JP2020040919A - Methane gas generator and methane gas generation method - Google Patents

Abstract

To provide a compact methane gas generator and a methane gas generation method effectively producing a methane gas.SOLUTION: There is provided a methane gas generator generating a methane gas by a methanation reaction, having a reaction part for an exothermic reaction of a reactant containing carbon dioxide and hydrogen and production of a product material containing the methane gas and steam and having higher temperature than the reactant, and a heat exchanger for heating the reactant sent to the reaction part in advance and cooling the product material flowed out from the reaction part by heat exchange of the reactant sent to the reaction part and the production material flowed out from the reaction part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a methane gas generation device and a methane gas generation method.

  Efforts are being made to reduce carbon dioxide, a greenhouse gas, to reduce global warming. Further, for example, Patent Documents 1-2 disclose a technique relating to a methanation reaction in which carbon dioxide and hydrogen are reacted to generate methane gas.

Japanese Patent No. 6299347 JP 2017-052669 A

  When methane gas is generated, it is conceivable to promote a methanation reaction in order to improve methane gas generation efficiency. It is desirable to preheat the reactants to promote the methanation reaction. However, energy is naturally required to preheat the reactants, and the effect of reducing greenhouse gases may be reduced.

  In addition, since the methanation reaction is a reaction that generates water as a by-product, it is desirable to condense and remove moisture as a by-product by cooling or the like in order to effectively use the generated methane gas. Conceivable. That is, when methane gas is generated by the methanation reaction, energy for cooling the methane gas is also required.

  That is, when methane gas is generated by the methanation reaction, it is considered desirable to perform preheating of the reactant or cooling of the methane gas, but this requires energy, and the effect of reducing the greenhouse gas may be reduced. Conceivable. In addition, a device for preheating the reactants and cooling the methane gas is also required, and there is a possibility that the entire production device may become large.

  Therefore, an object of the present invention is to provide a compact methane gas generation device and a methane gas generation method that efficiently generate methane gas.

  In order to solve the above-mentioned problems, the present invention is to make a heat exchange between a reactant that undergoes a methanation reaction and methane gas generated by the methanation reaction.

  In detail, the present invention is a methane gas generating apparatus that generates methane gas by a methanation reaction, wherein a reactant containing carbon dioxide and hydrogen is caused to undergo an exothermic reaction, and a product containing methane gas and water vapor, Preheating the reactant to be sent to the reaction unit by exchanging heat between the reaction unit that generates a product having a higher temperature than the reaction product sent to the reaction unit and the product flowing out of the reaction unit, And a heat exchanger for cooling a product flowing out of the methane gas generator.

  In such a methane gas generator, the reactant before the methanation reaction is preheated. Thus, the methanation reaction is promoted.

  Further, when the product is cooled, and the water vapor contained in the product is condensed and separated, the saturated vapor pressure of the product decreases. That is, handling of the product becomes easy.

  Further, the product may include an unreacted reactant. And the methanation reaction is a reversible reaction. That is, when an unreacted reactant is included in the product, the product is in a chemical equilibrium state with the unreacted reactant. Here, when steam is condensed by cooling the product and condensed water is separated from the product, the chemical equilibrium state changes, and methane gas and steam are newly generated from unreacted reactants. . That is, with the methane gas generator as described above, the purity of the generated methane gas is increased.

  Further, by performing heat exchange between the reactant and the product, preheating of the reactant and cooling of the methane gas are realized. That is, since the preheating of the reactant and the cooling of the methane gas are not separately performed, the energy required for preheating the reactant and cooling the methane gas is reduced. Therefore, the reduction of the greenhouse gas reduction effect is suppressed, and the methane gas generation efficiency is improved.

  Also, unlike such a methane gas generator, when the reactant and the product are not heat-exchanged and the preheating of the reactant and the cooling of the product are performed separately, when the amount of the reactant fluctuates, the reaction occurs. The temperature after the preheating of the reactant will fluctuate as compared to before the fluctuation of the physical quantity. Therefore, in order to suppress the fluctuation in the temperature of the reactant after preheating, it is necessary to control the flow rate of the heat medium that exchanges heat with the reactant according to the amount of the reactant.

  In addition, the amount of methane gas generated needs to be adjusted depending on circumstances such as the demand for gas and the change in the supply amount of reactants. In comparison, the temperature of the product after cooling will fluctuate. Therefore, in order to suppress fluctuations in the temperature of the product after cooling, it is necessary to control the flow rate of the heat medium that exchanges heat with the product according to the amount of the product. However, in the methane gas generator as described above, when the amount of the reactant fluctuates, the amount of the product that exchanges heat with the reactant fluctuates similarly to the amount of the reactant. That is, even when the reactant amount fluctuates, the flow rate of the heat medium that exchanges heat with the reactant does not need to be controlled according to the reactant amount in order to suppress the fluctuation in the temperature of the reactant after preheating. Further, even when the amount of the product changes, the flow rate of the heat medium that exchanges heat with the product does not need to be controlled according to the amount of the product in order to suppress the change in the temperature of the product after cooling. That is, there is no need for a configuration for suppressing the temperature fluctuation after the preheating of the reactant or the temperature fluctuation after cooling the product.

  In the methane gas generator as described above, preheating of the reactant and cooling of the product can be performed in one heat exchanger. In this case, the methane gas generator can be made more compact than when the preheating of the reactants and cooling of the products are performed in separate heat exchangers.

  By the way, the heat exchanger is a shell and tube heat exchanger, and the reactant passes through the shell of the shell and tube heat exchanger, and the product passes through the tube of the shell and tube heat exchanger. You may pass.

  In such a methane gas generator, the reactant passes through the shell part of the shell and tube heat exchanger. Thus, the mixing of the reactants is promoted while exchanging heat with the product. Since the reactants are sufficiently mixed and stirred before being charged into the reactor, the methanation reaction of the reactants passed through the heat exchanger is promoted. Therefore, methane gas generation efficiency is improved. The preheating of the reactants and the mixing and stirring of the reactants can be performed in one heat exchanger. Further, since a mixing and stirring function can be provided by the method of using the heat exchanger according to the present invention without separately providing a stirrer for mixing the reactants, the methane gas generation device can be downsized.

  By the way, the heat exchanger exchanges heat between the reactant sent to the reaction part and the water vapor of the product flowing out of the reaction part, thereby increasing the heat exchange area capable of condensing the water vapor of the product flowing out of the reaction part. May have.

  With the methane gas generator as described above, at least a part of the water vapor is condensed into water. Thus, the water vapor is easily separated from the methane gas. Further, the product may include an unreacted reactant. And the methanation reaction is a reversible reaction. That is, when an unreacted reactant is included in the product, the product is in a chemical equilibrium state with the unreacted reactant. Here, when condensed water is separated from the product, the chemical equilibrium state changes, and methane gas and water vapor are newly generated from unreacted reactants. That is, with the methane gas generator as described above, the purity of the generated methane gas is increased.

  Further, when the generated condensed water is drained, the heat capacity of the entire product is reduced. Therefore, the cooling efficiency of the methane gas is improved. Therefore, the methane gas generator can be made compact.

  Incidentally, a plurality of heat exchangers may be connected in series.

  With such a methane gas generator, the heat exchange efficiency between the reactant and the product increases. In other words, one heat exchanger can be made compact.

  Further, a drainage unit for draining water condensed in each of the plurality of heat exchangers connected in series may be further provided.

  The product may include unreacted reactants. And the methanation reaction is a reversible reaction. That is, when an unreacted reactant is included in the product, the product is in a chemical equilibrium state with the unreacted reactant. Therefore, when the condensed water is drained from the heat exchanger, the chemical equilibrium state changes, and methane gas and water vapor are newly generated from unreacted reactants. That is, with the methane gas generator as described above, the purity of the generated methane gas is increased.

  In addition, in such a methane gas generator, the heat capacity of the entire product is reduced by discharging the condensed water from the heat exchanger. Therefore, the cooling efficiency of the methane gas is improved. Therefore, one heat exchanger can be made compact.

  In the methane gas generator as described above, steam is condensed stepwise in each of the plurality of heat exchangers connected in series. Therefore, condensed water having different temperatures can be obtained from each heat exchanger. Therefore, when the condensed water having different temperatures is reused, energy saving is realized.

  Further, the total heat transfer surface of the plurality of heat exchangers connected in series may have an area for condensing steam into water.

  With the methane gas generator as described above, condensed water can be obtained from products passing through a plurality of heat exchangers connected in series. Further, when the condensed water is drained from the heat exchanger in which the condensed water is generated, the heat capacity of the entire product is reduced. Therefore, the cooling efficiency of the methane gas is improved. Therefore, the heat exchanger can be made compact.

  Further, the product may include an unreacted reactant. And the methanation reaction is a reversible reaction. That is, when an unreacted reactant is included in the product, the product is in a chemical equilibrium state with the unreacted reactant. Therefore, when the condensed water is drained from the heat exchanger where the condensed water is generated, the chemical equilibrium state changes, and methane gas and water vapor are newly generated from unreacted reactants. That is, the purity of the generated methane gas is increased.

  The present invention can also be grasped from the aspect of a method. That is, for example, in a methane gas generation method of generating methane gas by a methanation reaction, a reactant containing carbon dioxide and hydrogen is caused to undergo an exothermic reaction, and is a product containing methane gas and water vapor, and has a higher temperature than the reactant. A reaction step for producing a high product, and a heat exchange between a reactant sent to the reaction step and a product generated in the reaction step, preheats the reactant sent to the reaction step, and is generated in the reaction step. And a heat exchange step of cooling the produced product.

  With the methane gas generation device and the methane gas generation method described above, a compact device that efficiently generates methane gas can be realized.

FIG. 1 shows an example of an outline of a methane gas generator according to an embodiment of the present invention. FIG. 2 shows an example of the outline of the heat exchanger. FIG. 3 shows an example of a flowchart in which methane gas is generated by the methane gas generation device. FIG. 4 shows an example of a graph of a temperature difference of a reactant flowing into and out of a heat exchanger with respect to a heat transfer area per reactant flow rate. FIG. 5 shows an example of an outline of a configuration when two heat exchangers are arranged in series in FIG. 4 and an example of an outline of a configuration when one heat exchanger is used. FIG. 6 shows an example of an outline of a methane gas generator including one heat exchanger as an alternative to two heat exchangers arranged in series. FIG. 7 shows an example of the temperature of the first product flowing out of the heat exchanger with respect to the heat exchange area of the heat exchanger per flow rate of the reactant. FIG. 8 shows an example of the boiling point of water with respect to pressure.

  Hereinafter, embodiments of the present invention will be described. The embodiment shown below is an example of the embodiment of the present invention, and does not limit the technical scope of the present invention to the following aspects.

<Apparatus configuration>
FIG. 1 shows an example of an outline of a methane gas generator 100 according to an embodiment of the present invention. The methane gas generator 100 shown in FIG. 1 generates a product containing methane gas and water vapor by an exothermic reaction of a reactant containing gaseous carbon dioxide gas and hydrogen gas. Such a chemical reaction is called a methanation reaction. The above chemical reaction is also a reversible reaction. The above chemical reaction formula is represented as follows.

4H ₂ + CO ₂ ⇔CH ₄ + 2H ₂ O (1)

The methane gas generator 100 includes reaction towers 1A and 1B. Reaction tower 1A and reaction tower 1B are connected in series. The reaction towers 1A and 1B include reactors 2A and 2B, respectively. Inside the reactors 2A and 2B, a methanation reaction of the formula (1) is performed. Here, the reactors 2A and 2B are an example of the “reaction unit” of the present invention. Further, the reactors 2A and 2B are filled with a catalyst for promoting the methanation reaction. The catalyst includes, for example, a stabilized zirconia support having a tetragonal and / or cubic crystal structure in which a stabilizing element is dissolved, and Ni supported on the stabilized zirconia support. The stabilizing element is made of at least one transition element selected from the group consisting of, for example, Mn, Fe, and Co. It is known that these catalysts have high activity, and the reaction temperature which is the object of the present invention is, for example, one at around 200 ° C. (473 K). Although not shown, the reaction towers 1A and 1B are provided with thermometers for measuring the temperatures in the reactors 2A and 2B.

  Further, the methane gas generator 100 includes heat exchangers 3A and 3B. The heat exchangers 3A and 3B are provided in series. The heat exchangers 3A and 3B are connected to the reaction tower 1A. Here, each of the heat exchangers 3A and 3B is an example of the “heat exchanger” of the present invention, and is also an example of the “heat exchangers connected in series” of the present invention. The number of heat exchangers is not limited to two, and any number may be provided in series.

  The type of the heat exchangers 3A and 3B is, for example, a shell and tube type heat exchanger. Heat exchangers other than the shell-and-tube type heat exchanger are also used industrially, but if the temperature difference between the inlet and outlet is large as in the present invention, the heat exchanger may be damaged by other methods. May occur. Therefore, in the present embodiment, shell and tube type heat exchangers are employed as the heat exchangers 3A and 3B. Of course, heat exchangers other than the shell and tube type may be used as the heat exchangers 3A and 3B. FIG. 2 shows an example of the outline of the heat exchanger 3A. As shown in FIG. 2, the heat exchanger 3A includes inner walls 30 which are alternately arranged from the inlet to the outlet of the shell portion (the same applies to the heat exchanger 3B). Further, as shown in FIG. 2, in the heat exchanger 3A, the reactant sent to the reactor 2A passes through the shell portion. The tube portion of the heat exchanger 3A is a product (hereinafter, referred to as a first product) generated by the methanation reaction of the formula (1) in the reactor 2A, and is a tube portion of the heat exchanger 3B. Will pass through the first product. Here, the first product contains methane gas, water vapor, and unreacted reactants. The first product is an example of the “product” of the present invention.

  Further, the shell part of the heat exchanger 3B passes through the shell part of the heat exchanger 3A, and the reactant sent to the reactor 2A passes. The first product flowing out of the reactor 2A passes through the tube portion of the heat exchanger 3B. The sum of the heat transfer exchange areas of the heat exchangers 3A and 3B is a value that condenses steam contained in the first product into water.

  The methane gas generator 100 also includes a condensed water tank 4A for storing the generated condensed water when condensed water is generated in the tubes of the heat exchangers 3A and 3B when the water vapor contained in the first product is condensed. , 4B. As shown in FIG. 2, the condensed water tank 4A is provided so as to communicate with the bottom of the outlet of the tube portion of the heat exchanger 3A. Further, the methane gas generator 100 includes a float type drain valve 5A between the bottom of the outlet of the tube portion of the heat exchanger 3A and the condensed water tank 4A. Although not shown, the condensed water tank 4B is also provided so as to communicate with the bottom of the outlet of the tube portion of the heat exchanger 3B. In addition, the methane gas generator 100 includes a float type drain valve 5B between the bottom of the outlet of the tube portion of the heat exchanger 3B and the condensed water tank 4B. Here, the condensed water tanks 4A and 4B and the drain valves 5A and 5B are examples of the "drain means" of the present invention.

In addition, the methane gas generation device 100 includes a drain pipe that is connected to the condensed water tanks 4A and 4B, respectively, and drains the condensed water from the condensed water tanks 4A and 4B. Further, the methane gas generation device 100 includes adjustment valves 6A and 6B for adjusting the amount of drainage and valve control devices 7A and 7B for controlling the adjustment valves 6A and 6B, respectively, in the middle of the water distribution pipe. The valve control devices 7A and 7B are provided with regulating valves 6A and 6
By controlling B respectively, the amount of condensed water stored in the condensed water tanks 4A and 4B is adjusted.

  Further, the methane gas generator 100 includes a heat exchanger 3C between the heat exchanger 3A and the reaction tower 1B. The heat exchanger 3C is, for example, a shell-and-tube heat exchanger, and has a staggered inner wall 30 like the heat exchangers 3A and 3B. Here, the heat exchanger 3C is an example of the “heat exchanger” of the present invention. The shell part of the heat exchanger 3C is connected to the tube part of the heat exchanger 3A and the reactor 2B through piping. Further, a tube portion of the heat exchanger 3C is connected to the reactor 2B through a pipe. That is, in the heat exchanger 3C, the first product flowing out of the tube portion of the heat exchanger 3A flows into the shell portion. Then, the first product is sent to the reactor 2B. Further, in the tube portion of the heat exchanger 3C, a product (hereinafter, referred to as a first product) generated by the methanation reaction of the unreacted reactant contained in the first product in the reactor 2B according to the formula (1). 2). Here, the second product includes a first product, a product generated by a methanation reaction of an unreacted reactant included in the first product in the reactor 2B, and a first product. Unreacted reactants contained in the product and not reacted in the reactor 2B. The second product is an example of the “product” of the present invention.

  In addition, the methane gas generator 100 includes a heat exchanger 3D connected to the heat exchanger 3C. The heat exchanger 3D is, for example, a shell and tube heat exchanger. The shell of the heat exchanger 3D is connected to the tube of the heat exchanger 3C through a pipe. That is, the second product flowing out of the reactor 2B and passing through the tube portion of the heat exchanger 3C flows into the shell portion of the heat exchanger 3D. Further, the heat exchanger 3D has a heat transfer area capable of condensing water vapor contained in the second product passing through the shell portion into water.

  Further, the methane gas generator 100 includes a chiller 8 that supplies cooling water to a shell portion of the heat exchanger 3D. Further, between the chiller 8 and the heat exchanger 3D, a circulation pipe through which the cooling water circulates is formed. Further, the methane gas generating device 100 includes valves 9A and 9B in the middle of the circulation line to control the flow rate of the cooling water flowing through the circulation line. In addition, the methane gas generation device 100 includes a pressure controller 10A that controls the pressure of the cooling water flowing through the pipeline in the middle of the pipeline from the chiller 8 to the heat exchanger 3D. In addition, the methane gas generator 100 includes a flow controller 11A that controls the flow rate of the cooling water flowing through the pipeline in the middle of the pipeline from the chiller 8 to the heat exchanger 3D. That is, the pressure and flow rate of the cooling water supplied from the chiller 8 to the heat exchanger 3D are controlled to desired values. Further, the methane gas generation device 100 includes a thermometer 12A that measures the temperature of the cooling water flowing through the pipeline in the middle of the pipeline from the chiller 8 to the heat exchanger 3D.

  In addition, the methane gas generator 100 includes a condensed water tank 4C for storing condensed water generated in a shell portion of the heat exchanger 3D. The condensed water tank 4C is provided so as to communicate with the bottom of the shell of the heat exchanger 3D. Further, the methane gas generator 100 includes a float type drain valve 5C between the bottom of the shell portion of the heat exchanger 3D and the condensed water tank 4C.

  Further, the methane gas generator 100 includes a drain pipe connected to the condensed water tank 4C and draining the condensed water from the condensed water tank 4C. Further, the methane gas generator 100 includes a regulating valve 6C for adjusting the amount of drainage and a valve control device 7C for controlling the regulating valve 6C in the middle of the water distribution pipe. The valve control device 7C controls the amount of condensed water in the condensed water tank 4C by controlling the adjustment valve 6C.

Further, the methane gas generator 100 includes a pipe connected to the shell part of the heat exchanger 3D and through which the methane gas flowing out of the shell part of the heat exchanger 3D passes. In addition, the methane gas generator 100 includes a thermometer 12B, a pressure instruction controller 13, and a pressure control valve 14 in the middle of the pipe. The thermometer 12B measures the temperature of the methane gas flowing through the pipe. Further, the pressure in the pipe is adjusted by controlling the pressure control valve 14 by the pressure indicating controller 13.

  Further, the methane gas generator 100 includes a pipe for supplying methane gas flowing out of the shell part of the heat exchanger 3D to the outside of the system as a product gas, and a pipe branched from the pipe and connected to the purge device 50. Here, the purge device 50 purges impurities such as unreacted reactants contained in the methane gas from the methane gas.

  In addition, the methane gas generation device 100 is provided in the middle of a pipe that supplies the methane gas flowing out of the shell portion of the heat exchanger 3D as a product gas to the outside of the system, and the middle of a pipe that branches from the pipe and connects to the purge device 50. , On-Off valves 15A and 15B. By controlling the On-Off valves 15A and 15B, it is determined whether the methane gas flowing out of the heat exchanger 3D is supplied as a product gas or the methane gas flowing out of the heat exchanger 3D is sent to the purge device 50 for purging. It is determined.

  Further, the methane gas generator 100 includes a damper 16 with a valve between the shell of the heat exchanger 3D and the purge device 50. The pulsation of the methane gas sent to the purge device 50 is suppressed by passing through the damper 16 with a valve.

  In addition, the reaction towers 1A and 1B of the methane gas generator 100 include jackets 17A and 17B so as to surround the reactors 2A and 2B, respectively. Heat medium oil flows into the jackets 17A and 17B. When the heat transfer medium oil flows into the jackets 17A and 17B, heat exchange occurs between the substance in the reactors 2A and 2B and the heat transfer medium oil, and fluctuations in the temperature of the substance in the reactors 2A and 2B are suppressed. That is, the methanation reaction of the formula (1) proceeds stably in the reactors 2A and 2B.

  Further, the methane gas generating device 100 includes a heat medium oil tank 18 for storing the above heat medium oil. Further, the methane gas generator 100 includes a heater 19 for heating the heat transfer oil in the heat transfer oil tank 18.

  Further, the methane gas generator 100 includes a discharge pipe connected to the heat medium oil tank 18 and configured to discharge the heat medium oil from the heat medium oil tank 18. Further, the methane gas generator 100 includes valves 9C and 9D and a valve control device 20 for controlling the valves 9C and 9D in the middle of the discharge pipe. The valve control device 20 adjusts the amount of the heat transfer oil stored in the heat transfer oil tank 18 by controlling the valves 9C and 9D.

  In addition, the methane gas generating device 100 is connected to the heating medium oil tank 18 and the jackets 17A and 17B, and includes a circulation pipe for circulating the heating medium oil. The methane gas generation device 100 includes a valve 9E for adjusting the amount of the heat transfer oil flowing out of the heat transfer oil tank 18 and a jacket in the pipeline between the heat transfer oil tank 18 and the jacket 17A. The pump 21 for pumping to 17A is provided. Further, the methane gas generator 100 includes a pressure controller 10B that controls the pressure of the heat transfer oil sent to the jacket 17A, a valve 9F, and a flow controller 11B that controls the flow rate of the heat transfer oil sent to the jacket 17A. .

  In addition, the methane gas generator 100 includes a temperature instruction controller 22A that measures the temperature of the heat transfer oil and controls the heater 19 in the middle of the heat transfer oil circulation pipe and upstream of the jacket 17A. Further, the methane gas generator 100 includes a thermometer 12C in the middle of the heat transfer oil circulation pipe and between the jacket 17A and the jacket 17B.

  Further, the methane gas generator 100 includes a heat medium oil cooler 23 that cools the heat medium oil in the middle of the heat medium oil circulation pipe and downstream of the jacket 17B. The heat medium oil cooler 23 is, for example, a shell and tube heat exchanger. The heat medium oil flowing out of the jacket 17B flows into the shell portion of the heat medium oil cooler 23. On the other hand, cooling water is supplied to the tube portion of the heat medium oil cooler 23 from outside the system.

  Further, the methane gas generator 100 includes a thermometer 12D that measures the temperature of the heat transfer oil between the jacket 17B and the heat transfer oil cooler 23 in the middle of the heat transfer oil circulation pipe. In addition, the methane gas generator 100 branches off from the heat medium oil circulation pipe between the jacket 17B and the heat medium oil cooler 23, and is connected to the heat medium oil tank 18 without passing through the heat medium oil cooler 23. Branch piping. The methane gas generator 100 includes a temperature control valve 24 in the middle of the branch pipe. Further, the methane gas generator 100 includes a thermometer 12E for measuring the temperature of the heat transfer oil flowing between the heat transfer oil cooler 23 and the heat transfer oil tank 18, and a temperature control valve 24 based on the measurement value of the thermometer 12E. Is provided with a temperature instruction controller 22B for controlling the temperature. By controlling the temperature control valve 24, the amount of the heat medium oil flowing out of the jacket 17B that is cooled back to the heat medium oil tank 18 via the heat medium oil cooler 23 and the heat medium oil cooler The amount that returns to the heat medium oil tank 18 without passing through 23 is determined. Thus, the cooling amount of the heat transfer oil is adjusted.

<Example of generation flow>
Next, an example of a flow in which methane gas is generated by the operation of the methane gas generation device 100 will be described. In generating methane gas, the heater 19 shown in FIG. 1 is started. Then, the heat medium oil in the heat medium oil tank 18 is heated. Then, the valve 9E is opened, and the pump 21 is started. By such an operation, the heat medium oil is circulated to the jackets 17A and 17B. The pressure at which the heat transfer oil is pressure-fed to the jacket 17A is controlled to a desired value by the pressure controller 10B. Further, the circulation flow rate of the heat transfer oil is controlled to a desired value by the flow rate controller 11B. Further, the heater 19 is configured to heat the heat transfer oil in the heat transfer oil tank 18 to a temperature near the temperature at which the reaction of the reactants proceeds in the reaction towers 2A and 2B, based on an instruction from the temperature instruction controller 22A. Controlled. In this way, the heat medium oil at a desired temperature and pressure circulates in the jackets 17A and 17B. Here, the desired temperature of the heat transfer oil flowing into the jackets 17A and 17B is a temperature at which the methanation reaction of the formula (1) can proceed, for example, about 200 ° C. Cooling water is supplied to the tube portion of the heat medium oil cooler 23. Cooling water is circulated between the chiller 8 and the heat exchanger 3D.

  FIG. 3 shows an example of a flowchart in which methane gas is generated by the methane gas generation device 100 after preparation for methane gas generation is performed in the methane gas generation device 100 as described above.

(Step S101)
In step S101, a reactant containing carbon dioxide gas and hydrogen gas is caused to flow into the shell of the heat exchanger 3A. Then, the reactant containing the carbon dioxide gas and the hydrogen gas flowing into the shell portion does not proceed linearly but is diffused by hitting the inner wall 30 of the heat exchanger 3A. Therefore, the reactants are mixed and stirred. The reaction product thus mixed and stirred flows out of the shell of the heat exchanger 3A and flows into the shell of the heat exchanger 3B. Then, the above-mentioned reactant is further mixed and stirred in the same manner, and flows into the reactor 2A.

(Step S102)
In step S102, a methanation reaction of the inflowing reactant proceeds in the reactor 2A. As the methanation reaction proceeds, methane gas is generated as a product. In addition, steam is generated as a by-product. When the methanation reaction is in progress, the heat generated by the methanation reaction is absorbed by the heat transfer oil flowing through the jacket 17A. That is, the fluctuation of the temperature in the reactor 2A is suppressed, and the methanation reaction in the reactor 2A proceeds stably.

  Part of the heat generated by the methanation reaction is also absorbed by a first product including a product containing methane gas and water vapor and an unreacted reactant. That is, the temperature of the first product is higher than the temperature of the reactant flowing into the reactor 2A. Then, the first products flow out of the reactor 2A due to the pressure generated by the methanation reaction, and flow into the tube portion of the heat exchanger 3B.

(Step S103)
In step S103, in the heat exchanger 3B, the first product and the reactant before being sent to the reactor 2A exchange heat. The first product that has flowed into the tube portion of the heat exchanger 3B exchanges heat with the reactant that has not flowed to the reactor 2A that has flowed into the shell portion of the heat exchanger 3B. Here, the temperature of the first product is higher than the temperature of the reactant before being sent to the reactor 2A. Therefore, in the shell portion of the heat exchanger 3B, the reactants before being sent to the reactor 2A are preheated while being mixed and stirred.

  On the other hand, the first product flowing through the tube portion of the heat exchanger 3B is cooled by exchanging heat with the reactant. When the water vapor contained in the first product is cooled to generate condensed water, the generated condensed water accumulates at the bottom of the outlet of the tube portion of the heat exchanger 3B. The condensed water accumulated at the bottom of the outlet of the tube portion of the heat exchanger 3B flows into the condensed water tank 4B by opening the drain valve 5B. The temperature of the condensed water stored in the condensed water tank 4B is, for example, 100 degrees or more. Further, the first product flowing through the tube portion of the heat exchanger 3B flows into the tube portion of the heat exchanger 3A after cooling.

(Step S104)
In step S105, in addition to the heat exchanger 3B, in the heat exchanger 3A, the first product and the reactant before being sent to the reactor 2A and before being sent to the heat exchanger 3B Exchange heat. The first product is further cooled in the heat exchanger 3A. Here, the sum of the heat transfer exchange areas of the heat exchangers 3A and 3B is a value that condenses steam contained in the product passing through the tube portion into water. Therefore, in the heat exchanger 3A, the steam contained in the first product is cooled, and condensed water is generated. Then, the generated condensed water accumulates at the bottom of the outlet of the tube portion of the heat exchanger 3A. The condensed water accumulated at the bottom of the outlet of the tube portion of the heat exchanger 3A flows into the condensed water tank 4A by opening the drain valve 5A. The temperature of the condensed water stored in the condensed water tank 4A is, for example, 100 degrees or more. Further, the steam is gradually cooled from the heat exchanger 3B to the heat exchanger 3A. Therefore, the temperature of the condensed water stored in the condensed water tank 4A is lower than the temperature of the condensed water stored in the condensed water tank 4B. Further, the reactant passing through the shell portion of the heat exchanger 3A exchanges heat with the first product having a higher temperature than the reactant, so that the reactant is preheated even before being sent to the heat exchanger 3B. .

(Step S105)
In step S105, the first product cooled in the tube part of the heat exchanger 3A flows into the shell part of the heat exchanger 3C. Then, the first product does not proceed linearly, but is diffused by hitting the inner wall 30 of the heat exchanger 3C. Therefore, the first product is mixed and stirred. Thereafter, the first product mixed and stirred in the shell portion of the heat exchanger 3C is sent to the reactor 2B.

  Here, since the sum of the heat transfer exchange areas of the heat exchangers 3A and 3B is a value for condensing the water vapor contained in the product passing through the tube portion into water, one of the heat exchanges in the heat exchanger 3A or 3B is performed. The parts are separated as condensed water. That is, the relationship between the unreacted reactant and the product contained in the first product is not in a chemical equilibrium state due to the separation of water vapor. Therefore, unreacted reactants contained in the first product sent to the reactor 2B undergo a methanation reaction.

(Step S106)
In step S106, methane gas is further generated from the unreacted reactant contained in the first product flowing into the reactor 2B by a methanation reaction. The heat generated by the methanation reaction is absorbed by the heat transfer oil flowing through the jacket 17B. That is, the fluctuation of the temperature in the reactor 2B is suppressed, and the methanation reaction in the reactor 2B proceeds stably.

  In the reactor 2B, methane gas is newly generated as a product, and steam is further generated as a by-product. That is, the second product including the first product and the product newly generated in the reactor 2B exists in the reactor 2B. The temperature of the second product absorbs at least a part of the heat generated by the exothermic methanation reaction and is higher than the temperature of the reactant (first product) flowing into the reactor 2B. Has become. Then, these second products flow out of the reactor 2B due to the pressure generated by the methanation reaction, and are sent to the tube portion of the heat exchanger 3C.

  At least a portion of the heat transfer oil that has absorbed the reaction heat flows out of the jacket 17B and flows into the shell portion of the heat transfer oil cooler 23. In the heat medium oil cooler 23, the heat medium oil exchanges heat with cooling water and is cooled. Then, the cooled heat medium oil is returned to the heat medium oil tank 18. The temperature of the heat transfer oil returned from the heat transfer oil cooler 23 to the heat transfer oil tank 18 is measured by the temperature instruction controller 22B. Then, the temperature control valve 24 is controlled based on the measured temperature. In other words, by controlling the temperature control valve 24, the amount of heat flowing from the jacket 17 </ b> B to the heat medium oil cooler 23 and the flow directly from the jacket 17 </ b> B to the heat medium oil tank without passing through the heat medium oil cooler 23. The balance with the amount of the heat transfer oil is adjusted. In this way, fluctuations in the temperature of the circulating heat transfer oil are suppressed. Further, after the supply of the reactant is started and the reaction is started, the operation of the heater 19 may be stopped since the reaction heat exceeds the heat radiation amount. When the operation of the heater 19 is stopped, the energy used for the heating amount is reduced.

(Step S107)
In Step S107, the second product having a higher temperature than the first product flows into the tube portion of the heat exchanger 3C. On the other hand, the first product before flowing into the reactor 2B flows into the shell portion of the heat exchanger 3C. That is, the first product and the second product exchange heat in the heat exchanger 3C. In the heat exchanger 3C, heat exchange between the first product and the second product preheats the first product and cools the second product.

(Step S108)
In step S108, the second product cooled in the heat exchanger 3C is sent to the shell part of the heat exchanger 3D. In the heat exchanger 3D, the second product is further cooled by the cooling water flowing through the tube portion. Here, the heat exchanger 3D has a heat transfer area capable of condensing steam contained in the second product passing through the shell portion into water. That is, in the heat exchanger 3D, most of the water vapor contained in the second product becomes condensed water and accumulates at the bottom of the shell portion of the heat exchanger 3D. Then, the condensed water accumulated at the bottom of the shell portion of the heat exchanger 3D flows into the condensed water tank 4C by opening the drain valve 5C. The temperature of the condensed water stored in the condensed water tank 4C is, for example, 100 degrees or more.

  In addition, the second product cooled in the shell portion of the heat exchanger 3D contains almost no steam because the heat exchanger 3D has a heat transfer area for condensing steam into water. Unreacted reactants remaining in the second product are almost eliminated by the methanation reaction in the reactor 2B. Therefore, the methane gas flowing out of the shell portion of the heat exchanger 3D can be supplied to the outside as a product gas. When methane gas is supplied to the outside of the system as a product gas, the On-Off valve 15A is closed and the On-Off valve 15B is opened. Further, the methane gas generator 100 can also send the methane gas flowing out of the shell part of the heat exchanger 3D to the purge device 50 to purge a small amount of impurities mixed with the methane gas. When the methane gas is sent to the purge device 50 to be purged, the On-Off valve 15A is opened and the On-Off valve 15B is closed.

<Action and effect>
In the methane gas generator 100 as described above, the reactants before the methanation reaction flowing into the reactor 2A are preheated in the heat exchangers 3A and 3B. In the heat exchanger 3C, the first product flowing into the reactor 2B is preheated. Therefore, the methanation reaction is promoted in the reactors 2A and 2B.

  The methane gas generated in the reactor 2A is cooled in the heat exchangers 3A, 3B, 3C, 3D. When the steam contained in the methane gas is condensed and discharged in the heat exchangers 3A, 3B, 3C and 3D, the saturated vapor pressure of the methane gas decreases. That is, handling of methane gas becomes easy.

  Further, in the heat exchangers 3A and 3B, the reactant before the methanation reaction is performed in the reactor 2A and the first product containing the methane gas generated by the methanation reaction exchange heat, so that the reaction is performed. Preheating of the product and cooling of the first product are realized. Further, in the heat exchanger 3C, a reactant before the methanation reaction is performed in the reactor 2B (an unreacted reactant included in the first product) and a methane gas including a methane gas generated by the methanation reaction The heat exchange between the second product and the second product realizes the preheating of the reactant and the cooling of the second product. That is, the methane gas generator 100 as described above does not include separate heat exchangers for preheating the reactants and cooling the products containing methane gas. Therefore, the methane gas generator 100 as described above can save energy for preheating the reactants and cooling the methane gas. That is, the methane gas generator 100 as described above can improve the methane gas generation efficiency. Further, with the methane gas generator 100 as described above, the methane gas generator can be made more compact than in the case where preheating of a reactant and cooling of a product are performed separately.

Also, if separate heat exchangers are provided for preheating the reactants and cooling the product containing methane gas, respectively, if the amount of the reactants fluctuates, the amount of the reactants after the preheating of the reactants compared to before the amount of the reactants changes. The temperature will fluctuate. Therefore, in order to suppress the fluctuation in the temperature of the reactant after preheating, it is necessary to control the flow rate of the heat medium that exchanges heat with the reactant according to the amount of the reactant. Also, when the amount of the product fluctuates, similarly, the temperature after cooling the product fluctuates compared to before the fluctuation of the amount of the product. Therefore, in order to suppress the fluctuation of the temperature after cooling the product, it is necessary to control the flow rate of the heat medium that exchanges heat with the product according to the amount of the product. However, with the methane gas generator 100 as described above, when the amount of reactants flowing into the heat exchangers 3A and 3B fluctuates, the reactants flow out of the reactor 2A and flow into the heat exchangers 3A and 3B, and react with the reactants. The amount of the first product that exchanges heat will vary according to the amount of the reactants. That is, even when the amount of reactants flowing into the heat exchangers 3A and 3B fluctuates, the flow rate of the first product that exchanges heat with the reactants in the heat exchangers 3A and 3B is controlled according to the amount of reactants. At least, the fluctuation of the temperature after the preheating of the reactant is suppressed autonomously.

  Even when the amount of the first product flowing out of the heat exchangers 3A and 3B fluctuates, the flow rate of the reactant that exchanges heat with the first product in the heat exchangers 3A and 3B is similarly reduced. Even if the control is not performed in accordance with the amount of the first product, the temperature fluctuation of the first product after cooling is suppressed autonomously. That is, there is no need for a configuration for suppressing fluctuations in preheating of the reactant and fluctuations in cooling of the first product. The same can be said for the heat exchanger 3C, and there is no need for a configuration for suppressing fluctuations in preheating of the first product and fluctuations in cooling of the second product.

  In the methane gas generator 100 as described above, the reactants pass through the shell portions of the shell and tube heat exchangers in the heat exchangers 3A and 3B. Therefore, the reactant is diffused when the reactant hits the inner wall 30 of the shell portion. That is, the mixing and stirring of the reactants is promoted. Therefore, the methanation reaction is promoted in the reactor 2A into which the reactants preheated and mixed and stirred in the heat exchangers 3A and 3B flow.

  Also in the heat exchanger 3C, the first product passes through the shell of the shell-and-tube heat exchanger. The heat exchanger 3C is the same type of heat exchanger as the heat exchangers 3A and 3B. Therefore, the first product is diffused when the reactant hits the inner wall 30 of the shell portion of the heat exchanger 3C. Therefore, mixing and stirring of the first product is promoted. Therefore, the methanation reaction is promoted in the reactor 2B into which the first product that has been preheated and mixed and stirred in the heat exchanger 3C flows. That is, in order to promote the methanation reaction, new equipment is provided in addition to the heat exchangers 3A, 3B, and 3C, and the mixing and stirring of the reactants can be omitted. Therefore, methane gas generation efficiency is improved. Further, the methane gas generator 100 can be made compact.

  Further, the first and second products flowing out of the reactors 2A and 2B receive the pressure in the reactors 2A and 2B and pass through the tube portions of the heat exchangers 3A, 3B and 3C, respectively. . That is, it is not necessary to newly provide pumping means such as a pump and a compressor for passing the first product and the second product through the heat exchangers 3A, 3B, and 3C. That is, the power required for the first product and the pumping can be reduced, and energy saving can be realized.

  In the methane gas generator 100 as described above, the sum of the heat transfer exchange areas of the heat exchangers 3A and 3B is a value that condenses water vapor contained in the first product passing through the tube portion into water. It is. Therefore, in the heat exchangers 3A and 3B, at least a part of the steam contained in the product is condensed into water. That is, steam is easily separated from methane gas. Therefore, the purity of methane gas can be easily increased.

  In the methane gas generator 100 as described above, the first product flowing out of the reactor 2A contains an unreacted reactant. And the methanation reaction is a reversible reaction. That is, the unreacted reactant contained in the first product is in a chemical equilibrium state with the methane gas and water vapor contained in the first product. Here, when steam is separated from the first product in the heat exchanger 3A or the heat exchanger 3B, the relationship of the chemical equilibrium state changes. That is, the relationship between the unreacted reactant contained in the first product, the methane gas, and the water vapor is no longer in a chemical equilibrium state due to the separation of the water vapor. Therefore, the first product that has passed through the heat exchangers 3A and 3B and sent to the reactor 2B undergoes a methanation reaction of the unreacted reactant contained therein. That is, methane gas is generated again from unreacted reactants contained in the first product. That is, the proportion of unreacted reactants contained in the first product decreases, and the proportion of methane gas contained in the first product increases. That is, with the methane gas generator 100 as described above, the purity of the generated methane gas is increased.

  In the methane gas generator 100, the first product that has flowed out of the heat exchanger 3B in the heat exchanger 3C is preheated again, mixed and stirred, and then sent to the reactor 2B. Therefore, the methanation reaction in the reactor 2B is promoted, and the methane gas generation efficiency is improved.

  Further, when the condensed water is separated from the first product in the heat exchanger 3A and discharged from the heat exchanger 3A, the heat capacity of the entire first product is reduced. In other words, the first product can be cooled more quickly than before the condensed water is separated. Therefore, in the heat exchangers 3A and 3B connected in series as described above, the heat exchange area of the heat exchanger 3A can be reduced, and the heat exchanger 3A can be made compact.

  When condensed water is generated in both the heat exchangers 3A and 3B, the condensed water having different temperatures is stored in the condensed water tanks 4A and 4B. If the condensed water having different temperatures is reused, energy saving can be realized. As an example of the reuse of the condensed water, when the purge device 50 is a device provided with a membrane that allows methane gas to pass therethrough and does not allow impurities contained in the methane gas to pass, it is used to heat the methane gas before passing through the membrane. It is mentioned that it is done. With such a methane gas generation device 100, dew condensation of the methane gas flowing into the film is suppressed, and influence on the operation of the purge device 50 is suppressed.

  In the above embodiment, if the supply pressure of the reactant is sufficient, it is not necessary to heat the raw material by adiabatic compression of the compressor.

<Modification 1>
In the methane gas generator 100 described above, when condensed water is generated in the heat exchangers 3A and 3B, the generated condensed water is drained from the heat exchangers 3A and 3B. However, even when condensed water is generated in the heat exchangers 3A and 3B, the generated condensed water does not have to be drained from the heat exchangers 3A and 3B. The configuration of the methane gas generator 100A is different from that of the methane gas generator 100 in that the methane gas generator 100A does not include the condensed water tanks 4A and 4B and the drain valves 5A and 5B that communicate with the bottoms of the outlets of the tube portions of the heat exchangers 3A and 3B.

  Here, the heat exchange efficiency between the reactant and the product when two heat exchangers were arranged in series without providing the drainage means for the condensed water as in the methane gas generator 100A was verified. FIG. 4 shows the temperature and heat exchange of the reactant flowing out of the heat exchanger with respect to the heat exchange area per flow rate of the reactant when two heat exchangers are arranged in series (hereinafter referred to as (A)). The difference from the temperature of the reactants entering the vessel is illustrated. FIG. 4 shows the temperature and heat of the reactant flowing out of the heat exchanger with respect to the heat exchange area per reactant flow rate when one heat exchanger is provided (hereinafter referred to as (B)). The difference from the temperature of the reactants entering the exchanger is also illustrated.

  FIG. 5 shows an example of an outline of the configuration of FIG. 5A and an example of an outline of the configuration of FIG. As shown in FIG. 5, (A) is formed from heat exchangers 3A and 3B provided in methane gas generator 100A and reaction tower 1A. Then, the reactant before the methanation reaction flows into the shell part of the heat exchanger 3A and the shell part of the heat exchanger 3B. Then, the product after the methanation reaction flows into the tube portion of the heat exchanger 3A and the tube portion of the heat exchanger 3B.

Further, the heat exchange area per flow rate of the reactant shown in FIG. 4 is the sum of the heat exchange area of the heat exchanger 3A and the heat exchange area of the heat exchanger 3B. Further, the temperature difference between the reactants flowing into and out of the heat exchanger shown in FIG. 4 is based on the temperature of the reactant flowing from the shell portion of the heat exchanger 3B (T
This is a value obtained by subtracting the temperature (T2A) of the reactant flowing into the shell portion of the heat exchanger 3A from 1A).

  On the other hand, (B) is formed from one heat exchanger 3E and reaction tower 1A. Then, the reactant before the methanation reaction flows into the shell portion of the heat exchanger 3E. Then, the product after the methanation reaction flows into the tube portion of the heat exchanger 3E. The heat transfer area per flow rate of the reactant shown in FIG. 4 is the heat transfer area of the heat exchanger 3E. The temperature difference between the reactants flowing into and out of the heat exchanger shown in FIG. 4 is based on the temperature (T1B) of the reactants flowing out of the shell part of the heat exchanger 3E and flowing into the shell part of the heat exchanger 3E. This is a value obtained by subtracting the temperature (T2B) of the reactant before the reaction.

  As shown in FIG. 4, in the case of (A), regardless of the heat exchange area of the heat exchanger per flow rate of the reactant, the amount of the reactant flowing into and out of the heat exchanger is higher than in the case of (B). The temperature difference is a large result. That is, it has been confirmed that the configuration in which two heat exchangers are arranged in series has higher heat exchange efficiency than the configuration in which one heat exchanger is provided. In addition, it was confirmed that the configuration in which two heat exchangers were arranged in series improved the heat exchange efficiency even without a drainage unit for draining condensed water. In other words, in the case of (A), even if the heat exchanger is downsized and the heat exchange area of the heat exchanger is reduced, the same preheating effect and generation of the reactant as in (B) are obtained. It can be said that a cooling effect of the object can be obtained. Therefore, in the case of (A), the entire device can be made compact. From the verification results of FIGS. 4 and 5, the methane gas generator 100 </ b> A can reduce the size of the heat exchangers 3 </ b> A and 3 </ b> B to make the entire methane gas generator more compact than in the case of a single heat exchanger. It can be said that it can be done. Further, it can be said that the methane gas generator 100A can realize the same heat exchange efficiency as that in the case of a single heat exchanger, while making the entire apparatus compact.

<Modification 2>
Further, the methane gas generator may include one heat exchanger as an alternative to the heat exchangers 3A and 3B. FIG. 6 shows an example of the outline of a methane gas generator 100B including a heat exchanger 3F as an alternative to the heat exchangers 3A and 3B. Although not shown, the shell portion of the heat exchanger 3F includes, similarly to the heat exchanger 3A, inner walls arranged alternately from the inlet to the outlet of the shell portion. And the reactant sent to the reactor 2A flows into the shell part of the heat exchanger 3F. On the other hand, the first product flowing out of the reactor 2A flows into the tube portion of the heat exchanger 3F. That is, in the heat exchanger 3F, the reactant sent to the reactor 2A and the first product exchange heat. Then, the reactant sent to the reactor 2A is preheated, and the first product is cooled. The reactants are mixed and stirred in the shell part of the heat exchanger 3F.

  In the methane gas generator 100 as described above, the reactant before the methanation reaction flowing into the reactor 2A is preheated in the heat exchanger 3F. In the heat exchanger 3C, the first product flowing into the reactor 2B is preheated. Therefore, the methanation reaction is promoted in the reactors 2A and 2B.

  Further, the methane gas generated in the reactor 2A is cooled in the heat exchangers 3F, 3C, 3D. Further, the methane gas generated in the reactor 2B is cooled in the heat exchangers 3C and 3D. When the steam contained in the methane gas is condensed and discharged in the heat exchangers 3F, 3C, and 3D, the saturated vapor pressure of the methane gas decreases. That is, handling of methane gas becomes easy.

Further, in the heat exchanger 3F, the reactant before the methanation reaction is performed in the reactor 2A and the first product containing methane gas generated by the methanation reaction exchange heat, so that the reactant Preheating and cooling of the first product are realized. In addition, heat exchanger 3
In C, the reactant (the unreacted reactant contained in the first product) before the methanation reaction is performed in the reactor 2B and the second product containing methane gas generated by the methanation reaction Heat exchange achieves preheating of the reactants and cooling of the second product. That is, the methane gas generator 100B as described above does not include separate heat exchangers for preheating the reactant and cooling the product containing methane gas. Therefore, the methane gas generator 100B as described above can save energy for preheating the reactants and cooling the methane gas. That is, the methane gas generator 100B as described above can improve the methane gas generation efficiency. Further, with the methane gas generator 100B as described above, the methane gas generator can be made more compact than in the case where the preheating of the reactant and the cooling of the product are performed separately.

  Also, if separate heat exchangers are provided for preheating the reactants and cooling the product containing methane gas, respectively, if the amount of the reactants fluctuates, the amount of the reactants after the preheating of the reactants compared to before the amount of the reactants changes. The temperature will fluctuate. Therefore, in order to suppress the fluctuation in the temperature of the reactant after preheating, it is necessary to control the flow rate of the heat medium that exchanges heat with the reactant according to the amount of the reactant. Further, even when the amount of the product fluctuates, the temperature after cooling the product fluctuates similarly as compared to before the fluctuation of the amount of the product. Therefore, in order to suppress the fluctuation of the temperature after cooling the product, it is necessary to control the flow rate of the heat medium that exchanges heat with the product according to the amount of the product. However, in the case of the methane gas generator 100B as described above, when the amount of the reactant flowing into the heat exchanger 3F fluctuates, the reactant flows out of the reactor 2A and flows into the heat exchanger 3F to exchange heat with the reactant. The amount of one product will vary according to the amount of the reactants. That is, even when the amount of reactant flowing into the heat exchanger 3F fluctuates, the reaction can be performed without controlling the flow rate of the first product that exchanges heat with the reactant in the heat exchanger 3F according to the amount of reactant. Fluctuations in temperature after preheating of the object are suppressed autonomously.

  Also, even when the amount of the first product flowing out of the heat exchanger 3F fluctuates, the flow rate of the reactant that exchanges heat with the first product in the heat exchanger 3F is changed according to the first product amount. Even without control, fluctuations in the temperature of the first product after cooling are autonomously suppressed. That is, there is no need for a configuration for suppressing fluctuations in preheating of the reactant and fluctuations in cooling of the first product. The same can be said for the heat exchanger 3C, and there is no need for a configuration for suppressing fluctuations in preheating of the first product and fluctuations in cooling of the second product.

  In the case of the methane gas generator 100B as described above, the reactant passes through the shell of the shell and tube heat exchanger in the heat exchanger 3F. Therefore, the reactant is diffused when the reactant hits the alternately provided inner walls of the shell portion. Thus, mixing and stirring of the reactants is promoted. Therefore, the methanation reaction is promoted in the reactor 2A into which the reactant preheated and mixed and stirred in the heat exchanger 3F flows. Similarly, in the heat exchanger 3C, the first product passes through the shell portion of the shell-and-tube heat exchanger. Therefore, mixing and stirring of the first product is promoted. Therefore, the methanation reaction is promoted in the reactor 2B into which the first product that has been preheated and mixed and stirred in the heat exchanger 3C flows. That is, in order to promote the methanation reaction, new equipment is provided in addition to the heat exchangers 3F and 3C, and it is not necessary to mix and stir the reactants. Therefore, methane gas generation efficiency is improved. In addition, the methane gas generator 100B can be downsized.

  The first product and the second product flowing out of the reactors 2A and 2B receive the pressure in the reactors 2A and 2B and pass through the tube portions of the heat exchangers 3F and 3C, respectively. That is, it is not necessary to newly provide a means such as a pump or a compressor for allowing the first product and the second product to pass through the heat exchangers 3F and 3C. Therefore, the power required for pumping can be reduced, and energy saving can be achieved.

  In the methane gas generator 100B as described above, the first product flowing out of the reactor 2A contains an unreacted reactant. And the methanation reaction is a reversible reaction. That is, the unreacted reactant contained in the first product is in a chemical equilibrium state with the methane gas and water vapor contained in the first product. Here, when steam is separated from the first product in the heat exchanger 3F, the relationship of the chemical equilibrium state changes. That is, the relationship between the unreacted reactant contained in the first product, the methane gas, and the water vapor is no longer in a chemical equilibrium state due to the separation of the water vapor. Therefore, the first product sent to the reactor 2B after passing through the heat exchanger 3C undergoes a methanation reaction of the unreacted reactant contained therein. That is, methane gas is generated again from unreacted reactants contained in the first product. That is, the proportion of unreacted reactants contained in the first product decreases, and the proportion of methane gas contained in the first product increases. That is, with the methane gas generator 100B as described above, the purity of the generated methane gas is increased.

  In the methane gas generator 100B, the first product that has flowed out of the heat exchanger 3B in the heat exchanger 3C is preheated again, mixed and stirred, and then sent to the reactor 2B. Therefore, the methanation reaction in the reactor 2B is promoted, and the methane gas generation efficiency is improved.

Further, the heat transfer exchange area of the heat exchanger 3F may be 0.005 [m ² / (L / min)] or more. FIG. 7 shows an example of the temperature of the first product flowing out of the heat exchanger 3F with respect to the heat exchange area of the heat exchanger 3F per flow rate of the reactant. FIG. 7 shows the case where the pressure in the tube of the heat exchanger 3F is the rated pressure (0.4 MPaG) in the tube of the heat exchanger 3F, the atmospheric pressure lower than the rated pressure, and The first product temperature is plotted for each of the three different cases of 0.7 MPaG, which is also higher. FIG. 8 shows an example of the boiling point of water with respect to pressure. 7 and 8, if the heat transfer exchange area of the heat exchanger 3F is 0.005 [m ² / (L / min)] or more, regardless of the pressure in the tube of the heat exchanger 3F, steam Turns into condensed water. Therefore, with the methane gas generator 100B as described above, a large amount of condensed water is generated. Therefore, the generated condensed water can be discharged from the heat exchanger 3F, and the methanation reaction of the unreacted reactant contained in the first product can be promoted. Therefore, methane gas can be highly purified. Further, the obtained condensed water can be reused like the methane gas generator 100 to realize energy saving.

  In the above heat exchangers 3A and 3B, the reactant passes through the shell portion and the first product passes through the tube portion. However, the first product passes through the shell portion and the tube portion. The reactants may pass through. In such a case, the condensed water tanks 4A and 4B are provided so as to communicate with the bottoms of the shell portions of the heat exchangers 3A and 3B, respectively.

  Further, in the methane gas generator as described above, two reaction towers are provided, but the number of reaction towers may be any number. The heat medium oil may be another heat medium such as water. The cooling water supplied to the heat medium oil cooler 23 may be supplied from the chiller 8.

  The embodiments and modifications disclosed above can be combined with each other.

1A, 1B ··· reaction tower; 2A, 2B · · · reactor; 3A, 3B, 3C, 3D, 3E, 3F · · · heat exchanger; 4A, 4B, 4C · · · condensed water tank; 5A, 5B, 5C ·・ Drainage valve; 6A, 6B, 6C ・ ・ Regulatory valve; 7A, 7B, 7C ・ ・ Valve control device; 8 ・ ・ Chiller; 9A, 9B, 9C, 9D, 9E, 9F ・ ・ Valve; Pressure controllers; 11A, 11B, flow rate controllers; 12A, 12B, 12C, 12D, 12E, thermometers; 13, pressure regulators; 14, pressure control valves; 15A, 15B, On-Off Valve: 16 ··· Dampener with valve; 17A, 17B ··· Jacket; 18 ··· Heat medium oil tank; 19 ··· Heater; 20 ··· Valve control device; 21 ··· Pump; 22A, 22B ··· Temperature controller 23..Heat medium oil cooler; 24..Temperature control valve 30 ... internal wall; 50 · purge device; 100, 100A, 100B ... methane gas generator

Claims (7)

A methane gas generator that generates methane gas by a methanation reaction,
A reaction unit that causes a reactant containing carbon dioxide and hydrogen to generate an exothermic reaction and generates a product containing methane gas and water vapor and having a higher temperature than the reactant,
By exchanging heat between the reactant sent to the reaction section and the product flowing out of the reaction section, heat exchange to preheat the reactant sent to the reaction section and cool the product flowing out of the reaction section And a container,
Methane gas generator. The heat exchanger is a shell and tube type heat exchanger,
The reactant passes through a shell portion of the shell and tube heat exchanger,
The product passes through a tube portion of the shell and tube heat exchanger,
The methane gas generator according to claim 1. The heat exchanger exchanges heat between a reactant sent to the reaction section and water vapor of a product flowing out of the reaction section, so that heat exchange capable of condensing water vapor of a product flowing out of the reaction section can be performed. Having an area,
The methane gas generator according to claim 1. A plurality of the heat exchangers are connected in series,
The methane gas generator according to any one of claims 1 to 3. Drainage means for draining water condensed in each of the plurality of heat exchangers connected in series,
The methane gas generator according to claim 4. The total heat transfer surface of the plurality of heat exchangers connected in series has an area for condensing water vapor into water,
The methane gas generator according to claim 4. A methane gas generation method for generating methane gas by a methanation reaction,
A reaction step of causing an exothermic reaction of a reactant containing carbon dioxide and hydrogen to produce a product containing methane gas and water vapor and having a higher temperature than the reactant,
By performing heat exchange between the reactant sent to the reaction step and the product generated in the reaction step, the reactant sent to the reaction step is preheated, and the product generated in the reaction step is cooled. A heat exchange step;
Methane gas generation method.