Sewage sludge dryer, Sewage sludge drying

The wet product fed through the inlet nozzle is picked up by the rotor blades, applied on the hot wall and simultaneously conveyed towards the outlet nozzle at the opposite end of the body. The generated vapours are streaming counter-currently to the product flow and are leaving the dryer close to the feed nozzle. Evaporating and conveying capacity are adapted by the right rotor blade arrangement. Entrained particles from the dry zone are removed in the wet zone. Moisture levels of less than 1 % can be achieved. The residence time of the product is typically between 5 and 15 minutes. The outstanding heat transfer rate for hot solid products enables cooling of large amounts of solids in a compact machine compared to usually used cooling screws and without cooling air.In product melting like the melting of urea, the particles are heated up and molten inside the dryer. The melt can be mixed with other liquid and solid additives to improve the properties of the final products.

The vertical thin film dryer consists of a cylindrical, vertically arranged body with heating jacket and a rotor inside. The rotor is equipped with rows of pendulum blades all over the length of the dryer. The hinged blades spread the wet feed product in a thin product layer over the heated wall and mix the product layer material intensively. Therefore the volatile components evaporate continuously from the product layer with high evaporation rates. The hinged blades are designed with a minimum gap to prevent fouling of the heating surface by product, but are never in contact with the heated wall. The product enters the dryer at its top. The evaporation starts after heating to the boiling point. In the slurry zone first solids are formed and with advancing evaporation of the volatiles and continued shearing by the hinged blades the paste breaks up to powder. The final solid product is discharged by gravity at the bottom of the dryer via a suitable air lock.