PUTTART®

The PUTTART® vertical dryer-granulator is a high-capa city installation for simultaneous sludge drying and granulating.

Mechanically dewatered sludge (dry solids content between 15 and 30%) is extracted from the reception bunker and pumped to the coater. In the coater the wet sludge is mixed with already dried granules that are recycled to the coater, in such a way that each dry granule is coated with a thin layer of wet sludge.

The coated granules enter the dryer from the top and fall onto the first tray. The tray is a double steel plate, internally heated with thermal oil. This means that drying is done in an indirect way (no contact between heating medium and product to be dried) and this is inherently much safer (no explosion risks) than direct drying.The granules are transported from the inner to the outer circumference of the tray by raking arms which are mounted on a slowly rotating central shaft.

At the outer side of the tray, the granules fall on the tray below, which is slightly larger in diameter than the one above. The granules are now transported back to the centre. This movement is repeated on the trays below. At the bottom of the dryer the granules are collected and transported by a screw system and a bucket elevator to a sieve. The sieve separates the larger granules from the smaller ones. The small granules are recycled to the coater, the large granules are cooled and evacuated to storage. The vapours created in the dryer are condensed in a contact condenser, using cooling water. Uncondensable gases (such as odours, VOCs) are evacuated to the thermal oil boiler where they are destroyed by thermal oxidation (see also DYNAFLUID® section). The heat created is recovered to heat up the thermal oil. Usually additional fuel is necessary to reach energy equilibrium.

Applications

municipal sludge (primary, secondary, digested,...)