Patent ID: 9382389
Filing Date: 2016-07-05
CPC Classification: C08H,D21C,Y02P

Claim Text:
1. A method for separation of lignin from black liquor, comprising: precipitating lignin by acidifying black liquor with carbon dioxide resulting in a first lignin suspension; separation to form a lignin cake of a solid material of a first filter cake and a first filtrate, suspending the first filter cake to obtain a second lignin suspension, separating the second lignin suspension to form a second lignin cake of a solid material of the second filter cake and a second filtrate, adding a washing liquid for displacement washing of the second filter cake, enhancing a dryness of the second filter cake, obtaining filtrate from the displacement washing, the filtrate forming a part of the second filtrate, increasing an ionic strength by adding recovery boiler precipitator dust to at least a first portion of the second filtrate and adjusting the pH of the second filtrate to a value below 6, washing the first filter cake with the first portion of the second filtrate, the recovery boiler precipitator dust of the second filtrate keeping lignin in the first filter cake in solid form, and sending the first portion of the second filtrate to recovery after use as washing liquid, and adding a second portion of the second filtrate to the washed first filter cake to form the second lignin suspension, adjusting the pH level of the second lignin suspension to a value below 6 and approximately the pH level of the washing liquid added to the second filter cake.