JPH0681287A - Method for removing lightweight foreign material in pulp - Google Patents

Abstract

PURPOSE:To reduce the loss of pulp fiber and separate and remove lightweight foreign materials in pulp by separating the lightweight foreign materials from a pulp slurry in a waste paper centrifugal separator and then filtering the separated liquid discharged from the waste paper centrifugal separator. CONSTITUTION:A pulp slurry separated from coarse undigested materials and foreign materials with screens 3, 4 and 6 is passed through a level tank 8 and then fed to a centrifugal separator 7. The resultant separated liquid discharged from the centrifugal separator is filtered through a filter 9 to separate lightweight foreign materials. The obtained pulp is then discharged from the side of a concentrated solid substance in the centrifugal separator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is lighter than wood pulp such as polyethylene, polypropylene, polystyrene or sticky substances mixed in pulp in the cooking / papermaking process due to wood chips, which is a pulp raw material, and recovered waste paper. Light foreign matter,
The present invention relates to a method for removing lightweight foreign matter in pulp that can be separated and removed by a means simpler than the conventional industrial technology.

[0002]

BACKGROUND OF THE INVENTION As is well known, it is unavoidable that various foreign substances are mixed in wood chips, which are pulp raw materials, and recovered waste paper. In particular, the mixing ratio has increased with the recent diversification of raw materials and suppliers.

There are many kinds of such foreign substances, and in particular, when the light weight foreign substances, which are lighter than wood pulp, are mixed in the pulp and processed in the papermaking process, they give a visual defect to the product and seriously impair the quality.

Therefore, even in the current manufacturing process, the conventional technique is used to remove these foreign substances.

Conventional methods, particularly for removing foreign matters in pulp slurry, include a liquid cyclone (cleaner) treatment method and a screen treatment method.

[0006] The screen treatment method is equipment for removing foreign matters and coarse fibers by passing the pulp slurry through slits or round holes, but due to its nature, if the foreign matter removal rate is to be increased, rejecting is performed. It is necessary to have a high rate, and it is unavoidable that a large amount of pulp is discharged together with the foreign substances to be removed.

Therefore, in the conventional screen equipment, in order to reduce the loss amount of the pulp, a method for recovering the pulp by re-screening the pulp mixed with the foreign matter discharged from the screen and performing the multi-stage treatment. However, in this case, there is a problem that equipment cost and power cost increase.

Further, as is well known, the foreign matter separation by the cleaner treatment method utilizes a centrifugal action based on the difference in specific gravity between pulp and foreign matter. Due to its nature, mineral substances and metals having a large difference in specific gravity from pulp are used. However, it has a problem that it is not effective for removing foreign matters having a small relative specific gravity difference from wood pulp.

Further, a reverse cleaner has been conventionally used for the purpose of eliminating a light foreign substance having a specific gravity smaller than that of wood pulp, but since the centrifugal force acting is weak, its separating effect is not so high. Had a problem.

By the way, conventionally, a method of centrifuging a suspension of a general solid (hereinafter referred to as slurry) by a decanter type centrifuge is also known.

This decanter type centrifuge is generally used in the mining industry and food industry for dehydration / concentration of products and intermediate raw materials and concentration of wastewater sludge. When the slurry is subjected to centrifugal treatment, it is generally operated so as to obtain a centrifugal force of 2000 G or more, which is the most effective operating condition for concentrating and dehydrating a target solid substance.

Therefore, the present inventors have tried to remove the lightweight foreign matter from the pulp by using the decanter type centrifuge, and the above-mentioned 20 by using the decanter type centrifuge.
When light foreign matter is removed with a centrifugal force of 00G, the pulp concentration discharged from the decanter centrifuge is about 20% when the pulp slurry before treatment is about 3%.
In addition, the light foreign matter was separated from the black liquor and discharged in the state of being mixed in the pulp. That is, under these conditions, the pulp and the light foreign matter could not be separated.

The inventors have made various studies on the operating conditions of the decanter type centrifugal separator, and the decanter type centrifugal separator is operated at a centrifugal force much lower than the centrifugal force of 2000 G which is a general operating condition. In this case, it was found that the pulp and the light weight foreign matter were reliably separated, and the light weight foreign matter was mixed with the black liquor and discharged from the decanter type centrifuge.

The present invention was devised on the basis of such knowledge, and its purpose is to efficiently separate the above-mentioned lightweight foreign substances mixed in pulp by using, for example, a decanter type centrifuge. The present invention aims to provide a method for removing lightweight foreign matter in pulp, which can be removed, resulting in extremely low loss of pulp fiber, and which is also capable of significantly improving the quality of pulp, and which is also excellent in economic efficiency. Is.

[0015]

In order to achieve the above object, according to the present invention, light foreign matter is separated from pulp slurry by centrifugal force by a centrifugal separator and then discharged from the centrifugal separator. By filtering the separated liquid,
The present invention is characterized in that the lightweight foreign matter is taken out from the separated liquid.

Further, according to the present invention, in order to remove light foreign substances from pulp such as recovered waste paper with high efficiency,
After separating the lightweight foreign matter from the pulp slurry through the centrifugal force of the centrifuge, the step of filtering the separated liquid discharged from the centrifuge is configured to be repeated a plurality of times. .

In the present invention, the centrifugal force of the centrifugal separator is set to 2000 G or less, preferably about 500 G.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the accompanying drawings.

FIG. 1 shows a lightweight foreign matter removing device for pulp according to a first embodiment of the present invention. More specifically, it shows an example in a cooking step for cooking wood chips to produce kraft pulp. There is.

In the figure, reference numerals 3, 4 and 6 are screens for decomposing coarse undigested matter and foreign matters from pulp, and reference numeral 8 is a level for containing pulp containing knots and foreign matters separated by the screens 4, 6. A tank, reference numeral 7 is, for example, a decanter centrifuge for separating lightweight foreign matter in the reject pulp supplied from the level tank 8, and reference numeral 9 is a cooking effluent containing light foreign matter discharged from the decanter centrifuge 7. Each of the filtering devices for separating light foreign matter from (hereinafter, referred to as black liquor) is shown. Of course,
The centrifuge 7 is not limited to the decanter type.

In the separation work by the decanter type centrifugal separator 7, the separation of pulp and light weight foreign matter was recognized in the range of centrifugal force of 2000 G or less, and particularly, the separation of pulp and light weight foreign matter was more effective at 500 to 1000 G. Was recognized.

That is, under these conditions, the lightweight foreign matter was completely separated from the pulp, and the lightweight foreign matter was discharged together with the black liquor.

In this case, it was confirmed that the pulp did not exist in the discharge liquid and was discharged from the solid content concentration side of the decanter type centrifugal separator 7. This means that under the conditions of the present invention, about 100% of the light foreign material is separated from the pulp and at the same time about 100% of the pulp is recovered.

As shown in FIG. 2, when the centrifugal force exceeds 1000 G, the efficiency of separating pulp and light foreign matter decreases.

Then, as shown in FIG.
Under the condition of G or less, the pulp is discharged from the liquid side of the decanter type centrifugal separator 7 and the recovery rate of the pulp decreases.

As is apparent from the above, in order to efficiently separate the above-mentioned lightweight foreign matter from pulp, the centrifugal force by the decanter type centrifugal separator 7 is the dehydration of products and intermediate raw materials in general mining industry. However, it is important to treat with a gentler centrifugal force of 2000 G or less than the operating conditions for the purpose of concentration.

The filtering device 9 separates the light foreign matter and the black liquor separated from the pulp by the above decanter type centrifugal separator with, for example, a wire mesh having a filtration surface of about 0.5 mm opening or a slant type filter. Is configured to.

The black liquor discharged from the decanter type centrifuge 7 and containing the light foreign matter is filtered by the filtering device 9 into the light foreign matter and the black liquor.

The lightweight foreign matter separated by filtration is separated as a residue on the filtration surface, simply scraped by hand at any time, or continuously discharged through mechanical means.

The black liquor that has passed through the filtration surface is mixed with the concentrated pulp black liquor discharged from the decanter type centrifugal separator 7 and returned to the process.

Since the black liquor in the kraft pulp manufacturing process contains a high concentration of alkali and organic components, if a light foreign substance leaks into the environment from the manufacturing process, it will face a serious environmental problem. However, as in the present invention, by combining the decanter type centrifuge 7 and the filtering device 9, the black liquor is completely recovered and is not discharged to the outside of the process. Separation / removal can be performed safely.

FIG. 4 shows a second embodiment which is an application example of the light foreign matter removing device for pulp in the pulp according to the first embodiment at the main line in the cooking process. In this embodiment, the screen 4 is The process of treating the pulp that has passed through the screen 4 with the decanter centrifuge 7 is shown for the purpose of separating and removing finer foreign matter contained in the passed pulp that is finer than that in the first embodiment.

In this embodiment, since the screen 4 normally has an opening of about 2 mm, some of the lightweight foreign matter passes through the filtering surface of the screen 4. In order to separate light foreign substances from the complete pulp, it is necessary to treat the pulp having passed through the screen 4 with the decanter type centrifugal separator 7.

The combination, function and usage of the decanter centrifuge 7 and the filtering device 9 for treating the separated liquid discharged from the decanter centrifuge 7 are the same as in the first embodiment.

FIG. 5 shows a light foreign matter removing device for pulp according to a third embodiment of the present invention, and this embodiment shows separation and removal of light foreign matter in the waste paper treatment of the corrugated board base paper manufacturing process. .

In the figure, reference numeral 12 is a pulper (defibration machine), reference numeral 13 is a double separator, reference numeral 14 is a screen, reference numeral 15 is a concentrator, reference numeral 16 is a disintegrator, and reference numeral 17 is a decanter type centrifugal separator. The reference numeral 18 indicates a screen, the reference numeral 19 indicates a foreign substance discharged from the screen, and the reference numeral 20 indicates a rejected paper pulp.

In the prior art, in order to separate the lightweight foreign matter 11 contained in the waste paper material disentangled by the pulper 12, a complicated waste paper treatment process composed of a plurality of screens, disintegrators and cleaners is used. Although it was necessary to repeatedly execute the process, in this embodiment, since the decanter type centrifuge 17 is provided in the waste paper treatment process, it is possible to remove lightweight foreign matter with a high efficiency in one operation, so Can be greatly simplified.

Table 1 shows the results of separation and removal of the lightweight foreign matter in the waste paper pulp treatment according to this embodiment having the above-mentioned structure.

[0039]

[Table 1]

As is clear from Table 1, each time the treatment by the decanter type centrifugal separator 17 is repeated a plurality of times,
The efficiency of separating and removing light foreign matter was improved, and the pulp recovery rate was greatly improved.

In the present invention, the location of the decanter type centrifugal separators 7 and 17 is not limited to the illustrated example.

Further, according to the present invention, the centrifugal force of the decanter type centrifuge is controlled according to the difference in specific gravity between the pulp and various lightweight foreign substances, so that the lightweight foreign substances can be removed more efficiently. It can also be configured.

[0043]

As described above, in the method for removing lightweight foreign matter in pulp according to the present invention, the lightweight foreign matter mixed in the pulp is efficiently separated and removed by using a centrifuge. Therefore, the loss of pulp fiber can be extremely reduced, and besides, the quality of pulp can be significantly improved, and it is also excellent in economic efficiency.
It has many excellent effects.

[Brief description of drawings]

FIG. 1 is a flow chart schematically showing a foreign matter removing step in pulp according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a centrifugal force and a lightweight foreign matter removal rate in the same process.

FIG. 3 is a graph showing the relationship between centrifugal force and pulp recovery rate in the same process.

FIG. 4 is a flow chart schematically showing a second embodiment of the step of removing foreign matter in pulp.

FIG. 5 is a flow chart schematically showing a third embodiment in which the present invention is applied to the step of removing foreign matter in waste paper pulp.

[Explanation of symbols]

 3,4,14,18 Screen 7,17 Decanter type centrifuge 11 Light weight foreign material

Front page continued (72) Inventor Meiji Matsuura 4379 Shimada City, Shizuoka Prefecture Tokai Pulp Stock Company In-house

Claims (3)

[Claims] 1. A method for separating light foreign matter from pulp slurry through centrifugal force of a waste paper centrifuge, and then filtering the separated liquid discharged from the centrifugal separator to remove the light foreign matter from the separated liquid. A method for removing lightweight foreign matter in pulp, characterized by: 2. A pulp characterized in that a step of separating a light foreign substance from a pulp slurry through a centrifugal force by a centrifugal separator and then filtering a separated liquid discharged from the centrifugal separator is repeated a plurality of times. How to remove lightweight foreign matter. 3. The centrifugal force of the centrifuge is 2000 G
The method for removing lightweight foreign matter in pulp according to claim 1 or 2, wherein the amount is preferably around 500 G.