Question

The gas distribution in a blast furnace is controlled by the shape of

• A. Cohesive zone
• B. Deadman zone
• C. Raceway zone
• D. Chemical reserve zone

Hint:

Think of the cohesive zone as a "dam" or an "umbrella" for gas flow inside the blast furnace. The gas must flow around this impermeable region, so its shape and position are crucial for controlling where the hot gases go.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question asks about the primary factor controlling the flow pattern of the hot reducing gases as they ascend through the burden (layers of coke, iron ore, and flux) in an ironmaking blast furnace.
Step 2: Detailed Explanation:
- (A) Cohesive zone: This is the region within the furnace where the iron-bearing materials (sinter, pellets) begin to soften and melt. As they soften, they lose their permeability to gas flow. This zone forms a semi-molten, relatively impermeable layer, often with an inverted 'V' shape. The ascending hot gases generated in the raceway cannot easily pass through this zone and are forced to flow around it, primarily towards the furnace walls. Therefore, the shape, level, and permeability of the cohesive zone are the most critical factors that dictate the overall gas distribution in the furnace stack, which in turn affects heat transfer, reduction reactions, and overall furnace efficiency.
- (B) Deadman zone: This is a stagnant column of coke located in the center of the furnace hearth. It has very low permeability and gas flow is minimal through it. While it influences flow at the very bottom of the furnace, it doesn't control the overall distribution throughout the main stack like the cohesive zone does.
- (C) Raceway zone: This is the region in front of the tuyeres (air inlets) where coke combusts at very high temperatures. It is the source of the hot reducing gas, but the raceway's shape itself does not control the subsequent distribution of that gas through the many meters of burden above it.
- (D) Chemical reserve zone: This is a region of thermal and chemical equilibrium where the temperature is around 1000 \(^{\circ}\)C. It relates to the efficiency of chemical reactions but does not physically control the gas flow path.
Step 3: Final Answer:
The cohesive zone acts as a gas distributor, and its shape is the most influential factor in determining the gas flow pattern within the blast furnace.
Step 4: Why This is Correct:
The low permeability of the cohesive zone forces the gas to flow around it, making its geometry the primary controller of gas distribution in the furnace's upper sections. Controlling the cohesive zone shape is a key aspect of modern blast furnace operation.