La-Mont boiler: typical working pressure range (forced-circulation water-tube) Select the usual working pressure range for a La-Mont boiler from the options below.

Introduction / Context:
The La-Mont boiler is a high-pressure, forced-circulation, water-tube design. It circulates water through small-diameter tubes at high velocity using an external pump to prevent film boiling and ensure excellent heat transfer. Recognizing its pressure band distinguishes it from low-pressure shell boilers and from ultra-high-pressure once-through units.

Given Data / Assumptions:

• Pressure units: 1 MN/m^2 = 1 MPa ≈ 10 bar.
• La-Mont design emphasizes high circulation ratios (typically >5) to avoid tube overheating.
• Industrial practice places La-Mont in a high but not supercritical pressure class.

Concept / Approach:
La-Mont boilers were developed to operate efficiently at high subcritical pressures. Typical ranges cited in teaching texts span roughly 2.5–15 MN/m^2 (≈25–150 bar), covering many high-pressure process and power duties without entering supercritical territory, which would be handled by Benson/once-through types.

Step-by-Step Solution:
Convert ranges to bar to build intuition: 2.5–15 MN/m^2 ≈ 25–150 bar.Compare with known La-Mont use: high-pressure but subcritical.Therefore, select 2.5 to 15 MN/m^2 from the choices.This fits the classic classification for La-Mont boilers.

Verification / Alternative check:
Design notes and exam references list La-Mont within this pressure span, emphasizing forced circulation to maintain stable boiling at elevated heat fluxes.

Why Other Options Are Wrong:
0.5–10 MN/m^2 is too broad and includes very low pressures; 1–15 overlaps but includes many low-pressure cases atypical of La-Mont; 3.5–20 or “above 25” shift the range unnecessarily high, encroaching on regimes typical of other designs.

Common Pitfalls:
Confusing pressure capability with circulation method; assuming forced circulation implies supercritical operation—it does not.

Final Answer:
2.5 to 15 MN/m^2