Segregation and mixing of particles of different size and shape in a rotating drum

L'elaborato affronta il fenomeno della segregazione radiale per forma e dimensione di particelle in un tamburo rotante. Sono state considerate miscele binarie di particelle di diversa forma e dimensione. L'analisi del sistema è stata effettuata mediante analisi di immagine; la procedura di analisi è stata sviluppata col software ImageJ. Infine, sono stati calcolati anche l'angolo di massima stabilità, l'angolo di riposo e l'angolo di riposo dinamico per le miscele considerat

Particle-scale numerical study on screening processes

The present study aimed to increase the understanding of the industrial screening process by using the discrete element method simulation (DEM) and machine learning modelling. Thus, the study focused on understanding the fundamentals of the complicated screening processes by investigating the process model with different controlling factors through particle-scale analysis. The particle-scale analysis was also linked to several macroscopic models and screening processes such as percolation of particles under vibration, the local passing of particles from the screen, choking of screening, non-spherical shaped particles contact detection and packing and machine learning modelling. The computational and theoretical analyses as well as machine leaning helped to clarify the use of particle-scale analysis and screening processes in several areas. The outcomes of this thesis include: (i) the percolation of particles under vibration and the machine learning modelling of percolation velocity to predict the size ratio threshold; (ii) a better understanding of screening process based on local passing of inclined and multi-deck screen and physics informed machine learning modelling to predict the particles passing; (iii) a logical model to predict the choking judgement of screen while combining the numerical results and machine learning and (iv) a novel contact force model for non-spherical particles by Fourier transformation and packing. The research in this thesis is useful for the fundamental understanding of the effect of particles’ contact force, operational conditions, particle properties, percolation and sieving on the screening process. Moreover, the novel process models based on artificial intelligence modelling, DEM simulation, and physics laws can help the design, control and optimisation of screening processes

Discrete element method modelling of complex granular motion in mixing vessels: evaluation and validation

In recent years, it has been recognised that a better understanding of processes involving particulate material is necessary to improve manufacturing capabilities and product quality. The use of Discrete Element Modeling (DEM) for more complicated particulate systems has increased concordantly with hardware and code developments, making this tool more accessible to industry. The principal aim of this project was to study DEM capabilities and limitations with the final goal of applying the technique to relevant Johnson Matthey operations. This work challenged the DEM numerical technique by modelling a mixer with a complex motion, the Turbula mixer. The simulations revealed an unexpected trend for rate of mixing with speed, initially decreasing between 23 rpm and 46 rpm, then increasing between 46 rpm and 69 rpm. The DEM results were qualitatively validated with measurements from Positron Emission Particle Tracking (PEPT), which revealed a similar pattern regarding the mixing behaviour for a similar system. The effect of particle size and speed on segregation were also shown, confirming comparable results observed in the literature. Overall, the findings illustrated that DEM could be an effective tool for modelling and improving processes related to particulate material

Multiscale investigation of the dynamic behaviour of particles in an inclined rotating drum

The simple geometry and multiple applications of a rotating drum, such as mixing, segregation, drying, and coating in chemical, mining, chemical, metallurgy, civil, food processing, and waste management industries, have made it a focus of studies on the behaviour of granular particles. Studying that behaviour experimentally is very expensive and simulations require very high computational power. But with the advent of greater and cheaper computational power, it has become economical to use simulations. The dynamic properties and behaviours of particles in a drum and their mixing and segregation have been the main fields of study. Those studies have dealt with problems related to drums rotating horizontally. However, very few studies have analysed particle behavior in an inclined rotating drum (IRD), although those drums have long been used in waste management and process industries. Therefore, in this study, a comprehensive focus was given to particle behavior in an IRD and its applications. This study took an overview and brief look at various aspects of particle behavior in the IRD, because to the author’s knowledge, no study of this scale has focused on that type of drum. The discrete element method (DEM) was used to study particle behavior in the IRD. Because research related to that behaviour is at a very early stage, the DEM simulations required experimental validation. Therefore, an experimental setup was designed and fabricated, and its results were used to validate the DEM results with the help of Altair’s EDEM simulation software. In this study, the DEM model was implemented on the EDEM platform. Initially, a system using only one particle type was used to validate the DEM results with the experimental results, and after that, a two-particle system was used for segregation. The particles were spherical. The experimental and simulation results had similar patterns, which validated the DEM simulation results, thus justifying the use of DEM to study the particles in an IRD system. The DEM is a contact-based model, where particle behavior broadly depends on the velocity of the particles. Hence, dynamic properties such as velocity, contact forces, torque, and coordination number of the particles in a rotating drum with the inclined axis of rotation play a major role in understanding particle behavior

Fast, flexible particle simulations — An introduction to MercuryDPM

We introduce the open-source package MercuryDPM, which we have been developing over the last few years. MercuryDPM is a code for discrete particle simulations. It simulates the motion of particles by applying forces and torques that stem either from external body forces, (gravity, magnetic fields, etc.) or particle interactions. The code has been developed extensively for granular applications, and in this case these are typically (elastic, plastic, viscous, frictional) contact forces or (adhesive) short-range forces. However, it could be adapted to include long-range (molecular, self-gravity) interactions as well. MercuryDPM is an object-oriented algorithm with an easy-to-use user interface and a flexible core, allowing developers to quickly add new features. It is parallelised using MPI and released under the BSD 3-clause licence. Its open-source developers’ community has developed many features, including moving and curved walls; state-of-the-art granular contact models; specialised classes for common geometries; non-spherical particles; general interfaces; restarting; visualisation; a large self-test suite; extensive documentation; and numerous tutorials and demos. In addition, MercuryDPM has three major components that were originally invented and developed by its team: an advanced contact detection method, which allows for the first time large simulations with wide size distributions; curved (non-triangulated) walls; and multicomponent, spatial and temporal coarse-graining, a novel way to extract continuum fields from discrete particle systems. We illustrate these tools and a selection of other MercuryDPM features via various applications, including size-driven segregation down inclined planes, rotating drums, and dosing silos. Program summary: Program Title: MercuryDPM Program Files doi: http://dx.doi.org/10.17632/n7jmdrdc52.1 Licensing provisions: BSD 3-Clause Programming language: C++, Fortran Supplementary material: http://mercurydpm.org Nature of problem: Simulation of granular materials, i.e. conglomerations of discrete, macroscopic particles. The interaction between individual grains is characterised by a loss of energy, making the behaviour of granular materials distinct from atomistic materials, i.e. solids, liquids and gases. Solution method: MercuryDPM (Thornton et al., 2013, 2019; Weinhart et al., 2016, 2017, 2019) is an implementation of the Discrete Particle Method (DPM), also known as the Discrete Element Method (DEM) (Cundall and Strack, 1979). It simulates the motion of individual particles by applying forces and torques that stem either from external forces (gravity, magnetic fields, etc.) or from particle-pair and particle–wall interactions (typically elastic, plastic, dissipative, frictional, and adhesive contact forces). DPM simulations have been successfully used to understand the many unique granular phenomena – sudden phase transitions, jamming, force localisation, etc. – that cannot be explained without considering the granular microstructure. Unusual features: MercuryDPM was designed ab initio with the aim of allowing the simulation of realistic geometries and materials found in industrial and geotechnical applications. It thus contains several bespoke features invented by the MercuryDPM team: (i) a neighbourhood detection algorithm (Krijgsman et al., 2014) that can efficiently simulate highly polydisperse packings, which are common in industry; (ii) curved walls (Weinhart et al., 2016) making it possible to model real industrial geometries exactly, without triangulation errors; and (iii) MercuryCG (Weinhart et al., 2012, 2013, 2016; Tunuguntla et al., 2016), a state-of-the-art analysis tool that extracts local continuum fields, providing accurate analytical/rheological information often not available from experiments or pilot plants. It further contains a large range of contact models to simulate complex interactions such as elasto-plastic deformation (Luding, 2008), sintering (Fuchs et al., 2017), melting (Weinhart et al., 2019), breaking, wet and dry cohesion (Roy et al., 2016, 2017), and liquid migration (Roy et al., 2018), all of which have important industrial applications

DEM Study on the Mixing Behaviour of U-shaped Ribbon Mixers

Particle mixing is widely practised in a broad range of powder processing, including ceramics, pharmaceutical, food, and chemical industries. Although significant developments have been made in understanding the mixing performance by conducting experiments during the last decades, the detailed solid mixing information cannot be obtained by experiments because of the complicated mixing mechanisms in the system and backward measuring equipment. Numerical simulation has become the primary method to accelerate the development of solid mixing technology, reduce the cost of design and operating time, as well as provide more particle information. Therefore, in this thesis, a deep investigation of industrial-scale U-shaped ribbon mixer is conducted to reveal the complex solid mixing behviours and optimise the mixing efficiency based on the Discrete element method. Specifically, it covers the following five aspects: 1. The accuracy of some commonly used mixing indices for mixing of uniform particles in a horizontal cylindrical ribbon mixer is comprehensively investigated to help select proper mixing indices for solid mixing in the ribbon mixer. 2. The effect of operating condition and particle property on mixing performance in a U-shape ribbon mixer is investigated. This work evaluates the effect of operating conditions and material properties on the mixing performance in an industrial-scale U-shaped ribbon mixer and provides an effective way to assist the practical industrial operation in an economical and safe manner. 3. The effect of particle cohesion on mixing performance in a U-shape ribbon mixer is investigated. This chapter sheds light on the detailed mixing behaviour of the U-shaped ribbon mixer for cohesive particle mixing and provides the operational guide for the practical food mixing process. 4. The effect of particle shape on mixing performance in a U-shape ribbon mixer is investigated. The work contributes to optimisation of the mixer design and the operational conditions in chemical, food, and pharmaceutical engineering fields. 5. The effect of impeller design on mixing performance in a U-shape ribbon mixer is investigated. This work provides an effective way to assistant industrial design in an economical and safe manner. These studies contribute to the deep understanding and further optimization of industrial-scale ribbon mixer

Impact de la ségrégation granulaire sur le transfert de chaleur dans un lit rotatif

RÉSUMÉ: Alors que les conséquences de la crise environnementale se font sentir partout autour de la planète, il devient urgent de trouver des sources d’énergie alternatives pour remplacer les ressources fossiles. Ecolomondo, une compagnie montréalaise, désire répondre à cette recherche d’énergie propre en proposant un procédé de pyrolyse de pneus usés. Ce procédé permet de convertir des pneus usés, qui représentent souvent de hauts risques de contamination des sols, des nappes phréatiques et de l’air, en biodiésel pouvant remplacer l’essence issue du pétrole. Cependant, lors de la conversion thermique des morceaux de pneus dans un four rotatif à l’échelle industrielle, plusieurs problèmes peuvent survenir. Entre autres, la température à l’intérieur du réacteur, mesurée à un endroit précis grâce à un thermocouple, subit des changements brusques et imprévus de valeurs. Ces mesures de température variables rendent le contrôle et l’optimisation de la réaction très difficiles, voire dangereux.----------ABSTRACT:Climate change consequences have started to be omnipresent all around the world. To respond to these challenges, many industries are trying to find renewable energy sources to lower our dependency to fossil fuels. One example of these new technologies is the production of biofuel from waste, such as scrap tire pieces. In addition of producing biofuel that can replace fuel from oil resources, the pyrolysis of scrap tires is a good avenue to get rid of a waste that accumulates in many places in the world and represents a hazard for wild fires, which can pollute soils, waters and airs. However, pyrolysis of scrap tires is not easy to scale up at an industrial level to be competitive. In the big rotary kilns that are used to heat up the pieces of tires, the temperature is measured at a specific location using a thermocouple probe. This temperature fluctuates a lot in time and makes the process very hard to control and optimize

CONTROLLING MIXING AND SEGREGATION IN TIME PERIODIC GRANULAR FLOWS

Segregation is a major problem for many solids processing industries. Differences in particle size or density can lead to flow-induced segregation. In the present work, we employ the discrete element method (DEM) – one type of particle dynamics (PD) technique – to investigate the mixing and segregation of granular material in some prototypical solid handling devices, such as a rotating drum and chute. In DEM, one calculates the trajectories of individual particles based on Newton’s laws of motion by employing suitable contact force models and a collision detection algorithm. Recently, it has been suggested that segregation in particle mixers can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. Further, it has been hypothesized that, for a rotating drum, the effectiveness of this technique can be linked to the probability distribution of the number of times a particle passes through the flowing layer per rotation of the drum. In the first portion of this work, various configurations of solid mixers are numerically and experimentally studied to investigate the conditions for improved mixing in light of these hypotheses. Besides rotating drums, many studies of granular flow have focused on gravity driven chute flows owing to its practical importance in granular transportation and to the fact that the relative simplicity of this type of flow allows for development and testing of new theories. In this part of the work, we observe the deposition behavior of both mono-sized and polydisperse dry granular materials in an inclined chute flow. The effects of different parameters such as chute angle, particle size, falling height and charge amount on the mass fraction distribution of granular materials after deposition are investigated. The simulation results obtained using DEM are compared with the experimental findings and a high degree of agreement is observed. Tuning of the underlying contact force parameters allows the achievement of realistic results and is used as a means of validating the model against available experimental data. The tuned model is then used to find the critical chute length for segregation based on the hypothesis that segregation can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. The critical frequency, fcrit, is inversely proportional to the characteristic time of segregation, ts. Mixing is observed instead of segregation when the chute length L < Uavg*ts, where Uavg denotes the average stream-wise flow velocity of the particles. While segregation is often an undesired effect, sometimes separating the components of a particle mixture is the ultimate goal. Rate-based separation processes hold promise as both more environmentally benign as well as less energy intensive when compared to conventional particle separations technologies such as vibrating screens or flotation methods. This approach is based on differences in the kinetic properties of the components of a mixture, such as the velocity of migration or diffusivity. In this portion of the work, two examples of novel rate-based separation devices are demonstrated. The first example involves the study of the dynamics of gravity-driven particles through an array of obstacles. Both discrete element (DEM) simulations and experiments are used to augment the understanding of this device. Dissipative collisions (both between the particles themselves and with the obstacles) give rise to a diffusive motion of particles perpendicular to the flow direction and the differences in diffusion lengths are exploited to separate the particles. The second example employs DEM to analyze a ratchet mechanism where a current of particles can be produced in a direction perpendicular to the energy input. In this setup, a vibrating saw-toothed base is employed to induce different mobility for different types of particles. The effect of operating conditions and design parameters on the separation efficiency are discussed