Slime control method

Abstract

To provide a method capable of efficiently controlling slime in a paper making process.SOLUTION: The present invention relates to a method of controlling slime in a paper making process. The method of controlling slime according to the present invention includes supplying a slime controlling agent to at least one of whitewater storages of a whitewater recovery system or a whitewater circulation system in the paper making process. The slime controlling agent is supplied from the lower part of the whitewater storage.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a slime control method in a papermaking process.

Background Art

[0002] Since the pulp and paper industry is a water-intensive industry, a large amount of water is used and discharged in pulp and paper mills. One of the discharged waters is white water containing fine pulp fibers, which is discharged when papermaking pulp slurry. From the perspective of effective utilization of water resources, regeneration and reuse of water such as white water discharged in the manufacturing process are widely carried out. As an example, the recovered white water is reused as shower water for paper machines and the like.

[0003] On the other hand, since white water contains a large amount of organic substances that are nutrients for microorganisms and bacteria, there is a problem that slime derived from microorganisms and bacteria occurs in the circulating water system, each facility, and pipes connecting them. In addition, there is a problem that the generated slime mixes into the papermaking raw material, causing a decrease in production efficiency due to paper breakage or a decrease in the quality of paper products.

[0004] In order to solve the problem of slime generation, various methods have been proposed (for example, Patent Documents 1 and 2). Patent Document 1 discloses controlling the broke system corresponding to the raw material system upstream of the papermaking process using an antibacterial agent so that the number of bacteria is always maintained at 1 × 10 7 or less per mL until immediately before being mixed with other raw materials. Patent Document 2 discloses adding a bactericide so that the bactericidal rate of the bactericide against papermaking process water is 50% or more and less than 90%.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, conventional methods sometimes fail to adequately control slime. Therefore, there is a need for a method that can efficiently control slime in the papermaking process.

[0007] This disclosure provides a method for efficiently controlling slime in the papermaking process. [Means for solving the problem]

[0008] This disclosure relates to a slime control method in a papermaking process, comprising supplying a slime control agent to at least one white water storage section of a white water recovery system or white water circulation system in the papermaking process, wherein the supply of the slime control agent is carried out from the lower part of the white water storage section. [Effects of the Invention]

[0009] According to this disclosure, slime can be efficiently controlled in the papermaking process. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram illustrating an example of the papermaking process related to this disclosure. [Figure 2] Figure 2 is a diagram illustrating one embodiment of a slime control method described herein. [Figure 3] Figure 3 is a diagram illustrating one embodiment of a slime control method described herein. [Modes for carrying out the invention]

[0011] In this disclosure, “slime control in the papermaking process” means controlling or suppressing microbial deposits and / or adhering materials in the papermaking process. In one or more embodiments, slime control in this disclosure includes reducing the amount of deposits generated or accumulated in the white water reservoir, suppressing the generation of deposits, suppressing the generation or formation of adhering materials, and suppressing the growth of microorganisms. In one embodiment, “microbial deposits and / or adhering materials” in this disclosure may include slime and may also include materials that show a positive result in the ninhydrin test used for slime detection.

[0012] In this disclosure, the “white water storage section” may include one or more storage tanks for storing white water present in the white water recovery system or white water circulation system in the papermaking process. In one or more embodiments, the white water storage section may include a location where white water temporarily accumulates. Examples of white water storage sections in one or more embodiments include tanks (white water silos / white water pits) for recovering and storing white water discharged from the paper machine (e.g., wire section), excess white water pits, and seal pits. In one or more embodiments, the slime control method of this disclosure can be performed in a storage tank (e.g., excess white water pit and white water pit) that introduces white water into the inlet supplying raw pulp slurry to the paper machine (wire section), thereby enabling more efficient slime control in the papermaking process. The slime control method of the present disclosure can be suitably carried out in one or more embodiments in a papermaking process that incorporates a CP device for locally adjusting the pulp concentration of the inlet.

[0013] In this disclosure, "papermaking process" refers not only to the process of making paper from pulp slurry (raw pulp) using a papermaking machine, but also to a white water recovery system for recovering the white water discharged in large quantities during papermaking and a white water circulation system for reusing the recovered white water (hereinafter, these are collectively referred to as the "circulating water system"). In this disclosure, "white water" refers to an aqueous solution discharged from the wire section, press section, etc., in the papermaking machine. In one or more embodiments, the white water may contain fine fibers derived from the raw pulp used during papermaking, and other papermaking chemicals, etc.

[0014] In this disclosure, "papermaking process water" may, in one or more embodiments, include pulp slurry and white water, as well as process water in circulating water systems such as the raw material system, raw material preparation system, white water circulation system, and white water recovery system, and industrial water or recycled water supplied to the water circulation process water system. In this disclosure, pulp may, in one or more embodiments, include bleached chemical pulp, unbleached chemical pulp, bleached mechanical pulp, unbleached mechanical pulp, recycled paper pulp (DIP), and broken pulp. Examples of bleached and unbleached chemical pulp include kraft pulp (KP) and sulfite pulp (SP). Examples of bleached and unbleached mechanical pulp include wood pulp (GP) and thermomechanical pulp (TMP).

[0015] FIG. 1 shows a schematic diagram for explaining an example of a papermaking process in the present disclosure. The raw material pulp slurry prepared in the raw material preparation process is stored in the seed box 1. The raw material pulp slurry stored in the seed box 1 is sent to the cleaner 2 by the primary fan pump 11, and after chemicals such as calcium carbonate are added in the tank 4 via the deculator 3, it is sent to the inlet 6 by the secondary fan pump 12 via the primary screen 5. The raw material pulp slurry sent to the inlet 6 is supplied to the wire part (dewatering part) 7, where it is dewatered. The dewatered wet sheet is sent from the press part (pressing and squeezing part, not shown) to the dryer part (drying part, not shown). The white water discharged by the dewatering in the wire part 7 is recovered and stored in the white water silo 8. The white water (surplus white water) overflowing from the white water silo 8 is introduced into the surplus white water pit 9, and from there it is introduced into the inlet 6 via the MJ screen 13 and reused, and / or introduced into the cleaner 2 via the secondary screen 14 and the primary fan pump 11 and reused.

[0016] In FIG. 1, the form in which the surplus white water pit 9 is arranged between the white water silo 8 and the inlet 6 is taken as an example for explanation, but the method of the present disclosure is not limited to this form. For example, the white water in the white water silo 8 may be introduced into the inlet 6 via the screen 13 without passing through the surplus white water pit 9.

[0017] In FIG. 1, the form in which the white water discharged from the wire part 7 is recovered and stored in the white water silo 8 is taken as an example for explanation, but the white water stored in the white water silo 8 is not limited to the white water discharged from the wire part 7. In one or more embodiments, the white water discharged from a wet part other than the wire part such as the press part in the paper machine may be recovered and stored in the white water silo 8.

[0018] [Slime control method] The present disclosure relates to a slime control method in a papermaking process. The slime control method of the present disclosure includes supplying a slime control agent from the lower part of at least one white water storage section in a white water recovery system or a white water circulation system in the papermaking process. According to the slime control method of the present disclosure, in one or more embodiments, it is possible to reduce or decrease the deposits derived from microorganisms in the white water storage.

[0019] According to the slime control method of the present disclosure, furthermore, in one or more embodiments, it may be possible to reduce or decrease the deposits derived from microorganisms in each facility in the papermaking process and in the piping connecting them. Also, according to the slime control method of the present disclosure, in one or more embodiments, it is possible to suppress the occurrence of blockage in each pipe in the papermaking process. According to the slime control method of the present disclosure, in one or more embodiments, it may also be possible to suppress the occurrence of defects in paper products. According to the slime control method of the present disclosure, in one or more embodiments, it is possible to extend the interval between planned cleanings that are carried out by stopping the production of ordinary paper.

[0020] The slime control method of the present disclosure includes supplying a slime control agent from the lower part of the white water storage section. In the present disclosure, "supplying from the lower part of the white water storage section" includes, in one or more embodiments, supplying from near the bottom surface of the white water storage section. From the point of more efficiently performing slime control, it is preferable that the slime control agent is supplied from a position closer to the bottom surface of the white water storage section, and from the point of more efficiently performing slime control, it is more preferable to supply from an injection port (nozzle) arranged on the bottom surface of the white water storage section.

[0021] In one or more embodiments, the flow rate of the slime control agent is 10 L / min or more, from the standpoint of more efficient slime control. In one or more embodiments, the flow rate of the slime control agent is 20 L / min or more, 30 L / min or more, 40 L / min or more, or 50 L / min or more, from the standpoint of more efficient slime control. In one or more embodiments, the flow rate of the slime control agent is 100 L / min or less, 80 L / min or less, or 70 L / min or less, from the standpoint of more efficient slime control.

[0022] In this disclosure, from the viewpoint of more efficient slime control, it is preferable in one or more embodiments that the slime control agent is supplied from the lower part of the white water reservoir in a substantially horizontal direction to the bottom surface of the white water reservoir. In this disclosure, from the viewpoint of more efficient slime control, it is preferable in one or more embodiments that the slime control agent is supplied horizontally to the bottom surface from a drug inlet located at the bottom of the white water reservoir.

[0023] In order to control slime more efficiently, in one or more embodiments, the slime control agent is preferably supplied from the upstream side to the downstream side of the water flow in the white water storage section. In order to control slime more efficiently, in one or more embodiments, the slime control agent may also be supplied toward the outlet side for discharging white water to the outside.

[0024] In one or more embodiments, the slime control agent may be supplied from a single agent inlet located within the white water reservoir, or from two or more agent inlets located within the white water reservoir. From the viewpoint of more efficient slime control, it is preferable to supply the agent from multiple agent inlets located at the bottom of the white water reservoir.

[0025] In one or more embodiments, the supply of the slime control agent may be continuous or intermittent, and intermittent supply is preferred from the standpoint of more efficient slime control.

[0026] When supplying slime control agents intermittently, in one or more embodiments, the slime control agents are supplied at predetermined time intervals. The supply time per instance is 1 minute or more, 2 minutes or more, 3 minutes or more, 4 minutes or more, or 5 minutes or more in one or more embodiments, from the standpoint of more efficient slime control. Similarly, the supply time per instance is 60 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, or 10 minutes or less in one or more embodiments. The supply frequency (number of times) per day is 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more in one or more embodiments. The supply frequency (number of times) per day is 20 times or less, 15 times or less, 14 times or less, 13 times or less, 12 times or less, 11 times or less, or 10 times or less in one or more embodiments.

[0027] Examples of slime control agents include, in one or more embodiments, bound halogens, hypochlorites, chlorites, chlorine dioxide, and hydrogen peroxide.

[0028] Examples of bound halogens include bound chlorine and bound bromine in one or more embodiments. Monochloramine and / or monobrolamine are preferred in one or more embodiments from the viewpoint of more efficient slime control. Monochloramine and monobrolamine are OCl - (Br - )+NH4 +→It is produced by a reaction such as NH2Cl(Br) + H2O. In one or more embodiments, monochloramine can be produced by mixing a hypochlorite and an ammonium compound. Examples of ammonium compounds in one or more embodiments include ammonium sulfate, ammonium bromide, ammonium chloride, and ammonium sulfamate. These may be used individually or in combination of two or more.

[0029] Examples of slime control agents containing monochloramine and / or monobroramine include, in one or more embodiments, agents produced by mixing an aqueous solution of sodium hypochlorite, potassium hypochlorite, or calcium hypochlorite hypochlorite with an aqueous solution of a water-soluble inorganic ammonium salt of ammonium chloride, ammonium bromide, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium sulfate, or ammonium nitrate, or with ammonia water. In one or more embodiments, the molar ratio of hypochlorite to ammonium salt is 1:1 to 1:2, 1:1.1 to 1:2, 1:1.2 to 1:2, or 1:1.2 to 1:1.6, as the molar ratio of nitrogen to the total residual chlorine. In this disclosure, "total residual chlorine" refers to free residual chlorine (HOCl, OCl). - This refers to the sum of free residual chlorine and combined residual chlorine (chloramine). In this disclosure, "total residual chlorine amount" means the sum of free residual chlorine and combined residual chlorine, and in this disclosure, "total residual chlorine concentration" means the sum of free residual chlorine concentration and combined residual chlorine concentration. The total residual chlorine concentration can be measured by the method described in the examples.

[0030] Examples of hypochlorites in one or more embodiments include sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite. These may be used individually or in combination of two or more.

[0031] Examples of chlorites in one or more embodiments include sodium chlorite, potassium chlorite, and calcium chlorite. These may be used individually or in combination of two or more.

[0032] Chlorine dioxide is an extremely unstable chemical substance, making its storage and transportation very difficult. It is preferable to produce (generate) chlorine dioxide on-site using known methods and adjust its concentration for use. Chlorine dioxide can be produced by the following reaction in one or more embodiments. Alternatively, it may be produced using a commercially available chlorine dioxide generator (device). (1) Reaction of sodium hypochlorite, hydrochloric acid, and sodium hypochlorite NaOCl+2HCl+2NaClO2→2ClO2+3NaCl+H2O (2) Reaction of sodium chlorite with hydrochloric acid 5NaClO2+4HCl→4ClO2+5NaCl+2H2O (3) Reactions with sodium chlorate, hydrogen peroxide and sulfuric acid 2NaClO3+H2O2+H2SO4→2ClO2+Na2SO4+O2+2H2O

[0033] The slime control agent can be supplied in such a way that the total residual chlorine concentration (in the case of monobrolamine, as a value converted to total residual chlorine concentration) in the liquid (white water) stored in the white water reservoir is 0.5 mg / L to 30 mg / L in one or more embodiments. From the viewpoint of more efficient slime control, the supply amount (concentration) of the slime control agent can be 1 mg / L or more, 1.5 mg / L or more, or 2 mg / L or more in one or more embodiments. Similarly, from the viewpoint of the slime control agent supply amount (total residual chlorine concentration), can be 20 mg / L or less, 15 mg / L or less, 10 mg / L or less, 7.5 mg / L or less, or 5 mg / L or less in one or more embodiments.

[0034] In one or more embodiments, the slime control agent may be supplied from a single white water storage unit located within the white water recovery system or white water circulation system, or from multiple white water storage units located within the system.

[0035] The slime control method of this disclosure may include supplying papermaking process water along the bottom surface of a white water reservoir where a slime control agent is supplied, from the viewpoint of more efficient slime control. In this disclosure, "supplying along the bottom surface" means, in one or more embodiments, supplying papermaking process water so as to move along the bottom surface of the white water reservoir, supplying papermaking process water in a substantially horizontal direction with respect to the bottom surface of the white water reservoir, or supplying papermaking process water in a substantially horizontal direction with respect to the bottom surface from an inlet (nozzle) located at the bottom of the white water reservoir. From the viewpoint of more efficient slime control, it is preferable to supply the papermaking process water from a position closer to the bottom surface of the white water reservoir, and from the viewpoint of even more efficient slime control, it is preferable to supply it from an inlet (nozzle) located at the bottom surface of the white water reservoir.

[0036] In one or more embodiments, the water for the papermaking process may be supplied from a single chemical inlet located within the white water storage section, or from two or more chemical inlets. From the viewpoint of more efficient slime control, it is preferable to supply the water from multiple chemical inlets located at the bottom of the white water storage section.

[0037] In one or more embodiments, the supply of water for the papermaking process may be continuous or intermittent.

[0038] In order to more efficiently control slime, in one or more embodiments, the water used in the papermaking process is preferably supplied from the upstream side to the downstream side of the water flow in the white water storage section. In order to more efficiently control slime, in one or more embodiments, the water used in the papermaking process may also be supplied from the inlet side for introducing white water into the white water storage section to the outlet side for discharging white water to the outside.

[0039] In one or more embodiments, the water used in the papermaking process may be supplied from near the supply location of the slime control agent. In one or more embodiments, the slime control method of the present disclosure includes supplying the water used in the papermaking process from an inlet located near the chemical inlet for supplying the slime control agent.

[0040] In one or more embodiments, the flow rate of water in the papermaking process is 20 L / min or more, from the standpoint of more efficient slime control. In one or more embodiments, the flow rate of water in the papermaking process is 30 L / min or more, 40 L / min or more, or 50 L / min or more, from the standpoint of more efficient slime control. In one or more embodiments, the flow rate of water in the papermaking process is 500 L / min or less, 400 L / min or less, or 300 L / min or less, from the standpoint of more efficient slime control.

[0041] The slime control method of this disclosure, in one or more embodiments, does not include agitation to reduce the amount of sediment in the white water storage section to which the slime control agent has been supplied. Agitation in this disclosure, in one or more embodiments, includes agitation by injecting a water flow in a lateral, downward, or diagonally downward direction using an underwater agitator or the like. The slime control method of this disclosure, in one or more embodiments, does not include agitation in the white water storage section using a jet-type underwater agitator.

[0042] <Embodiment 1> One embodiment of the present disclosure, which is not particularly limited, will be described with reference to the drawings. In this embodiment 1, the white water storage section is an excess white water pit 9, the slime control agent is a bound halogen (monochloramine), and the case in which monochloramine is supplied from the bottom of the excess white water pit 9 will be described as an example. The excess white water pit 9 is a tank into which excess white water overflowing from the white water silo 8 is introduced. In one embodiment of the slime control method of this disclosure, slime control is performed by supplying monochloramine from the bottom of the excess white water pit 9.

[0043] The white water stored in the excess white water pit 9 contains a large amount of organic matter, which serves as a nutrient source for microorganisms and bacteria. This organic matter (solids and suspended matter) can accumulate at the bottom of the excess white water pit 9, potentially generating slime that can cause defects in the product. Normally, the production line is stopped and production halted for cleaning approximately twice a month. In addition, measures are taken to suppress slime generation during normal operation by adding chemicals such as slime control agents. In particular, the white water supplied to inlet 6 is used to adjust the concentration of the pulp slurry at the inlet. Therefore, the generation of slime (sediment) in white water storage areas connected to inlet 6 (located upstream of inlet 6), such as the excess white water pit 9, directly leads to a decrease in product (paper) quality and production efficiency, making slime control in these areas extremely important.

[0044] Figures 2A and 2B show schematic diagrams illustrating an example of the configuration of the excess white water pit 9 in this embodiment. Figure 2A is a schematic cross-sectional view, and Figure 2B is a schematic top view. A chemical inlet (nozzle) 23 for supplying monochloramine is located at the bottom of the excess white water pit 9. The inlet 23 is connected to a vertically extending pipe 24, and the other end of the pipe 24 is connected to a pump 25, etc. Excess white water overflowing from a white water silo (not shown) is introduced into the excess white water pit 9 from its top surface (not shown). Outlets 21 and 22 for discharging the white water in the pit are formed on one wall of the excess white water pit 9. Outlet 22 is connected to the inlet 6 via an MJ screen, and outlet 23 is connected between the seed box 1 and the primary fan pump 11 via a secondary screen 14.

[0045] The inlet 23 for supplying monochloramine is located near the upstream wall of the excess white water pit 9 (the wall opposite to the wall where the white water outlets 22 and 23 are formed), and is positioned so that its tip is in contact with the bottom of the excess white water pit 9, allowing monochloramine to be supplied horizontally along the bottom of the excess white water pit 9 toward the outlets 22 and 23. As shown in Figure 2, multiple inlets 23 are installed so as to be evenly spaced along one wall of the excess white water pit 9.

[0046] By supplying monochloramine at the lower part (near the bottom) of the excess white water pit 9, the amount of microbial deposits on the bottom of the excess white water pit can be suppressed or reduced, and the production of metabolites by microorganisms associated with the deposits can also be suppressed.

[0047] The supply of monochloramine is not limited, but should be intermittent, with a supply duration of 5 to 20 minutes, at a frequency of 6 or 12 times per day. The flow rate of monochloramine is not limited, but can range from 20 L / min to 70 L / min.

[0048] In addition to monochloramine, recovered white water (water used in the papermaking process) may be supplied from the inlet 23. The supply of recovered white water may be done simultaneously with the supply of monochloramine, or at a time when monochloramine is not being supplied. The supply of recovered white water from the inlet 23 is not limited, but can be done continuously or intermittently at a flow rate of 20 L / min to 250 L / min.

[0049] <Embodiment 2> As another embodiment, we will describe an example in which, in addition to the chemical inlet for supplying monochloramine, a chemical inlet for supplying recovered white water (papermaking process water) is located at the bottom of the excess white water pit 9. This embodiment is the same as Embodiment 1, except that a chemical inlet for supplying recovered white water is further located in the excess white water pit 9, and recovered white water is supplied from there.

[0050] Figures 3A and 3B show schematic diagrams illustrating an example of the configuration of the excess white water pit in this embodiment. Figure 3A is a schematic cross-sectional view, and Figure 3B is a schematic top view. As shown in Figures 3A and 3B, in this embodiment, an inlet 23 for supplying monochloramine and an inlet 31 for supplying recovered white water are located at the bottom of the excess white water pit. The inlet 23 is connected to a pump 25 via a vertically extending pipe 24, and the inlet 31 is connected to a pump 33 via a vertically extending pipe 32.

[0051] The inlet 23 for supplying monochloramine and the inlet 31 for supplying recovered white water are located adjacent to each other near the upstream wall of the excess white water pit 9 (the wall opposite to the wall where the white water outlets 22 and 23 are formed). The tips of the inlets 23 and 31 are positioned in contact with the bottom of the excess white water pit 9 so that monochloramine can be supplied horizontally along the bottom of the excess white water pit 9. As shown in Figure 3, the inlet ports 23 and 31 are installed in multiple locations so as to divide one wall of the excess white water pit 9 equally.

[0052] By supplying monochloramine and recovered white water to the lower part (near the bottom) of the excess white water pit, the amount of microbial deposits on the bottom of the excess white water pit can be suppressed or reduced, and the production of metabolites by microorganisms associated with the deposits can also be suppressed.

[0053] The supply of monochloramine is not limited, but should be intermittent, with a supply duration of 5 to 20 minutes, at a frequency of 6 or 12 times per day. The flow rate of monochloramine is not limited, but can range from 20 L / min to 70 L / min.

[0054] The supply of recovered white water is not limited, but can be carried out continuously or intermittently at a flow rate of 20 L / min to 250 L / min.

[0055] [Paper manufacturing method] This disclosure also relates to a method for manufacturing paper, which includes performing slime control in the papermaking process using the slime control method of this disclosure. Slime control in the method for manufacturing paper of this disclosure can be performed in the same manner as the slime control method of this disclosure described above.

[0056] The types of paper manufactured are not particularly limited, and in one or more embodiments, examples include newsprint, printing paper, information paper, packaging paper, sanitary paper, miscellaneous paper, corrugated cardboard base paper, cardboard for paper packaging, and miscellaneous cardboard. Examples of printing paper include fine paper and coated paper; examples of information paper include PPC paper and thermal paper base paper; examples of packaging paper include pure white roll paper and bleached kraft paper; examples of sanitary paper include tissue paper and toilet paper; examples of miscellaneous paper include food container base paper and coated printing base paper; examples of corrugated cardboard base paper include liner and core base paper; examples of cardboard for paper packaging include white cardboard and colored cardboard; and examples of miscellaneous cardboard include gypsum board and paper tube base paper.

[0057] This disclosure further relates to one or more embodiments described below. [1] A method for controlling slime in the papermaking process, This includes supplying a slime control agent to at least one white water storage section of a white water recovery system or white water circulation system in the papermaking process, The method involves supplying the slime control agent from the lower part of the white water storage section. [2] The slime control agent is supplied by supplying it horizontally to the bottom surface from a drug inlet located at the bottom of the white water storage section, according to the method described in [1]. [3] The method according to [1] or [2], comprising supplying the slime control agent at a flow rate of 20 L / min or more. [4] The method according to any one of [1] to [3], wherein the slime control agent is supplied intermittently or continuously. [5] The slime control agent is supplied from the upstream side to the downstream side in the white water storage section, according to any one of the methods in [1] to [4]. [6] The slime control agent is selected from the group consisting of bound halogens, hypochlorites, chlorites, chlorine dioxide and hydrogen peroxide, according to any one of [1] to [5].

[0058] The present disclosure will be described in further detail below with reference to examples and comparative examples, but these are illustrative examples and the disclosure is not limited to these examples. [Examples]

[0059] Monochloramine aqueous solution and monobroramine aqueous solution were prepared according to the following preparation examples 1 to 4.

[0060] [Preparation Example 1] Preparation of monochloramine aqueous solution using a mixture of sodium hypochlorite and ammonium sulfate A sodium hypochlorite aqueous solution (total residual chlorine content: 140 g / L) was diluted with deionized water to a total residual chlorine content of 2 g / L. Then, a 30% ammonium sulfate aqueous solution (30 g of ammonium sulfate (manufactured by Kishida Chemical Co., Ltd.) dissolved in deionized water to a total volume of 100 g) was mixed in to prepare a monochloramine aqueous solution with a molar ratio of total residual chlorine to nitrogen of 1:1.2.

[0061] [Preparation Example 2] Preparation of monochloramine aqueous solution using a mixture of sodium hypochlorite and ammonium sulfate The preparation was carried out in the same manner as in Preparation Example 1, except that the molar ratio of total residual chlorine to nitrogen was set to 1:1.6.

[0062] [Preparation Example 3] Preparation of monochloramine aqueous solution using a mixture of sodium hypochlorite and ammonium chloride A sodium hypochlorite aqueous solution (total residual chlorine content: 140 g / L) was diluted with deionized water to a total residual chlorine content of 2 g / L. Then, a 20% ammonium chloride aqueous solution (20 g of ammonium chloride (manufactured by Kishida Chemical Co., Ltd.) dissolved in deionized water to a total volume of 100 g) was mixed in to prepare a monochloramine aqueous solution with a molar ratio of total residual chlorine to nitrogen of 1:1.2.

[0063] [Preparation Example 4] Preparation of monobromamine aqueous solution using a mixture of sodium hypochlorite and ammonium bromide A sodium hypochlorite aqueous solution (total residual chlorine content: 140 g / L) was diluted with deionized water to a total residual chlorine content of 2 g / L. Then, 30 ml / L of 1% sodium hydroxide aqueous solution was added, and a 30% ammonium bromide aqueous solution (30 g of ammonium bromide (manufactured by Kishida Chemical Co., Ltd.) dissolved in deionized water to a total volume of 100 g) was mixed in to prepare a monobroramine aqueous solution so that the molar ratio of total residual chlorine to nitrogen was 1:1.2.

[0064] [Test Method] At a certain paper mill (manufacturing of high-quality paper for printing), the chemical prepared in Preparation Example 1 was added to a surplus white water pit (length: 10m x width: 4-5m, height: 3-4m, draft: depth: 2-3m) so that the total residual chlorine concentration (mg / L) at the time of addition was as shown in Table 1 below. The addition time per addition, the number of additions per day, the addition location, the water flow conditions at the bottom of the white water pit, and the number of operating days were as shown in Table 1 below. The amount of sediment at the bottom of the excess white water pit after a certain number of operating days, as shown in Table 1, was visually inspected. The difference in operating days is due to emergency shutdowns caused by trouble or shutdowns due to paper changes. Each example and comparative example will be described in detail below.

[0065] [Example 1] In Example 1, as shown in Figure 3, an inlet 23 for supplying the chemical agent and an inlet 31 for supplying recovered white water were arranged in contact with the bottom surface of the excess white water pit 9. These inlets 23 and 31 were laid parallel to the wall opposite to the outlets 21 and 22 (the upstream side of the excess white water pit). The chemical agent and recovered white water were supplied horizontally from the upstream side to the downstream side of the bottom surface of the excess white water pit through these inlets 23 and 31. The chemical (Preparation Example 1) was supplied at a flow rate of 50-60 L / min, with each addition taking 10 minutes and adding every 4 hours, six times a day, so that the total residual chlorine concentration at the time of addition was 3.8 mg / L. The recovered white water was supplied continuously at 200 L / min for 24 hours.

[0066] The amount of sediment at the bottom of the excess white water pit after 11 days of operation was visually observed and evaluated according to the evaluation criteria shown in Table 1 below. The results are shown in Table 1 below. The sediment at the bottom of the excess white water pit showed a positive result in the ninhydrin test used for slime detection. On Days 1, 4, 7, and 11, the total residual chlorine concentration was measured before and after the addition of the drug after multiple drug supply cycles using the method described below. An example of the results is shown in Table 2 below. In addition, the number of viable bacteria before and after the addition of the drug was measured using the method described below, along with the total residual chlorine concentration. The results are shown in Table 3 below. "Before drug addition" refers to 30 minutes before the start of drug addition, and "after drug addition" refers to immediately before the drug addition is stopped. Samples for measuring the total residual chlorine concentration and the number of viable bacteria were taken from the piping immediately preceding the MJ screen 13.

[0067] [Method for measuring total residual chlorine concentration] The total residual chlorine concentration was measured using the diethyl-p-phenylenediamine (DPD) colorimetric method described in JIS K0101 "Test Methods for Industrial Water". [Method for measuring the number of viable bacteria] Viable cell counts were determined by gradually diluting the collected samples as needed, culturing them on standard agar plates for general viability for 48 hours, and counting the number of colonies formed.

[0068] [Comparative Example 1] In Comparative Example 1, an inlet for supplying the chemical was laid below the waterline of the excess white water pit (approximately 1 / 3 of the way from the top of the pit depth), and the chemical (Preparation Example 1) was supplied from there. The chemical (Preparation Example 1) was supplied at a flow rate of 50-60 L / min, with an addition time of 5 minutes per addition and an interval of 4 hours between additions, 6 times a day, so that the total residual chlorine concentration at the time of addition was 2.4 mg / L. In Comparative Example 1, recovered white water was not supplied. The amount of sediment at the bottom of the excess white water pit after three days of operation was visually observed and evaluated according to the evaluation criteria shown in Table 1 below. The results are shown in Table 1 below. The reason the operation lasted only three days was that it was shut down urgently due to a problem caused by sediment at the bottom of the excess white water pit.

[0069] [Comparative Example 2] In Comparative Example 2, the procedure was the same as in Comparative Example 1, except that the recovered white water was continuously supplied at a rate of 200 L / min for 24 hours. The inlet for supplying the recovered white water was laid on the bottom surface of the excess white water pit. The amount of sediment at the bottom of the excess white water pit after four days of operation was visually observed and evaluated according to the evaluation criteria shown in Table 1 below. The results are shown in Table 1 below. The operation period was four days because it was shut down urgently due to a problem caused by sediment at the bottom of the excess white water pit.

[0070] [Comparative Example 3] In Comparative Example 3, the procedure was the same as in Example 1, except that the drug was supplied from an inlet laid below the waterline of the excess white water pit (approximately 1 / 3 of the way from the top edge of the pit depth). The amount of sediment at the bottom of the excess white water pit after 5 days of operation was visually observed and evaluated according to the evaluation criteria shown in Table 1 below. The results are shown in Table 1 below. The operation period was 5 days because the system was shut down urgently due to a problem caused by sediment at the bottom of the excess white water pit. Furthermore, similar to Example 1, the total residual chlorine concentration and viable bacterial count were measured before and after the addition of the drug after supplying the drug multiple times on Days 1, 2, 4, and 5. The results are shown in Tables 2 and 3 below.

[0071] [Table 1] Visual Inspection Criteria 5: Sediment covering the entire bottom surface of the pit can be seen. 4: Approximately three-quarters of the pit bottom is covered with sediment. 3: About half of the pit bottom is covered with sediment. 2: One-third of the pit bottom is covered with sediment. 1: A small amount of sediment is visible covering the bottom of the pit. 0: No sediment is observed at the bottom of the pit.

[0072] [Table 2] [Table 3]

[0073] In Example 1, the chemical agent was supplied from an inlet located at the bottom of the excess white water pit, and the recovered white water was continuously supplied from an inlet located at the bottom of the pit. As a result, as shown in Table 1, in Example 1, after 11 days of operation, no sediment was observed at all at the bottom of the excess white water pit, or if any was observed, it was only a small amount. On the other hand, in Comparative Examples 1 to 3, where the chemical was added from the top of the excess white water pit, one or half of the bottom surface of the excess white water pit was covered with sediment, resulting in a shorter operating period of 3 to 5 days, less than half that of the Example. Furthermore, in Comparative Example 3, the chemical addition time was doubled compared to Comparative Example 2, but similar to Comparative Example 2, about half of the bottom surface of the excess white water pit was covered with sediment. In Example 1, blockage of each pipe was suppressed, and a reduction in defects in the paper product was also confirmed. In contrast, in Comparative Examples 1 to 3, neither suppression of blockage of each pipe nor a reduction in defects in the paper product was confirmed. As a result of the effects described above, according to Example 1, by extending the number of operating days, it was possible to improve paper productivity and shorten the time required for cleaning the equipment during downtime due to paper changes.

[0074] The pre-addition measurement results shown in Tables 2 and 3 illustrate how the atmosphere within the system changed after the intermittent addition of the drug. As shown in Tables 2 and 3, comparing Example 1 with Comparative Example 3, both the total residual chlorine concentration and the number of viable cells improved in Example 1. Note that in Table 3, the low value of 300 for the number of viable cells before addition on Day 1 in Example 1 is because this measurement was taken after multiple applications of monochloramine on Day 1.

[0075] [Example 2] In a certain paper mill (for the production of high-quality paper for printing), an inlet 23 for supplying chemicals to an excess white water pit (length: 10m x width: 4-5m, height: 3-4m, draft: depth: 2-3m) was placed on the wall opposite to the outlets 21 and 22 (upstream side of the excess white water pit), as shown in Figure 2, so as to be in contact with the bottom surface of the excess white water pit. The drug (Preparation Example 1) was supplied at a flow rate of 50-60 L / min, with an addition time of 15 minutes per application and an interval of 2 hours between applications, 12 times a day, so that the total residual chlorine concentration at the time of addition was 3.8 mg / L. In Example 2, the recovered white water was not supplied. As a result of operating the system in the same manner as in Example 1, no sediment was found at all on the bottom of the excess white water pit, or if any was found, it was only a small amount, similar to Example 1.

Claims

1. A method for controlling slime in the papermaking process, This includes supplying a slime control agent to at least one white water storage section of a white water recovery system or white water circulation system in the papermaking process, The slime control agent is supplied from the bottom of the white water storage section (however, this method does not include stirring in the white water storage section using a jet-type underwater agitator).

2. The method according to claim 1, wherein the slime control agent is supplied horizontally to the bottom surface from a drug inlet located at the bottom of the white water storage section.

3. The method according to claim 1, comprising supplying the slime control agent at a flow rate of 20 L / min or more.

4. The method according to claim 1, wherein the supply of the slime control agent is performed intermittently or continuously.

5. The method according to claim 1, comprising supplying the slime control agent from the upstream side to the downstream side in the white water storage section.

6. The method according to any one of claims 1 to 5, wherein the slime control agent is selected from the group consisting of bound halogens, hypochlorites, chlorites, chlorine dioxide, and hydrogen peroxide.

7. The method according to any one of claims 1 to 4, further comprising supplying the slime control agent from a position closer to the bottom surface of the white water reservoir.

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