The effect of the wetting droplets size on power consumption during drum granulation

Changes of torque during fine material (foundry dolomite) granulation in a horizontal drum granulator at changing wetting parameters were studied. The variable parameters were droplet diameter and wetting of granular material. The bed of loose material was sprayed during feeding, at a constant liquid flow rate V-l=0.012 m(3)/h. The size of wetting liquid droplets was changed using different rates of air flow through pneumatic spraying nozzles in the range from V-p=1.0 to 3.0 m(3)/h and applying a sprinkler which supplied (drop-wise) the liquid uniformly along the entire drum length. In each test, instantaneous values of torque on the granulator shaft were measured in 1 s time intervals. The effect of droplet size and moisture content of the bed of granular material on torque in the whole granulation cycle was estimated. It was found that bed wetting conditions had a significant influence on the nucleation and growth of agglomerates. A minimum (boundary) size of liquid droplets, at which the bed is not transformed into granulated material, depends on the total amount of liquid supplied at the wetting stage. Changes of torque during the drum granulation are a good representation of the phenomena related to the transformation of wetted feed into granulated product and can be an easy indicator of the process.