Patent ID: 8877007

Claim:
A method of refining sulfite rejects obtained during acid sulfite pulping or bisulfite pulping, the method comprising: providing wood chips and a sulfite cooking liquor to a digester and digesting the wood chips at a suitable temperature for obtaining delignification; screening a slurry obtained from the digester to separate a reject portion from an accept portion, the reject portion including sulfite rejects comprising condensed lignin, wherein the condensed lignin was formed by acid-induced condensation; providing the sulfite rejects to a refiner, wherein the refiner is adapted to disintegrate the sulfite rejects; refining the sulfite rejects to obtain refined sulfite rejects having a Canadian standard freeness between approximately 600 ml and 900 ml; and returning at least a portion of the refined sulfite rejects to the digester for re-cooking in the sulfite cooking liquor with additional wood chips.