JP2013212457A - Scale preventing apparatus, and geothermal power generation system using the apparatus, and scale preventing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scale preventing apparatus capable of preventing silica scale and calcium scale by a low cost method with respect to an inflow water containing at least a silica component and a calcium component, to provide a power generation system employing the same, and to provide a scale preventing method.SOLUTION: A scale preventing apparatus includes: an insoluble chelate member 1a for catching a calcium component of inflow water; a container 1 for containing the insoluble chelate member; an alkaline material addition device for adding an alkaline material to the inflow water obtained after being contacted with the insoluble chelate member to thereby raise the pH of the inflow water more than 7; an acidic substance addition device for adding an acidic substance to the inflow water before being contacted with the insoluble chelate member and for adjusting the pH of the inflow water to less than 7; and a control device 11 for alternately switching between the operation of the alkaline material addition device and the operation of the acidic substance addition device.

Description

  The present invention relates to a scale suppression device, a geothermal power generation system using the device, and a scale suppression method.

  The geothermal power generation system generates power using steam or hot water ejected from the production well, and then returns the hot water whose temperature has decreased to the reduction well. High-temperature hot water ejected from the production well contains more calcium and dissolved silica than well water and river water, and thus easily deposits such as calcium carbonate and amorphous silica. Particularly in the above-ground part and the reduction well, it is a problem to suppress the silica scale generated by the temperature drop of the hot water in the above-ground part.

  In general, a sulfuric acid injection method is used as a silica scale suppression method. In the sulfuric acid injection method, the polymerization rate of silica is suppressed by lowering the pH of hot water, and the amount of scale deposition is reduced. However, since the sulfuric acid injection method only decreases the polymerization rate of silica, it is expected that silica will precipitate after a sufficient amount of time has passed in the reduction well. Moreover, since sulfate ion concentration rises, possibility that scales, such as anhydrite, will precipitate increases. There is also a problem that pipes and the like are corroded by acid.

  One method for solving these problems is to make hot water alkaline (for example, see Non-Patent Document 1). That is, the solubility of amorphous silica increases as it becomes alkaline, and increases rapidly, particularly at pH 8 or higher. Therefore, silica scale hardly occurs in a high pH solution. Furthermore, unlike the above-described method for suppressing the rate of silica polymerization, this effect continues even in the reduction well because the amount of precipitated silica does not increase over time. Furthermore, a method of suppressing precipitation of calcium carbonate, anhydrite, and magnesium silicate in the production well by using a chelating agent that captures calcium and magnesium in the production well is disclosed.

  Patent Document 1 describes that a cation exchange resin and an anion exchange resin are arranged in series along a direction in which regenerated water flows, and the regenerated water is supplied to the ion exchange resin to regenerate the ion exchange resin. Yes.

Daisuke Fukuda, Geothermal Technology, Vol. 34, Nos. 1 & 2 (Ser. No. 74) 51-57, 2009

JP 2007-260633 A

  In the method disclosed in Non-Patent Document 1, a chelating agent is injected into the production well, and an alkaline agent is injected in the above-ground part. However, when a sufficient amount of chelating agent captures calcium ions, it is possible to prevent the formation of calcium silicate hydrate (hereinafter abbreviated as CSH), but a large amount of chelating agent can be injected. Necessary. In general, a chelating agent is an expensive drug, so there is a problem that it is not economical.

  As disclosed in Patent Document 1, as a method of capturing metal ions without using a chelating agent, a method of capturing metal ions using an ion exchange resin is known. However, since the ion exchange resin preferentially captures monovalent ions (such as sodium ions), there is a problem that it is difficult to capture divalent ions (such as calcium ions). For this reason, there is a problem that it is not suitable for suppressing the production of scales containing divalent ions.

  The present invention provides a scale suppression device capable of suppressing silica-based scale and calcium-based scale by an inexpensive method against inflow water containing at least a silica component and a calcium component, a power generation system using the scale, and a scale suppression method. It is an object.

  In order to solve the above-described problem, an embodiment of the present invention provides an insoluble chelate member that captures polyvalent metal ions of the inflow water in a scale suppression device that suppresses scale generation of the inflow water containing at least a silica component and a calcium component. A container containing the insoluble chelate member, an alkaline substance addition device for adding an alkaline substance to the inflow water after contacting the insoluble chelate member to make the pH of the inflow water higher than 7, and the insoluble chelate An acidic substance adding device that adds an acidic substance to the influent water before contacting the member to lower the pH of the influent water to less than 7, and an operation of the alkaline substance adding device and an operation of the acidic substance adding device alternately The control apparatus which switches to is provided.

  FIG. 14 shows the relationship between the precipitate and the dissolved matter when the influent water is made alkaline (first step) and made acidic (second step). When the influent water is made alkaline (first step), a compound (for example, CSH) that reacts with the polyvalent metal ions and precipitates is precipitated, and amorphous silica is dissolved. When the influent water is acidified (second step), amorphous silica is precipitated, and a compound (for example, CSH) that precipitates by reacting with the polyvalent metal ions is dissolved.

  When operating the alkaline substance addition device, the polyvalent metal ions in the influent water are removed by the insoluble chelate member upstream from the place where the alkaline substance is added to the influent water, and react with the polyvalent metal ions to precipitate. The production | generation of the compound to suppress can be suppressed. However, if the influent water is passed through the insoluble chelate member beyond the capture capacity of the insoluble chelate member, the polyvalent metal ions cannot be sufficiently removed. Then, the polyvalent metal ions not captured and the silica component react to gradually generate scale. In particular, calcium ions react with the silica component to produce CSH. When the alkaline substance addition apparatus is operated, the amorphous silica produced when the acidic substance addition apparatus is operated can be dissolved. Examples of polyvalent metal ions include calcium ions, iron ions, and aluminum ions. As the insoluble chelate member, a resin having a chelating ability, a fiber having a chelating ability, or a material in which a molecule having a chelating ability is bound to an insoluble carrier can be used. For example, Kirest Fiber (registered trademark) manufactured by Kirest Co., Ltd. can be used as the fiber having chelating ability.

  On the other hand, when the acidic substance addition apparatus is operated, the silica component in the inflowing water gradually precipitates as amorphous silica. It should be noted that the generation rate of amorphous silica can be reduced under acidic conditions as compared with neutral conditions. When the acidic substance addition apparatus is operated, the compound that has reacted with the polyvalent metal ions and precipitated is dissolved by the acid. The insoluble chelate member that has captured the polyvalent metal ion releases the captured polyvalent metal ion. Thereby, the insoluble chelate member recovers the polyvalent metal ion capturing ability. By using an insoluble chelate member, it is possible to operate more economically than the method of adding a chelating agent to the influent water, and adding an acidic substance upstream of the insoluble chelate member, and downstream of the insoluble chelate member By alternately adding the alkaline substance to the amorphous silica, it is possible to alternately dissolve the amorphous silica and the compound (for example, CSH) that reacts with the polyvalent metal ions and precipitates.

The control device may alternately switch the operation of the alkaline substance addition device and the operation of the acidic substance addition device at a preset interval.
According to such a configuration, the switching operation can be automatically performed at intervals set in advance by the timer function of the control device.

  The scale suppression device further includes a scale detection device that detects the degree of scale deposition downstream of the container, the control device includes a storage unit that stores an output signal of the scale detection device, and the scale detection device includes: When calculating based on the signal to be output and the value of the calculated result exceeds the upper threshold, the operation is switched from the alkaline substance addition device to the acidic substance addition device, and the calculated result is less than the lower threshold, A calculation unit that switches operation from the acidic substance addition device to the alkaline substance addition device, and the control device may operate the alkaline substance addition device before the acidic substance addition device.

According to said structure, according to the output value of a scale detection apparatus, it becomes possible to determine automatically the addition time of an alkaline substance, and the addition time of an acidic substance.
FIG. 12 shows the change over time in the output value of the scale detection apparatus when the alkaline substance addition apparatus is operated prior to the acidic substance addition apparatus. In FIG. 12, during operation of the alkaline substance addition device (first step), the silica component in the inflowing water reacts with the polyvalent metal ions to gradually produce a solid compound. As a result, the output value of the scale detector gradually increases. At the same time, the inflowing water is made alkaline so that amorphous silica is dissolved.

  The alkaline substance addition apparatus is stopped when the output value of the scale detection apparatus corresponding to the amount of the solid compound exceeds the upper threshold. Then, the acidic substance adding device is operated (second step). By making the influent water acidic, the solid compound that has reacted and precipitated with the polyvalent metal ions is dissolved, and the output value of the scale detector decreases. At the same time, the insoluble chelate member that has captured the polyvalent metal ion releases the captured polyvalent metal ion. Thereby, the insoluble chelate member recovers the polyvalent metal ion capturing ability.

Next, triggered by the fact that the output value of the scale detection device is less than the lower limit threshold, the acidic substance addition device is stopped and the alkaline substance addition device is operated (first step).
In this manner, the control device can automatically and alternately switch the operation of the alkaline substance addition device and the acidic substance addition device, and can automatically recover the polyvalent metal ion capturing ability of the insoluble chelate member.

  The scale suppression device further includes a scale detection device that detects the degree of scale deposition downstream of the container, the control device includes a storage unit that stores an output signal of the scale detection device, and the scale detection device includes: When calculating based on the signal to be output and the value of the calculated result exceeds the upper threshold, the operation is switched from the acidic substance adding device to the alkaline substance adding device, and the calculated result is less than the lower threshold, A calculation unit that switches operation from the alkaline substance addition apparatus to the acidic substance addition apparatus, and the control device may operate the acidic substance addition apparatus prior to the alkaline substance addition apparatus.

According to said structure, according to the output value of a scale detection apparatus, it becomes possible to determine automatically the addition time of an alkaline substance, and the addition time of an acidic substance.
As another operation, FIG. 13 shows a change with time of the output value of the scale detection device when the acidic substance addition device is operated prior to the alkaline substance addition device. In FIG. 13, during operation of the acidic substance addition device (second step), the silica components in the inflowing water gradually react to produce amorphous silica. As a result, the output value of the scale detector gradually increases. At the same time, the inflowing water is made acidic, so that the solid compound that has reacted and precipitated with the polyvalent metal ions is dissolved. Further, the insoluble chelate member that has captured the polyvalent metal ion releases the captured polyvalent metal ion. Thereby, the insoluble chelate member recovers the polyvalent metal ion capturing ability.

  The acidic substance addition apparatus is stopped when the output value of the scale detection apparatus corresponding to the generation amount of amorphous silica exceeds the upper threshold. And an alkaline substance addition apparatus is operated (1st process). By making inflow water alkaline, an amorphous silica is melt | dissolved and the output value of a scale detection apparatus reduces. At the same time, the insoluble chelate member captures polyvalent metal ions in the inflow water. Thereby, an insoluble chelate member suppresses that the silica component and polyvalent metal ion in inflow water react, and a solid compound is produced | generated.

Next, the alkaline substance addition apparatus is stopped and the acidic substance addition apparatus is operated (second step), triggered by the output value of the scale detection apparatus becoming less than the lower limit threshold.
In this way, the control device can automatically and alternately switch the operation of the acidic substance addition device and the alkaline substance addition device, and can automatically recover the polyvalent metal ion capturing ability of the insoluble chelate member.

  In general, alkaline materials are more expensive than acidic materials. When the acidic substance adding device is operated prior to the alkaline substance adding device, the period for using the acidic substance that is less expensive than the alkaline substance becomes longer, so that the amount of the alkaline substance used can be suppressed and economical operation can be performed.

  Further, in the scale suppression device, the scale detection device includes a scale deposition unit, an upstream pressure gauge that measures a pressure upstream of the scale deposition unit and outputs a signal to the control device, and a scale deposition unit. It is good also as providing the downstream pressure gauge which measures the pressure of a downstream side and outputs a signal to the said control apparatus. As a modification of this configuration, instead of installing the upstream pressure gauge and the downstream pressure gauge, a differential pressure gauge that obtains the pressure difference before and after the scale depositing portion is used, and the pressure difference signal output from the differential pressure gauge is Input to the control device is also included in the scope of the present invention.

  According to such a configuration, the control device calculates the pressure difference from the output values of the pressure gauges before and after the scale depositing portion, and when the pressure difference exceeds the upper limit threshold or when the pressure difference is less than the lower limit threshold, The operation of the alkaline substance addition apparatus and the acidic substance addition apparatus is switched. Therefore, the insoluble chelate member can be regenerated by automatically switching the flow path according to the pressure difference that changes in accordance with the amount of scale attached to the scale depositing portion.

  Further, in the scale suppression device, the scale detection device includes a flow meter that measures a flow rate of the inflow water and outputs a signal to the calculation unit, and the control device includes the alkaline substance addition device or the acidic substance addition device. A value obtained by subtracting the subsequent flow rate of the flow meter from the flow rate of the flow meter at the start of operation of the apparatus may be calculated.

  According to such a configuration, the control device calculates a value obtained by subtracting the flow rate of the flow meter from the flow rate of the flow meter at the start of operation of the alkaline substance addition device or the acidic substance addition device, and When the flow rate difference exceeds the upper limit threshold value or when the flow rate difference is less than the lower limit threshold value, the operation of the alkaline substance addition device and the acidic substance addition device is switched. Accordingly, it is possible to automatically switch the flow path according to the flow rate difference that changes according to the amount of scale attached to the scale depositing portion, and to regenerate the insoluble chelate member.

Further, in the scale suppression device, the control device switches the operation state of the alkaline substance addition device from the operation state of the acidic substance addition device, and from the operation state of the acidic substance addition device to the alkaline substance addition device. It is good also as providing the period which stops addition of the said alkaline substance and the said acidic substance at the time of at least one of the time of switching to the operation state.
In the influent water which is made acidic by adding an acidic substance, the metal is ionized. When the pH of the inflowing water changes to the alkali side, the ionized metal becomes a hydroxide, thereby increasing the effect of aggregating the scale and increasing the generation rate of amorphous silica. By providing a period for stopping the addition of the alkaline substance and the acidic substance, the mixing of the influent water to which the acidic substance is added and the influent water to which the alkaline substance is added does not occur, and the second step of adding the acidic substance from the second step Generation of amorphous silica can be suppressed when the operation is switched to the first step of adding the alkaline substance. Moreover, it can suppress that the alkaline substance supplied from an alkaline substance storage tank and the acidic substance supplied from an acidic substance storage tank directly mix, and a precipitate arises or the heat of neutralization arises.

  Further, in the scale control device, an alkaline discharge pipe for passing the influent water after adding the alkaline substance, an acidic discharge pipe for passing the influent water after adding the acidic substance, and the influent water A valve for switching the flow path to the alkaline discharge pipe or the acidic discharge pipe, and the control device connects the flow path of the influent water to the alkaline discharge pipe while adding the alkaline substance, During addition of the acidic substance, the valve may be controlled so as to connect the flow path of the influent water to the acid discharge pipe.

According to such a configuration, alkaline water and acidic water can be separated and discharged.
In the scale control device, the alkaline discharge pipe may be connected to an alkaline well, and the acidic discharge pipe may be connected to an acidic well.

  According to such a configuration, the discharge water at the alkaline operation and the discharge water at the acidic operation can be discharged to different discharge destinations instead of being discharged to one discharge destination. Therefore, it is possible to prevent neutral water and acid water from being mixed and neutral, so that scale generation is suppressed and the maintenance frequency of the discharge destination can be reduced.

  The scale suppression device further includes a pH meter that measures the pH of the inflow water downstream from the place where the alkaline substance is added, and at least one of the alkaline substance addition device and the acidic substance addition device includes the pH meter. May be controlled so as to approach the target pH when the alkaline substance is added and the target pH when the acidic substance is added.

According to such a structure, compared with the case where a fixed amount is added excessively, the addition amount of an alkaline substance or an acidic substance can be suppressed, and cost can be reduced.
Further, an evaporator that evaporates a medium with geothermal water, a turbine that rotates with the medium, a generator that is connected to the turbine and generates electric power with the rotational force of the turbine, and condenses the medium that has exited the turbine Geothermal power generation comprising a condenser and a circulation pump for sending the medium exiting the condenser to the evaporator, and comprising the scale suppression device that uses the geothermal water after passing through the evaporator as inflow water It is good also as a system.

According to such a structure, since the production | generation of the amorphous silica and CSH adhering to ground piping or a reduction | restoration well can be suppressed, the maintenance frequency of ground piping or a reduction | restoration well can be reduced.
The scale suppression method of the present invention is the scale suppression method for suppressing the generation of scale of influent water containing at least a silica component and a calcium component, wherein the insoluble chelate member captures the polyvalent metal ions of the inflow water. A first step of adding an alkaline substance to the inflow water to raise the pH of the inflow water above 7, and an acidic substance to the inflow water before contacting the insoluble chelate member to adjust the pH of the inflow water to 7 And a second step of contacting with the insoluble chelate member, wherein the first step and the second step are alternately switched.

  According to such a configuration, in the first step of capturing the polyvalent metal ion from the inflow water, the scale (for example, forming a compound with the polyvalent metal ion by capturing the polyvalent metal ion in the insoluble chelate member (for example, In addition, by adding an alkaline substance to the influent water after contact with the insoluble chelate member, the solubility of amorphous silica can be increased, so that the formation of amorphous silica can also be suppressed. In the first step, when the ability of the insoluble chelate member to capture polyvalent metal ions becomes weak, CSH gradually precipitates, but amorphous silica can be dissolved.

  On the other hand, in the second step shown below, amorphous silica gradually precipitates, but CSH can be dissolved. In the second step, the polyvalent metal ion capturing ability of the insoluble chelate member can be recovered by detaching the polyvalent metal ion from the insoluble chelate member capturing the polyvalent metal ion. Furthermore, since the inflowing water becomes acidic, the silica polymerization reaction rate can be reduced, and the formation of amorphous silica can be suppressed. And, by adding an acidic substance to the influent water, the solubility of CSH can be increased, so that the generation of CSH can also be suppressed. Furthermore, by using an insoluble chelate member, the cost can be reduced compared to adding a chelating agent to the influent water.

  In the scale suppression method, the addition of the alkaline substance and the acidic substance is stopped when switching from the first process to the second process and at least one of switching from the second process to the first process. It is good also as providing the period to make.

  In the influent water to which the acidic substance is added, the metal is ionized. When the pH of the inflowing water suddenly changes to the alkali side, the effect of aggregating the scale increases due to the ionized metal becoming a hydroxide, and the silica polymerization reaction rate tends to increase. By providing a period for stopping the addition of the alkaline substance and the acidic substance, the mixing of the influent water to which the acidic substance is added and the influent water to which the alkaline substance is added does not occur, and the second step of adding the acidic substance from the second step Generation of amorphous silica can be suppressed when the operation is switched to the first step of adding the alkaline substance.

  ADVANTAGE OF THE INVENTION According to this invention, a silica type scale and a calcium type scale can be suppressed by the cheaper method of adding a chelating agent with respect to the inflow water containing a silica component and a calcium component at least.

Schematic block diagram according to the first embodiment of the present invention (when alkali is added) Schematic block diagram according to the first embodiment of the present invention (at the time of acid addition) Schematic configuration diagram according to the second embodiment of the present invention (when alkali is added) Schematic block diagram according to the second embodiment of the present invention (at the time of acid addition) Schematic configuration diagram according to the third embodiment of the present invention (when alkali is added) Schematic block diagram according to the third embodiment of the present invention (at the time of acid addition) Schematic configuration diagram according to the fourth embodiment of the present invention (when alkali is added) Schematic configuration diagram according to the fourth embodiment of the present invention (at the time of acid addition) Schematic configuration diagram according to the fifth embodiment of the present invention Schematic configuration diagram according to the sixth embodiment of the present invention. The flowchart which concerns on each Example of this invention Change with time of output value of scale detecting device according to embodiment of the present invention (first step precedes) Change with time of output value of scale detection device according to embodiment of the present invention (preceding second step) The figure which showed the relationship between the precipitate and dissolved matter when the influent water was made alkaline (first step) and made acidic (second step) Schematic configuration diagram according to the seventh embodiment of the present invention Schematic configuration diagram according to the eighth embodiment of the present invention

Hereinafter, embodiments of a scale suppression method according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following Example, In the range which does not change the summary, it can deform | transform suitably and can be implemented.
(First embodiment)
FIG. 1 is a schematic configuration diagram according to a first embodiment of the present invention. The scale suppression device of the first embodiment of the present invention is a device that suppresses the generation of scale of influent water containing at least a silica component and a calcium component, and an insoluble chelate member 1a that captures polyvalent metal ions of the inflow water. A container 1 containing the insoluble chelate member 1a, and an alkaline substance addition device 50a for adding an alkaline substance to the inflow water after contacting the insoluble chelate member 1a to make the pH of the inflow water higher than 7. , An acidic substance adding device 40a for adding an acidic substance to the influent water before contacting the insoluble chelate member to make the pH of the influent water less than 7, an operation of the alkaline substance adding apparatus 50a and the addition of the acidic substance There is provided a control device 11a that alternately switches the operation of the device 40a. Inflow water taken in from the inflow water inlet 12 flows into the container 1 through the pipe L2. As an example of the insoluble chelate member 1 a put in the container 1, Kyrest Fiber (registered trademark) manufactured by Kyrest Co., Ltd. can be used. A valve 3 is installed in the middle of the pipe L2. The pipe L3 connects the container 1 and the reduction well 13. A valve 4 is installed in the middle of the pipe L3, and a pipe L5 is connected to the pipe L3 between the container 1 and the valve 4. A pump 8 is installed at the other end of the pipe L5. The pipe L6 connects the pump 8 and the alkaline substance storage tank 6. A valve 7 is provided in the middle of the pipe L6. One end of the pipe L7 is connected to a portion of the pipe L6 between the pump 8 and the valve 7, and the other end of the pipe L7 is connected to the acidic substance storage tank 9. A valve 10 is installed in the middle of the pipe L7. Alkaline substance is stored in the alkaline substance storage tank 6. An acidic substance is stored in the acidic substance storage tank 9. The alkaline substance addition device 50a corresponds to a part constituted by the pipe L5, the pump 8, the pipe L6, the alkaline substance storage tank 6, and the valve 7. The acidic substance addition device 40a shares the pipe L5 and the pump 8 of the alkaline substance addition device 50a, and corresponds to a portion constituted by the pipe L7, the acidic substance storage tank 9, and the valve 10. One end of the pipe L1 is connected to a portion between the inlet water inlet 12 and the valve 3 of the pipe L2. The other end of the pipe L1 is connected to a portion between the container 1 and the valve 4 of the pipe L3. A valve 2 is installed in the middle of the pipe L1. One end of the pipe L4 is connected to a portion between the valve 3 and the container 1 of the pipe L2. The other end of the pipe L4 is connected to a portion between the valve 4 and the reduction well 13 of the pipe L3. A valve 5 is installed in the middle of the pipe L4. A pH meter 26 is provided downstream of the place where the pipe L3 and the pipe L4 merge. The control device 11a is connected to the valve 2, the valve 3, the valve 4, the valve 5, the valve 7, the valve 10, and the pump 8 through a control line, and controls them. The output signal of the pH meter 26 is taken into the control device 11a. Furthermore, a pH meter 26 for measuring the pH of the inflow water downstream from the place where the alkaline substance is added is provided, and at least one of the alkaline substance addition device 50a and the acidic substance addition device 40a has a value of the pH meter 26 of the alkaline substance. Control is performed so as to approach the target pH at the time of addition and the target pH at the time of addition of the acidic substance, respectively.

  Next, an outline of the main operation of each embodiment of the present invention will be described. The operation flow is shown in FIG. The scale suppression method of the scale suppression device of the present invention is a first step in which an alkaline substance is added to the influent water after the polyvalent metal ions are trapped by the insoluble chelate member 1a to make the pH of the inflow water higher than 7. S2) and a second step (S3) in which an acidic substance is added to the inflow water before contacting the insoluble chelate member 1a to bring the pH of the inflow water to less than 7 and contact the insoluble chelate member 1a. It is characterized in that the process and the second process are alternately switched (S1). Regarding this switching, as shown in FIGS. 12 and 13, there are a method of executing the first step first and a method of executing the second step first. Moreover, you may decide to provide the period which stops addition of an alkaline substance and an acidic substance at the time of switching from a 1st process to a 2nd process, and at least one at the time of switching from a 2nd process to a 1st process.

  The timing of switching between the first step and the second step is when the amount of the insoluble chelate member 1a with respect to the flow rate of the influent water and the calcium concentration exceeds the allowable range of the polyvalent metal ion capturing ability of the insoluble chelate member 1a. It is desirable to switch between the first step and the second step.

  As a simple operation, the time required for the insoluble chelate member 1a to capture the polyvalent metal ion in advance exceeds the allowable range, and the time required for the insoluble chelate member 1a to recover the polyvalent metal ion capture capability. Predicted by experiments, a time shorter than these times may be set as a time for switching from the first step to the second step and a time for switching from the second step to the first step. That is, the control device 11a may alternately switch the operation of the alkaline substance addition device and the operation of the acidic substance addition device at a preset interval.

Various scale suppression methods as described above can also be executed in the scale suppression devices of the embodiments described later.
Next, an example of the operation in the first embodiment will be described in more detail with reference to FIGS. Thick line arrows represent the flow of water or chemicals. FIG. 1 shows the flow of liquid at the time of alkali addition, and FIG. 2 shows the flow of liquid at the time of acid addition. First, the valve 3, the valve 4 and the valve 7 are opened, the valve 2, the valve 5 and the valve 10 are closed, and the pump 8 is operated, while the inflowing water is passed from the inflowing water inlet 12 through the pipe L2, the container 1, and the pipe L3. The water is passed through the reduction well 13. At this time, polyvalent metal ions of the influent water are captured by the insoluble chelate member 1a, and then the pump 8 is operated to add an alkaline substance to the influent water downstream from the container 1 so that the pH of the influent water is higher than 7. (See FIG. 1. First step).

  When the ability of the insoluble chelate member 1a to capture polyvalent metal ions has decreased, the valve 2, the valve 5 and the valve 10 are opened, the valve 3, the valve 4 and the valve 7 are closed, and the pump 8 is operated while the inflowing water flows in. Water is passed from the water inlet 12 to the reduction well 13 via the pipe L1, the container 1, and the pipe L4. At this time, an acidic substance is added to the inflow water before the pump 8 is operated to come into contact with the insoluble chelate member 1 a so that the pH of the inflow water is less than 7 and is brought into contact with the insoluble chelate member 1 a. Then, polyvalent metal ions are released from the insoluble chelate member 1a, and the polyvalent metal ion capturing ability of the insoluble chelate member 1a is restored (see FIG. 2, second step).

  FIG. 14 shows the correspondence between precipitates and dissolved matters when the influent water is made alkaline (first step) and acid (second step). When the influent water is made alkaline (first step), a compound (for example, CSH) that reacts with the polyvalent metal ions and precipitates is precipitated, and amorphous silica is dissolved. When the influent water is acidified (second step), amorphous silica is precipitated, and a compound (for example, CSH) that precipitates by reacting with the polyvalent metal ions is dissolved.

Since the flow rate of the pump 8 is controlled so that the value of the pH meter 26 approaches the target pH at the time of addition of the alkaline substance and the target pH at the time of addition of the acidic substance, the alkaline substance or the The amount of the acidic substance added can be suppressed, and the cost can be reduced.
(Second embodiment)
Next, a second embodiment having another mechanism in terms of switching between the first step and the second step will be described with reference to FIGS. Thick line arrows represent the flow of water or chemicals. FIG. 3 shows the flow of liquid at the time of alkali addition, and FIG. 4 shows the flow of liquid at the time of acid addition. The main difference between the first embodiment (FIGS. 1 and 2) and the second embodiment (FIGS. 3 and 4) is that the scale detector 60 detects the degree of scale deposition downstream of the container 1. Is different from the control method of the control device.

  The scale detector 60 includes a scale depositing unit 16, an upstream pressure gauge 17 that measures a pressure upstream of the scale depositing unit 16 and outputs a signal to the control device 11 b, and a pressure downstream of the scale depositing unit 16. And a downstream pressure gauge 18 that outputs a signal to the control device 11b. The pipe L8, one end of the container 1 and the scale depositing portion 16 are connected, and the pipe L9 is connected to the other end of the container 1 and downstream of the valve 4 of the pipe L8. The pipe L10 connects the scale depositing part 16 and the reduction well 13.

  The control device 11b calculates the differential pressure based on the storage unit 25 that stores the output signal of the scale detection device 60 and the signal output by the scale detection device 60, and the value (differential pressure) of the calculated result has the upper limit threshold value. If exceeded, the operation is switched from the alkaline substance addition device to the acidic substance addition device, and if the calculated result value (differential pressure) is less than the lower limit threshold, the operation is switched from the acidic substance addition device to the alkaline substance addition device. A calculation unit 24 is provided. The differential pressure is calculated by subtracting the value of the downstream pressure gauge 18 from the value of the upstream pressure gauge 17.

  FIG. 12 shows the change over time in the output value of the scale detection apparatus when the apparatus is operated. As the first step proceeds, the output value (differential pressure) of the scale detector 60 gradually increases. When the output value (differential pressure) of the scale detection device exceeds the upper limit threshold value, the first process is switched to the second process. In the second step, the insoluble chelate member 1a is exposed to inflow water having a pH of less than 7, and polyvalent metal ions are released from the insoluble chelate member 1a. In the second step, the scale deposited on the scale depositing portion 16 is also dissolved, so the output value (differential pressure) of the scale detection device 60 decreases. When the output value (differential pressure) of the scale detection device becomes less than the lower threshold, the second process is switched to the first process. Thereafter, the switching between the first step and the second step is repeated as described above.

  Further, in each of the scale suppression devices, the alkaline substance and the acidic substance are at least one of when switching from the first process to the second process and when switching from the second process to the first process. You may control to provide the period which stops addition of this.

  As another type of scale detection device, instead of the scale detection device 60 of FIG. 3, the flow rate of the inflowing water is measured and a signal is output to the calculation unit 24, as in a scale detection device 61 of FIG. 10 described later. You may decide to provide the flowmeter 21 and the scale precipitation part 16. FIG. And the control apparatus 11b calculates the value which subtracted the flow volume of the said flow meter 21 from the flow volume of the said flow meter 21 at the time of the operation | movement start of the alkaline substance addition apparatus 50a. The calculation result at this time is the output value of the scale detection apparatus of FIG. The control device 11b performs a calculation based on the storage unit 25 that stores the output signal of the scale detection device 60 and the signal output by the scale detection device 61, and when the calculated result value exceeds the upper limit threshold, the alkaline property When the operation is switched from the substance addition apparatus 50a to the acidic substance addition apparatus 40a and the calculated value is less than the lower limit threshold, the calculation unit 24 that switches the operation from the acidic substance addition apparatus 40a to the alkaline substance addition apparatus 50a is provided. The control device 11b operates the alkaline substance addition device 50a prior to the acidic substance addition device 40a (see FIG. 12).

As another form, instead of the scale detection device 60 of FIG. 3, a flow meter 21 that measures the flow rate of influent water and outputs a signal to the calculation unit 24 as in a scale detection device 61 of FIG. 10 described later. And the scale depositing unit 16, and the control device 11 b calculates a value obtained by subtracting the subsequent flow rate of the flow meter 21 from the flow rate of the flow meter 21 at the start of operation of the acidic substance addition device 40 a. Also good. And the control apparatus 11b calculates based on the signal which the memory | storage part 25 which memorize | stores the output signal of the said scale detection apparatus 60, and the said scale detection apparatus 61 outputs, and the value of the calculated result exceeds an upper limit threshold value The operation unit that switches the operation from the acidic substance addition apparatus 40a to the alkaline substance addition apparatus 50a and switches the operation from the alkaline substance addition apparatus 50a to the acidic substance addition apparatus 40a when the calculated value is less than the lower limit threshold. 24, and the control device 11b may operate the acidic substance addition device 40a before the alkaline substance addition device 50a (see FIG. 13).
(Third embodiment)
Next, a third embodiment will be described with reference to FIGS. Thick line arrows represent the flow of water or chemicals. FIG. 5 shows the flow of the liquid when adding the alkali, and FIG. 6 shows the flow of the liquid when adding the acid. The differences between the first embodiment (FIGS. 1 and 2) and the third embodiment (FIGS. 5 and 6) are as follows.

In the first embodiment, both the acidic inflow water that has passed through the pipe L4 and the alkaline inflow water that has passed through the pipe L3 have been discharged to the reduction well 13.
On the other hand, in the third embodiment, one end of the pipe L12 is connected to a portion between the valve 3 of the pipe L2 and the container 1, and the other end of the pipe L12 is connected to the acidic reducing well 15, One end of the pipe L11 is connected to the container 1, and the other end of the pipe L11 is connected to the alkaline reducing well 14. As a result, the acidic influent water is discharged to the acidic reducing well 15 and the alkaline influent water is discharged to the alkaline reducing well 15. Other operations are the same as those in the first embodiment. The alkaline discharge pipe through which the inflow water after adding the alkaline substance is passed corresponds to the pipe L11. The acid discharge pipe through which the inflow water after the acidic substance is added corresponds to the pipe L12.

  By adopting such a configuration, it is possible to prevent neutral water and acidic water from being mixed and become neutral at the discharge destination, so that scale generation is suppressed and the maintenance frequency of the discharge destination can be reduced. It was.

As in the third embodiment, alkaline discharge is also performed in the later-described embodiment 4 (FIGS. 7 and 8), embodiment 5 (FIG. 9), embodiment 6 (FIG. 10), and embodiment 8 (FIG. 16). The pipes (L11, L13, L18, L22) are connected to the alkaline reducing well 14, and the acidic discharge pipes (L12, L14, L17, L21) are connected to the acidic reducing well 15.
(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIGS. Thick line arrows represent the flow of water or chemicals. FIG. 7 shows the flow of liquid at the time of alkali addition, and FIG. 8 shows the flow of liquid at the time of acid addition. The differences between the second embodiment (FIGS. 3 and 4) and the fourth embodiment (FIGS. 7 and 8) are as follows. In the second embodiment (FIGS. 3 and 4), the pipe L <b> 10 is connected to one reducing well 13. On the other hand, in FIGS. 7 and 8, the end of the pipe L13 is connected to the alkaline reducing well 14, and a valve 19 is installed in the middle of the pipe L13. Furthermore, one end of the pipe L14 is connected to the upstream side of the valve 19 of the pipe L13, the other end of the pipe L14 is connected to the acidic reducing well 15, and the valve 20 is installed in the middle of the pipe L14. . The control device 11d can control the valve 19 and the valve 20 in addition to the function of the control device 11b of FIGS. When alkaline material is added to the incoming water, valve 19 is opened and valve 20 is closed. On the other hand, when the acidic substance is added to the influent water, the valve 20 is opened and the valve 19 is closed. Other operations are the same as those in the second embodiment.
(Fifth embodiment)
Next, a fifth embodiment will be described with reference to FIG.

The inflow water inlet 12 is connected to the container 1 by a pipe L15.
The acidic substance addition device 40b supplies the acidic substance to the pipe L15 through the pipe L19. The acidic substance addition device 40b includes an acidic substance storage tank 9 that stores an acidic substance, a pump 8a, a pipe L7 that connects the acidic substance storage tank 9 and the pump 8a, a valve 10 that is provided in the middle of the pipe L7, A pipe L19 connecting the pump 8a and the pipe L15 and a valve 22 provided in the middle of the pipe L19 are provided.

  In the container 1, an insoluble chelate member 1a is provided. As an example of the insoluble chelate member 1a, Kyrest Fiber (registered trademark) manufactured by Kyrest Co., Ltd. can be used. The scale detection device 60 is connected to the container 1 by a pipe L16.

  The alkaline substance addition device 50b supplies an alkaline substance to the pipe L16 through the pipe L20. The alkaline substance addition device 50b includes an alkaline substance storage tank 6 that stores an alkaline substance, a pump 8b, a pipe L6 that connects the alkaline substance storage tank 6 and the pump 8b, a valve 7 provided in the middle of the pipe L6, A pipe L20 connecting the pump 8b and the pipe L16 and a valve 23 provided in the middle of the pipe L20 are provided.

  The scale detection device 60 includes a scale depositing unit 16, a pressure gauge 17 installed in piping upstream of the scale depositing unit 16, and a pressure gauge 18 installed in piping downstream of the scale depositing unit 16. . The upstream side of the scale depositing part 16 is connected to the container 1 by a pipe L16, and the downstream side of the scale depositing part 16 is connected to the alkaline reducing well 14 by a pipe L18.

A pH meter 26 for measuring the pH of the influent water downstream from the place where the alkaline substance is added is provided.
The pipe L17 branches from the pipe L18 on the downstream side of the pH meter 26 and is connected to the acidic reducing well 15. A valve 19 is installed in the middle of the pipe L18. A valve 20 is installed in the middle of the pipe L17.

  The control device 11e is connected to the valve 10, the valve 22, the valve 7, the valve 23, the valve 19, the valve 20, the pump 8a and the pump 8b through control lines, and controls them. Output signals from the pressure gauge 17, the pressure gauge 18, and the pH gauge 26 are taken into the control device 11e. Furthermore, at least one of the alkaline substance addition device 50b and the acidic substance addition device 40b is controlled such that the value of the pH meter 26 approaches the target pH when the alkaline substance is added and the target pH when the acidic substance is added. .

  Next, an outline of the main operation of each embodiment of the present invention will be described. The main operation flow is shown in FIG. The scale suppression method of the scale suppression device of the present invention is a first step in which an alkaline substance is added to the influent water after the polyvalent metal ions are trapped by the insoluble chelate member 1a to make the pH of the inflow water higher than 7. S2) and a second step (S3) in which an acidic substance is added to the inflow water before contacting the insoluble chelate member 1a to bring the pH of the inflow water to less than 7 and contact the insoluble chelate member 1a. It is characterized in that the process and the second process are alternately switched (S1). Regarding this switching, as shown in FIGS. 12 and 13, there are a method of executing the first step first and a method of executing the second step first. Moreover, you may decide to provide the period which stops addition of an alkaline substance and an acidic substance at the time of switching from a 1st process to a 2nd process, and at least one at the time of switching from a 2nd process to a 1st process.

  The timing of switching between the first step and the second step is when the capture capacity of the insoluble chelate member 1a exceeds the allowable range in consideration of the flow rate of the influent water and the amount of the insoluble chelate member 1a with respect to the calcium concentration. It is desirable to switch between the first step and the second step.

  As a simple operation, the time required for the insoluble chelate member 1a to capture the polyvalent metal ion in advance exceeds the allowable range, and the time required for the insoluble chelate member 1a to recover the polyvalent metal ion capture capability. Predicted by experiments, a time shorter than these times may be set as a time for switching from the first step to the second step and a time for switching from the second step to the first step. That is, the control device 11a may alternately switch the operation of the alkaline substance addition device 50b and the operation of the acidic substance addition device 40b at predetermined intervals.

Various scale suppression methods as described above can also be executed in the scale suppression devices of the embodiments described later.
Next, the operation of each process in the fifth embodiment will be described in more detail with reference to FIG.

  In the first step, the valve 7, the valve 23 and the valve 19 are opened, the valve 10, the valve 22 and the valve 20 are closed, and the pump 8 b is operated, and the inflow water is supplied from the inflow water inlet 12 to the pipe L 15, the container 1 and the pipe L 16. Then, water is passed through the scale detection device 60 and the piping L18 to the alkaline reduction well 14. At this time, polyvalent metal ions of the influent water are captured by the insoluble chelate member 1a, and then the pump 8b is operated to add an alkaline substance to the influent water downstream from the container 1 so that the pH of the influent water is higher than 7. ing.

  In the second step, the valve 10, the valve 22 and the valve 20 are opened, the valve 7, the valve 23 and the valve 19 are closed, and the pump 8a is operated, and the inflowing water is supplied from the inflowing water inlet 12 to the pipe L15, the container 1, and the pipe L16. Then, water is passed through the scale detection device 60 and the piping L18 to the acidic reduction well 15. At this time, an acidic substance is added to the inflow water before the pump 8a is operated to come into contact with the insoluble chelate member 1a so that the pH of the inflow water is less than 7 and is brought into contact with the insoluble chelate member 1a. If it does so, a polyvalent metal ion will be discharge | released from the insoluble chelate member 1a, and the capture | acquisition capability of the insoluble chelate member 1a of the polyvalent metal ion will be recovered.

Generation of scale can be suppressed by alternately executing the first step and the second step as described above with various variations as described above.
FIG. 14 shows the correspondence between precipitates and dissolved matters when the influent water is made alkaline (first step) and acid (second step). When the influent water is made alkaline (first step), a compound (for example, CSH) that reacts with the polyvalent metal ions and precipitates is precipitated, and amorphous silica is dissolved. When the influent water is acidified (second step), amorphous silica is precipitated, and a compound (for example, CSH) that precipitates by reacting with the polyvalent metal ions is dissolved.

Further, since the flow rate of the pump 8a and the pump 8b is controlled so that the value of the pH meter 26 approaches the target pH at the time of adding an alkaline substance and the target pH at the time of adding an acidic substance, respectively, compared with the case where a constant amount is added excessively. Thus, the amount of alkaline substance or acidic substance added can be suppressed, and the cost can be reduced.
(Sixth embodiment)
Next, a sixth embodiment will be described with reference to FIG. The sixth embodiment is different from the fifth embodiment in that the scale detection device 60 of the fifth embodiment is replaced with a scale detection device 61, and the calculation method of the control device 11f is changed accordingly. It is. Scale detector 61 includes a scale detector 16 and a flow meter 21. The scale detection device 61 includes a flow meter that measures the flow rate of influent water and outputs a signal to the calculation unit 24 of the control device 11f. The control device 11f starts the operation of the alkaline substance addition device 50b or the acidic substance addition device 40b. The value obtained by subtracting the flow rate of the subsequent flow meter from the flow rate of the current flow meter is calculated. In FIG. 12 and FIG. 13, this calculated value is handled as the output value of the scale detection device 61.

The control devices (11a, 11b, 11c, 11d, 11e, 11f) of the above embodiments are various set values such as an upper limit threshold value and a lower limit threshold value, and output values of the scale detection device as shown in FIGS. Are stored in the storage unit 25. The control devices (11a, 11b, 11c, 11d, 11e, and 11f) can be connected to an input / output device (not shown), and can change various setting values and retrieve data using the input / output device.
(Seventh embodiment)
Next, a seventh embodiment will be described with reference to FIG. The seventh embodiment is a geothermal power generation system including any one of the above-described scale suppression devices. Specifically, an evaporator 71 that evaporates a medium with geothermal water taken out from the production well 70, a turbine 72 that rotates with the medium, and a power generation that is connected to the turbine 72 and generates electric power by the rotational force of the turbine 72. Machine 73, a condenser 74 that condenses the medium exiting from the turbine 72, and a circulation pump 75 that sends the medium exiting from the condenser 74 to the evaporator 71, and has passed through the evaporator 71. The later geothermal water is used as the inflow water of the scale suppression device 100. The geothermal water produced from the scale suppression device 100 is supplied to the reduction well 13. The electric power generated by the generator 73 is input to the conditioner 77 through the power wiring 76, converted into a desired voltage / current by the conditioner 77, and output to the outside through the power output wiring 78 to the outside.
(Eighth embodiment)
Next, an eighth embodiment will be described with reference to FIG. In the eighth embodiment, any one of the scale suppression devices of the third embodiment, the fourth embodiment, the fifth embodiment, and the sixth embodiment is replaced with the scale of the seventh embodiment. The geothermal power generation system is incorporated into the suppression device 101. Alkaline drainage from the scale control device 101 is caused to flow into the alkaline reduction well 14, and acidic wastewater is allowed to flow into the acidic reduction well 15.

  By adopting such a configuration, it is possible to prevent neutral water and acidic water from being mixed and become neutral at the discharge destination, so that scale generation is suppressed and the maintenance frequency of the discharge destination can be reduced. It was.

  As mentioned above, if it carries out like each Example of this invention, it can suppress a silica type scale and a calcium type scale by the cheaper method of adding a chelating agent with respect to the inflow water which contains a silica component and a calcium component at least. .

DESCRIPTION OF SYMBOLS 1 Container 1a Insoluble chelate member 2, 3, 4, 5, 7, 10, 19, 20, 22, 23 Valve 6 Alkaline substance storage tank 8, 8a, 8b Pump 9 Acid substance storage tank 11a, 11b, 11c, 11d, 11e, 11f Control device 12 Inflow water inlet 13 Reducing well 14 Alkaline reducing well 15 Acidic reducing well 16 Scale precipitation unit 17, 18 Pressure gauge 21 Flow meter 24 Calculation unit 25 Storage units 26, 27, 28 pH meters 40a, 40b Acidic substance addition apparatus 50a, 50b Alkaline substance addition apparatus 60, 61 Scale detection apparatus 70 Production well 71 Evaporator 72 Turbine 73 Generator 74 Condenser 75 Circulation pump 76 Power wiring 77 Conditioner 78 External power output wiring 100, 101 Scale Suppressors L1, L2, L3, L4, L5, L6, L7, L8, L9, L 0, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20 piping

Claims (13)

In a scale suppression device that suppresses the generation of scale of influent water containing at least a silica component and a calcium component,
An insoluble chelate member for capturing the polyvalent metal ions of the inflow water;
A container containing the insoluble chelate member;
An alkaline substance addition device for adding an alkaline substance to the influent water after contacting the insoluble chelate member to make the pH of the influent water higher than 7.
An acidic substance adding device that adds an acidic substance to the influent before contacting the insoluble chelate member to make the pH of the influent below 7;
A scale suppression device comprising a control device that alternately switches between the operation of the alkaline substance addition device and the operation of the acidic substance addition device. The scale control device according to claim 1, wherein the control device alternately switches the operation of the alkaline substance addition device and the operation of the acidic substance addition device at a preset interval. A scale detection device that detects the degree of scale deposition downstream of the container,
The control device includes a storage unit that stores an output signal of the scale detection device;
When the calculation result is based on the signal output from the scale detection device and the calculated result value exceeds the upper threshold, the operation is switched from the alkaline substance addition device to the acidic substance addition device, and the calculated result value is the lower limit. If less than the threshold, comprising an arithmetic unit that switches the operation from the acidic substance addition device to the alkaline substance addition device,
The scale control device according to claim 1, wherein the control device operates the alkaline substance addition device before the acidic substance addition device. A scale detection device that detects the degree of scale deposition downstream of the container,
The control device includes a storage unit that stores an output signal of the scale detection device;
The calculation is performed based on the signal output from the scale detection device, and when the calculated result value exceeds the upper limit threshold, the operation is switched from the acidic substance addition device to the alkaline substance addition device, and the calculated result value is the lower limit. If less than the threshold, comprising an arithmetic unit that switches the operation from the alkaline substance addition device to the acidic substance addition device,
The scale control device according to claim 1, wherein the control device operates the acidic substance adding device before the alkaline substance adding device. The scale detector includes a scale depositing unit, an upstream pressure gauge that measures a pressure upstream of the scale depositing unit and outputs a signal to the control device, and measures a pressure downstream of the scale depositing unit, The scale suppression device according to claim 3, further comprising a downstream pressure gauge that outputs a signal to the control device. The scale detection device includes a flow meter that measures a flow rate of the influent water and outputs a signal to the calculation unit,
The scale according to claim 3 or 4, wherein the control device calculates a value obtained by subtracting a flow rate of the flow meter after that from a flow rate of the flow meter at the start of operation of the alkaline substance addition device or the acidic substance addition device. Suppression device. The control device is at least when switching from an operating state of the alkaline substance adding device to an operating state of the acidic substance adding device, and when switching from an operating state of the acidic substance adding device to an operating state of the alkaline substance adding device. The scale suppression device according to any one of claims 1 to 6, wherein a period for stopping the addition of the alkaline substance and the acidic substance is provided at one time. A discharge pipe for alkalinity through which the influent water is added after the alkaline substance is added;
An acid discharge pipe for passing the influent water after adding the acidic substance;
A valve for switching the flow path of the influent water to the alkaline discharge pipe or the acidic discharge pipe,
The controller connects the flow path of the influent water to the alkaline discharge pipe while adding the alkaline substance, and connects the flow path of the influent water to the acidic discharge pipe while adding the acidic substance. The scale suppression device according to any one of claims 1 to 7, wherein the valve is controlled so as to perform. The scale suppression device according to claim 7, wherein the alkaline discharge pipe is connected to an alkaline well, and the acidic discharge pipe is connected to an acidic well. A pH meter that measures the pH of the influent water downstream from the place where the alkaline substance is added,
The at least one of the alkaline substance addition device and the acidic substance addition device is controlled so that a value of the pH meter approaches a target pH when an alkaline substance is added and a target pH when an acidic substance is added, respectively. The scale suppression apparatus as described in any one of 1 to 9. An evaporator for evaporating the medium with geothermal water;
A turbine rotating with the medium;
A generator connected to the turbine and generating electric power by the rotational force of the turbine;
A condenser for condensing the medium exiting the turbine;
A circulation pump for sending the medium exiting the condenser to the evaporator;
The geothermal power generation system provided with the scale suppression apparatus as described in any one of Claim 1 to 10 which makes the said geothermal water after passing the said evaporator into inflow water. In a scale suppression method for suppressing scale generation of influent water containing at least a silica component and a calcium component,
A first step of adding an alkaline substance to the inflow water after the polyvalent metal ions of the inflow water are captured by an insoluble chelate member to make the pH of the inflow water higher than 7.
A second step of adding an acidic substance to the influent before contact with the insoluble chelate member to bring the pH of the inflow water to less than 7 and bringing it into contact with the insoluble chelate member;
A scale suppression method for alternately switching between the first step and the second step. A period for stopping the addition of the alkaline substance and the acidic substance is provided when switching from the first process to the second process and at least one of switching from the second process to the first process. The scale suppression method according to claim 12.

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