pH estimation device and pH estimation method for silica-supersaturated fluid

Abstract

In the present invention, the pH of a fluid is estimated without using a pH gauge.　Provided is a pH estimation system 10 for a silica-oversaturated fluid, said system comprising: a first flow path L1 which is branched from a pipe 20, through which a silica-containing fluid flows, and extracts a portion of the fluid; a first measurement part 1 which is connected to the first flow path via an open / close valve B2; a retention section L2 which is connected to the first flow path; a second flow path L3 which is connected to the retention section and returns the fluid to the pipe; a second measurement part 2 which is connected to the second flow path via an open / close valve B3; and a calculation device 3 which is electrically connected to the first measurement part and the second measurement part. The first measurement part and the second measurement part comprise a fluid temperature measurement device and a silica concentration measurement device; and the calculation device stores a silica concentration reduction rate, a silica saturation concentration, and a temperature-pH relational expression and calculates the pH of the fluid on the basis of measurement results obtained at the first measurement part and the second measurement part and the relational expression.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for estimating the pH of a silica-supersaturated fluid. [Background technology]

[0002] Conventionally, scale deposition has been a problem in systems that include a fluid distribution system, such as power plants, ship systems, boiler systems, and steel plants. In particular, silica-based scale deposition is a problem in systems that utilize geothermal fluids, such as geothermal power plants. In order to suppress silica scale deposition, attempts have been made in various plants to measure the silica concentration in the fluid and to control the generation and adhesion of scale based on this measurement.

[0003] An automatic geothermal steam well component analyzer is known that measures the silica content or electrical conductivity of sample water obtained from two-phase fluid extracted from the steam well, and that has an air or nitrogen gas bubbling tank in the front stage (see, for example, Patent Document 1). Patent Document 1 discloses that the silica concentration and electrical conductivity can be measured by automatically analyzing the components in the steam at the outlet of the steam turbine.

[0004] A method is known in which, for the purpose of suppressing damage caused by scale deposition, a coloring reagent whose absorbance in the ultraviolet-visible region varies with pH fluctuations is added to test water collected from boiler water, the absorbance is measured, and the pH of the test water is determined based on the absorbance (see, for example, Patent Document 2). Patent Document 2 discloses that the pH of highly alkaline boiler water can be measured without using a glass electrode pH meter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-250760 [Patent Document 2] Patent Publication No. 2021-67430 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology disclosed in Patent Document 1, the silica content is automatically measured by sampling the steam at the outlet of the steam turbine in a geothermal power plant. However, because silica that adheres to the steam turbine before reaching the outlet is not included in the measurement, the silica content is underestimated and cannot be said to be an accurate measurement. It has become clear that various factors are involved in the formation of silica scale. While the silica concentration in a fluid is an important factor in scaling, the pH of a fluid containing silica is also an important factor.

[0007] Commonly used pH meters are made up of porous glass electrodes, which means that their heat resistance temperature is low (approximately 80°C or less), and there is a risk that the electrode will dissolve if a pH meter measures an alkaline fluid with a pH of 8 or higher.

[0008] Furthermore, when high-temperature silica-supersaturated fluids are measured with commercially available pH meters, there is the problem that accurate responses cannot be expected due to the buildup of scale on the porous glass electrode.When using a pH meter for automatic measurement of the pH of silica-supersaturated fluids, a dedicated system with measures to prevent scale formation is required to improve the measurement accuracy of the pH meter, which incurs additional costs.

[0009] Patent Document 2 describes a technique in which a pH indicator reagent is mixed with test water and the pH is measured based on the absorbance of the resulting mixture, but this is a relatively complicated method. Furthermore, since geothermal water is composed of multiple components rather than a single component, the color development of the pH indicator reagent may be inhibited, potentially making accurate measurements impossible. Furthermore, scale may build up on transparent quartz cells used to measure absorbance, potentially making accurate measurements impossible.

[0010] The inventors have experimentally and theoretically investigated the deposition of scale caused by silica polymerization in a silica-supersaturated fluid, and established a formula for predicting silica precipitation accompanying the time-dependent silica polymerization reaction. They then discovered a system and method for accurately measuring the pH of a silica-supersaturated fluid based on the measured values ​​of the silica concentration and temperature in the silica-supersaturated fluid and the previously obtained relationships between the rate of decrease of the silica concentration in the fluid, the silica saturation concentration, the temperature, and the pH, and thus completed the present invention.

[0011] According to one embodiment, the present invention provides a system for estimating pH of a silica-supersaturated fluid, comprising: a first flow path branching from a pipe through which a silica-containing fluid flows and extracting a portion of the fluid; a first measuring unit connected to the first flow path via an on-off valve; a retention section connected to the first flow path; a second flow path connected to the retention portion and returning the fluid to the piping; a second measurement unit connected to the second flow path via an on-off valve; a computing device electrically connected to the first measurement unit and the second measurement unit; Equipped with the first measurement unit and the second measurement unit include a fluid temperature measurement device and a silica concentration measurement device, The calculation device stores a relational expression between the rate of decrease in silica concentration of the fluid, the silica saturation concentration, the temperature, and the pH, and is provided with a means for calculating the pH of the fluid based on the measurement results in the first measurement unit and the second measurement unit and the relational expression.

[0012] The pH estimation system preferably includes a temperature maintaining device for the first flow path, the stagnation section, and the second flow path.

[0013] The pH estimation system preferably includes a cooler upstream of the first flow path.

[0014] According to another embodiment, the present invention relates to a geothermal power generation facility including a piping through which a geothermal fluid flows and a power generation device that generates electricity by rotating a steam turbine using steam contained in the geothermal fluid, and including any of the pH estimation systems described above attached to the piping through which the geothermal fluid flows at the inlet of the steam turbine.

[0015] According to another aspect, the present invention provides a method for estimating pH of a silica-supersaturated fluid flowing through a flow path, comprising: measuring a first silica concentration and a first temperature of the silica-supersaturated fluid at a first measurement point in the flow path; measuring a second silica concentration and a second temperature of the silica-supersaturated fluid that reaches a second measurement point downstream of the first measurement point in the flow path; obtaining a rate of decrease in the silica concentration of the fluid from the measurement time difference between the first measurement point and the second measurement point, the first silica concentration, and the second silica concentration; obtaining the pH of the silica-supersaturated fluid based on the previously obtained relationship between the rate of decrease in the silica concentration of the fluid, the silica saturation concentration, the temperature, and the pH; This relates to a pH estimation method, including:

[0016] In the pH estimation method, the step of obtaining the pH is carried out by using a silica precipitation prediction formula dC / dt=-k(C t -C e ) n (where k is the reaction rate constant of the silica polymerization reaction, C t is the silica concentration of the fluid at time t, and C e is the silica saturation concentration, and n is an integer from 1 to 5. It is preferable to use

[0017] In the pH estimation method, it is preferable that the measurement time difference between the first measurement point and the second measurement point is 5 minutes or more. [Effects of the Invention]

[0018] The pH estimation system and method according to the present invention can estimate the pH of a fluid based on the measured values ​​of the silica concentration and temperature of the fluid without using a pH meter. This makes it possible to accurately obtain the pH of a fluid in a facility such as a plant through which a silica-supersaturated fluid flows. This makes it possible to obtain information useful for inhibiting silica scale in a simple and economical manner. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram conceptually showing a pH estimation system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic graph showing the silica deposition prediction formula. [Figure 3] FIG. 3 is a graph showing the relationship between temperature and dissolved silica concentration at acidic, neutral, and alkaline pH. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to the embodiments described below.

[0021] According to one embodiment, the present invention relates to a pH estimation system and method for estimating the pH of a silica-supersaturated fluid, the pH estimation system comprising: a first flow path branching from a pipe through which a silica-containing fluid flows and extracting a portion of the fluid; a first measuring unit connected to the first flow path via an on-off valve; a retention section connected to the first flow path; a second flow path connected to the retention portion and returning the fluid to the piping; a second measurement unit connected to the second flow path via an on-off valve; a computing device electrically connected to the first measurement unit and the second measurement unit; Equipped with.

[0022] The pH estimation system and method according to this embodiment relate to a system and method for estimating the pH of a fluid sample to be measured, based on a calculation formula and accumulated data, from the fluid temperature and silica concentration at two or more measurement points in the fluid, without directly measuring the pH of the fluid.

[0023] In this embodiment, the fluid to be measured is a silica-supersaturated fluid. More specifically, the fluid contains silica in excess of its solubility at the fluid temperature, and is composed of Si(OH)4, Si(OH)3O. - , SiO2(OH)2 2- , Si2O2(OH)5 - , and / or Si2O3(OH)4 2- The term "fluid" refers to a fluid containing Si- and OH-containing species, including but not limited to, and may refer to a liquid such as water, or a substance that forms a two-phase flow, which is a mixture of a liquid such as water and a gas such as steam.

[0024] The silica-supersaturated fluid to be measured may also be a fluid flowing through a plant. The plant is a plant where a fluid containing silica flows and where the adhesion of silica scale can cause the plant to shut down or malfunction. Examples of plants include, but are not limited to, geothermal power plants, boiler systems, systems equipped with cooling water piping, and water treatment systems. Note that the fluid flowing through the plant does not necessarily have to be a silica-supersaturated fluid. If the fluid flowing through the plant is a fluid that does not reach supersaturation, the temperature of the fluid can be lowered by a cooler optionally provided in the pH estimation system according to this embodiment, and the fluid can then be made into a supersaturated state before being used as a measurement target. Details will be described later.

[0025] The present invention will be described below using a geothermal fluid flowing through a geothermal power plant as an example, but the present invention is not limited to estimating the pH of geothermal fluid. Figure 1 is a conceptual diagram of a pH estimation system according to a first embodiment. The pH estimation system 10 shown in Figure 1 mainly includes a first flow path L1, a retention section L2, a second flow path L3, a first measurement section 1, a second measurement section 2, and a calculation device 3.

[0026] The pH estimation system 10 according to this embodiment can be configured with a flow path branched from a pipe 20 through which a silica-supersaturated fluid flows, and a unit for measuring the physical properties of the fluid flowing through the flow path. Hereinafter, the silica-supersaturated fluid will be abbreviated to "fluid." The pipe 20 may be any pipe and is not particularly limited. In a geothermal power generation facility, the pipe 20 may be a pipe at a location where it is beneficial to obtain the pH of the fluid, and in particular, the pipe may be a pipe upstream of a steam turbine.

[0027] The first flow path L1 is a pipe that branches off from the pipe 20 and introduces a portion of the fluid flowing through the pipe 20 into the pH estimation system 10. The first flow path L1 only needs to be able to send a portion of the fluid flowing through the pipe 20 to the subsequent first measurement unit 1 while maintaining the temperature, and may be a pipe made of a metal such as carbon steel or stainless steel.

[0028] The diameter of the first flow path L1 is not particularly limited, but may be, for example, an outer diameter of 2 to 12.7 mm, which may be the same diameter as the retention section L2 described below. An inlet valve B1 may be provided at the inlet of the first flow path L1, i.e., between the piping 20 and the first flow path L1. This allows a configuration in which a portion of the fluid flowing through the piping 20 flows into the first flow path L1 only when the valve B1 is in an open state. The length of the first flow path L1 is defined as the distance from the inlet valve B1 to the valve B2 at the inlet of the first measurement section 1. The length of the first flow path L1 is not particularly limited, but it is preferable to keep the length of the flow path as short as possible to suppress heat radiation from the flow path and minimize temperature drop. For example, it may be 0.1 to 1 m.

[0029] The first measurement unit 1 measures the temperature and silica concentration of the fluid at the inlet of the pH estimation system 10. The first measurement unit 1 is connected to the first flow path L1 via valve B2. When valve B2 is open, a portion of the fluid extracted from the pipe 20 is sent to the first measurement unit 1, where the temperature and silica concentration of the fluid can be measured. Before measurement, valves B1 and B4 are opened to allow the fluid to flow. After the flow stabilizes, B2 is opened and the fluid is sampled. After a predetermined amount of fluid has been sampled, B2 is closed. The amount of fluid required for measurement in the first measurement unit 1 can be 5 to 10 mL, depending on the configuration of the first measurement unit 1.

[0030] The first measurement unit 1 includes a thermometer for measuring a first temperature T0 of the fluid. It is preferable to measure the temperature of the fluid without contacting the fluid; for example, it is preferable to measure the temperature of a sampled fluid from outside the container. This is to eliminate the effect of scale formation on the thermometer. Alternatively, a thermometer may be inserted into the sampled fluid to directly measure the temperature of the fluid. In this case, it is preferable to provide a washable configuration for the part of the thermometer that comes into contact with the fluid to prevent scale buildup. The first measurement unit 1 also includes an online silica concentration measurement device for measuring a first silica concentration C0 of the fluid. The online silica concentration measurement device may be configured as an automatic silica concentration measurement device using the molybdenum yellow method. The automatic silica concentration measurement device may be, for example, a device manufactured by Mettler-Toledo, but is not limited to a specific device.

[0031] It is desirable to provide a waste tank within the online silica concentration measuring device for storing the fluid used to measure the temperature and silica concentration in the first measurement section 1, and to collect and finally dispose of the fluid in accordance with regulations during plant or equipment maintenance. In the pH estimation method described below, the first measurement section 1 can be considered as the first measurement point for obtaining the first silica concentration C0 and first temperature T0.

[0032] The retention section L2, branching from the first flow path L1, is a relatively long flow path located between the first flow path L1 and the second flow path L3. The retention section L2 is provided for the purpose of increasing the time interval Δt, preferably 5 minutes or more, for the fluid Fs extracted from the piping 20 from the first measurement section 1 to the second measurement section 2. The type and diameter of the piping constituting the retention section L2 may be the same as those of the piping constituting the first flow path L1, and it is preferable that the piping be made of a material that is resistant to scale deposition and heat resistant. The structure of the retention section L2 is not particularly limited as long as it can ensure the above-mentioned time interval Δt, but it can be, for example, a spiral structure (also referred to as a loop structure). By making the retention section L2 a spiral structure, the flow path length can be ensured, and the pH estimation system 10 can be made compact. The length of the retention section L2 is also not particularly limited as long as it can ensure the above-mentioned time interval Δt, but it can be, for example, approximately 3 to 300 m.

[0033] The second flow path L3 is a flow path that returns the fluid Fs flowing through the first flow path L1 and the retention section L2 to the pipe 20 through which the silica-supersaturated fluid flows. The preferred type, diameter, and length of the pipe constituting the flow path may be the same as those of the first flow path L1. The second flow path L3 is connected to the pipe 20 through which the silica-supersaturated fluid flows, and a valve B4 is provided at the outlet of the second flow path L3. The connection position between the second flow path L3 and the pipe 20 is preferably downstream of the connection position between the first flow path L1 and the pipe 20 in the flow of the fluid F flowing through the pipe 20.

[0034] The second measurement unit 2 measures the temperature and silica concentration of the fluid Fs that flows through the retention unit L2 and enters the second flow path L3, i.e., the temperature and silica concentration of the fluid Fs at the outlet of the pH estimation system 10. The second measurement unit 2 is connected to the second flow path L2 via valve B3. When valve B3 is open, a portion of the fluid that flows through the retention unit L2 is sent to the second measurement unit 2, where the temperature and silica concentration of the fluid can be measured. The sampling operation can be the same as that of the first measurement unit. Therefore, before measurement, valves B1 and B4 are opened to allow the fluid to flow. After the flow stabilizes, B3 is opened to sample the fluid. After sampling of a predetermined amount of fluid is completed, B3 is closed. The amount of fluid required for measurement in the second measurement unit 2 can also be the same as that in the first measurement unit 1.

[0035] The calculation device 3 stores the previously obtained relationship between the rate of decrease of the silica concentration of the fluid, the silica saturation concentration, the temperature, and the pH, and calculates the pH of the fluid based on the measurement results from the first measurement unit 1 and the second measurement unit. The calculation device 3 may be, for example, a computer, but is not limited to a specific device. The calculation device 3 is electrically connected to the first measurement unit 1 and the second measurement unit 2 in a manner that allows it to receive data on the silica concentration and temperature from the first measurement unit 1 and the second measurement unit 2. The calculation device 3 can optionally function as a display device that displays the estimated pH result, and may be configured to allow the estimated pH result to be monitored.

[0036] The temperature maintaining device 4 covers at least the periphery of the first flow path L1, the retention portion L2, and the second flow path L3 to prevent a drop in the temperature of the fluid passing through these flow paths. The temperature maintaining device 4 may be a heat insulating material provided around each flow path, or may be a device such as a constant temperature bath that heats or cools the flow paths from the outside to maintain a specific temperature.

[0037] According to an embodiment, the pH estimation system 10 may include a cooler (not shown) at the inlet of the first flow path L1. The cooler may be any cooler capable of lowering the temperature of the fluid flowing through the first flow path L1. When the fluid flowing through the pipe 20 is not in a silica-supersaturated state, the fluid temperature can be lowered to generate a pseudo-silica-supersaturated fluid, enabling pH estimation. When the pH estimation system 10 includes a cooler, the system may be configured to control the temperature after cooling based on the temperature measurement results in the first measurement unit 1, and may include a control device.

[0038] According to another embodiment, the pH estimation system 10 can be removably installed in the pipe 20 through which the silica-supersaturated fluid flows. In this case, the pipe 20 through which the silica-supersaturated fluid flows can be provided with a port communicating with the first flow path and a port communicating with the second flow path. Therefore, it is possible to measure the pH in any pipe provided with such ports within the geothermal power generation facility.

[0039] According to yet another embodiment, the pH estimation system 10 may further include an additional measurement unit and an additional retention unit. For example, instead of the retention unit L2 shown in the figure, a first retention unit connected to the first flow path L1, a second retention unit downstream of the first retention unit and connected to the second flow path L3, and a third measurement unit connected to the second retention unit so as to be able to measure the temperature and silica concentration of the fluid between the first retention unit and the second retention unit may be provided. A similar configuration may also be provided with three retention units and two additional measurement units, or more retention units and additional measurement units. Providing multiple measurement units has the advantage of improving the accuracy of the pH estimation method described below.

[0040] Next, the invention according to the first embodiment will be described from the viewpoint of a pH estimation method. The pH estimation method according to this embodiment is a method for estimating the pH of a silica-supersaturated fluid flowing through a flow path, and includes the following steps. (1) measuring a first silica concentration and a first temperature of the silica-supersaturated fluid at a first measurement point in the flow path; (2) measuring a second silica concentration and a second temperature of the silica-supersaturated fluid that has reached a second measurement point downstream of the first measurement point in the flow path; (3) A step of obtaining a rate of decrease in silica concentration from the measurement time difference between the first measurement point and the second measurement point, the first silica concentration, and the second silica concentration. (4) A step of obtaining the pH of the silica-supersaturated fluid based on the previously obtained relationship between the rate of decrease in silica concentration, the silica saturation concentration, the temperature, and the pH.

[0041] The pH estimation method according to this embodiment is based on the experimental fact and theoretical basis that in a fluid supersaturated with silica, the silica polymerization reaction progresses over time, causing the silica concentration in the fluid to decrease, and the rate of decrease depends on the temperature and pH. If the temperature can be maintained constant and the change in silica concentration over time and the temperature can be measured, the pH can be estimated based on the silica precipitation prediction equation experimentally established by the inventors.

[0042] The pH estimation method according to this embodiment uses the following silica precipitation prediction formula (formula (I)) and the formula for the reaction rate constant k (formula (II)). dC / dt=-k(C t -C e ) n (I) (where k is the reaction rate constant of the silica polymerization reaction, C t is the silica concentration of the fluid at time t, and C e is the silica saturation concentration, and n is an integer from 1 to 5. k=A·exp(-E a / RT) (II) where A is the frequency factor and E a is the activation energy, R is the gas constant, and T is the silica polymerization reaction temperature, which is the temperature of the fluid exemplified by geothermal water.

[0043] Figure 2 is a graph that shows a schematic representation of the silica precipitation prediction formula (formula (I)) when the temperature T is constant, and is a graph in the case of n=2. The prediction curves for acidic, neutral, and alkaline conditions are experimentally derived curves, and the value of k varies depending on the pH. Figure 2 shows that in a silica-supersaturated fluid, the silica concentration C0 at time t=0 and the silica concentration C at time t after Δt have elapsed t By measuring the rate of decrease in silica concentration, expressed as dC / dt, the decrease rate varies depending on the pH. Referring to the definition formula of the reaction rate constant k (Equation (II)), the frequency factor A and the activation energy E a Since is a value that depends on pH, it can be understood theoretically that the reaction rate constant k in equation (I) is a term that depends on pH. The frequency factor A can be calculated by fitting, and E a can be theoretically calculated from elementary reactions. An elementary reaction refers to each reaction in the process of silica scaling during the silica polymerization reaction. For example, the reaction in which monomeric silica grows into tetrameric silica is a combination of the following reactions: Monomer + Monomer → Dimer, Monomer + Dimer → Trimer, Monomer + Trimer → tetramer, Dimer + Dimer → tetramer. Each reaction is an elementary reaction. Monomeric silica is defined as a structure with one Si atom, and dimeric silica is defined as a structure with two Si atoms.

[0044] 2 shows a schematic representation of silica precipitation prediction curves for three typical pH values: acidic, neutral, and alkaline, but in practice, it is preferable to experimentally obtain silica precipitation prediction curves in advance at pH increments of, for example, 0.1 in the range of 5.5 to 9. Similarly, it is preferable to experimentally obtain silica precipitation prediction curves in advance at temperature increments of, for example, 15°C in the range of 25°C to 200°C.

[0045] In addition, in formula (I), C eis the silica saturation concentration, which is also a value that depends on pH and temperature. The temperature dependency of the silica saturation concentration can also be experimentally obtained in advance. FIG. 3 is a graph showing the relationship between the temperature and the dissolved silica concentration (saturation concentration) of a fluid in acidic, neutral, and alkaline conditions. The plots in the graph are examples of experimental data and represent a predicted curve for the temperature dependency of the silica saturation concentration. It is also preferable to experimentally obtain in advance the predicted curve for the silica saturation concentration, for example, in the pH range of 5.5 to 9, for example, in increments of 0.1.

[0046] Each step will be explained below using the pH estimation system shown in Figure 1. However, the above steps are not necessarily limited to the method performed using the pH estimation system shown in Figure 1.

[0047] In step (1), a first silica concentration C0 and a first temperature T0 of the silica-supersaturated fluid are measured at a first measurement point in the flow path. The measurement of the first silica concentration and the measurement of the first temperature can be performed by a first measurement unit 1 shown in FIG. 1. The obtained measured values ​​can be electrically transmitted to a calculation device 3.

[0048] Before carrying out step (1), a step of obtaining a silica-supersaturated fluid may be carried out as a preparatory step. For example, if the silica-containing fluid is undersaturated, the temperature of the fluid can be lowered to bring it into a pseudo-supersaturated state before measurement.

[0049] In step (2), a second silica concentration C of the silica-supersaturated fluid that has reached a second measurement point downstream of the first measurement point in the flow path is measured. t and the second temperature T tis measured. The time required for the fluid to travel from the first measurement point to the second measurement point can also be considered as the measurement time difference between the first and second measurement points, and is represented as Δt. Δt can vary depending on the shape and pressure of the flow path, so it is preferable to obtain it in advance through a preliminary experiment or calculation. It is preferable to determine the first and second measurement points so that Δt is 5 minutes or more, and when using the device shown in Figure 1, it is preferable to design the flow path length of the retention section L2 so that Δt is 5 minutes or more. The reason for setting Δt in this manner is that in the pH estimation method of this embodiment, the silica concentration reduction rate is used as one of the parameters and estimation is performed based on this, so the silica polymerization reaction changes abruptly and the difference in parameters is easy to grasp. Second silica concentration C t and the second temperature T t The measurement method can be the same as that of step (1), and can be performed by the second measurement unit 2 shown in Figure 1. The obtained measured value can be electrically transmitted to the calculation device 3.

[0050] In carrying out the method of the present invention, the temperature of the fluid to be measured for silica concentration and temperature is kept constant. More specifically, the temperature of the fluid is kept constant from the time it passes through the first measurement point until it reaches the second measurement point. When the apparatus shown in FIG. 1 is used, the temperature of the first flow path L1, the retention section L2, and the second flow path L3 can be kept constant by the temperature maintaining device 4. In steps (1) and (2), the first temperature T0 and the second temperature T t is measured, but it is a confirmatory measurement, and T0 = T t It is preferable to control the temperature of the fluid so that

[0051] In step (3), the rate of decrease in silica concentration is obtained from the measurement time difference between the first measurement point and the second measurement point, the first silica concentration, and the second silica concentration. The rate of decrease in silica concentration is expressed as dC / dt, and is calculated by multiplying C0 obtained in step (1) and C1 obtained in step (2). t The rate of decrease in silica concentration can be obtained by calculation using Δt.

[0052] In step (4), the pH is calculated based on the previously obtained relationship between the rate of decrease in the silica concentration, the silica saturation concentration, the temperature, and the pH. More specifically, step (4) includes step (a) of inputting the calculation result of step (3) into a silica precipitation prediction formula, step (b) of calculating values ​​of a reaction rate constant k and a silica saturation concentration Ce that fit the silica precipitation prediction formula, and step (c) of extracting the pH that gives the calculated reaction rate constant k and silica saturation concentration Ce.

[0053] In step (a), the value of dC / dt obtained in step (3) and the second silica concentration C obtained in step (2) are added to formula (I). t The value n can be calculated using an integer between 1 and 5, and it is preferable to set n=2.

[0054] In step (b), dC / dt and C t For the entered formula (I), the values ​​of k and Ce are varied and calculations are performed to calculate the values ​​of k and Ce that satisfy formula (I). The temperature T in the reaction rate constant k is calculated based on the measured first temperature T0 (second temperature T t Once the temperature is determined, k and Ce can be determined experimentally for each pH.

[0055] In step (c), dC / dt and C t For equation (I) into which the above equations have been input, the pH that gives the reaction rate constant k and silica saturation concentration Ce calculated in step (b) is extracted. The data to be extracted can be the predicted curve of pH and temperature dependence of silica saturation concentration obtained in advance, as shown in Figure 3.

[0056] In the estimation method according to this embodiment, steps (3) and (4) can be considered as a pH estimation program, and the present invention includes the following. A program for estimating the pH of a silica-supersaturated fluid flowing through a flow path, comprising: acquiring a first silica concentration and a first temperature of the silica-supersaturated fluid at a first measurement point in a flow path through which the silica-supersaturated fluid flows; acquiring a second silica concentration and a second temperature of the silica-supersaturated fluid that has reached a second measurement point downstream of the first measurement point in the flow path; obtaining a rate of decrease of the silica concentration from the measurement time difference between the first measurement point and the second measurement point, the first silica concentration, and the second silica concentration; obtaining the pH of the silica-supersaturated fluid based on the previously obtained relationship between the rate of decrease of the silica concentration, the silica saturation concentration, the temperature, and the pH; A pH estimation program that runs on a computer. The operation of each step is as described in the pH estimation method.

[0057] According to the pH estimation method of this embodiment, the silica concentration and temperature of the silica-supersaturated fluid are measured at two locations, thereby making it possible to obtain the pH of the silica-supersaturated fluid.

[0058] [Second embodiment: geothermal power generation facility] According to a second embodiment, the present invention relates to a geothermal power generation facility. The geothermal power generation facility includes a piping through which a geothermal fluid flows, a power generation device that generates electricity by rotating a steam turbine using steam contained in the geothermal fluid, and the pH estimation system according to the first embodiment is attached to the piping through which the geothermal fluid flows at an inlet of the steam turbine.

[0059] A geothermal power generation facility is a facility that generates electricity using geothermal fluid as a power source, and mainly comprises a production well, a steam separator, a steam turbine, a reinjection well, and piping connecting these through which geothermal fluid flows. In a geothermal power generation facility according to a second embodiment, the pH estimation system according to the first embodiment is connected to the piping. Preferably, the facility is located upstream of the steam turbine, and the pH estimation system according to the first embodiment is connected to the piping that supplies geothermal fluid to the steam turbine.

[0060] This section explains the flow of geothermal fluid in a geothermal power generation system. A production well is a well that ejects geothermal fluid, which is hot water, steam, or a mixture of these, from an underground geothermal reservoir onto the surface. The geothermal fluid ejected from the production well is separated into gaseous steam and liquid hot water in a steam separator. The separated steam is led to a steam turbine and used to rotate the turbine, producing electricity in a generator. The steam that has done work in the turbine is cooled and condensed and sent to a cooling tower. Meanwhile, the hot water separated in the steam separator is returned to the injection well via a heat exchanger, a hot water pit, etc.

[0061] In the case of a binary power generation system, a second steam separator is provided downstream of the steam separator, and the steam separated in the second steam separator heats a low boiling point medium. The heated low boiling point medium is used to rotate the second turbine. The low boiling point medium is used by repeating evaporation and condensation while circulating, and the hot water separated in the steam separator may also be used to heat the low boiling point medium. The geothermal power generation facility according to this embodiment describes a configuration common to both a binary power generation system and a system that operates a turbine using only geothermal steam, and both the binary power generation system and the system that operates a turbine using only geothermal steam are considered to fall within the scope of the present invention.

[0062] The geothermal power generation facility according to the second embodiment of the present invention is equipped with the pH estimation system shown in Figure 1, and when information about the pH of the geothermal fluid is needed, valves B1 and B4 can be opened to estimate the pH. This allows the pH of the geothermal fluid in the geothermal power generation facility to be accurately determined, and the necessary operations to suppress the deposition of silica scale can be carried out. [Explanation of symbols]

[0063] L1: First flow path, L2: Retention area, L3: Second flow path B1, B2, B3, B4 valves 1 1st measurement section, 2 2nd measurement section, 3 calculation device, 4 temperature maintenance device 10 pH estimation systems, 20 piping F fluid, Fs fluid extracted from the pipe

Claims

1. 1. A system for estimating pH of a silica-supersaturated fluid, comprising: a first flow path branching from a pipe through which a silica-containing fluid flows and extracting a portion of the fluid; a first measuring unit connected to the first flow path via an on-off valve; a retention section connected to the first flow path; a second flow path connected to the retention portion and returning the fluid to the piping; a second measuring unit connected to the second flow path via an on-off valve; a computing device electrically connected to the first measurement unit and the second measurement unit; Equipped with the first measurement unit and the second measurement unit include a fluid temperature measurement device and a silica concentration measurement device, The calculation device is configured to store a relational expression between the rate of decrease of the silica concentration of the fluid, the silica saturation concentration, the temperature, and the pH, and to calculate the pH of the fluid based on the measurement results in the first measurement unit and the second measurement unit and the relational expression.

2. The pH estimation system according to claim 1 , further comprising a temperature maintaining device for the first flow path, the retention section, and the second flow path.

3. The pH estimation system according to claim 1 , further comprising a cooler provided upstream of the first flow path.

4. A pipe through which geothermal fluid flows; a power generation device that generates electricity by rotating a steam turbine using steam contained in the geothermal fluid; Including, A geothermal power generation facility comprising the pH estimation system according to claim 1 , which is attached to a pipe through which geothermal fluid flows at an inlet of the steam turbine.

5. A method for estimating pH of a silica-supersaturated fluid flowing through a flow path, comprising: measuring a first silica concentration and a first temperature of the silica-supersaturated fluid at a first measurement point in the flow path; measuring a second silica concentration and a second temperature of the silica-supersaturated fluid that reaches a second measurement point downstream of the first measurement point in the flow path; obtaining a rate of decrease of the silica concentration from the measurement time difference between the first measurement point and the second measurement point, the first silica concentration, and the second silica concentration; obtaining the pH of the silica-supersaturated fluid based on the previously obtained relationship between the rate of decrease of the silica concentration, the silica saturation concentration, the temperature, and the pH; A method for estimating pH, comprising:

6. The step of obtaining the pH is carried out by using a silica precipitation prediction formula dC / dt=-k(C ｔ -C ｅ ) ｎ (where k is the reaction rate constant of the silica polymerization reaction, C ｔ is the silica concentration of the fluid at time t, and C ｅ is the silica saturation concentration, and n is an integer from 1 to 5. The pH estimation method according to claim 5, wherein

7. The pH estimation method according to claim 5, wherein the measurement time difference between the first measurement point and the second measurement point is 5 minutes or more.

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