2-1 Recausticizing - Principles & Practice

1 1 TAPPI KRAFT RECOVERYSHORT COURSERECAUSTICIZINGCHAPTER - Principles AND PRACTICEBYDALE SANCHEZVECTOR PROCESS EQUIPMENT BASIC CHEMISTRY FLOWSHEET OPTIONS GREEN LIQUOR PREPARATION WHITE LIQUOR PREPARATION LIME MUD WASHING CONTROLS2 LIME KILNLIME MUDWASHINGWEAK WASHLIMEMUDWATERWHITELIQUORCLARIFICATION LIME MUDWHITE LIQUORSMELTDISSOLVINGSMELTFROMRECOVERYBO ILERGREENLIQUORCLARIFICATIONDREGSSLAKER/ CAUSTICIZERSLIMEGREENLIQUORGRITRECAUSTIC IZING CYCLEBASIC CHEMISTRYGREENLIQUOR+LIMEWHITELIQUORLIME MUD=+Na2CO3+ H2O + CaO = 2 NaOH + CaCO33 CHEMICAL REACTIONS SLAKINGCaO + H2O Ca(OH)2+ Heat CAUSTICIZINGCa(OH)2 + Na2CO3 2 NaOH + CaCO3 OVERALL REACTIONNa2CO3 + H2O + CaO 2 NaOH + CaCO3 EQUILIBRIUM REACTION REVERSIBLE INCOMPLETE4 REACTION AT SOLID/ LIQUID INTERFACEUNREACTEDCORENa+CO3=OH-CaOCaCO3 DEFINITIONSTTA = TOTAL TITRATABLE ALKALINaOH + Na2S + Na2CO3AA = ACTIVE ALKALINaOH + Na2S EA = EFFECTIVE ALKALINaOH + Na2S SULFIDITY %Na2S / AA or Na2S / TTA5 DEFINITIONSCE = CAUSTICITY %NaOH x 100 NaOH + Na2CO3 Lime Availability %CaO / Kiln ProductNote.

2 All chemical concentrations are expressed on a Na2O basis TTA = 120 g/l as Na2 OOther units of measure are lb/ft3& lb/galOPERATING CAUSTICIZING EFFICIENCY7580859095100105050100150200 TTA g/l% C ESULFIDITY=0%SULFIDITY=15%SULFIDITY=30%O PERATING CE5%6 FREE CaO vs CAUSTICITY0123456770758085% CAUSTICITY% FREE LIMEFLOWSHEETWITH CLARIFIERSS melt TankGreen LiquorClarifierDregs FilterSlaker /CausticizersWhiteLiquorClarifierLime MudWasherLime KilnWhite LiquorWeak WashWaterLime Mud FilterLimeGreen LiquorStabilization7 Smelt TankGreenLiquorClarifierDregs FilterSlaker / CausticizersLime KilnWhite LiquorWeak WashFLOWSHEET WITH PRESSURE FILTERSW aterLime Mud FilterPressure FiltersLimeGreen LiquorStabilizationWaterSmelt TankGreen LiquorClarifierDregs FilterSlaker /CausticizersLime KilnWhiteLiquorWeak WashFLOWSHEET WITH PRESSURE DISC FILTERW aterLime Mud FilterPressure Disc FilterLimeGreen LiquorStabilizationWater8 GREEN LIQUOR PREPARATIONS meltWeak WashSmelt DissolvingTankStabilizationTankClarifier Dregs Holding TankDregs FilterClarifiedGreen LiquorVariation in Green Liquor Density or Temperature in Stabilization TankTimeDensity or Temperature InletOutlet9 OPTIONAL SIDEMOUNT AGITATORINLET PIPEDOWN COMERRAW GREEN LIQUORTOP MOUNTED AGITATORPUMP TO GREEN LIQUORCLARIFIERRAW GREEN LIQUOR STABILIZATION TANKGREEN LIQUOR CLARIFICATION OPTIONS SEDIMENTATION CLARIFIERS PRESSURE FILTERS CROSS FLOW FILTERS SOCK TYPE FILTERS10 GREEN LIQUOR CLARIFIERFEEDWELLSTORAGE ZONEMAX LLMIN LLCLARIFIEDLIQUOR OUTCLARIFIERFEEDUNDERFLOW OUTRAKE DRIVECLARIFICATION ZONECLARIFIER INTERNALSP hoto courtesy of Dorr-Oliver Eimco11 Clean Green Liquor!

3 Clarifier FeedClarified Green LiquorPhoto courtesy of Dorr-Oliver EimcoGREEN LIQUOR CLARIFIER PROBLEMSDIRTY GREEN LIQUOR Clarifier too small (rise rate too high) Properly designed internal components Use of Contaminated condensate Lack of Stabilization tank Settling aid addition problem (Polymer)12 DREGS PRECOAT FILTERP hoto courtesy of Dorr-Oliver EimcoDREGS FILTER OPERATIONAL PROBLEMS Wet cake discharge High soda loss Difficulty forming a precoat13 ClarifierWHITE LIQUOR PREPARATIONG reen Liquor LimeWhite LiquorLime MudLime SlakerCausticizersGritLIMEGREEN LIQUORAGITATORTO VENT SCRUBBERSECONDARY GREENLIQUOR FEEDOVERFLOW TROUGHSLAKING COMPARTMENTCLASSIFIER COMPARTMENTGRITLIME SLAKERTO CAUSTICIZERSSCREWCLASSIFIER DRIVE14 LIME SLAKERP hoto courtesy of Kadant Black Clawson Inc. Goslin Products GroupLIME SLAKER Sized based on retention time in slaking compartment. For Clarifiers 15 to 20 mins For Pressure filters 20 to 25 mins Correct operation determines white liquor strength15 LIME SLAKER PROBLEMS OVERLIMING Lime feed rate and or GL flow and strength BOILING GL Temperature control and or lime feed rate GREEN LIQUOR TEMPERATURE Heating Direct and indirect type heaters Cooling Indirect heat exchangers FRESH LIME MAKE-UP - the way it is added GRIT too much or too little grit can be an indicator of a problemFRESH LIME MAKE-UPSingle SiloSLAKERFrom KilnFRESHLIMESLAKERTwo SilosReburnedFreshSLAKER16 SLAKER GRIT HANDLING WASH GRIT TO pH LESS THAN WITH GRIT WASHER Photo courtesy of Kadant Black Clawson Goslin Products GroupSLAKER GRIT HANDLING GRIND OR PULVERIZE GRIT AND FILTER ON DREGS FILTER OR RECYCLE TO LIME SLAKERP hoto courtesy of Kadant Black Clawson Goslin Products Group17 INLETINLETOUTLETOUTLETRISERPIPECAUSTICIZ ERSWHITE LIQUOR CLARIFICATIONOPTIONS SEDIMENTATION CLARIFIERS VERTICAL TUBE TYPE PRESSURE FILTERS

4 PRESSURE DISC FILTERS18 WHITE LIQUOR CLARIFIERFEEDWELLSTORAGE ZONEMAX LLMIN LLCLARIFIEDLIQUOR OUTCLARIFIERFEEDUNDERFLOW OUTRAKE DRIVECLARIFICATION ZONEWHITE LIQUOR CLARIFIERFor successful clarifier operation Causticizer retention of 90 minutes Good accurate torque indication on rakes Properly sized variable speed underflow pumps with density and flow measurement19 WHITE LIQUOR CLARIFIER PROBLEMS CLOUDY OVERFLOW Over Liming Fresh Lime LOW UNDERFLOW SOLIDS Over Liming Fresh Lime Rat Holing Pumping Rate Rat HolingWHITE LIQUOR CLARIFIER PROBLEMSDEFE20 Pumping RateWHITE LIQUOR CLARIFIER PROBLEMSDEFEFEHOT WATERUNDERFLOWPUMPQDQS+ QLQUFQUF=QS+QL+QD Pumping Rate Mass flow of solids = Slaker solids output. Slaker solids output calculated from Green Liquor flow and Lime LIQUOR CLARIFIER PROBLEMS21 VERTICAL PRESSURE FILTERP hoto courtesy of Kadant Black Clawson Goslin Products GroupVERTICAL TUBE TYPE PRESSURE FILTERP hoto courtesy of Kadant Black Clawson Goslin Products Group22 PRESSURE TUBE TYPE FILTERSFEEDTANKMUDTANKDFABWHITE LIQUOR TOSTORAGE TANKFROMCAUSTICIZERSTO LIME MUDWASHER (WEAKWASH FILTER)DpWATERFILTRATION CYCLEF ilter 3-5 minsBackwash 3-5 secsRest 25-35 secsPRESSURE TUBE TYPE FILTERSAcid washing Interval between washes 4 8 weeks Acid types Sulphamic, Hydrochloric, Formic Alternative strategy Change filter socks every 6 months or when TUBE TYPE FILTERSFor successful operation of pressure filters.

5 Clean green liquor < 100 mg/l Causticizer retention time 150 -180 minutes. Causticizing control FILTER INTERNALSP hoto courtesy of Kadant Black Clawson Goslin Products Group24 PRESSURE FILTER PROBLEMS FREQUENT ACID WASHING Green Liquor Dregs contaminates filter socks Overliming temporary blinding of filter socks HIGH PRESSURE DROP Overliming Dregs High Mud Level SHORT FILTER SOCK LIFE Dregs contaminationWL PRESSURE DISC FILTERP hoto courtesy of Dorr-Oliver Eimco25 FEEDTANKWHITE LIQUOR PRESSURE DISC FILTERCOMPRESSORLIME MUDSLURRY TANKTO LIME MUD STORAGEWHITELIQUORWHITELIQUORSEPARATORFR OMCAUSTICIZERSCAKEWASH WATERWATERLIQUOR ticizedSlurry GravitySystem (35%Solids)Disc FilterSystem(75%Solids)White Liquor with MudWhite Liquor to Digester26 LIME MUD WASHINGLime Mud WasherLime MudStorageLime MudFilterLimeMud MixerWeak WashFiltrateWaterLime MudWaterLIME MUD WASHING SEDIMENTATION CLARIFIERS VERTICAL PRESSURE FILTERS NOT REQUIRED WITH PRESSURE DISC FILTERS27 LIME MUD WASHER PROBLEMS CLOUDY OVERFLOW Over Liming, Fresh Lime, Scrubber Dust, Contaminated Condensate.

6 LOW UNDERFLOW SOLIDS Over Liming, Fresh Lime, U/Flow Pumping HIGH SODA IN WEAK WASH AND LIME MUD Water Balance, U/Flow Pumping TOO MUCH WEAK WASH Water BalanceLIME MUD PRECOAT DRUM FILTERP hoto courtesy of Dorr-Oliver Eimco28 LIME MUD PRECOAT DISC FILTERP hoto courtesy of Dorr-Oliver EimcoLIME MUD FILTER PROBLEMS HIGH MOISTURE IN KILN FEED Over Liming, Fresh Lime, Dregs, Overloaded FREQUENT PRECOAT CHANGES Blinding of Precoat Over Liming, Fresh Lime, Dregs, Wash Water HIGH SODA IN KILN FEED Cake Wash, High Moisture TRS EMISSIONS FROM KILN Cake Wash, Overloaded29 TRS Control viaMud Dewatering & OxidationTO WaterSoluble SodaWITHOXIDATIONNa2S = = CAUSTICIZING CONTROLC onductivityOn-Line TitrationNear Infrared Spectrometry GREEN LIQUOR TEMPERATURE AND DENSITY LIME MUD DENSITY CONTROL30 SLAKER CONTROLCONTROLCONTROLSYSTEMSYSTEMSCREWCC CDTFGREEN LIQUORLIME SLAKERCAUSTICIZERSLIMELIMECONDUCTIVITY BASED CONTROL SYSTEMSLAKER CONTROLCONTROLCONTROLSYSTEMSYSTEMSCREWDT FGREEN LIQUORLIME SLAKERCAUSTICIZERSLIMELIMETITRATION BASED CONTROL SYSTEMSAMPLE LINEAUTOMATICAUTOMATICTITRATORTITRATORWL FILTER31 SLAKER CONTROLCONTROLCONTROLSYSTEMSYSTEMSCREWDT FGREEN LIQUORLIME SLAKERCAUSTICIZERSLIMELIMENEAR-INFRARED BASED CONTROL SYSTEMSAMPLE LINENIRNIRSENSOR(S)SENSOR(S)

7 WLFILTERSLAKER CONTROLCONTROLCONTROLSYSTEMSYSTEMSCREWTT FGREEN LIQUORLIME SLAKERLIMELIMESTEAM CONTROL VALVEHEATER T SLAKER CONTROL ANDGREEN LIQUOR DENSITYDWEAKWASH32 Smelt TankGreen LiquorClarifierDregs FilterSlaker /CausticizersWhiteLiquorClarifierLime MudWasherLime KilnWhite LiquorWeak WashWaterLime Mud FilterLimeGreen LiquorStabilizationDENSITY CONTROL LOCATIONSEFFECT OF DENSITY CONTROLON WHITE LIQUOR CLARIFIER UNDERFLOW BASED ON 1000 GPM OR LPM TO DIGESTERALL SOLIDS EXPRESSED AS SUSPENDED SOLIDS NOT TOTAL SOLIDS1217113540021713510001000100014000 200400600800100012001400160025% solids35% solids45% solidsgpm or lpmGreen LiquorWhite Liquor withMudWhite Liquor toDigester33 OTHER TECHNOLOGIES PRESSURE GREEN LIQUOR FILTERS FILTER PRESS FOR DREGS DEWATERINGSUMMARYWHAT IS IMPORTANT? GOOD GREEN LIQUOR Raw Green Liquor Stabilization Tank Conservatively Sized Clarifier Density and temperature control DO NOT OVERLIME Causticizing Control Fresh Lime Make-up. 34 CONCLUSIONFOR TROUBLE FREE OPERATION ADEQUATELY SIZED EQUIPMENT GOOD GREEN LIQUOR QUALITY GOOD LIME QUALITY EFFECTIVE CAUSTICIZING CONTROL Slaker and Density controls LIME MUD WASHING