Steam Boiler, Classification of Steam Boiler

Steam Boiler and types of Boiler

Steam Boiler

A boiler may be defined as a closed vessel in which steam is produced from water by combustion of fuel.
According to American Society of Mechanical Engineers (A.S.M.E) a steam generating unit is defined as "A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for transferring the heat so made available to the fluid being heated and vapourised."

Steam Generator is Employed

(a) for generating power in steam engines or steam turbines.
(b) in the textile industries for sizing and bleaching etc.
(c) for heating the building in cold weather and for producing hot water for hot water supply.

Primary Requirements of Steam Generators of Boilers.

(a) The water must be contained safety.
(b) The steam must be safely delivered in desired condition.


Classification of Boilers.

Boiler are classified on the following basis

(1) Tube contents.

According to tube contents boiler are classified in following

(a) Fire tube Boiler:

      In which hot gases pass through the tubes and water surrounds them. The products of combustion leaving the furnace pass through fire tubes which are surrounded by water.
For example:- Cochram;Lancashire; Cornish and locomotive boilers.

(b) water tube boiler:

      In water tube boiler, water flows inside the tubes and the hot flue gases flow outside the tubes.
A bank of water tubes containing water is connected with a steam water drum by means of two sets of headers. The hot flue gases from the furnaces pass over the tubes and are discharged through the chimney.
For example: Babcock and Wilcox boiler which usually have straight but inclined water tubes, and stirling boiler,which has bent water tubes ,power boiler, etc.


(2) Method of Firing.

On the basis of method of firing, boilers are classified as

(a) internally fired boiler:

      The furnace region is provided inside the boiler shell and is completely surrounded by water cooled surfaces.
For example: Lancashire boiler; Locomotive, and scotch boilers

(b) Externally fired boiler.

          In externally fired boilers, the furnace region is provided outside the boiler. Its furnace region is simple and easy to construct.
For example: Babcock and Wilcox boiler.

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