Patent ID: 8691049

Claim:
A method for the production of cellulose pulp in a continuous digestion system in an energy-efficient manner, the method comprising the following steps: providing a digester vessel having an inlet defined therein at a top thereof and an outlet defined therein at a bottom thereof; continuously feeding chips (CH) to an inlet of an impregnation vessel; impregnating the chips in an impregnation fluid in the impregnation vessel at a pre-determined impregnation temperature (T imp ); feeding the impregnated chips and a transfer fluid to the inlet at the top of the digester vessel; cooking the impregnated chips in the digester vessel at a pre-determined cooking temperature (T kok ); feeding out dissolved pulp from the digester vessel through the outlet arranged at the bottom of the digester vessel; withdrawing black liquor essentially at the cooking temperature (T kok ) from the digester vessel, leading the withdrawn black liquor directly to a bottom of the impregnation vessel; mixing the black liquor with a chips mixture of the impregnated chips and the impregnation fluid; the black liquor increasing a temperature of the chips mixture at the bottom of the impregnation vessel, the temperature of the black liquor being at least 135° C. in association with the withdrawal of the black liquor from the digester; withdrawing a portion of a transfer fluid from the top of the digester; leading the portion of the transfer fluid to a position where the transfer fluid is given time to work as impregnation fluid accounting for at least 25% of a total impregnation time for the cellulose chips disposed in the impregnation vessel, the portion of the transfer fluid passing a first indirect heat exchanger; the first indirect heat exchanger indirectly subjecting the portion of the transfer fluid to a first fluid for a production of pure steam from the first fluid and for cooling of the portion of the transfer fluid; leading the pure steam that is produced to a steam pre-treatment position, upstream of the impregnation vessel; heating the chips at the steam pre-treatment position, and using the cooled transfer fluid as impregnation fluid in the impregnation vessel.