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1、MECHANISMS OF LO-SOLIDS PULPING: EFFECT OF FIBRE WALL DISORDERJOHN A. LLOYD, ROBERT W. ALLISON, JIAN ER JIANG AND BRUNO S. MARCOCCIA 1998 Tappi Pulping ConferenceIntroductionHigh Dissolved Solids in kraft pulping: -increases alkali consumption -decreases pulp brightness and bleachability -lowers fin
2、al pulp strength2IntroductionLo-Solids process developed by Ahlstrm Machinery -easy retro-fit to continuous digesters-exchange spent impregnation stage liquor with wash filtrate + white liquor -lower DS in bulk and final phases3Continuous DigesterWhite Liquor Wash Filtrate4Lo-Solids MechanismDiffusi
3、vity differences in ordered vs disordered regions of cell wall Over-pulping in disordered regions -faster diffusion of OH- in &DS out -less 2 reactions with organics -greater OH- Weak points created along fibre Effect exacerbated by high DS5Concentration GradientsOrderedDisorderedRelative Concentrat
4、ion100%0%Cell WallBulk Liquor100%0%Dissolved Solids6Concentration GradientsOrderedDisorderedRelative Concentration100%0%Cell WallBulk Liquor100%0%OH-7Concentration GradientsOrderedDisorderedRelative Concentration100%0%Cell WallBulk Liquor100%0%Dissolved Solids8Concentration GradientsOrderedDisordere
5、dRelative Concentration100%0%Cell WallBulk Liquor100%0%OH-9Study ObjectivesEvidence to support Marcoccia hypothesis -increase proportion of disorder ?use chipper damaged chips -pulp with high and low solids liquors -measure pulping response ?look for greater DS effect10Experimental ApproachSplit tec
6、hnical chips (high &low density)DamagedUndamagedChipperBladeLog- Whole- Undamaged- Damaged11Experimental ApproachContinuous digester simulation -Mill liquors with high dissolved solidsLiquorEA g/LSulfidity %Total Solids g/L Feed42.539.0 52 U pper C irc.20.945.5 96 Low er C irc.19.246.7108 Extraction
7、11.164.2142 W ash Filtr. 0.964.0 5412Experimental ApproachRepeat continuous digester simulation -lab liquors with low dissolved solids -prepared from fresh NaOH and Na2S -similar EA and sulfidity as mill liquors Pulping with mill liquors normal DS Pulping with lab liquors very low DS13Laboratory Sys
8、tem14Laboratory SystemA1A3A2Central digesterChipsHeat exchangerCirculation pumpMetering pumpsAccumulatorsMP1MP215Pulping ResponseAlkali profile Pulping rate Total yield Brightness/bleachability16Effective Alkali Profile0102030400246Cooking Time, hrEA, g/LLab LiquorsA BCDEMill Liquors17Pulping RateCh
9、ip TypePulpingKappa Number LiquorRangeMean Low DensityMill22-2522.6 Lab18-2018.5 High DensityMill20-2321.3 Lab1817.918Pulping Yield4244464850161820222426Kappa NumberTotal Yield, %WholeUndamagedDamagedHigh DensityLow Density19Unbleached Brightness 500 PFI revs05101520253035Low DensityHigh DensityMill
10、 Lab20Bleachability D0.35ACMED1%ClO2808182838485868788Low DensityHigh DensityMill Lab21Fibre PropertiesCarbohydrate composition Fibre length Fibre dimensions Fibre deformations Fibre wall lignin content22Carbohydrate CompositionWRO1286.doc2 23/04/98Liquor TypeCell. GGM Axylan g/100g pulpHemi:Cell Ra
11、tioLow DensityMill79.58.59.50.23Lab80.89.87.20.21High DensityMill81.78.46.90.19Lab83.58.75.30.1723Carbohydrate RetentionWRO0001.doc1 25/05/98ChipLiquorCelluloseGGMAxylan Type% retained during pulpingLow densityMill962458 Lab942742 High densityMill962364 Lab96234924Fibre LengthWRO0001.doc1 25/05/98Ch
12、ip TypeFibre Length (mm)Ave LWFLLow DensityUndamaged0.771.26Damaged0.781.28 High DensityUndamaged1.672.43Damaged1.542.2925Fibre Dimensions Undamaged chipsWRO2678.doc1 25/05/98Chip TypeLiquorWall Area (m2)Wall Thick. (m)Fibre Perimeter (m)Collapse PotentialLow densityMill1982.9986.43.11 Lab1642.5581.
13、43.48 High densityMill2603.7493.02.21 Lab2753.7996.22.28 LSD(95%) 150.16 3.60.1926Fibre Deformations Low densityChip TypeLiquorFibre Wall Dislocations (#/mm)Curl Index UndamagedMill 3.1 89 Lab 4.9132 DamagedMill 6.4 86 Lab 5.6108 LSD(95%) 2.1 1327Fibre Deformations High densityChip TypeLiquorFibre W
14、all Dislocations (#/mm)Curl Index UndamagedMill 8.9 89 Lab15.1126 DamagedMill14.8109 Lab19.9 91 LSD(95%) 2.1 1328Fibre Wall KinkDistance, mmGrey Scale50100150200250010203040506029Fibre Wall Dislocation5 01 0 01 5 02 0 001 02 03 04 05 06 0d is t a n c e ( m )grey scale Distance, mmGrey Scale30Pulp St
15、rengthViscosity-kappa relations WZSTI Tear-tensile relations Other handsheet properties31Pulping Selectivity2630343842161820222426Kappa NumberViscosity, mPa.sLab LiquorsMill LiquorsWholeUndamagedDamaged32Wet Zero Span Tensile IndexWRO3388.doc1 25/05/98Chip TypeWZSTI, Nm/g Lab Liquor Mill LiquorDiffe
16、rence %Low DensityUndamaged1031012Damaged 98 944 High DensityUndamaged1531456Damaged151138933Tear-Tensile Relations0510152025303540405060708090100110Tensile Index, N.m/gTear Index, mN.m2/gU D /lab U D /m ill D /lab D /m illHigh densityLow densityUndam, Lab Undam, Mill Dam, Lab Dam, Mill34Tear at Constant TensileWRO0003.doc1 24/04/98Chip TypeLab
