JP5891084B2 - Scale removing agent, scale removing method and scale removing apparatus - Google Patents

Description

  The present invention relates to a scale removing agent having tropolones and a removing method for removing silica-based scale generated in a geothermal power generation facility using the removing agent.

  In a geothermal power generation facility, a scale in which calcium carbonate, calcium sulfate, calcium sulfide, calcium phosphate, magnesium hydroxide, calcium silicate, etc., dissolved in hot water is deposited. In particular, the scale containing silica has a poor thermal conductivity and is generally hard, which is a big problem in heat exchange facilities.

  In addition, generation of silica scale has been confirmed in the reservoir around the reduction well of the geothermal power generation facility. When this scale is generated, the water permeability in the reservoir layer is remarkably deteriorated and the diffusion of the reduced hot water is prevented, and the performance of the reducing well is deteriorated with time. If the performance of the reduction well deteriorates, it will be in a situation where it cannot be fully reduced. The reduction well that eventually fell in performance became an abandoned mine, and equipment users would need to re-dig a new well to reduce hot water.

  Silica-based scales generated in geothermal power generation facilities include both general silica scales where silica in hot water precipitates as amorphous silica alone and silicate scales complexed with metal cations in hot water. Yes. The scale exists in a crystalline or amorphous form, and specifically includes aluminum silicate, iron silicate, magnesium silicate, and the like.

  As a technique for removing the silica-based scale, techniques using hydrofluoric acid or fluoride are known (for example, Patent Document 1 and Patent Document 2). In this silica-based scale removal technology, fluoride ions contained in hydrofluoric acid or fluoride react with silica to dissolve and remove scale in a form that forms a complex of silica and fluorine.

  However, hydrofluoric acid is a deleterious substance-designated drug, and it is an extremely dangerous environment for removing scale. As for fluoride, when the temperature is raised to increase the dissolving power, highly toxic hydrofluoric acid is volatilized and a similar dangerous working environment is created. Furthermore, hydrofluoric acid and fluoride are chemicals that have a very high impact on the environment. In scale removal work that uses a large amount of chemicals, it is necessary to pay close attention to its disposal and discharge.

  Nitric acid is used for removal of silica scale by chemicals other than hydrofluoric acid and fluoride. However, since it does not show complex dissolution like fluorine, the removal ability of silica scale is small and practical. Absent.

  There is also a scale removal method using an alkaline solution, which also has a dissolving power for silica-based scales, but has a poor silicate scale dissolving power and is not practical.

  Although it is not a scale removal technology, there is a case where a method of adjusting the pH of hot water by adding a small amount of acid such as sulfuric acid to prevent the generation of scale in a hot water pipe of a geothermal power generation facility (for example, patent document) 3, Patent Document 4).

  This method has a low running cost and is widely used. In order to prevent the generation of scale, since the solubility of silica-based scale in hot water is larger as the pH is smaller, it is better to keep the pH as small as possible. Can only be lowered to Although this level of pH adjustment prevents a certain degree of occurrence, depending on the conditions of the formation such as the underground reservoir, the pH of hot water becomes high at the moment of exposure to the formation and there is a possibility of losing its suppression effect. I'm worried and I don't know if it will be effective enough.

  In addition, there are cases where the reservoir clogging has occurred over time even in the power generation facilities that are actually performing the treatment.

  As described above, at present, there is no method for removing silica-based scale with a practical chemical that is safe and has sufficient dissolving power.

Japanese Patent Laid-Open No. 63-179086 JP 63-179087 A JP 61-257220 A JP-A-4-371214

  An object of the present invention is to provide a technique for efficiently dissolving and removing scales safely using an environmentally friendly chemical in removing scales generated in geothermal power generation facilities.

  As a result of intensive studies on chemical removal of silica-based scales, the present inventors have found that silica-based scales can be removed safely and efficiently by using tropolones.

  The scale remover of the present invention is characterized by containing tropolones.

  A preferred embodiment of the present invention is characterized in that the scale remover contains at least one of hydrochloric acid, sulfuric acid and nitric acid, and the pH is adjusted to 1-2.

  The scale removal method of the present invention is characterized by removing silica-based scale generated in a geothermal power generation facility using the scale remover.

  The scale removing device of the present invention includes a tank that stores the scale removing agent, and a pump that circulates the scale removing agent between the tank and a geothermal power generation facility.

  According to the present invention, not only the scale is efficiently removed, but also hazardous materials such as hydrofluoric acid and fluoride are not used, so that the operation can be performed safely. Moreover, when applied to the reduction well reservoir of the geothermal power generation facility, the removal capability is exhibited and the scale can be efficiently removed regardless of the soil environment.

Change in silica concentration over time according to removal solution concentration in dissolution test (concentration dependence of silica dissolution) Change with time of silica concentration according to removal solution temperature in dissolution test (temperature dependence of silica dissolution) Change with time of silica concentration according to removal solution pH in dissolution test (pH dependence of silica dissolution) Diagram showing the structure of the tropolone form Schematic diagram of demonstration test equipment Change with time of silica concentration in removal solution in demonstration test equipment Diagram showing a simulated reservoir specimen Temporal change of head height in simulated reservoir test body

  The scale removal solution as the scale remover of the embodiment of the invention will be described in detail below. The scale removal solution of the present embodiment is used for removing silica-based scale generated in geothermal power generation facilities. A geothermal power generation facility is a power generation facility that uses geothermal heat, which is a type of renewable thermal energy. It uses a natural steam erupted from a well drilled underground to generate electricity and use it for power generation. The later steam and hot water are returned to the basement through the reduction well.

  The scale removal solution of this embodiment is a solution containing tropolones. The solvent is water or an organic solvent.

  Tropolones are one of aromatic compounds in which a hydroxyl group is introduced into a seven-membered tropolone (cycloputatrienone) skeleton. In general, it often refers only to α-tropolone. It can also be isolated from the essential oils of conifers such as natural hiba and cypress.

  The concentration of tropolones in the descaling solution is usually in the range of 0.01% to 3.5% by weight. When the concentration of tropolones is less than 0.01% by mass, the dissolution rate of the scale is slow, which is not practical. On the other hand, when the concentration of tropolones exceeds 3.5% by mass, tropolones dissolve well in organic solvents, but their solubility in water is not so high, so they are saturated due to changes in the environment of the target equipment. Therefore, it may be deposited in the facility and become a different harmful element, which is not preferable.

  Since the descaling ability of tropolone becomes stronger as the temperature is higher, the temperature of the descaling solution is preferably higher. However, if the temperature exceeds 110 ° C., it becomes difficult to apply it to the ground facility of the geothermal power generation facility. Therefore, it is preferable that the temperature of the scale removal solution is appropriately selected according to the state of the scale. On the other hand, if it is applied to the permeable layer of the reduction well reservoir of the geothermal power generation facility, the temperature range naturally exceeds 80 ° C., and the dissolution rate is also increased.

  The pH of the descaling solution is usually 3.5 or less. Most tropolones exhibit weakly acidic properties, but in some cases, it is preferable to add a solution having a low pH, for example, an acid such as hydrochloric acid, sulfuric acid, or nitric acid, to adjust the pH to an appropriate value according to the state of the scale.

  In the complex reaction between tropolones and silica contained in the descaling solution, the pH decreases, and the dissolution rate increases as the structure of the tropolones changes. Since dissolution with the scale proceeds mainly by a complex reaction, the dissolution of the silica-based scale can be accelerated as the pH of the removal solution is decreased. However, if the pH is lowered, the corrosion risk of the geothermal power generation equipment and the apparatus for transporting the removal solution is increased, so the pH is preferably about 1-2.

  The scale removal method of the present embodiment is a method of removing the scale removal solution by continuously or intermittently contacting the silica-based scale. For example, there is a method in which a scale removing solution is circulated with a pump and brought into contact with a silica-based scale of a ground hot water pipe or a heat exchanger in a geothermal power generation facility. Moreover, the method etc. which spray a scale removal solution directly to this silica type scale by spray etc. are also considered.

  The scale removal apparatus of the present embodiment includes a tank that stores the scale removal solution, and a pump that circulates the scale removal solution between the tank and the geothermal power generation facility. When the pump circulates the descaling solution, the descaling solution contacts the ground hot water piping in the geothermal power generation facility or the silica-based scale of the heat exchanger to remove it.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

  A silica-based scale dissolution test was carried out using the troponan aqueous solution (scale removal solution) of the example.

  Α-tropolone, which is a tropolone, was dissolved in ultrapure water to prepare an aqueous tropolone solution adjusted to pH 1 to 5 with an aqueous hydrochloric acid solution. An aqueous tropolone solution was placed in a beaker, and 5 g of silica-based scale adhering to the ground piping of the geothermal power generation facility in a mortar was added to the beaker.

  Stir the tropolone aqueous solution to which the silica-based scale added to powder is stirred with a shaker, collect an appropriate amount of the suspension at regular intervals, filter through a membrane filter, and then measure the Si concentration in the filtrate with an ICP emission spectrometer did. The results are shown in FIGS.

  FIG. 1 shows the change over time of the Si concentration in the solution at each solution concentration when the pH of the tropolone aqueous solution is 1 and the temperature is 30 ° C. It can be seen that the higher the solution concentration, the higher the Si concentration in the solution, and the higher the solubility in silica-based scale.

  FIG. 2 shows changes with time of the Si concentration in the solution at each pH and temperature of the solution when the tropolone aqueous solution concentration is 1.0 mass%. It can be seen that the lower the pH, the higher the Si concentration in the solution, and the higher the solution temperature, the higher the Si concentration in the solution, which increases the dissolving ability of the silica-based scale.

  FIG. 3 shows changes with time of the Si concentration in the solution at each pH when the temperature of the tropolone aqueous solution is 30 ° C. and the concentration is 1.0 mass%. It can be seen that the lower the pH, the higher the Si concentration in the solution, and in particular, the dissolution rate increases rapidly in the pH range of 1-2.

  FIG. 4 shows three types of structures in tropolone.

4 (a) is a protonated form [H ₂ L ⁺ ], FIG. 4 (b) is a normal α-tropolone form [HL], and FIG. 4 (c) is a troponate form [L ⁻ ]. It expresses. Here, L means a ligand, and the expression of each form expresses a proton in the same manner as a metal ion, and expresses it as a proton complex in a broad sense. For example, L means the following structural formula in which two protons are dissociated from tropolone.

The distribution of these forms is determined by the following balanced equations (1) and (2).

As the environment becomes acidic, the reaction of formula (1) proceeds to the right and the reaction of formula (2) proceeds to the left. Therefore, it is considered that tropolone is almost transformed into a protonated form of [H ₂ L ⁺ ] under strong acidity such as pH of 1. In this protonated form, tropolone is considered to exhibit a strong complex reaction with silica and increase the dissolution rate of the silica-based scale.

  The test which removes the silica-type scale produced | generated in the heat exchanger which heat-exchanges the temperature of geothermal water and a vapor | steam in a geothermal power generation equipment using the tropolone aqueous solution of an Example was implemented.

  As shown in FIG. 5, the tropolone aqueous solution tank 1 was installed in a device that circulates geothermal water inside the heat exchanger 6 generated by the silica-based scale in the geothermal power generation facility. After the geothermal water was temporarily stopped, a 1.0 mass% tropolone aqueous solution adjusted to pH 1 was circulated for 72 hours. The Si concentration in the solution at this time was measured with an ICP emission spectrometer.

  FIG. 6 shows the change over time in the Si concentration in the solution circulating in the heat exchanger. As time passed, the Si concentration increased, and it was confirmed that the silica-based scale in the heat exchanger was removed.

  In order to confirm the effect of the removal solution in the reduction well where the scale blockage was observed over time in the geothermal power generation facility, a scale removal test was conducted on a test body that simulated the reservoir part of the reduction well.

  FIG. 7 shows a simulated specimen. A half-sand blend of red sand and red sand, mixed with a simulated base layer adjusted to neutral (pH 5) and weakly alkaline (pH 8) and silica gel at a ratio of 7: 3, and a stainless steel pipe (made of SUS304) with a diameter of 100 mm and a length of 4000 mm. ) And filled up to a depth of 1000 mm from the lower surface to prepare a test body simulating the scale blockage of the reservoir portion of the reduction well.

  A mesh-like wire net that can withstand the weight of the formation made of the same material was installed on the lower surface of the stainless steel pipe, and filter paper was laid on the mesh to simulate the state of the removal solution in the formation in the reduction well for a certain period of time.

  While maintaining the temperature of the steel pipe inner layer at 80 ° C. with a heating ribbon heater from the side of the test body, a 1 mass% tropolone aqueous solution adjusted to pH 1 was poured into the 30 L test body from the upper part of the steel pipe, and the scale was removed for 72 hours. After 72 hours, tap water was poured from the upper part of the stainless steel pipe so that the water head was 4000 mm from the lower end of the steel pipe, and the temporal change of the water head height from that point was measured. Here, the head height at the start of measurement is 0 mm, and the head height is 4000 mm if the entire solution flows out.

  A similar test was performed on unadjusted tap water and a sulfuric acid aqueous solution adjusted to pH 1 as a removal solution instead of the tropolone aqueous solution.

  FIG. 8 shows the temporal change of the head height under each condition. When the tropolone aqueous solution is used, the improvement of water penetration is noticeable as compared with the case where tap water is used regardless of whether the formation is neutral or weakly alkaline. It is thought that the silica gel mixed as a silica-based scale simulant dissolved by tropolone and the penetration was improved. Comparing the neutrality and weak alkalinity of the strata, it can be seen that the environment where the stratum is neutral can be expected to improve the infiltration early.

  On the other hand, with respect to the sulfuric acid aqueous solution, improvement of water penetration is recognized when the formation is in a neutral environment. However, the effect is smaller than when the tropolone aqueous solution is used. When the formation becomes weakly alkaline, the improvement in infiltration is small. Moreover, it is suggested that it may be difficult to remove the silica-based scale in the formation close to the alkaline environment, because it is more sensitive to the properties of the formation than when the tropolone aqueous solution is used.

1: Tropolone aqueous solution tank 2: Circulation pump 3: Removal solution circulation valve (outward)
4: Geothermal water circulation shut-off valve 5: Geothermal water bypass valve 6: Heat exchanger 7: Removal solution circulation valve (return)
8: Removal solution blocking valve 11: Stainless steel pipe 12: Removal solution 13: Simulated formation 14: Filter paper 15: Mesh wire mesh 16: Specimen support base 17: Removal solution receiver 18: Ribbon heater

Claims (4)

  A scale remover comprising tropolones.   The scale remover according to claim 1, comprising at least one of hydrochloric acid, sulfuric acid, and nitric acid, and having a pH adjusted to 1 to 2.   A scale removal method comprising removing a silica-based scale generated in a geothermal power generation facility using the scale remover according to claim 1. A tank for storing the descaling agent according to claim 1 or 2,
And a pump that circulates the scale remover between the tank and a geothermal power generation facility.

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