Rae Cunnington chaired this Technical Session.

There were three parts to the Technical Session. Part One consisted of Doug Pryke and Chris Kanters presenting the Softwood Analysis from the ECF Survey. Part Two consisted of a panel of mill members answering 6 questions composed by Rae. Part Three consisted of the group answering thirteen questions composed by Rae.

Part 1: Softwood analysis was presented today.

Chris Kanters, Ted Tam and Doug Pryke were the surveyors.

Sent survey to 42 mill sites – got 42 responses – 38 SW and 11 HW – 49 Bleach Plants.

Do Stage. Presenters to make note on how they calculated Kappa Factor. Used ClO2 application per ADt bleached pulp / Kappa # entering Bleach Plant. Where had K#, multiplied it by 1.5.

Eop. End pH most common control.

No semi-bleached included. 3, 4 or 5 stages - 90 to 91 brightness.

Second E or Ep stage – total bleach plants, i.e. DnD included where couldn’t add anyway.

Cost discussion. 0.5 kg equiv. Cl2 for each 1 kg of carryover. Doesn’t include mag. sulfate; sulfuric acid for pH control of Do; antichlor; or chemicals in O2 delig. stage. Bleaching chemicals only. Does include NaOH used in D1 stage.

Bleaching cost $4.63/ADmt less in low chemical consuming vs. high chemical consuming bleach plants despite higher Kappa No. feeding the bleach plants.

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$5.31 /ADMt less in low vs. high despite higher Kappa!

Why is cost data contrary to expectations? Data too sketchy to discern why? Better control? More Kappa analyzers? More medium consistency first stages? Not enough to make conclusion. Not necessarily furnish.

Approx. $11/tonne less bleaching cost in O2 delig. vs. conventional. $50 vs. $39/tonne.

No significant bleach cost change since 1996 survey. More O2 delig.

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A panel discussion of 6 questions posed by Rae Cunnington followed. The panel included: Weyerhaeuser, Grande Prairie; EB Eddy, Espanola; Irving, St. John; and James River, Marathon. Others from the audience also contributed answers to the questions.

1. Does your mill split the addition of ClO2 to the first stage? Has the mill examined the benefits of altering this addition? What do you believe is the best manner in which to add the ClO2 to this stage? Why? Do you have any hydraulic limitations that prevent you from making a more optimal split?
2. What do you believe is the best distribution of hydrogen peroxide in the bleach plant, (Eo, E2, both)? What factors do you think should influence where peroxide is added and how much is added? Has your mill conducted any trials recently to look at this distribution? What were the results?
3. What is the best material of construction for a Do/D1/D2 tower? Why?
4. What is the best material of construction for bleach plant washers?
5. What is the optimum distribution of ClO2 in Do, D1, D2 stages?
6. What is the best mixing strategy for ClO2 addition to a Do stage?

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Does your mill split the addition of chlorine dioxide to the first stage? Explain results from trials.

Just went from 2 mixers to 1. Did trial using both or one and saw no actual difference in results. Both high shear mixers. Medium consistency. Using compensated brightness and saw no difference. 100 horsepower less due to one mixer. Only concern – used to have on-line spare. If have good mixing need only one mixer.

No split, only have one IMPCO high shear mixer.

Don’t split addition to Do. SW runs low consistency Do. Dioxide added ahead of static – works well. HW add to Ahlmixer. Runs well. Use chlorine on SW line. Need to set up Ahlmixers correctly to optimize mixing. ClO2 addition counter to the stock flow.

Low consistency D100, add all at once. Found no difference when trialed in past. Two in-line static mixers.

Had two Sunds. Now one and no difference.

Have 3.

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Found no difference. Had a Sunds and static. Got rid of static, then replaced Sunds with an Ahlmix.

Static after Ahlmix. Never use second.

Two Kamyr high shear mixers. Put all to one mixer.

Have 4 going down to 3 soon. All MC.

Had 2 static and high shear mixer. Use only high shear mixer now, low consistency.

Rae Cunnington summary: General consensus appears to be no difference between single or multiple injection, and one mixer is adequate provided it mixes well. May need to have dual injection points just because of hydraulic capacity of existing pipe lines

What do you believe to be the best distribution of peroxide in the bleach plant?

Not a lot of experience at Grande Prairie. Have peroxide in Eo stage. Did trials on E2p. Jury is out on where is best application. Was originally added at the top of the pre-retention tube, now MC pump. Were adding 6 kg/tonne Eop for effluent colour. Did trials and found 4 kg/tonne was fine for colour. Jim Collins, James River, Marathon

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No peroxide in E2 stage. No real provision to add but would if could. Add to Eop since 1991. Put in standpipe just before pump suction. 4 kg/tonne. Considering adding magnesium sulfate due to pulp strength issues. Have they tried higher levels? Planning to trial. Did add 7 kg/t by mistake. Add as 5% peroxide. Increased temperature to 85 degrees C. Brought pH down to 10.6. Got caustic reduction. Any problems running washer – no. Want 50 to 52 brite on Eop.

Don’t use peroxide on reg. basis. DEDnD both on HW and SW so can only use in E1 or final storage. Run only for high brite. Peroxide at 5% dilution. Used to have too much metal carryover from first stages but have improved. When they used to bleach in high D they added 1.1 lb. NaOH/1 lb. peroxide. 2 ½ to 3 hours in high D. pH of 10 in high D. Head box 5 or 6. Using sour water to kill peroxide. HW no peroxide, run 60 to 65 and SW 58 – can get to 78 on SW with peroxide.

Were adding to both E stages. Discontinued adding to E2, found no change in chemical consumption or brightness. Doing on/off trials in Eop with peroxide to gauge impact on effluent. What caused you to take off second E2p? Were originally doing it to get better brightness stability for certain customers but now have different customers and products. Can still add E2p when having problems. E2 peroxide was 1.5 kg/t. D1 84 to 86.5 brightness.

Doug Pryke: In the survey, the mills with low chemical consumption had 3 kg. in Eop, high chemical consumption mills had 4.5 in Eop. Half mills in both categories used E2 peroxide at 1.2 to 1.6 kg/t. Peroxide doing more brightening in high cost mills.

Eop and Ep. Limited to 1.5 kg. 82 degrees C, 1 to 1.5 hours. Thinks it is the better place to put it, i.e. second extraction. Hard to consume all the peroxide though.

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Add on E2 stage to catch up. Soda carryover 12 to 25 kg saltcake/ADt on good day up to 45 on bad day. 1 to 1.5% kg. peroxide will get 20 points of brightness. Just on "B" bleach. Use on A Bleach as well but B bleach aggressively. Add magnesium sulfate at E1 stage only. Believe it carries through. Two stage O2 delig. in middle of bleach sequence. Trying to save quality. D1 brightness is only typically 56 when they do this peroxide addition. Add at D2 .35 to 0.45% ClO2 to catch up, i.e. higher than normal but not much. Sequence is Do with a low Kappa factor, OOD1 Ep D2.

Add manganese sulfate which kills peroxide carryover from peroxide treatment in high density storage. Worried about paper machines with carryover. Add very small amount of manganese sulfate. Run 92 degrees at first washer.

Run a pressure of 300 kPa at top of upflow tower for best performance.

Individual?: Who has tried Quick Brite and found it did not give reliable measurement. Many mills have found this, especially on Eop pulp. As brightness is increased, the reliability improves.

What is the best material of construction for Do, D1 and D2 towers?

Have acid tile on 3 towers, but have to put up with the associated maintenance costs.

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Best is not necessarily cheapest. Run acid tile on D1 and D2 – old towers, annual inspection. New MC Do tower on hardwood bleach line, chosen for lowest cost, is FRP, N710 double Nexus veil. Had 20 year lifespan on FRP – 60 C in softwood bleach plant. New tower will be FRP, with double nexus veil and new N710 resin. Inspect FRP tower every year. Hard to get good repair on corrosion veil. Big job. Watch with FRP lines – used to be hand-laid up now filament wound. Don’t stand up to abuse.

All bleaching towers are acid tile lined. There since 1950’s. When they had damage got past membrane and corroded tower. Have FRP on D1 – needed emergency repair after 7 years.

Do is FRP – 9 years old. Having damage. Feel can’t predict failure. Is cheaper material worth it? – don’t know how to predict life service. Have gone to Kynar lined for ClO2 pipe. Found risk of ClO2 leak from pipe unacceptable. Coring pipe is only method to determine integrity. What are using for nozzles? Some FRP and some titanium and SMO.

In the US, mills have replaced FRP when it was considered unpredictable.

What is the best distribution of ClO2 in Do, D1, D2 stages?

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Survey results. Do = Conventional 2.1 % on pulp for low chemical consumers. 2.3% is for high chemical consumers. D1 is 1.1 and 1.2. D2 is 0.32 and 0.37.

A bleach is 2.5, 1.0 and 0.15. B bleach is 1.4, 1.0 and 0.35.

2.0, 1.1 and 0.5.

2.3, 0.45 and 0.23.

2.1, 1.2 and 0.3.

1.5, 1.0, 0.35.

1.7, 1.0, 0.28.

1.3, 0.9 and 0.25.

Sterling advised that 55 to 65% of ClO2 in first stage (Do) is preferable to keep overall chemical consumption low.

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Rae provided 13 questions for the group as a whole to answer. Tables were given a number and the individuals at that table were asked to answer certain of the following questions.

1. For O2 mills. Has your mill explored the best combination of pulping and O2 delignification, in terms of yield, bleachability?
2. Have many people in the audience explored the relationship between their unbleached Kappa number and their bleaching costs? What type of relationship have they found?
3. Has your mill switched recently from measurement of saltcake losses to COD losses? What do you consider the benefits of switching? Do you believe that COD is a better predictor of bleaching chemical consumption by organic carryover? For the people who have not switched, what are the primary reasons for not switching? Cost? Easement of measurement?
4. Has your mill recently switched to MC Do stage? If so what were the quantifiable benefits from this switch? What type of ROI did you find for this project?
5. For people who have increased their Eop temperature, (say from 70 – 80 or higher), what were the quantitative benefits of doing so? Was there a cost benefit when steam was factored in?
6. If you have an Eop stage has your mill tried adding MgSO4 to this stage? If so what was your objective for trialing it? What were the benefits/results? If not, why?
7. If you have a kappa analyzer on brownstock and/or Eop stage, what control strategy are you using? Kappa factor or compensated kappa factor? What benefits has this additional control provided? Cost, variability, etc.?
8. D1 stage. What measure do you think is the best measurement of bleachability? Eop kappa or Eop brightness?
9. For those mills with Eop kappa analyzer, have you tried using Eop feed forward control for D1 brightness?
10. The survey found that oxygen mills with a post oxygen kappa number of 20 had significantly lower bleaching costs, (~ $4.63/MT), than those with a post oxygen kappa number of 16. Why do believe this is the case?
11. For a DEopDED sequence, what is the best filtrate recycle scheme? Why? (Assume 2 zones per washer white water and hot water available for equivalent of one complete washer each).
12. What is the best way of measuring/controlling pH in a D1 stage?
13. Does and oxygen delig. system impact pulp strength, even with MgSO4?

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For mills with O2 delig, has your mill examined the best combination of pulping and oxygen delignification in terms of yield, bleachability?

Low solids at 30 Kappa and O2 is equiv. to 38 Kappa and O2 delignification in yield. Pioneer and Ahlstrom with U. of Maine doing laboratory study, 15 to 40 Kappa and 10 to 13 from O2 delignification, and will look at yield – expect results at end of year. Student at Paprican working on this.

One mill optimized for other factor, i.e. environmental

Have you explored the relationship between unbleached Kappa No. and bleaching costs?

Answers to Question 2.

Kamloops - 2 lbs. ClO2 per Kappa. After installation of O2 delignification this changed.

Higher Kappa pulp lignin seems to be easier to remove. Less lignin re-precipitation in BS with high Kappa? When low Kappa number may get lignin re-precipitation. Loss of digester residual?

One mill reported 3.33 kg equiv. Cl2/Kappa increase. Linear relationship normally but not linear during upset.

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How do you measure black liquor carryover to the bleach plant, COD or saltcake?

All used saltcake. COD too time consuming.

COD is best predicator of chemical consumption but not easiest. Most mills using conductivity for ease of use and good relationship between soda loss and chemical consumption. Some chemicals like methanol show up as COD demand but do not demand chem.

Mills measure conductivity in and out of BSW.

Has your mill switched to MC Do from LC? What were results?

One mill had without doing anything else. No change in chemical consumption observed.

Weyerhaeuser, Grande Prairie had switched. Quantifying ROI difficult because other changes went on at same time.

For mills that have increased the Eop stage temperature, were there quantitative benefits from doing so, after factoring in steam costs?

Crofton results from their OO stages part way through the bleach plant.

Agreement that high temperatures are beneficial.

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For Eop stages, have you tried the addition of magnesium sulfate?

Most mills have not tried it.

Crofton said 0.2% magnesium sulfate with 0.6% peroxide resulted in a 2 to 3 pt. viscosity increase. May carry forward.

Fred Munro agrees that magnesium sulfate carries forward.

If you have a Kappa analyzer, what control strategy are you using?

Cariboo does have Kappa analyzer but not using – using brightness control. Need to improve reliability.

Hinton has Kajaani Kappa Analyzer. Still evaluating benefits.

One mill has a CEK analyzer – don’t know if it is a measure of bleachability.

Thunder Bay at inlet.

Northwood have inlet and CEK. Have Kappa factor control on Do and D1.

Crofton has one and uses at inlet and CEK.

Halsey has one at inlet and CEK.

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What do you think is the best measure for bleachability, Eop brightness or CEK No?

Eop brightness is a better measurement. CEK was measured but down in range 1 to 3 it is too low to use accurately.

CEK test is too variable so use brightness.

For mills with Eop Kappa Analyzer, have you tried feed forward control for D1 brightness?

No experience reported.

The survey found mills with oxygen delignification and a post oxygen Kappa No. of 20 had significantly lower bleaching costs (~$4.63) than those with a Kappa No. of 16. What might contribute to this?

Species? :

• One mill normally uses IDF, and tried coastal species and found the same bleaching costs.

• Hexaneuronic acids can be removed by acid stage. Different amount of acid solubles that survive O2 delignification.

Lignin reprecipitation:

• Loss of digester residual
• After O2 delignification

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Carryover?

High variability in Kappa number?

Not sharing the load between stages?

Was the conversion of K. No to Kappa done right?

Small bleach plant, i.e. retention time, poor mixing?

Std. deviations of Kappa’s or coefficient of variability?

Bad O2 delignification reactions if hitting too hard?

Higher sulfidity pulp may be easier to bleach?

Artifact of panicky chemical operators? May not get benefit of lower Kappa because overadding chemicals.

pH control strategy not adjusted to account for different incoming conditions?

Mill water quality.

Pulp cleanliness.

Mill that put in O2 delignification maybe stuck with small bleach plants.

Some kind of kinetic reaction?

Were the pulps bleached to the same brightness?

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For the standard DEopDED sequence, what is the best filtrate recycle scheme to use?

Jump stage counter current. Costs. Lower water use, steam savings, better chemical use.

Recycle of white water to D2 stage is most common.

Most mills do not use Eop filtrate.

E2 back to Eop and top shower bars D1.

Question 12.

What is best way of measuring/controlling pH in a D1 stage?

In line pH probes and some with sample extraction and offline measurement. High pH for bleaching and lower for shive control.

No resolution. Where to put probe. Up in tower or right after in vat. Only ones controlling higher pH were controlling scheme around that.

Most mills have in-line pH control. 2 mills let pH float. One uses spent acid, one mill caustic.

Does an O2 delig system impact pulp strength even with the addition of magnesium sulfate?

Most pulp strength loss results from what is done in the digester. Total viscosity loss across bleach plant is the same if you do or do not have O2 delig.

Depends upon how you run O2 delig.

Most add magnesium sulfate. Viscosity will go down a bit.

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Verbal report by Fred Munro.

Have new Z/D stage on hardwood line. React ozone immediately then add ClO2. Can use as ClO2 only stage. Since end April 1999. Running in campaigns. Found very effective bleaching agent for high brightness. Low 2’s to 4 as replacement, i.e. replace 2 to 4 kg ClO2 for every kg. ozone. Gone 50% and up of ozone substitution. Make 100% birch, aspen or maple. 600 tpd. Paper machine loves it – something about it they like. Ahlstrom ALZ mixers, two mixers ozone then Ahl mixer for CLO2 special med. consistency ozone mixers. No ozone left after mixing. Retention. Mixers fraction second. Transition tube 20 seconds. Most reaction happens in mixers. 60 minutes retention in downflow Do. Capability of adding 6 kg/tonne ozone. Started at 3 and moving up. Conc. of ozone is 12.5% - running now at 10 or 11. How decide how much ClO2? Ozone is a fixed charge. ClO2 added to give CE brightness. Stable. Different strength viscosity relationship – haven’t seen deterioration in paper strength. Not expecting problem.