Importance

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Abstract

The invention relates to a process for continuous cooking of cellulose. In the process, wood chips (11) are impregnated (1) with cooking lye (10), after which the wood chips impregnated with cooking lye is mixed (27) with spent liquor (18) in order to transfer (12) it into the upper portion of a pressurized digester (2). The transfer liquor used for the transfer of the wood chips in the preceding step is separated (26) from the impregnated wood chips in the upper portion of the digester (2) and is recycled (13,14) to the preceding step. After this, the chips are conducted from the digester (2) downwards into the cooking zone (24) and from there on to the washing zone (24), whereby a mixture of spent lye and wash lye, i.e. spent liquor (18) is removed from between the cooking and washing zones (19) and a portion (21) of the liquor removed from the digester (2) is expansion evaporized (5,6) in order to recover heat in the form of steam (22,23). In order to improve the heat consumption of the method and to reduce the steam consumption, the spent liquor (18) is mixed with the impregnated chips before transferring these into the upper portion of the digester (2), whereas a corresponding portion (21) of the transfer liquor (13) separated from the upper part of the digester (2) is conducted to the expansion evaporation (5,6) and from there on to the chemicals recovery (17). The invention also relates to a device for implementing the above process.

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First Claim