Concentration measurement device, reactor, and concentration measurement method

Abstract

To provide: a concentration measurement device in which an effect of pressure in measurement of concentration of methane contained in produced gases can be reduced; a reactor; and a concentration measurement method.SOLUTION: A concentration measurement device includes: a thermometer which detects the temperature of produced gases obtained by methanation reaction between carbon dioxide and hydrogen; a pressure gage which detects the pressure of the produced gases; a flowmeter which detects the flow rate of the produced gases or the flow rate of water included in the produced gases; and an arithmetic device which calculates a methane concentration on the basis of detection results detected by the thermometer, the pressure gage, and the flowmeter.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane concentration measuring device, a reaction device, and a concentration measuring method for methane contained in a product gas obtained by a methanation reaction.

Background Art

[0002] There is a demand for measuring the concentration of methane contained in a product gas obtained by a methanation reaction of carbon dioxide and hydrogen. The prior art disclosed in Patent Document 1 quantifies the carbon dioxide concentration of the product gas and determines the conversion rate from carbon dioxide to methane.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When determining the conversion rate from carbon dioxide to methane in the prior art, when measuring the carbon dioxide concentration of the product gas with a concentration meter, the measurement result is affected by the pressure of the product gas, so it lacks accuracy. Directly measuring the concentration of methane in the product gas with a concentration meter also has the problem of lacking accuracy because the measurement result is affected by the pressure of the product gas.

[0005] The present invention has been made to solve this problem, and an object thereof is to provide a concentration measuring device, a reaction device, and a concentration measuring method capable of reducing the influence of pressure when measuring the concentration of methane contained in a product gas.

Means for Solving the Problems

[0006] A first aspect for achieving this object is a methane concentration measuring device included in a product gas obtained by a methanation reaction of carbon dioxide and hydrogen, the device including a thermometer configured to detect the temperature of the product gas, a pressure gauge configured to detect the pressure of the product gas, a flow meter configured to detect the flow rate of the product gas, and an arithmetic unit configured to calculate the concentration of methane based on detection results of the thermometer, the pressure gauge, and the flow meter.

[0007] A second aspect is that, in the first aspect, the arithmetic unit obtains the volume flow rate of saturated water vapor in the product gas based on the amount of saturated water vapor in the product gas at the temperature detected by the thermometer and the pressure of the product gas detected by the pressure gauge, obtains the flow rate of carbon dioxide based on the flow rate of the product gas detected by the flow meter and the volume flow rate, and calculates the concentration of methane included in the product gas.

[0008] A third aspect is a methane concentration measuring device included in a product gas obtained by a methanation reaction of carbon dioxide and hydrogen, the device including a thermometer configured to detect the temperature of the product gas, a pressure gauge configured to detect the pressure of the product gas, a flow meter configured to detect the flow rate of the product gas, a water flow meter configured to detect the flow rate of water formed by condensation of the product gas, and an arithmetic unit configured to calculate the concentration of methane based on detection results of the thermometer, the pressure gauge, the flow meter, and the water flow meter.

[0009] A fourth aspect is that, in the third aspect, the arithmetic unit obtains the volume flow rate of saturated water vapor in the product gas based on the amount of saturated water vapor in the product gas at the temperature detected by the thermometer and the pressure of the product gas detected by the pressure gauge, obtains the flow rate of carbon dioxide based on the flow rate detected by the water flow meter and the volume flow rate, and calculates the concentration of methane included in the product gas based on the flow rate of the product gas detected by the flow meter and the flow rate of carbon dioxide.

[0010] A fifth aspect is that, in any one of the first to fourth aspects, the absolute pressure of the product gas is 0.1 MPa or more.

[0011] The sixth aspect is a reaction apparatus, which includes the concentration measurement device in any one of the first to fifth aspects, and a reactor containing a catalyst that promotes the methanation reaction of carbon dioxide and hydrogen.

[0012] The seventh aspect is, in the sixth aspect, including a plurality of reactors, a communication path that connects adjacent reactors and sends the product gas generated in the previous-stage reactor to the subsequent-stage reactor, and a separation device that separates water from the product gas in the communication path, and the concentration measurement device measures the concentration of methane contained in the product gas generated in a reactor previous to the last subsequent-stage reactor.

[0013] The eighth aspect is a method for measuring the concentration of methane contained in the product gas obtained by the methanation reaction of carbon dioxide and hydrogen, which includes detecting the temperature of the product gas, detecting the pressure of the product gas, detecting the flow rate of the product gas or the flow rate of water contained in the product gas, and calculating the concentration of methane based on the temperature of the product gas, the pressure of the product gas, and the flow rate of the product gas or the flow rate of water contained in the product gas.

Advantages of the Invention

[0014] According to the present invention, since the concentration of methane is calculated without using a concentration meter based on the temperature of the product gas, the pressure of the product gas, and the flow rate of the product gas or the flow rate of water contained in the product gas obtained by the methanation reaction of carbon dioxide and hydrogen, the influence of the pressure of the product gas can be reduced. Furthermore, the concentration meter can be omitted.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of a reactor 10 according to the first embodiment. The reactor 10 includes a reactor 11 containing a catalyst 12, a carbon dioxide introduction unit 13 for introducing carbon dioxide into the reactor 11, and a hydrogen introduction unit 14 for introducing hydrogen into the reactor 11. In the reactor 11 into which a raw material gas containing carbon dioxide and hydrogen is introduced, a methanation reaction represented by the chemical reaction formula CO2 + 4H2 → CH4 + 2H2O proceeds. The reactor 10 includes a concentration measuring device 20 for measuring the concentration of methane contained in the product gas obtained by the methanation reaction.

[0017] The catalyst 12 suitable for the methanation reaction can be used without limitation. Examples of the catalyst 12 include a powder, pellet, or porous structure in which particles are supported on a carrier. Examples of the carrier include powders, pellets, or porous structures of oxides containing one or more of alumina, silica, magnesia, titania, zirconia, niobia, silica-alumina, zeolite, and calcium phosphate. The porous structure has air permeability through which the raw material gas can pass. Also, the raw material gas passes through the gaps between the powder and the pellets. Examples of the particles supported on the carrier include metals such as Ni.

[0018] The reactor 10 includes a plurality (three in this embodiment) of reactors 11 and has a connecting passage 15 connecting adjacent reactors 11. The connecting passage 15 sends the product gas generated by the methanation reaction in the previous-stage reactor 11 to the subsequent-stage reactor 11. Since no catalyst 12 is arranged in the connecting passage 15, the methanation reaction does not proceed when the product gas passes through the connecting passage 15. The number of reactors 11 is not limited to three, and two or more are sufficient.

[0019] A cooler 16 is arranged in the communication path 15. The cooler 16 is also arranged downstream of the final reactor 11. As the cooler 16, anything that can cool the product gas, such as a heat exchanger, can be used without limitation. The cooler 16 cools the product gas generated in the previous reactor 11, and the communication path 15 sends the cooled product gas to the subsequent reactor 11. The cooler 16 cools the product gas to, for example, the lowest temperature at which the methanation reaction starts. Since the methanation reaction is an exothermic reaction, when the surface of the catalyst 12 becomes hot, the reverse reaction becomes dominant and the conversion rate of methane decreases. The cooler 16 is provided to reduce the reverse reaction and increase the conversion rate of methane.

[0020] A separator 17 for separating water from the product gas is arranged downstream of the cooler 16 in the communication path 15. The cooler 16 arranged upstream of the separator 17 cools the product gas to the dew point, and the separator 17 separates the water condensed by the cooler 16. When the amount of water contained in the product gas is reduced by the separator 17, the rate of the forward reaction of the methanation reaction becomes larger than the rate of the reverse reaction in the reactor 11 downstream of the separator 17, so that the conversion rate of methane can be increased.

[0021] The concentration measuring device 20 is a device that measures the concentration of methane contained in the product gas. The concentration measuring device 20 measures the concentration of methane contained in the product gas flowing downstream of the reactor 11 in the previous stage rather than the last reactor 11. The absolute pressure of the product gas for which the concentration measuring device 20 measures the concentration is, for example, 0.1 MPa or more. The concentration of methane contained in the product gas of the last reactor 11 can be measured using a concentration meter after reducing the pressure of the product gas to atmospheric pressure.

[0022] The concentration measuring device 20 includes an arithmetic unit 21, a flow meter 22 that measures the flow rate of the product gas, a thermometer 23 that detects the temperature of the product gas, and a pressure gauge 24 that detects the pressure of the product gas. The flow meter 22, the thermometer 23, and the pressure gauge 24 input their respective detection results into the arithmetic unit 21.

[0023] The arithmetic unit 21 includes a CPU, a ROM, a RAM, and a backup RAM (none of which are shown in the figure). The ROM is a non-volatile memory that stores programs executed by the CPU. The CPU executes arithmetic processing based on the programs stored in the ROM. The RAM is a memory that temporarily stores the arithmetic results of the CPU and data input from each sensor. The backup RAM is a non-volatile memory that stores data to be saved and the like.

[0024] Since the chemical reaction formula of the methanation reaction is CO2 + 4H2 → CH4 + 2H2O, among the flow rates of the product gas after the reaction, if the flow rate of CO2 is x [L / min], the flow rate of H2 is 4x [L / min]. Considering the conversion rate from CO2 to CH4, the flow rate of CH4 contained in the product gas is 1 - x [L / min]. Since the product gas also contains saturated water vapor, if the amount of saturated water vapor is α [L / min], the flow rate F of the product gas detected by the flow meter 22 is F = x + 4x + (1 - x) + α = 4x + 1 + α [L / min].

[0025] The amount of saturated water vapor [g / m 3 is a value determined by the temperature of the product gas detected by the thermometer 23. In the ROM of the arithmetic unit 21, the amount of saturated water vapor [g / m 3 for each temperature is stored. The arithmetic unit 21 uses the formula Q = A·V = A·(2q / P) 1 / 2 to convert the fluid density [g / m 3 to the volume flow rate [L / min]. Here, Q is the volume flow rate = the amount of saturated water vapor [L / min], A is the cross-sectional area of the communication path 15, V is the flow velocity, q is the pressure of the product gas detected by the pressure gauge 24, and P is the fluid density = the amount of saturated water vapor [g / m 3 . In the formula Q = A·(2q / P) 1 / 2 since A is a known constant, the arithmetic unit 21 substitutes the pressure of the product gas detected by the pressure gauge 24 and the amount of saturated water vapor [g / m 3 determined by the temperature detected by the thermometer 23 to calculate the amount of saturated water vapor α [L / min] contained in the product gas.

[0026] The arithmetic unit 21 acquires the flow rate F [L / min] of the generated gas detected by the flow meter 22, substitutes the saturated water vapor amount α [L / min] into the algebraic expression F = 4x + 1 + α, and calculates x. Since the flow rate of CH4 contained in the generated gas is 1 - x [L / min], the concentration [vol%] of CH4 contained in the generated gas is (1 - x) / F. The arithmetic unit 21 substitutes x and F into this algebraic expression to calculate the concentration [vol%] of CH4 contained in the generated gas.

[0027] Since the concentration measuring device 20 measures the concentration of methane contained in the generated gas without using a concentration meter whose measurement result is easily affected by pressure, the influence of pressure during concentration measurement can be reduced. As a result, the concentration of methane contained in the high-pressure generated gas flowing through the communication path 15 connecting the adjacent reactors 11 can be measured. By arranging the concentration measuring device 20 for each communication path 15, the methane concentration for each reactor 11 can be measured. Therefore, by comparing the designed methane concentration for each reaction stage with the actual methane concentration, the deterioration state of the catalyst 12 accommodated in the reactor 11 can be detected. Since the deteriorated catalyst 12 can be appropriately replaced, the maintenance of the reaction apparatus 10 becomes easier. Since a concentration meter for detecting the concentration of the components of the generated gas can be omitted, maintenance of the concentration meter, which was part of the maintenance of the reaction apparatus, becomes unnecessary.

[0028] By arranging the concentration measuring device 20 for each communication path 15, the methane concentration for each reactor 11 can be measured. Therefore, by comparing the methane concentration of the generated gas in the reactor 11 at the forefront stage with the designed methane concentration for each reaction stage, an abnormality in the carbon dioxide concentration introduced into the reactor 11 by the carbon dioxide introduction unit 13 can be detected. Thereby, an abnormality in the raw material gas can be detected.

[0029] The second embodiment will be described with reference to FIG. 2. In the first embodiment, the case of detecting the flow rate of the generated gas and obtaining the methane concentration of the generated gas was described. In contrast, in the second embodiment, the case of detecting the flow rate of the water condensed from the water vapor contained in the generated gas and obtaining the methane concentration of the generated gas will be described. In the second embodiment, the same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description is omitted.

[0030] Figure 2 is a block diagram of the reaction apparatus 30 in the second embodiment. The reaction apparatus 30 includes a concentration measuring device 40. The concentration measuring device 40 measures the concentration of methane contained in the product gas flowing downstream of the reactor 11 upstream of the last reactor 11.

[0031] The concentration measuring device 40 includes an arithmetic unit 21, a flow meter 22, a thermometer 23, a pressure gauge 24, and a water flow meter 41 (flow meter) that detects the flow rate of the water separated by the separation device 17. The flow meter 22 detects the flow rate F of the product gas upstream of the separation device 17. The thermometer 23 and the pressure gauge 24 detect the temperature and pressure of the product gas downstream of the separation device 17. The water flow meter 41, the flow meter 22, the thermometer 23, and the pressure gauge 24 input their respective detection results into the arithmetic unit 21.

[0032] Since the chemical reaction formula of the methanation reaction is CO2 + 4H2 → CH4 + 2H2O, if the flow rate of CO2 is x [L / min] among the flow rates of the product gas after the reaction, the flow rate of H2 is 4x [L / min]. Considering the conversion rate from CO2 to CH4, the flow rate of CH4 contained in the product gas is 1 - x [L / min], and the flow rate of H2O (gas) is 2(1 - x) [L / min].

[0033] If the flow rate detected by the water flow meter 41, that is, the flow rate of H2O (liquid) separated by the separation device 17, is β [L / min], then β [L / min] = β [g / mol] = β / 18 [mol / min]. Therefore, according to Avogadro's law, the flow rate of H2O (gas) separated by the separation device 17 is β / 18 [mol / min] · 22.4 [L / mol] = 22.4β / 18 [L / min]. Since the product gas also contains saturated water vapor, if the amount of saturated water vapor in the product gas flowing downstream of the separation device 17 is α [L / min], the flow rate of H2O (gas) contained in the product gas flowing upstream of the separation device 17 is 22.4β / 18 + α [L / min].

[0034] Focusing on the flow rate [L / min] of H2O (gas) contained in the generated gas, the equation 2(1 - x) = 22.4β / 18 + α holds. Similar to the first embodiment, the arithmetic unit 21 calculates the amount of saturated water vapor α [L / min] contained in the generated gas from the pressure of the generated gas detected by the pressure gauge 24 and the temperature detected by the thermometer 23, based on the amount of saturated water vapor [g / m 3 . The arithmetic unit 21 substitutes the saturated water vapor amount α and the flow rate β detected by the water flow meter 41 into the equation 2(1 - x) = 22.4β / 18 + α to calculate x.

[0035] The arithmetic unit 21 acquires the flow rate F [L / min] of the generated gas detected by the flow meter 22. Since the flow rate of CH4 contained in the generated gas is 1 - x [L / min], the concentration [vol%] of CH4 contained in the generated gas is (1 - x) / F. The arithmetic unit 21 substitutes x and F into this algebraic expression to calculate the concentration [vol%] of CH4 contained in the generated gas.

[0036] According to the concentration measuring device 40 and the reaction device 30 including the concentration measuring device 40, the same operational effects as those of the concentration measuring device 20 and the reaction device 10 in the first embodiment can be achieved.

[0037] Although the present invention has been described based on the embodiments, it is easily conceivable that the present invention is not limited to the above embodiments at all, and various improvements and modifications are possible without departing from the spirit of the present invention.

[0038] In the first embodiment, the flow rate, temperature, and pressure of the generated gas flowing downstream of the cooler 16 in the communication path 15 are detected to calculate the methane concentration of the generated gas, but it is not necessarily limited to this. It is of course possible to detect the flow rate, temperature, and pressure of the generated gas flowing upstream of the cooler 16 in the communication path 15 to calculate the methane concentration of the generated gas.

[0039] Although the case where the separation device 17 is arranged in one of the three communication paths 15 has been described in the embodiment, it is not necessarily limited to this. It is of course possible to arrange the separation device 17 in each of the three communication paths 15, or to arrange the separation device 17 in two of the three communication paths 15. It is of course possible to arrange a plurality of separation devices 17 in one communication path 15.

[0040] Although the reactor 10, 30 including the separation device 17 for separating the water condensed by the cooler 16 has been described in the embodiment, the separation device 17 is not limited to this. The separation device 17 may use a desiccant such as slaked lime, an adsorbent such as activated carbon or zeolite, a water separation membrane, etc., and separate the water vapor without condensing it with the cooler 16.

[0041] Although the case where the cooler 16 cools the product gas to the lowest temperature at which the methanation reaction starts has been described in the embodiment, it is not necessarily limited to this. The temperature at which the cooler 16 cools the product gas may be lower than the temperature at which the methanation reaction reaches equilibrium.

[0042] Although the description has been omitted in the embodiment, it is of course possible to arrange a heater in the communication path 15 or the reactor 11 to heat the gas introduced into the reactor 11 to a temperature equal to or higher than the starting temperature of the methanation reaction. Examples of the heater include those that heat the heat source by the combustion heat of the gas or electricity to heat the product gas, those that utilize induction heating, and heat exchangers.

Explanation of reference numerals

[0043] 10, 30 Reactor 11 Reactor 12 Catalyst 15 Communication path 17 Separation device 20, 40 Concentration measuring device 21 Arithmetic unit 22 Flow meter 23 Thermometer 24 Pressure gauge 41 Water meter

Claims

1. A methane concentration measuring device for a product gas obtained by a methanation reaction of carbon dioxide and hydrogen, comprising: a thermometer for detecting the temperature of the product gas; a pressure gauge for detecting the pressure of the product gas; a flow meter for detecting the flow rate of the product gas; an arithmetic unit for calculating the concentration of methane based on the detection results of the thermometer, the pressure gauge, and the flow meter.

2. A methane concentration measuring device for a product gas obtained by a methanation reaction of carbon dioxide and hydrogen, comprising: a thermometer for detecting the temperature of the product gas; a pressure gauge for detecting the pressure of the product gas; a flow meter for detecting the flow rate of the product gas; a water flow meter for detecting the flow rate of water formed by condensation of the product gas; an arithmetic unit for calculating the concentration of methane based on the detection results of the thermometer, the pressure gauge, the flow meter, and the water flow meter.

3. The concentration measuring device according to claim 1 or 2, wherein the product gas has an absolute pressure of 0.1 MPa or more.

4. A reaction device comprising the concentration measuring device according to claim 1 or 2, and a reactor containing a catalyst for promoting the methanation reaction of carbon dioxide and hydrogen.

5. A plurality of the reactors, a connecting passage connecting adjacent reactors and sending the product gas generated in the previous-stage reactor to the subsequent-stage reactor, a separating device for separating water from the product gas in the connecting passage, wherein the concentration measuring device measures the concentration of methane contained in the product gas generated in a reactor upstream of the last-stage reactor.

6. A method for measuring the concentration of methane contained in a product gas obtained by a methanation reaction of carbon dioxide and hydrogen, comprising: detecting the temperature of the product gas, detecting the pressure of the product gas, and detecting the flow rate of the product gas or the flow rate of water contained in the product gas; calculating the concentration of methane based on the temperature of the product gas, the pressure of the product gas, and the flow rate of the product gas or the flow rate of water contained in the product gas.

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