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  • CHLORINE DIOXIDE BLEACHING

    Presented by:

    Scott CarmichaelSenior Process Engineer

    Eka Chemicals

  • PURPOSE OF CHEMICAL BLEACHING

    Selectively Remove Lignin

    Brighten Pulp Remove Contaminants Remove Extractives

  • MAJOR WOOD COMPONENTSAT DIFFERENT STAGES OF

    DELIGNIFICATION

    30

    40

    50

    60

    70

    80

    90

    100

    0 20 40 60 80 100Lignin Removed, %

    Y

    i

    e

    l

    d

    ,

    %

    (

    O

    n

    W

    o

    o

    d

    )

    Lignin Content

    Hemicellulose Content

    Pure Cellulose Content

    Total Pulp Yield

    Extractives

    Bulk Delignification

    MacLeod, M., PAPRICAN, TAPPI Kraft Pulping

  • FOUR STAGE BLEACH LINE

    `

    D0Eop D1 D2

  • BLEACHING OF PULP

    Sequence Development - Chemical Pulps Pre-bleaching to remove residual lignin

    Fragmentation from the cellulose portion in an oxidation/substitution step

    Solution of fragments for removal in washing Final bleaching or brightening by oxidation of coloring

    material Chemical selectivity important because of low lignin to

    cellulose ratio

  • BLEACHING AGENTS

    Chlorine SodiumHypochlorite

    ChlorineDioxide

    Oxygen HydrogenPeroxide

    Ozone

    Stage Design. C H D O P ZChem. Form. Cl2 NaOCl ClO2 O2 H2O2 O3Delig. Eff. E E E P/F F GBright. Eff. P E E P E GSelectivity G F/P E F E PShive Reduct. E E E F F PEnvir. Impact P P G/E G/E G/E G/ETotal Cost I I Ex I M/Ex VE

    E = Excellent G = Good F = Fair P = PoorI = Inexpensive M = Moderate Ex = Expensive VE = Very Expensive

    Developed from TAPPI: Pulp Bleaching, Principles and Practice

  • COMMON BLEACHING TERMS

    Kappa number (Kp#) measure of lignin content Lignin~(Kp#)*0.15

    Permanganate number (K#) measure of lignin content K# ~ (Kp#)*0.67

    Active chlorine (aCl) term used to relate chlorine based bleaching compounds aCl = (2.63* ClO2) + Cl2

    Kappa Factor = (aCl as % on pulp)/ (kappa number) Oxidative Equivalents (OXE) term used to convert bleaching

    compounds. OXE is the quantity of substance that receives one mole of

    electrons when a substance is reduced.

  • OXE FOR BLEACHING CHEMICALS

    Chemical OXE/kg aCl

    Cl2 28.20 1.0ClO2 74.12 2.63O2 125.00 4.43H2O2 58.79 2.09O3 125.00 4.43

  • FACTORS EFFECTING ClO2 PERFORMANCE

    Active Chlorine Distribution

    pH

    Charge

    Retention Time / Temperature

    Chemical Variants

    mixing, lignin, carryover, consistency

  • MULTI-STAGE BLEACHING

    72

    76

    80

    84

    88

    92

    96

    0.2 0.6 1 1.4 1.8

    Chlorine Dioxide, %

    B

    r

    i

    g

    h

    t

    n

    e

    s

    s

    %

    I

    S

    O

    Do-EoD1D2

  • ClO2 DISTRIBUTION EFFECT ON TOTAL USAGE

    Sequence: D (EO) D, 14 Kappa (9.4 K#)Reference: EC bleaching model

    35

    37

    39

    41

    43

    45

    35 45 55 65 75 85

    % of total ClO2 in first D

    T

    o

    t

    a

    l

    C

    l

    O

    2

    l

    b

    /

    T

  • D1 VERSUS D1+ D2 ClO2 DEMAND FOR BRIGHTENING

    10

    15

    20

    25

    30

    35

    40

    45

    0 25 50 75 100 125

    T

    o

    t

    a

    l

    C

    l

    O

    2

    C

    o

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    s

    u

    m

    e

    d

    I

    n

    D

    1

    a

    n

    d

    D

    2

    S

    t

    a

    g

    e

    s

    k

    g

    e

    q

    .

    C

    l

    2

    /

    t

    p

    u

    l

    p

    92 ISO90 ISO88 ISO87 ISO

    % ClO2 Consumed in the D1 Stage

    Reference: Axegard, et al., E2 Stage Improves the Reactivity of Pulp Towards Chlorine Dioxide

  • D0 STAGE OPERATIONS

  • EFFECT OF pH IN D0 STAGE(SW)

    6

    9

    12

    15

    18

    21

    1 2 3 4 5pH

    D

    0

    K

    a

    p

    p

    a

    N

    u

    m

    b

    e

    r

    KF = 0. 10

    KF = 0. 17

    KF = 0. 23

    KF = 0. 17 DE

    20

    25

    30

    35

    40

    45

    1 2 3 4 5pH

    D

    0

    I

    S

    O

    B

    r

    i

    g

    h

    t

    n

    e

    s

    s

    ,

    %

    KF = 0. 23

    KF = 0. 17

    KF = 0. 10

    Reference: Basta, et al., New and Improved Possibilities in D100 Bleaching,Proceedings of 1992 TAPPI Pulping Conference

  • DELIGNIFICATION EFFICIENCY

    23456789

    101112

    0.1 0.15 0.2 0.25 0.3Kappa Factor

    E

    o

    p

    K

    a

    p

    p

    a

    #

    SWHW

  • KAPPA NUMBER VS TIME

    Minutes

    Source: A Mathematical Model for Chlorine Dioxide Delignification; Savoie, Martin and Tessier, Patrick, TAPPI Journal June 1997

  • EFFECT OF COD CARRYOVER (SW - O2 Delig.)

    1.6

    2.0

    2.4

    2.8

    3.2

    3.6

    0.17 0.19 0.21 0.23 0.25 0.27 0.29KF

    E

    K

    a

    p

    p

    a 10 kg/t COD15 kg/t COD20 kg/t COD

  • BLEACH PLANT OPERATIONSD0 STAGE SUMMARY

    D0 Stage pH optimum at 2.5 - 3.2 Temperature 120 - 130 F, depending on time Allow for COD carryover in charge D0 Kappa Factor 0.18 - 0.22 for Economic &

    Environmental Residual not necessary Charge approx. 50 - 60 % of total active chlorine for D0 Brightness / Kappa relationship difference for Hardwood

  • D1 STAGE OPERATIONS

  • EFFECT OF TERMINAL pH ON D1 STAGE

    68

    70

    72

    74

    76

    78

    80

    82

    84

    86

    2 3 4 5 6 7 8 9

    pH at End of D1

    B

    r

    i

    g

    h

    t

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    e

    s

    s

    a

    t

    E

    n

    d

    o

    f

    D

    1

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    1.6

    1.8

    %

    A

    c

    t

    i

    v

    e

    C

    h

    l

    o

    r

    i

    n

    e

    Brightness

    Chlorate + Chlorite

    Chlorite

    Chlorate

  • EFFECT OF pH AND ClO2 CHARGEON D1 STAGE BRIGHTNESS

    78

    80

    82

    84

    86

    88

    1.5 2.5 3.5 4.5 5.5pH D1

    B

    r

    i

    g

    h

    t

    n

    e

    s

    s

    D

    1

    %

    I

    S

    O

    O2 - Delignified ECF Softwood Kraft, Kappa # 18 (K# 11.3)Reference: Basta, et al., Reducing of AOX Levels,

    Proceedings of 1991 Appita Annual General Conference

    K# E1 = 2.28% ISO E1 = 63.5Viscosity E1 = 31.8 cPs

    K# E1 = 2.28% ISO E1 = 63.5Viscosity E1 = 31.8 cPs

    23 lb/T D (as ClO2)

    15 lb/T D (as ClO2)

    8 lb/T D (as ClO2)

  • EFFECT OF END pH IN D1 STAGE ONSHIVES IN PULP AFTER THE D1 STAGE

    02468

    10121416182022

    3.0 3.5 4.0 4.5 5.0 5.5 6.0

    D1 Tower Terminal pH

    D

    1

    W

    a

    s

    h

    e

    r

    S

    h

    i

    v

    e

    C

    o

    u

    n

    t

    Reference: Pulp Bleaching - Principles and Practice; C. Dence & D. Reeve

  • BLEACH PLANT OPERATIONSD1 STAGE SUMMARY

    Maintain residual 0.02-0.05 gpl for brightness

    Operate pH 3.5-4.5

    Lower pH leads to improved shive bleaching but also strength and viscosity loss

    Temperature range 160-175 F

    Charge approx 30-40% of total active chlorine

  • EFFECT OF RESIDUAL ANDTEMPERATURE ON BRIGHTNESS

    74

    76

    78

    80

    82

    84

    86

    1 2 0 1 5 0 1 8 0 2 1 0 2 4 0 2 7 0 3 00

    Time (min)

    B

    r

    i

    g

    h

    t

    n

    e

    s

    s

    ,

    %

    I

    S

    O

    40 lb/T ClO2

    30 lb/T ClO2

    20 lb/T ClO2

    Residual ClO2 No residual

  • D1 EFFECT ON D2 BRIGHTNESS CEILING

    30

    40

    50

    60

    70

    80

    90

    100

    0 0.25 0.5 0.75 1 1.25 1.5

    D1 Chlorine Dioxide, % on Pulp

    B

    r

    i

    g

    h

    t

    n

    e

    s

    s

    ,

    %

    G

    E

    Rapson, W.H., Bleaching of Pulp. Tappi Monograph

    D1

    D2

    D2 ClO2 = 0.5% on pulp

  • BLEACH PLANT OPERATIONSD2 STAGE SUMMARY

    Operate pH 3.5 - 5.0

    Temperature range 155 - 175 F

    Maintain residual at 0.02 - 0.05 gpl

    Residual important for brightness stability

    Important to stay away from brightness ceiling

  • QUESTIONS?

    PURPOSE OF CHEMICAL BLEACHINGFOUR STAGE BLEACH LINEBLEACHING OF PULPCOMMON BLEACHING TERMSOXE FOR BLEACHING CHEMICALSMULTI-STAGE BLEACHINGClO2 DISTRIBUTION EFFECT ON TOTAL USAGED1 VERSUS D1+ D2 ClO2 DEMAND FOR BRIGHTENINGDELIGNIFICATION EFFICIENCYEFFECT OF COD CARRYOVER (SW - O2 Delig.)BLEACH PLANT OPERATIONSD0 STAGE SUMMARYD1 STAGE OPERATIONSEFFECT OF pH AND ClO2 CHARGEON D1 STAGE BRIGHTNESSEFFECT OF END pH IN D1 STAGE ONSHIVES IN PULP AFTER THE D1 STAGEBLEACH PLANT OPERATIONSD1 STAGE SUMMARYEFFECT OF RESIDUAL ANDTEMPERATURE ON BRIGHTNESSD1 EFFECT ON D2 BRIGHTNESS CEILINGBLEACH PLANT OPERATIONSD2 STAGE SUMMARYQUESTIONS?