US 5,207,870 AGranted

Process and equipment for pretreatment of cellulosic raw material

AssigneeOsmo Aho

InventorsOsmo Aho, Antti Aho

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Abstract

The invention concerns a process for pretreatment of cellulosic chip-formed raw material by impregnation. In the process, first a vacuum treatment is carried out without preceding moistening treatment, and as soon as possible after the vacuum treatment penetration is carried out with a solution of chemicals or with water at the atmospheric or a higher solution pressure. In this way the fiber cavities can be filled optimally, which promotes a uniform and adequate diffusion of the solution into the fiber walls significantly. The process can be carried out, e.g., in a device which comprises a tank (11) for the treatment of the raw material and therein a feed opening (18) for the solution as well as an opening (14) for removal of the raw material, which said opening (14) communicates preferably with a reception tank, wherein the atmospheric or a higher pressure prevails.

Claims9

Dependent claims

A process for the pretreatment of cellulose chips, comprising the steps of:

(a) removing air from the cellulose chips by exposing the chips to subatmospheric pressure;
(b) contacting the chips from step (a) with a penetrating liquid having a temperature lower than the liquid's boiling point at said subatmospheric pressure, said contacting taking place within about 0.5 minute after said exposure to subatmospheric pressure in step (a) and under conditions such that a pressure gradient is maintained between the liquid and the fiber cavities;
and
(c) exposing the chips and the liquid to a pressure of atmospheric or above within said 0.5 minutes and for a time sufficient to allow the solution to penetrate into the chips;
wherein said subatmospheric pressure in step (a) is from about 0.1 to about 0.5 bar, and wherein the penetrating liquid has a temperature of from about 35.degree. to about 85.degree. C.;
and
wherein the cellulose chips, prior to removal of air in step (a), are substantially unmoistened.

4 more elements

Dependencies are inferred from the claim text.