Discharging Characteristics of Particles from the Drying Tank in a Thermal Jet Dryer

Authors are developing a thermal jet dryer for the purpose of weight and volume reduction and recycling of sludge dehydrated cake. In order to investigate the discharging characteristics of particles from the drying tank, which is disc type and set vertically, experiments using a cold model equipment with airflow at ambient temperature and calculations using a CFD software FLUENT were carried out. The following results were obtained. (1) Velocity and its tangential component of airflow in the tank are almost the same, so they could be measured by a one dimension anemometer. It suggests that the Rankine eddy is generated in the tank. (2) By calculations using FLUENT, tangential velocity and direction profile of airflow in the tank were almost corresponding to experimental ones. (3) After feeding particles in the tank, velocity of airflow has decreased. Therefore, particles could not circulate along the inner wall and took off from it. This phenomenon contributed to the discharge of particles from the tank, and it was shown by FLUENT using two-way coupling calculation for gas-solid multiphase flow. (4) Experimental and calculated average residence time of particles in the tank were in the order of hundreds seconds. They corresponded with each other when the horizontal velocity ratio of particles-wall collisions was between 0.8 and 0.9.