Thread: Degeneration of Lumps due to Multiple Transfers

1. Degeneration of Lumps due to Multiple Transfers

I am looking for a public database which provides data on the quantum of fines generated while conveying different material like coal, limestone,clinker, iron ore, lime etc. through a conveyor line involving multiple transfer points.

I expect the variables to include : the height of fall, the material, number of transfer points etc.

Is there any empirical formula to derive the quantum of such fines generation ?

2. Fines Generation in Belt Transfers

Kayem:

We too have searched world-wide for such information. I can tell you it is a solvable problem and some have made measurements on the production of fines in transfers of coal and iron ore. There are two reasons for the studies: 1) product degradation and 2) dust emissions

When fines generation influences large commerce, people study the problem. Large coal producers have made such studies to limit the loss of lump. Fluized bed combustion chambers require a close variance on lump size to stablize the combustion cycle and flow dynamics in the bed. Iron ore value is lost, if fines are present. The steel making process is influenced in a similar manner to the coal fluidized bed.

COAL:
South Africa's SASOL and ESKOM have made coal measurements. As I recall, they claim over 1% loss of premium lump to fines.

We have measured and made such study in coal and iron ore using Discrete Element Method (DEM) modeling. We have repeated measurement of a single transfer to demonstrate it is possible to classify the degree of breakage from field measurements. After 10 carefully taken samples, before and after the transfer, each test showed a 1% increase in fines below 20 microns. In fact, the whole cummulative damage curve shifted accounting for sieve damage during the measurement. We then took the same sample and passed it through the same chute and saw a systematic increase of about 1% per pass. The coal was a very friable type and the transfer a typical stop-and-go with about a 3 meter drop directly onto the receiving belt. We have also studied and measured the effect of long distance transport on conveyor belts due to idler agitation.

IRON ORE:
Hamersley Iron (HI), Australia, have made such measurements and found about 1% increase in undesirable fines for each transfer. Conveyor Dynamics, Inc. (CDI) is has and is presently studying fines generation and its control using curved transfer chutes. We can quantify the breakage of all particles, in the transfer using a combination of DEM and Population Balance Modeling (PBM). THe DEM gives the energy breakage spectrum for the range of particles the DEM can handle ( usually 20:1 max. in 3-Dimensions) and the PBM can extend the range when a sufficient size class of particles are tested for breakage energy. Changing the transfer chute geometry, significant reduction in breakage and fugitive dust can be achieved.

BHP, Australia, have also studied fines generation of raw iron ore and in DRI briquettes, for belt transfers and ship loading operation. Their claims are similar to HI. BHP is also introducing curved chutes to control breakage.

DEM:
DEM can quantify both: 1) breakage of lump to fines by impact and shear breakage through an orchestrated test and analysis program for all manner of transported materials and 2) dust emissions via gas dynamics in chutes. The lessons learned in mineral process equipment design has led to such developments and will be published by CDI in 2003. There will be a section posted in December on Chute Flow Dynamics (curved chute granular flow) that introduces the subject with some examples. See our web site in the first quarter 2003 for breakage developments and gas flow-fugitive dust migration:
www.conveyor-dynamics.com

It is not possible, in my opinion, to classify such breakage, by some simple algorithm. To many variables are at work including material properties, their size distribution and chute configurations.

Not a clear answer, but a beginning. Hopefully, others will contribute to this worthy cause.

Lawrence Nordell
President
Conveyor Dynamics, Inc.

3. Particle beakdown

There are so many variables that effect breakage of bulk lumps that I would question the validity of a database except for closely defined materials and transfer conditions.

I chaired a working party for the British Materials Handling Board that published a ‘User Guide to Particle Attrition in Materials Handling Equipment’. This document sets out a structured approach to the circumstances and characteristics of breakage mechanisms, the influence of particle properties on attrition and flow processes that cause attrition, test procedures and the like. From this, and representative tests on specific materials, it should be practical to extrapolate predictions for a given system.

I also published a paper, available on application to tech@ajax.co.uk, on ‘Minimising Particle Attrition in Mechanical Handling Equipment’. This brings out various design techniques and features of good practice for reducing breakage and dust generation.

Lyn Bates