Apparatus, system and method for producing nitrogen gas using fuel cell exhaust gas

Abstract

To provide a method of effectively generating a nitrogen gas with high purity by using a fuel battery.SOLUTION: A method for producing nitrogen gas is characterized in that a gas containing air, nitrogen or oxygen, and a fuel gas are supplied to a fuel battery to operate the fuel battery; an exhaust gas having an oxygen concentration lower than that of the air is taken out of the fuel battery; the exhaust gas is made to act on a filter using fibers having different penetration level of nitrogen and oxygen to take out the exhaust gas where a nitrogen concentration is increased from this filter. Here, it is preferable that the air or the gas, having a pressure exceeding an atmospheric pressure and the fuel gas having a pressure exceeding the atmospheric pressure are supplied to the fuel battery, and the exhaust gas having the pressure exceeding the atmospheric pressure and the oxygen concentration lower than the air is taken out from this fuel battery, and the exhaust gas is made to act on the filter with the pressure exceeding the atmospheric pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for producing highly pure nitrogen gas. [Background technology]

[0002] In recent years, the use of fuel cells has been actively promoted. For example, fuel cell vehicles have been put into practical use, and fuel cell equipment for home and industrial use is also becoming more widespread. Fuel cells not only enable highly efficient power generation, but also, unlike conventional power generation methods using internal combustion engines, make it possible to reduce carbon dioxide emissions to almost zero. For these reasons, fuel cell technology is expected to significantly contribute to the realization of a low-carbon society.

[0003] The inventors of the present application have focused on the potential of fuel cells and have invented a soldering device that utilizes a fuel cell, as described in Patent Documents 1 and 2. This soldering device utilizes not only the electricity generated by the fuel cell, but also the exhaust gases generated by the power generation, which are supplied to the soldering device.

[0004] Furthermore, the present inventors have also invented a power generation device that uses a fuel cell to supply an inert gas and electricity to a processing device that processes an object to be heated by electrically heating the inert gas, as described in Patent Documents 3 and 4. This power generation device can remove or reduce the oxygen, water vapor, and moisture contained in the exhaust gas from the fuel cell, and convert the exhaust gas into an inert gas suitable for use in the processing device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-233549 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-164987 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-084796 [Patent Document 4] Japanese Patent Application Laid-Open No. 2018-163890 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors of the present invention then came to the realization that if fuel cells were used in the same way, it would also be possible to supply highly pure nitrogen gas, which is in high demand at various production and service sites.

[0007] Such high-purity nitrogen gas is an inert gas that has no combustion-supporting or combustion-promoting properties, making it a very useful gas. However, currently, it is produced using air as a raw material through methods such as pressure swing adsorption (PSA), cryogenic air separation, and membrane separation.

[0008] Here, we thought that if we used the exhaust gas from a fuel cell instead of using air as a raw material as in the past, we might be able to efficiently produce high-purity nitrogen gas.Of course, because we use a fuel cell, it would also be possible to supply electricity along with the high-purity nitrogen gas.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for efficiently producing highly pure nitrogen gas using a fuel cell. [Means for solving the problem]

[0010] According to the present invention, a fuel cell that operates by taking in air or a gas containing nitrogen and oxygen, and a fuel gas, and that discharges exhaust gas having an oxygen concentration lower than that of air from an oxygen electrode side; a fuel gas delivery means, different from the fuel cell, for delivering the fuel gas; The exhaust gas; The fuel gas delivered from the delivery means The fuel gas Import Reacted over a combustion catalyst height, catalytic combustion means for converting the exhaust gas into a nitrogen-enriched exhaust gas having a lower oxygen concentration; With doA nitrogen gas generator, or system, is provided.

[0012] The nitrogen gas generator according to the present invention or system As one embodiment of the present invention, The system further comprises a filter means for applying the received exhaust gas with an increased nitrogen concentration to a filter capable of separating at least the fuel gas, separating the fuel gas remaining in the exhaust gas from the exhaust gas, and extracting the exhaust gas with an increased nitrogen concentration from the filter. It is also preferable.

[0013] The nitrogen gas generator according to the present invention or system In The filter is a filter including high molecular weight polymer hollow fiber fibers that are more selectively permeable to not only fuel gas molecules but also oxygen molecules compared to nitrogen molecules, and the filter means outputs the exhaust gas having a lower fuel gas concentration and a lower oxygen concentration and an increased nitrogen concentration compared to the received exhaust gas having a lower oxygen concentration and an increased nitrogen concentration. It is also preferable.

[0014] Furthermore, the nitrogen gas generating device according to the present invention In another embodiment of the system, the device or system further includes an oxygen filter means for filtering the exhaust gas discharged from the fuel cell through a filter having hollow fiber fibers that selectively transmit oxygen molecules compared to nitrogen molecules, and extracting the exhaust gas with a lowered oxygen concentration from the filter, and the catalytic combustion means for reacting the exhaust gas with a lowered oxygen concentration with the fuel gas on a combustion catalyst. It is also preferable.

[0015] Furthermore, in the nitrogen gas generating device or system according to the present invention, Fuel gas delivery means teeth, at least The fuel gas recovered from the exhaust gas discharged from the fuel electrode side of the fuel cell , and deliver it to the catalytic combustion means. It is also preferable.

[0016] The nitrogen gas generator according to the present invention or system In another embodiment of the present invention, The device or system further includes a dehumidifying means for extracting moisture or water vapor from the exhaust gas discharged from the fuel cell and converting the exhaust gas into an exhaust gas with a lower moisture or water vapor content. It is also preferable.

[0019] Furthermore, the nitrogen gas generating device according to the present invention or system In The fuel cell is a solid oxide fuel cell (SOFC). is also preferred.

[0024] According to the present invention, supplying air or a gas containing nitrogen and oxygen and a fuel gas to the fuel cell to operate the fuel cell; An exhaust gas having an oxygen concentration lower than that of air is extracted from the oxygen electrode side of the fuel cell, The exhaust gas; The fuel gas is delivered from a fuel gas delivery means other than the fuel cell, which is capable of delivering the fuel gas. The fuel gas is reacted on a combustion catalyst. 、 The exhaust gas is converted into an exhaust gas having a lower oxygen concentration and an increased nitrogen concentration. R child A method for producing nitrogen gas is provided. [Effects of the Invention]

[0025] According to the present invention, it is possible to efficiently generate highly pure nitrogen gas using a fuel cell. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram illustrating one embodiment of a nitrogen gas generation system according to the present invention. [Figure 2] 1 is a graph for explaining Example 1 of the nitrogen gas generation process according to the present invention. [Figure 3] 1 is a graph for explaining Example 1 of the nitrogen gas generation process according to the present invention. [Figure 4] 1 is a graph for explaining Example 1 of the nitrogen gas generation process according to the present invention. [Figure 5] 10 is a graph illustrating Example 2 in which the recovery rate of a nitrogen gas filter in a nitrogen gas generation process according to the present invention was examined. [Figure 6] FIG. 10 is a schematic diagram for explaining another embodiment of the nitrogen filter U according to the present invention. [Figure 7] 1 is a graph showing the relationship between the oxygen concentration introduced into the nitrogen gas filter according to the present invention and the oxygen concentration in the gas discharged from the filter. [Figure 8] FIG. 10 is a schematic diagram for explaining another embodiment of the "fuel cell" according to the present invention. [Figure 9] FIG. 10 is a schematic diagram for explaining yet another embodiment of the "fuel cell" according to the present invention. [Figure 10] FIG. 10 is a schematic diagram illustrating yet another embodiment of the nitrogen gas generation system according to the present invention. [Figure 11] FIG. 10 is a schematic diagram illustrating yet another embodiment of the nitrogen gas generation system according to the present invention. [Figure 12] 1 is a graph showing the relationship between current and voltage in a "fuel cell" according to an embodiment of the present invention, in which the operating state of the "fuel cell" was examined. [Figure 13]1 is a graph showing the relationship between cell temperature and power in a "fuel cell" according to an embodiment of the present invention, in which the operating state of the "fuel cell" was examined. [Figure 14] 10 is a graph showing the relationship between the cell temperature of the "fuel cell" and the relative humidity of the exhaust gas in an example in which the operating state of the "fuel cell" according to the present invention was examined. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same components are designated by the same reference numerals. In addition, components that may have similar structures and functions may also be designated by the same reference numerals. Furthermore, dimensional ratios within and between components in the drawings are arbitrary for ease of viewing the drawings.

[0028] [Nitrogen gas generation system / device] FIG. 1 is a schematic diagram showing one embodiment of a nitrogen gas generation system according to the present invention.

[0029] The nitrogen gas generation system 1 according to one embodiment of the present invention shown in FIG. 1 has the following notable features: (A) "Air or a gas containing nitrogen and oxygen" and "fuel gas" (hydrogen in this embodiment) are supplied to the "fuel cell (in the fuel cell U11)" to operate this "fuel cell"; (B) Extract "exhaust gas (off-gas)" from the "fuel cell" which has a lower oxygen concentration than air, (C) The "exhaust gas" is made to act on a "nitrogen gas filter 12f" using fibers (e.g., hollow fiber fibers) with different permeability for nitrogen and oxygen, and the "exhaust gas" with an increased nitrogen concentration is extracted from this "nitrogen gas filter 12f." This system is capable of implementing the following distinctive nitrogen gas generation methods:

[0030] Here, the "nitrogen gas filter 12f" in (C) above is a filter that uses fibers with different degrees of permeability for nitrogen and oxygen, as described above, and the inventors of the present application have confirmed through experiments (the details of which will be explained later) that in a filter that uses such fibers, the "oxygen concentration reduction index" of "exhaust gas" that has an oxygen concentration (in ml per 100 ml of medium, expressed in volume (vol)%) lower than that of air increases the lower the oxygen concentration.

[0031] In this way, the nitrogen gas generation system 1 makes it possible to efficiently generate nitrogen gas with a low oxygen concentration, i.e., high purity, by combining a fuel cell and a nitrogen gas filter 12f, which are highly compatible from the perspective of low oxygen concentration.

[0032] Incidentally, as will be explained in more detail later, the inventors of the present application have confirmed through experiments that by applying "exhaust gas" with an oxygen concentration of 2.5 vol% or less to "nitrogen gas filter 12f," it is possible to extract "exhaust gas" from "nitrogen gas filter 12f" with an oxygen concentration that is 1 / 10 or less of the result when air is applied.

[0033] Furthermore, the inventors of the present application have experimentally confirmed that the nitrogen gas filter 12f used in this embodiment has a higher recovery rate as the oxygen concentration of the gas to be filtered decreases. Therefore, by using such a nitrogen gas filter 12f to filter exhaust gases having an oxygen concentration lower than that of air, it is possible to further increase the recovery rate of high-purity nitrogen gas. This recovery rate will also be described in detail later.

[0034] Furthermore, in the embodiment shown in FIG. 1, the nitrogen gas generation system 1 includes: (A') "Air or a gas containing nitrogen and oxygen" having a pressure exceeding atmospheric pressure (1 atmosphere (atm)) and "fuel gas" having a pressure exceeding atmospheric pressure are supplied to a "fuel cell," (B') Extracting from the fuel cell exhaust gases having a pressure exceeding atmospheric pressure and a lower oxygen concentration than air; (C') The "exhaust gas" is applied to the "nitrogen gas filter 12f" at a pressure exceeding atmospheric pressure. This has become possible.

[0035] Here, the "nitrogen gas filter 12f" is a filter using fibers with different degrees of permeability for nitrogen and oxygen, and the inventors of the present application have confirmed through experiments (also described in detail later) that in a filter using such fibers, the higher the pressure of the "exhaust gas" applied, the lower the oxygen concentration of the "exhaust gas" extracted from the filter, i.e., the higher the purity of the nitrogen gas obtained. From the perspective of such pressure control, the nitrogen gas generation system 1 can efficiently generate nitrogen gas with a low oxygen concentration, i.e., high purity.

[0036] Incidentally, as will be explained in more detail later, experiments have confirmed that it is also preferable to set the pressure of the "exhaust gas" acting on the "nitrogen gas filter 12f" to a pressure value that exceeds a pressure threshold determined by the "nitrogen gas filter 12f," a pressure threshold that increases as the flow rate of the "exhaust gas" when extracted from the "nitrogen gas filter 12f" increases.

[0037] Furthermore, in the nitrogen gas generation system 1 of this embodiment, in the above embodiments (A') to (C'), a high-pressure "exhaust gas" is generated using a "fuel cell" and this is used to act on a "filter," so there is no need to (in one go) increase the pressure from atmospheric pressure to a desired high pressure (for example, 7 atmospheres). As a result, it is possible to efficiently generate high-purity nitrogen gas.

[0038] The terms "high purity" and "high purity" used above refer to a state in which the oxygen concentration in the nitrogen gas is sufficiently reduced. Specifically, the nitrogen concentration (in ml per 100 ml of medium, expressed as vol%) in the "high purity" or "high purity" nitrogen gas produced in this embodiment may be, for example, 95 vol% or more, 99 vol% or more, or even 99.9 vol% or more, depending on the field and application of the nitrogen gas.

[0039] [Configuration of nitrogen gas generation system] As also shown in FIG. 1, the nitrogen gas generation system 1 of this embodiment includes: (a) Fuel cell U11 having a "fuel cell"; (b) A natural energy power generation unit (U) 101, a power storage unit U101s, a hydrogen generation unit U102, a hydrogen generation reforming unit U103, a hydrogen tank 104, a flow control unit U105, an air compressor U106, an air tank 107, a filter U108, and a flow control unit U109 are provided in a position preceding the fuel cell U11. (c) A drain 111, a pressure control unit U113, a gas-liquid separation unit U114, and a hydrogen recovery unit U115 are provided at the downstream side of the hydrogen electrode of the fuel cell U11. (d) At a position downstream of the air electrode side of the fuel cell U11, there are provided a drain 112, a pressure control U121, a gas-liquid separation U122, an off-gas buffer tank 123, a pressure booster U124, a corrosive gas removal unit U125, a temperature adjustment unit U126, a flow control unit U127, a nitrogen filter U12 equipped with a nitrogen gas filter 12f, a pressure booster U128, and a nitrogen tank 129. (e) Overall control U131 and The system is equipped with a system that can take in natural energy such as air, water, and sunlight, and in some cases city gas and even commercial electricity, and can supply highly pure nitrogen gas, electricity, and thermal energy to the outside.

[0040] In other words, the nitrogen gas generation system 1 of this embodiment is also capable of providing the electricity and thermal energy generated by the operating "fuel cell" to the outside in addition to the generated nitrogen gas, and can also be considered as a nitrogen gas, electricity and heat supply system (device).

[0041] The nitrogen gas generation system 1 can be configured as a single nitrogen gas generation device including the components described above. Alternatively, the nitrogen gas generation system 1 can be configured as a nitrogen gas generation device including at least a fuel cell U11 and components directly connected thereto, and a nitrogen filter U12, with at least the natural energy generator U101 being external to the device.

[0042] For example, it is possible to configure a nitrogen gas generation device in which all components other than the natural energy power generation U101, power storage U101s, hydrogen generation U102, hydrogen generation reforming U103, hydrogen tank 104, air compression U106, air tank 107, pressure booster U128, and nitrogen tank 129 are device components.

[0043] Furthermore, it is also possible to configure a nitrogen gas generator having a nitrogen filter 12 that includes the pressure control U121 to flow control U127, the pressure booster U124 to flow control U127, or the corrosive gas removal U125 to flow control U127 as upstream and downstream filtering stages. Of course, a downstream filtering stage up to the nitrogen tank 129 may also be provided.

[0044] Furthermore, such a nitrogen gas generator may be provided with a piping joint as an exhaust gas intake that can be connected to the exhaust gas outlet of an externally installed "fuel cell," and may be a device that takes in exhaust gas discharged from this external "fuel cell" and outputs nitrogen gas with a reduced oxygen concentration. In other words, it may be a "fuel cell-mounted filtering device" that can be attached to a "fuel cell." [Possible invention claims] A method for generating nitrogen gas, characterized in that a gas containing nitrogen and oxygen and having an oxygen concentration lower than that of air is applied to a filter made of fibers having different degrees of permeability for nitrogen and oxygen, and the gas with an increased nitrogen concentration is extracted from the filter. [Possible invention claims] an exhaust gas intake port for receiving exhaust gas emitted from an external fuel cell; A filter using fibers with different permeability to nitrogen and oxygen, which receives the exhaust gas and outputs the exhaust gas with an increased nitrogen concentration. A nitrogen gas generating device comprising:

[0045] Incidentally, the flow of material and energy transfer and the processing steps shown by connecting the components with arrows in the system configuration diagram of FIG. 1 can also be understood as one embodiment of a nitrogen gas generation method in the nitrogen gas generation system 1.

[0046] Also in Figure 1, the natural energy power generation unit U101 may be a solar cell power generation unit equipped with a solar cell and converting sunlight into electricity, or a wind power generation unit that uses wind power to rotate a rotor with blades to drive a generator and generate electricity, or a micro-hydro power generation unit that uses water flow (hydropower) to rotate a turbine (water wheel) to drive a generator and generate electricity.

[0047] Also, various other power generation units can be adopted as the natural energy power generation unit 101 as long as they ultimately convert the light energy of sunlight or the kinetic energy of wind and water currents into electrical energy. Furthermore, the natural energy power generation unit 101 may be a combination of two or more of the power generation units described above. In any case, it is preferable that the output section of the generated power is equipped with a wattmeter so that it is possible to measure whether or not power is being generated at each point in time and the amount of power generated.

[0048] The power storage U101s is a power storage unit that includes a secondary battery such as a lithium (Li) battery or a lead (Pb) battery, and stores and preserves the power supplied from the natural energy power generation unit 101. It is also preferable that the power storage U101s includes a power storage meter that can measure the amount of power stored at each point in time and whether or not it is fully charged.

[0049] Here, power is supplied from the power storage unit U101s to the hydrogen generator U102 (which performs water electrolysis) and the air compressor U106, which will be described later, but instead of or in addition to these, commercial power may be supplied to the hydrogen generator U102 and the air compressor U106.

[0050] Furthermore, it is also preferable to supply power directly from the renewable energy power generation unit 101 to the hydrogen generator U102 and air compressor U106 without using a storage battery U101s with a secondary battery, which has a certain limit on the amount of stored power (or is provided only as an auxiliary). In this case, renewable energy is directly converted into the chemical energy of hydrogen and the physical energy of compressed air and then used.

[0051] When the renewable energy power generation unit 101 generates AC power (for example, when it is equipped with an AC generator), this AC power or commercial power is converted to DC by a converter and then supplied to the power storage U101s or hydrogen generation U102. Also, when the air compressor U106 is equipped with a DC-driven compressor 22, the power is also converted to DC and then supplied to the air compressor U106.

[0052] In any case, the overall control U131 can appropriately switch and control the power supply to the hydrogen generation U102 and air compression U106 as described above, while monitoring, for example, the power generation status in the natural energy power generation unit 101 and the power storage status in the power storage U101s.

[0053] 1, the hydrogen generator U102 is a hydrogen supply unit equipped with an electrolysis section capable of generating hydrogen and oxygen by electrolyzing the obtained water using supplied power. Various known electrolysis methods can be used here, but for example, electrolysis may be performed using a stack of multiple electrolysis cells, each having a structure in which a solid polymer electrolyte membrane is sandwiched between catalysts and electrodes on both sides.

[0054] The hydrogen generator U102 is also preferably equipped with a dehumidifying unit that removes moisture from the generated hydrogen and oxygen. Furthermore, a mechanism may be provided in which the moisture removed here is returned to the electrolysis unit for electrolysis. It is also preferable to have a wattmeter that can measure the amount of power consumed at each point in time and whether or not power is being consumed, and may also have a flow meter or gas pressure meter that can measure the amount of hydrogen and oxygen generated and whether or not they are being generated.

[0055] The hydrogen generation reformer U103 takes in a hydrocarbon gas such as city gas or LPG, mixes this hydrocarbon gas with steam, and generates a hydrogen-containing gas containing hydrogen (H2) as a main component from this mixed gas through a steam reforming reaction. It is also preferable to have a mechanism for reducing the carbon monoxide gas content in the generated hydrogen-containing gas using a CO conversion catalyst or the like, and further reducing the carbon monoxide concentration using a CO selective oxidation catalyst.

[0056] Incidentally, if an SOFC (solid oxide fuel cell) is used as the "fuel cell" of the fuel cell U11 described below, the high temperature (large amount of heat) required for steam reforming in the hydrogen generation reformer U103 can be met by the exhaust heat from this "fuel cell."

[0057] The nitrogen gas generation system 1 may be equipped with either a hydrogen generation unit 102 or a hydrogen generation and reforming unit 103 as a hydrogen (fuel) supply source, or it is preferable to have both units to ensure a variety of supply sources. Furthermore, instead of or in addition to these supply sources, hydrogen gas itself may be supplied from another system or device.

[0058] The hydrogen tank 104 is a gas tank that temporarily stores and preserves the hydrogen gas supplied from the hydrogen generator U102 or hydrogen generator / reformer U103 in a compressed (high-pressure) state, and may be equipped with a hydrogen storage alloy cylinder. It is also preferable that the hydrogen tank 104 is equipped with a gas pressure gauge so that the gas pressure inside the tank can be measured at any time.

[0059] The flow control U105 is a unit that controls the pressure and flow rate of hydrogen gas supplied from the hydrogen tank 104 to the fuel cell U11. Specifically, it may be equipped with a hydrogen gas regulator and a hydrogen gas mass flow controller (or flow switch).

[0060] Here, hydrogen gas may be supplied to the hydrogen electrode side of the fuel cell U11 at a high pressure (e.g., 2 to 7 atmospheres) that exceeds atmospheric pressure (1 atmosphere). That is, in this embodiment, the back pressure of the "fuel cell" provided in the fuel cell U11 can be set to a pressure that exceeds atmospheric pressure. Note that this back pressure is set to 1 atmosphere when the outlet side of the "fuel cell" is in an open state, i.e., when the exhaust gas pressure is atmospheric pressure.

[0061] However, when a mass flow controller is used in the flow control U105, a pressure difference loss usually occurs here, so it is also preferable to receive hydrogen gas from the hydrogen tank 104 at a pressure, for example, 1 to 2 atmospheres higher than the set pressure (back pressure), adjust that pressure with a regulator, and then flow that hydrogen gas to the mass flow controller. Incidentally, it has been found through experiments that the above-mentioned pressure difference loss increases as the flow rate decreases (the more the flow is restricted).

[0062] Also in Figure 1, the air compressor U106 is a unit equipped with a compressor that compresses (high-pressures) air taken in from the atmosphere and supplies it to an air tank 107. As a compression method for this compressor, various methods can be used, such as a reciprocating type, scroll type, screw type, rotary type, swing type, or a combination of two or more of these.

[0063] The air tank 107 is a gas tank that temporarily stores and preserves the compressed air supplied from the air compressor U106 in a compressed state. It is also preferable that the air tank 107 is provided with a gas pressure gauge so that the gas pressure inside the tank can be measured at any time.

[0064] The filter U108 is a unit that includes an air filter and an oil filter, and removes minute dust particles, oil components, and the like from the high-pressure air supplied from the air tank 107 using these filters.

[0065] The flow control U109 is a unit that controls the pressure and flow rate of compressed air supplied from the air tank 107 to the air electrode side of the fuel cell U11 via the filter U108. Specifically, it may be equipped with a gas regulator and a mass flow controller (or a flow switch).

[0066] In this embodiment, this compressed air may also be supplied to the air electrode side of the fuel cell U11 (set with a back pressure above atmospheric pressure) while still in a high pressure (for example, 2 to 7 atmospheres) state exceeding atmospheric pressure (1 atmosphere). In this case, taking into account the pressure difference loss of the mass flow controller, compressed air at a pressure, for example, 1 to 2 atmospheres higher than the set back pressure may be received from the air tank 107, and the pressure may be adjusted by a regulator before the compressed air is passed to the mass flow controller, just as in the case of hydrogen gas described above.

[0067] Also in Figure 1, fuel cell U11 is a unit that has a "fuel cell" and extracts and outputs exhaust gas having an oxygen concentration lower than that of air, electricity, heat, and water (water vapor) from this "fuel cell."

[0068] Of course, this fuel cell U11 can be used with the back pressure of the "fuel cell" set to 1 atmosphere (atmospheric pressure), but as a preferred embodiment, (a) The back pressure is set to exceed atmospheric pressure (e.g., 2 to 7 atmospheres), (b) receiving hydrogen gas having a pressure above atmospheric pressure (e.g., 2 to 7 atmospheres) from flow control U105, and further receiving compressed air having a pressure above atmospheric pressure (e.g., 2 to 7 atmospheres) from flow control U109; (c) Discharge exhaust gases with pressures exceeding atmospheric pressure (e.g., 2 to 7 atmospheres). It is also preferable that the unit is equipped with a "fuel cell."

[0069] Here, this "fuel cell" may be of a known configuration, and may have a structure in which multiple cells, each having a structure in which an electrolyte is sandwiched between a hydrogen electrode (fuel electrode, positive electrode, anode) and an air electrode (oxygen electrode, negative electrode, cathode), are stacked (laminated) with separators interposed between them.

[0070] Furthermore, as the cell type for "fuel cells," various types of fuel cells can be used, including polymer electrolyte fuel cells (PEFCs), solid oxide fuel cells (SOFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs). Of these, SOFCs have high power generation efficiency and typically operate at approximately 700 to 1000°C, making them capable of supplying considerably high-temperature exhaust gases. As mentioned above, when hydrogen gas is produced from city gas or the like using hydrogen generation reforming (U103), SOFCs can also provide the large amount of heat required for the steam reforming. Furthermore, the PEFC system operates at relatively low temperatures and allows for compact cell size, which is why it is used in many fuel cell vehicles, for example.

[0071] If the "fuel cell" in Fuel Cell U11 is a PEFC, it is also possible to use, for example, a JARI-type fuel cell developed for research and development by the Japan Automobile Research Institute (JARI), a general incorporated foundation. JARI-type fuel cells are designed to be able to increase back pressure and apply pressure to the cell, and also to recover all exhaust gases with high back pressure.

[0072] In this embodiment, the pressure inside the "fuel cell", i.e., the back pressure, is adjusted and controlled by the back pressure valve of the pressure control U113 and the back pressure valve of the pressure control U121, which will be described later. (a) The back pressure on the hydrogen electrode side, which is mainly adjusted by the back pressure valve of the pressure control U113, (b) The back pressure on the air electrode side, which is mainly adjusted by the back pressure valve of the pressure control U121, and It is also preferable to control the back pressures so that they are nearly equal. In fact, if there is a difference of about 0.1 atmospheres between the two back pressures, some gas leakage may occur from the "fuel cell," but it has been experimentally shown that if the two back pressures are equal, no problems will occur even with a fairly high back pressure. In particular, if the "fuel cell" is a PEFC, it is more preferable to make the two back pressures equal, since its electrolytic membrane is relatively thin.

[0073] Furthermore, the fuel cell U11 equipped with the "fuel cell" described above is equipped with a measurement system and a group of sensors that can measure the amount, pressure, and temperature of hydrogen gas and compressed air flowing into the "fuel cell," as well as the amount, pressure, and temperature of exhaust gas, exhaust water vapor, and moisture emitted from the "fuel cell." Furthermore, it is preferable that the operation of the "fuel cell" be controlled by an overall control U131 that receives information from the measurement system and group of sensors.

[0074] It is also preferable that a heat exchanger that circulates a heat exchange medium such as water is placed inside or around the fuel cell to extract heat from the operating fuel cell that generates heat and transfer it to the outside of the unit. Alternatively, instead of a heat exchanger, a thermoelectric system that connects a conductive separator in the fuel cell with a heat pipe can be used to directly extract heat from the fuel cell to the outside.

[0075] Incidentally, the heat transferred by the heat exchange medium or heat pipe in this way is supplied not only to the outside but also to within the system for use, and in this embodiment, it is supplied to an off-gas buffer tank 123, which will be described later, and makes it possible to further increase the temperature (for example, 45°C) of the exhaust gas supplied to the nitrogen filter U12. Of course, if the temperature of the exhaust gas is sufficiently high, such heating treatment in the off-gas buffer tank 123 is not necessary.

[0076] The heat can also be transferred to the hydrogen generation reformer U103 using such a heat exchange medium or heat pipe to replenish the heat required for steam reforming. The heat can also be used to convert water to be electrolyzed in the hydrogen generation unit U102 into steam or to raise the temperature of the water, thereby improving the efficiency of hydrogen generation during electrolysis.

[0077] In this case, in order to achieve and stably maintain the desired hydrogen generation efficiency, it is also preferable to monitor the temperature of the electrolytic cell with an installed temperature sensor and control the electrolysis operation with the overall control U131. Furthermore, it is also possible to perform electrolysis without using an electrolyte by increasing the voltage applied between the electrodes, thereby eliminating the need for monitoring and maintenance of the electrolyte.

[0078] Furthermore, as another embodiment of the fuel cell U11, two or more "fuel cells" can be connected in series, and exhaust gas from the preceding fuel cell can be sequentially taken in and used for the cell reaction, making it easy to ultimately extract exhaust gas with a lower oxygen concentration, for example, exhaust gas with an oxygen concentration of 2.5 vol% or less. The inventors of the present application have disclosed a fuel cell system with this configuration that they invented in JP 2019-129110 A.

[0079] Also in FIG. 1, drains 111 and 112 are provided at the fuel passage outlet (on the hydrogen electrode side) and the air passage outlet (on the air electrode side) of the "fuel cell" in fuel cell U11, respectively, to recover water produced by condensation of water vapor contained in the exhaust gas (which usually has a relative humidity of approximately 100%). This makes it possible to suppress adverse effects on the cell reaction due to the so-called flooding phenomenon. The water recovered in this way may also be sent to hydrogen generator U102 and reused as a hydrogen generating material.

[0080] Here, by setting the back pressure of the "fuel cell" to a value exceeding atmospheric pressure (for example, 2 to 7 atmospheres), the dew point can be raised, increasing the amount of water that falls into drains 111 and 112, and improving the dehumidification effect. It is also preferable that drains 111 and 112 have an auto-drain function that automatically discharges water to the outside when a predetermined amount of water has accumulated. An example of the dehumidification process in drain 112 will be described in detail later using FIG. 14.

[0081] The pressure control U113 is a unit for returning the hydrogen gas that has been dehumidified in the drain 111 to the fuel line inlet (on the hydrogen electrode side) of the fuel cell (for example, downstream of the flow control U105) via, for example, a hydrogen mixer, while maintaining the set back pressure of the fuel cell. Specifically, the pressure control U113 is equipped with a back pressure valve and a pressure gauge, and controls the pressure (back pressure) within the fuel cell, particularly on the hydrogen electrode side, by adjusting this back pressure valve.

[0082] The gas-liquid separator U114 is a unit for removing residual water vapor and moisture from the exhaust gas discharged from the fuel passage outlet (on the hydrogen electrode side) of the fuel cell and passing through the drain 111 and pressure control U113. Specifically, water vapor and moisture can be removed using a dehumidifier, a dry filter, a dehumidifying device equipped with a pressurizing mechanism, or a gas-liquid separator. Dehumidifiers containing silica gel and / or zeolite can be used. The gas-liquid separator can be a gravity separator, a centrifugal separator, a mist eliminator pad, a vane separator, or a pneumatic separator coalescer.

[0083] The hydrogen recovery unit U115 uses a known hydrogen gas filter and executor to extract and reuse unreacted residual hydrogen gas from the exhaust gas discharged from the fuel passage outlet (on the hydrogen electrode side). The extracted hydrogen gas can be sent back to the hydrogen mixer downstream of the flow control unit U105, for example. The extracted hydrogen gas may also be discharged to the outside.

[0084] Also in Figure 1, the pressure control U121 is a unit for sending the exhaust gas (on the cathode side) that has been dehumidified in the drain 112 to the gas-liquid separator U122 while maintaining the set back pressure of the "fuel cell." Specifically, like the pressure control U113, this pressure control U121 is equipped with a back pressure valve and a pressure gauge, and by adjusting this back pressure valve, the pressure (back pressure) within the "fuel cell," particularly on the cathode side, is controlled.

[0085] The gas-liquid separator U122 is a unit for removing residual water vapor and moisture from the high-pressure (e.g., 2 to 7 atmospheres) exhaust gas that is discharged from the air passage outlet (on the air electrode side) of the "fuel cell" and passes through the drain 112 and pressure control U121. Specifically, like the gas-liquid separator U114 described above, it can remove water vapor and moisture using a dehumidifier equipped with a dehumidifier, dry filter, or pressurization mechanism, or a gas-liquid separator. Incidentally, as one standard, it is also preferable for the gas-liquid separator U122 to keep the relative humidity in the exhaust gas below 20 to 30%.

[0086] This gas-liquid separator U122 is a very important unit, particularly in an embodiment in which the back pressure of the "fuel cell" is not high (for example, 2 atmospheres or less), since an increase in the amount of water recovered in the drain 112 due to an increase in the dew point cannot be expected. However, in one embodiment, when the exhaust gas coming out of the drain 112 is stored in the off-gas buffer tank 123 described later, it is possible to pressurize the gas by, for example, a compressor (pressure booster) device provided in the upstream stage of the tank, and dehumidify the gas by an auto-drain installed in the tank 123. In this case, the gas-liquid separator U122 may be omitted.

[0087] The off-gas buffer tank 123 is a gas tank that temporarily preserves and stores the exhaust gas introduced from the gas-liquid separator U122. This exhaust gas is introduced into the off-gas buffer tank 123 until the pressure reaches the same as the set back pressure (for example, 2 to 7 atmospheres). Furthermore, in order to allow the exhaust gas to flow into the nitrogen filter U12 (described later) at a desired pressure (for example, 7 atmospheres), it is also preferable that the flow rate of this exhaust gas into the off-gas buffer tank 123 be set to a flow rate equal to or exceeding the required introduction flow rate into the nitrogen filter U12.

[0088] Incidentally, when the "fuel cell" is stopped, the pressure in the piping to the off-gas buffer tank 123 returns to, for example, atmospheric pressure. Therefore, it is preferable that the off-gas buffer tank 123 is equipped with a check valve to prevent backflow of exhaust gas to the "fuel cell." It is also preferable that the off-gas buffer tank 123 is equipped with a gas pressure gauge so that the gas pressure in the tank can be measured at each point in time.

[0089] Furthermore, it is also preferable that the off-gas buffer tank 123 uses a "heating means" capable of performing a heating process using the heat generated by the "fuel cell" in the fuel cell U11 to heat the exhaust gas in the tank to a temperature higher than room temperature (for example, 30 to 45°C). This makes it possible to supply exhaust gas at a temperature suitable for nitrogen filtering to the nitrogen gas filter 12f of the nitrogen filter U12, which will be described later.

[0090] Here, the above-mentioned "heating means" may be a heat exchanger or a separator-heat pipe connection system, as already explained. This makes it possible to effectively utilize the heat of the "fuel cell" to perform an appropriate nitrogen filtering process without using an energy consuming means such as an electric heater. Of course, if the temperature of the exhaust gas introduced into the off-gas buffer tank 123 is sufficiently high, such a "heating means" is not necessary.

[0091] The pressure booster U124 further boosts the pressure of the exhaust gas extracted from the "fuel cell" of the fuel cell U11 (for example, to a pressure of 7 atmospheres) and supplies it to the nitrogen filter U12. A known pressure booster valve, such as the inert gas booster valve VB11A or VBA42 manufactured by SMC Corporation, can be used as this pressure booster U124. It is also preferable to provide a pressure gauge to monitor the boosted exhaust gas pressure.

[0092] Here, most of the known booster valves are of the air-driven type, and in this case, the booster valve may be driven using a portion of the compressed air supplied to the "fuel cell", i.e., compressed air taken out from the air tank 107, as support gas. This eliminates the need for additional power consumption for driving the booster valve. It is also preferable to use a booster-type compressor as the booster valve U124.

[0093] As mentioned above, if the pressure of the exhaust gas from the off-gas buffer tank 123 is sufficiently high (for example, 7 atmospheres), the pressure booster U124 is of course not required. Also, although care must be taken in handling it, it is possible to use hydrogen gas extracted from the hydrogen tank 104 as this support gas.

[0094] Also in Figure 1, the corrosive gas removal unit U125 is a unit that can perform processing to remove or reduce at least one of sulfides, chlorides, hydrocarbons, fluorides, and strong alkaline compounds from exhaust gas (extracted from the "fuel cell") that is then to be applied to the nitrogen gas filter 12f of the nitrogen filter U12.

[0095] For example, if hydrogen gas is generated from city gas or other sources using the hydrogen generation reformer U103 and used as fuel in a fuel cell, the resulting exhaust gas will contain various gas components other than hydrogen gas, such as hydrogen sulfide, sulfur dioxide, hydrocarbon gases such as methane, ammonia, and formaldehyde. Furthermore, if an SOFC is used in a fuel cell, nitrogen gas in the air can combine with oxygen in a high-temperature atmosphere of around 800°C, generating nitrogen oxides (NOx). These gases not only become impurities in the final nitrogen gas product, but also pose a risk of adversely affecting the hollow fiber fibers of the nitrogen gas filter 12f.

[0096] Therefore, the corrosive gas removal unit U125 is equipped with, for example, an activated carbon filter, and serves to remove or minimize the amount of impurity gases in the exhaust gas. Incidentally, one standard for the corrosive gas removal unit U125 is to limit the concentration of hydrocarbon gases to 0.013 mg / Nm3. 3 It is also preferable to keep the concentrations of strongly acidic gases such as hydrogen sulfide, sulfur dioxide, hydrogen chloride, and fluorine, and strongly alkaline gases such as amines, ammonia, and caustic soda below the detection limit of a predetermined detection method.

[0097] Furthermore, as shown in Figure 1, it is also preferable to install a mist filter and a dust filter before and after the corrosive gas removal unit U125. Of these, the mist filter is a filter that removes or reduces mist such as water mist, solvent mist, and oil mist in the exhaust gas. As one standard, this mist filter reduces the concentration of residual oil from these mist to 0.01 mg / Nm3. 3 It is also preferable to keep it to 0.008 ppm wt or less. On the other hand, a dust filter is a filter that removes or reduces dust in exhaust gas. As one standard, it is also preferable for a dust filter to remove almost all particles with a particle size of 0.01 μm or more.

[0098] The temperature regulator U126 is a unit equipped with, for example, an electric heater, for adjusting the temperature of the exhaust gas taken in to approach or match a preset suitable temperature based on the characteristics of the nitrogen gas filter 12f, and supplying the temperature-adjusted exhaust gas to the nitrogen filter U12. In one preferred embodiment, the temperature regulator U126 may receive heat supplied from the fuel cell U11 via a heat exchanger and use it for temperature adjustment, or may adjust the exhaust gas temperature using power supplied from the fuel cell U11.

[0099] Incidentally, the UBE N2 separator NM-B01A manufactured by Ube Industries, which can be used as the nitrogen gas filter 12f (described in detail later), is said to have a high filtering effect when the temperature of the introduced gas is 30 to 45°C, which is higher than room temperature (25°C). In this case, when the exhaust gas from the "fuel cell" is higher than room temperature (25°C), it is possible to enjoy this high filtering effect without using the temperature adjustment unit U126. It is also possible to reduce the amount of power consumed for temperature adjustment.

[0100] It is also known that in the nitrogen gas filter 12f, which uses fibers with different permeabilities for nitrogen and oxygen, the recovery rate drops significantly as the temperature of the introduced exhaust gas increases. Therefore, depending on the nitrogen gas output performance set in this system, it may be possible to maintain the temperature of the exhaust gas at approximately the same temperature as in the off-gas buffer tank 123 without using the temperature regulator U126 in order to ensure a predetermined recovery rate.

[0101] Also in Figure 1, the nitrogen filter U12 is a unit that applies exhaust gas supplied from the flow control U127 to a nitrogen gas filter 12f made of fibers with different permeability to nitrogen and oxygen, and extracts exhaust gas with an increased nitrogen concentration, i.e., high-purity nitrogen gas in this embodiment, from this nitrogen gas filter 12f.

[0102] Specifically, in this embodiment, the nitrogen filter U12 is (a) a nitrogen gas filter 12f; (b) a filter input / output section that introduces exhaust gas into the nitrogen gas filter 12f to act on it and extracts exhaust gas with an increased nitrogen concentration from the nitrogen gas filter 12f; (c) A filter purge section that extracts gas containing oxygen molecules (hereinafter referred to as filter exhaust gas) separated from nitrogen molecules (in the exhaust gas) by the nitrogen gas filter 12f separately from the exhaust gas extracted in (b) above. It is equipped with:

[0103] Specifically, the nitrogen gas filter 12f can be a hollow fiber filter (hollow fiber filter) made of a polymer fiber material that preferentially transmits oxygen molecules over nitrogen molecules. For example, the UBE N2 Separator NM-B01A manufactured by Ube Industries, Ltd., which uses polyimide hollow fibers, can be used. As high-pressure exhaust gas flows through the hollow fibers, oxygen molecules selectively permeate the hollow fiber membrane, ultimately producing highly purified nitrogen gas at the hollow fiber outlet. Of course, the nitrogen gas filter 12f is not limited to this separator. For example, separators from the UBE N2 Separator NM series manufactured by Ube Industries or SEPURAN N2 membrane modules manufactured by Daicel-Evonik can also be used as the nitrogen gas filter 12f.

[0104] Here, in such a nitrogen gas filter 12f, (a) The oxygen concentration of the introduced exhaust gas (introducing oxygen concentration), the pressure of the introduced exhaust gas (introducing pressure), and the flow rate of the exhaust gas at the outlet of the filter 12f (outlet flow rate), (b) The oxygen concentration of the exhaust gas at the outlet of the filter 12f (outlet oxygen concentration) and the recovery rate of the filter 12f The relationship between these two will be explained in detail later using examples shown in Figures 3 to 5. Various conditions for obtaining highly pure nitrogen gas will also be explained there.

[0105] The outlet flow rate (a) above can be measured by a flow meter installed on the outlet side of the nitrogen filter U12 and controlled by the flow control U127 described below. Similarly, the outlet oxygen concentration (b) above can be measured by an oxygen concentration meter installed on the outlet side of the nitrogen filter U12. Of course, it is also preferable to install the flow control U127 immediately after these oxygen concentration meter and flow meter.

[0106] Furthermore, in this embodiment, based on the outlet oxygen concentration measured by this oxygen concentration meter, the overall control U131 can, for example, control the back pressure valve of the pressure control U121 to adjust the set back pressure of the "fuel cell", or control the mass flow controller of the flow control U127 to adjust the exhaust gas flow rate to the "filter", thereby making it possible to supply high-purity nitrogen gas with the desired extremely low oxygen concentration.

[0107] 1, the flow control U127 is a unit that controls the flow rate of the exhaust gas with an increased nitrogen concentration generated by the nitrogen filter U12, i.e., high-purity nitrogen gas in this embodiment, and sends the nitrogen gas to the nitrogen tank 129 via the pressure booster U128. That is, as described above, this is a unit that controls the outlet flow rate (f_out) of the nitrogen gas filter 12f. Specifically, it can be equipped with a gas regulator and a mass flow controller (or a flow switch).

[0108] In this embodiment, the pressure booster U128 is a unit that further boosts the pressure of the high-purity nitrogen gas whose flow rate has been controlled by the flow control U127 (for example, to a pressure of 8 to 15 atmospheres) and sends it to the nitrogen tank 129, thereby preserving and storing a larger amount of high-purity nitrogen gas in the nitrogen tank 129. For example, a boost pressure booster valve or a boost compressor can be used as this pressure booster U128. It is also preferable that a pressure gauge be provided to monitor the pressure boost.

[0109] The nitrogen tank 129 temporarily stores and preserves the high-purity nitrogen gas supplied from the nitrogen filter U12 via the pressure booster U128, and serves as a nitrogen gas supply interface that stably supplies the high-purity nitrogen gas to the outside, for example, under the control of the overall control U131. It is also preferable that the nitrogen tank 129 is provided with a gas pressure gauge so that the gas pressure inside the tank can be measured at any time.

[0110] It is also possible to supply the generated nitrogen gas directly to the outside from the nitrogen filter U12 via a predetermined flow control means without using the nitrogen tank 129 (and pressure booster U128) as such a nitrogen gas supply interface. For example, if the supply destination is a soldering device or the like, high-purity nitrogen gas that is supplied directly and has a temperature at least above room temperature (25°C) is more preferable because it saves the amount of heat required to further increase the temperature when used as a soldering atmosphere.

[0111] The overall control U131 is capable of communicating with the main components, including the fuel cell U11 and nitrogen filter U12 described above, and preferably with all components, via a wired or wireless communication network.It receives measured quantities output from the measuring units and sensors of each component, such as pressure, gas flow rate, temperature, nitrogen concentration, oxygen concentration, hydrogen concentration, and the presence or absence of hydrogen leaks, and monitors them appropriately to monitor and control each component.

[0112] For example, it is also preferable that the overall control U131 is equipped with a processor and memory, and that the memory stores and is equipped with a nitrogen gas generation system monitoring and control program for monitoring and controlling each component, and that the program is executed by the processor.

[0113] The control performed by the overall control U131 includes adjustment and control of the pressure, gas flow rate, temperature, nitrogen concentration, oxygen concentration, hydrogen concentration, etc., in each component and between each component. In particular, it is also preferable to control the back pressure in the "fuel cell" of the fuel cell U11 and to control the balance between the back pressure on the hydrogen electrode side and the back pressure on the air electrode side.

[0114] It is also preferable that the overall control U131 monitors the temperature (cell temperature) of the "fuel cell" of the fuel cell U11, the temperature of the exhaust gas introduced into the nitrogen gas filter 12f of the nitrogen filter U12, and the temperature of the hydrogen generation U102, etc., to appropriately control the fuel cell reaction, filtering operation, and hydrogen generation (electrolysis) reaction in the nitrogen gas generation system 1. Furthermore, it is also preferable to monitor the presence or absence of hydrogen leakage in each component and between each component, and if it is determined that a problem has occurred, to send an alarm containing information about the location of the hydrogen leakage to the outside.

[0115] [Example 1] 2 to 4 are graphs for explaining Example 1 of the nitrogen gas generation process according to the present invention.

[0116] In Example 1, the measurement results and analysis results of which are shown in FIGS. 2 to 4, a UBE N2 separator NM-B01A manufactured by Ube Industries was used as the nitrogen gas filter 12f (FIG. 1). Air having an oxygen concentration of 20.8 vol% and three types of mixed gases of nitrogen gas and oxygen gas having oxygen concentrations of 10.3 vol%, 5.1 vol%, and 1.1 vol%, respectively, were introduced into this nitrogen gas filter 12f at room temperature (25°C). (a) The oxygen concentration of the introduced gas (introduced oxygen concentration c_in_O2 (vol%)), the pressure of the introduced gas (introduced pressure p_in (atmospheric pressure)), and the flow rate of the exhaust gas at the outlet of the nitrogen gas filter 12f (outlet flow rate f_out (L / min, liters / minute)), (b) Oxygen concentration of the gas at the outlet of the nitrogen gas filter 12f (outlet oxygen concentration c_out_O2 (ppm vol)) We measured the above and investigated the relationship between (a) and (b).

[0117] Incidentally, the oxygen concentrations of 10.3 vol%, 5.1 vol%, and 1.1 vol% in the introduced gas are all values that are realized in the exhaust gas of an actual "fuel cell."

[0118] Figures 2(A), (B), and (C) show graphs showing the relationship between the inlet oxygen concentration c_in_O2 and the outlet oxygen concentration c_out_O2 when the outlet flow rate f_out is 2.0 L / min, 1.5 L / min, and 1.0 L / min, respectively.

[0119] According to these graphs, (a) The smaller the introduced oxygen concentration c_in_O2, (b) The larger the introduction pressure p_in, (c) The smaller the outlet flow rate f_out, It can be seen that the outlet oxygen concentration c_out_O2 becomes smaller, and nitrogen gas with higher purity is output from the nitrogen gas filter 12f.

[0120] For example, if the inlet oxygen concentration c_in_O2 is set to 1.1%, the inlet pressure p_in is set to 7.0 atmospheres, and the outlet flow rate f_out is set to 1.0 L / min, the outlet oxygen concentration c_out_O2 will be 325 ppm (0.0325 vol%) (as shown in Figure 2(C)). Incidentally, if the outlet flow rate f_out is set to an even smaller value of 0.75 L / min under the same inlet oxygen concentration and inlet pressure, the outlet oxygen concentration c_out_O2 will be a very small value of 190 ppm (0.0190 vol%), and high-purity nitrogen gas with an extremely low oxygen concentration will be obtained. Incidentally, experiments have confirmed that this tendency in results remains roughly unchanged even when the temperature of the gas introduced into the nitrogen gas filter 12f is 40°C or 50°C.

[0121] <Outlet flow rate and outlet oxygen concentration> First, a more specific relationship between the outlet flow rate f_out and the outlet oxygen concentration c_out_O2 will be described. From the data of the graphs shown in Figures 2(A) to 2(C), the relationship between the two is expressed by the following equation: (1) (c_out_O2)=C·(f_out) a It is derived that the relationship expressed as follows holds. The coefficient C of the (a) term takes a positive value, and the smaller the introduced oxygen concentration c_in_O2 is and the larger the introduced pressure p_in is, the smaller the value becomes. For example, when the introduced oxygen concentration c_in_O2 is 1.1% and the introduced pressure p_in is 7.0 atmospheres, the C value becomes 319 (ppm), which is a very small value. (b) The power coefficient a is almost independent of the introduced oxygen concentration c_in_O2, and is around 1.6 when the introduced pressure p_in is 4.0 atmospheres. The larger the introduced pressure p_in, the larger the value becomes, reaching around 2.0 when the introduced pressure p_in is 7.0 atmospheres.

[0122] Therefore, in any case, it can be understood that the smaller the outlet flow rate f_out, the smaller the outlet oxygen concentration c_out_O2 can be, that is, high-purity nitrogen gas with a lower oxygen concentration can be obtained. Here, since the power coefficient a is determined only by the introduction pressure p_in, the mechanism by which the outlet flow rate contributes to the outlet oxygen concentration is thought to be dynamic and related to the state of the fibers of the filter 12f, which is determined by the introduction pressure.

[0123] <Introduced oxygen concentration and filtering effect> Next, the relationship between the introduced oxygen concentration c_in_O2 and the filtering effect of the nitrogen gas filter 12f, that is, the degree of the oxygen concentration reduction effect, will be described using the analysis results shown in FIG.

[0124] 3(A), (B), and (C) show graphs illustrating the relationship between the introduced oxygen concentration c_in_O2 and the oxygen concentration reduction index when the outlet flow rate f_out is 2.0 L / min, 1.5 L / min, and 1.0 L / min, respectively. Note that the four curves shown in each of these graphs are power approximation curves for data points when the introduced pressure p_in is 4.0 atmospheres, 5.0 atmospheres, 6.0 atmospheres, and 7.0 atmospheres, respectively.

[0125] Here, the oxygen concentration reduction index is calculated by the following formula, where c_out_O2(Air) is the outlet oxygen concentration when air with an oxygen concentration of 20.8 vol% is introduced into the nitrogen gas filter 12f. (2) (Oxygen concentration reduction index)=c_out_O2(Air) / c_out_O2 It is an index calculated using the results of filtering with air as the standard, and represents the absolute degree of reduction in oxygen concentration due to filtering, that is, the magnitude of the filtering effect (relative to the case of air as the standard).

[0126] According to the graphs in Figures 3(A), (B) and (C), (a) The oxygen concentration reduction index increases as the introduced oxygen concentration c_in_O2 decreases. In particular, the rate of increase becomes rapidly larger when the introduced oxygen concentration c_in_O2 exceeds 10 vol%. (b) The oxygen concentration reduction index does not show a significant dependency on the inlet pressure p_in. (c) The oxygen concentration reduction index does not show any significant dependency on the outlet flow rate f_out. Incidentally, the introduced oxygen concentration c_in_O2=10 vol%, at which the rate of increase of the oxygen concentration reduction index in (a) above begins to increase sharply, roughly corresponds to the oxygen concentration in the exhaust gas of a "fuel cell" with an oxygen utilization rate of 50%.

[0127] Furthermore, from the above analysis results, it can be seen that, for example, to find filtering conditions that result in an oxygen concentration reduction index of 10, i.e., a filtering effect that is 10 times (one order of magnitude higher) (compared to that of air), it is sufficient to set the introduction oxygen concentration c_in_O2 to 2.5 vol% or less, regardless of the settings of the introduction pressure p_in or the outlet flow rate f_out. Here, the value c_in_O2 = 2.5 vol% is the average introduction oxygen concentration value at which the oxygen concentration reduction index is 10 in the four power approximation curves in each graph. Incidentally, the horizontal axis intercept of the tangent line at around c_in_O2 = 1.1 vol% in each graph curve also has a value near 2.5 vol% (= c_in_O2).

[0128] Therefore, in the nitrogen gas generation system 1 of the embodiment shown in Figure 1, by applying exhaust gas with an oxygen concentration of 2.5 vol% or less to the nitrogen gas filter 12f, it is possible to extract exhaust gas from this filter 12f with an oxygen concentration of 1 / 10 or less compared to the result when air is applied. Incidentally, it has been confirmed through experiments that the graph of Figure 3 described above is generally consistent, especially in the low oxygen concentration range, even when the temperature of the gas introduced into the nitrogen gas filter 12f is 40°C and 50°C.

[0129] <Inlet pressure and outlet oxygen concentration> Next, the relationship between the introduction pressure p_in and the outlet oxygen concentration c_out_O2 will be explained using the analysis results shown in FIG.

[0130] FIG. 4 shows the ratio of the quadratic coefficient to the linear coefficient in the four polynomial (quadratic) approximation equations corresponding to the four graph curves in each of the graphs shown in FIGS. 2(A) to 2(C). Relationship between inlet pressure p_in and (second-order coefficient) / (first-order coefficient) The graph shows:

[0131] 2(A) to 2(C) show four graph curves that represent the relationship between the inlet oxygen concentration c_in_O2 and the outlet oxygen concentration c_out_O2 when the inlet pressure p_in is 4.0 atmospheres, 5.0 atmospheres, 6.0 atmospheres, and 7.0 atmospheres, respectively. In addition, a polynomial (quadratic) approximation formula corresponding to each graph curve is written near the graph curve for p_in=7.0 atmospheres (and f_out=1.0 L / min) in the graph of FIG. 2(C). (3) y=6.6246x 2 +161.96 where y is c_out_O2 (vol%) and x is c_in_O2 (vol%) In this case, the quadratic coefficient is 6.6246 and the linear coefficient is 161.96.

[0132] As described above, the introduced oxygen concentration c_in_O2 not only contributes (proportionally) to the outlet oxygen concentration c_out_O2 as a linear term, but also has an effect as a quadratic term. In other words, if the introduced oxygen concentration c_in_O2 becomes 1 / N, the outlet oxygen concentration c_out_O2 does not simply become 1 / N, but the quadratic term of the introduced oxygen concentration c_in_O2 affects the outlet oxygen concentration c_out_O2.

[0133] The ratio of the second-order coefficient to the first-order coefficient, (second-order coefficient) / (first-order coefficient), as described above, was calculated for each curve in each of the graphs in Figures 2(A) to (C), and these calculated values were plotted on a graph with the vertical axis representing (second-order coefficient) / (first-order coefficient) and the horizontal axis representing the introduction pressure p_in, resulting in the graph in Figure 4.

[0134] According to the graph in Figure 4, three graph curves (straight lines in Figure 4) are obtained where the outlet flow rates f_out are 1.0 L / min, 1.5 L / min, and 2.0 L / min, respectively, and it can be seen that the graph points in Figure 4 can be approximated by a linear approximation formula determined for each outlet flow rate.

[0135] According to these graph curves (straight lines), the (quadratic coefficient) / (linear coefficient) ratio increases as the inlet pressure p_in increases and as the outlet flow rate f_out decreases. Therefore, it can be seen that the quadratic term of the inlet oxygen concentration c_in_O2 contributes to reducing the outlet oxygen concentration c_out_O2.

[0136] From this, it can be understood that in order to obtain nitrogen gas with higher purity (to reduce the outlet oxygen concentration c_out_O2), it is preferable to increase the proportion of the quadratic term in the inlet oxygen concentration c_in_O2, i.e., (quadratic coefficient) / (linear coefficient), in positive values, and that it is important to set it to a value exceeding 0 (zero), at which the contribution of the quadratic term disappears. In other words, it is preferable to express the quadratic term exceeding a positive value.

[0137] Therefore, from the graph of FIG. 4, the conditions under which the (second-order coefficient) / (first-order coefficient) ratio exceeds 0 (zero) were found. It was found that the conditions are when the outlet flow rate f_out is 1.0 L / min, 1.5 L / min, and 2.0 L / min and the inlet pressure p_in exceeds 2.94 atmospheres, 3.40 atmospheres, and 3.86 atmospheres, respectively. It can also be understood that these pressure thresholds increase as the outlet flow rate f_out increases. In other words, when the outlet flow rate f_out is set to a smaller value, the inlet pressure p_in can be set based on a smaller pressure threshold.

[0138] Furthermore, from the above analysis results, it can be understood that in the nitrogen gas generation system 1 of the embodiment shown in Figure 1, it is also preferable to set the exhaust gas pressure (inlet pressure) acting on the nitrogen gas filter 12f to a pressure value that exceeds the pressure threshold determined by the nitrogen gas filter 12f, and which takes on a larger value as the flow rate (outlet flow rate) of the exhaust gas when extracted from the nitrogen gas filter 12f increases.

[0139] [Example 2] FIG. 5 is a graph for explaining Example 2 in which the recovery rate of the nitrogen gas filter 12f in the nitrogen gas generation process according to the present invention was examined.

[0140] In Example 2, the recovery rate of the nitrogen gas filter 12f is measured using the same system as in Example 1, with the same conditions set as in Example 1 for the introduced oxygen concentration, introduction pressure, and outlet flow rate. However, in Example 2, measurements are also made when the introduced oxygen concentration c_in_O2=0 (zero), that is, when pure nitrogen gas is introduced into the filter 12f. The recovery rate, which is a measurement item in Example 2, is the degree of gas recovery in the filter 12f, and is calculated using the following equation, where the flow rate of the introduced gas at the inlet of the filter 12f (introduced flow rate) is f_in: (4) (recovery rate) = (f_out) / (f_in) The ratio is calculated as follows:

[0141] Figures 5(A), (B), and (C) show graphs showing the relationship between the introduced oxygen concentration c_in_O2 and the recovery rate under conditions where the outlet flow rate f_out is 2.0 L / min, 1.5 L / min, and 1.0 L / min, respectively.

[0142] According to these graphs, (a) (Although this may be slightly different under conditions of 4.0 atmospheres) The smaller the introduced oxygen concentration c_in_O2, (b) The smaller the inlet pressure p_in (although the difference between 4.0 and 5.0 atmospheres is very small), the further (c) (This is highly probable given the definition of recovery rate) The larger the outlet flow rate f_out, The recovery rate becomes larger, and it can be seen that even if a predetermined flow rate of exhaust gas is introduced into the nitrogen gas filter 12f, a larger amount of nitrogen gas (which is exhaust gas with a reduced oxygen concentration) is obtained.

[0143] Regarding the inlet oxygen concentration c_in_O2 in (a) above, the direction of increasing the recovery rate and the direction of decreasing the outlet oxygen concentration c_out_O2 (as shown in FIG. 2, for example) are consistent. Specifically, by decreasing the inlet oxygen concentration c_in_O2, it is possible to further reduce the outlet oxygen concentration and increase the recovery rate. Therefore, in order to generate more nitrogen gas with higher purity, it is more preferable to use a nitrogen gas filter that increases the recovery rate as the oxygen concentration of the gas to be filtered decreases.

[0144] This also shows that a combined system of a "fuel cell" that outputs exhaust gas with a low oxygen concentration and the above-mentioned "nitrogen gas filter" that utilizes that exhaust gas is a very compatible system, in other words, a system that can efficiently generate nitrogen gas, from the standpoint of both the outlet oxygen concentration and the recovery rate.

[0145] On the other hand, with regard to the inlet pressure p_in (b) and the outlet flow rate f_out (c) above, the direction of increasing the recovery rate and the direction of decreasing the outlet oxygen concentration c_out_O2 (as shown in Figure 2, for example) are opposite directions, and the recovery rate and the outlet oxygen concentration c_out_O2 are in a so-called trade-off relationship.

[0146] Therefore, for example, if the inlet pressure p_in is increased, high-purity nitrogen gas with a lower oxygen concentration can be obtained, but on the other hand, the amount of exhaust gas required to obtain a predetermined amount of that nitrogen gas, and therefore the amount of air required to be input into the ``fuel cell'', will increase.

[0147] Therefore, it is also preferable to adjust the settings of the inlet pressure p_in and the outlet flow rate f_out to ensure a predetermined recovery rate while realizing a desired low outlet oxygen concentration c_out_O2 in accordance with the nitrogen gas output performance content set in the nitrogen gas generation system 1 (FIG. 1). For example, it is also preferable to determine while controlling the inlet pressure p_in and the outlet flow rate f_out (and the recovery rate, which depends on these) in order to realize the performance content of producing nitrogen gas of a predetermined purity or higher (e.g., 99.9 vol% or higher) at a predetermined production cost (e.g., at a production cost equal to or lower than that of a PSA apparatus as described below).

[0148] Regarding the trade-off between the recovery rate and the outlet oxygen concentration c_out_O2 with respect to the inlet pressure p_in in (b) above, the inventors of the present application believe that this is also related to the fact that in the nitrogen gas filter 12f of Example 2 (Example 1), in which the filter fibers are hollow fibers, as the inlet pressure p_in increases, the hollow fibers expand, causing changes not only in the oxygen molecule selectivity of the filter fibers but also in their permeability to molecules other than oxygen molecules.

[0149] Furthermore, with regard to the recovery rate described above, the inventors of the present application have confirmed that the higher the temperature of the gas introduced into the nitrogen gas filter 12f, the smaller the recovery rate becomes, and that the recovery rate drops significantly at temperatures above a certain level. Therefore, it is also preferable that the temperature regulator U126 (FIG. 1) installed upstream of the nitrogen filter U12 in the nitrogen gas generation system 1 (FIG. 1) adjusts the temperature of the exhaust gas, taking into consideration the need to ensure a predetermined recovery rate in the nitrogen gas filter 12f.

[0150] Regarding the effect of the temperature of the introduced gas on the recovery rate, the inventors of the present application believe that as the temperature increases, the hollow fibers of the nitrogen gas filter 12f expand, which changes not only the oxygen molecule selectivity of the filter fibers but also their permeability to molecules other than oxygen molecules.

[0151] 2 to 5, Examples 1 and 2 have been described above. Based on the findings obtained from these experiments, the inventors of the present application have succeeded in using the nitrogen gas generation system 1 to generate high-purity nitrogen gas having a purity (nitrogen concentration) exceeding 99.9 vol% and an oxygen concentration of less than 0.1 vol% (1000 ppm vol). Such high-purity nitrogen gas can be used in reflow soldering equipment, which has strict purity requirements. Incidentally, even in reflow soldering equipment, nitrogen gas with a purity (nitrogen concentration) of 99 vol% can be used, depending on the type of solder paste used.

[0152] Needless to say, the demand for nitrogen gas is not limited to electronic and electrical fields that use soldering equipment. In fact, nitrogen gas is used for a variety of purposes in a wide range of fields, including the metal and resin fields, which use nitrogen gas for laser processing and heat treatment, the transportation field, which requires nitrogen gas for tire filling and shipboard purging equipment, the chemical field, which uses nitrogen gas as a process gas, pressure transport gas, and cooling gas, the machinery field, which requires nitrogen gas for dry cutting equipment, and the food field, which uses nitrogen gas for food preservation and gas filling, and in CA (Controlled Atmosphere) storage atmosphere supply equipment and fryer equipment.

[0153] Therefore, the required purity (nitrogen concentration) of nitrogen gas also varies depending on the field and application. For example, in some cases the concentration of oxygen gas as an impurity gas (oxygen concentration) is required to be on the order of 0.01 vol% (100 ppm vol), while in other cases an oxygen concentration of up to a few vol% is acceptable.

[0154] In such a situation, the nitrogen gas generation system 1 can appropriately provide nitrogen gas in which the residual oxygen is suppressed to the required upper limit of the oxygen concentration by adjusting, for example, the inlet oxygen concentration c_in_O2, the inlet pressure p_in, and the outlet flow rate f_out. For example, in a case where the oxygen concentration can be as low as a few vol%, it is possible to increase the recovery rate by setting the inlet oxygen concentration c_in_O2 to, for example, 10 vol%, suppressing the inlet pressure p_in lower, and increasing the outlet flow rate f_out.

[0155] Furthermore, the nitrogen gas generation system 1 can also provide the electricity and heat required for the generated nitrogen gas, depending on the field and application. In this regard, it is naturally difficult or impossible for conventional nitrogen gas generators to provide such energy supplies.

[0156] Furthermore, based on the findings described above, the inventors have confirmed that the nitrogen gas generation system 1 according to the present invention can significantly reduce the cost of generating nitrogen gas. For example, according to research by the inventors, the current selling price of a nitrogen gas cylinder is, for example, 430 yen / Nm 3 The selling price of liquid nitrogen is about 120 yen / Nm 3 In addition, the cost of generating nitrogen gas using a PSA (pressure swing adsorption) device, which is a widely used nitrogen gas generating device, is about 48 yen / Nm 3 It will be about that amount.

[0157] In response to these issues, calculations have confirmed that with the nitrogen gas generation system 1, by setting appropriate conditions, including the standard output and possible exhaust gas flow rate of the "fuel cell," as well as the expected hydrogen procurement cost, it is possible to achieve generation costs that are equal to or lower than those of, for example, the PSA device described above. Furthermore, in cases where the nitrogen gas generation system 1 also provides the (required) electricity and heat, as described above, the overall procurement costs, including these, can be significantly reduced compared to conventional methods.

[0158] [Another embodiment of the nitrogen filter U] Another preferred embodiment of the nitrogen filter U12 will be described below. As described above, the nitrogen filter U12 shown in Fig. 1 is equipped with a filter purge section that extracts a "filter discharge gas" containing oxygen molecules that have been separated from nitrogen molecules (in the exhaust gas) by passing through the hollow fiber fibers of the nitrogen gas filter 12f. Here, the "filter discharge gas" discharged from this filter purge section contains a considerable amount of oxygen molecules, and is therefore a gas that can be reused in the fuel cell reaction or can be subjected to another filtering process.

[0159] Incidentally, when gas with an oxygen concentration of 10.2 vol% was introduced into the nitrogen gas filter 12f under conditions of an inlet pressure of 6.0 atmospheres and an outlet flow rate of 1.0 L / min, and the oxygen concentration of the filter exhaust gas discharged from there was examined, the experimental result was 14.9 vol%, and furthermore, the experimental result was obtained that the recovery rate was 0.29.

[0160] If we assume that almost all of the oxygen molecules in the introduced gas are discharged from the filter purge section of the nitrogen gas filter 12f (because the oxygen concentration at the outlet of the filter 12f is orders of magnitude smaller), the oxygen concentration in the filter discharge gas is calculated to be 0.102 / 0.71 = 14.4 using the recovery rate (0.29) obtained from the above experiment, which roughly matches the 14.9 vol% obtained from the above experiment. Therefore, it can be seen that almost all of the oxygen gas separated as unnecessary is recovered from the filter purge section of the nitrogen gas filter 12f.

[0161] Therefore, the nitrogen gas generation system 1 of this embodiment, as shown by the circled "B" in FIG. 1, (a) Returning the gas to the flow control U109 located before the cathode of the Fuel Cell to be reused in the Fuel Cell as a gas containing oxygen and nitrogen; and / or (b) Return the exhaust gas to the off-gas buffer tank 123 installed in front of the nitrogen filter U12, and let it act on the nitrogen gas filter 12f again together with the exhaust gas. This makes it possible to use oxygen gas more effectively and extract nitrogen gas with a lower oxygen concentration.

[0162] If the filter exhaust gas, which has a lower oxygen concentration than air, is reused in a fuel cell, the exhaust gas from the fuel cell can be made into exhaust gas with a lower oxygen concentration. This increases the recovery rate in the nitrogen gas filter 12f into which such exhaust gas is introduced (as explained using FIG. 5), making it possible to ultimately extract more nitrogen gas. Furthermore, although this depends on the settings of various conditions in the nitrogen gas generation system 1, increasing the final recovery rate in the nitrogen gas filter 12f in this way can also significantly reduce the cost of generating nitrogen gas.

[0163] Incidentally, as will be explained in detail later using Figure 7, under conditions where the oxygen concentration of the exhaust gas from the "fuel cell" is about 15 vol% and the oxygen concentration of the filter exhaust gas is, for example (typically) 1.4 times the introduced oxygen concentration c_in_O2, the oxygen concentration of the filter exhaust gas will be the same as or higher than that of air (20.8 vol%), and as a result, the above-mentioned benefits of returning the filter exhaust gas to the air electrode side of the "fuel cell" will not be realized.

[0164] On the other hand, if the oxygen concentration of the filter exhaust gas is also 1.4 times the inlet oxygen concentration c_in_O2, and the oxygen concentration of the exhaust gas from the "fuel cell" is about 10 vol%, the oxygen concentration of the filter exhaust gas will be around 14 vol% (<20.8 vol%), and the above-mentioned return of the filter exhaust gas becomes meaningful. Furthermore, if the oxygen concentration of the exhaust gas from the "fuel cell" is about 5 vol%, the oxygen concentration of the filter exhaust gas will be around 7 vol%, which not only is expected to improve the recovery rate, but depending on the system settings, it may also have the economic effect of significantly reducing the cost of generating nitrogen gas.

[0165] Another preferred embodiment for reusing the filter exhaust gas as described above will be described below. Figure 6 is a schematic diagram for explaining another embodiment of the nitrogen filter U12 according to the present invention.

[0166] 6(A), the nitrogen filter U12 is equipped with three nitrogen gas filters 12f1, 12f2, and 12f3 connected in series. Specifically, the exhaust gas taken into the nitrogen filter U12 is first introduced into nitrogen gas filter 12f1, and the exhaust gas with an increased nitrogen concentration that emerges from this nitrogen gas filter 12f1 is introduced into the next nitrogen gas filter 12f2. Furthermore, the exhaust gas with an increased nitrogen concentration that emerges from nitrogen gas filter 12f2 is introduced into the last nitrogen gas filter 12f3, and finally, nitrogen gas with a higher purity is extracted from this nitrogen gas filter 12f3.

[0167] Here, from the results of Examples 1 and 2 described above, it can be seen that the later the nitrogen gas filter is, the lower the oxygen concentration of the exhaust gas is output with a higher recovery rate.

[0168] In this embodiment, the filter exhaust gases discharged from the nitrogen gas filters 12f1, 12f2, and 12f3 are returned together to the flow control U109 (FIG. 1) upstream of the fuel cell and / or the off-gas buffer tank 123 (FIG. 1) upstream of the nitrogen filter U12 for reuse. This makes it possible to more effectively utilize the oxygen gas content and extract nitrogen gas with a lower oxygen concentration.

[0169] It should be noted that the number of nitrogen gas filters used in this embodiment is not limited to three. Specifically, it is possible to use N nitrogen gas filters, from the first nitrogen gas filter to the Nth nitrogen gas filter (N is an integer of 2 or more). In this case, Extracting exhaust gas with an increased nitrogen concentration from the nth nitrogen gas filter (n is an integer greater than or equal to 1 and up to (N-1)), allowing the extracted exhaust gas to act on the (n+1)th filter, and extracting the exhaust gas with an increased nitrogen concentration from the (n+1)th filter; This process is repeated from n=1 to (N-1).

[0170] 6(B), the nitrogen filter U12 is provided with three nitrogen gas filters 12f1, 12f2, and 12f3 connected in cascade. Specifically, the exhaust gas taken into the nitrogen filter U12 is first introduced into the nitrogen gas filter 12f1, and the filter exhaust gas discharged from this nitrogen gas filter 12f1 is introduced into the next nitrogen gas filter 12f1.

[0171] Furthermore, the filter exhaust gas discharged from this nitrogen gas filter 12f2 is introduced into the final nitrogen gas filter 12f3, and the filter exhaust gas discharged from this nitrogen gas filter 12f3 is sent back to the flow control U109 (Figure 1) in front of the "fuel cell" and / or the off-gas buffer tank 123 (Figure 1) in front of the nitrogen filter U12, and is reused.

[0172] Furthermore, if the oxygen concentration in the filter discharge gas discharged from the nitrogen gas filter 12f3 is equal to or higher than a predetermined value, the filter discharge gas may be sent to an external oxygen tank for storage. In any case, such processing makes it possible to more effectively utilize the oxygen gas and to extract nitrogen gas with a lower oxygen concentration.

[0173] Here, the exhaust gases with increased nitrogen concentrations that have come out of the nitrogen gas filters 12f1, 12f2 and 12f3 are combined and output as highly pure nitrogen gas.

[0174] In addition, since the flow rate of the introduced gas (introduced flow rate) decreases from nitrogen gas filter 12f1 to 12f3, it is preferable to use, for example, nitrogen gas filter 12f2 that is smaller than 12f1 (compatible with small flow rates), and further, to use nitrogen gas filter 12f3 that is smaller than 12f2 (compatible with small flow rates).

[0175] Naturally, the number of nitrogen gas filters used in this embodiment is not limited to 3. Specifically, it is possible to use N nitrogen gas filters, from the first nitrogen gas filter to the Nth nitrogen gas filter (N is an integer of 2 or more).

[0176] When N nitrogen gas filters are used in this way, Extracting exhaust gas with an increased nitrogen concentration (or filter exhaust gas with an increased nitrogen concentration) and another filter exhaust gas from the nth nitrogen gas filter (n is an integer of 1 or more and up to (N-1)), causing the extracted filter exhaust gas to act on the (n+1)th filter, and extracting the filter exhaust gas with an increased nitrogen concentration from the (n+1)th filter; This process is repeated from n=1 to (N-1).

[0177] Here, the return effect and recovery rate of the filter exhaust gas in the cascade filter system shown in Figure 6(B) will be explained. First, the experimental results of the oxygen concentration of the filter exhaust gas in one nitrogen gas filter 12f will be shown.

[0178] 7A and 7B are graphs showing the relationship between the oxygen concentration c_in_O2 introduced into the nitrogen gas filter 12f according to the present invention and the oxygen concentration c_fout_O2 of the filter exhaust gas. The graph in Fig. 7A shows the results of an experiment in which the outlet flow rate f_out was set to 2.0 L / min, while the graph in Fig. 7B shows the results of an experiment in which the outlet flow rate f_out was set to 1.0 L / min.

[0179] According to the graphs in FIGS. 7(A) and (B), (a) The larger the introduced oxygen concentration c_in_O2, (b) The smaller the introduction pressure p_in, the more (c) The larger the outlet flow rate f_out, It can be seen that the oxygen concentration c_fout_O2 of the filtered exhaust gas becomes larger. Here, it has been confirmed that the calculated value of the oxygen concentration c_fout_O2 of the filtered exhaust gas calculated from the measured value of the outlet flow rate f_out above (c) using the inlet flow rate f_in and the inlet oxygen concentration c_in_O2 matches very well with the measured value of c_fout_O2 this time.

[0180] In addition, the relationship between the introduced oxygen concentration c_in_O2 (vol%) in (a) and the oxygen concentration c_fout_O2 (vol%) in the filter exhaust gas is expressed by the following equation, as shown in the approximate curves (straight lines) in FIGS. 7(A) and 7(B). (5) (c_fout_O2)=b·(c_in_O2) Here, the proportionality coefficient b takes a larger value as the inlet pressure p_in decreases, and when the outlet flow rate f_out is 2.0 L / min, b = 1.6 to 2.1 in the range of the graph in Figure 7(A), while when the outlet flow rate f_out is 1.0 L / min, b = 1.3 to 1.7 in the range of the graph in Figure 7(B).

[0181] As described above, under the conditions of a predetermined inlet pressure p_in and outlet flow rate f_out, the oxygen concentration c_fout_O2 of the filter exhaust gas increases to a value approximately 1.3 to 2.1 times the inlet oxygen concentration c_in_O2.

[0182] As a typical example, the proportionality coefficient b is set to 1.4, that is, the following equation is used: (5') (c_fout_O2)=1.4·(c_in_O2) Assuming that the above holds, let us consider the effect of returning the filter exhaust gas in the cascade filter system shown in Figure 6(B) above.

[0183] Returning to Figure 6(B), as shown in the figure, the oxygen concentration c_in_O2 introduced into nitrogen gas filter 12f1 is defined as C1, the oxygen concentration c_fout_O2 of the filter exhaust gas from nitrogen gas filter 12f1 that is introduced into nitrogen gas filter 12f2 is defined as C2, the oxygen concentration c_fout_O2 of the filter exhaust gas from nitrogen gas filter 12f2 that is introduced into nitrogen gas filter 12f3 is defined as C3, and the oxygen concentration c_fout_O2 of the filter exhaust gas from nitrogen gas filter 12f3 is defined as C4.

[0184] Here, for example, when air (with an oxygen concentration of 20.8 vol%) is introduced into a "fuel cell" with an oxygen utilization rate of 50%, and the resulting exhaust gas is introduced into the nitrogen gas filter 12f1, according to the above formula (5'), C1=10.4(vol%),C2=14.6(vol%),C3=20.4(vol%),C4=28.5(vol%) From this result, it can be seen that in this case, the oxygen concentration (i.e., C4) in the filter exhaust gas from the third nitrogen gas filter 12f3 exceeds that of air (20.8 vol%), and there is no effect in returning this gas to the "fuel cell." Incidentally, such filter exhaust gas may be stored as oxygen-rich gas in a separate tank, for example, and used separately.

[0185] On the other hand, when considering the case where exhaust gas having an oxygen concentration of 5.0 vol% is introduced into the nitrogen gas filter 12f1, according to the same above formula (5'), C1=5.0(vol%),C2=7.0(vol%),C3=9.8(vol%),C4=13.7(vol%) From this result, in this case, the oxygen concentration in the filter exhaust gas from the third nitrogen gas filter 12f3 is lower than that of air (20.8 vol%), and it is expected that the final recovery rate will be improved by returning this gas to the "fuel cell." Furthermore, depending on the system settings, it is also possible to achieve an economic effect by significantly reducing the cost of generating nitrogen gas.

[0186] Next, the final recovery rate in the cascade filter system shown in FIG. 6(B) will be considered.

[0187] First, as shown in Figure 6(B), the flow rate f_in introduced into nitrogen gas filter 12f1 is set to f1, the flow rate f_fout of filter exhaust gas from nitrogen gas filter 12f1 (which is the flow rate introduced into nitrogen gas filter 12f2) is set to f2, the flow rate f_fout of filter exhaust gas from nitrogen gas filter 12f2 (which is the flow rate introduced into nitrogen gas filter 12f3) is set to f3, and the flow rate f_fout of filter exhaust gas from nitrogen gas filter 12f3 is set to f4.

[0188] To simplify the calculation, the flow rate f1 introduced into the nitrogen gas filter 12f1 is set to 1, and the recovery rates of the three nitrogen gas filters 12f1, 12f2, and 12f3 are all set to 0.3. Then, taking the above formula (5') into consideration, f2=1×(1-0.3)=0.7,f3=1×(1-0.3) 2 =0.49,f4=1×(1-0.3) 3 =0.34 From this result, the final recovery rate in the cascade filter system shown in Figure 6(B) is (6) (Recovery rate) = (1 - 0.34) / 1 = 0.66 This achieves a recovery rate that far exceeds the recovery rate of 0.3 for individual filters.

[0189] The calculation results of the above formula (6) are for the case where the recovery rate of each filter is fixed at 0.3, but in reality, as described above, the introduced oxygen concentration c_in_O2 increases from nitrogen gas filter 12f1 to 12f3, working to lower the recovery rate. However, on the other hand, the introduced pressure p_in decreases, working to raise the recovery rate. In the end, the final recovery rate is not significantly different from the above formula (6), and is thought to be at least a value considerably higher than the recovery rate of each filter, 0.3.

[0190] Thus, even when considering the recovery rate of each individual filter, the cascade filter system shown in Figure 6(B) is expected to improve the final recovery rate, and furthermore, depending on the system settings, it may be possible to achieve an economical effect by significantly reducing the cost of producing nitrogen gas.

[0191] Various embodiments relating to the nitrogen filter U12 have been described above, but even in these embodiments, it is preferable that the overall control U131 (Figure 1) constantly monitors the oxygen concentration, pressure, and flow rate of the exhaust gas from the "fuel cell," as well as the inlet oxygen concentration, inlet pressure, inlet flow rate, inlet gas temperature, outlet oxygen concentration, outlet pressure, outlet flow rate, etc. of each nitrogen gas filter, and controls each unit so that a predetermined amount (predetermined flow rate) of nitrogen gas having a predetermined high nitrogen concentration can be provided at the appropriate time.

[0192] In this case, the overall control U131 (Figure 1) may use the oxygen concentration, pressure, and flow rate of the exhaust gas from the "fuel cell," as well as the measured values of the inlet oxygen concentration, inlet pressure, inlet flow rate, inlet gas temperature, outlet oxygen concentration, outlet pressure, and outlet flow rate at each nitrogen gas filter as learning data to construct a control model that can estimate the optimal control value of each unit and the achievable nitrogen gas production cost using a known machine learning algorithm, such as a neural network, and control each unit using this constructed control model.

[0193] As mentioned above, nitrogen gas users' requirements for nitrogen gas purity (nitrogen concentration) and generation costs vary widely depending on the field and specific application. For example, some users require a purity of 99.9 vol% or higher, while others require a purity of around 95 vol% but require generation costs to be kept below a certain level. The overall control U131 (Figure 1) preferably selects a control model based on the requirements of each individual user and uses the appropriately selected control model to enable the nitrogen gas generation system 1 to deliver high performance that meets the user's requirements.

[0194] [Another embodiment of a fuel cell] Figure 8 is a schematic diagram for explaining another embodiment of the "fuel cell" according to the present invention. Note that Figures 8(A) to (C) show cross sections of each fuel cell, and linearly extending air and fuel paths appear in these cross sections, but these shapes are merely simple examples for explaining this embodiment, and the air and fuel paths of this embodiment are not limited to these shapes.

[0195] First, according to the embodiment shown in Fig. 8(A), the fuel cell 20 has a configuration in which a plurality of battery cells, such as a first cell 201, a second cell 202, etc., are stacked (laminated) and separated by separators. (a) an air passage through which air (or a gas containing nitrogen and oxygen) flows, and an air electrode having an electrode surface exposed to the air passage; (b) a fuel path through which hydrogen gas, which is a fuel gas, flows, and a fuel electrode having an electrode surface exposed to the fuel path; (c) an electrolyte sandwiched between the air electrode and the fuel electrode; As with known fuel cells, when the fuel cell is in operation, it is possible to provide the electric power generated between the air electrode and the fuel electrode to the outside.

[0196] In the fuel cell 20 of this embodiment, in each of the first cell 201, the second cell 202, etc., air and hydrogen are introduced into the cell from opposite sides. That is, each cell is configured such that the vicinity of the outlet of the air path and the vicinity of the inlet of the fuel path are adjacent to each other with the electrolyte interposed therebetween. Note that in this embodiment, the flow direction of air through the air path and the flow direction of hydrogen through the fuel path are consistently opposite to each other.

[0197] With the configuration described above, near the outlet of the air passage of each battery cell, the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact, via the electrolyte, in a reactive state with a sufficient amount of hydrogen gas that has begun to flow near the inlet of the fuel passage. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0198] In other words, in the fuel cell 20 of this embodiment, the vicinity of the outlet of the air passage and the vicinity of the inlet of the fuel passage of each battery cell are adjacent to each other via the electrolyte, so a "high oxygen consumption area" (FIG. 8(A)) is formed near the outlet of the air passage, where most of the residual oxygen is used for the fuel cell reaction. As a result, it is also possible to extract nitrogen gas with a sufficiently or considerably low residual oxygen concentration.

[0199] Incidentally, a configuration similar to the fuel cell 20 described above can be realized not only in polymer electrolyte fuel cells (PEFCs) and solid oxide fuel cells (SOFCs), but also in phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), etc.

[0200] Next, according to the embodiment shown in Fig. 8(B), a plurality of (three in this figure) fuel cells 31, 32, and 33 having known internal structures are connected in series with respect to the air and fuel paths to form a fuel cell system. (a) The air passage outlet of each battery cell (311, 312, ...) in the fuel cell 31 is connected to the air passage inlet of each battery cell (321, 322, ...) in the fuel cell 32 by piping; (b) The air passage outlets of the respective battery cells (321, 322, . . . ) in the fuel cell 32 are connected to the air passage inlets of the respective battery cells (331, 332, . . . ) in the fuel cell 33 by piping, and further, (c) a fuel passage outlet on the same side as the air passage inlet of each battery cell (331, 332,...) of the fuel cell 33 is connected by a pipe to a fuel passage inlet on the same side as the air passage outlet of each battery cell (321, 322,...) of the fuel cell 32; (d) The fuel path outlet, which is on the same side as the air path inlet, of each battery cell (321, 322, ...) of the fuel cell 32 is connected by piping to the fuel path inlet, which is on the same side as the air path outlet of each battery cell (311, 312, ...) of the fuel cell 31.

[0201] In this embodiment, under such a configuration, air (or a nitrogen and oxygen mixture) is introduced from the air passage inlet of each cell in fuel cell 31, while hydrogen is introduced from the fuel passage inlet of each cell in fuel cell 33, which is located on the opposite side. As a result, in each fuel cell, the flow direction of air through the air passage and the flow direction of hydrogen through the fuel passage are opposite to each other, and the vicinity of the final outlet for air (which serves as the air passage of each cell in fuel cell 33) and the vicinity of the initial inlet for hydrogen (which serves as the fuel passage of each cell in fuel cell 33) are located close to each other with the electrolyte interposed therebetween.

[0202] Furthermore, with this configuration, in the air passage of each cell in the fuel cell 33 (near the final outlet for the air), the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact, via the electrolyte, with a sufficient amount of hydrogen gas that has just begun to flow through the fuel passage of each cell in the fuel cell 33, in a manner that allows it to react. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0203] Incidentally, any of the fuel cells 31 to 33 constituting the above fuel cell system may be not only PEFC or SOFC but also PAFC, MCFC, etc. Also, the number of fuel cells constituting the fuel cell system is not limited to three, and may be two or four or more.

[0204] Next, according to the embodiment shown in Fig. 8(C), the cylindrical stack type fuel cell 40 has a configuration in which a plurality of cylindrical cells 401 are stacked (laminated) with their cell axes aligned in parallel. (a) an air passage through which air (or a gas containing nitrogen and oxygen) flows, and a cylindrical air electrode that surrounds the air passage on its inner surface; (c) a cylindrical electrolyte that encases the outside of the cylindrical air electrode; (b) a cylindrical fuel electrode further encasing the outside of the cylindrical electrolyte, and a fuel path surrounding the outer surface of the fuel electrode through which hydrogen gas, which is a fuel gas, flows; As with known fuel cells, when the fuel cell is in operation, it is possible to provide the electric power generated between the air electrode and the fuel electrode to the outside.

[0205] In the cylindrical stack fuel cell 40 of this embodiment, air and hydrogen are introduced into each battery cell 401 from opposite sides of the battery cell 401. That is, each battery cell 401 is configured such that the vicinity of the outlet of the air path and the vicinity of the inlet of the fuel path are close to each other with the electrolyte interposed therebetween. Note that this embodiment is also configured such that the flow direction of air through the air path and the flow direction of hydrogen through the fuel path are consistently opposite to each other.

[0206] With this configuration, near the outlet of the air path of each battery cell 401, the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact with a sufficient amount of hydrogen gas that has begun to flow near the inlet of the fuel path further outside, via the electrolyte that surrounds it, in a manner that allows it to react with it. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0207] That is, in the cylindrical stack fuel cell 40 of this embodiment, the vicinity of the outlet of the air passage and the vicinity of the inlet of the fuel passage of each battery cell 401 are adjacent to each other via the electrolyte, so a "high oxygen consumption area" (FIG. 8(C)) is formed near the outlet of the air passage, where most of the residual oxygen is used for the fuel cell reaction. As a result, it is also possible to extract nitrogen gas with a sufficiently or considerably low residual oxygen concentration.

[0208] Incidentally, a configuration similar to the cylindrical stack fuel cell 40 described above can be realized not only in SOFCs but also in PEFCs, PAFCs, and even MCFCs.

[0209] 9A to 9C are schematic diagrams illustrating still another embodiment of the "fuel cell" according to the present invention. Note that, although cross sections of each fuel cell are also shown in Figures 9A to 9C, and linearly extending air and fuel passages appear in these cross sections, these shapes are merely simple examples for the purpose of illustrating this embodiment, and the air and fuel passages of this embodiment are not limited to these shapes.

[0210] First, according to the embodiment shown in Fig. 9(A), a SOFC 51 and a PEFC 52, which are a solid oxide fuel cell and a polymer electrolyte fuel cell, respectively, are connected in series with respect to the air path and the fuel path to form a fuel cell system. (a) The air passage outlet of each battery cell (511, 512, . . . ) in the SOFC 51 is connected to the air passage inlet of each battery cell (521, 522, . . . ) in the PEFC 52 by piping; (b) The fuel path outlet, which is on the same side as the air path inlet, of each battery cell (521, 522, ...) of PEFC52 is connected by piping to the fuel path inlet, which is on the same side as the air path outlet of each battery cell (511, 512, ...) of SOFC51.

[0211] In this embodiment, under such a configuration, air (or a gas containing nitrogen and oxygen) is introduced from the air channel inlet of each battery cell in the SOFC 51, while hydrogen is introduced from the fuel channel inlet of each battery cell in the PEFC 52, which is on the opposite side. As a result, the flow direction of air through the air channel and the flow direction of hydrogen through the fuel channel are opposite to each other, and the vicinity of the final outlet for air (which becomes the air channel of each battery cell in the PEFC 52) and the vicinity of the initial inlet for hydrogen (which becomes the fuel channel of each battery cell in the PEFC 52) are configured to be adjacent to each other with the electrolyte interposed therebetween.

[0212] Furthermore, with this configuration, in the air passage of each battery cell in the PEFC 52 (near the final outlet for the air), the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact, via the electrolyte, with a sufficient amount of hydrogen gas that has just started to flow through the fuel passage of each battery cell in the PEFC 52, in a manner that allows it to react. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0213] Furthermore, the above-described interconnected system of the SOFC 51 and PEFC 52 suppresses the deterioration of the electrolyte in each fuel cell. Specifically, the electrolyte of the PEFC 52 is a solid polymer membrane made of a fluoropolymer or the like, and because the PEFC 52 maintains a sufficient amount of hydrogen, there is no shortage of hydrogen ions in the solid polymer membrane. As a result, it is possible to prevent the hydrogen atoms of the polymer in the solid polymer membrane from being absorbed into the fuel cell reaction, which would cause the solid polymer membrane to deteriorate.

[0214] On the other hand, the electrolyte of SOFC51 is a solid oxide membrane formed from stabilized zirconia or various perovskite oxides, and because SOFC51 has a sufficient amount of oxygen, there is no shortage of oxide ions in this solid oxide membrane. As a result, it is possible to avoid a situation in which the solid oxide membrane is exposed to a strongly reducing atmosphere (high temperatures of 700-800°C), and oxygen atoms in the solid oxide membrane are taken in by the fuel cell reaction, which would reduce and deteriorate the solid oxide membrane.

[0215] In addition, as one preferred embodiment, the SOFC51 and PEFC52 are fuel cells of equal efficiency, and it is also preferable to set the consumption of oxygen in the air and the consumption of hydrogen in the hydrogen gas to be approximately the same at the connection point between the SOFC51 and PEFC52, i.e., the piping position connecting the two.

[0216] Furthermore, it is preferable that a heat exchanger be connected to the air passage outlet of each battery cell in the SOFC 51, and that this heat exchanger recover heat from the high-temperature exhaust gas coming out of the air passage outlet. It is also preferable that a unit for removing corrosive gases, etc., using an activated carbon filter or the like be installed downstream of this heat exchanger. Furthermore, it is also preferable that a unit with a dehumidifying function, such as an auto-drain or a dehumidifier, be installed, particularly at the fuel passage outlet of each battery cell in the PEFC 52.

[0217] Next, according to the embodiment shown in Figure 9(B), a fuel cell system is constructed by connecting a fuel cell 61 and a fuel cell 62, both of which have known internal structures, in series with respect to the air passage. (a) The air passage outlets of the respective battery cells (611, 612, ...) in the fuel cell 61 are connected to the air passage inlets of the respective battery cells (621, 622, ...) in the fuel cell 62 by piping; (b) The fuel path outlet, which is on the same side as the air path inlet of each battery cell (621, 622, ...), of the fuel cell 62, is connected by piping to the fuel path inlet, which is on the same side as the air path inlet of each battery cell (611, 612, ...), of the fuel cell 61.

[0218] In this embodiment, under such a configuration, air (or a gas containing nitrogen and oxygen) is introduced from the air passage inlet of each cell in fuel cell 61, while hydrogen is introduced from the fuel passage inlet of each cell in fuel cell 62, which is located on the opposite side. This results in a configuration in which the vicinity of the final outlet for air (which serves as the air passage of each cell in fuel cell 62) and the vicinity of the initial inlet for hydrogen (which serves as the fuel passage of each cell in fuel cell 62) are close to each other with the electrolyte interposed therebetween.

[0219] In this embodiment, in each cell of the fuel cell 61, the flow direction of air through the air path and the flow direction of hydrogen through the fuel path are the same, but in each cell of the fuel cell 62, they are opposite to each other.

[0220] Furthermore, with the above-described configuration, in the air passage of each cell in the fuel cell 62 (near the final outlet for the air), the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact, via the electrolyte, with a sufficient amount of hydrogen gas that has just begun to flow through the fuel passage of each cell in the fuel cell 62, in a manner that allows it to react. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0221] Incidentally, the fuel cells 61 and 62 constituting the above fuel cell system may be not only PEFCs or SOFCs, but also PAFCs, MCFCs, etc. Here, in the fuel cell 61, although the flow direction of the air flowing through the air path and the flow direction of the hydrogen flowing through the fuel path are the same, the residual amount of hydrogen gas is small, so it is preferable that the fuel cell 61 is not a PEFC in order to avoid a situation in which the solid polymer membrane is deteriorated. On the other hand, it is also preferable that the fuel cell 62 is not an SOFC in order to avoid a situation in which the solid oxide membrane is reduced and deteriorated (as already explained).

[0222] Next, according to the embodiment shown in Figure 9(C), fuel cell 71 and fuel cell 72, both of which have known internal structures, are connected in series with respect to the air path and in parallel with respect to the fuel path to form a fuel cell system. (a) The air passage outlet of each battery cell (711, 712, ...) in the fuel cell 71 is connected to the air passage inlet of each battery cell (721, 722, ...) in the fuel cell 72 by piping; (b) The fuel passage inlet on the same side as the air passage inlet in each battery cell (711, 712, ...) of the fuel cell 71, and the fuel passage inlet on the same side as the air passage outlet in each battery cell (721, 722, ...) of the fuel cell 72 are both connected in parallel to piping from the hydrogen supply source.

[0223] In this embodiment, under such a configuration, air (or a nitrogen and oxygen mixture) is introduced from the air passage inlet of each cell in the fuel cell 71, while hydrogen is introduced into each fuel cell (71, 72) according to the piping (b) above. This results in a configuration in which the vicinity of the final outlet for air (which serves as the air passage of each cell in the fuel cell 72) and the vicinity of the initial inlet for hydrogen (which serves as the fuel passage of each cell in the fuel cell 72) are adjacent to each other with the electrolyte interposed therebetween.

[0224] Incidentally, in this embodiment, as in the embodiment of Figure 9(B) above, in each cell of the fuel cell 71, the flow direction of air flowing through the air path and the flow direction of hydrogen flowing through the fuel path are the same, but in each cell of the fuel cell 72, they are opposite to each other.

[0225] Furthermore, with the configuration described above, in the air passages of each cell in the fuel cell 72 (near the final outlet for the air), the air that has consumed its own oxygen through the fuel cell reaction up to that point comes into contact, via the electrolyte, with a sufficient amount of hydrogen gas that has just begun to flow through the fuel passages of each cell in the fuel cell 72 in a manner that allows it to react. As a result, much of the small amount of oxygen remaining in the air is actively consumed by the sufficient amount of hydrogen, and the air is ultimately output as nitrogen gas with a sufficiently or significantly low residual oxygen concentration.

[0226] Incidentally, the fuel cells 71 and 72 constituting the above fuel cell system may be not only PEFCs or SOFCs, but also PAFCs, MCFCs, etc. Here, in the fuel cell 71, air and hydrogen are introduced from the same side of the fuel cell 71, and the flow direction of the air through the air path and the flow direction of the hydrogen through the fuel path are the same, which is the same as that of a normal fuel cell. Therefore, the fuel cell 71 may be any of the above types. On the other hand, it is also preferable that the fuel cell 72 is not an SOFC in order to avoid the situation where the solid oxide film is reduced or deteriorated (as already explained).

[0227] 8(A)-(C) and 9(A)-(C), the fuel cell 20, the fuel cell system of fuel cells 31-33, the cylindrical stack fuel cell 40, the fuel cell system of SOFC 51 and PEFC 52, the fuel cell system of fuel cells 61 and 62, and the fuel cell system of fuel cells 71 and 72 have been described. These fuel cells (systems) may be used as components of the fuel cell U11 in the nitrogen gas generation system 1 shown in FIG. 1, contributing to the generation of nitrogen gas with a lower oxygen concentration. Of course, they may also be used as components of the fuel cell U11 in the nitrogen gas generation system 1 that employs the combustion catalyst U90 (FIG. 11), which will be described later.

[0228] Alternatively, these fuel cells (systems) may be used as a main component in an apparatus for producing high-purity nitrogen gas or low-oxygen-concentration exhaust gas (nitrogen gas) without relying on a nitrogen gas filter. For example, it may be possible to efficiently produce nitrogen gas with a lower oxygen concentration using only these fuel cells (systems) without using the nitrogen filter U12 (FIG. 1). [Possible invention claims] A method for generating nitrogen gas, characterized by supplying air or a gas containing nitrogen and oxygen to a fuel cell capable of causing a fuel cell reaction by bringing an oxygen-containing gas that has been supplied into the cell and undergone a fuel cell reaction into close proximity with the original fuel gas that was supplied into the cell via an electrolyte, to operate the fuel cell, and extracting the air or gas with a lowered oxygen concentration from the fuel cell. [Possible invention claims] A method for generating a low-oxygen concentration gas, characterized by supplying an oxygen-containing gas to a fuel cell capable of causing a fuel cell reaction by bringing an oxygen-containing gas that has been supplied into the cell and undergone a fuel cell reaction into close proximity with the original fuel gas that was supplied into the cell via an electrolyte, operating the fuel cell, and extracting the gas with a lower oxygen concentration from the fuel cell.

[0229] FIG. 10 is a schematic diagram for explaining still another embodiment of the nitrogen gas generating system according to the present invention.

[0230] In the embodiment shown in FIG. 10, a new fuel cell U80 separate from the fuel cell U11 is provided downstream of the nitrogen filter U12 (for example, immediately after the flow control U127) in the nitrogen gas generation system 1 shown in FIG.

[0231] Here, the "fuel cell" of fuel cell U80 and the "fuel cell" of fuel cell U11 roughly correspond to (or correspond to) fuel cell 61 and fuel cell 62 shown in Figure 9(B), respectively. That is, as already explained in detail, in the "fuel cell" of fuel cell U80, the vicinity of the final outlet for air (which is the air path of each cell of the "fuel cell") and the vicinity of the initial inlet for hydrogen (which is the fuel path of each cell of the "fuel cell") are configured to be adjacent to each other with the electrolyte interposed therebetween.

[0232] Specifically, the "fuel cell" of the fuel cell U80 takes in nitrogen gas with a low oxygen concentration (for example, an oxygen concentration of 0.1 to several vol%) extracted from the nitrogen filter U12 through an air passage inlet (on the air electrode side), and introduces hydrogen through a fuel passage inlet (on the fuel electrode side) on the opposite side of the air passage inlet to cause a fuel cell reaction, actively consuming much of the residual oxygen in the taken-in nitrogen gas with a sufficient amount of hydrogen, and ultimately outputting high-purity nitrogen gas with a sufficiently low residual oxygen concentration (for example, an oxygen concentration of less than 0.1 vol%).

[0233] Here, it is also preferable that the high-purity nitrogen gas is first stored and stored in a nitrogen tank 129 (FIG. 1) via a drain 802, a gas-liquid separator U, an oxygen concentration meter, a flow meter, and a pressure booster U128 (FIG. 1), and then supplied to the outside as appropriate.

[0234] In addition, hydrogen gas (containing a considerable amount of residual hydrogen) extracted from the fuel path outlet, which is on the same side as the air path inlet in the "fuel cell" of fuel cell U80, is sent to hydrogen recovery U115 via drain 801, gas-liquid separator U803, check valve, and flow control U804, and is then fed into the "fuel cell" of fuel cell U11 through the fuel path inlet (on the hydrogen electrode side) of that "fuel cell" and used again in the fuel cell reaction.

[0235] In this embodiment, it is preferable that the "fuel cell" of the fuel cell U11 and the "fuel cell" of the fuel cell U80 are both PEFCs, or they may be SOFCs and PEFCs, respectively. In either case, the problem of electrolyte degradation as already explained can be avoided.

[0236] Furthermore, in the nitrogen gas generating system of the embodiment shown in FIG. 10, it is also possible to generate nitrogen gas with a lower oxygen concentration using only the fuel cells U11 and 80, without using the nitrogen filter U12.

[0237] [Another embodiment using a combustion catalyst] FIG. 11 is a schematic diagram for explaining still another embodiment of the nitrogen gas generating system according to the present invention.

[0238] In the embodiment shown in Fig. 11, a combustion catalyst U90 is provided downstream of the nitrogen filter U12 (for example, immediately after the flow control U127) in the nitrogen gas generation system 1 shown in Fig. 1. Here, this combustion catalyst U90 is a unit that brings hydrogen gas and oxygen in the exhaust gas into contact on a solid catalyst made of a compound of a noble metal such as palladium (Pd) or platinum (Pt), or a compound of another transition metal, to perform catalytic combustion, which is an oxidation reaction that is more controlled than flame combustion.

[0239] Specifically, in this embodiment, the combustion catalyst U90 is (a) Nitrogen gas with a low oxygen concentration (for example, an oxygen concentration of 0.1 to several vol%) extracted from the nitrogen filter U12, (b) Hydrogen gas taken out from the fuel line outlet of the fuel cell U11, passed through the drain 111, pressure control U113, and gas-liquid separation U114, and then recovered in the hydrogen recovery U115, and then sent through the flow control U902 and check valve. The unit takes in nitrogen and brings them into contact on a "solid catalyst" installed inside the unit, causing a catalytic combustion reaction, and ultimately outputs nitrogen gas with a sufficiently low residual oxygen concentration (for example, an oxygen concentration on the order of 0.01 vol% (100 ppm vol)). Of course, instead of the hydrogen gas in (b) above, it is also possible to supply hydrogen gas to the combustion catalyst U90 from, for example, the hydrogen generation U102 or the hydrogen generation reforming U103.

[0240] Here, the "solid catalyst" installed in the combustion catalyst U90 is preferably a ceramic honeycomb with many fine holes and a catalyst such as platinum (Pt) or palladium (Pd) supported on the surface, including the inside of the holes. In this case, the total area of the catalyst surface where the catalytic combustion reaction takes place can be made sufficiently large, making it possible to carry out efficient catalytic combustion.

[0241] Furthermore, the nitrogen gas with extremely low oxygen concentration output from the combustion catalyst U90 comes out in a high-temperature state, and the heat may be recovered by a heat exchanger 901 installed at the outlet of the combustion catalyst U90. In this case, the heat recovered by the heat exchanger 901, like the heat recovered from the fuel cell U11, is preferably supplied to the off-gas buffer tank 123 and used to further heat up the exhaust gas to be supplied to the nitrogen filter U12 (for example, 45°C), or it may be supplied to the outside. Note that when the temperature of the nitrogen gas output from the combustion catalyst U90 is not very high, it may be sent to the hydrogen filter U903, which will be described later, without passing through the heat exchanger 901.

[0242] The extremely low-oxygen nitrogen gas output from the combustion catalyst U90 typically contains residual hydrogen gas that was not combusted in the catalytic combustion reaction. In this embodiment, the hydrogen filter U903 takes in the high-purity nitrogen gas that has passed through the heat exchanger U901, and separates the residual hydrogen gas from the extremely low-oxygen nitrogen gas using a known hydrogen gas filter installed inside, thereby outputting nitrogen gas of higher purity. This output high-purity nitrogen gas is then preferably stored in a nitrogen tank 129 (FIG. 1) via a check valve, an oxygen concentration meter, a flow meter, and a pressure booster U128 (FIG. 1), and is then provided to the outside as appropriate.

[0243] The hydrogen gas filter may be a filter equipped with a palladium (Pd)-based hydrogen permeable membrane, or a hydrogen gas filter equipped with an aromatic polyimide-based gas separation membrane. For example, UBE GAS SEPARATOR manufactured by Ube Industries, which uses a pipe made of bundled hollow fiber membranes, or SEPURUN Noble manufactured by EVONIK can be used.

[0244] In this embodiment, the hydrogen gas separated from the nitrogen gas by the hydrogen filter U903 is sent to the hydrogen recovery U115 via the flow control U904, where it can be reused in the fuel cell U11 or subjected to catalytic combustion again in the combustion catalyst U90.

[0245] Furthermore, as a preferred embodiment, by employing the combustion catalyst U90 in the nitrogen gas generation system 1 (FIG. 1) as described above, it is possible to improve the recovery rate in the nitrogen gas filter 12f (FIG. 1) of the nitrogen filter U12. That is, if the oxygen concentration of the gas output from the nitrogen gas filter 12f is set to, for example, several vol%, with the ultimate goal of achieving an extremely low oxygen concentration in the combustion catalyst U90, it becomes possible to introduce a significantly large flow rate (outlet flow rate) of exhaust gas into the nitrogen gas filter 12f (as can be seen from the graph in FIG. 2). As a result, it is possible to increase the recovery rate in the nitrogen gas filter 12f (as can be seen from the graph in FIG. 5). Furthermore, if a cascade-type filter system such as that shown in FIG. 6(B) is employed as the nitrogen gas filter of the nitrogen filter U12, it is possible to achieve a recovery rate of nearly 1.0 (100%) depending on the design.

[0246] 11, it is also possible to efficiently generate nitrogen gas with a lower oxygen concentration using only the fuel cell U11 and the combustion catalyst U90, without using the nitrogen filter U12. In any case, it is understood that the combined system of a "fuel cell" and a "combustion catalyst" is a highly compatible system capable of efficiently generating nitrogen gas, since the required hydrogen gas can be shared. [Possible invention claims] supplying air or a gas containing nitrogen and oxygen and a fuel gas to the fuel cell to operate the fuel cell; extracting exhaust gas from the fuel cell, the exhaust gas having an oxygen concentration lower than that of air; The extracted exhaust gas and the fuel gas are reacted on a combustion catalyst to convert the exhaust gas into an exhaust gas having a lower oxygen concentration. A method for generating nitrogen gas.

[0247] [Fuel cell characteristics] FIG. 12 is a graph showing the relationship between current and voltage in a "fuel cell" according to an embodiment of the present invention, in which the operating state of the "fuel cell" was examined.

[0248] In this example, a JARI-type PEFC was used as the "fuel cell" of fuel cell U11, and the current flowing between the air electrode and fuel electrode of the "fuel cell" and the voltage between the air electrode and fuel electrode were measured when the cell temperature of the "fuel cell" during operation was 80°C and the back pressure of the "fuel cell," i.e., the pressure of the air and hydrogen introduced into the "fuel cell," was 4.0 atmospheres, 5.0 atmospheres, 6.0 atmospheres, and 7.0 atmospheres. The resistance value of the external resistor connected between the two electrodes as a load was 0.075 Ω.

[0249] According to the graph in Figure 12, the voltage of the "fuel cell" decreases as the current increases, but the degree of this decrease (the slope of the graph line) becomes gentler as the pressure of the introduced air and hydrogen increases. Thus, in the "fuel cell," at higher pressures, even if the fuel cell reaction progresses and the current increases, the voltage does not decrease as much and is maintained at a higher value.

[0250] Therefore, it can be understood that the higher the pressure of the air and hydrogen introduced into the "fuel cell", the more stable the voltage of the electric power that can be provided.

[0251] FIG. 13 is a graph showing the relationship between cell temperature and power in a "fuel cell" according to an example in which the operating state of the "fuel cell" according to the present invention was examined.

[0252] 12 except for the cell temperature, and the normalized power was measured while the cell temperature was varied from about 45°C to about 80°C. Note that this normalized power is calculated by normalizing the power values at each pressure (4.0 atmospheres, 5.0 atmospheres, 6.0 atmospheres, 7.0 atmospheres) with the power value (= voltage value × current value) on the low-temperature side of the graph when the pressure of the introduced air and hydrogen is atmospheric pressure (1 atmosphere) set to 1.

[0253] 13, the normalized power of the "fuel cell" tends to decrease as the cell temperature increases when the pressure of the introduced air and hydrogen is 4.0 atmospheres, but the tendency to decrease becomes smaller as the pressure increases. Furthermore, when the pressure of the introduced air and hydrogen is 6.0 atmospheres and 7.0 atmospheres, the normalized power is almost constant, largely independent of the cell temperature.

[0254] Therefore, it can be understood that the higher the pressure of the air and hydrogen introduced into the "fuel cell", the more stable the power that can be provided, with less fluctuation due to cell temperature.

[0255] FIG. 14 is a graph showing the relationship between the cell temperature of the "fuel cell" and the relative humidity of the exhaust gas in an example in which the operating state of the "fuel cell" according to the present invention was examined.

[0256] The experimental conditions in this example were generally the same as those in the example described in Fig. 13, and the cell temperature was changed from 35°C to 80°C, and the relative humidity of the exhaust gas on the air electrode side (discharged from the air passage outlet) after passing through drain 112 (Fig. 1) was measured. Incidentally, this relative humidity was measured using a thermo-hygrometer after the exhaust gas that had passed through drain 112 was taken out and placed in a measurement container.

[0257] 14, the relative humidity of the exhaust gas passing through drain 112 exceeds 80% when the pressure of the introduced air and hydrogen is atmospheric pressure (1.0 atmosphere) and the cell temperature is in the range of 35°C to 80°C, but decreases to about 30% and about 20%, respectively, when the pressure is 3.0 atmospheres and 5.0 atmospheres. This result is thought to be because the higher the pressure of the introduced air and hydrogen, the higher the dew point of the exhaust gas in drain 112, and more moisture and water vapor in the exhaust gas condenses and is removed.

[0258] Therefore, it can be understood that the higher the pressure of the air and hydrogen introduced into the "fuel cell," the drier the exhaust gas (with less moisture and water vapor) that can be obtained.

[0259] As explained in detail above, according to the present invention, it is possible to efficiently generate high-purity nitrogen gas using a fuel cell. In particular, by using a nitrogen gas filter or even a combustion catalyst, it is possible to generate even higher-purity nitrogen gas.

[0260] Furthermore, when a hydrogen gas society arrives in the future, it is expected that the use of fuel cells that use hydrogen gas as a fuel gas will become widespread. In such an era, this invention will make a significant contribution to the efficient production of nitrogen gas. Naturally, it will also be possible to meet the need for on-site supply of electricity and heat. In other words, this invention is expected to make a significant contribution to the establishment of an energy and product supply and demand system based on local production and consumption, which is considered to be one ideal form for the future.

[0261] Furthermore, although this is merely one embodiment of the present invention, it is also possible to supply hydrogen gas as fuel gas to a fuel cell with a high back pressure setting by utilizing a hydrogen generator U equipped with an electrolysis unit. This type of configuration is also expected to be widely used in the hydrogen gas society described above.

[0262] It should be noted that the above-described embodiments are merely illustrative of the present invention and are not limiting, and the present invention can be embodied in various other modified and altered forms. Therefore, the scope of the present invention is defined only by the claims and their equivalents. [Explanation of symbols]

[0263] 1. Nitrogen gas generation system and equipment 101 Renewable Energy Power Generation Unit (U) 101s Energy storage U 102 Hydrogen Generation U 103 Hydrogen Generation and Reforming U 104 Hydrogen Tank 105, 109, 127, 804, 902, 904 Flow Control U 106 Air Compressor U 107 Air Tank 108 Filter U 11, 80 Fuel Cell U 111, 112, 801, 802 Drain 113, 121 Pressure Control U 114, 122, 803 Gas-liquid separation U 115 Hydrogen Recovery U 12 Nitrogen Filter U 12f, 12f1, 12f2, 12f3 Nitrogen Gas Filter 123 Off-gas buffer tank 124, 128 Pressure Booster U 125 Corrosive gas removal U 126 Temperature adjustment U 129 Nitrogen Tank 131 Overall Control U 20, 31, 32, 33, 61, 62, 71, 72 fuel cell 201, 311, 321, 331, 511, 521, 611, 621, 711, 721 Cell 1 202, 312, 322, 332, 512, 522, 612, 622, 712, 722 Second cell 40 Cylindrical stack fuel cell 401 Cylindrical Cell 51 SOFC 52 PEFC 90 Combustion Catalyst U 901 Heat exchange U 903 Hydrogen Filter U

Claims

1. a fuel cell that operates by taking in air or a gas containing nitrogen and oxygen, and a fuel gas, and that discharges exhaust gas having an oxygen concentration lower than that of air from an oxygen electrode side; a fuel gas delivery means, different from the fuel cell, for delivering a fuel gas; a catalytic combustion means for taking in the exhaust gas and the fuel gas delivered from the fuel gas delivery means and reacting them on a combustion catalyst to convert the exhaust gas into an exhaust gas having a lower oxygen concentration and an increased nitrogen concentration; A nitrogen gas generating device comprising:

2. The nitrogen gas generating device according to claim 1, further comprising a filter means for applying the received exhaust gas with an increased nitrogen concentration to a filter capable of separating at least the fuel gas, separating the fuel gas remaining in the exhaust gas from the exhaust gas, and extracting the exhaust gas with an increased nitrogen concentration from the filter.

3. the filter is a filter including a high molecular weight polymer hollow fiber that is more selectively permeable to not only the molecules of the fuel gas but also oxygen molecules compared to nitrogen molecules, The filter means discharges the nitrogen-enriched exhaust gas, which has a lower fuel gas concentration and a lower oxygen concentration than the received nitrogen-enriched exhaust gas.

3. The nitrogen gas generator according to claim 2.

4. The system further comprises an oxygen filter means for passing the exhaust gas discharged from the fuel cell through a filter having hollow fiber fibers that selectively transmit oxygen molecules compared to nitrogen molecules, and extracting the exhaust gas with a lowered oxygen concentration from the filter; The catalytic combustion means reacts the exhaust gas, the oxygen concentration of which has been reduced, with the fuel gas on a combustion catalyst.

4. The nitrogen gas generating device according to claim 1, wherein the nitrogen gas generating device is a nitrogen gas generating device.

5. A nitrogen gas generating device as described in any one of claims 1 to 4, characterized in that the fuel gas delivery means delivers the fuel gas recovered from at least the exhaust gas discharged from the fuel electrode side of the fuel cell to the catalytic combustion means.

6. 6. The nitrogen gas generating device according to claim 1, further comprising a dehumidifying means for extracting moisture or water vapor from the exhaust gas discharged from the fuel cell, thereby converting the exhaust gas into an exhaust gas with a lower moisture or water vapor content.

7. 6. The nitrogen gas generator according to claim 1, wherein the fuel cell is a solid oxide fuel cell (SOFC).

8. a fuel cell that operates by taking in air or a gas containing nitrogen and oxygen, and a fuel gas, and that discharges exhaust gas having an oxygen concentration lower than that of air from an oxygen electrode side; a fuel gas delivery means, different from the fuel cell, for delivering a fuel gas; a catalytic combustion means for taking in the exhaust gas and the fuel gas delivered from the fuel gas delivery means and reacting them on a combustion catalyst to convert the exhaust gas into an exhaust gas having a lower oxygen concentration and an increased nitrogen concentration; A nitrogen gas generating system comprising:

9. supplying air or a gas containing nitrogen and oxygen and a fuel gas to the fuel cell to operate the fuel cell; extracting exhaust gas having an oxygen concentration lower than that of air from the oxygen electrode side of the fuel cell; The exhaust gas is reacted with the fuel gas delivered from a fuel gas delivery means other than the fuel cell, which is capable of delivering the fuel gas, on a combustion catalyst, to convert the exhaust gas into an exhaust gas having a lower oxygen concentration and an increased nitrogen concentration. A method for generating nitrogen gas.

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