DEWATERING OF FINE GRANULAR MATERIALS BY VIBRATING SCREENS WITH SUPERPOSED CAPILLARY SUCTION

摘要

Vibrating screens are widely used for dewatering bulk materials in the mineral-processing industries. Advantages are high throughput and low capital costs. However, the residual moisture of bulk materials after conventional vibrational dewatering often turns out to be only a little lower than the moisture achievable by stationary draining. There is strong evidence that the mechanism of drop formation and dripping off the screen is usually the limiting factor of dewatering kinetics on vibrating screens. Pilot scale studies at the Institut fuer Mechanische Verfahrenstechnik und Mechanik have shown that the additional use of capillary suction media can considerably lower residual moisture, compared to conventional vibrational dewatering. The suction medium is designed as an endless textile belt, which is constantly moved in a counterflow mode along the underside of the screen of a modified vibrating screen. All water that has left the bulk due to vibrational acceleration gets immediately absorbed by the porous belt, thus being removed by active transport, instead of having to drip off. In addition, the capillary suction caused by the fine pores of the suction media acts as a superposed driving force on the water in the bulk, resulting in further dewatering. In the work presented, this modified pilot scale vibrating screen has been used for dewatering quartz sand. The influence of bulk height, residence time, frequency of vibration and acceleration on dewatering have been studied with throughputs ranging up to 5 t/h. By comparison with lab-scale batch experiments, methods for scale up calculations have been developed and verified. Possible fields of application for the process presented can be found in processing industries, as well as in chemical industries.