JP2018003275A - Geothermal utilization system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a geothermal utilization system that suppresses precipitation of a scale on pipeline through which geothermal fluid flows and a heat exchanger and other external facilities, at the same time prolonging a maintenance frequency for the pipeline, etc.SOLUTION: A geothermal utilization system 1 according to an embodiment includes: an air-water separation tank 2 that separates a geothermal fluid that has flown out from an outlet port 11a of a geothermal fluid extraction pipe 11 into geothermal water and geothermal steam, at the same time maintaining carbon dioxide partial pressure of the geothermal steam at a partial pressure value of deaeration suppression or higher; and an aeration tank 3 for aerating the geothermal water that has flown in from the air-water separation tank 2 through a check valve 21, thus deaerating carbon dioxide contained in the geothermal water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a geothermal utilization system, and more particularly to a system that uses a geothermal fluid taken from a source.

  Conventionally, a geothermal utilization system that takes out a geothermal fluid including geothermal steam and geothermal water from an underground source (production well) and uses the geothermal steam for power generation or the like is known (see Patent Document 1). In addition, a geothermal utilization system that performs binary power generation by heating and evaporating a low boiling point medium using geothermal water and rotating a turbine with the steam is also known.

JP2013-180912A

  In the geothermal utilization system, scales are provided on the inner wall of piping for extracting geothermal fluid from the source, piping for transporting geothermal water to external equipment such as a heat exchanger, and external equipment (hereinafter collectively referred to as “piping etc.”). Adhere to. The scale is a deposit of inorganic salts contained in the fluid on the inner wall, and is very hard and difficult to dissolve in water. Conventionally, calcium carbonate and silica have been known as scales for geothermal water. However, the inventors' research has revealed that magnesium silicate is also included in the scale components.

  As the scale grows, the flow path in the piping and external equipment becomes narrower, so it is necessary to perform maintenance and remove the scale. The removal of the scale is performed by a method such as dissolving the scale with a chemical, scraping it, or crushing it. Regardless of which method is used, fluid cannot flow through the piping or the like during maintenance. For this reason, for example, when generating electricity using geothermal fluid, the operation must be stopped during the maintenance period. Therefore, it is required to suppress the precipitation of scale as much as possible.

  Then, an object of this invention is to provide the geothermal utilization system which can suppress that a scale deposits in the piping and external equipment through which a geothermal fluid flows, and can extend the maintenance period of piping etc.

The geothermal utilization system according to the present invention is:
Separating the geothermal fluid flowing out from the outlet of the geothermal fluid outlet pipe into geothermal water and geothermal steam, and maintaining the carbon dioxide partial pressure of the geothermal steam above the deaeration suppression partial pressure value; and
An aeration tank for aeration of geothermal water flowing from the air / water separation tank through a backflow prevention valve to degas carbon dioxide in the geothermal water;
It is characterized by providing.

In the geothermal utilization system,
The apparatus further comprises a hot water transport pipe for transporting geothermal water stored in the aeration tank to an external facility, and the temperature of the geothermal water flowing in the hot water transport pipe is maintained at a temperature higher than a temperature at which silicon oxide does not precipitate. You may be made to do.

In the geothermal utilization system,
A backflow prevention valve that prevents backflow of geothermal steam exhausted from the steam-water separation tank and keeps the carbon dioxide partial pressure of the geothermal steam in the steam-water separation tank at a constant value may be further provided.

In the geothermal utilization system,
The said backflow prevention valve may be provided, and you may further provide the steam exhaust pipe which exhausts the geothermal steam of the said steam separation tank.

In the geothermal utilization system,
The outlet of the geothermal fluid outlet pipe may be disposed in the gas phase of the steam separator.

In the geothermal utilization system,
The outlet of the geothermal fluid outlet pipe may be provided with a sudden pressure reduction preventing means for preventing the geothermal fluid pressure from suddenly decreasing.

In the geothermal utilization system,
The outlet of the geothermal fluid outlet pipe may be disposed in the liquid phase of the steam / water separation tank.

In the geothermal utilization system,
The steam / water separation tank and the aeration tank may be connected so as to connect the liquid phases to each other via a connection pipe provided with the backflow prevention valve.

In the geothermal utilization system,
In the aeration tank, calcium ions dissolved in the geothermal water may be precipitated as insoluble calcium carbonate, and magnesium ions dissolved in the geothermal water may be precipitated as insoluble magnesium silicate.

  In the present invention, in the steam-water separation tank, the geothermal water is made acidic by maintaining the carbon dioxide partial pressure of the geothermal steam at or above the degassing suppression partial pressure value, and the precipitation of calcium carbonate and magnesium silicate is suppressed. Thereby, it can suppress that a scale adheres to a geothermal fluid extraction pipe. On the other hand, in the aeration tank, geothermal water is aerated to degas carbon dioxide, thereby making the geothermal water alkaline and forcing calcium carbonate and magnesium silicate to precipitate. And geothermal water is supplied to external facilities, such as a heat exchanger, via a hot water transport pipe. Thereby, it can suppress that the scale of calcium carbonate and magnesium silicate precipitates in external facilities, such as a hot-water transport pipe and a heat exchanger.

  Therefore, according to this invention, it can suppress that a scale deposits in external facilities, such as piping and a heat exchanger with which a geothermal fluid flows, and can extend the maintenance period of piping etc. significantly.

1 is a schematic configuration diagram of a geothermal utilization system 1 according to an embodiment of the present invention. CO ₂ is a graph showing the relationship between the solubility and carbon dioxide partial pressure (p _CO2). (A) is a temperature-pH correlation diagram of calcium carbonate, and (b) is a temperature-pH correlation diagram of silica (SiO ₂ ). (A) and (b) are both temperature-pH correlation diagrams of magnesium silicate (MgSiO ₃ .H ₂ O).

  Hereinafter, a geothermal utilization system according to an embodiment of the present invention will be described with reference to the drawings.

  First, before describing the geothermal utilization system, the deposition conditions of various scales (calcium carbonate, silica, and magnesium silicate) are shown in FIGS. 3 (a), 3 (b), 4 (a), and 4 (b). ) Will be described. In addition, although FIG. 3 (a), FIG.3 (b), FIG.4 (a) and FIG.4 (b) are the results derived | led-out using the component of the hot spring water of Obama hot spring of Unzen City, Nagasaki Prefecture, The tendencies and characteristics explained in the above are the same for other hot spring waters.

The precipitation reaction of calcium carbonate is as shown in chemical formula (1).
CaCO ₃ Ｃａ Ca ²⁺ + CO ₃ ²⁻ (1)

  FIG. 3A is an example of a graph showing the relationship between the temperature and pH of calcium carbonate using the saturation index (SI) as a parameter. As can be seen from FIG. 3A, the precipitation of calcium carbonate is suppressed as the pH decreases.

The precipitation reaction of silica is as shown in chemical formulas (2) and (3).
SiO ₂ + 2H ₂ O⇔H ₂ SiO ₄ (aq) (2)
SiO ₂ + 2H ₂ O⇔H ₃ SiO ₄ ⁻ + H ⁺ (aq) (3)

FIG. 3B is an example of a graph showing the relationship between the temperature and pH of silica (SiO ₂ ) using the saturation index as a parameter. As can be seen from FIG. 3B, in the region where the temperature of the geothermal water is high to some extent (for example, 64 ° C. or higher), the precipitation of silica is suppressed regardless of the pH value.

The precipitation reaction of magnesium silicate is as shown in chemical formulas (4) and (5).
MgSiO ₃ .H ₂ O + H ₂ O⇔Mg ²⁺ + H ₃ SiO ₄ ⁻ + OH ⁻
... (4)
Mg ₃ Si ₂ O ₅ (OH) ₄ + 6H ^{+ ３} 3Mg ²⁺ + 2H ₄ SiO ₄ ⁰ + H ₂ O
... (5)

FIG. 4A is an example of a graph showing the relationship between the temperature and pH of magnesium silicate (MgSiO ₃ .H ₂ O) using the saturation index as a parameter. FIG. 4B is an example of a graph showing the relationship between the temperature and pH of magnesium silicate (Mg ₃ Si ₂ O ₅ (OH ₄ )) using the saturation index as a parameter. As can be seen from FIG. 4A and FIG. 4B, the precipitation of magnesium silicate is suppressed as the pH is lowered. In particular, Mg ₃ Si ₂ O ₅ (OH ₄ ) is sensitive to pH as shown in FIG.

  Next, the geothermal utilization system 1 according to the present embodiment will be described.

  As shown in FIG. 1, the geothermal utilization system 1 includes an air / water separation tank 2, an aeration tank 3, a geothermal fluid extraction pipe 11, a hot water transport pipe 12, a connection pipe 13, and a steam exhaust pipe 14. I have.

The geothermal fluid take-out pipe 11 takes out a geothermal fluid from a source (production well) and causes it to flow out from the outlet 11a. This geothermal fluid is composed of geothermal water and geothermal steam. Geothermal water contains calcium ions (Ca ²⁺ ), magnesium ions (Mg ²⁺ ), and hydrogen carbonate ions (HCO ₃ ⁻ ), and geothermal steam contains carbon dioxide (CO ₂ ).

  In this embodiment, as shown in FIG. 1, the geothermal fluid outlet pipe 11 has an outlet 11 a arranged in the gas phase of the steam separator 2. Thereby, geothermal steam can be efficiently taken out via the steam exhaust pipe 14. The extracted geothermal steam is sent to a steam turbine or the like.

  The hot water transport pipe 12 transports the geothermal water stored in the aeration tank 3 to external equipment. External facilities include binary power generation heat exchangers, cooking utensils, and hot springs.

  As shown in FIG. 1, the connection pipe 13 is a pipe that connects the steam / water separation tank 2 and the aeration tank 3. More specifically, the steam separation tank 2 and the aeration tank 3 are connected to each other via the connection pipe 13 so as to connect the liquid phases. The connection pipe 13 is provided with a backflow prevention valve 21. The check valve 21 is a check valve for preventing the backflow of geothermal water from the aeration tank 3 to the steam separation tank 2. The backflow prevention valve 21 can prevent the concentration of carbon dioxide in the geothermal water of the steam / water separation tank 2 from decreasing.

  Next, the steam / water separation tank 2 will be described in detail.

  The steam-water separation tank 2 separates the geothermal fluid flowing out from the outlet 11a of the geothermal fluid outlet pipe 11 into geothermal water and geothermal steam. The geothermal water is stored in the steam / water separation tank 2, and the geothermal steam is led to an external device such as a steam turbine through the steam exhaust pipe 14.

The steam-water separation tank 2 maintains the carbon dioxide partial pressure (p _CO2 ) of the geothermal steam at or above the degassing suppression partial pressure value. By maintaining the carbon dioxide partial pressure of the geothermal steam at or above the degassing suppression partial pressure value, it is possible to suppress degassing of carbon dioxide from the geothermal water in the steam-water separation tank 2. By suppressing the deaeration of carbon dioxide, the pH of the geothermal water in the steam separator 2 is lowered.

Incidentally, degassed suppression value of the partial pressure, with a graph showing the relationship between CO ₂ solubility and CO ₂ partial pressure (see FIG. 2), bicarbonate ion concentration of the geothermal water ^- obtained from measured values of (HCO ₃ concentration) It is possible. For example, when the bicarbonate ion concentration in the geothermal water is 2.7 × 10 ⁻³ mol / L, the degassing suppression partial pressure value is obtained as about 0.2 to 0.25 atm using the graph of FIG.

  By maintaining the carbon dioxide partial pressure of the geothermal steam in the steam-water separation tank 2 at or above the degassing suppression partial pressure value as described above, suppressing the degassing of carbon dioxide in the steam-water separation tank 2, The pH of the water becomes acidic (for example, pH = 4.5 to 6.5). Thereby, as can be seen from FIGS. 3A, 4A, and 4B, precipitation of calcium carbonate and magnesium silicate is suppressed. As a result, it can suppress that the scale which consists of these substances adheres to the inside of the geothermal fluid extraction pipe | tube 11, and the outflow port 11a. In addition, since geothermal water is high temperature in the geothermal fluid extraction pipe | tube 11 and the steam-water separation tank 2, precipitation of a silica is suppressed.

  As shown in FIG. 1, in this embodiment, a backflow prevention valve 22 is provided to keep the carbon dioxide partial pressure constant. The backflow prevention valve 22 is configured to prevent the backflow of the geothermal steam exhausted from the steam-water separation tank 2 and keep the carbon dioxide partial pressure of the geothermal steam in the steam-water separation tank 2 at a constant value. In the present embodiment, the backflow prevention valve 22 is provided in the steam exhaust pipe 14 that exhausts the geothermal steam in the steam separation tank 2. In addition, the backflow prevention valve 22 may be provided not only in the steam exhaust pipe 14 but in the gas phase part (top surface, upper side surface, etc.) of the steam-water separation tank 2.

  Next, the aeration tank 3 will be described in detail.

  The aeration tank 3 aerates geothermal water flowing from the steam / water separation tank 2 through the backflow prevention valve 21 to degas carbon dioxide in the geothermal water. Thereby, calcium ions and magnesium ions dissolved in the geothermal water are forcibly deposited as scales. That is, the aeration tank 3 precipitates calcium ions dissolved in the geothermal water as insoluble calcium carbonate and precipitates magnesium ions dissolved in the geothermal water as insoluble magnesium silicate. As a result, scale components in geothermal water are reduced.

  More specifically, in the aeration tank 3, the geothermal water in the aeration tank 3 becomes alkaline (for example, pH = 8 to 9) by performing deaeration of carbon dioxide in the geothermal water flowing from the air / water separation tank 2. . Thereby, as can be seen from FIGS. 3A, 4A, and 4B, the precipitation reaction of calcium carbonate and magnesium silicate is promoted. In addition, about a silica, since geothermal water is alkaline, precipitation reaction is suppressed so that FIG.3 (b) may show.

  The geothermal water in the aeration tank 3 is transported to an external facility such as a binary power generation heat exchanger through the hot water transport pipe 12. Since calcium carbonate and magnesium silicate are already deposited in the aeration tank 3, the scale of calcium carbonate and magnesium silicate is suppressed from being deposited on the hot water transport pipe 12 and external equipment.

In order to suppress the precipitation of silica in the hot water transport pipe 12, it is preferable that the temperature of the geothermal water flowing in the hot water transport pipe 12 is set to a predetermined temperature. That is, the temperature of the geothermal water flowing in the hot water transport pipe 12 is preferably maintained at a temperature not lower than the temperature at which silicon oxide (SiO ₂ ) does not precipitate (for example, 64 ° C. or higher). For example, by covering the outer periphery of the hot water transport pipe 12 with a heat insulating material, the temperature of the geothermal water in the hot water transport pipe 12 is maintained at a temperature at which silicon oxide does not precipitate. The temperature is maintained at 70 ° C. to 100 ° C., for example. Thereby, it can suppress that silica also precipitates in the hot water transport pipe 12.

  As described above, in the geothermal utilization system 1 according to the present embodiment, in the steam-water separation tank 2, the geothermal water is made acidic by maintaining the carbon dioxide partial pressure of the geothermal steam at or above the degassing suppression partial pressure value. Inhibits precipitation of calcium carbonate and magnesium silicate. Since geothermal water is high temperature, silica precipitation is also suppressed. Thereby, it can suppress that a scale adheres to the geothermal fluid extraction pipe | tube 11. FIG. In the aeration tank 3, the geothermal water is aerated and the carbon dioxide is deaerated to make the geothermal water alkaline and forcibly precipitate calcium carbonate and magnesium silicate. Since geothermal water is alkaline, precipitation of silica is also suppressed. Then, geothermal water is supplied to external equipment such as a heat exchanger via the hot water transport pipe 12. Thereby, it can suppress that the scale of calcium carbonate and magnesium silicate precipitates in the hot-water transport pipe 12 and external equipment. Furthermore, by keeping the temperature of the geothermal water in the hot water transport pipe 12 at such a temperature that silicon oxide does not precipitate, it is possible to suppress the precipitation of silica in the hot water transport pipe 12.

  As described above, according to the geothermal utilization system of the present embodiment, the scale is prevented from depositing on the external equipment such as the piping and heat exchanger through which the geothermal fluid flows, and the maintenance cycle of the piping and the like is greatly extended. Can do. For example, piping maintenance, which has been conventionally performed every two months, can be made one year.

  In addition, the geothermal utilization system which concerns on this invention is not restricted to said embodiment. For example, the outflow port 11 a of the geothermal fluid extraction pipe 11 may be arranged in the liquid phase of the steam-water separation tank 2. Thereby, since the carbon dioxide concentration in the geothermal water stored in the steam-water separation tank 2 becomes high, precipitation of calcium carbonate can be further suppressed.

  In addition, the outlet 11a of the geothermal fluid extraction pipe 11 may be provided with a sudden pressure reduction preventing means 25 for preventing the pressure of the geothermal fluid from rapidly decreasing. Thereby, sudden pressure reduction when the geothermal fluid flows out from the geothermal fluid take-out pipe 11 is prevented, and precipitation of scale such as calcium carbonate at the outlet 11a can be suppressed. Examples of the sudden pressure reduction preventing means 25 include a net-like member provided so as to cover the outlet 11a and a throttle member for reducing the diameter of the outlet 11a.

  In the above embodiment, the steam / water separation tank 2 and the aeration tank 3 are connected by the connection pipe 13. However, the steam / water separation tank 2 and the aeration tank 3 are arranged directly adjacent to each other without using the connection pipe 13. May be. In this case, the backflow prevention valve 21 is provided on the wall surface shared by the steam separation tank 2 and the aeration tank 3. Thereby, the maintenance work of the connecting pipe 13 can be made unnecessary.

  Based on the above description, those skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the above-described embodiments. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Geothermal utilization system 2 Steam / water separation tank 3 Aeration tank 11 Geothermal fluid extraction pipe 11a Outlet 12 Hot water transport pipe 13 Connection pipe 14 Steam exhaust pipe 21, 22 Backflow prevention valve 25 Rapid decompression prevention means

Claims (9)

Separating the geothermal fluid flowing out from the outlet of the geothermal fluid outlet pipe into geothermal water and geothermal steam, and maintaining the carbon dioxide partial pressure of the geothermal steam above the deaeration suppression partial pressure value; and
An aeration tank for aeration of geothermal water flowing from the air / water separation tank through a backflow prevention valve to degas carbon dioxide in the geothermal water;
A geothermal utilization system characterized by comprising:   The apparatus further comprises a hot water transport pipe for transporting geothermal water stored in the aeration tank to an external facility, and the temperature of the geothermal water flowing in the hot water transport pipe is maintained at a temperature higher than a temperature at which silicon oxide does not precipitate. The geothermal utilization system according to claim 1, wherein   The backflow prevention valve which prevents the backflow of the geothermal steam exhausted from the said steam-water separation tank, and keeps the carbon dioxide partial pressure of the geothermal steam of the said steam-water separation tank at a fixed value is further provided. 2. The geothermal utilization system according to 2.   The geothermal heat utilization system according to claim 3, further comprising a steam exhaust pipe that is provided with the backflow prevention valve and exhausts the geothermal steam of the steam-water separation tank.   The geothermal heat utilization system according to any one of claims 1 to 4, wherein the outlet of the geothermal fluid outlet pipe is disposed in a gas phase of the steam separation tank.   6. The geothermal utilization system according to claim 5, wherein a sudden pressure reduction preventing means for preventing a sudden decrease in the pressure of the geothermal fluid is provided at the outlet of the geothermal fluid outlet pipe.   The geothermal heat utilization system according to any one of claims 1 to 4, wherein the outlet of the geothermal fluid outlet pipe is disposed in a liquid phase of the steam separator.   The said steam-water separation tank and the said aeration tank are connected so that a mutual liquid phase may be connected through the connection pipe provided with the said backflow prevention valve. The geothermal utilization system described.   The aeration tank deposits calcium ions dissolved in the geothermal water as insoluble calcium carbonate and precipitates magnesium ions dissolved in the geothermal water as insoluble magnesium silicate. The geothermal utilization system in any one of claim | item 1 -8.

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