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

5. 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. 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 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. 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 “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. 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. 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.