JP2020015003A - Ammonia decomposition method and fuel cell system - Google Patents

Abstract

To provide an ammonia decomposition method capable of inhibiting hydrazine from being decomposed to efficiently decompose ammonia, and a fuel cell system using the ammonia decomposition method.SOLUTION: An ammonia decomposition method including a concentrating step of concentrating a hydrazine aqueous solution containing ammonia to thereby adjust an ammonia concentration in the hydrazine aqueous solution to 2.0 mass% or more, a preparation step of oppositely arranging a pair of electrodes 62 in the hydrazine aqueous solution, and a decomposition step of applying an electric current to the electrodes 62 to boil the hydrazine aqueous solution in the vicinity of the electrodes 62 to thereby cause a gas phase between the electrodes 62 and producing plasma in the gas phase on a condition of causing dielectric breakdown in the gas phase to decompose the ammonia contained in the hydrazine aqueous solution.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ammonia decomposition method and a fuel cell system, and more particularly to an ammonia decomposition method effective for decomposing ammonia contained in liquid fuel circulating in a fuel cell system, and a fuel using the ammonia decomposition method. It relates to a battery system.

  Conventionally, ammonia may be generated from various devices that consume nitrogen compounds, such as a fuel cell using hydrazine as a liquid fuel. From the viewpoint of the global environment, such ammonia is usually required to be detoxified before being released to the atmosphere.

  As a method of treating ammonia, for example, a method of decomposing ammonia into nitrogen and hydrogen using a plasma reactor is known.

  More specifically, for example, a pair of electrodes are opposed to each other in an aqueous hydrazine solution containing ammonia at a concentration of 0.001 to 1 mol% (that is, 0.0014 to 1.4 mass%), The electrode is energized, and a hydrazine aqueous solution is boiled in the vicinity of the electrode to generate a gas phase between the electrodes, and a plasma is generated in the gas phase under conditions that cause dielectric breakdown in the gas phase, which is contained in the hydrazine aqueous solution. A method for decomposing ammonia has been proposed (for example, see Patent Document 1).

JP 2017-148745 A

  On the other hand, when ammonia is decomposed in an aqueous hydrazine solution, not only ammonia but also hydrazine may be decomposed, and as a result, nitrogen oxides and the like may be generated, which may require further purification treatment.

  The present invention relates to an ammonia decomposition method capable of suppressing the decomposition of hydrazine and efficiently decomposing ammonia, and a fuel cell system using the ammonia decomposition method.

  In the present invention [1], a concentration step of adjusting the ammonia concentration of the hydrazine aqueous solution to 2.0% by mass or more by concentrating the hydrazine aqueous solution containing ammonia, and disposing a pair of electrodes in the hydrazine aqueous solution to face each other. A preparing step, energizing the electrode, generating a gas phase between the electrodes by boiling the hydrazine aqueous solution in the vicinity of the electrode, and generating a plasma in the gas phase under conditions that cause dielectric breakdown in the gas phase. And a decomposition step of decomposing ammonia contained in the aqueous hydrazine solution.

  The present invention [2] is a fuel cell system capable of decomposing ammonia by the ammonia decomposing method according to the above [1], wherein a fuel cell to which a liquid fuel containing hydrazine is supplied, and a fuel in which the liquid fuel is stored A tank, a fuel supply path for supplying liquid fuel from the fuel tank to the fuel cell, a fuel discharge path for discharging a discharge liquid from the fuel cell, and transporting the discharge liquid from the fuel discharge path to the fuel tank. A recirculation path, a gas-liquid separator interposed between the fuel discharge path and the recirculation path, a water separation unit interposed in the recirculation path for separating moisture from liquid fuel, and the fuel tank. A fuel cell system comprising: a pair of electrodes disposed inside each other; and a plasma generator having a power supply for supplying electricity to the electrodes.

  In the ammonia decomposition method and the fuel cell system of the present invention, first, the ammonia concentration in the hydrazine aqueous solution (liquid fuel) containing ammonia is adjusted to 2.0% by mass or more, and then the electricity is supplied to the hydrazine aqueous solution (liquid fuel). As a result, a gas phase (bubbles) is generated in the hydrazine aqueous solution, and plasma is generated in the gas phase under conditions that cause dielectric breakdown due to the gas phase (bubbles).

  As a result, ammonia in the aqueous hydrazine solution can be efficiently decomposed while suppressing the decomposition of hydrazine.

FIG. 1 is a schematic diagram of an ammonia decomposition apparatus used to carry out one embodiment of the ammonia decomposition method of the present invention. FIG. 2 is a schematic diagram of a fuel cell system using the ammonia decomposition device shown in FIG. FIG. 3 is a schematic configuration diagram showing a concentrator installed in the fuel cell system shown in FIG.

1. Ammonia decomposition method and ammonia decomposition apparatus In the ammonia decomposition method of the present invention, as described later in detail, after adjusting the concentration of ammonia in the hydrazine aqueous solution, ammonia is generated by generating plasma in the hydrazine aqueous solution containing ammonia. (NH ₃ , NH ₄ ⁺ ) is decomposed into nitrogen (N ₂ ) and hydrogen (H ₂ ).

  The hydrazine aqueous solution is an aqueous solution of hydrazine, and contains hydrazine and water, and ammonia.

Examples of the hydrazine include anhydrous hydrazine (NH ₂ NH ₂ ), hydrazine hydrate (NH ₂ NH ₂ .H ₂ O), hydrazine carbonate ((NH ₂ NH ₂ ) ₂ CO ₂ ), and hydrazine sulfate (NH ₂ NH _2). H ₂ SO ₄ ), monomethylhydrazine (CH ₃ NHNH ₂ ), dimethylhydrazine ((CH ₃ ) ₂ NNH ₂ , CH ₃ NHNHCH ₃ ), carboxylic hydrazide ((NHNH ₂ ) ₂ CO) and the like. These hydrazines can be used alone or in combination of two or more. The hydrazine preferably includes anhydrous hydrazine (NH ₂ NH ₂ ) and hydrazine hydrate (NH ₂ NH ₂ .H ₂ O).

  In the aqueous hydrazine solution containing ammonia, the concentration of hydrazine (the concentration before concentration described later) is not particularly limited, but is, for example, 1.0% by mass or more, preferably 2.0% by mass, based on the total amount of the hydrazine aqueous solution. %, For example, 20.0% by mass or less, preferably 15.0% by mass or less.

  In the hydrazine aqueous solution containing ammonia, the concentration of ammonia (concentration before concentration described later) is, for example, 0.001% by mass or more, preferably 0.01% by mass or more based on the total amount of the hydrazine aqueous solution. Yes, for example, less than 2.0% by mass, preferably 1.5% by mass or less, more preferably 1.4% by mass or less, even more preferably 0.14% by mass or less.

  In addition, known additives (such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide) may be added to the aqueous hydrazine solution at an appropriate ratio, if necessary.

  The hydrazine aqueous solution containing such ammonia is treated, for example, by the ammonia decomposition apparatus 50 shown in FIG.

  In FIG. 1, the ammonia decomposition apparatus 50 includes a concentrator 51, a plasma reaction vessel 52, and a plasma generator 53.

  The concentration device 51 includes a storage tank 54 for retaining the hydrazine aqueous solution, a water separation pipe 55 arranged to pass through the storage tank 54, and a blower 56 for supplying air into the water separation pipe 55, A concentrated liquid transport line 57 is provided as a transport path for transporting the aqueous hydrazine solution from the storage tank 54 to the plasma reaction vessel 52.

  The storage tank 54 is a closed container that can store the hydrazine aqueous solution, and is formed of a material that is resistant to the hydrazine aqueous solution. A hydrazine aqueous solution containing ammonia is stored in the storage tank 54.

  Although not shown, the storage tank 54 is provided with an ammonia concentration meter capable of measuring the ammonia concentration in the hydrazine aqueous solution.

  The water separation tube 55 includes, for example, a hollow fiber (hollow fiber membrane) formed of a water separation membrane.

  A water separation membrane is a membrane that blocks ammonia and hydrazine while allowing water to permeate. For example, a carbon membrane, a hydrophobic porous membrane (eg, a polytetrafluoroethylene porous membrane, a polyethylene porous membrane, a polypropylene porous membrane) And the like). The pore size of the water separation membrane is not particularly limited, and is appropriately set within a range that blocks ammonia and hydrazine and allows water to pass therethrough.

  The inner diameter of the hollow fiber (hollow fiber membrane) composed of the water separation membrane is, for example, 200 μm or more, preferably 250 μm or more, and for example, 900 μm or less, preferably 850 μm or less.

  Although not shown in FIG. 1, the water separation tube 55 is preferably formed as a bundle of hollow fibers (hollow fiber membranes) formed of a water separation membrane. Specifically, a plurality of (for example, 500 to 2500) hollow fibers formed of a water separation membrane are bundled to obtain a collective tubular water separation tube 55.

  The water separation pipe 55 is provided so as to pass through the storage tank 54, and is immersed in a hydrazine aqueous solution containing ammonia.

  The blower 56 includes a blower pump 58 and a blower line 59, and is capable of supplying air to the blower line 59 by driving the blower pump 58.

  The water separation pipe 55 described above is disposed in the flow direction of the blower line 59 so as to be interposed in the blower line 59. Thus, air can be supplied from the blower pump 58 to the water separation pipe 55 via the blower line 59.

  The concentrate transport line 57 has an upstream end connected to the storage tank 54 and a downstream end connected to the plasma reaction vessel 52 described later.

  An on-off valve 60 is provided in the flow direction of the concentrated liquid transport line 57.

  The on-off valve 60 is a valve for opening and closing the concentrate transport line 57, and for example, a known on-off valve such as an electromagnetic valve is used. By opening and closing such an on-off valve 60, the hydrazine aqueous solution in the storage tank 54 can be transported to the plasma reaction vessel 52 at an arbitrary timing.

  The plasma reaction container 52 is a heat-resistant and pressure-resistant container that can be sealed, and is formed of a material that is stable with respect to an aqueous hydrazine solution containing ammonia. The shape and size of the plasma reaction vessel 52 are not particularly limited, and are appropriately set according to the purpose and use.

  The plasma generator 53 includes a power supply 61 and a pair of electrodes 62.

  The power source 61 is not particularly limited as long as it can generate plasma in the hydrazine aqueous solution by energizing the electrode 62, and includes, for example, a known pulse power source. The pulse power supply can generally adjust a pulse voltage, a pulse width, and a pulse repetition frequency to arbitrary values, and is electrically connected to the pair of electrodes 62 via wiring.

  The pair of electrodes 62 is formed in, for example, a plate shape, a rod shape, or the like. In FIG. 1, the electrode 62 is formed in a rod shape. Examples of an electrode material for forming the electrode 62 include nickel, copper, stainless steel, and tungsten, and preferably tungsten. The pair of electrodes 62 are fixed to the plasma reaction container 52 so as to penetrate the peripheral side surface of the plasma reaction container 52, and are spaced apart from each other by a predetermined distance in the plasma reaction container 52 so that the end faces face each other. And are arranged facing each other.

  The distance between the end faces of the pair of electrodes 62 is, for example, 0.5 mm or more, preferably 0.8 mm or more, and is, for example, 1.5 mm or less, preferably 1.2 mm or less.

  The cross-sectional shape of the electrode 62 (that is, the shape of the facing surface of the pair of electrodes 62) is not particularly limited, but various shapes such as a substantially circular shape in a cross-sectional view and a substantially square shape in a cross-sectional view are employed. . The cross section of the electrode 62 preferably has a substantially circular shape in cross section.

  For example, when the electrode 62 has a substantially circular shape in cross section, the diameter of the electrode 62 (that is, the diameter of the facing surface of the pair of electrodes 62) is 0.1 mm or more, preferably 0.2 mm or more. And 1.0 mm. Further, for example, when the electrode 62 has a substantially rectangular shape in cross section, the length of one side thereof (that is, the length of one side of the opposing surface of the pair of electrodes 62) is 0.1 mm or more, preferably 0.1 mm or more. 2 mm or more and 1.0 mm.

Further, the cross-sectional area of the electrode 62 (i.e., the area of the facing surfaces of the pair of electrodes 62), 0.007 mm ² or more, preferably is a 0.03 mm ² or more, e.g., 1 mm ² or less, preferably, 0 .8mm ² or less.

  When the size of the electrode 62 is in the above range, a gas phase (bubbles) can be favorably generated in the aqueous hydrazine solution containing ammonia, and dielectric breakdown due to the gas phase (bubbles) can be caused in the solution.

  Hereinafter, the plasma decomposition method using the ammonia decomposition apparatus 50 will be described in detail.

  In this method, first, the aqueous hydrazine solution containing ammonia is concentrated by the concentrating device 51, whereby the ammonia concentration of the aqueous hydrazine solution is adjusted (concentration step).

  More specifically, in this step, in the concentration device 51, the hydrazine aqueous solution is stored in the storage tank 54, and the water separation tube 55 is immersed in the hydrazine aqueous solution.

  In such a state, when the air supply pump 58 of the air blower 56 is driven to supply air to the water separation pipe 55 (hollow fiber membrane) through the air supply line 59, the water contained in the aqueous hydrazine solution around the water separation pipe 55 Is turned into steam, and the steam passes through the hollow fiber membrane of the water separation tube 55.

  As a result, moisture is introduced into the water separation pipe 55, while hydrazine and ammonia remain in the storage tank 54 without being vaporized. The water vapor introduced into the water separation pipe 55 is discharged while being mixed with air.

  As a result, part of the water is separated from the aqueous hydrazine solution, and ammonia and hydrazine are concentrated.

  In this method, preferably, the ammonia concentration of the aqueous hydrazine solution in the storage tank 54 is monitored by an ammonia concentration meter (not shown), and the aqueous hydrazine solution is concentrated by the above-described method until a predetermined ammonia concentration is reached.

  The ammonia concentration after concentration is higher than the ammonia concentration before concentration, and is 2.0% by mass or more, preferably 2.5% by mass or more, more preferably 3.0% by mass, based on the total amount of the hydrazine aqueous solution. As described above, the content is more preferably 3.5% by mass or more, further preferably 4.0% by mass or more, further preferably 4.5% by mass or more, and particularly preferably 5.0% by mass or more. It is 20.0% by mass or less, preferably 10.0% by mass or less.

  The concentration of hydrazine after concentration is not particularly limited, but is higher than the concentration of hydrazine before concentration, for example, 2.0% by mass or more, preferably 5.0% by mass or more. 0 mass% or less, preferably 20.0 mass% or less.

  In this step, by opening the on-off valve 60 of the concentrate transport line 57, the aqueous hydrazine solution in which ammonia has been concentrated is transported from the storage tank 54 to the plasma reaction vessel 52 via the concentrate transport line 57. I do.

  Thus, the aqueous hydrazine solution containing ammonia (ammonia concentrated solution) is stored in the plasma reaction vessel 52.

  Next, in this method, a pair of electrodes 62 are opposed to each other in an aqueous hydrazine solution containing ammonia (ammonia concentrated solution) (preparation step).

  That is, a hydrazine aqueous solution containing ammonia is transported into the plasma reaction vessel 52 in which the electrodes 62 are opposed to each other, so that the pair of electrodes 62 are opposed to each other in the hydrazine aqueous solution.

  Next, in this method, a current is applied to the electrode 62, and a hydrazine aqueous solution is boiled in the vicinity of the electrode 62 to generate a gas phase (bubbles) between the electrodes 62, and dielectric breakdown by the gas phase (bubbles) occurs in the solution. Under the conditions, a plasma is generated in the gas phase (bubbles) to decompose ammonia contained in the aqueous hydrazine solution (decomposition step).

  In the decomposition step, the conditions for generating a gas phase (bubbles) by boiling in an aqueous solution of hydrazine containing ammonia and causing dielectric breakdown in the solution by the gas phase (bubbles) are specifically described below. At least one of the conditions (a) to (c) is satisfied.

(A) Electrode size The size of the pair of electrodes 62 is set in the above-described range. Specifically, when the electrode 62 has a substantially circular shape in cross section, its diameter (that is, the diameter of the facing surface of the pair of electrodes 62) is, for example, 0.1 mm or more, preferably 0.2 mm or more. In addition, for example, it is set to 1.0 mm or less.

  When the size of the electrode 62 is in the above range, a gas phase (bubbles) can be more reliably generated in the hydrazine aqueous solution containing ammonia, and dielectric breakdown due to the gas phase (bubbles) can be caused in the solution. Therefore, ammonia in the hydrazine aqueous solution can be reliably decomposed.

(B) Frequency Among the energization conditions by the electrode 62 (pulse power supply), the pulse repetition frequency is adjusted to an appropriate range.

  Specifically, the pulse repetition frequency is, for example, 20 kHz or more, for example, 300 kHz or less, preferably 100 kHz or less, more preferably 50 kHz or less.

  When the pulse repetition frequency is in the above range, gas phase (bubbles) can be more reliably generated in the aqueous hydrazine solution containing ammonia, and dielectric breakdown by the gas phase (bubbles) can be caused in the solution. Therefore, ammonia in the hydrazine aqueous solution can be reliably decomposed.

(C) Conductance of Solution The conductance (ease of current flow) of the aqueous hydrazine solution containing ammonia is adjusted to an appropriate range.

  Specifically, the conductance of the aqueous hydrazine solution containing ammonia is, for example, 0.01 S / m or more, preferably 0.05 S / m or more, for example, 10 S / m or less, preferably 5 S / m or less. It is.

  If the conductance of the aqueous solution of hydrazine containing ammonia is within the above range, a gas phase (bubbles) is more reliably generated in the aqueous solution of hydrazine containing ammonia, and dielectric breakdown by the gas phase (bubbles) is caused in the solution. Can be. Therefore, ammonia in the hydrazine aqueous solution can be reliably decomposed.

  The method of adjusting the conductance is not particularly limited, and a known method can be adopted. Specifically, for example, a known additive such as an acid or an alkali is added to improve the conductivity of the solution. For example, a method of removing ions in a solution with an ion-adsorbing resin or the like to lower the conductivity, and the like can be mentioned.

  In this ammonia decomposition method, at least one or more of the above conditions (a) to (c) may be satisfied. Preferably, all of the above conditions (a) to (c) are satisfied. Satisfying. If all of the above conditions (a) to (c) are satisfied, a gas phase (bubbles) is generated in the hydrazine aqueous solution containing ammonia, and dielectric breakdown due to the gas phase (bubbles) is caused in the solution. Can be done. Therefore, ammonia in the hydrazine aqueous solution can be reliably decomposed.

  Note that conditions other than the above (a) to (c) are not particularly limited, and are appropriately set according to the purpose and use.

  Specifically, the amount of the aqueous hydrazine solution containing ammonia is, for example, 10 mL or more, preferably 20 mL or more, for example, 100 L or less, preferably 50 L or less.

  Further, among the energization conditions by the electrode 62 (pulse power supply), the pulse voltage is, for example, 1 kV or more, preferably 3 kV or more, for example, 20 kV or less, preferably 15 kV or less.

  The pulse width is, for example, 0.1 μs or more, preferably 1 μs or more, for example, 10 μs or less, preferably 5 μs or less.

  Further, the irradiation time (energization time) is, for example, 5 minutes or more, preferably 30 minutes or more, for example, 6 hours or less, preferably 2 hours or less.

  By energizing under such conditions, the hydrazine aqueous solution containing ammonia boils, and a gas phase (bubbles) is generated in the solution, and dielectric breakdown due to the gas phase (bubbles) occurs in the solution. At this time, the ammonia in the hydrazine aqueous solution moves into the gas phase (bubbles) and is gasified (ammonia gasified).

  In such a state, since the hydrazine aqueous solution containing ammonia is energized by the plasma generator 53, the ammonia gas in the gas phase (bubbles) is subjected to plasma processing and decomposed into nitrogen and hydrogen.

  In other words, in such an ammonia decomposition method, a gas phase (bubbles) is generated in a solution by energization, and plasma is generated in the gas phase (bubbles) under conditions that cause dielectric breakdown in the gas phase to occur in the solution. . At this time, the ammonia contained in the solution moves into the gas phase (bubbles), and the ammonia is decomposed in the gas phase (bubbles).

  According to such an ammonia decomposition method, ammonia can be efficiently decomposed at low cost in an aqueous hydrazine solution containing ammonia.

  Further, by satisfying at least one of the above conditions (a) to (c), dielectric breakdown in the gas phase can be reliably caused in the aqueous hydrazine solution containing ammonia. . Therefore, ammonia in the hydrazine aqueous solution can be reliably decomposed.

  In particular, in the above-described ammonia decomposition method, first, the ammonia concentration in the hydrazine aqueous solution containing ammonia is adjusted to 2.0% by mass or more, and thereafter, the current is passed through the hydrazine aqueous solution, so that the gas phase (bubbles) ) Is generated, and plasma is generated in the gaseous phase under conditions that cause dielectric breakdown by the gaseous phase (bubbles).

  In other words, when the plasma is generated, the ammonia concentration in the hydrazine aqueous solution is adjusted to 2.0% by mass or more.

  As a result, ammonia in the aqueous hydrazine solution can be efficiently decomposed while suppressing the decomposition of hydrazine.

  In the above ammonia decomposition method and ammonia decomposition apparatus, water was separated from the aqueous hydrazine solution by a water separation membrane and a blower to concentrate ammonia.However, the concentration method in the concentration step is not particularly limited, and a known method is employed. can do.

  Therefore, such an ammonia decomposition method can be used in various industrial fields, and in particular, can be suitably used in a fuel cell using hydrazine as a liquid fuel.

2. 2. Overall Configuration of Fuel Cell System In FIG. 2, an electric vehicle 1 is a hybrid vehicle that selectively uses a fuel cell and a battery as power sources, and has a fuel cell system 2 mounted thereon.

  The fuel cell system 2 is a fuel cell system capable of decomposing ammonia by the above-described ammonia decomposition method. The fuel cell system 2 includes a fuel cell 3, a fuel supply / discharge unit 4, an air supply / discharge unit 5, an ammonia decomposition device 50, a control unit 6, and a power unit 7.

(1) Fuel Cell The fuel cell 3 is, for example, an anion exchange type fuel cell or a cation exchange type fuel cell to which the liquid fuel is directly supplied and discharged, and is disposed below the center of the electric vehicle 1. Examples of the liquid fuel include a liquid fuel containing hydrazine as a fuel compound, and specifically, an aqueous solution of hydrazine. In addition, known additives (such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide) may be added to the liquid fuel at an appropriate ratio, if necessary.

  In the following, the liquid fuel supplied to the fuel cell 3 is a supply liquid, while the liquid fuel discharged from the fuel cell 3 (a reaction product of the liquid fuel supplied to the fuel cell 3 (nitrogen gas, ammonia, etc.) And water produced by the reaction) are distinguished from each other as effluents.

  The fuel cell 3 includes a unit cell 28 (fuel cell) having an electrolyte layer 8, an anode 9 disposed on one side of the electrolyte layer 8, and a cathode 10 disposed on the other side of the electrolyte layer 8. It is formed in a stack structure in which a plurality of layers are stacked via a not shown (not shown). That is, a plurality of unit cells 28 each having the anode 9 and the cathode 10 opposed to each other with the electrolyte layer 8 interposed therebetween are stacked. In FIG. 2, of the plurality of unit cells 28 that are stacked, only the unit cell 28 that is arranged in the front-rear direction of the electric vehicle 1 is shown in an enlarged manner, and the other unit cells 28 are described in a simplified manner. ing.

  The electrolyte layer 8 is a layer to which an anion component or a cation component can move, for example, and is formed using an anion exchange membrane or a cation exchange membrane. The electrolyte layer 8 is preferably formed using an anion exchange membrane.

  The anode 9 has an anode electrode 11 as a fuel-side electrode, and a fuel supply member 12 for supplying a liquid fuel (supply liquid) to the anode electrode 11.

  The anode electrode 11 is formed on one surface of the electrolyte layer 8. Examples of the electrode material of the anode electrode 11 include a porous carrier on which a catalyst is supported (a catalyst-supporting porous carrier).

  The fuel supply member 12 is also used as a separator, and is made of a gas-impermeable conductive member. The fuel supply member 12 is formed with a concave groove that is recessed from the surface. The grooved surface of the fuel supply member 12 is in contact with the anode electrode 11. As a result, a fuel supply passage for bringing the liquid fuel (supply liquid) into contact with the entire anode electrode 11 is provided between one surface of the anode electrode 11 and the other surface (the surface on which the groove is formed) of the fuel supply member 12. 13 are formed.

  A fuel supply port 15 is formed at one end (lower side) of the fuel supply passage 13 for allowing a liquid fuel (supply liquid) to flow into the anode 9, for discharging the liquid fuel (discharge liquid) from the anode 9. Is formed on the other end side (upper side).

  The cathode 10 has a cathode electrode 16 as an oxygen-side electrode, and an air supply member 17 for supplying air (oxygen) to the cathode electrode 16.

  Cathode electrode 16 is formed on the other surface of electrolyte layer 8.

  Examples of the electrode material of the cathode electrode 16 include a catalyst-supporting porous carrier exemplified as the electrode material of the anode electrode 11.

  The air supply member 17 is also used as a separator, and is made of a gas-impermeable conductive member. The air supply member 17 is formed with a concave groove that is recessed from the surface. The air-supplying member 17 has a surface on which the groove is formed, and is opposed to the cathode electrode 16. As a result, an air supply passage 18 is formed between the other surface of the cathode electrode 16 and one surface (the surface on which the groove is formed) of the air supply member 17 for bringing air into contact with the entire cathode electrode 16. .

  An air supply port 19 for allowing air to flow into the cathode 10 is formed at the other end (upper side) of the air supply path 18, and an air discharge port 20 for discharging air from the cathode 10 is formed at one end (lower side). Side).

  Further, in such a fuel cell 3, one separator that partitions each of the plurality of unit cells 28 has both the fuel supply member 12 and the air supply member 17. In other words, the separator acts on one side as the fuel supply member 12 and on the other side as the air supply member 17.

(2) Fuel supply / discharge unit The fuel supply / discharge unit 4 includes a high-concentration fuel tank 22 for storing liquid fuel containing hydrazine at a high concentration (high-concentration liquid fuel), a high-concentration fuel tank 22, and a fuel cell 3. A high-concentration fuel supply line 45 for supplying liquid fuel (primary (high-concentration) supply liquid) from the high-concentration fuel tank 22 to the circulation fuel tank 47; A fuel supply line 30 as a fuel supply path for supplying a supply liquid (secondary (low-concentration) supply liquid) from the circulating fuel tank 47 to the fuel cell 3 (specifically, the fuel supply path 13); Specifically, a fuel discharge line 31 serving as a fuel discharge path for discharging the discharge liquid from the fuel supply path 13), and a reflux line 3 serving as a return path for transporting the discharge liquid from the fuel discharge line 31 to the circulation fuel tank 47. 2 is provided.

  The fuel cell 3 is interposed between the fuel supply line 30 and the fuel discharge line 31, and a gas-liquid separator 23 (described later) is provided between the fuel discharge line 31 and the reflux line 32. Is interposed.

  The high concentration fuel tank 22 is disposed behind the fuel cell 3 and on the rear side of the electric vehicle 1. The high-concentration fuel tank 22 stores a high-concentration aqueous solution of hydrazine as a liquid fuel.

  The high concentration fuel supply line 45 has an upstream end connected to the high concentration fuel tank 22 and a downstream end connected to the circulation fuel tank 47.

  The high-concentration fuel supply line 45 is provided with a first supply pump 33 and a fuel supply valve 34.

  As the first supply pump 33, for example, a known liquid feed pump such as a rotary pump such as a rotary pump and a gear pump, a reciprocating pump such as a piston pump and a diaphragm pump is used. The first supply pump 33 is electrically connected to a control unit 29 (described later) (see a broken line in FIG. 2). Accordingly, a control signal from the control unit 29 (described later) is input to the first supply pump 33, and the control unit 29 (described later) controls driving and stopping of the first supply pump 33.

  The fuel supply valve 34 is a valve for opening and closing the high-concentration fuel supply line 45, and for example, a known on-off valve such as an electromagnetic valve is used. Further, the fuel supply valve 34 is electrically connected to a control unit 29 (described later) (see a broken line in FIG. 2). Accordingly, a control signal from the control unit 29 (described later) is input to the fuel supply valve 34, and the control unit 29 (described later) controls opening and closing of the fuel supply valve 34.

  By driving the first supply pump 33 and opening and closing the fuel supply valve 34, the liquid fuel (primary (high concentration) supply liquid) is supplied to the high concentration fuel tank 22 through the high concentration fuel supply line 45. Is supplied to the circulating fuel tank 47.

  The circulating fuel tank 47 is a tank for storing liquid fuel, and is formed of the above-mentioned material having resistance to liquid fuel.

  The downstream end of a reflux line 32 (described later) is connected to the circulating fuel tank 47, and the discharged liquid is supplied through the reflux line 32, as described in detail later. Thus, in the circulating fuel tank 47, the liquid fuel (primary supply liquid) transported from the high-concentration fuel tank 22 and the discharged liquid discharged from the fuel cell 3 are mixed at an appropriate ratio, and the fuel cell 3 The concentration of the liquid fuel (secondary supply liquid) supplied to is adjusted.

  The fuel supply line 30 has an upstream end connected to the circulating fuel tank 47 and a downstream end connected to the fuel cell 3 (specifically, the fuel supply passage 13 of the anode 9). I have.

  Further, a second supply pump 35 is provided in the fuel supply line 30.

  As the second supply pump 35, the above-described known liquid supply pump is used. The second supply pump 35 is electrically connected to a control unit 29 (described later) (see a broken line in FIG. 2). Accordingly, a control signal from the control unit 29 (described later) is input to the second supply pump 35, and the control unit 29 (described later) controls driving and stopping of the second supply pump 35.

  By driving the second supply pump 35, a liquid fuel (secondary (low concentration) supply liquid) containing hydrazine at a relatively low concentration is supplied from the circulating fuel tank 47 to the fuel cell 3 via the fuel supply line 30. Supplied to

  The fuel discharge line 31 has an upstream end connected to the fuel cell 3 (specifically, the fuel supply passage 13 of the anode 9), and a downstream end connected to the gas-liquid separator 23. ing.

  With such a fuel discharge line 31, the discharged liquid is discharged from the fuel cell 3 and transported to the gas-liquid separator 23.

  The gas-liquid separator 23 is formed of, for example, a hollow container, and has two bottom circulation ports 24 formed at the lower portion thereof to allow the inside and outside of the gas-liquid separator 23 to flow.

  In addition, one upper circulation port 25 for circulating the inside and outside of the gas-liquid separator 23 is formed in the upper part of the gas-liquid separator 23.

  In the gas-liquid separator 23, two bottom circulation ports 24 are formed in the fuel discharge line 31 and the reflux line 32 (rearward in the front-rear direction of the electric vehicle 1 and in the vertical direction of the electric vehicle 1). (Described later).

  A gas discharge pipe 26 for discharging the gas (gas) separated by the gas-liquid separator 23 is connected to the upper circulation port 25. The gas discharge pipe 26 is connected to the upper circulation port 25. A gas discharge valve 27 is provided in the gas discharge pipe 26.

  The gas discharge valve 27 is a valve for opening the gas discharge pipe 26 to release the pressure in the gas-liquid separator 23. For example, a known on-off valve such as an electromagnetic valve is used. The gas discharge valve 27 is electrically connected to a control unit 29 (described later) (see a broken line in FIG. 2). Accordingly, a control signal from a control unit 29 (described later) is input to the gas discharge valve 27, and the control unit 29 (described later) controls opening and closing of the gas discharge valve 27.

  The reflux line 32 has an upstream end connected to the gas-liquid separator 23 and a downstream end connected to the upper wall of the circulating fuel tank 47.

  Thereby, the discharged liquid transported in the fuel discharge line 31 is transported to the circulating fuel tank 47 via the gas-liquid separator 23 and the reflux line 32, and further via the storage tank 54 described later. Then, in the circulating fuel tank 47, the fuel is mixed with the liquid fuel (primary supply liquid) transported from the high-concentration fuel tank 22, adjusted in concentration, and supplied to the fuel cell 3 as a supply liquid (secondary supply liquid). By returning, a closed line (closed flow path) circulating through the anode 9 is formed. That is, the circulating fuel tank 47, the fuel supply line 30, the fuel supply path 13, the fuel discharge line 31, the gas-liquid separator 23, the reflux line 32, and the storage tank 54 (described later) form a closed line (closed flow path). .

(3) Air supply / discharge unit The air supply / discharge unit 5 includes an air supply line 41 for supplying air to the fuel cell 3 (cathode 10), and an air discharge for discharging air discharged from the cathode 10 to the outside. And a line 42.

  One end (upstream) of the air supply line 41 is open to the atmosphere, and the other end (downstream) is connected to the air supply port 19. An air supply pump 43 is interposed in the air supply line 41, and an air supply valve 44 is provided downstream of the air supply pump 43.

  The air supply pump 43 is electrically connected to the control unit 29 (described later), and a control signal from the control unit 29 (described later) is input to the air supply pump 43, and the control unit 29 (described later) is controlled. , And controls the driving and stopping of the air supply pump 43.

  The air supply valve 44 is a valve for opening and closing the air supply line 41, and for example, a known on-off valve such as a solenoid valve is used.

  The air supply valves 44 are each electrically connected to a control unit 29 (described later), and a control signal from the control unit 29 (described later) is input to the air supply valve 44 and the control unit 29 (described later) is controlled. ) Controls the opening and closing of the air supply valve 44.

  Further, as described later, the air supply line 41 is disposed downstream of the air supply pump 43 and the air supply valve 44 so as to pass through a storage tank 54 (described later).

  One end (upstream side) of the air discharge line 42 is connected to the air discharge port 20, and the other end (downstream side) is drained.

(4) Ammonia Decomposition Device The ammonia decomposition device 50 is provided in the fuel cell system 2 in order to decompose ammonia in a liquid fuel (that is, an aqueous hydrazine solution).

  The ammonia decomposing device 50 is provided in the reflux line 32 and includes a concentrating device 51 as a water separating means for separating water from the liquid fuel, and a plasma generating device 53 for generating plasma in the circulating fuel tank 47. Have.

  As shown in FIG. 3, the concentration device 51 includes a storage tank 54 for retaining the liquid fuel, and a water separation pipe 55 interposed in the air supply line 41 and disposed so as to pass through the storage tank 54. Have.

  The storage tank 54 is the same as the storage tank 54 of the ammonia decomposer 50 shown in FIG. 1, is a closed container capable of retaining liquid fuel, and is formed of the above-described material resistant to liquid fuel.

  In the fuel cell system 2, the storage tank 54 is interposed in the return line 32, as shown in FIG. Specifically, the reflux line 32 is divided by the storage tank 54. The reflux line 32 is connected to the upper wall of the storage tank 54, and the reflux line 32 is also connected to the bottom wall of the storage tank 54. Liquid fuel is temporarily stored in the storage tank 54 by the operation of the fuel cell system 2.

  The water separation pipe 55 is the same as the water separation pipe 55 of the ammonia decomposition apparatus 50 shown in FIG. 1, and includes a hollow fiber (hollow fiber membrane) formed of a water separation membrane. Preferably, it is formed as a bundle of hollow fibers (hollow fiber membranes) composed of a water separation membrane. Specifically, a plurality of (for example, 500 to 2500) hollow fibers formed of a water separation membrane are bundled to obtain a collective tubular water separation tube 55.

  The water separation pipe 55 is disposed in the storage tank 54 so as to be interposed in the air supply line 41 (see a thick broken line in FIG. 3).

  More specifically, one or more (one in FIG. 3) water separation pipes 55 are arranged in the storage tank 54, and are immersed in a liquid fuel (not shown).

  In the ammonia decomposition apparatus 50, the circulation line 32 is also used as the concentrated liquid transport line 57 shown in FIG. 1 on the downstream side of the storage tank 54.

  On the downstream side of the storage tank 54, an on-off valve 60 is provided in the flow direction of the circulation line 32 (concentrated liquid transport line 57).

  The on-off valve 60 is a valve for opening and closing the concentrate transport line 57, and for example, a known on-off valve such as an electromagnetic valve is used. The on-off valve 60 is electrically connected to a control unit 29 (described later) (see a broken line in FIG. 2). Thereby, a control signal from the control unit 29 (described later) is input to the on-off valve 60, and the control unit 29 (described later) controls opening and closing of the on-off valve 60.

  Further, although not shown, an ammonia concentration meter capable of measuring the concentration of ammonia in the liquid fuel (hydrazine aqueous solution) in the storage tank 54 is provided in the storage tank 54, and the ammonia concentration in the storage tank 54 is monitored. It is possible to input the ammonia concentration to the control unit 29.

  The plasma generating device 53 includes a pair of electrodes 62 disposed facing each other in the circulating fuel tank 47, and a power supply 61 for energizing the electrodes 62.

  The pair of electrodes 62 is the same as the pair of electrodes 62 of the ammonia decomposition device 50 shown in FIG. 1, and is fixed to the circulating fuel tank 47 so as to penetrate the peripheral side wall of the circulating fuel tank 47. In the fuel tank 47, the fuel tanks 47 are arranged so as to face each other at a predetermined interval so that the end faces face each other.

  The power supply 61 is the same as the power supply 61 of the ammonia decomposition apparatus 50 shown in FIG. 1, and includes, for example, a known pulse power supply. The pulse power supply can generally adjust a pulse voltage, a pulse width, and a pulse repetition frequency to arbitrary values, and is electrically connected to the pair of electrodes 62 via wiring.

  That is, the circulating fuel tank 47 shown in FIG. 2 is also used as the plasma reaction vessel 52, and the pair of electrodes 62 is fixed to the peripheral wall thereof, and the power supply 61 and the electrode 62 are connected to each other, so that the plasma generator 53 are configured.

(5) Control Unit The control unit 6 includes a control unit 29.

  The control unit 29 is a control unit (for example, an electronic control unit (ECU)) that executes electric control in the electric vehicle 1, and is configured by a microcomputer including a CPU, a ROM, a RAM, and the like.

  In the control unit 6, as will be described in detail later, for example, driving and stopping of the first supply pump 33 and the second supply pump 35, and, for example, the fuel supply valve 34, the gas discharge valve 27, the air supply valve 44, the on-off valve Opening / closing of 60 or the like is appropriately controlled.

(6) Power Unit The power unit 7 includes a motor 37 for converting electric energy output from the fuel cell 3 into mechanical energy as a driving force of the electric vehicle 1, and an inverter 38 electrically connected to the motor 37. , A power battery 40 for storing regenerative energy from the motor 37, and a DC / DC converter 36.

  The motor 37 is disposed forward of the fuel cell 3 and in front of the electric vehicle 1. Examples of the motor 37 include a known three-phase motor such as a three-phase induction motor and a three-phase synchronous motor.

  The inverter 38 is disposed between the motor 37 and the fuel cell 3. The inverter 38 is a device that converts DC power generated by the fuel cell 3 into AC power, and includes, for example, a power conversion device incorporating a known inverter circuit. The inverter 38 is electrically connected to the fuel cell 3 and the motor 37 by wiring.

  Examples of the power battery 40 include a known secondary battery such as a nickel-metal hydride battery having a rated voltage of about 100 V and a lithium-ion battery. The power battery 40 is connected to the wiring between the inverter 38 and the fuel cell 3, whereby power from the fuel cell 3 can be stored and power can be supplied to the motor 37.

  The DC / DC converter 36 is arranged between the power battery 40 and the fuel cell 3. The DC / DC converter 36 has a function of raising and lowering the output voltage of the fuel cell 3 and a function of adjusting the power of the fuel cell 3 and the input / output power of the power battery 40.

  The DC / DC converter 36 is electrically connected to the control unit 29 (see the broken line in FIG. 2), so that the fuel cell 3 is controlled according to the output control signal output from the control unit 29. Output (output voltage).

  The DC / DC converter 36 is electrically connected to the fuel cell 3 and the power battery 40 by wiring, and is electrically connected to the inverter 38 by branching of the wiring.

  Thus, the power from the DC / DC converter 36 to the motor 37 is converted from the DC power into three-phase AC power in the inverter 38 and supplied to the motor 37 as three-phase AC power.

3. In the above-described fuel cell system 2, the fuel supply valve 34 is opened under the control of the control unit 29, and the first supply pump 33 is driven, so that the liquid stored in the high-concentration fuel tank 22 is controlled. Fuel (primary supply liquid) is supplied to the circulating fuel tank 47 via the high-concentration fuel supply line 45. Further, under the control of the control unit 29, the second supply pump 35 is driven, and the liquid fuel (secondary supply liquid) in the circulation fuel tank 47 is supplied to the anode 9 via the fuel supply line 30. On the other hand, when the air supply valve 44 is opened and the air supply pump 43 is driven, air is supplied to the cathode 10 via the air supply line 41. The fuel supply valve 34 is closed after a predetermined amount of liquid fuel is supplied.

  At the anode 9, the liquid fuel passes through the fuel supply path 13 while being in contact with the anode electrode 11. On the other hand, in the cathode 10, air passes through the air supply path 18 while contacting the cathode electrode 16.

  Then, an electrochemical reaction occurs in each electrode (the anode electrode 11 and the cathode electrode 16), and an electromotive force is generated.

For example, when the electrolyte layer 8 is an anion exchange membrane and the liquid fuel is an aqueous hydrazine solution, for example, an aqueous solution of anhydrous hydrazine (N ₂ H ₄ ), the following equations (1) to (3) are obtained.
(1) N ₂ H ₄ + 4OH ⁻ → N ₂ + 4H ₂ O + 4e ⁻ (reaction at the anode electrode 11)
(2) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at cathode electrode 16)
(3) N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O (reaction in the entire fuel cell 3)
That is, at the anode electrode 11 to which hydrazine is supplied, hydrazine (N ₂ H ₄ ) reacts with hydroxide ions (OH ⁻ ) generated by the reaction at the cathode electrode 16 to form nitrogen (N ₂ (gas). ) And water (H ₂ O) are generated, and electrons (e ⁻ ) are generated (see the above formula (1)).

In addition, in the reaction shown in the above (1), ammonia (NH ₃ , NH ₄ ⁺ ) is actually produced as a by-product in addition to nitrogen (N ₂ (gas)) and water (H ₂ O).

The electrons (e ⁻ ) generated at the anode electrode 11 reach the cathode electrode 16 via an external circuit (not shown). That is, the electrons (e ⁻ ) passing through the external circuit become currents.

On the other hand, at the cathode electrode 16, electrons (e ⁻ ), water (H ₂ O) generated from an external supply or a reaction in the fuel cell 3, and oxygen (O ₂ ) in the air flowing through the air supply passage 18. Reacts with to generate hydroxide ions (OH ⁻ ) (see the above formula (2)).

Then, the generated hydroxide ion (OH ⁻ ) passes through the electrolyte layer 8 and reaches the anode electrode 11, and the same reaction as described above (see the above formula (1)) occurs.

  When the electrochemical reaction at the anode electrode 11 and the cathode electrode 16 occurs continuously, the reaction represented by the above formula (3) occurs in the fuel cell 3 as a whole, and the electromotive force is generated in the fuel cell 3. appear.

  Then, the generated electromotive force is transmitted to the DC / DC converter 36 via the wiring, and the power unit 7 transmits the power to the inverter 38 and the motor 37 and / or the power battery 40. Then, in the motor 37, the electric energy converted into three-phase AC power by the inverter 38 is converted into mechanical energy for driving the wheels of the electric vehicle 1. On the other hand, the power battery 40 charges the electric power.

In the fuel supply / discharge unit 4, the liquid fuel discharged from the anode 9 (including used and unreacted liquid fuel, nitrogen gas (N ₂ ) by-produced, and ammonia (NH ₃ , NH ₄ ⁺ )). Passes through the fuel discharge line 31 and flows into the gas-liquid separator 23 from the bottom circulation port 24 on the upstream side.

In the gas-liquid separator 23, a liquid pool due to the discharged liquid is generated in a hollow portion of the gas-liquid separator 23, and a part of the gas (such as nitrogen gas (N ₂ )) contained in the discharged liquid is located above the liquid pool. Separated into space.

  Thus, in the gas-liquid separator 23, the discharged liquid is separated into the liquid fuel and the gas.

  The gas separated in the gas-liquid separator 23 is discharged to the outside via the gas discharge pipe 26 when the gas discharge valve 27 is opened.

  On the other hand, the liquid fuel separated in the gas-liquid separator 23 flows into the circulating fuel tank 47 via the reflux line 32, is circulated as a supply liquid (secondary supply liquid), and is again supplied from the fuel supply port 15 through the fuel supply port 15. It flows into the supply path 13.

  When the fuel concentration in the liquid fuel decreases with the circulating use of the secondary supply liquid, the liquid fuel separated in the gas-liquid separator 23 and flowing into the circulating fuel tank 47 is supplied to the fuel supply valve 34. The liquid supply (primary (high-concentration) supply liquid) transported from the high-concentration fuel tank 22 by the opening and closing of the fuel tank 22 is mixed and adjusted in concentration, and then, as a supply liquid (secondary supply liquid), again into the fuel supply port 15. From the fuel supply passage 13.

  In this way, the liquid fuel circulates in the fuel circulation path (recirculation line 32, circulation fuel tank 47, fuel supply line 30, fuel discharge line 31, gas-liquid separator 23, and fuel supply path 13).

4. As shown in the above formula (3), in the fuel cell system 2, when an aqueous hydrazine solution is used as the liquid fuel, the reaction between hydrazine (N ₂ H ₄ ) and oxygen (O ₂ ) causes nitrogen gas to be removed. (N ₂ ) and water (H ₂ O).

Further, in this reaction, ammonia (NH ₃ , NH ₄ ⁺ ) is by-produced in addition to nitrogen gas (N ₂ ) and water (H ₂ O), and ammonia is contained in the liquid fuel.

  Therefore, in the fuel cell system 2, the above-described ammonia decomposition method is performed in the storage tank 54 and the circulating fuel tank 47 interposed in the fuel circulation path (closed line).

  More specifically, in this method, first, in the storage tank 54, a part of the water contained in the aqueous hydrazine solution is separated, and the aqueous hydrazine solution is concentrated (concentration step).

  That is, when ammonia is generated in the fuel cell 3, the liquid fuel containing ammonia (that is, the aqueous solution of hydrazine containing ammonia) is discharged from the fuel cell 3 to the fuel discharge line 31 and passes through the gas-liquid separator 23. Then, the fuel is accumulated in the storage tank 54.

  On the other hand, in the storage tank 54, the air flowing through the air supply line 41 is supplied into the water separation pipe 55 (hollow fiber membrane).

  That is, in the concentration device 51, the liquid fuel (hydrazine aqueous solution containing ammonia) is retained in the storage tank 54, the water separation pipe 55 is immersed in the liquid fuel (hydrazine aqueous solution containing ammonia), and Air passes through the inside of the separation tube 55.

  In such a concentrating device 51, when air passes through the inside of the water separation tube 55, part of the water contained in the liquid fuel around the water separation tube 55 is steamed, and the steam is removed from the water separation tube 55. Pass through a water separation membrane. That is, thereby, a part of the water in the liquid fuel (hydrazine aqueous solution containing ammonia) is introduced into the water separation pipe 55.

  On the other hand, hydrazine and ammonia in the liquid fuel remain in the storage tank 54 without being vaporized.

  Thereby, only water is separated from the liquid fuel, and hydrazine and ammonia are concentrated. The hydrazine concentration and the ammonia concentration after the concentration are within the above ranges.

  Specifically, in the storage tank 54, the ammonia concentration of the liquid fuel is measured by an ammonia concentration meter (not shown). The liquid fuel is concentrated until the ammonia concentration is equal to or higher than the lower limit, that is, equal to or higher than 2.0% by mass based on the total amount of the liquid fuel.

  Then, when the ammonia concentration of the liquid fuel becomes equal to or more than the above lower limit, the on-off valve 60 is opened by operating the control unit 29.

  Thereby, the concentrated liquid fuel (hydrazine aqueous solution containing ammonia) is supplied to the circulating fuel tank 47 via the reflux line 32 as shown in FIG.

  At this time, the circulating fuel tank 47 is also used as the plasma reaction vessel 52 in the ammonia decomposition device 50, and a pair of electrodes 62 is provided on the peripheral wall surface.

  Therefore, when the concentrated liquid fuel is supplied to the circulation fuel tank 47, the pair of electrodes 62 are arranged to face each other in the liquid fuel (preparation step).

  Thereafter, the electrode 62 is energized under the above-described conditions (that is, conditions for generating bubbles in the solution) to generate plasma in the hydrazine aqueous solution. Thereby, the ammonia contained in the aqueous hydrazine solution can be decomposed.

  Then, as described above, the liquid fuel in which the ammonia has been decomposed is mixed with the liquid fuel (primary (high-concentration) supply liquid) transported from the high-concentration fuel tank 22 as necessary, and the concentration thereof is adjusted. , Again flows into the fuel supply path 13 from the fuel supply port 15 as a supply liquid (secondary supply liquid).

  According to such an ammonia decomposition method, in the fuel cell system 2, ammonia contained in the circulating liquid fuel can be decomposed in the liquid fuel.

  Particularly, in the above-described ammonia decomposition method, first, the ammonia concentration in the liquid fuel is adjusted to 2.0% by mass or more, and thereafter, the gas is generated in the liquid fuel by energizing the liquid fuel. In addition, a plasma is generated in the gas phase under the condition that dielectric breakdown occurs due to the gas phase (bubbles).

  In other words, when the plasma is generated, the ammonia concentration in the hydrazine aqueous solution is adjusted to 2.0% by mass or more.

  As a result, it is possible to efficiently decompose ammonia in the liquid fuel while suppressing the decomposition of hydrazine.

  As a result, the power generation can be efficiently performed by the fuel cell system 2 without the necessity of further purification treatment of nitrogen oxides.

  The water separated from the liquid fuel is introduced into the water separation pipe 55 and mixed with air. Thereby, the air is humidified. The humidified air passes through the water separation pipe 55 (hollow fiber membrane) and is supplied to the fuel cell 3 via the air supply line 41 (the air supply line 41 downstream of the storage tank 54).

  In such a fuel cell system 2, the water contained in the effluent discharged from the fuel cell 3 is recovered, and the water can be used to wet the electrolyte layer 8, thereby improving the power generation efficiency. Can be.

5. Modifications In the above description, first, the liquid fuel is concentrated to a predetermined concentration by the concentration device 51, and then the opening and closing of the on-off valve 60 is controlled to intermittently supply the liquid fuel to the circulating fuel tank 47. Although the ammonia in the liquid fuel is intermittently decomposed, for example, by controlling the drive of the second supply pump 35 and adjusting the flow rate of the circulating liquid fuel, the on-off valve 60 is always opened, The liquid fuel is continuously supplied to the circulation fuel tank 47, whereby the ammonia in the liquid fuel can be continuously decomposed.

  Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Note that “parts” and “%” are based on mass unless otherwise specified. Specific numerical values such as the mixing ratio (content ratio), physical property values, and parameters used in the following description are the mixing ratios (corresponding to them) described in the above-mentioned “Embodiments of the Invention”. Substitute the upper limit value (value defined as “less than” or “less than”) or the lower limit value (value defined as “over” or “exceeding”) such as content ratio, physical property value, parameter, etc. be able to.

Example 1
An ammonia decomposition apparatus shown in FIG. 1 was prepared. The capacity of the plasma reaction vessel was 50 to 100 mL, and a tungsten electrode having a substantially circular shape in cross section (1 mm in diameter) was used as the electrode.

  In addition, as a solution containing ammonia, an aqueous solution of hydrazine containing ammonia was used. In addition, potassium hydroxide was added to the hydrazine aqueous solution, and the conductance was 0.08 S / m.

  Further, when 50 mL of the hydrazine aqueous solution was measured by ion chromatography analysis, the hydrazine concentration was 5.2% by mass, and the ammonia concentration was below the detection limit.

  Next, a hollow fiber (hollow fiber membrane) composed of a water separation membrane was immersed in 50 mL of a hydrazine aqueous solution containing ammonia, and air was passed through the hollow fiber to concentrate the aqueous hydrazine solution. The hydrazine concentration after concentration was 5.0% by mass, and the ammonia concentration was 2.0% by mass.

  Then, in an argon atmosphere, a power supply was operated under the conditions of a pulse voltage of 5 kV, a frequency of 20 kHz, a pulse width of 2 μs, and an irradiation time of 30 minutes, and electricity was supplied to the electrode in a hydrazine aqueous solution to generate bubbles in the solution. Dielectric breakdown was caused by the bubbles, and plasma was generated in the bubbles. In addition, during the operation, the reaction vessel was cooled to 20 to 30 ° C with a chiller.

  Thereafter, the power was turned off, and the hydrazine aqueous solution after the above treatment was measured by ion chromatography analysis. As a result, the hydrazine concentration was 5.0% by mass and the ammonia concentration was 1.2% by mass.

  That is, ammonia could be decomposed without decomposing hydrazine.

Comparative Example 1
In the concentration of the hydrazine aqueous solution, plasma was generated in the hydrazine aqueous solution in the same manner as in Example 1 except that the hydrazine concentration after concentration was changed to 5.0% by mass and the ammonia concentration was changed to 1.0% by mass.

  Thereafter, the power was turned off, and the hydrazine aqueous solution after the above treatment was measured by ion chromatography to find that the hydrazine concentration was 4.9% by mass and the ammonia concentration was 0.68% by mass.

  That is, not only ammonia but also hydrazine was decomposed.

DESCRIPTION OF SYMBOLS 1 Electric vehicle 2 Fuel cell system 3 Fuel cell 23 Gas-liquid separator 30 Fuel supply line 31 Fuel discharge line 32 Reflux line 41 Air supply line 47 Circulating fuel tank 51 Concentrator 53 Plasma generator

Claims (2)

A concentration step of adjusting the ammonia concentration of the aqueous hydrazine solution to 2.0% by mass or more by concentrating the aqueous hydrazine solution containing ammonia;
A step of preparing a pair of electrodes facing each other in the hydrazine aqueous solution;
Energizing the electrode, and generating a gas phase between the electrodes by boiling the hydrazine aqueous solution in the vicinity of the electrode, and generating plasma in the gas phase under conditions that cause dielectric breakdown in the gas phase, A decomposing step of decomposing ammonia contained in the aqueous hydrazine solution. A fuel cell system capable of decomposing ammonia by the ammonia decomposition method according to claim 1,
A fuel cell to which a liquid fuel containing hydrazine is supplied,
A fuel tank for storing liquid fuel,
A fuel supply path for supplying liquid fuel from the fuel tank to the fuel cell,
A fuel discharge path for discharging a discharge liquid from the fuel cell;
A reflux path for transporting the effluent from the fuel discharge path to the fuel tank;
A gas-liquid separator interposed between the fuel discharge path and the return path,
Water separation means interposed in the reflux path for separating water from the liquid fuel,
A fuel cell system comprising: a pair of electrodes opposed to each other in the fuel tank; and a plasma generator having a power supply for supplying electricity to the electrodes.

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