To increase the efficiency of boilers equipment like economiser, air pre heater and super heater are added to the boiler. These are known as boiler accessories. They mainly serve the purpose of existing maximum heat from flue gases.
Brief description of accessories used in modern boilers is given below.
Air Pre Heater
It is a heat exchanger used to heat the air entering furnace by extracting heat from flue gas. Combustion of fuel using hot air improves furnace temperature and also improves the thermal efficiency of the boiler.
This is also a heat exchanger but heats the feed water again using flue gases. It is placed in the path of flue gas just ahead of the air pre heater.
This heat exchanger heats the steam and raises the temperature. The radiant super heater taking radiant heat is inside the furnace and the connective super heater is having steam tubes across which the flue gases flow before entering the economiser.
Feed Water Pump
It forces the feed water into the boiler at the desirable operating pressure. It is a special type of pump and handles hot water coming from condenser or feed heater and raises its pressure to boiler pressure.
This is another type of heat exchanger used to condense exhaust steam from engine or turbine. The condensate obtained is re-circulated there by need for fresh feed water is minimised. The condenser maintains vacuum pressure and thus improves the driving potential of steam from boiler passing through turbine or engine and improves the expansion ratio and hence efficiency.
Found only in ships. It is used to get pure water from available sea (salt) water.
Pressure Reducing Valve
This valve throttles the flow into the turbine. When sudden fall in load occurs on the turbine this ensures that the power produced instantly matches with the load.
These are of two types namely induced draft and forced draft. These aid natural draft produced by the chimney and these fans ensure regulated supply of air for combustion. They also help the smooth flow of flue gases.
This helps to clean the external surfaces of water tubes by dislodging soot accumulated over them. Clean surfaces are essential for good heat transfer.
This collects the fine dust particles and soot carried by the flue gases. Now-a-days this is an essential component to ensure clean and safe environment surrounding power plants.
Cooling Tower and Pump
Used to cool the raw water and supply this to the condenser as coolant.
Ash Handling Equipment
These help continuous disposal of ash from the ash pit.