Steam Boilers

Steam Boilers

1 Fire Tube & Water Tube Boilers

2 Internally Fired Boiler

3 Externally Fired Boiler

4 Cochran Boiler

5 Lamont Boiler

STEAM BOILERS

• Generates 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

• According to flow of water and hot gases.

1.     Fire Tube Boilers

2.     Water Tube Boilers

• According to the method of firing.

1.       Internally fired boilers

2.     Externally fired boilers

• According to the Pressure developed

1.     Low pressure boilers

2.     High pressure boilers

In fire tube boilers,

•           The hot gases pass through the tubes surrounded by water.

•         The water is get heated up and converted into steam

•         The exhaust gases are sent to atmosphere through chimney.

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 and burnt.

•           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 convection.

•         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 tonnes/hr

•           Pressure of the steam generated is 170 bar.

•           Temperature of the steam produced is 500^o C

Working:

•           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 bar.

•           They can produce the steam at the rate of 45000 kg per hour.