Ten Key Steps to Minimise Particle Attrition during Handling
Ultimately, the formation of fresh product surfaces is proportional to the energy expended in its creation. Therefore, to reduce the total energy absorbed by a storage and handling system by way of good initial design, certain basic principles stand out as means to reduce the degree of particle attrition that a bulk material will suffer.
1. Establish the threshold strength at which the particles can sustain an applied load without breaking. Relate to the following:
2. Minimise or reduce free fall. Employ spirals or cascades to loose height with low contact forces. Use broad, deep and slow feed streams on chutes. If large drops are inevitable, disperse the flow stream as much as practical.
3. Minimise impact frequency and magnitude as practical. Try to ensure contact velocities are low, oblique to contact surfaces and employ resilient contact materials to reduce sharp, concentrated loads.
4. Avoid slip on rough surfaces, past flow obstructions or surface irregularities. Try to reduce contact pressures as far as practical.
5. Minimise overpressures on extracting devices in hoppers.
6. Avoid shearing the bulk in confined or high stress conditions. Allow room for local expansion when shearing a settled powder bed.
7. Allow generous working clearances that will not trap or wedge particles.
8. Move the material slowly and coherently wherever possible and expand the flow channel at changes of flow direction
9. Converge a flow stream gently, in dilate, low velocity conditions by way of smooth contact surfaces
10. If pneumatic conveying is deemed necessary, chose a dense phase system with low radius bends and minimum exit velocity without direct hard, end impact.
See also the Bulk Materials Handling Board publication:
’User Guide to Particle Attrition in Materials Handling Equipment’.
