Benson boiler Construction and Working

Published: 5 Oct 2025

The Benson boiler is one of the most efficient and advanced boilers used in modern power plants. Invented by Mark Benson in 1922, it introduced the idea of a drumless, once-through boiler that can operate at supercritical pressure. This design made boilers safer, lighter, and more efficient. Today, Benson boilers are widely used in power generation and the heavy industries because of their reliability and high steam output.

What is Benson Boiler?

A Benson boiler is a high-pressure, water-tube, supercritical boiler. Unlike ordinary boilers, it does not have a steam drum. Instead, water passes through tubes in a single cycle and directly turns into steam. Since it avoids bubble formation and circulation problems, the Benson boiler delivers dry, superheated steam that improves turbine efficiency and reduces maintenance issues.

Benson Boiler Diagram

Construction of Benson Boiler

The Benson boiler is compact, lightweight, and built to handle extreme pressure. Its construction includes several important parts:

Furnace: The chamber where fuel (coal, oil, or gas) is burned. Surrounded by water walls that absorb heat.
Economizer: Uses hot flue gases to preheat feedwater, saving fuel and improving efficiency.
Evaporator Tubes (Water Walls): Tubes around the furnace where water absorbs radiant heat and changes into steam.
Superheater: Heats steam above its saturation temperature so that it becomes dry steam for turbines.
Reheater: Heats steam again after partial expansion in the turbine to boost efficiency.
Separator: Removes any leftover water droplets before steam enters the turbine.
Air Preheater: Uses exhaust gases to preheat the combustion air, ensuring better fuel burning.
Feed Pump: A powerful pump that forces feedwater through all heating stages.

This design eliminates the heavy steam drum and makes the boiler more compact and quicker to operate.

Working of Benson Boiler

The Benson boiler works on the once-through principle with forced circulation. Its operation can be explained step by step:

Water is pumped into the system using a high-pressure feed pump.
It first passes through the economizer, where it absorbs heat from the hot flue gases.
The preheated water then enters the furnace water walls, where radiant heat from burning fuel increases its temperature.
As water flows through the tubes, it gradually converts into steam.
The steam moves to the superheater, where it becomes completely dry and superheated.
In some cases, the steam is reheated after turbine expansion to improve efficiency.
A separator ensures that no moisture remains in the steam before it enters the turbine.
The dry, superheated steam drives the turbines to generate electricity.
Finally, the exhaust gases flow through the air preheater before leaving through the chimney, ensuring maximum heat utilization.

Specification of Benson Boiler

Type: Supercritical, once-through, water tube boiler
Pressure: Above 221 bar
Efficiency: More than 90%
Capacity: Can generate up to 136,000 kg of steam per hour
Fuel: Coal, oil, or gas

Application of Benson Boiler

Benson boilers are used in industries where continuous, high-pressure steam is needed:

Power plants for electricity generation
Petrochemical industries
Refineries and chemical plants
The pulp and paper industries
Combined Heat and Power (CHP) systems

Advantages of Benson Boiler

High efficiency and rapid start-up
Compact and lighter in weight
Safer as it avoids drum explosion risks
Produces dry steam, protecting turbine blades

Disadvantages of Benson Boiler

High initial cost due to advanced design
Complex construction requires skilled operators
Precise water quality control is necessary

Conclusion

The Benson boiler is a powerful, efficient, and modern type of water-tube boiler. Its supercritical, once-through operation makes it far superior to traditional boilers. Although it is costly and more complex to maintain, its benefits in terms of efficiency, safety, and compact design make it an essential choice for power plants and industries worldwide.