Forced-circulation boilers — identify which use it Which of the following boilers operate with forced circulation of water (i.e., pumps circulate water through the evaporator)?

Introduction / Context:
Modern high-pressure boilers often rely on forced circulation to control heat transfer, avoid film boiling, and maintain stable flow in evaporator circuits. Recognizing which types employ pumps (as opposed to natural circulation) is core boiler knowledge.

Given Data / Assumptions:

• La-Mont: external circulation pump sends water through parallel evaporator tubes.
• Benson: once-through, supercritical or subcritical sliding pressure operation; feed pumps provide forced flow.
• Loeffler: evaporates feedwater using recirculated steam to avoid salt deposition; circulation by pumps.

Concept / Approach:
All three named boilers use forced circulation, albeit with different circuit philosophies. In contrast, Cornish, Lancashire, and simple natural-circulation water-tube units depend primarily on density differences between hot and cold legs (thermosyphon action) rather than pumps.

Step-by-Step Solution:

Verification / Alternative check:
Standard schematics for La-Mont and Loeffler show dedicated circulation pumps; Benson's once-through design relies entirely on feed pumps to push fluid through heating surfaces.

Why Other Options Are Wrong:

• Any single selection omits other forced-circulation designs.
• Cornish boiler: a fire-tube boiler without forced water circulation.

Common Pitfalls:
Assuming “once-through” means natural circulation; misclassifying Benson as natural because it lacks a steam drum.

Final Answer: