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Basics of KraftPulping & Recovery ProcessArt J. RagauskasInstitute of Paper Science and TechnologyGeorgia Institute of Technology
Outline HistoryGoalsProcess OverviewKraft Pulping ProcessKraft Recovery– Power Plant– Caustic Plant
History Soda pulping process patented, 1854. Soda recovery via incineration patented,1865. First successful soda mill, 1866. Kraft pulping process patented by Dahl, 1884. First commercially viable kraft mill, Sweden,1885. Kraft recovery furnace, 1930’s.
Kraft Pulping and Recovery:Overall ObjectivesChemical convert wood into cellulosic pulpHigh quality, strong pulp for papermakingOperate safelyMinimize impacts on air and waterSatisfy customer needs– Maximum product quality Minimize cost
Kraft Pulping Objectives Use chemicals, heat, pressure to liberatefibers. Operate safely. Minimize impacts on air and water. Satisfy customer needs - maximum productquality. Minimize cost.
Kraft Recovery Objective Concentrate and burn black liquor.– Provide energy produced from organics.– Provide partially reconstituted pulping chemicals. Operate safely.Minimize impacts on air and water.Satisfy customer needs, product quality.Minimize cost.
Kraft Caustic Plant Objective Final step in reconstituting pulping chemicals.– Provides fresh cooking liquor.– Regenerates lime from lime mud. Operate safely.Minimize impacts on air and water.Satisfy customer needs, product quality.Minimize cost.
The Kraft Pulping and RecoveryProcess Process overview.Dale Proctor, 2003
Dale Proctor, 2003
The Kraft Pulping and RecoveryProcess Flow DiagramPulp MillWhiteLiquorBlackLiquorCaustic PlantPower PlantGreenLiquor
The Kraft Pulping andRecovery Basic Process FlowPulpMillPulp Mill Cookingpulp WashingWhite LiquorBlack Liquor NaOHTurpentine Na2SDale Proctor, 2003
Raw Material
Structure of Wood FibersPS1S2S3LumenMiddle Lamella
Chemical Structure of HOOHHHHHOHOn40 – 47 %25 – 35 : 100 - 200H3COOHO-XylanOHOHSubstituted withOHHOOOCH320-30 %CH3
Physical Structure of FibersCellulose embeddedin lignin –hemicellulose matrix.
Kraft YieldsPine WoodLignin30 kg50% YieldKraft5 kgCellulose45 kg40 kgHemicellulose20 kg2.5 kgExtractives5 kg0 kg
Chip Quality Hardwood vs.Softwood Wood Density Roundwood vs.Chips– SMC– ThinningsJuvenile(8 – 12)Mature
Chip Storage Manage Chip Pile– By-Products– Acid Hydrolysis– Yield
Chip mChipperChip StorageChipScreensBoilerMagnetPulp MillRechipper
Kraft Pulping White Liquor– NaOH NaSH– Dissolve & FragmentLignin– Peeling and ChainScission ofPolysaccharidesDale Proctor, 2003Pulp MillBlackLiquorWhiteLiquorCaustic PlantPower PlantGreenLiquor
Kraft ChemistryNaOH Na OHNa2S 2 Na S2S2- H2O SH- OHNaOH Na2S H2O 3Na 2OH- SHNa2CO3
Kraft Pulping Digesters– Batch and ContinuousReactors– Dissolve & FragmentLignin– 341-350ºF– 105-120 psi– pH 12-14Dale Proctor, 2003
Kraft PulpingWhiteLiquorChipFeedSystemBlow tors(Recovery)
Batch Digesters 20 ft. Height 10 – 15 ft. Diameter Carbon Steel Pressure Vessel
Batch DigestersChip ChuteLocking PinLiquor Top OffLevel & PressureSensorsBlowlineCapping ValveGasoff VentTemperatureProbesWhite and BlackLiquor
Continuous Digesters: Chip FeedSystem Pressurized Feed System
Chip BinTopSeparatorLow Pressure FeederImpregnation ZoneSteaming VesselChip ChuteHighPressureFeederWhiteLiquorInline Drainers
Continuous Digesting System Carbon Steel Pressure Vessel 200 – 250 ft Height.
Liquor HeatersFlashTankHeatingZoneScreensFlash Steam to SVCookingZoneLiquor to EvaporatorsExtractionZoneScreensWashing& CoolingZoneBlow TankOutlet DeviceCold Blow
Pulp PreparationHot Water toFinal WashingStage ShowerBlow TankKnottersChip BinLiquor fromLater Stages toShower EarlierCounterCurrentWashersScreens/CleanersLiquor fromFirst Stage toEvaporatorsPulp Storage
Kraft Chemistry Extractives– Dissolved– Turpentine– Tall Oil
ExtractivesDigester ReliefCycloneSeparatorsBlack LiquorCondensersDecanterStorage
The Kraft Pulping and Recovery ProcessFlow DiagramPulp MillWhiteLiquorBlackLiquorCaustic PlantPower PlantGreenLiquor
Power Plant Kraft Recovery– Black Liquor Evaporation– Recovery Boiler
Kraft Power PlantBlack Liquor from Pulp MillWasher Filtrate & Flash TankBlack LiquorOxidation?GreenLiquor toCausticPlantSmelt DissolvingTankConcentratedBlack LiquorConcentratoror DirectContactEvaporatorRecoverBoiler
Kraft Multiple Effect EvaporatorsWeakBlackLiquorSteamFlashTankSoap SkimmerConcentrated Liquor Tank
The Kraft Recovery Boiler Recovery Boiler– Water Evaporation– Burns Organics– Steam– Reduces Oxidized Sulfur Compounds– Recovers Inorganics as Smelt
Kraft Recovery Boiler Green LiquorPulp Mill– Na2CO3– Na2SBlackLiquorWhiteLiquorCaustic PlantPower PlantGreenLiquorDale Proctor, 2003
The Kraft Recovery BoilerPrecipitatorConcentrated BL from ConcentratorSalt CakeBlack LiquorMix TankLiquor HeaterSteamDissolvingTank
PrecipitatorSuperheater and ScreenEconomizersFlue GasWaterwallsBoiler BankForced Air FanSecondary AirAir HeatersBlack LiquorSmelt SpoutsPrimary AirSmeltDissolvingTank
The Kraft Recovery BoilerBoiler FeedWaterHot Combustion GasPrecipitatorEconomizerFurnace WallBoilerSectionScreenSuperheaterTurbines
The Kraft Recovery BoilerOxidationNa2S 3/2 O2 CO2 Na2CO3 SO2OxidizingPyrolysisNa2S H2O CO2 Na2CO3 H2SReductionDryingReductionNa2SO4 2C Na2S 2CO2Na2SO4 4C Na2S 4CO
The Kraft Pulping and RecoveryProcess Flow DiagramPulp MillWhiteLiquorBlackLiquorCaustic PlantPower PlantGreenLiquor
The Kraft Pulping and RecoveryProcess Flow Diagram
The Kraft Chemical RecoveryProcess Flow DiagramCaO (Lime)SlakerSmelt - Na2CO3CaO H2O Ca(OH)2 (Slaked Lime)Na2CO3 Ca(OH)2 NaOH (Caustic) CaCO3 (Lime Mud)Pulp Mill
The Kraft Caustic Plant ProcessFlow DiagramGreenLiquor ClarifierSlakerCausticizersDregsWasher orFilterWhiteLiquor ClarifierFilterLimeSiloKilnMud Washer
Safety Pulp Mill - Acid Cleaning– Digester, Liquor Heaters, Inline Drainers Power Plant - Smelt Water Explosions Caustic Plant - Gas in Kiln
Environmental Concerns Water– Acid Cleaning– Liquor Spills Air– Stacks
arthur.ragauskas@ipst.gatech.edu
Thank You!
History Soda pulping process patented, 1854. Soda recovery via incineration patented, 1865. First successful soda mill, 1866. Kraft pulping process patented by Dahl, 1884. First commercially viable kraft mill, Sweden, 1885. Kraft recovery furnace, 1930's.
