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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!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
• Constant or changing cross-sectional area!
• Operates full or partially full!• Full chute with changing cross-section
is a hopper!
What is a Chute?!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Flow Problems!
• Plugging!• Wear of chute surface!• Spillage!• Dustiness!• Excessive belt wear!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Example Chute Flow Problems!
Spillage!Buildup!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Dusting! Abrasive wear!
Example Chute Flow Problems!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
<---- Before!
After ---->!
Example Chute Flow Problems!Dusting!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Prevent Plugging!
• Prevent plugging at impact points!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
• Calculate V2 / V1!
Prevent Plugging!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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 $ %
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Prevent Plugging!
• If V2 near zero or negative, calculate impact pressure, run chute test!
• Calculate V2 / V1!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Normal Pressure (σn) = W / A!(apply & remove)!
Chute Test!
Sample of wall material
Bulk solid!
Cover
Ring
Tester platform!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Example of Chute Impact Test!
Critical!Chute!Angle!(deg)!
Impact Pressure (psf)!
0!75!25! 50!
20!
80!
60!
40!
0! 100!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Prevent Plugging!
• Consider gradual change in direction (e.g., two-half angles)!
• If V2 near zero or negative, calculate impact pressure, run chute test!
• Calculate V2 / V1!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
!
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!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Design Principles!
• Prevent plugging at impact points!• Sufficient cross-sectional area!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Sufficient Chute Area!
Q = VA!
Where:!Q=Volumetric flow rate (ft3/sec)!
V=Velocity (ft/sec)!
A=Area of material stream (ft2)!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Design Principles!
• Prevent plugging at impact points!• Sufficient cross-sectional area!• Control the stream of particles!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Load not!centered!on belt!
Trajectory!in chute!
Incoming stream!with horizontal!
velocity component!
Sloped chute!with circular!cross section!
Trajectory on ImproperlyDesigned Chute!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Control the Stream!
Chains used to reduce rock bouncing
Bulk Solids: Science / Engineering / Design!
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
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Hood and Spoon Design!
Proper belt loading with spoon
Proper stream capture with hood
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Controlling the Stream!
Solution to belt-to-belt transfer with space constraints
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
DEM for Chutes!
• Generalized mathematical solution!• Physical properties!
– Coefficient of friction!– Particle density!
• Boundary conditions!– Initial velocity!– Chute geometry!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Design Principles!
• Prevent plugging at impact points!• Sufficient cross-sectional area!• Control the stream of particles!• Minimize wear of chute surface!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Rock Box Configurations!
Rock box with sticky bauxite leads to frequent head box plugging
Heavy residual left in head box
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Design Principles!
• Prevent plugging at impact points!• Sufficient cross-sectional area!• Control the stream of particles!• Minimize wear of chute surface!• Control dust generation!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Control Dust Generation!
– Material not in contact with chute surface
– Stream not concentrated – Velocity not constant
– Well captured and guided stream
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
Chute Cross-Section to Concentrate Stream!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON Dust Pump Effect!
• Problem!– Excessive dusting during
unloading!• Possible solutions!
– Curved chute, rounded cross-section!
– Dust suppressant!– Telescoping chute!
Bulk Solids: Science / Engineering / Design!
JENIKE & JOHANSON
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!