Method for defoaming aqueous systems

Abstract

To provide a defoaming method capable of efficiently removing foams in an aqueous system, especially a defoaming method for an aqueous system capable of efficiently reducing foams in white water in a papermaking process.SOLUTION: The method for defoaming an aqueous system according to claim 1, further comprising at least one of a step of stirring the aqueous system using an underwater stirring device or a step of adding a defoaming agent to the aqueous system, in addition to the step of generating the ultrafine bubbles using the ultrafine bubble generating device in the aqueous system.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for defoaming an aqueous system, and in particular to a method for defoaming an aqueous system that efficiently reduces foam in white water during the papermaking process. [Background technology]

[0002] Papermaking is carried out by dispersing pulp raw materials in water and then making paper from this material. However, the white water discharged from the papermaking machine contains a lot of starch, sizing agents, latex, paper strength agents, etc. in addition to fine fibers and fillers, and is prone to foaming when the water falls into a pit or when cavitation occurs due to the pump. This foaming problem has led to reduced productivity and the frequent occurrence of product defects due to the production of paper from foam-containing stock, and as a countermeasure, vacuum degassing equipment and antifoaming agents have been used. However, the former has the problem of equipment cost, and the latter has the problem that after the antifoaming agent is added, it takes time for it to disperse well and demonstrate its function, in addition to the cost of the chemicals. Due to the recent increase in the speed of paper production, there is a demand, particularly in the papermaking process, for the defoaming agent to be added to a large volume of circulating water systems or to the water systems flowing into the circulating water systems, and for the defoaming effect to be exerted by diluting and mixing the agent uniformly and efficiently in a short period of time.

[0003] However, the above-mentioned conventional chemical mixers are insufficient for uniform mixing in a short time, and therefore, an excessive amount of antifoaming agent must be added to achieve the desired defoaming effect, which leads to problems such as defects due to residual antifoaming agent, deterioration of paper product properties such as poor sizing ability, and increased chemical costs. As mixing techniques used in fields other than paper manufacturing, Patent Document 1 discloses a method for mixing powder and liquid using jet injection when preparing chemical solutions, and Patent Document 2 discloses a chemical solution mixing device using a jet pump. The applicant also discloses in Patent Document 3 a method of dispersing a chemical solution containing an antifoaming agent by installing a submerged agitator in a water reservoir in a paper manufacturing process. However, none of these prior art documents or suggests that an ultra-fine bubble generator is effective in defoaming, or that an effective defoaming method can be achieved by using an ultra-fine bubble generator in combination with a defoaming agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-313909 [Patent Document 2] Japanese Patent Application Publication No. 3-229691 [Patent Document 3] Japanese Patent Application Publication No. 2019-183326 Summary of the Invention [Problem to be solved by the invention]

[0005] Adding an antifoaming agent is considered as a way to solve foam problems in aqueous systems, but there are concerns about the increased cost of the antifoaming agent and adverse effects such as staining caused by the antifoaming agent, particularly the occurrence of defects in paper products in papermaking and adverse effects on other chemicals such as sizing agents.

[0006] An object of the present invention is to solve the above-mentioned problems of the prior art, that is, to provide a defoaming method capable of efficiently removing foam in an aqueous system, particularly a defoaming method capable of efficiently reducing foam in white water in the papermaking process of papermaking. [Means for solving the problem]

[0007] (1) The method for defoaming an aqueous system of the present invention is a method for defoaming an aqueous system in which ultrafine bubbles are generated in the aqueous system using an ultrafine bubble generator.

[0008] (2) (1) The method for defoaming an aqueous system comprises, in addition to a step of generating ultrafine bubbles using an ultrafine bubble generator, at least one of a step of stirring the aqueous system using a submersible stirring device and a step of adding a defoaming agent to the aqueous system.

[0009] (3) In (1) or (2), the method is for defoaming an aqueous system in a papermaking process.

[0010] (4) (2) is a method for defoaming an aqueous system in which the submerged agitator is an eductor type.

[0011] (5) In (4), the method for defoaming an aqueous system is to introduce ultra-fine bubble-containing water generated by an ultra-fine bubble generator or water containing such ultra-fine bubbles into an eductor-type submersible agitator, mix it with intake water, and then discharge it to the outside.

[0012] (6) (5) is a defoaming method for an aqueous system in a papermaking process.

[0013] (7) (6) The method for defoaming an aqueous system includes the steps of stirring the aqueous system using a submersible stirring device and adding a defoaming agent to the aqueous system. [Effects of the Invention]

[0014] According to the aqueous defoaming method of the present invention, it is possible to efficiently remove aqueous bubbles, and particularly to efficiently reduce bubbles in white water in the papermaking process in papermaking. This makes it possible to achieve good paper product properties without paper breaks or defects due to foam, even with a reduced amount of defoaming agent used or even without using any defoaming agent, reduce the cost of defoaming agents, and prevent problems such as paper defects and reduced sizing effect caused by defoaming agents. In some fields, even if the product does not allow the use of antifoaming agents, the bubbles that cause problems can be reduced by using an ultra-fine bubble generator and a jet-type agitator such as an eductor type.

[0015] Furthermore, in the present invention, the configuration includes a step of measuring internal bubbles at least at one location in the circulating water system and in the water system flowing into the circulating water system, which makes it possible to monitor the state of the bubbles, and to select an appropriate location for installing the ultra-fine bubble generator and conditions for generating ultra-fine bubbles, an appropriate location for installing the jet-type agitator and conditions for agitation, and an appropriate location for adding the antifoaming agent and conditions for adding it. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a model diagram of an example of a papermaking process in which the aqueous defoaming method of the present invention is carried out. [Figure 2] FIG. 1 is a model diagram of a papermaking process using the underwater agitator of the present invention. [Figure 3] This is a model diagram of an eductor type as an example of a submersible agitator. [Figure 4] FIG. 1 is a diagram of a model used in Example 1 of the present invention. [Figure 5] FIG. 1 is a model diagram of the ultra-fine bubble generator used in Example 1 of the present invention. [Figure 6] FIG. 1 is a model diagram of an eductor-type submersible agitator used in Example 1 of the present invention. [Figure 7] FIG. 10 is a diagram showing an installation model of each device used in Example 2 of the present invention. [Figure 8] FIG. 10 is a diagram showing an installation model of each device used in Example 2 of the present invention. [Figure 9] FIG. 10 is a diagram showing an installation model of each device used in Example 2 of the present invention. [Figure 10] FIG. 10 is a diagram showing an installation model of each device used in Example 3 of the present invention. [Figure 11] FIG. 10 is a diagram showing an installation model of each device used in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described below with reference to the drawings, particularly when it is implemented in a papermaking process in papermaking.

[0018] <Paper making process> The aqueous defoaming method of the present invention is particularly preferably applied to the papermaking process carried out in the papermaking system of a paper mill.

[0019] In this invention, the term "papermaking process" refers to a process that includes a raw material preparation system, a white water circulation system, and a white water recovery system, and refers to the entire water circulation process, including the recovery and reuse system of the aqueous solution (so-called "white water") discharged in large quantities from a papermaking machine. White water usually contains fine fibers derived from the raw pulp used in papermaking, as well as other papermaking chemicals.

[0020] FIG. 1 shows an example of a papermaking system used to explain the defoaming method for a papermaking process as an aqueous system according to the present invention, but the present invention is not limited to this example.

[0021] First, the raw material is adjusted in the raw material adjustment system A1, which includes a raw material adjustment tank 1 and a machine chest 2 of the papermaking system A. Specifically, raw material containing pulp and water (not shown) are supplied to the raw material adjustment tank 1, and water delivered from a recovered water tank 12 by a pump 13 is added to prepare a pulp slurry. The adjusted pulp slurry is supplied to the machine chest 2, where various papermaking chemicals such as viscosity modifiers and paper strength agents are added as needed, and then supplied to the white water circulation system A2 by a pump 3. Before being supplied to the white water circulation system A2, the pulp slurry may pass through a seed box (not shown). The pulp slurry is then mixed with white water (water containing a certain amount of stock components) from the white water silo 5 and supplied as stock to the inlet 6, from which it is supplied to the rotating wire 7a of the wire part 7. The stock supplied to the wire part 7 is dewatered to form a sheet and sent to the papermaking process starting from the press part 8 to produce a paper product. Meanwhile, the water remaining in the wire part 7 is stored as white water in the white water silo 5. The white water stored in the white water silo 5 is supplied to the pump 4, forming a white water circulation system A2.

[0022] A portion of the white water stored in the white water silo 5 is supplied from the white water silo 5 to the excess white water pit 9 of the white water recovery system A3. The excess white water supplied to the excess white water pit 9 is pumped by pump 10 to a solid-liquid separator 11 for solid-liquid separation. The water from the solid-liquid separation is stored in a recovered water tank 12. A portion of the water is pumped by pump 13 to the raw material adjustment tank 1 of the raw material adjustment system A1 for use in adjusting the concentration of the pulp slurry. Another portion is reused as water for various purposes in the papermaking process, such as shower water for keeping the wire 7a of the wire part 7 and the felt of the press part 8 clean through piping (not shown). Thus, the white water recovery system A3, together with the raw material adjustment system A1 and the white water circulation system A2, constitutes the circulating water system of the papermaking process, and water circulates within this circulating water system. The remaining water in the recovered water tank 12 is discharged to the system for concentration adjustment and sent to a wastewater treatment facility (not shown).

[0023] Furthermore, if there is a shortage of water in the papermaking system A, in this example, water stored in the cushion tank 14 is supplied from the water line 15 and supplied to the excess white water pit 9 by a pump 16. The solid content of the components separated in the solid-liquid separator 11 is either reused as papermaking raw material or disposed of as waste.

[0024] In the papermaking system A of FIG. 1, water storage sections for storing water include a white water silo 5, an excess white water pit 9, a recovered water tank 12, and a cushion tank .

[0025] In the present invention, examples of water flowing into the circulating water system of the papermaking process include, but are not limited to, tap water, industrial water, and treated water from wastewater treatment facilities. While Fig. 1 shows an example in which water from a water line 15 flowing into the circulating water system of the papermaking process is supplied to the excess white water pit 9, the supply location is not limited to the excess white water pit 9. For example, if water from an external source other than the circulating water system is supplied as dilution water for pulp and various papermaking chemicals, the water from the external source will flow into the circulating water system of the papermaking process of the present invention. Water discharged from processes subsequent to the papermaking process, such as the press part 8, may also be collected in the white water silo 5 or the excess white water pit 9.

[0026] The submersible agitator S in Figure 1 is an ultra-fine bubble generator and a jet-type agitator of the present invention. Note that the installation locations of the ultra-fine bubble generator and the jet-type submersible agitator S in Figure 1 are examples and are not limited to these. Only the ultra-fine bubble generator may be installed underwater in the water storage section, only the jet-type agitator may be installed, or both may be installed. However, the ultra-fine bubble generator is installed at least underwater in the water storage section or in the air raised from the water.

[0027] Although there is no problem in adding the antifoaming agent anywhere in Figure 1, it is common to add the antifoaming agent to the water reservoir where bubbles are usually generated.

[0028] <Papermaking raw materials> In the present invention, examples of raw material pulp used in papermaking include groundwood pulp (ground pulp (GP)) such as softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (LBKP); mechanical pulp such as refiner mechanical pulp (RMP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP); chemical pulp such as kraft pulp (KP), sulfide pulp (SP), and alkaline pulp (AP); recycled waste paper pulp from used magazines, used newspapers, used cardboard, used liner paper, and used backing paper (ground paper); white waste paper pulp; and deinked pulp, but are not limited to these.

[0029] Examples of papermaking chemicals include, but are not limited to, fillers, surfactants, waxes, sizing agents, flocculants, coagulants, antifoaming agents, dispersants, viscosity modifiers, various paper strength agents, bulking agents, retention aids, paper dust prevention agents, rust inhibitors, and conductivity imparting agents.

[0030] <Stirring> In the method for defoaming an aqueous system of the present invention, at least one water storage section in the white water circulation system A2, white water recovery system A3, or raw material preparation system A1 (hereinafter collectively referred to as the "circulating water system"), or in the aqueous systems flowing into these circulation systems (reference numerals 14 to 16; the circulating water system and the aqueous systems flowing into the circulating water system are collectively referred to as the "aqueous system"), is agitated with a jet agitator or an ultra-fine bubble generator is installed. The agitation location or the location where the ultra-fine bubble generator is installed is not particularly limited, but it is suitable for use in water tanks and other locations within these aqueous systems where water temporarily accumulates and where foam problems occur. Specifically, in the circulating water system of a papermaking system, examples include the white water silo 5, the excess white water pit 9, and the recovered water tank 12, and in the aqueous system flowing into the circulating water system, the cushion tank 14.

[0031] It is possible to achieve a defoaming effect using only ultrafine bubbles or only antifoaming agents, but because stagnant water areas (areas where there is no water flow) will occur in the water storage area, it is effective to stir the inside of the pit to ensure that the ultrafine bubbles and antifoaming agent generated by the ultrafine bubble generator are distributed throughout the pit. In the present invention, it is preferable not only to introduce ultrafine bubbles into the water system but also to stir the water without increasing the bubbles in the water reservoir.

[0032] Here, the submerged agitator has the advantage that it can be installed in an existing papermaking system without large-scale modifications. It is preferable to use a submerged agitator of the horizontal or downward jet type. If an upward jet type submerged agitator is used, the water flow does not directly hit the bottom of the water storage section, which weakens the effect of eliminating stagnant areas at the bottom. Furthermore, the water flow creates waves at the gas-liquid interface, which increases the risk of air being entrained in the water as bubbles, making this undesirable.

[0033] Here, several examples of mixing methods using submersible agitators are explained using the model diagrams in Figure 2. Figure 2(a) shows an example in which a submersible agitator S is used as a downward jet type. The dashed arrows in the figure indicate the flow of water discharged from the submersible agitator S. In this example, the submersible agitator S is installed in the center of the water storage section 17, which is highly effective in preventing stagnant water. Figure 2(b) shows an example in which a submersible agitator S is used as a horizontal jet type, installed slightly higher than the bottom of the water storage section and at an angle so that the water flow faces downward. Figure 2(c) shows an example in which a horizontal jet type submersible agitator S is installed at the bottom of the water storage section. When installing a horizontal jet type submersible agitator in a cylindrical water storage section, it may be installed so that the water flow follows the inner surface of the water storage section 17, as shown in the model diagram in Figure 2(d), or it may be installed so that the water flow is directed in the diameter direction near the bottom of the cylindrical water storage section 17, as shown in the model diagram in Figure 2(e). In any case, it is necessary to select the type, capacity, installation location, etc. of the submersible agitator so that it is effective in preventing water stagnation, taking into account the capacity and shape of the water storage section. Also, in these examples, one submersible agitator S is installed in each water storage section 17, but multiple units can be installed if necessary. In this case, it is important to agitate the water without increasing the amount of bubbles in the water.

[0034] An eductor-type submersible agitator S preferably used in the present invention is illustrated in Figure 3. The eductor-type submersible agitator S in Figure 3 is equipped with a nozzle 18a inside, an inlet 19a for the driving water 18 through which the driving water 18 flows in from the nozzle 18a, and an outlet 20a through which the suction water 19 flows in with the inflow of the driving water 18, and the driving water 18 and the suction water 19 are mixed and discharged to the outside. The eductor-type submersible agitator S is preferred because it can generate a large agitating force with a small amount of water. It is preferable to supply water containing ultra-fine bubbles from an ultra-fine bubble generator as the driving water 18, but water containing ultra-fine bubbles may also be used. The eductor-type submersible agitator S in this patent is not limited to this.

[0035] The ultra-fine bubble generator used in this invention is a device that generates bubbles with a particle size of 1 μm or less, and any known device can be used. Examples include gas-liquid mixed shear type, static mixer type, Venturi type, cavitation type, steam condensation type, ultrasonic type, swirling jet type, pressurized dissolution type, and micro-hole type. Among these, the gas-liquid mixed shear type and swirling jet type are preferred because they can easily generate ultra-fine bubbles using a pump or other device. Furthermore, compared to conventional degassing devices, ultra-fine bubble generators have the advantage that they can be installed without major modifications. Figure 5 shows a model diagram of a mixed shear type ultra-fine bubble generator U.

[0036] Many manufacturers produce ultra-fine bubble generators, but since the water used in the papermaking process contains SS components, it is best to use a generator with as large a diameter as possible. Examples include, but are not limited to, the TH-03, TH-05, TH-07, and TH-10 models manufactured by Daisei Kogyo Co., Ltd.

[0037] In the present invention, an ultra-fine bubble generator is installed in at least one of the circulating water systems consisting of the raw material adjustment system, white water circulation system, and white water recovery system, and in the water reservoirs in the water systems flowing into the circulating water systems. Preferably, the installation of a submerged agitator or the addition of a defoaming agent enhances the defoaming effect, enabling a reduction in the amount of defoaming agent added. The installation of an ultra-fine bubble generator, a submerged agitator, and the addition of a defoaming agent further improves the defoaming effect. In particular, the most efficient defoaming effect can be achieved by adding a defoaming agent to the water reservoirs in which the ultra-fine bubble generator and the submerged agitator are installed.

[0038] <Addition of antifoaming agent> The present invention preferably includes a step of adding an antifoaming agent to at least one of the circulating water system in the papermaking process and the water system flowing into the circulating water system. This step is preferably carried out in a water system having a water reservoir where an ultrafine valve supply step is carried out, since a higher antifoaming effect can be obtained. The amount of the antifoaming agent added is generally 0.1 to 500 mg / L, preferably about 0.5 to 100 mg / L, of the active ingredient relative to the water system.

[0039] The antifoaming agents used in the present invention include, but are not limited to, emulsion types, water-soluble surfactant types, self-emulsifying types, and oil types. For example, for papermaking, self-emulsifying and emulsion-type defoamers are primarily used. Examples of self-emulsifying defoamers include surfactants such as polyoxyethylene polyoxypropylene distearate and polyoxyethylene polyoxypropylene monostearyl ether. Examples of self-emulsifying defoamers include conventionally used self-emulsifying defoamers, such as polyoxyethylene polyoxypropylene distearate and polyoxyethylene polyoxypropylene monoalkyl ethers such as polyoxyethylene polyoxypropylene monostearyl ether, and other surfactant-based defoamers. Examples of emulsion-type defoamers include agents in which a water-insoluble substance serving as a defoaming component is emulsified with an emulsifier and can be diluted with water. Examples of emulsion-type defoamers include conventionally used emulsion-type defoamers, such as those primarily composed of polyoxyalkylene polyalkylsiloxanes, polydimethylsiloxanes, higher alcohols, fatty acid esters, and hardened oils. Higher alcohols include saturated alcohols and unsaturated alcohols having about 12 to 30 carbon atoms, such as dodecanol, tetradecanol, dodecenol, and tetradecenol.

[0040] <Internal foam measurement and antifoam agent addition control> In the method for defoaming an aqueous system of the present invention, it is preferable to measure internal bubbles in the aqueous system during the papermaking process, since this makes it possible to monitor the foam state of the aqueous system to be defoamed. Such monitoring makes it possible to select appropriate stirring locations and stirring conditions, appropriate ultra-fine bubble generator locations and ultra-fine bubble generation conditions, and defoaming agent addition locations and addition conditions.

[0041] The amount of antifoaming agent to be added may be controlled based on the measured value (measurement result) obtained in this measurement, i.e., antifoaming agent may be added when the measured value is higher than a reference value, or the amount of antifoaming agent to be added may be controlled while simultaneously controlling the stirring or ultrafine bubble generation conditions.

[0042] <Other> According to the present invention, it is possible to suppress the generation of foam in a circulating water system in a papermaking process. Therefore, by applying the aqueous defoaming method of the present invention to a papermaking process, it is possible to reduce the amount of defoaming agent used, the amount of other chemicals used such as sizing agents, and to reduce stains and defects caused by the defoaming agent.

[0043] Although the present invention has been described above by citing preferred embodiments, the method for defoaming an aqueous system of the present invention is not limited to the configurations of the above-mentioned embodiments.

[0044] Those skilled in the art can appropriately modify the defoaming method for aqueous systems of the present invention in accordance with conventionally known knowledge. As long as such modifications still comprise the configuration of the defoaming method for aqueous systems of the present invention, they are of course included in the scope of the present invention. [Example]

[0045] Example 1 Figure 4 is an external view of the equipment used in the test. The dashed lines in the figure indicate the flow of water discharged from the submersible agitator S. The water tank is equipped with a magnetic pump 21 for circulating water, an ultra-fine bubble generator U, and an eductor-type submersible agitator S. The suction port 22 of the magnetic pump 21 was installed diagonally across from the discharge port 23 of the magnetic pump 21 (the driving water inlet of the ultra-fine bubble generator U). In addition, an air supply ball valve 25 and an air flow meter 26 were installed above the waterline to supply air to the ultra-fine bubble generator U through air supply piping 24 when generating microbubbles. 20 L (liters) of white water from the white water pit of an operating paperboard machine was placed in a water tank measuring 60 cm x 30 cm x 35 cm (height), and 10 mL of a general-purpose anionic rosin emulsion sizing agent (active ingredient concentration 50% by mass) and 10 mL of a general-purpose amphoteric modified polyacrylamide resin paper strength agent (active ingredient concentration 20% by mass) were added, and the mixture was stirred using a mixer (hand blender) capable of strong stirring nearby while aerating. The reason for adding the sizing agent and paper strength agent, and for stirring while aerating, was to increase the amount of foam in the white water, as the amount of foam in the tank was low. The white water, which had been forcibly foamed, was circulated within the system shown in Figure 4 using a magnetic pump 21. Table 1 shows the test conditions and the results of the defoaming effect. Depending on the test conditions, an eductor-type submersible agitator and an ultra-fine bubble generator were operated, and defoaming agent was added.

[0046] <Ultra-fine bubble generator> The TH-03 manufactured by Taisei Kogyo Co., Ltd. was used.

[0047] <<Mixing device>> An eductor-type submersible agitator S shown in the cross section of Figure 6 was fabricated and used.

[0048] 《Stirring conditions》 When there was no stirring (conditions 1, 2, and 3 in Table 1), the magnetic pump 21 was used to control the water volume and circulate the water to the extent that the water surface did not ripple. When there was stirring (no ultrafine bubbles or microbubbles) (conditions 4 and 9), an eductor-type water flow agitator S was installed on the outlet side (delivery side) of the magnetic pump 21. When there was stirring (with ultrafine bubbles and microbubbles) (conditions 5, 6, 7, 8, 10, 11), 12, and 13), an ultrafine bubble generator U, TH-03, was installed on the discharge port 23 side (delivery side) of the magnetic pump 21, and an eductor-type submersible agitator S was installed further ahead. The operating conditions for the ultra-fine bubble generator U were as follows: when ultra-fine bubbles were generated (conditions 7 and 10), the ball valve 25 connected to the air inlet 29 of the ultra-fine bubble generator U was fully closed, and the water pressure at the inlet 28 of the driving water 18 of the ultra-fine bubble generator U was 0.2 MPa. When microbubbles were generated (conditions 6 and 7), the ball valve 25 connected to the inlet 29 was slightly opened (air inflow rate adjusted to approximately 0.05 L / min), and the water pressure at the inlet 28 of the driving water 18 was 0.2 MPa. The operating conditions for the eductor-type submersible agitator S were such that the driving water 18 was supplied at a flow rate of approximately 10 L / min, and the discharge water 20 was agitated at a flow rate of 30 L / min.

[0049] <Antifoaming agent> The following antifoaming agents were used, and the amount added was 2 mg / L relative to the circulating water. A: Aquas "Aquascreen AW-210" surfactant-based defoamer (surfactant-based) manufactured by Aquas B: Aquas "Aquascreen AW-570" high-alcohol emulsion defoamer (high-alcohol type) manufactured by Aquas

[0050] Evaluation Method The evaluation was carried out by stirring and circulating for 10 minutes, then leaving it to stand for 10 minutes, and then measuring the amount of internal foam measured by an EGT (Entrained Gas Tester) and the amount of foam (foam area) as seen from above the water tank.

[0051] Test Method Tests were conducted under conditions 1 to 13 in Table 1, depending on the agitation, the presence or absence of ultrafine bubbles, and the presence or absence of an antifoaming agent. The antifoaming agent was added to give a concentration of 2 mg / L. In addition, the TH-03 manufactured by Daisei Kogyo Co., Ltd. can generate microbubbles by sucking in a very small amount of air.

[0052] [Table 1] *For example, a bubble area of ​​80% means that 80% of the bubble area is visible from the top of the tank, and 20% is visible on the water surface (water area) at the waterline.

[0053] Since there was no difference in the effect depending on the type of defoamer under conditions 2 and 3 in Table 1, it was decided to conduct the test using defoamer A.

[0054] From Table 1, it can be inferred that the ultrafine bubbles under Condition 12 have a defoaming effect, while the microbubbles under Condition 13 do not, compared to the comparative example in which the ultrafine bubble generator and submerged agitator under Condition 1 were not operated and no defoaming agent was added.

[0055] From Table 1, it can be inferred that the defoaming effect is greater when ultra-fine bubbles are used in combination with eductor-type submerged agitation (condition 10) than when they are used alone (condition 12).

[0056] Table 1 shows that the highest defoaming effect was achieved when using the ultra-fine bubble generator and submersible agitator (condition 5) and adding an antifoaming agent, compared to when using ultra-fine bubbles in combination with eductor-type submersible agitation (condition 10).

[0057] The reasons for these results are not entirely clear, but it is possible that without stirring, the ultrafine bubbles, which have a defoaming effect, are not sufficiently dispersed in the tank; that stirring makes it easier for bubbles in the water (bubbles that are larger than ultrafine bubbles and tend to float) to escape above the waterline; or that the eductor effect increases the efficiency of ultrafine bubble generation.

[0058] <Example 2> The defoaming effect was confirmed by installing an eductor-type submerged agitator S and an ultra-fine bubble generator U in a paperboard manufacturing machine. The operating condition of the paperboard manufacturing machine was 400 m / min. The antifoaming agent is A: Aquas Co., Ltd.'s "Aquascreen AW-210" surfactant-based defoamer (surfactant-based) was added to the influent water at 5 mg / L. B: Aquas Co., Ltd.'s "Aquascreen AW-570" high-alcohol emulsion defoamer (high-alcohol type) was added to the influent water at 2 mg / L. 7, 8, and 9 are diagrams showing the device layout during testing under conditions 1, 2, and 3 in Table 2, respectively. Each device is equipped with a white water silo 5, a pump 4, an inlet 6, a wire part 7, a pump 33 (33 is shown only in Figures 8 and 9) used in combination with an eductor-type submersible agitator S or an ultra-fine bubble generator U, an ultra-fine bubble generator U (U is shown only in Figures 8 and 9), and an eductor-type submersible agitator S (S is shown only in Figure 9). The antifoaming agent Aquascreen AW-210 was added using piping hose 31, and the antifoaming agent Aquascreen AW-570 was added using piping hose 32.

[0059] <Ultra-fine bubble generator> Two TH-10 units manufactured by Taisei Kogyo Co., Ltd. were used. The operating conditions were that the ball valve 25 connected to the air intake 29 was fully closed and the water pressure at the inlet 28 of the driving water 18 was approximately 0.2 MPa.

[0060] <<Mixing device>> An eductor-type submersible agitator S was used, as shown in the cross-sectional view of Figure 6. The operating conditions were to agitate the water in the white water silo 5 with a driving water 18 flow rate of approximately 100 L / min and a discharge water 20 flow rate of approximately 300 L / min.

[0061] Evaluation Method The evaluation was carried out based on the amount of foam inside the silo (EGT), the amount of foam seen from above the white water silo (5), and the hardness of the foam when collected in a plastic bottle. The test water was collected from white water silo (5) (1). The amount of foam seen from above the white water silo 5 was visually rated on a 5-point scale, with 5 being when foam was overflowing from the white water silo 5 and 1 being when there was no foam at all, and the hardness of the foam was checked by collecting it in a plastic bottle and checking whether it disappeared easily. Table 2 shows the test conditions and the results of the defoaming effect.

[0062] [Table 2] Condition 1 was tested using the device specifications shown in Figure 7, Condition 2 was tested using the device specifications shown in Figure 8, and Condition 3 was tested using the device specifications shown in Figure 9.

[0063] The results in Table 2 show that using the Ultrafine Bubble Generator U under Condition 2 reduced internal bubbles compared to Condition 1, in which only an antifoaming agent was added, and the bubbles generated on the water surface were softer (they were easier to dissipate when stirred with a glass rod, etc.). Furthermore, compared to Condition 2, in which white water containing ultrafine bubbles was directly poured into white water silo 5, Condition 3, in which the white water was further poured into white water silo 5 through an eductor-type submersible agitator, reduced internal bubbles more.

[0064] Example 3 Tests were also conducted on a different board machine than in Example 2. The ultra-fine bubble generator U was installed in a paperboard manufacturing machine that already had an eductor-type submersible agitator S installed, and the defoaming effect was confirmed. The antifoaming agent is A: Aquas Co., Ltd.'s "Aquascreen AW-210" surfactant-based defoamer (surfactant-based) was added to the influent water to a concentration of 5 mg / L. B: Aquas Co., Ltd.'s "Aquascreen AW-570" high-alcohol emulsion defoamer (high-alcohol type) was added to the influent water at 2 mg / L. Added. 10 and 11 are diagrams showing the device layout during testing under conditions 1 and 2 in Table 3, respectively. The apparatus includes a white water silo 5, a pump 4, an inlet 6, a wire part 7, a pump 33 for an eductor-type submersible agitator S, an eductor-type submersible agitator S, a pump 34 for an ultra-fine bubble generator U (33 is shown only in Figure 11), and an ultra-fine bubble generator U (U is shown only in Figure 11).

[0065] <Ultra-fine bubble generator> Two TH-10 pumps manufactured by Taisei Kogyo Co., Ltd. were used. The operating conditions for both pumps were that the ball valve 25 at the air intake 29 was fully closed and the water pressure at the inlet 28 of the driving water 18 was approximately 0.2 MPa.

[0066] <<Mixing device>> An eductor-type submersible agitator S has already been installed and is in use. It is agitating the driving water 18 at a flow rate of approximately 100 L / min at a flow rate of approximately 300 L / min.

[0067] Evaluation Method The evaluation was carried out based on the amount of internal foam measured by EGT, the amount of foam seen from above the white water silo 5, and the hardness of the foam when collected in a plastic bottle. The test water was collected from the white water silo 5. The amount of foam seen from above the white water silo 5 was visually evaluated on a 5-point scale, with 5 being when foam was overflowing from the white water silo 5 and 1 being when there was no foam at all, and the hardness of the foam was checked by collecting it in a plastic bottle and checking whether it disappeared easily. Table 3 shows the conditions and evaluation results.

[0068] [Table 3] Condition 1 was tested using the device specifications shown in Figure 10, and condition 2 was tested using the device specifications shown in Figure 11.

[0069] Compared to the use of the underwater stirring device S and the addition of an antifoaming agent under condition 1, the use of the ultra-fine bubble generator U under condition 2 also reduces internal bubbles and softens the bubbles that form on the waterline (the bubbles disappear more easily when stirred with a glass rod, etc.). [Explanation of symbols]

[0070] A Papermaking System A1 Raw material adjustment system A2 White water circulation system A3 White water recovery system 1 Raw material adjustment tank 2 Machine Chest 3. Pump 4. Pump 5. Shiramizu Silo 6 Inlet 7 Wire Part 7a wire 8 Press Section 9. Excess white water pit 10 Pump 11 Solid-liquid separator 12 Recovered water tank 13 Pump 14 Cushion Tank 15 Water Line 16 Pump S Submersible Mixer 17 Water storage section 18 Driving Water 18a nozzle 19 Inhalation water 19a Inlet 20 Discharge water 20a Discharge part 21 Magnetic Pump 22 Intake port 23 Discharge port 24 Air supply piping 25 Ball Valve 26 Air flow meter 27 Air Flow 28 Entrance 29 Air intake 30 Discharge water 31 Plumbing hose 32 Plumbing hose 33 Pump 34 Pump U Ultra Fine Bubble Generator

Claims

1. A method for defoaming an aqueous system, comprising generating ultrafine bubbles in the aqueous system using an ultrafine bubble generator.

2. 2. The method for defoaming an aqueous system according to claim 1, further comprising, in addition to a step of generating ultrafine bubbles using an ultrafine bubble generator, at least one of a step of stirring the aqueous system using a submersible stirring device and a step of adding a defoaming agent to the aqueous system.

3. 3. The method for defoaming an aqueous system according to claim 1, wherein the aqueous system is an aqueous system used in a papermaking process.

4. 3. The method for defoaming an aqueous system according to claim 2, wherein the submersible agitator is an eductor type.

5. The method for defoaming an aqueous system according to claim 4, characterized in that the ultra-fine bubble-containing water generated by the ultra-fine bubble generator or water containing such water is introduced into an eductor-type submersible agitator, mixed with intake water, and then discharged to the outside.

6. 6. The method for defoaming an aqueous system according to claim 5, wherein the aqueous system is a papermaking process.

7. 7. The method for defoaming an aqueous system according to claim 6, further comprising the steps of: stirring the aqueous system using a submersible stirring device; and adding a defoaming agent to the aqueous system.

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