 Background Information › Spirals › Reflux Classifier  Advantages/Disadvantages  Influence of various size fractions and specific gravites  Performance of a reflux classifier  Conclusion

 Spirals are currently being used in most American coal preparation plants  The Australian-made reflux classifier could potentially replace spirals  Cost analysis would need to be done at each individual plant  A clear cut answer as to which is better cannot be expected

 To clean the 2 x 0.1 mm particle size fraction in coal  Separate rock based on specific gravity and size  Used in other facets of mining as well

 Not originally invented for use in coal industry  The Humphreys spiral was initially used to process chrome bearing sands in 1943  Originally a car tire that was cut and hung  First model made for coal in early 1980’s

 Feed pulp of 15%-45%  Size range of 2mm down to 0.1mm  Through gravity and centrifugal force: › Light particles (coal) pushed to outside › Heavy particles (rock) stay on inside  Other forces at work: › Differential settling rates › Interstitial trickling

Cross section of spiral stream

 Three product draws located at bottom of spiral › Tailing › Middling › Concentrate  Drawing on left is for hard rock Cross section of spiral stream

 Originally 5 turn, one-stage  Now typically 6 or 7 turn, two-stage

 Invented by K.P. Galvin at the University of Newcastle in Australia › Made by Ludowici › Used widely in Australia  Has its roots in: › Teetered bed separators (hindered settling column) › Lamella settlers  Lamella plates added to teetered bed separator to create reflux classifier

 Upward moving water current to separate particles of different size fractions and densities  Feed enters the unit tangentially into a feedwell  The addition of the lamella plates has allowed an increase of settling rate and capacity

Schematic representation of reflux classifier

 Faster settling particles fall to the underflow  Slower settling particles will rise to the overflow  Particles now travel greater distance with lamella plates › Where the term reflux is derived Schematic representation of reflux classifier

SpiralsReflux Classifier AdvantagesDisadvantagesAdvantagesDisadvantages Simple Design Near zero operating cost Small capital investment Low capacity (~2 MTPH) Need many spirals (takes space) High capicity (135 MTPH) Sharp separation High capital cost High maintenance cost Large material (>2mm can be lost)

 An important quality in determining the optimum size fraction is a graph of slip velocities vs. the particle size  Slip velocity is the velocity of the particle relative to the moving liquid › Would be zero if particle traveled same speed as water › Heavier and bigger particles have bigger slip velocities

Typical Teetered Bed Separator

Reflux Classifer from pilot trial by Galvin in 2002 Lamella plates set at 60º

 Reflux Classifier (right) is less uniform than the teetered bed separator  Much sharper separation can be seen from the reflux classifer

 Galvin’s pilot plant trial showed: › great separation between two gravities › significantly less variation in the separation density with size  A later full scale test by Galvin in 2005 showed similar results  In 2010, Galvin discovered found that moving the lamella plates to 70º would be beneficial to reduce influence of coarse particles

 Plant Engineer should obtain a test model from Ludowici › A plant manager can take the information presented to compare the performance on their own spirals. › A decision can then be made if a reflux classifier is a good choice for their particular plant

 Background Information › Spirals › Reflux Classifier  Advantages/Disadvantages  Influence of various size fractions and specific gravites  Performance of a reflux classifier

Drummond, R., Nicol, S. and Swanson, A Teetered bed separators: the Australian experience. The J. of the South Afr. Inst. of Min. and Metall. 16(10). October Accessed November Galvin, K.P., Callen, J., Zhou, E. and Doroodchi. E Gravity separation of coal in the reflux classifier: New mechanisms for suppressing the effects of particle size. Int. Coal Prep. Cong. 2010, Conf. Proc. Littleton, CO: SME Galvin, K.P., Doroodchi, E., Callen, J., Lambert, N. and Pratten, S.J Pilot plant trial of the reflux classifier. Min. Eng. 15(1) Accessed October Galvin, K.P., Doroodchi, E. Callen, J., and Spear, S Performance of the reflux classifier for gravity separation at full scale. Min. Eng. 18(1) Accessed October Ludowici Australia Products and Services Guide. Unpublished work. Nguyentranlam, G. and Galvin, K.P Particle classification in the reflux classifier. Miner. Eng. 14(1) Accessed November Wills, B.A. and Napier-Munn, T.J Mineral Processing Technology. Great Britian: Elsevier Ltd