Basic issues in blast furnace ironmaking

I’ll try to answer the original poster’s question. Blast furnace ironmaking certainly takes place in a reducing atmosphere; the process involves removing oxygen from iron oxides in the iron ore to produce pure iron. Maintaining this reducing atmosphere inside the furnace is achieved through coke and the carbon contained in the materials fed into the furnace, such as coal powder or oil. The carbon in coke can directly reduce iron oxides, a process known as direct reduction in ironmaking. Meanwhile, carbon monoxide generated by the combustion of coke, coal powder, or oil also plays a role in the reduction process as it rises upward, and this is referred to as indirect reduction. Therefore, the main components of the gas at the top of the blast furnace are nitrogen, carbon monoxide, and carbon dioxide. This gas, although produced through reduction, still has a high calorific value and can be used either within the factory or outside it as fuel. In terms of steel production, ironmaking is a reducing process, while steelmaking is an oxidizing process. I’m not sure if my answer addresses your question.

What was mentioned above relates to thermodynamics; let’s add something about dynamics as well. Coke is added to the blast furnace along with the feed material, that is, iron ore, from the top of the furnace. As molten iron is discharged from the bottom of the furnace, coke moves downward together with the feed material. At the lower part of the blast furnace, there are blowers and coal injection nozzles; gas is blown in from below and moves upward until it is discharged as blast furnace gas at the top of the furnace. Thus, due to this relative movement of solids, liquids, and gases, coke is reduced at a certain temperature, and carbon monoxide in the gas also undergoes reduction, creating a reducing atmosphere inside the blast furnace. Of course, this reducing atmosphere refers to the entire blast furnace as a whole.

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