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Investigations into the segregation of heaps of particulate materials with particular reference to the effects of particle size

Investigations into the segregation of heaps of particulate materials with particular reference to the effects of particle size

Salter, Guy Francis (1999) Investigations into the segregation of heaps of particulate materials with particular reference to the effects of particle size. PhD thesis, University of Greenwich.

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The object of the research programme forming the basis of this thesis has been to provide an improved understanding of the significance of principle variables that determine the propensity that a particulate solid bulk material will segregate. In spite of its ubiquity, and economic significance, segregation of bulk solids is a misinterpreted and vaguely understood phenomenon. An extensive literature review has been undertaken to establish different areas within industry where segregation has proved problematic. The literature review has related segregation and mixing terminology and helped to integrate and collate the current level of understanding of segregation. This review also established that the most productive way forward for enhancing knowledge was to undertake an experimental study into an area that focused on heap segregation and related fields. To achieve this two specially designed rigs were constructed which allowed independent control of variables that were widely documented as affecting the magnitude of material segregation produced when single point charging in plane-flow and conical vessel environments.

Analysis of video footage has provided an increased understanding of the heaping process. Perceived mechanisms of segregation and a recognition of their change in priority during the heaping process has been integrated with reported segregation mechanisms documented in literature. An enhanced and more detailed description of the heap segregation process is presented. It has been recognised that there is a significant facet of segregation behaviour that exists at the point where the vertical charging feed contacts the heap surface. This behaviour increases the severity of a 'hump' pattern that is produced within the vicinity of the heap apex. An embedding mechanism has been identified and attributed to the significant appearance of this behaviour. The significance of this mechanism has not been reported in existing literature and as such has not been incorporated into any predictive techniques used to model heap segregation of this form. Test conditions were configured that successfully removed this behaviour, which allowed the derivation of an empirical technique that successfully modelled segregation patterns being produced in a plane-flow vessel environment. Furthermore, existing predictive techniques published in literature are shown to accurately model the profiles of segregation produced for test results that were devoid of the 'hump' profile. A statistical appraisal of these segregation results was also undertaken that validated the hierarchy of principle particle, process and geometrical variables listed in literature and also provided added information on the significance of their interactions. Test work conducted that vertically filled a plane-flow vessel more commensurate with industrially relevant applications is also presented. Further work is recommended before specific conclusions can be stated regarding the influence that principle variables have on the resulting magnitude of the 'hump' profile produced.

The most important outcome of the work has been the development of a technique that can predict the profile of segregation produced in a conical heap formed under identical conditions to that produced in a plane-flow vessel. There is a significant difference in segregation profiles produced in both vessel geometries. This has been attributed to differences in surface area that the charging feed material is presented with as it descends across the surface of the heap and a model has been successfully developed based on this notion. Providing a relationship between these two vessel environments is of industrial relevance as materials are predominantly stored in a conical geometry as opposed to a plane-flow vessel environment synonymous with the majority of published literature on the topic.

Item Type: Thesis (PhD)
Additional Information: This research programme was carried out in collaboration with Mass Systems Co. Ltd.
Uncontrolled Keywords: Powder mixing; material separation; heap segregation;
Subjects: T Technology > TJ Mechanical engineering and machinery
Pre-2014 Departments: School of Engineering
School of Engineering > Wolfson Centre for Bulk Solids Handling Technology
Last Modified: 25 Jul 2019 13:58

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