carrie hartford - jenike & johanson pty ltd - ways to minimize particle attrition that can...

Bulk Solids: Science / Engineering / Design!

Ways to Minimise Particle Attrition

Carrie Hartford

Senior Engineer

[email protected]

08 9277 3303

Perth WA

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


What is attrition?

“Rubbing away or wearing down by friction”

“Gradual diminution in number or strength because of constant stress”

Example – bisphenol


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


Attrition is a concern in virtually every industry

� Chemicals, plastics � Foods � Pharmaceuticals � Power generation � Metals � Detergents


Effects of particle attrition

� Increased dust levels – safety hazard



� 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



� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing)



� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking



� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking � Off-spec product – too fine or too lumpy



� Increased dust levels – safety hazard � Flow stoppages (arching, ratholing) � Caking � Off-spec product – too fine or too lumpy � Increased segregation


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 !


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


System review Attrition mechanisms � Compression

� Failure along weak planes � Examples

�  Bin/silo

�  Railcar

�  Pinch point in feeders


System review Attrition mechanisms � Shear

� Edges of particles chipped off or worn away � Examples

�  Interparticle motion

�  Sliding along bin wall

� Cyclone travel


System review Attrition mechanisms � Compression and shear

� Examples � Converging flow channel

� Mechanical feeder (especially screw feeders)


Attrition tests

� Impact � Hopper flow � Compression � Pneumatic conveying


Attrition tests - impact

� Used to evaluate particle attrition during filling of silos, hoppers, and chutes


Attrition tests

� Impact � Hopper flow

� Evaluate particle attrition due to funnel or mass flow in a hopper

Flowing!

Stagnant!

Funnel Flow!

Mass Flow!


Attrition tests – hopper flow - rotational shear


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


Attrition tests

� Impact � Hopper flow � Compression

� Evaluate particle attrition due to loads acting on particle or bed


Attrition by Compression!

Principle Pressure, psf!

Perc

ent M

inus

2.5

mm

!


Attrition / friability tests - particle hardness


Attrition tests

� Impact � Hopper flow � Compression � Pneumatic conveying

� Measure particle size before and after conveying


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?


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


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

Bulk Solids: Science / Engineering / Design!

Questions?

Carrie Hartford

Senior Engineer

[email protected]

08 9277 3303

Perth WA