THE WOLFSON CENTRETHE WOLFSON CENTREfor Bulk Solids Handling Technologyfor Bulk Solids Handling Technology

B66: Direct On-Line MeasurementB66: Direct On-Line Measurementof Wall Friction of Coal as anof Wall Friction of Coal as anIndicator ofIndicator of HandleabilityHandleability

J RJ R PillaiPillai

ObjectiveObjective

To develop an on-line measuring instrument to give aTo develop an on-line measuring instrument to give acontinuous readout of wall friction of coal, to assess itscontinuous readout of wall friction of coal, to assess its‘‘handleabilityhandleability’’

To Prove or disprove whether there is a:To Prove or disprove whether there is a:–– consistent link between changes in wall failure and internalconsistent link between changes in wall failure and internal

failure properties based on moisture content,failure properties based on moisture content,–– correlation between on-line and off-line wall frictioncorrelation between on-line and off-line wall friction

measurements.measurements.

Why?Why?

Variation in Flow properties

Blockages in bunkers & chutes

Unscheduled downtime

Process stoppages

TrainingTime Money

Off-linemeasurement

Wall friction tester - SetupWall friction tester - Setup

JenikeJenike type walltype wallfriction testerfriction tester

150

100 95

2518

‘Skid’ plate (SS 304‘Skid’ plate (SS 3042b) finish2b) finish

On-line test rigOn-line test rig

Continuous & rapidContinuous & rapidstatus monitoringstatus monitoring

No samplingNo samplingNo manual operationNo manual operationSimple and ruggedSimple and rugged

sensorssensorsCost effectiveCost effective

W(cg)

Pivot

Direct i on of mat eri al fl ow

Li nkageDead weight

Sl i der Pl at e

HV

d

Load cell

Schematic of linkage & skid plate assemblySchematic of linkage & skid plate assembly

Test conducted

Jenikewall friction

On-line Trials

CrushedGlass

CoalEC2101(RuM3)

Load0.42 kg,2.7 kg,4.7 kg

Speed0.01m/sec0.1 m/sec1 m/sec

CrushedGlass

CoalEC2101

CleanPlate

UncleanPlate

CleanPlate

UncleanPlate

From eachbatch

Angle of wall friction as a function of shearAngle of wall friction as a function of sheardisplacement on crushed glassdisplacement on crushed glass

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Distance [m]

Fri

ctio

na

ng

le[d

eg]

0.1m/sec

1 m/sec

0.01m/sec

Crushed Glass

Crushed glassCrushed glass

Starting with a clean plate the trend measuredStarting with a clean plate the trend measuredon crushed glass can be broken down into 3on crushed glass can be broken down into 3stagesstages

An initial lead-in region, where the measuredAn initial lead-in region, where the measuredangle of wall friction was approximately constantangle of wall friction was approximately constant(0 – 50m)(0 – 50m)

••A transient condition, where the measured wallA transient condition, where the measured wallfriction increases, at a rate dependent on speedfriction increases, at a rate dependent on speed

••A final steady state wall friction value, obtainedA final steady state wall friction value, obtainedafter relatively large shear displacementafter relatively large shear displacement(~150m)(~150m)

Unlike crushed glass, the initial lower stable value for coal is notUnlike crushed glass, the initial lower stable value for coal is notwell definedwell defined

Gradual increase towards a higher steady state value at allGradual increase towards a higher steady state value at allspeed.speed.

Influence of velocity is negligible unlike with crushed glass.Influence of velocity is negligible unlike with crushed glass. More consistent result compared to crushed glassMore consistent result compared to crushed glass

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Distance [m]

Fri

ctio

nan

gle

[deg

]

0.01m/seccoal

0.1m/seccoal

1 m/seccoal

Angle of wall friction as a function of shearAngle of wall friction as a function of sheardisplacement on coal (RuM3)displacement on coal (RuM3)

Comparison between failure loci obtained fromComparison between failure loci obtained fromon-line &on-line & JenikeJenike (“clean” & “unclean” Plate) for(“clean” & “unclean” Plate) for

crushed glasscrushed glass

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Normal Stress [kPa]

Sh

ear

Str

ess

[kP

a]

0.01 m/sec {Initialvalue}

~0.01 m/sec {Finalvalue}

0.1 m/sec {Initialvalue}

0.1 m/sec {Finalvalue}

Jenike (clean)

Jenike (unclean)

Final value

Initial value

“Unclean”

“clean”

Comparison between failure loci obtained fromComparison between failure loci obtained fromon-line &on-line & JenikeJenike (“Clean” & “Unclean” Plate) for(“Clean” & “Unclean” Plate) for

coal (RuM3)coal (RuM3)

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Normal force [kg]

Sh

ear

forc

e[k

g]

0.01 m/sec2% mois ture

0.01 m/sec(initialvalues )

unclean -2.4%mois ture

clean tes t3s t - 2.8%mois ture

Final values Initial values“unclean”

“clean”

–– TheThe JenikeJenike wall friction loci obtained from the “clean”wall friction loci obtained from the “clean”plate tests were similar & comparable to the lociplate tests were similar & comparable to the lociobtained from the initial stable values measured onobtained from the initial stable values measured onthe on-line wall friction testerthe on-line wall friction tester

–– TheThe JenikeJenike wall friction loci obtained from thewall friction loci obtained from the“unclean” plate tests showed significantly higher“unclean” plate tests showed significantly highershear force (than the clean plates) but lower valuesshear force (than the clean plates) but lower valuesthan the final stable value measured on the on-linethan the final stable value measured on the on-linewall friction testerwall friction tester

For both the crushed glass and the coal samples…For both the crushed glass and the coal samples…

Plausible causesPlausible causes

Effect of particle size and distribution in the on-line wallEffect of particle size and distribution in the on-line wallfriction testerfriction tester

In on-line tester ‘Skid’ plate is sheared over a large shearIn on-line tester ‘Skid’ plate is sheared over a large sheardisplacementdisplacement

Dynamic effect on the on-line wall friction tester withDynamic effect on the on-line wall friction tester withrespect to speed and load unlikerespect to speed and load unlike JenikeJenike type wall frictiontype wall frictiontestertester

By comparison in theBy comparison in the JenikeJenike wall friction testwall friction testthe powder sample used is very small andthe powder sample used is very small andmay not be representative samplemay not be representative sample

Effect of particle size onEffect of particle size on JenikeJenike type walltype wallfriction testerfriction tester

Results suggest that as the maximum particle sizereduces the wall friction increases

Angle of wall friction- Jenike - Coal EC2101 Particle size comparison

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5

Normal load (kPa)

An

gle

ofW

allf

rictio

n(d

eg)

<1mm - samp 1[5%]

<1mm - samp 2[4%]

2~1mm - samp 1[5%]

2~1mm - samp 2[5%]

3~2mm - samp 1[5.3%]

3~2mm - samp 2[5.3%]

<1mm - samp 3[4.5%]

<1mm - samp 4[4.5%]

<1mm - samp 5[4.4%]

Interim ConclusionsInterim Conclusions

There is a significant difference in the angle of wallThere is a significant difference in the angle of wallfriction of a “clean” and “unclean “ surfacefriction of a “clean” and “unclean “ surface

Surface wear on the “skid” plate does not have aSurface wear on the “skid” plate does not have asignificant effect on the wall friction measurementsignificant effect on the wall friction measurement

The rate at which the wall friction increases is bulk solidThe rate at which the wall friction increases is bulk soliddependent, the glass showing a gradual transitiondependent, the glass showing a gradual transitionwhereas the coal increases rapidlywhereas the coal increases rapidly

From the tests carried out both theFrom the tests carried out both the JenikeJenike and the onlineand the onlinetester shows the same trend, though there are sometester shows the same trend, though there are somevariation seen quantitativelyvariation seen quantitatively

JenikeJenike wall friction testerwall friction tester

–– Test varying the moisture content on coalTest varying the moisture content on coal

Test on Annular shear cell varying the moisture contentTest on Annular shear cell varying the moisture content

Existing Online TesterExisting Online Tester

–– Add moisture to coal to find if it can sense the differenceAdd moisture to coal to find if it can sense the difference–– Test by introducing Pre-consolidation plateTest by introducing Pre-consolidation plate

Development of a separate pilot scale rig with trough shape beltDevelopment of a separate pilot scale rig with trough shape belt Other option considered for comparisonOther option considered for comparison

–– HopperHopper flowabilityflowability testertester

Proposed workProposed work

Schematic of on-line test unitSchematic of on-line test unit

Winch for up & downmovement

Roller forhorizontalmovement

Linkage

Materialflow

Enclosure

Loadcell set-up

‘Skid’Plate

Conveyor belt

Frame

Thanks .…Any Questions??Thanks .…Any Questions??