Abstract
Authors have been developing a thermal jet dryer for the purpose of weight and volume reduction and recycling of organic sludge dehydrated cake. A new sludge feeding system was introduced to avoid the compression of the sludge in a screw feeder. Sewage sludge was able to be dried by this improvement. The experimental results for the sewage sludge were compared with those of bean curd refuse and waste water sludge from a dye works. The simulations of the air-solid multiphase flow accompanying drying process were made using a CFD software and its results were compared with the experimental ones.
(1) There was little difference about the particles' average residence times in the drying tank for three samples, although experimental results showed large difference about the effective diameters of dried product. Therefore, there is little influence of disintegration, drying, kinds and physical properties of samples on the fundamental particles' flow.
(2) CFD calculations of particles' trajectories with heat transfer and drying were made by two-way coupling method. Similar calculation results were obtained with the experimental data for setting the vertical restitution coefficient between particles-wall to 1, and setting the horizontal one to 0.6-0.7. In order to carry out better predictions, development of the disintegration process model is needed.
(3) Unlike conventional pneumatic dryers or rotary dryers, the particles in the drying tank are in the almost same drying conditions through the drying process. Moreover, it turned out that a gas-solid multiphase flow in the drying tank is assumed to be a complete-mixing flow.
