IntroductionModernizing or building their pulp mills, severalpulp producers still consider the 30 years oldECF bleaching as the only option.But, considering the very good and reliableresults achieved by industrial ozone bleaching,such a conservative attitude can not be justifiedany longer.
IntroductionFirst industrial production of ozone bleached pulpstarted in 1992.At the beginning, ozone bleaching developmentwas linked to the increasing environmentalpressure.
IntroductionToday the choice of ozone is mostly justified bythe economical savings resulting from chemicalscosts cut-off.In May 2011, 22 mills worldwide use ozonebleaching and deliver a pulp quality similar orbetter than conventional ECF bleaching would do.
Ozone Generation Ozone production requires only Oxygen & Energy.It is a pure on-site technology needing neither delivery nor storage Producing 1 kg ozone requires: - 10 kWh (all included) - 8.3 kg of pure oxygen At the generator’s outlet, the gas mixture contains 7.3 kg oxygen and 1 kg ozone(concentration of 12 % by weight)
Ozone Generation• Since 2000, ITT WEDECO has developed Z-Compact system which is an ozone plant completely pre-assembled at factory offering the following advantages:• Complete test run before shipment• Solution “plug & play”• Fully protected from ambient conditions• Minimal foundation work & foot print Modularity combining “on site” chemical production & supply is today a key success factor for ozone production . Example : Fibria Jacarei with 4 Z-Compact systems in operation • Nominal ozone production on site : 750 kg/h (18 tons/day ozone) • Peak capacity : 1 ton/h (24 tons/day ozone)
Z-stage – High Consistency C-Free® ZeTracTMHC ozonation is carried out at atmospheric pressure in 1 min.Ozonated pulp is then sent without intermediate washing to a 5-10minutes long extraction stage.Such a solution allows to recycle the E filtrate back to the furnaceand lower the total bleaching effluent to 4-8 m3/adt.
Z-stage – Medium ConsistencyIn 2004, Lenzing upgraded its 2 bleaching lines with modernmixers: it resulted in a 2.5 ISO brightness points increase for thesame ozone dose.
Z-stage – Operating Parameters for HWInitially Z-stages were operated at 40-45°C.In Mondi Ruzomberok increased temperatures improve ozonebleaching efficiency but do not impact mechanical properties: Temp in Z 43°C 43°C 58°C 61°C Kappa number after Z(EO) 4.1 4.0 4.0 3.8 ClO2 charge, kg/adt (DCS data) 24.5 23.5 24.7 24.4 Brightness, % ISO 85.9 85.2 86.6 87.7 Reverted Brightness, % ISO 81.8 82.2 83.9 85.9A similar study made Domtar Espanola operating the Z-stage at70°C. Today most of the HW Z-stages operate in the 55-70°C range.
Z-stage – Operating Parameters for HWAs a result of an increasedtemperature, steam requirementscan be 75% lower when ozonebleaching is implemented:(industrial figures)
Green Bleaching Green Bleaching consists in maximizing the use of green chemicals and their by-products.Example of Celtejo (Portugal): Pulp production: 720 adt/d (Eucalyptus, Pine) Brightness: 90 % ISO Flexible bleaching process: (OO)ZeDD, (OO)ZeDP & (OO)ZePP Total bleach plant effluent volume: 6-8 m3/adt for light-ECF 4-6 m3/adt for TCF
Green Bleaching Oxygen34 t/day O2 30 t/day O2 + Applications 4 t/day O3 Ozone 17.5 t/day 02 Generator Gas scrubber 30 t/day 02 available Oxygen Delignif. Compressor Pulp in Oxygen 12.5 t/day 02 Plant Oxygen TOWL Back-up Z-Stage LOX tank Pulp out Ozone Destruction System ambient air
1998: Domtar Espanola (Canada) Pulp production: 800 adt/d (Birch, Aspen, Maple) Brightness: 93 % ISOIn 1998, Domtar Espanola switched from O-A-D-E-DnD to O-A-ZD-E-DnD.It was noticed: 1. no impact on viscosity or mechanical strength 2. a replacement ratio from 2.2 to 3.5 3. a bleaching costs reduction of 10%
Mondi Ruzomberok (Slovakia) D PO PO Pulp production: 480,000 adt/y (HW and SW) Brightness: 89+ % ISO PFI 28 SR - HW: PFI 28 SR - SW: Breaking length (km) 7.8 - 8.5 Breaking length (km) 11 - 12 Tear index (mNm2/g) 5.8 - 6.5 Tear index (mNm2/g) 9.5 - 10.5 Stiffness (mN) 125 - 135 Stiffness (mN) 125 - 135 Viscosity (cm3/g) 650 - 700 Viscosity (cm3/g) 550 - 600In 2005, the mill set a new world record for copy paper production at 1500 m/min. The paper machine is still today the 3rd fastest worldwide for such a production
ITC Bhadrachalam (India) Line 2 Pulp production: 500 adt/d (Eucalyptus, Subabul and Casurina) Brightness: 89+ % ISOITC’s feedback concerning ozone bleaching is the following: 1. overall strength properties improved by 5% 2. about Rs 450 per MT saving in bleached pulp cost of production Savings of 7.25 €/adt 3. 1 kg of Ozone replaces 5-6 kg ClO2 as active Cl2
Fibria Jacarei (Brazil) Line C Eucalyptus pulp production: - 1,200 adt/d on line B - 2,500 adt/d on line C Brightness: 90+ % ISOProducing 1,300,000 adt/y, Fibria Jacarei is the biggest mill using ozone bleaching. The mill just contracted a new Z-Compact-System to increase capacity on line B.
Oji Paper Nantong (China) Pulp production: 1600 adt/d (Eucalyptus and Acacia) Brightness: 90+ % ISO Start-up: 2012 The Oji Paper mill in Nantong will bethe first Greenfield mill built with an ozone stage
In the near Future…Results presented by Metso - Zetrac forumApril 27– 28, 2011, Pousada do Crato, Flor da Rosa, Portugal
In the near Future… … an A(Ze)(PO) bleaching sequence would allow to bleacheucalyptus pulp to 92% ISO with 3.3 kg/adt O3 and 8 kg/adt H2O2!
ConclusionsOzone bleaching technology has improved a lot in the last 20 years. Itis today: - a well proven technology - a reliable on site chemical production - a safe, stable and flexible process - used by some reference pulp mills worldwide.Ozone bleaching allows to reach those 4 targets at once:1. Lower the effluents amount combined2.Improve effluents quality3. Produce pulp with similar or better strength properties,4. Lower bleaching chemical costs by at least 20%
Sustainable development is your ambition… Ozone Bleaching is our solution! Fibria Jacarei, Brazil MUITO OBRIGADO PELA VOSSA ATENÇÃO !