Valmet Ab

Valmet Aktiebolag

Stefan Antonsson

Jonas Saetherasen

Krister Olsson

Christofer Lindgren

Mikael Lindström

Jonas Saetheråsen

Lari Lammi

Petteri Kuusisto

Eva Hogebrandt

Sannet Minnaar

Lars Eriksson

Mikael LINDSTRÖM

Daniel Trolin

Bengt Wernersson ÖStberg

Håkan Dahllöf

Maria Wennerström

Lars Sjödin

Mikael Lindstrom

Fredrik Wilgotson

A method for obtaining a strong hydrolysate from cellulosic material after a hydrolysis in a batch digester is disclosed. According to the invention the cellulosic material is exposed to a 2 stage hydrolysis with a first steam phase hydrolysis followed by a liquid phase hydrolysis, and wherein the steam phase is conducted such that the degree of packing of the cellulosic material results in at least a 20% up to 100% packing increase. The liquid phase hydrolysis includes adding hot and preferably acidified hydrolysis liquid and not establishing a total L/W ratio above 3.5, but sufficient to keep the cellulosic material under the level of the hydrolysis liquid.

Method for recovering concentrated hydrolysate after hydrolysis of cellulose material

The invention is related to a method for the preparation of kraft pulp with increased pulping yield from lignin-containing cellulosic material using polysulfide cooking liquor. In order to obtain a cost efficient system both in aspects of investment costs but also in aspects of heat economy of operating the process is most of the total charge of alkali charged as heated polysulfide liquor to an first atmospheric vessel, wherein the hot polysulfide liquor flashes off steam providing most if not all of the necessary steaming effect for the cellulose material. The polysulfide liquor is then allowed to impregnate the cellulose material at a temperature closer to cooking temperature but still so low that essentially no delignification occurs in impregnation vessel, as the H-factor in impregnation vessel is kept within 1-20.

Cost efficient kraft cooking method using polysulfide cooking liquor

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Stockholm, Sweden

Stefan Antonsson