TAPPI KRAFT RECOVERY SHORT COURSE RECAUSTICIZING CHAPTER PRINCIPLES AND PRACTICE BY DALE SANCHEZ VECTOR PROCESS EQUIPMENT INC.

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1 TAPPI KRAFT RECOVERY SHORT COURSE RECAUSTICIZING CHAPTER PRINCIPLES AND PRACTICE BY DALE SANCHEZ VECTOR PROCESS EQUIPMENT INC. TOPICS BASIC CHEMISTRY FLOWSHEET OPTIONS GREEN LIQUOR PREPARATION WHITE LIQUOR PREPARATION LIME MUD WASHING CONTROLS 1

2 RECAUSTICIZING CYCLE SMELT DISSOLVING SMELT FROM RECOVERY BOILER GREEN LIQUOR CLARIFICATION GREEN LIQUOR WEAK WASH LIME KILN LIME LIME MUD LIME MUD WASHING WATER LIME MUD WHITE LIQUOR CLARIFICATION DREGS SLAKER GRIT /CAUSTICIZERS WHITE LIQUOR BASIC CHEMISTRY GREEN LIQUOR + LIME = WHITE + LIQUOR LIME MUD Na 2 CO 3 + H 2 O + CaO = 2NaOH + CaCO 3 2

3 CHEMICAL REACTIONS SLAKING CaO + H 2 O Ca(OH) 2 + Heat CAUSTICIZING Ca(OH) 2 + Na 2 CO 3 2NaOH + CaCO 3 OVERALL REACTION Na 2 CO 3 + H 2 O + CaO 2NaOH + CaCO 3 EQUILIBRIUM REACTION REVERSIBLE INCOMPLETE 3

4 REACTION AT SOLID/ LIQUID INTERFACE Na + CaCO 3 CO 3 = UNREACTED CORE CaO OH - DEFINITIONS TTA = TOTAL TITRATABLE ALKALI NaOH + Na 2 S + Na 2 CO 3 AA = ACTIVE ALKALI NaOH + Na 2 S EA = EFFECTIVE ALKALI NaOH + ½ Na 2 S SULFIDITY % Na 2 S / AA or Na 2 S / TTA 4

5 DEFINITIONS CE = CAUSTICITY % NaOH x 100 NaOH + Na 2 CO 3 Lime Availability % CaO / Kiln Product Note: All chemical concentrations are expressed on a Na 2 O basis e.g. TTA = 120 g/l as Na 2 O Other units of measure are lb/ft 3 & lb/gal % CE OPERATING CAUSTICIZING EFFICIENCY 105 SULFIDITY=0% SULFIDITY=15% 5% SULFIDITY=30% OPERATING CE TTA g/l 5

6 FREE CaO vs CAUSTICITY % FREE LIME % CAUSTICITY Smelt Tank FLOWSHEET WITH CLARIFIERS Weak Wash Lime Kiln Green Liquor Stabilization Green Liquor Clarifier Dregs Filter Slaker / Causticizers Lime Mud Filter Lime Lime Mud Washer White Liquor White Liquor Clarifier Water 6

7 FLOWSHEET WITH PRESSURE FILTERS Weak Wash Smelt Tank Lime Kiln Green Liquor Stabilization Green Liquor Clarifier Lime White Liquor Lime Mud Filter Pressure Filters Water Dregs Filter Slaker / Causticizers Water FLOWSHEET WITH PRESSURE DISC FILTER Weak Wash Smelt Tank Lime Kiln Water Green Liquor Stabilization Lime Lime Mud Filter Green Liquor Clarifier Dregs Filter Slaker / Causticizers Pressure Disc Filter White Liquor Water 7

8 Smelt GREEN LIQUOR PREPARATION Weak Wash Stabilization Tank Clarified Green Liquor Smelt Dissolving Tank Clarifier Dregs Filter Dregs Holding Tank Variation in Green Liquor Density or Temperature in Stabilization Tank Inlet Density or Temperature Outlet Time 8

9 RAW GREEN LIQUOR STABILIZATION TANK RAW GREEN LIQUOR TOP MOUNTED AGITATOR INLET PIPE DOWN COMER OPTIONAL SIDE MOUNT AGITATOR PUMP TO GREEN LIQUOR CLARIFIER GREEN LIQUOR CLARIFICATION OPTIONS SEDIMENTATION CLARIFIERS PRESSURE FILTERS CROSS FLOW FILTERS SOCK TYPE FILTERS 9

10 GREEN LIQUOR CLARIFIER RAKE DRIVE MAX LL CLARIFIER FEED STORAGE ZONE MIN LL FEEDWELL CLARIFICATION ZONE CLARIFIED LIQUOR OUT UNDERFLOW OUT CLARIFIER INTERNALS Photo courtesy of Dorr-Oliver Eimco 10

11 Clean Green Liquor! Clarifier Feed Clarified Green Liquor Photo courtesy of Dorr-Oliver Eimco GREEN LIQUOR CLARIFIER PROBLEMS DIRTY 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) 11

12 DREGS PRECOAT FILTER Photo courtesy of Dorr-Oliver Eimco DREGS FILTER OPERATIONAL PROBLEMS Wet cake discharge High soda loss Difficulty forming a precoat 12

13 WHITE LIQUOR PREPARATION Green Liquor Lime White Liquor Grit Lime Slaker Causticizers Clarifier Lime Mud LIME SLAKER GREEN LIQUOR LIME TO VENT SCRUBBER AGITATOR OVERFLOW TROUGH SECONDARY GREEN LIQUOR FEED SCREW CLASSIFIER DRIVE GRIT TO CAUSTICIZERS CLASSIFIER COMPARTMENT SLAKING COMPARTMENT 13

14 LIME SLAKER Photo courtesy of Kadant Black Clawson Inc. Goslin Products Group LIME 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 strength 14

15 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 problem FRESH LIME MAKE-UP Single Silo Two Silos Reburned Fresh FRESH LIME SLAKER SLAKER From Kiln SLAKER 15

16 SLAKER GRIT HANDLING WASH GRIT TO ph LESS THAN 12.5 WITH GRIT WASHER Photo courtesy of Kadant Black Clawson Goslin Products Group GRIND OR PULVERIZE GRIT AND FILTER ON DREGS FILTER OR RECYCLE TO LIME SLAKER SLAKER GRIT HANDLING Photo courtesy of Kadant Black Clawson Goslin Products Group 16

17 CAUSTICIZERS INLET OUTLET INLET OUTLET RISER PIPE WHITE LIQUOR CLARIFICATION OPTIONS SEDIMENTATION CLARIFIERS VERTICAL TUBE TYPE PRESSURE FILTERS PRESSURE DISC FILTERS 17

18 WHITE LIQUOR CLARIFIER RAKE DRIVE MAX LL CLARIFIER FEED STORAGE ZONE MIN LL FEEDWELL CLARIFICATION ZONE CLARIFIED LIQUOR OUT UNDERFLOW OUT WHITE LIQUOR CLARIFIER For successful clarifier operation Causticizer retention of 90 minutes Good accurate torque indication on rakes Properly sized variable speed underflow pumps with density and flow measurement 18

19 WHITE LIQUOR CLARIFIER PROBLEMS CLOUDY OVERFLOW Over Liming Fresh Lime LOW UNDERFLOW SOLIDS Over Liming Fresh Lime Rat Holing Pumping Rate WHITE LIQUOR CLARIFIER PROBLEMS Rat Holing DE FE 19

20 WHITE LIQUOR CLARIFIER PROBLEMS Pumping Rate Q S + Q L UNDERFLOW PUMP Q UF DE FE FE Q D HOT WATER Q UF =Q S +Q L +Q D WHITE LIQUOR CLARIFIER PROBLEMS Pumping Rate Mass flow of solids = Slaker solids output. Slaker solids output calculated from Green Liquor flow and Lime rate. 20

21 VERTICAL PRESSURE FILTER Photo courtesy of Kadant Black Clawson Goslin Products Group VERTICAL TUBE TYPE PRESSURE FILTER Photo courtesy of Kadant Black Clawson Goslin Products Group 21

22 PRESSURE TUBE TYPE FILTERS FILTRATION CYCLE Filter 3-5 mins Backwash 3-5 secs Rest secs A B WHITE LIQUOR TO STORAGE TANK Dp WATER FROM CAUSTICIZERS D F TO LIME MUD WASHER (WEAK WASH FILTER) FEED TANK MUD TANK PRESSURE TUBE TYPE FILTERS Acid washing Interval between washes 4 8 weeks Acid types Sulphamic, Hydrochloric, Formic Alternative strategy Change filter socks every 6 months or when needed. 22

23 PRESSURE TUBE TYPE FILTERS For successful operation of pressure filters. Clean green liquor < 100 mg/l Causticizer retention time minutes. Causticizing control system. PRESSURE FILTER INTERNALS Photo courtesy of Kadant Black Clawson Goslin Products Group 23

24 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 contamination WL PRESSURE DISC FILTER Photo courtesy of Dorr-Oliver Eimco 24

25 WHITE LIQUOR PRESSURE DISC FILTER COMPRESSOR CAKE WASH WATER FROM CAUSTICIZERS WHITE LIQUOR SEPARATOR WATER WHITE LIQUOR FEED TANK LIME MUD SLURRY TANK TO LIME MUD STORAGE LIQUOR YIELD White Liquor with Mud White Liquor to Digester Causticized Slurry 17.9 Gravity System (35% Solids) 3.2 Disc Filter System(75% Solids) 25

26 LIME MUD WASHING Water Lime Mud Filtrate Lime Mud Mixer Weak Wash Water Lime Mud Washer Lime Mud Storage Lime Mud Filter LIME MUD WASHING SEDIMENTATION CLARIFIERS VERTICAL PRESSURE FILTERS NOT REQUIRED WITH PRESSURE DISC FILTERS 26

27 LIME MUD WASHER PROBLEMS CLOUDY OVERFLOW Over Liming, Fresh Lime, Scrubber Dust, Contaminated Condensate. 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 Balance LIME MUD PRECOAT DRUM FILTER Photo courtesy of Dorr-Oliver Eimco 27

28 LIME MUD PRECOAT DISC FILTER Photo courtesy of Dorr-Oliver Eimco LIME 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, Overloaded 28

29 TRS Control via Mud Dewatering & Oxidation AIR Washing Zone WITHOUT OXIDATION Na 2 S = 0.04% TO KILN 0.2% Water Soluble Soda WITH OXIDATION Na 2 S = 0.005% CONTROLS CAUSTICIZING CONTROL Conductivity On-Line Titration Near Infrared Spectrometry GREEN LIQUOR TEMPERATURE AND DENSITY LIME MUD DENSITY CONTROL 29

30 SLAKER CONTROL D C LIME CONTROL SYSTEM GREEN LIQUOR F SCREW T C C LIME SLAKER CAUSTICIZERS CONDUCTIVITY BASED CONTROL SYSTEM SLAKER CONTROL D LIME CONTROL SYSTEM AUTOMATIC TITRATOR GREEN LIQUOR F SCREW T LIME SLAKER SAMPLE LINE TITRATION BASED CONTROL SYSTEM CAUSTICIZERS WL FILTER 30

31 SLAKER CONTROL D LIME CONTROL SYSTEM NIR SENSOR(S) GREEN LIQUOR F SCREW T LIME SLAKER SAMPLE LINE CAUSTICIZERS NEAR-INFRARED BASED CONTROL SYSTEM WL FILTER WEAK WASH SLAKER CONTROL CONTROL SYSTEM HEATER D T LIME GREEN LIQUOR F T SCREW STEAM CONTROL VALVE ΔT SLAKER CONTROL AND GREEN LIQUOR DENSITY LIME SLAKER 31

32 Smelt Tank DENSITY CONTROL LOCATIONS Weak Wash Lime Kiln Green Liquor Stabilization Green Liquor Clarifier Dregs Filter Slaker / Causticizers Lime Mud Filter Lime Lime Mud Washer White Liquor White Liquor Clarifier Water gpm or lpm EFFECT OF DENSITY CONTROL ON WHITE LIQUOR CLARIFIER UNDERFLOW BASED ON 1000 GPM OR LPM TO DIGESTER % solids 35% solids 45% solids Green Liquor White Liquor with Mud White Liquor to Digester ALL SOLIDS EXPRESSED AS SUSPENDED SOLIDS NOT TOTAL SOLIDS 32

33 OTHER TECHNOLOGIES PRESSURE GREEN LIQUOR FILTERS FILTER PRESS FOR DREGS DEWATERING SUMMARY WHAT 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. 33

34 CONCLUSION FOR TROUBLE FREE OPERATION ADEQUATELY SIZED EQUIPMENT GOOD GREEN LIQUOR QUALITY GOOD LIME QUALITY EFFECTIVE CAUSTICIZING CONTROL Slaker and Density controls LIME MUD WASHING 34