Cooking process of lignocellulose material

摘要

A continuous cooking process making use of a digester, which includes therein, from a top toward a bottom of the digester, a top zone, an upper cooking zone, a lower cooking zone and a cooking/washing zone and also includes strainers provided at the bottom of the respective zones and wherein a cooking black liquor extracted from at least one of the strainers is discharged to outside a digestion system, a process for cooking a lignocellulose characterized by feeding, upstream of the top of the digester, a first cooking liquor containing an alkaline cooking liquor having a specified composition, feeding a second cooking liquor of an alkaline cooking liquor made mainly of sodium hydroxide to the upper cooking zone, and feeding a third cooking liquor of an alkaline cooking liquor similar to the second cooking liquor to the cooking/washing zone.

主权项

1. A continuous cooking process for cooking lignocellulose comprising the steps of:
providing a digester having, from the top to the bottom thereof, a top zone, an upper cooking zone, a lower cooking zone, a cooking/washing zone and strainers provided at the bottom of the respective zones; feeding a first cooking liquor comprising an alkaline cooking liquor containing polysulfide, sodium hydroxide and sodium sulfide or sodium carbonate and sodium sulfide as main components, polysulfide sulfur at a sulfur concentration of 3-20 g/L, not less than 99 mass % of a sulfur component to total sulfur component of cooking activity and 85-95 mass % of effective alkali relative to total effective alkali, respectively, in total amount of alkali cooking liquors to be introduced into the digester, upstream of the top zone of the digester; feeding a second cooking liquor comprising an alkaline cooking liquor made mainly of sodium hydroxide to the upper cooking zone; feeding a third cooking liquor comprising an alkaline cooking liquor made mainly of sodium hydroxide to the cooking/washing zone; and withdrawing a cooked pulp from the bottom of the digester, wherein a cooking black liquor is extracted from at least one of the strainers and discharged outside of the digester.