Carrie Hartford - JENIKE & JOHANSON PTY LTD - Ways to minimize particle attrition that can...

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Carrie Hartford delivered the presentation at the 2014 Dust Explosions Conference. The 2014 Dust Explosions Conference examined industrial hazards, the means to control or eliminate dust and analysed the latest technology to ensure the maximum protection and safety of organizations. The event also featured recent industrial case studies and new safety recommendations. For more information about the event, please visit: http://www.informa.com.au/dust14

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Bulk Solids: Science / Engineering / Design!

Ways to Minimise Particle Attrition

Carrie Hartford

Senior Engineer

chartford@jenike.com

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

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

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

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

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 6

Effects of particle attrition

� Increased dust levels – safety hazard

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

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 8

Effects of particle attrition

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

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 9

Effects of particle attrition

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

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

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

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 !

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

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

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

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)

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 17

Attrition tests

� Impact � Hopper flow � Compression � Pneumatic conveying

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 18

Attrition tests - impact

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

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!

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 20

Attrition tests – hopper flow - rotational shear

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

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

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 23

Attrition by Compression!

Principle Pressure, psf!

Perc

ent M

inus

2.5

mm

!

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 24

Attrition / friability tests - particle hardness

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 25

Attrition tests

� Impact � Hopper flow � Compression � Pneumatic conveying

� Measure particle size before and after conveying

Bulk Solids: Science / Engineering / Design!SCIENCE ⏐ ENGINEERING ⏐ DESIGN 26

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?

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

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

Bulk Solids: Science / Engineering / Design!

Questions?

Carrie Hartford

Senior Engineer

chartford@jenike.com

08 9277 3303

Perth WA

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