What Is a Benson Boiler?
A Benson boiler is a type of Once-Through Boiler patented by Marc Benson in Germany in 1923 and incorporates recirculation characteristics at part-load operation below about 60° MCR.
The Benson boiler usually consists of small diameter tubes (ca. 25 mm bore) spirally wound to form the furnace envelope. Feedwater enters the bottom of the furnace at high sub-critical or supercritical pressure and is evaporated to high quality in the spiral section.
A balancing header is commonly provided near the top of the furnace to alleviate any differences in steam quality resulting from variations in heat absorption in different parallel spiral circuits before the steam/water mixture is introduced to the open boiler pass.
Here, it is superheated in the upper parts of the furnace envelope and subsequently in pendant tube banks. The balancing header also serves as a means of separating excess liquid when, at low loads, the furnace flow rate exceeds the steam demand from the boiler as a whole.
As in other forms of Fossil Fuel-Fired Boilers, the flue gasses are used for reheat, economizer, and air-heating duties.
Parts Of Benson Boiler
The main parts of Benson boiler are:
- Air Preheater: It preheats the air before entering into the furnace. The preheated air increases the burning efficiency of the fuel.
- Economizer: It heats the water to a certain temperature.
- Radiant Superheater: It is superheater that heats the water with radiation produced by the burnt fuel. It raises the temperature to supercritical temperature.
- 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.
- Convection Superheater: It superheats the steam to the desired temperature (nearly 650 degree Celsius).
- Furnace: It is the place where the fuel is burnt.
- Feed Pump: It is used to supply the water inside the boiler at supercritical pressure of 225 bars.
Working Principle of Benson Boiler
The Benson boiler is a water tube boiler, which accomplishes its job on the principle of the critical pressure of water. As we mentioned before, Critical pressure is the pressure at which the water and gas states are in equilibrium.
The feedwater passes through the economizer to the water-cooled walls of the furnace. The water receives heat by radiation and the temperature increases to nearly critical temperature. It then moves to the evaporator and may get superheated to some degree. Finally, it is transferred through the superheater to achieve the desired superheated steam.
How Does a Benson Boiler Work?
in the previous sections, we talked about what a Benson Boiler is and upon what principle it works, in the present section, we elaborate on the 4 steps that indicate how exactly a Benson boiler processes its job.
Step 1: In a Benson boiler, there is no steam and water drop. It will directly convert water into steam. The blower will start working and it will blow air into the air preheater. Then, the air preheater heats the air and hot air will come out. This hot air will be used in the furnace for further process.
Step 2: The feed pump increases the pressure of the water to the supercritical pressure. Then, the water enters into the economizer. In the economizer, the water is preheated using combustion gases to increase the efficiency of the boiler.
Step 3: in this step, the water passes to the radiant superheater. In the radiant superheater, the water is heated using radiant heat transfer. Here heat is transferred from the combustion chamber to water and the water will partially convert into steam and partially it remains in the liquid form. Then this partial vapor and liquid will go to the convective superheater.
Step 4: In the last step where there is the convective superheater, the water will be fully converted into vapor or steam and the superheated steam will get to the prime mover and rotate the turbine. this is how a Benson Boiler works.
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 lightweight boiler.
- The boiler can be started within 15 minutes.
Disadvantages of Benson Boiler
The Following are the disadvantages of the 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 mechanical power.