PSE 476: Lecture #11 Pulping and Bleaching PSE 476 Lecture #1 Introduction Lecture #1 Introduction.
Modern & Eco-friendly Pulping & Bleaching Techniques...Modern & Eco-friendly Pulping & Bleaching...
Transcript of Modern & Eco-friendly Pulping & Bleaching Techniques...Modern & Eco-friendly Pulping & Bleaching...
Modern & Eco-friendly
Pulping & Bleaching
Techniques
By
Dr. Vimlesh Bist
Central Pulp & Paper Research Institute
Saharanpur, UP
CONTENT
� Pulping and bleaching scenario
� Modern Pulping Technologies
� Modern Bleaching Technologies
• Environment Norms* Increased environmental concern & awareness
* Environmental campaign on industrial usee of Chlorine and
release of Dioxin in Pulp Bleaching.
* Enforcement of stringent environmental regulations on discharge
of Organochlorine compounds which resulted in
- Wider use of extended delignification
- Oxygen Delignification
- Eop, Substitution of Chlorine with Chlorine
Dioxide
- Secondary treatment of effluents
• Pulp Quality* Paper Machine runnability
* Strength requirements of end products
• Market Force
* Customer requirement
The Need for Modern Developments
Limitations in Indian mills
� Variation in the capacity
� Variation in raw material
� Investment cost
Typical investment cost for 100000 TPA pulp mill
Extended delignification – 12 million USD
Oxygen delignification – 10 million USD
ClO2 generation plant – 16 million USD
Pulping & Bleaching Scenario (1970-2006)
1970
1975
1985
1990-2006
Conv.
CookingBleaching
O2 Delignification
Modified batch Cooking
Disp. - Super Batch/ RDH
Kappa No.30 25 20 15 10 5 0
Enzyme, ECF/TCF
Bleaching
Variables associated with the raw materials
•Fiber dimensions
•Chemical Composition
•Density- Bulk density/packing density
Physical size and shape of log
•Moisture content
•Porosity
•Storage conditions
� Chemical composition and sulphidity
� The amount of chemical added
� Bath ratio
� Time/temperature of digester, H factor
� Chip dimensions
� Chip impregnation
� Pressure
Major variables
H-FACTOR
The H-factor is a way of expressing
amount of Delignification, which takes
place during a cook. As Per definition the
H- factor is the area under a cooking
curve of relative reaction rates vs. time.
Developments in Pulping Technologies
�Developments in Batch cooking
�Developments in continuous cooking
Batch or Conventional Cooking
Until 1950’s only Batch digesters were used to produce Kraft Pulp
In late 70’s and early 80’s following developments took place
• Modified Cooking Chemistry Principles (Alkali Profiling
and low content of dissolved matter)
• Extended Cooking
• Energy Efficient Liquor Displacement Cooking
Batch or Conventional Cooking
1. Level out the alkali concentration- lower at
beginning, higher at end
2. High HS- concentration- specially at the start of
bulk delignification
3. Keep dissolved lignin low- especially at the end
of cooking
4. Low temperature.
Principles of Liquor Displacement Cooking / Extended Delignification
What is Liquor Displacement Cooking ?
Heat and residual chemicals remaining in Black liquor at the end of
the cooking are captured for reuse in subsequent batch cooking.
Conventional Batch Cooking Modified Batch Cooking
Loss of Cooking selectivity at
specific Kappa Number
Flexibility (Process & Raw
Material)
Hot Blow results in strength
degradation
Lower kappa numbers were
possible without loss in quality
The fiber undergo mechanical
stress resulting into poor pulp
strength
Respond to environmental
challenges
Terminal Displacement
- Digester contents are cooled to stop reaction after desired delignification is reached.
High pulp strength delivery and
yield
Digestor discharge by dilution and
pumping which is a gentle technique
77
95
0
10
20
30
40
50
60
70
80
90
100
Strength
Delivery %
Conventional Batch Liquor Displacement Batch
Strength Delivery of Pulp from Conventional &
Displacement Batch Digestors
42
44
46
48
50
52
54
10 20 30 40
Diplacement
Coventional
Yield vs Kappa Number for Conventional & Liquor
Displacement Batch Cooking of Soft wood Kraft Pulps
Cooking Cycle (Sunds Defibrator)
Chip
Fill
20
Chip
Steami
ng
20
Liq
Fill
15
Heating
90
Cooking
60
Degassin
g + Blow
25
Conventional Cooking
Displacement Batch Cooking
Chip
Fill
30
Warm
Liquor
Fill
30
Hot
Liquor
Fill
35
Heating
20
Cooking
45
Displacement
40
Discharge
30
Developments in Batch cooking
� RDH
� Super batch
� Enerbatch
� Cold Blow
Rapid
Displacement
Heating
(RDH)
Impregnation Temperature is 125-130oC
Addition of white Liquor in
Impregnation is necessary
Upward Flow Displacement
Super Batch Initial Impregnation with Black Liquor
at approximate 80-90o C Upward Flow
Displacement
EnerBatch Downward Flow Displacement
Clod Blow No warm Impregnation Stage
Development in Modified Batch Cooking
Developments in Continuous Cooking
• First Prototype Continuous Digestor started in 1938 at a mill in
Sweden with capacity of 20 t/d
• First commercial digestor with capacity 30 tons per day
commissioned in 1948 in a Swedish mill.
• In 1962 in digestor washing called high heat washing became
available
• High heat washing simplified the brown stock washing plant
• 1983 the first mill trials with modified Kraft cooking (MCC) were
performed in Finnish mill.
• MCC was developed by STFI & Royal Institute of Technology
Stockholm Sweden.
• 65% of global Kraft pulp production is manufactured by
continuous cooking.
Developments in Continuous cooking
� Modified Continuous
� Iso Thermal Cooking
� Black liquor impregnation
� Low Solid Cooking
MCC Split or multiple WL additions for alkali profiling and counter cooking
methods to minimize lignin concentration at the end of cook.
EMC High heat wash zone is simultaneously used for cooking and washing.
ITC
Advantages
High heat wash zone is simultaneously used for cooking and washing
� Low knots & rejects
� Uniform cook with high yield
� Improved Bleachability
� Higher brightness ceiling
Low Solids
Pulping
Dissolved wood solids are removed from the system by extracting spent
liquor at multiple locations
First commercial installation in 1993.
Black Liquor
Impregnation
Advantages
Black liquor pretreatment enhances the delignification during Kraft cooking
and improves the selectivity of the cook
Extracted Black liquor is added to the impregnation vessel with a retention
time of 45 minutes.
Improved pulp properties , improved tear strength(10 % Approx) at the
same tensile strength
Development in Continuous Cooking
Continuous Digester for Agro based Mills
(Pandya Type)
Cleaner Technology-Pulping
Technology Advantages
RDH, Super batch,
Enerbatch
CC +MCC+ITC
Reduced energy requirement,
high pulp yield, Better strength
& uniformity,Lower kappa,
Lower bleaching chemical
requirement.
1995- onward
CC+MCC+ITC
BLI+MCC+ITC
Low Solid Cooking
Better Pulp properties
Low temperature uniform
cooking, better yield
Adv/Disadvantages of
Conventional Batch
DigestingAdvantage•Operational flexibility
•Produce diff. Grades in same digester
•Sharp kappa number change
•Tolerant to pins and fines
•Capacity increased by adding
digesters
•Less sensitive to chips quality
Disadvantage
•High energy use
•Limited capability to extended
• Delignification
Adv/ Disadvantages of
Con. DigestingAdvantage
•More constant steam demand
•More compact less space requ.
•Uniformity in pulp quality
•Extended Delignification possibility
•Better pulp strength
Disadvantages
•High capital investment
•Restriction for type and raw
material quality
Pulping of casuarina- bole and branch (debarked)
Modern Development in
Bleaching Technology
Symbol Chemical Symbol Chemical
C Chlorine Z Ozone
D Chlorine dioxide E Sodium Hydroxide
H Hypochlorite X Enzymes
O Oxygen Q Chelating agents
(reduce the metal ion
Conc.Mn.,Fe,Cu)
EDTA,DTPA
P Hydrogen
peroxide
A Acid
Chemicals Used in Bleaching Processes
Oxidant Symbol Code/form Function Advantages Disadvantages
C Cl2 gas Oxidize &
chlorinate Lignin
Effective, Economical Can cause loss of
pulp strength
O O2 Gas used with
NaoH sol.
Oxidize &
solubilize lignin
Low chemical
cost,provide chloride
free effluent for
recovery
Large amount
required,expensi
ve equipment ,
lossof pulp
strength
H Ca(OCl)2 or NaOCl Oxidize, brighten &
solubilize lignin
Easy to make and use Can cause loss of
pulp strength
D Clo2 Oxidize, brighten &
solubilize lignin
Achieve high
brightnesswithout pulp
degradation,good
particle bleaching
Expensive, must
be made on site
P Na2O2(2-5%)Sol. Oxidize, brighten
lignin
Easy to use , high yield
& low cost
Expensive , poor
particle
bleaching
Z O3 gas Oxidize, brighten &
solubilize lignin
Effective, Provide
chlorine free effluent
for recovery
Expensive , poor
particle
bleaching
E NaoH(5-10%)Sol. Hydrolyze &
solubilize lignin
Effective &
economical
Darkens pulp
Functions & Economics and Technological Implications of Bleaching Agents
Formula
Weight
(g/mol)
Electron
transferred
/molecule
1 kg equal
to kg act.
Cl2
C12 + 2e- ���� 2Cl-
ClO2 + 2H2O + 5e- *���� Cl- + 4OH-
NaOCI + H2O + 5e-���� NaCl + 2OH-
O2 + 2H2O + 4e- ���� 4OH-
H2O2 + 2H+ + 2e- ���� 2H2O
O3 + 3H+ + 6 e- ���� 3OH-
7 1
67.5
133
32
34
48
2
5
2
4
2
6
1
2.63
0.53
4.43
2.094.43
Reactions and oxidizing equivalents of
bleaching agents
Selection of right sequence
• Cost of the bleaching chemical
• Selectivity
• Ex. Chlorine being less expensive & less
selective than Chlorine Dioxide was used in
the first stage CED instead of DEC
• In the end of the sequence its use may
cause degradation of carbohydrates due to low
amount of lignin
Pulp type Sequence
Sulphite & Bisulphite pulp
Three stages C-E-H
Four stages C-E-H-H
C-E-H-D
C-E-D-H
C-C-E-H
C-H-E-H
H-C-E-H
C-E-D-D/H
E-C-H-D
Five stages C-E-H-D-H
C-C-E-H-H
Kraft Pulp
Three stage ,semi-bleached C-E-H
D/C-O-D
Four Stage , Partly semi-bleached C-E-H-D
C-E-H-P
C-E-H-H
C-H-E-H
C-D-E-D
O-C-E-H
O-C-E-D
O-D-E-D
O-D-O-D
Established Pulp Bleaching Sequences showing the Predominant Role of
Chlorine & Chlorine Dioxide in the Industry
Pulp type Sequence
Sulphite & Bisulphite pulp
Five stages C-E-H-P-D
C-E-H-D-P
C-E-H-E-H
C-E-D-E-D
C-E-D-P-D
C-E-H-E-D
C-H-D-E-D-
D-E-D-E-D
C-C/H-E-H-H
Six stages C-H-E-D-E-D
C-E-H-D-E-D
C-E-H-E-H-D
C-E-H-D-P-D
C-E-H-E-P-D
C+D-E-H-D-E-D
O-C-E-D-E-D
O-C+D-E-D-E-D
O-D-E-D-E-D
O-C-D-E-H-D
Seven Stages C-H-H-D-D-D-P
Established Pulp Bleaching Sequences showing the Predominant Role of
Chlorine & Chlorine Dioxide in the Industry
� OXYGEN PRETREATMENT
� ENZYME PRETREATMENT
� OZONE BLEACHING
� ECF / TCF BLEACHING
Modern Development in
Bleaching Technology
Lignin removal before chlorination
Technology Advantages
Oxygen treatment-
Two stage Oxygen treatment
High kappa reduction (55%)
High brightness gain
Lower yield loss
More selective delignification
Ozone Treatment-TCF
Bleaching
Better effluent quality
Hot Chlorine Dioxide stage
Acid pre treatment
Saving of Chlorine dioxide
Better brightness development
Improves brightness stability/reduced
reduction.
Worldwide production capacity of Oxygen-
Delignified PulpCapacity, 1000 AD
tons/day
2 512
25
65
125
190
0
50
100
150
200
1970 1975 1980 1985 1990 1995 2000
Capacity 1000 AD Ton
Evolution of Oxygen-delignification Technology
OXYGEN DELIGNIFICATION
Conditions for the Oxygen Bleaching
Pulp Consistency 3-30%
Sodium Hydroxide 2% , 1.2%
Oxygen Pressure 5 Kg/cm2
Treatment
Temperature
120oC
Treatment Time 30 min
Oxygen Treatment of Wheat Straw Soda Pulp
Parameters A B C
Unbleached pulp kappa 48 33.6 11.8
Unbleached pulp
brightness
23.2 28.5 33.8
Unbleached pulp Viscosity 675.2 693.2 517.6
Oxygen treated pulp
kappa
29.5 21.5 6.0
% Kappa drop 38.5 36.0 49.15
Oxygen treated pulp
Brightness
30.4 32.7 46.8
Oxygen Treatment of Mix Hard Wood Pulp
Parameters A B C
Unbleached pulp kappa 16 16 16
Unbleached pulp brightness 27.2 27.2 27.2
Unbleached pulp Viscosity 685.2 685.2 685.2
Oxygen treated pulp kappa 7.0 7.2 8.4
% Kappa drop 56 56 47
Oxygen treated pulp
Brightness
45 45 42
CEH Bleaching of Untreated Oxygen Treated
Pulp of Bagasse
14.6
45
18
6.26.6
17
7 6.382 80
0
5
10
15
20
25
30
35
40
45
50
Kappa Number Total Cl2 NaOH Kg/t Brightness Viscosity
CEH OCEH
Single Stage Oxygen treatment
Two Stage Oxygen treatment
Typical Process Conditions for Two Stage ODL
Parameters First Stage Second Stage
Temp. 80-85 90-106
Pressure (top) ,bar 7-10 3-5
Retention time,min 20-40 60-80
Kappa Reduction High Low
Viscosity modest modest
Eo-Stage Oxygen Treatment
Effect of NaOH Addition
PROCESS VARIABLES IN OXYGEN
DELIGNIFICATION
PROCESS VARIABLES IN OXYGEN
DELIGNIFICATION
Effect of Temperature
PROCESS VARIABLES IN OXYGEN
DELIGNIFICATION
Effect of Oxygen Pressure
PROCESS VARIABLES IN OXYGEN
DELIGNIFICATION
Effect of Oxygen on final pulp brightness
Characteristics of CEH & OCEH Bleach
Effluent (Untreated) of Bagasse
8.8
33
4.184.5
16.3
1.27
0
5
10
15
20
25
30
35
BOD mg/l CODmg/l AOX Kg/t
BOD mg/l CODmg/l
Characteristics of CEH & OCEH Bleach
Effluent (Untreated) of Bamboo
12.8
43.5
4.636.3
20.4
1.32
0
5
10
15
20
25
30
35
40
45
50
BOD mg/l CODmg/l AOX Kg/t
OZONE BLEACHING
OZONE DELIGLIFICATION
• Ozone has property of de-lignifying the cellulose, was
discovered 150 Years back by Chinese and Japanies, but
commercialized in 1960s and 1970s.
• About 25 mills are using it for bleaching of chemical pulp
• It is a very powerful oxidizing agent
• Very poorly soluble in water, 1g/l
• When generated from oxygen, only 8-12% converts into ozone
• It is less selective toward lignin than chlorine or chlorine
dioxide
• It is a strong electrophile which reacts with functional group
in residual lignin.
• Most phenolic group in lignin is oxidized by ozone.
• More selective towards lignin but its intermediate inorganic
byproducts formed by direct decomposition as HO and Hoo
are very reactive with carbohydrates.
Process conditions•Consistency-
The consistency is maintained to enhance the mass transfer rate
between gas and liquid phase, eith high or medium consistency is
maintained during the reaction
•pH-
Ozone delignification is more efficient at pH value near 2. The low
kappa and better viscosity is achieved at pH 2 than pH 4 or 6.
•Temperature
The best selective temperature range is 25-30oC.
•Time - 2-5 Minutes
•Additives- several additives as formic acid, acetic acid, methanol
etc. are reported, for preservation of carbohydrates combination of
dioxide with ozone is also a good substitute..
OZONE AS REPLACEMENT OF CHLORINE-
• The ozone can be a substitute of chlorine, but this fact is
not realistic in case the initial kappa number is high. It
requires low kappa number entering to bleach plant (<10)
• Most commercial installation are after oxygen
delignification in DZ or ZD combinations
• Placing the Z stage towards the end of the sequences
found to increase the brightness and reduce the Ozone
requirement
• Placing Z stage between two peroxide stages reactivates
the pulps and it responsd better to the second peroxide
stage.
LABORATORY BLEACHING RESULT FOR A OXYGEN
DELIGNIFIED KRAFT PULP OF KAPPA 15
(OZONE 0.5%,CY 10%, EDTA AT PH 6.3 AND H2O2 2.5% AT PH
11)
Sequence Kappa number
after bleaching
Brightness,%ISO
Z 9.9 46.7
QP 7.1 71.1
QPP 5.9 77.9
ZQP 3.6 77.5
QPZ 2.7 77.6
ZQPP 2.8 83.9
QPZP ND 89.9
ECF / TCF BLEACHING
ECF/TCF Bleaching
DIFFERENT ECF/TCF BLEACHING SEQUENCESS
Application Bleach sequence
Reduced chlorine (C)-P-H
(C)-P-D-H
(C)-P-H-D-H
Peroxide replacement P-D-P
P-D-H
P-H-H
P-H-D
D-P-D
P-H-D-H
P-DP-D
Oxygen bleaching O-P
O-D
O-H
O-P-D
O-D-P
O-C-P
O-H-P
O-C-P-D
O-D-P-D
Ozone bleaching Z-E-P
Z-E-Z
Z-E-Z-P
Peracaetic acid P-A-P
A-E-A-E-A
others O-Q-P
O-Q-P-P
O-Q-P-Z-P
Bleaching Sequences Designed to reduce or Eliminate the use of Chlorine Based Compounds and Chlorine