Method of controlling methanol concentration, method of estimating methanol concentration, power generating system, and method of producing carbon dioxide

Abstract

To provide a method of controlling methanol concentration, etc., the method being capable of improving the accuracy of methanol concentration control while suppressing a control load.SOLUTION: There is provided a method of controlling methanol concentration within a predetermined range R1 in a methanol composition that causes changes with time in at least one selected from the group consisting of the methanol concentration, a density and a temperature. The method includes: a step (A) of obtaining a data group G1 of densities D and temperatures T measured during a control period P for the methanol composition; a step (B) of calculating a corresponding methanol concentration group G2 from the data group G1; and a step (C) of adding, to the methanol composition, a methanol composition MC1 with methanol concentration C1 and / or water on the basis of the average value α of the methanol concentration group G2. The added amount of the methanol composition MC1 and / or water is determined on the basis of a difference between target methanol concentration C0 selected from the predetermined range R1 and the average value α.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for controlling methanol concentration, a method for estimating methanol concentration, a power generation system, and a method for producing carbon dioxide.

Background Art

[0002] Non-Patent Document 1 discloses a method for calculating methanol concentration from the density and temperature of a methanol solution.

Prior Art Document

Non-Patent Document

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Methanol is known as a raw material for adhesives, agricultural chemicals, paints, synthetic resins, synthetic fibers, pharmaceuticals, etc., and there is also increasing expectation for its potential as future clean energy. Specific examples of the latter include fuel cells that use methanol as a direct fuel (direct methanol fuel cells). Taking the operation of a direct methanol fuel cell as an example, in the methanol composition that serves as its energy source (typically, a composition obtained by adding water to methanol), at least one selected from the group consisting of methanol concentration, density, and temperature changes over time. In such a system, when applying the method described in Non-Patent Document 1, for example, it is affected by bubbles that may occur due to liquid feeding by a pump, and the accuracy of the measurement results tends to decrease. To improve the above accuracy, it is also conceivable to use a degassing pump, but in this case, the control load becomes excessively high, and it tends to be inferior in terms of economy. Thus, it can be said that there is room for improvement in the prior art from the viewpoint of suppressing the control load while improving the accuracy in controlling methanol concentration.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a method for controlling the methanol concentration and the like that can improve the accuracy of methanol concentration control while suppressing the control load.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by implementing control based on the average value α of a predetermined data group, and have completed the present invention.

[0007] That is, the present invention includes the following aspects. [1] In a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, a method for controlling the methanol concentration within a predetermined range R1, a step (A) of obtaining a data group G1 of density D and temperature T measured during a control period P for the methanol composition; a step (B) of calculating a corresponding methanol concentration group G2 from the data group G1; a step (C) of adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on the average value α of the methanol concentration group G2; and a method in which the addition amount of the methanol composition MC1 and / or water is determined based on the difference between a target methanol concentration C0 selected from the predetermined range R1 and the average value α. [2] The method according to [1], wherein the measurement frequency during the control period P is 0.01 seconds / time to 1 second / time. [3] The method according to [1] or [2], wherein the number of data points in the methanol concentration group G2 is 10 to 1000 points. [4] The method according to any one of [1] to [3], wherein the density D is measured by a MEMS sensor. [5] The method according to any one of [1] to [4], wherein the target methanol concentration C0 is 0.5% by mass or more and 5.0% by mass or less. [6] The method according to any one of [1] to [5], wherein the methanol concentration C1 is 10% by mass or more and 100% by mass or less. [7] A method for estimating the methanol concentration in a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, comprising: Step (A') of obtaining a data group G1 of density D and temperature T measured during a prediction period P' for the methanol composition; Step (B') of calculating a corresponding methanol concentration group G2 from the data group G1; Step (C') of calculating an average value α of the methanol concentration group G2 as an estimated value of the methanol concentration of the methanol composition. A method comprising the above steps. [8] Power generation means using a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, A control unit connected to the power generation means, A power generation system comprising: The control unit is configured to execute control to adjust the methanol concentration to a predetermined range R1, The control includes: Control (a) of obtaining a data group G1 of density D and temperature T measured during a control period P for the methanol composition; Control (b) of calculating a corresponding methanol concentration group G2 from the data group G1; Based on the average value α of the methanol concentration group G2, control (c) of adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition; Including the above steps, In the control, the addition amount of the methanol composition MC1 and / or water is determined based on the difference between the target methanol concentration C0 selected from the predetermined range R1 and the average value α. A power generation system. [9] The power generation system according to [8], wherein the power generation means is a direct methanol fuel cell. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a method for controlling the methanol concentration and the like that can improve the accuracy of methanol concentration control while suppressing the control load. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

[0010] Hereinafter, modes for carrying out the present invention (hereinafter, also referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. The following present embodiment is an exemplification for explaining the present invention, and is not intended to limit the present invention to the following contents. The accompanying drawings show an example of the embodiment, and the embodiment is not to be construed as being limited thereto. The present invention can be appropriately modified and implemented within the scope of its gist. In each drawing, the same or similar elements are denoted by the same reference numerals, and duplicate explanations are omitted. Also, unless otherwise specified, positional relationships such as up, down, left, and right are described based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings do not represent actual ratios, and the actual ratios are not limited to the ratios shown in the drawings.

[0011] [Method for Controlling Methanol Concentration] The method for controlling the methanol concentration in this embodiment (hereinafter also referred to as the "first method") is a method for controlling the methanol concentration within a predetermined range R1 in a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time. The method includes a step (A) (corresponding to "step S1" described later) of obtaining a data group G1 of density D and temperature T measured during a control period P for the methanol composition, a step (B) (corresponding to "step S2" described later) of calculating a corresponding methanol concentration group G2 from the data group G1, and a step (C) (corresponding to "step S3" described later) of adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on the average value α of the methanol concentration group G2. The addition amount of the methanol composition MC1 and / or water is determined based on the difference between a target methanol concentration C0 selected from the predetermined range R1 and the average value α. Since the first method is configured in this way, it is possible to improve the accuracy of methanol concentration control while suppressing the control load.

[0012] FIG. 1 is a flowchart illustrating the first method. In the example of FIG. 1, the first method includes a step S1 of obtaining a data group G1 of density D and temperature T measured during a control period P for the methanol composition, a step S2 of calculating a corresponding methanol concentration group G2 from the data group G1, and a step S3 of adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on the average value α of the methanol concentration group G2. In the first method, after steps S1, S2, and S3 are executed in this order, if the methanol composition is further used, steps S1, S2, and S3 can be repeatedly executed one or more times, and if the methanol composition is not further used, the control can be terminated accordingly. Hereinafter, the methanol composition and the processes that can be performed on it will be described in detail.

[0013] (Controlled system) The first method is a method for controlling the methanol concentration of a methanol composition within a predetermined range R1, and can be applied to various controlled systems. That is, the predetermined range R1 can be arbitrarily set according to the controlled system to which the first method is applied. The controlled system to which the first method is applied is not particularly limited, and may be, for example, a synthesis system using methanol or a power generation system using methanol. The synthesis system is not particularly limited, and examples thereof include synthesis systems for adhesives, agricultural chemicals, paints, synthetic resins, synthetic fibers, pharmaceuticals, and the like. The power generation system is not particularly limited, and examples thereof include power generation systems such as direct methanol fuel cells and methanol reforming fuel cells. In the present embodiment, from the viewpoint of making the effect obtained by the first method more apparent, the controlled system to which the first method is applied is preferably a power generation system, and more preferably a direct methanol fuel cell. In other words, the first method can be preferably executed by a power generation system, and more preferably executed by a direct methanol fuel cell.

[0014] (Methanol composition) The methanol composition in the present embodiment is a composition containing at least methanol, and at least one selected from the group consisting of the methanol concentration, density, and temperature in the methanol composition changes over time (hereinafter, such a change is also simply referred to as "change over time"). The methanol composition in the present embodiment may be a mixture of methanol and water, or may contain substances other than these. In the present embodiment, from the viewpoint of the measurement accuracy of the methanol concentration, the total amount of methanol and water is preferably 99% by mass or more based on 100% by mass of the methanol composition.

[0015] The change over time in this embodiment can be said to occur under various environmental factors corresponding to the controlled system to which the first method is applied. Typical examples thereof include, but are not limited to, cases where a methanol composition in a raw material tank is fed as a synthesis raw material to a synthesis tank, reacted with other raw materials, and then unreacted components are circulated and returned to the raw material tank, or cases where a methanol composition in a fuel tank is directly fed as fuel to the fuel electrode side of a direct methanol fuel cell, reacted, and then unreacted components are circulated and returned to the fuel tank. In these typical examples, in particular, the methanol concentration of the methanol composition tends to decrease over time. Therefore, for the methanol composition in the synthesis tank or the fuel tank, methanol can be supplied from another tank to increase the methanol concentration and, as a result, control can be performed to maintain the concentration before use in the reaction. When there is some abnormality in the controlled system to which the first method is applied or when the methanol concentration of the methanol composition tends to increase over time, the amount of methanol supplied from another tank to the synthesis tank can be reduced and / or water can be supplied from a tank different from the methanol composition to the methanol composition to reduce the methanol concentration, and as a result, control can be performed to maintain the desired concentration.

[0016] (Step (A)) In step (A), for the methanol composition, a data group G1 of density D and temperature T measured during the control period P is acquired.

[0017] In this embodiment, the control period P is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. Specifically, the control period P can be 5 minutes or more, 30 minutes or more, 1 hour or more, or 1 day or more.

[0018] In this embodiment, the measurement frequency during the control period P is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. As the measurement frequency increases, the accuracy of methanol concentration control tends to increase, while as the measurement frequency decreases, an excessive measurement load can be avoided. From such a perspective, in this embodiment, it is preferable that the measurement frequency is 0.01 second / time to 1 second / time.

[0019] In this embodiment, the measurement locations of the density D and the temperature T are not particularly limited. For example, they can be measured at any point in a tank filled with a methanol composition. In this case, the data group G1 is a data group obtained by acquiring, for each time, values calculated from the density D and the temperature T measured at the arbitrary point. In this embodiment, there may be a plurality of measurement locations. In that case, the average value α is calculated as the average value of the methanol concentration group G2 obtained for all the measurement locations.

[0020] In this embodiment, the specific measurement methods for the density D and the temperature T are not particularly limited, and they can be measured based on various known methods. In this embodiment, from the perspective of the balance between measurement simplicity and measurement accuracy, the density D and the temperature T are preferably measured by a MEMS sensor and a temperature sensor, respectively. The MEMS sensor, the temperature sensor, and their usage methods are also not particularly limited, and they can be measured based on various known MEMS sensors, temperature sensors, and their usage methods. Specific examples of the MEMS sensor include, but are not limited to, those described in U.S. Patent No. 10935404. The temperature sensor may be a thermocouple.

[0021] In this embodiment, the values of the density D and the temperature T are not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. The value of the density D can be, for example, 0.9 g / mL to 1.0 g / mL. Also, the value of the temperature T can be, for example, 6°C to 90°C. In addition, when directly applying the first method to a direct methanol fuel cell, if the value of density D is 0.9 g / mL to 1.0 g / mL and the value of temperature T is 6 °C to 90 °C, the measurement accuracy of the methanol concentration tends to increase.

[0022] (Step (B)) In step (B), the corresponding methanol concentration group G2 is calculated from the data group G1. The specific calculation method of the methanol concentration group G2 is not particularly limited and can be measured based on various known methods. In the present embodiment, the methanol concentration group G2 can be measured based on the method described in JIS K1501:2005 Methanol 4. Test Methods and the like from the viewpoint of the balance between measurement simplicity and measurement accuracy. In this case, if necessary, the methanol concentration group G2 can also be obtained by creating an approximate line or the like.

[0023] In the present embodiment, the number of data points of the methanol concentration group G2 is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. While the accuracy of methanol concentration control tends to increase as the number of the above data points increases, an excessive measurement load can be avoided as the number of the above data points decreases. From such a viewpoint, in the present embodiment, the number of data points of the methanol concentration group G2 is preferably 10 to 1000 points.

[0024] (Step (C)) In step (C), based on the average value α of the methanol concentration group G2, for the methanol composition in the present embodiment, a methanol composition MC1 having a methanol concentration C1 and / or water is added. Here, the addition amount of the methanol composition MC1 and / or water is determined based on the difference between the target methanol concentration C0 selected from the predetermined range R1 and the average value α. In this specification, "average" means arithmetic mean. The first method can avoid the following problems by including step (C), and thus can improve the accuracy of methanol concentration control. The problems assumed when step (C) is not carried out include, but are not limited to, for example, being affected by bubbles or the like that may occur due to liquid feeding by a pump, and the measured density value deviating from the actual density. Also, in step (C), a determination index can be obtained by an operation with a relatively low load of calculating the average value α from the methanol concentration group G2, and it can be said to be advantageous from the viewpoint of control load. The method for calculating the average value α is not particularly limited. For example, in the present embodiment, the data group G1 and the methanol concentration group G2 are stored in a control unit connected to a MEMS sensor that can be used, and based on them, the calculation of the average value can be executed by various known processing means that may be provided in the control unit.

[0025] FIG. 2 is a flowchart illustrating a specific operation that can be executed in step S3 shown in FIG. 1. In the example illustrated in FIG. 2, step S3 includes a step S31 of calculating the average value α of the methanol concentration group G2, a step S32 of calculating the difference D between the target methanol concentration C0 and the average value α, and a step S33 of adding the methanol composition MC1 and / or water in an amount corresponding to the difference D to the methanol composition. The calculation of the average value α in step S31 can be executed by the method described above. In step S32, the target methanol concentration C0 can be any numerical value selected from a predetermined range R1. That is, the target methanol concentration C0 may be the upper limit value of the predetermined range R1, the lower limit value, or any numerical value greater than the lower limit value and less than the upper limit value. The method for calculating the difference D is not particularly limited. For example, in the present embodiment, the target methanol concentration C0 and the average value α are stored in a control unit connected to a MEMS sensor that can be used, and based on them, the calculation of the difference D can be executed by various known processing means that may be provided in the control unit. In step S33, in order to eliminate the difference D between the target methanol concentration C0 and the average value α, an amount of methanol composition MC1 and / or water corresponding to the difference D is added to the methanol composition. By such an operation, as a result, the average value α is controlled to be within a predetermined range R1. Note that when the difference D is a positive value (target methanol concentration C0 > average value α) as the target methanol concentration C0 - average value α, the concentration of the methanol composition may be controlled to increase. For example, a methanol composition MC1 having a methanol concentration C1 is added to the methanol composition. When an operation of already adding the methanol composition MC1 to the methanol composition has been executed, control to increase the addition amount can also be performed. On the other hand, when the difference D is a negative value (target methanol concentration C0 < average value α) as the target methanol concentration C0 - average value α, the concentration of the methanol composition may be controlled to decrease. For example, water is added to the methanol composition. When an operation of already adding the methanol composition MC1 to the methanol composition has been executed, control to decrease the addition amount can also be performed.

[0026] In the present embodiment, the target methanol concentration C0 is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. The target methanol concentration C0 can be, for example, 0.5 mass% or more and 5.0 mass% or less. Note that when the first method is directly applied to a direct methanol fuel cell, when the target methanol concentration C0 is 0.5 mass% or more, the reaction on the fuel electrode side tends to be promoted, and when it is 5.0 mass% or less, the generation of crossover (a phenomenon in which methanol on the fuel electrode side permeates through the electrolyte membrane and moves to the air electrode side, reacting with oxygen at the air electrode and lowering the efficiency) is suppressed, and the power generation efficiency tends to be higher. From the above viewpoints, when the first method is applied to a direct methanol fuel cell, the target methanol concentration C0 is preferably 0.5 mass% or more and 5.0 mass% or less.

[0027] In step (C), the water that can be added to the methanol composition is not particularly limited, and for example, pure water, ultrapure water, etc. can be used.

[0028] In step (C), the timing for adding methanol composition MC1 and / or water to the methanol composition is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. For example, during the control period P, methanol composition MC1 and / or water can be added to the methanol composition at a timing such that the difference between the target methanol concentration C0 and the average value α is maintained at 1.0 mass% or less. When directly applying the first method to a direct methanol fuel cell, by controlling (adding methanol composition MC1 and / or water) so that the difference between the target methanol concentration C0 and the average value α is maintained at 1.0 mass% or less, there is a tendency to operate more stably. From the above perspective, when directly applying the first method to a direct methanol fuel cell, it is preferable to control (add methanol composition MC1 and / or water) so that the difference between the target methanol concentration C0 and the average value α is maintained at 0.4 mass% or less during the control period P.

[0029] In the present embodiment, the methanol concentration C1 is not particularly limited and can be appropriately set according to the controlled system to which the first method is applied. The methanol concentration C1 can be, for example, 5 mass% or more and 100 mass% or less. When directly applying the first method to a direct methanol fuel cell, when the methanol concentration C1 is 5 mass% or more, the amount of methanol composition MC1 required assuming long-term operation tends to be small. The upper limit value of the methanol concentration C1 is not particularly limited and can be, for example, 100 mass%, less than 100 mass%, or 60 mass% or less. From the above perspective, when directly applying the first method to a direct methanol fuel cell, the methanol concentration C1 is preferably 5 mass% or more and 100 mass% or less, and more preferably 10 mass% or more and 100 mass% or less.

[0030] <Method for estimating methanol concentration> As described above, the method for controlling the methanol concentration (the first method) of the present embodiment has been explained. It can be said that the first method also includes the method for estimating the methanol concentration. That is, the method for estimating the methanol concentration (hereinafter, also referred to as the "second method") of the present embodiment is a method for estimating the methanol concentration in a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time. For the methanol composition, a step (A') of obtaining a data group G1 of density D and temperature T measured during a prediction period P' (corresponding to "step S1'" described later), a step (B') of calculating a corresponding methanol concentration group G2 from the data group G1 (corresponding to "step S2'" described later), and a step (C') of calculating an average value α of the methanol concentration group G2 as an estimated value of the methanol concentration of the methanol composition (corresponding to "step S3'" described later). Since the second method is configured in this way, it is possible to improve the estimation accuracy of the methanol concentration while suppressing the control load.

[0031] Figure 3 is a flowchart illustrating the second method. In the example of Figure 3, the second method includes a step S1' of obtaining a data group G1 of density D and temperature T measured during a prediction period P' for the methanol composition, a step S2' of calculating a corresponding methanol concentration group G2 from the data group G1, and a step S3' of calculating an average value α of the methanol concentration group G2 as an estimated value of the methanol concentration of the methanol composition. As described above, it can be said that the first method includes the second method, and each step in the second method can be implemented in the same manner as the first method. For example, steps S1' and S2' in the second method can be executed in the same manner as steps S1 and S2 in the first method, respectively. Step S3' can be executed in the same manner as the calculation of the average value α in step S3 of the first method. The setting of the prediction period P', density D, and temperature T in the second method is not particularly limited, and can be set in the same manner as the control period P, density D, and temperature T in the first method, respectively. The calculation method of the average value α in the second method can also be the same as the calculation method of the average value α in the first method.

[0032] <Power generation system> As described above, although the first method or the second method can be applied to various controlled systems, from the viewpoint of making the effects obtained by the first method more apparent, it is preferable to apply the first method or the second method to a power generation system. That is, the power generation system of the present embodiment includes a power generation means that utilizes a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, and a control unit connected to the power generation means. The control unit is configured to execute control for adjusting the methanol concentration to a predetermined range R1. The control includes control (a) for acquiring a data group G1 of density D and temperature T measured during a control period P for the methanol composition, control (b) for calculating a corresponding methanol concentration group G2 from the data group G1, and control (c) for adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on an average value α of the methanol concentration group G2. In the control, the addition amount of the methanol composition MC1 and / or water is determined based on the difference between a target methanol concentration C0 selected from the predetermined range R1 and the average value α. Since the power generation system of the present embodiment is configured in this way, it is possible to improve the accuracy of methanol concentration control while suppressing the control load, and as a result, it is possible to suppress a decrease in output over time. As described above, the power generation system of the present embodiment can be said to apply the first method or the second method to the power generation system. Controls (a) to (c) executed by the control unit in the power generation system of the present embodiment can be executed in the same manner as steps (A) to (C) in the first method, respectively. The setting of the predetermined range R1, control period P, density D, temperature T, methanol concentration C1, and target methanol concentration C0 in the power generation system of the present embodiment is not particularly limited, and can be set in the same manner as the control period P, density D, and temperature T in the first method, respectively. The calculation method of the average value α in the power generation system of the present embodiment can also be the same as the calculation method of the average value α in the first method.

[0033] Examples of the power generation means in the present embodiment include fuel cells such as direct methanol fuel cells and methanol reforming fuel cells. When a fuel cell is adopted as the power generation means in the present embodiment, the configuration of the fuel cell is not particularly limited, and various known configurations can be adopted. Specific examples thereof include, but are not limited to, the configuration of the fuel cell described in Japanese Patent Application Laid-Open No. 2009-176514. From the viewpoint of making the effects of the first method or the second method more apparent, the power generation means is preferably a direct methanol fuel cell. That is, the power generation system of the present embodiment is preferably a power generation system including a direct methanol fuel cell and a control unit connected thereto.

[0034] (Configuration example of power generation system) FIG. 4 is a diagram for explaining a configuration example of the power generation system. The power generation system 100 illustrated in FIG. 4 includes a power generation means 10 and a control unit 20 connected to the power generation means 10. In the example illustrated in FIG. 4, the case where the power generation means 10 is a direct methanol fuel cell, that is, the case where the first method and / or the second method is applied to the direct methanol fuel cell is taken as an example. The power generation means 10 (a direct methanol fuel cell in the example of FIG. 4) includes a cell stack 1 and a fuel tank 2, and the cell stack 1 and the fuel tank 2 are connected via a liquid feed pump 3a. The cell stack 1 is configured such that air or oxygen gas is supplied from the outside via an air pump 3b separately. The cell stack 1 is composed of a plurality of fuel cell cells (not shown), and the fuel cell cells include an air electrode (positive electrode), a fuel electrode (negative electrode), and an electrolyte membrane disposed between the air electrode and the fuel electrode. In the example of FIG. 4, when the methanol composition in the fuel tank 2 is supplied from the liquid feed pump 3a to the fuel electrode (negative electrode) and air or oxygen gas is supplied from the air pump 3b to the air electrode (positive electrode) of the fuel cell cell, reactions proceed at both electrodes and power generation is performed. The reactions at each electrode are as follows. Fuel electrode (negative electrode): CH3OH + H2O → 6H + + CO2 + 6e - Air electrode (positive electrode): 6H+ +3 / 2O2 + 6e - → 3H2O Overall reaction equation: CH3OH + 3 / 2O2 → CO2 + 2H2O

[0035] In the example of FIG. 4, the methanol composition after being supplied to the fuel electrode is circulated and returned to the fuel tank 2. Since at least a part of the methanol contained in the methanol composition is consumed in the reaction at the fuel electrode, in the example of FIG. 4, the methanol composition in the fuel tank 2 can vary over time at least in terms of its methanol concentration. To monitor such changes over time, a sensor 4 is connected to the fuel tank 2. That is, the methanol composition in the fuel tank 2 is sent to the sensor 4 by the liquid feed pump 3e to measure the density D and temperature T, and then returned to the fuel tank 2. The data on the density D and temperature T measured by the sensor 4 are sent to the control unit 20 each time, whereby the control unit 20 can execute control (a) to acquire a data group G1 of the density D and temperature T measured during the control period P. Subsequently, the control unit 20 executes control (b) to calculate a corresponding methanol concentration group G2 from the data group G1, and control (c) to add a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on the average value α of the methanol concentration group G2. To execute control (c), a methanol tank 5 and a water tank 6 are connected to the fuel tank 2 via liquid feed pumps 3c and 3d, respectively. That is, when the target methanol concentration C0 is greater than the average value α, the liquid feed pump 3c is operated to supply a methanol composition MC1 having a methanol concentration C1 from the methanol tank 5 to the fuel tank 2 to increase the methanol concentration. On the other hand, when the target methanol concentration C0 is less than the average value α, the liquid feed pump 3d is operated to supply water from the water tank 6 to the fuel tank 2 to decrease the methanol concentration.

[0036] As described above, in the example of FIG. 3, the control unit 20 is connected to at least the liquid feed pumps 3c to 3e and the sensor 4, and thereby can execute control (a), control (b), and control (c). In the control unit 20 of the power generation system, after executing control (a), control (b), and control (c) in this order, when further using the methanol composition (that is, when continuing power generation), control (a), control (b), and control (c) can be repeatedly executed one or more times, and when not further using the methanol composition (that is, when ending power generation), the control can be terminated accordingly.

[0037] The control unit 20 may be one as illustrated in FIG. 4, or a plurality of control units connected to at least any one of the liquid feed pumps 3c to 3e and the sensor 4 may be arranged. Further, the control unit 20 may be arranged outside the system of the power generation means 10 or incorporated in the system of the power generation means 10 as illustrated in FIG. 4. The control unit 20 can be configured to perform the following operations. That is, in an example where the controlled system is a direct methanol fuel cell (see FIG. 4), the control unit 20 supplies the methanol composition (aqueous methanol solution) in the tank 2 to the fuel cell stack 1 by the liquid feed pump 3a, and supplies air to the fuel cell stack 1 by the air pump 3b. When generating power, the control unit 20 controls so that the methanol concentration of the methanol composition in the tank 2 is maintained within a predetermined range R1. In such control, the change over time of the methanol concentration of the methanol composition in the tank 2 is confirmed by the sensor 4. As a result of the confirmation, when a decrease in the methanol concentration is detected, in order to supplement the shortage of methanol, the methanol composition MC1 having a methanol concentration C1 can be added from the methanol tank 5 to the tank 2 via the liquid feed pump 3c. As a result of the confirmation, when an increase in the methanol concentration is detected, the addition amount of the methanol composition MC1 can be reduced, and / or water can be added from the water tank 6 to the tank 2 via the liquid feed pump 3d in order to supplement the shortage of water. In the power generation system 100, continuously, the methanol composition (aqueous methanol solution) in the tank 2 is supplied to the fuel cell stack 1 by the liquid feed pump 3a, and air is supplied to the fuel cell stack 1 by the air pump 3b. While power generation is being performed, the methanol concentration control by the sensor 4, the liquid feed pump 3c, and the liquid feed pump 3d is continuously performed. When power generation is completed, or when the methanol concentration and the liquid volume of the tank become constant, the control by the control unit 20 (methanol concentration control by the sensor 4, the liquid feed pump 3c, and the liquid feed pump 3d) can be terminated or temporarily stopped. Note that the operations described above regarding the control unit 20 in the power generation system of the present embodiment can also be implemented as a first method and a second method.

[0038] <Method for producing carbon dioxide> As described above, when the first method or the second method is directly applied to a direct methanol fuel cell, that is, when the power generation means in the power generation system of the present embodiment is a direct methanol fuel cell, at least carbon dioxide can be produced by operating the power generation system (see the above-mentioned overall reaction formula (CH3OH + 3 / 2O2 → CO2 + 2H2O)). In other words, the method for producing carbon dioxide according to the present embodiment (hereinafter also referred to as the "third method") is a method for producing carbon dioxide using a power generation system including a power generation means and a control unit connected to the power generation means, the method including the step of supplying to the power generation means a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, the control unit being configured to execute control for adjusting the methanol concentration to a predetermined range R1, the control including control (a') for obtaining a data group G1 of density D and temperature T measured during a control period P for the methanol composition, control (b') for calculating a corresponding methanol concentration group G2 from the data group G1, and control (c') for adding a methanol composition MC1 having a methanol concentration C1 and / or water to the methanol composition based on an average value α of the methanol concentration group G2, in the control, the addition amount of the methanol composition MC1 and / or water being determined based on the difference between a target methanol concentration C0 selected from the predetermined range R1 and the average value α. Since the third method is configured in this way, it is possible to improve the accuracy of methanol concentration control while suppressing the control load, and as a result, it is possible to produce carbon dioxide while suppressing the output decrease over time.

[0039] Here, the power generation system in the third method can be configured in the same manner as the power generation system of the present embodiment. Also, the controls (a'), (b'), and (c') in the third method can be executed in the same manner as the controls (a), (b), and (c) executed in the power generation system of the present embodiment, respectively. The setting of the predetermined range R1, control period P, density D, temperature T, methanol concentration C1, and target methanol concentration C0 in the power generation system of the present embodiment is not particularly limited, and can be set in the same manner as the control period P, density D, and temperature T in the first method, respectively. The method for calculating the average value α in the power generation system of the present embodiment can also be the same as the method for calculating the average value α in the first method.

Example

[0040] Hereinafter, the present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to these examples.

[0041] [Example 1] The control method of the present embodiment was applied to a direct methanol fuel cell. That is, in a system having the same configuration as FIG. 4, the following operations were executed. In the power generation system 100, continuously, the methanol composition (methanol aqueous solution) in the tank 2 was supplied to the fuel cell stack 1 by the liquid feed pump 3a, and air was supplied to the fuel cell stack 1 by the air pump 3b to generate power. Here, in order to maintain the methanol concentration of the methanol composition in the tank 2 within a predetermined range, the methanol composition in the tank 2 is sent to the sensor 4 by the liquid feed pump 3e and then returned to the tank 2, and the methanol concentration is measured using the sensor 4. That is, as the sensor 4, a MEMS sensor (inline liquid density meter "VLO-M2"; manufactured by TrueDyne Sensors) is used, and from the data group G1 of the density D and temperature T measured for the methanol composition in the tank 2, based on the method described in JIS K1501:2005 Methanol 4. Test Methods (based on the relationship between the temperature, density, and methanol concentration described in JIS K1501:2005 Methanol 4. Test Methods), the corresponding methanol concentration group G2 is calculated. The measurement frequency during such a control period is set to 0.01 seconds / time, and the average value α (the average value of the methanol concentration group G2 for 100 times) of 100 measurement values (100 methanol concentration groups G2) is calculated. Since methanol in the methanol composition is consumed by power generation, when the average value α calculated from the detection result of the sensor 4 becomes <1.8%, the liquid feed pump 3c is turned ON, and when it becomes >2.0%, the liquid feed pump 3c is turned OFF. For 30 minutes, the average value α was in the range of 1.5 to 2.0%. During this period, separately, the methanol composition in the tank 2 was sampled for verification, and the methanol concentration was actually measured over time. It was also found that such actual measurement values were also in the range of 1.5 to 2.0% and the actual measurement values were in good agreement with the average value α. When the above actual measurement value becomes <0.5% or >10%, it was set to emergency stop, but continuous power generation for 30 minutes or more was possible without emergency stop.

[0042] [Comparative Example 1] In Example 1, power generation was performed in the same manner as in Example 1 except that the average value α was not calculated, and when each of the methanol concentration groups G2 calculated from the data group G1 became <1.8%, the liquid feed pump 3c was turned ON, and when it became >2.0%, the liquid feed pump 3c was turned OFF. Before 30 minutes had elapsed since the start of power generation, it was found that the methanol concentration group G2 contained a methanol concentration outside the range of 0.5 to 10%, and thus power generation was stopped urgently.

Explanation of symbols

[0043] 1 Cell stack 2 Tank (fuel tank) 3a, 3c to 3e Liquid feed pump 3b Air pump 4 Sensor 5 Methanol tank 6 Water tank 10 Power generation means 20 Control unit 100 Power generation system

Claims

1. In a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, the methanol concentration is within a predetermined range R 1 A method for controlling the methanol concentration, comprising: Obtaining a data group G of density D and temperature T measured during a control period P for the methanol composition 1 Step (A); From the data group G 1 Calculating a corresponding methanol concentration group G 2 Step (B); Based on the average value α of the methanol concentration group G 2 Adding methanol composition MC having a methanol concentration C 1 And / or water to the methanol composition 1 Step (C); And having The addition amount of the methanol composition MC 1 And / or water is determined based on the difference between the target methanol concentration C 1 Selected from the predetermined range R 0 And the average value α.

2. The method according to claim 1, wherein the measurement frequency during the control period P is from 0.01 second / time to 1 second / time.

3. The method according to claim 1, wherein the number of data points of the methanol concentration group G 2 Is from 10 points to 1000 points.

4. The method according to claim 1, wherein the density D is measured by a MEMS sensor.

5. The method according to claim 1, wherein the target methanol concentration C 0 Is from 0.5% by mass to 5.0% by mass.

6. The method according to claim 1, wherein the methanol concentration C 1 Is from 10% by mass to 100% by mass.

7. In a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, a method for estimating the methanol concentration, comprising: For the methanol composition, a data group G of density D and temperature T measured during a prediction period P'; 1 Obtaining step (A'); The data group G 1 From the corresponding methanol concentration group G 2 Calculating step (B'); As an estimated value of the methanol concentration of the methanol composition, calculating an average value α of the methanol concentration group G 2 Step (C'); A method comprising:

8. Power generation means using a methanol composition in which at least one selected from the group consisting of methanol concentration, density, and temperature changes over time, A control unit connected to the power generation means, A power generation system comprising: The control unit is configured to execute control for adjusting the methanol concentration to a predetermined range R 1 And the control is For the methanol composition, control (a) for obtaining a data group G of density D and temperature T measured during a control period P And the data group G 1 Control (b) for calculating the corresponding methanol concentration group G And the data group G 1 From the corresponding methanol concentration group G 2 Calculating control (b); Based on the average value α of the methanol concentration group G 2 For the methanol composition, control (c) for adding a methanol composition MC 1 Having a methanol concentration C 1 And / or water; Including In the control, the addition amount of the methanol composition MC 1 And / or water is a target methanol concentration C selected from the predetermined range R 1 And 0 ​A power generation system determined based on the difference from the average value α.

9. The power generation system according to claim 8, wherein the power generation means is a direct methanol fuel cell.

Images