Measurement and simulation of the contact drying of sewage sludge in aNara-type paddle dryer

摘要

Contact drying experiments were carried out in a Nara-type paddle dryer to study the drying kinetics ofsewage sludge in the presence of air. In order to have a better understanding of the sewage sludge dryingmechanism, a penetration model developed by Tsotsas and Schliinder is used to simulate the dryingkinetics of the pasty, lumpy and granular phase which the sludge experiences during the drying process.The pasty phase is assumed to be a saturated particulate phase, and the granular phase is consideredas a mono-dispersed particulate phase whose diameter was experimentally determined. In the lumpyphase, a sludge wall sticking still to the paddle-shaft surface was formed, and the heat transfer resistancefrom the sludge wall is considered during the model calculation. The influence of the drying parameters(temperature, stirrer speed and air flowrate) on the drying process is investigated experimentally andtheoretically. The result indicates that the penetration theory is able to describe the sludge drying kineticsof the three distinct phases. Experimental and calculated drying kinetics are in satisfactory agreement fordifferent drying parameters.