Process for treating clarified sludge

A method of treating an aqueous sludge containing combustible solid matter in a continuous process comprising the steps of

• a. mechanically dewatering the sludge;
• b. granulating the dewatered sludge;
• c. drying the dewatered, granulated sludge in a drier containing a fluidized bed consisting of the granulate to be dried at a temperature of 100.degree.-300.degree. C., but always less than the incineration point of the solid matter, the drying step involving the production of exhaust gases containing essentially inert steam;
• d. withdrawing the exhaust gases from the drier and dividing same into two parts;
• e. freeing one of the exhaust gas parts of dust and then recirculating it to the bed of the drier to serve as the sole fluidizing medium for that bed;
• f. condensing the steam in the remaining part of the exhaust gases;
• g. withdrawing dried granulate from the drier and adding a part thereof to the dewatered sludge in the granulating step;
• h. withdrawing dried granulate from the drier and burning same to an ash granulate in a fluidized bed boiler at a temperature of 800.degree.-900.degree. C., the bed of the boiler consisting essentially of the introduced dried granulate and the ash resulting from burning;
• i. heating the bed of the drier by heat exchangers incorporated in that bed which transfer to the bed only heat generated in the boiler;
• and
• j. removing the granulated ash resulting from the burning of the dried granulate in the boiler.