Kadant S23-2 Screw Press – SOLD!

KadantS23-2TaperedScrewDewateringPress Max176F/80C SSwithMotorandGearbox 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