Kraft Pulping and Recovery Process basics

1 basics of Kraft Pulping & Recovery ProcessArt J. Ragauskas Art J. Ragauskas Institute of Paper Science and TechnologyInstitute of Paper Science and TechnologyGeorgia Institute of TechnologyGeorgia Institute of TechnologyOutline History Goals Process Overview Kraft Pulping Process Kraft Recovery Power Plant Caustic PlantHistory 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 Pulping and Recovery :Overall Objectives Chemical convert wood into cellulosic pulp High quality, strong pulp for papermaking Operate safely Minimize impacts on air and water Satisfy customer needs Maximum product quality Minimize costKraft Pulping Objectives Use chemicals, heat, pressure to liberate fibers.

2 Operate safely. Minimize impacts on air and water. Satisfy customer needs - maximum product quality. Minimize 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 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 Kraft Pulping and Recovery ProcessDale Proctor, 2003 Process Proctor, 2003 The Kraft Pulping and Recovery Process Flow DiagramPower PlantCaustic PlantPulp MillBlack LiquorGreen LiquorWhite LiquorThe Kraft Pulping and Recovery Basic Process FlowPulp MillDale Proctor, 2003 White Liquor NaOH Na2 SPulp Mill Cooking WashingBlack LiquorTurpentinepulpRaw MaterialStructure of Wood FibersLumenPS1S2S3 Middle LamellaChemical Structure of FibersOOHOOHOOHOOHOHOOHOOHOOHO-XylanOn.

3 100 - 200 Substituted withOH3 COHOOHOHO2 COCH325 35 %Extractives2 8 %OOCH2 OHOCH3 OOHH3 COCHOHCH2CH2 OHH3 COOHOHOH3 COHOOHOH3 COOHOHOH3CO20-30 %OHHOHHOHHOHHHOOHHHOHHOHHOHOOHOHHOHHOHHO HOOHHHOHHOHHOHHOn40 47 %Physical Structure of FibersCellulose embedded in lignin hemicellulose Yields0 kg5 kg20 kgHemicellulose40 kg45 kgCellulose5 kg30 kgLignin50% Yield KraftPine WoodChip Quality Hardwood vs. Softwood Wood Density Roundwood vs. Chips SMC ThinningsJuvenile(8 12)MatureChip Storage Manage Chip Pile By-Products Acid Hydrolysis YieldChip PreparationChips RoundwoodChip ScreensMagnetPulp MillRechipperSlasherBarking DrumChip Storage ChipperLong-woodBoilerKraft PulpingDale Proctor, 2003 White Liquor NaOH + NaSH Dissolve & Fragment Lignin Peeling and Chain Scission of PolysaccharidesPower PlantCaustic PlantPulp MillBlack LiquorGreen LiquorWhite LiquorKraft ChemistryNaOH + Na2S + H2O 3Na+ + 2OH-+ SH-NaOH Na+ + OH-Na2S 2 Na+ + S2-S2-+ H2O SH-+ OH-Na2CO3 Dale Proctor, 2003 Kraft PulpingDale Proctor, 2003 Digesters Batch and Continuous Reactors Dissolve & Fragment Lignin 341-350 F 105-120 psi pH 12-14 Kraft PulpingBlow TankWashersEvaporators ( Recovery )

4 KnottersScreens/CleanersDigesterWhite LiquorChip Feed SystemBatch Digesters 20+ ft. Height 10 15 ft. Diameter Carbon Steel Pressure VesselBatch DigestersChip ChuteLocking PinLiquor Top OffLevel & Pressure SensorsBlowlineTemperature ProbesCapping ValveGasoff VentWhite and Black LiquorContinuous Digesters: Chip Feed System Pressurized Feed SystemLow Pressure FeederHigh Pressure FeederTop SeparatorChip BinSteaming VesselInline DrainersImpregnation ZoneChip ChuteWhite LiquorContinuous Digesting System Carbon Steel Pressure Vessel 200 250 ft DeviceBlow TankCold BlowHeating Zone ScreensCooking ZoneExtractionZone ScreensWashing & Cooling ZoneFlashTankLiquor to EvaporatorsFlash Steam to SVLiquor HeatersPulp PreparationBlow TankKnotters Counter CurrentWashers Screens/Cleaners Chip BinPulp StorageLiquor from First Stage to EvaporatorsLiquor from Later Stages to Shower EarlierHot Water to Final Washing Stage ShowerKraft Chemistry Extractives Dissolved Turpentine Tall OilExtractivesDigester ReliefBlack LiquorCondensersCyclone Separators

5 StorageDecanterThe Kraft Pulping and Recovery Process Flow DiagramPower PlantCaustic PlantPulp MillBlack LiquorGreen LiquorWhite LiquorPower Plant Kraft Recovery Black Liquor Evaporation Recovery BoilerBlack Liquor from Pulp Mill Washer Filtrate & Flash TankRecover BoilerGreen Liquor to Caustic PlantConcentratedBlack LiquorSmelt DissolvingTankKraft Power PlantBlack LiquorOxidation??Concentrator or Direct Contact EvaporatorKraft Multiple Effect EvaporatorsWeak Black Liquor SteamFlashTankConcentrated Liquor TankSoap SkimmerThe Kraft Recovery Boiler Recovery Boiler Water Evaporation Burns Organics Steam Reduces Oxidized Sulfur Compounds Recovers Inorganics as SmeltKraft Recovery BoilerDale Proctor, 2003 Green Liquor Na2CO3 Na2 SPower PlantCaustic PlantPulp MillBlack LiquorGreen LiquorWhite LiquorThe Kraft Recovery BoilerBlack LiquorMix TankConcentrated BL from ConcentratorSalt CakeLiquor HeaterPrecipitatorDissolvingTankSteamFor ced Air FanAir HeatersSmelt SpoutsWaterwallsBoiler BankFlue GasSmeltPrimary AirSecondary AirBlack LiquorSuperheater and ScreenEconomizersDissolvingTankPrecipita torEconomizerBoiler SectionSuperheaterFurnace WallScreenHot Combustion GasBoiler Feed WaterPrecipitatorTurbinesThe Kraft Recovery BoilerOxidizingDryingReductionThe Kraft Recovery BoilerOxidationNa2S + 3/2 O2 + CO2 Na2CO3+ SO2 PyrolysisNa2S+ H2O+ CO2 Na2CO3+ H2 SReductionNa2SO4 + 2C Na2S + 2CO2Na2SO4+ 4C Na2S + 4 COThe Kraft Pulping and Recovery Process Flow DiagramPower

6 PlantCaustic PlantPulp MillBlack LiquorGreen LiquorWhite LiquorThe Kraft Pulping and Recovery Process Flow DiagramSmelt - Na2CO3Na2CO3 + Ca(OH)2 NaOH (Caustic) + CaCO3 (Lime Mud)CaO + H2O Ca(OH)2 (Slaked Lime)CaO (Lime)SlakerThe Kraft Chemical Recovery Process Flow DiagramPulp MillThe Kraft Caustic Plant Process Flow DiagramDregs Washer or FilterSlakerCausticizersGreenLiquor ClarifierWhite Liquor ClarifierMud WasherFilterLime SiloKilnSafety Pulp Mill - Acid Cleaning Digester, Liquor Heaters, Inline Drainers Power Plant - Smelt Water Explosions Caustic Plant - Gas in KilnEnvironmental Concerns Water Acid Cleaning Liquor Spills Air You!