Method for displacement in batch digesters

摘要

The method is for producing pulp in batch digesters. More particularly, the method is for ending a treatment phase of the digester content. In order to obtain a more uniform pulp quality from the process is the treatment phase ended by displacing a liquor volume (WLP) through the digester vessel with an imposed increasing temperature in the displacement liquor added to digester.

主权项

1. A method for ending a heated treatment phase in a displacement batch pulping process in a digester vessel, where the treatment phase has been done at a treatment temperature above 130° C., said digester having at least a bottom, a mid-point and a top liquid exchange position, the method initiated after the heated treatment phase and comprising the following steps;
adding a first displacement liquor to the bottom liquid exchange position while having a first lower temperature in the first displacement liquor at start of the displacement filling of a part of the digester with a first volume of the first displacement liquor, wherein the first lower temperature is more than 20° C. below the treatment temperature of the treatment phase; continuing to add the same first displacement liquor to the bottom liquid exchange position while having a higher second temperature in the first displacement liquor in a later phase of the displacement filling at least a part of the digester with a total second volume of the first displacement liquor larger than the first volume; and continuing the displacement with a final displacement liquor; and the first lower temperature in the first displacement liquor is in a range 70-110° C.