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Question Video: Identifying the Composition of Blast Furnace Coke Chemistry

Which of the following substances is the coke that takes part in essential reactions inside a blast furnace? [A] Waste gas [B] Limestone [C] Slag [D] Carbon [E] Iron ore

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Video Transcript

Which of the following substances is the coke that takes part in essential reactions inside a blast furnace? (A) Waste gas, (B) limestone, (C) slag, (D) carbon, or (E) iron ore.

Blast furnaces can be used to extract iron from its ore. A lot of iron is used to produce steel. Iron metal is usually extracted from a hematite ore, which contains iron(III) oxide. The ore must be treated before it can be placed in a blast furnace. First, the ore is crushed to make smaller pieces; then impurities are removed. Once the impurities are removed from the ore, the treated iron ore is mixed with limestone and coke in centering beds. Limestone and iron ore are combined with the coke. So neither limestone nor iron ore can be described as coke. So neither option (B), limestone, or option (E), iron ore, can be the answer to this question.

The centering beds are used to compact the iron ore, limestone, and coke materials into a solid mass. The mixture of these three materials is known as the charge. This is what’s transported to the top of the blast furnace. When the charge enters the blast furnace, it is heated. This causes the limestone, which is mostly made up of calcium carbonate, to decompose into calcium oxide and carbon dioxide. The calcium oxide then reacts with sandy impurities, producing a molten slag byproduct, which is mostly made up of calcium silicate. We can therefore see that slag is not coke. Thus, option (C), slag, is not the answer to this question.

As well as calcium silicate and calcium oxide being produced, the waste gas carbon dioxide is formed. Carbon dioxide and nitrogen, another side product from a different reaction, leave through the top of the furnace as waste gases. We can see that these waste gases are not coke. Thus, option (A), waste gas, is not the answer to the question.

The only option left that we haven’t ruled out as incorrect is (D), carbon. When carbon in the form of coal is heated, it forms coke. The coke takes part in essential reactions, including reacting with oxygen from the hot air blast. So the answer to the question “Which of the following substances is the coke that takes part in essential reactions inside a blast furnace?” is (D), carbon.

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