Steam turbine plant

Abstract

To provide a steam turbine plant for enabling safe and low-cost electric power generation by utilizing accumulated heat using fluid bed and molten salt.SOLUTION: The steam turbine plant includes a molten salt heat accumulation tank capable of accumulating and releasing heat, a steam generator for heating water with the heat accumulated in the molten salt heat accumulation tank to form water vapor, a fluid bed for overheating the water vapor to form overheated water vapor, a steam turbine for generating motive power with the overheated water vapor, and an electricity generator for converting the motive power into electric power.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steam turbine plant. [Background technology]

[0002] The introduction of renewable energy is progressing in order to move towards a decarbonized society. In addition, CO2 emissions from thermal power generation using fossil fuels are a concern. As power supply and demand changes from moment to moment, thermal storage power generation is attracting attention from the perspective of fulfilling the power adjustment function that has traditionally been performed by thermal power. Thermal storage power generation stores electricity when surplus electricity is generated by renewable energy, and can supply the stored electricity when demand for electricity is high. Thermal storage power generation has the advantage of being less expensive than storage batteries or hydrogen.

[0003] Proposed heat storage methods for thermal power generation include a molten salt heat storage method and a fluidized bed heat storage method. Patent Document 1 (JP 2022-139945 A) discloses a heat storage-coupled steam generation system that includes a high-temperature heat medium supply unit that heats and supplies a molten salt heat medium, a heat storage unit having a high-temperature heat storage tank that stores the high-temperature heat medium supplied from the high-temperature heat medium supply unit and a low-temperature heat storage tank that stores the low-temperature heat medium after the high-temperature heat medium has been cooled, a steam generation unit that generates high-pressure steam and low-temperature heat medium to be supplied to a load unit by heat exchange between the heat medium and steam, and a circulation means for circulating the heat medium at a predetermined flow rate. Non-Patent Document 1 (Ishikawa, Atsushi, and four others, "Development of Evaluation Technology for Fixed-Bed Heat Storage Systems," IHI Technical Report, IHI Corporation, 2023, Vol. 62, No. 2, p. 16) discloses a fixed-bed heat storage system that stores heat in a fluidized bed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-139945 [Non-patent literature]

[0005] [Non-Patent Document 1] Atsushi Ishikawa and four others, "Development of Evaluation Technology for Fixed-Bed Thermal Storage Systems," IHI Technical Report, IHI Corporation, 2023, Vol. 62, No. 2, pp. 16-24 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the heat storage method using a fluidized bed has the advantage of being able to store high temperatures of over 800°C, it is necessary to inject gas to make the heat storage material flow, which requires power. Also, if the object to be heated is a liquid during heat dissipation, the system becomes a three-component system consisting of the object to be heated (liquid), the heat storage material (solid), and the gas for fluidization, which makes the structure of the fluidized bed complicated and raises concerns about high costs.

[0007] Furthermore, in the heat storage method using molten salt, if the temperature of the heat medium approaches or exceeds 600°C, the molten salt can corrode the tank containing the molten salt, posing a safety problem.

[0008] The present invention has been made in consideration of the above problems, and has as its object to provide a steam turbine plant that is capable of generating electricity safely and at low cost by utilizing heat stored using a fluidized bed and molten salt. [Means for solving the problem]

[0009] The steam turbine plant of the present invention comprises: a molten salt thermal storage tank capable of storing and releasing heat; a steam generator that heats water to generate steam using the heat stored in the molten salt thermal storage tank; a fluidized bed for superheating the steam to form superheated steam; a steam turbine that generates power using the superheated steam; a generator that converts the power into electricity; It has. The "steam" in the steam generator includes water in a supercritical state. The "superheated steam" in the fluidized bed may be steam in a supercritical state or not.

[0010] According to the steam turbine plant of this invention, water is heated to steam by the steam generator, and therefore the temperature of the molten salt thermal storage tank is kept below 600°C, preventing corrosion of the tank containing the molten salt by the molten salt, thereby enhancing safety. Furthermore, in the fluidized bed, fluidization is performed using steam, which is the heated object, and heat is added to the steam to superheat it and turn it into superheated steam, which simplifies the structure of the fluidized bed and reduces costs.

[0011] Steam turbine plants also include: It is preferable to have a steam heating line connected to the fluidized bed, which supplies steam to the fluidized bed and provides heat from the steam to the fluidized bed. The fluidized bed preferably has a solid heat storage material consisting of iron spheres or core-shell microcapsules.

[0012] The molten salt thermal storage tank comprises: a low-temperature section containing a heat transfer medium having a first temperature; a high temperature section containing a heat transfer medium having a second temperature higher than the first temperature; a first pipe capable of transporting a heat medium from the low temperature portion to the high temperature portion; a second pipe capable of transporting a heat medium from the high-temperature portion to the low-temperature portion; It is preferred that the compound has the following structure:

[0013] The heat transfer medium is preferably a solution containing a molten salt selected from the group consisting of NaNO2, LiNO3, NaNO3, KNO3, NaOH, KOH, LiCl, NaCl, KCl, Li2CO3, Na2CO3, K2CO3, a mixture of LiF and BeF2, a mixture of LiF, NaF and KF, and a mixture of LiF, BeF2, ThF4 and UF4.

[0014] The core-shell type microcapsules preferably comprise a core made of a metal alloy and a shell made of Al2O3 provided on the surface of the core. [Effects of the Invention]

[0015] By utilizing heat stored using a fluidized bed and molten salt, it is possible to provide a steam turbine plant that is capable of generating electricity safely and at low cost. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating a steam turbine plant according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a molten salt thermal storage system. [Figure 3] FIG. 3 is a schematic diagram showing an example of a fluidized bed. [Figure 4] FIG. 4 is a schematic diagram showing a modified fluidized bed. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described below with reference to the drawings. In the following description, for example, reference numerals in the drawings corresponding to the components of the invention will be enclosed in parentheses. It should be noted that the drawings are schematic, and the layout of each component, data format, communication method, etc. may differ from reality.

[0018] FIG. 1 is a schematic diagram illustrating a steam turbine plant 1 according to one embodiment. The steam turbine plant 1 includes a molten salt thermal storage system 6 that heats water to produce steam, a fluidized bed 2 that superheats the steam to produce superheated steam, a steam turbine 3 that generates power using the superheated steam, a generator 4 that converts the power into electricity, and a condenser 5 that cools the superheated steam from the steam turbine 3 to produce water. Liquid water is supplied to the molten salt thermal storage system 6 at a predetermined pressure by a pump (not shown), and liquid water is also supplied from the condenser 5. In the molten salt thermal storage system 6, liquid water is heated to produce steam. The steam in the molten salt thermal storage system 6 includes supercritical water. Steam from the molten salt thermal storage system 6 is supplied to the bottom of the fluidized bed 2, and as fluidization occurs within the fluidized bed 2, the steam is superheated to produce superheated steam. Although fluidization may not occur depending on conditions such as the steam flow rate, such a case is also included in the term "fluidized bed" herein. This superheated steam may be supercritical or non-supercritical steam. The superheated steam is supplied to a steam turbine 3, which is rotated by the superheated steam, thereby generating electricity 7 in a generator 4.

[0019] In the steam turbine plant 1 in Figure 1, water is heated to steam by the molten salt thermal storage system 6, and the molten salt flowing into the molten salt thermal storage system 6 is kept at a temperature of less than 600°C to prevent corrosion of the molten salt thermal storage tank by the molten salt, thereby improving safety. In the fluidized bed 2, fluidization is performed by the steam to be heated, and heat is added to the steam to superheat it and turn it into superheated steam, so the structure of the fluidized bed 2 can be simplified and costs can be reduced.

[0020] In the molten salt thermal storage system 6, the injected water gains (releases) heat from the heat medium, becomes water vapor, and is then discharged. The water vapor discharged from the molten salt thermal storage system 6 thus contains water in a supercritical state. The water vapor discharged from the molten salt thermal storage system 6 is sent to a fluidized bed. The heat medium flows into the molten salt thermal storage system 6 from direction d1 and is discharged from direction d2. The heat medium can be selected appropriately depending on the conditions for converting water into water vapor in the molten salt thermal storage system 6. However, because it is easy to handle and has a relatively low specific heat, the heat medium is preferably a solution containing a molten salt selected from the group consisting of NaNO2, LiNO3, NaNO3, KNO3, NaOH, KOH, LiCl, NaCl, KCl, Li2CO3, Na2CO3, K2CO3, a mixture of LiF and BeF2, a mixture of LiF, NaF, and KF, and a mixture of LiF, BeF2, ThF4, and UF4. Furthermore, in order to improve the heat storage density, the heat medium may contain a phase change material (PCM) such as crushed concrete, paraffin, fatty acid, sugar alcohol, etc. By heating the heat medium in the molten salt thermal storage system 6, heat can be stored (heat stored) in the molten salt thermal storage system 6.

[0021] It is preferable to supply liquid water at a pressure of, for example, 28 to 30 MPa to the molten salt thermal storage system 6. It is also preferable to supply liquid water at a temperature of, for example, 280°C to the molten salt thermal storage system 6. The steam supplied from the molten salt thermal storage system 6 to the fluidized bed 2 has a pressure of, for example, 27 MPa.

[0022] FIG. 2 is a schematic diagram illustrating an example of an overall thermal storage system. The molten salt thermal storage system 6 in FIG. 2 includes a low-temperature section 11 containing a heat transfer medium having a first temperature, a high-temperature section 10 containing a heat transfer medium having a second temperature higher than the first temperature, a first pipe 14 capable of transporting the heat transfer medium from the low-temperature section 11 to the high-temperature section 10, an electric heater 12 provided along the first pipe 14, a second pipe 15 capable of transporting the heat transfer medium from the high-temperature section 10 to the low-temperature section 11, and a steam generator 13 provided along the second pipe 15. A temperature stratification 16 is formed between the high-temperature section 10 and the low-temperature section 11, and the first and second temperatures are maintained such that the second temperature in the high-temperature section 10 is higher than the first temperature in the low-temperature section 11. Typically, the same heat transfer medium is stored in the low-temperature section 11 and the high-temperature section 10. The low-temperature section 11 and the high-temperature section 10 constitute a molten salt thermal storage tank, which is capable of storing and releasing heat.

[0023] The low-temperature section 11 and the high-temperature section 10 are connected by a first pipe 14 and a second pipe 15. A heat transfer medium can be transported between the low-temperature section 11 and the high-temperature section 10 via the first pipe 14 and the second pipe 15 in the direction of the arrows shown in FIG. 2 . That is, the heat transfer medium can be transported from the low-temperature section 11 to the high-temperature section 10 via the first pipe 14. The heat transfer medium can also be transported from the high-temperature section 10 to the low-temperature section 11 via the second pipe 15. An electric heater 12 is installed in the first pipe 14, which heats the heat transfer medium having a first temperature transported from the low-temperature section 11 to a second temperature. A steam generator 13 is installed in the second pipe 15. Heat exchange occurs between water injected by a pump from the direction D1 and the heat transfer medium having a second temperature, converting the water into steam. This steam is discharged from the steam generator 13 in the direction D2 and sent to the fluidized bed. At this time, the temperature of the heat medium is lowered from the second temperature to the first temperature by heat exchange with the water. In this way, in the molten salt thermal storage system 6, heat is stored (heat stored) in the molten salt thermal storage tank by the electric heater 12, and the heat is released (heat dissipated) by the steam generator 13.

[0024] The first and second temperatures can be selected appropriately depending on the type of heat medium and the conditions for converting water into steam in the molten salt thermal storage system 6. More specifically, the first temperature is, for example, 300°C, and the second temperature is, for example, 420°C.

[0025] The steam discharged in the direction D2 from the steam generator 13 in Fig. 2 contains water in a supercritical state. The molten salt thermal storage system 6 in Fig. 2 has the low temperature section 11 and the high temperature section 10 integrated together, which allows for space saving and cost reduction. In addition, by maintaining the temperature stratification 16 and having the high temperature section 10 at the second temperature, the steam discharged in the direction D2 can be efficiently heated to a high temperature.

[0026] FIG. 3 is a schematic diagram illustrating an example of a fluidized bed 2. Steam discharged from the molten salt thermal storage system 6 is injected into the bottom 24 of the fluidized bed 2 from the direction D3, and supercritical steam is discharged from the top 23 in the direction D4. A plurality of heaters 21 are disposed between the bottom 24 and the top 23 of the fluidized bed 2, and the heaters 21 heat the solid thermal storage material 22. The heaters 21 are not particularly limited as long as they can effectively heat the solid thermal storage material 22; for example, sheath heaters, electromagnetic heating devices, or electrical heating devices can be used. The solid thermal storage material 22 heated by the heaters 21 is fluidized by the steam injected from the bottom 24 of the fluidized bed 2, allowing efficient transfer of heat from the solid thermal storage material 22 to the steam. Furthermore, wire mesh 25 is provided near the bottom 24 and the top 23 of the fluidized bed 2 to prevent the solid thermal storage material 22 from scattering outside the fluidized bed 2.

[0027] The solid heat storage material is not particularly limited as long as it can exchange heat with water vapor, but solid heat storage materials made of iron balls or core-shell type microcapsules are preferred because of their excellent thermal conductivity and efficiency of heat exchange with water vapor. Also, examples of core-shell type microcapsules include microcapsules made of a core made of a metal alloy and a shell made of Al2O3 provided on the surface of the core.

[0028] FIG. 4 is a schematic diagram showing a modified example of the fluidized bed 2. A steam heating line 28 is connected to the fluidized bed 2, and a fan or compressor 26 and a heating section 27 are provided along the steam heating line 28. The steam heating line 28 can be used when storing heat in the fluidized bed 2 (during heat storage). When the steam heating line 28 is operated, the steam is compressed by the fan or compressor 26, thereby increasing the temperature of the steam through adiabatic compression, and the temperature of the steam is further increased by the heating section 27. The heating section 27 is not particularly limited, but may be, for example, a sheath heater. The high-temperature steam is then injected into the bottom 24 of the fluidized bed 2, thereby heating the solid heat storage material 22 in the fluidized bed 2 and storing heat within the fluidized bed 2. The steam injected into the bottom 24 of the fluidized bed 2 may be discharged from the top 23 of the fluidized bed 2 or may be circulated through the steam heating line 28 again via line 30. Alternatively, the steam to be injected into the bottom 24 of the fluidized bed 2 may be supplied from a separate line 29 for supplying steam. The above describes a method in which steam is taken out from the top of the fluidized bed 2, heated, and then returned from the bottom. However, the opposite method may be used in which steam is taken out from the bottom of the fluidized bed, heated, and then returned from the top. Although FIG. 4 shows an embodiment in which both the fan or compressor 26 and the heating unit 27 are arranged in the steam heating line 28, only the fan or compressor 26 or only the heating unit 27 may be arranged in the steam heating line 28 as long as it can heat the steam to a sufficiently high temperature. [Explanation of symbols]

[0029] 1...Steam turbine plant, 2...Fluidized bed, 3...Steam turbine, 4...Generator, 5...Condenser, 6...Molten salt thermal storage system, 7...Electric power, 10...High temperature section, 11...Low temperature section, 12...Electric heater, 13...Steam generator, 14...First pipe, 15...Second pipe, 16...Temperature stratification, 21...Heater, 22...Solid thermal storage material, 23...Top, 24...Bottom, 25...Wire mesh, 26...Fan or compressor, 27...Heating section, 28...Steam heating line

Claims

1. a molten salt thermal storage tank capable of storing and releasing heat; a steam generator that heats water to generate steam using the heat stored in the molten salt thermal storage tank; a fluidized bed for superheating the steam to form superheated steam; a steam turbine that generates power using the superheated steam; a generator that converts the power into electricity; A steam turbine plant having:

2. moreover, 2. The steam turbine plant according to claim 1, further comprising a steam warming line connected to the fluidized bed, the steam warming line supplying steam to the fluidized bed and imparting heat to the fluidized bed from the steam.

3. 3. The steam turbine plant according to claim 1, wherein the fluidized bed has a solid heat storage material made of iron balls or core-shell type microcapsules.

4. The molten salt thermal storage tank comprises: a low-temperature section containing a heat transfer medium having a first temperature; a high temperature section containing a heat transfer medium having a second temperature higher than the first temperature; a first pipe capable of transporting a heat medium from the low temperature portion to the high temperature portion; a second pipe capable of transporting a heat medium from the high-temperature portion to the low-temperature portion; The steam turbine plant according to claim 1 or 2, comprising:

5. The heat transfer medium is NaNO ２ , LiNO ３ , NaNO ３ , KNO ３ , NaOH, KOH, LiCl, NaCl, KCl, Li ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , LiF and BeF ２ a mixture of LiF, NaF and KF, and a mixture of LiF and BeF ２ and ThF ４ and UF ４ 5. The steam turbine plant according to claim 4, wherein the solution contains a molten salt selected from the group consisting of a mixture of

6. The core-shell type microcapsules have a core made of a metal alloy and an Al layer provided on the surface of the core. ２ O ３ 4. The steam turbine plant according to claim 3, further comprising a shell comprising:

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