Development of a dynamic-physical process model for sieving

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In mechanical process engineering and materials preparation technology, it is frequently required to separate disperse solid systems according to their particle sizes and shapes. This is necessary within combined processes because bulk materials often consist of particles of different, highly non-spherical form and broad size distribution but, defined narrow particle size distributions are needed for subsequent process steps. On this background, sieving is a technically simple but well-suited, separation process which can be performed discontinuously and continuously. Despite its established nature, the design, optimization and scaling of screening processes is not trivial since the process, plus its subprocesses and its dynamics, is still not satisfactorily understood. Although, good development takes place, there is still a lack of physically based process models.In order to design or optimize screening processes, particle-based simulation methods, such as the Discrete Element Method (DEM), are applied, which allows the modelling of the process step screening in detail after an appropriate validation. Likewise, phenomenological models are suitable for the optimization of apparatus-specific and operational parameters. Therein, simple models, which are used in stationary process simulation packages, only consider the integral outcome of the separation operation. Other models include the interactions between stratification and particle passage through the screen. Usually, the empirically determined, material-, operating-, and apparatus-specific parameters for phenomenological models were determined experimentally, whereas direct derivations of parameters for dynamic models for the process step screening were rarely carried out by DEM applications. Particularly, this applies to investigations of systems with real particles of complex shape under the influence of wetness.While during the first two funding periods of the proposed project, discontinuous and continuous sieving in realistic systems with dry and moist particles was investigated, wet screening will be focussed in the third phase. By means of DEM simulations, which were validated by experimental investigations within the SPP 1679 and will be validated for the new system properties, discontinuous and continuous screening processes are performed time resolved with different mechanical excitation for polydisperse systems of real particle shapes with the effect of wetness under changing operational conditions. Dynamic phenomenological models, which are extended by the observed relationships and predictive properties, are used to represent the numerical results. Simplified DEM simulations are applied to obtain the required parameters for the new, runtime efficient models which can be used in dynamic, combined bulk solids process simulations.