Investigation of a Hydraulic Channel for Plastic Particles Sorting via Experimental and Numerical Tools

In recent decades, the versatility of fossil-based polymers has led them to become one of the most used materials for the production of several consumer goods. The destiny of post-consumer plastics is crucial for environmental sustainability. Two are the alternatives to landfilling: (i) energy recovery, i.e., replacement of traditional fuel with plastic litter, and (ii) recycling, i.e., processing of plastic wastes to produce secondary raw materials that may substitute primary raw materials. This work presents the investigation of a device for the hydraulic separation of heterogeneous plastic wastes, which, when properly upscaled, may be efficiently used within recycling plants. This apparatus is suitable for the separation of granules or flakes of plastics with a density higher than 1000 Kg/m3 and may replace existing technologies for mechanical recycling. The purpose of the device is to separate the useful fraction from a mixture of plastics and water introduced inside. The separation procedure efficacy relies on the difference in density, dimension, and shape of the processed plastic particles and on the flow features within the device. Experiments were carried out to test the efficacy of the device as a function of those factors. To increase the range of variation in the key parameters influencing the apparatus’s working principles, Computational Fluid Dynamics was employed to build a numerical model of the device. The validated numerical model suitable to fully characterize the apparatus performance features a hybrid grid with an inner mesh of 3·10−3 m size, a careful modeling of the near-wall region, and the k-ω SST turbulent model.