Transfer Chute For Bulk Material

2009
Theoptimisationoftransferchutesinthebulkmaterials
industry
M.N.vanAarde
A dissertationsubmittedtotheFacultyofEngineeringinfulfilmentofthe
requirementforthedegree
MagisterIngeneriae
In
MechanicalEngineering
AttheNorth-WestUniversity,PotchefstroomCampus
Promoter: Dr. M. Kleingeld
Pretoria
ABSTRACT
ABSTRACT
Bulk materials handling is a rapidly growing global industry. Immense challenges
exist to improve the efficiency and cost effectiveness of transporting and handling
bulk materials continuously. The nature and scale of bulk materials handling
varies from country to country. This study specifically focuses on the handling of
bulk materials in the mining sector.
Within this industry, transfer chutes are a key component used for transferring
bulk material from one conveyor to another. Among other uses it can also be
used under hoppers or silos to transfer material to conveyors, trains, trucks or
ships. In a continuous effort to improve the efficiency of processes the industry is
bombarded with transfer chute problems that include:
blocked chutes
high wear of liner materials
spillage due to skew loading
conveyor belt wear at loading points.
Thorough investigation of existing transfer points, before modifying or replacing
them with another configuration, gives better insight into the problems. This aids
the designer to come up with the optimum solution for a speci"Ac transfer point. In
this dissertation a study is done on the configuration of dynamic chutes or hood
and spoon chutes. After completing a detailed investigation of existing problems,
the study focuses on rectifying material transfer problems and designing for ease
of maintenance.
Adding to the improved flow in the new design, for the specific case study
discussed in this dissertation, other design details are discussed which further
validates the new design. This design improves the wear life of the liners inside
the chute and minimises down time by reducing maintenance shutdowns.
The optimisation of transfer chutes in the bulk materials industry
M.N. van Aarde
ii
ABSTRACT
There are literally endless possibilities when it comes to chute configurations due
to the uniqueness of each plant, material type and layout constraints. It is
therefore beneficial to know what issues to address in the process of chute
design or optimisation.
This study focuses on a specific case study with unique problems and solutions.
It should however give further insight and a basic understanding of what a chute
designer must consider, and the methods taken, to optimise an existing material
transfer point. The purpose of this document is therefore not to provide the
reader with a recipe for chute optimisation but rather with the knowledge to
comprehend the problems and solutions by discussing a specific industry case
study.
M.N. van Aarde
iii
SAMEVATTING
SAMEVATTING
Materiaal handteringis 'n vinnig groeiendewereldwyeindustrie. Hierdieindustrie
word gekonfronteer deur groot uitdagings om die effektiwiteit van materiaal
handtering te verbeter en sodoende die koste daaraan verbonde te verminder.
Die aard en skaalvan materiaal handtering varieervan land totland afhangende
van dievereisteswatgestelword deurdaardieland seindustrielesektor. Hierdie
studie fokus spesifiek op materiaal handtering in die mynbou sektor waar
hoofsaaklikgeprosesseerdeerts handteerword. ,
In hierdieindustrie is oordrag geute 'n sleutel komponenten word dithoofsaaklik
gebruik om erts te vervoervanafeen vervoerband na 'n volgende. Dit kan ook
onderandere gebruikword onder hoppers ofsillos waar materiaal vervoerword
'na vervoerbande, treine, vragmotors ofskepe. In die strewe om die effektiwiteit
van prosesse te verbeter word die industrie gekonfronteer met probleme wat
onderandereinsluit:
geblokkeerdeoordrag geute
hoeslytasieop geut-voerring materiale
vermorsing van materiaal as gevolg van geute wat skeef aflaai op
vervoerbande
hoeslytasievan vervoerbandeby uitlaai punte
Voordatbestaandeprobleem geutevervang word met'n nuwe konfigurasieis dit
belangrik om 'n deeglike ondersoek te doen. Hierdie ondersoek skep 'n beter
insig oordie problemewatbestaan in die oordrag geute. 'n Beterinsig rondom
die probleme gee aan die ontwerper die vermoe om die optimale oplossing vir
die probleme te kry. In hierdie skripsie is 'n studie gedoen oordie konfigurasie
van dinamiese geute of sogenaamde "hood and spoon" geute. Bestaande
probleme word in ag geneem en die studie fokus op die verbetering van
materiaalvloeisowel asIn ontwerpwatinstandhoudingvergemaklik.

M.N.vanAarde
iv
SAMEVATTING
As 'n toevoegsel tot die verbeterde vloei binne die nuwe ontwerp, vir die
spesifieke geut waarna gekyk word in hierdie studie, word daar ook ander
ontwerp toevoegings bespreek wat die waarde van die nuwe ontwerp verder
bevestig. Hierdie ontwerp verbeter die leeftyd van die geut-voerring en tyd wat
afgestaan moet word aan instandhouding word geminimeer.
Daar is letterlik eindelose moontlikhede wanneer dit kom by die konfigurasie van
oordrag geute as gevolg van die uniekheid van elke aanleg, materiaal tipe en
uitleg beperkings. Daarom is dit voordelig om te weet waaraan aandag gegee
moet word in die proses om geute te ontwerp of te optimiseer.
Hierdie studie fokus op 'n spesifieke oordrag geut binne 'n spesifieke industrie
met unieke probleme en oplossings. Dit behoort die geut ontwerper te bekwaam
met die basiese kennis en insig oor waarna om te kyk wanneer geute ontwerp of
geoptimiseer word. Die doel van hierdie skripsie is dus nie om die leser te
voorsien van 'n resep om geute te optimiseer nie maar wei die kennis om die
probleme en oplossings te verstaan deur gebruik te maak van 'n studie uit die
industrie.
M.N. van Aarde
v
ACKNOWLEDGEMENTS
ACKNOWLEDGEMENTS
I would like to thank Prof. E.H. Mathews for the opportunity to do my Masters
degree.
Special thanks to Dr. M. Kleingeld for his guidance and effort in assisting me in
my attempt to deliver a dissertation of this standard.
Thank you to Prof. Lesley Greyvenstein for the language editing.
To my family, thank you for all your support and encouragement throughout the
execution of this study.
------_..__.__.__._--_.._--,-----------
M.N. van Aarde
vi
TABLEOFCONTENTS
~ ~
TABLE OF CONTENTS
Abstract. ................................................................................................................ii
Samevatting.........................................................................................................iv
Acknowledgements..............................................................................................vi
Tableofcontents.................................................................................................vii
Listoffigures.......................................................................................................ix
Listoftables.........................................................................................................xii
Nomenclature.....................................................................................................xiii
Chapter1: Introductiontotransferchutes in the bulkmaterialshandling industry1
1.1 Introductiontotransferchutes..................................................................... 2
1.2Variousapplicationsand configurationsoftransferchutes .........................5
1.3Recurring chuteproblemsand countermeasuresfrom industry................11
1.4Purposeofthisresearch ...........................................................................18
1.5Synopsis ofthisdissertation......................................................................19
Chapter2: Basicconsiderationsin chute design............................................... 21
2.1 Preface......................................................................................................22
2.2Design objectives...........................................,..........................................22
2.3 Integratingamoreappropriatechute layoutwiththeplantconstraints......27
2.4Investigatingthe correctchuteprofileforreduced linerwear....................30
2.5 Feed chutegeometryforreduced beltwear.............................................. 34
2.6Conclusion................................................................................................. 37
Chapter3: Testsfortheidentification ofrecurring problemson existing chutes39
3.1 Preface......................................................................................................40
3.2Testmethodology......................................................................................40
3.3Chuteperformanceacceptancecriteria.....................................................42
3.4Discussion ofproblemareas.....................................................................42
3.5Summaryoftestresults............................................................................. 54
3.6Conclusion................................................................................................. 55
The optimisation oftransfer chutes in the bulk materials industry
M.N. vanAarde
vii
TABLEOF CONTENTS
Chapter4: Dynamicchutesfortheelimination ofrecurring problems................57
4.1 Preface...................................................................................................... 58
4.2Considerationoftheexistingtransferpointconstraints.............................59
4.3 Designofthechute profile......................................................................... 61
4.4Incorporating adead boxin theimpactareas............................................67
4.5 Designing thechuteforintegrationwith system requirements................. 73
4.6Conclusion................................................................................................. 75
Chapter5: Testing andverification ofthenewsolution......................................77
5.1 Preface......................................................................................................78
5.2Selecting atestmethodology.................................................................... 79
5.3Determination ofmaterial properties......................................................... 85
5.4Verification oftheselectedtestmethodologyforthis application..............88
5.5 Verification of new chute configuration and optimisation of the hood
location............................................................................................................92
5.6 Effectofthe honeycombstructurein highimpactzones...........................95
5.8Conclusion...........;.....................................................................................97
Chapter6: Conclusions and Recommendations................................................99
6.1 Conclusionsand recommendations........................................................100
6.2Recommendationsforfurtherstudy........................................................103
References.......................................................................................................105
AppendixA: MaterialTestsAnd LinerSelection............................................111
AppendixB: ChuteControl Philosophy..........................................................116
M.N.vanAarde
viii
LISTOFFIGURES
LIST OF FIGURES
Figure1: Growthin globalcrudesteelproductionfrom 1996to2006[2].............. 2
Figure2: Typicalin-linetransferpoint[6]. .............................................................4
Figure3: 90transferpoint[7J..............................................................................4
Figure4: Materiallumpsizesthroughacrushingplant......................................... 6
Figure5: StackerReclaimerin reclaimingmode..................... .............................. 7
Figure 6: Typicaldeadbox[11J.............................................................................9
Figure7: Typicalcascadechute[11]....................................................................9
Figure8: Typicaldynamicchute[12]..................................................................10
Figure9: Radialdoorusedin chutesunderorepassesorsilos[11]...................10
Figure 10: Floppergate divertingmaterialto differentreceivingconveyors[11J.11
Figure 11: Chutelinerdegradation................. .....................................................12
Figure12: Resultsofcontinuousbeltwearattransferpoints.............................13
Figure1 Dustfrom atransferpointontoastockpi/e......................................... 13
Figure 14: Ceramiccompositeliners[18]............................................................ 15
Figure 15: BenetechInteliflowJ-Glidetransferchute[19]..........:........................16
Figure16:FlowsimulationoftheBenetechIneliflo chute[19] ............................17
Figure 17: Fourstepprocessforplantdesignandcommissioning[1]................ 27
Figure18: Verticalcurveonincline conveyor..................................................... 28
Figure 19: Protectiverolleron atransferchute...................................................29
Figure20: Geometryoftheimpactplateandmaterialtrajectory[30J.................. 30
Figure21: Modelfortheimpactof aparticleonaflatsurface[29]..................... 31
Figure22: Oreflowpathin the curvedchuteontotheincline conveyor[31] ....... 35
Figure 23: Gentle deceleration ofthe productbeforeimpacton thereceivingbelt
[32]......................................................................................................................35
Figure24: Typicalfeedchutedischargemodel[33]............................................ 37
Figure25: Layoutofconveyorsforchutetestwork.............................................43
Figure26: Configurationof theexistingtransferchute........................................44
Figure27: Clearchuteindicatingcameraangle..................................................46
The optimisationoftransferchutesin thebulkmaterialsindustry
M.N.vanAarde
ix
LISTOF FIGURES
Figure28: Coarsematerialat8000tlh...............................................................46
Figure29: Finematerialat8 000tlh...................................................................47
Figure30: Blockedchutewith coarsematerialat8600tIh.................................47
Figure31: Damagedsideskirt............................................................................49
Figure32: Viewbehindthechuteofthereceivingconveyorbeforeloading.......50
Figure33: Viewbehindthe chuteofthereceivingconveyorduringloading.......50
Figure34: Peaksurgesexperiencedduringreclaimingoperations.................... 52
Figure35: Stockyardheadendlayout................................................................ 59
Figure36: Dimensionalconstraintsontheexistingtransferconfiguration..........60
Figure37:Hoodandspoonconfigurationforthe90transfer............................ 63
Figure38:Hoodvelocityprofile.......................................................................... 65
Figure39: Spoon velocityprofile.........................................................................66
Figure40: Chute crosssection........................................................................... 67
Figure43: Honeycomb wearboxpositioning...................................................... 69
Figure44: Wearboxin thehoodsection............................................................ 70
Figure45: Spacingarrangementofhoneycombribsinside thehood................. 71
Figure46: Wearboxin the spoonsection...........................................................72
Figure47: Linerdetailofthe spoonhoneycombwearbox .................................. 73
Figure41: Spoonin the operationalposition.......................................................74
Figure42: Spoon in the non operationalposition................................................75
Figure 48: Flow analysis examples: a) separation and screening, b) hoppers,
feeders[36J.........................................................................................................80
Figure49: Simulationsresultsfrom Fluent[4OJ...............................................83
Figure50: Simulationresultsfrom BulkFlowAnalyst[41J............................... 83
Figure51: Determination ofmaterialpropertiesforan accurateangleofrepose88
Figure Actualmaterialflowwithcoarse Sat10000tIh ................................ 89
Figure53: Materialflowpattemthrough the existingchute................................. 90
Figure54: Crosssectionalsideviewofmaterialflowthrough the existingchute91
Figure55: Materialflowthrough hoodat10000tlh............................................ 92
Figure56: Materialflowthroughspoon at10000tlh.......................................... 93
Figure57:Determination ofthe optimumhoodlocation...................................... 94
The optimisation oftransferchutesin thebulkmaterialsindustry
M.N. vanAarde
x
OFFIGURES
Figure58: Material behaviour through hood ................................... ............ ........96
Figure59: Material behaviour through spoon ..................................................... 96
M.N.vanAarde
xi
LIST OF TABLES
LIST OF TABLES
Table 1: DesignInputReferenceRequirements[24J.......................................... 24
Table 2: Iron aregradesusedforchutetestwork...............................................45
Table 3: Resultsfrom testprogramme................................................................54
The optimisationof transferchutesin the bulkmaterialsindustry
M. N. van Aarde
xii
---------------------------------
CV
NOMENCLATURE
NOMENCLATURE
SCADA
CCTV
CEMA
DEM
kPa
mm
MSHA
m/s
mt
MW
NIOSH
OSHA
R&D
tlh
3D
Supervisory Control And Data Acquisition
Closed Circuit Television
Conveyor Equipment Manufacturers Association
Conveyor
Discrete Element Method
Kilopascal
Millimetres
Mine Safety and Health Administration
Metres per second
Metric Tons
Megawatt
National Institute for Occupational Safety and Health
Occupational Safety and Health Administration
Radius of curvature
Research and Development
Tons per hour
Three Dimensional
M.N. van Aarde
xiii
CHAPTER 1
CHAPTER 1: INTRODUCTION TO TRANSFER CHUTES IN THE BULK
MATERIALS HANDLING INDUSTRY
M.N. van Aarde
1
CHAPTER 1
1.1 INTRODUCTION TO TRANSFER CHUTES
1.1.1 Bulk material handling industry
In order to comprehend the utilisation of transfer chutes fully it is imperative to
first understand the industry in which it is used. Transfer chutes are most
commonly used in the bulk materials handling industry. Bulk materials handling
operations perform a key function in a great number and variety of industries
throughout the world as stated in 1978 by Arnold, McLean, and Roberts [1 J.
The nature of materials handling and scale of industrial operation varies from
industry to industry and country to country. These variations are based on the
industrial and economic capacity and requirements of the specific industry or
country. Regardless of the variations in industry, the relative costs of storing,
handling and transporting bulk materials are, in the majority of cases, very
significant.
o
Figure 1: Growth in global crude steel production from 1996 to 2006 [2J
M.N. van Aarde
2
CHAPTER 1
The chart from BHP Billiton, shown in Figure 1, provides a clear indication of the
actual drivers of global materials demand. Figure 1 indicates the percentage
growth in crude steel production from all the major role players between 1996
and 2006. China accounted for 65% of the 494 million tonnes of global steel
production growth between 1996 and 2006. Europe grew by 6% while the "other"
countries grew by 20% [2].
These figures emphasise that bulk materials handling performs a key function in
the global industry and economy [1]. Because of market requirements, new
products continuously evolve. This is also true for the field of bulk conveying
technologies [3]. It can be assumed that the evolution of new technology is due
to the requirement for more efficient and cost effective operation.
The case study which will be discussed from Chapter 3 onwards is an iron ore
export facility. This facility exports approximately 50 million tonnes per annum.
With each hour of down time, the financial losses equate to approximately
R750 000. This highlights the fact that handling systems should be designed and
operated with a view to achieving maximum efficiency and reliability.
1.1.2 Function of transfer chutes
BS2890 (Specification for Troughed Belt Conveyors) gives the definition for
transfer chutes as follows: "A straight, curved or spiral, open topped or enclosed
smooth trough, by which materials are directed and lowered by gravity" [4]. For
any belt conveyor system to operate successfully the system requires that [5]:
the conveyor belt be loaded properly
the material transported by the conveyor is discharged properly.
The transfer of bulk material can either be from a belt, bin, hopper, feeder or
stockpile and occurs at a transfer point. In most cases this transfer point requires
optimisation of transfer chutes in the bulk materials industry
M.N. van Aarde
3
CHAPTER 1
- .. ~ ~ ~
a transfer chute [5]. In industry the most common use of transfer chutes is for
transferring bulk material from one conveyor belt to another. This transfer of
material can be done in any direction as simplistically explained in Figure 2 and
Figure 3.
Figure 2: Typical in-line transfer point [6J
Figure 2 shows a basic in-line transfer of material from the end of one conveyor
belt onto the start of another conveyor belt. Figure 3 illustrates a more intricate
design where the direction of material transport is changed by an angle of 90
0

This design, or any other design entailing a directional change in flow, normally
requires more detailed engineering [7}.
M.N. van Aarde
4
CHAPTER 1
Regardless of the direction or type of transfer, there are some design
requirements that always need special attention. Some of these requirements
are reduced wear on chute liners, correct discharge velocity, minimum material
degradation and minimum belt abrasion. The correct design will also eliminate
blockages, shape the load correctly and minimise the creation of dust [7].
1.2 VARIOUS APPLICATIONS AND CONFIGURATIONS OF TRANSFER CHUTES
The application of transfer chutes is central to any operation in the bulk handling
industry. Whether it is mining operations, storing, stacking, importing or
exporting of bulk material, the transfer of material is always required. On the
mining side the challenges involved with materials handling are probably some of
the most extreme.
This is due to the great variation in lump sizes that must be catered for. At
Sishen iron ore mine, seven iron ore products are produced, conforming to
different chemical and physical specifications. The current mining process at
Sishen entails [8]:
Removal of topsoil and stockpiling
Drilling and blasting of ore
Loading of iron ore and transporting to the crushers
Crushing and screening into size fractions
Beneficiation of all size fractions
Stockpiling onto various product beds.
The processes with the most intricate and complex chute arrangements are
probably crushing and screening as well as stacking and reclaiming of material.
1\/1. N. van Aarde
5
CHAPTER 1
1.2.1 Crushing
An excavator or wheeled loader transfers the rock to be crushed into the feed
hopper of the primary crusher. The primary crusher breaks the large rock
boulders, or "run of mine" material, into smaller grain sizes. Some of the bigger
crushers in the industry can crack boulders that are about one cubic meter in
size. All the crushed material passes over a screen to separate the different
lump sizes. The material that falls through the screen is transferred via a series
of transfer chutes and conveyor belts to the stockpile area [9].
Where the material does not pass through the screen another system of transfer
chutes and conveyor belts transfers this material to a secondary crusher. The
material is fed into this crusher via a transfer chute from the discharge of a
conveyor belt. All the processed material is then transferred to the stockpile area
via a separate series of transfer chutes and conveyor systems [9]. Throughout
this whole process the material lump size changes and with it the transfer chute
requirements.
Figure 4: Material lump sizes through a crushing plant
M.N. van Aarde
6
CHAPTER 1
Figure 4 shows some spillage from a conveyor between a primary and secondary
crusher. The shovel in the picture provides a good reference as to the variation
in material lump size on the walkway.
1.2.2 Stacking and Rec/aiming
Normally the stockyard area has an elongated yard conveyor for moving bulk
material in the longitudinal direction of the stockyard. Straddling the yard
conveyor transversely is the rail mounted undercarriage of the stacker reclaimer.
Three main chutes transfer material through the machine [10]. Figure 5 shows
this machine in action while reclaiming material from a stockpile.
Figure 5: Stacker Reclaimer in reclaiming mode
The first chute will transfer material to the incline conveyor of the machine when
the material has to be stacked on the stockpile. In the case where the material
must bypass the machine, this chute will transfer material from the tripper, back
onto the yard conveyor [10].
M.N. van Aarde
7
CHAPTER 1
The second chute transfers material from the incline conveyor onto the boom
conveyor. This is normally a difficult process because the boom conveyor is
never in the same direction as the incline conveyor. From the end of the boom
conveyor the material is Simply discharged onto the stockpile [10].
When reclaiming stockpile material, the bucket whee! at the head end of the
boom conveyor scoops up material and deposits it back onto the boom conveyor.
From here it is discharged into the centre chute of the machine. This chute then
discharges the material onto the yard conveyor for further processing. In some
cases the bottom section of this centre chute must be moved out of the way to
allow free passage of material discharged from the tripper chute onto the yard
conveyor [10].
1.2.3 Chute configurations
Various chute configurations are used in the bulk materials handling industry.
These configurations depend on the specific requirements of the system layout
or material properties. There are basically two main configurations, consisting of
dead box chutes and dynamic chutes. Both of these configurations have their
specific applications in industry. The major difference is that dead box chutes
use the material being transferred as a chute liner, whereas dynamic chutes are
lined with a high wear resistant material. A combination of both can also be
used.
If the material being transferred is relatively dry, such as goid ore, dead boxes
prove to be more beneficial. One of the applications of a de?d box is to absorb
the direct impact of material discharged from aconveyor into a head chute as
can be seen in Figure 6. Other applications are in long or high transfer points. In
these transfers the momentum of falling material must be reduced before
reaching the receiving conveyor belt in order to reduce wear of the belt [11].
M.N. van Aarde
8
CHAPTER 1
Figure 6: Typical dead box [11]
As shown in Figure 7 dead boxes are also used to accomplish changes in the
vertical flow direction, by inserting angled panels. This configuration where dead
boxes are used as deflection plates or impact wear plates is known as a cascade
chute. In this case the deflection plate or the impact wear plate hardness is
equal to that of the feed material [11].
Figure 7: Typical cascade chute [11]
The hood and spoon chute or dynamic chute is configured so that the hood
catches and changes the material trajectory path to exit with a vertical velocity.
When the material impacts the spoon it slides down the smooth spoon surface.
The material flow direction is changed to the direction of the receiving conveyor
as shown in Figure 8 [12].
M.N. van Aarde
9
CHAPTER 1
Figure 8: Typical dynamic chute [12J
Ancillary equipment used with this configuration of chutes is radial doors and
flopper gates. Radial doors are used successfully below ore passes or silos for
an on/off feed control as shown by Figure 9. One drawback of radial doors is the
possibility of jamming while closing. In order to counteract this problem a
knocker arm between the cylinder door and the rod can be added. This helps to
close the door with full force, open with reduced force, or hammered open [11]
Figure 9: Radial door used in chutes under ore passes or silos [11J
M.N. van Aarde
10
CHAPTER 1
The function of a f10pper gate is to divert the flow of material in a chute when one
conveyor is required to feed either of two discharge points as shown in Figure 10.
For this same purpose a diverter car can also be used where a section of the
chute moves in and out of the path of material flow. The critical area in the
design of a flop per gate is the hinge point. In order for the gate to be self
cleaning the hinge point should be placed above the apex of the double chute.
This also prevents rock traps that can jam the gate [11].
COVERE;D
Figure 10: Flopper gate diverling material to different receiving conveyors [11J
1.3 RECURRING CHUTE PROBLEMS AND COUNTERMEASURES FROM INDUSTRY
Transfer chutes are a fundamental link when conveying ore and, therefore, it is
important to get it right at the outset of design and fabrication. Design and
fabrication issues can cause numerous problems when transferring material.
Historically, conveyor system design focused on the system's overall structural
integrity, while ensuring that the equipment would fit within the facility's
constraints [13], [14], [15].
M.N. van Aarde
11
CHAPTER 1
Little attention was given to design analysis or consideration for material flow
characteristics. Normally the solution for controlling flow was to implement
simplerock boxes [15]. Thistype ofchute configuration is still commonly used in
industry but with more emphasis on the flow of material. The most recurrent
problemson transferchutesare[13] ,[14] :
Spillage
Blocked chutes
High wear on the receiving belt due to major differences between the
materialvelocityand the beltvelocity
Rapid chutewear
Degradation ofthematerialbeing transferred
Excessivegenerationofdustand noise
Miss tracking ofthe receiving conveyor belt due to skew loading from the
transferchute.
Figure 11: Chute liner degradation
Figure 11 shows the excessive wear on ceramic tiles where the material
trajectory from the feeding belt impacts the chute. These tiles are replaceable
and a maintenance schedule normally specifies the replacement intervals. A
The optimisation oftransfer chutes in the bulk materials industry 12
M.N.van Aarde
CHAPTER 1
problem arises when the frequency of these maintenance intervals is too high
due to excessive wear on the liners.
Figure 12: Results of continuous belt wear at transfer points
The conveyor belt can account for up to 60% of the capital cost of a bulk
materials handling plant. This means that the cost implications of constant
replacement of a conveyor belt, due to wear, can become significantly higher
than the original capital investment [16]. Figure 12 shows the extreme damage
on a conveyor belt caused by abrasion and gouging.
Figure 13: Dust from a transfer point onto a stockpile
M.N. van Aarde
13
CHAPTER 1
.. ----------------------------
The presence of dust is an indisputable fact in many industries concerned with
the handling or processing of products such as coal, mineral ores and many
others [17]. As in the case of spillage, it is easy to identify transfer systems that
cause dust clouds. Environmental regulations are in place to prevent excessive
I
dust emissions.
Government organisations such as the Occupational Safety and Health
Administration (OSHA), the Mine Safety and Health Administration (MSHA) and
the National Institute for Occupational Safety and Health (NIOSH) closely monitor
dust levels at all coal handling facilities [13]. Therefore, it is imperative that the
chute design process caters for limiting dust emissions.
Systems normally used in industry are enclosed skirting systems, bag houses
and dust collectors. This, however, is only treating the symptom rather than
eliminating the primary cause. In order to minimise dust generation the use of
low impact angles and minimal chute contact is required (14]. One of the most
successful methods of controlling dust is atomised water spray systems using a
combination of high pressure water and chemical substances.
Over the years, considerable research has gone into minimising wear on transfer
chutes. There are currently a few different liner types to choose from, depending
on the configuration and application of the chute. These include ceramic tiles;
chrome carbide overlay materials and hardened steel plates such as
VRN. A combination of liner materials can also be used, similar to the one
. shown in Figure 14.
The opUmisation of transfer chutes in the bulk materials industry
M.N. van Aarde
14
CHAPTER 1
Figure 14: Ceramic composite liners [18J
This ceramic composite liner is an example of the new technology available in
chute lining materials. It is a high wear resistant surface made from cylindrical
alumina ceramic pellets bound within a resilient rubber base. The purpose of this
material is to provide wear resistance through the use of ceramics while the
rubber dampens the impact forces [18].
Some innovative concepts for chute design have been implemented since the
materials handling industry started to incorporate new ideas. Benetech Inc.
installed a new generation hood and spoon type chute at Dominion's 1200 MW
Kincaid coal powered generating station as shown in Figure 15. This chute
replaced the conventional dead box chute [19]. Their innovation is to use a pipe
configuration combined with the hood and spoon concept.
M.N. van Aarde
15
CHAPTER 1
Figure 15: Benetech Inteliflow J-G/ide transfer chute [19J
This chute has sufficient chute wall slope and cross sectional area to prevent
material build-up and blocked chutes. Reduced collision forces in the chute
minimize material degradation and the creation of excessive dust. The material
velocity in the chute is controlled by the wall angles to obtain a discharge velocity
with the same horizontal component as the belt velocity [19]. Figure 16 shows a
flow simulation of the Benetech concept. The simulation shows that this concept
will result in lower impact forces and reduce belt abrasion.
M.N. van Aarde
16
CHAPTER 1
Figure 16: Flow simulation ofthe Benetech Ineliflo chute [19J
C.B.P. Engineering Corp. also considers the concept of pipe type sections to be
the answer to most of the transfer chute problems. They describe it as a curved
or half round chute. The modern perception is to gently guide the material in the
required direction rather than use a square box design or deflector doors which
turns or deflects the flow [20].
The industry is striving towards developing new technology in transfer chute
design. One solution is to incorporate soft loading transfer chutes to alter the
material flow direction with minimum impact on the side walls of chute and
receiving conveyor. As experienced by many' industries, these types of chutes
can transfer material onto the receiving conveyor at almost the same velocity as
the conveyor. By doing so, many of the problems with material transfer can be
eliminated [13].
Most of these solutions, as proposed by industry, only address a few of the
numerous problems experienced with transfer chutes. The dynamic hood and
M.N. van Aarde
17
CHAPTER 1
spoon chute appears to afford the best opportunity for solving most of the
problems. There are still however many unanswered questions surrounding this
design.
Figure 11 shows the installation of a hood type chute in the iron ore industry. It is
clear from this image that liner wear in the higher impact areas is still an area of
concern. Improvements can still be made to this design in order to further
enhance its performance.
1.4 PURPOSE OF THIS RESEARCH
The bulk materials handling industry is constantly facing the challenge of
implementing transfer chutes that satisfy all the system requirements. Problems
such as high wear, spillage, blockages and the control of material flow are just
some of the major challenges faced by the industry.
The objective of this research is to identify problems experienced with transfer
chutes of an existing bulk handling system and to apply current design solutions
in eliminating these problems. In doing so the research aims to introduce a new
method of minimising liner wear caused by high impact velocities.
Dynamic chutes are
,
discussed in particular where the entire design process
addresses the problems identified on chutes in brown field projects. Approaching
! chute design from a maintenance point of view, with the focus on reducing liner
I
degradation, will provide a fresh approach to transfer chute design. The
concepts d i s ~ s s e d in this dissertation, (dynamic and dead box chutes), are
commonly used in industry. However, some research is done to determine
whether a combination of these concepts can solve some of the problems
experienced by industry.
The optimisation of transfer chutes in the bulk materials industry 18
M.N. van Aarde
CHAPTER 1
At the hand of all the information provided in this dissertation its purpose is to
enable the chute designers to better understand the process of "chute
optimisation and design. This is achieved through the discussion of a case study
where the chutes are evaluated and re-designed to achieve the desired
performance.
1.5 SYNOPSIS OF THIS DISSERTATION
Chapter 1 gives an introduction to the bulk materials industry and the role that
transfer chutes plays in this industry. Some of the problems that the industries
have been experiencing with transfer chutes were identified and the diverse
solutions to these problems discussed. These solutions were reviewed to
identify whether improvement would be possible.
Chapter 2 provides a better understanding of the functionality and the
conceptualisation of transfer chutes as well as investigating the theory behind
material flow through transfer chutes. This theory reviews the research and
design objectives used as a guideline when approaching a new chute
configuration. The guidelines for evaluating and designing transfer chutes are
used to verify the performance of these chutes in the" iron ore industry.
Chapter 3 identifies some practical problems experienced on transfer chutes ~
an existing bulk transfer facility. These problems are identified through a series
of tests where the actual flow inside the chutes is monitored via CCTV cameras.
\
The results obtained from these tests are specific to this facility but can provide
insight into the cause of some problems generally experienced in the in,dustry.
These results can provide helpful information when modifying or re-designing
new transfer chutes.
Chapter 4 uses the theory discussed in Chapter 2 to conceptualise a new
transfer chute configuration for the transfer points that were tested. All the facility
The optimisation of transfer chutes in the bulk materials industry 19"
M.N. van Aarde
CHAPTER 1
constraints are taken into account during the process in order to obtain an
optimum solution to the problems identified during the chute test work. The old
chutes did not have major problems with liner wear due to large dead boxes.
Ho.wever, this remains a serious consideration for the new dynamic chute design
due to its configuration where there is continuous sliding abrasion of the chute
surface. A new concept for the reduction of liner degradation is introduced in this
chapter.
Before manufacturing and installing this new concept, it is important to verify that
it will perform according to conceptual design. Chapter 5 is a discussion on the
use of the Discrete Element Method as a verification tool. A simulation of the
new transfer chute concept is done to visualise the behaviour of the material as it
passes through the new transfer chute configuration.
Chapter 6 discusses the benefits of the new transfer chute configuration. A
conclusion is made as to what the financial implications will be with the
implementation of this new concept. Recommendations are made for future
studies in the field of bulk materials handling. These recommendations focus on
the optimisation of processes and the reduction of maintenance cost to the
facility.
M.N. van Aarde
20
CHAPTER 2
CHAPTER 2: BASIC CONSIDERATIONS IN CHUTE DESIGN
M.N. van Aarde
21
CHAPTER2
2.1 PREFACE
In an economicdrivenworld the pressureforproduction is often the causeofthe
loss ofproduction. This is a bold statement and is more factual than what the
industry would like to admit. This is also valid in the bulk materials handling
industry. Production targets seldom allow time for investigation into the root
causeofthe problems. Thequickfixoptionis often adopted, butisfrequentlythe
causeofevenmoremaintenancestoppages.
Existing chutes on brown field projects often fail dueto an initialdisregard forthe
design criteria, changes in the system parameters or lack of maintenance.
Thesetransferpoints areoften repaired on site by adding orremoving platework
and ignoring the secondary functions of a transfer chute. Therefore, it is
imperative to always considerthe basic chute specifications when addressing a
materialtransferproblem[21].
2.2DESIGNOBJECTIVES
In the questto improve ordesign anytransfer point, some ground rules mustbe
set. This can be seen as a check list when evaluating an existing chute or
designing a new chute. Transfer chutes should aim to meet the following
requirementsasfaras possible[21], [22], [23]:
Ensurethatthe required capacitycan be obtainedwith noriskofblockage
Eliminatespillage
Minimise wear on all components,and provide the optimal value life cycle
solution
Minimisedegradationofmaterialand generation ofexcessivedust
Accommodate and transfer primary and secondary scraper dribblings onto
thereceiving conveyor
M.N. vanAarde
22
CHAPTER2
Ensure that any differences between the flow offine and coarse grades are
catered for.
Transfer material onto the receiving conveyor so that at the feed point onto
theconveyor:
the componentofthematerial'now(parallelto thereceiving conveydr) is as
close as possibleto the beltvelocity (atleastwithin 10%), to minimisethe
powerrequired to acceleratethematerial and to minimiseabrasivewearof
thebelt
theverticalvelocitycomponentofthematerialflowis as lowas possible so
asto minimisewearand damageto the belt, aswellasto minimisespillage
dueto material bouncing offthebelt
The flow is centralised on the beltand the lateral flow is minimised so as
notto affectbelttracking and avoid spillage.
With the design ofanewchutethere are upto 46 differentdesign inputswith 19
ofthese being absolutelycritical to the success ofthedesign. Some ofthemost
critical preliminarydesignconsiderationsareshown inTable 1[24].
M.N. van Aarde
23
CHAPTER 2
Table 1: Design Input Reference Requirements [24J
Aria Unit
Feed Conveyor
Belt Speed
r
m/s
Belt Width mm
Jib/Head Pulley Dia mm
Pulley Width mm
Angle to Horizontal at the Head Pulley degrees
Belt Troughing Angle degrees
Sight Height Data
Feed Conveyor Top of Belt to Roof mm
Drop Height mm
Receiving Conveyor Top of Belt to Floor mm
Receiving Conveyor
Belt Speed m/s
Belt Width mm
Belt Thickness mm
Angle of Intersection degrees
Angle to Horizontal degrees
Belt Troughing Angle degrees
Material Properties
Max. Oversize Lump (on top) mm
Max. Oversize Lump (on top) degrees
studies done by Jenike and Johanson Inc. have identified six design principles
that can serve as a guideline in chute optimisation exercises. These six
principles focus on the accelerated flow in the chute which they identified as the
most critical mode [25].
Within accelerated flow the six problem areas identified by Jenike and Johanson
Inc. are [25]:
The optimisation of transfer chufes in the bulk materials industry
M.N. van Aarde
24
CHAPTER 2
plugging of chutes at the impact points
insufficient cross sectional area
uncontrolled flow of material
excessive wear on chute surfaces
excessive generation of dust
attrition or breakdown of particles.
2.2.1 Plugging of chutes
In order to prevent plugging inside the chute, the sliding surface inside the chute
must be sufficiently smooth to allow the material to slide and to clean off the most
frictional bulk solid that it handles. This philosophy is particularly important
where the material irnpacts on a sliding surface. Where material is prone to stick
to a surface, the sliding angle increases proportionally to the force with which it
impacts the sliding surface. In order to minimise material velocities and excessive
wear, the sliding surface angle should not be steeper than required [25].
2.2.2 Insufficient cross sectional area
The cross section of the stream of material inside the chute is a function of the
velocity of flow. Therefore, it is critical to be able to calculate the velocity of the
stream of material particles at any point in the chute. From industry experience a
good rule of thumb is that the cross section of the chute should have at least two
thirds of its cross section open at the lowest material velocity [25]. When the
material'is at its lowest velocity it takes up a larger cross section of chute than at
higher velocities. Therefore, this cross section is used as a reference.
2.2.3 Uncontrolled flow of material
Due to free falling material with high velocities, excessive wear on chutes and
conveyor belt surfaces are inevitable. Therefore, it is more advantageous to
M.N. van Aarde
25
CHAPTER 2
have the particles impact the hood as soon as possible, with a small impact
angle after discharge from the conveyor. With the material flowing against the
sloped chute walls, instead of free falling, the material velocity can be controlled
more carefully through the chute [25].
2.2.4 Excessive wear on chute surfaces
Free flowing abrasive materials do not normally present a large wear problem.
The easiest solution to this problem is to introduce rock boxes to facilitate
material on material flow. Chute surfaces that are subjected to fast flowing,
sticky and abrasive materials, are the most difficult to design.
A solution to this problem is to keep the impact pressure on the chute surface as
low as possible. This is done by designing the chute profile to follow the material
trajectory path as closely as possible. By doing so the material is less prone to
stick to the chute surface and the material velocity will keep the chute surface
clean [25].
2.2.5 Excessive generation of dust
Material flowing inside a transfer chute causes turbulence in the air and
excessive dust is created. In order to minimise the amount of dust, the stream of
material must be kept in contact with the chute surface as far as possible. The
material stream must be compact and all impact angles against the chute walls
must be minimised. A compact stream of material means that. the material
particles are flowing tightly together. At the chute discharge point the material
velocity must be as close as possible to the velocity of the receiving belt [25].
The optimisation of transfer in the bulk materials industry
M. N. van Aarde
26
CHAPTER2
2.2.6 Attrition or breakdown of particles
The break up of particles is more likely to occur when large impact forces are
experienced inside a chute than on smooth sliding surfaces. Therefore, in most
cases, the attrition of material particles can be minimised by considering the
following guidelines when designing a transfer chute: minimise the material
impact angles, concentrate the stream of material, keep the material stream in
contactwith the chute surface and keep the material velocity constantas far as
possible[25].
2.3 INTEGRATING A MORE APPROPRIATE CHUTE LAYOUT WITH THE PLANT
CONSTRAINTS
According to Tunra Bulk Solids in Australia, the process for design and
commissioning of a new plant basically consists of four steps. The entire
process is based on understanding the properties of the material to be
handled. [1]
R&DCENTRE CONSULTING CONTRACTOR
ENGINEERING ANDPLANT
COMPANY OPERATOR
r--------------,
I TESTINGOf CONCEPTUAl
I
DETAILED DESIGN CONSTRUCTION &.
I
BULKSOUDS
-.
DESIGN .,.. COMMISSIONING
-.
I
, -
I
FlowProper1ies LiningMaterial ; tu,et; Equipment
Selection Procurement_
I
I
I
I
I
FlowPat1erns
,SS.l!!pment
QualityControl
I
I I
FeederLoads& Process Performance
I
Power
I
Optimisation Assessment
I I
L J
-
I I
BinLoads
I I
I WearPredictions I
FEEDBACK
I I
I I
ModelStudi!?'>
L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ J
i FEEDBACK r--
Figure17:Four step process for plant design and commissioning [1J
M.N. vanAarde
27
CHAPTER 2
Figure 17 illustrates this four step process. These steps are a good guideline in
order to incorporate a more appropriate chute layout for the plant constraints.
This is an iterative process where all the possible solutions to a problem are
measured against all the possible plant constraints. This section focuses more
on the second column of Figure 17 and specifically on structures and equipment.
During this stage of design the utilisation of 3D parametric modelling also creates
an intimate and very accurate communication between the designer and the
project engineer or client. This effective communication tool will save time and
improve the engineering process [24].
A good example of obtaining an appropriate chute layout for the plant constraints
can be explained as follows. On an existing plant, a transfer point will have a
specific transfer height from the top of the feed conveyor to the top of the
receiving conveyor. If the feed conveyor has an incline section, to obtain the
required transfer height, it will also have a curve in the vertical plane of that
incline section. This curve has a certain minimum radius in order to keep the belt
on the idlers at high belt tensions [26].
Figure 18: Vertical curve on incline conveyor
M.N. van Aarde
28
CHAPTER 2
If the transfer height at a transfer point is changed, the path of the feeding
conveyor should always be taken into consideration. With an increase in transfer
height, the vertical curve radius will increase as well in order to prevent the
conveyor from lifting off the idlers in the curve. This will require expensive
modifications to conveyor structures and, therefore, in most cases be a pointless
exercise. Figure 18 shows clearly the large radius required to obtain a vertical
curve in a belt conveyor.
Other considerations on brown field projects might be lift off of the receiving
conveyor at start up, before or after the vertical curve. This is caused by peaks
in belt tension at start up which may cause the belt to lift off the idlers and chafe
against the chute. In some cases this can be solved by fitting a roller, as shown
in Figure 19, to the underside of the chute to protect it from being damaged by
the belt or to protect the belt from being damaged by the chute. The position of
this specific chute is just after a vertical curve where the belt tends to lift off at
start up.
Figure 19: Protective roller on a transfer chute
M.N. van Aarde
29
CHAPTER 2
2.4INVESTIGATING THE CORRECT CHUTE PROFILE FOR REDUCED LINER WEAR
In order to reduce chute wear, the curved-profile variable chute concept is
introduced [27]. This concept was originally developed by Professor Roberts for
the grain industry in 1969 [28]. After many years of research and investigation,
CMR Engineers and Project managers (pty) Ltd., came to the following
conclusion: any improvement in coal degradation, dust generation and chute
wear can only be achieved by avoiding high impact forces or reducing them as
much as possible [27].
At any impact point of material in a chute or conveyor, kinetic energy is
dissipated. This increases material degradation and wear on liners and conveyor
belt covers. Therefore, it is good practise to redirect the kinetic energy in a
useful manner. This action will help to reduce liner and belt wear [32].
x
Vo
- Impact Plate
Figure 20: Geometry of the impact plate and material trajectory [30J
The optimisation oftransfer chutes ;n the bulk materials industry
M.N. van Aarde
30
CHAPTER 2
The path followed by the material discharged over the end pulley of a belt
conveyor is known as its trajectory and is a function of the discharge velocity of
the material from the conveyor [29]. Figure 20 shows the material trajectory as
weI! as the radius and location of the impact plate. In the case of dynamic chutes
this impact plate represents the back plate of the chute.
The correct chute profile to reduce wear must cater for the proper location of the
chute covers and wearing plates. This location depends upon the path of the
trajectory which must be predicted as accurately as possible.
Figure 21: Mode! for the impact of a particle on a flat surface [29]
Figure 21 illustrates a material particle impinging on a flat chute surface at an
angle of approach 91, and with approach velocity V1. This particle will then
,
rebound off the chute plate at an angel 9
2
, and velocity V
2
. The wear on the
chute liners, or the surface, shown in Figure 21, will be a function of the vector
change in momentum of the particle. One component will be normal to and the
other component parallel to the flat surface. The parallel component is referred
\
to as the scouring component along the surface. [29].
It is important to determine the radius of curvature of material within the
trajectory. It is now a simple exercise to determine the chute hood radius
depending on plant constraints. Firstly the material trajectory must be calculated.
M.N. van Aarde
31
CHAPTER 2

According to the mechanical handling engineers association in Perth, Australia, it
is beneficial to keep the impact angle as small as possible. Impact angle less
than 20 are recommended for most liner materials. This will ensure an
acceptably small impulse force component normal to the surface. The at
which the material is gouging away the chute liner at the impact point will be
reduced [29].
The material trajectory is determined by equation l'
(1)
Where the origin of the x and y axis is taken at the mean material height, h, and
the discharge point on the pulley as shown in Figure 20. The variables involved
in the calculation of the material trajectory are [30]:
y =vertical position on the grid where the trajectory is determined
x = position parallel to the receiving belt line where the trajectory is determined
v = material speed
g =gravitational constant
a =inclination angle of the feeding conveyor
After the material leaves the belt, a simplified assumption can be made that it ,
falls under gravity. It is quite clear that in order to minimise the impact angle,
the impact plate must follow the path of the material trajectory as far as possible.
It will almost never be possible to obtain a contact point between the material and
the chute where there is a smooth contact with no impact angle.
This radius of curvature of the material is determined as follows [30}:
The optimisation of transfer chutes in the bulk materials industry i 32
M.N. van Aarde
CHAPTER 2
[1 + ( gx )]1.5
R = vcos8
c
(2)
vcos8
Where:
g == gravitational constant
v == material speed
8 == Angle at discharge
In order to simplify the manufacturing process of a curved chute, the radius must
be constant. For a relatively smooth contact between the material and the chute
plate, the radius of the curved chute, at the point of contact, is as close as
possible to the material discharge curvature radius [30]. This is rarely possible
on brown field projects due to facility constraints. In this case there will be higher
probability for rapid liner wear. Each situation must be individually assessed to
determine the best solution.
Cross sectional dimensions of the transfer chute must be sufficient to collect the
material and ensure continuous flow without causing blockages. At the same
time, the chute profile must not result in excessive material speed. Material
speed inside the chute will be considered to be excessive when it can not be
controlled to exit the chute at approximately the same velocity to that of the
receiving conveyor. Chutes may block for the following reasons [29]:
Mechanical bridging due to large lumps locking into one another
Insufficient cross section causing cohesive material to choke or bridge
Inadequate chute inclination causing fines build-up
Corner effects or cohesion causing material to stick to the chute walls.
M.N. van Aarde
33
CHAPTER 2
For the handling of large lumps of material, field experience has shown that the
chute cross sectional area should be 2.5 times the major dimension of the largest
lumps. To avoid possible bridging of the material in the chute, the
recommendation is to make the inner chute volume as large as possible. This
will be guided by the support steelwork around the transfer point [29].
Field experience has shown that it is advisable, depending on the material being
transferred, that the chute inclination angles be no less than 65 to 70
0
Corner
effects should also be avoided where material gets stuck in the inner corners of
chute plate work. These angles should preferably be no less than 70
0

2.5 FEED CHUTE GEOMETRY FOR REDUCED BELT WEAR
The design parameters to reduce both chute and belt wear are interrelated.
Research done at the Phalaborwa copper mine is a good case study to prove the
concept of a curved chute profile. This mine had specific problems with high belt
wear at transfer points. At this facility an in-pit 60 x 89 gyratory crusher and
incline tunnel conveyor was commissioned to haul primary crushed ore. A
conventional dead box chute transfers ore from the crusher to a 1800 mm wide
incline conveyor [31].
The maximum lump size handled by this section of the facility is 600 mm (60 kg).
An 18 mm thick top cover was specified for this conveyor with an 'X' grade
rubber according to DIN (abrasion value < 100 mm). This belt had an original
warranty 'of 10 years. After 3.5 years, the top cover started to show signs of
excessive wear and the tensile cords of the 18 mm thick cover were visible [31].
In April 1994, Phalaborwa commissioned the curved chute concept and a new
belt on the incline conveyor. Six months after commissioning, no gouging or
pitting damage was evident. The material velocity through this curved chute onto
the incline conveyor is shown in Figure 22 [31].
M.N. van Aarde
34
CHAPTER2
VELOCITY (m I aec )
_ .nm
_ . m
_ 1.211
_ UTI
_ U16
_ ' I.IU
_ I.m
_ I .rn
_ .171
-1'1'1
_ u n
_ ~ . l
_ 4 . ~
_ 4.1.,
_ 4.'"
\.141
CJ Uti
I.'"
'.1
-
,.1t5
, . ~
1.m
UI2
Material Flow Velocity Gradient
Figure22: Ore flow path in the curved chute onto the incline conveyor [31]
TENDENCYTOFORM
STAGNANTLAYERLEADING
TO INSTABILITYIN
DEPTHOF FLOW
C8FLOWIN CURVEDCHUTES
Figure23: Gentle deceleration of the product before impact on the receiving belt [32]
M.N.vanAarde
35
CHAPTER 2
Figure 23 illustrates the gentle deceleration of material that is achieved with the
curved chute concept. This helps to reduce belt wear because it is relatively
easy to discharge the material at the same velocity as the receiving conveyor.
The material speed, v, can be calculated at any point in the chute using equation
3 and equation 4 [33]:
v
~ R [(2,ue
2
-l)sin(O) +3,ue cos(O)] + Ke
2
,u,B (3)
4,ue +1
This equation is only applicable if the curved section of the chute has a constant
radius Rand I-Ie is assumed constant at an average value for the stream [33].
I-Ie = friction coefficient
8 = angle between the horizontal and the section of the spoon where the velocity
is determined and
(4)
The optimisation of transfer chutes in the bulk materja/s industry
M.N. van Aarde
36
CHAPTER2
MassFlowRate
Om
h
Figure 24: Typical feed chute discharge model [33J
ThevelocityV
e
, atthedischargeofthechute, can be determinedfrom equation 3
and equation 4. The components, Vey and Vex of the discharge velocity, as
shown in Figure 24, can now be calculated. This investigation should aid the
optimisationofthe chute profile in orderto [33]:
match the horisontal componentVex, ofthe material exitvelocity, as close
as possibletothebeltspeed
reduce the vertical componentV
ey
, ofthe material exitvelocity, in orderto
minimizeabrasivewearon thereceiving conveyor.
2.6 CONCLUSION
This section discussed the technical background necessary for the optimisation
of transfer chutes, on an existing iron ore plant, which will be discussed in
Chapter4. Thefocus isspecificallyaimed atreducing impactwearon chuteliner
materials and abrasivewearon receiving conveyorbelts. Importantto notefrom
M.N. vanAarde
37
CHAPTER2
this section is the acceptable limits of dynamic chute optimisation or design.
Theselimitsare:
amaterialimpactangleoflessthan20
a variance ofless than 10% between the receiving belt velocity and the
materialdischargevelocitycomponentparalleltothe receiving conveyor.
An important aspect of chute optimisation is to consider the facility constraints.
These constraints are in some cases flexible, but in most cases the chute
optimisation process mustbe designedwithin these constraints. This meansthat
any new concept will have to be measured againstwhat is possible within the
facilitylimits.
It is importantto notethat only the most common transfer chute problems were
mentioned in this chapter. Otherpossible problems were not addressed in this
chapter as it is normally related to detail design issues. Solutions to these
problems are uniqueto each type ofchute and will be addressed forthespecific
casestudyin Chapter4.
The optimisafjon oftransfer chutes in the bulk materials industry
M.N. vanAarde
38
CHAPTER 3
M.N. van Aarde
CHAPTER 3: TESTS FOR THE IDENTIFICATION OF RECURRING
PROBLEMS ON EXISTING CHUTES
39
CHAPTER 3 .
3.1 PREFACE
Since the completion of a certain iron ore handling facility, it has been
experiencing recurring material transfer problems at high capacities. In order to
investigate the problem, it was decided that performance testing of the chutes
should be carried out. The purpose of these tests was to monitor chute
performance at transfer rates of up to the design capacity of 10 000 tlh for
various grades of iron ore handled by the facility. Some of the methodologies
used in testing are only applicable to this specific facility.
Due to variations and surges associated with the reclaim operations at the
facility, performance testing focused on reclaim side chutes. This means that all
the transfer points at the exit points of the stockyard conveyors were tested.
Nineteen tests were conducted on various stockyard transfers. Information such
as the specific facility or conveyor numbers cannot be disclosed due to the
confidentiality of information.
To analyse SCADA data, the stacker reclaimer scale is used to determine the
peak surges passing through the transfer under investigation. The reason for
this is that the peaks in flow, due to reclaiming operations, flatten out when
passing through the transfer points. This is due to chute throat limitations and
small variations in belt speeds. If the down stream scales are used it would give
an inaccurate indication of the amount of ore that passed through the transfer
chute.
3.2 TEST METHODOLOGY
A CCTV camera was installed in a strategic position inside the head chute of the
stockyard conveyors. These cameras provided valuable information on the
physical behaviour of the material flow inside the transfer chutes. Where
possible, cameras were also placed on the receiving belt in front of and behind
M.N. van Aarde
40
CHAPTER3
the chute. Thiswas doneto monitorbelttracking and spillage. A high frequency
radio link between the head chute and the control tower made it possible to
monitorthecamerasatall times.
SCADA data was used to determine and establish the condition ofthe material
transferatthetimeofthetest. Data from various scales en routewere obtained
as well as confirmation ofblocked chutesignals. In analysing the SCADAdata,
thestackerreclaimerscaleis usedto determinethepeaksurges passingthrough
thetransferbeingtested.
Data was recorded from a sampling plantatthe facility. This data provides the
actual characteristics of representative samples taken and analysed by the
sampling plant during the duration of the test. The data gathered consist of
moisturecontentofthematerialsampleaswellasthesizedistributionoftheore.
Where possible, an inspector was placed at the transfer point being tested to
observe and record the performance. The inspector had a two way radio for
communication with the test co-ordinator in the central control room. Hewould
also be responsible for the monitoring ofany spillage, dust emissions etc. that
maynotbepicked up bythecameras.
Prior to commencing a test on a specific conveyor route, the following checks
hadto beperformed on allthematerial conveying equipment:
Clean out all transfer chutes and remove any material build-up from the
sidewalls
Checkthatfeed skirtsare properlyin position on thebelt
Checkthattheconveyorbeltistracking properlyatno load
Checkconveyoridlersareall in position and freeto rotate
Checkblocked chutedetectorsareoperational and in thecorrectlocation
M.N.vanAarde
CHAPTER3
Changethe position ofthe blocked chutedetectorifrequired to improveits
fUnction
Testand confirmthattheCCTVsystemsarefunctioning correctly
Assign persons with 2 way radios and cameras to monitorand record the
I
results ateachtransferpointontheroute.
3.3 CHUTEPERFORMANCE ACCEPTANCE CRITERIA
A material transfer chute performs to specification ifit transfers a maximum of
10000 tlh ofa specificiron are gradewithoutexperiencing any ofthe following
problems:
Material build up insidethe chute orblocking the chute, i.e. material is not
exitingthechuteatthesamerate asitis entering
Materialspillageencounteredfrom thetop ofthetransferchute
Material spillage encountered where material is loaded onto the receiving
conveyor
Belt tracking of the receiving conveyor is significantly displaced by the
loading ofmaterialfromthetransferchute ontotheconveyor.
Tests were conducted over a period ofone month and in such a short period
visible wear is difficultto quantify. Due to the sensitivity ofthe information no
historical data in terms ofchute orbeltwearwere madeavailable bythefacility.
Therefore it is not part ofthe criteria for these specific tests. Should a chute
however fail to perform according to the set criteria it validates the need for
modificationsornewdesigns.
3.4 DISCUSSION OF PROBLEM AREAS
The major concern during the testwork is material flow at the transfer points.
Secondary concerns are spillage, tracking of the receiving belt and material
M.N. vanAarde
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loading onto the receiving belt. One of the external factors that playa significant
role in material flow rate is the method and process of reclaiming. This section
will highlight all the problem areas observed during the test work.
Figure 25 shows the layout of the stockyard area. This layout will serve as a
reference when the specific test results at each transfer point are discussed. The
legends for Figure 25 are as follows.
c:::=> Transfer points where performance tests have been done
Direction that the conveyors are moving in
CV#4 CV#3 CV#2 CV#1
Figure 25: Layout of conveyors for chute test work
All four stockyard conveyors have a moving head arrangement. This means that
the chutes are split up into two sections. A moving head discharges material
onto either conveyor (CV) #5 or CV #6 via a static transfer chute. The moving
head positions are shown by A, Band C in Figure 25.
M.N. van Aarde
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CHAPTER 3
Position C is the purging or dump position. This position is used when the
stacker reclaimer is in stacking mode and any material left on the stockyard
conveyor gets dumped. The material does not end up on the stockpiles,
preventing contamination.
90 de-g TRANSFBt
OfAO BOX IN MOVING HEAD
Figure 26: Configuration of the existing transfer chute
Figure 26 shows the configuration of the existing transfer chutes. These chutes
capture the trajectory from the head pulley in a dead box situated in the top part
of the chute. The material then cascades down a series of smaller dead boxes
onto the receiving conveyor below.
Various grades of iron ore were tested during the testing period. These different
grades of iron ore are shown in Table 2. Three fine grades and four coarse
grades were used. The coarse material is defined as particles with a diameter of
M.N. van Aarde
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CHAPTER3
between 12 mm and 34mm and the fine material with diameters of between
4 mm and 12mm.
Table2: Iron are grades used for chute test work
Material PredominantLumpSize
Fine K 5mm
FineN 8mm
FineA 8mm
Coarse K 25mm
CoarseD 34mm
CoarseS 12mm
CoarseA 20mm
The CCTVcameras were placed inside the moving head pointing down into the
static chute overlooking the receiving conveyor. Figure 27 shows the camera
angle used during testing. This is a view ofa clear chute before testing. The
legendsforclarificationofall thevideo imagesare asfollows:
Frontofthechutethroatopening
Topofflowing materialatthechutethroatopening
Flowpattern ofthematerial
Direction ofthereceiving belt
M.N.vanAarde
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CHAPTER 3
Figure 27: Clear chute indicating camera angle
3.4.1 Coarse Material vs. Fine Material
Differences in transfer rates between coarse material and fine material are
evident from the data gathered during the test programme. These results are
discussed later in this chapter. The area between the yellow arrows and the red
line is the amount of 'freeboard' available. Freeboard is the open space available
between the top of the flowing stream of material and the chute plate work.
Figure 28 and Figure 29 shows the flow of coarse ore and fine ore respectively in
the same chute at 8 000 tlh.
Figure 28: Coarse material at 8 000 tlh
M.N. van Aarde
46
CHAPTER 3
Figure 29: Fine material at 8 000 tlh
The amount of 'freeboard' with fine material is much larger than with coarse
material. It is, therefore, obvious that coarse material is more likely to block a
chute when peak surges occur. This is due to particles that interlock in the small
discharge opening of the chute.
Figure 30: Blocked chute with coarse material at 8 600 tIh
Figure 30 is a snap shot of a chute blocked with coarse ore due to the material
interlocking at the discharge opening. The time from material free flowing to a
blocked chute signal was approximately 10 seconds. This is determined by
comparing the CCTV camera time to the blocked signal time on the SCADA.
M.N. van Aarde
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CHAPTER 3
The high clay content in finer material can also cause problems in the long run.
When wet 'Anes are fed through the chutes a thin layer of 'Anes builds up and
sticks to the sides of the chute. As this layer dries out it forms a new chute liner
i
and the next layer builds up. This process occurs gradually and will eventually
cause the chute to block.
3.4.2 Cross Sectional Area
Video images of a blocked chute on the receiving belts were analysed to
determine whether the blockage was caused by material build up on the belt
underneath the chute. This indicated that with the occurrence of a blocked chute
the material keeps flowing out of the chute at a constant rate without build up.
From this the assumption can be made that, in the case of a blocked chute, the
material enters the chute at a higher rate than it is discharged at the bottom.
Therefore, the conclusion can be made that the chute cross sectional area at the
discharge is insufficient to handle the volume of ore at high throughput rates.
Tests with a certain type of coarse material yielded a very low flow rate requiring
adjustment to the chute choke plate on the transfer between CV #3 and CV #5.
The chute choke plate is basically a sliding door at the bottom of the chute to
adjust the discharge flow of material. Tests with another type of coarse material,
shown in the summary of test results, indicates how the choke plate adjustment
can increase the throughput of material in the chute.
Data of all the different types of ore at the facility are obtained at the sampling
building. This data shows that the material size distribution for the two types of
coarse material, used in the tests mentioned above, are the same. This indicates
that the test results with the second coarse material are an accurate reflection of
what will be experienced with the first type of coarse material. Special care
M.N. van Aarde
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CHAPTER 3
should be taken when adjusting the choke plate to make sure that skew loading
is not induced by the modification.
3.4.3 Spillag/3
During one of the first tests on the transfer between CV #2 and CV #6, spillage
was observed at one of the side skirts on the receiving belt. A piece of the side
skirt had been damaged and pushed off the belt as shown by Figure 31. This
caused some of the material to be pushed off the belt when skew loading from
the chute caused the belt to miss track. In this case, spillage was not caused by
the skirt but by skew loading from the chute onto the receiving conveyor.
Figure 31: Damaged side skirt
A greater concern is spillage on the moving head chute of CV #3 and CV #4
loading onto CV #6. It appears as if the head chute creeps during material
transfer onto CV #6. As the chute creeps, the horizontal gap between the
moving head chute and the transfer chute reaches approximately 180 mm.
Facility operations proposed a temporary solution by moving the head chute to
the dumping or purging position and back to CV #5 before stopping over CV #6.
The reason for this creep could be attributed to slack in the moving head winch
cable.
M.N. van Aarde
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CHAPTER 3
3.4.5 Belt Tracking and Material Loading
The only belt tracking and material loading problems observed occurred on the
transfer between CV #2 and CV #5 I CV #6. A diverter plate was installed at the
bottom of the chute in order to force material flow onto the centre of the receiving
,
conveyor belt. This plate now causes material to fall to the left of the receiving
belt causing the belt to track to the right.
Figure 32: View behind the chute of the receiving conveyor before loading
Figure 32 shows the view from a CCTV camera placed over the receiving
conveyor behind the chute. Note the amount of the idler roller that is visible
before loading.
Figure 33: View behind the chute of the receiving conveyor during loading
M.N. van Aarde
50
CHAPTER 3
Figure 33 shows the view from a CCTV camera placed over the receiving
conveyor behind the chute during loading. Note the difference between the
amount of the idler roller that is visible between Figure 33 and Figure 32. This is
a clear indication of off centre belt tracking due to skew loading.
I
At the same transfer point it appears as if the configuration of the chute causes
the material to be dropped directly onto the receiving belt from the dead box in
the moving head. This will cause high impact wear on the belt in the long run.
High maintenance frequencies will be required on the impact rollers underneath
the chute and the roller bearings will have to be replaced frequently.
3.4.6 Reclaiming Operations
Reclaim operations are done from the stacker reclaimer that scoops up the
material with a bucket wheel from the stockpile. The machine starts at the top
bench of the stockpile and reclaims sideways until it is through the stockpile.
This sideways movement is repeated while the machine moves down the
stockpile. If the machine digs too deep into the stockpile small avalanches can
occur that over fill the buckets. This causes peak surges in the flow on the
conveyor system.
With an increase in the peak digging or reclaim rate, as requested for test work, it
seemed that the peak surges increased 'as well. In normal reclaiming operations
(average reclaim rate of 6 000 tlh to 7000 tlh) the peaks in reclaim surges do not
usually exceed 1 000 tlh. This is, however, dependent on the level of the
stockpile from where the machine is reclaiming.
At a peak digging or reclaim rate of 8 000 tlh, peak surges of up to 2 000 tlh were
observed as can be seen from Figure 34. All stacker reclaimers are operated
manually and the depth of the bucket wheel is determined by monitoring the
M.N. van Aarde
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CHAPTER3
reclaimerboom scalereading (yellowline). This makes itdifficultto reclaim ata
constantrate.
The reason for the high peak surges is due to avalanches on the stockpile
caused by reclaiming on the lower benches without first taking away the top
material. The blue line in Figure 34 represents a conveyor scale reading after
the material has passed through a series oftransfer chutes. It is clear that the
peaks tend to dissipate over time as the peaks on the blue line are lower and
smootherthan thaton theyellowline.
IlmJ
I _ It.. .. .. ..
:: J::::]:::-::-EiE:
::'.... 1::-
5. i .. i 1
.s:::. --.. ----.... .. -. _..- ....... --------............ -.-.. .. ..... --... - .._--.-- ... . .... --.. ................. "-r .. - ..---. . ................-._- p"
C) :::.: : : : : : : : : : :
: :::::::1::::::r =r=:l:::::::;::::::'[:::=1:::::-I:::::::t:-:::::1::::: -':::- -:::t=::::---
...._ ....-r............r.... ".. .. [ ......_......r...._...._.. r- ........ .. r ...... -r..- ..r--........;- .. ...... -r...... .. .......... .. -r""-"r"............:.. ..
:lX>O ["l,.lir-..............j... 1'..1"1', .....l....tj..
........["[, ' 1..11 ,i...... ..r..
t)
i i l i i i i i i i it
8
;;. ;;
S :l i
';'
!
"
Ii
g
i 'i '4. !1 :J. i
s a e 1':1 J!I as $ $ IS
"
IS e I!t
Time
___ SCALE
Figure34:Peak surges experienced during reclaiming operations
3.4.7 Other Problem Areas
Some blockages on other chutes at the facility occurred while testing the
stockyard chutes. These blockages are also shown in Table 3, where the test
M.N. vanAarde
52
CHAPTER 3
results are discussed, and to raise awareness that the bottlenecks on site are not
only caused by problems on the tested chutes.
A chute downstream from the stockyard:s encountered a blockage with fine
I
material when the flow rate reached 11 OOb tfh. Although this is higher than the
test maximum of 10 000 tfh, it still raises concern as to why the chute blocked so
severely that it took approximately two hours to clear.
Another bottleneck is the transfer point between the feed conveyor of CV #2 and
the discharge chute on CV #2. This transfer point blocked with fine material at a
peak just below 10 000 tfh. It should be even worse with coarse are as
previously discussed. Due to the configuration of the head chute, spillage of
scraper dribblings is also of great concern. The main stream of material
interferes with the flow path of the dribbling material. Therefore, the carry back,
scraped off the bottom of the feeding belt, cannot ~ o w down the chute and is
pushed over the sides of the chute.
The optimisation of transfer chutes in the bulk maferia/s industry
M.N. van Aarde
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3.5 SUMMARY OF TEST RESULTS
Table 3: Results from test programme
Transfer Point Material Tested Test No. Peak Capacity Blocked Chute
CV#11 CV#5 Yes
Fines N 14 10000 tlh No
Fines N 15 10000tlh No
CV #11 CV#6 Coarse K 20 9300 tlh No
Fines K 4 10600tlh No
Fines A 19 9633 tlh No
CV#31 CV#5 Yes
Yes
Yes
Coarse A 17 9427 tlh No
CV#31 CV#6 Coarse K 7 10195t1h Yes
Coarse K 8 11 000 tlh Yes
CV#41 CV#5 Coarse A 16 10307 tlh No
No (Mech trip on
CV#4/CV#6 Fines K 10 10815 tlh downstream conveyor)
Coarse K 11 8000 tlh No
Fines A 18 10328 tlh No
No (Feed to CV #2
CV#21 CV#5 Fines N 13 10 000 tlh blocked)
CV#21 Coarse K 1 & 2 10 153 tlh No
No (Blocked chute on
Fines K 3 11 000 tlh downstream transfer)
M.N. van Aarde
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CHAPTER 3
Table 3 shows the results obtained from all the tests on the stockyard conveyor
discharge chutes. Where possible, the same material grade was tested more
than once on the same transfer in order to confirm the repetitiveness of the test.
The tests shown in red indicate the transfers that blocked at a flow rate of less
than 10000 tlh.
Coarse K and Coarse 0 are noted as the critical materials for blocked chutes
caused by a peak surge. Tests with Coarse K and Coarse S, where a blocked
chute occurred at just over 10 000 tlh, can also be considered as failed tests.
This is due to the lack of a safety margin 'freeboard' inside the chute. When
analysing the video images, a build up can be seen at a flow rate of less than
10000 tlh.
Table 3 indicates that the fine material did not cause blocked chutes, but it was
seen that it did fill up the chute throat area in some cases. Although the coarse
material grades are shown as being least suitable for high flow rates, the fine
material should not be underestimated for its ability to cause blockages. The
finer materials normally have higher clay contents than the coarse grades and
therefore stick to the chute walls more easily_
3.6 CONCLUSION
At lower capacities (7 000 tlh to 8 000 tlh) the material appear to flow smoothly
inside the chutes without surging or building up in the chute., This flow rate
normally does not cause spillage or skew loading on the receiving conveyor belt.
On average, as the flow rate approaches 9 000 tlh, the material in the chute
throat area starts packing together and finally blocks up the chute.
At transfer rates greater than 9 000 tlh the available area inside the chutes is
completely filled up. This causes material to build up or surge inside the chute
which eventually results in the chute choking and the inlet flow becomes greater
M.N. van Aarde
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CHAPTER 3
than the outlet flow. Depending on the volume of the chute, the choked state can
only be maintained for a certain period of time. If the inlet flow does not
decrease it will cause a blocked chute.
Peak surges of up to 10 000 tfh were recorded in most tests which involved a
material surge inside the chute but without the occurrence of a blocked chute trip.
Although no blocked chute signal was given in these cases, the ability of the
chutes to transfer continuously at flow rates of between 9 000 tfh and 10 000 tfh
is not very reliable.
Continuous transfer at flow rates approaching 9 000 tfh seems attainable in most
cases, but due to the limited 'freeboard' available in the chute throat area, the
chutes will easily become prone to blocking. Due to the high peak surges at an
increased maximum reclaim rate, the amount of 'freeboard' is critical. If the
design criteria of the chute were intended to accommodate these large surges,
then all the chutes failed this test. This can be attributed to the fact that no
'freeboard' is left at a maximum reclaim rate of 9 000 tfh.
With the background available from the test programme, it is clear that further
investigation is required to obtain a solution to these problems. All the
information gathered can be integrated and utilised to provide a solution. A
possible solution can then be tested against the problems found with the current
transfer chutes.
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CHAPTER 4
CHAPTER 4: DYNAMIC CHUTES FOR THE ELIMINATION OF
RECURRING PROBLEMS
M.N. van Aarde
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4.1 PREFACE
After completion of the chute test programme the decision was made to improve
the old transfer configuration by installing a dynamic chute. The reason for the
dynamic chute is to increase the material speed and decrease the stream cross
sectional area. The dead boxes in the older chute slowed the material down and
the restriction on transfer height resulted in the material not being able to gain
enough speed after impacting on the dead boxes.
A dynamic chute configuration is investigated in this chapter. As the new chute
is fitted within the existing steelwork there are certain constraints that determine
the new configuration. All the constraints and limitations discussed in this section
are specific to the facility under discussion.
The new chute design basically consists of a hood and spoon which retains the
kinetic energy in the material stream as it is transferred from one conveyor to the
other. This will reduce the creation of dust in the chute and help to discharge the
material at a velocity closer to that of the receiving conveyor. The new design
does however experience high wear which was not a problem with the old chutes
due to large dead boxes.
In order to fit the optimum design of a dynamic chute within the existing structure
some changes are required to the positioning of the feed conveyor head pulley.
These changes are necessary to accommodate the discharge trajectory from the
feeding conveyor.
The radii of the hood and spoon are specified in such a way that the impact wear
is reduced significantly. In addition, both the hood and spoon are fitted with a
removable dead box section in the impact zones. The incorporation of these
sections makes this chute revolutionary in the sense of ease of maintenance.
M.N. van Aarde
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CHAPTER4
This new chute addresses all problems identified at the facility and aims to
eliminatemostofthem.
Tests were carried out to identify worst case materials for flow and wear.
Different liner materials were tested for both flow and wear conditions. The
outcome ofthese tests is used as the basis for the design of a newchute. As
different conditions for flow and wear inside the chute exist, different liners are
investigatedforeachsectioninsidethechute.
4.2CONSIDERATIONOFTHEEXISTINGTRANSFERPOINTCONSTRAINTS
The stockyard consists of four stacker reclaimers and several transfer points
feeding onto the two downstream conveyors, resulting in avery intricate system.
This system has numerous requirements which need to be addressed when
considering a new transfer chute configuration. The transfers under discussion
aresituatedatthe head end ofthe stockyard conveyors.
MOV1NGHEADO\'ER MOvm!ADOVER
CVI6 CVIS
t4CLIESECTION
PURGINGPOSmON
Figure35: Stockyard head end layout
The design ofa newtransfer chute configuration is restricted to a certain extent
by the existing structures on site. Figure 35 provides an overall view of the
existing steelworkatthe head end ofthe stockyard conveyor. Thisexisting steel
structure can be modified to suit a newconfiguration but does have some fixed
M.N. vanAarde
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CHAPTER 4
constraints. A good example of these constraints is the transfer height between
the stockyard conveyor and the downstream conveyors CV #5 and #6.
On both sides of the stockyard conveyor, stockpiles of ore can be reclaimed and
deposited onto the conveyor. This facility allows a certain travel for the stacker
reclaimer along the stockyard conveyor for the stacking and reclaiming of
material. The most forward position of the stacker reclaimer is at the beginning
of the incline section of the stockyard conveyor. As previously explained, any
curvature in a conveyor requires a certain minimum radius. When the transfer
height is raised, the radius constraints on that curvature in the stockyard
conveyor will reduce stockyard space. This means that the storage capacity at
the facility will be greatly diminished.
I

j
Figure 36: Dimensional constraints on the existing transfer configuration
The ideal is to stay within the eXisting critical dimensions as shown in Figure 36.
As functionality of the chute dictates the chute configuration, these dimensions
can be modified within certain constraints. These critical dimensions on the
existing configuration are:
M.N. van Aarde
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CHAPTER 4
Centre of receiving belt to centre of the head pulley 800 mm
Bottom of receiving belt to top of the head pulley 4048 mm
The head pulley can, however, be moved back a certain amount before it
becomes necessary to change the entire incline section of the stockyard
conveyor. As the moving head moves forward and backward there are idler cars
trailing behind the moving head carriage as shown in Figure 35. The purpose of
these idler cars is to support the belt when the moving head is feeding onto
CV #6 or when it is standing in the purging position.
4.3 DESIGN OF THE CHUTE PROFILE
4.3.1 Design Methodology
Proven standard methods for the functional design of the chute are used. These
hand calculation methods are based on the Conveyor Equipment Manufacturers
Association (CEMA) standard as well as papers from Prof. A.W. Roberts. These
are typically calculations for determining the discharge trajectory, optimal radius
of the hood and spoon as well as the velocity of material passing through the
chute.
In addition to standard methods of carrying out conceptual flow design, it is
supplemented by the use of Discrete Element Modelling (OEM) simulation
software. This is done to visualise the flow of material through the chute.
Results from standard calculation methods are compared to the outputs of the
OEM simulations to confirm both results. Chapter 5 will focus on the use of
Discrete Element Modelling for the design and verification of chute concepts.
M.N. van Aarde
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-_..._-----_._---_.-----------
4.3.2 Design Development
Figure 37 shows the concept of the hood and spoon chute for a 90 transfer as
required by the facility layout. The decision to opt for a hood and spoon chute is
based on trying to retain the material velocity when transferring material from the
feeding conveyor to the receiving conveyors. Retention of material velocity is
critical as the transfer height is restricted. The overall facility constraints for
design are as follows:
Feeding belt speed - 4.5 m/s
Receiving belt speed - 4.5 m/s
Transfer height - 4.01 m
Belt widths
-1650 mm
Maximum material throughput -10000 tlh
As this is a retrofit of an existing facility, some of the facility constraints cannot be
changed. This forms part of the design development as it steers the design in a
certain direction. Due to the fact that the transfer height cannot be changed, the
chute profile will be dependent on the transfer height restriction.
The optimisation of transfer chutes in the bulk matef;ials industry
M.N. van Aarde
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CHAPTER 4
START-UP CHrrl:E
DRlBBIlNGCHUTE.
Figure 37: Hood and spoon configuration for the 90' transfer
The optimum solution for the correct chute profile, in this situation, would be to
move the head pulley back far enough. This should be done so that the hood
can receive the material trajectory at a small impact angle and still discharge
centrally onto the spoon. However, the head pulley can only be moved back a
certain amount. Any further movement will require changes to the structure of
the feeding conveyor incline section.
As the stockyard conveyors feed onto two receiving conveyors, the head pulley
of the stockyard conveyors is situated on a moving head rail car. This enables
the conveyor to discharge either on CV #5 or CV #6 as shown in Figure 25.
Taking the movement of the head pulley into account, the moving head rail car
can be shortened by 1000 mm in order to move the head pulley back. As stated
in the preface, all changes are distinctive to this facility alone. However, it is
important to be aware of the consequences of every modification.
:The optimisation of transfer chutes in the bulk materials industry
M.N. van Aarde
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-_......._----- -------
4.3.3 Determination of the Profile
An important of the hood and spoon design is to ensure a
discharge from the hood onto the centre of the spoon. The is
determined using equation (1) in section 2.4. Although various material
are transferred it does not have a significant effect on the calculated trajectory
the bulk properties of the materials are very similar. It is however important
to the material which will transferred obtain the flow angles and wear
This information the will be
the Liner selection for this case study is discussed in Appendix A.
After the trajectory has been determined, the hood radius can determined by
using equation (2). As head pulley can move 1 000 mm backward, the
possible hood radius was determined to 2 577 mm. This hood radius is
VI'"U::'(,,"I""'('1 to produce the wear on the zone in chute.
The impact angle at this radius is 11" which is less than the maximum
allowable limit of 20".
The hood radius is chosen to as close as possible to radius of curvature of
the material trajectory. The point where the hood radius and the trajectory radius
cross is known as the impact point. In to determine the velocity
point in hood, the at is required. on the
hood from the horizontal where the material impacts and to slide down the
hood surface.
In this case the position impact hood is at 55.8r from the horizontal.
In to determine the velocity, this angle {e} is used as starting
point in (3). obtain a complete velocity profile, angle from where
the material impacts hood is decreased in increments 5" up to the
discharge point which is normally 0".
The optimisation chutes in the bulk materials industry
M.N. van Aarde
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-----
CHAPTER 4
Hood Velocity Profile
7.0
-
.--
--

6.0
5 . 0
4.0 _

3.0 g
---
a;
2.0 >
1.0
0.0
60 50 40 30 20 10 o
Theta (Position inside the hood)
Figure 38: Hood velocity profile
The spoon radius is determined in such a way that the wear at the point of impact
is kept to a minimum. At the same time the horizontal component of the material
exit velocity is as close as possible to the receiving belt speed. Firstly the
assumption is made that the initial velocity of material in the spoon is equal to the
exit velocity of material from the hood. This yields a spoon entry velocity of
6.33 m/s and can also be seen from Figure 38.
By reiterating various radii for the spoon, the optimum exit velocity, Ve can be
obtained. These radii are selected according to the available space in which the
spoon must fit and also to produce the smallest impact angle for material
discharging from the hood. This table is set up to display the different exit
velocities at various spoon radii. The exit velocity is also dependent on the exit
angle which is determined by the length of the spoon arc. In this case the spoon
radius is chosen as 3 575 mm. An exit angle of 38from the horizontal yields an
exit velocity closer to the receiving belt speed.
M.N. van Aarde
65
CHAPTER 4
Spoon Velocity Profile
6.7
6.6
...... 6.5
.!!!
S. 6.4
&;0
.g 6.3
V
/'
v-- ~
' ~
"'"
"ii
~
> 6.2
6.1
I'
'"
I
6.0
o 10 20 30 40 50 60
Theta (position inside the spoon)
Figure 39: Spoon velocity profile
Taken from the origin of the spoon radius, the material position in the spoon at
discharge is sr. The selection of this angle is guided by the geometry of the
chute and surrounding structures. This angle is then used to calculate the exit
velocity as shown in Figure 39. At this point the discharge angle relative to the
conveyor angle is 38. Ve is then determined to be 6.087 m/s with a velocity
component of 4.79 m/s in the direction of the belt. This value is 6.18% higher
than the belt speed of 4.S m/s which is acceptable as it is within the allowable
10% range of variation. Minimal spillage and reduced wear on the receiving
conveyor is expected.
Both the hood and spoon have a converged profile. This is done in order to
minimise spillage and ensure a smooth transfer of material from the hood to the
spoon and from the spoon to the receiving conveyor. The converged profile
starts out wide to capture any stray particles and converges to bring the material
particles closer together at the discharge. This profile does not influence the
transfer rate of the chute as the stream of material through the chute is no more
M.N. van Aarde
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CHAPTER 4
compact than the material on the conveyor belt before and after the transfer
chute.
4.4 INCORPORATING ADEAD BOX IN THE IMPACT AREAS
In chapter 1 reference is made to a chute design utilising pipe sections with a
rounded profile. The flat back plate is chosen instead of a rounded pipe type
section to house the honeycomb dead box configuration. It would be possible to
fit the honeycomb into a rounded back section but manufacturing and
maintenance would be unnecessarily difficult and expensive.
Furthermore, the cross section profile of the chute shows three sliding surfaces
as shown in. These surfaces consist of the back plate, two vertical side plates
and two diagonal plates. This is done in order to increase the angle between
adjoining plates so that the probability of material hanging up in the corners is
reduced. This helps to alleviate the risk of experiencing blocked chutes.
Figure 40: Chute cross section
M. N. van Aarde
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CHAPTER 4
4.4.1 Honeycomb Wear Box in the Hood
A honeycomb or wear box is incorporated into this chute configuration in order to
further minimise wear in the hood and spoon. The honeycomb configuration is
clearly shown in and is typical for both the hood and spoon. Reduced wear will
I
be achieved as impact and sliding will take place on the basis of material on
material flow. Ore is captured inside the honeycomb pockets which protects the
ceramic lining in the section of the honeycomb and creates another sliding face
made of the material being transferred. The ribs in the wear box do not protrude
from the sliding face of the chute and, therefore, do not interfere with the main
stream flow of material.
Positioning of the honeycomb is critical as the point of impact on the hood needs
to be on the honeycomb. This is required in order to assure that the highest
material impact is absorbed by a layer of static material inside the honeycomb
and not the chute liners. All the basic steps for designing a normal hood and
spoon chute are followed. Firstly the angle at impact (8
e
) is calculated to
determine where the trajectory of material will cross the radius of the hood. This
shows the position of the impact point on the hood. Figure 20 indicates where 8
e
is calculated. As previously stated, the angle at impact for this situation is
55.8r. This is calculated using [33]:
e =tan-
I
( 1/ ) (5)
C Ii
And y is defined by equation 1.
This gives an indication as to where the honeycomb should be situated in order
to capture the material impacting the hood fully. A flow simulation package can
also be used to determine the position of this honeycomb structure. shows an
opening for the honeycomb which starts at 40 clockwise from the vertical. This
The optimisation of transfer chutes in the bulk materials industry 68
M.N. van Aarde
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means that there are almost 16 of free space in the honeycomb to ensure that
the material will always impact inside the wear box.
There is no set specification as to the size of this free space. This is just to
accommodate any surges of m t ~ r i l on the feeding conveyor. As discussed in
Chapter 3, due to avalanches while reclaiming from the stockpiles, material
surges on the conveyors is a reality.
Figure 41: Honeycomb wear box positioning
illustrates exactly where this wear box is situated on the back plate of the hood.
This configuration is very similar to that of the spoon as both wear boxes only
cover the width of the flat back plate of the hood and spoon. The reason for this
is that most of the material impact and mainstream flow strikes the back plate.
M.N. van Aarde
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CHAPTER 4
WEAR BOX
Figure 42: Wear box in the hood section
All the horizontal ribs of the honeycomb are spaced 5 apart and there are 5
vertical ribs following the converging contour of the hood as shown in. Spacing
of the ribs depends largely on the maximum lump size handled by the transfer.
In this case the largest lumps are approximately 34 mm in diameter. The idea is
to get as many dead boxes into the honeycomb as possible. These small
cavities should, however, be large enough to capture a substantial amount of ore
inside.
M.N. van Aarde
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CHAPTER 4
----_. -----'------------
Figure 43: Spacing arrangement of honeycomb ribs inside the hood
The two vertical liners on the edges of the honeycomb are only 65 mm high while
the rest of the vertical liners are 120 mm high. This is done so that the flat liners
in the chute surface can overlap the edge liners of the honeycomb. An open
groove between the tiles along the flow of material would cause the liners to be
worn through much faster than in normal sliding abrasion conditions. Due to the
high wear characteristics of the ore all openings between tiles should be kept out
of the mainstream flow.
All the ribs in the honeycomb are 50 mm thick and vary in depth. The vertical
ribs protrude the horizontal ribs by 30 mm in order to channel the flow. These
vertical ribs are all flush with the surrounding tiles on the flat sliding surface of the
hood. All the pockets of the wear box are 120 mm deep measured from the top
of the vertical ribs. Again, dimension is dependent on the maximum lump size
handled by the transfer. There are no specifications as to the relation between
the pocket size and the lump size. These dimensions were chosen to be
approximately 4 times the lump size. Computer simulations can be used to test
the feasibility of this concept while commissioning of the equipment will ultimately
show whether this method works.
M.N. van Aarde
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CHAPTER 4
------------_.. -- - ----------------
4.4.2 Honeycomb wear box in the spoon
The honeycomb wear box in the spoon has the same configuration as in the
hood. It also covers the entire width of the back plate and fully accommodates
the material impacting on the spoon from the hood. The entire spoon is broken
up into three sections and the honeycomb wear box is situated in the back
section as shown in .
Figure 44: Wear box in the spoon section
With almost the same configuration as the hood, the spoon also has a corner
liner to ensure a continuous lined face between the flat surface liners and the
honeycomb ribs. The detail of these liners and ribs are shown in. A 90transfer
with a hood and spoon chute means that the stream received by the spoon is
narrower and longer than the stream received by the hood. This is caused when
the material takes the shape of the hood before it is discharged into the spoon.
The converged configuration causes the stream to flatten against the sliding
surface in the chute.
M.N. van Aarde
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CHAPTER 4
Due to the spoon honeycomb being a bit narrower than the hood there are only
three vertical ribs. The number of ribs had to be reduced to be able to
accommodate the preferred cavity size of the honeycomb boxes. These ribs now
form two channels in which the stream of material can be directed.
Figure 45: Liner detail of the spoon honeycomb wear box
As shown in there is a 3 mm gap between the honeycomb section and the chute
plate work. This is to ensure that the honeycomb section can be easily removed
for maintenance on the liners. All the edges of the liners have rounded corners
to reduce stress concentrations which can cause rapid liner failure.
4.5 DESIGNING THE CHUTE FOR INTEGRATION WITH SYSTEM REQUIREMENTS
The arc length of the spoon back plate is longer and closer to the belt in order to
ensure a smooth transfer of material from the chute to the receiving conveyor. A
small gap of 75 mm is left between the bottom of the spoon and the receiving
conveyor. Due to the fact that material can also be fed from another upstream
M.N. van Aarde
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CHAPTER 4
stockyard conveyor, this configuration will not be suitable. This means that the
gap of 75 mm is not enough to allow material to pass underneath the chute.
To accommodate this situation the spoon is split into different sections where the
bottom section lifts up to make room for material from behind. In the raised
position the gap between the chute and the belt is 450 mm. When the lower belt
is loaded to full capacity the material height is 380 mm. This means that the
clearance to the belt in the non operational position is sufficient. and show the
operational and non operational positions of the spoon .
."
"" .,'
.....
"T" ....,,-'t, .. ~ ....r_'-+-:w.*'tIY
,
1'.',-
Figure 46: Spoon in the operational position
M.N. van Aarde
74
CHAPTER 4
Figure 47: Spoon in the non operational position
This section is a discussion on how this new transfer chute configuration should
be operated in order to comply with the facility requirements. The bottom section
of the chute can be lifted out of the way of material from behind on the receiving
conveyor. Therefore, a control philosophy is required for this movement.
Referring to Figure 25, positions A and B indicate where these new chutes will be
installed. As previously stated position C is the purging or dump position. and
show the actuated spoon section in the operating and non operating positions.
The conditions for these positions are explained as follows.
4.6 CONCLUSION
With the consideration of all the facility constraints and a conceptual idea of what
the transfer configuration should look like, the design can be optimised. When
the feeding belt velocity is known, the material trajectory and optimum chute
radius can be determined. This radius and the radius of the spoon must then be
corrected to comply with the facility constraints but still deliver the required
material transfer rate.
M.N. van Aarde
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CHAPTER 4
With the high cost implications of regular maintenance intervals on chute liners
and facility downtime, a honeycomb structure is incorporated into the high impact
areas. The purpose of this honeycomb structure is to form small pockets similar
to dead boxes in order to promote material on material flow. This increases the
lifetime of the chute liners and reduces maintenance intervals.
This specific transfer chute splits up easily into separate sections and will help to
simplify maintenance. The bottom section of the chute is actuated to move up
and down depending on whether the chute is in operation or not. This will ensure
optimum transfer of material while in operation and provide sufficient clearance
when not in operation. This is again guided by the facility requirements.
In the design of all the transfer chute components the physical properties of the
ore should always be considered. This determines the chute profile in terms of
flow angles and liner selection. With maximum material flow ability, high
resistance to sliding abrasion and reduced maintenance cost in mind, 94%
alumina ceramics is the liner of choice. This is only in the main flow areas of the
chute. For the dribbling chute a polyurethane liner is used to promote the flow of
this sticky material.
M.N. van Aarde
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CHAPTER 5
CHAPTER 5: TESTING AND VERIFICATION OF THE NEW SOLUTION
- ,.'
S,
'i'
", .
77 ,
M.N. van Aarde
CHAPTER 5
5.1 PREFACE
Although hand calculations have been a proven method of design for many
years, it is important to verify any new chute concept before fabrication and
implementation. Confirming the concept can save time and money as it reduces
the risk of on-site modifications. Hand calculations only supply a two
dimensional solution to the problem which does not always provide accurate
material flow profiles.
In recent years a few material flow simulation packages have been developed to
aid the design of material handling equipment. The use of software packages
can be beneficial to the design process as it gives a three dimensional view of
the material behaviour in the chute. This means that changes to the chute
concept can be made prior to fabrication.
It is, however, important to verify that the solution obtained from the software
package is an accurate reflection of actual design model. Therefore, the material
being handled should be thoroughly tested to obtain the correct physical
properties required to obtain an accurate simulation result.
The use of material flow simulation software does not replace the necessity for
hand calculations. All the basic steps should still be done to derive a conceptual
chute configuration. Material flow simulation software should be used as a
complimentary tool to analytical hand calculations in the design process.
The optimisation of transfer chutes in the/bulk materials industry
M.N. van Aarde
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CHAPTER 5
5.2 SELECTING A TEST METHODOLOGY
Traditionally, transfer chutes were designed by using basic analytical calculations
and relying on empirical data from past experiences with other chutes. Mostly
these analytical methods only cater for the initial part of the chute such as the
parabolic discharge trajectory. It is difficult to determine what happens to the
flow of material after it strikes the chute wall [34].
Two methods of verification were usually applied to evaluate a new transfer
chute configuration. Trial and error' can be used but obviously this is not desired
due to the high cost implications. A second method is to build a small scale
model of the chute in which tests can be carried out before a final design can be
adopted. This physical modelling is, however, time consuming and
expensive [34].
Granular or particulate materials are composed of a large number of loosely
packed individual particles or grains. The flow of such granular materials forms
an intricate part of the materials handling industry. Small reductions in energy
consumption or increases in production can have great financial advantages.
Therefore, significant efforts are put into improving the efficiency of these
facilities. The important role of numerical simUlations is becoming more evident
in these optimisation procedures [35]. Due to these efforts this technology is
becoming more powerful and is easy to use as a verification method for transfer
chute designs.
The behaviour of bulk material particles is unique in the sense that it exhibits
some of the properties associated with the gaseous, liquid and solid states of
matter. The granular state of bulk materials cannot be characterised by anyone
of these states alone. The research that captures the contact between individual
particles in an explicit manner is known as discrete element methods (OEM) [36].
M.N. van Aarde
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CHAPTER 5
In basic terms, OEM explicitly models the dynamic motion and mechanical
interactions of each body or particle as seen in the physical material flow. It is
also possible to obtain a detailed description of the velocities, position, and force
acting on each particle at a discrete point during the analysis. This is achieved
by focusing on the individual grain or body rather than focusing on the global
body as is the case with the 'finite element approach [36].
Figure 48 illustrates two examples of how this OEM software can be applied.
Obviously the flow characteristics differ between the applications shown in Figure
48. This is, however, catered for by the mathematical simulation of each particle
collision.
Figure 48: Flow analysis examples: a) separation and screening, b) hoppers, feeders {36]
Continuous improvements in the performance of computing systems make OEM
a realistic tool for use in a wide range of process design and optimisation
applications. During the last 20 years the capabilities of OEM have progressed
from small scale two dimensional simulations to much more complex 3D
applications. The latest high performance desk top computers make it possible
to simulate systems containing large numbers of particles within a reasonable
time [37].
M.N. van Aarde
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CHAPTER5
According to the institute for conveyor technologies at the Otto-von-Guericke
University of Magdeburg in Germany, using OEM for bulk solid handling
equipmentprovides[38]:
A cost effective method of simulating the utility of materials handling
equipment-
Precise control over complicated problem zones e.g. transfer chutes,
redirection stationsand highwearareas
The possibilityto integrate processes in onesimulationsuchas mixing and
segregation
The possibility to involve the customer more extensively in the design
process
Anadvantagein the marketdueto attractivevideosequencesand pictures
ofthesimulation
The possibility to prevent facility damages and increase the efficiency of
conveyorsystemsextensively.
As a good example of the advantages of the discrete element method the
University ofWitwatersrand in Johannesburg did studies on rotary grinding mills.
The university studies have shown that the OEM qualitatively predicts the load
motion ofthe mill verywell. The improved knowledge ofthe behaviour ofmills
can, therefore, increasetheprofitabilityofmineralprocessing operations[39].
This material handling equipmentis generallycostlyto operate and inefficientin
the utilisation ofenergy for breakage. In order to understand the behaviour of
millsbetter, the OEM method isincreasinglybeing appliedtothemodelling ofthe
load behaviour ofgrinding mills. These results indicate thatthis method can be
appliedsuccessfullyinthebulkmaterialshandling industry.
The apUmisatian af transfer chutes in the bulk materials industry
M.N.vanAarde
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CHAPTERS
Another example where this technology has been used with great success is with
the design of a new load out chute for the Immingham coal import terminal in
Britain. By simulating the flow with a OEM package the designers were aided in
the fact that they were supplied with a quantitative description of the bulk ,solid
movement through the chute. In the opinion of Professor Franz Kessler
(University of Leoben) the Discrete Element Method provides the engineer with
unique detailed information to assist in the design of transfer points [3].
These simulation packages are at the moment very expensive and not widely
used in transfer chute design. It can be anticipated that the utilisation of these
packages will increase as the technology improves and the cost of the software
goes down [40]. To get the best value out of the simulation it is important to
compare simulation packages and select the one most suitable to the complexity
of the design.
Fluent is a two dimensional computational fluid dynamics (CFD) software
package which can also be used as a chute design aid through the simulation of
material flow. It must however be noted that this is not a OEM simulation
package. This software package simulates the flow of material by considering
the material particles as a liquid substance. The output of the simulation is the
same as can be seen in the example of Figure 49. "The colours in the simulation
represent the average particle spacing [40]. Due to the fact that this package
can, at this stage, only deliver two dimensional simulations it is considered
inadequate to perform detailed simulations on the intricate desig'n piscussed in
this dissertation.
The optjmisation of transfer chutes in the bulk materials industry
M.N. van Aarde
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CHAPTER 5
COnroUf !; ,:,,! Votume 01 ( 00\ 00) C3_2002
f.LUENT 6.0 (2<1 "'9" 9"'40, "'''' ',n, 1M>. u" . ,.ody)
Figure 49: Simulations results from Fluent [40]
The Overland Conveyor Company provides another alternative to the Fluent
software package. Applied OEM is a technology company that provides discrete
element software to a variety of users in the bulk materials industry. Bulk Flow
Analyst is an entry level package that they provide. This package is very
powerful in the sense that it can accurately predict flow patterns depending on
the accuracy of the inputs. An example of this is shown in Figure 50. It also has
the capability to show material segregation, dynamic forces and velocities [41].
Figure 50: Simulation results from Bulk Flow Analyst [41]
M.N. van Aarde
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OEM Solutions is a world leader in discrete element modelling software. They
recently announced the release of the latest version of their flow simulation
package called EOEM 2.1. This package can be used to simulate and optimise
bulk material handling and processing operations [41]. Oue to the capabilities of
this software package it is a very attractive option for designing transfer chutes.
With the development of EOEM 2.1, OEM Solutions worked in collaboration with
customers in the Bulk Handling, Mining and Construction, Pharmaceutical,
Chemical and Agricultural sectors. This enables the end users to perform more
sophisticated particle simulations specific to their unique applications. Also
incorporated into this package is the ability and flexibility to customise and
personalise advanced particle properties [42].
This specific package has been proven successful by industry leaders. Martin
Engineering (Neponset, Illinois) is a leading global supplier of solids handling
systems. This company continues to expand their use of EOEM software in
design optimisation and development of bulk materials handling products. These
optimisation and development actions include all aspects of conveyor systems
and transfer points for numerous industrial sectors [43].
There are several other OEM simulation packages such as ESYS Particle,
Passage-OEM and YAOE. However, none of these software packages seem be
major industry role players in the discipline of chute design, although they might
have the capability. In adjudicating the three big role players in bulk material flow
simulation packages there are a few factors taken into consideration. It appears
thatthe advantages of 30 capabilities are non negotiable. Therefore Fluent is
not really a consideration. From the literature review of the Bulk Flow Analyst
and the EOEM packages it seems that these two will provide more or less the
same performance. It does seem, however, that the EOEM software is a bigger
role player in various industries. Due to the possible future capabilities of EOEM
M.N. van Aarde
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through its association with numerous industries, this simulation package is the
softwareofchoice.
In orderto retrofitordesign anewtransferpointwith theaid oftheselected OEM
software package there:are a fewsteps that a designermustfollow to gain the
full benefitofthistool [36]:
1. An accurate 3D orCAD representation ofthe new or old transferchute
mustbe rendered
2. Identify restrictions and limitations in terms of chute geometry and
manufacturing
3. Identifydesired design goals (Le. dustemissions, flowrestrictions, etc.)
4. Identifyrepresentativematerial propertiesand particledescriptions
5. In caseofaretrofit, makedesignchangesto chutegeometrywith CAD
6. Simulatetheperformanceofthenewdesign using OEM software
7. Evaluateresultsobtainedfrom thesimulation (reiteratesteps5, 6and 7)
8. Perform and finalisedetaildesignsteps
9. Manufacture
10.Installation
The above mentioned steps found in references [6] and [36] only provides
information regarding retrofitting or designing chutes with the, aid of OEM.
Although itis a powerful design 1001, the design process should not discard the
useofanalytical hand Someofthemostimportantdesign decisions
regarding chute profiles are made with analytical har'd calculations such as
plottingthematerialtrajectorY.
5.3 DETERMINATION OF MATERIAL PROPERTIES
The discrete element method is a promising approach to the simUlation of
granularmaterial interaction. The accuracy ofthe outcome ofthe simulation is,
M.N. vanAarde
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CHAPTER 5
however, dependent upon accurate information on the material properties and
input parameters [44]. These inputs basically consist of the following
fundamental parameters: size and shape factors, bulk density, angle of repose,
cohesion and adhesion parameters and restitution coefficients [45].
The determination of most of these parameters are explained and defined in the
following paragraphs. The parameters that are changed in the simulation
according to the reaction of the flow are not discussed and are typically
parameters such as the internal coefficient of friction between a number of
particles. A collaborated effort by the bulk handling industry aims to find ways in
which all parameters can be accurately determined through scientific methods.
This has however still not been achieved. The objective is to achieve a realistic
representation and therefore some parameters are altered in the simulation.
It is important to note that the computation time increases as the particle size
becomes smaller and the amount of particles increase. In most granular flow
problems the characteristics of the material stream are largely determined by
particles greater than 10 - 20 mm in size [45]. Therefore, in order to reduce
computation time, the selected particle size for simUlations should be the same
as the largest particles handled by the facility namely 34 mm diameter.
Although fines have a higher internal friction coefficient and more cohesiveness,
these properties can be averaged into the input parameters to obtain the same'
overall effect [45]. Therefore, only a single particle size is used in the simulation
and the properties optimised to obtain the same result under actual operating
conditions. Some of the material properties can be easily obtained from the
facility. The rest of the properties are obtained from tests carried out by expert
conSUltants in this field.
The size factor and bulk density are obtained from the facility. Materia! tests
carried out by external consultants provide the coefficient of friction and also the
M.N. van Aarde
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wall friction angle. This is the angle at which the material will start to slide under
its own mass. To determine these material properties the external consultants
normally use sophisticated and expensive equipment. Data gathered from these
tests are used for the hand calculation of the chute profile. The angle of repose
can normally be observed from a stockpile and is the angle that the side of the
stockpile makes with the horizontal.
For the OEM simulation the coefficient of friction is one of the main determining
factors of the wall friction angle. Data provided by the material tests can not be
used as a direct input into OEM. In the software package the coefficient of
friction is represented by a factor between 0 and 1. The material test data can
however provide some insight into where on this scale the factor is. This factor
can be derived from a few small simulation iterations as there is no method of
direct conversion between the test result data and the OEM input.
To determine this factor a plate is modelled with a single layer of particles. This
plate is then rotated within the simulation at approximately 2 per second. As
soon as the particles begin to slide the time is taken from which the angle can be
calculated. This process is repeated with different friction coefficients until the
correct wall friction angle is obtained. After the coefficient of friction factor is
determined between the particles and the chute wall, the material restitution
factor and coefficient of internal friction can be obtained.
The restitution factor is obtained by measurir;tg the rebound height of a particle
when it is dropped from a certain height. This is usually difficult to determine due
to the variation in shape of the material particles. If the, particle lands on a
surface it rarely bounces straight back up. Therefore, the test is repeated
numerous times and an average is taken to obtain the final result.
Coefficient of internal friction is a property that describes the particles ability to
slide across each other. A simUlation is set up to create a small stockpile of
The optimisation of transfer chutes in the blJlk materials industry
M.N. van Aarde
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CHAPTER 5
material particles. The angle of repose can be obtained by measuring the
average apex angle of the stockpiles. In this simulation the coefficient of internal
friction and restitution factors are iterated. This is done in order to simulate the
accurate behaviour of particles falling onto the stockpile and forming the correct
angle of repose. Figure 51 shows what this simulation typically looks like.
Figure51: Determinationofmaterialpropertiesforanaccurateangleofrepose
5.4 VERIFICATION OF THE SELECTED TEST METHODOLOGY FOR THIS
APPLICATION
The best verification is to compare the simulation results with an actual material
flow situation. Therefore, a comparison is made between the actual flow in the
existing transfer configuration and the simulation of this same transfer. This is
also a good test to see if the parameters changed in the simulation were done
correctly.
During the chute test programme CCTV cameras were installed in the problem
transfer chutes at the facility. The cameras are positioned to provide an accurate
view of the material flow behaviour inside the chutes. As explained in Chapter 3,
The optimisationoftransferchutesinthe bulkmaterialsindustry 88
M.N. van Aarde
CHAPTER 5
the behaviour of the material flow inside the chutes changes with the variation of
ore type.
Due to the fact that only 34 mm diameter particles are used in the simulation, a
test using coarse ore was chosen for the veri'fication of the simulation.
Therefore, test #12 is used as reference for the verification. In this test, coarse S
with the particle size distribution between 28 mm and 34 mm was used at the
transfer from CV #3 to CV #5.
Figure 52 shows an image taken from the CCTV camera inside the transfer chute
between CV #3 and CV #5. The red line indicates the top of the chute throat
opening and the yellow arrows show the top of material flow. This screen shot
was taken at a flow rate of 10 000 tlh. It can be deduced from this view and the
chute test work that the chute is choking at a throughput rate of 10 000 tlh.
Figure 52: Actual material flow with coarse S at 10000 tIh
The transfer chute from Figure 52 was modelled in CAD and the model imported
into the discrete element package, EDEM. All the material input parameters as
discussed in section 5.3 were used in the simulation. 10 000 tlh was used as the
M.N. van Aarde
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CHAPTER5
flowrate parameterin an attemptto simulateand recreate thesituation asshown
by Figure52.
Test#12, ofthe chute performancetests, gavethefollowing resultswhichcan be
comparedtothe EDEM simulation:
Chutestartedto chokerapidlyat10 000 tlh
Slightoffcentre loadingontothe receiving conveyorCV#5
A lowervelocitylayerofmaterialcloseto thedischargeofthechute
Material roll backonthe receiving conveyordueto significantdifferencesin
thevelocityofthematerialflowand the receiving conveyor.
Off-centreloading
L.
Figure53: Material flow pattern through the existing chute
M.N. vanAarde
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Flow restricted in this
area
Low velocity layer
Low discharge velocity
rollback
Figure 54: Cross sectional side view of material flow through the existing chute
Figure 53 shows the material flow pattern in the existing chute where the thick
red arrows indicate the direction of flow. The legend on the left of the figure
indicates the material velocity in m/s. Slow flowing material is shown in blue and
the colour turns to red as the material velocity increases. Slight off centre
loading onto the receiving conveyor CV #5 can be seen from Figure 53. This
correlates well with the actual observations during the physical testing of this
transfer point.
Figure 54 shows the more determining factors for correlation between actual flow
and simulated flow where the legend on the left indicates the material velocity in
m/s. This is a cross sectional view through the centre of the chute. From this
view a build up of material can be seen in the chute throat area. The slow
flowing material on the back of the chute also helps to restrict the flow. Due to
the fact that the material speed at the discharge of the chute is much slower than
the receiving belt speed, a stack of turbulent flowing material is formed behind
the discharge point on the receiving conveyor.
M.N. van Aarde
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There is a good correlation between the simulated and actual material flow
pattern.The simulation method can therefore be considered as a valid alternate
or additional method to standard analytical chute design. Attention should be
giventhough tothe inputofmaterialpropertiesin ordertoobtainarealisticresult.
5.5 VERIFICATION OF NEW CHUTE CONFIGURATION AND OPTIMISATION OF THE
HOODLOCATION
Afterestablishing thatthe OEM is a reliable design and verification tool ,the new
transfer chute configuration can be simulated. Firstly, this configuration is
modelled without the honeycombs inside the hood and spoon. This is done in
ordertoverifythe material flowpattern and velocitythrough thehood and spoon.
Results obtained from this simulation can then be compared to the hand
calculation results. An iterative process is followed with simulations and hand
calculations to obtain the bestflow results. The simulation results are shown in
Figure55and Figure56.
I.'
L
Figure55: Material flow through hood at 10 000 tIh
M.N. vanAarde
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CHAPTER 5
Figure 56: Material flow through spoon at 10 000 tlh
The hood velocity profile shown in Figure 38 gives the same result as obtained
from the DEM simulation. The calculated hood exit velocity is 6.33 m/s. This is
the same result obtained from the simulation and shown by the red colouring in
Figure 55. As the material enters the spoon it is falling under gravity and ,
therefore, still accelerating. At impact with the chute wall it slows down and exits
the spoon with approximately the same velocity as the receiving conveyor.
Figure 56 shows the material flow through the spoon section. This can also be
compared to the spoon velocity profile in Figure 39. The behaviour of the
material inside the spoon, as shown by the simulation, correlates with the results
obtained from the hand calculations. This is another indication that with accurate
input parameters the DEM can be used as a useful verification tool.
M.N. van Aarde
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Skew loading
into spoon
Slower
material
L.
Figure 57: Determination of the optimum hood location
The hood is supported by a shaft at the top and can be moved horizontally. This
function is incorporated into the design in order to optimise the hood location
during commissioning of the transfer chute. It is critical to discharge centrally into
the spoon in order to eliminate skew loading onto the receiving conveyor.
Figure 57 illustrates the effect that the hood location has on material flow. When
comparing the flow from Figure 55 to the flow in Figure 57, it is clear that skew
loading is a direct result of an incorrect hood position. The circled area in Figure
57 illustrates how the flow reacts to the incorrect hood location.
Material is discharged to the right side of the spoon which causes a slight build-
up of material on the left. This causes the material to flow slightly from side to
side as it passes through the spoon. Figure 57 indicates that the material to the
M.N. van Aarde
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CHAPTERS
--...--------------- -------_....__... _---
right at the spoon discharge is slightly slower than the material on the left. This is
a clear indication of skew loading onto the receiving conveyor.
The material flow pattern in Figure 55 is symmetrical and, therefore, will not
cause skew loading. The OEM can give a good indication of the required hood
setup before commissioning. However, adjustments can still be made during the
commissioning process. The tracking of the receiving belt should give a good
indication of when the hood is in the optimum position.
5.6 EFFECT OF THE HONEYCOMB STRUCTURE IN HIGH IMPACT ZONES
The purpose of the honeycomb dead box structure in the high impact zones is to
capture material inside the pockets and induce material on material flow. This
requires that the material inside the honeycombs should be stationary while the
main stream material flow moves over the dead boxes. OEM can, therefore, be
set up in such a way that the material velocities can be visualised inside the
chute.
In Chapter 4 the logic of how this honeycomb should be structured and
positioned was discussed. The simulations shown in Figure 58 and Figure 59
illustrate how a OEM p c k ~ g e can also be used to determine the positioning of
these honeycomb structures. Impact points in the hood and spoon must be
inside the honeycomb in all situations of flow inside the chute. The spacing of
dead box pockets can be altered to ensure that a continuous layer of stationary
material is formed in the honeycomb area. Various geometries for this
honeycomb structure can be simulated with OEM to obtain the best results.
M.N. van Aarde
95
CHAPTER 5
Large radius hood
Hood honeycomb
box to minimise
wear in impact
Vertical discharge
from hood,
centralising flow on
,, belt
L
Figure 58: Material behaviour through hood
Spoon
Spoon honeycomb
box to minimise wear
in impact area
Improved spoon
discharge flow
Figure 59: Material behaviour through spoon
M.N. van Aarde
96
CHAPTERS
The legends on the left of Figure 58 and Figure 59 indicate the material velocity
in m/s. Dark blue indicates stationary material and bright red indicates a
maximum material velocity of 8 m/s. Using this information, the functionality of
the honeycomb dead boxes can now be analysed. The velocity of the material
captured by the dead boxes is indicated as dark blue. This means that all the
material in the dead boxes is stationary.
With the result obtained from the OEM simulation it is clear that material on
material flow will be induced by the honeycomb dead boxes. The pockets of the
honeycomb capture the material and will, therefore, have reduced wear in the
high impact areas. This material on material flow does, however, induce a
coarser sliding surface than the smooth ceramic liner tiles. Due to the high
velocity of material through the chute the effect of the coarser sliding surface is,
however, minimised.
5.8 CONCLUSION
The Discrete Element Method is proven to be a successful design and
verification tool in the bulk materials industry. This method is used widely in the
global bulk materials industry. The successful outcome of the OEM simulation is,
however, dependent on the correct material input parameters. Some of these
parameters are readily available from the facility that handles the material. The
rest of the parameters can be determined by setting up simple test simulations
with OEM.
To verify that the OEM simulation is a correct indication of the actual condition,
the simulation is compared to CCTV images taken from the same transfer chute.
The results show that the OEM simulation does provide a true reflection of the
actual material flow through the transfer chute. Therefore, the same material
input parameters can be used to simulate the new transfer chute configuration.
M.N. van Aarde
97
CHAPTER 5
From the simulations done on the new transfer chute configuration the effect of
the honeycomb dead boxes can be examined. These simulation results show
that the honeycomb dead box configuration is effective in capturing material
inside the honeycomb cavities. This results in material on material flow and
reduces impact abrasion on the ceramic chute liners.
Results obtained from the OEM simulation of the new transfer configuration are
compared to the hand calculation results. This comparison indicates that the
material velocity calculated in the hood and spoon correlates well with the
material velocity calculated by the OEM. The overall results obtained from
simulating the new transfer chute configuration have been shown to provide a
true reflection of the actual flow through the chute.
M.N. van Aarde
98
CHAPTER 6
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS
M.N. van Aarde
99
CHAPTER 6
6.1 CONCLUSIONS AND RECOMMENDATIONS
Bulk materials handling is a key role player in the global industrial industry.
Within this field the industry faces many challenges on a daily basis. These
challenges, as with any industry, are to limit expenses and increase profit. Some
of the limiting factors of achieving this goal in the bulk materials handling industry
are: lost time due to unscheduled maintenance, product losses due to spillage
andhigh costs incurred by increased maintenance.
The focus of this study was on the optimisation of transfer chutes and
investigations were carried out to determine the core problems. These
investigations were done by observing and monitoring various grades of iron ore
passing through transfer chutes known to have throughput problems. The core
problems were identified as high wear on liners in the impact zones, skew
loading on receiving conveyors, material spillage and chute blockages.
These problems cause financial losses to the facility either directly or indirectly.
Direct financial losses can be attributed to the frequent replacement of chute
liners while the indirect financial losses are caused by facility down time: This is
why it is imperative to optimise the manner in which the transfer of material is
approached. A new transfer chute configuration addresses the problems
identified at the facility and the core concepts can be adopted at any bulk
materials handling facility.
This new concept examines the utilisation of the hood and spoon concept rather
than the conventional dead box configuration. By using the hood and spoon
configuration the material discharge velocity is utilised and carried through to the
discharge onto the receiving conveyor. Adding to this design is a honeycomb
dead box configuration in the high impact zones of the hood and spoon. This
initiates material on material flow and prolongs the lifetime of the chute liners.
M.N. van Aarde
100
CHAPTER 6
The radius of the hood should be designed so that it follows the path of the
material trajectory as closely as possible. Some facility constraints prohibit this
hood radius from following exactly the same path as the material. The radius of
the spoon is designed in such a manner that it receives the material from the
hood and slows it down while turning it into the direction in which the belt is
running. Ideally, the material should be discharged from the spoon at
approximately the same velocity as the receiving conveyor.
If this can be achieved then some major problems suffered by the industry will
have been resolved. With the hood having almost the same radius as the
material trajectory impact wear on liners can be significantly reduced. By
discharging material from the chute onto the receiving conveyor at the same
velocity as the conveyor belt, excessive belt wear and material spillage will be
avoided. Further optimisation is however still possible by investigating the
implementation of various skirting options to the side of the conveyor.
This new transfer chute configuration also boasts an articulated bottom section in
the spoon. The purpose of the adjustable bottom section is to create greater
clearance below the spoon. This will allow material on the belt below, to pass
unimpeded underneath the spoon. In some cases there can be several chutes in
series that discharge onto the same conveyor. In these cases it is beneficial to
incorporate an articulated chute in order to have the capability of having a small
drop height between the discharge point in the chute and the receiving conveyor.
This low drop height also minimises turbulent flow at the chute discharge point on
the receiving conveyor.
The most unique feature to the new design is the implementation of the
honeycomb dead box configuration in the high impact zones. Due to these high
impact areas the liners will experience the most wear. This section of the chute
is flanged and can be removed separately from the rest of the chute to aid
maintenance. In most maintenance operations it may only be necessary to reline
M.N. van Aarde
101
CHAPTER 6
this small section of the chute. Costs are minimised by reducing the time
required for maintenance and the cost of replacing liners.
Previously, testing of new transfer chute configurations normally involved
implementing the chute and obseNing its ability to perform according to
specification. This can, however, be a costly exercise as it is possible that further
modifications to the chute will be required after implementation. Therefore, it is
beneficial to verify the new chute configuration before implementation.
This is done by simulating the material flow through the chute using Discrete
Element Method. A comparison was done between the actual flow in an eXisting
chute and the simulated flow in the same chute configuration. This comparison
showed the same result obtained from the simulation and the actual material
flow. This method can therefore be used as an accurate simulation tool for
evaluating transfer chute performance.
The mathematical calculations describing the material flow in and over the
honeycomb dead box structures are complex. Therefore simulation models are
used to show the material behaviour in those areas. Simulations show that the
material captured within the dead boxes remains stationary, thus protecting the
ceramic liners behind it. This is the desired result as it prolongs the life of the
chute liners and reduces maintenance frequencies.
If the work is done efficiently it normally takes two days to remove a worn chute
of this configuration fully and replace it with a new one. This is normally done
once a year due to the design lifetime of the chute. With the new chute
configuration this maintenance schedule can be reduced to two hours, once a
year, for the replacement of the honeycomb sections only. The exposed face of
the honeycomb ribs will wear through until the efficiency of the honeycomb
design is reduced.
M.N. van Aarde
102
CHAPTER 6
This specific iron ore facility has approximately fifty transfer points. During this
exercise only two of these transfer points were replaced with the new chute
configuration. The combined annual maintenance time for replacement of these
50 chutes is 100 days. If the new chute philosophy is adopted on all these
transfers the annual maintenance time can be reduced to as little as 100 hours.
This excludes the unplanned work for cleaning of spillages and fixing or replacing
worn conveyors.
There are significant benefits to investigating the problems at specific transfer
points before attempting a new design. This gives good insight into where the
focus should be during the design process. a ~ y identification and
understanding of the problem areas is essential for a new chute configuration.
The new design features can provide a vast improvement and a large benefit to
the bulk materials handling industry.
6.2 RECOMMENDATIONS FOR FURTHER STUDY
During the chute performance tests it was noted that avalanches on the
stockpiles during reclaiming of material causes peaks on the conveyor systems.
These peaks in the material stream increase the probability of blockages in the
transfer chutes. As a result, material spillage occurs and the conveyor belts can
be easily overloaded.
This occurrence creates the requirement for further studies on the reclaiming
operations. All stacker reclaimers are operated manually which creates ample
room for error. Investigations can be done to determine the value of automating
the reclaiming operations. Manual interaction cannot be avoided, but an
automated system will reduce the possibility for error.
Visual inspections on the transfer chute liners indicate that the material tends to
erode the liners away quicker in the grooves between liner plates or ceramic
M.N. van Aarde
103
CHAPTER 6
tiles. This occurrence seems to be worse in areas of the chute where the
material velocity is the highest.
This problem was specifically noticed with ceramic liner tiles. The tiles are glued
to the chute surface with an epoxy and this substance also fills the crevices
between the tiles. This epoxy is, however, not resistant to any type of sliding or
impact abrasion. If the material gains speed in such a groove between the tiles it
simply erodes the epoxy away. Studies to reduce or even eliminate this problem
should be examined.
In some situations the layout and configuration of the chute prohibits the tiles
from being inserted in a staggered manner. Studies can be done on the
composition of this epoxy in order to increase its resistance to sliding and impact
abrasion. By doing so the lifetime of the chute liners can be increased which will
result in minimised facility down time due to maintenance.
It seems that it is a global industry problem to find accurate scientific methods of
determining material input parameters for OEM simulations. Although most of
the material properties can be determined through testing, it is still a challenge to
convert that information into a representative input parameter into OEM. It is
therefore recommended that further studies be undertaken to determine a
method by which material test data can be successfully converted into OEM input
parameters.
M.N. van Aarde
104
REFERENCES
-.-..-----
REFERENCES
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[2] ANON. 2008. Peak(Export) Oil/USD Survival, Dec.
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[3] KESSLER, F. 2006. Recentdevelopmentsin thefield ofbulk conveying.
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[4] ANON. 2007. Specification for Troughed Belt Conveyors. British
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[5] CEMA(ConveyorEquipmentManufacturersAssociation). BeltConveyors
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[6] DEWICKI, G. 2003. Computer Simulation of Granular Material Flows.
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[7] AMERICAN COALCOUNCIL. 2009. Engineered chutes control dustfor
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[8] KUMBAIRONORE. 2008. Annual FinancialStatements2008.
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[10] ALTHOFF, H. 1977. Reclaiming and Stacking System. Patent: US
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[11] THE SOUTH AFRICAN INSTITUTE OF MATERIALS HANDLING.
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[12] CLARKE, R. 2008. Hood and spoon internal flow belt conveyortransfer
systems. SACEA- seminar. 22 Aug. http://WWvV.sacea.org.za/Date of
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[13] TW WOODS CONSTRUCTION. 2009. Design problemsin coal transfer
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[14] LOUGHRAN, J. 2009. Theflowofcoalthrough transferchutes. 20Aug.
Showcaseofresearch excellence. JamesCookUniversity,Australia.
[15] O'NEIL, M. 2006. Aguideto coal chute replacement. PowerEngineering
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guide-to-coal-chute.html Dateofaccess: 3Jul. 2009.
[16] NORDELL, L.K. 1992. A new era in overland conveyor belt design.
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[17] Rowland, C. 1992. DustControl atTransferPoints.
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[18] KRAM ENGINEERING. Ceramiccompositeimpactblocks.
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I19] BLAZEK, C. 2005. Kinkaid InteliFloInstallation. Source for Plats
Power Atticle, Oct.
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[20] C.RP. Engineering Corp. ModernTransferChute DesignsforUsein
Material Handling.
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26Apr2010.
[21] ROZENTALS, J. 2008. Rational design of conveyor chutes. Bionic
Research Institute, SouthAfrican InstituteofMaterials Handling.
[22] ROBERTS, A.W" SCOTT, O.J. 1981. Flow of bulk solids through
transfer chutes ofvariable geometry and profile. Bulk Solids Handling,
1(4) Dec.
[23] CARSON, J.W., ROYAL, T.A., GOODWILL, D.J. 1986. Understanding
and Eliminating Particle Segregation Problems. Bulk Solids Handling,
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[24] BENJAMIN, C.W. 2004. The use of parametric modelling to design
transferchutes and otherkeycomponents. GulfConveyorGroup.
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l25] STUART DICK, D., ROYAL, T.A 1992. Design Principles for Chutes to
Handle Bulk Solids. Bulk Solids Handling, 12(3), Sep.
[26J REICKS, AV., RUDOLPHI, T.J. 2004. The Importance and Prediction of
Tension Distribution around the Conveyor Belt Path. Bulk materials
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[28] ROBERTS, AW. 1969. An investigation of the gravity flow of non
cohesive granular materials through discharge chutes. Transactions of
the ACMEjournal of engineering for n u s t ~ May.
[29] TAYLOR, H.J. 1989. Guide to the design of transfer chutes and chute
linings for bulk materials.
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mechanical handling engineers
[30] ROBERTS, AW. 1999. Chute design application transfer chute design.
Design guide for chutes in bulk solids handling, The University of
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[31] NORDELL, L.K. 1994. Palabora installs Curved Transfer Chute in Hard
Rock to Minimise Belt Cover Wear. Bulk Solids Handling, 14, Dec.
[32] ROZENTALS, J. 1991. Flow of Bulk Solids in Chute Design.
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chute-design-software Dateofaccess: 12Aug. 2009.
[35J SAWLEY, M.L., CLEARY, P.W. 1999. A Parallel Discrete Element
Method for Industrial Granular Flow SimUlations. EPFL - Super
ComputingReview, (11).
[36] DEWICKI, G. 2003. Bulk Material Handling and Processing - Numerical
Techniques and Simulation of Granular Material. Overland Conveyor
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[37J FA VIER, J. 2009. Continuing Improvements Boost use of Discrete
ElementMethod. OilandGasEngineer- ProductionProcessing, 7 Oct. .
[38] KRAUSE, F., KA TTERFELD,A Usageofthe Discrete ElementMethodin
ConveyorTechnologies. Institute forConveyorTechnologies (IFSL), The
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[39] MOYS, M.H., VAN NIEROP, M.A, VAN TONDER, J.C., GLOVER, G.
2005. Validation of the Discrete Element Method (OEM) by Comparing
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[40J MciLVINA, P., MOSSAD, R. 2003. Two dimensional transfer chute
analysis using a continuum method. Third international conference on
CFD in the Minerals and Process Industry, CSIRO, Melbourne, Australia.
(41J Overland Conveyor Company Inc. 2009. Applied DEM.
http://www.applieddem.com/Date of access: 26Apr 2010.
(42] DEM SOLUTIONS. 2008. Advanced Particle Simulation Capabilities with
EDEM 2.1. Press release, 5 Nov.
[43J DEM SOLUTIONS. 2008. Martin Engineering Expands use of EDEMTM
Software in Design of Solids Handling Equipment. Press release, 20Feb.
(44] COETZEE, C.J., ELS, D.N.J. 2009. Calibration of Discrete Element
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[45] DAVID, J., KRUSES, P.E. Conveyor Belt Transfer Chute Modelling and
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bulk materials industry
M.N. van Aarde
110
ApPENDIXA
ApPENDIX A: MATERIAL TESTS AND LINER SELECTiON
The optimisation of-transfer chutes in the bulk materials industry
M.N. van Aarde
11-1
ApPENDIX A
MATERIAL TEST WORK AND LINER SELECTION
Material samples were taken from the stockpile area for evaluation and testing.
These samples represent the worst case materials for" impact wear and flow
problems. Tests were conducted by external consultants as this is a speciality
field. Therefore no detail information on how the tests are conducted is currently
available. Results from these tests should indicate the worst case parameters for
chute design according to each specific liner type tested.
The material handled by the facility varied from 4 mm to 34 mm lump size. A mid
range lump size ore was identified as the preferred material to use for wear
testing. This decision was based on the specific ore type maximum lump size of
15 mm as required for the wear test. The wear test apparatus used cannot
provide conclusive results with the larger lump sizes of 34 mm and thus smaller
sizes are used. Guidance on which ore samples to take was given by the
external consultants tasked with performing the test work.
The test work is divided into two sections. Firstly the flow test work is carried out
on the finer material with a higher clay content known to have bad flow angles.
Included in the selection of fine materials is a sample of the scraper dribblings.
This is the material scraped off the belt underneath the head pulley. Secondly,
the wear tests were conducted on 15 mm samples as explained above.
A few common liners were selected for testing. These liners are shown in
Table A. Some of these liners are known for their specific purpose and
characteristics. Polyurethane is known to have a very good coefficient of friction
and will, therefore, improve the flow of material. This material does, however,
wear out quicker in high impact applications. Therefore, it is only considered for
use inside the dribbling chute.
M.N. van Aarde
112
ApPENDIX A
As can be seen from Figure 37 in section 4.3.2, the dribbling chute will only see
scraper dribblings from the primary and secondary scrapers. It is protected from
any main stream flow of material by the start up chute. This makes the
polyurethane liner a prime candidate for lining this section of the chute.
Table A: Material tested vs. liner type
I
Flow Tests Wear Tests
Liner
!
T"""
en
aJ
c
u::::
I
i
N
en
aJ
c
u::::
Cf)
en
aJ
c
u::::
I
en
'-
OJ
aJ C
0.. .-
{\j -
'- .0
u :
(f) '-
0
T"""
aJ

{\j
0
0
N
aJ

{\j
0
0
i
I Chrome
x x x x ! x
Carbide
x x x x x
I VRN 500 I
x x x x x x
94%
Alumina
: Ceramic
i I
Poly
x !
Urethane I
I I
FLOW TEST WORK
The fines 1 sample was tested at three different moisture contents of 3.6%, 4.1 %
and 4.7%. This is 70%, 80% and 90% of saturation moisture respectively. No
noticeable difference was observed in the wall friction angles .. Therefore, the
fines 2 and fines 3 samples were tested at 80% of saturation which is 4.2% and
4.3% moisture content respectively.
Test work showed that the minimum chute angle required for flow increased as
the impact pressure increased. Chute angles were measured up to impact
pressures of about 8 kPa. The worst chute angle obtained was 62. This means
that no angle inside the chute should be less than 62from the horizontal.
The industry 113
M.N. van Aarde
ApPENDIXA
Thescraperdribblings were tested at a moisture content of12%. This material
possesses the most clay content and, therefore, has the worst flow properties.
During testing of this material, water was added to improve the flow. At an
impactpressureof0.3 kPathe minimum chuteangledrops from 62to 56when
adding afinemistsprayofwater.
WEARTESTWORK
As stated in chapter 4, wear tests were conducted on the chrome carbide
overlay, ceramics and VRN500. The results ofthese tests are shown as non
dimensional wear ratios ofmm wear/mm travel ofbulk solid sliding on the wear
liners coupon at a given force. Test results shown in Table B indicate thatthe
chrome carbidewill have about1.85timesthe lifetime of94% alumina ceramics.
TheVRN500 linerwill wearabout6times fasterthan the 94% alumina ceramics
atthesameforce.
TableB: Wear ratios of liners at two different pressure ranges
lore/WallCoupon 65kPa . 163kPa-173kPa
I
i
Coarse1on 94% Alumina Ceramic 9.0 E-9 3.7E-8
Coarse 1on ChromeCarbide 8.7 E-9 2.0 E-8
Coarse1on VRN500 9.1 E-8
I
2.4 E-7
i
: Coarse2 on 94%Alumina Ceramics 3.8 E-9 2.2 E-8
Coarse2 on ChromeCarbide 5.5 E-9 1.5E-8
:
Coarse2 on VRN500 6.6 E-8 2.5 E-7
I
LINER SELECTION
The lifetime ofthe liners is notthe only criteria. Maintainability and costarealso
factors thatmustbe considered. Chromecarbideseemsto be the linerofchoice
for this application. However, the specifictype ofchrome carbide tested is not
The optimisation of transfer chutes industry 114
M.N.vanAarde
ApPEND[xA
manufactured locally and the imported cost is approximately three times that of
ceramics.
VRN500 is slightly cheaper than ceramics and can easily be bolted to the back
plate of the chute which makes maintenance very simple. Ceramics are,
however, widely used on the facility and the maintenance teams are well trained
for this specific liner. Therefore, 94% alumina ceramics is chosen for this
application.
M.N. van Aarde
115
ApPENOD< B
ApPENDIX B: CHUTE CONTROL PHILOSOPHY
The optfmisation of transfer chutes in the bulk materials industry
M.N. van Aarde
116
ApPENDIX B
SPOON IN THE OPERATING POSITION
For the spoon to be in the operating position the moving head must be over that
specific spoon and the feeding stockyard conveyor must be running. This means
that material will be fed through the chute. In this case the spoon needs to be in
the operating position to prevent spillage.
However, when the chute is in the operating position and the feeding conveyor
trips for any reason, the actuated spoon section must not move to the non
operating position. If the spoon position feedback fails then the system must trip
and the spoon must remain in its last position. The downstream conveyor must
also fail to start with this condition.
SPOON IN THE NON OPERATING POSITION
As a rule the spoon needs to be in the non operating position when the moving
head, on that specific stockyard conveyor, is in the purging position (position C).
The reason is that when a stacker reclaimer is in stacking mode, any upstream
stacker reclaimer can be reclaiming. The reclaimed material on CV #5 or CV #6
will have to pass underneath the actuated chute.
ACTUATED SPOON OVER CV #5
As an example for the movement of any actuated spoon on CV #5 the following
are considered. When the moving heads of any of the stockyard conveyors are
in position A and that specific stockyard conveyor is running then the rest of the
actuated spoons over CV #5 must be in the non operating position. The
following scenario provides a better understanding.
CV #4 is running
CV #4 moving head is in position A.
M.N. van Aarde
117
ApPENDIXB
In this situation all the actuated spoons on CV #5, except underneath CV #4,
must be in the non operating position.
ACTUATED SPOON OVER CV #6
As an example for the movement of any actuated spoon on CV #6 the following
are considered. When the moving heads of any of the stockyard conveyors are
in position B and that specific stockyard conveyor is running then the rest of the
actuated spoons over CV #6 must be in the non operating position. The
following scenario is similar to 4.5.3 but explains the control philosophy for the
moving head in position B.
CV #2 is running
CV #2 moving head is in position B.
In this situation all the actuated spoons on CV #6, except underneath CV #2,
must be in the non operating position.
The optimisation of transfer chutes in bulk materials industry
M.N. van Aarde
118

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