Boilers are closed vessels made of steel that transfer heat from fuel combustion to water to generate steam. They come in two main types: fire tube boilers where hot gases pass through tubes surrounded by water, and water tube boilers where water passes through tubes surrounded by hot gases. Boilers must generate maximum steam, be lightweight, safe, affordable, and easy to access for maintenance. Steam is used for power generation, heating, and in chemical processes. Boiler efficiency is important and various accessories like economizers and superheaters are used to improve it. Understanding boilers is essential for the chemical industry as most used are high efficiency, safe water tube designs.

1. Boilers
By: Khalid Nawaz
Institute Of Chemical Engineering And Technology
University Of the Punjab Lahore Pakistan

3. What is a boiler/steam
generator..??
• A closed vessel made up of steel to transfer heat
produced by combustion of fuel to water and ultimately
generate steam .
It may be defined as:
 A steam generator or boiler is usually a closed vessel
made of steel. Its function is to transfer the heat
produced by the combustion of fuel to water and
ultimately to generate steam.

4. What should characteristics
of boiler..?
Generate maximum steam.
Light in weight and not occupy large space.
Proper safety regulations.
Cheaper in cost.
Easy cope up with fluctuating demands of
requirements.
Easily accessible for inspection and repair.

5. Where Steam is Used
 Steam is used in steam generators for production of
electricity.
 It is used as heating source for different purposes
 Steam is used for production of different products in
chemical industry.

6. Sources of heat in boiler..??
WOOD
COAL
DIESEL
NATURAL GAS
NUCLEAR ENERGY

7. Method of
firing
Boilers
Pressure of
steam
Circulation
of water
Tube contain
Water tube Fire tube
HighExternally
Natural Forced
LowInternally

8. Classification of Boilers:
Boilers may be classified according to the following-
1. Relative position of Hot gases and Water
a) Fire tube boiler:
The hot gases passes through the tubes that are
surrounded by water. Fire tube boilers are also known by
certain common names-
i) Horizontal return tubular
ii) Locomotive fire box
iii) Scotch marine and,
iv) Vertical tubular

9. b) Water tube Boiler:
The water passes through the tubes and the hot gases
produced by combustion of fuel, flow outside. This
type of Boilers designated by the following
common names:
i) Babcock and Wilcox Boiler (straight but inclined
tubes which connect the headers).
ii) Stirling Boiler (multitubular boiler having bent
tubes that connect boiler drums to headers).

10. BOILER MOUNTINGS AND ACCESSORIES
Boiler Accessories for efficient operation:
1. Water heating devices.
2. Water feeding devices.
3. Super heater
4. Economizer
5. Air preheater

11. Mountings..??
The boiler mountings are the part of the boiler and are
required for proper functioning.
In accordance with the Pakistan Boiler regulations, of the
boiler mountings is essential fitting for
safe working of a boiler.

12. Water level indicator..??
 Water level indicator is
located in front of boiler
in such a position that
the level of water can
easily be seen by
attendant. Two water
level indicators are used
on all boilers.

13. Pressure gauge..??
 A pressure gauge is
fitted in front of boiler
in such a position that
the operator can
 conveniently read it. It
reads the pressure of
steam in the boiler and
is connected to steam
 space by a siphon tube.

 The most commonly, the
Bourdon pressure gauge
is used

14. Safety valve..??
 Safety valves are located on the top of the boiler. They guard the boiler
against the excessive
 high pressure of steam inside the drum. If the pressure of steam in the boiler
drum exceeds
 the working pressure then the safety valve allows blow-off the excess
quantity of steam to
 atmosphere. Thus the pressure of steam in the drum falls. The escape of
steam makes a
 audio noise to warm the boiler attendant.

 There are four types of safety valve.
 1. Dead weight safety valve.
 2. Spring loaded safety valve
 3. Lever loaded safety valve
 4. High steam and low water safety valve

15. Dead weight safety valve Spring loaded safety valve
Lever loaded safety valve

16. Fusible Plug
It is very important safety device, which
protects the fire tube boiler against
overheating. It is
located just above the furnace in the boiler. It
consists of gun metal plug fixed in a gun metal
body with fusible molten metal.
During the normal boiler operation, the fusible
plug is covered by water and its temperature
does not rise to its melting state. But when the
water level falls too low in the boiler, it
uncovers the fusible plug. The furnace gases
heat up the plug and fusible metal of plug
melts,
the inner plug falls down The water and steam
then rush through the hole and extinguish the
fire before any major damage occurs to the
boiler due to overheating.

17. Blow-Off Cock
The function of blow-off cock is to
discharge mud and other
sediments deposited in the
bottom most part of the water
space in the boiler, while boiler is
in operation. It can also be
used to drain-off boiler water.
Hence it is mounted at the lowest
part of the boiler. When it is
open, water under the pressure
rushes out, thus carrying
sediments and mud.

18. Feed Check Valve
The feed check valve is fitted
to the boiler, slightly below the
working level in the boiler. It
is used to supply high pressure
feed water to boiler. It also
prevents the returning of feed
water from the boiler if feed
pump fails to work.

19. Steam Stop Valve
The steam stop valve is
located on the highest part of
the steam space. It regulates
the steam
supply to use. The steam stop
valve can be operated
manually or automatically.

20. Air preheater : It utilize the heat of exhaust
gases.
Economizer: Heat is used to raise the
temperature of feed water supplied to the boiler.
Steam super heater: Used to super heat the
steam.
Feed pump: Raise the pressure of water and
force it into the boiler.

21.  Function:
An economizer is a device in which
the waste heat of the flue gases is
utilized for heating the feed water.
 Economizer are of two types :
a) Independent type, and
b) Integral type

22.  Function:
The function of an injector is to
feed water into the boiler. It is also
used where the space is not
available for the installation of a
feed pump

23.  Function:
Its is a pump which is used to deliver
feed water to the boiler.
 The appliances in common use for
delivering the feed-water into the
steam boilers are:
a) Reciprocating pump
b) Rotary pump

24. Boiler efficiency
 Ratio of heat actually utilized in the generator to the heat
supplied by the fuel.
 Efficiency= ma ( h –
hf)/c
 Where, C is the calorific value of the
fuel.

25. Conclusion:
 Boilers are most important part of chemical industry.99
% boilers used in Pakistan chemical industries are water
tube boilers because of their high efficiency and
safety.so we should have cler understanding about the
boilers.