Method for avoiding mechanical damage of pulp
AssigneeMetso Chemical Pulping Oy
InventorMikael Svedman
Life of this patent
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Abstract
A method for producing chemical pulp from cellulosic material by means of alkaline cooking, including cooking the material to pulp at cooking temperature in a digester, reducing the temperature at the end of the cook, substantially relieving the overpressure in the digester and then discharging the pulp from the digester by means of pumping. The method is characterized in that the pulp is cooled to essentially 85° C. to 70° C. before pumping cooked material as a fluid suspension from the digester, and that the temperature of the cooked material is maintained in the same temperature range and at a pH level being between 10 and 13, between the digester and a first delignification/bleaching stage, thus avoiding mechanical damage of cellulosic material.
Claims14
A method for producing chemical pulp from lignocellulosic material by means of alkaline cooking, comprising:
- cooking the material to pulp at a cooking temperature in a batch digester, to produce a cooked material;
- essentially relieving overpressure by cooling the cooked material to a temperature between about 60° C. and about 85° C. using a wash liquor;
- discharging the cooked and cooled material from the digester by means of pumping;
- and
- treating the pulp in equipment operating essentially at atmospheric or higher pressure, wherein the temperature of the cooked and cooled material is maintained during processing stages between the digester and a first substantial delignification/bleaching stage.
Dependencies are inferred from the claim text.