Boiler Classification — Benson Boiler Pressure Level Benson boiler is a __________ water-tube steam boiler that employs forced circulation (once-through) without a steam drum. Choose the correct pressure range classification.

Introduction:
The Benson boiler is a once-through, forced-circulation boiler widely cited for supercritical and high-pressure operation. Understanding its classification clarifies why it omits a steam drum and how it achieves high efficiency with sliding pressure control.

Given Data / Assumptions:

• Water-tube, once-through design; feedwater flows through economiser, evaporator, and superheater in series.
• Forced circulation by pumps; no steam drum in supercritical versions.
• Designed for high and supercritical pressures.

Concept / Approach:
“High pressure” boilers operate far above simple shell-boiler pressures. The Benson concept is synonymous with high-pressure and, in many installations, supercritical operation where phase change occurs without a distinct boiling interface. Hence, it is correctly classified as a high-pressure water-tube boiler using forced circulation.

Step-by-Step Solution:
Identify design: once-through path with pumps ⇒ forced circulation.Recognize pressure regime: designed for very high to supercritical pressures.Therefore, select “high pressure”.

Verification / Alternative check:
Plant engineering references list Benson as a canonical high-pressure, once-through boiler, contrasting with drum-type subcritical units.

Why Other Options Are Wrong:

• Low pressure or vacuum: contrary to intended service.
• “Subcritical only”: many Benson units are explicitly supercritical.

Common Pitfalls:
Confusing forced circulation (Benson) with natural circulation (e.g., Babcock & Wilcox) and assuming a steam drum is universal.

Final Answer:
high pressure