THE STRESS ANALYSIS OF HIGH SHEAR MIXER GRANULATOR USING DISCRETE ELEMENT METHOD (DEM)

A. Hassanpour, B. Ng, S. J. Antony, M. Ghadiri

Institute of Particle Science & Engineering

University of Leeds, Leeds, LS2 9JT, U.K.

Abstract

High shear mixer granulators are typically found in pharmaceutical and detergent industries, and are capable of reducing processing time and producing agglomerates of high strength and density. Generally, several granulation scale-up stages are involved before commencing production. During such scale-up processes, the mechanics of particle interactions and prevailing levels of compressive stresses and strains are affected by the variation in hydrodynamics within granulators of different scales. This in turn affects the final structure of the agglomerates. In this paper the effect of velocity field of two different scales of high shear mixer granulator (1 l and 5 l) on the structure of the evolved agglomerates is analysed. The study is based on computer simulation using Distinct Element Method (DEM). A single agglomerate is generated using DEM and is placed in a bed of primary particles. The bed is sheared by imposing a velocity field obtained from Positron Emission Particle Tracking (PEPT) measurements on 1 l and 5 l granulators which were scaled up based on constant shear stress condition.

The results show that when the velocity profile of the 1 l granulator is used, the resulting agglomerate is more elongated, has a smaller packing fraction and therefore is weaker.

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REPRESENTING PARTICLE SHAPE IN DISCRETE ELEMENT MODELLING

E. Tijskens1 and F. Rioual2

1. DEM Research Group, K.U.Leuven

Leuven, BELGIUM

2. Cemagref

Clermont-Ferrand, FRANCE

Abstract

An overview is given of techniques to represent particle shape in discrete element models. The authors discuss issues related to computational complexity, implementation, experimental determination of model parameters. Finally, they present a new shape model based on rounded polyhedra.

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A NUMERICAL STUDY OF THE INFLUENCE OF PARTICLE FRICTION AND WALL FRICTION ON SILO FLOW

J. Härtl1, J.Y. Ooi1, J. Theuerkauf2

1. Institute for Infrastructure & Environment, The King's Buildings,

University of Edinburgh, Edinburgh EH9 3JL, U.K.

2. The Dow Chemical Company, Core R&D, EP&S, Solids Processing Laboratory,

2301 North Brazosport Blvd, Freeport, TX, USA

Abstract

A numerical study of flow and pressure in a silo using the discrete element method is presented. An attempt was made to use the Jenike direct shear tests to calibrate the DEM material model. The results show that DEM, using non-spherical particles, can produce reasonable predictions of both the flow behaviour and the wall pressure distribution in a silo. Temporally averaged pressure distributions are found to be in good agreement with established silo theories. A summary of the parametric study to explore the influence of particle and wall friction on the criteria for mass flow and funnel flow is also presented.

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Pressure development along the walls of a conical hopper with a steep inclination angle

S. Ding1, M. Rotter2, J. Ooi2 and G. Enstad1

1. POSTEC av Tel-Tek, 3914 Porsgrunn, Norway

2. The School of Engineering and Electronics, The University of Edinburgh, Scotland

Abstract

A progressive filling approach was adopted in a numerical effort to represent the filling process of particulate solids. It was implemented in a finite element analysis to investigate the development of loads on a conical steep hopper during filling. The loads developed along the walls of the hopper in a concentric-filling were addressed. An analysis of the conventional so-called ‘switch on’ filling was also conducted. The predictions of such numerical approaches are compared with predictions of classical theories for the loads acting on the wall of the hopper.

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EXPERIMENTAL INVESTIGATION OF A FULL SCALE SILO WITH A LARGE INNER TUBE

J.Y. Ooi1, J.F. Chen1, J.M. Rotter1, Z. Zhong1, J. Härtl1, M. Johnstone1, S.E. Forsmo2,

B. Andreasson2, D. Thulin2

1. School of Engineering & Electronics, University of Edinburgh, Edinburgh EH9 3JL, U.K.

2. LKAB, Malmberget SE-983 81, Sweden

ABSTRACT

This paper describes an investigation to support the design of full scale silos with large perforated inner concrete tubes. The group of silos are blasted and formed out of solid rock underground to store iron ore pellets. A 1:25th scale model was constructed to investigate the flow pattern and stress regime for the pellets and to evaluate the loading on the concrete tube. A total of 15 tests were conducted to measure the flow pattern using a combination of top surface observations and residence times of tracers, to measure pellets stresses and to observe the structural response of the inner tube subject to the pellets filling and discharge using fibre optics strain gauges. The main test results and the key findings relating to the flow pattern measurements are described in this paper.

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DRYING OF HEAT SENSITIVE MATERIALS OF HIGH MOISTURE CONTENT IN MECHANICALLY SPOUTED BED OF INERT PARTICLES

Janos Gyenis1 , Elisabeth Pallai –Varsnyi1 and Judit Tth2

1. Research Institute of Chemical and Process Engineering,

University of Pannonia, H-8200 Veszprm, HUNGARY

2. Institute of Materials and Environmental Chemistry,

Chemical Research Center, Hungarian Academy of Sciences,

H-1025 Budapest, HUNGARY

Abstract

In drying operation the material characteristics such as heat sensitivity, moisture content and particle size are of great importance, which should be taken into account in selection of proper design and conditions for the process. Rigorous quality requirements, i.e. gentle drying of heat sensitive materials, stable, well-controlled and economic operation can be fulfilled by using Mechanically Spouted Bed (MSB) dryer with inert particles developed to eliminate some drawbacks of the conventional spouted bed dryers. In this paper the construction and the main features of MSB-dryer are presented. Different tasks with special quality demands, namely drying of bovine serum albumin and moisture removal from tomato pulp of thermoplastic behaviour, and a method to accomplish these requirements are shown.

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PREDICTION OF POWDER AGGLOMERATION DURING SPRAY DRYING PROCESS

Gianfrancesco A.1*, Turchiuli C.1, Sommier A.1, Palzer S.2, Dumoulin E.1

1. Agroparistech, SPAB Department, UMR GenIAl 1145

1 avenue des Olympiades, 91300 Massy (France)

2. Nestl Research Center, Food Science and Technology Department.

Vers-Chez-Les-Blanc CH-1000 Lausanne 26 (Switzerland)

Abstract

Spray drying process is a convective drying of liquid droplets through their surface by hot air. Initially drop water activity is close to 1 and drying is fast. Then drop surface aw decreases and viscosity increases reaching a sticky rubbery state. Drying being fast, this behavior is generally observed close to the atomizer. But, for some specific conditions and materials, sticking is observed along the chamber, on walls or between particles (agglomeration).

In this study air properties evolution (temperature, relative humidity) during drying was considered as representative of drop drying. Trials were performed with a model product (maltodextrin DE12) in a co-current pilot spray dryer, varying parameters as liquid flow rate (25-50-75 mL.min-1), air temperature (144-174-200°C), air flow rate (80-110 kg.h-1) and rotary atomizer speed (22500 to 30000 rpm). From air cartographies and powders properties the evolution of temperature and mean water content of drying drops was described. These results combined with sorption isotherms and glass transition temperatures allowed to predict particles stickiness during drying.

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ANALYSIS OF THE DYNAMIC RESPONSE OF A MIXED-FLOW GRAIN DRYER ON THE BASIS OF REVERSING EXPERIMENTS

J. Mellmann1, L. Kocsis1 and I. Farkas2

1. Department of Post Harvest Technology,

Leibniz Institute of Agricultural Engineering Potsdam-Bornim (ATB),

Potsdam, GERMANY

2. Department of Physics and Process Control,

Szent Istvn University, Gödöll, HUNGARY

Abstract

Mixed-flow dryers are widely used for hot-air drying of grain, maize, and rice and considered to be well-engineered. Regardless there is still a need to optimize the process control as well as the dryer apparatus. To produce grain with equilibrium moisture content is an important objective of drying process control. However, fluctuations of grain moisture content at the dryer entrance are still a major problem resulting in quality and economic losses due to under-drying or over-drying. A multitude of disturbance variables, nonlinearity, and long reaction times complicate the dryer control. Therefore, the authors aim to develop a new model-based control system for the mixed-flow dryer enabling the operator to superiorly equalize the fluctuations of the moisture content of the dried grain. The objective of this study is to analyse the dynamic response of the dryer on the basis of reversing experiments. As a

result, model parameters for the process control model can be estimated. For this purpose jump functions of the inlet moisture content are inserted at the dryer entrance. The response functions measured at the dryer outlet are evaluated.

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FAST DETERMINATION OF PARTICLE SIZE DISTRIBUTION BY MEANS OF THE SETTLING RATES MEASURED IN A MICROSCOPE

“SEDIMENTATION BALANCE”

K. Sommer1, H. Dauth1

1. Technische Universität München, Center of Life Sciences Weihenstephan, Lehrstuhl für

Maschinen- und Apparatekunde, GERMANY

Abstract

The settling rate and the calculated equivalent diameter derived from that is one of the best and most important values to determine the particles size. A lot of processes dealing with particles are influenced by the settling rate, e.g. air separators, centrifugal separators or cyclones as well as the separation of particles from air or fluids. So far two well known sedimentation analysis are used to determine the particle size distribution by means of the settling rate, the sedimentation balance or the pipette analysis. Both methods have a few drawbacks. A long analysis time caused by small particles associated with the risk of thermal convection. In the case of the sedimentation balance a large amount of product is needed, because it is necessary to weigh the sediment.

Based on this background knowledge a new method to measure the particle size distribution by means of the equivalent diameter calculated from the settling rate is being developed. The aim was to avoid the known drawbacks of the common analysis methods. Therefore an inverted microscope is used to measure the increase of the settled particles at the bottom of a small cuvette (settling tank) by automatic image analysis. Hereby the measured quantity is not the mass but the increase of the total projected area. In addition the method needs just a small amount of particles which means it has a small sedimentation height and a relatively quick sedimentation time. As a result of the illumination in an inverted microscope from the top, a thermal convection could nearly be avoided. The results with selected products of spherical and non spherical shape will be presented and compared with other particle size measurement methods e.g. laser diffraction.

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THE APPARENT VISCOCITY OF AERATED ALUMINA POWDER USING A SPHERE DROP TECHNIQUE

K.C. Williams, G. Seswai and M.G. Jones

Centre for Bulk Solids and Particulate Technologies

University of Newcastle, AUSTRALIA

Abstract

With the increase in the development of CFD based codes for gas-solids flows, the viscous nature of gas-solid behaviour is becoming an increasing important parameter to determine. Generally, the assumption on the viscous behaviour of gas-solid flows is that the viscosity is only related to the interstitial gases rate of deformation rather than the overall gas-solids deformation response. This deformation response can vary from the conveying gas viscosity response for dilute gas-solid systems to apparent gas-solid viscosity behaviour for material that exhibits high air retention. (e.g. fluidised material). The apparent viscosity calculations for an alumina powder were

based on the resistance force of a sphere passing vertically through the aerated alumina bed. Initial results of the drag force of the sphere found that its associated co-efficient of drag within the aerated bed could vary between 1.2 and 2.5 with the aerated alumina bed exhibiting shear thinning (pseudo-plastic) viscosity behaviour.

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A STUDY ON THE EFFECT OF AIR HUMIDITY ON POWDER FLOW PROPERTIES

Giovanna Landi, Diego Barletta, Giorgio Dons, Giovanna Ferrari and Massimo Poletto

Department of Chemical and Food Engineering, University of Salerno

Via Ponte don Melillo, I-84084 Fisciano (SA), Italy

Abstract

In this work the effect of air humidity on the flow properties of a 48 µm glass beads powder was studied by means of a ring shear tester. Powder sample moisture content was conditioned by humid air in a fluidization column. In spite of the very low moisture contents in the

powder (<0.2%) obtained by this technique, a significant change in the powder cohesion was observed. The Kelvin equation was used to infer on the pressure increase inside the capillary bridge and the resulting typical interparticle force. This result was used to derive the powder tensile strength following the Rumpf approach and compare it with values derived from shear experiments. A single fitted value of the unknown capillary bridge gap is able to provide quantitative agreement for experiments with highly humid air. Model estimation indicates that water mainly condenses on rough surfaces of the particles and only a small portion of this condensed humidity contributes to change the powder flow properties in interparticle capillary bridges.

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POWDER FLOW AND DUST EMISSIONS

R. Ansart, A. de Ryck and J. A. Dodds

Centre RAPSODEE-UMR CNRS 2392, Ecole des Mines d’Albi-Carmaux

F-81000 Albi, France

Abstract

The handling of bulk materials in free streams of particles is a source of dust emission during the fall or at the impact on a pile, if fines are present. To quantify it, we discuss the physics of the phenomenon and focus on the role of air entrainment.

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WEAR OF STRAIGHT PIPELINE IN PNEUMATIC CONVEYING SYSTEMS

V. K. Agarwal1 and D. Mills2

1. Indian Institute of Technology

New Delhi, India

2. Pneumatic Conveying Consultant

Garelochead, UK

Abstract

The wear of bends in pneumatic conveying system pipelines is a topic that has been given much consideration in technical papers. Bends, of course, can fail in a matter of hours if conveying conditions or bend materials are inappropriate for the duty. Straight pipeline, however, is also susceptible to wear, and particularly so in sections following a bend. The authors have both undertaken research into these problems and in this paper they combine their findings and examine the influence of many of the parameters that they have investigated.

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DEVELOPMENT OF AN EROSION TESTER

- SOME THEORETICAL & EXPERIMENTAL ASPECTS

M. Wolf1, C. Ratnayake2, G.G. Enstad2, B.K. Datta3, P. A. Amundsen4, W. Schubert5

1. MCE Industrietechnik Salzburg GmbH & Co, Salzburg, Austria

2. Dept. of Powder Science & Technology (POSTEC), Telemark Technical R & D Centre (Tel-tek),

Porsgrunn, Norway

3. Aker Kværner Subsea AS, Fornebu, Norway

4. Dept. of Mathematics and Natural Science, University of Stavanger, Norway

5. Faculty of Process and Chemical Engineering, University of Applied Sciences, Mannheim, Germany

Abstract

In pneumatic conveying plants, wear has been identified as one of their major drawbacks. When a system is running in dilute phase mode, wear can be very effective, lead to unplanned maintenance due to leakage of pipes etc, discharge of bulk material to the surroundings with associated occupational hygiene problems and problems caused by contamination of their transported material by eroded particles. Particularly in oil and gas industry, this phenomenon has been recognised as a major problem for its effective operation. Even though quite a lot of scientific investigations have been carried out on wear in industrial pneumatic conveying systems, the problem is still with us, because the basic mechanisms of wear

are only partly understood. In an early investigation [1], some weaknesses of currently used measurement techniques were identified and a novel method to measure and predict the erosion of a pneumatic conveying pipeline system was proposed, as an on-line measurement technique.

This paper briefs the development of an erosion tester based on those proposals, together with some theoretical and practical problems involved with it. In addition, some observations made during the test using the newly developed erosion tester are also presented.

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WEAR TESTING OF POLYMERS IN PNEUMATIC CONVEYING SYSTEMS

Hans Schneider, Harald Wilms

Zeppelin Silos & Systems GmbH, Friedrichshafen, GERMANY

Abstract

Polymer pellets generate fines and streamers in dilute-phase pneumatic conveying systems. Fines generation depends on many parameters, which make comparison of industrial data and prediction for new systems difficult. In order to predict fines generation levels in pneumatic conveying systems, Zeppelin has installed in its test facility a conveying system dedicated for running wear tests under defined conditions. A respective test procedure has been defined. Conveying tests with numerous polymers have been performed in the meantime and quantitative results from this test facility are presented. A database is being built up for different polymers.

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FLOWABILITY TESTING FOR PRODUCT DEVELOPMENT AND QUALITY CONTROL

T. A Bell

DuPont Engineering Research and Technology

Wilmington, Delaware, USA

Abstract

The design of silos for reliable discharge and predictable flow patterns is the most

discussed application of shear testing. However, silo design activities are only a fraction of the

possible uses of shear testing. The assessment of powder flowability for quality control and product

development is a far larger potential use for shear testers, since powders are manufactured every

day, while silos are built infrequently. This paper presents examples of the application of shear

testing and other forms of flowability assessment in the chemical industry. Jenike, Schulze,

Johanson, and Edinburgh (EPT) testers have all been employed. Even the widely discredited Carr

Indices (powder dispersibility, Hausner ratio, etc) contain useful elements for quality control

purposes. The key issues for quality control and product development are often different than those

for designing silos, and the measure of a successful test program is also much different. Despite the

many places where shear testing could be used in industries manufacturing and consuming powders,

the acceptance of the technology is low and, in the author’s experience, has improved very little in

the past 15-20 years. The cost to industry is large but is often unrecognized. Successful advocacy

of powder testing requires an understanding of the needs and motivations that exist in an industrial

environment. This paper suggests technical areas in which the academic and industrial powder

testing communities can work together more effectively.

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PREDICTION OF POWDER BULK FLOWABILITY USING WATER MIGRATION, GLASS TRANSITION AND SINTERING KINETICS

N. Descamps1*, J. Fitzpatrick2, S. Palzer1

1 Nestl Product Technology Centre, 778224 Singen, Germany

2Department of Chemical and Process Engineering, University College, Cork, Ireland

* Corresponding author. Present address: Department of Process and Chemical Engineering,

University College, Cork, Ireland

Abstract

Powder agglomeration is important in the pharmaceutical, chemical and food industry. Agglomeration can be either desired (fluid bed agglomeration and tabletting) or undesired (caking and stickiness). This paper discusses the effect of water plasticization on the agglomeration and flowability of water-soluble amorphous powders. Water leads to a plasticization phenomena migrating into the amorphous matrix, which decreases the glass transition temperature Tg and the viscosity. The decreasing viscosity favours the creation of viscous bridges between particles, that is to say sintering. The formation of such bridges leads to a decrease of the powder flowability. This decrease of the flowability is directly linked to the strength of the bridges which depends on their radius X and on the mechanical properties (viscosity h and elasticity E) of the material.

The kinetics of the growth of such inter-particle bridges was modelled. The calculation was based on equations from sinter technology, which were combined with an estimation of the viscosity based on the theory of glass transition. The result was the diameter of the bridge as a function of viscosity and contact time between particles1. The influence of moisture on the viscosity was calculated using the Gordon and Taylor relation2 and the Williams, Landel and Ferry3 equations. The validity of this approach was then tested using maltodextrin (DE 21), by measuring the velocity with which an inter particle bridge was formed, using microscopic pictures. In addition, the water migration kinetics was studied and modelled using Fick’s law. Combining the sintering equation with the moisture migration model, it was then possible to estimate the sinter bridge radius as a function of time, water content and powder depth. Finally, the sintering kinetics was compared with the evolution of the flowability measured by a Ring Shear Tester after several storage times at a number of temperatures above Tg and under different pressures.

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FLOW BEHAVIOUR OF NONDRAINED LIMESTONE PARTICLE BEDS

Theodor Mladenchev and Jürgen Tomas

Mechanical Process Engineering, The Otto-von-Guericke-University

Universitätsplatz 2, D – 39 106 Magdeburg, Germany

Abstract

In this work a rheological model is assumed to describe the transition between “metastable” viscous paste and frictional packing flow. The aim is to determine the flow function tau = f(sigma, shear rate) of the limestone particle beds using both a normal stress dependent Coulomb-friction term and a viscous term for the paste flow. The experiments were carried out with a modified Press-Shear-Cell [1]. Shear ring and bottom surface are profiled by a wafer pattern to obtain a thin shear zone [2]. Direct wall sliding is avoided by this pyramidal roughness pattern. For the shear experiments two shear zone heights of 3 and 5 mm are used. The shear rates vary from 25.2 to 252 mm/min. The medium pressure range with normal stresses from 100 to 400 kPa was applied on each particle bed height and shear velocity. Electrolytes and flocculants were inserted to influence microscopically the surface forces between the particles.

The paste state is predefined by the packing density of a loose packing without any particle contact displacement. The packing densities were experimentally determined by means of shear experiments by fitting the compression function average pressure = f(bulk density).

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Dispersive and convective transport processes in continuous dynamic powder mixers

D. Dopfer1, V. Zerbes1 and K. Sommer1

1. Technische Universität München, Lehrstuhl für Maschinen- und Apparatekunde Freising, GERMANY

Abstract

For safe and reliable industrial continuous powder mixing processes the reduction of entering dosage fluctuations is very important. This reduction is influenced by the average residence time in the mixer. The convective and dispersive transport processes in a continuous mixer are influencing the overall mixer mass and thus, the average residence time. A new method is introduced to determine the filling degree gradient as well as the transport coefficient U and the dispersion coefficient D determining the convective and dispersive transport processes described by the Fokker-Planck-Equation. Strong influences of the rotational speed and the type of the mixing device as well as the position of the weir on the overall mixer mass occur and have to be considered in industrial production processes.

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QUANTIFYING SEGREGATION OF BINARY MIXTURES OF PARTICULATE SOLIDS BY IMAGE ANALYSIS

M. Eggert, A. Hassanpour, N. Gedney and M. Ghadiri

Institute of Particle Science and Engineering

University of Leeds, Leeds LS2 9JT, UK

Abstract

Understanding the segregation tendencies of particulate mixtures where homogeneity is a critical requirement – for example, in nuclear fuel manufacturing and pharmaceutical processing – is of great industrial interest. In spite of a considerable amount of research done on the segregation of binary mixtures, there is still no universally accepted technique for quantifying segregation. In this paper a method based on image analysis is proposed to quantify segregation of a vibrated heap. Three different systems made of a

binary mixture of glass beads of two different sizes and densities (fine hollow and coarse solid glass beads) with different levels of cohesion (made cohesive by silanisation) were analysed, i.e. (i) both hollow and solid beads free-flowing, showing a tendency to

segregate, (ii) hollow beads cohesive and solids beads free-flowing, showing a high level of segregation, (iii) solid beads cohesive and hollow beads free-flowing, tending not to segregate. Using an image analysis technique, a segregation index based on variation of concentration of hollow beads in the bed is suggested for all three systems.

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THEORETICAL STUDY OF SUPERPOSITION OF MACRO- AND MICROSCALE MIXING AND ITS INFLUENCE ON MIXING KINETICS AND MIXTURE QUALITY

V. Mizonov1, H. Berthiaux2, E. Barantseva1, C. Gatumel2, Y. Khokhlova1

1. Ivanovo Power Eng. State University, Ivanovo, Russia

2. Ecole des Mines d’Albi – Carmaux, UMR CNRS 2392, Albi, France

Abstract

The objective of the study is to build a model that describes evolution of the state of a mixture when the micro-scale mixing (penetration of particles into the closest neighborhood of its position during a small period of time) is accompanied by the macro-scale mixing (periodical

exchange of large parts of the mixture inside a mixing volume after a certain period of time). The mixing kinetics for segregation and non-segregation mixtures, agitated by blades placed in a certain sequence inside the mixing volume, is modeled. The case of exchange by the halves of material is examined as well. The two variants of the exchange are examined: the parallel displacement and the

symmetric turn. It is shown that there exist optimal parameters of the macro-scale transitions providing the highest rate of mixing. The proposed model helps better understanding the process and suggests some ideas to improve the design of the mixers.

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COMPARISON OF THE STABLE MICROSYSTEMS TEXTURE ANALYSER WITH THE SCHULZE RING SHEAR TESTER

A. Cowell1 and D. McGlinchey1

School of Engineering and Computing, Glasgow Caledonian University, Cowcaddens Road,

Glasgow G4 0BA, United Kingdom

Abstract

The Stable Microsystems Texture Analyser has been adapted to be used as a linear powder friction testing device. This device is capable of measuring both wall friction and internal friction at a range of consolidation loads. This device has been used to test a number of materials at

a variety of linear speeds. This paper presents a comparison of internal friction test results for one of these test speeds with internal friction test measurements made with the Schulze Ring Shear Test device. A range of materials, from nominally free flowing materials, to more cohesive materials, were selected in order to compare the results across a variety of powder types. The relationship between the friction measurements from these two devices was analysed. It was found that the Texture Analyser Friction Tester (TAFT) could be used as a ranking tool, but the results for the internal friction angles vary significantly from the Schulze Ring Shear Tester, so are not suitable for use in equipment design using the present procedure.

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Effect of Machine Dependence on Wall Failure Property Measurements, Jenike Versus An Annular Shear Tester

R.J. Berry, M.S.A. Bradley, R.J. Farnish & O.A. Angulo

The Wolfson Centre for Bulk Solids Handling Technology, The University of Greenwich,

Central Avenue, Chatham Maritime, Chatham, Kent, ME4 4TB, UK.

Abstract

Annular, ring or torsional shear testers are commonly used in bulk solids handling research for the purpose of powder characterisation or equipment design. This paper reports from a Defra sponsored project which aims to develop a powder flow-ability tester for industry. This paper compares the wall failure loci measured with an annular shear cell with measurements obtained using a Jenike cell. These wall failure loci have been measured for several bulk solids ranging from fine cohesive powders to free-flowing granular materials, on a stainless steel 304 2B wall surface.

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THE DEFORMATION AND BREAKAGE BEHAVIOUR OF IRREGULARLY SHAPED PARTICLES

Sergej Aman *, Jürgen Tomas*, Haim Kalman**, Evgeny Rozenblat**

*Mechanical Process Engineering, the Otto-von-Guericke-University

Universitätsplatz 2, D – 39 106 Magdeburg, Germany

**Laboratory for Conveying and Handling of Particulate Solids, Department of Mechanical Engineering,

Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel

Abstract

Investigation of breakage probability by the compression of single particles was carried out. Five size fractions of glass spheres and NaCl crystals from Dead Sea were tested. The stressing rate varies from 0.01 mm/s to 9 mm/s. The force-displacement diagrams ware used to obtain the

breakage force and the compression work up to the breakage. Usually, the breakage probability can be found from stress or energy approach. The first one uses the stress on the particle surface as variable for calculating the breakage probability distribution. The second approach uses the work done up to the breakage of the particle. In terms of irregularly shaped particles the application of stress approach is restricted due to undefined contact and/or cross-sectional area of particles. In our work, we prefer to use the breakage force as a variable. There exists an apparent link between the force and energy at a given value of breakage probability. In other words, the force distribution can be transformed to the energy distribution and vice versa. The transformation procedure was found to be size independent. It is not necessary to take into account the particle size by the transformation of energy distribution to force distribution. The energy was found to be linearly proportional to the breakage force.

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DEVELOPMENTS IN MECHANICAL TRANSPORT OF BULK SOLIDS

Alan W. Roberts1 and Mark G. Jones2

1. Emeritus Professor 2. Professor and Director, Centre for Bulk Solids and Particulate

Technologies, The University of Newcastle, NSW 2308 Australia

Abstract

This paper presents a brief overview of the various modes of transporting bulk solids with guidelines concerning factors to be considered regarding conveyor selection. The main emphasis of the paper is on mechanical conveyors in which salient aspects of research and technological developments are highlighted. Since the subject of mechanical conveying is indeed quite broad, the paper focuses primarily, by way of example, on belt and screw conveyors and bucket elevators. Of paramount importance to the design and selection process is the characterization of the flow and handling properties of the bulk solid to be conveyed. This aspect of conveyor design forms the main theme of the paper. The paper is illustrated by case study examples.

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The role of cohesive force on the relationship between the bulk density and the connectivity of the contact network of a granular material

F.A. Gilabert1, J.-!. Roux2 and A. Castellanos1

1. Faculty of Physics, University of Seville, Avda. Reina Mercedes s/n, 41012 Seville, Spain.

2. Laboratoire des Matriaux et des Structures du Gnie Civil. Institut Navier, 2 Alle Kepler,

Cit Descartes, 77420 Champs-sur-Marne, France.

Abstract

This work presents a numerical study of a model cohesive granular material based on the Discrete Element Method. The model is carried out by means of a set of thousands of grains represented by disks confined in a rectangular and periodic cell. Grains are able to interact with each other elastically with translational and rotational friction at all their contacts. The study subject is devoted to throw light on the relation between the volume solid fraction and the average number of contacts per grain. This granular system is subjected to an external and isotropic servo-controlled pressure, which can be varied within five orders of magnitude. Along this range of pressure, the effect of the interparticle adhesive force has been analyzed, observing how the system rearranges itself once the cohesion at each interparticle contact is removed during certain intermediate levels of pressure. From the results, we confirm the non-existence of a well-established relation between density and coordination number as in non-cohesive granular systems. This fact is essentially caused by a combined effect between the cohesion and the type of preparation process. Nevertheless and surprisingly, when the cohesion is abruptly removed from the system, both macroscopic and microscopic magnitudes converge very closely to the classical values of a non-cohesive system, which is moreover apparently independent from the preparation process. This result may be considered as an initial but fundamental point to understand the microscopic features, particularly since for fine powders their mechanical properties are enormously affected by their past history.

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MULTI-SPHERE ELLIPSOIDAL PARTICLES IN DEM SIMULATIONS OF PILING PROBLEM

D. Markauskas1, R. Kacianauskas1 and A. Diugys2,

1. Vilnius Gediminas Technical University

Vilnius, LITHUANIA

2. Lithuanian Energy Institute

Kaunas, LITHUANIA

Abstract

The multi-sphere (MS) approximation approach of the 3D axi-symmetric ellipsoidal particle is considered. An algorithm for hierarchical description of ellipsoid is suggested. Non-cohesive frictional visco-elastic MS ellipsoidal particle model is developed and implemented into the original DEM code. Performance of the MS approach is examined by solving a piling problem. A set of 1000 mono-sized ellipsoidal particles characterized by the aspects ratio s = 2.35 is employed for simulation. Concentrated sequential particle piling was considered and a repose angle is studied. Approximation effect is investigated by the increased number of spheres ranging from 3 to 17. The deviation of a multi-sphere shape from ellipsoid at the particle level is evaluated by the suggested shape distortion factors. It has been found, that convergence of repose angle obtained by MS model to ellipsoidal model when the number of spheres increases, has similar tendency as that of variation of distortion factors.

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DISCRETE ELEMENT SIMULATION OF A STOCKPILE WITH SPHERICAL AND NON-SPHERICAL PARTICLES

Chong Zhou, Jin Ooi

Institute for Infrastructure & Environment, School of Engineering & Electronics

University of Edinburgh, Edinburgh EH9 3JL, U.K

Abstract

The stress distribution beneath a stockpile is carefully investigated by using the discrete element method. Simulations were performed using both spherical and non-spherical particles in several numerical models of stockpiles. A robust and reproducible pressure profile with a significant pressure dip under the apex was predicted for all three models under certain conditions. The spherical assembly appears to produce a more erratic pressure profile with a less significant pressure dip. The history of the heap preparation is shown to be important whilst the base deflection is shown to be not a requirement for the dip to form. Specifically, piles constructed by pouring from a concentrated source show a stronger pressure minimum than that from an extended source. The results are in good agreement with some published experimental observations.

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EXPERIMENTAL AND CALCULATED LOADS ON "CONE IN CONE" INSERTS

Schuricht, T1., C. Fürll1 and G.G. Enstad2

1. Leibniz-Institut für Agrartechnik

Potsdam-Bornim, GERMANY

2. Telemark University College

Porsgrunn, NORWAY

Abstract

The examinations focused on the installation of small hopper inserts designed for mass flow. A FEM-"Silo-Flow-Program-System" was used for the calculations. Using full-scale silo experiments, the loads on the “cone in cone” inserts were measured as a function of the installed

positions. The results obtained for all experimental series in the experiment and in the numerical simulation showed a rise of the vertical loads on the hopper inserts as the height position increased. The comparisons between experiment and calculation with the more complex material law variant show relatively good agreement above all for the lower to middle height positions.

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AN EXPERIMENTAL STUDY OF CONE-IN-CONE INSERT CONFIGURATIONS IN A FULL-SCALE SILO

J. Härtl1, J.Y. Ooi1, G. Enstad2

1. School of Engineering & Electronics, University of Edinburgh, Edinburgh EH9 3JL, U.K

2. Tel-Tek. dept. POSTEC, Porsgrunn, Norway

ABSTRACT

This paper describes a comprehensive study of the influence of cone-in-cone inserts on flow pattern and wall pressure in a full-scale silo. A total of 8 insert configurations were investigated. The results were carefully analysed to evaluate the pattern of solids flow and wall pressure. Significant changes in the solids flow pattern and the silo wall pressures were observed when an insert was deployed. The results showed that when no insert was present, the silo exhibited funnel flow with a relatively narrow internal pipe flow and the flow boundary is between the central axis and the mid-radius of the silo. With the use of any of the insert configurations tested, the flow channel widened significantly to varying degrees but pure mass flow was never achieved. Furthermore in the presence of an insert, the normal wall pressure on the cylindrical section was observed to increase during discharge with a larger pressure fluctuation, which is probably caused by the flow channel being closer to the silo wall when the insert was deployed. Each insert also appears to cause the hopper wall pressure to increase near the transition and to decrease near the outlet. These and other relevant findings are summarized and discussed in this paper.

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Tracer Technique for Flow Profile Of Solid in Silo

Shantanu K. Nandgavkar, R.Pichumani and B.Pitchumani.

Particle Science & Technology Laboratory, Chemical Engineering Department,

Indian Institute Of Technology, New Delhi, India

Conclusion

The application of tracer has been successfully demonstrated to change funnel flow silo to mass flow silo. It was found that by use of cone in cone method in silo funnel flow can be converted into mass flow. Mass flow is obtained with binsert while keeping the inlet of binsert above the transition position. Binsert with 30o angle was found to be best, position of the binsert in silo depends on I and O. The study requires flow properties from Jenike shear tester.

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INVESTIGATION INTO THE SEGREGATION OF ALUMINA ON BOARD SHIPS AND IN THE SILOS

Are Dyroy, Jim M Scotland and Erik Tveten

1. Hydro Aluminium, NORWAY

2. Malvern Instruments, UK

Abstract

Norsk Hydro produce Aluminium by the electrolysis of Alumina (Al2O3). The Alumina feedstock material is delivered by ship and Norsk Hydro are very active in taking shares in Bauxite deposits from which Alumina is processed from around the globe. Alumina arrives typically in 10k + tonne loads and particle size distribution (PSD) information is not really known in advance. Norse Hydro used the Insitec Voyager (a mobile on-line laser diffraction based particle size measurement device) to investigate segregation of Alumina during discharge from the ships, silos and when transferring to production pots. The continuous sampling and measurement by the Insitec facilitated by several orders a much higher frequency of measurement than would have been previously. Large populations of fines that are transported from the silos produce blockages and create handling difficulties in the transport system. In addition the volumetric dosing of the electrolytic pots is adversely affected. By measuring the powder that is being transported from the silos to the process we can learn how the powder has segregated during delivery and storage into the silos and also how the PSD of the material delivered to the process is related to process events. Powder unloading from the ship to the silos is conveyed at 500+ t/h and is then conveyed to the process at 150+ t/h which results in a highly concentrated sampling point. One of the key features of the Insitec is its ability to measure at high concentrations without loss of accuracy. Norsk Hydro measured the Alumina at the intersection of 2 belt conveyors where the powder falls under gravity. The sampling system had no moving parts, diluted the sample concentration delivering representative samples and providing samples for continuous measurement.

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CONTROLLING PARTICLE SEGREGATION WITH A SPECIALLY SHAPED STANDPIPE

W.G. Halford, O.C. Kennedy and P.C. Arnold

Centre for Bulk Solids and Particulate Technologies

Faculty of Engineering

University of Wollongong

Wollongong NSW 2522 AUSTRALIA

Abstract

Natural segregation of particles often needs to be controlled directing the bulk solids into downstream processes. Such control is especially a requirement when the downstream flow is to be split into separate streams and/or evenly spread across processing equipment.

This paper reports on a model study where segregation was controlled by employing a square standpipe with a helical twist down the axis of the standpipe. A summary of the outcomes is provided where it was shown that it is possible to control the flow of a bulk solid down a vertical choked flow standpipe by inducing a helical twist in the standpipe and hence providing a positive influence on the downstream segregation issues.

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EXPERIMENTAL INVESTIGATION ON AIR CURRENT SEGREGATION IN CYLINDRICAL LABORATORY SILOS

Stefan Zigan1, Rex B. Thorpe1, Ugur Tuzun1 and Gisle G. Enstad2

1. Faculty of Engineering and physical sciences, University of Surrey, Guildford, GU2 7XH,

United Kingdom,

2. Telemark University College, Porsgrunn, Norway

Abstract

In this experimental investigation, the drop height of material was varied in a cylindrical silo. Process parameters, such as powder feeding rate and air extraction, were kept constant. It was found, that with increasing silo filling height the material masses in the compartments of the middle and outer rings amplified. One reason for the higher masses in the outside compartments in the experiments with higher powder drop heights was the break up of the particle jet which increased the value for the segregation index.

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The Reliable way to convey inconsistent Materials such as Drill Cuttings for all Applications

Abstract

Due to improved environmental awareness and legislation stringency there has been a substantial increase in the requirement for the “ship to shore” disposal of drill cuttings.

Many advantages are associated with the use of Positive Pressure Pneumatic Conveying Systems in order to store and transfer the drill cuttings to onshore processing facilities. These include reduced handling, rig/boat space and manpower

requirements, total enclosure and minimised waste volumes thereby resulting in reduced risk analysis with regards to the environment and safety.

However due to the heterogeneous nature of drill cuttings influenced by mud type, formation lithology, drilling conditions, solids control methodology and treatment/storage techniques, a large variance in performance can be expected which if not controlled may result in erratic performance or system failure.

This paper provides a Brandt FreeFlow design overview outlining the potential hazards that may affect drill cutting conveyance. It highlights the solutions utilised within Brandt Freeflow technology in order to ensure reliable, consistent, high transfer rates for all applications including inter field transfer.

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STARTUP AND RUNNING FORCES ON BULK SOLIDS FEEDERS:

EXPERIMENTAL FINDINGS VERSUS AVAILABLE MODELS

C.P.M Holmes1,M.S.A Bradley2, Alan R. Reed and R.J Berry2

1. Jenike & Johanson Ltd.

Toronto, Canada

2. The Wolfson Centre for Bulk Solids Handling

University of Greenwich, Chatham, United Kingdom

Abstract

Many different models have been postulated over the years for sizing of feeder drives; these models have different bases, some rationally based and others more rule-of-thumb. Experience of Jenike & Johanson and likewise of The Wolfson Centre in trouble-shooting feeder drives has shown that drive powers are often poorly matched, so there is clearly still some way to go towards establishing a universally-used reliable approach.

This paper presents an on-going programme of work designed to measure feeder forces experimentally on a purpose designed testing rig, and to compare these against some of the best known available models, and also against a full size installation. One aspect which is novel is the monitoring of the transition between the “filling stress field” load on the feeder and the “flowing stress field” load.

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Transitional Concentration Measurement of Powder Flow in Vertical Pipe for Petroleum Refinery Process

Tong ZHAO1, Masahiro TAKEI1

1. Department of Mechanical Engineering, Nihon University, 1-8-14, Kanda Surugadai,

Chiyoda-ku, Tokyo 101-8308, Japan

Abstract

An Electrical Capacitance Tomography (ECT) system has been developed to noninvasively measure the transitional powder concentration in a down powder flow. Three CT sensors are attached to different vertical position of the pipe. As results, the powder concentration distribution images are obtained under different parameter conditions. The particle flow rate was proved to influence the uniformity of the particle concentration directly. Particle concentration becomes partial with the increase of particle flow rate. Based on the reconstructed image obtained at different position, the axial and radial profiles of particle volume fraction and its fluctuation were also put forward. The results agreed well with the theoretical analysis.

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ANALYSIS OF TRANSIENT BEHAVIOUR IN THE DENSE PHASE CONVEYING OF POWDERS

M.G. Jones, K.C. Williams and S.S. Busteed

Centre for Bulk Solids and Particulate Technologies

University of Newcastle, AUSTRALIA

Abstract

With the increase in the development of CFD based codes for gas-solids flows, the viscous nature of gas-solid behaviour is becoming an increasing important parameter to determine. Generally, the assumption on the viscous behaviour of gas-solid flows is that the viscosity is only related to the interstitial gas rate of deformation rather than the overall gas-solids deformation

response. This deformation response can vary from the conveying gas viscosity response for dilute gas-solid systems to apparent gas-solid viscosity behaviour for material that exhibits high air retention. (e.g. fluidised material). The apparent viscosity calculations for an alumina powder were based on the resistance force of a sphere passing vertically through the aerated alumina bed. Initial

results of the drag force of the sphere found that the associated Cd of the aerated bed could vary between 0.1 and 2.0 with the aerated alumina bed exhibiting shear thinning (pseudo-plastic) viscosity behaviour.

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EVALUATION OF SCALE-UP PROCEDURES FOR DENSE-PHASE PNEUMATIC CONVEYING OF POWDERS

S.S. MALLICK and P.W. WYPYCH

Centre for Bulk Solids & Particulate Technologies, Faculty of Engineering,

University of Wollongong, Wollongong N.S.W. 2522, Australia

ABSTRACT

This paper presents the results of an ongoing project aimed towards developing a new validated testdesign procedure for the accurate prediction of pressure drop for dense-phase pneumatic conveying of powders. Models for combined pressure drop coefficient (“K”) for the solids-gas mixture were derived using the concept of “suspension density” by using the steady-state “straight pipe” pressure drop data between two different tapping locations of the same pipe and also for two different diameter pipes. It was observed that the derived models were different depending on the location of tapping points (for the same pipe) and selected pipe diameters. The derived models were then evaluated by predicting the pressure drop for pipelines with various diameters or lengths (viz. 69 mm I.D. 168 m; 105 mm I.D. 168 m; 69 mm I.D. 554 m) for the conveying of power-station fly ash. A comparison between the predicted pneumatic conveying characteristics (PCC) and the experimental plots showed that the models resulted in significant over-predictions. In the second part of the paper, the “Macro” or “Systems” approach of scale-up was evaluated. “Total” pipeline pressure drop data from the 69 mm I.D. 168 m pipe were scaled up to predict the PCC for 105 mm I.D. 168 m and 69 mm I.D. 554 m pipes. It was found that “Macro” method resulted in gross over-predictions for diameter scale-up.

However, much better predictions were obtained for length scale-up condition. It was concluded that further studies are needed to be carried out for a better understanding of the solids-gas flow mechanism under dense-phase conditions.

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EVALUATION OF PRESSURE GRADIENT DATA FOR THE PNEUMATIC CONVEYING OF SAND

A.N. Hari Rao1, David Mills2 and V K Agarwal3

1 SJCE College

Mysore, India

2 Pneumatic Conveying Consultant

Canterbury, UK

3 Indian Institute of Technology

New Delhi, India

Abstract

The design of pneumatic conveying systems is dependent upon the material properties and the conveying duty. The conveying line inlet air velocity is an important design criterion which is influenced by the mode of flow and the properties of the material to be conveyed. High inlet air velocity is required for dilute phase suspension flow. The value of inlet air velocity can significantly change for different materials even for dilute phase flow. Another major design consideration is the evaluation of conveying line pressure drop for the conveying duty specified. The minimum inlet air velocity and conveying line pressure drop can both be evaluated from the conveying characteristics of the material derived in a test pipeline. The value of pressure drop thus obtained will, however, be for the total pipeline which includes the horizontal sections, vertical sections and the bends. The pressure drop across the bends is much higher than in the horizontal pipeline.

Tests have been carried out with sand in a pneumatic conveying system and a set of conveying characteristics for the sand in the test pipeline have been obtained. The test data has been analysed in such a way that it is possible to derive a similar set of conveying characteristics in terms of the pressure gradient, in mbar/m, for the conveying of the sand through the straight horizontal pipeline. The results show the relationship between the pressure gradient data for different material flow rates and conveying line inlet air velocity.

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REVIEW OF MODELS FOR PREDICTING THE DISCHARGE RATES OF BULK PARTICULATES FROM SILOS AND BINS

K. Ariza-Zafra, R.J. Berry and M.S.A. Bradley

The Wolfson Centre for Bulk Solids Handling Technology,

University of Greenwich, Central Avenue,

Chatham Maritime, Kent ME4 4TB

Abstract

Various models for predicting discharge rates have been developed over the last four decades by many research workers (notably Beverloo [1], Johanson [2], Brown [3], Carleton [4], Crewdson [5], Nedderman [6], Gu [7].). In many cases these models offer comparable approaches to the prediction of discharge rates of bulk particulates from storage equipment when solely gravity is acting to initiate flow (since they invariably consider the use of mass-flow design equipment). The models that have been developed consider a wide range of bulk particulates (coarse, incompressible, fine, cohesive) and most contemporary works have incorporated validation against test programmes.

Research currently underway at The Wolfson Centre for Bulk Solids Handling Technology, University of Greenwich, has considered the relative performance of these models with respect to a range of bulk properties and with particular focus upon the flexibility of the models to cater for different geometrical factors for vessels.

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CAN GRANULAR MEDIA BE MODELLED IN TERMS OF CONTINUUM MECHANICS?

E.F. Grekova1,2, A. Castellanos1, S.N. Gavrilov2

1. University of Seville

Seville, SPAIN

2. Research Institute for Mechanical Engineering Problems of Russian Academy of Sciences

St. Petersburg, RUSSIA

Abstract

In the literature there is a discussion about the model appropriate for the granular material: if its equations in statics should be elliptic, parabolic, or hyperbolic, and even if a granular medium could be modelled in terms of continuum. We discuss the results of an experiment: a “granular plate” made from small photoelastic blocks, loaded by a vertical point force under various boundary conditions. This experiment proves that the granular medium under consideration is nonlinear even for infinitesimal stresses and strains. The reason is that this material cannot support tensile stresses: the contacts between the grains open, and the material fails. We suggest a variant of heteromodular theory which could be appropriate for the description of such a material. The equations are piece-wise linear, and can be classified as elliptic or parabolic only locally. Then we discuss some preliminary ideas on the construction of constitutive equations of a granular material taking into account the evolution of the system of contacts on the phenomenological (continuum) level.

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DEFORMATION AND BREAKAGE BEHAVIOUR OF DRY CYLINDRICAL AGGLOMERATES

S. Antonyuk and J. Tomas

Mechanical Process Engineering, Otto-von-Guericke-University of Magdeburg

Universitätsplatz 2, D–39 106 Magdeburg, GERMANY

Abstract

The effects of the particle size and the binder concentration (hydroxypropyl methylcellulose) in dry cylindrical -Al2O3 agglomerates on their force-displacement and breakage behaviour during the compression were experimentally investigated. The modulus of elasticity, stiffness, yield pressure and strength of agglomerates have been measured by single particle compression tests. The elastic compression behaviour was described by application of contact mechanics. The elastic stiffness of agglomerate increases linearly with the height of the cylinder. To approximate the ideally plastic force-displacement behaviour beyond the yield point, a simple

contact model was developed. With increasing binder content the elastic and plastic stiffness, the yield and breakage limits as well as modulus of elasticity increase.

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SEGREGATION OF BULK PARTICULATES THROUGH MULTIPLE PROCESS HANDLING STEPS

R.J.Farnish, P.Kulkani and M.S.A.Bradley

The Wolfson Centre for Bulk Solids Handling Technology,

University of Greenwich, Chatham, Kent ME4 4TB, UK

Abstract

Segregation or de-blending of bulk particulates is a problem that is encountered in many industrial sectors. The magnitude of segregation can often determine whether a complete production batch can be transferred for onward processing within the plant or released to market. It is a phenomenon that impacts directly upon the profitability of a process. Segregation can occur through a

coincidence of a range of variables that relate to the process and bulk particulate properties, common mechanisms for this include; percolation, surface effect (rolling) and elutriation. The importance to industry of predicting the sensitivity of bulk particulates to segregation cannot be under-estimated, and to this end various test procedures have been developed.

Within many industries striving to improve product quality and reduce wastage, the determination of variability in blend consistency caused by segregation is an increasing priority. This paper considers recent work undertaken to evaluate the effects of multiple handling operations on the degree of segregation that results. The bulk properties of segregability (and resulting flowability) can not only influence the product consistency, but can have great influence over the process (production) control and performance.

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RELIABLE FLOW OF POWDERS IN BLENDING SILOS

- NEW BLENDER DESIGN AS A CHANCE FOR PROCESS OPTIMISATION -

Dr. Hans Hoppe1 and Michael Dürr2

1. Coperion Waeschle GmbH & Co. KG

Weingarten, GERMANY

2. Coperion Waeschle GmbH & Co. KG

Weingarten, GERMANY

Abstract

Homogenization and mixing of bulk solids in silos is commonly used in industry when large quantities of material have to be handled. The use of those blenders is however limited to free flowing products with no risk for time consolidation (gravity blenders) or special bulk solids characteristics (fluid bed blenders). Consequently, the existing blending techniques were analyzed. As a result, a new blending silo design was established, which shows reliable and effective operation not only for free flowing bulk solids but also for products with more complicated flow properties. This new technological step opens various possibilities of optimization in all fields of industry when powder of varying quality has to be processed or a final product has to be homogenized before bagging.

Examples are:

- Blending powder instead of pellets in polyolefin industry (significant cost benefit).

- Blending PVC Dryblend before processing (higher stability of compounding process).

- Homogenization of powder in food industry, which is made of raw material with natural variation (constant quality of final product).

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ASSESSMENT OF METHODOLOGIES FOR SCALING-UP OF HIGH SHEAR MIXER GRANULATORS

N. Rahmanian*, M. Ghadiri, Y. Ding, X. Jia

Institute of Particle Science and Engineering

University of Leeds, LS2 9JT, UK

Abstract

Scaling up of the granulation process from laboratory to pilot scale and finally to industrial scale is necessary for obtaining appropriate product characteristics. However, there is little work on the engineering science of scaling up of granulators and in particular on the granule strength, size distribution and structure.

In this paper the effect of scale-up of high shear mixer granulators (Cyclomix), manufactured by Hosokawa Micron BV., on granule strength and size distribution of granules is addressed. Calcium carbonate (Durcal) is used for the powder and aqueous polyethylene glycol (PEG) as the binder.

The size and strength characterisation of granules produced at various scales, 1, 5, 50 and 250 L using three scale-up rules: i.e. constant tip speed, constant shear stress based on the methodology of Tardos et al. (2004) and constant Froude number is reported.

It is found that in each scale of granulator, the mean size of granules reduces and a more uniform strength and size distribution is obtained as the tip speed is increased. This can be the result of granule breakage and attrition at high impeller tip speeds.

Comparing all scales studied here, a similar size and strength distribution is found for all scales by adopting the constant tip speed rule. It is also found that the wall make up is extensively reduced as the process is scaled-up, most likely because the ratio of surface area to volume of the powder mass inside granulator decreases as the granulator is scaled up.

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RELIABLE HANDLING OF AL2O3-POWDER IN THE ALUMINUM SMELTER INDUSTRY

Dr. Hans Hoppe and Stefan Skirde

Coperion Waeschle GmbH & Co. KG

Weingarten, GERMANY

Abstract

The demands for aluminum is rising more and more due to the advantages, e.g. in the automotive industry and for other applications. For the production of aluminum metal, big capacities of Al2O3 have to be handled, from railcar or ship unloading down to smelter pots. A mixture of pneumatic and mechanical conveying is applicable to lead to the most reliable and economical plant layout. In ship unloading, conveying capacities of 600 t/h are common. The use of roots blowers increases the reliability by stable operating conditions. In case of silo charging, the application of airlifts, bucket conveyors or hose conveyors has to be decided. Inside the pot rooms, air slides can avoid so called scaling. Another option is a pneumatic conveying system with very low transport velocities by innovative bypass technologies.

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DEVELOPMENT AND INSTALLATION OF A NEW ALUMINA FEEDING SYSTEM TO ALUMINIUM POTS

Sivert Ose, Geir Wedde, Anders Sørhuus, Odd Bjarnø, Jon Kristian Bøckman

ALSTOM Norway AS

Oslo, Norway

Abstract

A new alumina distribution and feed system for use in the aluminium industry has been developed and installed. The alumina distribution system to aluminium production pots contains several new features which are improvements above existing systems.

The system will automatically keep a pot full of alumina at all times, and eliminates the need for crane filling. The pots are fed from silos to a horizontal airslide (actively fluidised) transporting alumina to smaller individual pot slides that are passively (hyperdense) fluidised. The alumina distribution system has several key features:

• Slim design - making retrofit easy

• Completely enclosed and self regulating system

• Keep pots automatically topped up all the time

• Avoids recycling of fines in the process

• Transports coarse material to the pot

• No attrition of the material

The system has been developed during several years, and a large scale test installation was installed at Dubal (Dubai Aluminium Company) in autumn 2006. This installation feeds 30 pots from a 180 m long horizontal airslide. During design and installation of the test installation, a number of experiences have been made, which were valuable in turning it into a product with improvements above other systems.

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EFFECTIVE DESIGN OF BELT FEEDER INTERFACES TO ACHIEVE RELIABLE OPERATION

John Carson1, Francisco Cabrejos2 and Michael Rulff3

1. Jenike & Johanson, Inc., Tyngsboro MA, USA

2. Jenike & Johanson Chile S.A., Via del Mar, Chile

3. Jenike & Johanson, Ltd., Mississauga, ON, Canada

Abstract

Belt feeders are commonly used to control the flow of bulk solids from bins and hoppers. If the interface between the hopper outlet and belt feeder is not designed correctly, solids flow may be severely compromised, resulting in no-flow, segregation, flooding, etc. Belt power and wear may also be compromised. By knowing the flow characteristics of the bulk solid being handled and applying proven design techniques, such problems can be avoided.

Design procedures for correcting problems with existing feeders as well as proper design of new feeders are presented.

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SIZE REDUCTION OF PARTICLES

Haim Kalman

Ben-Gurion University of the Negev

Beer Sheva, ISRAEL

Abstract

The ability to design a size reduction system prior to full scale experiments and to optimize existing systems has long been a goal of designers. Such a design and optimization could be achieved by correctly simulating any system under any operating condition. In this paper we present a new and innovative procedure to implement empirical comminution functions into DEMCFD simulations. The comminution functions include: initial strength distribution, selection function, breakage function and fatigue function. First, the traditional comminution functions (strength distribution and selection and breakage functions) and the recently investigated fatigue function are briefly described and modified. Then a procedure for implementing the functions into a DEM-CFD model is described in detail. The implementation involves converting the probability comminution functions into individual particle properties by a random method and then converting the velocity dependent comminution functions into strength dependent ones. In this way, and mainly owing to the use of the fatigue function (which defines the weakening of those particles that are not breaking), a real size reduction system, in which each particle is subjected to multiple impacts at various velocities can be simulated. Three case studies for multiple impact conditions at the same average velocity (several impacts at the same velocity, various velocities at each impact and randomly selected velocities) are presented and analyzed in order to confirm qualitatively the procedure, although the comminution functions need to be further quantitatively modified.

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