Understanding Benson Boilers and Water Drums

The question asks about the number of water drums present in Benson boilers. Benson boilers are a specific type of steam generator known for their unique design, particularly regarding the absence of steam and water drums.

Design Principle of Benson Boilers

Benson boilers operate on the "once-through" principle. In this design, feedwater is pumped into tubes at one end, and it flows continuously through heated sections, turning into steam and then superheated steam, exiting at the other end. There is no large reservoir for water or steam separation within a drum.

Absence of Water and Steam Drums

A key characteristic of Benson boilers is that they do not have traditional water drums or steam drums. This is primarily because they are designed to operate at very high pressures, often in the supercritical range (above 22.1 MPa or 221 bar). At supercritical pressure, the distinction between liquid water and steam disappears, eliminating the need for a steam-water separation drum.

Even when operating below supercritical pressure, the once-through design means that water enters one end, flows through evaporation tubes, and exits as steam, without accumulating in a water drum. The entire process happens in a continuous flow through the tubes.

Conclusion

Due to their unique once-through design and often supercritical pressure operation, Benson boilers are constructed without water drums (or steam drums). Therefore, the number of water drums in Benson boilers is zero.

Let's look at the options provided:

• zero: This aligns with the design principle of Benson boilers.
• two: Traditional boilers might have multiple drums, but not Benson boilers.
• three: More than two drums is also characteristic of different boiler types, not Benson.
• one: Some boilers have one water drum, but Benson boilers do not.

Based on the operational principles and design of Benson boilers, they have zero water drums.