Patent ID: 9475833
Filing Date: 2016-10-25
CPC Classification: C07G,C08H,D21C,Y02P

Claim Text:
1. A method for separation of lignin from original black liquor (BL IN ) handled in chemical recovery operations with evaporation stages receiving black liquor from a digester, said original black liquor having a first pH value, comprising the following phases in sequence: a first precipitation stage (PR) wherein an acidifier charge, comprising carbon dioxide, is added to the original black liquor in order to decrease the first pH value of the original black liquor to a second pH level and to initiate precipitation of lignin wherein the second pH level is above pH 7 and below 11.5, followed by a separation phase (FP suspending the lignin cake in a strong sulfuric acid solution establishing a pH level below 5 and maintaining the acidified lignin slurry in this slurry state for at least 2 minutes, dewatering the acidified lignin slurry (FP subjecting the acidic liquid phase (FL separating the solid gypsum (WG) from the acidic liquid phase and bleeding out the solid gypsum from the chemical recovery operations while sending the remaining liquid phase (FL using at least a part of the carbon dioxide released in the sulfur removal process as part of the acidifier charge added to the original black liquor.