Boilers with and without forced circulation In which of the following boilers does forced circulation of water not take place?

Introduction / Context:Boiler circulation refers to how water/steam moves through heated circuits. Modern high-pressure water-tube designs often employ forced circulation using pumps or gas-dynamic effects, whereas classic shell-type fire-tube boilers rely on natural convection.

Given Data / Assumptions:

• La-Mont and Velox are water-tube designs with explicit circulation enhancement.
• Benson and once-through supercritical designs use pumped flow through evaporator tubes.
• Lancashire is a large shell fire-tube boiler.

Concept / Approach:La-Mont employs an external circulating pump to force water through evaporator tubes. Velox uses high-velocity gas flow and pressure to enhance heat transfer and circulation. Benson/once-through boilers pump feedwater through the heating circuit without a steam drum—flow is definitely forced. Lancashire boilers, however, are fire-tube shells with a big water space where circulation is natural (density differences) rather than pump-driven.

Step-by-Step Solution:Identify water-tube forced-circulation examples: La-Mont, Velox, Benson.Identify the outlier: Lancashire (fire-tube) with natural circulation.Therefore, forced circulation does not occur in Lancashire boilers.

Verification / Alternative check:Design schematics show no circulation pump in Lancashire; modern high-pressure units always show pumps driving flow through small-diameter tubes.

Why Other Options Are Wrong:All others listed apply forced or once-through circulation; selecting them would contradict their defining features.

Common Pitfalls:Assuming “once-through” implies natural circulation; it actually relies on feed pumps for flow through the circuit.

Final Answer:Lancashire boiler