Change in the properties of beds granulated in disc granulators
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Technical University of Lodz
Publication date: 2010-01-01
Physicochem. Probl. Miner. Process. 2010;44(1):53–62
During tumbling of a powder bed wetted with liquid, material particles are agglomerated. Both the formation of granules and increase of the bed moisture content cause changes in bulk density and the coefficient of material friction against the granulator surface. They in turn determine energy transfer to the granulated material. In the present study, a change of the above mentioned parameters during batch granulation was investigated by comparing results obtained with a change in granulation degree and torque on the granulator shaft. Experiments were made in three disc granulators of diameters 0.5, 0.7 and 1 m, with rotational speeds equal to 0.2 of critical velocity. Variable parameters were the degree of disc filling and the angle of inclination of the disc axis to the level. The experimental material was bentonite with particles from 0 to 0.16 mm in diameter (dm = 0.056 mm), specific density 2420 kg/m3 and bulk density 790 kg/m3. The material was wetted drop-wise with water during the granulation at constant liquid flow rate Q = 0.7 ml/s. The angle of disc axis inclination in the applied range of its changes had no effect on the process and layer properties. In all cases, bulk density of the bed during granulation decreased. When observing change of the coefficient of friction between the bed and disc surface during granulation, three ranges of this parameter change were found. In the first, the coefficient was growing. In the second, short period, the coefficient decreased slightly. In the third, it increased again. Changing the in torque on the granulator shaft was also analysed. Three ranges could be distinguished here as well. In the first, unit moment increased to up to 50%. In the second, it dropped. In the third, it remained constant.