Heat recovery system

Abstract

To provide a heat recovery system which can preferably recover heat from a high temperature fluid to molten salt.SOLUTION: According to the invention, a heat recovery system includes a heat receiving part, a heat passage, a first heat recovery part, and a second heat recovery part. The heat receiving part is configured to receive a high temperature fluid. The heat passage is configured so that the high temperature fluid received by the heat receiving part circulates therein. The first heat recovery part is configured to recover heat of the high temperature fluid through heat exchange with a first heat medium. The second heat recovery part is disposed downstream of the first heat recovery part in the heat passage and is configured to recover, through heat exchange with molten salt, heat of the high temperature fluid which has passed through the first heat recovery part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat recovery system for recovering heat from a high temperature fluid. [Background technology]

[0002] One method for storing and transporting hydrogen is the organic chemical hydride method, in which aromatic compounds such as toluene are hydrogenated and stored or transported in the form of hydrogenated aromatic compounds (organic hydrides).The dehydrogenation reaction of hydrogenated aromatic compounds is an endothermic reaction, so heat must be added from an external source.

[0003] Patent Document 1 discloses a hydrogen production facility that uses electric power to heat a molten salt and dehydrogenates an organic compound using the heat of the heated molten salt. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6812252 Summary of the Invention [Problem to be solved by the invention]

[0005] Molten salt has the advantages of having a large heat capacity and low safety risks, but when heated with electricity, a large amount of electricity is required until the molten salt stores enough heat. Also, when molten salt is used at temperatures higher than the appropriate operating temperature range, degradation such as decomposition and corrosion progresses significantly, so it is not easy to heat the molten salt using high-temperature waste heat.

[0006] The present invention has been made in view of the above circumstances, and provides a heat recovery system that can suitably recover heat from a high-temperature fluid to a molten salt. [Means for solving the problem]

[0007] According to the present invention, the following inventions are provided. [1] A heat recovery system comprising a heat receiving section, a heat flow path, a first heat recovery section, and a second heat recovery section, wherein the heat receiving section is configured to receive a high-temperature fluid, the heat flow path is configured to allow the high-temperature fluid received by the heat receiving section to flow, the first heat recovery section is configured to recover heat from the high-temperature fluid by heat exchange with a first heat medium, and the second heat recovery section is disposed downstream of the first heat recovery section in the heat flow path and is configured to recover heat from the high-temperature fluid after passing through the first heat recovery section by heat exchange with molten salt. [2] The heat recovery system according to [1], wherein the high-temperature fluid has a temperature of 250 to 700°C after passing through the first heat recovery section. [3] A heat recovery system according to [1] or [2], further comprising a third heat recovery section, the third heat recovery section being arranged downstream of the second heat recovery section in the heat flow path and configured to recover heat from the high-temperature fluid after passing through the second heat recovery section by heat exchange with a second heat medium. [4] A heat recovery system as described in [3], wherein the first heat recovery unit has a first steam generator that uses the heat of the high-temperature fluid to generate steam and supplies the generated steam to a heat demand unit, and the third heat recovery unit has a feedwater preheater that uses the heat of the high-temperature fluid to preheat water to be supplied to the first steam generator. [5] The heat recovery system according to [4], further comprising a second steam generator, wherein the second steam generator is configured to generate steam from water preheated by the third heat recovery section by utilizing the heat stored in the molten salt, and the first steam generator and the second steam generator are configured to supply steam to the same heat demand section. [6] A heat recovery system according to any one of [1] to [5], wherein the second heat recovery unit is configured to supply the heat stored in the molten salt to a hydrogen generation unit configured to generate hydrogen from a hydrogenated aromatic compound. [7] A heat recovery system according to any one of [1] to [6], wherein the heat receiving section is configured to receive high-temperature gas from at least one of a gas turbine power generation facility, a fuel cell, an electric arc furnace, a blast furnace, and a waste incineration facility. [Effects of the Invention]

[0008] The heat recovery system of the present invention makes it possible to preferably recover heat from a high-temperature fluid to a molten salt. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing a schematic configuration of a heat recovery system 1 according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a schematic configuration of a heat recovery system 1A according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing a schematic configuration of a heat recovery system 1B according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0011] 1. First embodiment The heat recovery system 1 includes a heat receiving section 2, a heat flow path 2A, a first heat recovery section 3, a second heat recovery section 4, and a third heat recovery section 5. The heat receiving section 2 is configured to receive a high-temperature fluid. In this embodiment, the high-temperature fluid is a high-temperature gas (with a temperature range of, for example, 800°C to 1400°C) discharged from an industrial furnace such as an electric arc furnace or a blast furnace in a steel mill. However, the high-temperature fluid is not limited to this, and the heat receiving section 2 may also receive a high-temperature fluid discharged from a gas turbine or a fuel cell, or a high-temperature fluid from a combustion heat source such as a waste incineration facility, a solar heat source (concentrating type), a nuclear heat source, a geothermal heat source, or the like.

[0012] The heat flow path 2A is configured to allow the flow of high-temperature fluid received by the heat receiving section 2. The configuration of the heat flow path 2A can be, for example, a metal pipe configured to allow high-temperature fluid exceeding 1000°C to flow therethrough, but is not limited to this.

[0013] <First heat recovery section 3> The first heat recovery section 3 is configured to recover heat from the high-temperature gas flowing through the heat flow path 2A by heat exchange with a first heat medium. In this embodiment, the first heat recovery section 3 has a first steam generator 3A, and water (steam) is used as the first heat medium. The first steam generator 3A recovers heat from the high-temperature gas flowing through the heat flow path 2A and uses the recovered heat to evaporate supplied water. However, the first heat medium is not limited to this. For example, when recovering ultra-high temperature heat (approximately 1000°C to 1500°C) from a nuclear heat source, it is preferable to use carbon dioxide gas, helium, or the like as the first heat medium.

[0014] <Second heat recovery section 4> The second heat recovery section 4 is located downstream of the first heat recovery section 3 in the heat flow path 2A. The second heat recovery section 4 is configured to recover heat from the high-temperature gas flowing through the heat flow path 2A by heat exchange with molten salt. The exhaust gas from electric arc furnaces and blast furnaces typically exceeds the appropriate operating temperature range of molten salt, and contact with the molten salt often causes degradation, such as decomposition. However, the second heat recovery section 4 receives the heat from the high-temperature gas that has passed through the first heat recovery section 3 and been cooled by heat recovery in the first steam generator 3A. This prevents the molten salt from coming into contact with excessively high-temperature heat. Furthermore, when the high-temperature fluid is cooled to match the operating temperature of the molten salt, heat recovery is performed rather than simply dissipating it, preventing waste of thermal energy.

[0015] The temperature of the exhaust gas after passing through the first heat recovery unit 3 is preferably set to 250 to 700°C. If the temperature of the exhaust gas is less than 250°C, there is a risk that the molten salt will solidify. If the temperature of the exhaust gas exceeds 700°C, there is a risk that the molten salt will decompose or otherwise deteriorate. The set temperature of the exhaust gas after passing through the first heat recovery unit 3 is more preferably, for example, 300 to 650°C, and even more preferably 350 to 600°C. Within these temperature ranges, it becomes easier to supply heat at an optimal temperature from the second heat recovery unit 4 to the hydrogen generation unit 10, which will be described later.

[0016] The second heat recovery section 4 has a heater 4A. The heater 4A is configured to heat the molten salt by heat exchange between the high-temperature gas flowing through the heat flow path 2A and the molten salt. An example of the molten salt is, but is not limited to, a molten mixture of potassium nitrate and sodium nitrate. Molten salts generally have a large heat capacity and a high operating temperature, so it is advisable to appropriately select and use a molten salt with a known composition depending on the required heat storage capacity, temperature, etc.

[0017] The second heat recovery section 4 further includes a high-temperature tank 4B, a heat exchanger 4C, and a low-temperature tank 4D. A circulation path 40 for the molten salt is provided so that the molten salt passes from the heater 4A through the high-temperature tank 4B, the heat exchanger 4C, and the low-temperature tank 4D and returns to the heater 4A. A liquid delivery device such as a pump is appropriately disposed in the circulation path 40.

[0018] The high-temperature tank 4B is configured to store molten salt heated by the heater 4A. The high-temperature tank 4B stores molten salt at a temperature (for example, about 650°C) close to the upper limit of the operating temperature (250 to 700°C). The capacity of the high-temperature tank 4B and the temperature of the stored molten salt can be set appropriately depending on the amount of heat required to be stored.

[0019] The heat exchanger 4C is configured to supply heat from the molten salt supplied from the high-temperature tank 4B to the heat demand section through heat exchange. In the heat exchanger 4C, the high-temperature molten salt is cooled by heat exchange with thermal oil (hot oil), while the heated thermal oil supplies heat to the heat demand section. For example, the heat exchanger 4C may be configured such that the molten salt flows through a pipe and the thermal oil passes around the pipe, but this is not limitative. In this embodiment, the heat exchanger 4C supplies heat to the hydrogen generation section 10. The hydrogen generation section 10 is configured to generate hydrogen from a hydrogenated aromatic compound using the heat transferred from the molten salt to the thermal oil.

[0020] A thermal oil at about 400°C is constantly circulated between the heat exchanger 4C and the hydrogen generation unit 10. A mixture of diphenyl oxide and biphenyl can be suitably used as the thermal oil. However, other types of thermal oil may be used as long as they have good chemical stability under the temperature conditions used as the heat source for the dehydrogenation reaction. It is also possible to use a heat exchange medium other than thermal oil (high-pressure steam, gas, etc.) between the heat exchanger 4C and the hydrogen generation unit 10.

[0021] The low-temperature tank 4D is configured to store the molten salt cooled in the heat exchanger 4C. The high-temperature tank 4B stores molten salt at a temperature (for example, about 350°C) close to the lower limit of the operating temperature (250 to 700°C). The molten salt in the low-temperature tank 4D is sent again to the heater 4A, where it is heated, and then stored in the high-temperature tank 4B.

[0022] <Third heat recovery section 5> The third heat recovery section 5 is disposed downstream of the second heat recovery section 4 in the heat flow path 2A. The third heat recovery section 5 is configured to recover heat (for example, a temperature of about 250 to 300°C) from the high-temperature fluid after passing through the second heat recovery section 4 by heat exchange with water (second heat medium). The third heat recovery section 5 has a feedwater preheater 5A that uses the heat of the high-temperature fluid to preheat water to be supplied to the first steam generator 3A.

[0023] <Second steam generator 3B> The heat recovery system 1 further includes a second steam generator 3B. The second steam generator 3B is configured to generate steam from water preheated by a feedwater preheater 5A, utilizing the heat stored in the molten salt. The second steam generator 3B evaporates the preheated water using the heat of the molten salt supplied from the high-temperature tank 4B via a branch point 41. The molten salt that has passed through the second steam generator 3B returns to the circulation path 40 via a junction 42 and is sent to the low-temperature tank 4D.

[0024] The first steam generator 3A and the second steam generator 3B are configured to supply steam to the same heat demand section. Specifically, the steam generated by the first steam generator 3A and the second steam generator 3B passes through a junction 61 and a heat supply section 6 and is then supplied to the heat demand section.

[0025] In this embodiment, the heat demand unit that supplies heat from the heat supply unit 6 is a power generation facility 11. The power generation facility 11 includes a steam turbine 11A, a generator 11B, and a condenser 11C. The steam turbine 11A is configured to be driven by steam sent from the heat supply unit 6 of the heat recovery system 1. The generator 11B is configured to be driven by the rotational force of the steam turbine 11A. The condenser 11C is configured to condense the steam from the steam turbine 11A. The condensate from the condenser 11C is sent to the feedwater preheater 5A and is reused.

[0026] In the above-described heat recovery system 1, high-temperature gas (800°C to 1400°C) discharged from industrial furnaces such as electric arc furnaces and blast furnaces can be efficiently recovered by three stages of heat recovery means: the first heat recovery section 3, the second heat recovery section 4, and the third heat recovery section 5. This makes it possible to improve the heat recovery exergy efficiency when utilizing waste heat from industrial furnaces such as electric arc furnaces and blast furnaces.

[0027] In particular, compared to a normal heat recovery boiler, the addition of a heat recovery means (second heat recovery section 4) using molten salt with a large heat capacity in the middle stage of the two-stage steam generator makes it possible to achieve superior heat recovery exergy efficiency. Also, it becomes possible to supply the heat recovered in the first heat recovery section 3 and the third heat recovery section 5, and the heat recovered in the second heat recovery section 4 to multiple heat demand sections (in this embodiment, the hydrogen generation section 10 and the power generation facility 11).

[0028] In the second heat recovery unit 4, heat can be stored by utilizing the heat storage capacity of the molten salt, so even if the heat source input to the heat receiving unit 2 is unstable, heat can be stably supplied from the heat exchanger 4C to the hydrogen generation unit 10. Furthermore, because steam can be generated in the second steam generator 3B using the molten salt stored in the high-temperature tank 4B, steam can be stably supplied from the heat supply unit 6 to the power generation equipment 11 even if the heat input to the heat receiving unit 2 is unstable. Therefore, even if heat only enters the heat receiving unit 2 intermittently, heat supply from the heat exchanger 4C and the heat supply unit 6 can be stabilized.

[0029] 2. Second embodiment Next, a heat recovery system 1A according to a second embodiment will be described with reference to Fig. 2. The basic configuration of the heat recovery system 1A is the same as that of the heat recovery system 1. However, in this embodiment, heat is supplied from the heat exchanger 4C of the second heat recovery unit 4 to the power generation equipment 11, not to the hydrogen generation unit 10.

[0030] Condensate from the condenser 11C of the power generation facility 11 is sent to the feedwater preheater 5A on one side and to the heat exchanger 4C on the other side via a branch point 63. The condensate is evaporated in the heat exchanger 4C, and the generated steam is supplied to the power generation facility 11 via a junction point 62 and the heat supply unit 6.

[0031] In this embodiment, it is possible to centrally supply the heat recovered in the first heat recovery section 3, the second heat recovery section 4, and the third heat recovery section 5 to the power generation facility 11. For example, by employing the heat recovery system 1A in a combined cycle power generation facility and recovering the exhaust gas that has finished rotating the gas turbine of a gas turbine power generation facility in the heat recovery system 1A, it is possible to improve the power generation efficiency.

[0032] 3. Third embodiment In the above embodiment, an example was shown in which the heat receiving section 2 receives heat from the outside and sends it to a single heat flow path 2A, but a configuration in which heat sources of different temperature ranges are received and sent to different heat flow paths 2A to 2C may also be adopted. In Fig. 3, there are three heat flow paths 2A to 2C, but there may also be two, or four or more.

[0033] For example, when heat in the temperature range of the operating temperature of molten salt (250 to 700°C) enters the heat receiving section 2, it is advisable to send the heat to heat flow path 2B, which does not pass through the first steam generator 3A of the first heat recovery section 3. Heat flow path 2B merges with heat flow path 2A at junction 21. By being able to heat the molten salt with heat from multiple systems, it is possible to maintain the molten salt at a temperature above its melting point and prevent solidification, even in cases where the exhaust heat from industrial furnaces such as electric arc furnaces and blast furnaces is stopped for an extended period of time.

[0034] Furthermore, when heat in the temperature range of about 150 to 250°C enters the heat receiving section 2, it is preferable to send the heat directly to the feedwater preheater 5A of the third heat recovery section 5 through the heat flow path 2C, without passing through the first heat recovery section 3 and the second heat recovery section 4. The heat flow path 2C merges with the heat flow path 2A at the junction 22. In this way, by adopting a configuration that accepts heat sources in multiple temperature ranges and sends them to the optimal heat recovery section, it becomes possible to effectively use more heat sources.

[0035] In the above-described embodiments, high heat recovery exergy efficiency is achieved by efficiently recovering the high-temperature heat source received by the heat recovery systems 1, 1A, and 1B using molten salt and other heat transfer media (steam, helium, carbon dioxide, etc.). The heat recovery systems 1, 1A, and 1B are capable of storing heat using molten salt, which has a large heat capacity, and therefore have excellent heat storage capacity. Furthermore, the heat recovery systems 1, 1A, and 1B can supply heat by appropriately utilizing the stored heat. Therefore, even if it is not possible to receive stable exhaust heat from upstream equipment (such as a steelworks), the heat recovery systems 1, 1A, and 1B can stably supply heat to downstream equipment (heat demand units).

[0036] 4. Other embodiments When nuclear heat is recovered using helium, carbon dioxide, or the like as a heat medium in the first heat recovery section 3, the recovered heat may be supplied to a gas turbine. The high-temperature fluid received by the heat receiving portion 2 is not limited to gas or steam, but may be a liquid. The heat exchangers and heat transfer media used in each location are not limited to specific ones, and publicly known ones can be selected and used as appropriate. [Explanation of symbols]

[0037] 1: Heat recovery system 1A: Heat recovery system 1B: Heat recovery system 2:Heat receiving part 2A: Heat flow path 2B: Heat flow path 2C: Heat flow path 3: First heat recovery section 3A: First steam generator 3B: Second steam generator 4: Second heat recovery section 4A: Heater 4B: High temperature tank 4C: Heat exchanger 4D: Cryogenic tank 5: Third heat recovery section 5A: Feedwater preheater 6:Heat supply section 10: Hydrogen generation unit 11: Power generation facilities 11A: Steam turbine 11B: Generator 11C: Condenser 21: Confluence 22: Confluence 40: Circulation route 41: Branching point 42: Confluence 61: Confluence 62: Confluence 63: Branching point

Claims

1. A heat recovery system including a heat receiving section, a heat flow path, a first heat recovery section, and a second heat recovery section, the heat receiving portion is configured to receive a high-temperature fluid; the heat flow path is configured so that the high-temperature fluid received by the heat receiving portion flows through the heat flow path; the first heat recovery unit is configured to recover heat from the high-temperature fluid by heat exchange with a first heat medium; a second heat recovery section disposed downstream of the first heat recovery section in the heat flow path and configured to recover heat from the high-temperature fluid after passing through the first heat recovery section by heat exchange with molten salt.

2. 10. The heat recovery system of claim 1, A heat recovery system, wherein the temperature of the high-temperature fluid after passing through the first heat recovery section is 250 to 700°C.

3. The heat recovery system according to claim 1, further comprising a third heat recovery unit, a third heat recovery section disposed downstream of the second heat recovery section in the heat flow path and configured to recover heat from the high-temperature fluid after passing through the second heat recovery section by heat exchange with a second heat medium.

4. 4. The heat recovery system of claim 3, the first heat recovery unit has a first steam generator that generates steam by utilizing heat of the high-temperature fluid and supplies the generated steam to a heat demand unit, a heat recovery system, wherein the third heat recovery section has a feedwater preheater that uses heat of the high-temperature fluid to preheat water to be supplied to the first steam generator;

5. 5. The heat recovery system of claim 4, further comprising a second steam generator; the second steam generator is configured to generate steam from water preheated by the third heat recovery section by utilizing heat stored in the molten salt, A heat recovery system, wherein the first steam generator and the second steam generator are configured to supply steam to the same heat demand.

6. 10. The heat recovery system of claim 1, a second heat recovery unit configured to supply the heat stored in the molten salt to a hydrogen generation unit configured to generate hydrogen from a hydrogenated aromatic compound.

7. 10. The heat recovery system of claim 1, A heat recovery system, wherein the heat receiving section is configured to receive hot gas from at least one of a gas turbine power plant, a fuel cell, an electric arc furnace, a blast furnace, and a waste incineration plant.

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