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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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Conventional Batch Cooking Problems

  • Poor cooking uniformity

  • Cannot cook to a desired (low) kappa number without sacrificing pulp strength and/or yield


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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


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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 Benefits

  • Variability is improved over conventional cooking from better cooking uniformity and higher pulp strength


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Modern Digester Configurations – SuperBatch Cooking Benefits

SuperBatch pulps exhibit higher strength properties than conventional batch pulps.


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Modern Digester Configurations – SuperBatch Cooking Benefits

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


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Modern Digester Configurations – SuperBatch Cooking Benefits

Improved within-chip kappa variability


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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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