The Benson boiler is a high pressure, drumless, water tube steam boiler using forced circulation. In this boiler, the feed water enters at one and discharges superheated steam at the other end. The feed pump increases the pressure of water to supercritical pressure (i.e. above the critical pressure 225 bar) and thus the water directly transforms into steam without boiling.
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Parts of Benson Boiler
The following are the construction parts of Benson boiler:
- Feed pump
- Steam outlet pipe
- Air Pre-heater
- Radiant superheater
- Convection superheater
- Convection evaporator
It is the space, above the grate and below the boiler shell, in which the fuel is actually burnt. The furnace is also called firebox.
2. Feed Pump
It is a boiler accessory needed to force the feed water at high pressure into the boiler.
3. Steam Outlet Pipe
The superheated steam is supplied to the steam turbine by a steam outlet pipe.
4. Air Pre-heater
The air preheater is a necessary accessory that develops the heat in the exhaust gases by heating the air supplied to the furnace of the boiler. The Preheated air improves the thermal efficiency of the fuel.
In economiser, burning the feed water to a certain temperature. It makes the recovery of heat in the exhaust gases. Economiser improves the overall efficiency of the boiler by reducing fuel consumption.
6. Radiant Superheater
It is a superheater that heats water from radiation generated by burnt fuel. This increases the temperature to supercritical temperature.
7. Convection Superheater
The convection superheater superheats the steam to the desired temperature (about 650° C).
8. Convection Evaporator
In convection evaporator, it evaporates superheated water and transforms them into steam. It does this by the convection method of heat transfer from hot exhaust gases to water.
Working of Benson Boiler
The diagrammatic sketch of a Benson boiler is shown in the figure. It is a water tube boiler, which works on the principle of the critical pressure of water. Critical pressure is the pressure at which the water and gas states are in equilibrium.
The feedwater passes through the economiser to the water-cooled walls of the furnace. The water receives heat by radiation and the temperature increases to nearly critical temperature. It then enters the evaporator and may get superheated to some degree. Finally, it is transferred through the superheater to achieve desired superheated steam.
This boiler is also known as light-weight boiler as there is no large water and steam drum. The thermal efficiency of up to 90% may be achieved by this boiler. The average working pressure and capacity of this type of boiler is 250 bar and 135 ton/hour. It can be within 15 minutes.
Features of Benson Boiler
The following are the important features of Benson boiler:
- The weight of this boiler is less than other boilers. Which reduces the cost of boilers.
- With no drums in this boiler, its parts transfer is easy. All parts are likely to be transported to the site, without pre-assembly.
- Once the feedwater entering at one end is discharged as superheated steam at the other end.
Advantages of Benson Boiler
The following are the advantages of Benson boiler:
- The cost of the boiler is low because there is no water and steam drum.
- There is no pressure limit, therefore supercritical pressure may be used.
- The high pressure avoids the bubble formation in the tubes which increases the heat transfer rate.
- It is a light weight boiler.
- The boiler can be started within 15 minutes.
Disadvantages of Benson Boiler
The Following are the disadvantages of Benson boiler:
- Due to the supercritical type of boiler, its control requires to be inspected every time to prevent an explosion.
- This Boiler control is difficult for variable loads.
Application of Benson Boiler
The Following are the applications of Benson Boiler:
- The supercritical boiler is used in various industries to generate steam for the production of electrical power.
- This boiler has an average operating pressure, temperature and capacity of 650 ° C, 250 bar and 135 ton/hour, so used to generate the mechanical power.
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