No Slide Title

FiltrationChapter 4 in Fundamentals

Professor Richard HoldichR.G.Holdich@Lboro.ac.uk Course details: Particle Technology, module code: CGB019 and CGB919, 2nd year of study.Watch this lecture at http://www.vimeo.com/10201620 Visit http://www.midlandit.co.uk/particletechnology.htm for further resources.1FiltrationTypesCake filtration mechanismModification of Darcy's lawConstant pressure filtrationConstant rate filtrationVariable rate & pressure filtrationIndustrial equipment2Types of filtrationNormally batch (in duplicate) but some continuous ones:Deep bed - clarification

Image supplied by DynaSand and Hydro International (Wastewater) Ltd. 3Types - membrane

Clarification on filtering membranes4Types - Clarification

Cartridge and candle filtration5Cake filtration mechanismMultifilament filter cloth p. 40

6Cake filtration mechanismMonofilament filter cloth

7Cake filtration mechanismMonofilament open filter cloth/mesh

8Cake filtration mechanism p.31Why cant we simply measure Rm for each medium?

9Cake filtration mechanism reality p 41Why cant we simply measure Rm for each medium?

i.e. Rm = f(material to be filtered)10Modification of Darcy's lawPorosity or voidageand Concentration

11Modification of Darcy's lawDarcys law:

Kozeny-Carman equation:

Pressure/LFlow rate

use:12Modification of Darcy's lawDarcys law/Kozeny:

Pressure/LFlow rate

What do the graphs tell us about these equations? How will this vary for filtration? Think about a given material and filter in these equations what is constant, what varies, look at the graphWhat are the independent and dependent variables?

TimeVolume liquid13Modification of Darcy's law p.29Darcys law:

Q is constant - permeation

TimeFiltrate volume

Q decreases - filtrationAt constant pressure drop:14Modification of Darcy's law p. 32

Build up of incompressible filter cake:Filter mediumFilter cakeformation15Modification of Darcy's law

16Modification of Darcy's lawPressure drops are additive:PcakePmedium

17Modification of Darcy's lawPressure drops are additive:P

Ratio: cake volume:filtrate = constant =

18Modification of Darcy's law

Ratio: cake volume:filtrate = constant =

What doesRepresent in English, see the graph

What doesRepresent in English19Modification of Darcy's law p.36where c is the dry cake mass per unit volume of filtrate:and is the specific resistance to filtration (m/kg).

s is feed slurry mass fraction and m is the moisture ratio of the cake (mass cake wet/mass cake dry - or sample). In some instances one can assume m=1; i.e. neglect liquid in cake.20Modification of Darcy's law p.36

wRc

alpha = Rc/wConsidering Rc & alpha some more:w is dry mass/unit area solids:

so:

21Modification of Darcy's law equation (4.11)

General filtration equation:22Constant pressure filtrationConstant P filtration - integrate general equation:to give:

i.e:Time over filtrate volumeFiltrate volumeba23Constant pressure filtrationsummary:Need to know:

viscosity, pressure, and filter area & slurry mass fraction, liquid density (and cake moisture - if poss.)Time over filtrate volumeFiltrate volumebaNeed to calculate:c then and Rm24Constant pressure filtrationGeneral filtration equation:Constant pressure:

y = m x + c25Constant pressure filtrationFiltration Testing in the Laboratory:effect of pressure,different cloths or media,slurry agitation,filter aids and flocculantseffect of slurry pre-concentrationHigh permeability: vacuum leafLow permeability: pressure bombTests:26Constant pressure filtrationFiltration Testing in the Laboratory:specific resistance - possibly as f(pressure),medium resistancecake concentration - possibly as f(pressure) or moisture ratioHigh permeability: vacuum leafLow permeability: pressure bombTo obtain values of:27Constant pressure filtrationFiltration Testing in the Laboratory:Liquid viscosityfiltration pressurefilter areaHigh permeability: vacuum leafLow permeability: pressure bombAlso required for scale-up or simulation:Slurry mass fractionliquid densitysolid density - if cake height is required28Constant pressure filtration p. 41 vacuum filter leaf

Experimental characterisation29Constant pressure filtration

30Constant rate filtration p. 36Constant rate:General filtration equation:

Filtration pressureFiltrate volumeba31Variable rate & pressure filtrationGeneral filtration equation:Variable pressure and rate equation:

plotnumerical integration of:

32Industrial equipment p. 35

Rotary vacuum filter (continuous)Stagescake formation in slurry tank (F)drying and/or washing (D and W)discharge - then back to formation (D & Di)FDWD & Di33Industrial equipmentConstant pressure:

Rearrange for a quadratic:

34Industrial equipment p. 36Simulation of Rotary Vacuum Filter:

i.e. aV2 + bV - t = 0

where form time t = F/n (submergence/speed)35Industrial equipmentper cycle of drum:Mass dry cake deposited = cV (kg)Mass wet cake deposited = mcV (kg)mass slurry filtered = mcV + V (kg)

Calculate volume, hence:All above is per cycle, hence 3600/t for output per hour.36Industrial equipmentVacuum belt filter (continuous)

Image appears courtesy of Polyfilters UK Limited www.polyfilters.com 37Industrial equipmentVacuum belt filter (continuous)Image supplied courteousy of BHS-Sonthofen GmbH, Germany www.bhs-sonthofen.de

38Industrial equipmentVacuum disc filter (continuous)

Image courtesy of FLSmidth, Inc. 39Industrial equipmentTube pressure filter (batch)

Image courtesy of Mesto Minerals (Sala) AB40FiltrationTypesCake filtration mechanismModification of Darcy's lawConstant pressure filtrationConstant rate filtrationVariable rate & pressure filtrationIndustrial equipment41

This resource was created 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. Image of a DynaSand is provided courtesy of Hydro International (wastewater) Limited. See http://www.hydro-international.biz/irl/wastewater/dynasand.php for more details.

Slide 37. The image of a vacuum belt filter (continuous is provided with the permission of Polyfilters (UK) Limited. See http://www.polyfilters.com/process.html for more details.

Slide 38. Image provided courtesy of BHS-Sonthofen GmbH. See www.bhs-sonthofen.de for more details.

Slide 39. Image provided courtesy of FLSmidth Inc. See http://www.flsmidthminerals.com/Products/Filtration/Vacuum+Filtration/Vacuum+Disc+Filters/Agidisc+Vacuum+Filters/Agidisc+Vacuum+Filters.htm for more details.

Slide 40. Image of a tube press discharge, provided courtesy of Mesto Minerals (Sala) AB. See http://www.metso.com/miningandconstruction/MaTobox7.nsf/DocsByID/C44A6B216E52C95142256AF6002D6148/$File/Tube_Press_ES.pdf for more details.

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