CA1055291A

CA1055291A - Method of treating ligno-cellulose containing material

Info

Publication number: CA1055291A
Application number: CA254,213A
Authority: CA
Inventors: Karl B. Steenberg
Original assignee: SCA Development AB
Current assignee: SCA Development AB
Priority date: 1975-06-16
Filing date: 1976-06-07
Publication date: 1979-05-29
Also published as: BR7603721A; FI761732A; SE7506876L; SE402606B; NZ181172A; NO762057L; JPS521101A; AU1407976A

Abstract

Abstract of the Disclosure An improved method for treating ligno-cellulose containing material is disclosed which comprises disintegrating the material in a refiner to obtain a mechanical pulp having a high concentration and a low coarse material content, passing the thus formed pulp to storage chests located at a wet-lap forming machine for storage, removing the stored pulp and cleaning it by diluting and screening to reduce the coarse material content and to obtain a pulp concentration suitable for further processing in the wet part of a wet-lap forming machine, and passing the cleaned pulp to the wet-lap forming machine for further processing.

Description

lOSSZ9~
The present invention relates to a method of treating ligno-cellulose containing materials and the like.
During the manufacture of mechanical pulp, wood, or other ligno-cellulose containing material, the material is normally disintegrated in grinders or refiners. The resuling mechanical pulp normally contains substantial amounts of coarse material, such as shives and splinters. There-fore, it is necessary to clean the pulp to remove the coarse material so that the pulp can then be transported to a series of storage chests where it can be stored for further processing. The cleaning process requires diluting the pulp to a concentration so that screening can be effected, and then screening the diluted pulp in one or more steps. The stored pulp can, when desired, be further processed in a paper making machine, or other wet-lap forming apparatus.
In order to keep the dimensions of the storage chests in which the cleaned pulp is stored within reasonable limits, the cleaned pulp must first be thickened. Thus, it is necessary to utilize water extractors which take up a good deal of space and give rise to substantial water circulation within the plant. Further, the heat losses during each processing are very great.
It is an object of the present invention to provide a method for the treatment of ligno-cellulose containing material which is to be stored for further processing, which permits maintaining the dimensions of the stor-age chests within reasonable limits but eliminates the necessity of cleaning and thereafter thickening the pulp prior to storage, and the problems conse-quent thereto.
According to the present invention, a process is provided for the treatmen~ of ligno-cellulose containing material which comprises finely dis-integrating the material in a refiner to obtain a pulp of high concentration and which contains very small amounts of coarse material, and then transport-ing the thus formed pulp, without any preceding separation of coarse material, o to storage chests for storage pending further desired processing "without any prior screening and cleaning or dilution to a concentration suitable for screening and cleaning". The stored pulp can then be passed from the storage chests directly to a cleaning operat--la-ion wherein the pulp will first be diluted to a concentration suitable for screening and then screened to remove the coarse material content of the pulp and to provide the pulp with a final concentration suitable for further proces-sing in the wet part of a paper making machine or other wet-lap forming apparatus, without any prior thickening and further storage.
Although it was previously known that the use of refiners, or more particularly disc refiners, enabled a pulp having a high concentration and containing a very small amount of coarse material to be obtained, it was not heretofore recogni~ed that such material could be passed to storage chests without the necessity of prior separation of coarse material after the disin-tegrating step. Thus, such recognition has enabled virtually a complete elim-ination of the thickening operations which were necessary subsequent to the cleaning step so that the pulp which was to be transported to the storage chests, could be of a high enough concentration so that the dimensions of the storage chests could be maintained within reasonable limits. Further, by passing the pulp from the refiner to the storage chests and conducting the cleaning operation subsequent to storage and prior to further processing in the wet-lap forming machine, there is a reduction in the amount of water circulation necessary in the plant and consequently in the amount of heat losses. The dimensions of the storage chests are reduced and the necessity for water extractors eliminated to the greatest extent possible.
A particular and at present preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawing in which the Figure is a schematic representation of the preferred process.
In accordance with the preferred embodiment of the present inven-tion, the ligno-cellulose containing raw material 1 is finely disintegrated to a high concentration of from 15%-40% and preferably from 25%-35%, in one or more refiners 2. The pulp, which has a coarse material content of 0.31%-1.5%
and preferably 0.4%-0.8% Sommerville, is then passed to storage chests 3.

10~;5291 The preferred pulp concentration for storage is from 3%-20% depending upon the kind of storage container and discharge equipment used. Therefore, it may be necessary to dilute the pulp obtained from the refiners to such a concentration, However, in no event is the pulp diluted to such a low con-centration as would be required for screening, such concentration normally being below 1%. The thus formed pulp is, when further processing is desired, removed from the storage chests and passed to a cleaning operation wherein it is diluted and passed through screens and cleaners 4 whereby the pulp is brought to a final concentration suitable for further processing in a wet-lap forming machine. The pulp having such final concentration is passed directly to the wet part 5 in a wet-lap forming machine. In this regard, other types of pulps and chemicals can be admixed with the pulp, such other pulps and chemicals being supplied from tanks 6.
As a result of the novel process of the present invention, it is also possible that the conventional water circulation system 7 at the wet part of the wet-lap forming machine can be extended to comprise the cleaning and screening system as well. For example, the back-water from the wet part 5 can be utilized to effect the dilution of the pulp prior to the cleaning and screening operations. The flow of such back-water can be controlled by the valves 8 and 9. If desired, the ligno-cellulose containing material can be pre-heated prior to the disintegrating step. Furthermore, any steam produced in the refiners can be conducted away and utili~ed as steam heat or, after concentration with water, as hot water. The steam drain 10 has the effect of avoiding any unnecessary dilution of the pulp produced in the refiners which serves to maintain the concentration of the pulp produced at the highest possible level.
While the invention has been described with a certain degree of particularity, it is to be understood that the present disclosure is made by way of example only and that numerous variations as may become apparent to those skilled in the art may be made without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for treating a ligno-cellulose containing material comp-rising the steps of finely disintegrating said ligno-cellulose containing material in a refiner to obtain a mechanical pulp having a high concentration and a low coarse material content, passing the thus formed pulp to at least one storage chest for storing until further processing is desired, "without any prior screening and cleaning or dilution to a concentration suitable for screening and cleaning", removing said pulp from storage, cleaning said pulp by first diluting it with a liquid to a concentration suitable for screening and then screening said diluted pulp to reduce its coarse material content, and passing the thus cleaned pulp to the wet part of a wet-lap forming machine, without any prior thickening and further storage.

2. The method of claim 1 wherein said pulp is subjected to further processing in said wet-lap forming machine and at least part of said liquid utilized to dilute said pulp prior to screening is supplied from the circula-tion system at said wet part of said wet-lap forming machines.

3. The method of claim 2 wherein the back-water from said wet part of said wet-lap forming machine is utilized to dilute said pulp prior to screening.

4. The method of claim 1 wherein steam is produced in the refiner during disintegration of the ligno-cellulose containing material, and said steam is removed during said disintegration to avoid dilution of said pulp whereby the concentration of the pulp formed in the refiner is maintained at as high a level as possible.

5. The method of claim 1 wherein the mechanical pulp obtained from the refiner has a concentration of 15%-40%, and a coarse material content of 0.3%-1.5% Sommerville.

6. The method of claim 5 wherein the concentration of said mechanical pulp is 25%-35%.

7. The method of claim 5 wherein said level of coarse material is 0,4%-0.8% Sommerville.

8. The method of claim 1 wherein said pulp is diluted to a concentra-tion of 0%-1% prior to screening.

9. The method of claim 1 further including the step of diluting the pulp obtained from the refiner to a concentration of 3%-20% prior to passing said pulp to said at least one storage chest.