JP7245492B2 - geothermal power plant - Google Patents

Description

The present invention is a second operation in which heat is exchanged underground via a first working medium using a geothermal heat source as a heat source, and the heat of the first working medium is heat-exchanged in a heat exchanger. The present invention relates to a geothermal power generation device that generates power using a medium.

Conventionally, geothermal power generation equipment extracts natural steam existing in the geotropics using natural pressure and separates it from water. contains a large amount of impurities. This impurity becomes scale and adheres to thermal wells, pipes, turbine blades, and the like. When scale adheres, the amount of power generated decreases over time, making long-term use difficult.

In Patent Document 1, in a binary power generation system, a heat source fluid absorbs heat through heat exchange with a geothermal fluid or geothermal heat, releases heat in an evaporator, and recirculates for heat exchange with the geothermal fluid or geothermal heat. In addition, for the cooling fluid that cools the low boiling point medium, either a closed loop flow path is configured in the ground for heat radiation cooling, or the heat source fluid after passing through the evaporator is used as the driving heat source. A geothermal power generation system has been proposed that comprises a closed loop flow path that controls the temperature of the cooling fluid and supplies the cooling fluid to the condenser so that the condensing of the low boiling point medium in the condenser can be optimized.

JP 2014-84857 A

As described above, in the power generation method that pumps up and utilizes geothermal fluid, scale adheres to facilities such as piping facilities and turbines, and the amount of power generated decreases over time, or maintenance is required. In terms of the environment, it is possible that the amount of discharge of hot spring water will be affected because the geothermal fluid will be pumped up and used. After the geothermal fluid is pumped up and used for power generation, the water is returned to the earth from the return well. However, it contains chemical substances for removing scale, and has a considerable impact on the environment.
Furthermore, the method of generating power using only underground heat as seen in Patent Document 1 is effective because it is environmentally friendly and there is no need to consider the amount of hot spring water, chemical substances, and the like.

In a volcanic zone where magma is near the surface, even if the excavation distance is short, heat can be exchanged with a high-temperature geotropical zone of 300°C or higher.
However, in the case of using pure water as the first working medium as in the conventional method, if hot water is circulated in a closed loop instead of being steamed, the pressure must be maintained at a temperature at which it does not evaporate. There is a problem of burden.
For example, a pressure of 8587 kPa or more is required when conveying water at 300° C. without steaming it.

The present invention has been made in view of such problems, and effectively uses the amount of heat obtained from the geotropical zone on the ground to reduce the burden on the load equipment on the ground, while the high-temperature geotropical zone in the ground. An object of the present invention is to provide a geothermal power generation device capable of heat exchange.

In order to achieve the above object, the present invention employs the following means.

A geothermal power plant that recovers underground heat using a first working medium, has a heat exchanger that performs heat exchange on the ground with a second working medium, and uses the second working medium to drive a steam turbine to generate power. The power generating device, wherein the first working medium comprises a molten salt, is located in a geotropical region below the melting point of the first working medium, and is at a temperature that does not solidify the first working medium. It is characterized by comprising a heat medium transfer pipe provided with a heat insulating structure for keeping the inside of the pipe.

Due to the above characteristics, by using molten salt, the first working medium can be conveyed as a liquid without increasing the pump pressure even at high temperatures. Moreover, by using molten salt, even if an unexpected situation occurs, it does not become a harmful substance, so it is environmentally friendly. Moreover, solidification of the molten salt can be prevented by providing a heat insulating structure.

FIG. 1 is a schematic diagram showing the configuration of a geothermal power generator of the present invention according to an embodiment. FIG. 2 is a schematic diagram showing the temperature states of the geothermal zone and the first working medium of the present invention according to the embodiment. FIG. 3 is a schematic diagram showing the configuration of the heat medium transfer pipe of the present invention according to the embodiment.

An embodiment of a geothermal power generator 1 according to the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments and drawings described below illustrate a part of the embodiments of the present invention, and are not used for the purpose of limiting to these configurations, and are within the scope of the present invention. can be changed as appropriate. Corresponding components in each figure are labeled with the same or similar reference numerals.

FIG. 1 is a schematic diagram showing the configuration of a geothermal power generator 1 of the present invention according to an embodiment. The geothermal power generation device 1 uses molten salt as the first working medium (I1 to I5). Molten salts include, for example, CaCl2, NaF--AlF3 and LiF--BeF2 in the alkali metal halogen system. Also, in the oxyacid system, there are KNO3-NaNO3 and LiNO3-AgNO3. Among molecular molten salt systems, there is AlCl3-NaCl. This example shows an example using a molten salt of NaNO3, KNO3 and NaNO2 at a ratio of 7:44:9. NaNO3/KNO3/NaNO2 exhibits a melting point of 140°C and no decomposition occurs up to 550°C.

Water is used as the second working medium (J1 to J4). In addition, the second working medium (J1 to J6) is not only water, but also HFC-245fa, R245fa, etc., which are inert inert gases that are not flammable or toxic, or media with a low boiling point (a mixture of water and ammonia, etc.). Hydrogen (pentane) may also be used.

The geothermal power generation device 1 mainly includes a heat medium transfer pipe 10, an evaporator 50, a circulation pump 5, a steam turbine T, a generator G, a medium pump 55, a power receiving equipment H, and a cooler 56.

In the present invention, the first working medium (I1 to I5) reaches the evaporator 50 via the heat medium transfer pipe 10 and piping on the ground, and forms a closed loop that circulates to the heat medium transfer pipe 10 again.
The second working medium (J1 to J4) also forms a closed loop that circulates through the evaporator 50, the steam turbine T, the cooler 56, the medium pump 55 and the preheater 51.

FIG. 1 shows a heat medium transfer pipe 10 and a second working medium (J1 to J4) is divided into a device that generates steam power.

First, a system for recovering geothermal heat using the first working medium (I1 to I5) will be described. The first working medium I1 is sent to the heat medium transfer pipe 10 through the pipe by the circulation pump 5 . A heat medium transfer pipe 10 is buried from the ground surface K to a geotropical zone S serving as a heat source deep underground.

The heat medium transfer pipe 10 will be described below with reference to FIG. The heat medium transfer pipe 10 shown in FIG. 3 has a cylindrical medium injection pipe 11 embedded on the outside. The underground area with a temperature lower than the temperature is hardened with geothermal cement 15 so that there is no danger of collapse, and it also has a heat insulating function.

The heat medium transfer pipe 10 absorbs heat from the fluid or bedrock of the geotropical zone S located at the deepest part of the medium injection pipe 11 of the heat medium transfer pipe 10 . The length of the heat medium transfer pipe 10 varies depending on the temperature of the geotropical zone S, and extends to the geological zone capable of absorbing around 350° C. as heat.

The medium injection pipe 11 is made of a material such as stainless steel. In the region of the geotropical zone U where the temperature is high, the medium injection pipe 11 is attached with fins or the like by welding or the like in order to expand the heat transfer area.
In addition, acid-resistant paint is used as a countermeasure against acid resistance of the heat medium transfer pipe 10 found in volcanic areas and hot spring areas. It can also be painted.

A heat insulating structure 16, such as a heat insulating material such as heat insulating paint or resin, or an air layer, is provided so that the heat of the first working medium I1 is not removed. Also, the heat medium transfer pipe 10 may have a triple pipe structure for the heat insulating region that requires heat insulation in order to take the heat insulating structure.

The medium injection pipe 11 is heated by the heater 8 in the region near the ground surface K where the temperature of the underground heat is low, when the molten salt I1 drops below the melting point and solidifies or to prevent solidification.
The heater 8 may have a structure that uses electricity to apply electric power to the heating element, or a structure that warms the medium injection pipe 11 with a heat transfer pipe through which a heat medium passes.

The heat medium transfer pipe 10 is provided with a cylindrical medium take-out pipe 12 for transferring water heated in the geotropical zone S inside the medium injection pipe 11 . The medium take-out pipe 12 is formed in a cylindrical shape coaxially inside the medium injection pipe 11 . The medium take-out tube 12 has a cylindrical inner side through which the first working medium I3 can pass, and an outer side of which has a vacuum insulating structure or a heat insulating structure 17 provided with a heat insulating material along the vertical direction. The heat insulating structure 17 has a structure capable of transporting the first working medium I3 to the ground surface K without lowering the temperature of the first working medium recovered in the deepest part S of the earth.

FIG. 2 shows the temperature distribution 20 , and according to the geothermal temperature distribution 21 , the heat transfer pipe 10 is provided with the heat insulating structures 16 and 17 , the heat absorbing structure and the heater 8 . The vicinity of the point A is a position where the heat insulating structure 16 and the heater 8 are attached because there is a water vein in the temperature distribution of the geotropical zone and this is the point where the temperature drops the lowest. In addition, since the melting point 26 of the molten salt (NaNO3/KNO3/NaNO2), which is the first working medium (I1 to I5), is 140°C (one-dot two-dot chain line), Adiabatic structures 16 and 17 are required as an adiabatic region with a boundary 24 (one-dot chain line) as a boundary.

By adopting the above structure, the first working medium (I1 to I3) is conveyed to the ground surface S while maintaining a temperature of 300° C. as shown in the molten salt temperature distribution 25 .

As shown in FIG. 1, the first working medium I3 conveyed to the ground surface K flows into the evaporator 50 that also serves as heat exchange, and then the first working medium I4 that has passed through the evaporator 50 is heat exchanged. flows into the preheater 51 which also has the role of The first working medium I5 that has passed through the evaporator 50 exchanges heat while passing through the preheater 51 to preheat the second working medium.
A control valve 6 for adjusting the flow rate of the first working medium (I1 to I5) is provided before and after the evaporator 50 or the preheater 51 and on the inflow side of the circulation pump 5 to the heat medium transfer pipe 10 . The control valve 6 can adjust the temperature and flow rate of the first working medium (I1 to I5).

Regarding the use of the circulation pump 5, the first working medium (I) is basically driven by natural circulation due to the temperature difference between the inlet and outlet of the heat medium transfer pipe 10, e.g. The circulation pump 5 is used additionally if no difference is obtained. Further, the circulation pump 5 is used when the natural circulation is driven but the required flow rate cannot be obtained, or when the first working fluid (I1) is initially charged or drained.
In this embodiment, molten salt is used as a medium for heat exchange in the geotropical zone U. However, even if the heat medium transfer pipe 10 is damaged and flows out to the outside, it will not harm the environment and the work surface will not be damaged. can be safely handled even in

The circulation pump 5 is formed using an alkali-resistant metal, which is abundant in molten salt, and by using a material different from the alkali-resistant metal for the bearings, it is possible to prevent welding by the same kind of metal. no burden on

Next, a device for generating steam power using the second working medium (J1 to J4) will be described with reference to FIG.
As described above, the first working medium (I4) passing through the evaporator 50 maintains a temperature of 300° C., keeping the inside of the evaporator 50 at a high temperature. The second working medium (J4) becomes vapor in the evaporator 50 because it has a boiling point lower than 300°C (100°C for water). The second working medium (J1) turned into steam rotates the steam turbine T, and the generator G generates power.

The second working medium (J2), which is steam after being used in the steam turbine T, is returned to water by a cooler 56 having a cooling tower 57 and becomes the second working medium (J3). is sent to the preheater 51 by . The inside of the preheater 51 is heat-exchanged with the first working medium (I5) that has passed through the evaporator 50 and is kept at a high temperature. Also, the heat in the preheater 51 preheats the second working medium (J3), and the preheated second working medium (J4) flows into the evaporator 50 .

(Technical signs)
Examples of technical features of the present embodiment are shown in parentheses below, but they are not particularly limited, but merely illustrative, and the effects conceivable from these features will also be described.

<First feature point>
Underground heat is recovered by a first working medium (for example, mainly the first working medium (I1 to I5)), and is recovered by a second working medium (for example, mainly the second working medium (J1 ~ J4))) to perform heat exchange (e.g., mainly an evaporator 50 and a preheater 51), and the second working medium drives a steam turbine (e.g., mainly a steam turbine T). A geothermal power generation device that generates power,
the first working medium comprises a molten salt (e.g., primarily NaNO3/KNO3/NaNO2);
A heat insulating structure (e.g., heat insulating structures 16, 17, geothermal cement 15) that maintains the inside of the pipe at a temperature that does not solidify the first working medium and is located in a geotropical region that is lower than the melting point of the first working medium. provided with a heat medium transfer pipe (for example, mainly the heat medium transfer pipe 10).

Due to the above characteristics, by using molten salt, the first working medium can be conveyed in a liquid state without using a large pump power even at a high temperature. Moreover, by using molten salt, even if an unexpected situation occurs, it does not become a harmful substance, so it is environmentally friendly. Moreover, solidification of the molten salt can be prevented by providing a heat insulating structure.

<Second feature point>
The heat insulating structure is characterized by comprising geothermal cement (mainly geothermal cement 15, for example) covering the outer periphery of the heat medium transfer pipe.
Due to the above characteristics, the geothermal cement has the function of preventing collapse when the heat medium transfer pipe is buried, and can also have a heat insulating structure.

<Third Characteristic Point>
It is characterized by comprising a heater (for example, a heater 8) that covers the outer periphery of the heat medium transfer pipe and generates heat by heat obtained from the outside.
Due to the above features, even if the first working medium is unexpectedly solidified, it is possible to change the solidified state to the molten state by means of the heater, and it is also possible to prevent solidification in advance.

<Fourth characteristic point>
The heat medium transfer pipe is characterized in that the outer periphery thereof is coated with a resin.
Due to the above features, it is possible to prevent corrosion of the heat medium transfer pipe against acidic soil found in high-temperature volcanic areas.

As shown in the above embodiment, it can be used not only in volcanic areas, but also in geotropics where hot springs flow, volcanic areas in the sea, and the like.

DESCRIPTION OF SYMBOLS 1... Geothermal power generator, 5... Circulation pump, 8... Heater, 10... Heat medium transfer pipe,
DESCRIPTION OF SYMBOLS 11... Medium injection pipe, 12... Medium extraction pipe, 15... Geothermal cement, 16, 17... Thermal insulation structure,
20... Temperature distribution, 21... Geotropical temperature distribution, 24... Boundary, 25... Molten salt temperature distribution,
26 Melting point 50 Evaporator 51 Preheater 55 Medium pump T Steam turbine
G... generator, H... power receiving equipment, K... ground surface,
I, I1, I2, I3, I4, I5... first working medium,
J1, J2, J3, J4...second working medium, S...geotropic zone.

Claims (1)

A heat exchanger that recovers underground heat with a first working medium using molten salt and exchanges heat with a second working medium on the ground, and a steam turbine is driven with the second working medium. A geothermal power generation device that generates power by
a heat medium transfer pipe, which is located in a geotropical region lower than the melting point of the first working medium and has a heat insulating structure that keeps the inside of the pipe at a temperature that does not solidify the first working medium;
a heater that covers the outer periphery of the heat medium transfer pipe and generates heat by heat obtained from the outside;
A geothermal power generation device comprising:

Images