Construction and operation of Benson boilers

The Benson boiler is a supercritical, high pressure, drumless, forced circulation water tube steam boiler. This boiler was invented in the year 1922 by Mark Benson. This boiler is a supercritical boiler in which the feed water is compressed to a supercritical pressure and this prevents the formation of bubbles on the surface of the water tube. Bubbles do not form because at supercritical pressure the density of water and vapor becomes the same. It was Mark Benson who first proposed the idea of ​​compressing water to supercritical pressure before heating it in the boiler and due to this the latent heat of the water is reduced to zero. As the latent heat of the water reduces to zero, the water turns directly into vapor without the formation of bubbles.

Features of Benson boilers:

The main difficulty experienced in the La Mont boiler is the formation and fixation of bubbles on the internal surfaces of the heating tubes. The attached bubbles reduce heat flow and vapor generation as they offer greater thermal resistance compared to water film:

(a) If the boiler pressure were raised to a critical pressure (225 atm), the steam and water would have the same density and therefore the danger of bubble formation could be completely avoided.

(b) Natural circulation boilers require expansion joints, but these are not necessary for Benson because the tubes are welded. Assembling the Benson boiler is easier and faster, as all parts are welded on site and the work of expanding the tube in the workshop is completely avoided.

(c) Transportation of Benson boiler parts is easy as no drums are required and most parts are transported to site without pre-assembly.

(d) The Benson boiler can be assembled in a comparatively smaller area. The space problem does not control the size of the Benson boiler used.

(e) Boiler furnace walls can be protected more efficiently by using small-diameter, narrow-pitch tubes.

(f) The superheater in the Benson boiler is an integral part of the forced circulation system, therefore no special starting arrangement for the superheater is required.

(g) The Benson boiler can be turned on very quickly due to the welded joints.

(h) The Benson boiler can be operated more economically by varying the temperature and pressure at part loads and overloads. The desired temperature can also be kept constant at any pressure.

(i) The sudden drop in demand creates circulation problems due to the formation of bubbles in the natural circulation boiler, which never occurs in the Benson boiler. This feature of insensitivity to load fluctuations makes it more suitable for grid power plants as it has better adaptive capacity to meet sudden load fluctuations.

(j) Benson boiler blowdown losses hardly reach 4% of natural circulation boilers of the same capacity.

(k) Risks of explosion are not serious at all as it consists of only small diameter tubes and has very little storage capacity compared to drum boiler. During start-up, water passes through the economizer, evaporator, superheater and returns to the supply line through the start valve. During start-up, first the circulation pumps are activated and then the burners are activated to prevent the evaporator and superheater tubes from overheating.

Construction or Main Parts

Benson Boilers

1 . Air preheater- Preheats the air before it enters the oven. Preheated air increases fuel burning efficiency.

2. Economizer- Heats water to a certain temperature.

3. Radiant Superheater- It is a superheater that heats the water with the radiation produced by the burned fuel. Raises the temperature to supercritical temperature.

4. Convection Evaporator- Evaporates superheated water and converts it into steam. This is done by the convection mode of transferring heat to the water from the hot combustion gases.

5. Convection superheater- Superheats the steam to the desired temperature (almost 650 degrees Celsius).

6. Furnace- This is the place where the fuel is burned.

7. Feed pump- It is used to supply water inside the boiler at a supercritical pressure of 225 bar.

Working principle

It works on the principle that water pressure is increased to supercritical pressure (i.e. above the critical pressure of 225 bar). When the water pressure is increased to the supercritical level, the latent heat of the water becomes Zero and therefore it turns directly into steam without boiling. And this prevents the formation of bubbles on the surface of the tube.

In the Benson boiler, the feed pump increases the water pressure to supercritical pressure and then enters the economizer. From the economizer, water passes to the radiant heater. Here the water receives heat through radiation and is partially converted into steam. The temperature rises almost to the supercritical temperature. After this mixture of steam and water enters the convective evaporator where it is completely converted into steam and can superheat to some extent. Finally it is passed through the superheater to obtain the desired superheated steam. This superheated steam is then used by turbines or engines to produce electricity.

Benefits

• He sees.
• Occupy less useful area for assembly.
• The risk of explosion is almost negligible due to the use of smaller diameter pipes.
• It can be started easily in 15 minutes.
• Prevents the formation of bubbles due to supercritical water pressure.
• Transport is easy.
• This boiler can achieve a thermal efficiency of up to 90%.

Application

This supercritical boiler is used in various industries to generate steam for the production of electricity or mechanical energy. The average operating pressure, temperature and capacity of the Benson boiler is 650 degrees Celsius, 250 bar and 135 tons/h.