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Why is coke used as a reducing agent to reduce FeO to produce iron instead of coal.I admit that coke is carbonaceous but what is it that compels us to use coke instead of the naturally available coal?

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    $\begingroup$ coke burns hotter than coal. $\endgroup$ – MaxW Aug 8 at 15:32
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    $\begingroup$ When coke burns, it leaves little ash or smoke, it contains less impurities, and as @MaxW said, it produces a higher temperature. $\endgroup$ – Greg Aug 8 at 16:12
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The single most important factor is strength ( mechanical compressive ); coal is heated to make coke, the resulting coke is stronger than the original coal. Also, coke helps to make the charge of iron oxides and limestone more porous to permit gas flow up and droplets of liquid iron and slag down. The coke oven heating drives off volatiles from the coal, which are a valuable source of chemicals, and contain much of the undesirable $\ce{S}$ and $\ce{P}$, which would otherwise go into the pig iron. Minerals like silica (ash) remain in the coke but they are easily collected by the slag. A bit off topic, but powdered coke and gasses are blown into the bottom of the blast furnace to provide more $\ce{C}$, which makes modern blast furnaces much more productive than 60+ years ago.

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  • $\begingroup$ "Strength" is a bit dubious quantity. ;-) Coke reacts faster (with CO2 to form CO) because it is more porous, and thus always keeps a large surface area. The gas flow argument isn't really one. $\endgroup$ – Karl Aug 9 at 6:44
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    $\begingroup$ If you are unfamiliar with a blast furnace think of a 20 ft diameter tube 100 ft high filled with dense gravel ( iron oxide, lime stone and coke) at temperatures approaching 2500 F . It is critical that this "gravel" not collapse and maintain porosity for very high gas flow up though the column. So the strength of the coke is critical. $\endgroup$ – blacksmith37 Aug 10 at 3:21
  • $\begingroup$ The word "strength" means nothing. Strength of what? Mechanical? If you say "coke is more porous", that describes the individual coke particle (remember you are on a chemistry site here). You mean the bulk density and porosity of the coke/ore mixture, right? $\endgroup$ – Karl Aug 10 at 13:28
  • $\begingroup$ You should edit your answer accordingly if you want my upvote. ;-) $\endgroup$ – Karl Aug 10 at 15:55

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