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Boiler Accessories and their functions

The devices used in a Boiler as an integral part and help to run the Boiler efficiently are called  Boiler Accessories. Boiler accessories are optional in a boiler. Without Accessories, the boiler can produce steam with low efficiency. To increase the efficiency of the boiler, accessories are used.

Boiler Accessories list

  • Superheater
  • Economizer
  • Air Pre-heater
  • Feed Pump
  • Soot Blower
  • ID and FD fans
  • Ash Removal system
  • Fuel supply system
  • Dosing system
  • Deaerator
  • Draught Gauge
  • Steam & Water flow meter
  • Pyrometer
  • Evaporator oil gas filter
  • Carbon di Oxide Recorder


Superheater increases the temperature of saturated steam without raising its pressure. It consists of a bundle of small tubes. It installed in the path of hot flue gases from the furnace. Saturated steam passes inside the heater tubes and hot flue gasses passes outside the tubes. Thus heat transfer takes place from hot flue gases to saturated steam and raising the steam temperature without raising its pressure. Convection superheaters and radiation superheaters are used for this purpose. Increase in steam temperature depends on superheater place, hot flue gases temperature, superheater design, and steam flow. If the temperature of saturated steam increases up to 100C with the help of superheater then 1% fuel saving can be achieved.


Economizer used to heat the feed water through exhaust flue gases before leaving the chimney. It consists of steel or cast iron tubes. Mostly steel tubes used because steel has good heat transfer rate and bear high-pressure conditions. Feed water passes inside the tubes and exhaust flue gases pass outside the tubes. Economizer improves the economy of the boiler. Following are the advantages of using an economizer in the boiler:

  • Almost 15 to 20% fuel saving
  • Increase boiler efficiency
  • Minimize expansion and contraction
  • It increases the steam raising capacity of a boiler because it shortens the time required to convert water into steam
  • Prevents scale formation in boiler water tubes, scale forms in economizer tubes that can be clean easily
  • Entering hot feed water in the boiler reduces strains due to unequal thermal expansion
Boiler Accessories
Boiler Accessories

Air Preheater:

Air preheater used to recover heat from exhaust flue gases. It installed between the economizer and chimney. Air for combustion purpose passes from the air preheater. It increases combustion air temperature with the help of exhaust flue gases. Air passes through the heater tubes and flue gases pass over the outside of the heater tubes. Thus heat transfer takes place from flue gases to air required for combustion. If combustion air temperature increases up to 1000F with the help of air preheater then 2.3 to 2.6% fuels can be saved. In some conditions, 5 to 10% fuel saving also achievable.  Following advantages obtained with the help of Air preheater:

  • Increases the evaporative capacity per kg of fuel
  • Increases 2% boiler efficiency for each 35-400C rise in temperature of the air
  • Gives better combustion with less smoke, soot, and ash
  • Enables a low-grade fuel to burn with less excess air

Feed Pump:

Feed pump used to feed the high-pressure water in the boiler. Generally, feed water pressure is 20% more than that in the boiler pressure. Feed pump can be centrifugal or reciprocating type.

Soot Blower:

During combustion, soot deposits on the internal furnace tubes and plugged the gases passes. Ultimately soot deposition decreases boiler efficiency. Soot blower then used to remove soot from tubes to prevent plugging of gas passes.


The injector uses boiler steam or steam from another source to feed the water in the boiler. Injector works on Bernoulli theorem. It consists of two parts. One part contains a water cone and a steam cone. This part converts pressure into velocity and sends high-velocity mixer jet to the second part of the injector. Second part converts velocity or kinetic energy into potential energy. Thus increases 20% of pressure and water enter the boiler through the feed check valve. The injector has less cost and no moving part. It mostly used in locomotive boilers.

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