Habib, Muddasar
(2011)
Designing and assessing a novel vertical vibrated particle separator.
PhD thesis, University of Nottingham.
Abstract
Uncontrolled segregation in particulate mixtures has long been considered as an annoying, and costly, feature encountered in many materials handling operations and although the onset is not clear, many believe it to be driven by the differences in particulate physical properties. An increasing number of usefully scaled laboratory and computer simulation investigations are being carried, particularly by the physics community, to help our understanding of this phenomenon. Physicists at the University of Nottingham have identified that through careful control of frequency and acceleration during vertical vibration, different types of particles can be positioned and/or segregated in a small rectangular cell. An extension of this work resulted in the design of a new small scale batch separator capable of recovering at least one separated particle layer in a different chamber.
This work has explored the scale up of the small particle separator to operate in a semi-continuous mode. Since complete experimental know how of particle segregation phenomena is still deficient an empirical design strategy was used. This scaled up particle separator was driven by a pneumatically powered vertical vibration bench in which dry, non-cohesive particulate mixtures of varying densities and sizes (<1000µm) were vertically vibrated under different conditions to assess their separation behaviours. Experiments with regular (e.g. glass and bronze) and irregular shaped particle mixtures (e.g. comminuted glass and bronze) showed that lower magnitudes of vertical vibration frequency (30±10%), dimensionless acceleration (3±10%), particle bed heights (20 and 40mm in majority of the investigated cases) and partition gap sizes (5 and 10mm) were important for separation. Finally, the technique was employed to separate various industrially relevant particle mixtures (shredded printed circuit boards, iridium and aluminium oxide and shredded personal computer wires).
Two-dimensional Discrete Element Modelling (DEM) with interstitial fluid interactions simulated with a maximum of 1000 virtual glass and bronze particles showed some important aspects of particle segregation such as; layered particle separation, high density particles ending on top and bottom of the particle bed, convection currents, particle bed tilting and partitioned particle separation.
The application of Positron Emission Particle Tracking (PEPT) to glass, bronze, ilmenite and sand particles showed distinct trajectory maps in three dimension (X,Y and Z) with varying particle speeds in the vertically vibrated particle mixtures. The low density particles were mostly observed to move in the middle while the high density particles patrolled in the outer periphery of the separation cell. These distinct particle motions suggested that convection currents played an important role in controlling segregation. Furthermore, the application of a smoke blanket visualization technique showed the existence of air convection currents on top of the vertically vibrating particle mixtures.
The experiments on the scaled up semi-continuous particle separator confirmed what was identified previously in that good particle separation could be achieved through careful control of the frequency and acceleration during vertical vibration. This information lays the foundations for a new breed of low cost, dry separator for fine particulate mixtures.
Key Words: Vertical vibration, particle separator, fine particle mixtures, dry separation, PEPT, DEM, smoke visualizations.
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