JP2019044690A - Geothermal power generation system and power generation method utilizing geothermal power - Google Patents

Abstract

To provide a geothermal power generation system capable of facilitating maintenance, and also linking with a low-pressure system to sell power.SOLUTION: A geothermal power generation system comprises: an induction generator; a binary power generator comprising a screw connected to the induction generator and rotating with movement of working medium, and an evaporator configured to introduce into the screw the working medium as steam; a first inverter configured to convert AC power output by the induction generator into DC power, and convert DC power into AC power for regeneration in the induction generator; and a second inverter configured to convert DC power from the first inverter into AC power to supply it to a low-pressure system, and convert AC power of the low-pressure system into DC power to supply it to the first inverter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a geothermal power generation system and a power generation method using geothermal heat.

  In recent years, the need for promotion of renewable energy has increased, and the development of geothermal power plants has been actively promoted in Japan.

However, Japan's geothermal power plants are often installed in mountainous areas due to the terrain of Japan, and traffic access is inconvenient, and in many cases it is not easy to enter large vehicles and heavy machinery. For this reason, a geothermal power generation system that is resistant to failure and easy to maintain is desired.
In addition, facilities for supplying generated electricity are important, and power facilities are necessary near the power plant. Since power equipment and low-voltage wires are relatively covered even in mountainous areas, connection to low piezoelectric lines is desired.

  On the other hand, the current geothermal power generation system supplies electric power generated to a high-voltage transmission line, but it is desired to sell power by connecting to a low-voltage system (commercial power network). However, for reasons such as securing electric power quality, the power conversion method must be limited for the sale of power linked to the low voltage system, using an inverse converter. If the geothermal power generation cannot be connected to the low-voltage system, it is an obstacle to the spread of the geothermal power generation system for small-scale power generation companies.

JP 2016-164395 A

  An object of the present invention is to provide a geothermal power generation system that can be linked to a low-voltage system while facilitating maintenance.

  A geothermal power generation system according to the present invention includes an induction generator, a screw connected to the induction generator and rotated by movement of an operating medium, and a vaporizer that introduces the operating medium into the screw as steam. A first inverter that converts the alternating current power output from the induction generator into direct current power, converts the direct current power into alternating current power, and supplies the alternating current power to the induction generator; and direct current power from the first inverter is alternating current A second inverter is provided that converts the electric power into electric power and supplies it to the low-voltage system, and converts alternating-current power of the low-voltage system into direct-current power and supplies it to the first inverter. The power generation method using geothermal heat according to the present invention vaporizes the working medium with hot water based on geothermal heat and supplies it to the screw, thereby rotating the screw and rotating the screw to rotate the rotor of the induction generator. To generate AC power, convert the AC power into DC power using a first inverter, further convert the DC power into AC power using a second inverter, and supply the AC power to a low-voltage system. AC power of a system is converted to DC power by the second inverter and supplied to the first inverter, and the DC power is converted to AC power by the first inverter and supplied to the induction generator. And

  In the geothermal power generation system of the present invention, an induction generator is used in the binary generator. After the first inverter converts the AC power of the induction generator into DC power, the second inverter converts the DC power into AC power that matches the low voltage system and supplies (sells) power to the low voltage system. The induction generator has a simpler structure than other generators, so maintenance is easy and the system can be installed in mountainous areas where large vehicles and heavy machinery are difficult to enter. Become.

  On the other hand, the induction generator must obtain an exciting current from the outside and cannot be operated independently. However, in the geothermal power generation system of the present invention, the AC power of the low-voltage system is converted into DC power by the second inverter. The DC power is further converted into AC power by the first inverter, and the induction generator is excited based on the excitation current of the AC power, thereby enabling the operation of the induction generator.

  As described above, according to the geothermal power generation system of the present invention, it is possible to provide a geothermal power generation system that can be linked to a low-voltage system while facilitating maintenance.

It is the schematic which shows the whole structure of the geothermal power generation system of embodiment. 3 is a block diagram showing a detailed configuration example of a binary generator 50. FIG. A detailed configuration of the grid interconnection control unit 70 will be described.

  Next, a geothermal power generation system according to an embodiment of the present invention will be described with reference to the drawings.

  Drawing 1 is a schematic diagram showing the whole composition of the geothermal power generation system of an embodiment.

  This system is mainly composed of a brackish water separator 10, a hot spring tank 20, a silencer 30, an external heat exchanger 40, a binary generator 50, a cooling tower 60, and a grid interconnection control unit 70.

  In this system, as an example, a fluid (two-phase flow) in which hot water ejected from a hot spring well or the like obtained in a hot spring area and the steam is mixed through a pipe P1 in which valves V1 and V2 are arranged. The steam is led to the brackish water separator 10 and the steam is separated and discharged. After being separated, the steam is discharged to the outside through the valve V5. The pipe P1 partially branches to the pipe P2 where the valve V3 is disposed. The pipe P <b> 2 is led to the hot spring tank 20.

  On the other hand, hot water is introduced into the external heat exchanger 40 through the pipe P3. The pipe P3 is branched into pipes P4 and P5, and the hot water entering the pipe P4 is silenced by the silencer 30 and discharged to the outside. In FIG. 1, valves V6 and V8 and a pump for supplying or shutting off hot water are provided in the pipe P3, but this is merely an example. The external heat exchanger 40 manages heat exchange between hot water that passes through the pipe P3 and hot water that passes through the pipe P6 (which has a temperature lower than that of hot water).

  The hot water in the pipe P3 leaves the external heat exchanger 40, enters the pipe P5, and is stored in the hot spring tank 20. The hot water remaining in the brackish water separator 10 is discharged toward the hot spring tank 20 through the valve V4 and the pipe P0. The hot water or hot water stored in the hot spring tank 20 is secondarily used for applications not shown.

  Various pipes in FIG. 1 are provided with various valves V1, V2, V3, V4, V5, V6, V7, and V8 in order to block or open the passage of hot water and hot water flowing therethrough. It goes without saying that the positions of these valves V are merely examples, and are not limited to the illustrated examples.

  In the external heat exchanger 40, a pipe P6 is also disposed adjacent to the pipe P3. The heat of the hot water passing through the pipe P3 is transferred (heat exchanged) to the water passing through the pipe P6, and the hot water in the pipe P6 given heat is introduced into the binary generator 50 by the pump PM1. Cooling water stored in the cooling tower 60 is also introduced into the binary generator 50 through the pipe P7 and the pump PM2. The binary generator 50 includes an induction generator as a generator inside, and operates the induction generator with an operation medium such as an alternative chlorofluorocarbon as will be described later. These hot water and cooling water are used for vaporization and condensation of the working medium. The electric power generated by the binary generator 50 is transmitted to the low-voltage system (power network) via the system interconnection control unit 70 and the overhead wire pulling column.

  FIG. 2 is a block diagram illustrating a detailed configuration example of the binary generator 50. As an example, the binary generator 50 includes a hot water inlet 501, a hot water outlet 502, a preheater 503, a vaporizer 504, an induction generator 505, twin screws 506 A and 506 B, a working medium tank 507, a pump 508, and cooling water introduction. A port 509, a cooling water discharge port 510, a condenser 512, and a condenser 513 are provided. The binary generator 50 rotates the induction generator 505 using an operating medium (for example, an alternative CFC such as HFC-245fa (boiling point 15.3 ° C.)) stored in the operating medium tank 507 to generate electric power. The above-mentioned hot water and cooling water are used to vaporize and condense this alternative CFC.

  The hot water inlet 501 and the hot water outlet 502 are connected to the above-described pipe P <b> 6, and introduce the above-mentioned hot water into the binary generator 50 and discharge it from the binary generator 50. Hot water introduced from the hot water introduction port 501 is sequentially introduced into the vaporizer 504 and the preheater 503, and is again discharged from the hot water discharge port 502 to the pipe P6.

  The working medium conveyed from the working medium tank 507 via the valve V11 and the pump 508 is heated (preheated) to a predetermined temperature by the heat of hot water introduced from the hot water inlet 501 in the preheater 503. The working medium heated to a predetermined temperature by the preheater 503 is further heated by the vaporizer 504, and changes from liquid to gas (vaporizes). The vaporized working medium is introduced into twin screws 506A and 506B connected to the induction generator 505, and rotates the twin screws 506A and 506B. The liquid working medium supplied from the working medium tank 507 may also be selectively introduced into the twin screws 506A and 506B.

  The induction generator 505 may be a general induction machine (an electric motor or a generator) and includes a stator and a rotor. The rotor of the induction generator 505 may be a so-called cage rotor or a wound rotor. Twin screws 506A and 506B are connected to the rotating shaft of the rotor. As the twin screws 506A and 506B rotate based on the movement of the working medium, the induction generator 505 generates electric power.

  When the slip s of the induction generator 505 is a negative value, the induction generator 505 functions as a generator. On the other hand, as will be described later, the induction generator 505 can be excited by power supplied from a low-voltage system and function as an induction motor (slip s is a positive value).

  The vaporized working medium that has passed through the induction generator 505 is condensed and liquefied by the condensers 512 and 513 and returned to the working medium tank 507. Cooling water introduced from the cooling tower 60 to the cooling water inlet 509 is introduced into the condensers 512 and 513, whereby the working medium can be cooled and liquefied. The valve V12 adjusts the flow rate of the working medium from the induction generator 505 to the condensers 512 and 513. The cooling water passes through the condensers 512 and 513 and is then returned to the cooling tower 60 via the cooling water discharge port 510.

  Next, a detailed configuration of the grid interconnection control unit 70 will be described with reference to FIG. For example, the grid interconnection control unit 70 includes an AC reactor 71, a first inverter 72, a second inverter 73, an AC reactor 74, a harmonic filter 75, a circuit breaker 76, and a controller 77. The controller 77 controls the entire system interconnection control unit 70.

The AC reactor 71 is provided to mitigate the inrush current from the induction generator 505.
The first inverter 72 converts AC power generated by the induction generator 505 introduced via the AC reactor 71 into DC power and supplies the DC power to the second inverter 73. The second inverter 73 converts this direct-current power into alternating-current power having a quality adapted to the low-voltage system.
Each of the first inverter 72 and the second inverter 73 includes a bidirectional inverter, both of which have a function (forward conversion) for converting AC power into DC power, and also convert DC power into AC power. It also has a function (inverse conversion). That is, the first inverter 72 generates AC power that gives a rotating magnetic field having a synchronous speed in the induction generator 505 and supplies the AC power to the induction generator 505. Further, the second inverter 73 converts the AC power of the low-voltage system into a DC voltage, and supplies this to the first inverter 72.
When the abnormality is detected, the second inverter 73 outputs a cutoff signal Soff to the controller 77 to turn off the breaker 76 connected between the second inverter 73 and the low-voltage system. It also has a function of shutting off from the low-voltage system.

  The AC reactor 74 is provided to smooth the waveform of the AC power from the second inverter 73. The harmonic filter 75 has a function of removing harmonic components contained in the AC power.

  In this configuration, the induction generator 505 generates power by receiving energy supply from the geothermal system (in this case, the induction generator 505 is in a state where the rotational speed of the rotor is faster than the rotating magnetic field of the synchronous speed, and the slip s is Electricity flows from the first inverter 72 side toward the second inverter 73, and DC power is converted into AC power in the second inverter 73 and supplied to the low-voltage system.

  On the other hand, when the energy from the geothermal system is low (not at the time) such as when starting, the rotational energy given to the twin screws 506A and 506B is small, and the rotational speed of the rotor of the induction generator 505 is higher than the rotational speed of the rotating magnetic field. The slip s is a positive value. In this case, the AC power supplied to the low-voltage system is converted into DC power by the second inverter 73, and the DC power is further converted into AC power by the first inverter 72 and supplied to the induction generator 505. The With this electric power, a rotating magnetic field is generated in the induction generator 505 and the slip s has a positive value, and the induction generator 505 functions as an induction motor.

  As described above, since the geothermal power generation system according to the present embodiment uses the induction generator 505 having a simple structure in the binary generator 50, the geothermal power generation system is installed in an area where a large vehicle or heavy machinery is difficult to enter, such as a mountain area. Even if it is, maintenance management is easy.

  Then, AC power generated by the induction generator 505 in response to energy supply from the geothermal system is converted to DC power by the first inverter 72, converted again to AC power by the second inverter 73, and supplied to the low-voltage system. . On the other hand, when the energy from the geothermal system is low (not at the time), such as at the time of starting, AC power of the low-voltage system is supplied via the second inverter 73 and the first inverter 72, and a rotating magnetic field is generated by this power to induce induction power generation. The machine 505 can be driven as an induction motor. In this way, high-quality power using the reverse conversion device can be supplied to the low-voltage system by the induction generator 505 via the first inverter 72 and the second inverter 73. Therefore, in the geothermal power generation system according to the present embodiment, it is possible to sell electric power connected to a low-voltage system while using an induction generator.

DESCRIPTION OF SYMBOLS 10 ... Brackish water separator 20 ... Hot spring tank 30 ... Silencer 40 ... External heat exchanger 50 ... Binary generator 60 ... Cooling tower 70 ... System interconnection control part 71, 74 ... AC reactor 72 ... 1st inverter 73 ... 2nd inverter 75 ... harmonic filter 76 ... breaker 77 ... controller 501 ... warm water inlet 502 ... warm water outlet 503 ... preheater 504 ... vaporizer 505 ... induction generator 506A, 506B ... twin screw 507 ... operating medium tank 508 ... pump 509 ... cooling water inlet 510 ... cooling water outlet 512, 513 ... condenser

Claims (3)

A binary generator comprising: an induction generator; a screw connected to the induction generator and rotated by movement of a working medium; and a vaporizer for introducing the working medium into the screw as steam.
A first inverter that converts AC power output from the induction generator into DC power, converts DC power to AC power, and supplies the AC power to the induction generator;
A second inverter that converts the DC power from the first inverter into AC power and supplies it to the low-voltage system, and converts the AC power of the low-voltage system into DC power and supplies it to the first inverter. A geothermal power generation system characterized by   2. The circuit breaker according to claim 1, further comprising a circuit breaker that is connected between the second inverter and the low-voltage system and that disconnects the connection between the second inverter and the low-voltage system when an abnormality is detected. Geothermal power generation system. The working medium is vaporized by hot water based on geothermal heat and supplied to the screw, thereby rotating the screw,
Rotating the rotor of the induction generator by rotating the screw to generate AC power,
The AC power is converted into DC power using the first inverter, and the DC power is further converted into AC power by the second inverter and supplied to the low-voltage system.
AC power of the low-voltage system is converted into DC power by the second inverter and supplied to the first inverter, and the DC power is converted to AC power by the first inverter and supplied to the induction generator. A power generation method using geothermal heat.

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