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Bulk Solids: Science / Engineering / Design!
Ways to Minimise Particle Attrition
Carrie Hartford
Senior Engineer
08 9277 3303
Perth WA
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 2
Outline
� Discuss causes and effects of particle attrition with granular products
� Evaluate where most of the dust is generated � Characterize material’s attrition behavior through
various attrition tests � Engineer solutions to reduce dust generation
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 3
What is attrition?
“Rubbing away or wearing down by friction”
“Gradual diminution in number or strength because of constant stress”
Example – bisphenol
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 4
Other terms
Degradation - Decline to a lower condition, quality or level. Usually associated with changes in chemical or physical condition
Friability - tendency to readily crumble; brittle
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 5
Attrition is a concern in virtually every industry
� Chemicals, plastics � Foods � Pharmaceuticals � Power generation � Metals � Detergents
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 6
Effects of particle attrition
� Increased dust levels – safety hazard
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 7
Effects of particle attrition
� Increased dust levels – safety hazard � 281 combustible dust fires and explosions in industry
between 1980 and 2005 causing 119 fatalities and 718 injuries in the USA alone
� Investigation performed after 3 catastrophic dust explosions killed 14 workers in 2003.
� Secondary dust explosions, due to inadequate housekeeping and excessive dust accumulations, caused much of the damage and casualties in recent catastrophic incidents.
“Investigation Report – Combustible Dust Hazard Study”, US Chemical Safety and Hazard Investigation Board. November 2006
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 8
Effects of particle attrition
� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing)
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 9
Effects of particle attrition
� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 10
Effects of particle attrition
� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking � Off-spec product – too fine or too lumpy
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 11
Effects of particle attrition
� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking � Off-spec product – too fine or too lumpy � Increased segregation
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 12
Factors that affect particle attrition � Particle hardness � Particle shape and size � Energy of particle impact � Surface impact � Particle bed impact � Compression � Shear
� Surface hardness and roughness
� Particle chemistry � Propensity to melt
or smear !
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 13
System review Attrition mechanisms � Impact
� Particles shatter � Occurs when material stream is redirected � Examples
� Drop onto pile
� Drop into bin
� Belt-to-belt transfer chute
� Bends/diverters in pneumatic conveying line
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 14
System review Attrition mechanisms � Compression
� Failure along weak planes � Examples
� Bin/silo
� Railcar
� Pinch point in feeders
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 15
System review Attrition mechanisms � Shear
� Edges of particles chipped off or worn away � Examples
� Interparticle motion
� Sliding along bin wall
� Cyclone travel
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 16
System review Attrition mechanisms � Compression and shear
� Examples � Converging flow channel
� Mechanical feeder (especially screw feeders)
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 17
Attrition tests
� Impact � Hopper flow � Compression � Pneumatic conveying
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 18
Attrition tests - impact
� Used to evaluate particle attrition during filling of silos, hoppers, and chutes
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 19
Attrition tests
� Impact � Hopper flow
� Evaluate particle attrition due to funnel or mass flow in a hopper
Flowing!
Stagnant!
Funnel Flow!
Mass Flow!
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 20
Attrition tests – hopper flow - rotational shear
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 21
Attrition and shear strain
+16 +20 +30 +35 +40 +50 +70 +100 Pan
-4
-3
-2
-1
0
1
2
3
4
Change in percentage after test
Mesh sizes
Chan
ge
in p
erce
nta
ge
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 22
Attrition tests
� Impact � Hopper flow � Compression
� Evaluate particle attrition due to loads acting on particle or bed
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 23
Attrition by Compression!
Principle Pressure, psf!
Perc
ent M
inus
2.5
mm
!
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 24
Attrition / friability tests - particle hardness
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 25
Attrition tests
� Impact � Hopper flow � Compression � Pneumatic conveying
� Measure particle size before and after conveying
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Engineered solutions
� Can you change the material? � Increase particle hardness � Decrease particle size � Make particles rounded vs. angular or flaky
� Can you change the handling equipment?
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 27
Engineered solutions
� Transfer chutes � Control the flow of material � Minimise drop heights
� Bins/hoppers and feeders � Evaluate the appropriate flow method to minimise
attrition
� Pneumatic conveying systems � Minimise conveying velocities � Streamline the layout to minimise bends � Consider dense phase vs. dilute phase conveying
� Dense phase is not suitable for all materials
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Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 28
Summary
� The effects of particle attrition can be costly � Increased dusting � Powder caking � Decreased product performance � Creation of safety hazards such as dust explosions
� Particle attrition can be minimised through proper engineering � Attrition tests � Change the material and/or
change the equipment
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Bulk Solids: Science / Engineering / Design!
Questions?
Carrie Hartford
Senior Engineer
08 9277 3303
Perth WA