Advanced Positron Imaging and Numerical Modelling of Segregation and Transport of Plastics in Fluidised Beds: Toward a Circular Economy for Plastics

Abstract: The plastic waste crisis is one of the great global challenges facing modern society. In this talk, we discuss a new technology designed to recycle mixed plastic waste, converting it into new, virgin-quality plastic feedstocks, clean, low-sulphur fuels, and other useful products. We also introduce Positron Emission Particle Tracking (PEPT), a technique which allows the interior dynamics of large, optically-opaque systems such as these to be imaged with high spatial and temporal resolution, and explore how this technique – combined with advanced numerical modelling techniques – is being used to help optimise this nascent recycling method, and thus bring a promising concept toward industrial reality. Biography: Gaining his PhD in Nuclear Physics at the University of Birmingham in 2015, Dr. Windows-Yule has worked as a researcher in Mechanical Engineering at the University of Twente in the Netherlands, and in Chemical and Bioengineering at the Friedrich-Alexander-Universität Erlangen-Nürnberg, before returning to the University of Birmingham as an Assistant Professor in the School of Chemical Engineering. This diverse and highly multi-disciplinary experience has armed Dr. Windows-Yule with a variety of experimental and numerical techniques, from PEPT and PTV to DEM, CFD and MP-PIC, which he applies to a variety of scientific and industrial problems. His current research focuses on three main areas: Addressing climate change, in particular through the development of novel plastic and heavy metal recycling techniques and the production of novel biofuels the advancement and optimisation of industrial process equipment The optimisation of industrial process equipment, working with industrial partners including AstraZeneca, GlaxoSmithKline, Mondelēz, Procter and Gamble, and Unilever The development of novel positron imaging methodologies, and the application of these both to the above and other important contemporary problems.Ope

Density-Driven segregation in Binary and Ternary Granular Systems

We present a first experimental study of density-induced segregation within a three-dimensional, vibrofluidised, ternary granular system. Using Positron Emission Particle Tracking (PEPT), we study the steady-state particle distributions achieved by binary and ternary granular beds under a variety of differing system parameters. In doing so, we determine the extent to which the segregative processes in ternary systems resemble their comparatively well-researched binary counterparts. We examine the influence of particle elasticity on the system, demonstrating the existence of a significant parameter range for which the effects of inelasticity-induced segregation may be safely neglected. Finally, we investigate the existence of a causal link between convective motion within a system and the segregative behaviours observed

Competition between geometrically induced and density-driven segregation mechanisms in vibrofluidized granular systems

The behaviors of granular systems are sensitive to a wide variety of particle properties, including size, density, elasticity, and shape. Differences in any of these properties between particles in a granular mixture may lead to segregation, or “demixing,” a process of great industrial relevance. Despite the known influence of particle geometry in granular systems, a considerable fraction of research into these systems concerns only uniformly spherical particles. We address, for the case of vertically vibrated granular systems, the important question of whether the introduction of differing particle geometries entirely invalidates our existing knowledge based on purely spherical granulates, or whether current models may simply be adapted to account for the effects of particle shape. We demonstrate that while shape effects can indeed influence the dynamical and segregative behaviors of a granular system, the segregative mechanisms associated with particle geometry are decidedly secondary to those related to particle density. The relevant control parameters determining the extent of geometrically induced segregation are established. Finally, a manner in which shape effects may be accounted for in simulations utilizing purely spherical particles is proposed

Numerical modelling of granular flows: a reality check

Discrete particle simulations provide a powerful tool for the advancement of our understanding of granular media, and the development and refinement of the multitudinous techniques used to handle and process these ubiquitous materials. However, in order to ensure that this tool can be successfully utilised in a meaningful and reliable manner, it is of paramount importance that we fully understand the degree to which numerical models can be trusted to accurately and quantitatively recreate and predict the behaviours of the real-world systems they are designed to emulate. Due to the complexity and diverse variety of physical states and dynamical behaviours exhibited by granular media, a simulation algorithm capable of closely reproducing the behaviours of a given system may be entirely unsuitable for other systems with different physical properties, or even similar systems exposed to differing control parameters. In this paper, we focus on two widely used forms of granular flow, for which discrete particle simulations are shown to provide a full, quantitative replication of the behaviours of real industrial and experimental systems. We identify also situations for which quantitative agreement may fail are identified, but important general, qualitative trends are still recreated, as well as cases for which computational models are entirely unsuitable. By assembling this information into a single document, we hope not only to provide researchers with a useful point of reference when designing and executing future studies, but also to equip those involved in the design of simulation algorithms with a clear picture of the current strengths and shortcomings of contemporary models, and hence an improved knowledge of the most valuable areas on which to focus their work

An experimental, theoretical and event-driven computational study of narrow vibrofluidised granular materials

We review simulations, experiments and a theoretical treatment of vertically vibrated granular media. The systems considered are confined in narrow quasi-two-dimensional and quasi-one-dimensional (column) geometries, where the vertical extension of the container is much larger than one or both horizontal lengths. The additional geometric constraint present in the column setup frustrates the convection state that is normally observed in wider geometries. We start by showing that the Event Driven (ED) simulation method is able to accurately reproduce the previously experimentally determined phase-diagram for vibrofludised granular materials. We then review two papers that used ED simulations to study narrow quasi-one-dimensional systems revealing a new phenomenon: collective oscillations of the grains with a characteristic frequency that is much lower than the frequency of energy injection. Theoretical work was then undertaken that is able to accurately predict the frequency of such an oscillation and Positron Emission Particle Tracking (PEPT) experiments were undertaken to provide the first experimental evidence of this new phenomenon. Finally, we briefly discuss ongoing work to create an open-source version of this ED via its integration in the existing open-source package MercuryDPM (http://MercuryDPM.org); which has many advanced features that are not found in other codes

An experimental, theoretical and event-driven computational study of narrow vibrofluidised granular materials

We review simulations, experiments and a theoretical treatment of vertically vibrated granular media. The systems considered are confined in narrow quasi-two-dimensional and quasi-one-dimensional (column) geometries, where the vertical extension of the container is much larger than one or both horizontal lengths. The additional geometric constraint present in the column setup frustrates the convection state that is normally observed in wider geometries. We start by showing that the Event Driven (ED) simulation method is able to accurately reproduce the previously experimentally determined phase-diagram for vibrofludised granular materials. We then review two papers that used ED simulations to study narrow quasi-one-dimensional systems revealing a new phenomenon: collective oscillations of the grains with a characteristic frequency that is much lower than the frequency of energy injection. Theoretical work was then undertaken that is able to accurately predict the frequency of such an oscillation and Positron Emission Particle Tracking (PEPT) experiments were undertaken to provide the first experimental evidence of this new phenomenon. Finally, we briefly discuss ongoing work to create an open-source version of this ED via its integration in the existing open-source package MercuryDPM (http://MercuryDPM.org); which has many advanced features that are not found in other codes

Micromechanics of non-active clays in saturated state and DEM modelling

The paper presents a conceptual micromechanical model for 1-D compression behaviour of non-active clays in saturated state. An experimental investigation was carried out on kaolin clay samples saturated with fluids of different pH and dielectric permittivity. The effect of pore fluid characteristics on one-dimensional compressibility behaviour of kaolin was investigated. A three dimensional Discrete Element Method (DEM) was implemented in order to simulate the response of saturated kaolin observed during the experiments. A complex contact model was introduced, considering both the mechanical and physico-chemical microscopic interactions between clay particles. A simple analysis with spherical particles only was performed as a preliminary step in the DEM study in the elastic regime

Maximizing energy transfer in vibrofluidized granular systems

Using discrete particle simulations validated by experimental data acquired using the positron emission particle tracking technique, we study the efficiency of energy transfer from a vibrating wall to a system of discrete, macroscopic particles. We demonstrate that even for a fixed input energy from the wall, energy conveyed to the granular system under excitation may vary significantly dependent on the frequency and amplitude of the driving oscillations. We investigate the manner in which the efficiency with which energy is transferred to the system depends on the system variables and determine the key control parameters governing the optimization of this energy transfer. A mechanism capable of explaining our results is proposed, and the implications of our findings in the research field of granular dynamics as well as their possible utilization in industrial applications are discussed