in the atmospheric air a weight regulator of sucked in air 26 in modulation with the booster 25 an air humidifier saturator 27 operating on hot water at an adjustable and constant temperature depending on the amount of water vapor desired to be introduced into the gasification combustion chamber items 28 29 and 30 show with their regulating meters the intakes for the hot water the water vapor the gases or fumes which it is desired to introduce into the reaction system of the gasification combustion zone an assembly for cooling the spent schist so as to allow recovery of the tangible heat and to lower the temperature sufficiently for facilitating emptying of the kiln this assembly is formed by a fan 31 which sucks in the gases at the ends of the ramps 14 it is provided by a heat exchanger 32 and a hot water generator the latter may be used for example for conditioning air saturated with the humidifier 27 connected to the hot water reserve 33 regulated by 34 to a constant temperature or else it may be intended for other uses the gases cooled at 32 are mixed at 35 with incondensible gases from the kiln they are then injected at both ends of the ramps 16 they pass through the spent schist to be cooled by direct contact a large part is taken.