In blast furnace–hot-blast practice, what medium do the blast furnace stoves heat and deliver to the furnace to enable efficient ironmaking? Specify the intended heating target (not the fuel or the off-gas).

Introduction / Context:
Blast furnace stoves (often called Cowper stoves) are classic regenerator units used in ironmaking. They cyclically store heat in checker bricks and then release that heat to a flowing stream. Understanding exactly which stream they heat is essential for furnace technology: it determines combustion needs, stove sizing, and overall blast furnace efficiency.

Given Data / Assumptions:

• The ironmaking blast furnace requires a pressurized hot blast for tuyeres.
• Stoves operate in alternating “on-gas” (heating bricks) and “on-blast” (heating air) modes.
• The goal is to raise the temperature of the oxidant entering the furnace, thereby improving thermal efficiency and reducing coke rate.

Concept / Approach:
In “on-gas” mode, fuel gas is burned and flue gases heat the checkerwork. After sufficient heating, flows are reversed to “on-blast” mode, where cold air passes through the hot checker bricks and emerges as hot blast. This hot air (not steam, not blast furnace gas) feeds the tuyeres to combust injected fuels/coke at the raceway, elevating flame temperatures and improving meltdown and reduction kinetics.

Step-by-Step Solution:
Identify the end-use stream that must be hot at the tuyeres: combustion air (the “blast”).Recognize that stoves are regenerator heat exchangers transferring stored heat to this air.Conclude that the stoves are designed to heat air, typically to several hundred degrees Celsius (often above 900°C in large plants).

Verification / Alternative check:
Operational descriptions of Cowper stoves uniformly state that they preheat the blast air. Process flow diagrams show air compressors/blowers feeding stoves and then the hot blast main to the tuyeres.

Why Other Options Are Wrong:
Blast furnace gas: Used as a fuel for the stove in “on-gas” phase, but the product stream heated for the furnace is air.Steam: Not generated by stoves; steam systems are separate utilities.None of these: Incorrect because “air” is correct.

Common Pitfalls:

• Confusing the stove fuel (often blast furnace gas) with the stream being heated for the furnace.
• Assuming any hot gas leaving the stove is the same as the blast—only the “on-blast” stream is the hot air product.

Final Answer:
air