1. The boiler as a steam
generator.

2. Steam Generators/Boilers
• “A combination of apparatus for producing, furnishing or
recovering heat together with apparatus for transferring
the heat so made available to water which would be
heated and vaporized to steam form” (ASME).
• Basis for classification of boilers
o Contents inside the tube
o Firing system
o Position of drum
o Pressure
o Nature of water circulation

3. Water Tube and Fire Tube Boilers

4. Requirements of a Good Boiler
• Low cost of installation, operation and maintenance
• Easy maintenance
• High efficiency
• Safety
• High transportability
• High steam production rate
• Good quality of steam
• Quick steam generation capacity
• Meeting fluctuating demand of steam

5. Cochran Boiler

6. Babcock and Wilcox Boiler

7. Locomotive Boiler

8. Lancashire Boiler

10. Boiler Accessories
• Economiser
• Air preheater
• Super heater
• Steam trap
• Steam separator
• Injector

11. Economiser

12. Air Preheater

13. Superheater

14. Steam Separator

15. Boiler Performance
Heat loss in the boiler
Heat balance sheet

16. E-1
E-2
E-3
ECONOMISER
EVAPORATOR
STEAM
DRUM
SUPERHEATER

17. • 1. Introduction,
• 2. Equivalent Evaporation
• 3. Boiler Efficiency.
• 4. Boiler Trial
• 5. Heat Losses in a boiler
• 6. Heat balance sheet

18. • Introduction
• The performance of a steam boiler is measured in
terms of its ‘evaporative capacity
• In actual practice, the feed water temperature and
working pressure varies considerably.
• The feed temperature usually adopted is 100° C
and the working pressure as normal atmospheric
pressure, i.e. 1.013 bar. It is assumed that the
boiler is supplied with water at the boiling
temperature (100°C) corresponding to the
atmospheric pressure.

19. Equivalent evaporation
• It is the amount of water evaporated from feed
water at 100° C and formed into dry and saturated
steam at 100° C at normal atmospheric pressure. It
is, usually, written as “from and at 100 °C”
• As the water is already at the boiling temperature.
it requires only latent heat at 1.013 bar to convert
it into steam at the temperature (100° C). The value
of this latent heat is taken as 2257 kJ/kg. (hfg at
100°C)

21. Equivalent evaporation E
me = Kg/h or kg/kg of fuel burnt

22. Is called the factor of evaporation Fe and is
always greater than unity for all boilers.
𝐹𝑒 =
ℎ − ℎ𝑓1
2257

23. Boiler Efficiency
• It may be defined as the ratio of heat actually used in
producing the steam to the heat liberated in the
furnace. It is also known as thermal efficiency of the
boiler.

24. Worked example
• A boiler was used to produce wet steam at 11 bar with a
dryness fraction of 0.8 from water at 12 C. Fuel is supplied to
the furnace of the boiler at a rate of 325 kg per hour. The
calorific value of the fuel is 35700 kJ/kg. The mass of water
supplied to the boiler in
5 hrs 23 minutes = 15630 kg.
• The mass of water was measured before and after the steam
generation process and it was discovered that in order to
restore the original level in the boiler 1200 kg of water was
required.
• Evaluate:
• Actual evaporation per kilogram of coal
• Equivalent evaporation from and at 100 C
• Thermal efficiency of the boiler.

25. Performance of Boilers
• Evaporation Rate: It is steam generation rate of boilers
which may be expressed in terms of kg of steam per unit
heating surface area or kg of steam per cubic metre of
furnace volume or kg of steam per kg fuel burnt.
• Equivalent Evaporation: It is equivalent of energy of
evaporation of 1 kg of water at 100°C to dry and
saturated steam at 100°C, standard atmospheric
pressure of 1.013 bar. Hence, the equivalent
evaporation of 1 kg of water at 100°C needs 2,257 kJ.
• Factor of Evaporation: It is ratio of heat absorbed by 1 kg
of feed water under working conditions to latent heat of
steam at atmospheric pressure.

26. • Boiler Efficiency: It is ratio of heat absorbed by
water in boiler to heat supplied to boiler per unit
time.

27. Thank You.

29. Worked example
• A boiler was used to produce wet steam at 11 bar with a
dryness fraction of 0.8 from water at 12 C. Fuel is supplied to
the furnace of the boiler at a rate of 325 kg per hour. The
calorific value of the fuel is 35700 kJ/kg. The mass of water
supplied to the boiler in
5 hrs 23 minutes = 15630 kg.
• The mass of water was measured before and after the steam
generation process and it was discovered that in order to
restore the original level in the boiler 1200 kg of water was
required.
• Evaluate:
• Actual evaporation per kilogram of coal
• Equivalent evaporation from and at 100 C
• Thermal efficiency of the boiler.

30. Boiler trial
The main objectives of a boiler trial are:
1. To determine the generating capacity of the
boiler.
2. To determine the thermal efficiency of the
boiler when working at a definite pressure.
3. To prepare heat balance sheet for the boiler.

31. Heat loss in a boiler
• We know that the efficiency of a boiler is the ratio
of heat utilised in producing steam to the heat
liberated in the furnace.
• The heat utilised is always less than the heat
liberated in the furnace.
• The difference of heat liberated in the furnace and
heat utilised in producing steam is known as heat
lost in the boiler.

32. hf1
hf2
h3 = hf + x hfg
h4 = hsup
1
2
3
4
Evaporator Economiser
Superheater
Steam Drum

33. Heat lost to dry flue gases per kg of
fuel

34. Heat lost in moisture present in the
fuel
It is assumed that the moisture is converted into superheated
steam at atmospheric pressure 1.013 bar).
•Heat lost in moisture present in the fuel

35. heat lost to steam formed by combustion of hydrogen
per kg of fuel

36. 4 The heat lost due to unburned
carbon per kg of fuel

37. Heat lost due to incomplete combustion of carbon to
carbon monoxide.
• This loss generally occurs in the boiler due to
insufficient air supply.

38. Heat lost due to radiation.
• There is no direct method for finding the heat lost
due to radiation. This loss is calculated subtracting the
heat utilised in raising steam and heat losses from the
heat supplied.
• A Heat balance sheet shows the complete account of
heat supplied by 1 kg of dry fuel and heat consumed.
The heat supplied is mainly utilised for raising the
steam and the remaining heat is lost.

39. Heat balance sheet
Heat supplied kJ Heat consumed kJ %
Heat supplied by
1 kg of fuel
Xf 1 Heat lost to dry flue gases per kg of fuel
2 Heat lost in moisture present in the fuel.
3 heat lost to steam formed by combustion
of hydrogen per kg of fuel
4 The heat lost due to unburned carbon per
kg of fuel
5. Heat lost due to incomplete combustion
of carbon to carbon monoxide.
6. Heat lost due to radiation etc.
X6 = Xf – (x1 + x2 + x3 + x4 + x5)
X1
X2
X3
X4
X5
X6

40. Example
• In a boiler the following observations were made
• Pressure of steam 10 bar
• Steam condensed 540 kg/hr
• Fuel used 65 kg/hr
• Moisture in fuel 2% by mass
• Mass of dry flue gas 9 kg/kg of fuel
• Lower calorific value of fuel 32000 kJ/kg
• Temperature of flue gases 325°C
• Temperature of boiler house 28°C
• Feed water temperature 50°C
• Mean specific heat (flue gases) 1 kJ/kgK
• Dryness fraction of steam 0.95
Draw up a heat balance sheet for the boiler

41. • Heat supplied by 1 kg of fuel
• =(1 - 0.02) x 32000 = 31360KJ
• Heat utilised in raising steam per kg of fuel
• From steam tables, for a feed water temp of 50°C
• hf = 209.3 kJ/kg
kg
31
.
8
65
540
m
m
me
f
s




42. • Correspondingly for steam at 10 bar
• hf = 762.6 kJ/kg, hfg = 2013.6kJ/kg
• Heat utilised in raising steam per kg of fuel
• Heat carried away by dry flue gas
    kJ
t
t
c
m b
g
pg
g 2673
28
325
1
9 






   
  kJ
h
xh
h
m
h
h
m f
fg
f
e
f
f
e
20495
3
.
209
6
.
2013
95
.
0
6
.
762
31
.
8
1
1
2













43. • Heat carried away by moisture in fuel per kg of fuel
• From tables @ 28°C, hb = 117.3 kJ/kg
• Heat carried away by moisture in fuel
 
 
 
  kJ
h
t
c
m b
g
p
m
6
.
60
3
.
117
100
325
1
.
2
2676
02
.
0
100
2676










Cp for steam = 2.1 kJ/kgK

44. Heat balance sheet
Heat supplied kJ Heat consumed kJ %
Heat supplied
by 1 kg of
fuel
31360
1 Heat utilised in raising steam
2 Heat carried away by flue gases.
3 Heat lost in moisture present in the
fuel.
4. Heat lost due to radiation etc.
X6 = Xf – (x1 + x2 + x3)
20495
2673
60.6
= 8131.4
Totals 31360 31360

45. The following particulars were recorded during a steam
boiler trial
Pressure of steam = 11 bar;
mass of feed water = 4600 kg/hr;
Temperature of feed water = 75C;
dryness fraction of steam = 0.96;
coal used 490 kg/hr;
calorific value of coal 35700 kJ/kg;
Moisture in coal 4% by mass;
Mass of hydrogen in fuel 18% by mass
mass of flue gases 18.57 kg/kg coal;
temperature of flue gases = 300C;
Boiler house temperature = 16C;
specific heat of flue gases = 0.97 kJ/kg K
Draw the heat balance sheet of the boiler per kg of

46. In a boiler trial, the following observations were obtained.
Pressure of steam = 8.5 bar;
mass of feed water = 1520 kg/hr;
Temperature of feed water = 30C;
dryness fraction of steam = 0.95;
coal used 200 kg/hr;
Ash and unburnt coal collected = 16 kg/hr
Calorific value of ash and unburnt coal = 3780 kJ/kg
calorific value of coal 27300 kJ/kg;
Moisture in coal 4% by mass;
mass of flue gases 17.3 kg/kg coal;
temperature of flue gases = 330C;
Boiler house temperature = 17C;
specific heat of flue gases = 1 kJ/kg K
Draw the heat balance sheet of the boiler per kg of coal.

48. Heat balance sheet
Heat supplied kJ Heat consumed kJ %
Heat supplied
by 1 kg of
(dry) fuel
(1-%m)CV 1 Heat utilised in raising steam per kg of
steam
𝑚𝑒 ℎ𝑓 + 𝑥ℎ𝑓𝑔 − ℎ𝑓1
2 Heat carried away by flue gases.
𝑚𝑔𝐶𝑝𝑔 𝑡𝑔 − 𝑡𝑏
3 Heat lost in moisture present in the fuel.
𝑚𝑚 ℎ𝑔 + 𝐶𝑝𝑠 𝑡𝑔 − 100 − ℎ𝑏
4 Heat lost in water formed from
hydrogen present in the fuel.
𝑚𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛 ℎ𝑔 + 𝐶𝑝𝑠 𝑡𝑔 − 100 − ℎ𝑏
4. Heat lost due to radiation etc.
X6 = Xf – (x1 + x2 +x3 +x4)
Totals