PURPOSE: To reduce the generation of bad smell and unburnt gas in case dehydrated sludge, having a high calorific value, is incinerated by a method wherein gas, discharged from a drying stage above a furnace, is cooled and dehumidified, thereafter, is re-circulated to a cooling stage below the furnace, while exhaust gas of a combustion stage effects heat exchange between combustion air, thereafter, is passed through a scrubber.

CONSTITUTION: The exhaust gas, containing smelly constituents discharged from the multistage furnace 1, is introduced into a cooling and cleaning tower 32 through a duct 8, is cooled, dehumidified and cleaned here by contacting with original or treated water or the like sprayed from a spraying nozzle 30, thereafter, is returned to the cooling stage 17 of the multistage furnace through a pipeline 34 and the unburnt gas, containing the smelly constituents, is burnt perfectly in the combustion stage 16 above the cooling stage. The heat of the exhaust gas, extracted from the combustion stage 16, effects the heat exchange between the combustion air in a heater 42, thereafter, alkali washing of the gas is effected in the scrubber (or a mist cottrel) 44 and, then, the washed gas 48 is dissipated into atmosphere.