Analysis of Granules Behavior in Continuous Drum Mixer by DEM

Abstract

Fig. 1. Principle of the simulation model. model for granulation should be discussed. There are two models for the simulation of granulation process. One is trace movement of all particles. The other is trace movement of granulated particle only as one particle. The former might be better to analyze granulation mechanism. However, it is not realistic to simulate them because particles traced are enormous and it would take a long time to simulate the behavior of granules. Therefore the latter is adopted in this work. The assumptions in this simulation model are follows; 1) Granules are treated as one particle. 2) Particle shape is sphere. 3) Particle diameter is uniformly. 4) Particle diameter and other parameter is fixed in the simulation. 5) Effect of moisture is ignored.Physical constants and simulation conditions are shown in Table 1. Figure 2 shows the schematic diagram of a continuous drum mixer used in the simulation. Table 2 lists the size of drum mixer. Drum length and gradient angle were changed to investigate their effects on the granule behavior. The granules are fed at the extreme right of the drum mixer and granules drop from the extreme left (Fig. 2). Feeding rate is fixed at 100 kg/min. Continuous Drum Mixer Determination of ParametersThe simulation parameters are needed to be determined so that the granules behavior simulated correspond to the experimental results. Particularly the frictional coefficient has to be determined carefully since it strongly affects granules behavior. The simulation of granules behavior was performed to investigate the frictional coefficient on the behavior. The snapshots are shown in Fig. 3. The granules behavior is influenced by the frictional coefficient and a rising angle increases with an increase in the frictional coefficient. The rising angle was defined as shown in Fig. 4(a) to evaluate the granule behavior and to compare to experimental results. Figure 4 (b) shows relationship between the friction coefficient used in the simulation and the rising angle. The rising angle obtained from the experiment was also shown in Fig. 3. The rising angle increases with an increase in the ISIJ International, Vol. 49 (2009) frictional coefficient until the coefficient is 0.5, and then, the rising angle is going to be constant value about 100 degrees. The frictional coefficient was determined as 0.7, at which the rising angle obtained from the simulation is the closest to experimental one, although the rising angle obtained from the simulation does not agree with experimental results completely. This difference between them could be due to the assumption of sphere in the granules. The reason of this difference will be investigated more detail in the future. ExperimentGranulation experiment has been performed by using the continuous dram mixer. Granulator consists of rotating drum mixer, water nozzle and feed hopper (Fig. 5). The raw materials used in the actual process are supplied continuously at the extreme right of the drum mixer. Water is sprinkled by a nozzle, and ...

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