Cooling towers

1. Yashvir Singh
Department of Mechanical Engineering
Condensers
and
Cooling Towers
Applied Thermodynamics-II 1

2. 2
Outline
• Introduction
• Types of condensers
• Sources of air in condenser
• Effects of air leakage
• Methods of obtaining maximum vacuum in condenser
• Vacuum & condenser efficiency
• Mass of cooling water required
• Edward air pump
• Necessity of cooling ponds and cooling towers
• Condenser water cooling systems
• Types of cooling towers and cooling ponds

3. Introduction :
3
• Objective of a steam condenser:
– To create low back pressure for turbine exhaust
– To condense the exhaust steam from the turbine

4. 4
Introduction :
Advantages :
• Increases work done per kg of steam
• Increases thermal efficiency of plant
• Condensed steam provides a source of good pure feed
water.
• High temperature condensate water reduces amount of
heat supplied per kg of steam
• Reduces corrosion of boiler tube

5. 5
Introduction :
Elements of steam condensing plant :
• Condenser
• Supply of cooling water
• Condenser cooling water pump
• Air extraction pump
• Make up water pump
• Condensate extraction pump
• Boiler feed pump
• Hot well
• Cooling tower

6. Introduction :
6

7. 7
Types of Condensers :
Two main types :
• Jet condenser
• Surface condenser

8. 8
Jet Condenser :
• It is further classified on the basis of Direction of
flow of the condensate and Arrangement of the
tubing system.
Types:
• Low level jet condenser
– Parallel flow type
– Counter flow type
• High level jet condenser
• Ejector jet condenser

9. Low Level Parallel Flow Jet Condenser :
9

10. Low Level Counter Flow Jet Condenser :
10

11. High Level Jet Condenser :
11

12. Ejector Condenser :
12

13. 13
Jet Condenser :
Advantages :
• Lower quantity of cooling water required
• Simple in design
• Require less floor space
• Lower capital and maintenance cost
• Due to direct contact heat transfer is more effective
Disadvantages :
• Condensate cannot be directly used as feed water
• Power consumption in pump is more
• Piping cost is high.

14. 14
Surface Condenser :
• It is further classified as follows :
• According to number of cooling water passes
– Single pass
– Multi pass
• According to direction of condensate flow
– Down flow condenser
– Central flow condenser

15. Double Pass Surface Condenser :
15

16. Down Flow Surface Condenser :
16

17. Down Flow Surface Condenser :
17

18. Central Flow Surface Condenser :
18

19. Evaporative Condenser :
19

20. Evaporative Condenser :
20

21. 21
Evaporative Condenser :
Advantages:
• Simple in design and low initial cost
• Low quantity cooling water required
• Small capacity cooling water pump
•Low operating cost.
Disadvantages:
• Vacuum maintained is less
• Due to less vacuum work done per kg of steam is less
• Not suitable for medium and large power plant

22. 22
Surface Condenser :
Advantages:
• Due to high vacuum increases thermal efficiency and
output of plant
• Condensate can be reused as boiler feed water
• Auxiliary power requirement is less
• Less amount of air is carried to the boiler
• Any kind of feed water can be used
• Can develop high vacuum, so suitable for medium
and large power plants

23. 23
Surface Condenser :
Disadvantages:
• Very bulky and requires more floor space
• High manufacturing, running and maintenance cost
• Requires large quantity of cooling water

24. 24
Surface Condenser :
Requirement of good surface condenser:
• There should be uniform distribution of exhaust steam
throughout the heat transfer surface of the condenser
• There should not be any leakage of air into the
condenser
• There should not be any tube leakage
• The heat transfer surface in contact with cooling water
must be free from any deposit as scaling reduces the
efficiency of heat exchangers.

25. 25
Comparison :
Jet Condenser Surface Condenser
Cooling water and steam
come in direct contact
Cooling water and steam
do not come in direct
contact
Maintenance cost is low Maintenance cost is high
More suitable for low
capacity plants
More suitable for high
capacity plants
Condensate is not used as
boiler feed water
Condensate is directly used
as boiler feed water

26. 26
Comparison :
Jet Condenser Surface Condenser
Condensation of steam is
due to heat transfer by
mixing of steam with water
Condensation of steam is
due to heat transfer by
steam to water through
tubes
Economic and simple
condensing plant
Costly and complicated
condensing plant
More power consumption
in air pump
Less power consumption in
air pump

27. 27
Sources of Air in Condenser:
• The boiler feed water contains dissolved air. From the
boiler it is carried off by steam and to the turbine and
finally to the condenser
• The air leaks through the joints, packing and glands
into the condenser where the pressure is below the
atmospheric pressure.
• Air dissolved with cooling water is carried in case of
jet condensers.

28. 28
Effects of Air Leakage :
• Increases the back pressure on the turbine with the
effect that there is low thermal efficiency of the
plant
• Reduces the rate of condensation of steam because air
having poor thermal conductivity, reduces the
overall heat transfer from the steam air mixture.
• The presence of air in the condenser increases the
corrosive action.

29. 29
Method of obtaining max vacuum :
• Air pump : extract the air and other non-condensable
gases from the condenser to maintain a desired
vacuum.
– Wet pump : removes a mixture of condensate and air
with other non-condensable gases.
– Dry pump : removes the air and other non-condensable
gases only.

30. Method of obtaining max vacuum :
• Steam Jet Air Ejector : remove air from condenser
when a wet pump is employed. It consist of
convergent – divergent nozzle and a diffuser.
30

31. 31
Method of obtaining max vacuum :
• De-aerated feed water : the de-aeration is the
process of removal of non condensable gases from
feed water. It helps both in maintaining better vacuum
in the condenser and controlling corrosion of the steel
and piping of the steam power plant.
• Air tight joints : the air leaks through the joints,
packings and glands into the condenser. This can be
reduced by proper workmanship while making the
joints and these are maintained as such by proper
inspection from time to time.

32. 32
Vacuum & Condenser Efficiency :
• The minimum absolute pressure at the steam inlet of
a condenser is the saturation pressure corresponding
to the temperature of the condensed steam. This
vacuum is called Ideal Vacuum. It is the maximum
vacuum that can be obtained in a condensing plant,
with no air present at that temperature.
• The actual pressure in the condenser is greater than
the ideal pressure by an amount equal to the pressure
of air present in the condenser.
• The ratio of the actual vacuum to the ideal vacuum is
known as Vacuum Efficiency.

33. Vacuum & Condenser Efficiency :
33
• If,
Ps = Saturation pressure of steam corresponding to the steam
temperature entering into condenser
Pc = Total pressure of air and steam in the condenser (Pa + Ps).
Pb =Atmospheric pressure.
• Ideal vacuum possible without air leakage = (Pb - Ps)
• Actual vacuum existing in condenser due to air
leakage

34. Vacuum & Condenser Efficiency :
34
• It is the ratio of actual rise in the temperature of
cooling water to the maximum possible rise in
temperature of cooling water.

35. Mass of Cooling Water Required :
35

36. Mass of Cooling Water Required :
36

37. Edward Air Pump :
37

38. Edward Air Pump :
38

39. 39
Necessity of Cooling Ponds & Towers :
• To absorb the heat from steam.
• It is necessary to pre-cool the water coming out of
condenser before using again in a closed system. As
with increase in temperature pressure also increases.

40. 40
Condenser Water Cooling System :
• Cooling water systems used in practice according to
availability of water are :
– Open Cooling System (Once Through System)
– Closed Cooling System
– Mixed Cooling System

41. Open Cooling System (Once Through System) :
41

42. Closed Cooling System :
42

43. Mixed Cooling System :
43

44. 44
Types of Cooling Towers & Ponds :
• Cooling towers cool the warm water discharged from
the condenser and feed the cooled water back to the
condenser.
• Types of cooling towers :
– Natural draught cooling towers
– Mechanical cooling towers
• Forced draught cooling towers
• Induced draught cooling towers

45. Natural Draught Cooling Towers :
45

46. Natural Draught Cooling Towers :
AjaypalsinhBarad 46

47. 47
Natural Draught Cooling Towers :
Advantages :
• Its operating and maintenance costs are less since no
fans are needed.
• It creates its own draft assuring efficient operation
even when there is no wind.
•Longer life.
Disadvantages :
• High capital cost
• Performance varies with the seasonal changes

48. Forced Draught Cooling Tower :
48

49. Forced Draught Cooling Tower :
49

50. 50
Forced Draught Cooling Tower :
Advantages:
• More efficient
• Problems of blade erosion are avoided
• Fan is located at ground so more safe
• Vibration and noise are less as mechanical equipments are
set on a solid foundation.
Disadvantages :
• Possibility of recirculation of hot humid exhaust air
coming out from the top of the tower
• Fan size is limited to 4 meters
• Possibility of ice formation on fan blades in cold weather

51. Induced Draught Cooling Tower (Counter) :
51

52. Induced Draught Cooling Tower (Counter) :
52

53. Induced Draught Cooling Tower (Cross) :
53

54. 54
Induced Draught Cooling Tower :
Advantages:
• Coldest water comes in contact with the driest air and
the warmest water comes in contact with the most air.
• The recirculation of hot humid air is not a major
problem.
• Larger fan size can be used.
• Lower first cost due to the reduced pump capacity
• Capable of cooling through a wide range.

55. 55
Induced Draught Cooling Tower :
Disadvantages:
• Not economical up to the capacity of 15000 liters of
water per minute.
• Higher power motor is required to drive the fan
compared to forced draught.
• Maintenance cost is high.
• Fan bearings need to be cooled.

56. 56
Terms related with Cooling Tower:
Fill:
• The hot water from the condenser is sprayed through
the nozzles over a series of horizontal bars called fill
or packing.
Drift:
• When the air flows from bottom to top of the cooling
tower, it carries fine water droplets along with the air.
These fine droplets of water are called drift.

57. 57
Terms related with Cooling Tower:
Approach (A):
• It is defined as the difference between the exit
temperature of the cooling water (tc2) and the wet
bulb temperature of the ambient air (twb).
A = tc2 -twb
Cooling range (R):
• It is the difference in temperature of the incoming
warm water (tc1) and the exit temperature of cooled
water (tc2).
R = tc1 -tc2

58. 58
Cooling Ponds :
• The cooling pond is one of the simplest method of
cooling the condenser water. This method is less
efficient than cooling tower.
• Types of cooling ponds:
1. Natural and Directed flow cooling pond
2. Single deck and Double deck cooling pond
3. Open and Louvre fence cooling pond.

59. Cooling Ponds :
Natural flow cooling pond
59

60. Cooling Ponds :
Directed flow cooling pond
60

61. Cooling Ponds :
Single deck cooling pond
61

62. Cooling Ponds :
Double deck cooling pond
62

63. Cooling Ponds :
Single deck cooling pond
63

64. Cooling Ponds :
• Spray pond with Louvre fence
Ajaypalsinh Barad 64

65. 65
Cooling Ponds :
Advantages:
• Initial cost is less
•Simple in design and arrangement
Disadvantages:
• Requires large area for cooling.