JPH11293587A - Scaling prevention in paper pulp production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scaling prevention method that can efficiently prevent the formation of scales in paper pulp production with a reduced amount of addition of a slurry and provide the slurry for this purpose. SOLUTION: The formation of scale is prevented by adding a slurry that contains a crystalline powder that becomes the deposition nuclei of the scale component included in the paper pulp production system, and a thickener having a carboxyl group content of <=1 m-equivalent and a rotational viscosity of >=600 cP to the paper pulp production process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing the formation of scale attached to a paper pulp production system and a slurry for use in the method.

[0002]

2. Description of the Related Art Pulp, which is a raw material for paper, contains calcium salts and barium salts, and elutes as calcium ions and barium ions in raw water or white water. Particularly, in the case of pulp using recovered waste paper as a raw material, a large amount of an inorganic filler is present in the waste paper, and calcium elution is particularly large. Also,
In the papermaking process of pulp and paper mills, fixing of sizing agents,
Sulfate bands are widely used primarily for pH adjustment. In some cases, sulfuric acid is added for pH adjustment. In addition, oxalate ions are present in the pulp,
May elute as oxalate ions.

[0003] In a paper pulp production system, calcium ions and barium ions combine with sulfate ions and oxalate ions derived therefrom, and calcium sulfate, barium sulfate, and calcium oxalate, which are extremely hardly soluble in water, are used as a scale. Generate. These scales include mixing chests, tanks, seed boxes, piping, fan pumps,
It not only reduces the original performance of the equipment by adhering to various papermaking equipment such as screens, inlet outlets, suction rolls, suction pumps, etc. It can cause large losses in production, such as causing spotting or spotting on the paper product and impairing quality.

[0004] Pulp, which is a raw material for paper, is obtained by digesting wood chips with sodium hydroxide.
Since a large amount of sodium hydroxide and water are used in pulp production, sodium hydroxide is generally recovered by an alkali recovery step, and effective use of water is achieved. This alkali recovery process comprises a wood pot for digesting wood chips, an evaporator for concentrating black liquor, a boiler, a dissolver tank, a green liquor thickener, a causticizing tank, and a rotary kiln for converting recovered calcium carbonate into quicklime.

The water flowing through the alkali recovery step has a high pH,
At a high temperature, it contains calcium ions and carbonate ions derived from wood. In the causticizing step, sodium hydroxide is recovered by adding quick lime, and is reused for cooking wood chips again. As described above, in this water, calcium carbonate is in a highly supersaturated state, so that the scale containing calcium carbonate as a main component is constantly adhered to the inner wall of the apparatus or the piping. If the scale adheres to the apparatus or the inner wall of the pipe in the alkali recovery step, not only does the flow rate decrease, thereby lowering the productivity, but also, in some cases, the pipe may be blocked, causing a great deal of trouble.

[0006] When the scale adheres to the apparatus or the pipe as described above, it is often performed by hand such as spraying high-pressure water or hitting it off with a hammer, which requires a great deal of labor and time. When knocking off the attached scale,
There is a problem in terms of work safety because scale fragments are scattered. In addition, calcium carbonate is soluble in acid, so it may be washed with hydrochloric acid or the like.However, since sulfur components derived from wood chips easily react with hydrochloric acid to generate hydrogen sulfide, the work is extremely dangerous. is there.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for preventing scale in a paper pulp manufacturing process which can efficiently prevent the formation of scale in a paper pulp manufacturing system with a small amount of addition. Is to provide a slurry.

[0008]

SUMMARY OF THE INVENTION The present invention relates to the following method for preventing scale in a paper pulp production system and a slurry. (1) A slurry containing a crystal powder serving as a precipitation nucleus of a scale component contained in a paper pulp production system and a thickener having a carboxyl group content of 1 meq / g or less and a rotational viscosity at 20 ° C. of 600 cP or more. A method for preventing scale in a paper pulp production system, comprising adding pulp to a paper pulp production process. (2) The method according to the above (1), wherein the slurry contains a dispersant for dispersing the crystal powder. (3) A slurry containing a crystal powder as a precipitation nucleus of a scale component contained in a paper pulp production system, a thickener having a carboxyl group content of 1 meq / g or less, and a rotational viscosity of 600 cP or more. A slurry for preventing scale of a paper pulp production system, characterized by comprising: (4) The above (3) containing a dispersant for dispersing the crystal powder.
The described slurry.

The paper pulp production system to be treated in the present invention is a system for producing paper and / or pulp, which means all the processes for producing scale, and includes a papermaking process, a raw material preparation process, and a pulp production process. Process, an alkali recovery process and the like. A large amount of water is used in these systems,
Sulfate ions and oxalate ions contained therein are combined with calcium ions and barium ions to form calcium sulfate, barium sulfate, and calcium oxalate, which are extremely hardly soluble in water, as scales.

[0010] In the present invention, such a paper pulp production system includes:
By adding a slurry containing crystal powder to be a nucleus, scale formation is prevented. The slurry is a slurry containing a crystal powder and a thickener having a carboxyl group content of 1 meq / g or less, a rotational viscosity at 20 ° C. of 600 cP or more, and preferably further contains a dispersant.

The crystal powder used in the present invention is not limited in its component, shape, particle size, etc., as long as it serves as a nucleus for depositing scale components contained in the paper pulp production system. Those composed of the same or similar components as the scale are preferred. As such a crystal powder,
Crystals having the same or similar crystal lattice structure to the scale species adhered in the above-mentioned system are preferred, and calcium sulfate, barium sulfate, calcium oxalate and calcium carbonate identical to the scale species are particularly preferred. The particle size is not particularly limited, but is preferably from 0.01 to 100 μm, and more preferably from 1 to 50 μm, from the viewpoint of the scale prevention effect.

As a thickener, when the above-mentioned crystal powder is converted into a slurry, the viscosity of the slurry is increased to maintain a stable dispersion state, and when added to a paper pulp production system, the crystal powder is uniformly dispersed in the system. A thickener having a carboxyl group content of 1 meq / g or less is used. Examples of such thickeners include high-molecular polysaccharides (ramsan gum, xanthan gum, guar gum, etc.), cellulose derivatives (methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, etc.), starches (hydroxypropyl starch, etc.), synthetic polymers (polyvinyl alcohol,
Polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylamide, etc.), inorganic compounds (talc, mica,
Smectite, bentonite, magnesium aluminum silicate, etc.). Among these, organic compounds such as high molecular polysaccharides and cellulose derivatives are preferred.

These compounds can be directly dissolved or dispersed in water and used as they are. In particular, in the case of high molecular weight polymers, they are dispersed in a solvent such as ethylene glycol to prevent mamako when added to water. It can be added to water afterwards. The solvent used here is preferably a solvent that dissolves in the organic compound and water.

[0014] In addition to the above essential components, a dispersant may be added to the slurry of the present invention in order to prevent agglomeration of particles. As the dispersant, a water-soluble polymer having a carboxyl group content of 1 meq / g or less can be used, and a polymer containing a sulfonic acid group is particularly preferable. For example, polystyrene sulfonic acid, polyvinyl sulfonic acid,
Polyisoprenesulfonic acid, poly2-acrylamide-
2-methylpropanesulfonic acid, poly 2-hydroxy-
Sulfonic acid homopolymers such as 2-allyloxypropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid,
Copolymers of sulfonic acid monomers such as isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-hydroxy-2-allyloxypropanesulfonic acid with vinyl monomers, ligninsulfonic acid, and naphthalenesulfonic acid Examples include, but are not limited to, acid formalin condensates. The number average molecular weight is 1,000 to 500,000, preferably 300
0 to 50,000 is preferred.

The above-mentioned crystal powder, thickener, dispersant and the like are dispersed or dissolved in water to form a slurry. In this case, if necessary, additives such as a solvent and a stabilizer can be added. . The concentration of the crystal powder in the slurry is 1 to 80% by weight, preferably 20 to 50% by weight, and the concentration of the thickener is 0.1%.
01-20% by weight, preferably 0.1-5% by weight, the concentration of the dispersant is 0-20% by weight, preferably 0-5% by weight,
The concentration of the solvent and other additives is 0 to 10% by weight.

The method for producing a slurry of the present invention can be produced by adding the above-mentioned components to water, stirring, mixing and dispersing. In this case, the order of addition of each component is not limited, and each component may be added at the same time, a crystal powder may be added to water, and a thickener and other components may be added with stirring. The crystal powder may be added while adding a thickener to the mixture and stirring, or a mixture of the crystal powder and the thickener may be added to water and stirred.

In the above case, the concentration of each component, especially the thickener, is adjusted so that the rotational viscosity at 20 ° C. of the slurry (JIS K-7117) is 600 cP or more. The upper limit of rotational viscosity is determined by the handling properties as a slurry,
Generally, it is 10,000 cP. The preferred rotational viscosity of the slurry is between 600 and 2000 cP.

By adjusting the rotational viscosity of the slurry of the present invention to a specific value by adding a thickener, the crystal powder maintains a stable dispersion state and exhibits a long-term dispersion stability. The dispersion stability is further increased by adding a dispersant.

This slurry is added as it is or diluted with water or the like to a paper pulp production system, and dispersed in a liquid such as white water to prevent scale. The amount of the slurry added is 0.1 to 200 mg / l, preferably 0.5 to 100 mg / l, more preferably 1 to 50 m / l as the concentration of the crystal powder.
g / l.

Even if the crystal powder is added as it is to the paper pulp production system, the dispersibility is poor and the effect of preventing the scale is small due to sedimentation. However, when the slurry is added in the state of the slurry of the present invention, the dispersibility in the liquid becomes poor. Excellent, high scale prevention effect. Although the mechanism is not clear, since the crystal powder and the thickener are combined and dispersed in the liquid in the system, the crystal powder is retained in the liquid and acts as a nucleus for precipitation of scale components. It is estimated that there is.

The scale-preventing effect of the present invention is as follows.
It is presumed that precipitation on the vessel wall is prevented,
Since the crystal powder is combined with the thickener and has good dispersibility, the effect of preventing scale can be obtained with a small amount of addition.

In this case, when a compound having a carboxyl group such as polyacrylic acid, maleic acid-based polymer, or CMC is used as a thickener, the surface of the crystal powder is covered with the carboxyl group, and the chelating action causes calcium ions or the like to form. The complex of the cation is formed on the surface, and the precipitation of the scale component on the crystal surface is inhibited.However, in the present invention, since a thickener having a small carboxyl group content is used, there is no such inhibition, and the crystal surface is not affected. Scale components are efficiently precipitated, and the scale prevention effect is high.

In the present invention, the dispersing agent is added to the slurry to increase the dispersibility of the crystals, so that the effect of preventing the scale by the slurry is further enhanced. Even in this case, by using a dispersant having a small carboxylic acid content, inhibition of precipitation of scale components on crystals can be reduced.

[0024]

The slurry for preventing scale of the present invention has a long-term dispersion stability because it has a specific rotational viscosity by mixing a crystal powder and a thickener, and has a dispersibility when added to a paper pulp production system. And the scale can be prevented efficiently. When a dispersant is added, the effect is further enhanced.

In the scale prevention method of the present invention, since the above-mentioned slurry is added to the paper pulp production system, it is possible to efficiently prevent the formation of scale in the paper pulp production system with a small amount of addition. When a dispersant is added, the effect is further enhanced.

[0026]

Embodiments of the present invention will be described below.

Examples 1 to 5 and Comparative Examples 1 to 3 According to the compositions shown in Tables 1 and 2, a predetermined amount of water was placed in a 300 ml beaker, and a predetermined amount of crystal powder was added with stirring.
The mixture was stirred for 1 hour or more to prepare a uniform slurry. Meanwhile, a predetermined amount of rum sun gum and 10 times the amount of propylene glycol were prepared, and 1/100 of the propylene glycol was prepared.
The ramsan gum was dissolved in the amount of 2 and added to the crystalline powder slurry. The vessel in which the ramsangum was dissolved was washed with the remaining propylene glycol and added to the slurry. When further additives (mixed and used drugs) were added, they were added after this. Stirring was continued for about 2 hours to prepare a uniform slurry. The crystal powder slurry prepared as described above is placed in a sample bottle with a lid having an outer diameter of 40 mm and a height of 120 mm, and is allowed to stand in a 40 ° C constant temperature bath. After one week, one month, two months, and three months, the state of separation of the slurry was observed to evaluate the dispersion stability. The evaluation is 100 height from the bottom to the liquid level.
%, And when separation occurred, the height from the bottom to the interface of the separated slurry was expressed in%. That is, if there was no separation, it was 100%, and if there was a separated slurry interface at half the height of the entire surface, the value was 50%. Table 3 shows the results.

[0028]

[Table 1]

[Table 2] (Note) PG: propylene glycol

[0029]

[Table 3]

From the above results, it can be seen that all of the examples show long-term dispersion stability. On the other hand, Comparative Example 1 containing no thickener has poor dispersion stability, and Comparative Example 2 using a crystal powder having a large particle size and Comparative Example 3 having low rotational viscosity also have poor long-term dispersion stability. I understand.

Example 6, Comparative Examples 4 and 5 The case where the calcium sulfate slurry of Example 1 (Example 6) and the powdered calcium sulfate dihydrate (Comparative Example 4) were added, and the case where no calcium sulfate slurry was added (Comparative Example 5) In the case of (1), the difference in the scale deposition effect was examined. The operation is as follows. Using calcium chloride dihydrate and anhydrous sodium sulfate,
1 calcium ion concentration in 3 500 ml beakers
An aqueous solution of 200 mg / l and a sulfate ion concentration of 3600 mg / l was prepared for each 500 ml. 3 solutions at 40
° C and stirred with a magnetic stirrer, and the calcium sulfate slurry of Example 1 and the powdered calcium sulfate dihydrate were converted to powder in two beakers in a quantity of 25.
mg / l was added. The remaining one was blank without adding any crystals. 10 ml per hour from 3 solutions
Each sample was sampled and filtered through a 0.22 μm filter paper, and the calcium ion concentration was measured to compare the rate of decrease in calcium ion concentration, ie, the rate of scale deposition. Table 4 shows the measurement results of the calcium ion concentration after 3 hours as a representative example of the results.

[0032]

[Table 4]

As can be seen from the results in Table 4, it is clear that the addition of the slurry reduces the calcium ion concentration, that is, the deposition rate of the calcium sulfate scale is higher than that of the addition of the powder.

Example 7 A copolymer of acrylamide / sodium acrylate having a molecular weight of 5,000 = 80/20 mol% (carboxyl group content: 2.6 meq / g) was added to the calcium sulfate slurry of Example 1.
g) (1% by weight) (Example 7) and those without (Acrylamide / sodium acrylate not added (Example 6), and no drug added (Comparative Example 5)) The difference in precipitation effect was investigated. The test conditions and operation were the same as in Comparative Example 1. Table 5 shows the results.

[0035]

[Table 5]

As can be seen from the results in Table 5, the addition of the carboxyl group-containing polymer did not decrease the calcium ion concentration similarly to the blank, and clearly inhibited the scale deposition.

Claims (4)

[Claims] Claims: 1. A crystal powder which is a precipitation nucleus of a scale component contained in a paper pulp production system, and a thickener having a carboxyl group content of 1 meq / g or less, and a rotational viscosity at 20 ° C of 600 cP or more. A method for preventing scale in a paper pulp production system, comprising adding the slurry of the above to a paper pulp production process. 2. The method according to claim 1, wherein the slurry contains a dispersant for dispersing the crystalline powder. 3. A crystal powder, which serves as a precipitation nucleus for a scale component contained in a paper pulp production system, and has a carboxyl group content of 1
A thickener not more than milliequivalents / g and a rotational viscosity of 600
A slurry for preventing scale in a paper pulp production system, comprising a slurry having cP or more. 4. The slurry according to claim 3, further comprising a dispersant for dispersing the crystal powder.