INNOVATIVE GRAVITY-BASED TECHNOLOGIES AND
INNOVATIVE GRAVITY-BASEDTECHNOLOGIES AND CIRCUITSFOR FINE COAL CLEANINGR. Q. HonakerUniversity of KentuckyDepartment of Mining EngineeringWorkshop on Coal Beneficiation andUtilization of Rejects : Initiatives, Policies and Best PracticesRanchi, IndiaAugust 22 – 24, 2007
U. S. COAL PREPARATIONCoal preparationinvolves processing toachieve the requiredquality for end users.636 Mt of coalprocessed annually.Coal is sized andcleaned in variouscircuits.Fine (-1 mm) coaltypically accounts for12%-15% of feed (75– 95 Mt annually)
TYPICAL loneUltrafineFineCoal reensBasketCentrifugeScreen-BowlCentrifugesDisc FilterFrothFlotation
Minus 0.15 mmCommon U.S. FineCoal Circuit38cmClassifyingCyclone1 x 0.15 mmColumnFlotationCompoundSpiralConcentrator1 ctSieveBendScreenBowlCentrifugeCleanCoalThickener
Spiral ConcentratorsFlowing film separator.Produces three product streams.3-3.5 tph/start; 30 gpm/start.Three starts on one axis.Separation density 1.8 RD; Ep 0.15 – 0.18.Typical 5-10% high densityparticle by-pass.SpiralCoalRocknrtiSogZone
Spiral Performance ImprovementsLuttrell et al. performed circuitanalysis to reduce separationdensity and improve efficiency.Rougher-Cleaner arrangementwith middling recycle the mostpractical.Separation densities of around1.7 at Ep 0.18.Commercial manufacturershave since produced spiralsthat achieve the RougherCleaner cleaning action in asingle unit.Primary-Secondary(Midds Only)FeedProductRefuse
Water-Only Cyclone – Spiral Circuit100Water-Only Cyclone (WOC)SpiralWOC-Spiral Circuit80Probability to Product (%)Recent emphasis inmetallurgical coalproduction is loweringthe separation densityof the fine circuit.Water-only cyclonesprovide a low densitycut but tend to lose coal.Spirals tend to ensure100% coal recovery buthave a high density cut.Combining the two unitsprovides an efficient lowdensity separation.604020011.21.41.61.822.2Relative Particle DensityWOC: Ep 0.10Spiral: Ep 0.15WOC-Spiral: Ep 0.062.42.6
Water-Only/Spiral Fine Coal ralConcentrator38mmClassifyingCycloneSieveBend1 enScreenBowlCentrifugeCleanCoalThickener
Teeter-Bed SeparationsLow pressure waterinjection at the bottom ofthe separation chamberfluidizes the high-densityparticles.Fluidized particle bed autogenous medium.Can be used as analternative or inconjunction with spirals.2 tph/ft2 capacity.Effective over a particlesize range 5:1.
Teeter-Bed Installation650 ton/hr plantHMC/Teeterbed/Flotation plant140 tph, 2 x 0.25mm treated byTeeter-Bed.3 x 3 m2 CrossflowTeeter-Bed unitused.
Teeter-Bed Performance10090Recovery (%)Parametric evaluationwas performed toimprove start-upperformance.9% ash productachieved with organicefficiency greaterthan 95%.80Ken America WashabilityTest Set 3Test Set 2Test Set 1Start-Up7060024681012Product Ash (%)14161820
Particle Size-by-Size PerformanceParticleSize(mesh) 88 x 1616 x ECOVERY(%)87.387.089.588.895.895.295.595.6A particle size-by-size analysis of the process streamsshows that 56.5% of the ash-bearing material is removedfrom the 8 and 8 x 16 mesh fractions while recovering95% of the combustible material.A significant finding is the high ash contents in the 8mesh tailings material ( 70%). The ash content of thisfraction in the initial tests was around 48%.
Crossflow Coal PerformanceAsh Content 010:0011:0012:0013:0014:0015:00Operating Time (hrs)The average feed, product and tailing ash contents were15.97%, 9.99% and 64.34%, respectively.
-1 mmFineCircuitFeedUltrafine Gravity CircuitClassifyingCyclones- 0.250 eject0.25 x 0.044 mm1.0 x 0.25 mmCleanCoal
Spiral Concentrator Application forUltrafine Coal CleaningRecent studies have foundthat spirals such as the SX7can provide an effectivegravity-based separationperformance for -100 meshcoal.Required volumetric flowrate is around 15 gpm/startand feed solids contentshould be nearly 15% byweight.Currently, two U.S. coalpreparation plants usespirals in this application.
Ultrafine Spiral ConcentratorAsh Rejection PerformanceTest 1 Performance (Higher Yield)Spiral FeedParticle Size(mesh)Weight (%) Ash (%)16 x 10019.608.44100 x 325-325Total45.1335.2810019.3353.7429.34Spiral ProductSpiral Mids 1Spiral Mids 2Spiral TailingsWeight (%)16.34Ash (%)5.22Weight (%)25.52Ash (%)6.80Weight (%)16.75Ash (%)14.77Weight (%)15.49Ash 5310057.8474.4959.54Test 2 Performance (Lower Product Ash)Spiral FeedParticle Size(mesh)Weight (%) Ash (%)16 x 10019.608.44100 x 32545.1319.33-32535.2853.74Total10029.34Spiral ProductWeight (%)17.5058.2624.24100Ash (%)4.9410.7147.1318.53Spiral Mids 1Weight (%)25.2642.2732.47100Ash (%)5.9912.0051.6423.35Spiral Mids 2Weight (%)21.9247.1830.91100Ash (%)6.8016.1957.5326.91Spiral TailingsWeight (%)20.1652.5627.29100Ash (%)36.8756.3368.6855.78
Ultrafine Spiral ConcentratorTotal Sulfur Rejection PerformanceTest 1 PerformanceSpiral FeedSpiral ProductSpiral Mids 1Spiral Mids 2Spiral TailingsParticle Size(mesh)Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%)16 x 0 x l1004.071002.501003.631005.401006.32Test 2 PerformanceSpiral FeedSpiral ProductSpiral Mids 1Spiral Mids 2Spiral TailingsParticle Size(mesh)Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%) Weight (%) T. Sulfur (%)16 x 0 x l1004.071003.041003.501004.971006.67
Enhanced Gravity ConcentrationFeedCommercial units availablethat provide up to 300 g’sUnits utilize basic principlesof jigging, tabling, fluidizedbed or flowing film.The Knelson Concentratoris a fluidized bed unit.Feed slurry is injected intothe center and acceleratedby mechanical action.High density particlesmigrate to the bowl wall anddischarged throughcontrolled pinch valves.Low density particles flownaturally over the top lip ofthe gsUnderflowTailingsFluidizationWaterProductReject
Knelson Steam Coal Performance100Recovery (%)9080706050Steam Coal40WashabilityWithout Air InjectionAir InjectionFlotation Release3020100048121620Product Ash (%) Knelson concentrator provided superior performance compared to flotation.
Knelson Separation PerformanceRecovery (%)1008060Metallurgical Coal40WashabilityWithout Air InjectionWith Air Injection20Optimized Air Injection0024681012Product Ash (%)141618
Falcon ConcentratorCentrifugal flowing filmseparator.Feed slurry containing20% solids is injectedonto a spinning rotorand accelerated.Particle bed is formedwith heaviest particlesnear the bowl wall.Valves along topcircumference of bowlare controlled todischarge the reject.
Combustible Recovery (%)Water-Only Enhanced Gravity Separations on300 x 45 Micron Coal1008060Altair JigFalcon40Release Analysis20Washability00204060Ash Rejection (%)80100
Dense-Medium Application in the Falcon SeparatorPittsburgh No. 8 CoalClean CoalYield Yield(%)CleanCoal(%)100100808060604040Dense Medium FalconWashabilityOptimized Dense Medium202000005510101515ProductAsh (%)ProductAsh2020(%)2525
Sulfur Rejection PerformanceCombustible Recovery (%)100806040Pittsburgh No. 8 coalWashability20Dense Medium00204060Total Sulfur Rejection (%)80100
Ultrafine Gravity-Based CircuitRequirementTo produce an acceptableultrafine clean coal productfrom a gravity-based system,the high clay slimes must beremoved.Unfortunately, the slimes tendto report with the water inclassification systems.When water recovery isrestricted, density effectsresults in the loss of coal to theslime stream.Screening is typically limited bya low open area and blinding.The most efficient deslimingprocess commercially availableis column flotation.-1 mmFineCircuitFeedUltrafine Gravity CircuitClassifyingCyclones- 0.250 ngCycloneCyclonesReject0.25 x 0.044 mm1.0 x 0.25 mmCleanCoal
Enhanced Gravity-Flotation Circuit-0.045 mm-0.15 mmNominal-1 ifyingCyclones1 x 0.15 mmSpiralsEnhancedGravitySeparatorFrothFlotation BankRejectFine CleanCoalProduct
Summary – Fine Gravity CircuitsInnovative fine coalcircuits involving twostage, rougher-cleanerspiral units have beensuccessful commerciallyusing conventional lowcost dryers for productdewatering.Teeter-bed separatorshave been found toprovide very efficient finecoal cleaning for nominal2 x 0.25 mm coal.
Summary-Ultrafine Gravity CircuitsSpiral concentrators operated underspecified feed conditions providesignificant ash and total sulfurrejections for the 44 microns coal.Similar results have been achievedfrom enhanced gravity separators onfull-scale units.However, the inability to commerciallyachieve efficient ultrafineclassification limits gravity-basedtechnologies.Column flotation is the most efficientdesliming technology.For coals containing a relatively highlevel of pyritic sulfur and/or middlingparticles, a spiral/enhanced gravityand froth flotation circuit providesbetter technical performance;economics must be proven.
INNOVATIVE GRAVITY-BASED TECHNOLOGIES AND CIRCUITS FOR FINE COAL CLEANING R. Q. Honaker . 38cm Coal Circuit Classifying Cyclone Compound Spiral Concentrator Clean Coal 1 mm Deslime Screen Unders Thickener Sieve Bend . desliming technology. For coals containing a relatively high level of pyritic sulfur and/or middling
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