24941-100-30R-G01-00073 Tunra 6299 Report Final[1]

TUNRA BULK SOLIDS HANDLING RESEARCH ASSOCIATES(a division of The University of Newcastle Research Associates Ltd - inc. in NSW. ACN 000 710 074)

in association with the

Centre for Bulk Solids & Particulate Technologies

FLOW PROPERTIES OFAZ ZABIRAH BAUXITE

Report No. 6299 June, 2004

Client: Hatch Associates Pty. Ltd.

Address: GPO Box L923Perth, WA 6842 Australia

Telephone: 08 9428 5000Facsimile: 08 9428 5555

Attention: John Rosten

This report has been checked and authorised by the undersigned

Signed .................................................

for Tunra Bulk Solids Handling Research Associates

Users of this report are invited to contact Tunra Bulk Solids if clarification of any aspect is required.

The test results presented are for a client supplied bulkmaterial sample. Should the material handled

in practice vary from this test sample thenthe results in this report

may be far from optimal. In addition, any extrapolationof the data and / or recommendations to

situations other than those for which they werespecifically intended without confirmation

by Tunra Bulk Solids may lead to erroneous conclusions.

The contents of this report may not be reproducedwithout the consent of the client;

and then only in full.

This investigation was performedusing the facilities of the

Bulk Solids Handling Laboratoriesof

Tunra Bulk Solids Handling Research Associatesand the

Centre for Bulk Solids & Particulate Technologiesat

The University of Newcastle

POSTAL ADDRESS: COPIES LIST:

Tunra Bulk Solids Client (2)University of Newcastle Stephen J. WicheUniversity Drive, Callaghan Alan W. RobertsNSW 2308 AUSTRALIA Office File

Telephone: +61 2 4921 7127Facsimile: +61 2 4921 6094Email: [email protected]

i

TABLE OF CONTENTSPage

1 EXECUTIVE SUMMARY............................................................... 1

2 FLOW PROPERTY TESTS ............................................................ 62.1 Direct Shear Test ................................................................ 62.2 Wall Friction Test............................................................... 82.3 Compressibility Test........................................................... 92.4 Moisture Content Test ........................................................ 92.5 Surface Roughness Test ..................................................... 92.6 Particle Size Test................................................................. 92.7 Angle of Repose Test........................................................ 102.8 Belt Conveyor Surcharge Angle Test................................ 102.9 Dust Extinction Moisture Tests ........................................ 102.10 Unconfined Uniaxial Test................................................. 10

3 FLOW PROPERTY RESULTS..................................................... 113.1 Particle Size Range ........................................................... 113.2 Moisture Content.............................................................. 123.3 Shear Tests ....................................................................... 153.4 Compressibility Tests ....................................................... 173.5 Wall Friction Tests ........................................................... 183.6 Angle of Repose ............................................................... 193.7 Belt Conveyor Surcharge Angle Tests .............................. 203.8 Dust Extinction Moisture Tests ........................................ 20

4 STORAGE FACILITY DESIGN................................................... 214.1 Mass Flow Design............................................................ 214.2 Funnel Flow Design ......................................................... 244.3 Chute Design.................................................................... 24

5 REFERENCES............................................................................... 25

Appendix

Test Results AModes of Flow BStorage Plant Design C

ii

GLOSSARY OF TERMS

Arching - a dome shaped obstruction formed by a bulk material usually at ahopper outlet

Angle of Repose - the angle between the horizontal and the surface of a poured bulkmaterial

Axi-Symmetric Flow - a flow pattern formed during the discharge from a bin of a bulkmaterial and characterised by particle trajectories that aresymmetrical about the vertical axis of the bin

Bin - a container or vessel for holding a bulk material, frequentlyconsisting of a vertical cylinder section with a converging hopper -see Appendix A

Bulk Solid - an assembly of solid particles handled in sufficient quantities suchthat the characteristics can be described by the properties of themass of the particles rather than the characteristics of eachindividual particle. May also be referred to as a granular material,particulate solid, or powder.

Cohesive Arch - an arch that depends on interparticle, cohesive strength (eg.unconfined yield strength) for its stability

Cylinder - vertical part of a binDead Zone - an amount of material that cannot be discharged from a binExpanded-Flow - flow pattern which is a combination of mass-flow and funnel-flow

- see Appendix BFeeder - device for controlling the rate of withdrawal of a bulk material

from a binFlow Channel - space in bin through which a bulk solid is actually flowing during

dischargeFlow Properties - bulk material characteristic properties utilised to define their

behaviour during storage and flowFunnel-Flow - the bulk material sloughs off the top surface and discharges

through a vertical channel which forms within the stored bulkmaterial above the outlet - see Appendix A

Gravity Flow - the flow of a bulk material is induced by gravity aloneHopper - the converging portion of a binMass-Flow - flow pattern in which all the solids in a bin are in motion whenever

any of it is withdrawn - see Appendix AMoisture Content - quoted as a percentage of wet weight (%wb)Plane Flow - a flow pattern characterised by flow trajectories that are

symmetrical about the vertical plane through the longitudinal axisof the outlet slot

Ratholing / Piping - a no-flow condition in which material forms a stable vertical holewithin a funnel-flow bin - the diameter of the rathole is governedby the diagonal dimension of the outlet

Silo - As per 'Bin' definition

iii

NOMENCLATURE

a - average vertical acceleration of bulk material in hopper [m/s2]ac - acceleration of bulk material in hopper due to the

convergence of the flow channel [m/s2]av - acceleration of bulk material in hopper due to the increase

in the velocity after discharge commences [m/s2]B - outlet dimension of the silo [m]Bc - minimum outlet dimension for conical hopper [m]Bf - dimension of central flow channel in funnel-flow silo [m]Bmin - minimum outlet dimension for cohesive arch [m]Bp - minimum outlet dimension for plane flow hopper [m]D - diameter of silo [m]Df - critical rathole dimension [m]Df m - critical rathole dimension calculated for the base of the silo [m]Dg - diagonal dimension of the hopper at the transition with the

base of the stockpile [m]e, exp - base of Napierian logarithms [-]EYL - effective yield locus [-]ff - critical flow factor based upon minimum opening dimension [-]ffa - actual flow factor based upon actual opening dimension [-]FF - flow function - the plot of unconfined yield strength versus

major consolidation stress for one specific bulk material [-]g - acceleration due to gravity [m/s2]G(φt) - function based upon the static angle of internal friction [2] [-]h - actual head of solids [m]hD - effective draw-down of material in funnel flow silo [m]hf - effective head of bulk material [m]H - surcharge level of bulk material [m]Hcr - critical surcharge of bulk material to ensure total mass-flow

in silo [m]H(α) - factor to take into account the variation in arch thickness,

hopper half angle and hopper type [-]Kf - rathole geometry factor [-]Kj - normal stress ratio [-]L - length of slot hopper [m]Lh - length of slot hopper at the transition with the base of the stockpile [m]m - silo geometry parameter [-]

m = 0 for plane flow (end effects neglected)m =1 for axi-symmetric flow

iv

Q - mass flow rate [kg/s]R - hydraulic radius [m]Ra - average surface roughness [µm]TYL - time yield locus [-]v - velocity of bulk material in silo [m/s]vav - average velocity of bulk material in silo [m/s]WYL - wall yield locus [-]

α - hopper half angle, or slope of hopper, measured from the vertical [˚]αc - critical hopper half angle for mass-flow for conical hopper [˚]αp - critical hopper half angle for mass-flow for plane flow hopper [˚]γ - bulk material specific weight [kg/m2s2]δ - effective angle of internal friction - the inclination of the effective

yield locus [˚]θR - angle of repose of bulk material [˚]π - constant [-]ρ - bulk material density - mass of a quantity of a bulk material

divided by its total volume [kg/m3]σc - unconfined yield strength - the major principal stress of the

Mohr stress circle being tangential to the yield locus with theminor principal stress being zero [Pa]

σo - adhesion [Pa]σw - the normal stress present at a confining wall [Pa]σ1 - major consolidating stress - the major principal stress given

by the Mohr stress circle of steady state flow [Pa]

σ_

1 - stress acting in equilibrium arch [Pa]τo - cohesion [Pa]τw - the shear stress present at a confining wall [Pa]φ - kinematic angle of internal friction - the tangent to the yield

locus and the abscissa [˚]φt - static angle of internal friction [˚]φw - fully developed or kinematic wall friction angle - describes the

arctan of the ratio of the wall shear stress to the wall normal stress [˚]

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 1____________________________________________________________________________________________1 EXECUTIVE SUMMARY

This report has been commissioned by Hatch Associates Pty. Ltd. to determine the flow propertiesof a number of samples of Az Zabirah Bauxite so as to provide relevant parameters for the designof efficient and reliable bulk storage and handling facilities.

Due to the number of samples being referred to in this report, the following abbreviations will beused in order to identify the material:

ROM AB – Run Of Mine Average Grade BauxiteROM HB – Run Of Mine High Grade BauxiteROM LB – Run Of Mine Low Grade Bauxite

SSP AB (-80) – Secondary Sizer Product Average Grade BauxiteSSP HB – Secondary Sizer Product High Grade BauxiteSSP LB – Secondary Sizer Product Low Grade Bauxite

T2 CAB – Rod Mill Feed Combined Average Grade BauxiteT2 CHB – Rod Mill Feed Combined High Grade BauxiteT2 LB – Rod Mill Feed Low Grade BauxiteUCZ D1-45 to UCZ D3-45 – Rod Mill Feed Upper Clay ZoneLCZ D43-45 to LCZ D45-45 – Rod Mill Feed Lower Clay Zone

SSP AB (-25) – Secondary Sizer Product Undersize Average Grade BauxiteT1 OAB – Oversize Average Grade BauxiteT2 OAB – Oversize Average Grade BauxiteT1 OHB – Oversize High Grade BauxiteT2 OHB – Oversize High Grade BauxiteT1 CAB – Combined Average Grade BauxiteT1 CHB – Combined High Grade BauxiteT1 LB – Undersize Low Grade BauxiteAGB RSP – Combined Average Grade Bauxite Roller Screen Product

How these samples were derived is illustrated in Figure 1. T1 refers to 22mm crusher. T2 refers to16mm crusher.

A particle size distribution only was performed on the following samples, SSP AB (-25), T1 OAB,T2 OAB, T1 OHB, T2 OHB, T1 CAB, T1 CHB, T1 LB and AGB RSP.

The following samples had particle size distribution, angle of repose, worst case determination, andwall friction tests (at worst case moisture) performed, ROM AB, ROM HB, ROM LB, SSP AB (-80), SSP HB, SSP LB.

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 2____________________________________________________________________________________________

ROM BAUXITE

HB AB LB

SECONDARYCRUSHER

80mm

SSP

HB AB LB

25mmSCREEN

COMBINED-80 mm

OVERSIZE-80 mm +25 mm

UNDERSIZE-25 mm

ROLLERSCREEN

AGB RSP

T1 22 mm T2 16 mm T1 22 mm T2 16 mm

T2 CHBT2 CABT2 CLB

T2 OHBT2 OABT2 OLB

T2 OHBT2 OAB

T1 CHBT1 CAB

SSP AGB -80mm

SSP AGB-25mm

ROMCLAY ZONES

UPPERD1-45D2-45D3-45

LOWERD43-45D44-45D45-45

UCZ D-451UCZ D2-45UCZ D3-45LCZ D43-45LCZ D44-45LCZ D45-45

T2 16 mm

Figure 1 – Sample Collection Flow Chart

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 3____________________________________________________________________________________________The following samples had particle size distribution, angle of repose, belt surcharge angle and worstcase determination tests performed, T2 CAB, T2 CHB, T2 LB, and UCZ D1-45 to UCZ D3-45 andLCZ D43-45 to LCZ D45-45.

A full range of tests was carried out at the worst case moisture level for T2 CAB, T2 CHB, T2 LB,and LCZ D44-45 and at best case moisture level for UCZ D3-45 samples.

The requirements of this study are encompassed by Hatch Associates Pty. Ltd. order no.4500001419 dated 19. 2. 2004.

The bulk material tests depicted in this report were performed using the Jenike type direct sheartester [3, 4] in order to obtain the relevant material strength and frictional characteristics, and thecompressibility tester [1] for the measurement of the bulk density. Also the worst casedetermination of specified samples was undertaken using a uniaxial flowability tester. Thefollowing material flow properties and design parameters are presented in Appendix A:

• Particle Size Distributions• Worst Case Moisture Levels• Bulk material strength (Flow Function), effective, δ, and kinematic or static, φ or φt, angles of

internal friction, and bulk density, ρ• Wall friction characteristics for the lining materials:

(a) ‘Arco plate’ - Grade: Arco Alloy 1600,(b) Alumina Ceramic Wear Tile,(c) Mild Steel – mill scale finish,(d) ‘Tivar 88’ - Ultra High Molecular Weight Polyethylene (UHMWPE),(e) ‘Polycer’- ceramic in rubber wear pads(f) ‘Duaplate D60’ – Smooth Overlay(g) ‘Bisalloy 360’ - mill scale finish

• Mass flow hopper design parameters• Funnel flow design parameters• Dust Extinction Moisture Levels

For an explanation of the above terms the reader is referred to Appendices B and C, and [1-4].

Flow property testing on the Run Of Mine samples indicates the ROM AB, ROM HB and ROMLB have ‘worst case’ moisture levels of 18.2%, 21.1% and 22.4% respectively for the –4mm sizefraction which corresponds to a full size fraction moisture levels of 12%, 14.1% and 17.9%respectively. The results of testing at these moisture levels may be found in Appendix A.

Figure A2.1 contains the results of wall friction measurements at ‘worst case’ moisture levels onthe ROM samples. They indicate similar and high friction for ROM AB and ROM HB with ROMLB having lower frictional characteristics with increasing normal stress.

Flow property testing on the Secondary Sizer Product samples indicates the SSP AB, SSP HB andSSP LB have ‘worst case’ moisture levels of 12.9%, 15% and 22.2% respectively for the –4mm

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 4____________________________________________________________________________________________size fraction which corresponds to a full size fraction moisture levels of 9.2%, 7.2% and 19.2%respectively. The results of testing at these moisture levels may be found in Appendix A.

Figures A2.2 to A2.4 contain the results of wall friction measurements for SSP AB, SSP HB andSSP LB at 12.9%, 15% and 22.2% moisture respectively. They indicate reasonably lower wallfriction on the ‘Tivar 88’ material compared to Bisalloy 360 and Alumina Ceramic Tile, making itthe preferred wall lining material for the design of a mass-flow silo, or for when low frictionalcharacteristics between the bulk material and the wall lining material are required.

Flow property testing on the Rod Mill Feed samples indicates the T2 CAB, T2 CHB and T2 LBhave ‘worst case’ moisture levels of 15.2%, 16.1% and 19.9% for the –4mm size fraction whichcorresponds to a full size fraction moisture levels of 13%, 12.5% and 16.8% respectively. From theRod Mill Feed Clay Zone samples, the ‘best case’ moisture level was found to be 11.9% for theUCZ D3-45 sample and the ‘worst case’ moisture level was found to be 14.9% for the LCZ D44-45 sample. These -4mm size fraction moisture levels correspond to full size moisture levels of8.6% and 12.2% respectively. The results of testing at these moisture levels are contained inAppendix A.

Figures A1.1 to A1.4 show instantaneous and time consolidated flow functions, internal angles offriction and bulk density for T2 CAB and T2 CHB under low and high consolidation stresses. Theresults indicate T2 CAB has a high instantaneous flow function indicating high bulk strength with amoderate increase after 3 days storage. The T2 CAB would be classified as a difficult handlingmaterial. For the T2 CHB, the instantaneous flow function is moderately high indicating moderateto high bulk strength with a moderate increase after 3 days storage. The T2 CHB would beclassified as a moderately difficult handling material.

Figures A1.5 and A1.6 show instantaneous and time consolidated flow functions, internal angles offriction and bulk density for T2 LB under low and high consolidation stress. In general the resultsindicate an extremely difficult handling material with very high bulk strength which increasessignificantly after 3 days undisturbed storage.

Figures A1.7 and A1.8 show instantaneous and time consolidated flow functions, internal angles offriction and bulk density for UCZ D3-45 under low and high consolidation stress. In general theresults indicate a moderate handling material with moderate bulk strength which increasesmoderately after 3 days undisturbed storage.

Figures A1.9 and A1.10 show instantaneous and time consolidated flow functions, internal anglesof friction and bulk density for LCZ D44-45 under low and high consolidation stress. In generalthe results indicate a difficult handling material with high bulk strength which increases moderatelyafter 3 days undisturbed storage.

Figures A2.5 to A2.9 contain the results of wall friction measurements at aforementioned ‘worstcase’ moisture levels (‘best case’ for the upper clay zone). For all five samples, the Tivar ‘88’material indicates the lowest friction making it the preferred wall lining material for the design of a

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 5____________________________________________________________________________________________mass-flow silo, or for when low frictional characteristics between the bulk material and the walllining material are required.

Figure A3.1 contains graphs of mass flow hopper design parameters for the T2 CAB material.They show moderately large critical arching dimensions with a small increase after 3 day timestorage. Half hopper angles required for mass flow are steep for all the tested lining materials apartfrom ‘Tivar 88’.

Figure A3.2 contains graphs of mass flow hopper design parameters for the T2 CHB material.They show moderate critical arching dimensions with a small increase after 3 day time storage. Halfhopper angles required for mass flow are steep for all the tested lining materials apart from ‘Tivar88’.

Figure A3.3 contains graphs of mass flow hopper design parameters for the T2 LB material. Theyshow large critical arching dimensions under instantaneous conditions and 3 day time storagearching dimensions outside the graph boundary; that is the critical opening dimensions were greaterthan 4m for conical hoppers and 2 metres for plane flow hoppers. Half hoper angles for mass floware most favourable for ‘Tivar 88’.

Figure A3.4 contains graphs of mass flow hopper design parameters for the UCZ D3-45 material.They show small critical arching dimensions with a moderate increase after 3 day time storage.Tivar ‘88’ wall material provides the most favourable hopper half angle for mass flow.

Figure A3.5 contains graphs of mass flow hopper design parameters for the LCZ D44-45 material.They show moderate critical arching dimensions a with small increase after 3 day time storage.Tivar ‘88’ wall material provides the most favourable hopper half angle for mass flow.

Figures A4.1 to A4.5 contain graphs of critical piping diameter as a function of effective materialhead for the T2 CAB, T2 CHB, T2 LB and LCZ D44-45 samples at a ‘worst case’ moisture levelof 15.2%, 16.1%, 19.9% and 14.9% respectively and for the UCZ D3-45 sample at a ‘best case’moisture level of 11.9% . All graphs indicate a high propensity to form stable ratholes with the T2LB sample indicating the highest.

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 6____________________________________________________________________________________________2 FLOW PROPERTY TESTS

In order to determine the flow properties of bulk solids, some or all of the following range of testsmay be carried out.

2.1 Direct Shear Test

During the flow of a bulk solid with mixed particle sizes, the large particles move bodily while thematerial shears across the fines. Therefore, the strength of the bulk solid and its ability to causestoppages of flow is dependent on the strength of the fines component. To determine the strengthof a bulk solid containing large particles, the fines are generally screened through a 4 mm aperturesieve and tested using the following methods and procedures. The direct shear testing machine isequipped with a shear cell of circular cross section as shown in Figure 2. The normal load isapplied to the cell by means of a gravity vertical loading system and the shearing action is providedby means of an electro-mechanically driven loading stem which moves horizontally at a rate of 2.5mm/min. The shear force is measured with a strain gauge load cell and indicated on a chartrecorder.

Figure 2 - Jenike Shear Test Cell

The bulk material is sheared at a number of different normal loads to generate a series of yield locias shown in Figure 3. For each instantaneous yield locus, a minimum of six shear tests areperformed. A complete description of the testing technique is given in [3, 4]. The effect ofundisturbed storage time on consolidation may be determined using a consolidation bench inconjunction with the shear tester. The consolidated samples are placed in a consolidation bench forthe requisite time under the application of a consolidating pressure and then sheared. From theinstantaneous and time yield loci generated, the following properties of the bulk material may bedetermined:

2.1.1 Flow Functions

The flow function (FF) is a measure of the material's strength at a free surface as a function of themajor consolidating pressure and is obtained from the Yield Loci as illustrated in Figure 3. A flowfunction may be obtained for both instantaneous and time consolidated conditions.


Figure 3 - Yield Loci and Flow Function

2.1.2 Effective Angle of Internal Friction

The effective angle of internal friction (δ) is the slope angle of the Effective Yield Locus (EYL)which is a line from the origin, tangential to the Major Mohr circle shown in Figure 3.

2.1.3 Kinematic Angle of Internal Friction

The kinematic angle of internal friction (φ) is the slope angle of the Instantaneous Yield Locus atthe point of intersection with the Mohr circle through the origin.

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 8____________________________________________________________________________________________2.1.4 Static Angle of Internal Friction

The static angle of internal friction (φt) is the slope angle of the Time Yield Locus at the point ofintersection with the Mohr circle through the origin.

2.2 Wall Friction Test

The wall friction test was performed using the apparatus shown in Figure 4, which is similar to thedirect shear arrangement described in Section 2.1 with a sample of wall material in place of the cellbase. The bulk material is sheared across the wall material under reducing normal stress to generatea Wall Yield Locus (WYL). For each WYL a minimum of three wall friction tests are performed.

From the WYL the wall friction angle may be determined at any normal stress as:

φw = wall friction angle = tan -1 [ shear stress / normal stress at boundary] (1)

This is shown diagrammatically in Figure 5. A low wall friction angle is particularly important forpracticable mass-flow hopper design.

Figure 4 - Wall Yield Loci Test Apparatus

Figure 5 - Determination of Wall Friction Angle

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 9____________________________________________________________________________________________2.3 Compressibility Test

The bulk density is determined using a Compressibility Tester. This unit consists of a 63.5 mmdiameter by 19 mm deep cell, which is filled with a - 4 mm sample of the bulk material. Loads areapplied to the sample by means of a lid and weight carrier, and the compression of the sample ismeasured with a dial gauge. Knowing the sample volume, a mass and applied load allows therelationship between bulk density (ρ) and the major consolidation pressure (σ1) to be determined.

2.4 Moisture Content Test

Total moisture content for the test sample is determined using a method derived from AS 1038 Part1 Method C and is quoted as a percentage of wet weight (%wb).

2.5 Surface Roughness Test

The friction developed between a bulk material sliding on a wall lining material is a function ofvarious parameters including the bulk material / wall lining material combination, particle sizedistribution, and wall lining material surface roughness. Due to the importance of the surfaceroughness of the wall lining material in determining the subsequent storage facility designparameters, the average centreline, Ra, surface roughness of each wall lining material tested in thisreport is provided.

The surface roughness of the wall lining samples is determined by the procedure given in [5]. Inthis analysis, the roughness of a lining sample shall be given by the centreline average roughness,Ra, and shall be noted by

Ra = 1L ⌡⌠

0

L | y(x) | dx (2)

where y(x) is the coordinate height measured from the mean centreline shown in Figure 6.

Figure 6 - Surface Roughness

2.6 Particle Size Test

The particle size distribution of was determined using a dry sieving technique.


2.7 Angle of Repose Test

This was determined using the technique described in the International Maritime Organisations'Code of Safe Practice for Solid Bulk Cargoes' [6]. The method involved forming a conical pile ofthe material that was then digitally photographed from two directions at 90˚. The digital imageswere then imported into a computer drawing and the repose angles measured obtaining 4 resultsthat were then averaged. The tests were repeated three times for each material and the resultsaveraged to obtain the reported result.

2.8 Belt Conveyor Surcharge Angle Test

This test was conducted using a 70m long, 600mm wide belt conveyor located at the TUNRAlaboratories. The conveyor has an idler spacing of 1250mm and a troughing angle of 35˚. A sampleof the ore to be tested was placed along the conveyor belt a distance of 1500mm heaped at the angleof repose, then transported 30m and back to the original position. The included angle of the samplewas then measured at three points along the pile and the results averaged to obtain the surchargeangle.

2.9 Dust Extinction Moisture Tests

These tests were conducted in accordance with AS4156.6-2000 with the exception that the testquantity used in the test rig was 2.5 kg rather than the specified 1.2 kg due to the fact that thestandard was written for coal rather than bauxite.

2.10 Unconfined Uniaxial Test

The test was conducted by first forming a solid cylinder of the bulk material under ‘constrainedconsolidation’ and then ‘unconfined compression’ of the formed cylinder until failure occurred.This was achieved by utilising an arrangement shown schematically in Figure 7. For the‘constrained consolidation’ phase, three mould sections were pressed tightly together utilisingpneumatic actuators to form a hollow cylinder with an 80mm inside diameter. Consolidation of thebulk solid was performed by top and bottom pneumatic actuators connected to loading discs withsufficient clearance to fit inside the mould cylinder. The lower loading disc was located just insidethe mould cylinder and it was then filled with the bulk sample. The top was screeded off and theupper loading disc was then located on top of the sample. The top and bottom pneumatic actuatorsthen applied a pre-determined compressive force, measured by a load cell, for which thecorresponding stress was the major consolidation stress σ

1.


Figure 7 – Schematic of Unconfined Uniaxial Test Machine

With the lower disc clamped in place, the applied consolidation load was relaxed and the threemould sections retracted to expose the consolidated cylindrical bulk sample. The top pneumaticactuator then applied a slowly increasing compressive load until the sample failed. The stresscorresponding to the load, measured by the load cell, at which failure occurred, was the unconfinedyield stress σ

C. By measuring the unconfined yield stress σ

C obtained for a range of major

consolidation stresses σ1, a flow function was plotted that represents the cohesive strength of the

bulk solid.

3 FLOW PROPERTY RESULTS

3.1 Particle Size Range

Appendix A Figures A5.1 to A5.4 contain graphs showing the cumulative percent mass as afunction of particle size for all of the samples tested. The d5 0 equivalent diameters are summarizedin Table 1 below.


Table 1 – d5 0 equivalent diameter

Zone Sample d5 0 equivalentdiameter (mm)

Average Grade Bauxite ROM AB 28SSP AB (-80) 35SSP AB(-25) 8

T1 OAB 20T2 OAB 14T1 CAB 12T2 CAB 4

AGB RSP 3.5High Grade Bauxite ROM HB 14

SSP HB 30T1 OHB 20T2 OHB 12T1 CHB 5T2 CHB 9

Low Grade Bauxite ROM LB 4SSP LB 1.5T1 LB 3.5T2 LB 5

Upper Clay Zone UCZ D1-45 4UCZ D2-45 5UCZ D3-45 4

Lower Clay Zone LCZ D43-45 5.5LCZ D44-45 4LCZ D45-45 5

For convenience, the three ROM and Secondary Sizer Product, and five Rod Mill Feed samples(‘worst case’ and ‘best case’) have been plotted again in Figures A5.5 to A5.7.

3.2 Moisture Content

The finer portion of a bulk material will have a higher percentage moisture content than the coarserportion. By measuring the moisture contents at which the full size fraction and the -4 mm sizefraction of the sample supplied reached saturation, and by measuring a typical 'as supplied'moisture level of the full size fraction and the –4mm size fraction, the relationship between themoisture contents of the full size fraction and the tested -4 mm size fraction may be determined.The results of these measurements are given in Table 2 and are graphed in Figure 8 to Figure 10.Using these graphs, the relationship between the moisture content of the -4mm size fraction and thefull size fraction may be determined for any moisture level from zero to saturated.


Table 2 – Moisture Contents

Zone Sample Size Fraction ‘as supplied’ SaturatedAverage Grade Bauxite ROM AB Full 8.1 % 15.1 %

-4mm 11 % 26 %SSP AB (-80) Full 7.8 % 11.7 %

-4mm 10.5 % 25.9 %SSP AB(-25) Full 8.6 % N/A

T1 OAB Full 6.8 % N/AT2 OAB Full 6.7 % 11.6 %

-4mm 7.6 % 22.8 %T1 CAB Full 7.4 % N/AT2 CAB Full 7.8 % 18.4 %

-4mm 8.9 % 21.7 %AGB RSP Full 9.3 % N/A

High Grade Bauxite ROM HB Full 9.2 % 16.3%-4mm 11.4 % 26.4 %

SSP HB Full 6.7 % 9.9 %-4mm 10.9 % 25 %

T1 OHB Full 6.6 % N/AT2 OHB Full 6.3 % 13.8 %

-4mm 7.2 % 22.9 %T1 CHB Full 8.5 % N/AT2 CHB Full 6.8 % 16.6 %

-4mm 8.1 % 23 %Low Grade Bauxite ROM LB Full 11.6 % 21.9 %

-4mm 13.9 % 28 %SSP LB Full 12.4 % 23.4 %

-4mm 13.3 % 27.7 %T1 LB Full 11.4 % N/AT2 LB Full 10.6 % 21 %

-4mm 12.6 % 24.9 %Upper Clay Zone UCZ D1-45 Full 5.3 % 13.8 %

-4mm 5.7 % 23.7 %UCZ D2-45 Full 4.3 % 11.3 %

-4mm 4.7 % 23.2 %UCZ D3-45 Full 4.7 % 12.2 %

-4mm 5.6 % 19.8 %Lower Clay Zone LCZ D43-45 Full 8.3 % 16.1 %

-4mm 10.2 % 23.1 %LCZ D44-45 Full 8.7 % 18.2 %

-4mm 10.2 % 24.9 %LCZ D45-45 Full 8.9 % 15.6 %

-4mm 10.3 % 25.1 %


0

5

10

15

20

25

30

0 5 10 15 20 25 30

ROMABROMHBROMLB

-4mm Size FractionMoisture Content (%)

Full Size Fraction Moisture Content (%)

Saturated

As Supplied

Figure 8 - 4mm Versus Full Size Fraction Moisture Content (ROM)

0

5

10

15

20

25

30

0 5 10 15 20 25 30

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Figure 9 – 4mm Versus Full Size Fraction Moisture Content (SSP)


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Figure 10 – 4mm Versus Full Size Fraction Moisture Content (RMF)

3.3 Shear Tests

For flow property determination and performance evaluation it is advisable to examine samples ofthe bulk material which are likely to produce the most difficult flow conditions. Variations inmoisture content can have a major influence on the handleability of a bulk material. For most bulkmaterials the bulk strength tends to increase with increased moisture content, reaching a peak atbetween 60% and 80% of saturation. Beyond this peak the bulk strength generally reduces withadditional moisture.

3.3.1 Run of Mine Samples

To find the moisture level for maximum bulk strength the moisture content of several portions ofthe -4 mm sample of the ROM AB sample were modified from that supplied of 11% to levels of13%, 15.6%, 18.2%, and 20.8%. For the ROM HB sample, moisture content was modified fromthat supplied of 11.4% to levels of 13.2%, 15.8%, 18.5%, and 21.1%. For the ROM LB sample,moisture content was modified from that supplied of 13.9% to levels of 14%, 16.8%, 19.6%, and22.4%.

3.3.2 Secondary Sizer Product Samples

Several portions of the -4mm sample of the SSP AB sample were modified from that supplied of10.5% to levels of 12.9%, 15.5% and 18.1%. For the SSP HB sample, moisture content wasmodified from that supplied of 10.9% to levels of 12.5%, 15% and 17.5%. The SSP LB samplewas modified from that supplied of 13.3% to levels of 16.6%, 19.4% and 22.2%.


3.3.3 Rod Mill Feed Samples

Several portions of the -4mm sample of the T2 CAB sample were modified from that supplied of8.9% to levels of 10.8%, 13% and 15.2%. For the T2 CHB sample, moisture content was modifiedfrom that supplied of 8.1% to levels of 11.5%, 13.8% and 16.1%. The T2 LB sample was modifiedfrom that supplied of 12.6% to levels of 14.9%, 17.4% and 19.9%.

3.3.4 Rod Mill Feed Clay Zone Samples

The -4mm sample of the UCZ D1-45 sample was modified from that supplied of 5.7% to levels of9.4%, 11.8%, 14.2% and 16.6%. For the UCZ D2-45 sample, moisture content was modified fromthat supplied of 4.7% to levels of 9.3%, 11.6% and 13.9%. The UCZ D3-45 sample was modifiedfrom that supplied of 5.6% to levels of 7.9%, 9.9% and 11.9%.

The -4mm sample of the LCZ D43-45 sample was modified from that supplied of 10.2% to levelsof 11.6%, 13.9% and 16.2%. For the LCZ D44-45 sample, moisture content was modified fromthat supplied of 10.2% to levels of 12.5%, 14.9% and 17.4%. The LCZ D45-45 sample wasmodified from that supplied of 10.3% to levels of 12.5%, 15% and 17.5%.

3.3.5 Worst Case Determination

The uniaxial tester was used to obtain flow functions from which the worst case moisture levelswere determined. The results obtained from these tests may be found in Appendix A.

For the Run of Mine Samples the results of these tests may be found in Figure A6.1. The graphindicates that the ROM AB, ROM HB and ROM LB exhibit highest strength at a fines moisturelevel of 18.2 %, 21.1 % and 22.4 % respectively. Using the graph given in Figure 8, these moisturelevels equate to a moisture level of 12%, 14.1% and 17.9% respectively in the full size fraction.

For the Secondary Sizer Product Samples the results of these tests may be found in Figure A6.2.The graph indicates that the SSP AB, SSP HB and SSP LB exhibit highest strength at a finesmoisture level of 12.9%, 15% and 22.2% respectively. Using the graph given in Figure 9, thesemoisture levels equate to a moisture level of 9.2%, 7.2% and 19.2% respectively in the full sizefraction.

For the Rod Mill Feed Samples the results of these tests may be found in Figure A6.3. The graphindicates that the T2 CAB, T2 CHB and T2 LB exhibit highest strength at a fines moisture level of15.2%, 16.1% and 19.9% respectively. Using the graph given in Figure 10, these moisture levelsequate to a moisture level of 13%, 12.5% and 16.8% respectively in the full size fraction.

For the Rod Mill Feed Clay Zone Samples the results of these tests may be found in Figure A6.4and A6.5. The graphs indicate that the UCZ D3-45 exhibits lowest strength and LCZ D44-45exhibits the highest strength at a fines moisture level of 11.9% and 14.9% respectively. Using the

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 17____________________________________________________________________________________________graph given in Figure 10, these moisture levels equate to a moisture level of 8.6% and 12.2%respectively in the full size fraction.

3.3.6 Shear Testing of Rod Mill Feed Samples

A full range of tests under low and high consolidation was performed on the five Rod Mill Feedsamples at the aforementioned moisture levels, the results of which are given in Appendix A,Figures A1.1 to A1.10. The middle graph contains the effective and static angles of internal frictionand the lower graph contains the instantaneous and 3 day time storage flow functions.

For the T2 CAB, the instantaneous flow function is high indicating high bulk strength with amoderate increase after 3 days storage. The T2 CAB would be classified as a difficult handlingmaterial.

For the T2 CHB, the instantaneous flow function is moderately high indicating moderate to highbulk strength with a moderate increase after 3 days storage. The T2 CHB would be classified as amoderately difficult handling material.

For the T2 LB, the instantaneous flow function is very high indicating very high bulk strength witha large increase after 3 days storage. The T2 LB would be classified as an extremely difficulthandling material.

For the UCZ D3-45, the instantaneous flow function is moderate indicating moderate bulk strengthwith a moderate increase after 3 days storage. The UCZ D3-45 would be classified as a moderatehandling material.

For the LCZ D44-45, the instantaneous flow function is high indicating high bulk strength with amoderate increase after 3 days storage. The LCZ D44-45 would be classified as a difficult handlingmaterial.

3.4 Compressibility Tests

Compressibility tests were performed on the Rod Mill Feed samples. That is on the ‘worst case’T2 CAB, T2 CHB, T2 LB, and LCZ D44-45 and on the ‘best case’ UCZ D3-45 samples.

The results of these tests for low consolidation are contained in the upper graph of Appendix A,Figures A1.1, A1.3, A1.5, A1.7 and A1.9, and for high consolidation in the upper graph ofAppendix A, Figures A1.2, A1.4, A1.6, A1.8 and A1.10.

The results show the T2 CAB material is moderately compressible, the bulk density increasingabout 50% from an unconsolidated value of about 1200 kg/m3 to about 1800 kg/m3 at aconsolidation of 100 kPa.

The T2 CHB material is moderately compressible, the bulk density increasing about 40% from anunconsolidated value of about 1500 kg/m3 to about 2100 kg/m3 at a consolidation of 100 kPa.


Also the T2 LB material is highly compressible, the bulk density increasing about 70% from anunconsolidated value of about 1200 kg/m3 to about 2000 kg/m3 at a consolidation of 100 kPa.

Furthermore, the UCZ D3-45 material is poorly compressible, the bulk density increasing about20% from an unconsolidated value of about 1200 kg/m3 to about 1400 kg/m3 at a consolidation of100 kPa.

Finally, the LCZ D44-45 material is poorly compressible, the bulk density increasing about 20%from an unconsolidated value of about 1200 kg/m3 to about 1400 kg/m3 at a consolidation of 100kPa.

3.5 Wall Friction Tests

Appendix A, Figures A2.1 to A2.9 contain graphs of the wall yield loci and associated wall frictionangle for normal stresses up to 22 kPa for the wall materials indicated in Table 3. Also in Table 3are the results of surface roughness measurements on the wall samples. In practice the surfaceroughness, Ra, of the lining material should be similar to those values depicted in Table 3. Failure toadhere to these values may lead to storage facility designs that are not optimal.

Table 3 - Wall Lining Materials

Wall Material Surface Roughness 'Ra'(µm)

Arco plate 20.9Alumina Ceramic Tile 2.2

Mild Steel 5.6Tivar 88 1.3

PolyCeramic N/ADuaPlate D60 N/ABisalloy 360 5.9

The wall friction tests were carried out in the following format:

The ‘worst case’ Run of Mine samples, ROM AB, ROM HB and ROM LB were tested on theBisalloy 360 wall material.The ‘worst case’ Secondary Sizer Product samples, SSP AB, SSP HB and SSP LB were tested onTivar ‘88’, Bisalloy 360, and Alumina Ceramic Tile.The ‘worst case’ Rod Mill Feed samples, T2 CAB, T2 CHB, T2 LB, LCZ D44-45 and ‘best case’UCZ D3-45 were tested on Arcoplate, Alumina Ceramic Tile, Mild Steel, Tivar ‘88’, PolyCeramicand DuaPlate D60.

Figure A2.1 shows that the ROM LB has lowest frictional characteristics on the Bisalloy 360 wallmaterial when compared to ROM AB and ROM HB with increasing normal stress.


Figures A2.2 to A2.4 contain the wall friction results for SSP AB, SSP HB and SSP LB. Thegraphs show ‘Tivar 88’ has lower wall friction compared to Bisalloy 360 and Alumina CeramicTile, making it the preferred wall lining material for the design of a mass-flow silo, or for when lowfrictional characteristics between the bulk material and the wall lining material are required.

Figures A2.5 to A2.9 contain the results of wall friction measurements for the five Rod Mill Feedsamples. The results indicate that the Tivar ‘88’ material, followed by the Alumina Ceramic Tile,lowest friction making them the preferred wall lining materials for the design of a mass-flow silo, orfor when low frictional characteristics between the bulk material and the wall lining material arerequired.

Care should be taken in design to fully understand the normal wall pressures acting as this can havean effect on the wall friction coefficient.

3.6 Angle of Repose

Angle of Repose tests were carried out on the Run of Mine, Secondary Sizer Product and Rod MillFeed samples. Examples of the photographs taken during the measurements programm arecontained in AppendixA, Figures A8.1 to A8.15. The results of the tests are summarised in Table 4below. It should be noted that the results are for the full size fraction of the materials. The reposeangle measurements conducted indicate a maximum angle. Some reduction in the angle should beexpected in practice due to larger particles that roll down the pile surface and other effects such asdrop height.

Table 4 – Angle of Repose

Zone Sample Angle of Repose (0)Run Of Mine ROM AB 34

ROM HA 32ROM LB 32

Secondary Sizer Product SSP AB 36SSP HB 35SSP LB 31

Rod Mill Feed T2 CAB 34T2 CHB 35T2 LB 34

UCZ D1-45 34UCZ D2-45 34UCZ D3-45 34LCZ D43-45 36LCZ D44-45 37LCZ D45-45 36

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 20____________________________________________________________________________________________3.7 Belt Conveyor Surcharge Angle Tests

The conveyor belt surcharge angle tests were performed on the nine Rod Mill Feed samples and aresummarized in Table 5 below.

Table 5 – Belt Conveyor Surcharge Angle

Sample Included Angle (0) Belt SurchargeAngle (0)

T2 CAB 138 21T2 CHB 145 17.5T2 LB 128 26

UCZ D1-45 137 21.5UCZ D2-45 143 18.5UCZ D3-45 141 19.5LCZ D43-45 134 23LCZ D44-45 128 26LCZ D45-45 132 24

3.8 Dust Extinction Moisture Tests

The results of Dust Extinction Moisture (DEM) testing are given in Appendix A, Figure A7.1 forthe Rod Mill Feed materials. The Dust Extinction Moisture (DEM) levels determined from thegraph at a dust number of 10 are given in Table 6. As the dust tests were conducted on the –6.3mmsize fraction, the DEM relates to this size fraction only and as explained in Section 3.2, the fineswill hold a higher proportion of moisture than the larger size fraction. Figure 11 shows therelationship between the moisture content of the –6.3mm size fraction and the full size fraction forthe Rod Mill Feed materials. The equivalent full size fraction DEM levels are also indicated inTable 6.

Table 6 – Dust Extinction Moisture

Ore -6.3mm Size Fraction Full Size FractionT2 CAB 8.9 % 7.6 %T2 CHB 9.6 % 8 %T2 LB 11 % 9.5 %

UCZ D3-45 6.9 % 5.8 %LCZ D44-45 10.4 % 8.6 %


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Figure 11 – 6.3mm Versus Full Size Fraction Moisture Content

4 STORAGE FACILITY DESIGN

The reader is referred to Appendix B 'Material Flow Patterns in Silos' and Appendix C 'StorageFacility Design Notes' for background information. The results of the flow property tests given inAppendix A, Figures A1.1 to A1.10 and A2.5 to A2.9 can be used to generate storage facilitydesign information for the five Rod Mill Feed materials as follows.

4.1 Mass Flow Design

In order to design a silo to promote reliable mass-flow, two (2) parameters are of importance:

(a) the hopper (converging portion of the silo) outlet dimension, B, must be chosen to preventmechanical and cohesive arching, and

(b) the hopper half angle, α, must be selected to ensure flow of the bulk material along the wallsof the hopper.

The diameter, or width, of the silo, along with the height, are subsequently selected based upon thestorage capacity and silo height constraints.

Appendix A, Figures A3.1 to A3.5 detail plots of the maximum possible hopper half-angle 'α'required to achieve mass-flow as a function of the hopper outlet dimension 'B' for bins which havesignificant surcharge of material above the hopper section. A typical plot is also given in Figure 12.In hoppers without surcharge, some increase in these angles may be accommodated.


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Figure 12 - α Versus B Typical Plot

The basic methodology required to design a mass-flow silo is:

(1) decide whether an axi-symmetric (conical) or plane (slot) flow silo is required. A point tonote in this selection is that the minimum opening dimension for an axi-symmetric silo,based upon the strength of the material, is typically double that of a plane flow silo, howeverthese dimensions only apply to a plane flow shape where the outlet length is at least three (3)times the outlet width. In addition, plane flow hoppers show an advantage over conicalhoppers, with an increase of about 10˚ in the hopper half angle. This has implications inallowing a reduction in the total height of a plane flow silo for a given storage volume.

It should be noted when calculating critical hopper geometries that conical hoppers have a 3̊tolerance included in the hopper half-angle.

(2) once the geometry of the silo is selected, the opening dimension, B, must be chosen toprevent both mechanical and cohesive arches forming at the hopper outlet.

(i) The critical outlet dimensions given are to ensure cohesive arches do not form overhopper outlets. In order to prevent mechanical arching it is recommended that the minimumoutlet dimension be about five (5) times the maximum lump size for conical hoppers andthree (3) times for plane-flow hoppers.

(ii) The critical cohesive arching dimension for a hopper is that dimension at which a stablearch will not obstruct the outlet and flow will just initiate, based on a 'Flow - No Flow'criterion. The critical outlet dimensions for the five Rod Mill Feed samples at the 'worst case'moisture levels of 15.2%, 16.1%, 19.9% and 14.9% (T2 CAB, T2 CHB, T2 LB and LCZ


D44-45 respectively) and ‘best case’ moisture level of 11.9% (UCZ D3-45) are shown ongraphs contained in Appendix A, Figures A3.1 to A3.5. The results are given forinstantaneous conditions and after 3 days undisturbed storage. All results are presented forboth conical and plane flow hoppers with the tested lining materials. Looking at the plots inFigures A3.1 to A3.5 and the typical plot of Figure 12, the cohesive arching dimension is B1,if the material is to be stored in the silo for a minimal amount of time, or B2, if the material isto be stored undisturbed for a period of time.

The resulting minimum outlet dimension of the silo will be the larger outlet dimension asgiven in (i) and (ii). Note that the aforementioned minimum arching dimension is generallyincreased by 20% in order to guarantee flow.

(3) The hopper half angle, α, is chosen from the plots of Appendix A, Figures A3.1 to A3.5corresponding to the chosen outlet dimension determined from (2). For example, looking atFigure 12 and, say, that the dimension of B2, was selected as the minimum outlet dimension,then the hopper half angle would be α2.

(4) It is often possible to select a larger outlet dimension, B, over that determined in (2) in orderto increase the corresponding hopper half angle, α. This has the benefit of reducing the siloheight whilst still ensuring the capacity requirements of the silo. Hopper half-angles requiredto achieve mass-flow are usually greater at larger opening dimensions. As the outletdimension increases the maximum principal stress during discharge also increases. As can beseen from Appendix A, Figures A2.5 to A 2.9 the wall friction decreases with an increase innormal stress, within the range of stresses existing at the outlet, giving rise to an increase inthe required hopper half-angle for mass-flow. Tunra Bulk Solids should be contacted if halfhopper angles are required at outlet dimensions greater than those given in Figures A3.1 toA3.5.

If the plots of Figures A3.1 to A3.5 resemble the trend of Figure 12, then the aforementionedmay be utilised in the design process ie. select a larger B value and, correspondingly, a largerα value. If, on the other hand, there is no increase in hopper half angle with an increase inoutlet dimension, then there is no benefit from a flow standpoint to increase the silo outletdimension (Note: may need to increase the outlet dimension to promote the required flowrate; see (5)).

(5) The flow rate of a 'coarse' bulk material from a mass-flow silo is determined by the analysisin Appendix C. In the majority of situations the flow rate exceeds the required rate and afeeder must be incorporated to restrict the discharge. It must be noted, however, that theunrestricted flow rate from the silo, as given by the analysis of Appendix C, must be greaterthan the potential feed rate from the feeder in all instances. Estimates of the potential flow ratefrom mass flow hoppers are contained in Appendix A, Figures A3.1 to A3.5.

Attention must be given to the design of the feeder and feeder / hopper interface to ensure the entireoutlet is active to allow full mass flow to be realised. For plane flow hoppers the discharge capacityof the feeder needs to increase in the direction of feed to draw material from the entire slot length.

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 24____________________________________________________________________________________________In the case of belt or apron feeders this can be achieved using a tapered slot. Increasing the pitch ofscrew feeders toward the discharge end will have a similar effect.

It is advised to contact Tunra Bulk Solids to review proposed hopper and feeder designs.

4.2 Funnel Flow Design

The effective design of funnel flow discharge systems requires the outlet dimensions to be greaterthan the critical piping diameter, Df, to ensure that stable ratholes do not develop. The calculatedcritical piping diameter is an upper bound value which has been found in practice to be approachedin flat bottom storage systems with difficult handling materials. Appendix A, Figures A4.1 to A4.5shows the relationship between the critical piping diameter, Df, and effective head of solids, hf, forthe five Rod Mill Feed samples at moisture levels of 15.2%, 16.1%, 19.9% and 14.9% (T2 CAB,T2 CHB, T2 LB and LCZ D44-45 respectively) and 11.9% (UCZ D3-45) for both instantaneousconditions and after 3 days undisturbed storage. All graphs indicate a high propensity to formstable ratholes with graph A4.3 for the T2 LB sample indicating the largest diameter for a relativelysmall effective head of solids. Hence an extremely high propensity to form stable ratholes would beexpected for the T2 LB sample.

It should be noted that the critical piping dimension calculations are based on the bulk strength ofthe fines only. Should the tested bulk material have a significant proportion of lump then this willtend to reduce its ability to maintain a stable rathole particularly if segregation causes areas of lumpconcentration. The values given in Figures A4.1 to A4.5 should therefore be treated as the upperbound with some reductions expected in practice, particularly in bins which are not flat bottomed.

4.3 Chute Design

In many materials handling installations blocked chutes can be a significant cause of interruption toproduction. In chutes where bed depths are low, the normal pressures are also low. Appendix A,Figure A2.1 shows how the wall friction angles can be higher at these low consolidation pressures.

The wall friction angle, φw, is given by:

φw = tan-1 τwσw (3)

where τw is the shear stress, measured from the wall yield locus at a normal consolidation pressure,σw.

Equation (3) allows for an estimation of the required chute inclination angle for transfer chutedesign. The preferred angle of inclination of chutes can be determined by adding between 5˚ and10˚ to the measured wall friction angle at the consolidation pressure calculated from the nominalchute bed depth.

TBS Report # 6299 Flow Properties of Az Zabirah Bauxite Client: Hatch Associates Pty. Ltd. 25____________________________________________________________________________________________5 REFERENCES

[1] Arnold P. C., McLean A. G. and Roberts A. W. 'Bulk Solids: Storage Flow and Handling', TUNRA, The University of Newcastle, 2nd Edition, 1982.

[2] Roberts A.W. 'Basic Principles of Bulk Solids Storage, Flow and Handling'. The Institute for Bulk Materials Handling Research, University of Newcastle, Australia, 1993.

[3] Jenike, A.W. 'Storage and Flow of Solids', Bulletin 123, University of Utah, 7th Printing, Revised November 1976.

[4] 'Standard Shear Testing Technique for Particulate Solids using the Jenike Shear Cell'. The Institution of Chemical Engineers, England, 1989.

[5] Mitutoyo Operation Manual, 178 Series, Surftest 4, Manual No. 4128.[6] 'Code of Safe Practice for Solid Bulk Cargoes', The International Maritime

Organisation, London, Eighth Edition, 1991.

APPENDIX A

Results

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Figure A1.1 - Low Consolidation Shear Test Results 6299 - Rod Mill Feed Average Grade Bauxite @ 15.2% mc.

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Figure A1.2 - High Consolidation Shear Test Results 6299 - Rod Mill Feed Average Grade Bauxite @ 15.2% mc.

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Figure A1.3 - Low Consolidation Shear Test Results 6299 - Rod Mill Feed High Grade Bauxite @ 16.1% mc.

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Figure A1.4 - High Consolidation Shear Test Results 6299 - Rod Mill Feed High Grade Bauxite @ 16.1% mc.

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Figure A1.5 - Low Consolidation Shear Test Results 6299 - Rod Mill Feed Low Grade Bauxite @ 19.9% mc.

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Figure A1.6 - High Consolidation Shear Test Results 6299 - Rod Mill Feed Low Grade Bauxite @ 19.9% mc.

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Figure A1.7 - Low Consolidation Shear Test Results 6299 - Rod Mill Feed Upper Clay Zone @ 11.9% mc.

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Figure A1.8 - High Consolidation Shear Test Results 6299 - Rod Mill Feed Upper Clay Zone @ 11.9% mc.

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Figure A1.9 - Low Consolidation Shear Test Results 6299 - Rod Mill Feed Lower Clay Zone @ 14.9% mc.

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0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180



Figure A1.10 - High Consolidation Shear Test Results 6299 - Rod Mill Feed Lower Clay Zone @ 14.9% mc.

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a

Flow Function

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30

ROM Average Grade Bauxite @ 18.2% mc

ROM High Grade Bauxite @ 21.1% mc

ROM Low Grade Bauxite @ 22.4% mc

Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus

Figure A2.1 - Wall Friction Test Results 6299 - ROM Bauxite on Bisalloy 360 Mill Scale

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30

Bisalloy 360 Mill Scale

Ceramic Tile

Tivar 88

Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus

Figure A2.2 - Wall Friction Test Results 6299 - Secondary Sizer Product

Average Grade Bauxite @ 12.9% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ceramic Tile

Tivar 88

Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus


High Grade Bauxite @ 15.0% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ceramic Tile

Tivar 88

Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus


Low Grade Bauxite @ 22.2% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30

Mild Steel Mill ScaleArcoplateCeramic TilePolycerDuaplate D60Tivar 88

Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus

Figure A2.5 - Wall Friction Test Results 6299 - Rod Mill Feed

Average Grade Bauxite @ 15.2% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus


High Grade Bauxite @ 16.1% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus


Low Grade Bauxite @ 19.9% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus

Figure A2.8 - Wall Friction Test Results 6299 - Rod Mill Feed Upper Clay Zone @ 11.9% mc

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30


Ang

le -

deg

rees

Normal Stress (kPa)

Wall Friction Angle

0

5

10

15

20

0 5 10 15 20 25 30

Shea

r St

ress

(kP

a)

Normal Stress (kPa)

Wall Yield Locus

Figure A2.9 - Wall Friction Test Results 6299 - Rod Mill Feed Lower Clay Zone @ 19.9% mc

0

5

10

15

20

25

30

35

40

0

100,000

200,000

300,000

400,000

500,000

600,000α- Mild Steel Mill Scaleα- Arcoplateα- CeramicTileα- Polycerα- Duaplateα- Tivar 88

0 0.5 1 1.5 2 2.5 3 3.5 4

Q- Mild Steel Mill ScaleQ- ArcoplateQ- CeramicTileQ- PolycerQ- DuaplateQ- Tivar 88

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr

Outlet Diameter (B) - m

Half Hopper Angle & Flow Rate vs Outlet Diameterfor a Conical Hopper.

Hal

f H

oppe

r A

ngle

(α)

- D

eg

3 days time storage critical outlet dimension

Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

10,000

20,000

30,000

40,000

50,000

60,000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr/

m(l

engt

h)

Outlet Width (B)- m

Half Hopper Angle & Flow Rate vs Outlet Widthfor a Slotted Wedge Shaped Hopper.

Hal

f H

oppe

r A

ngle

( α)

- D

eg

Figure A3.1 - Mass Flow Hopper Design Parameters and Estimated Flow Rates 6299 - Rod Mill Feed Average Grade Bauxite @ 15.2% mc.


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

100,000

200,000

300,000

400,000

500,000

600,000α- Mild Steel Mill Scaleα- Arcoplateα- Ceramic Tileα- Polycerα- Duaplateα- Tivar 88

0 0.5 1 1.5 2 2.5 3 3.5 4

Q- Mild Steel Mill ScaleQ- ArcoplateQ- Ceramic TileQ- PolycerQ- DuaplateQ- Tivar 88

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr



Hal

f H

oppe

r A

ngle

(α)

- D

eg


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr/

m(l

engt

h)

Outlet Width (B)- m


Hal

f H

oppe

r A

ngle

( α)

- D

eg

Figure A3.2 - Mass Flow Hopper Design Parameters and Estimated Flow Rates 6299 - Rod Mill Feed High Grade Bauxite @ 16.1% mc.


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

50,000

100,000

150,000

200,000α- Mild Steel Mill Scaleα- Arcoplateα- CeramicTileα- Duaplateα- Tivar 88

0 0.5 1 1.5 2 2.5 3 3.5 4

Q- Mild Steel Mill ScaleQ- ArcoplateQ- CeramicTileQ- DuaplateQ- Tivar 88

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr



Hal

f H

oppe

r A

ngle

(α)

- D

eg

Inst

anta

neou

s cr

itica

l o

utle

t di

men

sion

s

0

5

10

15

20

25

30

35

40

0

10,000

20,000

30,000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr/

m(l

engt

h)

Outlet Width (B)- m


Hal

f H

oppe

r A

ngle

( α)

- D

eg

Figure A3.3 - Mass Flow Hopper Design Parameters and Estimated Flow Rates 6299 - Rod Mill Feed Low Grade Bauxite @ 19.9% mc.

Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

100,000

200,000

300,000

400,000α- Mild Steel Mill Scaleα- Arcoplateα- Ceramic Tileα- Duaplateα- Tivar 88

0 0.5 1 1.5 2 2.5 3 3.5 4

Q- Mild Steel Mill ScaleQ- ArcoplateQ- Ceramic TileQ- DuaplateQ- Tivar 88

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr



Hal

f H

oppe

r A

ngle

(α)

- D

eg


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

10,000

20,000

30,000

40,000

50,000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr/

m(l

engt

h)

Outlet Width (B)- m


Hal

f H

oppe

r A

ngle

( α)

- D

eg

Figure A3.4 - Mass Flow Hopper Design Parameters and Estimated Flow Rates 6299 - Rod Mill Feed Upper Clay Zone @ 11.9% mc.


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

50,000

100,000

150,000

200,000

250,000

300,000α- Mild Steel Mill Scaleα- Arcoplateα- CeramicTileα- Duaplateα- Tivar 88

0 0.5 1 1.5 2 2.5 3 3.5 4

Q- Mild Steel Mill ScaleQ- ArcoplateQ- CeramicTileQ- DuaplateQ- Tivar 88

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr



Hal

f H

oppe

r A

ngle

(α)

- D

eg


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

20

25

30

35

40

0

10,000

20,000

30,000

40,000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Pote

ntia

l Dis

char

ge R

ate

(Q)

- T

/hr/

m(l

engt

h)

Outlet Width (B)- m


Hal

f H

oppe

r A

ngle

( α)

- D

eg

Figure A3.5 - Mass Flow Hopper Design Parameters and Estimated Flow Rates 6299 - Rod Mill Feed Lower Clay Zone @ 14.9% mc.


Inst

anta

neou

s cr

itica

l ou

tlet

dim

ensi

on

0

5

10

15

0 5 10 15


Figure A4.1 - Critical Piping Diameter 6299 - Rod Mill Feed Average Grade Bauxite @ 15.2% mc.

Dia

met

er -

Met

res

Effective Head - Metres

Critical Piping Diameter

0

5

10

15

0 5 10 15


Figure A4.2 - Critical Piping Diameter 6299 - Rod Mill Feed High Grade Bauxite @ 16.1% mc.

Dia

met

er -

Met

res



0

5

10

15

0 5 10 15


Figure A4.3 - Critical Piping Diameter 6299 - Rod Mill Feed Low Grade Bauxite @ 19.9% mc.

Dia

met

er -

Met

res



0

5

10

15

0 5 10 15


Figure A4.4 - Critical Piping Diameter 6299 - Rod Mill Feed Upper Clay Zone @ 11.9% mc.

Dia

met

er -

Met

res



0

5

10

15

0 5 10 15


Figure A4.5 - Critical Piping Diameter 6299 - Rod Mill Feed Lower Clay Zone @ 14.9% mc.

Dia

met

er -

Met

res



0

20

40

60

80

100

0.01 0.1 1 10 100

ROM AB

SSP AB (-80mm)

T1 CAB

T2 CAB

T1 OAB

T2 OAB

SSP AB (-25mm)

AGB RSP

Perc

ent F

iner

Sieve Opening Size - mmFigure A5.1 - Particle Size Distribution 6299 - Average Grade Bauxite

Particle Size Distribution

0

20

40

60

80

100

0.01 0.1 1 10 100

ROM HB

SSP HB

T1 CHB

T2 CHB

T1 OHB

T2 OHB

Perc

ent F

iner

Sieve Opening Size - mmFigure A5.2 - Particle Size Distribution

6299 - High Grade Bauxite


DRAFT ONLY

0

20

40

60

80

100

0.01 0.1 1 10 100

ROM LB

SSP LB

T1 LB

T2 LB

Perc

ent F

iner


6299 - Low Grade Bauxite


0

20

40

60

80

100

0.01 0.1 1 10 100

Upper Clay Zone Drum 1 - 45



Lower Clay Zone Drum 43 - 45

Lower Clay Zone Drum 44 - 45

Lower Clay Zone Drum 45- 45

Perc

ent F

iner


6299 - Rod Mill Feed Clay Zones


0

20

40

60

80

100

0.01 0.1 1 10 100

ROM AB

ROM HB

ROM LB

Perc

ent F

iner

Sieve Opening Size - mm Figure A5.5 - Particle Size Distribution

6299 - ROM Bauxite


0

20

40

60

80

100

0.01 0.1 1 10 100

SSP AB

SSP HB

SSP LB

Perc

ent F

iner


6299 - Secondary Sizer Product Bauxite


0

20

40

60

80

100

0.01 0.1 1 10 100

T2 CAB

T2 CHB

T2 LB

Upper Clay Zone Drum3 - 45

Lower Clay Zone Drum44 - 45

Perc

ent F

iner


6299 - Rod Mill Feed Bauxite


0

5

10

15

20

0 5 10 15 20 25 30 35 40

ROM Average Grade Bauxite @ 13.0% mcROM Average Grade Bauxite @ 15.6% mcROM Average Grade Bauxite @ 18.2% mcROM Average Grade Bauxite @ 20.8% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

ROM High Grade Bauxite @ 13.2% mcROM High Grade Bauxite @ 15.8% mcROM High Grade Bauxite @ 18.5% mcROM High Grade Bauxite @ 21.1% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

ROM Low Grade Bauxite @ 14.0% mcROM Low Grade Bauxite @ 16.8% mcROM Low Grade Bauxite @ 119.6% mcROM Low Grade Bauxite @ 22.4% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a

Major Consolidation Stress - kPa Figure A6.1 - Flow Function Comparison Results

6299 - ROM Bauxite

0

5

10

15

20

0 5 10 15 20 25 30 35 40

SSP Average Grade Bauxite @ 12.9% mc

SSP Average Grade Bauxite @ 15.5% mc

SSP Average Grade Bauxite @ 18.1% mcU

ncon

fine

d Y

ield

Str

engt

h -

kPa


0

5

10

15

20

0 5 10 15 20 25 30 35 40

SSP High Grade Bauxite @ 12.5% mcSSP High Grade Bauxite @ 15.0% mcSSP High Grade Bauxite @ 17.5% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

SSP Low Grade Bauxite @ 13.3% mc




Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


6299 - Secondary Sizer Product

0

5

10

15

20

0 5 10 15 20 25 30 35 40

RMF Average Grade Bauxite @ 10.8% mcRMF Average Grade Bauxite @ 13.0% mcRMF Average Grade Bauxite @ 15.2% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

RMF High Grade Bauxite @ 11.5% mcRMF High Grade Bauxite @ 13.8% mcRMF High Grade Bauxite @ 16.1% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

RMF Low Grade Bauxite @ 12.6% mcRMF Low Grade Bauxite @ 14.9% mcRMF Low Grade Bauxite @ 17.4% mcRMF Low Grade Bauxite @ 19.9% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


6299 - Rod Mill Feed Bauxite

0

5

10

15

20

0 5 10 15 20 25 30 35 40

UCZD1-45 @ 9.4% mcUCZD1-45 @ 11.8% mcUCZD1-45 @ 14.2% mcUCZD1-45 @ 16.6% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

UCZD2-45 @ 9.3% mcUCZD2-45 @ 11.6% mcUCZD2-45 @ 13.9% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40

UCZD3-45 @ 7.9% mcUCZD3-45 @ 9.9% mcUCZD3-45 @ 11.9% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


6299 - Rod Mill Feed Upper Clay Zone

0

5

10

15

20

0 5 10 15 20 25 30 35 40

LCZD43-45 @ 10.2% mcLCZD43-45 @ 11.6% mcLCZD43-45 @ 13.9% mcLCZD43-45 @ 16.2% mc

Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40


Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


0

5

10

15

20

0 5 10 15 20 25 30 35 40


Unc

onfi

ned

Yie

ld S

tren

gth

- kP

a


6299 - Rod Mill Feed Lower Clay Zone

1

10

100

1000

4 5 6 7 8 9 10 11 12 13 14

Rod Mill Feed Average Grade Bauxite; DEM = 8.9%

Rod Mill Feed High Grade Bauxite; DEM = 9.6%

Rod Mill Feed Low Grade Bauxite; DEM = 11.0%

Rod Mill Feed Lower Clay Zone; DEM = 10.4%

Rod Mill Feed Upper Clay Zone; DEM = 6.9%

Moisture Content (%)

Figure A7.1 - Dust/Moisture Relationship Test 6299 - Rod Mill Feed

Dus

t Num

ber

Figure A8.1 – ROM AB Angle of Repose

Figure A8.2 – ROM HB Angle of Repose

Figure A8.3 – ROM LB Angle of Repose

Figure A8.4 – SSP AB Angle of Repose

Figure A8.5 – SSP HB Angle of Repose

Figure A8.6 – SSP LB Angle of Repose

Figure A8.7 – T2 CAB Angle of Repose

Figure A8.8 – T2 CHB Angle of Repose

Figure A8.9 – T2 LB Angle of Repose

Figure A8.10 – UCZ D1-45 Angle of Repose

APPENDIX B

Modes of Flow

TBS Flow Property Report, Appendix B Modes of Flow B2

__________________________________________________________________________________________

B. MODES OF FLOW

B.1 Flow Patterns

There are two basic modes of flow during gravity discharge from storage bins, mass-flow andfunnel-flow. In mass-flow the bulk solid is in motion at every point of the bin whenever materialis drawn from the outlet, Figure B1(a). This flow pattern is obtained when the walls of thehopper are sufficiently steep and smooth with no abrupt transitions or inflowing valleys and thefeeder or gate allows discharge over the entire outlet area. This flow pattern has the followingcharacteristics:

• First-in first-out flow sequence, useful for storage of solids which deteriorate withtime

• Where materials segregate on charging there is remixing in the hopper• Flow is uniform and well controlled giving a constant feed density which is

independent of the head of solids• There are no dead regions within the bin

Mass-flow is reliable and predictable and should be used where continuous feed of solids isrequired. Mass-flow bins may also be applied to the blending and mixing of bulk solids. Adisadvantage of mass-flow is wear of bin and hopper walls when handling abrasive bulkmaterials.

(a) Mass-Flow (b) Funnel-Flow

Figure B1: Flow Patterns in Bins

As illustrated in Figure B1(b) funnel-flow occurs when the bulk solid sloughs off the topsurface and discharges through a vertical channel which forms within the stored bulk solid abovethe outlet. This mode of flow occurs when the hopper walls are rough and/or insufficientlysteep. This flow pattern has the following characteristics:


__________________________________________________________________________________________

• First-in last-out flow sequence• Where materials segregate on charging there is no remixing in the hopper• Flow rate tends to be erratic with widely varying feed density• Erratic flow rates cause fine powders to aerate, fluidise and flood• Tendency for stable pipes or 'ratholes' to form resulting in reduced live capacity

Funnel-flow is generally an undesirable flow pattern, mainly due to loss in live capacity but hasthe compensating advantage of minimising bin wall wear for some applications.

It needs to be noted that there is a further mode of flow, other than strictly mass-flow, whichoften occurs when the surcharge head of material above the hopper is low. This mode of flow iscalled intermediate-flow and is characterised by the bulk material flowing more quickly in acentral flow channel and more slowly against the hopper walls.

Figure B3: Hopper Types for Conical and Plane Mass-Flow


__________________________________________________________________________________________

B.2 Mass Flow Hopper Types

Mass flow hoppers can be classified according to the geometry of the stress field which is set upin the flow channel as material discharges. Essentially, the stress field can be either symmetricabout a central axis, or symmetric about a central plane. The axi-symmetric case applies tohoppers which have conical or square outlets, and hoppers of this axi-symmetric nature areclassified as conical hoppers.

Transition hoppers use a slotted outlet with a combination of side walls inclined as appropriatefor plane flow, and end walls inclined at angles derived for the conical case. Figure A3 illustratessome of the principal mass-flow hopper types.

The planar case applies to slotted outlets, where the slot length to width ratio exceeds 3:1. Theend walls of such a hopper are often vertical, and hoppers of this nature are classified as planeflow hoppers.

When large quantities of bulk solids are to be stored, the expanded-flow bin shown in Figure A4can be used. This bin combines the storage capacity of the funnel-flow bin, which forms theupper section, with the reliable discharge characteristics of the mass-flow hopper. For bulkmaterials with large rathole dimensions Df (often several metres) the expanded-flow concept,which incorporates Df as the transition dimension, allows for 100% live capacity with reduced

head height. Expanded-flow bins also have the advantage of minimising bin wall wear. Inaddition, expanded flow may be readily applied to multi-outlet bins.

Figure B4: Expanded-Flow Bin

APPENDIX C

Storage Plant Design

TBS Flow Property Report, Appendix C Storage Plant Design C2

__________________________________________________________________________________________

C. STORAGE PLANT DESIGN

The following notes are offered as background information in the design methodology of bulkmaterials storage plant design. The subject is discussed in greater detail in [1, 2].

C.1 Critical Hopper Dimensions for Mass-Flow

The critical hopper parameters for mass-flow are the minimum or critical cohesive archdimension, Bmin, and the corresponding hopper half-angle, α, for flow to occur. Referring toFigure C1, the bulk strength, given by the unconfined yield strength, σc, is defined by the FlowFunction, FF, which is a plot of σc as a function of the major consolidation pressure, σ1. The

hopper half-angle is chosen from the mass-flow limits [1, 2]. The stress acting in the arch, -σ1 , is

defined by the Flow Factor, ff [2].

σ

σ

σ

σ

FlowNo Flow

FFff

1

c

c1=

σ corresponding to opening dimension B

1

ρ g ∆V

α

B

∆V

σ σ1 1

min(a) Flow - No Flow Condition

(b) Critical Arching Dimension

σ1

Figure C1: Critical Arching Condition for Flow

The critical arching dimension is determined for the condition when the stress in the arch is just

equal to the bulk strength, i.e. -σ1 = σc. This is obtained from the intersection point of the Flow

Factor, ff, line and Flow Function, FF. The Flow Function is a bulk solid parameter and theFlow Factor is a flow channel parameter.

The minimum opening dimension, Bmin , is given by

Bmin = -σ1 H(α)

ρ g (C.1)

where: H(α) = arch thickness factor given in [2]ρ = bulk density

g = gravitational acceleration

C.1.1 Variation of Hopper Half Angle and Flow Rate with Hopper Opening Dimension


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To generate the required discharge flow rate, a larger opening dimension than that determined byequation (C.1) is required. Since the consolidating pressures within a stored bulk solid in theregion of the outlet increase with an increase in outlet dimension, this is usually accompanied bya reduction in wall friction angle, φw; as illustrated by the graphs shown in Appendix A, Figures

A3. Thus, an increase in hopper half-angle is possible when a larger opening dimension isselected.

Referring to Figure C2, the critical Flow Factor, ff, corresponds to the minimum openingdimension, Bmin. The actual Flow Factor, ffa, defines the stress condition in the arch

corresponding to the actual opening dimension, B. For this stress condition, the stress in the

arch, -σ1 , exceeds the unconfined yield strength, σc, and accelerated flow will occur. For a coarse

bulk solid the stress in the arch is given by

-σ1 = ρ g BH(α) ( 1 -

ag ) (C.2)

Figure C2: Flow in a Hopper

It may be shown that the acceleration, a, in equation (C.2) becomes

a = g [ 1 - ffffa

] (C.3)

where: ffa = σ1σc for σc < -σ1 (C.4)


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σ1 = major consolidation pressure at outlet corresponding to

outlet dimension B

The acceleration, a, has two components:

a = ac + av (C.5)

where: ac = convergence component due to the flow channelav = component due to the velocity increase as flow is initiated

It may be shown that

av = g

1 - ffffa

- 2 v2 (m + 1)

B tanα (C.6)

This shows that as the discharge velocity increases, av → 0. Thus, an average terminal dischargevelocity va is reached. With av = 0

vav =

1 - ffffa

g B

2 tanα (m + 1) (C.7)

and the flow rate is

Q = ρ B(1+m) L(1-m)

π

4 m

vav (C.8)

where: m = 0 for a plane-flow hopperm = 1 for an axi-symmetric or conical hopperB = width of slot or diameter of circular openingL = length of slot

The flow rate given by equation (C.8) is the maximum possible for unrestricted discharge. In themajority of cases the discharge rate needs to be controlled and this is accomplished by means ofa feeder.

C.2 Funnel-Flow

Funnel-flow is depicted in Figure C3. In this case flow occurs by material sloughing off the topsurface and flowing down a central flow channel which forms above the opening. Flow isgenerally erratic and gives rise to segregation problems. In the case of cohesive bulk solids, flowwill continue until the level of the bulk solid in the bin drops an amount HD equal to the draw-

down. At this level, the bulk strength of the contained material is sufficient to sustain a stablerathole of diameter Df = Bf as illustrated in Figure C3. Bf will be slightly larger than the hopperopening, B. Once the level defined by HD is reached, there is no further flow and the material


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below this level represents 'dead' storage. For complete draw-down, Bf should be equal to Dfm,

which is the rathole diameter calculated for the base of the bin.

H

h

B

h

h

B

ff

f

D

Effective Head of Solids

EffectiveDraw-Down

D

'Dead'Capacity

B

fmRathole Diameter

f

D

D

Figure C3: Funnel-Flow

For a funnel-flow bin, the effective head of solids, hf, is defined as

hf = R

Kj tan φw ( 1 - e- Kj tan φw h/R ) (C.9)

where: R =area of bin cross-section

perimeter of bin cross-section Κj = ratio of horizontal to vertical pressure in the bin. Assumed

to be 0.4.φw = wall friction angle in degrees

h = actual head of solids

However, when the width of the storage bin is greater than or equal to the maximum height ofthe stored material then equation (C.9) can be simplified to :-

hf = h (C.10)

That is, the effective head, hf, is equal to the 'hydrostatic' head, h.

hf defines the major consolidation pressure, σ1, as follows

σ1 = ρ g hf (C.11)


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For the given value of σ1, the corresponding value of the stress -σ 1 = σc acting at the rathole is

obtained from the extended Flow Function in accordance with Figure C4.

Extended FF

σ

σ

σ σ

σ1

11

c

c

=

Figure B4: Extended Flow Function

The critical rathole dimension, Df, is determined from the following equation

Df = -σ1 G(φt)

ρ g (C.12)

where: φt = static angle of internal friction

ρ = bulk density

g = gravitational acceleration

The function G(φt) is given in graphical form in [2].

It should be noted that the critical rathole dimension calculations are based on the bulk strengthof the fines only. Should the bulk material tested have a significant proportion of lumps, thenthis will tend to weaken the rathole structure, particularly if segregation causes areas of lumpconcentration.

C.3 Expanded-Flow Bin Geometry

In view of the large rathole dimensions Df (often several metres) in funnel-flow, the expanded-flow type bin of Figure C5, which incorporates Df as the transition dimension, allows for 100%

live capacity with reduced head height. The effective design of an expanded-flow bin requires thetransition dimensions to be greater than the critical piping diameter, Df, to ensure that stable

ratholes cannot develop.


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D

D

H Funnel Flow

MassFlow

f

B

α

Figure B5: Expanded-Flow

C.4 Chute Design

In many materials handling installations blocked chutes can be a significant cause of interruptionto production. In chutes where bed depths are low, the normal pressures are also low. Graphsshown in Appendix A, Figures A3 show how the wall friction angles can be higher at these lowconsolidation pressures. The wall friction angle, φw, is given by:

φw = tan-1 τwσw (C.13)

where τw is the shear stress, measured from the wall yield locus, at a normal consolidationpressure, σw.

Equation (C.13) allows for an estimation of the required chute inclination angle for transferchute design. The preferred angle of inclination of chutes can be determined by adding between5˚ and 10˚ to the calculated wall friction angle at the consolidation pressure determined from thenominal chute bed depth.

C.5 Gravity Reclaim Stockpiles

Gravity reclaim stockpiles, such as that illustrated in Figure C6, operate on the expanded flowprinciple. It is essential that they be fitted with mass-flow hoppers which are correctly interfacedwith the feeders. The mass-flow hoppers guarantee reliable flow as well as ensuring that theloads on the feeders and corresponding drive torques remain within acceptable limits. This is


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made possible as a result of the 'arched stress field' that is established in the hoppers once flowhas occurred. Details of stockpile and feeder design are given in [2].

C.5.1 Draw-Down Characteristics

For a given hopper geometry, the ‘rathole’ diameter Df is based on the diagonal dimension, Dg,

of the hopper at the transition with the base of the stockpile. That is

Dg = Lh2 + D2 (C.14)

H

h

D

D

fθR

H

X X

T

Z Z

ε

D

L

Dg

h

Figure C6: Gravity Reclaim Stockpile (Example)


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The rathole will open out at some slope angle, ε, which may be in the order of 5o, but will depend

on the size distribution of the bulk material. Alternatively, it may be assumed that the ratholediameter, Df, is such that

Df = Kf Dg (C.15)

Kf is a rathole geometry factor to allow for the opening up of the rathole due to the variation in

particle size range of the stored bulk solid.

1.0 < Kf < 1.2 (C.16)

The draw-down is computed as follows. The stress acting at the surface of the rathole is

σ− 1 = γ DfG(φt) (C.17)

where: φt = static angle of internal friction. G(φt) = rathole factor [1]γ = ρ g

= bulk specific weightρ = bulk density

At the rathole surface, the unconfined yield strength σc = σ− 1. For this condition, thecorresponding major consolidation stress, or pressure, σ1 is read from the Flow Function curve

as illustrated in Figure C7.

Extended FF

σσ

σσ

11

cc

=

Figure C7: Use of Extended Flow Function to Obtain 1

σ1 is given by σ1 = γ hf (C.18)

where: hf = effective head of solids

The effective head of solids will vary according to the conditions as follows:


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(i) Upper Bound Value

This is the 'hydrostatic' head which might occur in a loosely packed stockpile

hf = hD (C.19)

where: hD = draw-down

(ii) Likely Value

A less conservative value of hf is

hf = hD cos θR (C.20)

where: θ R = angle of repose

(iii) Lower Bound Value

Where a flow channel is pre-formed, then hf may be estimated using equation (C.9) with the

'hydraulic radius' R = Df4 .

C.5.2 Live Capacity

The live capacity of a gravity reclaim stockpile may be optimised by strategically placing themass-flow reclaim hoppers and feeders to maximise the intersection of the flow channels. ACAD geometrical modelling package is used for this purpose as illustrated by the exampleshown in Figure C8.

Figure C8: Example of Three-Dimensional Stockpile Model

24941-100-30R-G01-00073 Tunra 6299 Report Final[1]

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