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 operates one or more of a turbine, an absorption type refrigerator, an adsorption type refrigerator and a turbo refrigerator driven using heat energy possessed by high temperature gaseous mixture containing methane gas and water vapor generated by methanation reaction, 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 methanation production device, and adiabatic expansion or 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 for recycling 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 (Patent Document 1 and Patent Document 2) have been proposed. [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, namely a mixture of carbon dioxide and hydrogen, and a mixture of methane gas and water vapor, and also includes heat exchange via hot water condensed from water vapor as a secondary method. However, the thermal energy contained in the mixture of methane gas and water vapor, which is the product of the methanation reaction and has been heated to a high temperature, cannot be directly used to compress or preheat the raw material gas, and there is an issue that it is difficult to achieve sufficient preheating of the raw material gas or efficient cooling of the produced gas.

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

[0010] The present invention has been made in consideration of these problems, and its purpose is to provide a method for utilizing the thermal energy contained in the product obtained in the methanation reaction to pressurize and preheat the reactants supplied to a 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 generation device of the present invention is characterized in that it cools a mixture of methane and water vapor obtained from the methane gas generation device using cold heat obtained from a gas compressor connected to a turbine driven by a mixture of methane gas and water vapor heated to a high temperature by reaction heat generated by a methanation reaction, or an electric gas compressor driven by the generated power of a generator connected to the turbine, or a gas expander connected to the turbine, or a binary generator or absorption type chiller driven by the mixture of heated methane gas and water vapor as a heat source, and an adsorption type chiller driven by the condensed hot water discharged after driving the binary generator or absorption type chiller as a heat source, or a turbo chiller driven by the generated power of the generator, and condenses and liquefies the water vapor to separate it, thereby increasing the purity of the methane.

[0012] 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.

[0013] 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; and a step of using the thermal energy of the high-temperature product gas produced in the reaction step to drive a turbine or generate electricity with a generator, thereby adiabatically compressing the feed gas to be subjected to the methanation reaction, or operating one or more of an absorption refrigerator, an adsorption refrigerator, or a turbo refrigerator to convert the heat into cold, thereby cooling the mixture of methane and water vapor produced by the methanation reaction. and a process for purifying and utilizing recovered water, in which water obtained by removing impurities or neutralizing and cooling the condensed water recovered in the reaction 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 an absorption chiller or an adsorption chiller, or both, for cooling a mixture of methane and water vapor. Effect of the Invention

[0014] According to the present invention, by operating one or more turbines or refrigerators using the thermal energy contained in the high-temperature mixture of methane and water vapor produced by the methanation reaction, the feed gas to be subjected to the methanation reaction is adiabatically compressed, or the mixture of methane and water vapor produced by the methanation reaction is cooled, thereby promoting the methanation reaction and improving the efficiency of methane gas production.

[0015] 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]

[0016] [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.

[0017] [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

[0018] 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.

[0019] (First 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, this methane gas generation device mixes hydrogen and carbon dioxide, which are the raw gases for generating methane gas, in a mixer 1, and then a methanation reactor 2 is connected to generate a mixture of high-temperature methane gas and steam using a catalyst that promotes the Sabatier reaction, and exhausts the mixture. The steam turbine 3 is driven by the high-temperature mixture exhausted from the reactor, and the high-temperature mixture generated by the heat generated by the Sabatier reaction is quickly drawn into the steam turbine and flows out, thereby keeping the temperature inside the reactor constant at around 200 to 300°C.

[0023] Here, the temperature and pressure of the resulting gas mixture are reduced by the steam turbine driven by the high-temperature, high-pressure resulting gas mixture, while the feed gas compressor 4 connected to the steam turbine shaft is driven to adiabatically compress the feed gas, including the unreacted reflux gas, and supply it to the methanation reactor as high-temperature, high-pressure feed gas. This makes it possible to promote the methane production reaction by preheating and pressurizing the feed gas.

[0024] In addition, by driving the steam turbine, the mixture discharged from the rear stage of the turbine in a state where the temperature and pressure have been reduced becomes a mixture containing the main component methane, unreacted hydrogen and carbon dioxide, and steam at less than 100 to 120°C. This mixture is supplied to absorption chiller 5 and operated, making it possible to circulate cooling water at 5 to 15°C, and the obtained cooling water is circulated while flowing through heat exchanger 6 for cooling the produced gas, thereby cooling the dew point of the produced gas to less than 15°C.

[0025] In order to gradually cool the high-temperature produced gas to below 15°C while condensing and liquefying the water content, it is effective to lower the temperature in the process of converting the thermal energy of the produced gas into cold energy and gradually use the cold energy obtained by the cold energy conversion to cool the produced gas. Therefore, the methane gas and condensed hot water discharged from the absorption chiller are separated from the condensed hot water, and the condensed hot water whose temperature has been reduced to about 50 to 80°C is supplied to the adsorption chiller 7 and operated, making it possible to circulate cold water at 10 to 15°C. The obtained cooling water is circulated while passing through the heat exchanger 8 for cooling the produced gas, thereby pre-cooling the dew point of the produced gas separated from the adsorption chiller outlet to about 30°C, and the final outlet temperature can be cooled to a dew point of about 15°C before being cooled with the cooling water obtained from the absorption chiller.

[0026] In this way, the water vapor contained in the generated gas is condensed and liquefied by cooling using the temperature drop associated with heat dissipation through multi-stage heat utilization and the cold energy obtained through cold energy conversion utilization, and is separated. The mixture containing the main component methane gas and the unreacted gases hydrogen and carbon dioxide is separated by filter 9, which separates methane from the unreacted gas. The methane gas is supplied as a product, while the unreacted gas is returned upstream of the raw gas compressor.

[0027] 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 10 that removes and neutralizes impurities, and after allowing the water to dissipate heat naturally through heat exchange with the outside air, it is stored in a water tank and can be used as make-up water for the cooling tower.

[0028] Furthermore, by supplying water from the water storage tank to the electrolysis device 11 while supplying electricity to electrolyze the water, it is possible to produce hydrogen required for the methane production reaction and make it available as raw material gas.

[0029] With the above configuration, the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane production reaction is converted into turbine driving force or cold energy, and used to compress the feed gas and remove moisture by cooling the produced gas. This makes it possible to promote the methane production reaction, increase the concentration of the obtained methane, and lower the dew point. Second embodiment

[0030] Next, a methane gas production apparatus according to a second embodiment of the present invention will be described with reference to FIG.

[0031] As shown in Figure 2, this system converts the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane production reaction into turbine driving force or cold energy, and uses it to compress the feed gas and cool the produced gas to remove moisture, while promoting the methane production reaction. This feature is similar to that of the first embodiment, but the means of implementation is different.

[0032] Specifically, although a steam turbine is driven by a mixture of high-temperature methane and water vapor discharged from the methanation reactor, a generator 12 is connected to the turbine shaft, and the electricity generated by this generation is supplied to various pumps for operating the motor-driven raw gas compressor 13 and the equipment that makes up the methane generation system, thereby reducing the power consumption related to the operation of the methane generation system.

[0033] Furthermore, in this apparatus, binary power generation is performed by exchanging heat between the steam mixture after driving the steam turbine and a low boiling point medium for binary power generation in the binary generator 14 in a heat exchanger 15, and the generated power obtained is supplied to the equipment that constitutes the methane generation apparatus, such as the absorption chiller 5 and the adsorption chiller 6. However, like the first embodiment, the absorption chiller and the adsorption chiller are operated in stages using the steam mixture whose temperature has been reduced by passing through the heat exchanger for binary power generation to reduce the temperature, and the separated gas is cooled with the cold obtained by operating the chillers while separating the gas and condensed water, and the mixture of methane gas and unreacted gas is cooled to a dew point of about 15°C. After that, the mixture is separated by a filter 9 that separates methane and unreacted gas, and the methane gas is supplied as a product, while the unreacted gas is returned upstream of the raw gas compressor.

[0034] With the above configuration, the thermal energy of the mixture of high-temperature methane and water vapor obtained by the methane production reaction can be converted into electricity or cold energy, and used to compress the feed gas or cool the produced gas to remove moisture, thereby promoting the methane production reaction, increasing the concentration of the produced methane, and lowering the dew point. [Industrial Applicability]

[0035] 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, and the high-temperature air-fuel mixture produced in the methanation reaction device may be decompressed and cooled to promote moisture removal, or a turbo chiller may be operated with power generated by steam turbine power generation or binary power generation, and the resulting cold heat may be used to cool the high-temperature air-fuel mixture produced in the methanation reaction device, thereby promoting the methane production reaction.

[0036] 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]

[0037] 1. Raw material gas mixer 2. Methanation reactor 3. Steam turbine 4. Raw gas compressor 5. Absorption chiller 6. Absorption chiller cold heat exchanger 7...Adsorption chiller 8. Adsorption chiller cold heat exchanger 9. Unreacted gas separation filter 10. Drain water purification device 11. Water electrolysis device 12. Generator 13. Motor-driven raw gas compressor 14. Binary generator 15. 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 compressor connected to a turbine driven by a mixture of high-temperature methane gas produced in a methanation reaction and water vapor, 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 generating apparatus, characterized in that the pressure and temperature of a mixture of methane and water vapor generated from a methane gas generating apparatus are reduced by adiabatic expansion of the mixture of methane and water vapor generated from the methane gas generating apparatus using an expander connected to a turbine driven by a mixture of high-temperature methane gas and water vapor generated in a methanation reaction.

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 mixture of high-temperature methane gas produced in the methanation reaction and water vapor, and the generated electricity is supplied to power consuming 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, characterized in that binary power generation is performed by a binary generator that uses a mixture of methane gas and water vapor discharged from the turbine described in any one of claims 1 to 3 as a heat source to heat and evaporate a heat medium via a heat exchanger to drive the binary generator, and the generated power obtained is supplied to power consumption devices that constitute the methane gas generation apparatus.

5. A methane gas generator for generating methane gas by a methanation reaction, A methane gas generation apparatus, characterized in that an absorption chiller is driven by a mixture of high-temperature methane gas and water vapor produced in conjunction with a methanation reaction, or by high-temperature steam obtained when methane gas is separated from the mixture, and the cold energy obtained by the absorption chiller cools either or both of the mixture of methane and water vapor produced in the methane gas generation apparatus, or the methane gas obtained when water vapor is separated from the mixture.

6. A methane gas generation device that generates methane gas by any one of the methods recited in claims 1 to 5, characterized in that an adsorption-type refrigerator is driven by high-temperature condensed water produced by a temperature drop of a mixture of methane and water vapor generated from the methane gas generation device by any one of the methods recited in claims 1 to 5, and the cold heat obtained by the adsorption-type refrigerator is used to cool either or both of the mixture of methane and water vapor generated from the methane gas generation device, or methane gas obtained when water vapor is separated from the mixture.

7. A methane gas generation device that generates methane gas by any one of the methods of claims 1 to 3, characterized in that the method of any one of claims 1 to 3 lowers the temperature of a mixture of methane and water vapor generated from the methane gas generation device while utilizing thermal energy held by the mixture, and then the method of claim 4 or claim 5 further cools the mixture whose temperature has been lowered while utilizing thermal energy held by the mixture whose temperature has been lowered or high-temperature water formed by condensing and liquefying the water vapor in the mixture to lower the temperature.

8. A methane gas generator according to any one of claims 1 to 7, characterized in that water condensed and liquefied when a mixture of methane and water vapor generated in 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 electrolysis of water, or after impurities are removed or neutralized, the water is cooled by radiating heat, and then supplied as make-up water for a cooling tower when operating either or both of the absorption chiller according to claim 5 or the adsorption chiller according to claim 6.

9. 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 process for converting and utilizing the heat contained in the produced mixture, in which the heat energy contained in the high-temperature mixture containing methane gas and water vapor produced in the reaction process is utilized to operate one or more of a turbine, an absorption type refrigerator, and an adsorption type refrigerator to adiabatically compress the feed gas to be subjected to the methanation reaction, or to adiabatically expand or cool the mixture of methane and water vapor produced by the methanation reaction, thereby converting and utilizing the heat energy contained in the mixture in the reaction process to promote the methanation reaction; a recovered water purification and utilization process, which uses water obtained by removing impurities or neutralizing and cooling condensed water recovered from the mixture of methane and steam in association with the conversion and utilization process 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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