Question

A large mass that gets stuck to the blast furnace wall leads to

• A. increase in fuel consumption
• B. chilling of the hearth
• C. failure of the bosh walls
• D. choking of gas offtakes

Hint:

In process control questions, think about the immediate, corrective action an operator would take. A process becoming inefficient or cold is almost always compensated for by increasing the energy input, which means higher fuel consumption.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The phenomenon described is the formation of a "scaffold" or "scab," which is a buildup of solidified and semi-fused material on the internal walls of the blast furnace. This accretion disrupts the normal operation of the furnace by interfering with the flow of materials and gases.

Step 3: Detailed Explanation:
The formation of a scaffold has several negative consequences:

• It reduces the effective working volume of the furnace.

• It obstructs the smooth descent of the burden (coke, ore, limestone).

• It forces the ascending hot gases to flow through a narrower channel, leading to "channeling."
These disruptions lead to inefficient heat transfer between the hot gases and the burden, and incomplete chemical reactions. The furnace operation becomes unstable and cooler than desired. To counteract this inefficiency, restore the thermal balance, and potentially melt the scaffold, operators are forced to take corrective actions. The most common action is to increase the amount of heat generated, which is typically achieved by:

• Increasing the coke rate (fuel consumption).

• Increasing the hot blast temperature or oxygen enrichment.
While other severe consequences like chilling of the hearth (if the problem escalates) can occur, the immediate operational response and consequence is an increase in the fuel rate to compensate for the process inefficiency. Choking of gas offtakes is more related to burden "slips" or fluidization, not scaffolds. Failure of bosh walls is an extreme and rare event.

Step 4: Final Answer:
A large mass stuck to the blast furnace wall disrupts efficient operation, necessitating an increase in fuel consumption to maintain temperature and productivity.