Bulk Solids Handling

392 bulk solids handling · Vol. 26 · 2006 · No. 6

Areview of the developments in Bulk Solids Storage,Flow and Handling is presented. While noting that thedevelopment of this subject spans a period of some

125 years, the paper focuses on the significant contributionsover the past 50 years both during, and subsequent to, thework of Jenike. The work has covered such topics as flowproperty testing, theories of flow, modelling of particle sys-tems by continuum theory and discrete elements, vibrationsof powders, blending and mixing and wall loads under initialfilling, flow and pulsing conditions. The problems in many in-dustrial operations are often orders of magnitude more diffi-cult than the level of fundamental research available to solvethem. So the approach is to apply a combination of theory atthe current state of knowledge, some basic mechanics and“engineering judgment”. While this may satisfy the immedi-ate needs of industry, the important “spin off” is the identifi-cation of areas for longer term research. While not diminish-ing the value of unconstrained, fundamental research, it isparticularly important that considerable research effort bedirected at those known, complex, industrial problems where

improved solutions leading to more efficient performancehave a high priority.These objectives are illustrated and somethoughts for future strategic research are presented.Keywords: Bulk Solids; Particle Technology; Silos; Bins; Feed-

ing; Flow; Stockpiles; Conveying

1 Introduction

Throughout the world, the handling and processing of pow-ders and bulk materials are key operations in a great numberand variety of industries. Such industries include those asso-ciated with mining, mineral processing, chemical processing,agriculture, power generation, food processing, manufactur-ing and pharmaceutical production. While the nature of thehandling and processing tasks and scale of operation varyfrom one industry to another and, on the international scene,from one country to another according to the industrial andeconomic base, the relative costs of processing, storing, han-dling and transporting bulk materials are, in the majority of

Special BULK EUROPE 2006Special BULK EUROPE 2006

Alan W. Roberts, AustraliaThe industrial world depends, to a very large extent, on bulk solidshandling operations. As tonnages increase, there is the ongoing needfor more efficient, higher capacity storage, processing and transportsystems. In turn, more sophisticated analysis and design proceduresare a continuing necessity. Some significant developments from thevarious fields of bulk solids handling are highlighted herein.

Bulk Solids HandlingAn Historical Overview and

Current Developments

“So

BSH-08-06-Roberts-final.indd 392BSH-08-06-Roberts-final.indd 392 04.10.2006 13:21:1204.10.2006 13:21:12

Special BULK EUROPE 2006

393bulk solids handling · Vol. 26 · 2006 · No. 6

cases, very significant. It is important, therefore, that handlingand processing plants be designed and operated with a viewto achieving maximum efficiency and reliability.

The advances that have been made over the past four dec-ades have emanated from the establishment of Particle Tech-nology and Bulk Solids Technology as discipline areas in theirown right with strong overlapping roles. The interdisciplinaryroles of these two technologies are well recognised, so muchso that reference to one very often implies the inclusion ofthe other. There is a third discipline, namely Geomechanics,which must not be overlooked in view of its obvious interac-tive role with the other two.

Focusing on Bulk Solids Technology, reliable test proceduresfor determining the strength and flow properties of bulk sol-ids have been developed and analytical methods have beenestablished to aid the design of bulk solids storage and dis-charge equipment.There has been wide acceptance by indus-try of these tests and design procedures and, as a result, thereare numerous examples throughout the world of modern in-dustrial bulk solids handling installations which reflect thetechnological advances that have taken place.

Notwithstanding the current situation, the level of sophistica-tion required by industry demands a better understanding ofthe behaviour of bulk solids and the associated performancecriteria for handling plant design. Experience indicates that thesolution of one problem, which leads to an improvement inplant performance, often exposes other problems which needto be solved. Problems in industry frequently multiply at afaster rate than research outcomes. The importance of indus-trial orientated research cannot be too strongly emphasised.

The purpose of this paper is threefold. Firstly, to review the his-torical research developments leading to the establishment of

1796, just 8 years following the establishment of the First Set-tlement by the English in Sydney in 1788. The first export ofcoal occurred from the port city of Newcastle in 1801, a load ofsome 600 tonnes bound for India. Newcastle, situated some160 km north of Sydney, became an active bulk export portduring the nineteenth century, increasing in tonnage capacitythroughout the 20th and now 21st centuries. It is now theworld’s largest coal exporting port with annual tonnages cur-rently in the order of 83x106 tonnes with the project expansiontaking this to over 100x106 tonnes.

Despite the design, engineering and construction of bulk han-dling port facilities that accompanied these early develop-ments, research publications did not start to appear until to-wards the end of the 19th century. The need to store grain inlarge quantities provided the impetus for research into silo wallloads with a series of papers on this subject commencing in the1880’s and spanning a period of some thirty years. These pa-pers, reviewed by R [1], emanated mainly from England,Germany, Canada and the USA, with undoubtedly, the bestknown work of this period being that of H.A. J, the Ger-man Engineer from Bremen, who published his epic paper onsilo loads in 1895 [2]. The lesser known work of J is ofparticular significance in view of its relevance to silo wall pres-sures during both symmetric and eccentric discharge [3,4].

2.2 Bulk Solids and Particle Technology -Disciplines in their Own Right

The first half of the 20th century saw increased research inseveral aspects of granular and powder mechanics includingsuch subjects as the flow rates of bulk solids through orificesin the bottom of bins and through transfer chutes. In the areaof powder mechanics, the work of S and E led to are-discovery of Janssen’s equation [5]. The various studies ofgranular flows relied heavily on experimental techniques,with empirical type performance equations being derived

“Some users of this text may feel that it touchesupon too many apparently unrelated fields.

This may be true, but the inclusion of such fieldswas made purposely to indicate the wide

applications of a subject which should receiverecognition as deserving a place in the

engineering sciences”.

“Some users of this text may feel that it touch“Some users of this text may feel that it touches“Some users of this text may feel that it touch“Some users of this text may feel that it toucheselds.upon too many apparently unrelated fi

“Some users of this text may feel that it touchthe disciplines of particle technology and bulk solids handling.Secondly, to review the current state of knowledge and the de-velopments in flow property testing. Thirdly, by means of casestudy examples, to illustrate solutions to industrial problemshighlighting areas where further research is required.

2 Historical Overview

2.1 Bulk Materials Handling -The FoundationsThroughout the 19th century, the emerging mining, manufac-turing and agricultural industries, gave rise to an increasedneed to store and handle bulk materials in large quantities.While the focus for this activitymay have beenNorth America,UK and Europe, industrial developments were also beingmadeelsewhere in the world, notably Asia and countries of theSouthern Hemisphere. Since communications had not beenwidely established at that time, these latter developmentswere not widely known, if at all. For example, coal was discov-ered in what is now known as the Hunter Valley of Australia in

from experimental results. Also the emphasis was mainly onfree flowing, non-cohesive granular type materials. Refs. [6-15] are a selection of references covering this work. This peri-od embraced included a number of studies into the perform-ance of mechanical handling and conveying equipment, suchas screw conveyors, for bulk granular materials [16-21].

It was during this period that Particle Technology had its foun-dations. Reference is made here to the major contribution byJ.M. D in his book entitled “Micromeritics” which wasfirst published in 1943 [22]. As D wrote in the Preface




Ph.D. student of J. A comprehensive historical review ofthe Jenike/Johanson story has been written by J [25].

J saw the need to learn from the research conducted insoil mechanics and relied heavily on the work of the Russianauthor S [26]. He also recognised the importanceof plasticity theory in order to explain the flow or yieldingconditions in deforming bulk solids [27, 28]. This led to theestablishment of the effective yield locus and the yieldingtheory associated with solids flow [29].

The original research of Jenike and Johanson was conductedat the University of Utah, with the three University of Utahpublications, Bulletins 108, 116 and 123, [30-32], and the pa-per by J [33] laying the foundations of the moderntheory of bulk solids storage and flow. The significant resultsand outcome of this work included the following:

• Establishment of the two principal flow modes, Mass-Flowand Funnel-Flow.

• Radial stress theory describing the flow in mass-flow hop-pers and limits for mass-flow which depend on the wall fric-tion angle φ for the bulk solid in contact with the hopperwall, the hopper half angleα and the effective angle of inter-nal friction δ.

• Flow/No-Flow criteria

• Direct shear apparatus for the determination of the flowproperties of bulk solids

The Jenike theory is well proven in its application to designand analysis associatedwith industrial problems and projects.Jenike’s work generated a great deal of interest and stimulateda new wave of research effort in the field of bulk solids han-dling throughout the world.

2.5 The Latter YearsThe last 30 to 40 years has seen important developments on sev-eral fronts including research into the properties and behaviourof particulate solids during storage and flow, further work on binloads and applied research aimed at improving the efficiency ofindustrial operations. Important ‘break-throughs’ have beenmade possible through more sophisticated scientific equipmentfor experimental work and modern computer technology to as-sist the solution of complex problems. A ‘snap-shot’ of some ofthese developments with selected references is presented:

• Re-examination of themass-flow and funnel-flow limits tak-ing account of the surcharge head at the hopper/cylindertransition and the establishment of the conditions for “in-termediate-flow” [34,35].

• Development of test equipment for characterising bulk solidsand powders in terms of their stress/strain relationships andflow properties including boundary or wall friction [36-51].

• Analysis of vibration of bulk solids in relation to flow pro-motion [52-54].

• Studies of friction, adhesion and wear in bulk solids han-dling operations [55-59].

to the First Edition, the title “Micromeritics” was coined to rep-resent the science of small particles”.The subjectmatter includ-ed in the text is broad ranging including such subjects as: dy-namics; shape and size; particle-size measurement; packings;behaviour of particles under pressure; diffusion; electrical, opti-cal, sonic, surface and chemical, properties; thermodynamics ofparticles; flow of fluids though packings; infiltration and parti-cle-moisture relationships; capillarity; particle surface determi-nation; muds and slurries; transport of particles; dust clouds;atmospheric and industrial dust; collection and separation ofparticulate matter from air; theory of fine grinding; sampling.

D also wrote,

“Some users of this text may feel that it touches upon toomany apparently unrelated fields. This may be true, but theinclusion of such fields was made purposely to indicate thewide applications of a subject which should receive recogni-tion as deserving a place in the engineering sciences”.

Clearly this statement reinforced the interdisciplinary natureof this new named science. While the name “Micromeritics”still remains, it has provided the foundation for what we un-derstand to be been embraced by the title ‘Particle Technol-ogy’. There can be no doubt that Particle Technology is nowvery firmly established amongst the engineering sciences.

2.3 The Influence of Soil MechanicsSoil mechanics as a field of science and technology had al-ready been well developed. Therefore, it is not surprising thatthis field of study had a significant influence on the researchinto various aspects of bulk solids handling. Since soil me-chanics is mainly concerned with retaining walls, buriedstructures and foundation design, naturally, the internalstresses are much higher than those encountered in bulk sol-ids handling. Furthermore the main concern of soil mechan-ics is with the conditions existing within soil prior to failure,whereas the primary interest in bulk solids handling is withthe conditions under which failure and flow can occur. Nev-ertheless, the general similarities between the two fields ofstudy permit some important comparisons to be made.

The work of H [23] is of particular importance to theunderstanding of the mechanism of consolidation and flowof bulk solids. H, who studied the stress condition incohesive soils, showed that the peak shear stress at failure is afunction of the effective normal stress on, and the voids ratio(or density) in the plane of failure; this condition is independ-ent of the stress history of the sample. The work of Hwas further extended by R et al [24], who establishedthe concept of a failure surface in the three dimensional spaceof shear stress, normal stress, and voids ratio. They alsoshowed the existence of a critical voids ratio boundary atwhich unlimited deformation could take place withoutchange in the stress condition and voids ratio.

2.4 Bulk Solids Handling Technology -The Jenike EraThe flow of cohesive bulk solids from storage bins is a complexproblem and it was not until the mid 1950’s before any realprogress into the fundamental behaviour of such materials be-gan to take place. The modern developments are very largelydue to the pioneering work of D. AW. J togetherwith D. J R. J, who commenced his research as a




• Flow property measurement and reactor vessel design forhandling and processing of stringy bulk solids, such as do-mestic waste [60], and wet bulk solids.

• Dust control and measurement of ‘dustiness’ [61].

• Flow rate predictions for fine powders discharging frommass-flow hoppers [62-64].

• Flow characteristics in hoppers and discharge equipment inrelation to anti-segregation and mixing including the appli-cation of inserts [65-68].

• A new look at the prediction of rat-hole geometry in funnel-flow bins [69].

• Wall load predictions for symmetrical mass and funnel-flowbins [70-86] as well as for eccentric discharge.

• Analysis of ‘silo quaking’ in bins of various geometrical con-figurations [87-93].

• Investigations of pressures acting at the base of stockpilesand procedures for predicting the live capacity during grav-ity reclaim [94-104].

• Hopper/feeder interfacing for optimum draw-down andfeeder load prediction and drive torque control [105-108].

• Performance characteristics of various feeder types includ-ing belt, apron, vibratory, screw, rotating table, tube, oscil-lating plate and rotary valves [108-120].

• Discrete and continuum approaches to the modelling ofbulk solids flow [121-124].

• Pilot scale testing of bulk solids equipment using dynamicsimulation [125,126].

• Studies of the flow of bulk solids through transfer chutesand development ofmodels for chute design, including ana-lytical and numerical methods for optimising chute profilesfor minimum wear [127-137].

• Mechanical conveying - belt, special belt, screw, bucket,chain [138-142 ].

• Pneumatic conveying - lean phase, dense phase, slug andplug flow [143-145].

• Hydraulic conveying, slurry, paste pumping [146, 147].

In parallel with the foregoing, research into the widely varyingareas of Particle Technology has been proceeding at a very im-pressive rate. Of particular note are the quite exciting devel-opments in nanotechnology, such as in applications to medi-cal science, particle flow analysis and computer technology.The spin-off from this research to the broader areas of particleand bulk solids technology will continue to be of great value.

2.6 Interdisciplinary RolesThe interrelation between Particle Technology and Bulk Sol-ids Technology requires clarification. While clearly there is a

great deal of overlap, perhaps the main distinction lies in therange of particle sizes involved and the associated fields ofapplication. Particle Technology is associated more with finerparticles commonly less than a few millimetres down to mi-cron size and currently, down to nanometres. On the otherhand, Bulk Solids Technology, while concerned with fine par-ticles in the micron size range when dealing with powdersand dust, the size range often extends to much larger ‘parti-cles’ which may exceed one metre in size. Such is the casewhen dealing with ROM ores in mining operations. Further-more bulk solids handling is often thought of as being ‘endon’ to the process when the operations of storage and trans-port are only considered. This is erroneous. While not dimin-ishing the importance of storage and transportation, bulksolids technology is very much an integral part of most, if notall, industrial process operations.

In considering the interdisciplinary nature of the subjects ofParticle and Bulk Solids Technologies, it is important not tooverlook a third research discipline, namely, Geomechanics,which embraces Soil Mechanics. All three share a commoncore area which embraces particle characterisation andmod-elling. The interactions between these three principal re-search disciplines are illustrated in Fig. 1.

3 Developments in Bulk Solids Testing

3.1 General RemarksThe foundations of process and handling plant design lies inthe determination of the bulk solid flow properties and thecorrect interpretation of these properties in relation to theparticular applications. Therefore, it is not surprising that thisis a subject that has received a great deal of attention over thepast three decades, with several new testers being introduced.A review of the various test methods has been presented byS [36]. Since its introduction, the Jenike direct sheartest has been under fairly intense scrutiny, perhaps more sothan other test methods.The EuropeanWorking Party on theMechanics of Particulate Solids of the European Federationof Chemical Engineering has completed a detailed study ofthe Jenike direct shear test [37].

A recent project of the Working Party was concerned withthe application of the Jenike shear tester for measurement ofwall or boundary friction, that is, the friction between a bulksolid and sample of hopper lining materials. Even though aseries of tests was performed using the same bulk solid andsame lining material, significant variations in the results oc-curred. Wall friction is one of the most important parametersin bulk solids handling systems. It is clear that it is a subjectnot fully understood and requiring significant research.

The limited travel of the Jenike type direct shear tester is over-come in the torsional or ring type shear testers which allowcontinuous shear strain to occur, making consolidation to crit-ical state conditions easier to achieve. While several torsionalor ring type testers have been developed, the more recentSchulze Tester is one which is being widely adopted [38].

The need to standardise various test methods for powdersand bulk solids has received the attention of various stand-ards organisations throughout the world. For example, the




Australian Standards Association recognises the Jenike testapplied to coal [39], and the American Society for TestingMaterials (ASTM) has established several standards on flowproperty testing such as the shear tests due to J [40] andS [41]. An alternative bulk solid shear test procedureis the Indicizer™ developed by J [42,43] which hasalso been taken up as an ASTM standard. A general commentneeds to be made: While these standards focus on the speci-fications for the test procedures, as far as it is known, there isno specification for the required stiffness of the load cells. Er-rors can occur when dynamic effects, such as slip-stick, arewrongly attributable to the bulk solid rather than to the testequipment.

The need for a greater fundamental understanding of thestress/strain behaviour of particulate solids created the needfor more sophisticated equipment, notably the biaxial tester[44-47]. The complexity of these testers rather restricts theirapplication to research rather than to flow property testingfor design applications. The uni-axial tester provides an alter-native to the direct shear apparatus, [48-51].

The extreme variability of both bulk solids and their indus-trial applications has necessitated special test equipment tobe developed. These include the dynamic shear test for bulksolid vibration analysis, inverted shear tests, large scale shearcell tests, shear tests for funnel flow where higher pressuresare experienced, submerged shear tests for wet solids and“flowability” tests for quality control analysis. These are nowbriefly discussed.

3.2 Dynamic Shear Test for Vibration AnalysisIn the area of flow promotion using vibrations, the reductionboth in bulk strength and wall friction as a function of vibra-tion frequency and amplitude have been investigated [52-54]. The vibrated shear cells used in this work are shown inFig. 2.

For a given consolidation condition, vibration excitation dur-ing shear deformation has shown that the shear strength re-duces exponentially as the amplitude of vibration velocity

increases, as indicated in Fig. 3. This is a similar characteristicto the reduction in shear strength with increase in voidage asin the H diagram. The shear stress as a function ofvibration velocity amplitude is given by

The constant U in Eq. (1) is the bulk solid vibration velocityconstant. The experimental evidence suggests that U is inde-pendent of the consolidation pressure and applied normalpressure. By way of example,U = 7mm/s for pyrophyllite andU= 10 mm/s for iron ore. Knowing the value of U for the particu-lar bulk solid, the values of the relative amplitude Xr and fre-quency f for maximum shear strength may be estimated from

From a practical point of view, the application of high fre-quency (f ≥ 100 hz) and low amplitude (≈ 0.1 mm) vibrationgenerally produces the best results in promoting flow. Somestudies of the transmission of vibration energy through con-solidated bulk solids have also been undertaken [53].

3.3 The Inverted Shear TesterA disadvantage of the Jenike direct shear tester for wall fric-tion measurement, Fig. 4(a), is the inability to determine thewall or boundary yield locus in the low pressure and tensilestress zones. This difficulty may be overcome by the invertedshear tester, Fig. 4(b). In this way the properties of adhesionand cohesion may be deduced [55-57]. The complete wallyield locus is depicted in Fig. 5. In the test equipment of Fig.4(b), the retaining shear cylinder is retracted during each test

Fig. 1: Interdisciplinary roles of particle technology

Fig. 2: Test arrangements for vibrated shear cells

Fig. 3: Shear stress attenuation as a function of relative velocity onshear plane: -1 mm Pyrophyllite; 5% M.C. (d.b.) consolida-tion pressure = 7.9 kPa; X1 = 0.01 mm




a sufficient amount clear of the lining material surface. Thelow pressure properties are relevant to chutes and standpipeswhere sufficient body forces must be generated to preventbuild up on inclined, vertical and overhead surfaces as illus-trated in Fig. 6.

3.4 Large Scale Shear TestersThe standard Jenike type shear testers employ shear cells of95 mm internal diameter, with the maximum particle sizecommonly limited to -4 mm. To allow higher consolidation

pressures to be achieved, a smaller shear cell of 65 mm diam-eter is often used. These cell sizes are satisfactory for mostapplications particularly for mass-flow design where the fo-cus is on the cohesive arch analysis for flow to occur.

However, there are applications where the restriction to thefiner particle size range is too conservative. This applies tofunnel-flow and expanded-flow, particularly in the case ofgravity reclaim stockpiles, where the ratholes are large in di-ameter and several metres high, being formed by a large sizerange of particles. For this reason a 300 mm diameter directshear tester has been developed at the University of Newcas-tle. Furthermore, in the case of ROM stockpiles for mineralores, it is not uncommon for consolidation stresses to ap-proach 1 MPa. Since it is not practical to achieve such pres-sures using weights, a hydraulic load cylinder is incorporatedin the large shear tester.

There are also advantages in wall friction measurement to beable to test a wider size range of bulk solids. For this reason, a300 mm diameter inverted shear tester based on Fig. 4(b) hasalso been manufactured. The larger diameter shear cells offeradvantages in testing stringy, fibrous bulk materials such asdomestic waste [60].

3.5 Shear Tests for Wet SolidsWet solids handling is an area of increasing interest. Atpresent, it seems to fall ‘in no man’s land’ between rheologyand bulk solids. Applications commonly concern the designof vessels for the storage and gravity flow of super-saturatedbulk solids. Where the solids may settle out of suspensionduring storage, it is necessary to ensure that gravity dischargemay occur without blockages due to arching or ‘ratholing’.For this reason the storage vessel should be designed formass-flow.The required hopper geometrical parameters maybe determined for saturated bulk solid samples using sub-merged shear tests as depicted in Fig. 7. Clearly, this is an arearequiring more research.

3.6 Flowability TesterA flowability tester, developed by University of Newcastle, isdepicted in Fig. 8 [51]. In effect, this is an unconfined com-pression test in which the lateral pressure is controllable dur-ing the consolidation phase by means of pneumatic actua-tors attached to the three segments of the mould cylinder.

Fig. 8(a) shows the segments of the mould cylinder retractedand their support arms swung clear. Fig. 8(b) shows the armslock in place and the segments clamped together to contain

Fig. 6: Build-up on surfacesS = shear force; B = body force; Fo = adhesive force

Fig. 4: Test arrangement for determination of Wall Yield Loci

Fig. 5: Wall friction and adhesion

Fig. 7: Submerged Shear Tests




the bulk solid or powder sample during the consolidationphase of the test. For the unconfined phase of the test, thesegments are retracted to leave the consolidated cylindricalsample exposed so that the axial load may be applied to ef-fect failure. When compared with the Jenike direct shear testwhich is somewhat time consuming, the flowability testerprovides a much quicker analysis of the flow properties of abulk solid, the device being particularly suitable for qualitycontrol testing.

3.7 Abrasive Wear TestsTest equipment to measure the wear characteristics of hop-per and chute lining materials has been developed. The test-er due to J and R [58] employs a screw extrud-er type apparatus which forces the bulk solid against a sam-ple of lining material prepared as circular disc and which isdriven in rotation by dynamometer device. A disadvantageof this arrangement is the preparation of the lining sample incircular form to fit the dynamometer. The difficulty is morepronounced in the case of hard lining surfaces which cannotbe machined.

The apparatus shown in Fig. 9 overcomes this difficulty sincethe test sample which is nominally 150 mm square does notneed to be prepared with great accuracy [55,56]. The belt de-livers a continuous supply of the bulk material at a requiredvelocity to the sample of material to be tested, which is heldin position by a retaining bracket secured to load cells thatmonitor the shear load. The bulk material is drawn under thesample to a depth of several millimetres by the wedge actionof the inclined belt.Three body wear conditions are thus gen-erated.

The required normal load is applied by weights on top of thesample holding bracket. The bulk material is cycled back tothe surge bin via a bucket elevator and chute. The apparatusis left to run for extended periods interrupted at intervals toallow measurement of the test sample’s weight and surfaceroughness as required. The measured weight loss is then con-verted to the loss in thickness of lining material.

While the linear action wear tester described above has beenshown to be a very effective wear tester, the disadvantage liesin the bucket elevator recirculating systemwhich is subject toequipment wear. To overcome this problem, the circular weartester illustrated in Fig. 10 has been developed [59]. In thistester a plough, followed by a surface levelling and consoli-dating device, is incorporated to turn over the bulk solid wearmedia to present a “fresh” surface of bulk solid to the testsample each revolution. The tester has the advantage of al-lowing two lining samples to be tested at the same time

3.8 Dustiness TestsFor obvious environmental reasons, the control of dust inbulk solids handling and processing plants has a high priority.Through proper design, passive (non energy) dust controlcan be achieved in process plants such as in conveyor feedingand transfer operation. In open transport operations such asrail wagons and large storage systems, notably stockpiles, thecontrol of dust generation due to windage needs to beachieved. This is particularly important in the case of thestorage and transport of mineral ores such as coal where thepropensity for dust generation will vary with moisture con-tent and coal type.

Australian Standard AS 4156.6-2000 [61] provides the specifi-cation of the test equipment and measurement proceduresfor the determination of the dust versus moisture relationshipfor coal. The test is also of value for the assessment of surfacesealing surfactants for controlling dust losses due to windagefrom open stockpiles. While the Standard refers specifically tocoal, it is equally useful as a test for virtually all bulk solids.

The test equipment is shown in Fig. 11. It consists of a rotatingdrum fitted with eight longitudinal vanes or lifters to assist thedust dispersion. The test sample is placed in this drum and airis drawn through the sample as it rotates carrying dust parti-cles to the stationary filter collection bag held within thesealed stationary compartment. The specific details of the testprocedure are given in the Standard. Besides this particulartest, wind tunnel tests are also used for dustiness tests.

4 Bin Wall Loads

4.1 Early Silo ResearchWhile silos have been in existence formany centuries, the firstmeaningful research into silo loads was performed over theperiod embracing of some 30 years commencing in the early1880’s. A review of this early silo load research is given in Ref.[1]. The most widely known work in the early period of siloresearch is that due to the German Engineer, H.A. J [2].This work is significant in that it recognised some fundamen-tal aspects of internal and boundary friction which limit themagnitude of the loads on silo floors and walls. By compari-son, little is known of the work of the Canadian Engineer, J.A.

a) Arms Swung Clear b) Mould Segments ClampedTogehter

Fig. 8: Flowability tester

Fig. 9: Linear action wear test apparatus




J [3,4], whose contributions over the period 1902-04are twofold. Firstly, during symmetrical discharge he showedthat the wall pressures increased above the filling pressuresduring discharge. Secondly, and even more significantly, heexamined eccentric discharge and showed that the wall loadson the side nearest the discharge outlet are lower than thosefor symmetrical discharge, but greater on the opposite side.Thus he demonstrated the non symmetry of the wall pres-sures. Had his research beenmore widely known, some of thesilo failures that occurred some 80 or more years later mayhave been avoided.

4.2 More Recent ResearchFollowing the foundation work of J, the study of bin wallloads gained new impetus [70-80]. With the flow modesclearly defined and the advantages of mass-flow being identi-fied, the need for determining the wall loadings in mass-flowbins became a necessity. In addition, the better understand-ing of the characteristics of funnel-flow and the definition ofthe ‘effective transition’ provided the scope for formalisingthe computation of wall loads in funnel-flow bins. There wasthe realisation that bin wall loads are directly related to theflow pattern developed during discharge, and this led to theconclusion that, wherever possible, bin shapes should be keptas simple as possible. While symmetry of the flow channel is

seen as a desirable goal, from a practical point of view, it isvirtually impossible to guarantee symmetrical loading. Forinstance the filling of the bin needs to be exactly centralwhich, from a practical point of view, is unlikely. Secondly, theinterfacing of the hopper with the feeder may skew the flowpattern.

The need for ongoing research into bin wall loads had alsobeen encouraged, to a significant extent, by an increase in thenumber of reported bin and silo failures. As a result, therewas a pressing need to revise existing bin load codes and todevelop new codes in countries where such codes have notpreviously existed. The Australian Standard AS3774-1996 isone example of the latter [81].This standard is quite compre-hensive, addressing a wide range of silo loading conditionsincluding eccentric loads due to non symmetrical flow pat-terns.The new Eurocode covers the subject of silo loadings ingreat detail [82].

Major advances in the study of bin loads have been achievedthrough the application of finite element analysis [83-86].This has greatly assisted the analysis of complex loading pat-terns in multi-outlet bins and bins operating with eccentricdischarge.

Other problems in silo loading have been investigated. Theseinclude grain silos where an increase in moisture content ofthe stored grain due to aeration can lead to grain swelling.This can cause reverse friction at the wall leading to an expo-nential increase in the normal wall pressure [80]. If this oc-curs, wall pressures several times the static value given byJ’ equation may result. A similar effect may occur as aresult of temperature variations on a daily as well as seasonalbasis. Settlement of the stored product during the expansionphase leads to increased pressures during the contractionphase. Other research has involved the application of anti-dynamic tubes to control the pressures in tall grain silos [79].

4.3 Silo Quaking and HonkingA recurring problem in bin and silo loadings is that due to thephenomenon of silo quaking. Gravity flow in bins and silos,characteristically, is a cyclic or pulsating type flow. The pulsa-tions arise as a result of changes in density and dilation duringflow and by varying degrees of mobilisation of the internal

a) Photograph of Wear Tester b) Elevation of Tester

Fig. 10: Circular action wear tester

Fig. 11: Dustiness tester




friction and boundary wall fric-tion. The quaking problem islargely a slip-stick effect and ismore pronounced at low flowrates where the period of puls-ing may be from a few secondsto many seconds or even min-utes. The outcome of the quak-ing may range from nuisancevalue arising from the transmis-sion of shock waves through theground to disturb neighbouringareas, to structural fatigue fail-ure when the natural frequen-cies of the silo and structure it-self are excited by the flow puls-es. Research into the quakingphenomenon, supported by in-dustrial case studies has beenreported by R and W- at the University of New-castle [87-91].

A variation of the silo quaking problem is silo music and silo‘honking’ have been reported by T and G[92,93]. The ‘honking’ phenomenon is known to occur in tallaluminium silos which store plastic powders. In this case thehigher frequency components of the flow pulsations can giverise to loud, periodic, fog horn type sounds that have a decid-edly nuisance effect.

‘Silo quaking’ can occur in bins of all shapes and under a vari-ety of flow patterns. The phenomenon has been experiencedin tall mass-flow silos, tall funnel-flow silos, squat funnel-flow,expanded-flow and intermediate flow bins and multi-outletbins. As an illustration, the case of the tall mass-flow silo de-picted in Fig. 12 is briefly reviewed.

W [89,90] used hypo-plasticity theory to study theshock waves travelling up tall silos during discharge. He showedthat the amplitude of the wave front increases exponentiallyup the cylindrical section of the silo as illustrated in Fig. 13.From a practical point of view, quaking is known to occur if theheight of fill is above a critical height Hcrwhere Hcr ≈ D, D beingthe silo diameter or width (Fig. 12). Above the height Hcr, plugtype flow occurs with the velocity profile substantially uniform

across the cross-section. Below the critical level, in the region ofthe transition, the flow starts to converge due to the influenceof the hopper and the velocity profile is no longer uniform.Thevelocity profile is further developed in the hopper as shown. Asthe flow pressures generate in the hopper, dilation of the bulksolid occurs. As a result of this dilation, it is possible that thevertical supporting pressures decrease slightly reducing thesupport given to the plug of bulk solid in the cylinder. Thiscauses the plug to dropmomentarily giving rise to a load pulse.The cycle is then repeated.

Based on the dynamic load condition as depicted in Fig. 13, atheory for predicting the pulse period T has been developed,the period being shown to be a function of the strain rate oraverage velocity of discharge in the upper cylindrical sectionof the bin. The period is also shown to be a function of theaverage particle size Δy. A sample set of pulse period resultsis shown in Fig. 14. These results compare closely to thosemeasured in the field.

A critical factor in the operation of silos under quaking con-ditions is the influence of the dynamic characteristics of theoverall structure. By way of illustration, Fig. 15 shows a typicalarrangement of a silo supported on columns from a concretebase which, in turn, is supported on piles driven into theground. In view of the significant decrease in the silo massfrom the full to the empty condition, there is a correspondingincrease in the natural frequencies as follows:

4.4 Dynamic Loads Due to High Load-Out RatesDynamic loads also occur during flood type loading of mineralores into rail wagons. As an illustration, the case of an iron oretrain loading bin, illustrated in Fig. 16, is considered. Each wagonholds 120 tonnes of ore, the filling time per wagon being ap-proximately 50 sec. The load out is controlled by a clam shellgate operating on a swinging chute as depicted. As an empty

Fig. 12: Tall mass-flow silo

Fig. 13: Dynamic loads induced in silo

Fig. 14: Pulse period versus velocity - a = 1 m/s2




wagon moves under thebin load-out chute, there isan initial surge in the flowrate peaking around 60,000t/h. This causes high verti-cal and lateral impact loads.Once the chute chokes, theremainder of the wagon isloaded at a rate of approxi-mately 7000 t/h, with theflow rate reduced to zero asthe gate closes with thewagon full. The shock loadson the bin and structureneed to be taken into ac-count in the design.

centre with the pressure at the centre decreasing as depicted inFig. 17. One of the earliest papers to show the existence of thedip in pressure towards the centre of the pile is due to S andN [94], who performed small scale, bench top experi-mental studies. The M-distribution has also been shown to oc-cur using DEM simulation. However, due to the current limita-tion in computing power, DEM is restricted to small heaps in-volving a few thousand particles, whereas actual industrialstockpiles may contain in excess of 1012 particles of widely vary-ing size and shape.

The problem has attracted the attention of a group of physi-cists whose aim was to produce a complete explanation ofthe central dip in pressure under small sand piles. As shownby W et al [99,100], the assumption of a “fixed princi-pal axis” (FPA) has allowed the development of a model thatcan reproduce the classic pressure dip. The complexity of theapparently simple sand pile problem has been highlighted byAW who wrote [101],

“the humble sand pile is to granularmechanics as Fermat’s LastTheorem was to number theory: a tantalising simple problemthat stubbornly eludes solution”.

The recent research confirming the existence of the M-distribu-tion by MB [102] is quite comprehensive and worthy of

particular note. MB conducted ex-periments on 2m high pilot scale conicalstockpiles formed by gravel. An exampleof his results is shown in Fig. 18(a). He alsoestablished a limit slope theory to predictM-distribution of stockpiles of conical andother geometries. H Y J con-

Fig. 15: Simplified dynamic modelof silos

5 Gravity Reclaim Stockpiles

A subject of importance to the mining and mineral process-ing industries concerns the design of gravity reclaim stock-piles. It involves the determination of live capacity, loads onreclaim tunnels and the loads on reclaim hoppers and feeders.Typically stockpiles range inheight from 20 to 40 metres,with one known copper orestockpile in Irian Jaya having aheight of 70 metres. On such ascale, the consequence of fail-ure of the reclaim tunnel due tothe high base pressures maywell be catastrophic, so thetemptation is to err on the con-servative side in the design. Yet,the cost of being too conserva-tive cannot be sustained oneconomic grounds. Hence, theneed to be able to predict thebase pressures under all loadingconditions is strongly empha-sised.

5.1 Base PressuresBy way of background, the fun-damental research into the pres-sure distributions under smallheaps or piles formed by freeflowing materials is reviewed.This research has been approached, essentially,on three fronts, experimentally, analytically andnumerically using Finite Element Analysis (FEA)and Discrete Element Modelling (DEM), [94-98].

Intuitively, it would seem that the pressures ex-erted at the base would be ‘hydrostatic’, the dis-tribution mirroring the conical shape of the pilewith themaximumpressure occurring at themidpoint directly under the apex. It is now knownthat the pressure distribution is M-shaped withthe maximum pressure occurring away from the

Fig. 16: Load-out bin for filling iron ore rail wagons

a) Train Loading Bin b) Bin Flow Patterns and Loads

c) Wagon Load Rates and Total Load d) Rail Wagon Load Patterns




ducted extensive numerical simulations using a special FEApackage [103]. He also assumed axi-symmetry to accommodatethe 2-dimensional stress field. As shown in Fig. 18(b), HY’ prediction of MB’ results show close agreement.In both cases the pressures, as plotted, are normalised.

H Y’ research has extended to the loads on softground and to the prediction of pressure distributions aroundreclaim tunnels.The limitation of his work is that the analysesare limited to free-flowing cohesionless materials, but followup research on stockpiles formed from cohesive materials isnow underway.

In mining operations, the bulk solid is quite heterogeneous,comprising a wide range of particle shapes and particle sizesfrom large rocks to a few microns in a random packing array.The random behaviour is influenced by the loading arrange-ment and consequent segregation that may result. The bulksolid is mostly cohesive, its strength varying with moistureand consolidation.The consolidation conditions will vary withtime throughout the stockpile and be influenced by the load-ing and unloading cycle, variations with weather conditionsand with external loading such as the use of large mobileequipment, for example bulldozers, that may be used to workthe surface of the pile. In addition, differential bonding or ce-menting of particles forming the pile usually occurs due todrying or baking of the bulk solid. Under extreme rainfall con-ditions, stockpile slumping may occur giving rise to complex,variable base loading conditions.

5.2 Loads on Reclaim Hoppers and FeedersIn order to relate current research to industrial stockpile designsome relevant aspects are briefly reviewed. The purpose of astockpile is to store bulk solids and reclaim them by either me-chanical means or by gravity flow as illustrated in Fig. 19. In thecase of gravity reclaim, mass-flow hoppers and feeders are em-ployed as illustrated, discharge being by expanded-flow.

Knowing the flow properties of the bulk solid, it is possible toestimate the draw-down hD and the corresponding shape ofthe crater formed by gravity discharge. The use of mass-flowreclaim hoppers interfaced with the feeders is importantfrom the point of view of achieving reliable feed, and, in par-ticular, for controlling the loads on the feeders and the cor-responding drive torques and powers. Due to the archedstress field conditions in the hopper after feeding has beeninitiated, even if the feeder is then stoppedwith the stockpilestill relatively full, the load Qf on the feeder is independent ofthe surcharge head.The loadQf is much lower than the initialloadQiwhich occurs when the crater is filled from the emptycondition.

The initial loadQi on the feeder is more difficult to predict andmay vary considerably fromwhen the stockpile is filled for thefirst time to when a pre-formed rathole or flow-channel isfilled from the empty condition after the stockpile has been inuse. While the very conservative approach is to assume thatthe surcharge pressure ps is equal to the hydrostatic pressure,this will normally result in an over-design which cannot bejustified on economic grounds. If a pre-formed flow channel

“The humble sand pile is to granular mechanicsas Fermat’s Last Theorem was to number theory:a tantalising simple problem that stubbornly

eludes solution”.

“The humble sand pile is to granular mechane humble sand pile is to granular mechanics“The humble sand pile is to granular mechan“Th “The humble sand pile is to granular mechanicseorem was to number theory:as Fermat’s Last Th

e humble sand pile is to granular mechan“Thmat’s Last Th

Fig. 17: Granular heap or stockpile

Fig. 18: Research into pressures under stockpiles

a) Experimental Work - McBride [102 ]

b) Numerical Simulation - H.Y. Jeong[103]




exists, then this channel will act as a pseudo bin or silo inwhich the shear stresses generated at the boundaries will pro-vide support for the load generated by the bulk solid and re-duce the surcharge pressure ps. Even when a stockpile is filledfor the first time, there is likely to be an initial settlement ofthe bulk solid at the transition level of the hopper and stock-pile. This will help to define the flow channel and reduce, atleast partially, the surcharge pressure ps.

So much depends on the characteristics of the bulk solid, itscompressibility, particle size range and moisture content. Al-so the physical scale of the operation needs to be noted. Forinstance, mass-flow hoppers, typically, may have dimensionsLT (Fig. 19) in the order of 10 to 15 m, while the apron feedersmay be such that B is 2 to 2.5 m.

5.3 Draw-Down and Live CapacityThe determination of draw-down and live capacity, based onFig. 20 is described in Ref. [104]. The procedures are adaptedfrom the J theory for funnel-flow design in which thecritical rathole diameter Df is determined from the followingequation:

where γ = γ g = bulk specific weight

φt = static angle of internal friction determinedfrom the Time Yield Loci

σc = unconfined yield strength

The function G(φt) is given by J as a design graph in Ref.[32]. It may be represented by the following empirical equa-tion

It is noted that the Jenike analysis is based on a 2-dimensionalstress field for both axi-symmetry and plane symmetry withvertical and radial coordinates andmajor andminor principalstresses σ1 and σ2 respectively. The strength of a rathole isgoverned by the hoop strength, which is a function of theconsolidation stressσ3 in the 3rd or circumferential direction.

As an approximation, it is reasonable to assume that σ3 isequal to the average consolidation stress

where δ = effective angle of internal friction

It has been found that an acceptable estimate of σ1 is given by

where z = depth below stockpile surface, and θr = angle ofrepose

By calculating σ1 for various values of z and applying Eq. (7) todetermine σ3, the corresponding values of σc are obtainedfrom the Time Flow Function determined from the flow prop-erty tests. Hence the critical rathole diameter Df as a functionof z = hD is obtained using Eq. (5). This enables the Df versus hDgraph shown in Fig. 20 to be obtained.

A somewhat empirical, but satisfactory approach to the de-termination of the draw-down and crater geometry is depict-ed in Fig. 20. It is assumed that the rathole forms as an ellipseabove the hopper transition with major axis DR equal to thediagonal of the rectangle defining the hopper transition andminor axis BR. The sides of the crater slope away at the angleεp on the sides and angle εc on the ends. At the height hc therathole becomes circular and continues to slope away at theangle εc. The angles εc and εp depend on the angle of internalfriction δ and are given in Ref. [104]. Where the crater expan-sion line intersects the Df versus hD graph the rathole be-comes critically stable. This defines the draw-down. Abovethis level the bulk solid sloughs off at angle approximatingthe effective angle of internal friction δ.

With the crater geometry determined as described, the pre-dicted live capacity can be readily obtained using by compu-ter simulation employing a suitable CAD package. As an ex-ample, Fig. 21 shows the simulation of a kidney-shaped ironore stockpile with twin outlets. The model was produced inadvance of the plant construction to predict the live capacity

han

Fig. 19: Gravity reclaim stockpile

Fig. 20: Determination of rathole geometry and stockpiledraw-down




and feeder loads. The photograph of the stockpile duringsubsequent operation indicates good agreement with theCAD model.

5.4 Areas for Further ResearchThe stockpile studies have highlighted areas for further re-search, particularly in the prediction of rathole geometryduring funnel-flow. It is noted that J has undertakenwork in this area with respect to funnel-flow and expandedflow bins, where the diameter of the bin is shown to have aninfluence on the rathole geometry [69]. This is not taken intoaccount in the original J theory. Since in the case of grav-ity reclaim stockpiles, there are no defining bin wall bounda-ries, the problem is more complex.

6 Feeding of Bulk Solids

There are many types of feeders such as belt, apron, oscillat-ing plate, screw, vibratory, rotary table, plough and rotaryvalve and their selection is based on the particular processrequirements and properties of the powder or bulk solid. Ingeneral, the subject of feeder loads and feeder design andperformance has been researched in some detail [105-120].

Two principal objectives need to be met. Firstly, to achievethe correct interfacing of the feeder with the mass-flow hop-per for optimum draw-down without segregation. Secondly,to determine the feeder loads and drive powers for bothstart-up and running conditions. These two objectives arebriefly discussed.

6.1 Hopper/Feeder InterfacingAs an example, the interfacing problem of belt feeders andmass-flow hoppers, illustrated in Fig. 22, has also been stud-ied in some detail by S and S [107], and byR [108]. The primary aim is to achieve uniform draw-down in the hopper in order to avoid localised wear of theback or front walls of the hopper depending on the flow pat-tern as well as avoiding segregation problems. As shown byR, the optimum divergence angle λ for uniform drawdown along the hopper varies with the length to width ratio,L/B, as illustrated in Fig. 23.

As a further example, the case of screw feeders is considered,where the optimum draw-down is achieved by combinations ofexpanding pitch and tapered shaft as illustrated in Fig. 24. Whereit is necessary to smooth the discharge, such as when feeding intoa pneumatic conveying system, this may be achieved by a combi-nation of plug extrusion and multi blade rotary scraper as illus-trated in Fig. 25 [111]. It needs to be noted that multiple startscrews give rise to jamming and should not be used [110].

6.2 Feeder Loads and Drive PowerThe determination of feeder loads and drive powers requires aknowledge of the stress fields generated in the hopper. The re-lationship between the vertical pressure pv generated in amass-flow bin during both filling and flow and the feeder loadV is illustrated in Fig. 26. Under filling conditions, a peaked or‘active’ stress field is generated throughout the entire bin asshown. Once flow is initiated, an arched or ‘passive’ stress fieldis generated in the hopper and a much greater proportion ofthe bin surcharge load on the hopper is supported by the up-

a) CAD Simulation of Draw-Down Cratersb) View of Actual Stockpile Showing Draw-Down and Craters

Fig. 21: Simulation and draw-down performance of iron ore stockpile

Fig. 22: Belt and apron feeders

Fig. 23: Optimum divergence angle versus L/B ratio for a range ofclearance ratios ηV = 0.75; Ce = 0.5




per part of the hopper walls. Consequently, the load acting onthe feeder substantially reduces as shown in Fig. 26(b).

It is quite common for the load acting on the feeder under flowconditions to be in the order of 20% of the initial load.The archedstress field is quite stable and is maintained even if the flow isstopped.This means that once flow is initiated and then the feed-er is stopped while the bin is still full, the arched stress field is re-tained and the load on the feeder remains at the reduced value.

The work on feeder loads [108] allows good predictions ofrunning torques and powers to bemade. Referring to the beltor apron feeder of Fig. 22, the analysis requires considerationof the various components of the drive resistance based onthe loading conditions depicted. These components are:

• shear resistance of bulk solid along shear surface

• skirtplate friction in the hopper zone and in the extendedzone beyond the hopper

• belt or apron support idler friction due to combined bulksolid and belt or apron load

• slope resistance due to the inclination (or declination) ofthe feeder

An important aspect of the design is to ensure that the hop-per and feeder interface geometry is satisfactory to ensurethat there is sufficient friction between the belt or apron sur-face to effect feeding without slip and consequent accelerat-ed wear of the feeder surface.

6.3 Controlling Feeder LoadsThe loads on feeders and the torque during start-up may becontrolled by ensuring that an arched stress field fully or par-

tially exists in the hopper just prior to starting. This may beachieved by such procedures as:

• Cushioning in the hopper, that is leaving a quantity ofmate-rial in the hopper as buffer storage. This preserves thearched stress field from the previous discharge

• Starting the feeder under the empty hopper before fillingcommences.

• Using transverse, triangular-shaped inserts

• Raising the feeder up against the hopper bottom duringfilling and then lowering the feeder to the operating condi-tion prior to starting. In this way an arched stress field maybe fully or partially established.

The choice ofmounting arrangement for a feeder can assist ingenerating a preliminary arched stress field near the outletsufficient to moderate both the initial feeder load and start-ing power. In some cases belt feeders are mounted on helicalsprings, where the initial deflection of the springs during fill-ing of the bin can assist in generating an arched pressure fieldnear the outlet and reduce the initial load. An alternative ar-rangement is to incorporate a jacking system to lift the feederup against the bottom of the hopper during filling. Beforestarting, the feeder is released to its operating position suffi-cient to cause some movement of the bulk solid in order togenerate a cushion effect. The use of a slide gate or valveabove the feeder is another way of limiting the initial loadand power. The gate is closed during filling and opened afterthe feeder has been started.

For ‘emergency’ purposes, the provision of jacking or capstanscrews as illustrated in Fig. 27 can be used to lower the feedershould a peaked stress field be established on filling and thereis insufficient power to start the feeder. Lowering the feedercan induce, either fully or partially, an arched stress field and

Fig. 24: Screw feeder

Fig. 25: Smoothing discharge

Fig. 26: Vertical pressure and load variations on feeder

Fig. 27: Use of jacking screws to lower the feeder




allow the feeder to be started. This precaution is useful forfeeders installed under stockpiles where surcharge pressuresas high as 1000 kPa may be experienced.

6.4 Further ResearchThere is a need for more fundamental research into the stressfields in the feed zones associated with the hopper and feederinterface. Using a continuum approach, this is a three dimen-sional stress problem.The current theories, as outlined in Sec-tion 6.2, are mainly based on a lateral two dimensional stressfield in the hopper with the application of ‘equivalent’ frictioncoefficients to allow the shear forces in the orthogonal direc-tion to the plane of stress symmetry to be computed.

7 Numerical and Experimental Simulation

Current advances in continuum and discrete element me-chanics, and their associated computational methods FEAand DEM respectively, are also helping push the frontiers ofparticle and bulk solids technology forward at an impressiverate. Such advances have been made possible through therapid developments of modern computing systems. Even so,the simulation of bulk granular solids by FEA andDEM can becostly in terms of computer time. While, for example, DEM iscurrently limited by the number, size range and shape of par-ticles to be handled, the method is particularly useful forstudying localised flow behaviour such as the interface zonesof hoppers and feeders. For such modelling to be accurate,the need for research into the constitutive relationships todescribe the bulk material assumes a high priority.

There is much to learn from the physics of particle interac-tions and considerable work has been done on this subject.As an example, the work of D [121] and of T- [122] is mentioned, as is the work of the author in theexamination of the energy losses due to boundary and inter-granular friction in chute flow [127]. There are many others,including those involved in the sixties with the gravity flow ofspheres in hoppers as part of the work at that time in nuclearscience when pebble bed reactors were in vogue. There arenow numerous papers showing DEM applied to a wide rangeof bulk solids handling problems. As an example, the work ofC [123] in simulating the operation of a ball mill is cited.A critical review of DEM has been presented by T [124].

In acknowledging the developments in numerical simulation,it is important not to neglect the ‘old and tried’ method ofexperimental simulation employing dimensional analysis anddynamic similarity. These procedures have been successfullyadapted inmodel testing and prototype performance predic-tion of a range of bulk solids handling equipment and opera-tions. These include gravity discharge from bins and bulk railwagons, stockpiles, screw conveyors for grain handling andlarge feeding equipment for handling run-of-mine (R.O.M.)prior to the primary crushing operation [125,126]. As an il-lustration, the simulation of the ROM feeder shown in Fig. 28is briefly reviewed.

Themechanics of such feeders as described in the cited refer-ences is based on several industrial projects performed at theUniversity of Newcastle. The feeding action is made possibleby the geometry of the hopper, which should be of mass-flow

design, and the inclination angle of the feeder. Since there isno front face in the hopper and shear gate, the feeding actionin this case is made possible by both the large inclination an-gle θ and release angle ψ. Typically, inclination angles rangefrom 18o to 26o.

While the scale for the model in relation to the prototype isselected largely on practical grounds, account must be takenof the measured flow properties of the bulk solid. The non-dimensional consolidation stress parameter Nσ1 is relevant inthis case

where σ1 = consolidation stress, ρ = bulk density and x =characteristic dimension, which may be the head of bulk sol-ids, h, or the hopper opening dimension B.

The corresponding speeds for the model tests are governedby the Froude Number

Hence the corresponding speed for the model tests is given by

where the subscripts “m” and “p” refer to the “model” and“prototype” respectively.

Thenon-dimensionalparameters governing themass through-put Q, torque T and power P are respectively,

8 Chutes for Feeding and Transfer

8.1 Chute Design ObjectivesThe efficient operation of belt conveyors depends onmany fac-tors, not the least of which is the effective loading or feeding ofbulk solids onto the belts at the feed end as illustrated in Fig. 29.Not only is the chute required to direct the bulk solid onto thebelt without spillage, but it must also accelerate the flow so

Fig. 28: Open front, inclined apron feeder




that at the point of discharge onto the belt, the horizontalcomponent, vey, of the discharge velocity matches, as close aspossible, the belt speed. For accelerated flow, it has been estab-lished that a lumped parameter model provides a satisfactoryway of analysing the flow for chute design purposes. An equiva-lent friction factor is introduced in order to account for bound-ary and inter-particle friction losses [127,131,132,134]. For thechute to be self cleaning during start-up after stopping, the cut-off angle ψ is governed by the condition, ψ > tan-1 (µe) + 5o.

Chute design needs to take wear into account. Chute wear isa combination of impact and abrasive wear. Impact wear mayoccur at points of entry or points of sudden change in direc-tion. Abrasive wear is a function of the normal pressure, thefriction coefficient and velocity at the chute boundaries. Itmay be expressed in non-dimensional form as

Chute geometry has an important influence on the perform-ance and wear.This is illustrated in the case shown in Fig. 30 inwhich three chute profiles are compared, constant curvature,

parabolic and optimum [135]. The optimum profile is deter-mined using an evolutionally computational technique thatmimics the process of biological “natural selection” based onthe work of W [136]. The particular case concerns thetransfer of Bauxite at a feed rate of 300 t/h from the belt feed-er with an effective width of 1.0 and speed of 0.1 m/s. Thedrop height HT = 2.5 m and the receiving belt speed is travel-ling at a speed of vb = 4 m/s. The bulk density of the bauxite is1.4 t/m3. The friction angle for the bauxite on the chute sur-face is φ = 25o and the chute cut-off angleψ = 35o for which θo= 55o. Since the feeder speed is quite small, it is assumed thatthe initial chute velocity Vo ≈ 0. Based on the measured wallfriction angle and flow pattern, an average value of the equiv-alent friction coefficient µe = 0.5 is assumed.

All three chute profiles satisfy the cut-off condition of θo =55o, and the “optimum” profile has been constrained to finishat the same point as the parabolic chute.The optimumprofileis remarkably similar to the parabolic chute. The difference ismainly in the first 1-1.5 m of the profile where the optimumchute has a slightly tighter radius of curvature. The velocitydistributions for the three chutes are shown in Fig. 31 and thecorresponding wear profiles are plotted in Fig. 32.

Fig. 33: Transfer chuteFig. 29: Feeding onto a belt conveyor

Fig. 30: Chute profiles Fig. 31: Chute velocity profiles Fig. 32: Chute wear distributions




8.2 Transfer ChutesTransfer chutes are employed to direct the flow of bulk materialfrom one conveyor belt to one or more conveyors, often via athree dimensional path. An example of such a transfer chute isshown in Fig. 33. In this case the delivering and receiving con-veyors are at 90o to each other.

8.3 Chute Design for Dust Control in Grain LoadingOperations

In grain loading operations, such as employed in loadingships, dust generation is a recurring problem. In view of thelarge drop heights, the grain velocities, which often reach ter-minal conditions, are well above the dust pick-up velocities.Slowing the grain velocities by using cascade chutes hasshown to be unsuccessful since there is excessive dust emis-sions from the top feed end of the chutes. Research conduct-ed at the University of Newcastle has shown that a much bet-ter approach is to entrain the dust within the flowing grainstream [137]. This has been achieved using the arrangementshown in Fig. 34(a) which consists of a long radius spoonload-out chute that is fitted with an air-restrictive flap. For agiven grain mass flow rate, the flap is designed to rest justabove the grain stream exiting the spoon. In the pilot scaletests, the flap consisted of a thin steel backing plate with at-tached reinforced rubber lip to allow for automatic adjust-ment for sudden changes in the productmass flow rate. Fromvisual observation, the flap successfully diverts the air streaminto the product stream exiting the spoon outlet. During pi-lot scale tests, reductions in dust emissions as much as 80%were recorded. In order to examine the risk of the flap result-ing in a pressure increase within the vertical chute, the topsection of the chute was vented to atmosphere, simulatingthe conditions on site. The tests showed no visible dust es-caping from the top vent. The engineering consulting com-pany, Sinclair Knight Merz, hasapplied the dustless chute de-sign to a grain ship loading fa-cility involving four load-outchutes. One of the chutes isshown in Fig. 34(b). Significantreductions in dust emissionshave been achieved.

9 Belt Conveying - Bulk Solids/ConveyorBelt Interactions

9.1 General RemarksOf the variousmodes of continuous conveying of bulk solids,belt conveyors are of considerable importance in view oftheir widespread use and proven reliability. Conventionaltroughed belt conveyors have been used extensively in in-dustry over a long period of time. While their usage is largelyassociated with in-plant movement of materials, their appli-cation to long distance overland transportation is now wide-ly established. This has been made possible through the de-velopment of steel cord reinforced belts, better quality con-trol in the belt manufacture, improved reliability and lifethrough the application of belt condition monitoring andgreatly improved design methodologies. There is a wealth ofpublished literature on the subject of belt conveying; a selec-tion of papers that illustrate the developments that havetaken place are given in a review paper by R [138].

Notable achievements in conveyor design include analysesof belt conveyor dynamics during starting and stopping,belt vibration analysis and improved models to predict belttracking under various loading and conveyor curvature con-ditions. Combinations of horizontal and vertical curveswhich permit conveyors to be effectively integrated into theterrain over which they traverse are now a proven reality.Modern installations include single flight lengths of 10 to 15km, increased belt speeds and increased tonnages typically2000 to 6000 t/h with one known installation in Germanyhaving a capacity of 37000 t/h. Developments in belt mate-rials include Aramid fibre reinforced belts which offer sig-nificant advantages due to weight reduction. The applica-tion of booster drives to reduce tensions in long overland

conveyors is a matter of some interestbut difficult to implement in practice

Recent research has shown that beltsranging in widths from 800 to 1200mm are the most viable in terms ofeconomics and efficiency. In this way,belt tensions are kept to acceptablelimits allowing longer, individual con-veying distances to be realised for thegiven range of belt SR values commer-cially available. For large tonnages, theuse of belts within the above men-tioned range of widths and running athigher speeds provides the best solu-tion.

With regard to belt speeds, the eco-nomic evaluations clearly highlightthe advantages of employing speedsgreater than 6 m/s where large ton-nage throughputs are involved. Forexample, a 9.4 km long bauxite con-veyor in Western Australia with 1060mm wide belt is operating at 7.3 m/s.This conveyor has machined and bal-anced idlers to reduce the noise emis-sion. Conveyors operating at speeds of8 and 9 m/s are a known reality and

Fig. 34: Constant radius spoonwith air restriction flap

a) Schematic of chute

b) Installation onship loader




speeds up to 16m/s are currently being investigated for longdistance transport.

The following list highlights some recent and current advanc-es in conveyor research and development:

• Conveyor dynamics - starting and stopping characteristicsand dynamic belt stresses.

• Transverse vibrations of conveyor belts and the associatedinfluence of idler spacing and troughing configurations onsuch vibrations.

• Conveyor belt idler resistance taking into account belt rub-ber hardness, sag, troughing configuration, idler/belt in-dentation and ambient operating temperature.

• Conveyor transition geometry.

• Stability of bulk solid on conveyor belts during motion onhorizontal and vertical curves.

• Conveyor belt/drive drum friction taking into account rub-ber hardness, surface roughness wrap angle.

• Steel cord splice design and analysis.

• Conveyor belt monitoring as applied to steel cord and fab-ric belts

• Belt rip detection employing ultra sonic devices.

• Belt tension monitoring during operation.

• Belt cleaning including carry back measurement and devel-opment of improved cleaning efficiencies.

• Economic analysis applied to conveyor design.

• Booster drives to reduce belt tensions and permit longerindividual flight length.

• Design of horizontal curves.

• Improved quality control in belt and component manufac-ture.

• Special belt conveyors such as the pipe belts, aero belt andSicon belt

It is beyond the scope of this paper to review the various as-pects of the foregoing developments. In keeping with the fo-cus on the handling of bulk solids, the area of belt conveyor of

Fig. 35: Bulk density and packing ratio for coal

Fig. 36: Conveyor load model

Fig. 37: Belt velocities for slip and lift offµE = 0.5; X = 1.0 m; σo= 0

interest concerns the interaction between the bulk solid andthe conveyor belt [139]. Some aspects are now discussed.

9.2 Correct Choice of Bulk DensityIn the past, insufficient attention has been given to the cor-rect choice of bulk density when determining the conveyorthroughput. Bulk density varies with the consolidation stressor pressure as illustrated by the results for a coal sampleshown in Fig. 35. Also shown is the packing ratio based on themeasured solids density.

As discussed in Ref. [139], when loading a bulk solid onto a beltconveyor, the bulk density will increase an amount Δp fromthe initial loaded condition, “L”, to the running condition, “R”,as illustrated in Fig. 35. At the load point the bulk density cor-responds to the major consolidation stress σ1L defined as




During running, after the load has settled, the bulk densitycorresponds to the dynamic major consolidation pressureσ1D defined as

where v = belt velocityKs = sag ratioX = idler spacingh = average height of bulk solid on belt

Research has shown that the increase in bulk density Δρ/ρ isin the order of 12% to 14%. This corresponds to the amountof load settlement.

9.3 Slip Back and Lift Off During ConveyingReferring to Fig. 36, as the belt moves between the idlers, thebulk solid is subject to transverse acceleration in ‘y’ direction. Asdiscussed in Ref. [139], this can result inreduced bulk solid and belt surface frictionleading to slip during inclined conveying. Ifthe belt speed is fast enough, then lift-offand fall-back may occur. Both slip and lift-off can give rise to spillage. The problemsbecome more pronounced at higher beltspeeds indicating that low sag ratios mustbe achieved and thismay result in the needto employ reduced idler spacing.

As an example, Fig. 37 shows the belt ve-locities for slip and lift-off as a function ofconveying inclination angle for belt sag ra-tios of 0.2% and 0.5%, idler spacing of 1.0 mand an equivalent friction factor of 0.5 forthe bulk solid in contact with the troughedbelt. The adhesive stress between the bulksolid and belt surface is taken to be zero.

At higher belt speeds, lower sag ratios must be employed.The influence of sag ratio on belt speeds for slip and lift-off fora conveyor inclined at 10o is shown in Fig. 38. The idler spac-ing in this example is X = 1 m. If, for example, a conveyingspeed of 15m/s is required, the sag ratio for X = 1mmust notexceed 0.0014 or 0.14%.

The interaction of bulk materials with belt conveyors hasbeen an ongoing research interest of the University of New-castle for several years. This work has involved a series of ex-perimental studies using a specially designed conveyor simu-lation test rig. The essential details of this rig are illustrated inFig. 39. This rig is used to simulate the conveying motion onhorizontal curves as well as inclined conveying.

9.4 Flexure of Bulk Solids on Conveyor Belts in Relationto Idler Resistance

There are many other applications of bulk solids handlingthat could be cited. As one further illustration, the flexing ofthe bulk solids during the motion of the belt as it moves overthe idlers is of particular interest. As the belt travels from oneidler set to the next, the bulk solid undergoes changes in thestress field from active to passive as illustrated in Fig. 40. Inlong distance overland conveying, this may contribute asmuch as 25% of the power consumption.The flexing problemhas been studied in some detail by W [140,141].

10 Mechanical Conveying - Importance OfFlow Properties

Apart from belt conveyors as discussed in the last section,there are a number of different types of mechanical conveyorsused in bulk solids handling operations, particularly for in-plant conveying loading and unloading and transfer. Typicalexamples include special belt, screw, bucket, chain and vibra-tory [138-142]. As in the case of belt conveyors, it is particu-larly important that the design of all mechanical conveyorstake into account the relevant flow properties of the bulksolid being conveyed. The following example illustrates theimportance of this approach.

Fig. 38: Belt velocities for slip and lift off as function of sagconveyor slope = 10o; µE = 0.5; σo = 0

Fig. 39: Photograph of test rig loaded with coal




Fig. 41 shows a ‘Siwertel’ type vertical screw conveyor used ata port facility for unloading coal from bulk ships [142]. Thescrew conveyor is forced fed by means of a counter rotatinglower casing with feed vanes as illustrated. Hence the capac-ity of the screw conveyor is controlled by the feeding deviceand not by the conveyor itself. To avoid blockages in thescrew intake, it is essential that the conveyor speed is highenough for the fill ratio ηF < 1.

In the example being considered, the screw has a diameter of790 mm with pitch of 540 mm and is 27 metres high. Theunloader failed to deliver the design throughput of 1400 t/hat 400 rev/min with the installed motor power of, nominally,430, kW. Samples of the coal were delivered to the Universityof Newcastle for testing. The moisture content of the coal,as-supplied, was 27%, which was at the top end of the speci-fied moisture level for acceptance. As it so happened, thismoisture content corresponded to the level at which thecoal gained its maximum bulk cohesive strength. It was thealso the level at which the coal has its lowest bulk densitywhich partly accounts for the possible shortfall in tonnagethroughput.

However, the most significant factors influencing the per-formance of such a screw elevator concerns the friction gen-erated between the bulk solid, in this case the coal, and thescrew and casing surfaces. The friction angles as functions ofnormal contact pressure for the coal in contact with steelsurfaces deemed to be similar to that of the screw and casingof the actual unloader were determined. The friction anglesfor the screw and casing so determined gave a value of 25ocorresponding to the relevant normal pressures. These valuesand the measured bulk densities were used to evaluate thescrew unloader performance for the specified throughput of1400 t/h. Under forced feeding at 1400 t/h, it was recom-mended that the feeder operate at or above 300 rev/min forwhich the fill ratio was calculated to be 74%. This fill ratio isdeemed to provide a satisfactory margin against jamming orblockages.The operating speed of 400 rev/min was chosen bythe consulting engineers on site.

The power versus screw speed graphs are illustrated in Fig.42. Also shown is the variation of screw fill ratio as a functionof speed. For the 400 rev/min, the required power for thescrew is 600 kW, this being the power that was finally in-

stalled. It is interesting to note that as polishing of the screwsurface takes place with use, and at lower moisture levels ofthe coal which give rise to less cohesion, the friction angle forthe coal on the screw surface could reduce. As an illustration,the power versus speed curve for the throughput of 1400 t/hfor a screw surface friction angle of 20o, and casing frictionangle of 25o is also illustrated in Fig. 16. At 400 rev/min, a re-duction of 5o in the screw surface friction angle reduces thepower from 600 kW to 400 kW, a reduction of 33%, which isquite significant.

11 Concluding Remarks

The past 125 years has seen a remarkablegrowth in the knowledge of the way pow-ders and bulk solids behave during thevariety of processing and handling opera-tions occurring in practice. In particular,the expansion of the knowledge base overthe past 50 years has been very significantindeed and there is absolutely no doubtthat the discipline of Bulk Solids Handlingis now firmly established as a professionaldiscipline in its own right. So much hasbeen achieved that it has been only pos-sible in this review paper to outline somesalient developments.

Figure 40. Dynamic Stress Sates in Bulk Solids During Belt Conveying (Wheeler [140]).

Fig. 41: Screw conveyor for ship unloading

Fig. 42: Power and fill ratio for ship unloader screwD = 790 mm, p = 540 mm, H = 27 m




“Resources are limited;Creativity is unlimited”

“Resources are limited; Creativity is unlimited“Resources are limited;“Resources are limited; Creativity is unlimited“Resources are limited;

References

[] R, A.W.: Particle Technology - Reflection andHorizons: An Engineering Perspective; Transactions,Institution of Chemical Engineering, Part A, Vol 76(1999) No A7, pp 775- 796.

[] J, H.A.: Versuche über Getreidedruck in Silozel-len (On the Measurement of Pressures in Grain Silos).Zeitschrift des Vereines Deutscher Ingenieure (1895)pp. 1045-1049.

[] J, J.A.: Grain Pressures in Deep Bins; Trans.Canadian Society of Civil Engineers, Vol. XVII (1903).

[] J, J.A.: Grain Pressures in Deep Bins; Engineer-ing News, Vol. LI (1904) No.10, pp. 236-243

[] S, J.H., and J.C. E: The Variation of Pressurewith Depth in Columns of Powders; Proc. Faraday So-ciety, (November 1922) pp. 60-72.

[] D, W.E., and A.L. M: The GravitationalFlow of Fertilizers and Other Comminuted Solids; In-dustrial and Engineering Chemistry. Vol. 21 (1959).

[] B, E.C., and R.W. W: The Flow of DrySand through Capillary Tubes. Jnl. of Rheology, Vol. 2(1931), No. 4.

[] W, E.F., and H.L. V H: ExperimentalStudy of the Flow of Coal in Chutes at the RiversideGenerating Station; Trans, ASME, Vol. 67 (1945).

[] B, R.L., and P.G. H: Internal Flow ofGranular Masses; Fuel. Vol. 26 (1947).

[] F, F.C., and L.N. J: Flow of GranularSolids Through Orifices; Chem. Eng. Science, Vol. 10(1955).

[] R, H.F., and T. T: Rate of Discharge of Granu-lar Materials from Bins and Hoppers; The Engineer,Vol. 208 (1959).

[] B, R.L., and J.C. R: Exploratory Study ofthe Flow of GranulesThrough Apertures; Trans. Instn.of Chem Engrs. Vol. 37 (1959) No. 2.

[] B, R.L., and J.C. R: Profile of Flow ofGranules Through Apertures; Trans. Instn. of ChemEngrs. Vol. 38 (1960) No. 5.

[] B, R.L.: Minimum Energy Theorem for Flow ofDry Granules Through Apertures; Nature, Vol. 191(1961) July 29.

The field of bulk solids handling has greatly benefited by ahealthy blend of fundamental and applied research. This hasbeen the underlying philosophy of many universities and re-search centres throughout the world specialising in this area. Inacknowledging the importance of unconstrained fundamentalresearch in view of the ‘spin offs’ to practical applications thatmay and do occur, the maintenance of a close rapport with in-dustry is essential to the objectives of providing strong guidancein directing research to the solution of important practicalproblems. The complexity of problems in industry often multi-ply at a faster rate than current research outcomes. Hence, inmany cases, research has to play a ‘catch up’ role. The ongoingprofessional development of the discipline depends to a verysignificant extent on the undergraduate, graduate and continu-ing education programs. International conferences focusing onthe science, technology and practice of the discipline of bulksolids handling will continue to have an important role to play.

In a climate of an ever expanding information and knowledgebase, the emerging generations of researchers in our field willneed to be more discerning than ever before. They will needto filter out the “signals” from the “noise” and not overlookthe important “classical” research contributions over the pastcentury that laid the foundations for the disciplines. Theyshould select the right problems to solve and not simply “re-invent the wheel”. They should be strongly encouraged to re-gard modern computer and instrumentation technology as a‘means to an end’ and not as ‘an end in itself’. The disciplinesof Particle and Bulk Solids Technology impact our lives in somany ways. The future is challenging and exciting.

“Resources are limited; Creativity is unlimited”

(Message spanning entrance gates of POSCO, Pohang Ironand Steel, Korea). ■

A. W. Roberts

Emeritus Professor Alan Roberts AM,holds BE and PhD degrees from theUniversity of NSW, Australia, as wellas two honorary doctoratesand is aFellow of the Australian Academy ofTechnological Sciences and Engineering. He has had over40 years experience in bulk materials handling researchand consulting. After retiring from the University ofNewcastle, where he was Dean of the Faculty of Engi-neering for just on 20 years, he remains as Director of theUniversity’s R&D company, TUNRA Bulk Solids whichhe established 31 years ago and which is currently aver-aging around 130 projects a year for industry. He is theauthor of numerous publications and has received sev-eral honours and awards.

About the Author




[] O’C, J.R.: Internal Flow in Moving Beds ofGranular Materials; J. Agric. Engng. Res. Vol. 5 (1960)No. 2.

[] B, R.F.: Rational Method for Selecting ScrewConveyors; Chem. Met. Engnr., Vol. 42 (1934) No. 9,September, p. 470.

[] G, E.M.: Elementarnaya Teoriya VertikalnovoVintovovo Transportera; Trudy Mosk. Inst. Mekh. iElek. Slesk. Khoz. im. V.M. Molotov (1956) No. 2, p.102.

[] R, G.E.: Performance Characteristics of FarmType Auger Elevators; Paper presented to North At-lantic Section, American Society of Agricultural Engi-neers, Sept. 1-3, 1959.

[] B, A., and W.L. S: Verticaal Transport metSchroeftransporteurs. Orgaan van Het NetherlandsInstituut van Register-Ingenieurs en Afgestudeerenvan Hogere Technische Scholen, 4-15c Jaarg (1960),February, p. 159.

[] R, A.W. and A.H. W: Performance of GrainAugers; Proc. Instn. of Mech. Engrs. U.K. Vol. 176(1962) No. 8, pp. 165-194.

[] R, A.W.: An Investigation of Grain Vortex Mo-tion with Relation to the Performance of VerticalGrain Augers, Part 1; Proc. Instn. of Mech. Engrs. U.K.Vol. 178 (1963-64) No. 12, pp. 293-310.

[] D, J.M.: Micromeritics; Pitman. 1st Edition(1943), 2nd Edition (1943)

[] H, M.J.: On the Physical Properties of Distrib-uted Cohesive Soils. Ingeniorvidensk Skr. 45 (1937).

[] R, K.H., A.N. S, and C.P. W:1958On the Yielding of Soils. Geotechnique 8. 22-53.

[] J, J.R.: Theory of Bulk Solids Flow - A Histori-cal Perspective; Intl.. Jnl. of Bulk Solids Storage in Silos.Vol. 3 (1987) No. 1, pp. 1-15.

[] S, V.V.: Statics of Soil Media; Butterworths(1960).

[] P, W., and G. H: Theory of Perfectly PlasticSolids; New York Dover Publications (1968) (OriginalWork 1951).

[] H, R.:TheMathematicalTheory of Plasticity; Claren-don Press, Oxford (1983).

[] J, A.W., and R.T. Shield: On the Plastic Flow ofCoulomb Solid Beyond Original Failure. ASME Jnl.App. Mech. (1959).

[] J, A.W.: Gravity Flow of Bulk Solids; Bul. 108(1961), The Univ. of Utah, Engng. Exp. Station, USA

[] J, J.R.: Stress and Velocity Fields in the Gravi-ty Flow of Bulk Solids; Bul. 116 (1961), The Univ. ofUtah, Engng. Exp. Station, USA.

[] J, A.W.: Storage and Flow of Solids; Bul. 123, TheUniv. of Utah, Engng. Exp. Station, USA (1964).

[] J, J.R.:. Stress and Velocity Fields in the Grav-ity Flow of Bulk Solids; ASME, Jnl. of Appl. Mechanics,Vol. 131 (1964), Ser. E, No. 3, pp. 499-506.

[] J, A.W.: A Theory of Flow of Particulate Solids inConverging and Diverging Channels Based on a Coni-cal Yield Function; Powder Tech., Vol. 50 (1987), pp.229-236.

[] B, E.J.: Flow and Stress Analysis of CohesionlessBulk Materials in Silos Related to Codes; DoctoralThesis,The University of Twente, Enschede,The Neth-erlands (1989).

[] S, J.: Testers for Measuring Flow Properties ofParticulate Solids; Proc. International Symposium onthe Reliable Flow of Particulate Solids III, Porsgrunn,Norway 1999.

[] Standard Shear Testing Technique for Particulate Sol-ids Using the Jenike Shear Cell. Report of the EFCEWorking Party on theMechanics of Particulate Solids,Published by the IChemE. 46p.

[] S, D.: New Ring Shear Tester for Flowabilityand Time Consolidation Measurements; Proc. FirstIntl. Particle Technology Forum, Part III, AIChE, Den-ver, Co. (1994), pp. 11-16.

[] Australian Standard AS 3880-1991. Bin Flow Proper-ties of Coal. Standards Association of Australia.

[] D6128-00 Standard Test Method for Shear Testing ofBulk Solids Using theThe Jenike Shear Cell.

[] D6773-02 Standard Test Method for Shear Testing ofBulk Solids Using the Schulze Ring Shear Tester

[] J, J.R.: The Johanson IndicizerTM System vs.the Jenike Shear Tester; bulk solids handling Vol. 12(1992), pp. 141-144.

[] B, T.A., B.J. E, R.J. G, W.J.F. S, andS, M.M.: Practical Evaluation of the JohansonHang-Up Indicizer; bulk solids handling Vol. 14 (1994)No.1, pp. 117-125.

[] The Development of a True Biaxial Shear Tester; Parti-cle Charact. Vol. 2 (1985), pp. 149-153.

ted




[] H, J. and J. S: Influence of Stress Historyon the Yield Limit of Bulk Solids. Proc. Second Intl.Conf. on Bulk Materials Storage, Handling and Trans-portation. Instn. of Engrs. Australia (1986). 94-97.

[] M, L.P.: Investigation of the Behaviour of PowdersUnder and After Consolidation. Doctoral Thesis, Tele-mark Institute of Technology, Porsgrunn, Norway (1993).

[] J, R.J.M., M. K, and B. S: Eval-uation of the Flexible Wall Biaxial Tester for the Meas-urement of BCR-Limestone; Proc. 6th InternationalConference on Bulk Materials Storage, Handling andTransportation,The Instn. of Engrs. Australia, Wollon-gong, NSW, Australia (1998), pp. 47-50.

[] M, L.P., and G.G. Enstad: Uniaxial Tester for QualityControl and Flow Property Characterisation of Powders;bulk solids handling Vol.13 (1993) No.1, pp. 135-139.

[] K, A., D. Schulze, and J. Schwedes: Determina-tion of the Stress Ratio in Uniaxial Compression Tests- Part 2; powder handling and processing Vol. 6 (1994)No. 2, pp. 199-203.

[] L, E.H., J.Y. O, J.M. R, and S. P:Assessment of Coal Handleability; Proc World Con-gress on Particle Technology 3, Brighton, UK (1998).

[] W, S.J., A.W. R, and W.A. MB: Flowa-bility Tester for Characterising Bulk Solids; Proc. 8thInternational Conference on Bulk Materials Storage,Handling and Transportation,The Instn. of Engrs. Aus-tralia, Wollongong, NSW, Australia (2004), pp. 79-83.

[] R, A.W., M. O, and O.J. S: Influence ofVibrations on the Strength and Boundary FrictionCharacteristics of Bulk Solids and the Effect on Bin De-sign; bulk solids handling, Vol. 6, No.1, February 1986.

[] R, A.W.: Vibrations of Fine Powders and itsApplication. Chapter 6, Handbook on Powder Sci-ence & Technology, (eds M.E. Fayed and L. Otten),2nd Edition, Chapman and Hall, London (1997).pp146-201.

[] K, T., J. T: The Influence of Vibra-tions on Flow Properties of Cohesive Powders. Proc.7th International Conference on Bulk Materials Stor-age, Handling and Transportation, The Instn. of Engrs.Australia, Wollongong, NSW, Australia (2001). pp.417-427.

[] R, A.W., Ooms, M. and Wiche, S.J.: Concepts ofBoundary Friction, Adhesion and Wear in bulk solidshandling Operations; bulk solids handling Vol. 10(1990) No. 2, pp. q189-198.

[] R, A.W.: Bulk Solids Handling - Recent Develop-ments and Future Directions. bulk solids handling, 10thAnniversary Edition, Vol. 10 (1991), No. 1. pp. 17-35.

[] R, A.W., L.A. S, and S.R. S: The Inter-action of Bulk Solid Characteristics and Surface Param-eters in Surface or Boundary Friction Measurements;Tribology Intl. Vo. 26 (1993) No. 5. pp. 335-343.

[] J, J.R., and T.A. R: Measuring and Use ofWear Properties for Predicting Life of Bulk MaterialsHandling Equipment; bulk solids handling Vol. 2(1982) No. 3, pp. 517-523.

[] W, S.J., S. K, and A.W. R: Abrasive WearTester for Bulk Solids Handling Applications; Wear, El-sevier No. 258 (2005), pp. 251-257.

[] R, A.W., M.G. J, C.A. W, and S.J.W: Controlling Consolidation Pressures, BulkDensity and Permeability in Storage Vessels for Com-pressible Bulk Material; Proc 8th Int. Conf. on BulkMaterials, Storage, Handling and TransportationWol-longong, July 2004. (pp.424-428)

[] Australian Standard, AS 4156.6-2000. Coal Prepara-tion. Part 6: Determination of Dust/Moisture Rela-tionship for Coal

[] ML, A.G.: Flow Rates of Simple Bulk Solids fromMass-Flow Bins; Ph.D. Thesis, The University of Wol-longong (1979), Australia.

[] A, P.C., and Z.H. G: The Effect of Permeabilityon the Flowrate of Bulk Solids from Mass-Flow Bins.powder handling & processing Vol. 2 (1990) No. 3, pp.229-238.

[] G, Z.H., P.C. A, and A.G. ML: A SimplifiedModel for Predicting Particle Flowrates of a Fine fromMass Flow Bins; Powder Technology, Vol. 74 (1993)No. 1, pp. 153-158.

[] J, J.R.: In-Bin Blending; Chem. Engng. Prog.Vol. 66 (1970) No. 6.

[] J, J.R.: Controlling Flow Patterns in Bins bythe Use of an Insert; bulk solids handling Vol. 2 (1982)No. 3, pp. 495-498.

[] C, D.A., A.W. R, K.S. M, and S.R. S: Utilising the Unit Impulse Concept to Pre-dict Blending Capabilities of Silos. bulk solids han-dling. Vol. 6, No. 4. 373-378.

[] K, C, A.W. R, and D.A. C: TheAnti-Segregation and Blending Characteristics of aMass-Flow Hopper and Rotary Valve; Paper forpresentation at 6th International Conference onBulk Materials, Storage, Handling and Conveying,The Institution of Engineers, Australia, September1998.

[] J, J.R.: Predicting Rathole Stability in Funnel-Flow Bins (1995).






[] J, A.W. and J: On the Theory of BinLoads. Trans. ASME., Jnl. of Engng. for Industry. SeriesB. Vol.91, No.2. 339.

[] J, A.W., J.R. J, and J.W. C: BinLoads - Part 2: Concepts. Trans. ASME., Jnl. of Engng.for Industry. Series B. Vol. 95 (1973), No.1, p. 1

[] J, A.W., J.R. J, and J.W. C: BinLoads - Part 3: Mass-Flow Bins. Trans. ASME., Jnl. ofEngng. for Industry, Series B. Vol. 95 (1973), No.1, p. 6.

[] J, A.W., J.R. J, and J.W. C: Bin Loads- Part 4: Funnel-Flow Bins; Trans. ASME., Jnl. of Engng.for Industry. Series B. Vol. 95 (1973) No. 1, p. 13.

[] W, D.M.: An Approximate Theory for Pressure andArching in Hoppers; Chem. Eng. Sci. Vol 22 (1967). p. 975.

[] W, J.K.: A Theoretical Analysis of Stresses in Siloswith Vertical Walls; Chem. Eng. Sci. Vol. 28 (1973) p. 13.

[] A, P.C., A.G. ML, and A.W. R: BulkSolids Theory, Flow and Handling; The University ofNewcastle Research Associates, Australia (1982).

[] T, O.F.: Failure of Reinforced Concrete Grain Si-los; Trans. ASME., Jnl. of Engng. for Industry. Series B.Vol. 91 (1969) No. 2. p. 460.

[] J, A.W.: Load Assumption and Distribution in Si-lo Design; Conf. on Construction of Concrete Silos.Oslo, Norway.

[] O, M. and A.W. R:The Reduction and Con-trol of Flow Pressures in Cracked Grain Silos; bulk sol-ids handling Vol. 5 (1985) No. 5, pp. 1009-1016.

[] R, A.W.: Some Aspects of Grain Silo Wall Pres-sure Research - Influence of Moisture Content onLoads Generated and Control of Pressures in Tall Mul-ti-Outlet Silos. Proc. Powder and Bulk Solids Confer-ence, Rosemont, Illiniois USA (1988), 11-24.

[] Australian Standard AS3774-1990. Loads on Bulk Sol-ids Containers. Standards Association of Australia.

[] EN 1091-4, Eurocode 1 - Action on Structures. Part 4:Silos and tanks. Final draft December 2005, EuropeanCommittee for Standardization, Central Secretariat,Brussels, Belgium.

[] R, G. and J. E: Numerical Simulation of Fill-ing and Discharging Processes in Silos;Third Intl. Conf.on Bulk Materials Storage, Handling and Transporta-tion, The Instn. of Engrs. Aust., Newcastle, Australia(1989), pp. 48-52.

[] O, J.Y. andM. R: Elastic and Plastic Predictionsof Storing Pressures in Conical Hoppers; Third Intl.Conf. on Bulk Materials Storage, Handling and Trans-portation, The Instn. of Engrs. Aust., Newcastle, Aus-tralia (1989), pp. 203-207.

[] W, Y.H.: Static and Dynamic Analysis of the Flow ofBulk Materials through Silos; Ph.D. Thesis (1990), TheUniversity of Wollongong, Australia.

[] R, C. and J. E: Silo Loading. Proc. FourthWorld Congress of Chemical Engineering. Karlsruhe,Germany 1991, pp. 902-920.

[] R, A.W.: Shock Loads in Silos - The ‘Silo Quak-ing’ Problem; bulk solids handling Vol. 16 (1996) No.2, pp. 59-73.

[] R, A.W., and C.M. Wensrich: Flow Dynamics or‘Quaking’ in Gravity Discharge from Bins. ChemicalEngineering Science Vol. 57 (2002), pp. 295-305.

[] W, C.M.: Analytical and Numerical Modellingof Quaking in Tall Silos; PhD Thesis (2002), The Uni-versity of Newcastle, Australia.

[] W, C.M.: Experimental Behaviour of Quaking inTall Silos; Powder Technology Vol. 127 (2002), pp. 87-94.

[] R, A.W.: Review of the “Silo Quaking” Problemin Bins of Various Geometrical Shapes and Flow Pat-terns”. Task Force Quarterly, Academic ComputerCentre in Gdansk, Poland, Vol 7 (2003), pp. 623-641.

[] G, G. and J. T: Silo Music and SiloQuake. Silos - Forschung und Praxis Tagung ‘92, Karls-ruhe University, pp. 103-110.

[] T, J. andG. G: SiloMusic and Silo-QuakeExperiments and a Numerical Cosserat Approach; Pow-der Technology Vol. 76 (1993), pp. 201-212.

[] S, J., and J. N: Pressure Distribution UnderHeaped Bulk Solids; Proc. Powtech Conference, Ind.Chem. Eng Symp 63 (1981): D3/V/1-D3/V/12.

[] R, A.W., and L.H. T: Design Considerationsfor Maximum Reclaim Capacity of Conical Stockpiles.bulk solids handling Vol. 10 (1990) No. 1, pp. 9-15.

[] L, E. and D.F. B: An IdealisedThree-Dimension-al Model of Heaped Granular Material; Powder Tech-nology 74 (1993), pp. 271-276.

[] B, D.F. and E. L: Further Developments in the3-DMicroscopicModelling of a Heap of GranularMa-terial. Proc. 5th International Conference on Bulk Ma-terials Storage, Handling and Transportation, The In-stitution of Engineers, Australia, Newcastle 10 - 12 July1995, pp. 445-450.

[] B, J., U. T, and D.M. H: Modelling ofGranular Interactions in the Formation of Stockpiles.Proc. Chemeca 97, Rotorua, New Zealand, 29 Septe-meber - 1 October 1997, pp. 245-256.

[] W, J.P., P. C, M.E. C, and J.-P. B-: An Explanation for the Central Stress Minimum inSand Piles; Nature, Vol. 382 (1996), 25 July, pp. 336-338.




[] W, J.P., M.E. C, and P. C: StressPropagation and Arching in Static Sandpiles; Jnl. Phys-ics I, France 7 (1997), pp. 39-80.

[] W, A.: Searching for the Sand-Pile Pressure Dip;Science, Vol. 273 (1996) 2. August, pp. 579-580.

[] MB, W.: Mechanics of Bulk Solids Stockpiles; PhDThesis (2001), The University of Newcastle, Australia.

[] J, Ho Young: Numerical Simulations of StressesUnder Stockpiled Mass Over Ground With or With-out Loadout Tunnel; PhDThesis (2005), The Universi-ty of Western Ontario, Canada.

[] R, A.W.: Characterisation for Hopper and Stock-pile Design, Chapter 3, Characterisation of Bulk Solids, EdD. McGlinchey, Blackwell Publishing (2005). pp. 85-131.

[] R, A.W., M. O, and K.S. Manjunath: FeederLoad and Power Requirements in the ControlledGravity Flow of Bulk Solids from Mass-Flow Bins;Trans.IEAust., Mechanical Engineering, Vol. ME9(1984), No.1, April, pp. 49-61.

[] M, K.S. and A.W. R: Wall Pressure-Feeder Load Interactions in Mass-Flow Hopper/Feed-er Combinations; bulk solids handling Part I - Vol 6(1986) No. 4, Part II - Vol. 6 No. 5 (1986).

[] S, D. and J. S: Bulk Solids Flow in theHopper/Feeder Interface; Proc. Symposium on Relia-ble Flow of Particulate Solids (RELPOWFLO II), Oslo,Norway, 23-25 August 1993.

[] R, A.W.: An Overview of Feeder Design Focus-ing on Belt and Apron Feeders; bulk solids handling,Vol. 21 (2001) No. 1.

[] R, A.W.: Predicting the Performance of ScrewConveyors; Transactions of Mechanical Engineering,The Instn. of Engrs. Aust. Vol. ME2O (1995) No. 3, pp.213-220

[] R, A.W.: Predicting the Volumetric and TorqueCharacteristics of Screw Feeders; bulk solids handlingVol. 16 (1996) No 2, pp. 233-244.

[] W S.J. and W. MB: Investigations into theSmooth Discharge Screw Feeders; Transactions ofMechanical Engineering, The Institution of Engineers,Australia. Vol. ME22 (1997) No. 1, pp. 17-21.

[] R, A.W, M. O, and O.J. S: PerformanceCharacteristics of a Ross Type Chain Feeder; 10th An-niversary Powder and Bulk Solids Conference, May 7-9, 1985, Chicago, USA.

[] R, A.W., M. Ooms, and K.S. Manjunath: Per-formance of Dump Hopper and Apron Feeder usingInserts to Control Feeder Loads. Journal of Bulk SolidsStorage in Silos (1990), U.K




[] Roberts, A.W. 2001. Recent Developments in FeederDesign and Performance”, Handbook of Conveyingand Handling of Particulate Solids, Levy and Kalman(Ed), Elsevier. pp. 211-223.

[] Roberts, A.W, and Ooms, M. 1989. Performance Char-acteristics of Reciprocating Plate Feeders. Proc. ThirdInternational Conference on Bulk Materials Storage,Handling and Conveying, The Institution of EngineersAustralia, Newcastle. pp.369-377.

[] Roberts, A.W., Harrison, A. and Wiche, S. 1990. Per-formance Characteristics of Plough Feeders. 15 thPowder and Bulk Solids Conference, Chicago. U.S.A.

[] Roberts, A.W. 1992. Mechanics of Shear-Gate TypePlate Feeder”, 17th Powder and Bulk Solids Confer-ence, Chicago, U.S.A. pp.287-302.

[] Roberts, A.W and McBride, B. 1994. Some Aspects ofTube Feeder Performance. 19th Powder and Bulk Sol-ids, Conference, Chicago, U.S.A. pp.157-170.

[] Manjunath K.S. and Roberts, A.W. 2003. Investigationinto the Performance of Tube Type Feeders. Proc. 4thInternational Conference for Conveying and Handlingof Bulk Solids, (CHOPS) Budapest, Hungary. pp14.25-14.30

[] Roberts, A.W. 2006. Performance of Orbiting ScrewReclaimers. bulk solids handling, Vol. 26, No 1.

[] Deresiewicz, 1958. Mechanics of Granular Matter. Ad-vances in Applied Mechanics, Vol V, Academic Press,New York.

[] Trollope, D.H., Mechanics of Discontinua of ClasticMechanics. (1967). Department of Engineering, Re-search Bulletin No.2, University College of Townsville(Now James Cook University)

[] Cleary, P.W. 1998. Ball Mill Simulation Using DEM:Charge Motion, Power Draw, Segregation and Wear.Proc. 8th International Conference on Bulk MaterialsStorage, Handling and Transportation, The Instn. ofEngrs. Australia, Wollongong, NSW, Australia. pp.381-387.

[] Tüzün, U. 1998. Computer Simulations of Bulk Solids; aCritical Review of Discrete Element Techniques. Proc.8th International Conference on Bulk Materials Stor-age, Handling and Transportation, The Instn. of Engrs.Australia, Wollongong, NSW, Australia. pp.35-39.

[] Roberts, A.W. 2000. DynamicModelling of Bulk SolidsStorage, Discharge and Handling Systems. bulk solidshandling, Vol. 20, No.2, 183-189

[] R, A.W.: Predicting the Performance of OpenFront Inclined Apron Feeders; Proc. From Powder toBulk Conference, The Institution of Mechanical Engi-neers, London 2000, pp. 443-452.

[] R, A.W.: An Investigation into the Gravity Flowof Non-Cohesive Granular Materials Through Dis-charge Chutes; Trans. A.S.M.E., Jnl. for Engng. in Indus-try, Vol. 91 (1969) Series B, No. 2, pp. 373-381.

[] C, C., W.H. C, and A.W. R:Optimum Chute Profiles in Gravity Flow of GranularMaterial: ADiscrete Segment Solution; Trans. A.S.M.E.Jnl. for Engng. in Industry, Vol. 91 (1969), Series B,No. 2.

[] C, C., W.H. C, and A.W. R:Chute Profile for Minimum Transit Time in the Grav-ity Flow of Granular Materials; Jnl. Agric. Engng. Res.,Vol. 17 (1972).

[] S, S.B.: Gravity Flow of Cohesionless GranularMaterials in Chute and Channels; J. Fluid Mech. Vol.92 (1979), Part 1, pp. 53-96.

[] R, A.W. andO.J. S: Flow of Bulk SolidsThroughTransfer Chutes of Variable Geometry and Profile; bulksolids handling Vol. 1 (1981) No. 4, pp. 715-727.

[] R, A.W.: Chute Design Considerations for Feed-ing and Transfer; Proc. Beltcon 11, International Mate-rials Handling Conference, Johannesburg, South Afri-ca, 1-2 August 2001.

[] H, J.M., and X.M. Z: Dilatant Double ShearingTheory Applied to Granular Chute Flow; Acta Me-chanica 118 (1996) Nos. 1-4, pp. 97-108.

[] R, A.W.: Chute Performance and Design forRapid Flow Conditions; Chemical Engineering Tech-nology, Vol. 26 (2003) No. 2, pp. 163-170.

[] R, A.W., C.M. W, and R.E. S: In-fluence of Flow Properties and Geometry on ChuteDesign and Performance; Proc. Particle Systems Anal-ysis Conference 2005, Stratford-Upon Avon, England.

[] W, C.M.: Evolutionary Optimisation in Chute De-sign; Powder Technology, Vol. 138 (2003), pp. 118-123.

[] R, A.W., C.A. W, T. K, and S.J. W:Dust Reduction in Delivery of Particulate Commodities;Provisional Patent filed with Australian Patent Office, USPatent Office and Canadian Patent Office, April 2006

[] R, A.W.: Mechanical Conveying; Proc. FromPowder to Bulk Conference, The Institution of Me-chanical Engineers, London 2000, pp. 377-410

[] R, A.W.: Bulk Solid and Conveyor Belt Inter-actions for Efficient Transportation Without Spill-age; bulk solids handling Vol. 18 (1998) No. 1, pp.49-57

[] W, C.A.: Analysis of Main Resistances of BeltConveyors; PhDThesis (2003), The University of New-castle, Australia




[] W, C.A., A.W. R, and M.G. J: Calcu-lating the Flexural Resistance of Bulk Solids Transport-ed on Belt Conveyors; Particle and Particle SystemsCharacterisation, Vol. 21 (2004), pp. 340-347.

[] R, A.W.: Design and Performance Criteria forScrew Conveyors in Bulk Solids Operations; bulk sol-ids handling Vol. 21 (2002) No. 6, pp. 436-444.

[] K, G.: Pneumatic Conveying: Transport Solu-tions, Pitfalls and Measurements; in: A. L and H.K (.): Handbook of Powder Technology, Vol.10, Elsevier (2001), pp. 291-301.

[] W, P.W.: Dilute-Phase Pneumatic Conveying -Problems and Solutions; in: A. L and H. K(.): Handbook of Powder Technology, Vol. 10, Else-vier (2001), pp. 303-318.

[] J, M.G.: Characterisation for Pneumatic Conveyor De-sign; Chapter 5 in: D. MG (.): Characterisationof Bulk Solids; Blackwell Publishing (2005), pp. 151-180.

[] B, T. F., and A.J. C: Experiences Pump-ing Dense Slurries Containing Large Particles, 46thJapanese National Conference on Rheology, August1998, Rakuno-Gakuen University, Sapporo, Japan,pp. 117-118.

[] B, T. F., and A.J. C: Pressure Loss Calcula-tions for Thickened Slurries Containing Large Parti-cles; 14th International Conference on Slurry Han-dling and Pipeline Transport, Maastricht, The Neth-erlands, 8 - 10 September 1999.


Bulk Solids Handling

Documents

Transcript of Bulk Solids Handling