Process for the preparation of groundwood pulp

Abstract

A process is provided for preparing groundwood pulp from debarked pulpwood logs, which comprises grinding the logs in the presence of water under a superatmospheric pressure of a gas selected from the group consisting of steam, air, and steam and air, and forming and discharging a pulp suspension in the resulting aqueous liquor, while continuously supplying water during the grinding in a volume of less than 35 parts per part of bone dry pulp at a rate of addition such that the temperature of the discharged pulp suspension is below 200.degree. C. and preferably below 180.degree. C. and within the range from about 1.5 to about 50, preferably from 2 to 8, times the temperature in .degree.C. of the added water at a pressure within the range from about 8 to about 40 kiloponds/cm.sup.2, preferably from 10 to 30 kiloponds/cm.sup.2, higher than the superatmospheric pressure and at a temperature within the range from about 2 to about 63.degree. C.; then, optionally, any one or more of the steps of centrifugally separating steam from the pulp suspension and using the separated hot steam for heating purposes; thickening the pulp suspension within the range from about 5 to about 50% and supplying water separated therefrom to the grinding; and adding bleaching chemicals to the pulp and bleaching the pulp; the groundwood pulp is obtained in a higher pulp concentration and at considerable saving in energy, can be used with our without bleaching, and has a high content of long flexible fibers.

Dependencies are inferred from the claim text.