decanter centriguge

7/29/2019 decanter centriguge

1/17

DRYCAKE:CBBDECANTERCENTRIFUGES

Themarket

for

decanter

centrifuges

is

very

competitive.

There

are

more

than

a

dozenmanufacturerswithverylittletodistinguishthedifferentequipmentfrom

oneandother.WiththeuseofaninnovativedesignDRYCAKE'sCBBcentrifuges

hascreatedtheirownadvantageinthemarket. Theintentofthisdocumentisto

outlinethoseadvantages,whileatthesamealsoprovidinganexplanationofhow

centrifugesoperateandtheiradvantages.AtthisJuncturehowever,Iwantto

stressthatDRYCAKEcompetesonprice,performance,andmaintenance. The

performanceandmaintenanceadvantagesoftheCBBcentrifugedonot

compromiseDRYCAKEspriceadvantage.

SOMEOTHERDEWATERINGTECHNOLOGIES:

BeltFilterPress FournierPress PlateandFramePress BaggingSystems(DRYCAKEDRAIMAD) ScrewPress(DRYCAKESLUDGLESS) DewateringBins Geotube

Whiletherearealotofoptionsoutthere,thecentrifugeiscurrentlythe

preferreddewateringtechnologies. However,itisalwaysgoodtoinformoneself

ontheotheroptionsonthemarketplace.


2/17

CENTRIFUGEOPERATIONALPRINCIPLES:

Adecantercentrifugebehaveslikeagravitysettlingtank,

thedifferenceisthecentrifugalforce:itimprovesthesettling

timeandefficiency!!

GRAVITYSETTLINGTANK

Inagravitysettlingtank,thesolidssettlebytheforceofgravity,whicharethen

dischargedoutoneendandtheclarifiedliquidareskimmedoffandcomeoutthe

otherend.

Alsothe

settling

area

is

increased

by

virtue

of

the

G

force

working

in

360degrees

towardstheoutsideofthebowl.


3/17

CENTRIFUGELIKEAGRAVITYSETTLINGTANK

Gforceisdefinedastheratiobetweenthecentrifugalacceleration

createdinsidethebowlandtheearthgravityaccelerationg=9.81m/s2

Acentrifugeworkslikeagravitysettlingtank,exceptinsteadofoperatingat1G,

thecentrifugeoperatesatseveralthousandGthusreducingthesettlingtime.

TheBowlrotatesat~3000RPM*,andtheScroll/Screwrotatesat~3010RPM,

creatingadifferentialspeedof10RPM(30103000). Thesolidsaremovedoutof

thecentrifugeatthisspeedof10RPM. Theclarifiedliquidcomesouttherearend

ofthecentrifuge,likeinagravitysettlingtank.

TheBowlandScrewRPMSwillvarydependingonthesizeofthecentrifuge. The

differentialspeed

can

be

set

according

the

application,

and

the

desired

retention

time.(thetimethesludgestaysinsidethecentrifugebeforedischarge)

Theliquidoutletlevelissetbyaliquidlevelweirplate.


4/17

EquivalentArea(Ae)

R=bowlradius

L=distance

between

feed

point

and

liquid

outlet

Area=2 R L

Thesettlingabilityindicatesthedecantersettlingcapacity,andiscalculatedas

thesurfaceareaneededforasettlingtanktoachievethesametask.

Centrifugalacceleration

TheangularvelocityisrelativetotheRotationSpeed Thecentrifugalaccelerationisrelativetotheangularvelocityandthediameterofthebowl.(angularvelocityisusuallyexpressedinGforce)

Ac= centrifugalacceleration

=angularvelocity(radians/sec)

n= rotationspeed(rpm)

r = radius

60

2 n

2

rAc


5/17

CENTRIFUGE

HowitWorks

Solidsdischarge:

Thisis

where

the

dewatered

solids

drop.

Normally,

ascrew

conveyorwithavalveoradivertergateispositionedbelowthedischarge. Thisis

becauseforthefirstfewsecondsafterstartup,liquidwillcomeoutofthesolids

dischargeofacentrifuge.

Solidsdeposited:Thesearethesettledsolids. Theyformanannular,360

degree,shapearoundthebowl,andbeingconveyedforwardbythescroll/screw

ofthecentrifugeataraterelativetothedifferentialspeed.

Liquidsdischarge:Thisistheliquidsdischargeendofthecentrifuge,thisliquidisstilldirty,andissentbacktotheheadofplant.Thewaterlooksclearorslightly

trouble,withausualcapturerateof9598%.


6/17

FeedPipe:Thisiswherethesludgeisfed,onesomemachine,thefeedpipeis

ontheotherendofthemachine. Thesludgeisfeduponhalfwaythroughthis

feedpipe,atwhichtimethesludgeisreleasedandbythecentrifugalforce,the

solidssettlealongtheoutsideofthebowl.Thisisadjustableforoptimization.

Clarifiedliquidpond:Thisistheseparatedliquidpartofthecentrifuge,once

theliquidreachestheoutletlevel,theliquidbeginstodischarge.

CylindricalSection:90%ofthedewateringoccursinthissection.

Beach(Conicalsection):Thissectionisdesignedtoexertadditionalforceon

the

solids,

squeezing

out

the

last

drops

of

liquid

as

we

are

not

only

applying

the

centrifugalGforcebutalsopushingthesolidsuphill.Itisdesignedtoelevatethe

solidsabovethewaterlineintothedischargechamber.

Theangleofinclinationcanvaryfrom8to15degreedependingonthesludge

characteristics.

Gearbox:Thecentrifugeisequippedwithadrivesystemcomposedofanelectricmotor,ahydraulicmotor,hydraulicpumpandacyclogearbox.Theelectricmotor

providesthepowerrequiredtoturnthecompleterotatingassemblydrivingthe

drum

directly

and

the

scroll

through

the

hydraulics.

Controlling

the

differential

speedbetweenthedrumandthescrollisPLCcontrolled.ThePLCcontrolsthe

workingcycleaswellastheprotectionincaseoftorqueoverload.


7/17

DECANTERFEEDZONE

PolymerInjection:Thepolymerisusuallyinjectedinlinerightbeforethesludge

feedpumpbeforegoingintothefeedpipe.

FeedZone: Thisis

the

point

at

which

the

solids

are

released

into

the

centrifuge.

BaffleDisc:Thisplateserverstwofunctions.

1. Withoutabaffledisc,theliquidlevelcannotbesethigherthanthesludgedischargelevel. Since,theliquidlevelisoneofthe

factorsindeterminingthecapacityofacentrifuge. Thebaffle

thereforeallowsasmallermachinetodewateralargervolume.

2. TheGforceislowestattheverycenterofthecentrifuge. Thebaffle

disc

allows

the

centrifuge

to

exert

more

pressure

on

the

sludge. Thisisdonebyformingaplug;thecentrifugeis

completelyfilledwithsludgeinthebeachsectionbeyondthe

baffledisc.Withoutthebaffledisc,thiswouldnotbepossibleas

thesludgewouldgotothecenterandtherewouldbenobaffle

disctoprotect. Thisespeciallyhelpswithperformancewith

viscoussludgethathasatendencytosplashbacklikeyoghurt.

With

a

baffle

disc,

if

you

choose

to

set

the

liquid

level

higher

than

the

solids

dischargelevel,thenuponstartupliquidwillcomeoutofthesolidsdischarge

untilaplugisformed. Also,iftheplugislostduringoperation,thesamewill

happenagain. Thisiswhyqualitycontrols,especiallytorquecontrol,areof

utmostimportanceandwhywerecommendahydraulicbackdrive.


8/17

Decanterwithvariabledifferentialspeed

(Hydraulic

back

drive)

DecanterwithElectricBackDrive

DifferentControlRegulation


9/17

Asmentionedbeforetorquecontrolisessentialtooptimal

performance. Hydraulicbackdriveshaveaflatperformancecurve;

electricbackdrivesontheotherhandhaveperformancepeaks,and

dontperformaswelloutsidecertainparameters. Hydraulicare

thereforealwayspreferabletoelectricbackdrives.


10/17

DECANTERREGULATIONANDOPTIMIZATION


11/17

PerformanceOptimizing

Tooptimizetheperformancesetthefollowingparameters:

Q=feedrate d=flocculation =viscosity n=RPM n=differentialspeed (Rr)=Ponddepth

PerformanceOptimizing

Influenceofflocculation,rotationalspeedandfeedrateon

separationefficiency


12/17

CBBBENEFITS

Scroll:wearresistentprotection

WithSolidSteelbarsifthereiswearonthescroll,itcanbefixedwith

aweld. Thehollowsteelbarsthatsomeothermanufacturersuse

cannotbefixedifdamaged,andrequirethecompletereplacementof

thescroll.


13/17

SCRAPER

Solidsbuildupinthesedimentroomisoneofthemajorreasonsthatacentrifuge

stalls.TheCBBcentrifugesareequippedwithaseparatescraperroomand

continuousfullgeared,independentlydrivenlowspeed(5RPM)solidsscraperto

preventthisfromhappening

Thedischargeofacentrifugeisthrownagainstthewallsofthesedimentroom

withaforceover1000G.Normally,thesedimentfallsdownbecauseofgravity,

butwithalumsludgeandotherstickysludges,thesedimentbuildupandclogthe

discharge.

Ifthedischargeisclogged,nosolidscanleavethecentrifuge,andthebowlofthe

centrifugewillfillupcompletely,causingthecentrifugetocometoastop. Itwill

thenbenecessarytoremovethescrollandcleanoutthebowl. Incertain

applications,thismightrequirea30tonpulley.


14/17

Someothermanufacturersalsohaveascraperbutitrunswiththebowl/scroll

assemblywhichresultsinexcessivewearinthescraperbladesandcancause

increaseinlossofbalance. Othersmayuseachaindrivenscrapermotorresulting

insealing

problems

in

the

discharge

chamber.

OurScraperisfullygeared,usesballbearings,andoperatesindependentlyfrom

thebowlandthescroll. ThisfeaturesetsthescraperoftheCBBcentrifugeapart

fromeveryothermajormanufacturer.


15/17

ADJUSTINGTHEWEIRPLATE

Allothermajormanufacturersmakeuseofseveraldifferent

bothersomeweirplatestochangeliquidlevels. Theseareusually

halfcrestmoonsthataredifficulttochangeandareoftenlostin

storage.

CBBonlymakesuseofoneplate. So,whentheliquidlevelsdoneed

changingtheplateisexactlywhereyouneedit,onthemachine.

ChangingtheliquidlevelsisalsoeasierontheCBBbecauseofthe

threesectionhingedcover,whichprovidedquickandeasyaccessto

theweirplate.


16/17

IntegratedHydraulicReservoir

Oneofthebiggestconcernswegetfromoperatorsinregardsto

hydraulicbackdrivesisthelocationandconnectionofthehydraulic

tank.Typicallyahydraulicunitisplacednexttothecentrifugeswith

thehydrauliclinesrunningonthegroundtothecentrifuge.

CBBhasaddressedthisissuebysimplyusingthelegsofthecentrifuge

ashydraulictank.Thisreducesthefootprintofthecompletesupply,

and

removes

any,

potentially

unsafe,

connection

lines

lying

around.

IneffectCBBoffersazerofootprinthydraulicbackdrive.


17/17

DISCHARGEBUSHINGREPLACEMENT

Thedischargebushingsareveryeasytoreplaceduetoourthree

sectionhingedcoverandtheuseofstandardtools.

Wecanalsorotateourdischargebushingstogetmorelifeoutof

them.Thewearonthebushingsisalwaysonthesameside,sosimply

rotatethebushinginplace1/4turntogainupto4timesmorewear

life.

Documents

decanter centriguge