Estimation device and gas composition control device

Abstract

To provide a technique which reduces a measurement delay of the density of a chemical species contained in mixed gas in an estimation device.SOLUTION: An estimation device comprises: an inlet flow rate detection unit which detects an inlet display flow rate Qdisplay_tank_in being a display flow rate of gas supplied to an inlet of a gas tank; an outlet flow rate detection unit which detects an outlet display flow rate Qdisplay_tank_out being a display flow rate of gas at an outlet of the gas tank; a pressure detection unit which detects a tank pressure measurement value Ptank being the pressure in the gas tank; a temperature detection unit which detects a tank temperature measurement value Ttank being the temperature in the gas tank; and an estimation unit which estimates the density XA_tank of a chemical species A and the density XB_tank of a chemical species B in the gas tank by using the inlet display flow rate Qdisplay_tank_in, the outlet display flow rate Qdisplay_tank_out, the tank pressure measurement value Ptank and the tank temperature measurement value Ttank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an estimation device. [Background technology]

[0002] Estimation devices for estimating the concentration of chemical species in a mixed gas have been known for some time. These estimation devices are applied, for example, to the methane production process, which produces methane gas through the chemical reaction of carbon dioxide and hydrogen, and are used to determine the composition of a mixed gas containing carbon dioxide and hydrogen. In such a methane production process, in order to stabilize the quality of methane gas, it is necessary to continuously measure the concentrations of carbon dioxide and hydrogen in the mixed gas using a gas concentration measuring device, and if these concentrations fall outside a predetermined range, it is necessary to add more carbon dioxide or hydrogen to control the concentrations. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-142806 [Patent Document 2] Japanese Patent Publication No. 2020-158403 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, gas concentration measuring devices may take several tens of seconds to determine the concentration of the gas being measured. In the methane production process described above, if there are rapid changes in the concentration of carbon dioxide or hydrogen in the mixed gas, the concentration control may not be able to keep up, and the quality of the methane gas may not be stable.

[0005] The present invention was made to solve the above-mentioned problems, and aims to provide a technique for estimating the concentration of chemical species contained in a mixed gas in a short time using an estimation device. [Means for solving the problem]

[0006] The present invention has been made to solve at least a part of the above-described problems and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided an estimation device for estimating the composition of a mixed gas containing two different chemical species A and chemical species B. This estimation device is the inlet display flow rate Q of the gas at the inlet of the gas tank of the gas supplied from the supply source of the mixed gas to the gas tank display_tank_in An inlet flow rate detection unit that detects, and an outlet display flow rate Q that is the displayed flow rate of the gas at the outlet of the gas tank display_tank_out An outlet flow rate detection unit that detects, a tank pressure measurement value P that is a measured value of the pressure in the gas tank tank A pressure detection unit that detects, a tank temperature measurement value T that is a measured value of the temperature in the gas tank tank A temperature detection unit that detects, the inlet display flow rate Q display_tank_in And the outlet display flow rate Q display_tank_out And the tank pressure measurement value P tank And the tank temperature measurement value T tank Using these, the concentration X of the chemical species A at the inlet of the gas tank A_tank_in And the concentration X of the chemical species B B_tank_in , The concentration X of the chemical species A in the gas tank A_tank And the concentration X of the chemical species B B_tank , The actual flow rate Q at the inlet of the gas tank real_tank_in , And the actual flow rate Q at the outlet of the gas tank real_tank_out , An estimation unit that estimates at least one of them.

[0008] According to this configuration, the estimation unit uses the inlet display flow rate Q of the inlet flow rate detection unit display_tank_in And the outlet display flow rate Q of the outlet flow rate detection unit display_tank_out And the tank pressure measurement value P of the pressure detection unit tank And the tank temperature measurement value T of the temperature detection unit tank To determine the concentration X of the chemical species A in the gas tank A_tank And the concentration X of the chemical species B B_tankThis allows for the estimation of various factors, such as the concentration of a chemical species. This makes it possible to estimate the concentration of a chemical species in a relatively short time, compared to gas analyzers that take several tens of seconds to determine the concentration of the target gas.

[0009] (2) In the estimation device of the above form, the estimation unit uses equations (1) and (2) to determine the actual flow rate Q at the inlet of the gas tank. real_tank_in [slm] is estimated, and the concentration X of chemical species A at the inlet of the gas tank is calculated using equations (3) and (4). A_tank_in [mol%] and the concentration X of the chemical species B. B_tank_in [mol%] may be estimated.

number

number

number

number

[0010] (3) In the estimation device of the above form, the estimation unit uses formula (5) to determine the concentration X of chemical species A at the inlet of the gas tank. A_tank_in [mol%] and the concentration X of the chemical species B. B_tank_in [mol%] may be estimated.

number

[0011] (4) In the estimation device of the above form, the estimation unit uses equation (6) to determine the control constant C of the outlet flow detection unit. real_tank_out [-] is estimated, and using equation (7), the actual flow rate Q at the outlet of the gas tank is calculated. real_tank_out You may estimate [slm].

number

number

[0012] (5) In the estimation device of the above form, the estimation unit uses equation (8) to determine the number of moles n of gas in the gas tank tank [-] is estimated, and the concentration X of chemical species A in the gas tank is calculated using equations (9) and (10). A_tank [mol%] and the concentration X of the chemical species B. B_tank [mol%] may be estimated.

number

number

number

[0013] (6) In the estimation device of the above form, a regulating gas supply unit is provided downstream of the outlet of the gas tank and supplies a gas containing one of the chemical species A and the chemical species B, and the concentration X of the chemical species A in the gas tank A_tank and the concentration X of the aforementioned chemical species B B_tank , the actual flow rate Q at the inlet of the gas tank real_tank_in , and the actual flow rate Q at the outlet of the gas tank real_tank_outThe configuration may include a control unit that changes the flow rate of the gas supplied by the regulating gas supply unit according to at least one of the following: A_tank and the concentration X of chemical species B B_tank The flow rate of the gas supplied by the adjustment gas supply unit is changed using methods such as [specific methods]. This allows for the estimation of the concentration of the target gas in a relatively short time, and therefore, even if the gas concentration changes rapidly, the desired concentration can be quickly achieved.

[0014] (7) In the estimation device of the above form, the adjustment gas supply unit supplies a gas containing the chemical species A, and the control unit may change the flow rate of the gas containing the chemical species A supplied by the adjustment gas supply unit to a flow rate calculated using formula (11).

number

[0015] (8) In the estimation device of the above form, the adjustment gas supply unit supplies a gas containing the chemical species B, and the control unit may change the flow rate of the gas containing the chemical species B supplied by the adjustment gas supply unit to a flow rate calculated using formula (12).

number

[0016] Furthermore, the present invention can be realized in various forms, for example, as a mixed gas supply system including an estimation device, a control method for these devices and systems, a computer program for executing a gas concentration estimation method in these devices and systems, a server device for distributing the computer program, and a non-temporary storage medium storing the computer program. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing the general configuration of the estimation device according to the first embodiment. [Figure 2] This is the first flowchart of the gas composition control method. [Figure 3] This is the second flowchart for the gas composition control method. [Figure 4] This figure illustrates the results of an evaluation test of the gas composition estimation method according to the first embodiment. [Figure 5] This is a schematic diagram showing the general configuration of the estimation device for the comparative example. [Figure 6] This diagram illustrates the characteristics of the comparative gas composition estimation method. [Modes for carrying out the invention]

[0018] <First Embodiment> Figure 1 is a schematic diagram showing the general configuration of the estimation device of the first embodiment. The estimation device 1 of this embodiment is included in a methane production system 5 that produces methane (CH4) from a mixed gas of carbon dioxide (CO2) and hydrogen (H2). The methane production system 5 comprises a mixed gas supply unit 6, a gas tank 7, a methane reactor 8, and the estimation device 1. The mixed gas supply unit 6 supplies a mixed gas consisting of CO2 and H2 to the methane reactor 8 via the gas tank 7 and the estimation device 1. The estimation device 1 controls the composition of the mixed gas supplied to the methane reactor 8 (combination of CO2 concentration and H2 concentration) so that both CO2 and H2 react stably without excess or deficiency. As a result, the methane reactor 8 can produce stable, high-quality CH4. In other words, the estimation device 1 has the function of mitigating and stabilizing fluctuations in gas concentration so that the composition of the mixed gas does not change over time.

[0019] The estimation device 1 comprises a first flow path 11, a second flow path 12, an inlet flow rate detection unit 21, an outlet flow rate detection unit 22, a pressure gauge 23, a thermometer 24, a regulating gas supply unit 31, a supply flow path 32, and a control unit 40. Based on the estimated CO2 concentration and H2 concentration of the mixed gas, the estimation device 1 adjusts the composition of the mixed gas flowing through the second flow path 12 using the regulating gas supplied by the regulating gas supply unit 31.

[0020] The first channel 11 is a channel connecting the mixed gas supply unit 6 and the gas tank 7, through which the mixed gas supplied by the mixed gas supply unit 6 flows. The mixed gas flowing through the first channel 11 is temporarily stored in the gas tank 7, where it is rectified and homogenized. The second channel 12 connects the gas tank 7 and the methane reactor 8, supplying the mixed gas stored in the gas tank 7 to the methane reactor 8.

[0021] The inlet flow rate detection unit 21 is a thermal mass flow meter (T-MFM) installed in the first flow path 11. The inlet flow rate detection unit 21 detects temperature changes due to heat transfer with the gas flowing through the first flow path 11 and calculates the flow rate of the gas flowing through the first flow path 11. Here, the flow rate calculated by the inlet flow rate detection unit 21 is called the "inlet display flow rate". The inlet flow rate detection unit 21 is electrically connected to the control unit 40, which will be described later, and outputs the calculated "inlet display flow rate" to the control unit 40.

[0022] The outlet flow rate detection unit 22 is a thermal mass flow meter installed in the second flow path 12. The outlet flow rate detection unit 22 detects temperature changes due to heat transfer with the gas flowing through the second flow path 12 and calculates the flow rate of the gas flowing through the second flow path 12. Here, the flow rate calculated by the outlet flow rate detection unit 22 is called the "outlet display flow rate". The outlet flow rate detection unit 22 is electrically connected to the control unit 40 and outputs the calculated "inlet display flow rate" to the control unit 40.

[0023] The pressure gauge 23 is installed in the gas tank 7 and detects the pressure inside the gas tank 7. Here, the pressure detected by the pressure gauge 23 is referred to as the "tank pressure measurement value". The pressure gauge 23 is electrically connected to the control unit 40 and outputs the detected "tank pressure measurement value" to the control unit 40.

[0024] The thermometer 24 is installed in the gas tank 7 and detects the temperature inside the gas tank 7. Here, the temperature detected by the thermometer 24 is referred to as the "tank temperature measurement value". The thermometer 24 is electrically connected to the control unit 40 and outputs the detected "tank temperature measurement value" to the control unit 40.

[0025] The regulating gas supply unit 31 is connected to the second flow path 12 via the supply flow path 32. The regulating gas supply unit 31 is electrically connected to the control unit 40. In this embodiment, the regulating gas supply unit 31 stores CO2 gas and H2 gas separately and supplies either CO2 gas or H2 gas to the second flow path 12 in response to a command from the control unit 40. The regulating gas supply unit 31 may store either CO2 gas or H2 gas, but not both.

[0026] The control unit 40 includes a storage medium consisting of a hard disk or the like, and a CPU that loads a computer program stored in ROM into RAM and executes it. The control unit 40 is electrically connected to an inlet flow rate detection unit 21, an outlet flow rate detection unit 22, a pressure gauge 23, a thermometer 24, and a regulating gas supply unit 31. The control unit 40 uses the displayed flow rates of the inlet flow rate detection unit 21, the displayed flow rates of the outlet flow rate detection unit 22, the detected values ​​of the pressure gauge 23, and the detected values ​​of the thermometer 24 to estimate at least one of the following: the CO2 concentration and H2 concentration at the inlet of the gas tank 7, the CO2 concentration and H2 concentration inside the gas tank 7, the actual flow rate of the mixed gas at the inlet of the gas tank 7, and the actual flow rate of the mixed gas at the outlet of the gas tank 7. The control unit 40 changes the flow rate of the gas supplied by the regulating gas supply unit 31 according to at least one of the CO2 concentration and H2 concentration inside the gas tank 7, the actual flow rate of the mixed gas at the inlet of the gas tank 7, and the actual flow rate of the mixed gas at the outlet of the gas tank 7.

[0027] Next, the details of the gas composition control method of this embodiment will be described. In the gas composition control method of this embodiment, when the production of CH4 is started in the methane production system 5, the composition of the mixed gas of CO2 and H2 supplied by the mixed gas supply unit 6 is controlled. As a result, the methane reactor 8 is supplied with a mixed gas of a predetermined composition, so that the methane reactor 8 can produce CH4 of a stable quality with a constant concentration. The gas composition control method of this embodiment consists of a gas composition estimation method for estimating the composition of the mixed gas in the gas tank 7, and a gas composition adjustment method for adjusting the composition of the mixed gas supplied to the methane reactor 8 using the estimated composition of the mixed gas in the gas tank 7.

[0028] Figure 2 is a flowchart of the first gas composition control method, which is a flowchart of the gas composition estimation method. The gas composition estimation method is started when the methane production system 5 starts producing CH4. In the gas composition estimation method, the composition and pressure in the gas tank 7 immediately before the start are first obtained (step S11). In step S11, the control unit 40 obtains the composition and pressure in the gas tank 7 immediately before the gas composition control method is started as initial values. In this embodiment, the control unit 40 obtains the CO2 concentration, H2 concentration, and tank pressure measurement value in the gas tank 7 that were measured before the gas composition control method started.

[0029] In step S11, the composition and pressure inside the gas tank 7 acquired by the control unit 40 can be expressed as follows, where t[s] is the current time and Δt[s] is the control period of the estimation device 1. For convenience, the time before the gas composition control method is started is taken as the current time minus the control period of the estimation device 1. In step S11, the control unit 40 sets the internal volume V of the gas tank 7 as a setting value for the estimation device 1. tank [L] will also be retrieved. CO2 molar concentration in gas tank 7: X CO2_tank (t-Δt)[mol%] H2 molar concentration in gas tank 7: X H2_tank (t-Δt)[mol%] Tank pressure detection value: P tank [kPa]

[0030] Next, the actual gas flow rate at the gas tank outlet is estimated from the composition inside the gas tank 7 before the start (step S12). In step S12, the control unit 40 first uses the initial values ​​obtained in step S11, specifically the CO2 molar concentration X inside the gas tank 7. CO2_tank (t-Δt) and H2 molar concentration X H2_tank Based on (t-Δt), the conversion coefficient C of the outlet flow detection unit 22 at the current time t is calculated using equation (6). real_tank_out Estimate [-].

number

[0031] Here, we will explain the conversion coefficient for a thermal mass flow meter. A thermal mass flow meter generally has a main channel through which most of the target gas flows and a bypass channel through which the remainder of the target gas flows. The thermal mass flow meter calculates the flow rate based on the extent to which the target gas flowing through the bypass channel carries heat away from the heating element built into the thermal mass flow meter. For this reason, a conversion coefficient for calculating the flow rate is set for each type of target gas, calibrated according to the relationship between the flow division ratio between the main channel and the bypass channel and the constant-pressure specific heat of the target gas. In other words, the conversion coefficient of a thermal mass flow meter will differ if the type of target gas changes. Therefore, in this embodiment, in order to correspond to a mixed gas with a changing composition, the conversion coefficient of the thermal mass flow meter is calculated according to the gas composition using equation (6). The conversion coefficient C of the outlet flow rate detection unit 22 at the current time t calculated by equation (6) real_tank_out This shows the conversion coefficient for measuring the flow rate of the gas flowing through the second flow path 12 at time t, expressed as the conversion coefficient at time (t-Δt). The conversion coefficient of the thermal mass flow meter in this embodiment corresponds to the "control constant" described in the claims.

[0032] In step S12, the conversion coefficient C of the outlet flow detection unit 22 at the current time t, estimated by equation (6), is further calculated. real_tank_out Based on this, the actual flow rate Q of the mixed gas at the gas tank outlet is calculated using equation (7). real_tank_out Estimate [slm].

number

[0033] Next, the change amount of the number of moles of the gas in the gas tank 7 is estimated from the pressure change in the gas tank 7 (step S13). In step S13, the control unit 40 uses the measured tank pressure value P of the pressure gauge 23 tank [kPa] to estimate the change amount of the number of moles of the gas in the gas tank 7, Δn tank [mol] using Equation (1).

Equation

[0034] Next, the actual flow rate of the gas at the gas tank inlet is estimated from the actual flow rate of the gas at the gas tank outlet and the change amount of the number of moles in the gas tank 7 (step S14). In step S14, the control unit 40 uses the actual flow rate Q of the gas at the gas tank outlet estimated in step S12 real_tank_out and the change amount of the number of moles Δn in the gas tank 7 estimated in step S13 tank to estimate the actual flow rate Q of the gas at the gas tank inlet using Equation (2). real_tank_in [slm].

Equation

[0035] Next, the conversion coefficient of the inlet flow rate detection unit 21 at the current time is estimated based on the actual flow rate of the gas at the gas tank inlet and the inlet display flow rate of the inlet flow rate detection unit 21 (step S15). In step S15, the control unit 40 uses the actual flow rate Q of the gas at the gas tank inlet estimated in step S14 real_tank_in and the inlet display flow rate Q of the inlet flow rate detection unit 21 display_tank_in [slm] to obtain the conversion coefficient C of the inlet flow rate detection unit 21 at the current time t real_tank_in [-] using Equation (3).

Number

[0036] Next, based on the conversion coefficient of the inlet flow rate detection unit 21 at the current time, the composition of the gas at the gas tank inlet is estimated (Step S16). In Step S16, the control unit 40 uses the conversion coefficient C real_tank_in of the inlet flow rate detection unit 21 at the current time t estimated in Step S15, and uses Equations (4) and (5) to estimate the CO2 molar concentration X CO2_tank_in (t - Δt) [mol%] and the H2 molar concentration X H2_tank_in (t - Δt) [mol%] at the gas tank inlet. Note that Equation (5) is an equation indicating that the mixed gas is composed only of CO2 gas and H2 gas.

Number

Number

[0037] Next, based on the detected pressure value in the gas tank 7, the change amount of the number of moles in the gas tank 7, and the composition of the gas at the gas tank inlet, the composition in the gas tank 7 is estimated (Step S17). In Step S17, the control unit 40 first uses Equation (8) based on the tank pressure measurement value P tank [kPa] to estimate the number of moles n tank [mol] in the gas tank 7.

Number

[0038] In step S17, the change in the number of moles in the gas tank 7 is Δn. tank [mol] and the composition of the gas at the gas tank inlet (CO2 molar concentration at the gas tank inlet X CO2_tank_in (t-Δt) and H2 molar concentration X H2_tank_in Based on (t-Δt), the molar concentration of CO2 in gas tank 7 is calculated using equations (9) and (10). CO2_tank (t) [mol%] and H2 molar concentration X H2_tank Estimate (t)[mol%].

number

number

[0039] The gas composition estimation method shown in Figure 2 proceeds to step S17, after which the control cycle Δt of the estimation device 1 has elapsed (step S18), and then the actual gas flow rate Q at the gas tank outlet is again determined. real_tank_out The actual gas flow rate Q at the gas tank outlet is estimated (step S12). real_tank_out The "composition in the gas tank 7 immediately prior to" needed to estimate this is the CO2 molar concentration X in the gas tank 7 estimated in step S17 before proceeding to step S12. co2_tank and H2 molar concentration X H2_tank This is used.

[0040] Figure 3 is a second flowchart of the gas composition control method, and is a flowchart of the gas composition adjustment method. In the gas composition adjustment method, once the gas composition in the gas tank 7 is estimated in step S17 described above, the adjustment gas supply unit 31 supplies adjustment gas to the second flow path 12 according to the estimation result.

[0041] In the gas composition adjustment method, first, the flow rate of the chemical species to be supplied to the second flow path 12 is calculated from the gas composition in the gas tank 7 (step S19). In step S19, the control unit 40 calculates the CO2 molar concentration X in the gas tank 7 estimated in step S17. co2_tank and H2 molar concentration X H2_tankAnd the actual gas flow rate Q at the gas tank outlet estimated in step S12 real_tank_out Based on this, the flow rate of CO2 gas is calculated using equation (11), and the flow rate of H2 gas is calculated using equation (12).

number

number

[0042] Next, a command to supply a predetermined chemical species of gas to the second flow path 12 is output to the regulating gas supply unit 31 (step S20). In step S20, the control unit 40 outputs a command to the regulating gas supply unit 31 to supply to the second flow path 12 based on the flow rate calculated in step S19. Specifically, the flow rate Q of CO2 gas calculated in step S20 CO2 , or the flow rate Q of H2 gas H2 One of these is supplied to the second flow path 12. This makes it possible to set the composition of the gas supplied to the methane reactor 8 to the target H2 / CO2 composition.

[0043] Next, the effects of the gas composition estimation method using the estimation device 1 of this embodiment will be described. Here, the time change of the gas composition estimated by the gas composition estimation method of this embodiment and the time change of the actual gas composition were measured experimentally and compared.

[0044] Figure 4 illustrates the results of an evaluation test of the gas composition estimation method of the first embodiment. In Figure 4, the horizontal axis shows time, and the vertical axis shows the H2 / CO2 (=X) in the gas tank 7. H2_tank / X co2_tankFigure 4 shows the measured (true) H2 / CO2 values ​​in the gas tank 7 as a solid line, and the estimated values ​​by the gas composition estimation method of this embodiment as a dotted line. As shown in Figure 4, it became clear that the estimated values ​​fluctuate in the same way as the measured values. Therefore, it became clear that the gas composition estimation method of this embodiment can accurately predict the H2 / CO2 in the gas tank 7.

[0045] In manufacturing processes that produce gas products through chemical reactions, precisely controlling the composition of the raw material gases is necessary to maintain a high level of quality in the generated gases. For example, the CH4 gas produced in a methane production process is strongly influenced by the H2 / CO2 ratio of the raw material gas. Specifically, if the H2 / CO2 ratio of the raw material gas is 4.0 and the CO2 conversion rate is 99%, the CH4 concentration in the generated gas will be 95%. However, when the H2 / CO2 ratio is 4.1, even with a CO2 conversion rate of 99%, the CH4 concentration in the generated gas will drop to 87%. Thus, to guarantee the quality of the generated gas, it is necessary to precisely control and stabilize the composition of the raw material gases.

[0046] Furthermore, when the target chemical reaction requires two or more types of gases as raw material gases, the gases of each type of gas are not necessarily supplied separately and independently. In some cases, a mixed gas, in which the gases of the chemical types are already mixed, may be supplied to the chemical reactor as raw material. In this case, if the composition of the mixed gas is suitable for the target chemical reaction and is stable over time, the mixed gas can be supplied directly to the reactor. However, for example, when trying to make effective use of gases discharged from other processes, such conditions are difficult to meet, and the composition of the mixed gas fluctuates over time, so it is necessary to adjust it in some way.

[0047] Figure 5 is a schematic diagram showing the general configuration of the estimation apparatus of the comparative example. The chemical reaction system 2 shown in Figure 5 includes a mixed gas supply unit 6, a gas tank 7, a methanation reactor 8, and an estimation apparatus 90. The estimation apparatus 90 of the comparative example includes a first mass flow controller (first MFC) 91, a gas analyzer 92, a regulating gas supply unit 93, and a second mass flow controller (second MFC) 94. In the chemical reaction system 2, the composition of the mixed gas flowing through the second flow path 12 is measured by the gas analyzer 92, and the first mass flow controller 91 and the second mass flow controller 94, which adjusts the flow rate of the mixed gas supplied by the regulating gas supply unit 93, are controlled according to the difference between the measurement result and the target H2 / CO2 value of the mixed gas. This sets the composition of the mixed gas supplied to the methanation reactor 8 to the target H2 / CO2 value. However, measurement of gas concentration by the gas analyzer 92 is prone to measurement delays.

[0048] Figure 6 illustrates the characteristics of the gas composition estimation method for the comparative example. Generally, gas analyzers take several tens of seconds to identify the analysis results ("measurement delay" shown in Figure 6(a)). Therefore, if the change in H2 / CO2 of the mixed gas is as steep as between time t1 and time t2 in Figure 6(a), there is a risk of supplying adjustment gas based on incorrect information, and fluctuations in H2 / CO2 will remain at the inlet of the methane reactor 8 (indicated by A1 in Figure 6(b)). If fluctuations in H2 / CO2 remain, the composition of the mixed gas will not easily reach a value suitable for the desired chemical reaction, nor will it be stable.

[0049] Furthermore, gas analyzers capable of continuously measuring gas concentration are generally expensive. Additionally, because gas analyzers require the extraction of a portion of the gas supplied to the reactor, exhausting the extracted raw material gas results in a loss of raw material gas. Moreover, since concentration measurements within the gas analyzer are generally performed at atmospheric pressure, recycling the extracted raw material gas requires repressurization using a blower or compressor. This necessitates power and results in energy loss.

[0050] According to the estimation device 1 of this embodiment described above, the control unit 40 controls the inlet display flow rate Q of the inlet flow rate detection unit 21. display_tank_in And the outlet flow rate displayed Q of the outlet flow rate detection unit 22. display_tank_out And the tank pressure measurement value P from pressure gauge 23. tank And the tank temperature measurement value T from thermometer 24 tank Using this, the molar concentration of CO2 in gas tank 7 is X CO2_tank and H2 molar concentration X B_tank This allows for the estimation of various factors, such as the target gas concentration. Compared to gas analyzers that take several tens of seconds to determine the target gas concentration, this method allows for the estimation of the target gas concentration in a relatively short time.

[0051] Furthermore, according to the estimation device 1 of this embodiment, the flow rate of the mixed gas is detected by the inlet flow rate detection unit 21 and the outlet flow rate detection unit 22, which are thermal mass flow meters, and the pressure inside the gas tank 7 is detected by the pressure gauge 23. Unlike gas analyzers, thermal mass flow meters and pressure gauges have a measurement delay of a sufficiently small order of sub-seconds. Therefore, the CO2 molar concentration X inside the gas tank 7 can be detected. CO2_tank and H2 molar concentration X B_tank These factors reduce measurement delays, and also minimize delays in H2 / CO2 control using the gas composition control method. Therefore, the composition of the mixed gas supplied to the methanation reactor 8 can be stabilized.

[0052] Furthermore, according to the estimation device 1 of this embodiment, the thermal mass flowmeters used as the inlet flow detection unit 21 and the outlet flow detection unit 22 are less expensive than gas analyzers. This makes it possible to create a gas concentration estimation device at a lower cost.

[0053] Furthermore, according to the estimation device 1 of this embodiment, the thermal mass flow meter used as the inlet flow detection unit 21 and the outlet flow detection unit 22 detects the flow rate using a portion of the mixed gas, but the mixed gas used for detection is supplied to the methane reactor 8. As a result, unlike gas analyzers that discard a portion of the mixed gas, no loss of the raw material mixed gas occurs due to the estimation of the gas concentration. Moreover, since the thermal mass flow meter detects the flow rate by directly utilizing the flow of the mixed gas, it does not require pressurizing the gas used for gas concentration detection, unlike gas analyzers that generally detect gas concentration at atmospheric pressure. Therefore, CH4 gas can be produced more economically.

[0054] Furthermore, according to the estimation device 1 of this embodiment, the control unit 40 uses equations (1) and (2) to determine the tank pressure measurement value P tank Based on the time variation, the actual flow rate Q at the inlet of gas tank 7 is determined. real_tank_in The control unit 40 estimates the actual flow rate Q at the inlet of the gas tank 7 using equations (3) and (4). real_tank_in and inlet display flow rate Q display_tank_in Based on this, the molar concentration of CO2 at the inlet of gas tank 7 is X CO2_tank_in and H2 molar concentration X H2_tank_in This allows us to estimate the composition of the mixed gas at the inlet of the gas tank 7 by using the inlet flow detection unit 21 and the pressure gauge 23.

[0055] Furthermore, according to the estimation device 1 of this embodiment, since the mixed gas consists of two types of gases, CO2 gas and H2 gas, in addition to equation (4), equation (5), in which the sum of the molar concentration of CO2 and the molar concentration of H2 equals 100, is used to estimate the concentration X of chemical species A at the inlet of the gas tank. A_tank_in and the concentration X of chemical species B B_tank_in This allows us to estimate the composition of a mixed gas consisting of two different chemical species.

[0056] Furthermore, according to the estimation device 1 of this embodiment, the control constant C of the outlet flow rate detection unit 22 at the current time is calculated using equations (6) and (7). real_tank_outAnd the conversion coefficient C of the outlet flow rate detection unit 22 during calibration. calib_tank_out Based on the ratio, the actual flow rate Q at the outlet of gas tank 7 real_tank_out This allows us to estimate the actual flow rate Q at the inlet of the gas tank 7 using equation (2). real_tank_in This can be easily estimated.

[0057] Furthermore, according to the estimation device 1 of this embodiment, the control unit 40 uses equation (8) to determine the number of moles n of gas in the gas tank. tank The control unit 40 estimates the molar concentration of CO2 at the inlet of the gas tank 7 using equations (9) and (10). CO2_tank (t-Δt) and H2 molar concentration X H2_tank Based on (t-Δt), the molar concentration of CO2 in gas tank 7 is X CO2_tank (t) and H2 molar concentration X H2_tank (t) can be estimated. This allows us to estimate the composition of the mixed gas inside gas tank 7 at the current time using the composition of the mixed gas at the inlet of gas tank 7 immediately before.

[0058] Furthermore, according to the estimation device 1 of this embodiment, the control unit 40 determines the estimated CO2 molar concentration X in the gas tank 7. CO2_tank (t) and H2 molar concentration X H2_tank (t), etc., is used to change the flow rate of the gas supplied by the adjustment gas supply unit 31. As a result, the estimation device 1 can estimate the concentration of the target gas in a relatively short time, and can quickly reach the desired concentration even if the gas concentration changes rapidly.

[0059] Furthermore, according to the estimation device 1 of this embodiment, the control unit 40 determines the actual flow rate Q of the outlet of the gas tank 7. real_tank_out And the target value ξ for H2 / CO2 target This allows the flow rate of CO2 and H2 gas supplied by the adjustment gas supply unit 31 to be changed. Therefore, the H2 / CO2 ratio of the mixed gas can be set to the target value relatively easily.

[0060] <Modified form of this embodiment> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit, for example, the following modifications are also possible.

[0061] [Example 1] In the above embodiment, the composition of the mixed gas was estimated using equations (1) to (10), and the composition of the mixed gas was controlled using equations (11) and (12). However, the method for estimating the gas composition of the mixed gas and the method for controlling the gas composition are not limited to these. For example, using equations (1) to (4), the actual flow rate Q at the inlet of the gas tank could be estimated. real_tank_in And, the CO2 molar concentration X at the gas tank inlet CO2_tank_in (t-Δt) and H2 molar concentration X H2_tank_in (t-Δt) is estimated, and the molar concentration of CO2 in gas tank 7 is calculated using equations (9) and (10). CO2_tank (t) and H2 molar concentration X H2_tank (t) may be estimated.

[0062] [Differentiation 2] In the above-described embodiment, the inlet display flow rate Q display_tank_in And, the outlet display flow rate Q display_tank_out And, the tank pressure measurement value P tank And, the tank temperature measurement value T tank Using this, the concentration X of mixed chemical species A in gas tank 7 A_tank and the concentration X of chemical species B B_tank The estimation device was designed to estimate the concentration of chemical species A at the inlet of the gas tank. A_tank_in and the concentration X of chemical species B B_tank_in Actual flow rate Q at the gas tank inlet real_tank_in Actual flow rate Q at the outlet of the gas tank real_tank_out It may be used only for estimation purposes.

[0063] [Difference 3] In the above embodiment, the tank temperature measurement value T tank The temperature is to be detected by a thermometer 24 installed in the gas tank 7. Since the temperature of the gas tank 7 matches the ambient temperature of the estimation device 1, the ambient temperature is used as the tank temperature measurement value T. tank That is also acceptable.

[0064] [Differentiation Example 4] In the above embodiment, the conversion coefficients (C) for CO2 and H2 are set for each of the inlet flow detection unit 21 and the outlet flow detection unit 22. CO2_tank_out , C H2_tank_out , C CO2_tank_in , C H2_tank_in The conversion coefficients C of the thermal mass flowmeter are provided by the manufacturer. However, the conversion coefficients are not limited to these. They may be adjusted to improve the estimation accuracy in estimating the gas composition in the estimation device 1. Typically, the conversion coefficients provided by the manufacturer are intended for steady-state use, so the estimation accuracy of the estimation device 1 can be improved by adjusting them in the field where the thermal mass flowmeter is used. Specifically, the conversion coefficients C of the inlet flow detection unit 21 and the outlet flow detection unit 22 are... calib_tank_out , C A_tank_out , C B_tank_out , C calib_tank_in , C A_tank_in , C B_tank_in The values ​​can be adjusted by comparing the estimated values ​​with the true values ​​of the concentrations shown in Figure 4.

[0065] [Difference 5] In the above embodiment, a thermal mass flow meter was used as the inlet flow detection unit 21 and the outlet flow detection unit 22, but a mass flow controller (T-MFC) with a flow control function added to the thermal mass flow meter may also be used. The T-MFC has an additional control valve inside and operates to keep the displayed flow rate constant by adjusting the opening of the control valve (therefore, the actual flow rate will not be kept constant under conditions where the composition fluctuates). Since the displayed flow rate of the T-MFC is detected by the same principle as the T-MFM, even if a T-MFC is used, the CO2 molar concentration X in the gas tank 7 can be determined from the displayed flow rate of the T-MFC. CO2_tank and H2 molar concentration X B_tank It is possible to estimate things like the above.

[0066] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate. [Explanation of Symbols]

[0067] 1... Estimation device 6…Mixed gas supply unit 7... Gas tank 21...Inlet flow detection unit 22...Outlet flow rate detection unit 23... Pressure gauge 24…Thermometer 31... Regulating gas supply unit 40... Control Unit Q display_tank_in …Inlet display flow rate Q display_tank_out …Outlet display flow rate Q real_tank_in ...Actual flow rate at the gas tank inlet Q real_tank_out ...Actual flow rate at the gas tank outlet X CO2_tank_in ...CO2 molar concentration at the gas tank inlet X H_tank_in ...H2 molar concentration at the gas tank inlet X CO2_tank ...CO2 molar concentration inside the gas tank X H_tank ...H2 molar concentration in the gas tank

Images