JP4972752B2 - Geothermal power generation method and system - Google Patents

Description

  The present invention relates to a geothermal power generation method and system. More specifically, the present invention relates to a geothermal power generation method and system suitable for use in combination with a large-scale emission source of carbon dioxide.

  In the present specification, the high-temperature rock ground means a rock having a low water content while being hot due to the heat of the underground magma.

  As a conventional geothermal power generation method, a plurality of wells are drilled in the underground hot rock ground, and water is injected from some wells of the plurality of wells. There is a method in which hot water or steam generated by heating by the ground heat while passing through the crack is recovered from another well and used for power generation. In this case, the recovered hot water is fed through the well and into the hot rock ground, and water is passed between the ground and underground hot rock ground through the injection well and the recovery well. A circulation system as a heat transfer medium is formed, and the heat of the underground hot rock ground can be taken out to the ground (Non-patent Document 1).

In addition, there is concern about global warming due to an increase in the concentration of greenhouse gases such as carbon dioxide (CO ₂ ) in the atmosphere accompanying the use of fossil fuels. And as a means for preventing global warming, a project to fix and store carbon dioxide in the formation is progressing in and outside Japan (Non-Patent Document 2). In other countries as well as in Japan, carbon dioxide is stored in aquifers that are mainly sandstone formations near large-scale sources of carbon dioxide, such as coal-fired power plants and cement plants, as carbon dioxide underground storage candidates. Underground storage is promising.

Central Research Institute of Electric Power Industry: Toward the development of unused geothermal resources -Efforts for high-temperature rock power generation-, Review of Denki Research Institute, No. 49, March 2003. Woking Group III of the Intergovernmental Panel on Climate Chang [Metz, B .; et al. ]: IPCC Special Report on Carbon Dioxide Capture and Storage, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 442pp.

  However, the geothermal power generation method of Non-Patent Document 1 has a problem that the power generation efficiency is low because the recovery rate of water injected from the well into the high temperature rock ground as a heat transfer medium is only about 25%. The water recovery rate is obtained by dividing the total weight of recovered steam / hot water by the total weight of injected water.

  In addition, a method for efficiently fixing and storing carbon dioxide in the formation is required from the viewpoint of preventing global warming.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a geothermal power generation method and system capable of performing high-temperature rock power generation with a high heat transfer medium recovery rate and high power generation efficiency, and capable of fixing and storing carbon dioxide in the formation. And

In order to achieve this object, the geothermal power generation method according to claim 1, injects a heat transfer medium containing at least carbon dioxide into at least one injection well drilled in the high temperature rock ground, The reaction with the components fixes the part of the carbon dioxide contained in the heat transfer medium at the edge of the geothermal reservoir in the high-temperature rock ground and exhibits a sealing function to prevent leakage of the heat transfer medium, After collecting the heat transfer medium heated by the heat of the high temperature rock ground from at least one production well excavated in the rock ground, generating electricity using the recovered heat transfer medium, The heat transfer medium is reinjected from the injection well into the hot rock ground.

The geothermal power generation system according to claim 2 is a reaction between at least one injection well and at least one production well excavated in the high temperature rock ground and components in the high temperature rock ground including at least carbon dioxide. the heat transfer medium for transferring heat energy of the immobilized allowed to Rutotomoni HDR ground to exert a sealing function of preventing its leakage a part of the carbon dioxide in the edge portion of the geothermal reservoir hot Dry rock in the ground by And an injection device for injecting a heat transfer medium into the injection well, and a generator for generating electricity using the heat transfer medium heated by the heat of the hot rock ground and recovered from the production well, and used for power generation After that, the heat transfer medium is injected again from the injection well into the hot rock ground.

  Therefore, according to this geothermal power generation method and system, by forming a circulation system using a medium containing carbon dioxide as a heat transfer medium between the generator and the underground high-temperature rock body ground, As heat is removed, some of the carbon dioxide is immobilized in the formation.

  Moreover, when a part of carbon dioxide injected into the formation is fixed, a solidified layer is formed at the edge of the geothermal reservoir in the high temperature rock ground.

  In addition, in this invention, an injection well means the well for making a heat transfer medium reach | attain an underground high temperature rock body ground in high temperature rock power generation. The production well is a well for recovering the heat transfer medium heated by the heat of the underground hot rock ground in the hot rock power generation to the ground.

  According to the geothermal power generation method and system of the present invention, the heat of the underground high-temperature rock body is taken out and a part of carbon dioxide is fixed in the formation, so that carbon dioxide is not newly generated. Furthermore, it is possible to generate energy while storing carbon dioxide underground, and it is possible to achieve both reduction of natural environmental load and energy generation.

  In addition, a part of the carbon dioxide injected into the formation is fixed to form a solidified layer at the edge of the geothermal reservoir in the high-temperature rock ground to extract the thermal energy of the high-temperature rock ground Since it is possible to increase the recovery rate of the heat transfer medium by preventing leakage of the heat transfer medium injected into the high temperature rock ground, the power generation efficiency can be improved.

  Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

  FIG. 1 shows an embodiment of a geothermal power generation method and system according to the present invention. In this geothermal power generation method, a heat transfer medium containing carbon dioxide is injected into an injection well 1a excavated in a high temperature rock ground, and a geothermal reservoir 14 in the high temperature rock ground is formed by reaction with components in the high temperature rock ground. The heat transfer medium heated by the heat of the high temperature rock ground from the production well 1b excavated in the high temperature rock ground is fixed while fixing a part of carbon dioxide at the edge of the water to prevent leakage of the heat transfer medium. The collected heat transfer medium is used for power generation, and the heat transfer medium used for power generation is injected again from the injection well 1a into the high-temperature rock ground.

  The geothermal power generation method is realized as a geothermal power generation system of the present invention. The geothermal power generation system of this embodiment includes an injection well 1a and a production well 1b excavated in a high-temperature rock ground, a high-pressure pump 3 for injecting water as a heat transfer medium into the injection well 1a, and heat transfer to the injection well 1a. A gas compressor 4 for injecting a gas 10 containing carbon dioxide as a medium; a separator 5 for separating a heat transfer medium recovered from the production well 1b heated by the heat of the high-temperature rock ground into hot water and steam; And a generator 6 that generates electricity using the steam separated by 5 and again injects hot water separated by the separator 5 from the injection well 1a into the high-temperature rock ground.

(1) Excavation of a well In the present invention, a plurality of wells 1a and 1b are excavated in the geothermal reservoir 14 of the formation 2 in a region where high-temperature rock power generation is performed. Here, since the present invention performs high-temperature rock power generation using carbon dioxide, a well is drilled in the vicinity of a large-scale emission source of carbon dioxide such as a coal-fired power plant or a cement factory. It is preferable to use carbon dioxide emitted from a large-scale emission source.

  In this embodiment, out of the plurality of wells 1a and 1b excavated in the formation 2, the well 1a is used as an injection well and the well 1b is used as a production well. A plurality of injection wells and production wells may be provided.

  The excavation depth of the wells 1a and 1b may be any depth as long as the temperature required for the functioning of the generator 6 is secured by the heat of the bottom of the well. It is sufficient if the depth is higher than ℃.

  Japan is a volcanic archipelago, and there are many areas where the geothermal power generation is possible in the shallower underground than in other countries. If the underground temperature at which geothermal power generation is possible is 150 ° C. and the depth at which a realistic well can be drilled is 3000 m, geothermal power generation is possible in an area having a geothermal gradient of 50 ° C./km or more.

  The formation near the bottom of the well is preferably a formation suitable for underground storage of the heat transfer medium. For example, the porosity is preferably several percent or more and the permeability is several tens of milliseas or more.

  In general, aquifer geological storage is intended for sandstone with high porosity and permeability, but when the porosity and permeability of the formation are small, cracks are formed in the formation by applying high water pressure to the wells. It may be generated, i.e., hydraulically crushed to improve the porosity and permeability and improve the conduction state to ensure conduction between the wells near the bottom of the well. Therefore, the present invention is applicable not only to sandstone formations but also to distribution areas such as volcanic rocks and granite.

  Moreover, the surroundings of the wells 1a and 1b from the ground well opening to the vicinity of the well bottom are covered with, for example, a cemented casing 26 in order to prevent leakage of the heat transfer medium.

(2) Injection of heat transfer medium containing carbon dioxide into injection well In this embodiment, water 11 and gas 10 containing carbon dioxide discharged from carbon dioxide discharge source 8 are used as the heat transfer medium.

  In this embodiment, the high pressure pump 3 is used as an injection device for injecting water 11 as a heat transfer medium into the injection well 1a. Then, the water 11 stored in the water tank 7 is sent to the high-pressure pump 3 through the pipe, and is press-fitted into the injection well 1a by the high-pressure pump 3.

  Further, a gas compressor 4 is used as an injection device for injecting a gas 10 as a heat transfer medium into the injection well 1a. And the gas 10 discharged | emitted from the carbon dioxide discharge source 8 is sent to the gas compressor 4 via piping, is compressed by the gas compressor 4, and press-fits into the injection well 1a. In addition, the valve 20 for controlling distribution | circulation and interruption | blocking of the water 11 between these in the piping between the water storage tank 7 and the high pressure pump 3 is provided.

The gas 10 as the heat transfer medium of the present embodiment is not limited as long as it contains at least carbon dioxide, and may be a gas containing components other than carbon dioxide. A gas having a high carbon dioxide concentration is preferred. In addition, as the carbon dioxide emission source 8 in the present invention, a coal-fired power plant and a cement factory are conceivable. In the case of a coal-fired power plant, the main components of the discharged gas 10 are nitrogen (N ₂ ) and carbon dioxide, The concentration of carbon dioxide is approximately 15%.

  And when using the gas 10 discharged | emitted from the carbon dioxide emission source 8 as it is like this embodiment, since it is not necessary to isolate | separate and collect | recover carbon dioxide from the gas 10, the structure of a geothermal power generation system becomes simple. At the same time, the cost can be reduced.

  In this embodiment, in order to inject water 11 and gas 10 into the injection well 1a as a heat transfer medium, the discharge pipe of water 11 from the high-pressure pump 3 and the discharge pipe of gas 10 from the gas compressor 4 merge. Inflow piping to the injection well 1a is provided. The discharge pipe from the high-pressure pump 3 is provided with a valve 21 for controlling the flow and blocking of the water 11 between the high-pressure pump 3 and the junction of the pipe, and the discharge pipe from the gas compressor 4 has a gas A valve 22 is provided for controlling the flow and blocking of the gas 10 between the compressor 4 and the junction of the pipes. Furthermore, the valve 23 for controlling distribution | circulation and interruption | blocking of the water 11 and the gas 10 between these is provided in the piping between the confluence | merging point of piping, and the wellhead of the injection well 1a.

  When the gas 10 and the water 11 are injected into the injection well 1a, the gas 10 and the water 11 are alternately injected. Specifically, the valve 21 of the discharge pipe from the high-pressure pump 3 is closed, the valve 22 of the discharge pipe from the gas compressor 4 and the valve 23 of the injection pipe to the injection well 1a are opened, and the carbon dioxide discharge source 8 is discharged. The gas 10 to be compressed is compressed by the gas compressor 4 and pressed into the injection well 1a (fluid flow indicated by reference numeral 13 in FIG. 1).

  Subsequently, the valve 23 of the injection pipe to the injection well 1 a is closed, the valve 22 of the discharge pipe from the gas compressor 4 is closed, the valve 20 of the discharge pipe from the water tank 7 and the valve of the discharge pipe from the high-pressure pump 3. 21 and then the valve 23 of the injection pipe to the injection well 1a is opened, so that the water 11 in the water tank 7 is pressed into the injection well 1a by the high-pressure pump 3 (the flow of the fluid indicated by reference numeral 13 in FIG. 1). ). As a result, the gas 10 previously injected into the injection well 1 a is pushed into the geothermal reservoir 14 of the high-temperature rock ground in the formation 2.

  Thereafter, similarly, the gas 10 and the water 11 are alternately injected into the injection well 1a. Note that the interval of switching the press-fitting between the gas 10 and the water 11 depends on the assumed carbon dioxide storable amount of the geothermal reservoir 14, the recovery rate of the heat transfer medium, the carbon dioxide saturation in water with respect to the gas / water ratio, and the like. It is set appropriately based on this. Specifically, for example, when the gas / water ratio is 1, it may be possible to switch between injection of 30 tons of water 11 in one hour and injection of 30 tons of gas 10 in one hour. The carbon dioxide storable amount is mainly determined from the volume and porosity of the geothermal reservoir 14.

  If technically possible, the gas 10 containing carbon dioxide as the heat transfer medium and the water 11 may be injected at the same time.

(3) Immobilization of carbon dioxide in the formation Geothermal storage while some of the carbon dioxide contained in the gas 10 injected into the underground hot rock ground through the injection well 1a flows through the cracks in the hot rock ground. Layer 14 is formed. Carbon dioxide contained in the gas 10 exists in the geothermal reservoir 14 in a supercritical state or a state dissolved in water (HCO ₃ ⁻ , H ₂ CO ₃ , CO ₃ ²⁻ ).

In addition, carbon dioxide (specifically calcite) and clay minerals (specifically, other carbon dioxide reacts with calcium (Ca) originally present in the formation 2 by the chemical formulas 1, 2, and 3). In particular, it is fixed as kaolinite). In Chemical Formula 3, CaAl ₂ Si ₂ O ₈ is plagioclase, CaCO ₃ is calcite, and Al ₂ Si ₂ O ₅ (OH) ₄ is kaolinite.

(Chemical formula 1) CO ₂ + H ₂ O → H ₂ CO ₃
(Chemical Formula 2) H ₂ CO ₃ → H ⁺ + HCO ₃ ⁻
(Chemical Formula 3) CaAl ₂ Si ₂ O ₈ + H ⁺ + HCO ₃ ⁻ + H ₂ O
→ CaCO ₃ + Al ₂ Si ₂ O ₅ (OH) ₄

  In addition, the reaction on which the left side of Chemical Formula 3, that is plagioclase, dissolves easily occurs in the vicinity of the well (injection well 1a, production well 1b in this embodiment). In addition, the reaction to be fixed as the right side of Formula 3, that is, carbonate or clay mineral, increases as the calcium concentration of the fluid containing carbon dioxide increases and the flow velocity decreases, that is, as the distance from the well is increased, that is, the edge of the geothermal reservoir 14 It is easy to proceed with.

  A part of the carbon dioxide is fixed at the upper part of the geothermal reservoir 14 and functions as a cap lock 15. That is, the cap lock 15 exhibits a self-seal function that prevents leakage of carbon dioxide to the ground.

  A part of carbon dioxide is fixed at the side edge of the geothermal reservoir 14 to form the fixed layer 16.

  In this way, a part of carbon dioxide injected from the injection well 1a as a heat transfer medium is fixed at the edge of the geothermal reservoir 14 and functions to seal the geothermal reservoir 14 by closing the cracks in the hot rock ground. As a result, the heat transfer medium injected from the injection well 1a can be prevented from leaking from the geothermal reservoir 14, and the recovery rate can be increased as compared with ordinary high-temperature rock power generation. Thereby, carbon dioxide can be fixed and stored in the formation, and the power generation efficiency can be increased.

(4) High temperature of water in the formation Water 11 injected as a heat transfer medium from the injection well 1a is heated by the heat of the rock body while passing through the cracks of the high temperature rock ground of the geothermal reservoir 14, and is heated. become. This hot water is recovered from the production well 1b together with carbon dioxide that has not contributed to storage and immobilization and components other than carbon dioxide contained in the gas 10, such as nitrogen.

  In underground aquifer storage, it is important to contain carbon dioxide underground so that it does not leak to the ground. In this regard, in the present invention, since the cap lock 15 and the fixed layer 16 are formed around the geothermal reservoir 14, it is considered that carbon dioxide is recovered to the ground through the production well 1b. That is, since it is possible to easily manage the carbon dioxide that reaches the ground, it is possible to prevent leakage of carbon dioxide to the ground, that is, release of carbon dioxide into the atmosphere, thereby suppressing the load on the natural environment. At the same time, it is possible to reduce the cost for the carbon dioxide leakage countermeasure assumed in the underground aquifer storage.

(5) Electricity generation Electricity is generated using hot water, which is a heat transfer medium recovered from the production well 1b, carbon dioxide and steam in a supercritical state or a state dissolved in water. In the present embodiment, power generation is performed using a separator system.

  When the gas 10 discharged from the carbon dioxide emission source 8 is injected as a heat transfer medium into the high temperature rock ground as in the present embodiment, a large amount of nitrogen mainly is recovered from the production well 1b together with hot water. (Fluid indicated by reference numeral 17 in FIG. 1).

  The fluid 17 recovered from the production well 1b is separated by the separator 5 into steam 18 mainly composed of nitrogen and water vapor and hot water 19 partially containing carbon dioxide. Then, the separated steam 18 is sent to the generator 6 having a steam turbine to generate power. In addition, since the separator itself which isolate | separates a fluid into gas and a liquid is a well-known technique, it abbreviate | omits for details here. In this embodiment, a centrifugal separator is used. Moreover, in FIG. 1, the code | symbol 24 is provided in piping between the ground well of the production well 1b, and the separator 5, and controls the inflow to the separator 5 of the heat transfer medium 17 collect | recovered via the production well 1b. It represents the valve for.

  In addition, since a part of carbon dioxide is fixed at the edge of the geothermal reservoir 14, the carbon dioxide concentration of the steam 18 is lower than the gas 10 injected from the injection well 1a into the formation 2. Therefore, when the environmental standard value of the carbon dioxide concentration related to the exhaust gas is not exceeded, the steam 18 after being used for power generation in the generator 6 may be directly released into the atmosphere. In addition, when the carbon dioxide concentration does not exceed the environmental standard value but it is not preferable to release it into the atmosphere as it is or when it exceeds the environmental standard value, the steam 18 used for power generation is converted into the gas compressor 4. May be sent to the formation 2 again from the injection well 1a.

  On the other hand, the hot water 19 separated by the separator 5 is sent to the high-pressure pump 3 and is again injected from the injection well 1 a into the high-temperature rock body ground of the formation 2. In FIG. 1, reference numeral 25 denotes a valve that is provided in a pipe between the separator 5 and the high-pressure pump 3 and controls the inflow of hot water 19 separated by the separator 5 into the high-pressure pump 3.

  When the hot water 19 recovered from the production well 1b is used as water injected as a heat transfer medium from the injection well 1a, the valve 20 of the discharge pipe from the water tank 7 is closed and the water tank 7 is closed. The supply of water 11 is suppressed. That is, in the initial operation of the geothermal power generation system, only the water 11 supplied from the water tank 7 is injected into the injection well 1a by the high-pressure pump 3, and after the supply of the hot water 19 from the separator 5 is started, from the separator 5 Water 11 is supplied from the water storage tank 7 when the amount of water to be injected as a heat transfer medium is not sufficient with only the supplied hot water 19.

  According to the geothermal power generation system described above, a circulation system using water and carbon dioxide as a heat transfer medium is formed between the ground and underground geothermal reservoirs 14 through the injection well 1a and the production well 1b. The heat from the hot rock ground is extracted to the ground. Furthermore, a part of the carbon dioxide contained in the heat transfer medium is fixed around the geothermal reservoir 14. Furthermore, carbon dioxide fixed around the geothermal reservoir 14 serves as a barrier to prevent the heat transfer medium from leaking from the geothermal reservoir 14 and increase the heat transfer medium recovery rate. Thereby, the natural environment improvement effect is exhibited and the power generation efficiency is increased.

  In addition, although the above-mentioned form is an example of the suitable form of this invention, it is not limited to this, A various deformation | transformation implementation is possible in the range which does not deviate from the summary of this invention. For example, in the present embodiment, an example has been described on the assumption that carbon dioxide contained in the gas 10 discharged from the carbon dioxide emission source 8 such as a coal-fired power plant is used as carbon dioxide contained in the heat transfer medium. However, the present invention is not limited to this, and carbon dioxide contained in steam discharged from a conventional geothermal power plant may be used. In a conventional geothermal power plant, electric power is generated using hot water or steam originally present in the basement, hot water after power generation is injected into an injection well after cooling, and steam is released into the atmosphere. Since this steam generally contains high-concentration carbon dioxide, if this steam is recovered and injected into the injection well, power generation that exhibits the same operations and effects as the geothermal power generation system of this embodiment is achieved. The system can be configured. And in the existing geothermal power plant, since several wells are already mined, there exists an advantage that this invention can be implemented easily.

  In this embodiment, an example in which water and a gas containing carbon dioxide are used as a heat transfer medium has been described. However, the present invention is not limited to this, and separated and recovered carbon dioxide may be used. Specifically, the gas 10 discharged from the carbon dioxide emission source 8 is made into 100% or almost 100% carbon dioxide (hereinafter referred to as 100% carbon dioxide) using a carbon dioxide separation / recovery technique such as an amine absorption method. May be injected into the injection well 1a as a heat transfer medium. In this case, carbon dioxide is injected into the injection well 1a in a liquid or supercritical state. A high pressure pump is used instead of the gas compressor 4.

  If 100% carbon dioxide is used as the heat transfer medium and the heat transfer medium required for the functioning of the generator 6 can be secured with only 100% carbon dioxide, water is injected as the heat transfer medium. You don't have to. In other words, when 100% carbon dioxide is used as the heat transfer medium, water may be supplementarily used to prevent a decrease in power generation efficiency due to insufficient supply of carbon dioxide, that is, insufficient supply of heat transfer medium. . Note that when 100% carbon dioxide is used as the heat transfer medium and water is injected when necessary, carbon dioxide and water are injected alternately or simultaneously by the operation of the valves 21 and 22.

  Moreover, although this embodiment demonstrated the example which uses a separator system as a system of the high temperature rock body power generation using the hot water and steam collect | recovered from the production well 1b, it is not restricted to this, A binary system is used. You may do it. Specifically, when 100% carbon dioxide is injected into the injection well 1a, the fluid 17 recovered from the production well 1b is mainly hot water containing carbon dioxide. Therefore, in this case, a binary system is used instead of the separator 5, and a secondary medium, which is a low boiling point medium obtained by heat exchange by a binary system, specifically, steam such as normal pentane is used for power generation. You may make it do. In this case, the hot water 19 after the heat exchange is sent from the binary system 5 to the high-pressure pump 3 through a pipe and is again injected from the injection well 1a into the high-temperature rock ground. In addition, when the binary method is used in the method of injecting the gas, the amount of carbon dioxide that can be stored becomes smaller due to the increase of the pressure due to the nitrogen gas in the formation 2, and the use of a pump at a higher pressure is necessary. There is a concern that the cost will increase. However, when these problems are solved, the gas injection method and the binary method may be combined.

It is a schematic structure figure showing an example of an embodiment of a geothermal power generation system of the present invention.

Explanation of symbols

1a injection well 1b production well 14 geothermal reservoir

Claims (2)

A heat transfer medium containing at least carbon dioxide is injected into at least one injection well drilled in the hot rock ground, and the reaction of the components in the hot rock ground causes reaction of the geothermal reservoir in the hot rock ground. At least one production excavated in the high-temperature rock ground while immobilizing a part of carbon dioxide contained in the heat transfer medium at the edge and exhibiting a sealing function to prevent leakage of the heat transfer medium The heat transfer medium heated by the heat of the high-temperature rock body ground is recovered from a well, power is generated using the recovered heat transfer medium, and the heat transfer medium after being used for the power generation is used as the injection well. The geothermal power generation method is characterized by injecting again into the high temperature rock ground. A geothermal reservoir in the hot rock ground by reaction of at least one injection well and at least one production well drilled in the hot rock ground with components in the hot rock ground including at least carbon dioxide a heat transfer medium for transferring heat energy the rewritable exert part by immobilized sealing function for preventing its leakage the HDR ground of the carbon dioxide in the edge portion of the heat to the injection well An injection device for injecting a transmission medium, and a generator that generates power using the heat transfer medium heated by the heat of the high-temperature rock body ground and recovered from the production well, were used for the power generation A later-described heat transfer medium is again injected from the injection well into the hot rock ground.

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