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Modern Digester Configurations – SuperBatch Cooking

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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Modern Digester Configurations – SuperBatch Cooking

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  1. Modern Digester Configurations – SuperBatch Cooking

  2. Conventional Batch Cooking Problems • Poor cooking uniformity • Cannot cook to a desired (low) kappa number without sacrificing pulp strength and/or yield

  3. 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.

  4. Modern Digester Configurations – SuperBatch Cooking Intensive HBL treatment allows for improved H-factor/kappa relationship

  5. Modern Digester Configurations – SuperBatch Cooking • Circular steam packing configuration to minimize void spaces

  6. 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.

  7. 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

  8. 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.

  9. Modern Digester Configurations – SuperBatch Cooking • Used cooking liquor is displaced by wash liquor into accumulators for use in later cooks.

  10. 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

  11. 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.

  12. Modern Digester Configurations – SuperBatch Cooking • Variability is improved over conventional cooking from better cooking uniformity and higher pulp strength

  13. Modern Digester Configurations – SuperBatch Cooking SuperBatch pulps exhibit higher strength properties than conventional batch pulps.

  14. Modern Digester Configurations – SuperBatch Cooking Lower kappas can be expected at the same relative H-factors.

  15. Modern Digester Configurations – SuperBatch Cooking Improved within-chip kappa variability

  16. 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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