Different Types of Boiler Accessories and Their Functions

Boiler Accessories Functions

Read: Difference between boiler mountings and accessories

Feed Pump

The pressure of steam inside the boiler is high, and so the feed water pressure must be raised before its entry into the boiler for consistent operation. Feed pump is a device which raises the pressure of water and forces it into the boiler. Feed water pressure must overcome the steam pressure for a steady flow of water to the boiler.

Injector

Boiler Water Injector
Drawing of the injector used in steam locomotives. - credit:wikimedia
The function of the injector is same as the feed pump; it is used where space is not available for feed pump installation. In an injector, the Kinetic energy of steam is used to increase the pressure and velocity of feed water in a convergent-divergent nozzle.

Advantages: Simplicity, Compactness, High thermal efficiency, Absence of dynamic part.
Disadvantages: Low pumping efficiency, Difficulty in operation under extreme variation in steam pressure.

  • When large quantities of feed water involved feed pump is preferred over the injector because they are more reliable and need less attention.

Economizer

Economizer is a heat exchange device which recover some of the heat from exhaust or flue gas and utilize it for heating feed water. Generally, economizer units are placed between boiler and chimney.

Advantages:
  1. Stress due to uneven expansion is reduced because the temperature range between boiler parts is reduced.
  2. Saving in the Fuel consumption.
  3. Overall efficiency increases.
  4. Evaporative capacity of the boiler is increased.
  5. Protection from chilling of boiler metal.

Air preheater

air preheater
Tubular type air preheater
Air preheater is a device which extract heat from exhaust gas to increase the air temperature before entering the furnace. It accelerates the combustion, enhance the burning of fuel and thus increase thermal efficiency. It is generally placed after the economizer. The degree of preheating depends on the type of fuel and rate at which boiler operates. Another advantage of air preheater is that it Reduce flue gas temperature that allows to simplify the design of ducting for flue gas.

Super heater

super heater diagram
Diagram of a locomotive type fire-tube boiler with superheater. - credit: wikimedia
The steam generated by a boiler is generally wet or at most dry saturated. Super heater is used to increase the temperature of steam above its saturation point, since superheating result in the increase in efficiency and economy of the steam plant.
There are two types of super heater, convective and radiant. Convective type uses heat from flue gases whereas radiant type (placed on combustion chamber) receives heat from burning fuel through the radiant process.

Advantages:
  1. Steam consumption is reduced.
  2. Protection from erosion of turbine.
  3. Losses due to condensation of steam in the cylinders and pipes are reduced.
  4. Plant efficiency increases.

Steam separator

Baffle Plate Steam Seperator
Baffle plate steam seperator
The use of wet steam in a turbine is uneconomical; hence a steam separator, also known as a moisture separator used.  The function of steam separators is to remove water droplet from steam. It is installed on the main steam pipe from the boiler. 

It is important to remove water residue steam because:
  • Water droplet in steam reduces the thermal efficiency.
  • Water may accumulate in cylinder and cause hydrostatic lock that damages the engine.
  • In thermal power plants, water droplets in high-velocity steam from nozzles erode turbine blades.
According to the principle of operation, they are classified into Impact or Baffle type, Reverse current type, Centrifugal type.

Steam trap

Steam traps are used to remove condensate as well as non-condensable gases from the steam with negligible loss of steam. Most of the steam traps are automatic valves.
Read: Comparison between Steam Separator and Steam Trap

Pressure reducing valve

The function of pressure reducing valve is to maintain constant pressure on its delivery side irrespective of boiler pressure.

Read:
Common Problems Associated With Steam System
Types of boiler


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