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

3.  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

4.  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

6.  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

7.  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

8. Cross section of spiral stream

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

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

12.  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

13.  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

14. Schematic representation of reflux classifier

15.  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

16. 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)

17.  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

18. Typical Teetered Bed Separator

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

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

21.  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

22.  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

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

24. Drummond, R., Nicol, S. and Swanson, A. 2001. Teetered bed separators: the Australian experience. The J. of the South Afr. Inst. of Min. and Metall. 16(10). October. 385-392. www.onemine.org. Accessed November 2011. Galvin, K.P., Callen, J., Zhou, E. and Doroodchi. E. 2010. 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. 345-351. Galvin, K.P., Doroodchi, E., Callen, J., Lambert, N. and Pratten, S.J. 2002. Pilot plant trial of the reflux classifier. Min. Eng. 15(1). 19-25. www.engineeringvillage2.org. Accessed October 2011. Galvin, K.P., Doroodchi, E. Callen, J., and Spear, S. 2005. Performance of the reflux classifier for gravity separation at full scale. Min. Eng. 18(1). 19-24. www.engineeringvillage2.org. Accessed October 2011. Ludowici Australia. 2011. Products and Services Guide. Unpublished work. Nguyentranlam, G. and Galvin, K.P. 2001. Particle classification in the reflux classifier. Miner. Eng. 14(1). 1081-1091. www.engineeringvillage2.org. Accessed November 2011. Wills, B.A. and Napier-Munn, T.J. 2006. Mineral Processing Technology. Great Britian: Elsevier Ltd. 236-238.