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Boiler-Definition,Principle & Working,Properties,Classification,Parts

Boiler

  • A Boiler or steam generator essentially is a container into which water can be fed and steam can be taken out at desired pressure,temperature and flow.
  • For that the boiler should have a facility to burn a fuel and release heat.

Schematic diagram of boiler

schematic diagram of boiler 

Definition of boiler 

  • It is define as a closed vessel in which steam is produced from water by combustion of fuel.

Principle

  • In a boiler, the heat energy of the flue gases transfer to the water through convection.The fuel is burn into the furnace which produces flue gases.
  • These flue gases pass over the water containing in shell or tube according to the type of boiler.The heat of the flue gases transfer to the water and convert it into steam.

working principle of boiler

Working

  • A boiler is simply  heat exchange in which, water is work as cold fluid and flue gases works as hot fluid.The heat flow is transfer from hot fluid to cold fluid through convection which increases the energy of water.
  • A container half filled with water. The fuel is burn and the flue gases flow over the container.These gases heat the water and covert it into steam.
  • This steam taken out from a tube situated upper side of the container.The equal amount of water is feed into the container by the feed valve which maintain the boiler pressure unchanged.
  • If the steam escaping rate is high compare to water feeding rate,the pressure of boiler decreases.And if the water feeding rate is high compare to steam escaping rate the pressure of the boiler increases.Thus pressure is control with the help of  fuel supply and water supply of container.

Function & Properties of a good boilers

  • To convert chemical energy of the fuel into heat energy.
  • To transfer this heat energy to water for evaporation as well to steam for super heating.
  • It can be started or stopped quickly.
  • It should have a constant and through circulation of water.
  • All parts of boiler should be accessible for cleaning and inspection.
  • It should be trouble  free & require less attention and less maintenance.
  • It should have high rate of heat transfer and better combustion efficiency.
  • They having free from manufacturing defects.
  • It should be able to accommodate the load variation.
  • They having maximum steam generation rate within minimum fuel consumption.
  • Initial cost, running cost & maintenance cost are not high.

Classification of Boilers

      The boilers may be classify mainly on the basis of the following parameters:

1. Axis of the shell

   a. Vertical 

   b. Horizontal 

   c. Inclined 

2. Use of boilers

 a. Stationary 

 b. Portable

 3. Tube contents

 a. Fire tube

 b. Water tube

  4. Furnace position

a. Externally fired

b. Internally fired

5. Method of water circulation

a. Natural circulation

b. Forced circulation

1. Axis of the shell

a. Vertical

  • If the axis of the boiler is vertical then it  called as vertical boiler.
  • It’s  occupy less floor space.

b. Horizontal 

  • If the axis is horizontal than it called as horizontal boiler.
  • The parts of a horizontal boiler can be inspected and repaired easily but it occupies more space.

c. Inclined

  • If the axis is inclined than it called as inclined boiler.

2. Use of boilers

a. Stationary 

  • Stationary boilers are used for power plant steam for central station utility power plants, for plant process steam etc.

 b. Portable

  • Portable boilers are portable and are of small size.
  • For example:- Locomotive and Marine boilers.

3. Tube contents

 a. Fire tube

  • In fire tube boilers, the hot gases are inside the tubes and the water surrounds the tubes.
  • For example:- Cochran, Lancashire and Locomotive boilers etc.

 b. Water tube

  • In this case of water tube boiler, the water is inside the tube and hot gases surround them.
  • For example:- Babcock and Wilcox, Stirling, Yarrow boiler etc.

4. Furnace position

a. Externally fired

  • The boiler is known as externally fired if the heat addition is done externally i.e. furnace is outside the unit.
  • For example:- Babcock & Wilcox etc.

b. Internally fired

  • In case of internally fired boiler, heat addition is done internally i.e. furnace is within the unit.
  • For example:- Cochran and Lancashire.

5. Method of water circulation

a. Natural circulation

  • In natural circulation boilers, the circulation of water/steam is caused by the density difference which is due to the temperature variation.
  • For example:- Lancashire

b. Forced circulation

  • In forced circulation type of boilers, the circulation of water is done by forced pump.
  • For example:- Velox, Lamont etc.
Basic components of Boiler
  • Furnace
  • Economiser
  • Air-Preheater
  • Super heater
  • Re-heater
  • De-Super heater
  • Condenser
  • Cooling tower
  • Fan or draught system
  • Ash handling system

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