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TYPES OF HIGH PRESSURE BOILERS ,WORKING PRINCIPLE OF BENSON BOILER ,MERITS AND DEMERITS ,APPLICATIONS

 High Pressure Boilers :

There are two types of High pressure boilers are as follows.

1.    Benson Boiler

2.  Lamont Boiler






FIGURE 1: BENSON BOILER

Construction

 1. Air Preheater: It preheats the air before entering into the furnace. The preheated air increases the burning efficiency of the fuel.

2. Economiser: It heats the water to a certain temperature.

3. Radiant Superheater: It is super heater which heats the water with radiation produced by the burnt fuel. It raises the temperature to supercritical temperature.

4. Convection Evaporator: It evaporates the superheated water and converts them into steam. It does so by the convection mode of heat transfer to the water from the hot flue gases.

5. Convection Superheater: It superheats the steam to the desired temperature (nearly 650 degree Celsius). 6. Furnace: It is the place where the fuel is burnt.

7. Feed Pump: It is used to supply the water inside the boiler at supercritical pressure of 225 bars.

 

Working Principle

 Benson boiler 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.

 

Working

In Benson Boiler, the feed pump increases the pressure of the water to the supercritical pressure and then it enters into the economiser. From economiser, the water the water passes to the radiant heater. Here the water receives the heat through radiation and partly gets converted into steam. The temperature raises almost to the supercritical temperature. After that mixture of steam and water enters into convective evaporator where it is completely converted into steam and may superheated to some degree. Finally it is passed through the superheater to obtained the desired superheated steam. This superheated steam is then used by turbines or engine to produce the electricity.

Merits of Benson boilers

The various advantages of the boiler are

• It is a drum less boiler and hence the weight of this type of boiler is 20 % less as compared with other types of boiler.

• It is light in weight.

• Occupy smaller floor area for its erection.

• Explosion hazard is almost negligible because of use of smaller diameter tubes.

• It can be started very easily within 15 minutes.

• It avoids bubble formation due to the super critical pressure of water.

• Transportation is easy.

 • This boiler may achieve thermal efficiency upto 90 %.

Demerits of Benson Boiler :

The Disadvantages of Benson boiler are as follows.

·         When water flow is not enough, there are chances that tubes are overheated.

·         When impure water is used, the formation of heavy deposits takes place on heated surfaces.

·         The control of boiler for variable loads is difficult.


Applications

This supercritical boiler is used in different industries to generate steam for the production of electricity or mechanical power. The average operating pressure, temperature and capacity of benson boiler is 650 degree Celsius, 250 bar and 135 tonnes/h.
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