Blast Furnace — Typical Maximum Internal Diameter Approximately what is the maximum internal diameter of a modern blast furnace in ironmaking practice?

Introduction / Context:
The internal geometry of a blast furnace (BF) governs gas–solid contact, burden descent, and thermal efficiency. The maximum internal diameter, typically measured near the belly or bosh depending on design, is a key design parameter affecting capacity and throughput.

Given Data / Assumptions:

• General ironmaking blast furnaces (not laboratory or mini-BFs).
• We refer to typical textbook values used in competitive exams and fundamentals courses.
• The question asks for an approximate representative size.

Concept / Approach:
Classical references often cite maximum internal diameters in the neighborhood of 8–10 m for conventional designs, with large modern plants sometimes exceeding this. The value 9 m is a commonly taught benchmark that balances practicality and historical data across installations worldwide.

Step-by-Step Solution:
Relate furnace productivity to cross-sectional area → depends on diameter squared.Standard teaching examples: many BFs cited around 9 m internal diameter.Choose the closest typical value among the options: 9 m.

Verification / Alternative check:
Engineering handbooks present BF diameters roughly 8–12 m for large units; 9 m is a representative, exam-friendly figure.

Why Other Options Are Wrong:
3 m and 6 m are too small for large-scale ironmaking.12 m and 15 m represent very large furnaces; while possible in some contexts, 9 m is the commonly referenced typical maximum in fundamentals problems.

Common Pitfalls:
Assuming a single global standard; designs vary, but the exam convention centers near 9 m.

Final Answer:
9 m