JP2017104787A - Method of using concentrated water as circulating cooling water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of using a concentrated water in which the concentrated water in RO unit is used as a circulating cooling water.SOLUTION: The method of using a RO concentrated water as a circulating cooling water is a method of using RO concentrated water in which a RO concentrated water produced by processing an ionic state silica-containing water through a reverse osmosis membrane unit 20 is used as a circulating cooling water for, for example, a cooling tower or the like, and the method includes a chemical feeding step for feeding a colloidal silica by a chemical feeding unit 40 to a water containing an ionic state silica and/or water containing a concentrated water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for using concentrated water, in which concentrated water produced by treating water containing ionic silica with a reverse osmosis membrane device is used as circulating cooling water.

  Conventionally, in the case of using tap water or industrial water containing ionic silica as boiler feed water or the like, a reverse osmosis membrane device (hereinafter referred to as “RO device”) that prevents deterioration of the device due to silica scaling has been used. Technology is known. The RO device uses permeated water and ionic silica from which ionic silica and the like are removed from water (supply water) containing dissolved salts and ionic silica and the like by a reverse osmosis membrane (hereinafter referred to as “RO membrane”). Etc. are separated into concentrated water, and scaling of silica is suppressed by using permeated water from which ionic silica or the like has been removed.

  Concentrated water enriched with ionic silica or the like is generally often discarded. However, if the concentrated water can be reused, it is desirable from the viewpoint of economy and environmental load suppression. However, for example, when concentrated water is used as circulating cooling water for a cooling tower or the like, water is evaporated in the cooling tower, and corrosive ions such as ionic silica, chloride ions, or sulfate ions are concentrated. Therefore, there is a problem that scale and corrosion are likely to occur in the piping used for the circulation path.

  As a means for removing ionic silica from circulating cooling water having a high concentration of ionic silica, for example, a silica removal device that makes the circulating cooling water come into contact with a seed such as silica gel packed in a column etc. and adsorbs the ionic silica to the seed. There has been proposed a method using an open circulation type cooling facility in which ionic silica is removed from the circulating cooling water by providing in the circulation path (see, for example, Patent Document 1 described later).

JP 2001-324296 A

However, since the open circulation type cooling facility described in Patent Document 1 removes ionic silica only in a part of the circulation path, for example, the ionic silica locally in the circulation path such as a cooling tower. Scale may occur at high concentrations. In addition, since it is not premised on the use of water with high supersaturation of ionic silica such as concentrated water as the circulating cooling water, when concentrated water is used as the circulating cooling water, silica precipitation in the desilicaizer The amount becomes excessive, and problems such as seed swelling occur. As a result, since the replacement frequency of the desilicaization device becomes high, it takes time and cost and is not realistic.
Therefore, the method of using water having high ionic silica concentration such as concentrated water as the circulating cooling water has not yet been studied.

  This invention is made | formed in view of the above, and it aims at providing the utilization method of the concentrated water which uses the concentrated water in RO apparatus as circulating cooling water.

  The present invention relates to a method for using concentrated water, in which concentrated water produced by treating water containing ionic silica with a reverse osmosis membrane device is used as circulating cooling water, the water containing ionic silica and / or The present invention relates to a method of using concentrated water used as circulating cooling water, which includes a chemical injection step of pouring colloidal silica into water containing the concentrated water.

  Moreover, in this invention, it is preferable to provide the corrosive ion removal step which removes a corrosive ion further in addition to the said chemical injection step.

  Moreover, in the said chemical injection step, it is preferable that colloidal silica is inject | poured so that the colloidal silica density | concentration in the said circulating cooling water may be 150 ppm or more.

  The corrosive ion removal step is provided on the primary side of the chemical injection step, and the corrosive ion removal step corrodes with a nanofiltration membrane that is permeable to ionic silica and suppresses the passage of corrosive ions. It is preferred that the neutral ions are removed.

  Moreover, in this invention, it is preferable that the average particle diameter of the said colloidal silica is less than 30 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the utilization method of the concentrated water which uses the concentrated water in RO apparatus as circulating cooling water can be provided.

1 is an overall schematic view of a water treatment apparatus to which a method for using concentrated water according to the present invention is applicable. 6 is a graph showing the results of Experimental Example 1. 10 is a graph showing the results of Experimental Example 2. 10 is a graph showing the results of Experimental Example 3.

Hereinafter, an embodiment of the present invention will be described. In addition, this invention is not limited to the following embodiment.
Used in the case of using tap water or industrial water containing ionic silica as boiler feed water, etc., in the RO device for removing impurities such as ionic silica from tap water or industrial water, ionic silica etc. from the RO device The concentrated RO water is discharged.
The method of using concentrated water according to the present embodiment aims to use such RO concentrated water as circulating cooling water for a cooling tower or the like.

FIG. 1 is an overall schematic diagram of a water treatment apparatus 1 to which a method for using concentrated water according to an embodiment of the present invention is applicable.
As shown in FIG. 1, the water treatment device 1 according to the present embodiment includes an RO device 20, a nanofiltration device (hereinafter referred to as “NF device”) 30, a chemical injection device 40, and a water storage tank 50. Prepare.

  As shown in FIG. 1, the water treatment apparatus 1 includes a water supply path 10 through which fluid can flow, an RO treatment water path 220, an RO drainage path 230, an NF treatment water path 320, an NF drainage path 330, A circulation path 331.

The water supply path 10 is a path through which the supply water circulates, and is a path that connects a supply source (not shown) of supply water supplied to the water treatment apparatus 1 and the RO apparatus 20. The upstream end of the water supply path 10 is connected to a supply source (not shown) of the supply water, and the downstream end is connected to the RO device 20. In addition, a circulation path 331 described later is connected to the water supply path 10.
The feed water flowing through the water supply path 10 contains ionic silica. The content of ionic silica varies depending on the intake source of the supply water. The supplied water may have been subjected to pretreatment such as softening treatment or activated carbon treatment. When polyvalent cations and contaminants in the feed water are reduced by the pretreatment, the dispersibility of colloidal silica described later increases and the scale suppression effect is improved.

  The RO device 20 concentrates dissolved components such as dissolved salts and ionic silica contained in the supply water supplied to the RO device 20, and RO permeated water from which the ionic silica has been removed by the RO membrane, ionic silica, and the like are concentrated. It is an apparatus which isolate | separates into made RO concentrated water. The upstream side of the RO device 20 is connected to the water supply path 10, and the downstream side is connected to the RO treatment water path 220 through which RO permeate flows and the RO drainage path 230 through which RO concentrated water flows. The RO device 20 includes a reverse osmosis membrane module (hereinafter referred to as “RO membrane module”) 211 and a pump 212.

  The RO membrane module 211 includes a single or a plurality of reverse osmosis membrane elements (not shown). Examples of the RO membrane forming the reverse osmosis membrane element include a cross-linked aromatic polyamide composite membrane. The RO membrane usually has micropores with a pore diameter of about 0.5 nm on the entire surface, and can filter out substances having a molecular weight of about several tens. That is, the RO membrane prevents contaminant components such as ionic silica contained in the supply water from passing through the RO membrane.

  The pump 212 pressurizes the supply water supplied from the water supply path 10 and supplies it to the RO membrane module 211. The upstream side of the pump 212 is connected to the water supply path 10, and the downstream side is connected to the RO membrane module 211. The supply water supplied from the water supply path 10 is pressurized to a pressure higher than the osmotic pressure in the RO membrane by the pump 212 and supplied to the RO membrane module 211.

  The RO treatment water channel 220 is a water channel through which RO permeated water separated by the RO device 20 flows. The upstream end of the treatment water channel 220 is connected to the RO device 20, and the downstream end is connected to a RO permeated water supply unit (not shown).

  The RO drainage channel 230 is a channel through which the RO concentrated water separated by the RO treatment device 20 flows. The upstream end of the RO drainage channel 230 is connected to the RO device 20, and the downstream end is connected to the NF device 30 described later. Further, the RO drainage channel 230 is provided with a regulating valve 231.

The NF device 30 uses the RO concentrated water separated by the RO membrane module 211, NF permeated water from which corrosive ions such as chloride ions (Cl ⁻ ) and sulfate ions (SO ₄ ²⁻ ) have been removed, and these It is an apparatus that separates into NF concentrated water containing corrosive ions. The upstream side of the NF device 30 is connected to the RO drainage channel 230, and the downstream side is connected to the NF treatment channel 320 through which NF permeated water flows and the NF drainage channel 330 through which NF concentrated water flows. The NF device 30 includes a nanofiltration module (hereinafter referred to as “NF module”) 311.

  The NF module 311 includes a single or a plurality of nanofiltration membranes (hereinafter referred to as “NF membrane”). Examples of the NF film include polyamide-based, polyether-based synthetic polymer films. The NF membrane has a function located between an RO membrane capable of filtering a substance having a molecular weight of about several tens and an ultrafiltration membrane capable of filtering a substance having a molecular weight of about 1,000 to 300,000. That is, the NF membrane can transmit ionic silica, but prevents corrosive ions such as chloride ions and sulfate ions from passing therethrough.

  The NF treatment water channel 320 is a water channel through which the NF permeated water separated by the NF device 30 flows. The upstream end of the NF treatment water channel 320 is connected to the NF device 30, and the downstream end is connected to a water storage tank 50 described later.

  The NF drainage channel 330 is a channel through which NF concentrated water separated by the NF device 30 flows. The upstream end of the NF drainage channel 330 is connected to the NF device 30, and the downstream end is connected to a discharge unit (not shown) of NF concentrated water. In addition, a circulation path 331 described later is connected to the NF drainage channel 330. Further, a drainage control valve 332 is provided in the NF drainage channel 330.

  The circulation path 331 is a path for returning a part of the NF concentrated water separated by the NF device 30 to the water supply path 10. The upstream end of the circulation path 331 is connected to the NF drainage channel 330, and the downstream end is connected to the water supply path 10. In addition, an adjustment valve 333 is provided in the circulation path 331.

  By controlling the opening of the regulating valve 231, the drainage control valve 332 and the regulating valve 333, the RO concentrated water flowing through the RO drainage channel 230 and the NF concentrated water discarded through the drainage channel 330 and the circulation channel 331 are circulated. The flow rate of the NF concentrated water is adjusted, and the pressure in the RO module 211 and the NF module 311 is adjusted.

The chemical injection device 40 is a device that injects colloidal silica into the NF permeated water separated by the NF device 30.
Colloidal silica is a dispersion containing silica (SiO ₂ ) particles in a dispersed state in water. In this embodiment, ionic silica that is supersaturated in concentrated water is adsorbed by a polymerization reaction, and the ionic state of concentrated water is obtained. It has a function of suppressing the supersaturated state of silica. Colloidal silica has an average particle size sufficiently larger than that of ionic silica and is susceptible to shearing force in running water, making it difficult to cause a scale.

The average particle size of the colloidal silica is preferably less than 30 nm, more preferably less than 15 nm, and even more preferably 4 to 6 nm because the adsorption efficiency of ionic silica increases. The reason why the adsorption efficiency of the ionic silica increases as the particle size of the colloidal silica is reduced may be that the adsorption amount of the ionic silica increases due to the increase in the specific surface area. In addition, "average particle diameter" here means a numerical value measured by the BET method or NaOH titration method in principle. However, for numerical values with an average particle size of 10 nm or less, it is preferable to refer to the measured values by the Sears method from the viewpoint of measurement accuracy.
Moreover, the content of colloidal silica in the aqueous dispersion is not particularly limited, but those having a silica content of about 5 to 50% by weight are preferably used.

  The colloidal silica is not particularly limited, and commercially available products can be used. For example, “Snowtex ST-XS” having an average particle size of 4 to 6 nm (manufactured by Nissan Chemical Industries, Ltd., measuring the average particle size by the Sears method), “Cataloid SI-550” having an average particle size of 4 to 6 nm (JGC Catalyst) “Snowtex ST-30” (manufactured by Kasei Co., Ltd., measured by NaOH method), “Snowtex ST-30” (manufactured by Nissan Chemical Industries, Ltd., measured by BET method), average particle size “Cataloid SI-30” of 10 to 14 nm (manufactured by JGC Catalysts & Chemicals Co., Ltd., average particle diameter measured by NaOH method), “Quatron PL-1” of 15 nm average primary particle diameter (manufactured by Fuso Chemical Industries, BET method) Can be used. In addition, that the average particle diameter of colloidal silica has a range means that a measured value is in the said range.

  Moreover, as a chemical | medical agent poured with the chemical injection apparatus 40, things other than colloidal silica may be contained. For example, a scale inhibitor for inhibiting scale by a hardness component, a fungicide for inhibiting fungal growth or slime production, and the like may be included. These drugs may be administered simultaneously with colloidal silica or individually.

  The water storage tank 50 stores the NF permeated water separated by the NF processing device 30. The upstream side of the water storage tank 50 is connected to the NF treatment water channel 320, and the downstream side is connected to a circulating cooling water supply unit (not shown) such as a cooling tower.

  Next, the operation of the water treatment apparatus 1 will be described with reference to FIG. When the water treatment apparatus 1 starts operation, the supply water is supplied to the RO apparatus 20 through the water supply path 10. The supply water supplied to the RO device 20 is pressurized to the RO membrane osmotic pressure or higher by the pump 212 and reaches the RO membrane module 211. The supply water that has reached the RO membrane module 211 is separated into RO permeated water from which contaminant components such as ionic silica are removed and RO concentrated water in which ionic silica is concentrated. . The RO permeated water is supplied through the RO treatment passage 220 as boiler feed water, cooling tower circulating cooling water, or the like. The RO concentrated water is supplied to the NF device 30 through the RO drainage channel 230. Since the RO concentrated water supplied to the NF device 30 is in a state of being pressurized by the pump 212, it reaches the NF membrane module 311 without requiring a new pump or the like, and permeates the NF membrane. Thus, the RO concentrated water is separated into NF permeated water from which corrosive ions such as chloride ions and sulfate ions have been removed, and NF concentrated water containing these corrosive ions. Colloidal silica is added to the NF permeated water by the chemical injection device 40 and stored in the water storage tank 50.

A part of the NF concentrated water is discharged out of the system through the NF drainage channel 330 due to the pressure applied to the supply water, and a part thereof is returned to the water supply channel 10 through the circulation channel 331. The flow rate of the supply water that circulates through the RO device 20 is increased by the returned NF concentrated water, and scaling and fouling are suppressed.
The flow rates of the RO concentrated water flowing through the RO drainage channel 230, the NF concentrated water discarded through the drainage channel 330, and the NF concentrated water flowing through the circulation channel 331 are the opening amounts of the regulating valve 231, the drainage control valve 332, and the regulating valve 333. It is adjusted by controlling. Similarly, the pressure in the RO module 211 and the pressure in the NF module 311 are adjusted by controlling the opening degree of the regulating valve 231, the drainage control valve 332 and the regulating valve 333.

The ratio of the RO permeate to the supply water supplied to the water treatment device 1 by the operation of the water treatment device 1 is referred to as a recovery rate. In the present embodiment, the recovery rate is expressed as a ratio (%) of the amount of RO permeated water (F ₂ ) to the amount of supplied water (F ₁ ) (ie, F ₂ / F ₁ × 100). The recovery rate can be adjusted by the opening degree of the drainage control valve 332. That is, when the opening degree of the drainage control valve 332 is large, the flow rate of concentrated water is increased, so that the recovery rate is lowered. When the opening degree of the drainage control valve 332 is small, the flow rate of the concentrated water is reduced, so that the recovery rate is high.

  Increasing the recovery rate can increase the use efficiency of the feed water, but at the same time the concentration of ionic silica in the concentrated water can be increased, resulting in a supersaturated state. When the concentrated water becomes supersaturated, scaling and fouling of the RO membrane surface occurs, and the RO permeate amount decreases. Therefore, it is required to suppress the supersaturated state of the concentrated water while maintaining a high recovery rate.

The ratio of the amount of RO concentrated water (F ₃ ) to the amount of RO permeated water (F ₂ ) is called the circulation ratio. Further, when the NF device is provided in addition to the RO device as in the present embodiment, the circulation ratio is calculated as a ratio of the NF concentrated water amount to the total water amount of the RO permeated water amount and the NF permeated water amount.
Further, the ratio (F ₁ / F ₃ ) of the amount (F ₁ ) of the supplied water supplied to the water treatment device 1 to the amount (F ₃ ) of the RO concentrated water discharged to the outside of the RO device 20 is predeterminedly concentrated. It is called magnification.

Next, the utilization method of the concentrated water used as the circulating cooling water of this embodiment applied to the said water treatment apparatus 1 is demonstrated.
The method of using concentrated water in the present embodiment includes a chemical injection step of injecting colloidal silica into water containing ionic silica and / or water containing concentrated water.

In the chemical injection step, colloidal silica is injected into water containing ionic silica and / or concentrated water by the chemical injection device 40. In the present embodiment, the chemical injection step is provided at the subsequent stage of the NF device 30.
The amount of colloidal silica used in the chemical injection step is not particularly limited. However, it is preferable that the colloidal silica is added so that the concentration of colloidal silica in the circulating cooling water is 150 ppm or more. In addition, as long as the dosage is increased within a range where the dispersibility of the colloidal silica is ensured, the reaction rate between the colloidal silica and the ionic silica increases as the dosage increases, resulting in a more reliable scale suppression effect. However, it is preferable to suppress it to less than 3000 ppm from the viewpoint of cost.
Even when the dosage is set to be less than 150 ppm, the polymerization reaction of ionic silica and colloidal silica can proceed when the concentration of ionic silica in the concentrated water used as circulating cooling water is sufficiently high. A certain scale suppression effect can be obtained.

  Moreover, the utilization method of the concentrated water used as the circulating cooling water in the present embodiment further includes a corrosive ion removing step for removing corrosive ions.

In the corrosive ion removal step, corrosive ions such as chloride ions and sulfate ions contained in the RO concentrated water are preferably removed by the NF device 30.
Since the RO apparatus 20 removes not only ionic silica but also corrosive ions such as chloride ions and sulfate ions, these corrosive ions are concentrated in the RO concentrated water. Considering the use of RO concentrated water as circulating cooling water, it is preferable to remove these corrosive ions as much as possible in order to prevent corrosion of piping and the like. Therefore, by removing these corrosive ions by the NF device 30, the RO concentrated water can be preferably used as the circulating cooling water.
The removal rate of corrosive ions by the NF apparatus is, for example, a chloride ion removal rate of 80% and a sulfate ion removal rate of about 95%. Moreover, the ionic silica contained in RO concentrated water can permeate | transmit NF membrane. The “removal rate” indicates the concentration of each component in the permeated water with respect to the concentration of each component in the concentrated water.

Here, Table 1 shows the component concentration and amount of water in each water treatment stage in the method of using RO concentrated water when no NF device is provided, and Table 2 shows the NF device 30 according to the present embodiment. In the method of using RO concentrated water in the case of the water, the component concentration in water and the amount of water in each water treatment stage are shown.
Both of the methods for using concentrated water according to Table 1 and Table 2 contain ionic silica at a concentration of 30 mg / L, chloride ions at 15 mg / L, and sulfate ions at a concentration of 15 mg / L, respectively. The RO device recovery rate is 75%, the RO device removal rate is 99.0% for ionic silica removal rate, 99.0% for chloride ion removal rate, and 99.5% for sulfate ion removal rate. In addition, the circulation ratio is 5.0, and the concentration of each component in the circulating cooling water is a numerical value assuming that the concentration is 4 times in the circulating cooling water.
Moreover, the removal rate of the NF apparatus in the utilization method of the concentrated water which concerns on Table 2 is 0% for ionic silica removal rate, 80.0% for chloride ion removal rate, and 95.0% for sulfate ion removal rate.

“Supply water” in Tables 1 and 2 refers to water supplied to the water treatment device, that is, raw water, and “circulation water” refers to a part of the concentrated water of the RO device or NF device being returned through the circulation path. Shown water. “RO supply water” refers to water supplied to the RO device, and is water in which the supply water and circulating water are mixed.
The method of using concentrated water without an NF device in Table 1 uses wastewater that is part of RO concentrated water as circulating cooling water. However, as a result of wastewater being concentrated four times in circulating cooling water, The product ion concentration was 233.01 mg / L and the sulfate ion concentration was 236.45 mg / L, both exceeding the 200 mg / L standard of the Japan Refrigeration and Air Conditioning Industry Association (JRA).
On the other hand, the method of using concentrated water according to the present embodiment provided with the NF device 30 in Table 2 uses NF permeated water obtained by removing corrosive ions from the RO concentrated water by the NF device 30 as circulating cooling water. Is. As a result of NF permeating water being concentrated four times in circulating cooling water, the chloride ion concentration was 178.51 mg / L and the sulfate ion concentration was 107.29 mg / L, both below the JRA standard of 200 mg / L. ing. The ionic silica concentration is 466.02 mg / L, which exceeds 150 mg / L, which is the solubility of ionic silica at pH 8 and 30 ° C., but the supersaturated state is suppressed by the chemical injection of colloidal silica by the chemical injection step. Therefore, it is possible to suppress scale deposition and the like.

  The location where the corrosive ion removing step is provided is not particularly limited, but it is preferably provided on the primary side of the chemical injection step.

  In the method of using concentrated water used as the circulating cooling water in the present embodiment, pretreatment such as softening treatment or activated carbon treatment may be performed on the supply water supplied to the water treatment apparatus 1. By pretreatment such as softening treatment or activated carbon treatment, impurities in the concentrated water used as supply water or circulating cooling water to the RO device or multivalent positive ions such as calcium ions, magnesium ions, iron ions, manganese ions, aluminum ions, etc. Since the dispersibility of colloidal silica increases by reducing ions, a higher scale suppression effect can be obtained.

As described above, the RO concentrated water treated by the method of using the concentrated water according to the present embodiment is preferably used as the circulating cooling water, and particularly preferably used as the circulating cooling water for the cooling tower.
The cooling tower is a device for cooling a load device such as a heat exchanger, and the circulating cooling water used in the cooling tower is cooled by evaporation of the circulating cooling water in the cooling tower and supplied to the load device through a supply line. The circulating cooling water heated by cooling the load device is recovered to the cooling tower through the recovery line. That is, the circulating cooling water circulates between the cooling tower and the load device.

  Since the circulating cooling water used in the cooling tower has a long residence time, a sufficient reaction time between the colloidal silica and the ionic silica can be secured. Moreover, since water is evaporated and concentrated in the circulating cooling water in the circulating cooling water, the concentrations of ionic silica and colloidal silica in the circulating cooling water increase, and the pH increases. Even under such conditions, the reactivity between colloidal silica and ionic silica is improved as the concentration of ionic silica increases, and the reactivity between colloidal silica and ionic silica is improved under high pH conditions. Since the dispersion stability of colloidal silica is improved, a preferable scale suppression effect is obtained.

  According to the method of using concentrated water used as the circulating cooling water of the present embodiment described above, for example, the following effects are exhibited.

The method for using concentrated water according to the present embodiment includes a chemical injection step of injecting colloidal silica into water containing ionic silica and / or water containing concentrated water using the chemical injection device 40.
Thereby, the ionic silica contained in the concentrated water is polymerized and adsorbed with the colloidal silica. Ionic silica adsorbed on colloidal silica is unlikely to cause scaling. Therefore, when the concentrated water into which such colloidal silica is poured is used as the circulating cooling water, the concentration of ionic silica in the concentrated water can be reduced and scaling is suppressed, so that the concentrated water can be used as the circulating cooling water.
In addition, since the rate of polymerization reaction between colloidal silica and ionic silica varies depending on the concentration of these substances, a sufficient scale-inhibiting effect can be obtained depending on the use of concentrated water into which such colloidal silica is poured. There may not be. However, if it is a use as circulating cooling water, since the reaction time of colloidal silica and ionic silica can be ensured, the sufficient scale suppression effect is acquired.

In the chemical injection step in the method of using concentrated water of the present embodiment, chemical injection is performed so that the colloidal silica concentration in the circulating cooling water is 150 ppm or more.
Thereby, since the preferable reaction rate of colloidal silica and ionic silica in concentrated water is obtained, when a concentrated water is utilized as circulating cooling water, a more reliable scale suppression effect is obtained.

The particle size of colloidal silica to be injected in the chemical injection step in the method of using concentrated water of the present embodiment is less than 30 nm.
Thereby, since the adsorption efficiency of the ionic silica by colloidal silica increases, a more preferable scale suppression effect is obtained.

The method for using concentrated water of the present embodiment further includes a corrosive ion removing step for removing corrosive ions.
Since corrosive ions such as chloride ions and sulfate ions do not permeate through the RO membrane, the corrosive ion concentration in RO concentrated water may be very high. Therefore, when RO concentrated water is used as circulating cooling water without performing any treatment on these corrosive ions, there is a risk of corrosion of piping or the like used in the circulation path. However, since corrosive ions are removed by the corrosive ion removal step in the present embodiment, corrosion of the circulation path and the like when RO concentrated water is used as the circulating cooling water can be prevented.

In the method of using concentrated water of the present embodiment, the corrosive ion removal step is provided on the primary side of the chemical injection step, and in the corrosive ion removal step, the ionic silica can be transmitted and the permeation of corrosive ions is suppressed. Corrosive ions are removed by the NF film.
In the corrosive ion removal step, a sufficient corrosive ion removal effect can be obtained by removing the corrosive ions with the NF film. Since ionic silica can permeate through the NF membrane, ionic silica is not captured by the NF membrane and the NF membrane is not clogged even if concentrated water is permeated through the NF membrane. Further, when the particle size of colloidal silica to be injected in the chemical injection step is larger than the pore size of the NF membrane, if the corrosive ion removal step is provided on the secondary side of the chemical injection step, the colloidal silica cannot permeate the NF membrane. Concentrated water to which colloidal silica is added cannot be obtained. However, in this embodiment, since the corrosive ion removal step is provided on the primary side of the chemical injection step, such a problem can be avoided.

  As mentioned above, although preferable embodiment to which the utilization method of the concentrated water used as circulating cooling water of this invention was applied was described, this invention is not restrict | limited to the above-mentioned embodiment, It can change suitably.

In the water treatment device 1 in FIG. 1, the chemical injection device 40 performs chemical injection on the NF treated water flowing through the NF treated water channel 320, but is not limited thereto, and water containing ionic silica is used. Or you may perform a chemical injection to the water containing concentrated water, or both of these.
That is, although the water treatment apparatus 1 in FIG. 1 is configured to include the NF apparatus 30, the present invention is not limited to this, and the NF apparatus may not be provided. In such a case, chemical injection may be performed on the supply water that circulates in the water supply path 10, or a storage tank for supply water to be supplied to the RO device 20 through the water supply path 10 is provided, and colloidal silica is provided in the storage tank. You may do the medicine. That is, what is necessary is just to be poured so that the concentrated water finally used as circulating cooling water contains colloidal silica.
Alternatively, the drug injection device 40 may be provided in the circulation path 331 or the drug injection device 40 may be provided in the RO drainage channel 230 to perform drug injection to the concentrated water. In this case, the injected colloidal silica is mixed into the supply water supplied from the water supply path 10 to the RO device 20 through the circulation path 331, and finally added to the circulating cooling water.
In addition, the colloidal silica may be directly poured into the circulating cooling water flowing through the cooling tower or the like.

  When supplying concentrated water from the water treatment device 1 as circulating cooling water, it is blended with clean water, other treated water, other waste water, etc. within a range that does not impede the effects of the invention, and is supplied as circulating cooling water. There may be. In this case, the colloidal silica may be injected into the water to be blended.

  Moreover, in the water treatment apparatus 1 in FIG. 1, the circulation path 331 is provided, but is not limited thereto, and the water treatment apparatus may be configured without the circulation path 331. That is, the NF concentrated water may be drained without being returned to the water supply path 10.

[Experimental example]
Next, an experimental example for verifying the effect of the method of using concentrated water used as the circulating cooling water of the present invention will be described. This experiment verifies the effect of suppressing the supersaturated state of ionic silica when colloidal silica is added to ionic silica-containing water under predetermined conditions. Note that the present invention is not limited to the following experimental examples.

<Experimental example 1>
Sodium metasilicate nonahydrate 532.9 mg and sodium bicarbonate 420 mg as a buffer component are added to 250 mL of ion-exchanged water and completely dissolved, and an ionic silica concentration of 450 mg SiO ₂ / L aqueous solution (ionic silica Of a supersaturated aqueous solution). Then, 60 mL of this aqueous solution was weighed into a polypropylene container and stirred with a stirrer, and 0.35 mL of 10% hydrochloric acid was added so that the final pH was about 8.3. After completion of the addition of 10% hydrochloric acid, colloidal silica (20 wt% aqueous solution: “Snowtex ST-XS”, manufactured by Nissan Chemical Industries, Ltd.) having an average particle size (Sears method) of 4 to 6 nm was 167 mg SiO ₂ / L, 333 mg SiO ₂ / L, 1,667 mg SiO ₂ / L, 3,333 mg SiO ₂ / L For aqueous solutions immediately added and not added, the concentration of ionic silica in the aqueous solution was measured according to JIS K 0101 (1998) “Industrial test. It was measured according to the molybdenum yellow spectrophotometry specified in “Method”. In addition, it measured by maintaining the temperature of aqueous solution at 25 degreeC. The results are shown in FIG. In FIG. 2, the vertical axis of the graph represents the ionic silica concentration (mgSiO ₂ / L), and the horizontal axis represents the reaction time (minutes). The reaction time (minutes) was set to 0 when the addition of 10% hydrochloric acid was completed with respect to the prepared aqueous solution.

<Experimental example 2>
Sodium metasilicate nonahydrate 592.1 mg and sodium hydrogen carbonate 840.1 mg as a buffer component are added to 500 mL of ion-exchanged water and completely dissolved, and an ionic silica concentration of 250 mg SiO ₂ / L aqueous solution (ion A supersaturated aqueous solution of glassy silica) was prepared. Then, 60 mL of this aqueous solution was weighed into a polypropylene container and stirred with a stirrer, and 0.20 mL of 10% hydrochloric acid was added so that the final pH was about 8.3. After the completion of the addition of 10% hydrochloric acid, an aqueous solution in which colloidal silica similar to Experimental Example 1 was added immediately at 333 mg / L, 1,667 mg / L, 3,333 mg / L in terms of SiO ₂ , and an aqueous solution not added The ionic silica concentration in the aqueous solution was measured under the same conditions as in Experimental Example 1. The results are shown in FIG. In FIG. 3, the vertical axis of the graph represents the ionic silica concentration (mgSiO2 / L), and the horizontal axis represents the reaction time (minutes). The reaction time (minutes) was set to 0 when the addition of 10% hydrochloric acid was completed with respect to the prepared aqueous solution.

<Experimental example 3>
1894.7 mg of sodium metasilicate nonahydrate and 1680.2 mg of sodium hydrogen carbonate as a buffer component are added to 1000 mL of ion-exchanged water and completely dissolved, and an aqueous solution of ionic silica concentration of 400 mg SiO ₂ / L (ion A supersaturated aqueous solution of glassy silica) was prepared. Then, 100 mL of this aqueous solution was weighed into a polypropylene container and stirred with a stirrer, and 0.47 mL of 10% hydrochloric acid was added so that the final pH was about 8.3. After completion of the addition of 10% hydrochloric acid, colloidal silica having an average particle size of 4 to 6 nm, 10 to 15 nm, 40 to 50 nm, and 70 to 100 nm (20 wt% aqueous solution: “ST-XS”, “ST-30”, “ ST-20L "," ST-ZL "(manufactured by Nissan Chemical Industries, Ltd.) were each added with 500 mg SiO ₂ / L immediately, and ionic silica in the aqueous solution under the same conditions as in Experimental Example 1 Concentration was measured. The results are shown in FIG.

From the results of Experimental Example 1 shown in FIG. 2, the amount of colloidal silica added to the supersaturated aqueous solution of ionic silica is 167 mgSiO ₂ / L, 333 mgSiO ₂ / L, 1,667 mgSiO ₂ / L, 3,333 mgSiO ₂ / L. It has been found that the effect of reducing the ionic silica concentration increases as the value increases. From this result, it was confirmed that the effect of suppressing the supersaturated state of the ionic silica can be obtained by increasing the amount of colloidal silica added to the concentrated water of the ionic silica to 150 mgSiO ₂ / L or more.

From the results of Experimental Example 2 shown in FIG. 3, the amount of colloidal silica added to the supersaturated aqueous solution of ionic silica in a relatively low supersaturated state (250 mg SiO ₂ / L) with the ionic silica concentration lower than that of Experimental Example 1 Even when the amount is changed, as the added amount is increased to 333 mgSiO ₂ / L, 1,667 mgSiO ₂ / L, 3,333 mgSiO ₂ / L, the effect of reducing the concentration of ionic silica becomes higher. I understood. From this result, even when colloidal silica is added to a supersaturated aqueous solution of ionic silica in a relatively low supersaturated state, the effect of suppressing the supersaturated state of ionic silica is increased by increasing the amount of colloidal silica added. It was confirmed that it was obtained.

  From the results of Experimental Example 3 shown in FIG. 4, when the average particle size of colloidal silica added to the supersaturated aqueous solution of ionic silica is changed, the average particle size is 70 to 100 nm, 40 to 50 nm, 10 to 15 nm, 4 It turned out that the reduction effect of ionic silica concentration becomes high as it is reduced to ˜6 nm. From this result, when the amount of colloidal silica added to the supersaturated water of ionic silica is constant, it is confirmed that the smaller the average particle size of colloidal silica, the higher the effect of suppressing the supersaturated state of ionic silica. It was.

20 Reverse osmosis membrane device (RO device)
30 Nanofiltration membrane device (NF device)
40 Chemical injection device

Claims (5)

Concentrated water utilization method using concentrated water produced by treating water containing ionic silica with a reverse osmosis membrane device as circulating cooling water,
A method of using concentrated water used as circulating cooling water, comprising a chemical injection step of pouring colloidal silica into water containing the ionic silica and / or water containing the concentrated water.   The method for using concentrated water according to claim 1, further comprising a corrosive ion removing step for removing corrosive ions in addition to the chemical injection step.   The method of using concentrated water according to claim 1 or 2, wherein in the chemical injection step, colloidal silica is injected in a chemical manner so that the colloidal silica concentration in the circulating cooling water is 150 ppm or more. The corrosive ion removal step is provided on the primary side of the chemical injection step,
The method of using concentrated water according to claim 2 or 3, wherein, in the corrosive ion removal step, corrosive ions are removed by a nanofiltration membrane that is permeable to ionic silica and suppresses permeation of corrosive ions.   The usage method of the concentrated water in any one of Claims 1-4 whose average particle diameter of the said colloidal silica is less than 30 nm.

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