1. Carbonization of coals

The fuel needed for large modern blast furnaces can be neither wood, whose combustion temperature is too low, nor hard coal, whose melting point between 350 and 500°C is an obstacle to the permeability essential for shaft furnace operation. Early blast furnaces were fuelled by charcoal, which is rich in carbon and non-fusible.

For reasons of wood availability, English metallurgists thought of using coal from their country's rich subsoil, by carbonizing it in millstones or beehives in a similar way to charcoal manufacture. This innovation, which dates back to the end of the 16th century, has been reported in both England and Germany.

Initial attempts to use coke in blast furnaces were unsuccessful, and it was Abraham Darby who first produced coke cast iron in 1709.

Today, almost all blast furnaces run on coke, with...