1 Fire Tube & Water Tube Boilers
2 Internally Fired Boiler
3 Externally Fired Boiler
4 Cochran Boiler
5 Lamont Boiler
steam by transferring heat by burning of fuel to water.
Energy released by burning fuel (solid, liquid or
gaseous) is transferred to the water in the boiler.
Classification of boilers:
The steam boilers are classified as
to flow of water and hot gases.
1. Fire Tube
to the method of firing.
to the Pressure developed
In fire tube boilers,
The hot gases pass through the tubes surrounded by
The water is get heated up and converted into
The exhaust gases are sent to atmosphere through
E.g Locomotive boiler, Lancashire boiler.
1 FIRE TUBE & WATER TUBE BOILERS
According to flow of water and hot gases:
In water tube boilers,
Water is circulated through number of tubes and
the hot flue gases flow over these tubes.
A number of tubes are connected
with boiler drum through headers.
The hot gases flow over these tubes many times
before escaping through the stack.
The water is converted into steam and steam
occupies steam space.
E.g. Babcock & Wilcox,
stirling, BHEL boiler, Velox, Lamont, Lo-effler boilers. According to the
method of firing:
In internally fired boilers, the
furnace grate is provided inside the boiler shell.(E.g Lancashire, Locomotive
boilers) In externally fired boilers,
• The furnace grate is provided
outside or built under the boiler shell.
2 INTERNALLY FIRED BOILER:
3 EXTERNALLY FIRED BOILER:
According to the Pressure Dev eloped:
In Low Pressure Boilers,Steam is produced at a pressure
lower than 80 bar. (E. g.
Cochran, Lancashire, Locomotiv e)
In High Pressure Boilers,Steam is produced at a
pressure more than 80 bar. (E. g.
Lamont, Velox, Benson, Lo-effl er boiler)
4 COCHRAN BOILER:
Coal is fed into the gr ate through the fire hole
Ash formed during t he burning is collected in the
ash pit provided just below the grate.
Ash is then removed manually.
The hot gases from the grate pass through the
combustion chamber to the horizontal fire tubes and transfer the heat by
The flue gases comi ng out of fire tubes pass
through the smoke bo x and escape to the atmosphere through the chimney.
Smoke box is provided with a door for cleaning the
fire tubes and sm oke box.
The working pressure and steam capacity of cochran
boiler are 6.5 bar and 3500 kg /hr respectively.
5 LAMONT BOILER:
It is a water tube, forced circulation and
externally fired high pressure boiler.
• The capacity of the p lant is 50
Pressure of the steam generated is 170 bar.
Temperature of the steam produced is 500o
Feed water is pumped to the boiler by the feed
pump through the eco nomiser.
Economiser preheats the feed water by using hot
gases leaving the b oiler.
The circulating pump circulates the water from the
drum under high pressure to prevent the tubes from being ove rheated
Water is evaporated into steam when passing
through these tubes.
The water and steam from the tube enters the
boiler drum where the steam is separator.
This steam is passed through a convection
superheater and the steam is superheated by the flue gases.
This super heated steam is supplied to the prime
mover through steam outlet.
The water level in the drum is kept constant by
pumping the feed water into the boiler drum.
The air is preheated by the flue gases before
entering the combustion chamber to aid the combustion of the fuel.
This type of boiler has a working pressure of 170
• They can produce the steam at the rate of 45000 kg per hour.