What fuel is produced by heating coal without air and was vital to iron smelting? Coke is produced by heating coal in the absence of air and became a crucial fuel and reducing agent in iron smelting.
The process, called coking, drives off volatile substances such as water, coal gas, and coal tar. What remains is a hard, porous, carbon-rich material. Unlike ordinary bituminous coal, coke can withstand the heavy burden inside a blast furnace without collapsing and blocking the movement of gases.
In the furnace, coke supplies heat and produces carbon monoxide. That carbon monoxide removes oxygen from iron oxides in the ore, leaving metallic iron. Coke therefore performs two jobs at once: it acts as fuel and participates chemically in reduction.
Abraham Darby I established a coke-fired blast furnace at Coalbrookdale in 1709, helping make large-scale cast-iron production more practical. Coke gradually replaced charcoal in Britain because charcoal depended on wood and could not easily support expanding industrial demand. Charcoal remains a possible alternative, but it is made from wood rather than coal and is a different fuel.