Kadant S23-2 Screw Press – SOLD!

KadantS23-2TaperedScrewDewateringPress

MaxHP:15

MaxSpeed: 30RPM

Serial:S23-2-002

Max176F/80C

SSwithMotorandGearbox 

Built:04/2012 

Principleofoperation 

TheKADANTS23-2ScrewPressthickenspulpfromafeedconsistencyof3%to4%toadischargeconsistencyof30%.Thepulpisfedintotheinletchamberandisconveyedtothedischargeopeninglocatedatthebottomofthedischargechamber.

Thescrewshaftturnsinsidetwocylindricalscreenbaskets.Eachbasketconsistsofasupportingbackingshellwithadrainagescreeninstalledineachofthebasketsections.Thewaterdrainedfromthepulpflowsbetweenthescreenplateandthebackingshellofthebasket.Thewateriscollectedatthebottomofthebasketandgoestoafiltratecollector.

Thevolumeavailableforthepulpdecreasesgraduallyasthepulpmovesforwardtowardthedischargeend.Thepulpisthereforesubjectedtoanincreasingpressureasitadvancesinthepresscausingthewatertodrainthroughtheperforatedscreenplatethusincreasingthepulpconsistency.Thepulpisretainedinsidethepressbythescreenswhilethewaterpassesthroughtheopeningsofthescreens. 

Thelastflight(spiral)ofthescrewendsbeforetheplugsleevewhichallowsfurtherthickeningofthepulpandformingofaplug.Thisplugalsoservestoisolatethedischargechamber.

Table1:         Parametersofoperation

Thereareotherfactorsthatcanhaveaneffectintheperformanceofthepress.Achangeinthetypeofwood/fiber,inthestoringtimeoramodificationoftheprocess(chemistry)caninfluencetheoperationofthepress.Shortfiberbuildupsonthewhitewaterwillalsoaffectthecapacityofthepress.

3.5.1   Speed

Thespeedofthescrewpress(inRPM)istheparameterthathasmostinfluenceonthecapacityandthedischargeconsistencyofthepress.

Withamechanicaldrive(fixspeed)itispossibletochangethespeedbymodifyingthegearratio.Fordifficultapplications,itisrecommendedtouseavariablespeeddrive.Thedrivecanbemechanicalorhydraulic.

Ingeneral,thespeedisadjustedtoobtaintherequireddischargeconsistency.Thespeedmustbereducedtoincreasetheconsistency.Ifthecapacityofthepressisnotsufficient,thenacompromisemustbedonebetweencapacityandconsistency.

3.5.2   Feedconsistency

Dependingofthetypeofpulpandtherequiredperformance,thecomfortablespanforthefeedconsistencyisbetween3%and8%.

Alowfeedconsistencywillreducethecapacityofthepressandthedischargeconsistency.

Theeasierthepulpistodrain,thelowerthefeedconsistencycanbeforacertainproductionrateordischargeconsistency.

Formostapplications,thefibercontentofthefiltrateishigherwhenthefeedconsistencyislower.

Ifpossible,atstart-ups,itisrecommendedtomakearecirculationofthepulpuntiltheconsistencyisstablebeforeopeningthefeedvalve. 

3.5.3   Feedpressure 

Thefeedpressureshouldneverexceed20psi(140kPa).Thebestresultsareobtainedunder5psi(35kPa).

Atoohighfeedpressureinmostcaseswillpushthefibers(particularlytheshortones)throughthescreenopenings.Thiswillcauseahighfiberlossinthefiltrate.Itisthereforeveryimportanttokeepthefeedpressureaslowaspossiblefortherequiredproductionrate.Rememberthatthepulpgoingtothefiltratemustbesubtractedfromtheproductionrate…

Incertaincases,highfeedpressurecanplugthefirstscreenandreducedrasticallythecapacityofthepress.

Insomecase,thepulpgoesdirectlytothedischargeendwithoutformingaplugonthethroatofthepress(seesection3.9.2).Thiscanindicatethatthefeedpressureistoohigh,thatthechemicalsareunbalanced(pH)orthatthepresshasreacheditsmaximumcapacity.Inthiscase,thefeedvalveshouldbeusedtodecreasethefeedpressure(andatthesametimetheflowrate)untilthepressformsaplug. 

Thefeedpressureshouldbelimitedtoamaximumof10psi(70kPa).Abovethisvaluethereshouldbeanalarm.Theopeningofthefeedvalveshouldbereducedautomaticallywhenthefeedpressureapproaches15psi(100kPa)toavoidlosingthepulpinthethroatofthepressandtopreventsealingthescreens.Above20psi(140kPa),thefeedvalveshouldbeclosedcompletelytoavoiddamagingthepress. 

3.5.4   Freeness(CSF)

TheperformanceofthepressisaffectedbytheFreenessofthepulp.ThehighertheFreeness,theeasieritwillbetoobtaintherequireddischargeconsistency.Thisallowsthepresstoberunatafasterspeedandtoincreasethecapacityofthepress. 

Ingeneral,themaximumspeedofthepress(anditscapacity)reduceswhentheFreenessreduces. 

ThequantityoffibersinthefiltrateincreaseswhentheFreenessreduces.Tocompensate,thefeedpressurecanbereduced.Thiswillinturnreducethecapacityofthepress. 

3.5.5   Temperatureofthepulp

Toolowapulptemperaturecanhaveanegativeeffectontheperformanceofthescrewpress.Anincreaseofthepulptemperaturewillnormallyimprovethedrainagecharacteristicsofthepulp.Itisthenpossibletoincreasethecapacityofthepressaswellasthedischargeconsistency.

MaxCapacityis25TPD 

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