Thermal profile of a blast furnace — comparing zones The temperature in the upper part of a blast furnace (zone of reduction) is __________ the temperature in the middle part of the furnace.

Introduction / Context:
Inside a blast furnace, temperature and chemical reactions vary by height. Understanding this thermal gradient helps explain the sequence of ore reduction, coke combustion, and slag formation.

Given Data / Assumptions:

• Upper part is the stack/zone of indirect reduction where gases ascend.
• Middle part (near the bosh) is much hotter due to combustion and heat release.
• Normal furnace operation is assumed.

Concept / Approach:
Hot air blasts injected near the tuyeres cause intense combustion of coke, producing very high temperatures in the lower to middle furnace (often exceeding 1500°C locally). As gases rise, they cool while reducing iron oxides indirectly, so the upper stack temperatures are significantly lower (few hundred to several hundred degrees Celsius). Thus, the upper zone temperature is less than that of the middle zone.

Step-by-Step Solution:
Identify thermal source: combustion near tuyeres raises middle/lower temperatures.Track gas path: rising gases transfer heat upward, cooling as they ascend.Conclude: upper zone is cooler than the middle zone.

Verification / Alternative check:
Temperature profiles measured in operating furnaces show a gradient: hottest near bosh/tuyeres, moderate in middle, and lowest at the top stack.

Why Other Options Are Wrong:

• Equal to/more than: contradicts the known downward-to-upward cooling gradient.
• “Always higher/equal”: ignores operational thermodynamics of counter-current heat exchange.

Common Pitfalls:
Assuming uniform temperature; the blast furnace operates as a counter-current reactor with strong gradients.

Final Answer:
less than