Glowing coke descending through a cooling duct in a coking plant is quenched by two gas flows respectively traversing an upper compartment and a lower compartment of the duct, the two compartments meeting at a restricted gate for the passage of the coke. At least the lower gas flow, passing in countercurrent to the descending coke charge, is also circulated through a drying and preheating oven for coal to be fed to a coke-oven battery of the plant, thus containing some water vapor. When the upper flow is also constituted by coal-drying gas, it is passed downward through the upper compartment in order to reduce the height of a high-temperature zone in which combustion and thus loss of coke could occur. The coke gate is formed by a funnel-shaped upper partition and an upwardly pointing conical lower partition between which a scavenger gas passes in cross-flow.