Addressing Plugging Wear Spillage Transferchutes

Bulk Solids: Science / Engineering / Design!

JENIKE & JOHANSON

!

Addressing Plugging, Wear and Spillage at Transfer Chutes!

Thomas G. Troxel, Vice PresidentJayant Khambekar, Project Engineer!

Jenike & Johanson!


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What is a Chute?!


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•  Constant or changing cross-sectional area!

•  Operates full or partially full!•  Full chute with changing cross-section

is a hopper!

What is a Chute?!


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Chute Flow Problems!

•  Plugging!•  Wear of chute surface!•  Spillage!•  Dustiness!•  Excessive belt wear!


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Example Chute Flow Problems!

Spillage!Buildup!


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Dusting! Abrasive wear!

Example Chute Flow Problems!


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<---- Before!

After ---->!

Example Chute Flow Problems!Dusting!


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Prevent Plugging!

•  Prevent plugging at impact points!


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•  Calculate V2 / V1!

Prevent Plugging!


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V2 != Velocity along chute!! after impact!

V1 != Impact velocity!θ != Impact angle!φʼ = Wall friction angle

Chute Velocity Calculations!

θ

V1!

V2!!

V2V1

= cos" # sin" tan $ %


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Prevent Plugging!

•  If V2 near zero or negative, calculate impact pressure, run chute test!



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γ != Bulk density!V1 != Impact velocity!θ != Impact angle!PI != !Impact pressure!g != Acceleration due to !

! gravity, 32 ft/sec2

Calculate Impact Pressure!

θ V1!

PI!

!

Impact Pressure ="V1

2 sin2#g


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Normal Pressure (σn) = W / A!(apply & remove)!

Chute Test!

Sample of wall material

Bulk solid!

Cover

Ring

Tester platform!


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Example of Chute Impact Test!

Critical!Chute!Angle!(deg)!

Impact Pressure (psf)!

0!75!25! 50!

20!

80!

60!

40!

0! 100!


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Prevent Plugging!

•  Consider gradual change in direction (e.g., two-half angles)!

•  If V2 near zero or negative, calculate impact pressure, run chute test!



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!

φ' (deg) 10! 20! 30! 40! 50!0!

1!

2!

3!

4!

5!

θ 2 V1!

VΙ Ι!VΙ!θ

2

VΙ Ι!

V2!

Velocity of a Particle after Impacting Two Half !Angles as a Ratio of Velocity after One Impact!

θ = 70°"

θ = 60°"

θ = 50°"

θ = 40°"

θ = 30°"

θ = 20°"

θ = 80°!

θ

V1!

V2!


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Chute Design Principles!

•  Prevent plugging at impact points!•  Sufficient cross-sectional area!


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Sufficient Cross-Sectional Area!

•  Calculate acceleration, velocity to determine capacity!

•  Don't decrease chute cross-sectional area!

•  Keep chute no more than 1/3 full!


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Sufficient Chute Area!

Q = VA!

Where:!Q=Volumetric flow rate (ft3/sec)!

V=Velocity (ft/sec)!

A=Area of material stream (ft2)!


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V  = Velocity at distance S!V0 != Initial velocity!a != Acceleration!

!= g cos α (tan α - tan φ ')!α != Chute angle (from horiz.)!φ' != Wall friction angle!

Chute Velocity Calculation!

2aSVV 20 +=

V0 V

α

S


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•  Prevent plugging at impact points!•  Sufficient cross-sectional area!•  Control the stream of particles!


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Control the Stream!

•  Use sloped chute, not vertical!•  Gain and maintain control!•  Use curved, not flat, chutes!•  Use rubber curtains, chains or ribs!•  Discharge should have velocity in

direction of belt, be centered, and be at slightly higher speed!


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Load not!centered!on belt!

Trajectory!in chute!

Incoming stream!with horizontal!

velocity component!

Sloped chute!with circular!cross section!

Trajectory on ImproperlyDesigned Chute!


JENIKE & JOHANSON Control the Stream!

Chains used to reduce rock bouncing


JENIKE & JOHANSON Hood and Spoon Design!

Sticky fines on impact plate leading to frequent plugging

Proper stream capture with hood

Proper stream control with spoon


JENIKE & JOHANSON Hood and Spoon Design!

Proper belt loading with spoon

Proper stream capture with hood


JENIKE & JOHANSON Controlling the Stream!

Solution to belt-to-belt transfer with space constraints


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DEM for Chutes!

•  Generalized mathematical solution!•  Physical properties!

– Coefficient of friction!– Particle density!

•  Boundary conditions!–  Initial velocity!– Chute geometry!


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DEM Analysis!

Chute for iron ore


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DEM Analysis!


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DEM Analysis!


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•  Prevent plugging at impact points!•  Sufficient cross-sectional area!•  Control the stream of particles!•  Minimize wear of chute surface!


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Minimize Abrasive Wear!

•  Limit free fall height!•  Avoid abrupt changes in direction!•  Use rock boxes only if free flowing!•  Use ribs as alternative!•  If material is sticky, chute surface

should follow natural trajectory!


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Rock Box Configurations!


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Rock box with sticky bauxite leads to frequent head box plugging

Heavy residual left in head box


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Rock Box with Ribs!


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•  Prevent plugging at impact points!•  Sufficient cross-sectional area!•  Control the stream of particles!•  Minimize wear of chute surface!•  Control dust generation!


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Control Dust Generation!

•  Keep material in contact with surface!•  Concentrate the material stream!•  Keep impact angles small!•  Keep velocity constant!•  Exit in direction of belt, at slightly higher

speed!

Severe dusting with uncontrolled stream


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–  Material not in contact with chute surface

–  Stream not concentrated –  Velocity not constant

–  Well captured and guided stream


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Chute Cross-Section to Concentrate Stream!


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Avoid Dust Pump Effect!

Air

Solids Solids

Air moving down with bouncing solids creates dust pump effect

Solids in control on sloping chute surface prevents excess air entrainment


JENIKE & JOHANSON Dust Pump Effect!

•  Problem!–  Excessive dusting during

unloading!•  Possible solutions!

–  Curved chute, rounded cross-section!

–  Dust suppressant!–  Telescoping chute!


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Conclusions!

•  Chute problems are preventable!– Plugging, spillage, wear, dusting!

•  Effective chute design principles!– Maintain velocity through impact!– Gain and control stream flow!– Keep impact angles small (< 30º)!– Use sloped, curved chutes!– Keep chute no more than 1/3 full!– Avoid rock boxes, unless mat. free-flowing!

Addressing Plugging Wear Spillage Transferchutes

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