1 Fire Tube & Water Tube Boilers
2 Internally Fired Boiler
3 Externally Fired Boiler
4 Cochran Boiler
5 Lamont Boiler
• 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 500o C
• 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.