chemical pulping（下）

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1、Chapter7Pulpwashingapplicationssurfaceofthedrumtogenerateaninsidenip.Naturally,thepressalsohasasystemforfeedingwashliquidtotheinsideofthedrumandamethodforcirculatingthefiltratesinacountercurrentflow.7.5.3.2OperatingprincipleTheoperationalcharacteristicsoftheWMpulpwashpresscomefromi

2、tslonginsidenipanditsabilitytoperformmultiplewashingsandcirculatethefiltratesinacountercurrentmanner.Figure32.OperatingprincipleofaWMwashpresscomparedwithatwinrollpress(AhlstromMachinery).AsFig.32shows,thescreendrumandthepressrolllocatedeccentricallyinsidethedrumformthelonginsideni

3、pwhichyieldshigherfiltrateflowsperrevolutionthanashortnipbetweentworollsofequalsize.InaWMpress,thechamberformedbetweenthedrumandtherollsinsideitnarrowsgraduallyintoathinnip.Thisallowsuseofalargeportionofthedrumsurfaceasafilteringandpressingzone.Theareaincreasesevenfurtherifthefilte

4、rispressurefedtogiveapositiveover-pressuregeneratedbythein-feedpumptothechamberformedbythedrum,itsendplateintheentranceend,andthedrypulpmatintheexitend.Thepressureinthischamberdrivesfiltratesoutthroughthescreendrumalmostalongitsentireperimeter.Thisgivesalargedewateringsurface.Thepu

5、lpfeedisnormally4.5%−10%consistencybetweenthepressrollandtheperforatedscreendrum.ThepulpmatmovesforwardinthedruminaspiralorbitaroundthepressrollandispressedeverytimeitgoesundertherollasFig.33shows.Thepressureofthepulppumpedintothedrumandasetofstationaryguideplatesmountedtothedoctor

6、bladeofthedrumgeneratetheforwardmotion.Thepulpfallsfreelyfromthedischargeendofthedrumtothedilutionscrewortothedilutiontank.Thewashfiltrategoesbetweenthepressrollandthepulpmatthroughaknife-likedevicemountedaxiallyontopofthepressroll.Thisdevicehasinternalchannelstoprovideseparatewash

7、filtratefeednozzlesforeachstage.Thewashfiltrategoestothepulplayerbetweenthepressrollandthepulpmat.Thewashfiltrateisthenpressedoutthroughthepulpmatandtheperforationsofthedrum.Thedirtierliquorispressedoutfirstbeforethewashfiltrate.Thefiltrateretainedinthepulpmatisthereforeprimarilywa

8、shedfiltrate.Thewashingisa