1. bleaching
By EMIL GERMER, ALEXIS MÉTAIS and JEAN-CHRISTOPHE HOSTACHY
The benefits of ozone are now well proven and can include cost
savings and reduced effluent load
ACHIEVEMENTS IN INDUSTRIAL
OZONE BLEACHING
T
he first industrial pulp bleaching line including effluents to 4-6 m3/air dry tonne4. Of course investors
an ozone stage started 19 years ago. Today there always focus on the return on investment (ROI) and it
are 22 mills worldwide using what is commonly has now become clear to all ozone users that bleach-
named light-ECF bleaching. Among those 22 mills, 16 ing costs are reduced by 20-32% when introducing an
produce solely hardwood pulps, four produce both soft- ozone stage in an ECF bleaching line 3,5,6,7 and even
wood and hardwood pulps while SCA in Östrand (Swe- more in the case of TCF bleaching 8. The high bleach-
den) and Rosenthal in Blankenstein (Germany) produce ing efficiency of ozone allows a drastic reduction in
exclusively softwood pulp1. Thirteen mills started ozone the consumption of expensive bleaching chemicals
bleaching in the early years of the 21st century and three - chlorine dioxide in ECF bleaching and hydrogen
mills equipped two of their bleaching lines with ozone: peroxide in TCF bleaching as well as sodium hydrox-
Oji Paper in Tomioka (Japan), Fibria in Jacarei (Brazil) ide in both cases - and the implementation of ozone
and ITC in Bhadrachalam (India). Fibria selected ozone bleaching also results in reduced of steam require-
bleaching in 2002 for Jacarei’s new 2,500-tonne/day line ments during the bleaching process. The ROI in the
C after having operated ozone bleaching as from 1995 replacement of a D0-stage by an ozone Z-stage lies
on its 900-tonne/day line B. This decision clearly shows between two and four years 1,6.
that ozone bleaching has met all requirements and Without affecting the pulp strength properties
expectations on line B for seven years. in comparison with conventional ECF sequences,
In April 2011, four new ozone generation sys- bleaching with an ozone stage additionally gives a
tems have been contracted and will start operating wide range of opportunities by:
in 2012 for: - making very high brightness levels possible (92-
- a 700,000-tonne/yr capacity Chinese greenfield mill 93% ISO)2,9;
owned by Oji Paper (the company already uses - decreasing brightness reversion2,8,10;
ozone in its Japanese mills); - reducing drastically the extractive content10,11 by
- a pulp production capacity increase in Austria at 50-75%8,12;
Lenzing; - reducing energy requirements during refining by at
- two pulp production capacity increases in Brazil least 10%3,13;
(confidential). - precisely controlling the viscosity in viscose pulp
production.
Ozone bleaching is efficiently used on hardwood
and softwood pulps, on kraft and sulphite pulps dedi- Nevertheless, arguing that ECF bleaching has
cated to all kinds of final applications. Pulp produc- already been used in the industry for 30 years, a
ers do not always evaluate the significant ecological number of conservative pulp producers still con-
advantages of ozone-based bleaching sequences over sider the bleaching sequence D0-Eop-D1-D2 and
the traditional ECF bleaching sequence D0-Eop-D1- its variants- as the best alternative today. One should
D2 (or its variants): the quality of wastewater is drasti- however be aware that within the next 20 years,
cally improved 2,3 as it is possible to lower bleaching the pulp and paper industry will have to carry out
34 August 2011 Pulp & Paper International (PPI)

2. bleaching
significant modernisations to retain its competitive- HIGH CONSISTENCY (HC) OZONE
ness and, in turn such a traditional ECF bleaching BLEACHING
will then be over 50 years old. This position could
be understood if no better technique was available. The first commercial HC ozone bleaching started in
But considering the very good results and proven 1992 at the Union Camp mill in Franklin, VA. Accord-
stable operation achieved today by a large number ing to the C-Free® process implemented there, the
of industrial ozone-based light-ECF and TCF bleach pulp was pH adjusted, pressed to high consistency
plants, such a conservative attitude can’t be justified (40%), fluffed and transferred to the ozone paddle
any longer. reactor operating at atmospheric pressure14. The C-
The industrial use of ozone has already under-
gone a long string of improvements and develop-
ments. As with other new technologies, ozone bleach-
ing did not immediately reach its optimal technical
efficiency but faced several issues during its early
years. All the same, achievements of ozone bleaching
have improved year in year out and it is now a well
proven technology. Nevertheless, some pulp produc-
Fig. 1 - OZONE FORMATION IN AN ELECTRICAL FIELD
ers still remember the difficulties faced in the early
years and, unfortunately, this still represents a very
serious drawback towards the modernization of their
pulp mills. By doing a brief survey of ozone applica-
tion in pulp bleaching development over the past 20
years, the present article aims to draw specialists’ and
investors’ attention to practices and technologies that
helped ozone bleaching become the most advanced
and promising technology.
O Z O N E G E N E R AT I O N
Ozone generation is a pure on-site technology requir-
ing only energy and oxygen (usually also produced on
site from a VPSA plant). Ozone (O3) is produced from
oxygen (O2) in an electrical field at a concentration of
12% by weight, Fig. 1.
Modern ozone generators are 50% more efficient
than the ones used in the first ozone pulp bleaching
Fig. 2 - Z-COMPACT SYSTEM IN CELTEJO (PORTUGAL)
applications. Z-Compact-Systems, Fig. 2, were spe-
cially designed for the pulp and paper industry and
they are able to produce up to 250kg O3/h (6 tons/
day) per unit.
Today, ozone production only requires 7 to 8
kWh/kg of ozone and as a result, 1 kg ozone is now
cheaper than 1 kg of chlorine dioxide. Based on a
“plug and play” principle, modern ozone genera-
tion units are easy to operate and can deliver the full
ozone capacity in less than one minute with an avail-
Fig. 3- HC OZONE BLEACHING IN THE 1990S AND TODAY
ability higher than 99%.
Pulp & Paper International (PPI) A u g u s t 2 0 1 1 35

3. bleaching
Free® was provided by Sunds Defibrator until the late MEDIUM CONSISTENCY (MC) OZONE
1990s in the US, Sweden, South Africa and Germany. BLEACHING
Modern HC ozone bleaching uses the ZeTracTM
technology provided by Metso which is a much Improvements in MC ozone bleaching consist in fact
simplified version of the C-Free, Fig. 35. The experi- of alterations to the ozone mixers. This is no wonder
ence gained from the first industrial installations since the ozone mixer is the core of the MC Z-stage
showed that ozone requires very short (around 1 and the quality of the final pulp depends on its ef-
minute) contacting time with the pulp and that a 5-10 ficiency. It is worth remembering that the very few
minute extraction stage after the Z-stage is in most mills which faced quality issues are those where the
cases sufficient. These observations allowed the size first MC ozone bleaching technique was implement-
of reactors to be reduced, which lowered investment ed: this was mainly due to a non homogenous mixing
costs. Then the plug screw feeder, the refiner fluffer and a mixer which mechanically affected the fibers.
and the washing stage prior to the extraction stage Andritz, GL&V and Lenzing Technik are the three
could all be eliminated. These drastic simplifications suppliers of MC ozone mixers and all MC Z-stages are
led to significant reduction of the capital expenditure, designed according to the same principles. Industrial
energy requirements, maintenance costs as well as practice has shown that Andritz technology requires
effluent volume5. two mixers in series for a 3-6 kg/tonne ozone dose to
Figure 3 shows the principle of the modern obtain the optimal bleaching efficiency while Lenzing
ZeTrac system. The pulp is acidified and then pressed Technik considers that one single mixer of its own is
to high consistency (38-42%). Such a high consis- sufficient for a 4-5 kg/tonne ozone charge.
tency is a prerequisite to facilitate the rapid contact Because of the larger amount of filtrate around
between ozone gas and well fluffed pulp and so the fibers at 12% pulp consistency, the reaction must
preserves the reaction efficiency. Once dewatered, take place in a pressurized (7-8 bar) reactor and con-
the pulp is fluffed in a shredder screw on the top of sequently the total gas flow (oxygen and ozone) must
the press and fed by gravity into the reactor. Ozone is be compressed accordingly. A typical MC ozone stage
added to the reactor which is operated at a pressure from Andritz, Fig. 4, features a MC pump that feeds
slightly below atmospheric. After the reactor, the pulp the pulp to the ozone stage, two ozone mixers in
is diluted with alkaline liquor. series, a pressurized reaction tube, a flow discharger
at the reactor top and a blow tube11.
It was noticed that the whole reaction process
takes place in the mixers while the “reactor” has no
effect on the ozone reaction but only guarantees a
stable flow to the blow tube11. It is now possible to
decrease the gas pressure from 12 bar to 9 bar and
thus reduce operating costs.
Andritz improved the original Ahlström mixer
efficiency by reducing the gas bubble size without
making any fundamental change in the design of the
mixer but only increasing turbulence and mitigating
the mechanical action12. It makes the mixing a lot
more homogenous and maintains pulp strength all
along ozonation.
Lenzing started a MC ozone mixing system
from Kvaerner in 1992 and has since investigated all
possible improvements in MC ozone bleaching. It
has been a pioneer in ozone bleaching for almost 20
Fig. 4 - TYPICAL MC OZONE STAGE AND MIXER
years. As a result, LenzingTechnik designed its own
36 August 2011 Pulp & Paper International (PPI)

4. bleaching
ozone MC mixers (called Eccentric Mixers) imple- lower than the ratio of softwood/hardwood bleached
menting the revolutionary idea of an asymmetric pulps produced in those countries.
design to increase both fluidization of the pulp and Numerous studies carried out during the 1990s
retention time16. and in the more recent years have shown that the se-
And this proved to work: Lenzing upgraded its lectivity of ozone against lignin is very high. It is now
two bleaching lines in 2004 with modern Eccentric established that the reaction kinetic of ozone with
Mixers and the use of the new mixing technology typical lignin structures is 10 to 1,000 times higher
resulted in a 2.5 ISO brightness points increase for than with carbohydrates, Fig. 517.
the same ozone dose! Actually, Lenzing reduced its This means that as long as there is some remain-
bleaching chemical costs by 50% on line 1 and 38% ing lignin (even only 0.5-1.5%) a well-operated ozone
on line B16. bleaching process does not impact the cellulose more
than any other bleaching stage (a chlorine dioxide
PULP QUALITY one for example). In fact, according to the best wood
chemistry specialists15,17, the reaction kinetic of ozone
Since the first commercial ozone bleaching instal- with lignin is 1,000 times higher than the kinetic of
lation was started, enhancements to the ozone cellulose oxidation or depolymerisation by ozone.
bleaching process have been conducted jointly by Those scientific results are confirmed by the follow-
laboratories on the chemical side and by both the ing industrial experience of ozone bleaching.
industry and equipment suppliers on the operational In 1998, the Domtar mill in Espanola, ON,
and technical sides. Improvements in ozone bleach- switched from the ECF O-A-D-E-DnD sequence to
ing efficiency were boosted by the development the light-ECF O-A-ZD-E-DnD sequence for bleach-
of automatic control systems, mainly as a result of ing pulp up to 93% ISO brightness. Comparing the
achievements in the accuracy and reliability of elec- two sequences Domtar noticed “ozone has no impact
tronics. It is now possible to adjust very precisely the on viscosity or PFI strength properties and in paper
ozone dosage, pH, retention time and temperature in machine performance”9.
the Z-stage. These improvements now fully guarantee The Mondi mill in Ruzomberok (Slovakia)
the pulp quality after ozone bleaching. produces hardwood and softwood pulps at 89% ISO
When ozone bleaching started to develop in the brightness and switched in 2004 from a D-Eop-D-
early 1990s, the use of such a powerful oxidant in com-
bination with yet non-optimized process parameters
(the most important issue being the mixing homogene-
ity) resulted sometimes in uneven pulp delignification
and affected the pulp mechanical properties. Practices
improved step by step and opportunities soon replaced
difficulties, yet many pulp producers still believe that
the quality of ozone bleached pulp, especially soft-
wood, is lower than traditional ECF bleached pulp.
Since most of the mills using ozone are produc-
ing hardwood pulps, some people even believe that
this evidence sustains the alleged lower strength of
softwood ozone bleached pulps. The true explana-
tion instead is rather simple: ozone bleaching is
mostly implemented in Europe, Brazil, South Africa,
Australia, India and Japan, all countries deficient in
softwood resources. Thus, such an argument does not
Fig. 5 - MAIN OZONE REACTIONS WITH LIGNIN COMPOUNDS
stand considering that 25% of the mills using ozone
AND CARBOHYDRATES
are producing softwood pulps. This proportion is not
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5. bleaching
E-D bleaching to a ZEo-DnD one. It should first be At this stage it is worth remembering that gener-
noticed that there was only one washing stage (after ally, the tensile index is increased by refining while
ZEo) in the new process. Mondi compared hardwood the tear index follows the opposite trend and it is
and softwood pulp strength parameters of the new impossible to increase both of them at the same time.
pulps with the ones of the former pulps set as the Nevertheless the mill reported that the paper machine
reference (100%); only minor differences could be runnability was not affected and the final paper prop-
seen in standard pulp properties, Table 118. erties were even better than expected (stiffness)13.
Hardwood pulp properties were particularly
excellent and the hardwood proportion in the paper
Table 1 - RELATIVE PULP QUALITY FOR ECF-Z COMPARED
WITH ECF AT 27°SR FOR BOTH HW AND SW machine furnish was increased over 90%13. In 2005
Mondi Ruzomberok set up a new world record for
Hardwood Softwood copy paper production at 1,500 m/min13,18. Of course,
PFI rev 89 90 these two achievements would not have been pos-
Burst Index 100 97 sible with a lower pulp quality than before.
Tear Index 92 90 Moreover, the Ruzomberok mill has kept improv-
Breaking Length 104 102 ing the Z-stage operation and its bleaching process
Tensile Index 102 102 by installing a pressurized (PO) stage in place of the
Stiffness 93 94 last D stage in August 2008. Current pulp strength
properties are excellent and would make most pulp
mills envious, Fig. 6.
Concerning hardwood pulp, energy requirements Ozone bleaching process improvements never
for refining dropped by 11%, burst was maintained, stopped. The ITC mill in Bhadrachalam (India)
breaking length and tensile index increased while started ozone bleaching in 2007 after five years of ECF
tear and stiffness decreased. Meanwhile, for softwood bleaching operation. Its results are clear19:
pulp, refining energy was again reduced significantly, • the breaking length increased by 5.5%;
tensile properties increased marginally while burst, • the burst factor increased by 10%;
tear and stiffness showed some reduction. • the tear factor increased by 6%;
Fig. 6 - BLEACHING LINE AT MONDI RUZOMBEROK AND PULP STRENGTH PROPERTIES
38 August 2011 Pulp & Paper International (PPI)

6. bleaching
• the bleaching chemicals cost decreased by about 65 kg/tonne of low-pressure steam only are necessary
450 Rs/tonne ($10/tonne). for the Ze-DD bleaching sequence.
As an example, implementation of the ozone
O P E R AT I N G PA R A M E T E R S stage at Bhadrachalam led to a 50% drop in steam
consumption in comparison to the former D-Eop-D
Pulp temperature is one important operating param- bleaching sequence21.
eter that has been tuned. Ozonation was initially car- Steam savings are the highest in the case of hard-
ried out at 40°C in the 1990s and such a low tempera- wood pulp bleaching where usually a first A-stage
ture was not very convenient as the Z-stage is located (acidic) or DHT-stage (D-stage at hot temperature) is
right after the 85-95°C oxygen delignification and implemented. Such A or DHT stages have 2 targets:
before an alkaline extraction or a chlorine dioxide • removing hexenuronic acids which are responsible
stage (after a few MC ozone stages) generally carried for parasite chlorine dioxide consumption and
out at around 60-80°C. Therefore, it is necessary to brightness reversion;
cool the pulp before reheating it. • cleaning the pulp from transition metals which
It was thought that a higher temperature would are known to decompose H2O2 and responsible
lower the Z-stage efficiency, speed up the ozone for weakening of the cellulose during peroxide
decomposition, increase the negative effect of transi- bleaching.
tion metals and ultimately decrease the pulp quality.
Slowly, throughout industrial trials, it appeared that By removing transition metals the A-stage ef-
such fears were totally unfounded. Several results fectively replaces the use of a chelating agent. Acidic
have demonstrated that for hardwood pulp the Z- stages were built prior to the ozone stage in the
stage temperature could be increased up to 60°C and 1990s at the UPM mill in Pietarsaari (Finland), at the
sometimes even higher without any negative effect Sateri mill in Bahia (Brazil), at Fibria Jacarei and at
on pulp strength and brightness9,13,18. Espanola. But today there is no doubt that the imple-
For example, data from Ruzomberok show that mentation of an A-stage reduces both pulp strength
an increase of the Z-stage temperature from 43°C to properties and pulp yield22.
61°C gives a higher brightness (+1.8% ISO), a lower Of course, there is no such problem of hex-
brightness reversion, a higher stiffness and a better enuronic acids in the case of softwood pulp bleach-
ozone delignification efficiency, with all other proper- ing. But the issue of transition metals remains and
ties (PFI rev, Burst Index, Tear Index, Tensile Index in the 1990s Swedish mills SCA Östrand and Nordic
and Bulk) unaltered, Table 213,20. Paper Säffle as well as the Rosenthal mill in Blan-
Domtar Espanola first operated the Z-stage at kenstein (Germany) chose to start their bleaching
55°C. When it decided to increase the ozone stage sequence with a Q-stage (chelation).
temperature to 60°C, it increased delignification by Such A-stages or Q-stages are costly because they
5-10% and gained 1 point ISO brightness. Today, it is require a tower (with 2-3 hours retention time for
operating the ozone stage at 70°C9. the later) and the use of expensive chemicals. Yet in-
All HW pulp mills which set up an ozone stage in dustrial light-ECF and ozone based TCF experiences
the past 5-6 years are running the Z stage at a 55°C mini-
mum. This also resulted in significant steam savings. For
Table 2 - IMPACT OF TEMPERATURE ON THE KAPPA INDEX, ISO BRIGHTNESS
example, Ruzomberok reduced its steam requirements AND BRIGHTNESS REVERSION AT MONDI RUZOMBEROK
by 75% by running the Z-stage at 58-61°C 13.
Metso has shown industrially that steam require- Temp in Z 43°C 43°C 58°C 61°C
ments for light-ECF bleaching are only 25% of steam Kappa number after Z(EO) 4.1 4.0 4.0 3.8
requirements for conventional ECF bleaching in ClO2 charge, kg/adt (DCS data) 24.5 23.5 24.7 24.4
the case of HW pulp8. While the bleaching sequence Brightness, % ISO 85.9 85.2 86.6 87.7
DHT-Eop-D requires 249 kg/tonne of low-pressure Reverted brightness, % ISO 81.8 82.2 83.9 85.9
steam and 40 kg/tonne of medium-pressure steam,
Pulp & Paper International (PPI) A u g u s t 2 0 1 1 39

7. bleaching
have shown that the installation of those A-stages or In the 1990s it was common to fully bleach the
Q-stages should be avoided. pulp with six or even seven stages as in the following
The hexenuronic acids content is reduced by at sequences:
least 60% in the ozone stage23. This makes the ozone - A-ZD-Eop-ZD-Ep in Pietarsaari (Finland);
stage even more efficient than any A-stage and it - Q-OP-D-Z-PO-P in Blankenstein;
partly explains why ozone bleached pulps have a - A-ZD-Eo-DnD in Espanola.
lower brightness reversion than other pulps.
Actually, removal of transition metals is efficiently Bleaching sequences built in the last decade for
carried out during the ozone stage where the pH both hardwood and softwood pulps usually have only
is acidic (usually 2.5-3). Awareness of this avoids three or four stages and vary little from one another:
investing in any acid or chelating stage when ozone - Z-D-Ep-D at Nippon PaperYufutsu (Japan);
is applied, and results in operating cost savings. As a - ZEop-D-P at Mondi Ruzomberok;
result, only two of the 16 pulp bleaching lines having - ZD-E-D at Nippon Paper Maryvale (Australia);
started ozone since 2000 use an A-stage and none of - Ze-DP at ITC Bhadrachalam, Fig. 7;
them use chelating agents. - Z(EOP)-(PO) at Sniace (Spain, sulphite pulp for
dissolving grades);
BLEACHING SEQUENCES - Ze-D-P at Celtejo (Portugal).
The proven economical, technical and environmen- These bleaching sequences reflect the continuous
tal advantages, the development of oxygen deligni- and impressive developments of ozone application
fication as well as improvements in ozone bleaching in light-ECF bleaching process and clearly show the
and in the whole pulping process over the last 20 worldwide interest of pulp makers in ozone bleaching.
years, have allowed the bleaching sequence to be
shortened by one, two or even three stages, while CONCLUSIONS
simultaneously increasing the brightness ceiling with
2-3 points compared with what was possible. Ozone bleaching has already been industrially imple-
Fig. 7 - LINE 2 AT ITC BHADRACHALAM
40 August 2011 Pulp & Paper International (PPI)

8. bleaching
mented, experienced and improved for 18 years. It 4. CAMPO, R. and MARQUES, P Results Pulp & Paper
.,
is a well proven and safe process, currently used by 3, 32 (2009).
some reference pulp mills among the most modern 5. BOKSTRÖM, M., African Pulp and Paper Week
in the world. Its advantages in terms of bleaching cost 2002, Durban, South Africa.
savings, effluent load reduction and ease of use can 6. HOSTACHY, J.-C., Tappi J., 9(8): 16(2010).
no longer be questioned. It is applicable to all kind of 7. CAMPO, R. and SUNDIN, M., Proceedings of the
pulps and has no negative effect on their mechanical EFPG Days 2004, Grenoble, France.
properties. 8. WENNERSTRÖM, M. et al, International Colloqui-
The Z-stage takes place in just one minute and um on Eucalyptus Pulp 2007, Belo Horizonte, Brazil.
both HC and MC technologies are recognized as fully 9. GARTLEY, B., Ozone Delignification at Domtar
reliable, safe and stable processes. Espanola, paper presented at the PAPTAC Bleaching
High-consistency ozone bleaching is performed Committee, Oct. 21-23 2002.
at atmospheric pressure. Behind the ozone reactor, 10. CHIRAT, C., et al., Proceedings of the ABTCP 2008,
it requires only a 5-10 minutes long extraction stage Sao Paulo, Brazil.
and no intermediate washing is necessary. This solu- 11. VEHMAA, J. and PIKKA, O., Proceedings of Paperex
tion allows the E filtrate to be recycled back to the 2007, New Delhi, India.
brown stock or post-oxygen washing and further to 12. PIKKA, O., Proceedings of the EFPG Days 2004,
the recovery boiler, and so the total bleaching effluent Grenoble, France.
can drop to 4-6 m3/tonne. 13. TOMIS, B. and TUOMI, A., Proceedings of
As a result of continuous improvements of the Zellcheming 2006, Wiesbaden, Germany.
equipment and process automation as well as tuning 14. FERGUSON, K., Pulp & Paper, 66(11): 42 (1992).
of the operating conditions over a period of almost 20 15. CHIRAT, C., Proceedings of the EFPG Days 2007,
years, modern ozone bleaching is now recognised as Grenoble, France.
a state of the art technology for both hardwood and 16. LenzingTechnik, Eccentric Mixer - an innovation
softwood pulps. from LenzingTechnik, commercial presentation.
There are neither technical nor economical 17. LACHENAL, D., Proceedings of the EFPG Days
reasons to stick to a 30-year-old conventional ECF 2005, Grenoble, France.
process. The use of a light-ECF bleaching sequence 18. NORSTEDT, Å. and LINDSTRÖM, L.-Å., ATCP Con-
can by itself decrease bleaching costs by more than ference 2006.
20% and lead to the same pulp strengths with better 19. KUMAR, K.R., Proceedings of Paperex 2009, New
optical properties and refining ability. Ozone bleach- Delhi, India.
ing is by far the most valuable solution not only for 20. BALAZ, P Proceedings of Zellcheming 2006, Wies-
.,
forerunners but for all pulp mills. PPI baden, Germany.
21. PADMANABHAN, A. et al, paper presented at the
Emil Germer, Saint-Petersburg State Forest Technical National Award for Excellence in Energy Management
Academy; Alexis Métais, Jean-Christophe Hostachy, 2007, 22-23 August 2008, Pune, India.
ITT Wedeco 22. KOBAYASHI, T. et al, Japan Tappi, 59 (2005).
23. NORDÉN, S., ZeTrac Forum 2004, Rochehaut,
LITERATURE Belgium.
1. MÉTAIS, A., Proceedings of the TAPPSA National 24. ENGELFELDT A., internal training for ITC.
Conference 2010, Durban, South Africa.
2. CARRÉ, G. and WENNERSTRÖM, M., Proceedings
of the International Pulp Bleaching Conference 2005,
Stockholm, Sweden.
3. NORDÉN, S. et al., Eco-Friendly Bleaching with To read more articles on Chemicals, visit our Chemicals
ZeTracTM, paper presented at the IPPTA Annual Gen- Technology Channel at www.risi.com/
technologychannels/chemicals
eral Meeting & Seminar 2006, Chennai, India.
Pulp & Paper International (PPI) A u g u s t 2 0 1 1 41