Question

The main reducing agent in blast furnace operation is

• A. Coke
• B. Coal
• C. Carbon monoxide
• D. Carbon dioxide

Hint:

Distinguish between the ultimate source of reducing potential (coke) and the active chemical agent (CO gas). In the blast furnace, the gaseous reduction by CO is far more significant than the solid-state reduction by coke.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A reducing agent in iron making is a substance that removes oxygen from iron ores (e.g., Fe\(_2\)O\(_3\)). The blast furnace process uses carbon in the form of coke, but it's important to understand the chemical form that performs the bulk of the reduction.

Step 3: Detailed Explanation:
Let's analyze the roles of the substances listed:

• Coke (C): Coke serves multiple crucial functions: it is the primary fuel, it provides structural support and permeability to the burden, and it is the source of carbon. Coke itself acts as a reducing agent in the lower part of the furnace (direct reduction: \( \text{FeO} + \text{C} \rightarrow \text{Fe} + \text{CO} \)). However, its most important role in reduction is to produce the main reducing agent.

• Carbon monoxide (CO): In the high-temperature raceway zone, coke reacts to form carbon monoxide gas (\( \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \)). This hot CO gas then ascends through the furnace stack. It is this gas that is responsible for the majority (around 70-80%) of the iron ore reduction (indirect reduction: \( \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \)). Because it performs the bulk of the reduction work throughout the largest volume of the furnace, carbon monoxide is considered the main reducing agent.

• Coal: Pulverized coal is often injected as an auxiliary fuel to reduce coke consumption, but CO is still the primary product of its combustion that performs reduction.

• Carbon dioxide (CO\(_2\)): This is a product of the reduction reactions and combustion. It is an oxidizing agent in certain conditions, not a reducing agent.

Step 4: Final Answer:
While coke is the source material, the chemical species that carries out the majority of the reduction in a blast furnace is carbon monoxide (CO).