Methane gas production device and methane gas production method

Abstract

To provide a methane gas production device and a methane gas production method for efficiently producing methane gas.SOLUTION: A methane gas production device recovers reaction heat generated accompanied by methanation reaction and heat energy possessed by gaseous mixture of methane and water vapor generated by the methanation reaction by a heat medium through a heat exchanger, operates a turbine operated using the recovered heat energy, or one or more of an absorption type refrigerator and an adsorption type refrigerator, and thereby promotes the methanation reaction by either or both of adiabatic compression of raw material gas subjected to the methanation reaction and supply of the adiabatically compressed raw material gas to a methane gas production device, and cooling of gaseous mixture of the methane generated by the methanation reaction and water vapor, and thereby improves production efficiency of methane gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a methane gas production device and a methane gas production method for producing methane gas by a methanation reaction. [Background technology]

[0002] In order to reduce emissions of carbon dioxide, a major greenhouse gas, methods of circulating and utilizing methane gas by reacting carbon dioxide with hydrogen have been studied, and devices and methods for efficiently reacting carbon dioxide with hydrogen to produce methane gas have been proposed (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-40919 A [Patent Document 2] JP 2023-98433 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, conventional technology uses carbon dioxide and hydrogen as feed gases and uses the heat-generating methane production reaction in a methane gas generator to generate a high-temperature mixture of methane gas and water vapor. This utilizes the thermal energy and water vapor contained in the mixture to change the equilibrium state of the methanation reaction, thereby increasing the concentration of the methane gas generated and enabling efficient production. However, this technology has the following four challenges.

[0005] First, in the method described in Patent Document 1, the main heat exchange method between the raw material and the product is heat exchange between gases, i.e., a mixture of carbon dioxide and hydrogen, and a mixture of methane gas and water vapor, and also includes heat exchange via condensed hot water of water vapor as a secondary step. However, since all of the heat exchange media are liquid-gas heat exchanges in which a liquid such as a heat transfer medium is circulated, and no heat exchange involving a reaction in which the liquid heat transfer medium absorbs latent heat and is vaporized is performed, the efficiency of heat exchange is low, making it difficult to sufficiently preheat the raw material gas and cool the product mixture. Furthermore, in order to perform sufficient heat exchange, it is necessary to increase the heat exchange area and install multiple heat exchangers, which poses the problem of the device becoming larger.

[0006] Furthermore, since heat exchange is limited to the product mixture and the feed gas, the cooling limit of the product mixture is approximately up to the inlet temperature of the feed gas to the heat exchanger. Therefore, it is difficult to liquefy, condense, and separate the water vapor in the product mixture by individually and additionally cooling the product mixture to a dew point of 5 to 15°C or less, which is necessary for the supply and use of methane gas, using the thermal energy contained in the product mixture. Therefore, unless the feed gas, which is the reactant, is sufficiently cooled, it is difficult to condense and remove moisture below the dew point from the product mixture. On the other hand, in order to condense and remove moisture below the dew point sufficiently, a large amount of cooling energy is required to sufficiently cool the feed gas, which has low heat exchange efficiency, resulting in a problem of reduced efficiency of methane generation.

[0007] Furthermore, even if the reactant mixture of carbon dioxide and hydrogen can be supplied at a sufficiently low temperature, it is easy to remove moisture by cooling the product, but because the raw gas is low temperature, it is difficult to sufficiently preheat it by heat exchange before supplying it to the methane generation device, which results in a decrease in the efficiency of the methanation reaction, or in order to maintain the efficiency of the methanation reaction, the device must be made larger and more complex, such as by increasing the heat transfer area or arranging multiple heat exchangers in series.

[0008] On the other hand, as described in Patent Document 2, water is supplied to a methanation reactor to generate water vapor, and the obtained water vapor is supplied to a solid oxide electrolysis cell to generate a mixture of carbon dioxide, hydrogen, and water vapor. This mixture is then cooled in a condenser to produce a mixture of hydrogen and carbon dioxide from which moisture has been removed, and this mixture is compressed and supplied to a methanation reactor, thereby efficiently absorbing the heat of methanation reaction by evaporating water and effectively utilizing the energy of the obtained water vapor. However, this method requires a large amount of external energy supply for a process of cooling and removing moisture from the high-temperature unreacted water vapor discharged from the solid oxide electrolysis cell, and for driving a compressor that compresses the mixture of hydrogen and carbon dioxide after moisture removal, resulting in a problem of reduced methane generation efficiency in the entire system.

[0009] Note that the above-mentioned conventional technology does not disclose a specific method for pressurizing and preheating the reactants or for removing moisture in the generated methane gas mixture by cooling it to a dew point of 15°C or lower by utilizing the heat of reaction generated in the methane generation device or the high-temperature thermal energy contained in the mixture of methane and water vapor generated from the methane generation device.

[0010] The present invention has been made in consideration of these problems, and its purpose is to provide a method for recovering, via a liquid heat transfer medium, the reaction heat generated in the methanation reaction and the thermal energy contained in the product obtained by the methanation reaction, to pressurize and preheat the reactants to be supplied to the methane generation device, or to cool the mixture of methane and water vapor generated from the methane generation device to condense and remove the water vapor, thereby changing the equilibrium state of the methane generation reaction to promote methane generation, and to sufficiently remove the water vapor contained in the product to increase the methane purity, and a methane generation device to which these methods are applied. [Means for solving the problem]

[0011] In order to solve the above problems, the methane gas generator of the present invention is characterized in that it cools a mixture of methane and water vapor generated from the methane gas generator with cold energy obtained by a heat medium that is heated or vaporized by recovering either or both of the reaction heat generated by the methanation reaction and the thermal energy possessed by the product obtained by the methanation reaction, a gas compressor connected to a turbine driven by the heated or vaporized heat medium, or an electric gas compressor driven by the generated power of a generator connected to a turbine driven by the heated or vaporized heat medium, a gas expander connected to a turbine driven by the heated or vaporized heat medium, or an absorption or adsorption refrigerator driven by the heated or vaporized heat medium, and a turbo refrigerator driven by the generated power of a generator connected to a turbine driven by the heated or vaporized heat medium.

[0012] The methane gas generator may have a circulation flow path in which a heat transfer medium, which recovers reaction heat and is heated or vaporized, dissipates the recovered heat through the device and is then returned to the methane gas generator to recover the reaction heat.

[0013] Furthermore, the methane gas generator of the present invention is characterized in that it comprises a recovered water purification and supply device which recovers water condensed and liquefied when the mixture of methane and water vapor generated by the methane gas generator is cooled, purifies the water by removing impurities and neutralizing it, and then supplies the water as raw material water for producing hydrogen to be supplied to the methane gas generator by water electrolysis, or, after removing impurities or neutralizing the water, dissipates heat into the outside air, a river, seawater, or the ground to cool it, and then supplies it as make-up water for a cooling tower when operating an absorption chiller or adsorption chiller which is driven to cool the mixture of methane and water vapor generated by the methane gas generator.

[0014] Thus, the present invention is a method for producing methane gas by a methanation reaction, comprising: a reaction step of producing a high-temperature mixture containing methane gas and water vapor, which generates heat, by the methanation reaction; a heat recovery step of recovering the heat generated in the reaction step by a heat exchanger via a heat medium to raise the temperature of the heat medium or vaporize it; and a heat energy recovered by the heat medium in the heat recovery step to operate one or more of a turbine, an absorption type refrigerator, or an adsorption type refrigerator to adiabatically compress a feed gas to be subjected to the methanation reaction, or to refrigerate the methane and water generated by the methanation reaction. The method for producing methane gas includes a recovered heat conversion and utilization process in which the thermal energy recovered in the heat recovery process is converted and utilized to promote a methanation reaction by cooling the steam mixture, and a recovered water purification and utilization process in which water obtained by removing impurities or neutralizing and cooling the condensed water recovered in the recovered heat conversion and utilization process is used to generate hydrogen to be used in the methanation reaction from water electrolysis, or to supply the water as make-up water for a cooling tower when operating either an absorption chiller or an adsorption chiller, or both, for cooling the methane and water vapor mixture. Effect of the Invention

[0015] According to the present invention, the reaction heat generated in the methanation reaction is efficiently recovered via a liquid heat transfer medium, and one or more of a turbine driven by the recovered thermal energy, an absorption chiller or an adsorption chiller are operated, thereby adiabatically compressing the feed gas to be subjected to the methanation reaction or cooling the mixture of methane and water vapor produced by the methanation reaction, thereby promoting the methanation reaction and improving the efficiency of methane gas production.

[0016] Furthermore, the water obtained by removing impurities from condensed water recovered from the methane and water vapor mixture, and by neutralizing and cooling it, can be used to generate hydrogen for the methanation reaction, or to supply as make-up water for a cooling tower when operating an absorption chiller or adsorption chiller, or both, for cooling the methane and water vapor mixture, or as make-up water for a cooling tower for operating a binary generator. This makes it possible to reduce the amount of water and electricity consumed when producing hydrogen for the methanation reaction or cooling the methane and water vapor mixture, and to increase the efficiency of water usage in methane gas production. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a configuration of a methane gas production device according to a first embodiment of the present invention. FIG.

[0018] [Diagram 2] FIG. 2 is a schematic diagram showing a configuration of a methane gas production device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. Note that the scope of the present invention is defined by the claims, and is not limited to the present embodiment.

[0020] (First embodiment)

[0021] First, a methane gas production apparatus according to a first embodiment of the present invention will be described with reference to FIG.

[0022] As shown in Figure 1, in this methane gas generation device 1, hydrogen and carbon dioxide, which are the raw gases for generating methane gas, are mixed in a mixer 2, and then a catalyst 3 that promotes the Sabatier reaction in an insulated container is introduced. A liquid heat transfer medium 5 is heated and vaporized as it flows through a heat exchanger 4 placed inside the container due to the heat generated by the reaction. This keeps the reaction section at a constant temperature of around 200 to 300°C, and generates a high-temperature mixture of 200 to 300°C, mainly composed of methane and water vapor.

[0023] In addition, in this methane gas generation device 1, the high-temperature mixture of methane and water vapor generated inside the insulated container is also cooled by exchanging heat with a heat medium via a heat exchanger 4 arranged inside the container, and the water vapor is condensed and liquefied to become high-temperature water 6 of less than 100°C. This accumulates at the bottom of the insulated container and is then discharged outside the container as drain water.

[0024] The mixture discharged from the insulated container in this way is a mixture of less than 100°C containing the main component methane, unreacted hydrogen, and carbon dioxide. This mixture is separated by filter 7, which separates the methane from the unreacted gases, and the methane gas is supplied as a product, while the unreacted gas is returned to the methane gas generator.

[0025] In this process, the heat exchanger inside the insulated container absorbs the heat of reaction between the high-temperature product mixture and the methane production reaction. The heat transfer steam heated to approximately 150 to 300°C is supplied to a steam turbine 8 located outside the insulated container to drive the turbine. By driving a feed gas compressor 9 connected to the steam turbine shaft, the feed gas including the unreacted reflux gas is adiabatically compressed and supplied to the methane production device as high-temperature, high-pressure feed gas. This makes it possible to promote the methane production reaction by preheating and pressurizing the feed gas.

[0026] Furthermore, steam discharged from the steam turbine and cooled to approximately 110 to 150°C is supplied to an absorption chiller 10 and operated, making it possible to circulate cold water at 5 to 15°C. The resulting cooling water is circulated while passing through a heat exchanger 11 for cooling the generated gas, thereby cooling the circulating heat medium and returning it to the methane gas generation device.

[0027] In addition, by driving the absorption chiller, the heat transfer liquid whose temperature has been reduced to about 50 to 80°C is supplied to the adsorption chiller 12 and operated, making it possible to circulate cold water at 10 to 15°C. The obtained cooling water is circulated while flowing through the heat exchanger 13 for cooling the produced gas, so that the circulating heat transfer liquid is pre-cooled before being cooled by the cold heat of the absorption chiller. By driving the adsorption chiller, the heat transfer liquid whose temperature has been reduced to about 30 to 60°C is pre-cooled and lowered in temperature, and then it is further cooled by the cold heat obtained by driving the absorption chiller, and then it can be returned to the methane generation device by operating the heat transfer liquid circulation pump 14.

[0028] In addition, the operation of the absorption and adsorption chillers requires the use of cooling towers to dissipate heat, and in these cooling towers, cooling water is circulated by a pump while some of the cooling water evaporates from the cooling tower, making it necessary to make up water. Therefore, in this configuration, the drain water recovered by condensing and liquefying the water vapor generated by the methane production reaction is purified through a drain water purifier 15 that removes and neutralizes impurities, and then the water is allowed to dissipate heat naturally through heat exchange with the outside air, after which it is stored in a water tank and can be used as make-up water for the cooling tower.

[0029] Furthermore, by supplying the water stored in the water tank to the water electrolysis device 16 while also supplying electricity to electrolyze water, it is possible to reduce the amount of water required for the methane production reaction and produce hydrogen that can be used as raw gas.

[0030] With the above configuration, the reaction heat during methane production and the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane production reaction can be efficiently recovered via the liquid circulating heat medium and used to compress and preheat the feed gas and to cool the produced gas and the circulating heat medium, thereby promoting the methane production reaction.

[0031] In addition, in this configuration, the circulating heat medium can be, for example, water, which evaporates in a heat exchanger in the methane generation apparatus to obtain latent heat of vaporization, allowing more heat to be recovered and used effectively within the methane generation apparatus. However, depending on the heat exchange specifications in the methane generation apparatus, it is also possible to use molten salt or heat medium oil which has a high boiling point and high thermal conductivity and heat capacity, or a low-boiling point medium which is easy to vaporize even at low temperatures, such as ammonia water, pentane, or alternative fluorocarbons. Second embodiment

[0032] Next, a methane gas production apparatus according to a second embodiment of the present invention will be described with reference to FIG.

[0033] As shown in Figure 2, this system recovers the heat of reaction in methane production and the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane production reaction via a circulating heat medium, and uses the recovered energy to compress the raw material gas and cool the produced gas and the circulating heat medium, thereby promoting the methane production reaction. This is similar to the first embodiment in terms of the feature, but the means of implementation is different.

[0034] Specifically, although the steam turbine is driven by the heat transfer steam discharged from the methane generation system, a generator 17 is connected to the turbine shaft, and the electricity generated by this generation is supplied to a motor-driven raw gas compressor 18 and a pump for operating the equipment that makes up the methane generation system, thereby reducing the power consumption related to the operation of the methane generation system.

[0035] Furthermore, in this apparatus, binary power generation is performed by exchanging heat between the steam after driving the steam turbine and the low boiling point medium for binary power generation of the binary generator 19 in a heat exchanger 20, and the generated power obtained is supplied to the equipment that constitutes the methane generation apparatus, such as the absorption chiller 10 and the adsorption chiller 12. However, like the first embodiment, the absorption chiller and the adsorption chiller are operated in stages using the heat medium that has been reduced in temperature and condensed and liquefied after passing through the heat exchanger for binary power generation to reduce the heat medium temperature, and the circulating heat medium is cooled with the obtained cold energy before being returned to the methane generation apparatus.

[0036] In addition, in this configuration, the circulating heat medium can be, for example, water, which evaporates in a heat exchanger in the methane generation device to obtain latent heat of evaporation, allowing more heat to be recovered and used effectively within the methane generation device. However, high boiling point heat medium oil or molten salt may also be used depending on the heat exchange specifications in the methane generation device. If such high boiling point heat medium does not vaporize to steam within the methane generation device, it is possible to reduce the power consumption associated with the operation of the methane generation device by directly supplying the high-temperature heat medium sent from the methane generation device to the heat exchanger of the binary power generation device to increase the output of the binary power generation device.

[0037] In addition, in this configuration, it is desirable to control the rotation speed of the pump that circulates the circulating heat transfer medium, the cold water pump that circulates the cooling water obtained from the refrigerator, and the pump that circulates the cold water to and from the cooling tower for driving the chiller and binary generator by measuring characteristic values ​​such as the temperature, concentration, pressure, and flow rate of the product mixture and the final product methane gas circulating within the methane generation device, and increasing or decreasing the pump rotation speed based on these measured values, thereby controlling the amount of heat exchange at each heat exchange part and maximizing the methane generation efficiency and methane purity.

[0038] With the above configuration, even when a high-boiling point heat medium is circulated to suit the temperature conditions of the methane generation equipment, the reaction heat from methane generation and the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane generation reaction can be recovered via the circulating heat medium and used to compress the raw material gas and cool the generated gas and the circulating heat medium, thereby promoting the methane generation reaction. [Industrial Applicability]

[0039] The present invention is not limited to the above-described embodiment. For example, the driving force of a steam turbine may be utilized to drive a turbine expander, thereby decompressing and cooling the high-temperature air-fuel mixture generated in the methane generation device to promote moisture removal, or a turbo chiller may be operated with the power generated by steam turbine power generation or binary power generation, and the resulting cold energy may be used to cool the high-temperature air-fuel mixture and heat transfer medium generated in the methane generation device, thereby promoting the methane generation reaction.

[0040] As described above, the above-described embodiments are merely illustrative, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0041] 1. Methane gas generator 2. Raw material gas mixer 3. Catalyst for promoting the Sabatier reaction 4. Heat exchanger in methane gas generator 5. Heat transfer medium 6. Condensed liquefied high-temperature water 7. Unreacted gas separation filter 8. Steam turbine 9. Raw gas compressor 10. Absorption chiller 11. Absorption chiller cold heat exchanger 12...Adsorption refrigerator 13... Adsorption chiller cold heat exchanger 14 Heat transfer medium circulating pump 15 Drain water purification device 16. Water electrolysis device 17 Generator 18. Motor-driven raw gas compressor 19. Binary generator 20. Low-boiling-point medium heat exchanger for binary power generation

Claims

1. A methane gas generator for generating methane gas by a methanation reaction, A methane gas generator, characterized in that a raw material gas to be supplied to the methane gas generator is adiabatically compressed by a heat medium that is heated or vaporized by reaction heat generated by a methanation reaction via a heat exchanger, and a compressor connected to a turbine driven by the heated or vaporized heat medium, thereby increasing the pressure and temperature of the raw material gas to be supplied to the methane gas generator and supplying it to the methane gas generator.

2. A methane gas generator for generating methane gas by a methanation reaction, A methane gas generator, characterized in that the pressure and temperature of a mixture of methane and water vapor generated in the methane gas generator are reduced by adiabatically expanding the mixture of methane and water vapor generated in the methane gas generator using an expander connected to a turbine driven by a heat medium that is heated or vaporized by reaction heat generated in a methanation reaction via a heat exchanger and the heated or vaporized heat medium.

3. A methane gas generator for generating methane gas by a methanation reaction, A methane gas generation apparatus, characterized in that electricity is generated by a generator connected to a turbine driven by a heat transfer medium that is heated or vaporized by reaction heat generated in a methanation reaction via a heat exchanger and the heated or vaporized heat transfer medium, and the generated electricity is supplied to power consumption devices that constitute the methane gas generation apparatus.

4. A methane gas generator for generating methane gas by a methanation reaction, A methane gas generation apparatus, comprising: a heat transfer medium which is heated or vaporized by reaction heat generated in a methanation reaction via a heat exchanger; an absorption chiller or an adsorption chiller which is driven by the heated or vaporized heat transfer medium; and a mixture of methane and water vapor generated in the methane gas generation apparatus which is cooled by the cold heat obtained via the chiller.

5. A methane gas generator for generating methane gas by a methanation reaction, A heat transfer medium is heated or vaporized by the heat of reaction generated by the methanation reaction through a heat exchanger, and the heated or vaporized heat transfer medium is supplied to an absorption chiller, and the mixture of methane and water vapor generated in the methane gas generator is cooled by the obtained cold heat, and then The methane gas generation apparatus further comprises supplying the heat transfer medium discharged from the absorption refrigerator after its temperature has been reduced to an adsorption refrigerator, and further cooling the mixture of methane and water vapor generated in the methane gas generation apparatus by using the obtained cold heat.

6. A methane gas generation device that generates methane gas by the method of any one of claims 1, 2, or 3, characterized in that an absorption or adsorption type refrigerator is driven by a heat medium that is heated or vaporized by reaction heat generated in a methanation reaction via a heat exchanger and a heat medium discharged from a turbine driven by the heated or vaporized heat medium, and a mixture of methane and water vapor generated in the methane gas generation device is cooled by the cold heat obtained via the refrigerator.

7. A methane gas generating apparatus for generating methane gas by any one of the methods of claims 1 to 3, comprising: a heat transfer medium that is heated or vaporized by reaction heat generated in a methanation reaction through a heat exchanger; and a heat transfer medium discharged from a turbine driven by the heated or vaporized heat transfer medium, which drives an absorption chiller; and a mixture of methane and water vapor generated in the methane gas generating apparatus is cooled by the cold heat obtained through the absorption chiller. A methane gas generation apparatus, characterized in that a heat transfer medium discharged from the absorption chiller after having its temperature lowered is supplied to an adsorption chiller, and the resulting cold heat is used to further cool a mixture of methane and water vapor generated in the methane gas generation apparatus.

8. A methane gas generating apparatus according to any one of claims 1 to 7, A methane gas generator, comprising: a heat transfer medium that is heated or vaporized by reaction heat generated in association with a methanation reaction in the methane gas generator via a heat exchanger, and after the heat transfer medium is lowered by dissipating the heat recovered by any one or more of the methods described in claims 1 to 7, is returned to the methane gas generator again to recover reaction heat, thereby forming a circulation flow path.

9. 9. The methane gas generator according to claim 8, A methane gas generator, characterized in that one or more of the circulation flow rate and circulation pressure of a heat medium refluxing through the methane gas generator, the heat medium temperature at the inlet of the methane gas generator and the heat medium temperature at the outlet of the methane gas generator are controlled in response to either the concentration or the temperature of the generated methane gas, or both.

10. A methane gas generating apparatus according to any one of claims 1 to 9, The methane gas generator is characterized in that water condensed and liquefied when the mixture of methane and water vapor generated from the methane gas generator is cooled is recovered, and after impurities are removed or neutralized, the water is supplied as raw material water for producing hydrogen to be supplied to the methane gas generator by water electrolysis, or after impurities are removed or neutralized, the water is cooled by heat dissipation and supplied as make-up water for a cooling tower when an absorption chiller or adsorption chiller is operated to cool the mixture of methane and water vapor generated from the methane gas generator.

11. A method for producing methane gas by a methanation reaction, comprising: A reaction step of generating a high-temperature mixture containing methane gas and water vapor, which generates heat, by the methanation reaction; A heat recovery process in which heat generated in the reaction process is recovered by a heat exchanger via a heat medium to raise the temperature or vaporize the heat medium; a recovered heat conversion and utilization process in which the thermal energy recovered by the heat medium in the heat recovery process is utilized to operate one or more of a turbine, an absorption type refrigerator, or an adsorption type refrigerator to adiabatically compress the raw material gas to be subjected to the methanation reaction, or to adiabatically expand or cool a mixture of methane and water vapor produced by the methanation reaction, thereby converting and utilizing the thermal energy recovered in the heat recovery process to promote the methanation reaction; a quality confirmation step of measuring the concentration or temperature of the methane gas obtained through the conversion and utilization step of the recovered heat; A heat medium amount control process for increasing or decreasing the amount of heat medium supplied in the heat recovery process or the recovered heat conversion and utilization process according to the results obtained in the methane gas quality confirmation process; a process for purifying and utilizing recovered water, which is obtained by removing impurities or by neutralizing and cooling condensed water recovered from the mixture of methane and steam in association with the process for converting and utilizing the recovered heat, and which uses the water to generate hydrogen to be used in a methanation reaction by electrolysis of water, or to supply the water as make-up water for a cooling tower when operating an absorption chiller or an adsorption chiller, or both, for cooling the mixture of methane and steam; 16. A method for producing methane gas, comprising:

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