Minutes of Meeting

1. IMPACT OF MINI 0₂ DELIGNIFICATION SYSTEM
ON PULP QUALITY AT HARMAC - (Murray Walters)

• See previous paper by Doug McKenzie for background on why the system was installed and its configuration.
  
• "Low AOX" pulp in 1990 did not require maximum pulp strength, so ran mini-0₂ without worrying too much about strength.
  
• 2 lines of mini-0₂.
  
• Target 25% Delignification, but have seen as high as 50%.

Lab Trials:

• No relationship between incoming COD and pulp strength.
  
• Lost 1 CP/P Number drop.

Mill Trials:

1994:

• 5 days on and 5 days off, composite samples. Trial aimed at economic evaluation.
  
• CED viscosity dropped 1, tear down by about 1 point for entire tensile.

1995:

• Ran system for "low AOX" production only, but wanted to run all the time, so did a MgS0₄ trial.
  
• Tear/tensile (intrinsic strength) lower than for no oxygen, BUT adding MgS0₄ resulted in HIGHER intrinsic strength when oxygen on.
  
• NOTE: Viscosity was 10% lower even though intrinsic strength was the same or higher - or 4 points viscosity drop/P Number drop with MgS0₄.
  
• MgS0₄ eliminated the strength loss that was inherent in oxygen delignification.
  
• Trying to get customers away from viscosity as a release test.
  
• Mill has found that (contrary to some published results) mini-0₂ pulp is easier to bleach.

Future:

• Looking for justification for automatic kappa analyzer.
  
• Planning for MgSO₄ optimization.

Norm:

• Adding borohydride in last D2 stage will raise the viscosity test result by 3 points.
  

Dennis:

• To put a mini-0₂ system in for $ 3.5 million must require an unused washer, or the cost goes to $ 4.5 million.

2. WHAT PULP STRENGTH IS AND HOW COOKING, BLEACHING AND MILL CLOSURE AFFECT IT - (Norm Liebergott)

What is pulp strength?

Three kinds:

1. Fibre strength
   
2. Pulp strength
   
3. Paper strength
   

1. Fibre Morphology      Different species    . Intrinsic
                                      Length                  . Kinks/Curls
                                      Bonding

• Fibre Strength: Zero span, fibre angle.
  
• Fibres Determining Fibre Strength:
  
  • Cellulose Content
    
  • Proportion of S2 in the Cell Wall
    
  • Fibril Angle in the S2 layer
    
  • Physical Properties of the Cellulose
    
  • Physical Properties of the Matrix
    
  • Pulping and Bleaching Processes
    
  • Defects in the Cell Wall.
    
• Defined by a number of factors including pulping and bleaching conditions.

2. Pulp Strength: Burst, Tearing, Tensile, Bulk, Porosity, Fold, Roughness.

• Viscosity = average length of the cellulose chains. Intrinsic fibre strength.
  

• Pulp strength loss can come from:
  
  • Fibre damage from chipping operation:
    
  • Reduction in fibre length
    
  • Overthick chips
    
  • Fibre damage in cooking:
    
  • Non uniformity
    
  • Short cooking cycle
    
  • Removal of various wood constituents
    
  • Cooking to low Kappa number
    
  • Degradation of cellulose polymers
    
  • Digester blowing
    
  • Fibre damage in bleaching:
    
  • Reduction in molecular weight.
    
  • Mechanical treatments that change the internal structure of the fibre.
    
  • Changes in bond strength related to changes in chemical composition and to changes in internal structure of the fibres.
    
  • Changes in bonded area - also related to changes in internal structure and composition of the fibres.

3. Paper Strength:

• Burst/tear/tensile at constant test conditions.
  
• Different pulps react differently to refining.
  
• Now - using tear VS. tensile (= intrinsic strength)
  
• Future - fracture resistance.

Strength Loss comes from:

• Chipping operation - overthick too short, uneven distribution.
  
• Damage during cooking - uneven cooking, over-chlorination, too high or too low pH at Do.

Lab Trials - Strength Loss:

• 100% base pulp (lab prepared).
  
• BS - 80% (pilot plant)
  
• 0₂ Delig. - 75%
  
• DeoDED - 70%

Mill Bleach Plants:

• Do - pH too high or low decreases viscosity.
  
• 0₂ delig. - too low Kappa, e.g., 30 - 11.2 tear after bleaching sequence, 20 - 9.8 tear
  
• Increasing % delig. from 30% to 44% resulted in strength loss due to blowing hot.
  
• Eop stage - 85 Deg. should add MgSO₄ to protect pulp strength.
  
• Acid treatment, if too hot, will reduce intrinsic strength.

• See Appendix 1 for slides presented

• Future is high yield ECF cooking with polysulphide, Z/D.
  
• Compared Canadian mill Z/D, D/Z, Do, found both ozone had higher tear. Tensile almost same at 500 csf.
  
• Ozone by itself resulted in 5 - 10% loss in tear/tensile, but the D/Z process does not show this. Theory is that the Cl0₂ (or Cl0₂ filtrate) stops the ozone-lignin residuals from degrading the cellulose.
  
• 6 Kg. ozone seems to be the maximum - using 8 Kg/t reduced all strength parameters significantly, but 6 Kg/tonne had little effect.
  
• Ozone replacement ratio is 1 Kg. ozone : 2 Kg/Cl0₂ for a large cost savings.
  
• D/Z is particularly effective on non-oxygen delignified pulp, but Z/D is better for 0₂ delig. pulp.
  
• 3 systems in world running D/Z today.