. Figure below shows the
Reaction turbine.
• Most of the steam turbine are of axial flow type devices
except Ljungstrom turbine which is a radial type.

11. ii. Impulse Turbine
• If the flow of steam through the nozzles and moving blades of a
turbine takes place in such a manner that the steam is expanded
only in nozzles and pressure at the outlet sides of the blades is
equal to that at inlet side; such a turbine is termed as impulse
turbine because it works on the principle of impulse.
• In other words, in impulse turbine, the drop in pressure of steam
takes place only in nozzles and not in moving blades.
• This is obtained by making the blade passage of constant cross-
section area
• As a general statement it may be stated that energy
transformation takes place only in nozzles and moving blades (rotor)
only cause energy transfer.
• Since the rotor blade passages do not cause any acceleration of fluid,
hence chances of flow separation are greater which results in lower
stage efficiency.

12. cont…
• In Impulse turbine, the enthalpy drop (pressure drop)
completely occurs in the nozzle itself and when the fluid
pass over the moving blades it will not suffer pressure
drop again.
• Hence pressure remain constant when the fluid pass over
the rotor blades. Figure below shows the schematic
diagram of Impulse turbine.

14. Losses in Steam Turbine
• Profile loss:- Due to formation of boundary layer on blade surfaces. Profile loss
is a boundary layer phenomenon and therefore subject to factors that influence
boundary layer development. These factors are Reynolds number, surface
roughness, exit Mach number and trailing edge thickness.
• Secondary loss:- Due to friction on the casing wall and on the blade root and
tip. It is a boundary layer effect and dependent upon the same considerations as
those of profile loss.
• Tip leakage loss:- Due to steam passing through the small clearances required
between the moving tip and casing or between the moving blade tip and rotating
shaft. The extend of leakage depends on the whether the turbine is impulse or
reaction. Due to pressure drop in moving blades of reaction turbine they are more
prone to leakages.
• Disc windage loss:- Due to surface friction created on the discs of an impulse
turbine as the disc rotates in steam atmosphere. The result is the forfeiture of
shaft power for an increase in kinetic energy and heat energy of steam.

15. Cont…
• Wetness loss: Due to moisture entrained in the low pressure steam at the
exit of LP turbine. The loss is a combination of two effects; firstly,
reduction in efficiency due to absorption of energy by the water droplets
and secondly, erosion of final moving blades leading edges.
• Leaving loss: Due to kinetic energy available at the steam leaving from
the last stage of LP turbine. In practice steam does slow down after
leaving the last blade, but through the conversion of its kinetic energy to
flow friction losses.
• Partial admission loss: Due to partial filling of steam, flow between the
blades is considerably accelerated causing a loss in power.

16. Merits and Demerits of Steam
Turbine
Merits:
• Ability to utilize high pressure and high temperature steam.
• High component efficiency.
• High rotational speed.
• High capacity/weight ratio.
• Smooth, nearly vibration-free operation.
• No internal lubrication.
• Oil free exhaust steam.
• Can be built in small or very large units (up to 1200 MW).
Demerits:
– For slow speed application reduction gears are required.
– The steam turbine cannot be made reversible.
– The efficiency of small simple steam turbines is poor.

17. Steam Turbine Stage

18. Turbine Selection
• In all fields of application the competitiveness of
a turbine is a combination of several factors:
– Efficiency
– Life
– Power density (power to weight ratio)
– Direct operation cost
– Manufacturing and maintenance costs

19. 6.2 Velocity Triangles
• The three velocity vectors namely, blade speed,
absolute velocity and relative velocity in relation
to the rotor are used to form a triangle called
velocity triangle.
• Velocity triangles are used to illustrate the flow in
the blading of turbo machinery.
• Changes in the flow direction and velocity are
easy to understand with the help of the velocity
triangles.
• Note that the velocity triangles are drawn for the
inlet and outlet of the rotor at certain radius.

20. Steam Turbine Blade Terminology

21. Cont…

22. Nomenclature of Velocity
– V Absolute velocity of steam
– U Blade velocity 𝑈 =
𝜋𝑁𝐷 𝑚
60
; where N in rpm
– W Relative velocity of steam
– Va=Vf = Vm Axial component or flow velocity
– Vw Whirl or tangential component
– α-Nozzle angle
– β Blade angle
• Suffix: 1 Inlet, 2 Outlet

23. Rotor inlet and outlet flow
velocity triangle
• Inlet Velocity Triangle • Outlet Velocity Triangles

24. Combined Velocity Triangles

25. Work Done–Impulse Steam Turbine
• The stream is delivered to the wheel at an angle a1 and velocity V1
and the selection of angle a1 is a compromise.
• An increase in a1, reduces the value of useful component (Absolute
circumferential Component).
• This is also called Inlet Whirl Velocity, Vw1 = V1 cos(a1).
• An increase in a1, increases the value of axial component, also
called as flow component velocity.
• This is responsible for definite mass flow rate between to successive
blade.
• Flow component Va1 = V1 sin(a1) = W1sin(b1).
• The absolute inlet velocity can be considered as a resultant of blade
velocity and inlet relative velocity.
• The two points of interest are those at the inlet and exit of the
blade.

26. Newton’s Second Law for an Impulse Blade:
The tangential force acting of the jet is:
F = mass flow rate X Change of velocity in the tangential direction
Tangential relative velocity at blade Inlet : W1 cos(b1).
Tangential relative velocity at blade exit : -W2 cos(b2).
Change in velocity in tangential direction: -W2 cos(b2) - W1cos(b1).
-(W2 cos(b2) + W1cos(b1)).
Tangential Force,
U
W1V1
W2
V2
b1a1a2 b2
 1122 coscos bb WWmFA 


27. The reaction to this force provides the driving thrust on the wheel.
The driving force on wheel
 1122 coscos bb WWmFR 

Power Output of the blade,
 1122 coscos bb WWUmPb 

Diagram efficiency or blade efficiency:
steaminletofPowerKinetic
ouputPower
d
 1coscos
2
1
122
Vm
WWUm
d 



bb


28.  
2
1
121 1coscos2
V
WkWU
d
bb



 
2
1
21 1coscos2
V
kUW
d
bb



U
W1V1
W2
V2
b1a1a2 b2
1111 coscos1 ba WUVVw 
1
11
1
cos
cos
b
a UV
W


 
2
1
2
11 1
1cos
cos
cos2
V
kUVU
d








b
b
a

Vw1
In actual case, the relative
velocity is reduced by friction
and expressed by a blade
velocity coefficient k.
Thus, k = W2/W1

29. 


























 1
1cos
2cos
cos2
2
1
1
1 b
b
a k
V
U
V
U
d
 
2
1
2
11 1
1cos
cos
cos2
V
kUVU
d








b
b
a

Define Blade Speed Ratio, ∅=U/V1
 












 1
1cos
cos
cos2 2
1
b
b
a kd

30. For a given shape of the blade, the efficiency is a strong function of 
Thus the maximum diagram efficiency of the blade is obtained by:
For maximum efficiency: 0


d
d d
  01
1cos
cos
2cos2 1
1 













b
b
a k
 
12
cos
02cos 1
1
V
U

a
a



















 1
1cos
cos
4
cos
2
cos
cos2 211
1max,
b
baa
a kd

31. 











 1
1cos
cos
2 22
max,
b
b
 kd
The maximum efficiency of the blade is
If the blade is symmetrical, then β1 = β2 and neglecting frictional effects of the
blades on the steam, W1 = W2.
In actual case, the relative velocity is reduced by friction and expressed by a blade
velocity coefficient k.
Thus, k = W2/W1=1
i.e., maximum diagram efficiency
ηd max= cos2α1







4
cos
2
cos
cos4 11
1max,
aa
ad
I. For the given steam velocity work done per kg
of steam would be maximum when cos2α1=1
at α1=0.
II. As α1 increase, the work done on the blades
reduces, but at the same times surface area of
blades reduces, therefore there are less friction
losses ᴓ

32. Work sheet
1. The velocity of steam entering a simple impulse turbine is 1000 m/se, and the
nozzle angle is 20o. The mean peripheral velocity of blade is 400 m/se and
blades are symmetrical. If the steam is to enter the blade without shock, what
will be the blade angle?
a) Neglecting the friction effects on the blades, calculate the tangential force
on the blade and the diagram power for mass flow of 0.75 kg/se. Estimate
also the axial thrust and diagram efficiency.
b) If the relative velocity at the exit is reduced by friction to 80 % of that at
the inlet, estimate the axial thrust, diagram power and diagram efficiency.
2. In the stage of an impulse turbine provided with a single row wheel, the mean
diameter of the blade ring is 800 mm and the speed of rotation is 3000 rpm.
The steam issues from the nozzle with velocity of 300 m/se and the nozzle
angle is 200. The rotor blades are equiangular and the blade friction factor is
0.86. What is the power developed in the blading when the axial thrust on the
blades is 140 Newton?

33. CHAPTER-7:
7. Steam condensers, condensate-feed
water and circulating water system
7.1 Introduction
•If the pressure of the exhaust steam reduced below the
atmospheric pressure and hence its energy, partially or
fully, can not be reutilized, then this phenomenon is called
Steam Condensation.

34. Steam Condensers and
Condensate
The heat transfer device in which the exhaust steam
of a turbine or an engine is condensed by means of
cooling water at pressure below atmospheric, is called
Steam Condenser.
The condensed Steam is called Condensate and can
be again returned to Boiler and It saves the cost of
water.

35. Principle of Condensation
• In order to attain maximum
work, according to Carnot
principle, the heat must be
supplied at Maximum pressure
and temperature and should be
rejected at Minimum pressure
and temperature.
• The steam from the steam
turbine or steam engine could be
exhausted to atmosphere in such
a manner that the back pressure
would below the atmospheric
pressure.

36. Advantages of Condensers
 It increases the work output per kg of steam
supplied to the power plant.
 Reduces the specific steam consumption.
 Reduces the size of power plant of given
capacity.
 Improves the thermal efficiency of power
plant.
 Saves the cost of water to be supplied to
boiler.

37. 7.2 Elements of Condensing Plant
 CONDENSER: In which the exhaust
steam of the turbine is condensed by
circulating cooling water.
 CONDENSATE EXTRACTION PUMP:
to remove the condensate from the
condenser and feed it into the hot-well.
The feed water from hot-well is further
pumped to boiler.
 AIR EXTRACTION PUMP: to remove
air from the condenser, such a pump is
called dry air pump. If air and
condensate both are removed, it is called
as wet air pump.
 CIRCULATING PUMP: used to supply
feed water either from river or from the
cooling tower pond to the condenser.

38. Cont…
 COOLING TOWER:
1. The Ferro concrete made
device (hyperbolic shape) in
which the hot water from the
condenser is cooled by
rejecting heat to current of air
passing in the counter
direction.
2. Ring troughs are placed 8-
10m above the ground level.

39. 7.3 Types of Condensers
i. JET CONDENSERS
The exhaust steam and cooling
water come in direct contact
and as a result the steam is
condensed. It is also called
direct contact condensers.
ii. SURFACE CONDENSERS
The cooling water flows
through a network of tubes
and the exhaust steam passes
over these tubes. The steam
gets condensed due to heat
transfer to coolant by
conduction and convection.

40. Comparison of jet and surface
condenser
S.no
Jet condensers
1. Steam and water comes in
direct contact.
2. Condensation is due to mixing
of coolant.
3. Condensate is not fit for use
as boiler feed until the treated
cooling water is supplied.
4. It is cheap. Does not affect
plant efficiency.
5. Maintenance cost is low.
6. Vacuum created is up to 600
mm of Hg.
Surface condensers
Steam and water does not come in
direct contact.
Condensation is due to heat transfer
by conduction and convection.
Condensate is fit for reuse as boiler
feed.
It is costly. Improves the plant
efficiency.
Maintenance cost is high.
Vacuum created is up to 730 mm of
Hg.

41. i. JET CONDENSERS
CLASSIFICATION OF JET CONDENSERS
1. Low level jet condensers
i) Counter flow type
ii) Parallel flow type
2. High level jet injectors
3. Ejector jet condensers

42. (i) LOW LEVEL COUNTER FLOW JET INJECTOR
• The cooling
water to be lifted
into the condenser
up to a height of
5.5m.
•It is having
disadvantage of
flooding the steam
turbine if the
condensate
extraction pump
fails.

43. 1.(ii) LOW LEVEL PARALLEL FLOW JET INJECTOR
• The mixture of
condensate, coolant and
air are extracted with the
help of wet air pump.
• Vacuum created in the
condenser limits up to
600 mm of Hg.

44. 2. HIGH LEVEL JET CONEDNSER/ BAROMETRIC JET CONDENSER
• It is also called
Barometric jet condenser
since it is placed above
the atmospheric pressure
equivalent to 10.33 m of
water pressure.
• Condensate extraction
pump is not required
because tail pipe has
incorporated in place of
it.

45. 3. EJECTOR JET CONDENSER
• The cooling water enters
the top of the condenser
at least under a head of
6m of water pressure
with the help of
centrifugal pump.
• This system is simple,
reliable and cheap.
• Disadvantage of mixing of
condensate with the
coolant.

46. ii. SURFACE CONDENSERS
Surface condensers are of two types
i. SURFACE CONDENSERS
In this steam flows
outside the network of
tubes and water flows
inside the tubes.
The number of water passes
it may be:
a. Single pass
b. Multipass
ii. EVAPORATIVE CONDENSERS
• In this condenser shell is
omitted.
• The steam passes through
condenser tubes, the water is
sprayed while the air passes
upward outside the tube.
• The direction of condensate
flow and tube arrangement:
a. Down flow condenser
b. Central flow condenser

47. DOUBLE PASS SURFACE CONDENSER
• It consist of air tight cast
iron cylindrical shell.
• If cooling water is impure,
condenser tubes are made
up of red brass.

48. DOWN FLOW SURFACE CONDENSER
This condenser employs two separate
pumps for the extraction of condensate
and the air.
Baffles are provided so that the air is
cooled to the minimum temperature
before it is extracted.
The specific volume of cooled air
reduces, thereby, reduces the pump
capacity to about 50%.
Therefore, it also reduces the energy
consumption fro running the air pump.

49. CENTRAL FLOW SURFACE CONDENSER
•Air extraction pump is
located at the centre of the
condenser tubes.
•Condensate is extracted
from the bottom of the
condenser with the help of
condensate extraction pump.
•Provides the better contact
of steam.

50. EVAPORATIVE CONDENSER
• The exhaust steam is passed through the
series of gilled tubes called condenser coils.
• Thin film of cooling water trickles over
these tubes continuously from water
nozzles.
• During the condensation of steam, this thin
film of water is evaporated and the
remainder water is collected in the water
tank.
• The condensate is extracted with the help of
wet air pump.
• The air passing over the tubes carries the
evaporated water in the form of vapour and
it is removed with the help of induced draft
fan installed at the top.

51. Merits And Demerits of Jet Condensers
MERITS
1. Less quantity of
cooling water is
required to condense
the steam.
2. Simple in construction
and low in cost.
3. Does not require
cooling water pump.
4. Less space is
required.
5. Low maintenance
cost.
DEMERITS
1. The condensate is a
waste.
2. Less suitable for high
capacity plants.
3. Large length of pipes
required, hence piping
cost is high.
4. Loss of vacuum due to
leakage of air from
long pipings.

52. Merits And Demerits of Surface Condensers
MERITS
1. No mixing of cooling
water and steam,
hence the condensate
directly pumped into
the boiler.
2. Any kind of feed
water can be used.
3. Develops high vacuum,
therefore suitable fro
large power plants.
4. Require less power to
run the air extraction
and water extraction
pump.
5. System is more
DEMERITS
1. Require large quantity
of cooling water.
2. System is complicated,
costly and requires
high maintenance cost.
3. Require large floor
space since it is bulky.

53. 7.4 AIR PUMPS
TYPES OF AIR PUMPS
1. WET AIR PUMP
2. DRY AIR PUMP

54. Cont…
WET AIR PUMP
Used to remove both
condensate and the
air from the
condenser.
These may be of type:
i) Reciprocating
ii) Rotary
DRY AIR PUMP
Used only to remove
moist air.
These may be of type:
i) Reciprocating
ii) Rotary

55. RECIPROCATING AIR PUMP
(Edward’s Air Pump)
• This pump is suitable
only for small power
plants.

56. STEAM JET AIR EJECTOR
• It consists of
convergent- divergent
nozzle and a diffuser.
• Steam from boiler
enters from ‘a’ nozzle
where its K.E increases
and pressure decreases.
• Pipe ‘c’ is connected to
condenser form where
the air mixes with low
pressure steam at ‘b’.
• The mixture of steam
and air moves to
diffuser ‘d’ where its
velocity decreases and
pressure increases at

57. STEAM JET AIR EJECTOR
• The system shows only one
ejector, if more ejectors
are introduced, a very low
pressure can be obtained
in the condenser.
• Usually up to four numbers
of ejectors are used which
can reduce the pressure in
the condenser up to 0.08
bar.
• It is simple in
construction, cheap, highly
efficient and don’t have