Paul W. Cleary

DEM modelling of industrial granular flows: 3D case studies and the effect of particle shape on hopper discharge

Abstract While the discrete element method (DEM) is attracting increasing interest for the simulation of industrial granular flow, much of the previous DEM modelling has considered two-dimensional (2D) flows and used circular particles. The inclusion of particle shape into DEM models is very important and allows many flow features, particularly in hoppers, to be more accurately reproduced than was possible when using only circular particles. Elongated particles are shown here to produce flow rates up to 30% lower than for circular particles and give flow patterns that are quite different. The yielding of the particle microstructure resembles more the tearing of a continuum solid, with large-scale quasi-stable voids being formed and large groups of particles moving together. The flow becomes increasingly concentrated in a relatively narrow funnel above the hopper opening. This encourages the hope that DEM may be able to predict important problems such as bridging and rat-holing. Increasing the blockiness or angularity of the particles is also shown to increase resistance to flow and reduces the flow rates by up to 28%, but without having perceptible effect on the nature of the flow. We also describe our methodology for constructing and modelling geometrically complex industrial applications in three dimensions and present a series of industrially important three-dimensional (3D) case studies. The charge motion in a 5 m diameter ball mill and in a Hicom nutating mill, discharge from single- and four-port cylindrical hoppers, and particle size separation by a vibrating screen are demonstrated. For each case, plausible particle size distributions (PSDs) have been used. The results obtained indicate that DEM modelling is now sufficiently advanced that it can make useful contributions to process optimisation and equipment design. Finally the parallelisation of such a DEM code is described and benchmark performance results for a large-scale 2D hopper flow are presented.

Large Scale Industrial DEM Modelling

Particle scale simulation of industrial particle flows using discrete element method (DEM) offers the opportunity for better understanding the flow dynamics leading to improvements in equipment design and operation that can potentially lead to large increases in equipment and process efficiency, throughput and/or product quality. Industrial applications can be characterized as large, involving complex particulate behaviour in typically complex geometries. In this paper, with a series of examples, we will explore the breadth of large scale modelling of industrial processes that is currently possible. Few of these applications will be examined in more detail to show how insights into the fundamentals of these processes can be gained through DEM modelling. Some examples of our collaborative validation efforts will also be described.

Predicting charge motion, power draw, segregation and wear in ball mills using discrete element methods☆

Abstract Discrete element modelling (DEM) of particle flows inside ball mills involves following the trajectories and spins of all the particles and objects in the system and predicting their interactions with other particles and with the mill. It is necessary to simulate particles of many different sizes and densities interacting with complex shaped lifters and liner. The key ingredients are a fast and robust algorithm to predict collisions, a good collision model and an efficient and powerful method for describing the mill. Particle fows in a S m diameter ball mill are presented The charge behaviour, torque and power draw are analysed for a range of rotation rates from SO to 130% of the critical speed Sensitivity of the results to the choice of friction and restitution coefficients and to the particle size distribution are examined. Segregation is an important issue in rotating mills. Size segregation of steel balls and size separation of small rocks from the larger bails are examined. Predictions of liner wear rates and distributions are made. Evolution of the liner profile can be modelled in order to predict the lifter life cycle and its effect on the mill operation. Collisional force distributions can be used as indicators of breakage and attrition. Such quantitative predictions, once validated, can be used as part of a program to optimise mill design and operation.

Large‐scale landslide simulations: Global deformation, velocities and basal friction

The cause of the apparent small friction exhibited by long runout landslides has long been speculated upon. In an attempt to provide some insight into the matter, this paper describes results obtained from a discrete particle computer simulation of landslides composed of up to 1,000,000 two-dimensional discs. While simplified, the results show many of the characteristics of field data (the volumetric effect on runout, preserved strata, etc.) and with allowances made for the two-dimensional nature of the simulation, the runouts compare well with those of actual landslides. The results challenge the current view that landslides travel as a nearly solid block riding atop a low friction basal layer. Instead, they show that the mass is completely shearing and indicate that the apparent friction coefficient is an increasing function of shear rate. The volumetric effect can then be understood. With all other conditions being equal, different size slides appear to travel with nearly the same average velocity; however, as the larger landslides are thicker, they experience smaller shear rates and correspondingly smaller fractional resistance.

Modelling confined multi-material heat and mass flows using SPH

Abstract Many applications in mineral and metal processing involve complex flows of multiple liquids and gases coupled with heat transfer. The motion of the surfaces of the liquids can involve sloshing, splashing and fragmentation. Substantially differing material properties are common. The flows are frequently complicated by other physical effects. Smoothed particle hydrodynamics (SPH) is a computational modelling technique that is ideally suited to such difficult flows. The Lagrangian framework means that momentum dominated flows and flows with complicated material interface behaviours are handled easily and naturally. To be able to model complex multi-physics flows, many aspects of SPH need to be explored. In this paper we describe developments that allow conductive and convective heat transfer to be modelled accurately for a sequence of idealised test problems.

Smooth particle hydrodynamics: status and future potential

SPH is a powerful mesh free method that is now able to solve very complex multi-physics flow and deformation problems in a broad number of fields. This paper concentrates on the use of SPH to simulate a broad range of complex industrial fluid flow problems. These include free surface fluid flow for the generation of digital content, geophysical flows such as volcanic lava flows and tsunamis, several types of die casting (gravity, high pressure and ingot casting), resin transfer moulding and flow in porous media, mixing of particulates in liquid, pyrometallurgy and slurry flow in semi-autogenous grinding mills. The strengths and weaknesses of SPH will be explored and future opportunities for using the method to make major modelling advances are discussed.

Discrete-element modelling and smoothed particle hydrodynamics: potential in the environmental sciences.

Particle–based simulation methods, such as the discrete–element method and smoothed particle hydrodynamics, have specific advantages in modelling complex three–dimensional (3D) environmental fluid and particulate flows. The theory of both these methods and their relative advantages compared with traditional methods will be discussed. Examples of 3D flows on realistic topography illustrate the environmental application of these methods. These include the flooding of a river valley as a result of a dam collapse, coastal inundation by a tsunami, volcanic lava flow and landslides. Issues related to validation and quality data availability are also discussed.

Charge behaviour and power consumption in ball mills : sensitivity to mill operating conditions, liner geometry and charge composition

Discrete element method (DEM) modelling has been used to systematically study the effects of changes in mill operating parameters and particle properties on the charge shape and power draw of a 5-m ball mill. Specifically, changes in charge fill level, lifter shape (either by design or wear) and lifter pattern are analysed. The effects of changes to the properties of the charge (ball fraction, ball and rock shape, type of ball and rock size distributions and the lower cutoff of the rock size distribution) can all be interpreted in terms of their effects on the shear strength of the charge. Some changes increase the shear strength leading to higher dynamic angles of repose of the charge, higher shoulder positions and higher power consumption for sub-critical speeds. For super-critical speeds, they lead to lower power consumption, due to lower particle mobility as the particles lock together better. Changes to the charge that weaken the interlocking of particles have the opposite effect on the charge shape and power consumption. The combination of these effects means that the speed for which peak power consumption occurs is predominantly determined by the shear strength of the charge material and the fill level. This demonstrates the sensitivity of mill behaviour to the charge characteristics and the critical importance of various assumptions used in DEM modelling.

Industrial particle flow modelling using discrete element method

– The purpose of this paper is to show how particle scale simulation of industrial particle flows using DEM (discrete element method) offers the opportunity for better understanding of the flow dynamics leading to improvements in equipment design and operation., – The paper explores the breadth of industrial applications that are now possible with a series of case studies., – The paper finds that the inclusion of cohesion, coupling to other physics such fluids, and its use in bubbly and reacting flows are becoming increasingly viable. Challenges remain in developing models that balance the depth of the physics with the computational expense that is affordable and in the development of measurement and characterization processes to provide this expanding array of input data required. Steadily increasing computer power has seen model sizes grow from thousands of particles to many millions over the last decade, which steadily increases the range of applications that can be modelled and the complexity of the physics that can be well represented., – The paper shows how better understanding of the flow dynamics leading to improvements in equipment design and operation can potentially lead to large increases in equipment and process efficiency, throughput and/or product quality. Industrial applications can be characterised as large, involving complex particulate behaviour in typically complex geometries. The critical importance of particle shape on the behaviour of granular systems is demonstrated. Shape needs to be adequately represented in order to obtain quantitative predictive accuracy for these systems.

DEM simulation of industrial particle flows: case studies of dragline excavators, mixing in tumblers and centrifugal mills

Abstract Discrete element methods (DEM) are now sufficiently well developed to plausibly model industrial and mining related particle flows. Three cases studies of such DEM simulations are presented here; dragline excavators, mixing in tumblers and charge motion in centrifugal mills. They show the breadth of application now possible and the types of predictions that can be made for each. More importantly, they demonstrate the critical role of particle shape in industrial particle flows. Detailed experimental data for two of these applications shows that the simulation predictions are qualitatively accurate.