It is a high pressure water tube boiler with forced circulation which works on basic principle of critical pressure of water.Bension boiler was invented in 1922 by Mark Benson.
This boiler is a supercritical boiler. In this boiler, no bubble is formed on the water surface as the water is compressed to supercritical pressure.
When the water enters the boiler, it suddenly converts to steam as it enters the boiler at just above the critical pressure. No air separator drum is required to separate air bubble from water.
The critical pressure is the pressure at which the liquid and gas phase are at equibrilium.
At supercritical pressure, the bubbles do not form because the density of water and steam becomes same.
As the water is compressed to supercritical pressure the latent heat of water reduces to zero.
As the latent heat of water reduces to zero the water directly changes into steam without the formation of bubbles.
Latent heat :- the heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, without change of temperature.
It works on the principle that the pressure of the water is increased to the supercritical pressure (i.e. above critical pressure of 225 bar). When the pressure of water is increased to the super critical level, the latent heat of water becomes Zero and due to this, it directly changes into steam without boiling. And this prevents the formation of bubbles at tube surface.
In this process, less heat is required to convert water to steam as water is already just above critical pressure and hence less fuel is required.
Parts of Benson Boiler :-
1) Benson Chamber :-
#This is the outermost chamber of Benson boiler in which all other parts of Benson Boiler are kept.
2) Water Feed Pump:-
#Benson boiler is a forced pumped water tube boiler. Water enter into boiler at critical pressure. Water Feed Pump is used to supply the water inside the boiler at a supercritical pressure of 225 bars.
3) Economizer :-
When the water feed pump feeds the water. This water before entering into tube first passes through economizer which uses the combustion gases to preheat the water which also increases the efficiency of water.
Blower blow air into air preheater and air preheater will heat the air and a hot air will be out. This hot air will be used in the furnace for further process.
5) Air Preheater :-
It preheats the air before entering into the furnace. The preheated air increases the burning efficiency of the fuel.
6) Radiant super heater:-
It heats the water with radiation produced by burnt fuel.It raises the temperature of water to supercritical temperature.
7) Convection Evaporator:-
In the convection evaporator , convection is used to transfer heat from the flue gases to water. In this evaporator, the water evaporates completely.
8) Convecting Super heater :-
It is the last chamber in Belox boiler through which the heated steam passes. It superheats the steam to the desired temperature and this superheated steam is taken out for the industrial work.
The first and biggest part in Benson Boiler is Benson Chamber. Inside ths chamber other parts are kept. Blower is connected to air pre heater. Below air preheater, feed pump is present. Feed pump is connected to economizer and transfer water to economizer. This economizer is connected to radiant super heater. Radiant super heater is present at bottom of the benson chamber. This radiant super heater is connected to convective super heater which is finally connected to turbine.
Step 1 :-
In bension boiler we are not using steam and water drop. It will directly convert water into steam. Blower will start working and it will blow air into air preheater and air preheater will heat the air and a hot air will be out. This hot air will be used in the furnace for further process.
The feed pump increases the pressure of the water to the supercritical pressure and then water enters into the economizer. In the economizer, the water is preheated using the combustion gases to increase the efficiency of boiler.
From economizer, the water passes to the radiant super heater. In the radiant super heater, the water is heated using radiant heat transfer method . Here heat is transferred fromcombustion chamber to water and water will partially convert into steam and partially it will stay in the liquid form. Then this partial vapour and liquid will go to the convective super heater .
In the convective super heater, it will be fully converted into vapour or steam and these superheated steam will got to the prime mover and rotate the turbine . This is the working of Benson Boiler.