1. STEAM BOILERS

2. Contents
 Classification of boilers
 Essentialities of boilers
 Selection of different types of boilers
 Study of boilers, boiler mountings and accessories
 Performance of boilers
 Working principle of steam turbines

3. Definition of Boiler
 A boiler is a device used to generate steam at a desired
pressure and temperature by transferring heat energy
produced by burning fuel to water to change it to steam.
 It is a combination of apparatus used for producing,
furnishing or recovering heat together with the apparatus for
transferring the heat so made available to the fluid being
heated and vaporized.

4. Function of a boiler
 The fluid is contained in the boiler drum called shell and the
thermal energy released during combustion of fuel is
transferred to water and this converts water into steam at the
desired temperature and pressure.

5. Applications of boilers
Power generation: Mechanical or electrical power may be
generated by expanding steam in the steam engine or steam
turbine.
Heating: The steam can be used for heating residential and
industrial buildings in cold weather and for producing hot waters
for hot water supply.
Industrial processes: Steam can also be used for industrial
processes such as for sizing and bleaching etc. in textile
industries and other applications like sugar mills, cement,
agricultural and chemical industries.

6. Requirements of an efficient boiler
 The boiler should generate maximum amount of steam at a
required pressure and temperature and quality with minimum
fuel consumption and expenses
 Steam production rate should be as per requirements
 It should be absolutely reliable
 It should be light in weight
 It should not occupy large space
 It should be capable of quick starting
 It should conform to safety regulations
 The boiler components should be transportable without difficulty

7.  The installation of the boiler should be simple
 It should have low initial cost, installation cost and maintenance
cost.
 It should be able to cope with fluctuating demands of steam
supply.
 All parts and components should be easily accessible for
inspection, repair and replacement.
 The tubes of the boiler should not accumulate soot or water
deposits and should be sufficiently strong to allow for wear and
corrosion
 The water and gas circuits should be such as to allow minimum
fluid velocity (for low frictional losses)

8. Factors to be considered for selection of good boilers
 The working pressure and quality of steam required
 Steam generation rate
 Floor area available
 Accessibility for repair and inspection
 Comparative initial cost
 Erection facilities
 The portable load factor
 The fuel and water available
 Operating and maintenance costs

9. Classification of boilers
 Relative position of hot gases and water
 Fire tube boilers (Cochran, Lancashire, Cornish, Locomotive)
 Water tube boilers (Babcock and Wilcox boiler, Stirling boiler)
 Method of firing
 Internally fired boilers ( Lancashire, Locomotive)
 Externally fired boilers (Babcock and Wilcox boiler)
 Pressure of steam
 High pressure boilers(>80 bars-Cochran, Lancashire, Cornish,
Locomotive)
 Low pressure boilers (<=80 bars-Babcock and Wilcox boiler,
Lamont boiler)

10.  Method of circulation of water
 Natural circulation boilers (Lancashire, Locomotive, Babcock
& Wilcox boilers)
 Forced circulation boilers (Two large fire tubes Lancashire
boiler, Single large fire tube Cornish boiler, Cochran boiler,
Many small tubes Locomotive boiler, Babcock Wilcox water
tube boiler)
 Nature of service to be performed
 Land boilers
 Mobile boilers (or) Portable boilers
 Position and number of drums
 Single drum boilers
 Multi-drum boilers(Longitudinal or crosswise)

11.  Design of gas passages
 Single pass boilers
 Return pass boilers
 Multi-pass boilers
 Nature of draught
 Natural draught boilers
 Artificial draught boilers
 Heat source
 Combustion of solid, liquid or gaseous fuels
 Electrical and nuclear energy
 Hot waste gases of other chemical reactions
 Fluid used
 Steam boilers
 Mercury boilers
 Special boilers for heating special chemicals
 Material of construction of boiler shell
 Cast iron boilers
 Steel boilers

12. At atmospheric pressure water volume increases 1,600 times
Fig. Schematic overview of boiler

13. Boiler systems
 Water treatment system
 Feed water system
 Steam System
 Blow down system
 Fuel supply system
 Air Supply system
 Flue gas system

14. Types of boilers
 Fire tube boilers
 Lancashire,
 Cornish,
 Cochran,
 Locomotive.
 Water tube boilers
 Babcock & Wilcox boiler,
 Stirling boiler.

15. 1.Fire tube boiler
 The combustion gases pass
inside boiler tubes, and heat is
transferred to water on the shell
side.
 Relatively small steam
capacities (12,000 kg/hour)
 Low to medium steam
pressures (18 kg/cm2)
 Operates with oil, gas or solid
fuels

16. 2.Water tube boiler
 In this type of boiler water
passes through the tubes while
the gases remain in the shell
side, passing over the tube
surfaces
 Used for high steam demand
and pressure requirements
 Capacity range of 4,500 –
120,000 kg/hour
 Lower tolerance for water
quality and needs water
treatment plant

17. 3.Packaged boiler
 Comes in complete package
 Features
 High heat transfer
 Faster evaporation
 Good convective heat transfer
 Good combustion efficiency
 High thermal efficiency
 Classified based on number of
passes

18. 1.Lancashire boiler
 It is stationary fire tube, internally fired, horizontal, natural
circulation boiler.
 This is a widely used boiler because of its good steaming quality
and its ability to burn coal of inferior quality.
 This boiler is set in brickwork forming external flue so that the
external part of the shell forms part of the heating surface.

24. Advantages
 The feed pipe projecting into the boiler is perforated to ensure
uniform water distribution.
 Its heating surface area per unit volume at the boiler is
considerably large.
 Its maintenance is easy.
 It is suitable where a large reserve of hot water is needed. This
boiler due to the large reserve capacity can easily meet load
fluctuations.
 Super‐heater and economizer can be easily incorporated into the
system, therefore; overall efficiency of the boiler can be
considerably increased (80‐85%).

26. Locomotive boiler
 Locomotive boiler is a
horizontal fire tube type
mobile boiler. The main
requirement of this boiler is
that it should produce steam
at a very high rate.
 Therefore, this boiler requires
a large amount of heating
surface and large grate area to
burn coal at a rapid rate.

27. 3.Cochran Boiler
 It is a multi-tubular vertical fire tube boiler having a number of
horizontal fire tubes. This is the modification of a simple vertical
boiler where the heating surface has been increased by means of
a number of fire tubes.
 It is very compact and requires minimum floor area.
 Any type of fuel can be used with this boiler.
 Well suited for small capacity requirements.

31. Advantages & Disadvantages of COCHRAN BOILER
 Advantages
 Cochran Boiler occupies less floor space.
 Construction cost of Cochran Boiler is Low.
 Cochran boiler is semi-portable and hence easy to install and
transport.
 Because of self contained furnace no brick work setting is
necessary.
 Disadvantages
 The capacity of the Cochran boiler is less because of the vertical
design.
 Cochran Boiler requires high head room space.
 Because of the vertical design, it often presents difficulty in
cleaning and inspection.

32. Water tube boiler
 Features of Babcock & Wilcox boiler:
 Horizontal, Straight & Stationary
 Externally fired
 Natural circulation
 Water tube boiler
 Minimum steam pressure of 10 bar
 Minimum evaporative capacity of 7000 kg of steam per
hour.

34. BABCOCK & WILCOX BOILER

35. Stirling boiler
 The Stirling boiler is an early
form of water-tube boiler, used
to generate steam in large land
based stationary plants.
 Stirling boilers are one of the
larger arrangements for a water
tube boiler.
 They consist of a large brick-
built chamber with a sinuous gas
path through it, passing over
near-vertical water tubes that
zigzag between multiple steam
drums and mud drums.

37. Differences between Water-tube and Fire-tube boilers
Particulars Fire tube boiler Water tube boiler
Position of water and hot
gases
Hot gases inside the tubes and
water outside the tube
Water inside the tube and
hot gases outside the tubes
Mode of firing Operating
pressure
Generally internally fired
Operating pressure limited to
16 bar
Externally fired Can work
under as high pressures as 100
bar
Rate of steam
consumption
Lower Higher
Suitability for large power
plants
Not suitable Suitable
Risk on explosion Involves lesser risk on explosion
due to lower Pressure
Involves more risk on bursting
due to high pressure
Floor area For a given power, occupies more For a given power, occupies
less

38. particulars Fire tube boiler Water tube boiler
Construction Difficult Simple
Transportation Difficult Simple
Shell diameter Large for same power Small for same power
Treatment of water Not so necessary More necessary
Accessibility of various
parts
Various parts are not so easily
accessible for cleaning, repair
and inspection
Various parts are more
accessible
Requirement of skill Require less skill for efficient and
economic working
Require more skill and careful
attention
Differences between Water-tube and Fire-tube boilers Contd…..