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1、Chapter7Thermomechanicalpulpingtheshortretentiontimeatthetemperaturepeakintherefiningzone.Thisshortretentioniscausedbythehighcentrifugalforceinhigh-speedoperations.Table8givessomepulppropertiesfromthefirstcommercialRTSoperation.Theoperatingexperiencesuggeststhatanene
2、rgyreductionintheorderof15%ispossibleusingthissystem.Table8.RTSTMPpropertiescomparedtohigh-speedTMP.Firstrefiningstageusinga2300rpmAndritzTwinTC66refinerandsecondstageusinga1500rpmAndritzSB150refiner28.ProcessHigh-speedTMPRTSTMPEnergyconsumption,MWh/t1.841.85Freeness
3、,ml9694Breakinglength,km3.523.74Tearstrength,cNm/m129144Brightness,%55.755.5Lightscatteringcoeff.,m2/kg60.958.87.6.8.3ThermopulpTheSundsDefibratorThermopulpprocess(Fig.33)hastworefiningstages.Intheprimarystage,refiningiscarriedoutbelowthesofteningtemperatureofligninb
4、ut,inthesecondaryrefining,temperatureandpressureareraisedto160°C−170°Cand600−700kPa.Thehighpressureincreasestherefiningintensitybycompressingthesteaminthegapwhichreducestherefinergapclearance.Inordertomakefiberslessbrittletowithstandthehighrefiningintensity,temperatu
5、reoffibersisraisedto160°C−170°CbeforeenteringtheThermopulprefining.Dynamictestingofwoodsamplesindicatesthatthebreakdownofwoodfibersismoreefficientathighertemperatures29.IntheThermopulpsystem,thedistributionofrefiningenergyisfocusedonthesecondaryrefiningstage,wherethe
6、higherrefiningintensityenablessavingsofoverallrefiningenergy.InmillscaleThermopulprefiningtrials,10%−20%energysavingscomparedtoconventionalTMPhavebeenreached36.Table9showsacomparisonofTMPandThermopulppropertiesinaNorthAmericanmill.Table9.MillcomparisonofThermopulpand
7、standardtwo-stageTMP.ThepulpsamplesarecollectedafterthemainlineRGP76CDrefiners.ProcessTMPThermopulpFreeness,ml180160SEC,MWh/t2.151.75Tensileindex,Nm/g37.537.1Tearindex,mNm2/g9.89.6Lightscattering,m2/kg54.354.8Brightness,%55.154.5Theretentiontimeoffibersattheelevatedt
8、emperatureiskeptshort(afewsecondsonly)inordertoavoidbrightnesslossofpulp.Inadditiontoreducedbrightness,toohighatemperaturealsoincre
