Unit for furnace loading (throughput intensity) Choose the correct engineering unit commonly used to express furnace loading for hearth-type furnaces.

Introduction / Context:
Furnace loading quantifies throughput intensity—how much product is processed per unit hearth area per unit time. This normalisation enables fair comparison among furnaces of different sizes and helps in design/scale-up and performance benchmarking.

Given Data / Assumptions:

• Hearth-type furnaces where floor (hearth) area constrains charge layout.
• Throughput measured as mass of stock processed per hour.
• Need to compare furnaces independent of absolute size.

Concept / Approach:
Normalising throughput by hearth area yields a characteristic loading rate. The standard practice is to use mass flow per time per area. Using only ton/hr hides geometry effects; using ton/m2 omits time. Thus, ton stock/hr/m2 hearth area is the meaningful unit for loading intensity.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals specify recommended loading ranges (e.g., t/h/m2) depending on product type and heating schedule.

Why Other Options Are Wrong:

• ton stock/hr: Not normalised to area; inadequate for comparison.
• ton stock/m2: Lacks time dimension; cannot indicate rate.
• both (b) and (c): Combining two incomplete measures does not make a correct unit.
• kJ/hr/m3 flue-gas: Not a standard loading metric for hearth furnaces.

Common Pitfalls:
Confusing burner heat-input density with furnace loading; they are related but distinct metrics.

Final Answer:
ton stock/hr/m2 hearth area