Scale generation evaluation method and scale generation evaluation device

Abstract

To provide a scale generation evaluation method and a scale generation evaluation device that can detect a scale in a shorter time and evaluate the scale generation state.SOLUTION: A scale generation evaluation device has a light source 12 which has light with a predetermine-bandwidth wavelength, and an optical fiber 14 which has one end connected to the light source 12 and through which the light from the light source 12 is transmitted. The scale generation evaluation device comprises a surface plasmon resonance scale sensor 16 which is exposed with a noble metal thin-film layer 18 formed on the core surface having the clad removed in part in the middle or at the end of the optical fiber 14. The scale generation evaluation device comprises a spectrum analysis device 20 which detects a spectrum of the light passed through the surface plasmon resonance scale sensor 18 of the optical fiber 14. The spectrum analysis device 20 detects temporal change in spectrum of the light transmitted from the light source 12 to the optical fiber 14 to enable the generation state of a scale 30 to be evaluated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates to a surface plasmon resonance (SPR) detector using an optical fiber. This invention relates to a scale formation evaluation method and a scale formation evaluation device that evaluate the state of scale formation adhering to pipes, etc., using a SPR (Surface Pressure Resonance) sensor. [Background technology]

[0002] In equipment that uses groundwater or hot spring water, such as boilers, heat exchangers, and hot spring facilities, scale formed by the deposition of inorganic components in the water adheres to and accumulates on the inner walls of pipes, the inner surfaces of water pipes in heat exchangers, etc. In particular, in facilities that use geothermal water, such as geothermal power plants and hot spring facilities, inorganic salts dissolved in the geothermal fluid become supersaturated due to changes in temperature, pH, and pressure, and are prone to depositing as scale inside the pipes.

[0003] For example, calcium carbonate scale is 2+ or HCO3 - The dissolved CO2 in hot water, which contains a lot of ions, moves to the vapor phase through gas-liquid separation, causing an increase in the pH of the hot water, which reduces the solubility of carbonate minerals and causes them to precipitate as scale. Silica scale also precipitates as silica becomes concentrated in the hot water due to gas-liquid separation in the production wells of geothermal power plants, resulting in supersaturation. When this scale precipitates in pipes or in the piping of heat exchangers, it can cause many problems, such as reduced flow rate due to blockage of piping, reduced heat exchange efficiency, and equipment failure.

[0004] Many research proposals have been made on measures to prevent scale formation, but determining the conditions for preventing scale formation required test periods of several days to several months. Previous evaluation methods, for example, involved immersing a glass plate or metal piece in hot water and evaluating the weight change associated with scale formation or visual inspection. Other evaluation tests have involved filling a metal column (cylinder) with rocks or glass beads and passing hot water through it to measure the change in water flow due to clogging. However, these conventional methods have problems such as high testing costs and a lack of simplicity. Furthermore, in order to investigate effective methods for preventing scale formation, a rapid, real-time method for evaluating scale formation is required.

[0005] Meanwhile, as shown in Patent Document 1, a method for quantitatively evaluating calcium carbonate scale has been proposed in which a device capable of localized heating is heated for a certain period of time, then removed from the target water, dried, and weighed using an electronic balance or the like to detect the adhesion of scale. Patent Document 1 further discloses a scale detection method that utilizes a quartz crystal microbalance (QCM) method to immerse a mass change detection device, which has electrodes formed on both sides of a thin piece of quartz, in the target water and measure changes in resonance frequency due to scale adhesion to the electrode surfaces of the mass change detection device.

[0006] In addition, as disclosed in Non-Patent Document 1 by the present inventors, a scale sensor using an optical fiber made of quartz or plastic has been proposed for evaluation of scale formation and evaluation tests of prevention conditions. An optical fiber has a three-layer structure of a jacket, a cladding, and a core, and light propagates while being totally reflected in the core. This scale sensor utilizes the fact that the jacket and cladding of the optical fiber are removed, the core is exposed, and it is immersed in hot water, and scale with a refractive index larger than that of the core is precipitated on the core surface, inhibiting total reflection and reducing the amount of light propagated. By using this sensor, scale formation can be evaluated in a few hours to a few days, and scale formation can be evaluated in about the same time as the QCM method. A silica-core optical fiber with excellent heat and pressure resistance is used as the optical fiber used as the scale sensor, and this scale sensor has been used to monitor calcium carbonate and silica scale precipitated from hot water in various facilities that handle geothermal water. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-27961 A [Non-patent literature]

[0008] [Non-Patent Document 1] Okazaki et al. Investigation of the effects of electromagnetic field treatment of hot spring water for scale inhibition using a fiber optic sensor. SCIENTIFICREPORTS.(2019)9:10719 https: / / doi.org / 10.1038 / s41598-019-47088-6 Summary of the Invention [Problem to be solved by the invention]

[0009] In the case of the scale evaluation method disclosed in the above Patent Document 1, a long time of several hours to half a day is required to perform a sufficient evaluation. In addition, the scale sensor using optical fiber disclosed in the above Non-Patent Document 1 utilizes the phenomenon that the refractive index of the surface changes when the core part of the optical fiber is immersed in the target hot water and scale adheres to the surface, and the light transmitted through the sensor is attenuated. Therefore, when silica scale is the target, the sensitivity is poor because the refractive index of the precipitated scale is close to that of the optical fiber, and a long measurement time is required. Even when this optical fiber scale sensor is used, it takes about half a day to perform a sufficient evaluation. Therefore, conventional scale sensors have a long measurement time, and a scale detection method that is closer to real time is required.

[0010] The present invention has been made in consideration of the above-mentioned conventional background technology, and has an object to provide a scale formation evaluation method and a scale formation evaluation device that can detect scale in a shorter time and accurately evaluate the state of scale formation. [Means for solving the problem]

[0011] This invention is a scale formation evaluation method for evaluating the state of scale formation, which uses a light source that emits light of a wavelength within a predetermined bandwidth, an optical fiber having one end connected to the light source and through which light from the light source passes, and a surface plasmon resonance scale sensor having a core surface from which the cladding has been partially removed at the middle or end of the optical fiber and a thin film layer of a precious metal formed thereon, exposed, and the surface plasmon resonance scale sensor is positioned within a scale detection area, and the method evaluates the state of scale formation by transmitting light from the light source through the optical fiber and detecting changes over time in the spectrum of the light that has passed through the surface plasmon resonance scale sensor.

[0012] The bandwidth of the light includes a wavelength range of 550 nm to 750 nm for the peak value of the spectrum of the light. The light is white light, and the change in the spectrum of the light over time is detected by detecting a change in the peak wavelength of the absorbance of the spectrum of the light over time.

[0013] The scale detection target area is a pipe for geothermal power generation, and geothermal water or hot spring water for geothermal power generation passes through the pipe.

[0014] The present invention also relates to a scale formation evaluation device for evaluating the state of scale formation, comprising a light source that emits light of a wavelength within a predetermined bandwidth, an optical fiber having one end connected to the light source and through which light from the light source passes, a surface plasmon resonance scale sensor in which a thin film layer of a precious metal is formed and exposed on the core surface of the optical fiber from which the cladding has been partially removed at the middle or end of the optical fiber, and a spectral analysis device that detects the spectrum of light that has passed through the surface plasmon resonance scale sensor of the optical fiber, wherein the spectral analysis device detects changes over time in the spectrum of light transmitted from the light source to the optical fiber, making it possible to evaluate the state of scale formation.A scale formation evaluation device using a surface plasmon resonance scale sensor.

[0015] The light source may be an LED white light source. The optical fiber is a multimode optical fiber, and a gold thin film is formed as the precious metal thin film layer on the entire peripheral surface of the core from which the cladding has been removed. The gold thin film preferably has a thickness of 20 nm to 50 nm. Effect of the Invention

[0016] The method and device for evaluating scale formation using a surface plasmon resonance sensor according to the present invention enable more rapid measurement and evaluation, and make it possible to detect a greater number of scale types. In particular, silica scale can be detected and evaluated quickly and accurately, and appropriate countermeasures against scale can be taken at the appropriate time. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a scale formation evaluation device according to an embodiment of the present invention. [Diagram 2] FIG. 1A is an enlarged schematic diagram of a surface plasmon resonance scale sensor using an optical fiber according to one embodiment of the present invention, FIG. 1B is a schematic diagram showing the detection principle using surface plasmon waves, and FIG. 1C is a schematic diagram showing the detection principle using surface plasmon waves with a scale attached. [Diagram 3] 4 is a graph showing a wavelength peak shift based on measurement results of one embodiment of the scale formation evaluation device of the present invention. [Figure 4] 1 is a graph showing the change in peak wavelength versus immersion time of a sensor in one embodiment of the scale formation evaluation device of the present invention. [Diagram 5] 1 is a graph showing the change in light transmittance versus immersion time for a conventional optical fiber scale sensor. [Figure 6] Graphs (a) and (b) show the change in absorbance when the gold thin film of a surface plasmon resonance scale sensor using an optical fiber according to an embodiment of the present invention has a thickness of 15 nm, and graph (c) shows the relationship between refractive index and peak wavelength. [Figure 7] Graphs (a) and (b) show the change in absorbance when the gold thin film of a surface plasmon resonance scale sensor using an optical fiber according to an embodiment of the present invention has a thickness of 30 nm, and graph (c) shows the relationship between refractive index and peak wavelength. [Figure 8] Graphs (a) and (b) show the change in absorbance when the gold thin film of a surface plasmon resonance scale sensor using an optical fiber according to an embodiment of the present invention has a thickness of 60 nm, and graph (c) shows the relationship between refractive index and peak wavelength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a surface plasmon resonance (SPR) measurement method according to an embodiment of the present invention will be described. A method and device for evaluating scale formation using an optical fiber sensor utilizing optical fiber spectroscopy (OES) and optical fiber spectroscopy (OFRS) using optical fiber spectroscopy (OFRS) and optical fiber spectroscopy (OFRS) using optical fiber spectroscopy (OFRS) and optical fiber spectroscopy (OFRS) using optical fiber spectroscopy (OFRS) will be described with reference to the drawings. The scale formation evaluation device of the present invention evaluates the state of scale formation that adheres to the surfaces of equipment such as piping, which is a pipeline through which hot water passes in contact with the equipment, for example, in equipment that uses hot water such as geothermal water for geothermal power generation or hot spring water. It can also be used to evaluate CO2 mineralization reactions in the fields of CCS (Concentrated Carbon Storage) and Enhanced Geothermal Systems (EGS).

[0019] 1 and 2, a scale generation evaluation device 10 according to one embodiment of the present invention includes a light source 12 and an optical fiber 14 having one end connected to the light source 12 and through which light from the light source 12 passes. A gold thin film 16, which is a thin precious metal layer, is formed on the core surface of the optical fiber 14 from which the cladding has been partially removed, midway or at the end of the optical fiber 14, and a surface plasmon resonance scale sensor 18 is provided with the gold thin film 16 exposed.

[0020] The scale generation evaluation device 10 of this embodiment further includes a general purpose spectrum analyzer 20 that detects the spectrum of light passing through the surface plasmon resonance scale sensor 18 of the optical fiber 14 .

[0021] Light source 12 is preferably a white light source, with the wavelength of the peak light intensity ranging from 550 nm to 750 nm. For example, a white light source such as an LED light source having a predetermined bandwidth can be used. Furthermore, monochromatic light may be used, in which case the scale is detected and evaluated by detecting changes in the light that has passed through surface plasmon resonance scale sensor 18.

[0022] The optical fiber 14 is a multimode optical fiber, and preferably uses a silica core optical fiber. The surface plasmon resonance scale sensor 18 formed in the optical fiber 14 has a gold thin film 16 formed as a precious metal thin film layer on the entire surface of the core 14a from which the cladding has been removed. The gold thin film 16 preferably has a thickness of 20 nm to 50 nm. The gold thin film 16 can be formed by a known method such as vapor deposition.

[0023] The spectrum analyzer 18 detects changes over time in the peak wavelength of absorbance of the spectrum of white light, etc., transmitted from the light source 12 to the optical fiber 14, and displays this in a specified waveform on a display, making it possible to evaluate the state of scale formation, as described below.

[0024] Next, the principle of the surface plasmon resonance scale sensor 18 used here will be described. As shown in FIG. 2, incident light L indicated by an arrow is transmitted from the back side of the gold thin film 16 so as to be totally reflected within the core 14a. At this time, resonant excitation of a surface plasmon wave p occurs on the surface of the gold thin film 16. When the surface plasmon wave is resonantly excited in the gold thin film 16, the energy of the incident light is consumed accordingly, and a decrease in the intensity (decrease in reflectance) of the reflected light passing through the core 14a of the optical fiber 14 occurs. Furthermore, the adhesion of a scale 30 to the surface of the gold thin film 16 changes the surface refractive index of the gold thin film 16, and the intensity of the surface plasmon wave p also changes. This change is correlated with the amount of adhesion of the scale 30, and the amount of adhesion of the scale is expressed as a change in the peak wavelength of the light irradiated from the light source 12, as in the embodiment described later.

[0025] In the scale formation evaluation method using the scale formation evaluation device 10 of this embodiment, as shown in FIG. 1, the scale detection target area is an evaluation hot water path 24 for monitoring hot water 22 such as geothermal water or hot spring water used for geothermal power generation. The hot water 22 is passed through the evaluation hot water path 24, and the surface plasmon resonance scale sensor 18 of the optical fiber 14 is immersed in the hot water 22 in the evaluation hot water path 24 to measure and evaluate the scale. The hot water 22 is supplied from a hot water supply source 26 such as a water intake well to the evaluation hot water path 24 provided in a hot water supply path 28, which is a predetermined pipe, and the hot water 22 that has passed through the evaluation hot water path 24 is introduced into the original hot water supply path 28. The evaluation hot water path 24 may be branched, and the branched hot water 22 may be discarded. In addition to constantly flowing the hot water 22 to be used for evaluation, it may also be stored in the evaluation hot water path 24 for a certain period of time to measure and evaluate the scale.

[0026] In this invention, the amount of scale adhering to the gold thin film 16 on the surface of the core 14a is measured by the surface plasmon resonance scale sensor 18 as a time-dependent change in the peak wavelength of light transmitted through the optical fiber 14, using a spectrum analyzer 20. The scale adhesion state is measured by detecting the formation state of scale adhering to the equipment through which hot water passes in almost real time, and the degree of the formation state, its quality, and its effect on the equipment can be evaluated. The hot water referred to here is geothermal water or hot spring water for geothermal power generation, and also includes steam erupting from underground, and may also include carbon dioxide injected underground for the purpose of CCS or EGS. The equipment also includes piping for passing hot water, heat exchangers, and other pipelines. Furthermore, even if monochromatic light is used for the light source 12, it is possible to simply detect scale and recognize changes in the adhesion state by detecting changes in the light passing through the surface plasmon resonance scale sensor 18, and to evaluate the formation of scale.

[0027] According to the scale formation evaluation device 10 and the scale formation evaluation method using the surface plasmon resonance sensor of this embodiment, more rapid measurement and evaluation are possible, and more types of scale can be detected. In particular, rapid detection and evaluation of silica scale is also possible, and appropriate countermeasures against scale can be taken at the appropriate time.

[0028] The scale formation evaluation method and scale formation evaluation device using a surface plasmon resonance sensor of the present invention are not limited to the above embodiment, and the light bandwidth of the light source 12 and the type of light source can be set as appropriate, and the material and structure of the optical fiber 14 of the surface plasmon resonance scale sensor can also be selected according to the application of the sensor and the hot water to be used, etc. Furthermore, the applicable groundwater such as hot water includes not only geothermal water for geothermal power generation, but also hot spring water and other groundwater, and also contains water vapor. EXAMPLES

[0029] An embodiment of the scale formation evaluation method and scale formation evaluation device using a surface plasmon resonance sensor according to the present invention will be described below. First, the light transmitted through the optical fiber 14 is measured by the scale 30 attached to the surface of the gold thin film 16 of the surface plasmon resonance scale sensor 18, and the change in the peak wavelength of the measured absorbance over time is shown in FIG. 3. FIG. 3 shows that the wavelength of the peak value of the spectrum shifts with the passage of time shown by the arrow when the surface plasmon resonance scale sensor 18 (gold thin film 16 has a film thickness of 30 nm) is immersed in hot water. FIG. 4 is a plot of the time (horizontal axis) and the peak wavelength (vertical axis) values ​​for each peak wavelength shown in FIG. 3 when the surface plasmon resonance scale sensor 18 is immersed in hot water. This shows that the immersion time of the surface plasmon resonance scale sensor 18 and the attachment of the scale show a very accurate positive correlation between the time change in the measured peak wavelength. It was found that the time during which the surface plasmon resonance scale sensor 18 can detect the adhesion state of the scale 30 can be measured in units of approximately minutes, as shown in FIG. 4, and the adhesion state of the scale can be evaluated in real time.

[0030] FIG. 5 shows the change in light transmittance versus immersion time when a conventional optical fiber sensor is used. Comparing the initial response (0 to 180 minutes) with FIG. 4 using the surface plasmon resonance scale sensor 18, the surface plasmon resonance scale sensor 18 in FIG. 4 responded immediately after immersion and had superior linearity. Linearity was also observed 180 minutes after measurement in the case of the conventional optical fiber sensor shown in FIG. 5, but it can be seen that the change shown in FIG. 4 using the surface plasmon resonance scale sensor 18 of the present invention has a larger rate of change and is more sensitive. Thus, the method of evaluating the state of scale formation based on the change over time of the peak wavelength using the surface plasmon resonance scale sensor 18 of the present invention can evaluate the state of scale formation quickly and with high accuracy, demonstrating the usefulness of the surface plasmon resonance scale sensor 18.

[0031] Next, the film thickness of the gold thin film 16 of the surface plasmon resonance scale sensor 18 was evaluated by laboratory testing. Using three types of surface plasmon resonance scale sensors with different film thicknesses, the surface plasmon resonance spectrum was measured in response to changes in absorbance in the laboratory testing. As a result, as shown in Figures 6 to 8, it was confirmed that the peak wavelength of the optical spectrum shifted to the longer wavelength side due to surface plasmon resonance as the refractive index increased in each of the three types of sensors.

[0032] In particular, as shown in Figures 6(a) and (b), 7(a) and (b), and 8(a) and (b), the shift of the peak wavelength increased with increasing film thickness. In addition, in all surface plasmon resonance scale sensors, the peak shift of the surface plasmon resonance spectrum with respect to the change in refractive index was linear, as shown in Figures 6(c), 7(c), and 8(c). The refractive index sensitivities (nm / refractive index unit; RIU) of the sensors with film thicknesses of 15 nm, 30 nm, and 60 nm were 833 nm / RIU, 2141 nm / RIU, and 2575 nm / RIU, respectively, with the 60 nm film thickness showing the highest refractive index sensitivity and being sensitive to changes in the refractive index of the surroundings.

[0033] As shown in Fig. 6(a), Fig. 7(a), and Fig. 8(a), the higher the refractive index of the solution into which the sensor was placed during the test, the more a peak unrelated to surface plasmon resonance appeared around 530 nm. This is believed to be due to the fact that the optical fiber of the surface plasmon resonance scale sensor in this embodiment uses a multimode optical fiber with a core diameter of 200 μm. Therefore, the optimal film thickness of the gold thin film 16 was set to 30 nm, which has a relatively high refractive index sensitivity and is less affected by the peak that appears at 530 nm. The thickness of the gold thin film 16 can be set appropriately in the range of 10 nm to 60 nm, but it is preferable that the thickness is 20 nm to 50 nm. [Industrial Applicability]

[0034] This invention makes it possible to measure the precipitation rate of scale within one hour by periodically immersing a surface plasmon resonance scale sensor in a pipe or an evaluation hot water path such as a hot water tank in, for example, a geothermal power plant or a hot spring binary power plant, and can be reflected in the creation of a schedule for cleaning of the pipe. The evaluation device can be driven by a battery, making it possible to evaluate scale generation in places without a commercial power source, and has a wide range of applications. The handling of the surface plasmon resonance scale sensor will lead to the development of a device that can be easily operated even by engineers without special skills. Furthermore, this invention can be used in the field of carbon dioxide capture and storage (CCS), and can be used to evaluate, for example, the mineralization reaction of CO2. [Explanation of symbols]

[0035] 10. Scale formation evaluation device 12 light source 14 Optical Fiber 16 Gold thin film 18 Surface Plasmon Resonance Scale Sensor 20 Spectral analysis equipment 24 Hot water path for evaluation 26 Hot water sources 28 Hot water supply route 30 Scale

Claims

1. A scale formation evaluation method for evaluating a scale formation state, comprising: A surface plasmon resonance scale sensor is provided by using a light source having a wavelength of light in a predetermined bandwidth, an optical fiber having one end connected to the light source and through which the light from the light source passes, and a surface plasmon resonance scale sensor having a precious metal thin film layer formed on a core surface from which the cladding is partially removed at a midpoint or end of the optical fiber, and exposed. A scale formation evaluation method characterized by evaluating the state of scale formation by transmitting light from the light source through the optical fiber while the surface plasmon resonance scale sensor is positioned within a scale detection area and detecting changes over time in the spectrum of the light that has passed through the surface plasmon resonance scale sensor.

2. 2. The method for evaluating scale formation according to claim 1, wherein the bandwidth of the light includes a range of wavelengths of peak values ​​of the spectrum of the light from 550 nm to 750 nm.

3. 2. The method for evaluating scale formation according to claim 1, wherein the light is white light, and the change in the spectrum of the light over time is detected by detecting a change in a peak wavelength of absorbance of the spectrum of the light over time.

4. 2. The method for evaluating scale formation according to claim 1, wherein the scale detection target area is a pipe for geothermal power generation, and geothermal water or hot spring water for geothermal power generation passes through the pipe.

5. A scale formation evaluation device for evaluating the state of scale formation adhering to a surface of a material through which hot water passes, comprising: a light source having light of a wavelength within a predetermined bandwidth; an optical fiber having one end connected to the light source and through which light from the light source passes; a surface plasmon resonance scale sensor having a precious metal thin film layer formed and exposed on a core surface from which cladding has been partially removed at a midpoint or end of the optical fiber; and a spectrum analyzer for detecting the spectrum of the light that has passed through the surface plasmon resonance scale sensor of the optical fiber; The spectrum analyzer detects changes over time in the spectrum of light transmitted from the light source to the optical fiber, thereby enabling the scale formation state to be evaluated.

6. 6. The scale formation evaluation device according to claim 5, wherein the light source is an LED white light source.

7. The scale formation evaluation device according to claim 5, wherein the optical fiber is a multimode optical fiber, and a gold thin film is formed as the precious metal thin film layer on the entire peripheral surface of the core from which the cladding has been removed. The optical fiber may have any structure capable of extracting evanescent light required for exciting surface plasmon resonance, and is not limited to the embodiment. For example, the optical fiber may include an end face of an optical fiber, a structure in which a fiber cladding is extended to the vicinity of the core, and a structure in which fibers of different diameters are combined.

8. 8. The scale formation evaluation device according to claim 7, wherein the gold thin film has a thickness of 20 nm to 50 nm.

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