Boilers

1. STEAM
GENERATORS/BOILERS
Presented By:
Saurabh Kumar
Assistant Professor
EEE, Deptt.

2. PPT OBJECTIVES
 This course provides a basic understanding of principles related To
Steam generators and their types.

3.  A steam generator or boiler is a combination of systems and equipment
in which the chemical energy of fossil fuels is converter into thermal
energy which is then transferred to a working fluid (water) so as to
convert it into steam at high pressure and temperature.
 This high pressure and temperature steam is then used for the
development of power in a steam engine or turbine.
INTRODUCTION

4.  There are many ways to classify the boilers:
1. According to capacity
(a) Low capacity boilers- capacity < 20 tonnes of steam per hr.
(b) Medium capacity boilers- capacity = 20 to 75 tonnes/hr
(c) High capacity boilers- capacity > 100 tonnes/hr.
2. According to pressure of steam
(a) Low pressure boilers – pressure < 30 atm.
(b) Medium pressure boilers – pressure = 30 to 70 atm.
(c) High Pressure boilers – pressure upto 150 atm.
(d) Super pressure boilers – 150 to 190 atm.
(e) Super critical boilers – pressure > 225 atm.
3. According to design
(a) Tank or shell boiler:
 Consists of a cylindrical water drum containing one or more flue tubes
through which the flue gases are circulated.
 Used for plants having small steam raising capacity.
 Efficiency: 80%
Classification of Boilers

5. (B) Fire tube or smoke tube boilers:
 Essentially composed of a water filled pressure vessel containing a nest
of tubes through which the hot flue gases flow and heat is transferred
from hot gases to water in vessel.
 Advantages:
1. Simple
2. Least expensive
3. Ability to raise rapidly large quantities of steam per unit area of fire
grate.
4. Entire heating surface is devoted to the production of saturated steam.
 Disadvantages:
1. High pressure water is placed on the external surface of the tubes.
 Tubes has essentially half the strength for external pressure then it has
for internal pressure, type is limited to relatively low steam pressures.
 Maximum drum diameter is about 2.5 m
 Maximum steam pressure is limited to 17 atm.
Classification of Boilers

6. 2. Event of sudden and major tube failure, the high pressure water rushes
into the hot combustion chamber generating large quantities of steam in
the furnace.
 Likely to produce steam explosion in the furnace.
3. For higher pressure boilers becomes extremely heavy.
Classification of Boilers

7. (C) Water tube boilers:
 High pressure water passes through nests of tubes which are in the path
of hot flue gases.
 Efficiency : 92 %
 Suitable where large quantities of steam are to be raised rapidly in a
limited space.
 For raising more than 375 t/hr. of steam at pressures upto 350 atm and
temperatures more than 550ᵒC are being used, in large power plants.
Classification of Boilers

8. (D) According to heating surface arrangement
1. Horizontal water tube boilers
2. Vertical water tube boilers
(E) According to the number of boiler passes: single two, three, multi-
pass boilers
(F) According to the purpose: Power plant, industrial, locomotive and
heating boilers.
(G) According to water circulation: Natural circulation or forced
circulation boilers.
Classification of Boilers

9. Boiler properties:
1. Safety: The boiler should be safe under operating conditions.
2. Accessibility: The various parts of the boiler should be accessible for repair and
maintenance.
3. Capacity: Should be capable of supplying steam according to the requirements.
4. Efficiency: Should be able to absorb a maximum amount of heat produced due
to burning of fuel in the furnace.
5. It should be simple in construction .
6. Its initial cost and maintenance cost should be low.
7. The boiler should have no joints exposed to flames.
8. Should be capable of quick starting and loading.

10. Selection of boiler
 Six criteria should be considered when selecting a
boiler to meet the application needs:
 1. Codes and standards requirements
 2. Steam or Hot Water
 3. Boiler load
 4. Number of boilers
 5. Performance considerations
 6. Special considerations

11. Boiler load
 heating,
 process,
 Combination,
 Defining Load Variations,
 Load Tracking.

12. Number of boilers
 Back-Up Boilers
 Type of Load
 Downtime
 Boiler Turndown

13. Performance considerations
 Fuels
 Emissions
 Efficiency
a. Combustion Efficiency
b. Thermal Efficiency
c. Boiler Efficiency
d. Fuel-to-Steam Efficiency
e. Stack Temperature and Losses
f. Excess Air
g. Radiation and Convection Losses
h. Heating Surface
i. Flue Gas Passes
j. Integral Boiler/Burner Package

14. Special considerations
 Replacement Boilers
 Floor space required.
 Total space requirements.
 Access space for maintenance.
 Size and characteristics of the boiler to be replaced, including location
of existing piping, the boiler stack and utilities.
 Boiler weight limitations.
 With little or no access to the boiler room, some bent-tube type boilers
can be carried into the boiler room in sections or pieces and easily
assembled, with no welding required.
 Electric boilers should also be considered, especially since they do not
require a stack.
 Vertical fire tube boilers have a small floor space requirement.

15. Special considerations
 PAYBACK ANALYSIS
1. Estimate boiler fuel consumption rate.
2. Estimate annual fuel use.
3. Estimate annual fuel cost.
4. Determine potential incremental efficiency
improvement.
5. Estimate potential annual fuel savings.
6. Determine the payback period for the investment.
7. Refine the analysis.

16. Locomotive boiler

17. Locomotive boiler
 Consists of cylindrical barrel with rectangular fire
box at one end and smoke box at another end
 Hot gases generated due to burning of coal are
deflected by an arch of fire bricks, so that walls of
the fire box may be heated properly
 The heat of the hot gases is transmitted into water
through the heating surfaces of fire tubes

18. Babcock and Wilcox boiler

19. Babcock and Wilcox boiler
 It consists of a drum connected to a series of front
end and rear end header by short riser tubes
 To these headers are connected a series of inclined
(150 or more) water tubes
 A hand hole is provided in the header in front of
each tube for cleaning and inspection of tubes

20. Babcock and Wilcox boiler
 Feed valve is provided to fill the drum and inclined
tubes with water
 Through the fire door fuel is supplied to grate
where it is burnt
 The hot gases are forced to move upwards between
the tubes by baffle plates
 The water from the drums flows through the
inclined tubes via down take header and goes back
into the shell in the form of water and steam via
uptake header

21. Cochran Boiler
 This boiler consists of a cylindrical shell with its crown
having a spherical shape.
 The furnace is also hemispherical in shape.
 The grate is also placed at the bottom of furnace and the ash
pit is located below the grate.
 The coal is fed into the grate through the fire door and ash
formed is collected in ash pit located just below the grate
and it is removed manually.
 The furnace and combustion chamber are connected
through a pipe.
 The back of the combustion chamber is lined with
firebricks.

22. Cochran Boiler
 The hot gases from the combustion chamber flow through the nest of
horizontal fire tubes (6.25 cm Φ and 165-170 in number).
 The passing through the fire tubes transfers a large portion of the heat to
the water by convection.
 The flue gases coming out of fire tubes are finally discharged to
atmosphere through chimney.
 The spherical top and spherical shape of firebox are the special features
of this boiler.
 These shapes require least material for the volume.
 The hemispherical crown of the boiler shell gives maximum strength to
withstand the pressure of the steam inside the boiler.
 The hemispherical crown of the fire box is advantageous for resisting
intense heat.
 This shape is also advantageous for the absorption of radiant heat from
the furnace.

23. Cochran Boiler
 Coal or oil can be used as fuel in this boiler.
 If oil is used as fuel, no grate is provided but the bottom of
the furnace is lined with firebricks.
 Oil burners are fitted at a suitable location below the fire
door.
 A manhole near the top of crown of shell is provided for
cleaning.
 A number of hand-holes are provided around the outer shell
for cleaning purposes additionally.
 The smoke box is provided with doors for cleaning of the
interior of the fire tubes.

24. Cochran Boiler
 The airflow through the grate is caused by means of the
draught produced by the chimney.
 A damper is placed inside the chimney (not shown) to
control the discharge of hot gases from the chimney and
thereby supply of air to the grate is controlled.
 The chimney may also be provided with a steam nozzle (not
shown) to discharge the flue gases faster through the
chimney.
 The steam to the nozzle is supplied from the boiler.

25. Cochran Boiler
 The outstanding features of this boiler are given below:-
(i) It is very compact and requires minimum floor area.
(ii) Any type of fuel can be used with this boiler.
(iii) It is well suited for small capacity requirements.
(iv) It gives about 70% thermal η with coal firing and about
75% with oil firing.
(v) The ratio of grate area to the heating surface area varies
from 10:1 to 25:1.
 It is provided with all required mountings. The function of
each is briefly described below:-

26. Cochran Boiler

27. THANK YOU