Scale suppression method, scale suppression device, geothermal power generation system, and fluid utilization system

Abstract

This invention provides a scale suppression method that can more accurately suppress the precipitation of silica scale. [Solution] The scale suppression method according to the present invention includes a cation concentration adjustment step of adjusting the concentration of cations in a fluid based on a dissolved silica concentration curve that shows the relationship between the concentration of a target cation contained in a fluid containing dissolved silica and water and the concentration of dissolved silica in the fluid, wherein the dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica rises above the initial concentration of dissolved silica as the concentration of cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of cations rises above the first concentration range, and the cation concentration adjustment step sets the concentration of cations in the fluid to be within the first concentration range or within the second concentration range that is equal to or greater than the initial concentration of dissolved silica.

Description

[Technical Field]

[0001] The present invention relates to a scale suppression method, a scale suppression device, a geothermal power generation system, and a fluid utilization system. [Background technology]

[0002] Geothermal power generation facilities are used that generate electricity by utilizing steam separated from high-temperature geothermal fluids (geothermal water and geothermal steam) extracted from production wells. The geothermal fluids extracted from production wells contain more dissolved silica and other elements than well water or river water.

[0003] High-temperature geothermal water pumped from production wells is depressurized to extract steam, which concentrates the dissolved silica in the water and lowers its temperature. As the geothermal water flows through the piping of the geothermal power generation equipment, it cools, reducing the solubility of the dissolved silica. When the dissolved silica in the geothermal water becomes supersaturated, it polymerizes to amorphous silica and precipitates as silica scale. Silica scale can adhere to the inner walls of pipes, potentially causing blockages.

[0004] As a method for suppressing the deposition of silica scale, a scale suppression method has been disclosed in which a scale inhibitor formed from a water-soluble compound or a solution thereof is added in atomized form to the steam introduced into the steam turbine to suppress the formation of silica scale adhering to the steam turbine (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-160842 [Overview of the project] [Problems that the invention aims to solve]

[0006] Here, the higher the concentration of metal ions contained in the geothermal fluid, the stronger the salting-out effect by the metal ions, and the more the polymerization reaction is promoted. Therefore, the concentration of dissolved silica contained in the geothermal fluid tends to decrease. For this reason, the concentration of metal ions contained in the geothermal fluid has been adjusted to be reduced as much as possible. However, in facilities that use fluids containing dissolved silica and water, such as geothermal power generation facilities, in order to suppress the deposition of silica scale on the flow paths through which the fluid flows, etc., a method that can more accurately suppress the deposition of silica scale is required.

[0007] An aspect of the present invention aims to provide a scale suppression method and a scale suppression device that can more accurately suppress the deposition of silica scale.

Means for Solving the Problems

[0008] An aspect of the present invention is a scale suppression method for suppressing the formation of silica scale in a fluid containing dissolved silica and water, comprising a cation concentration adjustment step of adjusting the concentration of the target cation contained in the fluid containing dissolved silica and water based on a dissolved silica concentration curve showing the relationship between the concentration of the target cation and the concentration of the dissolved silica in the fluid, the dissolved silica concentration curve includes a first concentration range in which the concentration of the dissolved silica increases above the initial concentration of the dissolved silica as the concentration of the cation increases, and a second concentration range in which the concentration of the dissolved silica decreases as the concentration of the cation increases beyond the first concentration range, the cation concentration adjustment step is a scale suppression method of setting the concentration of the cation in the fluid within the first concentration range or within the range in the second concentration range where the concentration of the dissolved silica is not less than the initial concentration of the dissolved silica.

[0009] Another aspect of the present invention is a scale suppression device for suppressing the formation of silica scale in a fluid containing dissolved silica and water, comprising An additive supply unit that supplies an additive to the fluid, which allows for adjustment of the concentration of a target cation in the fluid, A control unit controls the additive supply unit based on a dissolved silica concentration curve that shows the relationship between the concentration of the target cation in a fluid containing dissolved silica and water and the concentration of the dissolved silica in the fluid. Equipped with, The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica increases from the initial concentration of dissolved silica as the concentration of the cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cations increases from the first concentration range. The control unit is a scale suppression device that controls the amount of additive supplied from the additive supply unit into the fluid so that the concentration of the cations in the fluid is within the first concentration range, or within the second concentration range where it is equal to or greater than the initial concentration of dissolved silica. [Effects of the Invention]

[0010] One aspect of the present invention can suppress the precipitation of silica scale with greater precision. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an example of a geothermal power generation system to which the scale suppression method according to the first embodiment of the present invention is applied. [Figure 2] This figure shows an example of a dissolved silica concentration curve, which illustrates the change in silica concentration in a geothermal fluid with respect to the cation concentration. [Figure 3] This is a flowchart showing an example of a scale suppression method according to the first embodiment of the present invention. [Figure 4] This is a schematic diagram showing an example of a geothermal power generation system equipped with a scale suppression device according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. For ease of understanding, the same reference numerals are used for identical components in each drawing, and redundant explanations are omitted. Also, the scale of each component in the drawings may differ from the actual scale. In this specification, the "~" indicating a numerical range means that the values ​​before and after it are included as the lower and upper limits, respectively, unless otherwise specified. Furthermore, if only the upper limit of a numerical range represented by "~" has a unit specified, it means that the lower limit also has the same unit.

[0013] A scale suppression method according to an embodiment of the present invention is a scale suppression method that suppresses the formation of silica scale in a fluid containing dissolved silica and water. The scale suppression method according to an embodiment of the present invention includes a cation concentration adjustment step of adjusting the concentration of the cation in the fluid based on a dissolved silica concentration curve that shows the relationship between the concentration of a target cation contained in the fluid containing dissolved silica and water and the concentration of the dissolved silica in the fluid. The dissolved silica concentration curve includes a first concentration range in which the concentration of the dissolved silica rises above the initial concentration of the dissolved silica as the concentration of the cation increases, and a second concentration range in which the concentration of the dissolved silica decreases as the concentration of the cation increases above the first concentration range. The cation concentration adjustment step sets the concentration of the cation in the fluid to within the first concentration range, or within the second concentration range that is equal to or greater than the initial concentration of the dissolved silica.

[0014] The scale suppression method according to this embodiment can increase the concentration of dissolved silica in the fluid by adjusting the concentration of cations in the fluid in the cation concentration adjustment step so that the concentration of cations in the fluid is within the first concentration range or within the second concentration range which is greater than or equal to the initial concentration of dissolved silica in the dissolved silica concentration curve. By maintaining a high concentration of dissolved silica in the fluid, the scale suppression method according to this embodiment can suppress the precipitation of silica scale with greater precision by making it difficult for silica scale to form in the fluid.

[0015] A scale suppression device according to an embodiment of the present invention is a scale suppression device that suppresses the formation of silica scale in a fluid containing dissolved silica and water. The scale suppression device according to an embodiment of the present invention comprises an additive supply unit that supplies an additive to the fluid in which the concentration of a target cation in the fluid can be adjusted, and a control unit that controls the additive supply unit based on a dissolved silica concentration curve that shows the relationship between the concentration of a target cation contained in the fluid containing dissolved silica and water and the concentration of the dissolved silica in the fluid. The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica rises above the initial concentration of dissolved silica as the concentration of the cation increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cation increases above the first concentration range. The control unit controls the amount of the additive supplied from the additive supply unit to the fluid so that the concentration of the cation in the fluid is within the first concentration range or within the second concentration range that is equal to or greater than the initial concentration of dissolved silica.

[0016] The scale suppression device according to the embodiment of the present invention can increase the concentration of dissolved silica in the fluid by adjusting the concentration of cations in the fluid so that the concentration of cations in the fluid is within the first concentration range or within the second concentration range which is greater than or equal to the initial concentration of dissolved silica in the dissolved silica concentration curve. By maintaining a high concentration of dissolved silica in the fluid, the scale suppression device according to this embodiment can suppress the precipitation of silica scale with greater precision, thereby making it difficult for silica scale to form in the fluid.

[0017] <First Embodiment> In describing the scale suppression method according to an embodiment of the present invention, a geothermal power generation system to which this scale suppression method is applied will be described. In this embodiment, the case in which the fluid containing dissolved silica and water is a geothermal fluid pumped up from underground will be described, but the invention is not limited to this, and any fluid containing dissolved silica and water is acceptable. Examples of fluids containing dissolved silica and water include tap water and groundwater. The fluid may also be industrial water used in petroleum refining facilities, thermal power generation facilities and nuclear power generation facilities, or industrial wastewater discharged from these facilities.

[0018] [Geothermal power generation system] A geothermal power generation system to which a scale suppression method according to an embodiment of the present invention is applied will be described. Figure 1 is a schematic diagram showing an example of a geothermal power generation system to which the scale suppression method according to this embodiment is applied. The arrows in Figure 1 indicate the flow of geothermal fluid. As shown in Figure 1, the geothermal power generation system 1A has a steam-water separator 11, a turbine 12, a generator 13, a condenser 14, a cooling tower 15, a retention tank 16, piping L10, a temperature measuring unit 21, a pH measuring unit 22, a cation concentration measuring unit 23, an optimal cation concentration calculation unit 24, a comparison unit 25, a supply amount calculation unit 26, and an additive supply unit 27, and generates electricity using geothermal fluid pumped from the production well 2.

[0019] Production well 2 is a well that brings geothermal water, geothermal steam, or a mixture thereof (geothermal fluid) from an underground geothermal reservoir to the surface.

[0020] Geothermal fluids contain dissolved silica and water.

[0021] The steam-water separator 11 separates the geothermal fluid pumped up from the production well 2 by the feedwater pump P1 into geothermal water and geothermal steam.

[0022] The turbine 12 rotates by being supplied with geothermal steam separated by the steam-water separator 11. The turbine 12 is connected to the generator 13.

[0023] The generator 13 generates electricity by being driven by the rotation of the turbine 12.

[0024] The condenser 14 condenses the geothermal steam discharged from the turbine 12.

[0025] The cooling tower 15 cools the condensed water (hot water) that has been condensed in the condenser 14. The condensed water cooled in the cooling tower 15 is sent to the condenser 14 by the circulation pump P2 as cooling water and is used for condensing geothermal steam.

[0026] The retention tank 16 is located in the middle of the piping L15 through which the geothermal water separated by the steam-water separator 11 flows, and allows the polymerization reaction of silica in the geothermal water to proceed, retaining the water until the silica-based insoluble components have sufficiently flocculated and settled. The geothermal water from which the silica-based insoluble components have been separated in the retention tank 16 may be returned to the reinjection well 3 through piping L15 by the reinjection pump P3.

[0027] Piping L10 connects the various components that make up the geothermal power generation system 1A and includes piping L11 to L15.

[0028] Piping L11 is a pipe that introduces geothermal fluid pumped from production well 2 to the steam-water separator 11. The geothermal fluid is pumped from production well 2 by the feedwater pump P1 and supplied to the steam-water separator 11.

[0029] Pipe L12 is a pipe that introduces the geothermal steam separated by the steam-water separator 11 to the turbine 12.

[0030] Pipe L13 is a pipe that introduces the condensed water (hot water) condensed in the condenser 14 into the cooling tower 15.

[0031] Pipe L14 is the pipe that returns the condensed water cooled in the cooling tower 15 to the condenser 14 as cooling water. The condensed water cooled in the cooling tower 15 is transported to the condenser 14 by the circulation pump P2.

[0032] Pipe L15 is a pipe that introduces the geothermal water separated by the steam-water separator 11 into the retention tank 16.

[0033] The temperature measuring unit 21 is installed in the piping L11 and measures the temperature of the geothermal fluid pumped up from the production well 2. Examples of the temperature measuring unit 21 include a thermometer.

[0034] The pH measuring unit 22 is installed in the piping L11 and measures the pH of the geothermal fluid pumped up from the production well 2. Examples of the pH measuring unit 22 include a pH meter.

[0035] The cation concentration measuring unit 23 is installed in the piping L11 and detects the types of cations contained in the geothermal fluid pumped up from the production well 2, and measures the concentration of the target cations. The cation concentration measuring unit 23 can be any analytical device that can detect the types of cations and measure the concentration of cations, and examples of the cation concentration measuring unit 23 include ion meters.

[0036] The target cations can be one type or two or more types.

[0037] If multiple cations are present in the geothermal fluid, the cation concentration measuring unit 23 may measure ions of the same valency together, according to the valency of the ions.

[0038] The optimal cation concentration calculation unit 24 calculates the concentration of cations in the geothermal fluid at which the concentration of dissolved silica in the geothermal fluid becomes equal to or greater than the initial concentration of dissolved silica, based on the type of cations measured by the cation concentration measurement unit 23 and the dissolved silica concentration curve that shows the relationship between the concentration of cations contained in the geothermal fluid and the concentration of dissolved silica in the geothermal fluid.

[0039] Figure 2 shows an example of a dissolved silica concentration curve that illustrates the change in the concentration of dissolved silica in a geothermal fluid with respect to the cation concentration in the geothermal fluid. As shown in Figure 2, the dissolved silica concentration curve includes a first concentration range M1 in which the rate of change in silica concentration increases as the concentration of dissolved silica rises above the initial concentration C0 of dissolved silica in the geothermal fluid before cations are added to the geothermal fluid, and a second concentration range M2 in which the rate of change in silica concentration decreases as the concentration of dissolved silica in the geothermal fluid decreases as the cation concentration increases above the first concentration range M1.

[0040] The second concentration range M2 comprises a 21st concentration range M21 in which the initial concentration of dissolved silica in the geothermal fluid is equal to or greater than C0, and a 22nd concentration range M22 in which the concentration of dissolved silica is less than the initial concentration of dissolved silica in the geothermal fluid, C0.

[0041] In the dissolved silica concentration curve, the range in which the dissolved silica concentration is equal to or greater than the initial concentration C0 is defined as the first concentration range M1 and the 21st concentration range M21, and the boundary point between the first concentration range M1 and the second concentration range M2 is the maximum value C of the dissolved silica concentration. M Consequently, the change in silica concentration in the geothermal fluid is maximized.

[0042] When the concentration of cations in the geothermal fluid is within a first concentration range M1, supplying cations to the geothermal fluid increases the concentration of dissolved silica, thereby suppressing the formation of silica scale. When the concentration of cations in the geothermal fluid is within a first concentration range M1, supplying cations to the geothermal fluid inhibits the polymerization reaction of dissolved silica, thus increasing the concentration of dissolved silica. Therefore, when the concentration of cations in the geothermal fluid is within a first concentration range M1, it is preferable to supply cations to the geothermal fluid to increase the concentration of cations in the geothermal fluid.

[0043] When the concentration of cations in the geothermal fluid is within the second concentration range M2, supplying cations to the geothermal fluid reduces the concentration of dissolved silica, making it easier for dissolved silica to precipitate in the geothermal fluid. When the concentration of cations in the geothermal fluid is within the second concentration range M2, supplying cations to the geothermal fluid strengthens the salting-out effect by the cations, promoting the polymerization reaction of dissolved silica, thus reducing the concentration of dissolved silica. Therefore, when the concentration of cations in the geothermal fluid is within the second concentration range M2, silica scale is easily formed in the geothermal fluid, so it is preferable to reduce the amount of cations in the geothermal fluid to lower its concentration.

[0044] Assume that the concentration of cations in the geothermal fluid is within the first concentration range M1 or within the second concentration range M2, specifically within the 21st concentration range M21. In this case, the concentration of dissolved silica in the geothermal fluid is within the first concentration range M1 or the second concentration range M2, and the concentration of dissolved silica is within the maximum value C of the dissolved silica concentration. M The concentration at which this occurs, i.e., the maximum concentration C of dissolved silica. M At the boundary between the first concentration range M1 and the second concentration range M2, the change in silica concentration is highest, and the concentration of dissolved silica in the geothermal fluid is highest. Maximum value C of dissolved silica concentration M When this is the case, the precipitation of dissolved silica in the geothermal fluid can be suppressed to the greatest extent possible, and therefore the formation of silica scale in the geothermal fluid can be suppressed to the greatest extent possible. Therefore, when the concentration of cations in the geothermal fluid is within the first concentration range M1 or the 21st concentration range M21 within the second concentration range M2, the concentration of cations in the geothermal fluid is adjusted so that the concentration of cations in the geothermal fluid is within the first concentration range M1 or the 21st concentration range M21, and the concentration of dissolved silica is within the maximum value C of the dissolved silica concentration. M It is preferable to adjust the concentration to the point where the dissolved silica concentration is maximized.

[0045] The optimal cation concentration calculation unit 24 can determine the dissolved silica concentration curve using a calculation method commonly used for creating concentration curves, based on the temperature of the geothermal fluid measured by the temperature measurement unit 21, the pH of the geothermal fluid measured by the pH measurement unit 22, and the type and concentration of cations measured by the cation concentration measurement unit 23. The dissolved silica concentration curve can be determined, for example, by combining commonly available computational chemistry and the Debye-Hückel equation.

[0046] The optimal cation concentration calculation unit 24 calculates the concentration of cations in the geothermal fluid such that the dissolved silica concentration is within the first concentration range M1 or the 21st concentration range M21 in the dissolved silica concentration curve shown in Figure 2.

[0047] The optimal cation concentration calculation unit 24 can calculate the cation concentration at which the dissolved silica concentration in the dissolved silica concentration curve falls within the first concentration range M1 or the 21st concentration range M21, based on the change in silica concentration of the dissolved silica in the geothermal fluid. The optimal cation concentration calculation unit 24 can calculate the change in silica concentration of the dissolved silica in the geothermal fluid using the following formula (1). That is, it is preferable to use the amount obtained by subtracting the equilibrium concentration of unsaturated dissolved silica or the saturation concentration of dissolved silica in the geothermal fluid from the initial concentration of dissolved silica in the geothermal fluid. Change in silica concentration = Initial concentration of dissolved silica in geothermal fluid - (Equilibrium concentration of unsaturated dissolved silica or saturation concentration of dissolved silica in geothermal fluid) ... (1)

[0048] The dissolved silica concentration curve, which shows the relationship between the concentration of cations in a geothermal fluid and the concentration of dissolved silica in the geothermal fluid, can have a different shape depending on whether the dissolved silica in the geothermal fluid is saturated or not. Therefore, when calculating the change in silica concentration, if the dissolved silica is not saturated, the change in silica concentration can be obtained by dividing the initial concentration of dissolved silica in the geothermal fluid by the equilibrium concentration of dissolved silica. If the dissolved silica is saturated, the change in silica concentration can be obtained by dividing the initial concentration of dissolved silica in the geothermal fluid by the saturation concentration of dissolved silica.

[0049] Furthermore, the equilibrium concentration of dissolved silica refers to the state in which the dissolved silica concentration stabilizes after the reaction of dissolved silica has progressed from its initial concentration.

[0050] The optimal cation concentration calculation unit 24 calculates the maximum value C of the dissolved silica concentration in the dissolved silica concentration curve, based on the type of cation measured by the cation concentration measurement unit 23 and the dissolved silica concentration curve, such that the dissolved silica concentration is within the first concentration range M1 or the 21st concentration range M21. M It is preferable to calculate the concentration of cations in the geothermal fluid. In this case, the concentration of dissolved silica will be at its maximum, thus minimizing the precipitation of dissolved silica in the geothermal fluid.

[0051] The optimal cation concentration calculation unit 24 is preferable in that it calculates with greater accuracy whether the concentration falls within the first concentration range M1 or the 21st concentration range M21. Furthermore, it is preferable that the cation concentration in the geothermal fluid is within the first concentration range M1 or the 21st concentration range M21 in the dissolved silica concentration curve, based on the temperature of the geothermal fluid measured by the temperature measurement unit 21 and the pH of the geothermal fluid measured by the pH measurement unit 22.

[0052] The comparison unit 25 compares the measured value of the cation concentration measured by the cation concentration measurement unit 23 with the calculated value of the cation concentration in the geothermal fluid within the first concentration range M1 or the 21st concentration range M21, which is calculated by the optimal cation concentration calculation unit 24.

[0053] Furthermore, the optimal cation concentration calculation unit 24 calculates the maximum value C of the dissolved silica concentration. M When the cation concentration in is calculated, the comparison unit 25 compares the measured value of the cation concentration measured in the cation concentration measurement unit 23 with the maximum value C of the dissolved silica concentration calculated in the optimal cation concentration calculation unit 24. M It is preferable to compare this with the calculated value of the concentration of cations in the geothermal fluid.

[0054] Based on the comparison result between the measured value of the cation concentration and the calculated value of the cation concentration in the comparison unit 25, the supply amount calculation unit 26 calculates the supply amount of the additive such that the concentration of the cation in the geothermal fluid is within the first concentration range M1 or within the 21st concentration range M21.

[0055] Also, in the optimal cation concentration calculation unit 24, when the concentration of the cation at the maximum value C of the dissolved silica concentration M is calculated, it is preferable that the supply amount calculation unit 26 calculates the supply amount of the additive such that the concentration of the cation in the geothermal fluid becomes the maximum value C of the dissolved silica concentration in the geothermal fluid. M

[0056] The additive supply unit 27 supplies an additive whose concentration of the target cation in the geothermal fluid can be adjusted into the geothermal fluid. The additive supply unit 27 may supply the additive into the geothermal fluid based on the calculation result of the supply amount of the additive in the supply amount calculation unit 26. The additive supply unit 27 may have an additive storage unit 271 that stores the additive and a control valve V11 that controls the supply amount of the additive in the additive storage unit 271 to the pipe L11.

[0057] The additive is a reagent that can adjust the concentration of the cation in the geothermal fluid by generating cations in the geothermal fluid or reacting with cations to reduce the cations in the geothermal fluid.

[0058] As the additive, a reagent that generates cations in the geothermal fluid or a reagent that reacts with the cations in the geothermal fluid to reduce the cations in the geothermal fluid can be used. By including the above reagents in the additive, the concentration of the cation in the geothermal fluid can be adjusted.

[0059] ​The reagents that can adjust the concentration of cations in geothermal fluid are not particularly limited, as long as they are compounds that generate cations when added to the geothermal fluid or compounds that react with cations when added to the geothermal fluid to increase or decrease the concentration of cations in the geothermal fluid. As reagents that can adjust the concentration of cations in geothermal fluid, inorganic salts and organic salts can be used that do not promote the formation of silica scale while suppressing fluctuations in the pH of the geothermal fluid. Inorganic salts and organic salts may be used individually or in combination of two or more types.

[0060] When the additive is supplied into the geothermal fluid, the cations generated from the additive are preferably one or more of the following: monovalent cations, divalent cations, and Al ions.

[0061] A monovalent cation is H + na + Li + , K + and Rb + It is preferable that it be one or more of the following ions.

[0062] Divalent cations are Be 2+ Mg 2+ Ca 2+ Sr 2+ and Ba 2+ It is preferable that it be one or more of the following ions.

[0063] The additive supply unit 27 only needs to be able to supply the additive into the geothermal fluid, and a general supply method may be used. As a supply method, for example, it may be simply injected, or it may be supplied by other methods such as spraying and injection.

[0064] It is preferable that the additive supply unit 27 supplies the additive to the piping L11 of the piping L10 at a position downstream of the temperature measurement unit 21, pH measurement unit 22, and cation concentration measurement unit 23. This makes it easier to appropriately supply the additive to the geothermal fluid based on the concentration of cations in the geothermal fluid calculated by the optimal cation concentration calculation unit 24, thereby enabling appropriate adjustment of the cation concentration in the geothermal fluid.

[0065] In geothermal power generation system 1A, geothermal fluid pumped from production well 2 is sent to a gas-water separator 11 via piping L11 by feedwater pump P1. In the gas-water separator 11, the geothermal fluid is separated into geothermal steam, which is a gaseous component, and geothermal water, which is a liquid component. The separated geothermal steam is sent to the turbine 12 via piping L12 and used to rotate the turbine 12. The generator 13 generates electricity by being driven by the rotation of the turbine 12. The geothermal steam that has passed through the turbine 12 is sent to the condenser 14 to condense, and the condensed water is further sent to the cooling tower 15 via piping L13 to be cooled. The cooled condensed water is returned to the condenser 14 via piping L14 by circulation pump P2 and used as cooling water for the geothermal steam that has passed through the turbine 12. In addition, the geothermal water separated in the gas-water separator 11 is sent to the retention tank 16 via piping L15 to remove silica-based insoluble components. Geothermal water from which silica-based insoluble components have been removed in the retention tank 16 is discharged from the retention tank 16 into the piping L15 and returned to the reinjection well 3 by the reinjection pump P3.

[0066] The geothermal fluid pumped from production well 2 contains dissolved silica. Therefore, in the geothermal power generation system 1A, as the geothermal fluid cools as it passes through piping L10, silica scale precipitates from the geothermal fluid and adheres to surfaces that come into contact with the geothermal fluid, such as the inner surface of piping L10, the outer surface of turbine 12, and the inner wall of injection well 3. The parts of piping L10 and turbine 12 that come into contact with the geothermal fluid are generally made of steel, and silica easily bonds with the hydroxyl groups on the surface of steel, making it easy for silica scale to adhere to these areas. For this reason, it is necessary to suppress the formation of silica scale from the dissolved silica in the geothermal fluid.

[0067] <Scale suppression method> A scale suppression method according to an embodiment of the present invention will now be described. The scale suppression method according to this embodiment adjusts the cation concentration in the geothermal fluid based on a dissolved silica concentration curve in which the concentration of dissolved silica in the geothermal fluid increases from the initial concentration C0 of dissolved silica before cations are added to the geothermal fluid (see Figure 2) as the concentration of cations increases, reaches a maximum value at a predetermined concentration, and then decreases thereafter. Based on the dissolved silica concentration curve showing the above trend, the scale suppression method according to this embodiment adjusts the cation concentration in the geothermal fluid to a 21st concentration range M21 within a first concentration range M1 or a second concentration range M2 that increases from the initial concentration C0 (see Figure 2) as the concentration of cations increases, thereby making the concentration of dissolved silica in the geothermal fluid higher than the initial concentration C0 (see Figure 2), and more accurately suppressing the precipitation of silica scale in the geothermal fluid.

[0068] Figure 3 is a flowchart showing an example of a scale suppression method according to an embodiment of the present invention. As shown in Figure 3, in the scale suppression method according to this embodiment, the geothermal fluid is analyzed by the temperature measuring unit 21, the pH measuring unit 22, and the cation concentration measuring unit 23 (geothermal fluid analysis step: step S11).

[0069] In the geothermal fluid analysis step S11, the temperature and pH of the geothermal fluid are measured by the temperature measuring unit 21 and the pH measuring unit 22 (temperature and pH measurement step: step S111).

[0070] Next, the cation concentration measuring unit 23 detects the types of cations contained in the geothermal fluid pumped up from the production well 2 and measures the concentration of the detected target cations (cation concentration measurement process: step S112).

[0071] The temperature and pH measurement step S111 and the cation concentration measurement step S112 may be performed simultaneously, or the cation concentration measurement step S112 may be performed before the temperature and pH measurement step S111.

[0072] Next, the optimal cation concentration calculation unit 24 calculates the concentration of cations in the geothermal fluid such that the dissolved silica concentration in the dissolved silica concentration curve becomes either the first concentration range M1 or the 21st concentration range M21, based on the types of cations measured in the cation concentration measurement step S112 and the dissolved silica concentration curve (see Figure 2) (optimal cation concentration calculation step: step S12).

[0073] The optimal cation concentration calculation unit 24 further preferably calculates the concentration of cations in the geothermal fluid such that the dissolved silica concentration is within the first concentration range M1 or the 21st concentration range M21, in a dissolved silica concentration curve created based on the temperature and pH of the geothermal fluid measured in the temperature and pH measurement step S111.

[0074] In the optimal cation concentration calculation step S12, the optimal cation concentration calculation unit 24 calculates the maximum value C of the dissolved silica concentration. M Therefore, it is preferable to calculate the concentration of cations in the geothermal fluid.

[0075] Next, the comparison unit 25 compares the measured value of the cation concentration measured in the cation concentration measurement step S112 with the calculated value of the cation concentration in the geothermal fluid within the first concentration range M1 or the 21st concentration range M21, which was calculated based on the dissolved silica concentration curve in the optimal cation concentration calculation step S12 (comparison step: step S13).

[0076] In the comparison step S13, the maximum value C of the dissolved silica concentration in the optimal cation concentration calculation step S12 is used. M When the concentration of cations in the sample is calculated, the comparison unit 25 compares the measured value of the cation concentration measured in the cation concentration measurement step S112 with the maximum value C of the dissolved silica concentration calculated in the optimal cation concentration calculation step S12. M It is preferable to compare this with the calculated value of the concentration of cations in the geothermal fluid.

[0077] Next, the supply amount calculation unit 26 calculates the amount of additive to supply such that the concentration of cations in the geothermal fluid falls within the first concentration range M1 or within the second concentration range M2, specifically within the 21st concentration range M21, based on the comparison result between the measured value of the cation concentration in the comparison step S13 and the calculated value of the cation concentration (supply amount calculation step: step S14).

[0078] In other words, in the supply amount calculation step S14, the supply amount calculation unit 26 calculates the amount of additive to be supplied such that the concentration of cations in the geothermal fluid is equal to or greater than the initial concentration C0 (see Figure 2) of dissolved silica in the geothermal fluid.

[0079] In the supply amount calculation step S14, the maximum value C of the dissolved silica concentration is calculated in the optimal cation concentration calculation step S12. M When this is calculated, the supply amount calculation unit 26 determines that the concentration of cations in the geothermal fluid is equal to the maximum value C of the dissolved silica concentration in the geothermal fluid. M It is preferable to calculate the amount of additive to be supplied.

[0080] Next, the additive supply unit 27 adjusts the concentration of cations in the geothermal fluid based on the concentration of the target cations contained in the geothermal fluid and the dissolved silica concentration curve, so that the concentration of cations in the geothermal fluid falls within the first concentration range M1 or the 21st concentration range M21 (cation concentration adjustment step: step S15).

[0081] In other words, based on the calculation result of the amount of additive to be supplied in the supply amount calculation step S14, the additive is supplied to the geothermal fluid to adjust the concentration of cations in the geothermal fluid to be within the first concentration range M1 or the 21st concentration range M21.

[0082] In the cation concentration adjustment process S15, the concentration of dissolved silica in the geothermal fluid can be adjusted by controlling the amount of additive supplied to the geothermal fluid flowing through the piping L11 by controlling the control valve V11 of the additive supply unit 27, thereby adjusting the concentration of cations in the geothermal fluid.

[0083] When the concentration of cations in the geothermal fluid is within the first concentration range M1, it is preferable to supply an additive to the geothermal fluid flowing through the pipe L11 to increase the concentration of cations in the geothermal fluid. This increases the concentration of dissolved silica in the geothermal fluid, and the maximum value C of the dissolved silica concentration... M Approaching or the maximum value of dissolved silica concentration C M Because it can be adjusted in this way, the formation of silica scale in the geothermal fluid can be further suppressed.

[0084] When the concentration of cations in the geothermal fluid is within the 21st concentration range M21 of the second concentration range M2, it is preferable to reduce the concentration of cations in the geothermal fluid by supplying an additive to the geothermal fluid flowing through the pipe L11. This increases the concentration of dissolved silica in the geothermal fluid, and the maximum value C of the dissolved silica concentration... M Approaching or the maximum value of dissolved silica concentration C M Because it can be adjusted in this way, the formation of silica scale in the geothermal fluid can be further suppressed.

[0085] If the concentration of cations in the geothermal fluid is within the 22nd concentration range M22 of the second concentration range M2, the additive supplied to the geothermal fluid flowing through the pipe L11 reduces the concentration of cations in the geothermal fluid to within the first concentration range M1 or the 21st concentration range M21. This increases the concentration of dissolved silica in the geothermal fluid to the same or higher level as the initial concentration of dissolved silica C0 (see Figure 2), and further increases the maximum concentration C of the dissolved silica. M Approaching or the maximum value of dissolved silica concentration C M Because it can be adjusted in this way, the formation of silica scale in the geothermal fluid can be further suppressed.

[0086] In the optimal cation concentration calculation step S12, the maximum value C of the dissolved silica concentration M When calculated, the additive supply unit 27 determines the concentration of cations in the geothermal fluid, and the concentration of dissolved silica within the first concentration range M1 or the 21st concentration range M21 is the maximum value C of the dissolved silica concentration. MIn other words, it is preferable to adjust the cation concentration by supplying additives so that the concentration is at the boundary between the first concentration range M1 and the second concentration range M2. In this case, the concentration of dissolved silica in the geothermal fluid is highest, and the precipitation of dissolved silica in the geothermal fluid can be suppressed to the greatest extent. Therefore, the formation of silica scale in the geothermal fluid can be suppressed to the greatest extent.

[0087] The cation concentration adjustment step S15 may be determined arbitrarily as appropriate depending on the type of cation, but for example, it is preferable to set the concentration of dissolved silica in the geothermal fluid to more than 1.0 times and 1.3 times or less the initial concentration C0 of dissolved silica in the geothermal fluid, more preferably to 1.05 to 1.25 times, and even more preferably to 1.1 to 1.2 times. If the concentration of dissolved silica is within the above preferred range with respect to the initial concentration of dissolved silica in the geothermal fluid, it becomes easier to set the concentration of cations to be within the first concentration range M1 or the 21st concentration range M21.

[0088] The concentration of cations in the geothermal fluid can be arbitrarily selected as appropriate depending on the type of cation, but for example, it is preferably greater than 0 mol / L and less than or equal to 0.5 mol / L, more preferably between 0.05 mol / L and 0.45 mol / L, and even more preferably between 0.1 mol / L and 0.45 mol / L. If the concentration of cations in the geothermal fluid is within the above preferred range, it can be easily adjusted so that the concentration of cations falls within the first concentration range M1 or the 21st concentration range M21.

[0089] As described above, the scale suppression method according to this embodiment includes a cation concentration adjustment step S15, in which the cation concentration adjustment step S15 adjusts the concentration of cations in the geothermal fluid to within a first concentration range M1 or a 21st concentration range M21 based on a dissolved silica concentration curve (see Figure 2). The first concentration range M1 or the 21st concentration range M21 is the range within the dissolved silica concentration curve where the dissolved silica concentration has risen above the initial dissolved silica concentration C0, and within the first concentration range M1 or the 21st concentration range M21, the dissolved silica concentration is equal to the maximum value C of the dissolved silica concentration. MThe dissolved silica can be increased until the concentration reaches a certain level. Therefore, the cation concentration adjustment step S15 can be adjusted so that the concentration of cations in the geothermal fluid is within the range in which the dissolved silica concentration increases, by setting the concentration of cations in the geothermal fluid within the first concentration range M1 or the 21st concentration range M21. Thus, the precipitation of silica scale caused by dissolved silica in the geothermal fluid can be appropriately suppressed depending on the concentration of cations in the geothermal fluid. Accordingly, the scale suppression method according to this embodiment can suppress the precipitation of silica scale in the geothermal fluid with greater precision.

[0090] In the scale suppression method according to this embodiment, the cation concentration adjustment step S15 adjusts the dissolved silica concentration to the maximum value C of the dissolved silica concentration curve. M It is preferable to adjust the concentration of cations in the geothermal fluid to such a value. This allows the dissolved silica in the geothermal fluid to reach the maximum value C of the dissolved silica concentration. M This method can contain up to a certain amount of dissolved silica, and most effectively suppresses the precipitation of silica scale in the geothermal fluid due to dissolved silica. Therefore, the scale suppression method according to this embodiment can most reliably suppress the amount of silica scale precipitation in the geothermal fluid.

[0091] In the scale suppression method according to this embodiment, the cation concentration adjustment step S15 preferably involves supplying an additive into the geothermal fluid, and the additive is preferably a reagent that generates cations in the geothermal fluid, or a reagent that reacts with cations in the geothermal fluid to reduce the amount of cations in the geothermal fluid. As a result, in the scale suppression method according to this embodiment, the concentration of cations in the geothermal fluid can be easily adjusted within the first concentration range M1 or the 21st concentration range M21 by adding an additive to the geothermal fluid in the cation concentration adjustment step S15.

[0092] The scale suppression method according to this embodiment preferably includes a cation concentration measurement step S112 and an optimal cation concentration calculation step S12. In the scale suppression method according to this embodiment, the concentration of cations contained in the geothermal fluid is measured in the cation concentration measurement step S112, and the concentration of cations such that the concentration of dissolved silica in the geothermal fluid becomes a first concentration range M1 or a 21st concentration range M21 is calculated in the optimal cation concentration calculation step S12. As a result, the scale suppression method according to this embodiment can appropriately determine the amount of cations to supply in the cation concentration adjustment step S15, and thus can more appropriately control the deposition of silica scale.

[0093] In the scale suppression method according to this embodiment, it is preferable to use one or more of the following ions as cations: monovalent cations, divalent cations, and Al ions. By using one or more of these ions as cations, cations can be easily supplied to the geothermal fluid, and the concentration of cations in the geothermal fluid can be easily adjusted. Therefore, the scale suppression method according to this embodiment can easily adjust the concentration of dissolved silica, and thus can appropriately suppress the deposition of silica scale in the geothermal fluid.

[0094] In the scale suppression method according to this embodiment, H is used as the monovalent cation. + na + Li + , K + and Rb + It is preferable to use one or more of these ions. By using one or more of these ions as monovalent cations, cations can be easily supplied to the geothermal fluid, and the concentration of cations in the geothermal fluid can be easily adjusted. Therefore, the scale suppression method according to this embodiment can easily adjust the concentration of dissolved silica, and thus can appropriately suppress the deposition of silica scale in the geothermal fluid.

[0095] In the scale suppression method according to this embodiment, the divalent cation is Be 2+ Mg 2+ Ca 2+ Sr 2+ and Ba2+ It is preferable to use one or more of these ions. By using one or more of these ions as divalent cations, cations can be easily supplied to the geothermal fluid, similar to monovalent cations, and the concentration of cations in the geothermal fluid can be easily adjusted. Therefore, the scale suppression method according to this embodiment can easily adjust the concentration of dissolved silica, and thus can appropriately suppress the deposition of silica scale in the geothermal fluid.

[0096] In the scale suppression method according to this embodiment, it is preferable that the cation concentration adjustment step S15 sets the concentration of dissolved silica in the geothermal fluid to more than 1.0 times and 1.3 times or less the initial concentration of dissolved silica in the geothermal fluid. The scale suppression method according to this embodiment can appropriately suppress the precipitation of silica scale in the geothermal fluid by appropriately understanding the increase or decrease in the concentration of dissolved silica.

[0097] In the scale suppression method according to this embodiment, the first concentration range M1 of the dissolved silica concentration curve may be greater than 0 mol / L and less than or equal to 0.5 mol / L. As a result, in the scale suppression method according to this embodiment, the concentration of cations contained in the geothermal fluid can be appropriately adjusted in the cation concentration adjustment step S15 to be within the first concentration range M1, thereby effectively suppressing the deposition of silica scale in the geothermal fluid.

[0098] The scale suppression method according to this embodiment preferably includes a temperature and pH measurement step S111. In the scale suppression method according to this embodiment, by measuring the temperature and pH of the geothermal fluid in the temperature and pH measurement step S111, the cation concentration can be adjusted more accurately in the cation concentration adjustment step S15, thereby allowing for more appropriate control of silica scale deposition. Therefore, the scale suppression method according to this embodiment can appropriately suppress the deposition of silica scale in the geothermal fluid.

[0099] In the scale suppression method according to this embodiment, it is preferable to supply the additive into the geothermal fluid at a location upstream of the piping L11. By supplying the additive into the geothermal fluid at a location upstream of the piping L11 and adjusting the concentration of dissolved silica in the geothermal fluid to be within the first concentration range M1 or the 21st concentration range M21, silica scale is less likely to precipitate in the piping L10, and thus the precipitation of silica scale throughout the piping L10 can be suppressed.

[0100] The geothermal power generation system 1A can use the scale suppression method according to this embodiment. Because the scale suppression method according to this embodiment exhibits the effects described above, it can suppress the deposition of silica scale in the geothermal fluid flowing through the piping L10 of the geothermal power generation system 1A, which can cause blockage and attenuation. As a result, the geothermal power generation system 1A can be operated stably and continuously, and the burden required for repair and replacement of the piping L10 and other components can be reduced, thereby reducing the burden required for the operation and management of the geothermal power generation system 1A.

[0101] <Second Embodiment> [Geothermal power generation system] A geothermal power generation system equipped with a scale suppression device according to an embodiment of the present invention will be described. Figure 4 is a schematic diagram showing an example of a geothermal power generation system equipped with a scale suppression device according to this embodiment. The arrows in Figure 4 indicate the flow of geothermal fluid. As shown in Figure 4, the geothermal power generation system 1B has a gas-water separator 11, a turbine 12, a generator 13, a condenser 14, a cooling tower 15, a retention tank 16, piping L10 and a scale suppression device 20, and generates electricity using geothermal fluid pumped from the production well 2. The gas-water separator 11, turbine 12, generator 13, condenser 14, cooling tower 15, retention tank 16 and piping L10 are the same as in the first embodiment described above, so details are omitted.

[0102] The scale suppression device 20 includes a temperature measuring unit 21, a pH measuring unit 22, a cation concentration measuring unit 23, an optimal cation concentration calculation unit 24, a comparison unit 25, a supply amount calculation unit 26, an additive supply unit 27, and a control unit 28, and suppresses the formation of silica scale in the geothermal fluid. Note that the temperature measuring unit 21, pH measuring unit 22, cation concentration measuring unit 23, optimal cation concentration calculation unit 24, comparison unit 25, supply amount calculation unit 26, and additive supply unit 27 are the same as in the first embodiment described above, so details are omitted.

[0103] The control unit 28 controls the control valve V11 of the additive supply unit 27 so that the concentration of cations in the geothermal fluid is within the first concentration range M1 or the 21st concentration range M21, based on the dissolved silica concentration curve (see Figure 2). By controlling the amount of additive supplied from the additive supply unit 27 to the geothermal fluid flowing through the piping L11, the concentration of cations in the geothermal fluid is adjusted.

[0104] The control unit 28 has a storage unit that stores control programs and various stored information, and an arithmetic unit that operates based on the control programs. Memory is used as the storage unit, and memory includes RAM, ROM, and storage. The arithmetic unit is a processor such as a CPU. The control unit 28 is realized when the arithmetic unit reads and executes the control programs and other information stored in the storage unit. In addition, the storage unit of the control unit 28 may store information showing dissolved silica concentration curves for each type of cation, as shown in Figure 2.

[0105] The control unit 28 controls the control valve V11 of the additive supply unit 27 based on the calculation result of the additive supply amount in the supply amount calculation unit 26, and adjusts the content of the additive supplied from the additive storage unit 271 to the geothermal fluid, thereby adjusting the cation concentration in the geothermal fluid. This makes it possible to adjust the cation concentration in the geothermal fluid so that the cation concentration in the geothermal fluid falls within the first concentration range M1 or the 21st concentration range M21.

[0106] The control unit 28 determines the maximum value C of the dissolved silica concentration in the dissolved silica concentration curve. MIt is preferable to control the amount of additive supplied from the additive supply unit 27 to the geothermal fluid so that the concentration of cations in the geothermal fluid is equal to the maximum value C of the dissolved silica concentration. M In this case, the concentration of dissolved silica in the geothermal fluid will be maximized within the first concentration range M1 or the 21st concentration range M21, thus minimizing the precipitation of silica scale.

[0107] The scale suppression device 20 includes a cation concentration measuring unit 23, an optimal cation concentration calculation unit 24, an additive supply unit 27, and a control unit 28. This allows the device to automatically and appropriately supply additives to the geothermal fluid flowing through pipe L11 so that the concentration of cations in the geothermal fluid is within a first concentration range M1 or a 21st concentration range M21. As a result, the scale suppression device 20 can adjust the dissolved silica concentration to be within a range that increases above the initial concentration C0, thereby appropriately suppressing the deposition of silica scale in the geothermal fluid according to the concentration of cations in the geothermal fluid. Therefore, the scale suppression device 20 can suppress the deposition of silica scale in the geothermal fluid more accurately and easily.

[0108] By equipping the geothermal power generation system 1B with a scale suppression device 20, the deposition of silica scale in the geothermal fluid flowing through the piping L11 can be suppressed more accurately and easily, thereby reducing the burden required for the operation and management of the geothermal power generation system 1B.

[0109] (Methods for suppressing silica scale) The scale suppression method according to this embodiment is performed using a scale suppression device 20. The scale suppression method according to this embodiment is the same as the scale suppression method according to the first embodiment, except that the control unit 28 performs the cation concentration adjustment step S15 of the scale suppression method according to the first embodiment shown in Figure 3, so the details are omitted.

[0110] The scale suppression method according to this embodiment includes a cation concentration adjustment step S15, and by performing the cation concentration adjustment step S15 in the control unit 28, the deposition of silica scale in the geothermal fluid can be suppressed with greater precision.

[0111] In each of the above embodiments, the temperature measuring unit 21, pH measuring unit 22, cation concentration measuring unit 23, and additive supply unit 27 are connected to the piping L11, and the cation concentration in the geothermal fluid flowing through the piping L11 is detected and the additive is supplied to the geothermal fluid flowing through the piping L11. However, the additive may be supplied to any of the piping L12 to L15, or to one or more of the piping L11 to L15.

[0112] In the above embodiments, the case in which the scale suppression method or scale suppression device according to this embodiment is applied to a geothermal power generation system has been described. However, the scale suppression method or scale suppression device according to each embodiment may also be used in a fluid utilization system that utilizes a fluid containing dissolved silica and water, for example. Examples of fluid utilization systems include petroleum refining facilities, thermal power generation facilities, and nuclear power generation facilities. The fluid utilization system may include equipment having fluid passages, such as heat exchangers, fluid transport piping, and gas-liquid separators.

[0113] As described above, embodiments have been explained, but these embodiments are presented as examples only, and the present invention is not limited by these embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0114] The embodiments of the present invention are, for example, as follows. <1> A method for suppressing the formation of silica scale in a fluid containing dissolved silica and water, The process includes a cation concentration adjustment step, in which the concentration of the target cation in a fluid containing dissolved silica and water is adjusted based on a dissolved silica concentration curve that shows the relationship between the concentration of the target cation in the fluid and the concentration of the dissolved silica in the fluid. The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica increases from the initial concentration of dissolved silica as the concentration of the cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cations increases from the first concentration range. The cation concentration adjustment step is a scale suppression method in which the concentration of the cations in the fluid is set to a first concentration range, or to a range within the second concentration range that is equal to or greater than the initial concentration of dissolved silica. <2> The cation concentration adjustment step adjusts the concentration of the cations in the fluid to the point where the concentration of dissolved silica in the dissolved silica concentration curve reaches its maximum value. <1> The scaling suppression method described above. <3> The cation concentration adjustment step involves supplying an additive into the fluid that allows for adjustment of the concentration of the cations in the fluid. The additive is a reagent that generates the cations in the fluid, or a reagent that reacts with the cations in the fluid to reduce the amount of cations in the fluid. <1> or <2> The scaling suppression method described above. <4> A cation concentration measurement step for measuring the concentration of the cations contained in the fluid, An optimal cation concentration calculation step, based on the measured type of cation and the dissolved silica concentration curve, calculates the concentration of the cation in the dissolved silica concentration curve within the first concentration range or within the second concentration range where the concentration of dissolved silica is equal to or greater than the initial concentration of the cation; including, <1> ~ <3> A scaling suppression method described in any one of the following. <5> The aforementioned cation is one or more of the following: a monovalent cation, a divalent cation, and an Al ion. <1> ~ <4> A scaling suppression method described in any one of the following. <6> The aforementioned monovalent cation is H + na+ Li + , K + and Rb + One or more of the following ions: <5> The scaling suppression method described above. <7> The aforementioned divalent cation, Be 2+ Mg 2+ Ca 2+ Sr 2+ and Ba 2+ One or more of the following ions: <5> or <6> The scaling suppression method described above. <8> The cation concentration adjustment step involves adjusting the concentration of dissolved silica to be more than 1.0 times and less than or equal to 1.3 times the initial concentration of dissolved silica in the fluid. <1> ~ <7> A scaling suppression method described in any one of the following. <9> The first concentration range is greater than 0 mol / L and less than or equal to 0.5 mol / L. <1> ~ <8> A scaling suppression method described in any one of the following. <10> The fluid is a geothermal fluid. <1> ~ <9> A scaling suppression method described in any one of the following. <11> A scale suppression device that suppresses the formation of silica scale in a fluid containing dissolved silica and water, An additive supply unit that supplies an additive to the fluid, which allows for adjustment of the concentration of a target cation in the fluid, A control unit controls the additive supply unit based on a dissolved silica concentration curve that shows the relationship between the concentration of the target cation in a fluid containing dissolved silica and water and the concentration of the dissolved silica in the fluid. Equipped with, The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica increases from the initial concentration of dissolved silica as the concentration of the cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cations increases from the first concentration range. A scale suppression device in which the control unit controls the amount of additive supplied from the additive supply unit to the fluid so that the concentration of the cations in the fluid is within the first concentration range, or within the second concentration range that is equal to or greater than the initial concentration of dissolved silica. <12> The control unit controls the amount of the additive supplied from the additive supply unit into the fluid so that the concentration of the cations in the fluid becomes the maximum value of the dissolved silica concentration curve. <11> A scale suppression device as described above. <13> A cation concentration measuring unit for measuring the concentration of the cations contained in the fluid, An optimal cation concentration calculation unit calculates the concentration of the cations in the dissolved silica concentration curve in the first concentration range or the second concentration range in which the concentration of dissolved silica is equal to or greater than the initial concentration of dissolved silica, based on the measured type of cations and the dissolved silica concentration curve. Equipped with, <11> or <12> A scale suppression device as described above. <14> The system includes a supply amount calculation unit that calculates the amount of additive to be supplied such that the concentration of the cations in the fluid falls within the first concentration range, or within the second concentration range where the concentration of dissolved silica is equal to or greater than the initial concentration of the cations, based on a comparison between the measured value of the cation concentration measured by the cation concentration measuring unit and the calculated value of the cation concentration calculated by the optimal cation concentration calculation unit. <13> A scale suppression device as described above. <15> The supply amount calculation unit calculates the supply amount of the additive such that the concentration of the dissolved silica in the fluid reaches its maximum value within the first concentration range, or within the second concentration range where the concentration of the dissolved silica is equal to or greater than the initial concentration of the dissolved silica. <14> A scale suppression device as described above. <16> The additive is a reagent that generates the cations in the fluid, or a reagent that reacts with the cations in the fluid to reduce the amount of cations in the fluid. <11> ~ <15> A scale suppression device described in any one of the following. <17> A geothermal power generation system that generates electricity using a fluid containing dissolved silica and water, <11> ~ <16> The device comprises a scale suppression device as described in any one of the following: A geothermal power generation system in which the fluid is a geothermal fluid. <18> A fluid utilization system that utilizes a fluid containing dissolved silica and water, A device having a flow path through which the aforementioned fluid flows, <11> ~ <16> A scale suppression device described in any one of the following, A fluid utilization system equipped with the following features. [Explanation of Symbols]

[0115] 1A, 1B Geothermal Power Generation System 2 Production wells 3 Reinforcement well 11 Steam water separator 12 Turbines 13 Generators 14 Condenser 15 Cooling Tower 16 Retention tank 20 Scale suppression device 21 Temperature measurement part 22 pH measuring section 23. Cation concentration measurement section 24 Optimal Cation Concentration Calculation Unit 25 Comparison Section 26 Supply amount calculation section 27 Additive supply unit 28 Control Unit L10, L11, L12, L13, L14, L15 piping M1 First concentration range M2 Second concentration range M21 21st concentration range M22 Concentration range of 22 V11 control valve

Claims

1. A method for suppressing the formation of silica scale in a fluid containing dissolved silica and water, The process includes a cation concentration adjustment step, in which the concentration of the target cation in a fluid containing dissolved silica and water is adjusted based on a dissolved silica concentration curve that shows the relationship between the concentration of the target cation in the fluid and the concentration of the dissolved silica in the fluid. The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica increases from the initial concentration of dissolved silica as the concentration of the cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cations increases from the first concentration range. The cation concentration adjustment step is a scale suppression method in which the concentration of the cations in the fluid is set to a first concentration range, or to a range within the second concentration range that is equal to or greater than the initial concentration of dissolved silica.

2. The scale suppression method according to claim 1, wherein the cation concentration adjustment step adjusts the concentration of the cations in the fluid to the maximum value at which the concentration of dissolved silica in the dissolved silica concentration curve is reached.

3. The cation concentration adjustment step involves supplying an additive into the fluid that allows for adjustment of the concentration of the cations in the fluid. The scale suppression method according to claim 1 or 2, wherein the additive is a reagent that generates the cations in the fluid, or a reagent that reacts with the cations in the fluid to reduce the number of cations in the fluid.

4. A cation concentration measurement step for measuring the concentration of the cations contained in the fluid, An optimal cation concentration calculation step, based on the measured type of cation and the dissolved silica concentration curve, calculates the concentration of the cation within the first concentration range or within the second concentration range where the concentration of dissolved silica is equal to or greater than the initial concentration of the cation in the dissolved silica concentration curve; A method for suppressing scale according to claim 1 or 2, including the method described in claim 1 or 2.

5. The scale suppression method according to claim 1 or 2, wherein the cation is one or more of a monovalent cation, a divalent cation, and an Al ion.

6. The aforementioned monovalent cation is H ＋ Na ＋ Li ＋ _K ＋ and Rb ＋ The scale suppression method according to claim 5, wherein the ions are one or more of the ions.

7. The divalent cation is Be ２＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ and Ba ２＋ The scale inhibition method according to claim 5, which is any one or more ions of

8. The scale suppression method according to claim 1 or 2, wherein the cation concentration adjustment step is to set the concentration of dissolved silica to more than 1.0 times and less than or equal to 1.3 times the initial concentration of dissolved silica in the fluid.

9. The scale suppression method according to claim 1 or 2, wherein the first concentration range is greater than 0 mol / L and less than or equal to 0.5 mol / L.

10. The scale suppression method according to claim 1 or 2, wherein the fluid is a geothermal fluid.

11. A scale suppression device that suppresses the formation of silica scale in a fluid containing dissolved silica and water, An additive supply unit that supplies an additive to the fluid, which allows for adjustment of the concentration of a target cation in the fluid, A control unit controls the additive supply unit based on a dissolved silica concentration curve that shows the relationship between the concentration of the target cation in a fluid containing dissolved silica and water and the concentration of the dissolved silica in the fluid. Equipped with, The dissolved silica concentration curve includes a first concentration range in which the concentration of dissolved silica increases from the initial concentration of dissolved silica as the concentration of the cations increases, and a second concentration range in which the concentration of dissolved silica decreases as the concentration of the cations increases from the first concentration range. A scale suppression device in which the control unit controls the amount of additive supplied from the additive supply unit to the fluid so that the concentration of the cations in the fluid is within the first concentration range, or within the second concentration range that is equal to or greater than the initial concentration of dissolved silica.

12. The scale suppression device according to claim 11, wherein the control unit controls the amount of the additive supplied from the additive supply unit into the fluid so that the concentration of the cations in the fluid becomes the maximum value in the dissolved silica concentration curve.

13. A cation concentration measuring unit for measuring the concentration of the cations contained in the fluid, An optimal cation concentration calculation unit calculates the concentration of the cations in the dissolved silica concentration curve in the first concentration range or the second concentration range in which the concentration of dissolved silica is equal to or greater than the initial concentration of dissolved silica, based on the measured type of cations and the dissolved silica concentration curve. A scale suppression device according to claim 11, comprising:

14. The scale suppression device according to claim 13, further comprising a supply amount calculation unit that calculates the amount of additive to be supplied such that the concentration of the cations in the fluid falls within the first concentration range, or within the second concentration range where the concentration of the dissolved silica is equal to or greater than the initial concentration of the dissolved silica, based on a comparison result between the measured value of the concentration of the cations measured in the cation concentration measuring unit and the calculated value of the concentration of the cations calculated in the optimal cation concentration calculation unit.

15. The scale suppression device according to claim 14, wherein the supply amount calculation unit calculates the supply amount of the additive such that the concentration of the dissolved silica in the fluid reaches its maximum value within the first concentration range or within the second concentration range where the concentration of the dissolved silica is equal to or greater than the initial concentration of the dissolved silica.

16. The scale suppression device according to claim 11 or 12, wherein the additive is a reagent that generates the cations in the fluid, or a reagent that reacts with the cations in the fluid to reduce the cations in the fluid.

17. A geothermal power generation system that generates electricity using a fluid containing dissolved silica and water, A scale suppression device according to claim 11 or 12, A geothermal power generation system in which the fluid is a geothermal fluid.

18. A fluid utilization system that utilizes a fluid containing dissolved silica and water, A device having a flow path through which the aforementioned fluid flows, A scale suppression device according to claim 11 or 12, A fluid utilization system equipped with the following features.

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