Year

2010

Degree Name

Doctor of Philosophy

Department

Faculty of Engineering

Abstract

The purpose of this research was to determine if either analytical methods or numerical discrete element modelling could be used with accuracy to design conveyor transfers. This goal was achieved using two test materials, polyethylene pellets and corn, which were selected for their different particle and bulk properties and also for a third product, iron ore, but to a lesser extent due to test rig limitations. The design of conveyor transfers has traditionally been based on either trial and error or previous experience and seen as a “black art” rather than a science, as such very few design guides are available. The design of conveyor transfers can be based on experimental investigations, although this method can be costly to companies, taking vital resources away from the key goal of continuous production. The analytical models have existed for some time and have become widely accepted design tools; however, there is limited validation of these to determine their overall performance (both advantages and disadvantages). The analytical models are two dimensional in application and their accuracy with respect to the three dimensional nature of transfer chutes is not clear. This is an area which needs further investigation. The design of transfer chutes has undergone an evolution since the advent of discrete element modelling (DEM) as well as increases in computer processing power. The potential to simulate and predict the behaviour of a transfer chute design before it is constructed can be highly desirable with the prospect of saving substantial time and money. This being said, there has been little validation published on the application of DEM in industrial applications, although in recent years this has started to increase with the realisation that companies need to be convinced this is a legitimate design tool. Additional DEM validation is warranted with respect to conveyor transfers. An experimental test program was undertaken following the design and commissioning of a novel conveyor transfer research facility. This experimental work focussed on two main areas; investigation of particle flow of material through a conveyor transfer hood and spoon and the generation of conveyor trajectories. From these areas, ‘real’ data was obtained for a range of granular free-flowing products, using a combination of high-speed video capture and still photography, for the purposes of validation. The effect of belt speed, material feed rate and the positioning of the transfer hood and spoon were considered in these investigations. Additional to this experimental work was the testing and collection of a wide range of particle and system characteristics for use in the analytical modelling and discrete element modelling components of this research. Two analytical models were then used to predict the particle flow of the test materials through the conveyor transfer hood and spoon. Belt speed, material feed rate and positioning of the transfer hood and spoon were all considered as part of this analysis to provide direct comparisons with the data obtained from the experimental testing. Prediction of the conveyor trajectories was performed using seven trajectory models available in the literature. These comparisons investigated the effect of belt speed and mass flow rate on the trajectory profiles, again providing a direct link with the experimental data. The discrete element method was used to generate three dimensional simulations of the material flow through the conveyor transfer hood and spoon and also conveyor trajectories, based on 3D CAD models of the conveyor transfer research facility. These simulation outputs were then compared to both the experimental data and data obtained from the analytical models. Two software packages were used, Chute MavenTM and EDEM. Chute MavenTM was used to produce the initial transfer chute and trajectory simulations using spherical particles. High material feed rates corresponding to those tested experimentally could not be simulated and so EDEM was employed to develop further simulations. The fact that EDEM has the ability to model both spherical and shaped (clustered) particles was utilised to investigate the effect of shape on simulation output. A critical aspect of any discrete element modelling is whether the outputs are realistic. To minimise any potential issues, a wide range of bench-scale calibration experiments and simulations were also completed to validate both DEM packages used. It can be concluded that the analytical models for conveyor transfers provided close approximations from a two dimensional perspective, however, there were some slight over-predictions evident in some situations. For conveyor trajectories, the models presented a substantial variation in prediction, however, one method stood out as being accurate under all conditions for the materials tested experimentally. Findings from the discrete element modelling showed the dynamic behaviour mimics that of the experimental testing and there was a general agreement with both the experimental investigations and analytical models for the conveyor transfer comparisons. With respect to conveyor trajectories, the DEM results agreed with the results seen experimentally and also predicted the same trajectory path as the one “stand out” analytical trajectory method mentioned above. The importance of DEM calibration and validation has also been documented and shown to be an absolute necessity in the successful simulation of industrial applications.

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