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Modern Digester Configurations – SuperBatch Cooking. Conventional Batch Cooking Problems. Poor cooking uniformity Cannot cook to a desired (low) kappa number without sacrificing pulp strength and/or yield. Basis for improvements:.

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Presentation Transcript
conventional batch cooking problems
Conventional Batch Cooking Problems
  • Poor cooking uniformity
  • Cannot cook to a desired (low) kappa number without sacrificing pulp strength and/or yield
basis for improvements
Basis for improvements:
  • Hydroxyl content must be low at initial cooking, uniform through bulk phase.
  • [HS-] has to be high during initial cooking
    • Early sulfide - lignin reactions with little alkali present
  • Lignin and sodium levels need to be low at the end of the cook.
  • Temperature has to be decreased in the cooking cycle.
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Modern Digester Configurations – SuperBatch Cooking

Intensive HBL treatment allows for improved H-factor/kappa relationship

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Modern Digester Configurations – SuperBatch Cooking
  • Circular steam packing configuration to minimize void spaces
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Modern Digester Configurations – SuperBatch Cooking
  • Black liquor impregnation occurs at a temperature below 100 deg C.
  • Low alkali - neutralizes wood acidity.
  • Liquor has high sulfidity.
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Modern Digester Configurations – SuperBatch Cooking
  • Hot black liquor displaces impregnation liquor, then hot white liquor is added
  • Energy saved by conserving heat from previous cooks within hot black liquor
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Modern Digester Configurations – SuperBatch Cooking
  • Liquor re-circulated for uniformity’s sake.
  • White liquor may be added during cook to control alkalinity and final fiber quality.
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Modern Digester Configurations – SuperBatch Cooking
  • Used cooking liquor is displaced by wash liquor into accumulators for use in later cooks.
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Modern Digester Configurations – SuperBatch Cooking

“Gentle Blow”

  • Pulp is well below 100 degrees C at this point.
  • Digester is emptied with a centrifugal pump.
    • Reduce strength loss
modern digester configurations superbatch cooking benefits
Modern Digester Configurations – SuperBatch Cooking Benefits
  • Initial pulping sulfide reactions makes for a fast, intensive bulk delignification phase.
  • High initial temperature in white liquor addition phase (10-15 deg below cooking temp) means a very small amount of direct steam is required.
  • High liquor to wood ratio ensures uniform alkaline concentration.
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Modern Digester Configurations – SuperBatch Cooking
  • Variability is improved over conventional cooking from better cooking uniformity and higher pulp strength
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Modern Digester Configurations – SuperBatch Cooking

SuperBatch pulps exhibit higher strength properties than conventional batch pulps.

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Modern Digester Configurations – SuperBatch Cooking

Lower kappas can be expected at the same relative H-factors.

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Modern Digester Configurations – SuperBatch Cooking

Improved within-chip kappa variability

modern digester configurations superbatch cooking problems
Modern Digester Configurations – SuperBatch Cooking Problems
  • Scaling issue – calcium salts
  • More complicated to run than conventional batch
  • High rejects can be a problem when kappa (softwoods) raised much above 30 – 35.
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