JP7745149B2 - Silica scale modifier - Google Patents

Description

The present invention relates to a silica scale modifying agent and a plant system equipped with an apparatus for administering the agent. In particular, the present invention relates to a silica scale modifying agent that modifies silica scale and makes it easier to remove the scale in a plant system.

In plant systems that use groundwater, such as geothermal power plants, silica dissolved in the water causes silica scale to adhere to the equipment and piping that make up the plant system. Silica scale is a strong deposit composed primarily of polymers of Si and O, and is difficult to remove.

One conventional method for preventing the formation of silica scale is the pH adjustment method. It is known that the rate at which scale builds up decreases depending on the pH of the geothermal steam, and scaling can be suppressed to some extent by reducing the pH to 5 or below. Specific methods for achieving this include injecting sulfuric acid or hydrochloric acid into the geothermal fluid (see, for example, Patent Document 1).

On the other hand, a known method for removing silica scale that has already adhered is to use chemicals to dissolve and remove the silica scale.

JP 2017-160842 A

However, because silica scale adheres to all parts of a plant system, currently, even when the above methods are used, mechanical (physical) removal is carried out after chemical treatment using chemicals. This mechanical removal work is large-scale and labor-intensive, necessitating the shutdown of the plant system for an extended period of time. There is a need for a chemical agent and system that can easily remove silica scale with little effort and short shutdown time.

After extensive research, the inventors came up with the idea of introducing a chemical structure into the silica scale polymer that has weaker interatomic bonding strength than conventional silica scale, making it possible to remove the scale without the need for large-scale work or strong mechanical forces. More specifically, they came up with the idea of using a chemical agent that can be mixed with the fluid circulating through the plant system and that can be incorporated into the molecular structure of the silica scale as the main component of the silica scale modifier, leading to the completion of the present invention.

That is, according to one embodiment, the present invention relates to a silica scale modifying agent containing a silane coupling agent.

In the silica scale modifying agent, the silane coupling agent is preferably 3-glycidoxypropyltrimethoxysilane or 3-glycidoxypropyltriethoxysilane.

The silica scale modifying agent is preferably a silane coupling agent having a linear hydrocarbon group with 8 or more carbon atoms.

It is preferable that the silica scale modifier is one that is added to the circulating water of a plant system.

In the silica scale modifying agent, it is preferable that the plant system is a geothermal power generation system and the circulating water is geothermal fluid.

According to another embodiment, the present invention provides a geothermal power generation system, comprising:
a gas-liquid separator that separates the geothermal fluid pumped from the production well into gas and liquid components;
a turbine disposed downstream of the gas-liquid separator and configured to be rotatable by the gas components separated by the gas-liquid separator;
A pipe for delivering the liquid component separated in the gas-liquid separator to an injection well;
and an injection device that injects the silica scale modifying agent according to any one of the preceding claims into geothermal fluid.

In the geothermal power generation system, it is preferable that the injection device be installed in the piping between the production well and the gas-liquid separator, the piping between the gas-liquid separator and the turbine, or the piping between the gas-liquid separator and the reinjection well.

According to yet another embodiment, the present invention provides a method for modifying silica scale, comprising the steps of:
a gas-liquid separator that separates the geothermal fluid pumped from the production well into gas and liquid components;
a turbine disposed downstream of the gas-liquid separator and configured to be rotatable by the gas components separated by the gas-liquid separator;
a pipe for delivering the liquid component separated by the gas-liquid separator to an injection well,
The present invention relates to a method for modifying silica scale, which comprises the step of adding the silica scale modifying agent according to any one of the above items to a geothermal fluid circulating in the geothermal power generation system.

The silica scale modifying agent of the present invention can be added to the fluid circulating within a plant system during normal operation, modifying silica scale that may adhere to any part of the plant system and making it easier to remove. Because the silica scale modifying agent of the present invention can modify the chemical structure of silica scale during the process of its adhesion and growth, it can achieve significant removal effects, unlike conventional chemicals that were applied after the fact after adhesion.

FIG. 1 is a conceptual diagram illustrating a geothermal power generation system, which is an example of a plant system to which a silica scale modifying agent can be applied.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments described below.

According to one embodiment, the present invention relates to a silica scale modifying agent. The silica scale modifying agent contains a silane coupling agent as a main component.

A silane coupling agent is a compound that contains, in one molecule, an inorganic portion containing a Si atom and an alkoxy group directly bonded thereto, an organic portion containing an organic functional group, and a divalent hydrocarbon group bonding these together. The silane coupling agent may particularly be a compound represented by the formula A-B-Si(OR ¹ ) _n (R ² ) _3-n (wherein A is the organic portion, B is a divalent hydrocarbon group, and Si(OR ¹ ) _n (R ² ) _3-n is the inorganic portion. In the inorganic portion, R ¹ and R ² are independently linear or branched hydrocarbon groups having 1 to 3 carbon atoms, and n is an integer selected from 1, 2, and 3).

A includes a bonding portion to B and an organic functional group. The bonding portion to B can typically be represented by —O—(CH ₂ ) _m —, where m is an integer selected from 1, 2, and 3. The organic functional group may be, for example, an organic functional group including an epoxy group, a methacryl group, an amino group, and/or an isocyanate group, but is not limited to these.

B is a linear or branched, saturated or unsaturated divalent hydrocarbon group, preferably a linear saturated hydrocarbon group with 3 or more carbon atoms, preferably 5 or more, and more preferably 8 or more. The upper limit of the carbon number is not particularly limited, but may be, for example, 20 or less, preferably approximately 10 or less. Note that the number of carbon atoms here refers to the number of consecutive carbon-carbon bonds without a heteroatom such as an oxygen atom between the carbon atoms. Silane coupling agents with long linear saturated hydrocarbon groups are incorporated into the Si and O polymers that make up silica scale, weakening the bonding strength between atoms in the polymer. Furthermore, the presence of long linear saturated hydrocarbon groups at the interface with the equipment to which silica scale adheres can reduce the strong adhesion of silica scale to the equipment.

R ¹ and R ² may independently represent a propyl group, an ethyl group, or a methyl group, and are preferably methyl groups from the viewpoint of ease of hydrolysis.

Specific examples of silane coupling agents include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, amino N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propyl. Examples of suitable silanes include, but are not limited to, propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, octenyltrimethoxysilane, 8-glycidoxyoctyltrimethoxysilane, and methacryloxyoctyltrimethoxysilane.

The silica scale modifier according to this embodiment may contain only one type of silane coupling agent, or may contain a mixture of multiple different types of silane coupling agents. When containing a mixture of multiple different types of silane coupling agents, two or more types of silane coupling agents whose organic functional groups do not react with each other can be mixed.

The silica scale modifying agent may consist solely of a silane coupling agent, or may contain, in addition to the silane coupling agent, a catalyst and a pH adjuster (such as sulfuric acid or caustic soda). It may also contain a chemical previously known for use in removing silica scale, provided that the properties of the silane coupling agent are not impaired. Examples of chemicals include, but are not limited to, acetic acid and hydrofluoric acid.

Next, we will explain a plant system to ^which the silica scale modifying agent can be applied and a method of using the silica scale modifying agent. The silica scale modifying agent can _{be added to any plant system in which a fluid containing silicic acid (Si(OH)4, Si(OH)3O-, SiO2(OH)22-} ^, _{Si2O2 ( OH ) 5- , Si2O3 ( OH} ^{) 42-} , etc.) can be circulated, and in which the deposition of silica scale is a problem. Examples of plant systems include, but are not limited to, geothermal power generation systems, boiler systems, systems equipped with cooling water piping, and water treatment systems.

Next, the use of a silica scale modifier will be explained using a geothermal power generation system as an example of a plant system. A geothermal power generation system according to one embodiment of the present invention comprises a gas-liquid separator that separates geothermal fluid pumped from a production well into gas and liquid components, a turbine positioned downstream of the gas-liquid separator and configured to be rotatable by the gas components separated by the gas-liquid separator, piping that delivers the liquid components separated by the gas-liquid separator to a reinjection well, and an injection device that injects the silica scale modifier into the geothermal fluid.

Figure 1 is a conceptual diagram illustrating a geothermal power generation system. Referring to Figure 1, the geothermal power generation system is primarily composed of a production well 6, a gas-liquid separator 2, a turbine 3, a generator 4, a condenser 5, and a reinjection well 7, and is equipped with a silica scale modifier injection device 1 between the production well 6 and the gas-liquid separator 2.

The flow of materials in a geothermal power generation system will now be described. Production well 6 is a well that extracts hot water, steam, or a mixture thereof (hereinafter referred to as geothermal fluid) from an underground geothermal reservoir. The geothermal fluid extracted from production well 6 is separated into gaseous steam and liquid hot water in gas-liquid separator 2. The separated steam is guided to turbine 3 and used to rotate turbine 3, generating electricity in generator 4. The steam that passes through turbine 3 is cooled in condenser 5 and guided to reinjection well 7 through piping (not shown). Meanwhile, the hot water separated in gas-liquid separator 2 is cooled and guided to reinjection well 7. Note that there are two possible configurations: one in which the steam separated in gas-liquid separator 2 directly rotates the turbine, and another in which the steam heats a low-boiling-point solvent, which then rotates the turbine. In this specification, the term "turbine configured to be rotatable by gaseous components separated in a gas-liquid separator" encompasses both of these configurations.

Silica scale is primarily composed of a polymer of Si and O that is formed due to silicic acid dissolved in geothermal fluid, and depending on the geothermal power generation method, it can adhere to any part of a geothermal power generation system, including turbine components such as turbine blades and rotors, piping, and heat exchangers.

In a geothermal power generation system according to one embodiment of the present invention, the silica scale modifier injection device 1 is installed between the production well 6 shown in the figure and the gas-liquid separator 2, and is configured to be able to inject silica scale modifier into the geothermal fluid immediately after it is drawn from the production well to the surface.

The silica scale modifying agent dosing device 1 may be a device that mixes the silica scale modifying agent with water and can then be dosed into the fluid in the facility at the appropriate temperature and concentration. Optionally, the silica scale modifying agent dosing device 1 may be equipped with a calculation means that optimizes the amount and type of silica scale modifying agent to be dosed according to the temperature, pH, and other conditions of the fluid to be dosed.

The amount of silica scale modifying agent added depends on the pH and temperature conditions of the geothermal fluid, but it is preferable to add an amount that results in a silane coupling agent concentration in the geothermal fluid that is at least 50% of the silicic acid concentration (weight percent). There is no particular upper limit to the silane coupling agent concentration, but it is preferable to add it at a concentration equal to or lower than the silicic acid concentration. By adding it in this amount, the silane coupling agent bonds to the Si compound species in the geothermal fluid, making it easier to incorporate into the Si-O polymer structure as silica scale grows. This weakens the bonding strength of the Si-O that makes up the silica scale, making it easier to modify the silica scale to a chemical structure that is easier to remove.

It is preferable to mix the silica scale modifier with water before adding it and leave it to stand for 1 to 3 hours to allow a preliminary reaction to occur, which promotes the hydrolysis reaction of the alkoxy groups in the silane coupling agent. Without intending to be bound by theory, after the preliminary reaction, the Si-OH portion of the silane coupling agent added to the geothermal fluid reacts with silicic acid in the geothermal fluid. Normally, silica scale forms a strong polymer composed of Si and O. However, by adding the silica scale modifier, chemical species formed by the polymerization of silicic acid and the silane coupling agent adhere to the surface of the piping components, and carbon moieties derived from the silane coupling agent often come into contact with the interface between the piping and the geothermal fluid. This is thought to modify the chemical structure of the silica scale, making it easier to peel off from the piping surface.

In place of or in addition to the illustrated embodiment, the silica scale modifier injection device can be installed at a different location. For example, an injection device can be installed in the piping immediately before the gas-liquid separator 2, indicated by a in the figure, to inject the silica scale modifier. A mixture of hot water and steam flows through the piping indicated by a. By installing the silica scale modifier injection device at this location, the silica scale inside the gas-liquid separator 2 can be modified, facilitating maintenance of the gas-liquid separator 2. Furthermore, an injection device can be installed in the piping immediately after the gas-liquid separator 2, indicated by b in the figure, and immediately before the turbine 3. Steam primarily flows through the piping indicated by b. By installing the silica scale modifier injection device at this location, the silica scale adhering to the components that make up the turbine 3 can be modified. Furthermore, an injection device can be installed in the piping immediately before the reinjection well 7, indicated by c in the figure, to inject the silica scale modifier. By installing a silica scale modifying agent injection device at this location, it is possible to modify the silica scale adhering to the components that make up the reinjection well 7. Alternatively, by installing a silica scale modifying agent injection device immediately after the gas-liquid separator 2 in the piping leading to the reinjection well 7, as shown at c, it is possible to modify the silica scale adhering to the piping components leading to the reinjection well 7. In addition to the silica scale modifying agent injection device 1 in Figure 1, it is also possible to install injection devices at one or more locations a, b, and c, and operate only the injection devices at the necessary locations to inject the silica scale modifying agent when needed.

In Figure 1, a geothermal power generation system is used as an example, but the silica scale modifying agent injection device can be installed in any plant system through which a fluid containing water with dissolved silicic acid flows. In particular, it can be installed upstream of a location where silica scale buildup is a problem, contributing to the modification of silica scale and making it easier to remove.

The present invention will be described in more detail below using examples. However, the present invention is not limited to the scope of the following examples.

1. Concentration Dependence of Silane Coupling Agent In the geothermal power generation system shown in Figure 1, a silane coupling agent injection device is placed between the production well and the surface facility. In Examples 1 and 2, a silica scale modifier containing 3-glycidoxypropyltrimethoxysilane (KBM-403 manufactured by Shin-Etsu Silicones Co., Ltd.) is used as the silane coupling agent. In this example and the comparative example, the concentration of silicic acid contained in the geothermal fluid is assumed to be approximately 500 ppm. The silane coupling agent is injected into the geothermal fluid in an amount that results in the concentration shown in Table 1 below. Before injecting the silica scale modifier into the geothermal fluid, the silica scale modifier and water are mixed in the silica scale modifier injection device, heated to 25°C, and allowed to stand (stirred as necessary) for 2 to 3 hours before injection. This is to promote hydrolysis of the alkoxy groups in the silane coupling agent.

The results are shown in Table 1. Here, the silica scale bonding strength refers to the relative bonding strength, assuming that the bonding strength between silica particles in silica scale without a silica scale modifier is 100%. The silica scale bonding strength (estimated value) listed in Table 1 was calculated as follows: If 100 ppm of silane coupling agent is added to a silica concentration of 500 ppm, assuming all of the silane coupling agent bonds with the silica, the silane coupling agent will penetrate 17% by weight of the scale, resulting in a 17% decrease in bonding strength to 83%. The silica scale removal force is the load (unit: Newton) applied when the scale is peeled off in a scratch test. This silica scale removal force is also expressed as a relative value, with the load without a silica scale modifier set to 1. The criteria for ease of removal are: a removal force of 0.67 or less compared to Comparative Example 1 is considered "easy," and a removal force of greater than 0.67 is considered "difficult." The carbon concentration in the scale was calculated as follows: EDX analysis was used for concentration analysis. Because carbon also contains contaminants, the carbon concentration obtained by analyzing Comparative Example 1 was used as the contaminant, and this concentration was subtracted from the carbon concentrations obtained by analyzing Examples 1 and 2. The results are shown in Table 1. In Table 1, the value in parentheses next to the carbon concentration indicates the carbon:silicon atomic ratio.

As the amount of silane coupling agent added increases, the bonding strength between atoms in the silica scale decreases, predicting that the silica scale will be modified into a chemical structure that is easier to remove. However, adding a silane coupling agent at a concentration about half the silicic acid concentration makes silica scale removal easier (less force). EDX analysis of the carbon concentration (wt%) in the silica scale reveals that the ratio of carbon atoms to silicon atoms contained in the silica scale increases as the amount of silane coupling agent added increases. Furthermore, adding a silane coupling agent at a concentration more than half the silicic acid concentration makes it easier to remove silica scale that has adhered to pipe walls. In this example, 3-glycidoxypropyltrimethoxysilane was used, but similar effects can be achieved with 3-glycidoxypropyltriethoxysilane (KBE-403, manufactured by Shin-Etsu Silicones Co., Ltd.).

2. Dependence of Silane Coupling Agent Structure Next, an experiment was conducted using the same silane coupling agent concentration conditions and silicic acid concentration conditions as in Example 2, except that the silane coupling agent, the main component of the silica scale modifier, was changed to 8-glycidoxyoctyltrimethoxysilane (KBM-4803, manufactured by Shin-Etsu Silicones Co., Ltd.). This is designated Example 3. When the physical properties of the scale formed in Example 3 were examined, the force required to remove the silica scale was 0.3 relative to Comparative Example 1. In Example 2, the force required to remove the formed scale was 0.5 relative to Comparative Example 1. However, when a silane coupling agent with a larger number of linear carbon atoms between the inorganic and organic moieties was used, the force required to remove the silica scale was further reduced, making silica scale removal even easier.

1 Silica scale modifying agent injection device, 2 Gas-liquid separator, 3 Turbine, 4 Generator, 5 Condenser, 6 Production well, 7 Reinjection well

Claims (7)

A silica scale modifier containing a silane coupling agent for use by adding to the circulating water of a plant system , the silica scale modifier being incorporated into the polymer structure of the silica scale to modify the chemical structure of the silica scale . The silica scale modifier according to claim 1, wherein the silane coupling agent is 3-glycidoxypropyltrimethoxysilane or 3-glycidoxypropyltriethoxysilane. The silica scale modifier according to claim 1, wherein the silane coupling agent is a silane coupling agent having a linear hydrocarbon group with 8 or more carbon atoms. The silica scale modifying agent according to claim 1 , wherein the plant system is a geothermal power generation system and the circulating water is a geothermal fluid. a gas-liquid separator that separates the geothermal fluid pumped from the production well into gas and liquid components;
a turbine disposed downstream of the gas-liquid separator and configured to be rotatable by the gas components separated by the gas-liquid separator;
A pipe for delivering the liquid component separated in the gas-liquid separator to an injection well;
A geothermal power generation system comprising an injection device that injects the silica scale modifying agent according to any one of claims 1 to 4 into geothermal fluid. 6. The geothermal power generation system of claim 5, wherein the injection device is provided in a piping between the production well and the gas-liquid separator, a piping between the gas-liquid separator and the turbine, or a piping between the gas-liquid separator and the injection well . a gas-liquid separator that separates the geothermal fluid pumped from the production well into gas and liquid components;
a turbine disposed downstream of the gas-liquid separator and configured to be rotatable by the gas components separated by the gas-liquid separator;
a pipe for delivering the liquid component separated by the gas-liquid separator to an injection well,
A method for modifying silica scale, comprising the step of adding the silica scale modifying agent according to any one of claims 1 to 4 to a geothermal fluid circulating in the geothermal power generation system.