1、Ultrafine coal classification using 150 mm gMax cyclone circuitsR.Q.Honakera,*,F.Boatena,G.H.LuttrellbaDepartment of Mining Engineering,University of Kentucky,Lexington,KY 40506-0107,United StatesbDepartment of Mining and Minerals Engineering,Virginia Tech,Blacksburg,VA 24061,United StatesReceived 5
2、 March 2007;accepted 6 June 2007Available online 1 August 2007AbstractA two-stage classification circuit using 150 mm diameter gMax cyclones was installed and evaluated in a coal preparation plant in aneffort to achieve a clean coal product without the use of froth flotation.Particle size separation
3、s of around 37 lm were achieved whilelimiting ultrafine bypass to less than 10%in the circuit underflow stream.As a result,approximately 81%of the ash-bearing material inthe circuit feed was rejected to the circuit overflow stream.The feed ash content was reduced from around 50%to values in the rang
4、e of2230%in the circuit underflow stream with a mass recovery of about 30%.Further reductions in the coarse product ash content werelimited due to the particle density effect and the remaining presence of a significant quantity of high-ash slime material in the coarseproduct.The typical D50for the c
5、oal particles was 40 lm while the estimated value for mineral matter was 17 lm.Based on the findingsof the study,the use of classification to recover a low-ash,coarse fraction in the feed of a fine coal circuit is limited by the density effectregardless of the ability to eliminate ultrafine bypass.?
6、2007 Elsevier Ltd.All rights reserved.Keywords:Coal;Classification;Fine particle processing;Hydrocyclones;Modeling1.IntroductionThe interest in achieving ultrafine particle size separa-tions within the range of 2550 lm has developed over thepast decade in the coal industry as a result of the need to
7、reduce or eliminate material from froth flotation feed thatis typically high in ash content,elevates chemical consump-tion in the flotation process and generally contributes tohighproductmoisturevalues.Anotherpotentialapplicationis the production of a fine clean coal product.The ash con-tents ofthen
8、ominal 150 25 lmsize fraction intheprimarycyclone of several coal preparation plants are less than 10%.As such,an efficient ultrafine particle size separation couldprovide ahigh-quality productwithouttheneed offrothflo-tation or other fine coal cleaning technologies.The most direct means of achievin
9、g particle size separa-tions is through the use of screening.Low-capacity andblinding issues have generally prohibited the use of screen-ing below 300 lm in the coal industry.However,recentlydeveloped screening technologies provide the potential ofachieving efficient particle size separations around
10、 150 lmat capacities amenable for use in coal preparation plants.Plant data from a recent in-plant study have revealed thatthe SuperStacker technology by Derrick Screens providesa very efficient particle size separation at around 75 lm atmass throughput capacities of 3 tons/h/m2or 40 tons/hfor the t
11、otal unit which incorporates 5 screen decks and0.10 mm slot openings(Hollis,2006).Mohanty et al.(2002)evaluated the Pansep screen technology for its abilityto achieve ultrafine coal particle separations.Exceptionalscreening efficiencies(imperfection values below 0.30)wereobtained while separating pa
12、rticles at 45 lm.However,screening performance significantly deteriorated when thefeed mass rate was increased above 2.6 tons/h/m2of screenarea.In addition,undersize bypass to the screen overflowincreased with mass feed rate from 20%under the optimumconditions to around 50%.0892-6875/$-see front mat
13、ter?2007 Elsevier Ltd.All rights reserved.doi:10.1016/j.mineng.2007.06.004*Corresponding author.Tel.:+1 859 257 1108;fax:+1 859 323 1962.E-mail address:rhonakerengr.uky.edu(R.Q.Honaker).This article is also available online at: Engineering 20(2007)12181226Industrial practice typically uses hydraulic
14、 classificationprocesses,such as classifying cyclones,for ultrafine particlesize separations.Classification principles are based on dif-ferences in the settling rates of the particles in the system,i.e.,coarse particles settle at a higher rate than fine parti-cles.Classifying cyclones with a 150 mm
15、or 250 mm diam-eter are commonly used in the coal industry for ultrafinesizing applications due to their high-volumetric and massthroughput capacities and effective classification perfor-mance.Recently,advancements in cyclone design haveimproved performance and positively affected operationalcharact
16、eristicssuchasreducedoperatingpressures(Heiskanen,1996;Obeng and Morrell,2003;Rong andNaper-Munn,2003;Mohanty et al.,2002).However,inherent problems that have not been remedied includethe amount of hydraulically entrained undersize materialreporting to the coarse underflow stream and a densityeffect that occurs due to the density difference between coaland mineral matter.Both the entrainment and density effects hinder the abil-ity of using cyclones to produce a final clean coal productin the und
