2-1 PPT Recausticizing PDF [PDF]

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TAPPI KRAFT RECOVERY SHORT COURSE RECAUSTICIZING CHAPTER 2.1 - 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

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RECAUSTICIZING CYCLE WEAK WASH

SMELT DISSOLVING

LIME KILN

SMELT FROM RECOVERY BOILER

WATER

LIME MUD

GREEN LIQUOR CLARIFICATION

DREGS

LIME MUD WASHING

LIME MUD

WHITE LIQUOR CLARIFICATION

LIME GREEN LIQUOR

SLAKER GRIT /CAUSTICIZERS

WHITE LIQUOR

BASIC CHEMISTRY GREEN LIQUOR

+ LIME

= WHITE LIQUOR

+

LIME MUD

Na2CO3 + H2O + CaO = 2NaOH + CaCO3

2

CHEMICAL REACTIONS • SLAKING CaO + H2O

Ca(OH)2 + Heat

• CAUSTICIZING Ca(OH)2 + Na2CO3

2NaOH + CaCO3

OVERALL REACTION Na2CO3 + H2O + CaO

2NaOH + CaCO3

• EQUILIBRIUM REACTION • REVERSIBLE • INCOMPLETE

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REACTION AT SOLID/ LIQUID INTERFACE Na+ CaCO3 CO3= UNREACTED CORE

OH-

CaO

DEFINITIONS TTA = TOTAL TITRATABLE ALKALI NaOH + Na2S + Na2CO3 AA = ACTIVE ALKALI NaOH + Na2S EA = EFFECTIVE ALKALI NaOH + ½ Na2S SULFIDITY % Na2S / AA or Na2S / TTA

4

DEFINITIONS CE = CAUSTICITY % NaOH x 100 NaOH + Na2CO3 Lime Availability % CaO / Kiln Product

Note: All chemical concentrations are expressed on a Na2O basis e.g. TTA = 120 g/l as Na2O Other units of measure are lb/ft3 & lb/gal

OPERATING CAUSTICIZING EFFICIENCY 105 100 95

SULFIDITY=0%

% CE 90

SULFIDITY=15%

85

SULFIDITY=30%

5%

80

OPERATING CE

75 0

50

100

150

200

TTA g/l

5

FREE CaO vs CAUSTICITY 7 % FREE LIME

6 5 4 3 2 1 0 70

75

80

85

% CAUSTICITY

FLOWSHEET WITH CLARIFIERS Smelt Tank

Weak Wash Lime Kiln

Green Liquor Stabilization Green Liquor Clarifier

Dregs Filter

Lime Mud Filter Lime Lime Mud Washer White Liquor

Slaker / Causticizers

White Liquor Clarifier Water

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FLOWSHEET WITH PRESSURE FILTERS Weak Wash Smelt Tank Lime Kiln Green Liquor Stabilization Green Liquor Clarifier

Lime Mud Filter Lime Pressure Filters

White Liquor

Water

Dregs Filter

Slaker / Causticizers

Water

FLOWSHEET WITH PRESSURE DISC FILTER Weak Wash Smelt Tank Green Liquor Stabilization Green Liquor Clarifier

Water

Lime Kiln Lime Mud Filter Lime Pressure Disc Filter White Liquor Water

Dregs Filter

Slaker / Causticizers

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GREEN LIQUOR PREPARATION Smelt

Weak Wash Stabilization Tank

Smelt Dissolving Tank

Clarified Green Liquor

Clarifier

Dregs Filter

Dregs Holding Tank

Variation in Green Liquor Density or Temperature in Stabilization Tank

Density or Temperature

Inlet

Outlet

Time

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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

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GREEN LIQUOR CLARIFIER RAKE DRIVE

CLARIFIER FEED MAX LL STORAGE ZONE

MIN LL FEEDWELL CLARIFICATION

CLARIFIED LIQUOR OUT ZONE

UNDERFLOW OUT

CLARIFIER INTERNALS

Photo courtesy of Dorr-Oliver Eimco

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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)

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DREGS PRECOAT FILTER

Photo courtesy of Dorr-Oliver Eimco

DREGS FILTER OPERATIONAL PROBLEMS • Wet cake discharge • High soda loss • Difficulty forming a precoat

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WHITE LIQUOR PREPARATION Green Liquor Lime White Liquor Grit Lime Slaker Causticizers

Clarifier Lime Mud

LIME SLAKER OVERFLOW TROUGH LIME

TO VENT SCRUBBER

SCREW CLASSIFIER DRIVE

AGITATOR GREEN LIQUOR

SECONDARY GREEN LIQUOR FEED

GRIT

TO CAUSTICIZERS

CLASSIFIER COMPARTMENT SLAKING COMPARTMENT

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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

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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

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SLAKER GRIT HANDLING • WASH GRIT TO pH LESS THAN 12.5 WITH GRIT WASHER

Photo courtesy of Kadant Black Clawson – Goslin™ Products Group

SLAKER GRIT HANDLING • GRIND OR PULVERIZE GRIT AND FILTER ON DREGS FILTER OR RECYCLE TO LIME SLAKER

Photo courtesy of Kadant Black Clawson – Goslin™ Products Group

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CAUSTICIZERS INLET

OUTLET

INLET OUTLET

RISER PIPE

WHITE LIQUOR CLARIFICATION OPTIONS • SEDIMENTATION CLARIFIERS • VERTICAL TUBE TYPE PRESSURE FILTERS • PRESSURE DISC FILTERS

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WHITE LIQUOR CLARIFIER RAKE DRIVE

CLARIFIER FEED MAX LL STORAGE ZONE

MIN LL FEEDWELL CLARIFICATION

CLARIFIED LIQUOR OUT ZONE

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

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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

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WHITE LIQUOR CLARIFIER PROBLEMS • Pumping Rate QS+ QL

UNDERFLOW PUMP

QUF DE

FE

QD FE

HOT WATER

QUF=QS+QL+QD

WHITE LIQUOR CLARIFIER PROBLEMS • Pumping Rate – Mass flow of solids = Slaker solids output. – Slaker solids output calculated from Green Liquor flow and Lime rate.

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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

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PRESSURE TUBE TYPE FILTERS FILTRATION CYCLE Filter 3-5 mins Backwash 3-5 secs Rest 25-35 secs

WHITE LIQUOR TO STORAGE TANK

A

B

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.

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PRESSURE TUBE TYPE FILTERS For successful operation of pressure filters. • Clean green liquor < 100 mg/l • Causticizer retention time 150 -180 minutes. • Causticizing control system.

PRESSURE FILTER INTERNALS

Photo courtesy of Kadant Black Clawson – Goslin™ Products Group

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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

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WHITE LIQUOR PRESSURE DISC FILTER COMPRESSOR

CAKE WASH WATER

WHITE LIQUOR SEPARATOR

FROM CAUSTICIZERS

WHITE LIQUOR

WATER

LIME MUD SLURRY TANK

FEED TANK

TO LIME MUD STORAGE

LIQUOR YIELD 100

96.8

100 82.1

80 60

White Liquor with Mud White Liquor to Digester

40 17.9

20 0

3.2

0 Causticized Slurry

Disc Filter Gravity System (35% System(75% Solids) Solids)

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LIME MUD WASHING Water Lime Mud

Filtrate Weak Wash

Lime Mud Mixer

Water

Lime Mud Washer

Lime Mud Storage

Lime Mud Filter

LIME MUD WASHING • SEDIMENTATION CLARIFIERS • VERTICAL PRESSURE FILTERS • NOT REQUIRED WITH PRESSURE DISC FILTERS

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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

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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

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TRS Control via Mud Dewatering & Oxidation AIR Washing Zone

TO KILN 0.2% Water Soluble Soda WITHOUT OXIDATION Na2S = 0.04%

WITH OXIDATION Na2S = 0.005%

CONTROLS • CAUSTICIZING CONTROL Conductivity On-Line Titration Near Infrared Spectrometry

• GREEN LIQUOR TEMPERATURE AND DENSITY • LIME MUD DENSITY CONTROL

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SLAKER CONTROL CONTROL SYSTEM

D C

LIME GREEN LIQUOR

F

SCREW T

C C

LIME SLAKER CAUSTICIZERS CONDUCTIVITY BASED CONTROL SYSTEM

SLAKER CONTROL CONTROL SYSTEM

D

AUTOMATIC TITRATOR

LIME GREEN LIQUOR

F

SCREW T

LIME SLAKER SAMPLE LINE

CAUSTICIZERS

WL FILTER

TITRATION BASED CONTROL SYSTEM

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SLAKER CONTROL NIR SENSOR(S)

CONTROL SYSTEM

D

LIME GREEN LIQUOR

F

SCREW T

LIME SLAKER SAMPLE LINE

WL FILTER

CAUSTICIZERS

NEAR-INFRARED BASED CONTROL SYSTEM

WEAK WASH

SLAKER CONTROL CONTROL SYSTEM T D

LIME

HEATER

GREEN LIQUOR

F T

SCREW

STEAM CONTROL VALVE

ΔT SLAKER CONTROL AND GREEN LIQUOR DENSITY

LIME SLAKER

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DENSITY CONTROL LOCATIONS Weak Wash

Smelt Tank

Lime Kiln Green Liquor Stabilization

Lime Mud Filter Lime Lime Mud Washer White Liquor

Green Liquor Clarifier

Dregs Filter

White Liquor Clarifier

Slaker / Causticizers

Water

EFFECT OF DENSITY CONTROL ON WHITE LIQUOR CLARIFIER UNDERFLOW BASED ON 1000 GPM OR LPM TO DIGESTER 1600 1400 gpm or lpm

1200 1000

1400 1217 1000

1135 1000

1000

White Liquor with Mud White Liquor to Digester

800 600 400

400 217

200

135

0 25% solids

Green Liquor

35% solids

ALL SOLIDS EXPRESSED AS SUSPENDED SOLIDS NOT TOTAL SOLIDS

45% solids

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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.

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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

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