JP6416023B2 - Scale suppression method and apparatus - Google Patents

Description

  Embodiments described herein relate generally to a heat exchanger, a method for suppressing scales adhering to piping, and an apparatus therefor.

  In general, in the fields of boilers, cooling towers, geothermal power generation, etc., it is necessary to pass hot water containing calcium, iron, silica components, etc. through the pipes. Is known to occur.

  For calcium and iron scales, canning agents have been developed. By adjusting the conditions and injecting chemicals, scales can be prevented to some extent, and the generated scales can be washed and removed.

  However, there are few effective methods for silica scale, and so far, it has not been widely put into practical use. For example, if the silica component is in a low concentration, it can be dealt with by removing silicic acid using an ion exchange resin, but the ion exchange resin is expensive and the situation where it can be used is limited. Moreover, in the operation of circulation systems such as boilers and cooling towers, the concentration increase due to concentration is monitored, and dilution by partial drainage and water injection is performed to suppress scale deposition.

Moreover, in an environment that contains high-concentration silica of several hundred mg / L, such as a geothermal power plant, and operates a large amount of water of several hundred m ³ or more per hour, the amount of precipitated silica is enormous. It leads to blockage of piping and reduction well. As a result, it is an important issue for electric power companies because it causes a decrease in the amount of power generation due to a decrease in the amount of water flow, that is, a decrease in the amount of energy obtained.

  As a conventional technique in a geothermal power plant, there is a method of retaining water after flushing (air-water separation) and injecting sulfuric acid to lower pH to make it difficult to precipitate silica. There is a problem that it solidifies by reacting with the like and shortens the life of the well. In addition, there is a method of water supply to the reduction well in a high temperature range where scale does not occur, calculated from the silica concentration and saturation solubility, etc., but in the binary type geothermal power generation for the purpose of using heat to low temperatures Difficult to apply.

  In the method of adding silica seed crystals and precipitating silica on the surface, it is difficult to lower the saturation solubility at the concentration of monosilicic acid that causes scale, and in the binary type where the water temperature decreases when passing through the heat exchanger, the heat exchanger It is difficult to prevent scale deposition on the surface. Although some flocculants are added, monosilicic acid in geothermal water, which causes scale, has a low molecular weight and requires a large amount of flocculant.

Patent registration No. 4020288 Patent registration No. 5563854

“Characteristics of Iron-Silica Inorganic Polymer Aggregation and Water Treatment” Ehara et al. 2000.11 8th Sanitation Engineering Symposium

  In the above-described silica scale suppression technology in geothermal power generation, the problem is that scale cannot be prevented efficiently and sufficiently. The scale suppression method according to the embodiment of the present invention has been made to solve the above-described problem, and aims to suppress scale by obtaining water in which silica scale is hardly generated.

  Hereinafter, a preferred specific example of a scale suppression method and apparatus according to an embodiment of the present invention will be described with reference to the drawings as necessary.

  As described above, in the field of geothermal power generation and the like, it is necessary to pass hot water containing calcium, iron, silica components, etc. through the pipe, and scale is generated on the inner wall of the pipe during continuous operation for a long time. It is known.

  The occurrence of scale is remarkable in a place where the temperature of the hot water that has passed through rapidly decreases. The occurrence of such a scale can be observed, for example, in geothermal power generation, particularly geothermal binary cycle power generation.

FIG. 1 is a diagram showing an outline of geothermal binary cycle power generation.
In FIG. 1, the geothermal hot water obtained from the production well 1 is subjected to heat exchange with a low boiling point medium in a heat exchanger 2 called an evaporator. The geothermal hot water deprived of thermal energy by the low boiling point medium is discharged deeply into the ground through the reduction well 3.

On the other hand, the low boiling point medium takes heat energy from the geothermal hot water in the heat exchanger 2 and is gasified by the heat to increase the pressure. The gas of the low boiling point medium turns the turbine 4 and turns the generator 5 connected to the turbine 4 to generate electric power. Thereafter, the low-boiling point medium is passed through the condenser 6, and the pressure is reduced in the process of being deprived of heat and liquefied.
The above is the basic process in geothermal power generation.

In the process described above, there are mainly three places where scales are likely to occur.
The first is the stage in which hot water springs up from the inside of the production well 1 to the ground. Here, it is said that a scale mainly composed of calcium carbonate is likely to occur due to a decrease in the temperature and pressure of the geothermal hot water accompanying the hot water.
Second, the inside of the heat exchanger 2. Here, it is known that the temperature of hot water drops rapidly due to heat exchange with a low boiling point medium, and a scale mainly composed of amorphous silica or calcium is generated.
Third, it is a reduction pipe after the heat exchanger 2. Again, since the temperature of the hot water continues to decrease, a scale such as amorphous silica is generated.

  As a problem specific to binary systems compared to general flash systems as a method of geothermal power generation, hot water with a relatively low temperature range and 200 ° C or less is often used, so silica scale is generated inside the power generation equipment. It is easy to mention. Silica scale is firmly fixed inside the equipment and has poor chemical cleaning properties, such as calcium scale, which dissolves relatively easily with acid, shortening the equipment life, and accompanying well clogging / reduction in wells The power generation amount may be reduced.

Here, the generation mechanism of silica scale will be briefly described.
The geothermal hot water contains silicic acid [Si (OH) ₄ ] that is the basis of silica scale. Silicic acid changes in saturation solubility depending on temperature, pH, and coexisting salt. Referring to the published analysis results of geothermal hot water, the geothermal hot water contains a silica component of at least several hundred mg / L, more than 1000 mg / L in terms of SiO ₂ .

  In the binary system described above, the hot water is often used in a temperature range of about 150 ° C to 200 ° C and the temperature of the hot water to be reduced is about 100 ° C to 150 ° C. The temperature of hot water drops in the vessel. When the saturation solubility of silicic acid falls below the dissolution concentration as the temperature drops, the silicic acid becomes supersaturated and the scale is deposited.

  Silicic acid that has become supersaturated changes its form according to time. That is, it polymerizes.

2Si (OH) ₄ → (OH) ₃ Si—O—Si (OH) ₃ + H ₂ O Formula (1)
The reaction of silicic acid (Si (OH) ₄ ) is schematically shown in Formula (1). As in this formula (1), the OH group portion of silicic acid undergoes dehydration condensation. By repeating this reaction, silicic acid increases the molecular weight and becomes polysilicic acid.

The polysilicic acid eventually adheres to the pipe surface and grows so as to cover the pipe surface using the adhering material as a trigger. At first, it adheres in the form of a gel, but as time passes, it gradually becomes firmly fixed.
Although silica scale is generated as described above, there is a study that the coexistence of cations affects the generation of silica scale. Therefore, the following examination was conducted.

A 1700 mg-SiO ₂ / L silicic acid solution was prepared and dissolved well, and then adjusted to pH 8 with sulfuric acid to obtain a supersaturated silicic acid solution. No scale was found in the pipe that was circulated at 90 ° C. for 3 weeks using this supersaturated silicate solution. Therefore, a part of the supersaturated silicic acid solution was taken, and when a calcium chloride solution was added and stirred, a precipitate was obtained and observed.

  FIG. 2 is an image obtained by drying the precipitate obtained by the above precipitation and observing with an electron microscope (SEM). FIG. 2A shows a case where the calcium addition concentration is 1 mmol / L, and FIG. FIG. 2C shows the case where the calcium addition concentration is 10 mmol / L, and FIG. 2C shows the case where the calcium addition concentration is 100 mmol / L.

When the calcium addition concentration is 1 mmol / L and 10 mmol / L, amorphous silica (SiO ₂ ) is mainly used (FIGS. 2A and 2B), and when the calcium addition concentration is 100 mmol / L, a part of sulfuric acid Calcium precipitated (FIG. 2C). When the calcium addition concentration is 1 mmol / L and 10 mmol / L, fine gel particles are precipitated (FIG. 2A, FIG. 2B), and when 100 mmol / L, acicular crystallized calcium sulfate, Silica was observed as an amorphous part (FIG. 2C). From these results, it can be derived that amorphous silica is precipitated by the addition of calcium and that the composition of the precipitate is changed depending on the concentration.
A similar test was performed on iron (III) ions in the same manner.

  Then, the amount of added ions (calcium ions and iron ions) and the amount of precipitated silica were arranged (FIG. 3). When silicate and calcium simply form calcium silicate, the Si / Ca ratio is 0.5 to 1, but in practice, a relatively large amount of silica is precipitated, particularly in a region where the amount of calcium ion addition is small. Yes. The same applies to iron. This phenomenon can be explained by the following model.

  That is, silicic acid dissolved in geothermal hot water is polymerized to polysilicic acid when it becomes supersaturated due to a decrease in temperature. Polysilicic acid is cross-linked by coexisting polyvalent cations and has a large molecular weight. When the molecular weight is increased, an aggregating action by so-called intermolecular force also works, so that solidification is promoted and it is easy to adhere to the pipe. That is, the presence of multivalent cations will accelerate scale generation.

Embodiments of the present invention relate to a method for suppressing scale resulting from geothermal hot water.
Therefore, the scale suppression method according to the embodiment of the present invention is:
A method for suppressing scale formation by adding a chemical to geothermal hot water,
It is characterized in that at least two or more kinds of agents are used in combination among the agent 1 that binds to Ca ions, the agent 2 that promotes the dispersion of the silica colloid, and the agent 3 that promotes the formation of the silica colloid. is there.

  The scale suppressing device according to the embodiment of the present invention includes at least two of the agent 1 that binds to Ca ions, the agent 2 that promotes dispersion of silica and silica colloid, and the agent 3 that promotes the formation of silica colloid. It is characterized by comprising a device for adding more than one kind of medicine to geothermal hot water.

  According to the scale suppression method according to the embodiment of the present invention, the addition of a predetermined chemical makes it difficult for geothermal hot water to deposit scale-causing substances, and even if temporarily deposited, makes it difficult to adhere to and accumulate on pipes and the like. be able to.

  From this, according to embodiment of this invention, the various problems which were brought about by the scale which generate | occur | produced conventionally in various geothermal utilization systems can be solved.

  Such a scale suppression method according to the embodiment of the present invention has a remarkable effect in a geothermal power generation system, particularly in a geothermal binary cycle power generation.

  The scale suppression method according to the embodiment of the present invention not only suppresses the generation of scale in the flow path of the ground portion of the geothermal hot water but also reduces it before the geothermal hot water is jetted to the ground or into the ground. Even after being applied, problems due to scale can be prevented or suppressed.

Drawing which shows the outline of geothermal binary cycle power generation. An electron micrograph of a precipitate obtained by adding a calcium chloride solution to a supersaturated silicic acid solution. Drawing showing the influence of cations on scale deposition. 6 is a diagram illustrating a scale suppression method according to an embodiment of the present invention. The figure which shows the molecular weight change of the silicic acid polymer by the chemical | medical agent 2. FIG. FIG. 2 is an optical micrograph showing the situation inside the tube (without addition of a drug) confirmed in Example 1. FIG. The scanning electron microscope (SEM) photograph of the scale adhering in the pipe | tube confirmed in Example 1. FIG. The optical micrograph which shows the condition (with chemical | medical agent addition) confirmed in Example 1 in a pipe | tube. The figure showing the addition effect of the chemical | medical agent 1 and the addition effect of the chemical | medical agent 2 confirmed in Example 2. FIG.

<Scale suppression method>
A scale suppression method according to an embodiment of the present invention includes:
A method for suppressing scale formation by adding a chemical to geothermal hot water,
It is characterized in that at least two or more kinds of agents are used in combination among the agent 1 that binds to Ca ions, the agent 2 that promotes the dispersion of the silica colloid, and the agent 3 that promotes the formation of the silica colloid. is there.

  Such a scale suppression method according to an embodiment of the present invention is preferably applicable to, for example, a “geothermal power generation system”, and in particular, “heat from geothermal hot water collected from the ground through a production well. This is a method that can suppress the “scale generated in the flow path of the geothermal hot water in the geothermal power generation system that returns the geothermal hot water to the ground through the reduction well after extracting the energy”.

  In addition, as a utilization form of “thermal energy” taken out from geothermal hot water, heating of other materials (solid, liquid, gas alone or a mixture thereof) can be exemplified. Examples of the “heat energy” extraction device include a heat exchanger. For example, a geothermal power generation system in which the object to be heated is a low boiling point solvent and the extraction of “thermal energy” from geothermal hot water and the heating of the low boiling point medium are performed in a common heat exchanger is, for example, a “geothermal binary cycle power generation system”. Is included as a specific example.

  Therefore, a specific example of the geothermal power generation system is preferably a “geothermal binary cycle power generation system”. Here, “geothermal binary cycle power generation” means “electric power generation cycle in which the heat energy of geothermal fluid is transferred to other fluids such as low-boiling-point media in a heat exchanger, and the turbine is driven by a heated and vaporized medium” (JIS B0127 (2102) 7106).

FIG. 4 shows a case where the scale suppression method according to the embodiment of the present invention is applied to a “geothermal binary cycle power generation system”.
In FIG. 4, the geothermal hot water obtained from the production well 1 is subjected to heat exchange with a low boiling point medium in the heat exchanger 2. The geothermal hot water deprived of thermal energy by the low boiling point medium is discharged deeply into the ground through the reduction well 3. In addition, the silica separator 7 can be provided in the middle of the heat exchanger 2 and the reduction well 3 as needed. The production well 1, the heat exchanger 2, the silica separator 7, and the reduction well 3 are connected by a pipe 8 through which geothermal hot water flows.

  On the other hand, the low boiling point medium takes heat energy from the geothermal hot water in the heat exchanger 2 and is gasified by the heat to increase the pressure. The gas of the low boiling point medium turns the turbine 4 and turns the generator 5 connected to the turbine 4 to generate electric power. Thereafter, the low-boiling point medium is passed through the condenser 6, and the pressure is reduced in the process of being deprived of heat and liquefied.

  In FIG. 4, the addition position A of the medicine 1, the addition position B of the medicine 3, and the addition position C of the medicine 2 are shown. Needless to say, when any one of the drug 1, the drug 2, and the drug 3 is not used, the addition position of the drug can be omitted. Moreover, the addition position of each of the drug 1, the drug 2, and the drug 3 does not need to be one, and can be provided at a plurality of positions.

In the scale suppression method according to the embodiment of the invention, first, the drug 1 is added to the geothermal hot water.
The drug 1 is a drug that binds to Ca ions. This drug 1 mainly has an action of reducing the effects of polyvalent cations such as calcium and iron. That is, an organic polymer compound that binds to these cations by an ionic bond or the like and contains, for example, a carboxyl group, a phosphonic acid group, a sulfonic acid, or the like in the molecule can be used.

  Preferable specific examples of such a drug 1 include (1) a compound containing a carboxyl group, preferably polyacrylic acid, polymaleic acid, an acrylic acid / maleic acid copolymer, etc. (2) a compound containing a phosphate group Preferably, hydroxyethylidylenediphosphonic acid and the like (3) compounds containing sulfonic acid, preferably those obtained by copolymerizing a part of polyacrylic acid polymer with sulfonic acid, and the like. Moreover, what is marketed as a calcium scale inhibitor can be used.

  Among these, polyacrylic acid is most preferable, and is added so as to include a functional group amount equal to or more than the Ca ion contained in the geothermal hot water.

  Addition of the drug 1 to the geothermal hot water may be prior to the addition of the drug 2 and the addition of the drug 3. Therefore, it is most preferable that the drug 1 is added into the well of the production well 1 such as the addition position A as specifically shown in FIG.

  As for the addition amount of the chemical | medical agent 1, it is desirable to make it contain the amount of applicable functional groups more than an equivalent with respect to Ca ion contained in geothermal hot water. Moreover, it is desirable that the calcium ion concentration in the free state is less than 10 mg / L as a result of the addition. The calcium ion concentration in the free state can be measured by a colorimetric method using phthalein or the like. When the addition amount of the chemical | medical agent 1 exists in the said range, precipitation of the scale triggered by the reaction of calcium and silica can be suppressed.

  After the addition, it is desirable to promote the dispersion of the drug by stirring in the pipe, and a static mixer or the like may be used. However, since pressure loss occurs, care must be taken not to make it excessive.

  In addition, when the Ca ion density | concentration of geothermal hot water is low, the chemical | medical agent 1 can reduce the addition amount, and the addition can be abbreviate | omitted by the case.

Subsequently, drug 3 is added.
The drug 3 is a drug that promotes the formation of silica colloid. This medicine 3 has a function of promoting polymerization of silicic acid in geothermal hot water. For example, silicic acid that has been polymerized in advance, that is, polysilicic acid, can be used for the chemical 3 to promote polymerization of silicic acid in geothermal hot water.

  The change in molecular weight distribution associated with the polymerization of silicic acid in the liquid is that the polymerization proceeds uniformly in the initial stage, the molecular weight increases as a whole to form primary particles, and then the primary particles polymerize. It can be understood that it becomes a double peak of a group having a larger molecular weight.

Here, when polysilicic acid previously polymerized and increased in molecular weight as in Drug 3 is added to supersaturated geothermal hot water, silicic acid is further polymerized into polysilicic acid having a large molecular weight, A large polysilicic acid group having a molecular weight of 100,000 or more and a small polysilicic acid group having a molecular weight of 10,000 or less can be formed in a short time (FIG. 5). FIG. 5 shows that after adding 20 mg-SiO ₂ / L polysilicic acid to an 800 mg-SiO ₂ / L solution at 90 ° C. and pH 8 and stirring, a centrifugal filter (fractionated molecular weight 10,000, 100,000, 1,000,000) ) And the molecular weight distribution of silica drawn from the measurement of the silica concentration of each filtrate. By adding polysilicic acid, a polysilicic acid group having a molecular weight of 100,000 or more and a polysilicic acid group having a molecular weight of 10,000 or less were formed, and a group of 10,000 to 100,000 was not detected. In other words, the molecular weight of silicic acid can be controlled by the drug 3. Increasing the molecular weight with the drug 3 has the effect of reducing the number of molecules. That is, the number of molecules targeted by the drug 2 described later can be reduced, and the effect of the drug 2 is increased.

The addition amount of the medicine 3 is preferably 1% to 10%, particularly preferably 2 to 5%, in terms of SiO ₂ concentration, with respect to the silicic acid concentration contained in the geothermal hot water. When the addition amount of the medicine 3 is within the above range, the effects of increasing the silicic acid molecular weight and decreasing the number of polysilicic acid molecules can be easily obtained.

Subsequently, drug 2 is added.
The drug 2 has a function of promoting the dispersion of the silica colloid. By the chemical | medical agent 2, the microparticle in geothermal hot water is disperse | distributed uniformly. This medicine 2 has an action of preventing the polysilicic acid polymerized by the aforementioned medicine 3 or the like from adhering to the pipe.

  Examples of the drug 2 include (1) an anionic surfactant, preferably polyacrylic acid, alkylsulfonic acid and the like, (2) a cationic surfactant, preferably quaternary ammonium salt, and the like (3) an anionic polymer. It is desirable to use a dispersant, preferably a naphthalene sulfonic acid formalin polymer or the like, and (4) a dispersant having a mechanism for obtaining a dispersion effect by a structure polarized in the molecule, preferably polyvinylpyrrolidone or a copolymer thereof. Of these, polyvinyl pyrrolidone and polyacrylic acid are most preferred.

  Addition of chemical 2 prevents the scale-causing substances present in the hot water as fine particles from adhering to the pipe surface, and further prevents the scale from adhering to the scale already adhering to the pipe surface. it can.

  The addition of the drug 2 can be performed after the addition of the drug 1 and before the addition of the drug 3, for example. In this case, it is preferable to add the chemical | medical agent 2 in the ground part after the geothermal hot water springs out from the production well 1 like the addition position B of FIG.

  The addition amount of the medicine 2 is preferably 1% to 20%, particularly preferably 2% to 5% with respect to the silicic acid concentration in the geothermal hot water. When the addition amount of the chemical | medical agent 2 exists in the said range, the effect of adhesion suppression by the dispersibility improvement of a silica can be acquired easily.

  The addition of the medicine 3 can be performed after the addition of the medicine 1 and before the heat exchange treatment. However, when the drug 3 is added, polysilicic acid is formed, which itself promotes scale formation. Therefore, when the drug 3 is added, the drug 2 is preferably present in the geothermal hot water. .

  In general, the order of adding the drug 2 and the drug 3 can cover the process more widely when the drug 3 is added after the drug 2 is added. However, if the dispersing agent is added after sufficiently proceeding the polymerization of the silicic acid with the chemical 3, a higher dispersion effect can be obtained, so that the scale adhesion inside the heat exchanger can be suppressed to a small extent. Therefore, the addition order of the chemical | medical agent 2 and the chemical | medical agent 3 can be suitably selected according to the thought of plant design.

The geothermal hot water to which any two or more of the chemicals 1 to 3 are added has the property that the substance causing the scale is difficult to deposit, and even if it is deposited, it is difficult to adhere to and accumulate on the piping. Scale generation can be reduced.
Next, the chemical-added geothermal hot water can be returned to the ground through the reduction well 3 as shown in FIG.

  The scale deposition on the ground reduction pipe can be suppressed by the above-mentioned addition of the chemicals, but it is not necessarily limited in the ground, that is, the blockage of the ground water vein after the reduction well 3. The reduced hot water drained from the reduction well 3 into the ground penetrates into the reservoir through underground gravel. The reduction in the amount of water contained in the reduction well is said to be due to the blockage of the flow path due to the scale adhering to the reduction well pipe, and the penetration into the underground hot water reservoir will be worsened. Is difficult to assume and countermeasures because the phenomenon varies from site to site. There is a method of adding sulfuric acid to lower the pH of hot water to delay the polymerization of silicic acid, but as long as supersaturated silicic acid is present, it usually precipitates over time.

  Therefore, it is preferable to remove silica from the geothermal hot water before the geothermal hot water is returned from the reduction well 3 to the ground. For this purpose, as shown in FIG. 4, it is desirable to provide a silica separator 7 to remove supersaturated silica from hot water.

  In the process so far, the supersaturated silica is colloidalized with a molecular weight of 100,000 or more. Therefore, a specific separation apparatus can be used for flotation separation such as agglomeration by a drug, membrane separation, gravity sedimentation, and pressure flotation. Combinations thereof can be used. As the separation membrane, a ceramic membrane excellent in high temperature and pressure resistance can be used, and in this stage, the hot water temperature has already decreased to around 100 to 120 ° C., and an organic membrane is also used. it can. As the flocculant, separability can be enhanced by using a polymer flocculant in addition to aluminum-based and iron-based flocculants such as polyaluminum chloride and polyiron sulfate. The coagulant is efficient because it can concentrate a colloid group having a molecular weight of 100,000 or more.

  As described above, the scale suppression method according to the embodiment of the present invention is preferably applicable to, for example, a “geothermal power generation system”, and in particular, “geothermal hot water collected from the ground through a production well. The scale generated in the geothermal hot water flow path (especially the flow path inside the heat exchanger) in the geothermal power generation system that returns the geothermal hot water to the ground through the reduction well after extracting the thermal energy from It can be done.

As a preferred embodiment of the present invention, a scale inhibiting method that uses the agent 2 that promotes the dispersion of the silica colloid and the agent 3 that promotes the formation of the silica colloid, and the agent that binds to the Ca ion. 1 and a scale inhibiting method using the drug 2 that promotes the dispersion of the silica colloid and the drug 3 that promotes the formation of the silica colloid.

<Scale suppression device>
The scale suppressing device according to the embodiment of the present invention includes at least two or more kinds of agents 1 that bind to Ca ions, agents 2 that promote the dispersion of silica colloid, and agents 3 that promote the formation of silica colloid. A device for adding a drug to geothermal hot water is provided.

  As a preferred specific example of such a scale restraining device, (a) a device for collecting geothermal hot water from the ground, (b) a device for extracting thermal energy from the geothermal hot water, and (c) geothermal hot water for geothermal hot water. At least two or more kinds of agents among the device for returning to the inside, (d) the agent 1 that binds to Ca ions, the agent 2 that promotes the dispersion of the silica colloid, and the agent 3 that promotes the formation of the silica colloid, And (e) those having a device for circulating geothermal hot water in (i) to (d) above.

  Here, (b) As an apparatus for collecting geothermal hot water from the ground, the production well 1 shown in FIG. 4 can be cited. (B) As an apparatus for extracting thermal energy from geothermal hot water, FIG. (C) As an apparatus for returning geothermal hot water to the ground, the reduction well 3 shown in FIG. 4 can be cited, and (d) it binds with Ca ions. As an apparatus for adding at least two or more kinds of agents among the agent 1, the agent 2 that promotes the dispersion of the silica colloid, and the agent 3 that promotes the formation of the silica colloid, the agent shown in FIG. The addition position A of 1, the addition position B of the medicine 3, and the addition position C of the medicine 2 can be cited. (E) As an apparatus for circulating geothermal hot water to the above (a) to (d), FIG. The pipe 8 shown in FIG.

  In addition to the above (a) to (e), the apparatus for suppressing a scale according to the embodiment of the present invention preferably further comprises (f) an apparatus for removing scale from the geothermal hot water. In this case, “(e) the device for distributing geothermal hot water to (i) to (d)” described above is “(e) circulating geothermal hot water to (i) to (f) above”. It is changed to "device to let". As an apparatus for removing scale from this (f) geothermal hot water, there can be mentioned a silica separator 7 shown in FIG.

<Example 1>
A simulated geothermal water of 90 ° C. was circulated, and a pipe made of SUS316L was connected to a part as a test body, and the generation of scale was observed. The circulation period was 3 weeks, the initial silicic acid concentration was 500 mg-SiO ₂ / L, the calcium concentration was 14 mg / L, and the pH was 8.5.

  The inside of the tube after the circulation was observed with an optical microscope. The result is as shown in FIG. 6A is a view when observed at an observation magnification of 25 times, and FIG. 6B is a view when an area surrounded by a square in FIG. 6A is observed at an observation magnification of 100 times. As shown in FIGS. 6A and 6B, white precipitates were attached to the inner surface of the tube.

  The above precipitate was collected and observed with a scanning electron microscope (SEM). The result is as shown in FIG. Furthermore, as a result of elemental analysis, it was found that the main components are Si and O, and that Ca and Fe (considered to be eluted from the apparatus) are slightly contained. That is, the deposit was silica scale, and it was found that precipitation of silica scale proceeds under the present test conditions.

Subsequently, simulated geothermal water at 90 ° C. was circulated again, and a SUS316L tube was connected to a part as a test body, and the occurrence of scale was observed. The circulation period is 3 weeks, the initial silicic acid concentration is 500 mg-SiO ₂ / L, the calcium concentration is 14 mg / L, and the pH is 8.5. This time, a sodium polyacrylate solution was used as the drug 1 and a polyvinyl pyrrolidone solution was used as the drug 2, and 50 ppm and 20 ppm were added, respectively.

  The inside of the tube after the circulation was observed with an optical microscope. The result is as shown in FIG. 8A is a view when observed at an observation magnification of 25 times, and FIG. 8B is a view when an area surrounded by a square in FIG. 8A is observed at an observation magnification of 100 times.

  In this test, silica scale adhesion was not observed. That is, it was confirmed that the adhesion to the silica scale pipe can be suppressed by the chemical.

<Example 2>
Drugs 1 and 2 were added to and mixed with simulated geothermal water at an initial silicic acid concentration of 500 mg-SiO ₂ / L, calcium concentration of 14 mg / L, pH of 8.5, and 90 ° C. at a ratio of 2: 1. After the above mixing, a hot water filtrate was obtained with an ultrafiltration membrane (fractionation molecular weight 3000) that can be centrifuged. The silica and calcium concentrations before and after filtration were measured. For free calcium, the colorimetric method using phthalein, for soluble silica, the colorimetric method using molybdenum blue, and for other calcium and silica, the concentrations of Ca and Si were measured by ICP emission method and converted as necessary.

FIG. 9A shows the calcium concentration.
As the concentration of drug 1 increases, the free calcium concentration decreases. On the other hand, since the fraction having a molecular weight of 3000 or more is increased, it can be seen that the reactivity has been lost due to the binding of the drug to calcium. Drug 1 is separated by filtration and is not included in the filtrate.

FIG. 9B shows the silica concentration.
When the concentration of the drug 2 is increased, the concentration of soluble silica (silicate monomer and dimer is detected) once increases and then decreases. In contrast to the movement, small silica colloids with a molecular weight of 3000 or less are reduced and increased. Since drug 2 is a dispersant and does not form a strong bond with silica, it can be seen that the addition of drug 2 has an effect of slowing the polymerization rate of silica. Drug 2 is separated by filtration and is not included in the filtrate. The fraction with a molecular weight of 3000 or more increases and decreases because of an increase in the amount of silica that is involved in the drug and separated by filtration, and a decrease due to a decrease in the overall molecular weight due to slow polymerization. . That is, the scale suppression effect shown in Example 1 is supported from the viewpoint of a decrease in polymerization rate.

1 Production Well 2 Heat Exchanger 3 Reduction Well 4 Turbine 5 Generator 6 Condenser 7 Silica Separator 8 Piping A Addition Position of Drug 1 B Addition Position of Drug 3 C Addition Position of Drug 2

Claims (10)

A method to suppress the scale formation by adding chemicals to the geothermal hot water, and after extracting thermal energy from the geothermal hot water collected through the production well from the ground, the geothermal hot water is passed through the reduction well A method for suppressing scale generated in the geothermal hot water flow path in the geothermal power generation system
(1) a compound containing a carboxyl group selected from polyacrylic acid, polymaleic acid, and acrylic acid / maleic acid copolymer, (2) a compound having a phosphate group containing hydroxyethylidenediphosphonic acid, and (3) polyacrylic A drug 1 that binds to a Ca ion selected from any one of a compound containing a sulfonic acid obtained by copolymerizing a sulfonic acid with a part of the acid polymer;
An agent 2 that promotes dispersion of a silica colloid selected from any one of (1) a cationic surfactant containing a quaternary ammonium salt, and (2) a dispersant containing polyvinylpyrrolidone or a copolymer thereof;
Among the agents 3 that promote the production of silica colloid containing polysilicic acid ,
A method for suppressing scale, comprising using at least two kinds of drugs in combination.   The scale suppression method according to claim 1, wherein the agent 2 that promotes the dispersion of the silica colloid and the agent 3 that promotes the formation of the silica colloid are used in combination.   The scale suppression method according to claim 1, wherein the agent 1 that binds to the Ca ions, the agent 2 that promotes the dispersion of the silica colloid, and the agent 3 that promotes the formation of the silica colloid are used in combination. The scale suppression method according to claim 1 or 3 , wherein the drug 1 contains an anion equal to or more than an equivalent of Ca ion contained in the geothermal hot water. The scale suppression method according to any one of claims 1 , 3 , and 4 , wherein the order of adding the drug 1, the drug 2, and the drug 3 is the order of the drug 1, the drug 3, and the drug 2. The scale suppression method according to any one of claims 1 to 3 , wherein the addition of the drug 1 is performed in the well of the production well. The scale suppression method according to any one of claims 1 to 6 , wherein the addition of the drug 1, the drug 2, and the drug 3 is performed before the geothermal hot water flows into the heat exchanger. After removing the heat energy from the geothermal hot water, before returning the geothermal heat water from the reinjection wells into the ground, to remove the silica from the geothermal hot water, to any one of claims 1-7 The scale suppression method as described. (1) a compound containing a carboxyl group selected from polyacrylic acid, polymaleic acid, and acrylic acid / maleic acid copolymer, (2) a compound having a phosphate group containing hydroxyethylidenediphosphonic acid, and (3) polyacrylic A drug 1 that binds to a Ca ion selected from any one of a compound containing a sulfonic acid obtained by copolymerizing a sulfonic acid with a part of the acid polymer;
An agent 2 that promotes dispersion of a silica colloid selected from any one of (1) a cationic surfactant containing a quaternary ammonium salt, and (2) a dispersant containing polyvinylpyrrolidone or a copolymer thereof;
Among the agents 3 that promote the production of silica colloid containing polysilicic acid ,
A scale suppression device comprising a device for adding at least two kinds of chemicals to geothermal hot water. (B) A device for collecting geothermal hot water from the ground, (b) A device for extracting thermal energy from the geothermal hot water, (c) A device for returning the geothermal hot water to the ground, (d) Combined with the Ca ions drug 1, drug 2 to facilitate the dispersion of the colloidal silica, of an agent 3 to promote the production of the colloidal silica, at least two or more agents are added to the geothermal hot water apparatus, and (e) The scale suppression device according to claim 9 , further comprising a device that circulates geothermal hot water in the (i) to (d).