One of the requirements for reducing iron ore into molten iron in a steel plant is coke, which is a non-volatile residue resulting from the destructive distillation of coals. Destructive distillation is the process of decomposing a substance (wood or coal) by heating it in the absence of air. Air is kept out of the oven so that the wood or coal will not fire. Coke, along with many useful volatile by-products, is produced when carefully selected bituminous coals are heated in a closed atmosphere. Coke used in a blast furnace must have the following characteristics:

1. It must have enough strength to resist shattering by handling or crushing under the load of the blast furnace charge.

2. It must be free of dust and particles under 3/4 inches in diameter for speed of combustion.

3. It must contain as little sulphur and ash as possible as determined by the coals used in its manufacture.

Coke is a hard, greyish substance obtained when soft coal (bituminous) is heated in an airtight oven. Coke contains 87 to 89 per/cent carbon, is hard and porous, produces intense, smokeless heat when it burns and is valuable in smelting (melting) iron ore. Coke used in smelting is called metallurgical coke.
Coke was first produced in beehive ovens but is now produced in the more efficient by-product ovens. The advantages gained in these by-product ovens are; increased coke yield, through exclusion of air; shorter coking period through the narrower chambers in use and the more efficient means of utilising gases; saving in the heat of the oven through external quenching; saving of time and labour through the use of mechanical equipment.

Originally, charcoal was produced by stacking hard or soft wood in piles or long rows that were covered with earth; a small opening was left in the top through which a fire was lighted, and the wood was allowed to smoulder for about 10 days. The hole was then closed, the fire smothered, and the charcoal collected. This early wood charcoal was used in the production of pig iron because of its low sulphur content but was replaced by the more economical and efficient coke produced from bituminous coal.

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Last updated February 1, 2006