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Particle Technology- Centrifugal Separation
The document discusses centrifugal separation techniques in particle technology, focusing on sedimenting centrifuges, hydrocyclones, and filtering centrifuges. It provides insights into operational principles, efficiencies, and mathematical models used to analyze and compare various centrifuge designs and their applications. Additionally, resources and illustrations are referenced for further understanding of these processes.
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Introduction to centrifugal separation in particle technology and course details.
Overview of sedimenting centrifuges, including designs and functions such as scroll decanters.
Description of different centrifuge types like tubular bowl and disc stack centrifuges.
Analysis of sedimenting centrifuge geometries focusing on liquid flow and particle dynamics.
Critical trajectory model and implications for settling times and sigma values for efficiency.
Case studies on flue gas desulphurization, hydrocyclones, and operational parameters.
Principle of hydrocyclones including features, operating data, and types/configurations.
Description of filtering centrifuges and their various types including pusher and peeler.
Detailed cycle processes in filtering centrifuge operations, including washing and drainage.
Performance analysis of centrifuge drainage and saturation principles.
Credits for resources and images used in the presentation concerning centrifugal technologies.
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Particle Technology- Centrifugal Separation
- 1. Centrifugal SeparationChapter 8in FundamentalsWatch this lecture at http://www.vimeo.com/10203052Visit http://www.midlandit.co.uk/particletechnology.htm for further resources.Course details: Particle Technology, module code: CGB019 and CGB919, 2nd year of study.Professor Richard [email protected]
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- 3. Particle motion ina centrifugal field
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- 6. Grade efficiency &cut size
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- 8. Adaptation of filtrationequations
- 9. Washing (ratio) &DryingScroll Discharge Decanter Archimedian screw to convey solids out of the centrifugeImperforate bowl, i.e. sedimenting not filteringImage courtesy of Thomas Broadbent & Sons LimitedImage courtesy of Siebtechnik GmbH
- 10. Scroll Discharge DecanterScrew rotates at only slight differential speed to the centrifuge - solids leave at one end, centrate at the other.Image courtesy of Siebtechnik GmbH
- 11. Tubular bowl centrifugeThis one is vertical axis - simple design with no internals for clarification or liquid/liquid separation - a more complicated design is the chamber bowl.Image removed for copyright reasons. For an example product please see http://www.sharpenntechnologies.com/pcat-gifs/products-large2/high-speed-centrifuge1111-2.jpg.
- 12. Disc stack centrifugeLike a lamella clarifier: internal surfaces to encourage settling - usually used in oil/water separation and cream
- 13. Sedimenting Centrifuges āLetās confine our analysis to a simple geometry - ignoring the complicated internal structures required to remove deposited solids and oil concentrates.Liquid flow outInner radiusAir coreOuter radius
- 14. Gravity settlingField force(weight) is:Drag force is:
- 15. Giving:Centrifugal settling Fieldforce (weight) is:Drag force is:
- 16. Giving:Centrifugal settlingi.e. U= f(r)ri.e. U = dr/dtSedimenting Centrifuges
- 17. Centrifugal settlinglimits: r=r1at t=0 to r=r2 at t=t
- 18. Giving:i.e. the radialresidence time in the machine
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- 21. Critical trajectory modelResidencetime axially and radially is the same.Critical trajectory modelMultiply through by āgā:Critical trajectory modelMultiply through by āgā:
- 22. Square bracketed termis the terminal settling velocity of a particle of size x.Critical trajectory model- Eq 8.10 & 5.28!Rearrange:m2c.f. a gravity settling basinMachine parametersm2The theoretical settling basin equivalent PLAN area given the dimensions of the machine in question and its operating conditions.Process parametersm2The measured value given the process flow rate and operating performance for the 100% cut-off.Sigma valuesSigma machinem2Sigma processm2The two sigma values are equal for 100% efficient machines - normally 40 to 60% may be achieved.Uses of sigma valuesTo compare between different machines of same geometryAttempts to compare between different types of machinesEstimate of machine size required to replace gravity settling clarifierYou need a density difference!
- 23. Flue gas desulphurisationFeed:CaSO4- 35water - 65 100%Cake:CaSO4 - 70water - 30 100%Centrate:CaSO4 - 2.7water - 97.3 100%All concentrations as mass percent
- 24. HydrocycloneSingle unit andarray:Defined by diameterof cylindrical sectionImage showing "Krebs gMAXĀ® Hydrocyclones" courtesy of FLSmidth Krebs Inc.
- 25. Means of separationCentrifugal:800g in 300 mm hydrocyclone50000 g in 10 mm hydrocycloneType of separator:a classifier (i.e. splits into sizes)a thickener (i.e. concentrates suspensions)
- 26. Operating dataDiameters: 0.01 to1 metreSolid (cut) sizes: 2 to 250 micronsFlow rates (single unit): 0.1 - 5000 m3 h-1Pressure drop: 6 to 0.4 barU/F solid content: up to 50% v/v (claimed)
- 27. Principal featuresNote: primary& secondary vortex, air core, U/F, O/F, tangential feed
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- 31. Grade efficiency āCut PointFeed distribution is split into two fractions:OverflowUnderflow
- 32. Grade efficiencyFraction bymass of each grade entering the U/F of the hydrocyclone.
- 33. Recovery is theoverall fraction entering the U/F - usually by volume.Grade efficiencyEquation:Grade efficiencyWhat is the grade efficiency of the following?Overflow50 kg/hUnderflow50 kg/h
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- 35. Grade efficiencyi.e. weneed to correct for effect due to flow split in order to reliably record the ability of the device to act as a classifier.
- 36. The reduced gradeefficiency.Grade efficiency<100%Reduced grade efficiency:
- 37. Normalised reduced gradeefficiency:100%
- 38. Equilibrium Orbit TheoryAparticle orbiting on the LZVV has no net tendency to move into the primary vortex (then O/F) or secondary vortex (then U/F).It must be equal to the cut size x50%.
- 39. Equilibrium Orbit TheoryForcebalance:centrifugalTangential velocity:
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- 41. Hydrocyclones - typesand configurationsOil/water separation - often offshore
- 42. Filtering Centrifuges Aperforated bowl - similar to a spin dryerSee box on page 83 for descriptions
- 43. Filtering Centrifuge āSection 8.3Pushergenerally coarse solids > 50 microns(semi)-continuous solids outputcareful balance of slurry inImage courtesy of Siebtechnik GmbH
- 44. Filtering Centrifuge Peelergenerallysolids > 5 micronsusually intermittent solids output - slow to 50 rpmImage removed for copyright reasons.Please search online for an image of a peeler centrifuge.
- 45. Filtering Centrifuge InvertingBaggenerally solids > 5 micronsintermittent solids outputImage removed for copyright reasons.Please search online for an image of an inverting bag centrifuge.
- 46. Filtering centrifuge -full cycle Function Time(s) Time(%) Accelerate from 50 to 500 rpm 40 5 Load/Filter at 500 rpm 277 32Accelerate to 1050 rpm 90 10 Spin dry at 1050 rpm 119 14Wash at 1050 rpm 10 1 Spin dry at 1050 rpm 236 27Slow down to 50 rpm 90 10 Unload at 50 rpm 15 2 Total cycle time 877 100 Basket load per cycle of solids 140 kg Productivity 575 kg/hour
- 47. Centrifuge - simpleanalysis ā Fig 8.9ļPtotal= ļPcake+ ļPmediumDefinitions:
- 48. Centrifuge - simpleanalysis- same as for conventional filtrationHowever, the radius at which the cake forms is continually moving inwards and the geometry is not planar.where:
- 49. Centrifuge - simpleanalysisCentrifugal head - the driving pressure:where omega is in seconds-1 = (2 pi/60)RPMDensity is that of the slurry or liquid depending upon the operation: filtering or washing
- 50. Centrifuge - washingbutrc remains constant during the washing stage. The time to wash with Vw m3 of solvent is:
- 51. Centrifuge - washingTypicalwashing performance:1Solute concn.Initial concn.0.5Flooded cakeDewatered cake0123Wash volumes
- 52. Centrifuge - drainage1Relativesaturation0.5S* = SIrreducible saturationSinitial00.20.40.6Time or dimensionless drainage time
- 53. This resource wascreated by Loughborough University and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme.Slide 3 (Left). Image of a decanter centrifuge provided courtesy of Thomas Broadbent and Sons Ltd. See http://www.broadbent.co.uk/en/about for details.Slides 3 (right), 4, and 42. Images courtesy of Siebtechnik GmbH. See http://www.tema.co.uk/images/products/7_1.jpg for details.Slide 24. Image of"Krebs gMAXĀ® Hydrocyclones" photo courtesy of FLSmidth Krebs Inc. See http://www.flsmidthminerals.com/Products/Classification/Hydrocyclones/Hydrocyclones.htm for details. Ā© 2009 Loughborough UniversityThis work is licensed under a Creative Commons Attribution 2.0 License. The name of Loughborough University, and the Loughborough University logo are the name and registered marks of Loughborough University. To the fullest extent permitted by law Loughborough University reserves all its rights in its name and marks which may not be used except with its written permission.The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence. Ā All reproductions must comply with the terms of that licence.The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher.