ISSN Online: 2377-424X
International Heat Transfer Conference 12
Influence of the operating conditions on the heat transfer coefficient during agitated sludge drying
Abstract
In regard to the environmental legislation and regulation issues, partial or exhaustive drying offers significant
reduction in the volume of the sludge output, and turns it into a valuable product. But the mechanical and
thermal design of the dryers is still more a question of know-how than scientific knowledge. A batch laboratory
scale dryer was developed to investigate the contact drying of sewage sludge. Drying kinetics, local and mean
heat transfer coefficients at the dryer wall as well as the torque needed to keep a constant stirring speed can be
determined. To validate this set up, the drying kinetics obtained in this batch dryer have been compared with
kinetics determined in an industrial paddle dryer. The results are in good agreement. Then, this experimental
tool was used to investigate the influence of the sludge origin, the wall temperature and the stirring speed on the
mean heat transfer coefficient at the dryer wall. This gives some important information for the thermal design of
the industrial process and for optimization.