presented by: scott carmichael senior process engineer eka ...pplant.uga.edu/tappi/clo2...
TRANSCRIPT
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CHLORINE DIOXIDE BLEACHING
Presented by:
Scott CarmichaelSenior Process Engineer
Eka Chemicals
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PURPOSE OF CHEMICAL BLEACHING
• Selectively Remove Lignin
• Brighten Pulp• Remove Contaminants• Remove Extractives
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MAJOR WOOD COMPONENTSAT DIFFERENT STAGES OF
DELIGNIFICATION
30
40
50
60
70
80
90
100
0 20 40 60 80 100Lignin Removed, %
Yiel
d, %
(On
Woo
d)
Lignin Content
Hemicellulose Content
Pure Cellulose Content
Total Pulp Yield
Extractives
Bulk Delignification
MacLeod, M., PAPRICAN, TAPPI Kraft Pulping
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FOUR STAGE BLEACH LINE
`
D0Eop D1 D2
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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
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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
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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.
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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
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FACTORS EFFECTING ClO2 PERFORMANCE
• Active Chlorine Distribution
• pH
• Charge
• Retention Time / Temperature
• Chemical Variants
– mixing, lignin, carryover, consistency
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MULTI-STAGE BLEACHING
72
76
80
84
88
92
96
0.2 0.6 1 1.4 1.8
Chlorine Dioxide, %
Brig
htne
ss %
ISO
Do-EoD1D2
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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
Tota
l ClO
2 lb/
T
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D1 VERSUS D1+ D2 ClO2 DEMAND FOR BRIGHTENING
10
15
20
25
30
35
40
45
0 25 50 75 100 125
Tota
l ClO
2 C
onsu
med
In D
1 and
D2 St
ages
kg
eq.C
l2/t
pulp
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”
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D0 STAGE OPERATIONS
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EFFECT OF pH IN D0 STAGE(SW)
6
9
12
15
18
21
1 2 3 4 5pH
D 0 K
appa
Num
ber
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 IS
O B
right
ness
, %
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
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DELIGNIFICATION EFFICIENCY
23456789
101112
0.1 0.15 0.2 0.25 0.3Kappa Factor
Eop
Kapp
a #
SWHW
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KAPPA NUMBER VS TIME
Minutes
Source: A Mathematical Model for Chlorine Dioxide Delignification; Savoie, Martin and Tessier, Patrick, TAPPI Journal June 1997
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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
appa 10 kg/t COD
15 kg/t COD20 kg/t COD
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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
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D1 STAGE OPERATIONS
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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
Brig
htne
ss a
t End
of D
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
%A
ctiv
e C
hlor
ine
Brightness
Chlorate + Chlorite
Chlorite
Chlorate
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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
Brig
htne
ss D
1 %
ISO
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)
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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
D1 W
ashe
r Shi
ve C
ount
Reference: Pulp Bleaching - Principles and Practice; C. Dence & D. Reeve
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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 160-175º F
• Charge approx 30-40% of total active chlorine
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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)
Brig
htne
ss, %
ISO
40 lb/T ClO2
30 lb/T ClO2
20 lb/T ClO2
Residual ClO2 No residual
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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
Brig
htne
ss, %
GE
Rapson, W.H., “Bleaching of Pulp”. Tappi Monograph
D1
D2
D2 ClO2 = 0.5% on pulp
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BLEACH PLANT OPERATIONSD2 STAGE SUMMARY
• Operate pH 3.5 - 5.0
• Temperature range 155 - 175 ºF
• Maintain residual at 0.02 - 0.05 gpl
• Residual important for brightness stability
• Important to stay away from brightness ceiling
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QUESTIONS?