Patent ID: 9145642
Filing Date: 2015-09-29
Classification: D21C

Abstract:
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.