JP7496768B2 - Methane Production Equipment - Google Patents

Description

The present invention relates to a methane production device.

There is known a methane production apparatus that produces methane from carbon dioxide ( _CO2 ) contained in a mixed gas discharged from a factory or the like (see, for example, Patent Document 1). In the methane production apparatus described in Patent Document 1, the _CO2 in the mixed gas discharged from the factory is adsorbed by an adsorbent, and hydrogen ( _H2 ) as a purge gas is injected into the adsorbent that has adsorbed the _CO2 , thereby separating the _CO2 from the mixed gas.

JP 2019-142806 A

The mixed gas discharged from a factory or the like may contain H ₂ in addition to CO _2. The gas ratio of H ₂ to CO ₂ in the mixed gas discharged from the factory may vary over time. Here, the composition of the generated gas from the methane production apparatus is strongly affected by the gas ratio of H ₂ to CO _2. For example, when the gas ratio is 4.0 and the CO ₂ conversion rate is 99 percent (%), the methane concentration in the generated gas is 95%. On the other hand, when the gas ratio is 4.1 and the CO ₂ conversion rate is 99%, the methane concentration in the generated gas decreases to 87%. Therefore, in order to guarantee the quality of methane generated by the methanation production apparatus, it is preferable to stabilize the gas ratio in the mixed gas supplied to the methane production apparatus. In contrast, the methane production apparatus described in Patent Document 1 does not take into consideration the variation in the gas ratio in the mixed gas supplied from the factory or the like.

The present invention has been made to solve at least part of the above-mentioned problems, and has an object to stabilize the gas ratio in a reactor and ensure the quality of the generated methane even when a mixed gas with an unstable gas ratio of _H2 and _CO2 is supplied to the reactor.

The present invention has been made to solve the above-mentioned problems, and can be realized in the following form : A methane production apparatus, comprising: a first methanation reactor for producing methane from a mixed gas of carbon dioxide and hydrogen, a gas ratio acquisition unit for acquiring a gas ratio of the mixed gas supplied to the first methanation reactor, the gas ratio being a ratio of carbon dioxide to hydrogen, a flow rate adjustment unit for adjusting a flow rate of the mixed gas supplied to the first methanation reactor, a second methanation reactor to which exhaust gas discharged from the first methanation reactor is supplied and which produces methane from the exhaust gas, and a flow path through which the exhaust gas discharged from the first methanation reactor passes and through which the exhaust gas supplied to the second methanation reactor passes, a downstream gas supply unit that supplies carbon dioxide or hydrogen to the second methanation reactor, and a control unit that controls a flow rate of carbon dioxide or hydrogen to the second methanation reactor, wherein the control unit determines a downstream flow rate, which is the flow rate of carbon dioxide or hydrogen supplied from the downstream gas supply unit to the second methanation reactor, using the gas ratio acquired by the gas ratio acquisition unit, a transport delay time of the exhaust gas generated by the tank, and a measurement delay time that occurs from the time the gas ratio acquisition unit acquires the gas ratio to the time the gas ratio is identified. In addition, the present invention can be realized in the following forms.

(1) According to one aspect of the present invention, a methane production apparatus is provided. This methane production device includes a first methanation reactor that produces methane from a mixed gas of carbon dioxide and hydrogen, a gas ratio acquisition unit that acquires a gas ratio of the mixed gas supplied to the first methanation reactor, which is the ratio of carbon dioxide to hydrogen, a flow rate adjustment unit that adjusts the flow rate of the mixed gas supplied to the first methanation reactor, a second methanation reactor that is supplied with exhaust gas discharged from the first methanation reactor and produces methane from the exhaust gas, a tank arranged in the middle of a flow path through which the exhaust gas passes, a downstream gas supply unit that supplies carbon dioxide or hydrogen to the second methanation reactor, and a control unit that controls the flow rate of carbon dioxide or hydrogen supplied to the second methanation reactor. The control unit determines a downstream flow rate, which is the flow rate of carbon dioxide or hydrogen supplied from the downstream gas supply unit to the second methanation reactor, using the gas ratio acquired by the gas ratio acquisition unit, the transport delay time of the exhaust gas generated by the tank, and the measurement delay time that occurs from the time the gas ratio acquisition unit acquires the gas ratio to the time the gas ratio is identified.

According to this configuration, the flow rate of CO 2 or H 2 supplied to the second methanation reactor is determined by taking into consideration the measurement delay time required from when the gas ratio acquisition unit detects and acquires the _gas ratio of the mixed gas, and the transport delay time required from when the gas ratio of the mixed gas is detected until the mixed gas flows into the second methanation reactor as exhaust _gas . In this way, by taking the delay time into consideration, the control unit calculates a gas ratio closer to the actual gas ratio of the exhaust gas supplied to the second methanation reactor. Thereby, the measurement delay time is offset by the gas transport delay time. As a result, compared to when these delay times are not taken into consideration, the gas ratio in the second methanation reactor is closer to the target gas ratio, and the methane concentration in the generated gas of the methane production apparatus is improved. That is, according to the methane production apparatus of this configuration, even when a mixed gas with an unstable gas ratio is supplied to the methane production apparatus, the gas ratio in the second methanation reactor can be stabilized to ensure the quality of the generated methane. In addition, the capacity of the tank is only required to delay the inflow of exhaust gas into the second methanation reactor by the time from when the gas ratio acquisition unit detects the gas ratio to when it acquires the gas ratio. Therefore, the size of the tank only needs to mitigate the fluctuations in the gas ratio of the exhaust gas supplied to the second methanation reactor, and a large capacity like that of a surge tank is not required. As a result, according to the methane production apparatus of this configuration, it is possible to realize a miniaturized methane production apparatus while ensuring the quality of the generated methane, compared to a methane production apparatus in which a surge tank arranged between the first methanation reactor and the second methanation reactor is used to mitigate the fluctuations in the gas ratio of the exhaust gas.

(2) In the methane production apparatus of the above embodiment, the control unit may determine the downstream flow rate using a differential time obtained by subtracting the measurement delay time from the transport delay time, and the gas ratio acquired by the gas ratio acquisition unit at a time that is the differential time before the present.
According to this configuration, the control unit can determine the flow rate of _CO2 or _H2 to be supplied to the second methanation reactor based on a gas ratio closer to the actual gas ratio of the exhaust gas supplied to the second methanation reactor, thereby further improving the methane concentration in the gas generated by the methane production apparatus of this configuration.

(3) The methane production apparatus of the above embodiment may further include an upstream gas supply unit that supplies carbon dioxide or hydrogen to the first methanation reactor, and the control unit may use the gas ratio acquired by the gas ratio acquisition unit to determine an upstream flow rate, which is the flow rate of carbon dioxide or hydrogen supplied from the upstream gas supply unit to the first methanation reactor.

(4) In the methane production apparatus of the above-described embodiment, the control unit may determine the downstream flow rate using a differential time obtained by subtracting the measurement delay time from the transportation delay time, a gas ratio acquired by the gas ratio acquisition unit at a time that is the differential time before the present, and the upstream flow rate.
According to this configuration, CO ₂ or H _{2 with a controlled flow rate is supplied to both the first methanation reactor and the second methanation reactor. Therefore, in the methane production apparatus of this configuration, CO 2 or H 2 with} a rough flow rate that does not take into account the measurement delay time is supplied to the first methanation reactor, and CO ₂ or H ₂ with a flow rate that is finely adjusted taking into account the measurement delay time and the _like is supplied to the second methanation reactor. As a result, the gas ratio in the second methanation reactor can be made closer to the target gas ratio. This further improves the methane concentration in the gas generated by the methane production apparatus of this configuration.

(5) The methane production apparatus of the above embodiment may further include a tank volume adjustment unit that reduces a volume of the tank that can accommodate gas as a flow rate of the mixed gas supplied to the first methanation reactor decreases.
When the total capacity of the tank is set to match the maximum flow rate of the mixed gas supplied to the first methanation reactor, the transport delay time when the flow rate of the mixed gas is low becomes longer than the time when the flow rate of the mixed gas is maximum, and the accuracy of control decreases. The tank volume adjustment unit can prevent this lengthening of the transport delay time when the flow rate of the mixed gas is low.

(6) In the methane production apparatus according to the above aspect, the tank volume adjustment unit may change a volume of the tank capable of accommodating gas by changing an amount of water in the tank.
In a tank of this configuration, the volume inside the tank can be easily changed by using water.

The present invention can be realized in various forms, such as a gas supply device, a methane production device, a methane production system, a hydrogen or carbon dioxide flow control device, a gas supply method, a methane production method, a method for controlling a gas supply device and a methane production device, a computer program for executing these devices and methods, a server device for distributing this computer program, a non-transitory storage medium on which a computer program is stored, etc.

FIG. 1 is a block diagram of a methane production apparatus and a mixed gas supply unit according to an embodiment of the present invention. 1 is a flow chart showing the supply of _H2 to the second reactor. FIG. 2 is a block diagram of a methane production apparatus and a mixed gas supply unit of a comparative example. FIG. 4 is an explanatory diagram of the effects of the methane production apparatus of the first embodiment and the methane production apparatus of the comparative example. FIG. 4 is an explanatory diagram of the effects of the methane production apparatus of the first embodiment and the methane production apparatus of the comparative example. FIG. 4 is an explanatory diagram of the effects of the methane production apparatus of the first embodiment and the methane production apparatus of the comparative example. FIG. 11 is a block diagram of a methane production apparatus and a mixed gas supply unit according to a second embodiment. FIG. 1 is an illustration of the flow rate of H ₂ supplied to the first reactor. 13 is a flowchart showing a flow rate of H ₂ supplied in the second embodiment. FIG. 13 is an explanatory diagram of a delay generation tank in a modified example. FIG. 13 is an explanatory diagram of a delay generation tank in a modified example. FIG. 13 is an explanatory diagram of the flow rate of H ₂ supplied to the second reactor in the modified example.

First Embodiment
FIG. 1 is a block diagram of a methane production apparatus 100 and a mixed gas supply unit 50 according to an embodiment of the present invention. The methane production apparatus 100 produces methane (CH 4 ) as a product gas by causing a methanation reaction between carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) in a mixed gas supplied from a mixed gas supply unit 50. The mixed gas supply unit 50 is a factory or _the like, and the supplied mixed gas is a combustion gas from a factory or the like. In this embodiment, the amounts of CO ₂ and H ₂ contained in the mixed gas vary with time. That is, the gas ratio ξ _M (H ₂ /CO ₂ ratio), which is the amount of H ₂ relative to the amount of CO ₂ in the mixed gas, is unstable.

As shown in FIG. 1, the methane production apparatus 100 of the first embodiment includes a _first reactor (first methanation reactor) 4 on the upstream side and a _second reactor (second methanation reactor) 7 on the downstream side for producing methane from a mixed gas containing CO 2 and H 2 , a mass flow controller (flow rate adjustment unit) MFC0 for adjusting the flow rate of the mixed gas supplied to the first reactor 4, a gas analyzer (gas ratio acquisition unit) 3 for acquiring a gas ratio ξ _M of the mixed gas supplied to the first reactor 4 on the upstream side of the mass flow controller MFC0, a surge tank 10 arranged between the mixed gas supply unit 50 and the mass flow controller MFC0, a first condenser 5 for condensing water vapor in the exhaust gas (hereinafter also simply referred to as "exhaust gas") discharged from the first reactor 4, a delayed generation tank (tank) 6 arranged in the middle of a flow path through which the exhaust gas supplied to the second reactor 7 passes, a second condenser 8 for condensing water vapor in the exhaust gas discharged from the second reactor 7, and a gas analyzer (gas ratio acquisition unit) 9 for condensing water vapor in the exhaust gas discharged from the second reactor 7. The methane production apparatus ₁₀₀ further includes a downstream gas supply unit 2 that additionally supplies H 2 to the second reactor 7, a mass flow controller MFC2 that adjusts the flow rate of H ₂ supplied from the downstream gas supply unit 2 to the second reactor 7, and a control unit 1 that controls the two mass flow controllers using a gas ratio ξ _M acquired by a gas analyzer 3. In this embodiment, the mixed gas supply unit 50 supplies the mixed gas via an adsorber (not shown) arranged upstream to the methane production apparatus 100, so that the mixed gas contains only CO ₂ and H _2. The gas ratio of the mixed gas supplied from the mixed gas supply unit 50 to the methane production apparatus varies within a range smaller than 4.0.

A methanation catalyst that causes a methanation reaction is contained in the first reactor 4 and the second reactor 7. The methanation catalyst generates methane by causing a methanation reaction represented by the following formula (1) to occur with respect to CO ₂ and H ₂ in the first reactor 4 and the second reactor 7. An example of the methanation catalyst is a complex containing ruthenium. In other embodiments, a well-known methanation catalyst other than ruthenium may be used.

上記式（１）から、生成ガス中のメタン濃度を向上させるためには、混合ガスのガス比ξ_Mが４．０に近いほど好ましいことがわかる。

From the above formula (1), it can be seen that in order to improve the methane concentration in the generated gas, the gas ratio ξ _M of the mixed gas is preferably closer to 4.0.

The exhaust gas containing methane produced by the methanation reaction in the first reactor 4 and unreacted _CO2 and _H2 is cooled to room temperature (25 degrees Celsius (°C)) by the first condenser 5 when it is discharged from the first reactor 4. By cooling the exhaust gas, water condensed from the steam by the first condenser 5 is separated from the exhaust gas. The exhaust gas containing methane from which the steam has been separated is supplied to the second reactor 7 via the delayed generation tank 6. The gas containing methane produced by the methanation reaction in the second reactor 7 has its steam separated by the second condenser 8 having the same configuration as the first condenser 5. The gas containing methane from which the steam has been separated is supplied as a generated gas to another device or storage tank not shown in the figure.

The delay generation tank 6 is a tank with a larger volume than the flow path. The presence of the delay generation tank 6 makes it take longer for the exhaust gas discharged from the first reactor 4 to flow into the second reactor 7 compared to the case where the delay generation tank 6 is not present. The surge tank 10, located upstream of the first reactor 4, is a tank that temporarily stores the mixed gas supplied from the mixed gas supply unit 50.

The gas analyzer 3 detects the _CO2 concentration in the mixed gas, and identifies the gas ratio ξ _M using the detected _CO2 concentration. The gas analyzer 3 calculates the gas ratio ξ _M by substituting the detected _CO2 concentration into the following formula (2).

Ｘ_CO2（ｔ）：混合ガス中のＣＯ₂濃度
ガス分析計３は、混合ガス中のＣＯ₂濃度を検出した時点からガス比ξ_Mを同定するまでに、計測遅れ時間τ_{delay_M}（例えば１０秒）を要する。一方で、遅れ生成タンク６があるため、ガス分析計３によりガス比ξ_Mが検出された混合ガスが第２反応器７へと供給されるまでのガス輸送遅れ時間τ_{delay_T}が発生する。

_XCO2 (t): _CO2 concentration in the mixed gas The gas analyzer 3 requires a measurement delay time _{τdelay_M} (e.g., 10 seconds) from the time when the _CO2 concentration in the mixed gas is detected until the gas ratio _ξM is identified. Meanwhile, due to the presence of the delay generation tank 6, a gas transport delay time _{τdelay_T} occurs until the mixed gas whose gas ratio _ξM has been detected by the gas analyzer 3 is supplied to the second reactor 7.

The control unit 1 of this embodiment controls the flow rate Q2 of H2 supplied from the downstream gas supply unit 2 to the second reactor 7 (downstream flow rate) using the gas ratio _ξM identified by the gas analyzer 3, the measurement delay time τ _{delay_M} , and the gas transport delay time τ _{delay_T} . Specifically, the control unit 1 determines the flow rate Q2 of _H2 using the following formula (3).

Ａ：制御定数
上記式（３）における制御定数Ａは、制御部１がマスフローコントローラＭＦＣ０を制御することにより、第１反応器４へと供給される混合ガスの流量Ｑ０に応じて決まる定数である。上記式（３）に示されるように、制御部１は、ガス輸送遅れ時間τ_{delay_T}から計測遅れ時間τ_{delay_M}を差し引いた差分時間を用いて、Ｈ₂の流量Ｑ２を算出している。制御部１は、マスフローコントローラＭＦＣ２を制御することにより、流量Ｑ２のＨ₂を第２反応器７へと供給する。

A: Control constant The control constant A in the above formula (3) is a constant determined according to the flow rate Q0 of the mixed gas supplied to the first reactor 4 by the control unit 1 controlling the mass flow controller MFC0. As shown in the above formula (3), the control unit 1 calculates the flow rate Q2 of _H2 using the difference time obtained by subtracting the measurement delay time τ _{delay_M} from the gas transport delay time τ _{delay_T} . The control unit 1 supplies _H2 at the flow rate Q2 to the second reactor 7 by controlling the mass flow controller MFC2.

FIG. 2 is a flow chart until H ₂ is supplied to the second reactor 7. In the flow shown in FIG. 2, first, the gas analyzer 3 detects the CO ₂ concentration in the mixed gas (step S1). The gas analyzer 3 identifies the gas ratio ξ _M by substituting the detected CO 2 concentration into the above formula (2) (step S2). The control unit 1 calculates the flow rate Q2 of H ₂ to be supplied to the second reactor 7 using the identified gas ratio ξ _M (step S3). The control unit 1 calculates the flow rate Q2 by substituting the identified gas ratio ξ _M , the gas transport delay time _{delay_T} , and the measurement delay time τ _{delay_M} into the above formula (3). The control unit 1 controls the mass flow controller MFC2 to supply H ₂ at the calculated flow rate Q2 to the second reactor 7 (step S4). Thereafter, the control unit 1 determines the end of the process, such as accepting an end operation (step S5). If the control unit 1 has not accepted the end operation (step S5: NO), the control unit 1 repeats the process from step S1 onwards. When the control unit 1 receives an end operation or the like (step S5: YES), it ends various control processes.

Comparative Example
3 is a block diagram of a methane production apparatus 100x and a mixed gas supply unit 50 of a comparative example. The methane production apparatus 100x of the comparative example differs from the methane production apparatus 100 of the first embodiment in that it does not include a delay generation tank 6 and that the control unit 1x calculates the flow rate Q2x of _H2 to be supplied to the second reactor 7 regardless of the gas transport delay time τ _{delay_T} and the like. Therefore, in the comparative example, only the points different from the first embodiment will be described, and a description of the same configuration and control as the first embodiment will be omitted.

The control unit 1x of the comparative example determines the flow rate Q2x of H ₂ by substituting the gas ratio ξ _M identified by the gas analyzer 3 into the following formula (4).

Ａｘ：制御定数
制御定数Ａｘは、第１実施形態の制御定数Ａと同様に、第１反応器４へと供給される混合ガスの流量Ｑ０に応じて決まる定数である。上記式（４）に示されるように、比較例の制御部１ｘは、第１実施形態におけるガス輸送遅れ時間τ_{delay_T}および計測遅れ時間τ_{delay_M}を用いずに、ガス比ξ_Mを用いて流量Ｑ２ｘを算出している。なお、比較例のメタン製造装置１００ｘでは、遅れ生成タンク６がないため、第１反応器４からの排ガスが第２反応器７へと流入するまでの時間が第１実施形態よりも短い。

Ax: control constant The control constant Ax is a constant determined according to the flow rate Q0 of the mixed gas supplied to the first reactor 4, similar to the control constant A in the first embodiment. As shown in the above formula (4), the control unit 1x in the comparative example calculates the flow rate Q2x by using the gas ratio ξ _M without using the gas transport delay time τ _{delay_T} and the measurement delay time τ _{delay_M} in the first embodiment. Note that, in the methane production apparatus 100x in the comparative example, since there is no delay generation tank 6, the time until the exhaust gas from the first reactor 4 flows into the second reactor 7 is shorter than that in the first embodiment.

4 to 6 are diagrams illustrating the effects of the methane production apparatus 100 of the first embodiment and the methane production apparatus 100x of the comparative example. In Fig. 4, a curve CξM is shown which represents the time transition of the gas ratio _ξM of the mixed gas supplied from the mixed gas supply unit 50, with the horizontal axis representing time ( _min ).

5 shows curves Cξ _{_100} and Cξ _{_100x} representing the time transition of the gas ratio of the exhaust gas supplied to the second reactor 7 when the horizontal axis represents time (min) on the same scale as in FIG. 4. The curve Cξ _{_100} shown by a solid line represents the time transition of the gas ratio of the exhaust gas in the methane production apparatus 100 of the first embodiment. The curve Cξ _{_100x} shown by a dashed line represents the time transition of the gas ratio of the exhaust gas in the methane production apparatus 100x of the comparative example.

Fig. 6 shows curves _{CCH4_100 and CCH4_100x representing the time progression of the methane concentration (%) in the product gas generated from the methane production apparatus 100, 100x when the horizontal axis is time (min) on the same scale as in Fig. 4. The curve CCH4_100 shown by} a solid line represents the time progression of the methane concentration in the methane production apparatus 100 of the first embodiment. The curve _{CCH4_100x} shown by a dashed line represents the time progression of the methane concentration in the methane production apparatus 100x of the comparative example.

As shown in Fig. 5, the curve _{Cξ_100} of the first embodiment is closer to the gas ratio of 4.0, which is the target of the methanation reaction, than the curve _{Cξ_100x} of the comparative example. As a result, as shown in Fig. 6, the methane concentration in the generated gas is closer to 100% in the curve _{CCH4_100} of the first embodiment than in the curve _{CCH4_100x} of the comparative example.

As described above, the methane production apparatus 100 of the first embodiment includes the first reactor 4 and the second reactor 7 for producing methane from a mixed gas containing CO ₂ and H ₂ , the gas analyzer 3 for detecting the gas ratio ξ _M of the mixed gas supplied to the first reactor 4, the delay generation tank 6 arranged in the middle of the flow path through which the exhaust gas supplied to the second reactor 7 passes, the downstream gas supply unit 2 for supplying H ₂ to the second reactor 7, and the control unit 1 for controlling the flow rate Q2 of H ₂ supplied to the second reactor 7 using the gas ratio ξ _M detected by the gas analyzer 3. The control unit 1 determines the flow rate Q2 of H 2 supplied to the second reactor 7 using the gas ratio ξ _M identified by the gas analyzer 3, the measurement delay time τ _{delay_M} , and the gas transport delay time τ _{delay_T} . That is, in the methane production apparatus 100 of this embodiment, the flow rate _Q2 of H 2 supplied to the second reactor 7 is determined taking into consideration the measurement delay time τ _{delay_M} required from the detection of the gas ratio ξ _M of the mixed gas by the gas analyzer ₃ until it is identified, and the gas transport delay time τ _{delay_T} required from the detection of the gas ratio ξ M of the mixed gas until the mixed gas flows into the second reactor 7. In this way, by taking the delay time into consideration, the control unit 1 calculates a gas ratio closer to the actual gas ratio of the exhaust gas supplied to the second reactor 7. Thereby, the measurement delay time τ _{delay_M} is offset by the gas transport delay time τ _{delay_T} . As a result, compared to the comparative example in which these delay times are not taken into consideration, as shown in FIG. 5, the gas ratio in the second reactor 7 of this embodiment is closer to the target of 4.0 than the comparative example, and as shown in FIG. 6, the methane concentration in the generated gas is improved. That is, according to the methane production apparatus 100 of this embodiment, even if a mixed gas with an unstable gas ratio ξ _M is supplied to the methane production apparatus 100, the gas ratio in the second reactor 7 can be stabilized to ensure the quality of the methane produced. Furthermore, the capacity of the delayed generation tank 6 is sufficient to delay the inflow of the mixed gas into the second reactor 7 by the time from when the gas analyzer 3 detects the gas ratio ξ _M to when it is identified. Therefore, the size of the delayed generation tank 6 only needs to mitigate the fluctuation of the gas ratio of the exhaust gas supplied to the second reactor 7, and a large capacity like that of a surge tank is not required. As a result, according to the methane production apparatus 100 of this embodiment, the methane production apparatus 100 can be made smaller while ensuring the quality of the methane produced, compared to a methane production apparatus in which a surge tank arranged between the first reactor 4 and the second reactor 7 is used to mitigate the fluctuation of the gas ratio of the mixed gas.

In addition, the control unit 1 of this embodiment calculates the flow rate Q2 of _H2 using the difference time obtained by subtracting the measurement delay time τ _{delay_M} from the gas transport delay time τ _{delay_T} as shown in the above formula (3). Therefore, the control unit 1 can determine the flow rate Q2 of _H2 to be supplied to the second reactor 7 based on a gas ratio that is closer to the actual gas ratio of the exhaust gas supplied to the second reactor 7. This makes it possible to further improve the methane concentration in the generated gas from the methane production apparatus 100.

Second Embodiment
7 is a block diagram of a methane production apparatus 100a and a mixed gas supply unit 50 of the second embodiment. The methane production apparatus 100a of the second embodiment differs from the methane production apparatus 100 of the first embodiment in that it includes an upstream gas supply unit 11 and a mass flow controller MFC1, and that a control unit 1a controls the mass flow controller MFC1 in addition to the mass flow controllers MFC0 and MFC2. Therefore, in the second embodiment, only the points different from the first embodiment will be described, and a description of the same configuration and control as in the first embodiment will be omitted.

7, the methane production apparatus 100a of the second embodiment includes an upstream gas supply unit 11 that additionally supplies _H2 to the first reactor 4, and a mass flow controller MFC1 that adjusts the flow rate of _H2 supplied from the upstream gas supply unit 11 to the first reactor 4. The control unit 1a of the second embodiment uses the gas ratio _ξM acquired by the gas analyzer 3 to control the flow rate (upstream flow rate) Q1 of _H2 supplied from the upstream gas supply unit 11 to the first reactor 4.

Fig. 8 is an explanatory diagram of the flow rate Q1 of _H2 supplied to the first reactor 4. As shown in the table in Fig. 8, the control unit 1a of the second embodiment predetermines the flow rate Q1 of _H2 supplied to the first reactor 4 according to the gas ratio _ξM acquired by the gas analyzer 3. The table in Fig. 8 is a table created in advance by an experiment on the methane production apparatus 100a. In other embodiments, the flow rate Q1 of _H2 may be determined using, for example, the above formula (3), or may be determined by other well-known calculation methods.

The control unit 1a of the second embodiment determines the flow rate Q2a of _H2 (downstream flow rate) to be supplied to the second reactor 7 using the determined flow rate Q1 of H2, a difference time obtained by subtracting the measurement delay time τ _{delay_M} from the gas transport delay time τ _{delay_T} , and the gas ratio ξ _M acquired by the gas analyzer 3. Specifically, the control unit 1a calculates the flow rate Q2a of _H2 by substituting each value into the following formula (5).

Ａａ，Ｂ：制御定数
制御定数Ａａ，Ｂは、第１反応器４へと供給される混合ガスの流量Ｑ０に応じて決まる定数である。

Aa, B: Control Constants The control constants Aa and B are constants that are determined according to the flow rate Q0 of the mixed gas supplied to the first reactor 4.

In the second embodiment, the gas transport delay time τ _{delay_T} is calculated using the following formula (6).

Ｖ_delay：遅れ生成タンクの容積（Ｌ）
ｐ：遅れ生成タンクの運転圧力（ａｔｍ）
Ｃ₁：第１反応器の代表ＣＯ₂転化率
ξ_rep：混合ガスの代表ガス比
第１反応器４の代表ＣＯ₂転化率Ｃ₁および混合ガスの代表ガス比ξ_repは、予め設定される定数である。第２実施形態では、代表ガス比ξ_repとして、混合ガス供給部５０から供給される混合ガスの所定時間内におけるガス比ξ_Mの平均値を用いている。代表ＣＯ₂転化率Ｃ₁は、代表ガス比ξ_repの混合ガスが第１反応器４へと供給された場合に、第１反応器４内において混合ガス中のＣＯ₂がメタンへと転換される割合である。代表ＣＯ₂転化率Ｃ₁および代表ガス比ξ_repは、経験的に前もって定められる値であり、他の実施形態では異なる方法によって定められてもよい。

V _delay : Volume of delay generation tank (L)
p: Operating pressure of the delayed generation tank (atm)
C ₁ : Representative CO ₂ conversion rate of the first reactor ξ _rep : Representative gas ratio of the mixed gas The representative CO ₂ conversion rate C ₁ of the first reactor 4 and the representative gas ratio ξ _rep of the mixed gas are preset constants. In the second embodiment, the average value of the gas ratio ξ _M of the mixed gas supplied from the mixed gas supply unit 50 within a predetermined time is used as the representative gas ratio ξ _rep . The representative CO ₂ conversion rate C ₁ is the ratio of CO ₂ in the mixed gas converted to methane in the first reactor 4 when the mixed gas with the representative gas ratio ξ _rep is supplied to the first reactor 4. The representative CO ₂ conversion rate C ₁ and the representative gas ratio ξ _rep are values that are empirically determined in advance, and may be determined by different methods in other embodiments.

FIG. 9 is a flow chart until H ₂ at the flow rate Q2 is supplied in the second embodiment. In the flow shown in FIG. 9, the gas analyzer 3 detects the CO ₂ concentration in the mixed gas (step S11) and identifies the gas ratio ξ _M (step S12). The control unit 1a determines the flow rate Q1 of H ₂ to be supplied to the first reactor 4 by collating the identified gas ratio ξ _M with the table of FIG. 8 (step S13). The control unit 1a calculates the flow rate Q2a of H 2 to be supplied to the second reactor 7 by substituting the determined flow rate Q1, the identified gas ratio ξ _M , the gas transport delay time _{delay_T} , and the measurement delay time τ _{delay_M} into the above formula (5) (step S14). The control unit _{1a supplies H 2 at} the calculated flow rate Q2a to the second reactor 7 (step S15). Then, the end of the process of step S16 is determined.

As described above, the methane production apparatus 100a of the second embodiment includes the upstream gas supply unit 11 that supplies H 2 to the first reactor 4. The control unit 1a controls the flow rate Q1 of H ₂ supplied from the upstream gas supply unit 11 to the first reactor 4 using the gas ratio ξ _M acquired by the gas analyzer 3. That is, in the second embodiment, H ₂ with the flow rates Q1 and Q2a controlled is supplied to both the first reactor 4 and the second reactor 7. Therefore, in the methane production apparatus 100a of the second embodiment, H ₂ with a rough flow rate Q1 that does not take into account the measurement delay time τ _{delay_M} is supplied to the first reactor 4, and H ₂ with a flow rate Q2a that is finely adjusted taking into account the measurement delay time τ _{delay_M} and the _like is supplied to the second reactor 7. As a result, the gas ratio in the second reactor 7 can be made closer to the target gas ratio. This makes it possible to further improve the methane concentration in the generated gas of the methane production apparatus 100a.

In addition, as shown in the above formula (5), the control unit 1a of the second embodiment determines the flow rate Q2a of H ₂ to be supplied to the second reactor 7 by using the difference time obtained by subtracting the measurement delay time τ _{delay_M} from the gas transport delay time τ _{delay_T} and the flow rate Q1 of H 2 supplied to the first reactor 4. Therefore, the control unit 1a can determine the flow rate Q2a of H ₂ to be supplied to the second reactor 7 based on a gas ratio that is closer to the actual gas ratio of the exhaust gas to be supplied to the second reactor 7. This makes it possible to further improve the _methane concentration in the generated gas from the methane production apparatus 100a of the second embodiment.

<Modifications of the above embodiment>
The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

[Modification 1]
The methane production apparatus 100, 100a of the first and second embodiments is an example of an embodiment of the present invention, and the configuration of the methane production apparatus 100 and the control executed by the methane production apparatus 100 can be modified in various ways. For example, the methane production apparatus 100 does not need to include the two condensers 5, 8 and the surge tank 10, and the first condenser 5 may be provided in a system different from the methane production apparatus 100. The mass flow controllers MFC0, MFC1, and MFC2 are examples of flow rate adjustment devices, and known devices capable of flow rate adjustment can be applied. As the upstream gas supply unit 11 and the downstream gas supply unit 2, a hydrogen tank storing _H2 or the like can be applied, and the upstream gas supply unit 11 and the downstream gas supply unit 2 may be configured by one hydrogen tank. The control units 1, 1a are one control unit, but may be divided into multiple control units and various functions may be divided, or each of the multiple control units may control each unit. The methane production apparatus 100 may include three or more methanation reactors.

Further, instead of the upstream gas supply unit 11 and the downstream gas supply unit 2 that supply H ₂ , an upstream gas supply unit and a downstream gas supply unit that supply CO ₂ may be provided as the adjustment gas supply unit. In the above first and second embodiments, it is assumed that the gas ratio ξ _M of the mixed gas supplied from the mixed gas supply unit 50 is smaller than 4.0, but when the gas ratio ξ _M is 4.0 or more, it is preferable that the upstream gas supply unit and the downstream gas supply unit supply CO ₂ .

Although the gas analyzer 3 detects the concentration of CO ₂ in the mixed gas and identifies the gas ratio ξ _M of the mixed gas, other detectors may be used. For example, instead of the gas analyzer 3, the gas ratio ξ _M may be identified by a device that measures the concentration of H ₂ in the mixed gas, or the concentrations of both CO ₂ and H ₂ may be detected to identify the gas ratio ξ _M. The mixed gas supply unit 50 may not include an adsorber and may supply a mixed gas containing gases other than CO ₂ and H ₂ to the methane production apparatus 100. In this case, the gas analyzer only needs to have a function of acquiring the gas ratio ξ _M of CO ₂ to H ₂ in the mixed gas.

[Modification 2]
FIG. 10 is an explanatory diagram of the delayed generation tank 6b in the modified example. FIG. 10 shows a schematic cross-sectional view of the delayed generation tank 6b in the modified example. The delayed generation tank 6 in the modified example is a tank integrated with the first condenser 5 through which the exhaust gas from the first reactor 4 passes. In the delayed generation tank 6b in the modified example, condensed water accumulates in the tank as generated water, and as the generated water increases, the effective volume V _delay in which the tank can accommodate gas decreases. As shown in FIG. 10, the delayed generation tank 6b in the modified example is provided with a level sensor SN that detects the liquid level of the generated water. Therefore, the effective volume V _delay of the delayed generation tank 6b in this modified example is expressed by the following formula (7) as shown in FIG. 10.

Ｖ_tank：遅れ生成タンク内の全容積
Ｖ_w：遅れ生成タンク内の水量
この変形例では、より正確な遅れ生成タンク６ｂ内の有効容積Ｖ_delayが算出されるため、ガス輸送遅れ時間τ_{delay_T}がより正確に算出され、第２反応器７内のガス比がさらに安定して、メタン製造装置により生成されるメタンの品質が向上する。

V _tank : total volume in the delay generation tank V _w : volume of water in the delay generation tank In this modified example, the effective volume V _delay in the delay generation tank 6b is calculated more accurately, so that the gas transport delay time τ _{delay_T} is calculated more accurately, the gas ratio in the second reactor 7 becomes more stable, and the quality of methane generated by the methane production apparatus is improved.

[Modification 3]
Fig. 11 is an explanatory diagram of a modified delay generation tank 6c. As shown in Fig. 11, the delay generation tank 6c of this modified example is a tank equipped with a mechanism for supplying and draining water from the tank, in contrast to the delay generation tank 6b shown in Fig. 10.

The delay generation tank 6c includes a condenser-integrated tank 66 in which generated water accumulates, a water tank 63 that stores water to be supplied to and drained from the condenser-integrated tank 66, a pump (tank volume adjustment unit) 62 for draining water from the condenser-integrated tank 66 to the water tank 63, a check valve 61 that allows water to flow only from the condenser-integrated tank 66 to the water tank 63, a pump (tank volume adjustment unit) 65 for supplying water from the water tank 63 to the condenser-integrated tank 66, and a check valve 64 that allows water to flow only from the water tank 63 to the condenser-integrated tank 66. In this modification, a control unit (not shown) controls the pumps 62 and 65 in accordance with the flow rate Q0 of the mixed gas supplied to the first reactor 4. As a result, the pumps 62 and 65 change the amount of water in the condenser-integrated tank 66, thereby changing the effective volume V _delay in the tank. In this modification, the pumps 62 and 65 reduce the effective volume V _delay in the tank as the flow rate Q0 of the mixed gas supplied to the first reactor 4 decreases.

The pumps 62, 65 of this modification reduce the effective volume _Vdelay in the tank as the flow rate Q0 of the mixed gas supplied from the mixed gas supply unit 50 to the first reactor 4 decreases. According to this modification, it is possible to equalize the gas transport delay time _τdelay when the flow rate Q0 of the mass flow controller MFC0 is at its maximum (full load) and when the flow rate Q0 is low (low load). This makes it possible to improve the methane concentration in the product gas of the methane production apparatus even at low load.

In addition, in the delay generation tank 6c of this modified example, the pumps 62, 65 change the amount of water in the condenser integrated tank 66, thereby changing the effective volume _Vdelay in the condenser integrated tank 66. Therefore, in the delay generation tank 6c of this modified example, the volume of the effective volume _Vdelay can be easily changed by using water.

In the delay generation tank 6c of this modification, the volume of the effective volume _Vdelay may be changed using a liquid other than water. Also, without using a liquid, and without being integrated with a condenser, the volume of the effective volume _Vdelay may be changed by moving the bottom of the tank up and down relative to the side.

[Modification 4]
12 is an explanatory diagram of the flow rate Q2d of _H2 supplied to the second reactor 7 in the modified example. In this modified example, the flow rate Q2d of _H2 is determined by a method different from that in the first and second embodiments. Specifically, the flow rate Q2d of _H2 is determined according to the map shown in FIG. 12 using the following formulas (8) and (9).

図１２では、ハッチングの濃さにより流量Ｑ２ｄの大小が示されており、ハッチングが濃いほど流量Ｑ２ｄが多い。なお、図１２における実線は、流量Ｑ２ｄが同じである等高線である。図１２に示されるように、上記式（８），（９）の算出値Ｘ，Ｙが小さいほど、流量Ｑ２ｄが大きくなる。

In Fig. 12, the magnitude of the flow rate Q2d is indicated by the density of the hatching, and the thicker the hatching, the greater the flow rate Q2d. Note that the solid lines in Fig. 12 are contour lines with the same flow rate Q2d. As shown in Fig. 12, the smaller the calculated values X and Y of the above formulas (8) and (9), the greater the flow rate Q2d.

In the first and second embodiments, the above formulas (3) and (5) are given as methods for calculating the flow rates Q2 and Q2a of H2 supplied to the second reactor 7, but these calculation methods are merely examples, and known calculation methods and determination methods such as a method using the map of Fig. 12 can be applied within the range of using the gas ratio _ξM , the measurement delay time τ _{delay_M} , and the gas transport delay time τ _{delay_T} . Similarly, the gas transport delay time τ _{delay_T} shown in formula (6) of the second embodiment may also be obtained by other methods.

Although this aspect has been described above based on the embodiment and modified examples, the embodiment of the above-mentioned aspect is intended to facilitate understanding of this aspect and does not limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

1, 1a, 1x...control unit 2...downstream gas supply unit 3...gas analyzer (gas ratio acquisition unit)
4...First reactor (first methanation reactor)
5...First condenser 6, 6b, 6c...Delay generation tank (tank)
7...Second reactor (second methanation reactor)
8: Second condenser 10: Surge tank 11: Upstream gas supply section 50: Mixed gas supply section 61, 64: Check valve 62, 65: Pump (tank volume adjustment section)
63... Water tank 66... Condenser integrated tank 100, 100a, 100x... Methane production device A, Aa, Ax, B... Control constants _C1 ... Representative _CO2 conversion rate of first reactor ξ _rep ... Representative gas ratio of mixed gas ξ _M ... Gas ratio of mixed gas Cξ _M ... Time transition of gas ratio of mixed gas _{CCH4_100} , _{CCH4_100x} ... Time transition of methane concentration _{Cξ_100} , _{Cξ_100x} ... Time transition of gas ratio of exhaust gas MFC0... Mass flow controller (flow rate adjustment unit)
MFC1, MFC2...Mass flow controller Q0...Flow rate of mixed gas Q1...Flow rate of _H2 supplied to the first reactor Q2, Q2a, Q2d, Q2x...Flow rate of _H2 supplied to the second reactor SN...Level sensor V _delay ...Effective volume of delay generation tank V _tank ...Total volume in delay generation tank V _w ...Amount of water in delay generation tank X _CO2 ... _CO2 concentration in mixed gas τ _{delay_M} ...Measurement delay time τ _{delay_T} ...Gas transport delay time (transport delay time)

Claims (6)

1. A methane production apparatus comprising:
a first methanation reactor for producing methane from a mixed gas of carbon dioxide and hydrogen;
a gas ratio acquisition unit that acquires a gas ratio of the mixed gas supplied to the first methanation reactor, the gas ratio being a ratio of carbon dioxide to hydrogen;
a flow rate adjusting unit that adjusts a flow rate of the mixed gas supplied to the first methanation reactor;
a second methanation reactor to which the exhaust gas discharged from the first methanation reactor is supplied and which produces methane from the exhaust gas;
a tank disposed in a flow path through which the exhaust gas discharged from the first methanation reactor passes and through which the exhaust gas supplied to the second methanation reactor passes ;
a downstream gas supply section for supplying carbon dioxide or hydrogen to the second methanation reactor;
A control unit for controlling a flow rate of carbon dioxide or hydrogen supplied to the second methanation reactor;
Equipped with
The control unit determines a downstream flow rate, which is the flow rate of carbon dioxide or hydrogen supplied from the downstream gas supply unit to the second methanation reactor, using the gas ratio acquired by the gas ratio acquisition unit, a transportation delay time of the exhaust gas generated by the tank, and a measurement delay time that occurs from the time the gas ratio acquisition unit acquires the gas ratio to the time the gas ratio is identified. The methane production apparatus according to claim 1,
The control unit is
a gas ratio acquisition unit that acquires a difference time obtained by subtracting a measurement delay time from a transport delay time and a gas ratio acquired by the gas ratio acquisition unit at a time that is the difference time before the present, said downstream flow rate being determined. The methane production apparatus according to claim 1, further comprising:
an upstream gas supply unit for supplying carbon dioxide or hydrogen to the first methanation reactor;
The control unit uses the gas ratio acquired by the gas ratio acquisition unit to determine an upstream flow rate, which is the flow rate of carbon dioxide or hydrogen supplied from the upstream gas supply unit to the first methanation reactor. The methane production apparatus according to claim 3,
The control unit is
a gas ratio acquisition unit that acquires a difference time obtained by subtracting a measurement delay time from a transport delay time, the gas ratio acquired by the gas ratio acquisition unit at a time that is the difference time before the present, and the upstream flow rate, the methane production apparatus determining the downstream flow rate. The methane production apparatus according to any one of claims 1 to 4, further comprising:
a tank volume adjusting unit that reduces a volume of the tank capable of accommodating gas as a flow rate of the mixed gas supplied to the first methanation reactor decreases. The methane production apparatus according to claim 5,
The tank volume adjustment unit changes the volume of gas that can be stored in the tank by changing the amount of water in the tank.

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