Question

Which of the following is/are the role(s) of coke in a blast furnace?

• A. reducing agent
• B. heat source
• C. gas permeable medium
  (D) flux
• D. flux

Hint:

Remember the three 'C's of Coke in a blast furnace: 1. {Chemical:} Reducing agent (produces CO). 2. {Calorific:} Heat source (burns to provide energy). 3. {Column:} Structural support (maintains permeability).

Answer 1

The Correct Option is A, B, C

Step 1: Understanding the Concept:
This question asks for the multiple functions of coke in an ironmaking blast furnace. Coke is a specially prepared form of carbon, made by heating coal in the absence of air. It is a crucial raw material in the blast furnace process.
Step 2: Detailed Analysis of Each Role:
- (A) reducing agent: Coke plays a vital role as a reducing agent. It directly reduces iron oxide at high temperatures (\( \text{Fe}_{2}\text{O}_{3} + 3\text{C} ⇒ 2\text{Fe} + 3\text{CO} \)). More importantly, the carbon monoxide (CO) gas produced from the combustion of coke is the primary gaseous reducing agent in the upper parts of the furnace (\( \text{Fe}_{2}\text{O}_{3} + 3\text{CO} ⇒ 2\text{Fe} + 3\text{CO}_{2} \)). So, coke is both a direct and indirect reducing agent. This statement is correct.
- (B) heat source: In the lower part of the furnace (the raceway), coke combusts with the hot air blast in a highly exothermic reaction (\( \text{C} + \text{O}_{2} ⇒ \text{CO}_{2} \)). This combustion provides the necessary heat to melt the iron and slag and to sustain the endothermic reduction reactions occurring higher up in the furnace. This statement is correct.
- (C) gas permeable medium: The charge in a blast furnace consists of layers of iron ore, coke, and flux. The coke is strong and maintains its shape even at high temperatures and under the heavy load of the material above it. The coarse, porous nature of the coke layers creates a permeable bed that allows the hot reducing gases to flow upwards through the furnace stack, ensuring efficient heat and mass transfer. This structural role is critical for furnace operation. This statement is correct.
- (D) flux: A flux is a substance added to the furnace to combine with impurities (like silica and alumina from the ore) and form a low-melting-point liquid slag. In an ironmaking blast furnace, the flux is typically limestone (CaCO\(_3\)) or dolomite. Coke itself is primarily carbon and does not act as a flux. This statement is incorrect.
Step 3: Why This is Correct:
Coke serves three essential and distinct functions in a blast furnace: it provides the chemical reducing power, the thermal energy, and the physical structure/permeability required for the process. Fluxing is the role of other materials like limestone.