A steam generator or boiler is usually a closed vessel of steel used to transfer the heat produced by the combustion of fuel (solid,gas,liquid) to water and generate steam.The selection of type and size of the boiler depends upon the following factors.
1: The power and working pressure
2: Position of the power house
3: The probable permanency of the station
4: Load Factor
Classification of the Steam Boilers.
1: According to the content in the tube
a : fire tube or smoke tube
In fire tube boilers the flames or hot gases produced by combustion of fuel are in the tubes which are surrounded by water. Simple vertical,Cochran,Lancashire,Cornish,Scotch marine, Locomotive and Velcon boilers are the examples of fire tube boilers.
b: Water Tube
In water tube boiler, the water is inside the tubes and flames or hot gases are surrounded from outside. Babcock and wilcox, Striling, La-mont,Benson, Yarrow and Loeffler boilers are the water tube boilers
2 : According to the position of the furnace
a : Internally Fired
The furnace is located inside the boiler shell. Most of the fire tube steam boilers are internally fired.
b : Externally Fired
In externally fired boilers ,the furnace is setted underneath in a brick-work. Water tube boilers are always externally fire boilers.
3: According to the axis of the shell
a : Vertical
In vertical steam boiler the position of axis of the shell is vertical.
b: Horizontal
In horizontal steam boiler the position of axis of the shell is horizontal.
4 : According to the number of tubes.
a : Single tube
In single tube boiler, it consists of only one water or fire tube. Simple vertical and Cornish boiler are single tube steam boilers.
b: Multi tubular
As name indicates, these boilers consists of two or more tubes of water or fired tubes.
5 : According to the method of circulation of water and fire
a : Natural Circulation
The circulation of the water is by natural convection currents which are set up during the heating of water.
b : Forced Circulation
External power driven like centrifugal pump is used to force circulation of water is called forced circulation. Use of forced circulation is made in high pressure boilers like La-mont,benson and velcon boiler.
6 : According to the use
a : stationary
These boilers used in power plants and in industrial purposes. These are called stationary boiler because they are fixed in a one place.
b : Mobile
The mobile steam boilers are those which move from on place to another. Locomotive and Marine boilers are the examples of mobile boilers.
7 : According to the Source of heat
Steam boilers may also classified as according to the source of heat provided in the form of solid,liquid and gases fuels. Hot waste gases, by-products of other chemicals, electrical energy and nuclear energy are also form of source of heat.
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