Nitrogen gas generator and system for filtering high-pressure fuel cell exhaust gas

Abstract

To provide a device that efficiently generates high-purity nitrogen gas by using a fuel cell.SOLUTION: Provided is a nitrogen gas generation device comprising: a fuel cell; a filter that includes at least a hollow yarn capable of separating between nitrogen and oxygen and whose high lower-limit pressure is determined because of the use of the hollow yarn; pressure control means which is capable of supplying air or an oxygen-containing gas having pressure equal to or higher than a pressure threshold that is set based on said high lower-limit pressure to the fuel cell, and which enables an exhaust gas discharged from the activated fuel cell and having pressure equal to or higher than said pressure threshold to be supplied to the filter; a filter input / output unit that introduces into the filter the exhaust has having pressure equal to or higher than said pressure threshold while maintaining the pressure at said pressure threshold or higher, and which removes, from the filter, the exhaust gas whose nitrogen concentration has increased; and general control means that causes the pressure control means to exercise pressure control so that the nitrogen concentration in the exhaust gas whose nitrogen concentration has increased becomes a desired high nitrogen concentration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for producing high-purity 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 household fuel cell installations are also becoming more common. 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 make a significant contribution 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 inventors have also invented an inert gas / power generation device that supplies inert gas and electricity to a processing device that processes an object to be heated by electrically heating the object in the inert gas. This device is equipped with an exhaust gas conversion unit that converts at least a portion of the exhaust gas from the fuel cell into an inert gas that can be used in the processing device, making it possible to provide an inert gas with a sufficiently reduced oxygen concentration, for example. [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 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 high-purity nitrogen gas, which is in high demand at various production and service sites.

[0007] 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 cryogenic air separation, pressure swing adsorption (PSA), membrane separation, and other methods.

[0008] Here, we thought that if we used the exhaust gas from a fuel cell instead of directly using air as a raw material as in the past, we might be able to efficiently produce high-purity nitrogen gas.Of course, since a fuel cell is used, it would also be possible to supply electricity in addition to 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 high-purity nitrogen gas using a fuel cell. [Means for solving the problem]

[0010] According to the present invention, a fuel cell is provided which operates by taking in air or an oxygen-containing gas containing nitrogen and a fuel gas; a filter including hollow fibers capable of separating at least nitrogen and oxygen, wherein a lower limit pressure for obtaining a target nitrogen concentration in a filtered nitrogen-containing gas under a set gas flow rate of the introduced nitrogen-containing gas is determined by the use of the hollow fibers; a pressure increasing means for increasing the pressure of a filter-supply exhaust gas, which is exhaust gas extracted from the fuel cell and supplied to the filter; a pressure control means provided downstream of the fuel cell, which is capable of supplying the air or oxygen-containing gas having a pressure exceeding atmospheric pressure to the fuel cell, which is capable of supplying exhaust gas having a pressure exceeding atmospheric pressure discharged from the operating fuel cell to the pressure boosting means, and which is capable of supplying filter supply exhaust gas whose pressure has been increased by the pressure boosting means to the filter; a filter input / output section that introduces the filter supply exhaust gas with increased pressure into the filter and extracts the exhaust gas with increased nitrogen concentration from the filter; an overall control means for causing the pressure control means to adjust the pressure of the filter-supplied exhaust gas to a pressure equal to or higher than the lower limit pressure, taking into account the pressure increase by the pressure increase means, and at which the nitrogen concentration in the exhaust gas with increased nitrogen concentration becomes a target high nitrogen concentration, under conditions where the oxygen concentration of the filter-supplied exhaust gas has been made a predetermined low oxygen concentration by the fuel cell; and for causing the pressure control means to adjust the pressure of the air or oxygen-containing gas supplied to the fuel cell to a pressure at which the oxygen concentration of the filter-supplied exhaust gas extracted from the fuel cell becomes the predetermined low oxygen concentration. With death, The predetermined low oxygen concentration is determined from the characteristics of the filter relating to the relationship between the oxygen concentration of the gas introduced and the oxygen concentration of the gas after filtering, and the target high nitrogen concentration. child The nitrogen gas generating device and the nitrogen gas generating system are characterized by the above. In the nitrogen gas generator and nitrogen gas generation system according to the present invention, the fuel cell is preferably a solid oxide fuel cell (SOFC). According to the present invention, there is also provided a fuel cell that operates by taking in air or an oxygen-containing gas containing nitrogen and a fuel gas; a filter including hollow fibers capable of separating at least nitrogen and oxygen, wherein a lower limit pressure of 0.2 MPa (megapascals) or more is determined as the lower limit pressure of the introduced gas at a set gas flow rate due to the use of the hollow fibers; a pressure control means provided downstream of the fuel cell, which is capable of supplying the air or oxygen-containing gas having a pressure equal to or higher than a pressure threshold value of 0.2 MPa or higher, which is set based on the upper lower limit pressure, to the fuel cell, and is capable of supplying exhaust gas having a pressure equal to or higher than the pressure threshold value, which is discharged from the operating fuel cell, to the filter; a filter input / output unit that introduces exhaust gas having a pressure equal to or higher than the pressure threshold into the filter while maintaining the pressure equal to or higher than the pressure threshold, and extracts the exhaust gas having an increased nitrogen concentration from the filter; an overall control means for causing the pressure control means to set the pressure of the air or oxygen-containing gas supplied to the fuel cell and the pressure of the exhaust gas supplied to the filter to respective pressure values ​​equal to or higher than the pressure threshold value, at which the nitrogen concentration in the exhaust gas with increased nitrogen concentration becomes a target high nitrogen concentration; A nitrogen gas generator and a nitrogen gas generation system are provided.

[0011] In the nitrogen gas generating device according to the present invention, the device further comprises a moisture / water vapor removal means that performs a process to remove or reduce moisture or water vapor from exhaust gas having a pressure equal to or greater than the pressure threshold, and discharges the treated exhaust gas at a pressure equal to or greater than the pressure threshold, and the overall control means causes the pressure control means to set the pressure of the treated exhaust gas to the pressure value, and the filter input / output unit preferably introduces the treated exhaust gas, whose pressure has been set to the pressure value, into the filter.

[0012] It is also preferable that no pressure boosting means for increasing the pressure of the exhaust gas is provided between the fuel cell and the filter.

[0013] Furthermore, the exhaust gas is exhaust gas whose temperature has become higher than room temperature due to heat generated by the fuel cell, As the filter on which the exhaust gas acts, a filter that exhibits a higher filtering effect when the temperature of the gas to be filtered is higher than room temperature under specified conditions of use is used. It is also preferable.

[0014] Furthermore, as another embodiment of the nitrogen gas generating device according to the present invention, it is also preferable that the nitrogen gas generating device further comprises a booster valve that further increases the pressure of the exhaust gas extracted from the fuel cell and introduced into the filter, and that the booster valve is driven by a portion of the air or oxygen-containing gas having a pressure equal to or higher than the pressure threshold and supplied to the fuel cell, or by a portion of the fuel gas that has been boosted to a pressure equal to or higher than the pressure threshold.

[0015] In addition, as yet another embodiment of the nitrogen gas generator according to the present invention, it is also preferable that the nitrogen gas generator further comprises a temperature adjustment means for adjusting the cell temperature of the fuel cell to fall within a cell temperature range that is preset according to the pressure of the exhaust gas being extracted, within which the output power of the fuel cell peaks.

[0016] Furthermore, it is also preferable that the fuel cell is a type of fuel cell other than a solid oxide fuel cell in which the temperature of the exhaust gas exceeds the range of the operating temperature set for the filter.

[0017] According to the present invention, there is also provided a fuel cell; a filter capable of separating at least nitrogen and oxygen; a pressure control means for supplying air or oxygen-containing gas containing nitrogen having a pressure higher than atmospheric pressure and a fuel gas having a pressure higher than atmospheric pressure to the fuel cell; a pressure adjusting means for sequentially increasing the pressure of the air or oxygen-containing gas and the pressure of the fuel gas to a plurality of preset pressure levels based on the relationship between the pressure and the peak value of the output power of the fuel cell, or for continuously increasing the pressure at a preset pressure increase rate based on the relationship, to achieve a target pressure; a filter input / output unit that introduces exhaust gas having a pressure exceeding atmospheric pressure, which is discharged from the operating fuel cell, into the filter and extracts the exhaust gas with an increased nitrogen concentration from the filter; A nitrogen gas generator is provided, comprising:

[0018] Furthermore, as yet another embodiment of the nitrogen gas generator according to the present invention, it is also preferable that the nitrogen gas generator further comprises a pressure equalization means having two gas storage spaces sandwiched between them by a movable partition, which generates the air or oxygen-containing gas and the fuel gas having equal pressures that are equal to or greater than the pressure threshold and supply them to the fuel cell.

[0019] Furthermore, as yet another embodiment of the nitrogen gas generator according to the present invention, the nitrogen gas generator comprises: a hydrogen generating means for generating hydrogen gas contained in the fuel gas by electrolyzing water; an oxygen-containing gas generating means for generating an oxygen-containing gas having an oxygen concentration higher than that of air, including oxygen gas simultaneously generated by the hydrogen generating means; It is also preferable that it further has

[0020] Furthermore, as yet another embodiment of the nitrogen gas generator according to the present invention, it is also preferable that the nitrogen gas generator further comprises hydrogen generation means for generating hydrogen gas having a pressure equal to or greater than the pressure threshold, which is contained in the fuel gas having a pressure equal to or greater than the pressure threshold, by electrolyzing water.

[0021] According to the present invention, there is also provided a nitrogen gas generation method using a filter including hollow fibers capable of separating at least nitrogen and oxygen, wherein a high lower limit pressure of 0.2 MPa or more is determined as the lower limit pressure of the gas introduced into the filter due to the use of the hollow fibers, comprising: a first step of supplying air or oxygen-containing gas containing nitrogen having a pressure equal to or higher than a pressure threshold value of 0.2 MPa or higher, which is set based on the upper lower limit pressure, and a fuel gas having a pressure equal to or higher than the pressure threshold value to the fuel cell, thereby operating the fuel cell; a second step of extracting exhaust gas from the fuel cell having a pressure equal to or greater than the pressure threshold; a third step of introducing exhaust gas having a pressure equal to or greater than the pressure threshold into the filter while maintaining the pressure equal to or greater than the pressure threshold, and extracting the exhaust gas having an increased nitrogen concentration from the filter; and The pressure of the air or oxygen-containing gas supplied to the fuel cell in the first step and the pressure of the exhaust gas supplied to the filter in the third step are set to respective pressure values ​​equal to or higher than the pressure threshold value, and at which the nitrogen concentration in the exhaust gas with increased nitrogen concentration becomes a target high nitrogen concentration. A method for generating nitrogen gas is provided. [Effects of the Invention]

[0022] According to the present invention, it is possible to efficiently generate high-purity nitrogen gas using a fuel cell. [Brief explanation of the drawings]

[0023] [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 table for explaining Example 1 of the nitrogen gas generation process according to the present invention. [Figure 3] 1 is a graph illustrating Experimental Example 1 relating to a nitrogen gas generation process according to the present invention. [Figure 4] 10 is a graph for explaining Example 2 of the nitrogen gas generation process according to the present invention. [Figure 5] 10 is a graph for explaining Example 2 of the nitrogen gas generation process according to the present invention. [Figure 6] 10 is a graph illustrating Example 3 of the nitrogen gas generation process according to the present invention. [Figure 7] 10 is a graph illustrating Example 4 of the nitrogen gas generation process according to the present invention. [Figure 8] FIG. 2 is a schematic diagram illustrating another embodiment of a nitrogen gas generation system according to the present invention. [Figure 9]FIG. 10 is a schematic diagram illustrating yet another embodiment of the nitrogen gas generation system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] [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.

[0026] 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 oxygen-containing gas" having a pressure exceeding atmospheric pressure and "fuel gas" (hydrogen gas in this embodiment) having a pressure exceeding atmospheric pressure are supplied to the "fuel cell 11" to operate the "fuel cell 11", (B) Extracting high-pressure "off-gas" from the "fuel cell 11," which is exhaust gas having a pressure exceeding atmospheric pressure; (C) This high-pressure "off-gas (exhaust gas)" is applied at a pressure exceeding atmospheric pressure to a "filter" capable of separating at least nitrogen and oxygen (a filter provided in the "nitrogen filter U12" in this embodiment), and the "off-gas" with an increased nitrogen concentration, i.e., high-purity nitrogen gas, is extracted from this filter. This system is capable of implementing the nitrogen gas generation method described above.

[0027] Here, various known nitrogen / oxygen separation filters can be used as the "filter" in (C) above, but such nitrogen / oxygen separation filters have traditionally required the introduction of high-pressure compressed air for efficient filtering (at a specified yield or higher). In other words, as a pre-treatment step, an air compressor or the like had to be operated to pressurize the air to the desired pressure (e.g., 0.7 MPa).

[0028] In contrast, the nitrogen gas generation system 1 uses the fuel cell 11 to generate high-pressure off-gas, which is then used to act on the filter, eliminating the need to boost the pressure from atmospheric pressure (0.1 MPa) to a desired high pressure (e.g., 0.7 MPa). As a result, high-purity nitrogen gas can be generated efficiently.

[0029] Here, the "high purity" in high-purity nitrogen gas refers to a state in which the oxygen concentration in the nitrogen gas is sufficiently reduced. Specifically, the nitrogen concentration (volume ratio, ml per 100 ml of medium) in the "high-purity" nitrogen gas produced in this embodiment is sometimes specified as, for example, 99% or more, or, for example, 99.9% or more, depending on the field of use of the nitrogen gas.

[0030] Furthermore, as the "filter" in (C) above, it is also preferable to use a filter that exhibits a higher filtering effect as the oxygen concentration (volume ratio, ml per 100 ml of medium) of the gas to be filtered ("off-gas") decreases under specified conditions of use (for example, within a specified oxygen concentration range in the "off-gas" that is applied to the "filter").

[0031] In fact, the nitrogen gas generation system 1 uses a "fuel cell 11" to generate "off-gas" that has a lower oxygen concentration than air, and by applying such "off-gas" to the above-mentioned "filter," it is possible to generate high-purity nitrogen gas more efficiently (compared to, for example, conventional compressed air).

[0032] Furthermore, as the "filter" of (C) above, it is also preferable to use a filter that has a higher filtering effect when the temperature of the gas to be filtered ("off-gas") is higher than room temperature (e.g., 25°C) under specified conditions of use (e.g., within a specified temperature range of the "off-gas" to be applied to the "filter").

[0033] In fact, the nitrogen gas generation system 1 uses a fuel cell 11 to generate off-gas that is normally at a temperature higher than room temperature (e.g., 25°C). By applying this off-gas to a filter such as the one described above, it becomes possible to generate high-purity nitrogen gas more efficiently (compared to, for example, conventional compressed air at about room temperature).

[0034] Incidentally, depending on the fuel cell 11, the temperature of the off-gas may be around room temperature, but for such off-gas, the heat generated by the fuel cell 11 can be directly used to easily convert it into gas with a temperature higher than room temperature (for example, 25°C).

[0035] [Configuration of nitrogen gas generation system] As also shown in FIG. 1, the nitrogen gas generation system 1 of this embodiment includes: (a) a fuel cell U11; (b) A renewable energy power generation unit (U) 101, a power storage unit U102, a hydrogen generator 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 gas-liquid separator U113, a hydrogen recovery unit U114, and a pressure controller U115 are provided at the downstream side of the hydrogen electrode of the fuel cell U11. (d) A drain 112, a gas-liquid separator U121, an off-gas buffer tank 122, a pressure controller U123, a pressure booster U124, a nitrogen filter U12, a flow controller U125, and a nitrogen tank 126 are provided at a downstream position on the air electrode side of the fuel cell U11. (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 commercial electricity, and can supply high-purity nitrogen gas, electricity, and thermal energy to the outside.

[0036] That is, the nitrogen gas generation system 1 of this embodiment also serves as a nitrogen gas, power, and heat supply system.

[0037] 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.

[0038] For example, it is possible to construct a nitrogen gas generation device in which all components other than the natural energy power generation unit (U) 101, the power storage unit U102, the hydrogen generation unit U103, the hydrogen tank 104, the air compressor U106, the air tank 107, and the nitrogen tank 126 are device components.

[0039] 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.

[0040] Also in Figure 1, the natural energy power generation unit U101 may be a solar cell power generation unit equipped with a solar cell that converts sunlight into electricity, or a wind power generation unit that uses wind power to rotate a rotor with blades attached to drive a generator to generate electricity, or a micro-hydro power generation unit that uses water flow (hydropower) to rotate a turbine to drive a generator to generate electricity.

[0041] Also, various other power generation units can be adopted as the natural energy power generation unit 101 as long as they are capable of ultimately converting 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.

[0042] The power storage U102 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 U102 includes a power storage meter so that it can measure the amount of power stored at each point in time and whether it is fully charged or not.

[0043] Here, power is supplied from the power storage unit U102 to the hydrogen generator U103 (which performs water electrolysis) and the air compressor U106, which will be described later. However, instead of or in addition to these, commercial power may be supplied to the hydrogen generator U103. Furthermore, it is also preferable to supply power directly from the renewable energy power generation unit 101 to the hydrogen generator U103 and the air compressor U106 without using the power storage unit U102, which has a predetermined limit on the amount of power storage and is equipped with an expensive secondary battery (or to provide it only as an auxiliary). In this case, natural energy is directly converted into the chemical energy of hydrogen and the physical energy of compressed air and then used.

[0044] 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 U102 or hydrogen generation U103. Also, when the air compressor U106 (described later) is equipped with a DC-driven compressor 22, the AC power is also converted to DC and then supplied to the air compressor U106.

[0045] In any case, the overall control U131 can appropriately switch and control the power supply to the hydrogen generation U103 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 U102.

[0046] The hydrogen generator U103 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 can 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.

[0047] The hydrogen generator U103 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.

[0048] The hydrogen tank 104 is a gas tank that temporarily stores and preserves the hydrogen gas supplied from the hydrogen generator 103 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.

[0049] 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).

[0050] In this embodiment, hydrogen gas is supplied to the hydrogen electrode side of the fuel cell U11 at a high pressure (e.g., 0.2 to 0.7 MPa) that exceeds atmospheric pressure (approximately 0.1 MPa). That is, as will be described in detail later, in this embodiment, the back pressure of the "fuel cell" provided in the fuel cell U11 is set to a pressure (e.g., 0.2 to 0.7 MPa) that exceeds atmospheric pressure (approximately 0.1 MPa).

[0051] 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, 0.1 to 0.2 MPa 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 flow is throttled).

[0052] 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 the air tank 107. Various types of compression methods can be used in this compressor, such as a reciprocating type, scroll type, screw type, rotary type, swing type, or a combination of two or more of these.

[0053] The air tank 107 is a gas tank that temporarily stores the compressed air supplied from the air compressor U 106 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.

[0054] 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.

[0055] 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 fuel cell U11 via the filter U108. Specifically, it may include a gas regulator and a mass flow controller (or a flow switch).

[0056] In this embodiment, this compressed air is also supplied to the air electrode side of the fuel cell U11, which is set to a back pressure (e.g., 0.2 to 0.7 MPa) that exceeds atmospheric pressure (approximately 0.1 MPa) while still in a high pressure state (e.g., 0.2 to 0.7 MPa). In this case, taking into account the pressure difference loss of the mass flow controller, compressed air at a pressure that is, for example, 0.1 to 0.2 MPa higher than the set pressure (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.

[0057] Incidentally, the back pressure value below is the value that is 0.1 MPa when the outlet side of the "fuel cell" is in an open state, that is, when the pressure of the off-gas is 0.1 MPa (atmospheric pressure).

[0058] Also in FIG. 1, fuel cell U11 is (a) A back pressure exceeding atmospheric pressure (e.g., 0.2 to 0.7 MPa) is set. (b) It receives hydrogen gas having a pressure above atmospheric pressure (e.g., 0.2 to 0.7 MPa) from flow control U105, and further receives compressed air having a pressure above atmospheric pressure (e.g., 0.2 to 0.7 MPa) from flow control U109, and operates; (c) Discharge off-gas having a pressure exceeding atmospheric pressure (e.g., 0.2 to 0.7 MPa). It is a unit equipped with a "fuel cell."

[0059] Here, this "fuel cell" may have a known configuration, and may have a structure in which multiple cells, each having a structure in which an electrolyte is sandwiched between a fuel electrode (hydrogen electrode, positive electrode, anode) and an air electrode (oxygen electrode, negative electrode, cathode), are stacked with separators interposed between them.

[0060] Furthermore, as the cell type for the "fuel cell," a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), or the like can be used. Of these, the SOFC type has high power generation efficiency, typically operates at approximately 700 to 1000°C, and is capable of supplying considerably high-temperature off-gas. The PEFC type operates at a relatively low temperature and allows for compact cell size, so it is widely used in fuel cell vehicles.

[0061] If the "fuel cell" of fuel cell U11 is of this PEFC type, it is possible to use, for example, the JARI-type fuel cell developed for research and development purposes 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 inside the cell, and also to recover all off-gas at high back pressure.

[0062] 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 U115 and the back pressure valve of the pressure control U123, 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 U115, (b) The back pressure on the air electrode side, which is mainly adjusted by the back pressure valve of the pressure control U123, 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 MPa 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 if the back pressure is considerably high.

[0063] 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 off-gas, exhaust water vapor, and moisture emitted from the "fuel cell." Furthermore, it is preferable that the operation of the fuel cell U11 be controlled by an overall control U131 that receives information from the measurement system and group of sensors.

[0064] It is also preferable that a heat exchanger that circulates a heat exchange medium such as water is installed 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.

[0065] Incidentally, the heat transferred by the heat exchange medium or peat pipe in this way can be supplied to the outside and made available for use, and in this embodiment, it is supplied to an off-gas buffer tank 122 (described later) so that the off-gas supplied to the nitrogen filter U12 can be heated to an even higher temperature (for example, 45°C). Of course, if the temperature of the off-gas is sufficiently high, such heating treatment in the off-gas buffer tank 122 is not necessary.

[0066] Furthermore, the heat transferred by the heat exchange medium or peat pipe can be used to convert the water to be electrolyzed in the hydrogen generation U103 into steam or to raise the temperature of the water, thereby improving the efficiency of hydrogen generation in electrolysis.

[0067] 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 electrolytic operation with the overall control U131. Furthermore, it is also possible to perform electrolytic processing without using an electrolyte by increasing the voltage applied between the electrodes, thereby eliminating the need for monitoring and maintenance of the electrolyte.

[0068] In another embodiment of the fuel cell U11, two or more "fuel cells" may be connected in series, and the off-gas from the preceding fuel cell may be sequentially taken in and used in the cell reaction, ultimately resulting in an off-gas with a lower oxygen concentration. The inventors of the present application have invented a fuel cell system with such a configuration and have filed a patent application for it (Japanese Patent Application No. 2018-11343).

[0069] Also in Figure 1, drains 111 and 112 are provided at the hydrogen electrode side outlet and the air electrode side outlet of the "fuel cell" in fuel cell U11, respectively, to recover water produced by condensation of water vapor contained in the off-gas (which 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. Incidentally, the water recovered here may be sent to hydrogen generator U103 and reused as a hydrogen generating material.

[0070] The gas-liquid separator U113 is a unit for removing residual water vapor and moisture from the off-gas discharged from the hydrogen electrode side outlet of the "fuel cell." Specifically, water vapor and moisture can be removed using a dehumidifier, a dry filter, or a gas-liquid separator. Here, a dehumidifier containing silica gel and / or zeolite can be used. Furthermore, the gas-liquid separator can be of a gravity separation type, a centrifugal separation type, a mist eliminator pad type, a vane type separation type, or a pneumatic separation coalescer type.

[0071] The hydrogen recovery unit U114 is a unit that uses a known hydrogen gas filter to extract and reuse unreacted residual hydrogen gas from the off-gas discharged from the hydrogen electrode side outlet. Here, the gas after extraction of the hydrogen gas may be discharged to the outside.

[0072] The pressure control U115 is a unit that returns the hydrogen gas extracted by the hydrogen recovery U114 to the inlet of the hydrogen electrode side of the fuel cell (flow control U105) while maintaining the set back pressure of the "fuel cell." Specifically, the pressure control U115 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.

[0073] 1, the gas-liquid separator U121 is a unit for removing residual water vapor and moisture from the high-pressure (e.g., 0.2 to 0.7 MPa) off-gas discharged from the air electrode-side outlet of the “fuel cell.” Specifically, like the gas-liquid separator U113 described above, the gas-liquid separator U121 can remove water vapor and moisture using a dehumidifier, a dry filter, or a gas-liquid separator.

[0074] The pressure of the off-gas from which water vapor and moisture have been removed in the gas-liquid separator U121, i.e., the back pressure on the air electrode side, is controlled by a pressure controller U123 equipped with a back pressure valve and a pressure gauge. If necessary to maintain the set back pressure, the pressure controller U123 can also discharge a predetermined amount of off-gas to the outside.

[0075] The off-gas buffer tank 122 is a gas tank that temporarily preserves and stores the off-gas introduced from the gas-liquid separator U121. This off-gas is introduced into the off-gas buffer tank 122 until its pressure becomes equal to a set back pressure (e.g., 0.2 to 0.7 MPa). In order to allow the off-gas to flow into the nitrogen filter U12 (described later) at a desired pressure (e.g., 0.7 MPa), it is also preferable that the flow rate of this off-gas into the off-gas buffer tank 122 be set to a flow rate equal to or exceeding the required introduction flow rate into the nitrogen filter U12.

[0076] Incidentally, when the "fuel cell" is stopped, the pressure in the piping to the off-gas buffer tank 122 returns to, for example, atmospheric pressure. Therefore, it is preferable that the off-gas buffer tank 122 is equipped with a check valve to prevent backflow of off-gas to the "fuel cell." It is also preferable that the off-gas buffer tank 122 is equipped with a gas pressure gauge so that the gas pressure in the tank can be measured at each point in time.

[0077] Furthermore, it is also preferable that the off-gas buffer tank 122 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 off-gas in the tank to a temperature higher than room temperature (for example, 30 to 45°C). This makes it possible to supply the off-gas at a temperature suitable for nitrogen filtering to the nitrogen filter U12, which will be described later.

[0078] 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 off-gas introduced into the off-gas buffer tank 122 is sufficiently high, such a "heating means" is not necessary.

[0079] The pressure booster U124 further boosts the high-pressure off-gas extracted from the "fuel cell" of the fuel cell U11 (for example, to a pressure of 0.7 MPa) and supplies it to the nitrogen filter U12. Specifically, the pressure booster U124 can further increase the pressure of the high-pressure off-gas using a known booster valve, for example, the inert gas booster valve VB11A manufactured by SMC Corporation. It is also preferable to have a pressure gauge to monitor the boosted off-gas pressure.

[0080] Here, most booster valves are of the air-driven type. 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 extracted from the air tank 107, as support gas. This eliminates the need for additional power consumption and other burdens for driving the booster valve. Incidentally, as mentioned above, if the pressure of the off-gas from the off-gas buffer tank 122 is sufficiently high (for example, 0.7 MPa), the booster valve U124 is of course unnecessary. Furthermore, although care must be taken in handling it, hydrogen gas extracted from the hydrogen tank 104 can also be used as this support gas.

[0081] Also in Figure 1, the nitrogen filter U12 is a unit that applies high-pressure off-gas supplied from the off-gas buffer tank 122 or the booster U124 to a "filter" that can separate at least nitrogen and oxygen, and extracts off-gas with an increased nitrogen concentration, i.e., high-purity nitrogen gas, from this "filter." (a) "filter"; (b) A filter input / output section that introduces high-pressure off-gas to act on the "filter" and extracts off-gas with an increased nitrogen concentration from the "filter." It is equipped with:

[0082] Specifically, this "filter" can be a hollow fiber filter made of a polymeric material that allows oxygen molecules to pass through preferentially over nitrogen molecules. For example, the UBE N2 Separator NM-B01A manufactured by Ube Industries, Ltd., which uses polyimide hollow fibers, can be used. In this system, oxygen molecules selectively pass through the hollow fiber membrane as the high-pressure off-gas flows through the hollow fibers, ultimately resulting in high-purity nitrogen gas being extracted from the outlet of the hollow fibers.

[0083] Incidentally, the nitrogen concentration of the nitrogen gas obtained from such a hollow fiber filter generally depends on the pressure and flow rate of the gas to be filtered introduced into the hollow fiber filter, and the higher the pressure and the smaller the flow rate, the lower the residual oxygen concentration in the extracted gas. (a) Regarding the introduction pressure, the set back pressure of the "fuel cell" is set to the pressure desired by this "filter" (for example, 0.7 MPa), or the high-pressure off-gas from the "fuel cell" is further boosted by the booster U124, (b) The flow rate is adjusted to an appropriate level by the mass flow controller (or flow switch) of the flow control U125 installed on the outlet side of the nitrogen filter U12. Incidentally, the flow control U125 is also equipped with an oxygen concentration meter, which may be used to measure and check the oxygen concentration of the nitrogen gas extracted from the nitrogen filter U12.

[0084] Here, based on this oxygen concentration measurement value, the overall control U131 preferably controls, for example, the back pressure valve of the pressure control U123 to adjust the set back pressure of the "fuel cell", or controls the mass flow controller of the flow control U125 to adjust the off-gas flow rate to the "filter", thereby supplying high-purity nitrogen gas with the desired extremely low oxygen concentration.

[0085] Furthermore, the inventors of the present application have experimentally confirmed that with the hollow fiber filter described above, under specified conditions of use (for example, within a specified range of oxygen concentrations in the gas to be filtered that is applied to the "filter"), the lower the oxygen concentration of the gas to be filtered, the higher the filtering effect (the results of this experiment will be explained in detail later using Figure 3).

[0086] Therefore, when off-gas having an oxygen concentration lower than that of air is introduced into the nitrogen filter U12 as in this embodiment, a filtering process with a higher filtering effect is performed compared to, for example, the conventional case in which compressed air (with an oxygen concentration of 20.8%) is introduced, and as a result, nitrogen gas of higher purity is produced more efficiently.

[0087] Furthermore, it has been found that the filtering effect of hollow fiber filters such as those described above is enhanced when the temperature of the gas to be filtered is higher than room temperature (e.g., 25°C) under certain conditions of use (e.g., within a certain temperature range of the gas to be filtered that acts on the "filter"). For example, in the above-mentioned UBE N2 separator NM-B01A manufactured by Ube Industries, the temperature of the introduced gas is considered to be 30 to 45°C.

[0088] Therefore, when off-gas at a temperature higher than room temperature (e.g., 25°C) is introduced into the nitrogen filter U12 as in this embodiment, a filtering process with a higher filtering effect is performed compared to when compressed air at approximately room temperature is introduced, and as a result, nitrogen gas of higher purity is produced more efficiently. Furthermore, since it is not necessary to use an electric heater to increase the temperature of the gas to be filtered (off-gas) introduced into the nitrogen filter U12 as in the conventional case, it is possible to reduce power consumption accordingly.

[0089] As described above, it can be seen that high-purity nitrogen gas can be efficiently generated by filtering the off-gas discharged from the fuel cell U11 using the "filter" of the nitrogen filter U12. Here, in experiments using the nitrogen gas generation system 1 conducted by the inventors of the present application, high-purity nitrogen gas with a purity (nitrogen concentration) of 99.9% and an oxygen concentration of less than 0.1% (1000 ppm) was successfully generated. Such high-purity nitrogen gas can also 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% can be used, depending on the type of solder paste used.

[0090] 1, the nitrogen tank 126 temporarily stores and preserves the high-purity nitrogen gas supplied from the nitrogen filter U12 via the flow control U125, 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 126 is provided with a gas pressure gauge so that the gas pressure inside the tank can be measured at any time.

[0091] It is also possible to supply high-purity nitrogen gas generated from the nitrogen filter U12 directly to the outside via the flow control U125 without using the nitrogen tank 126 as a nitrogen gas supply interface. In this case, the high-purity nitrogen gas (off-gas) extracted at a high temperature can be supplied almost as is, that is, a considerable amount of thermal energy can also be supplied. This type of supply is very preferable when the supply destination is, for example, a reflow soldering device or flow soldering device that can utilize the thermal energy.

[0092] The overall control U131 is capable of communicating with the major components, preferably all components, including the fuel cell U11 and nitrogen filter U12 described above, via a wired or wireless communication network, and is a control unit that receives and appropriately monitors 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, to monitor and control each component. For example, the overall control U131 is equipped with a processor and memory, and it is also preferable that this memory stores and installs a nitrogen gas generation system monitoring and control program for monitoring and controlling each component, which can be executed by the processor.

[0093] 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.

[0094] The overall control U131 may also monitor the temperature (cell temperature) of the "fuel cell" of the fuel cell U11, the temperature of the off-gas introduced into the "filter" of the nitrogen filter U12, and the temperature of the hydrogen generator U103, etc., to 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.

[0095] [Example 1] FIG. 2 is a table for explaining Example 1 of the nitrogen gas generation process according to the present invention.

[0096] In Example 1, the results of which are shown in Figure 2, a JARI-type "fuel cell" was used as fuel cell U11 (Figure 1). This "fuel cell" was operated under conditions of a back pressure of 0.3 MPa, an air flow rate of 2.5 L / min, and a hydrogen flow rate of 0.5 L / min. The pressure and flow rate of the off-gas supplied from the off-gas buffer tank 122 (with an internal tank pressure of 0.3 MPa) to the nitrogen filter U12 were varied by controlling the pressure booster U124, and the oxygen concentration in the high-purity nitrogen gas produced under various pressures and flow rates was measured. The "filter" of the nitrogen filter U12 was a UBE N2 separator NM-B01A manufactured by Ube Industries.

[0097] Incidentally, the oxygen concentration and humidity in the off-gas buffer tank 122 were 12.6% and 4.9%, respectively, when the amount of power generated (electricity) by the "fuel cell" was approximately 8 W. It was also confirmed that the oxygen concentration of the off-gas in the off-gas buffer tank 122 changes depending on the amount of power generated by the "fuel cell," and the greater the amount of power generated, the lower the oxygen concentration of the off-gas.

[0098] As shown in the table in Figure 2(A), under the condition that the flow rate of the off-gas introduced into the nitrogen filter U12 is constant at 1.0 L / min, the oxygen concentration of the generated high-purity nitrogen gas decreases as the nitrogen filter pressure, which is the pressure applied to the "filter" (off-gas pressure), increases. In particular, at a nitrogen filter pressure of 0.7 MPa and above, 0.73 MPa, high-purity nitrogen gas with an oxygen concentration of 0.0% (<0.1%), which exceeds the measurement limit accuracy (0.1% = 1000 ppm), is obtained.

[0099] Furthermore, as shown in the table in Figure 2(B), under the condition that the nitrogen filter pressure (off-gas pressure) is kept constant at 0.7 MPa, even when the off-gas flow rate is 2.0 L / min, high-purity nitrogen gas with an oxygen concentration of 0.8 to 0.9% and a nitrogen concentration of 99% or more is obtained.

[0100] [Experimental Example 1] FIG. 3 is a graph for explaining Experimental Example 1 relating to the nitrogen gas generation process according to the present invention.

[0101] In Experimental Example 1, the results of which are shown in Figure 3, the same "filter" as in Example 1 was used, and the nitrogen filter pressure was kept constant at 0.7 MPa. The relationship between the flow rate of the introduced gas and the oxygen concentration of the nitrogen gas generated after filtering was investigated when introducing introduced gas (a mixture of nitrogen gas and oxygen gas) with various oxygen concentrations into the "filter." The temperature of the introduced gas was 21.1°C.

[0102] The graph in Figure 3 shows the relationship between the inlet gas flow rate and the oxygen concentration of the generated nitrogen gas (post-filter oxygen concentration) when the inlet gas oxygen concentration is 20.8% (equivalent to air), 14.0%, 10.4%, and 7.8%. The graph shows that for each inlet gas oxygen concentration, the smaller the inlet gas flow rate, the smaller the post-filter oxygen concentration, indicating that more oxygen molecules are separated and removed.

[0103] Furthermore, the graph shows that the lower the oxygen concentration of the introduced gas, the lower the post-filter oxygen concentration and the greater the filtering effect. Here, the filtering effect refers to the degree of low oxygen concentration in the (extremely) low-oxygen gas generated as a result of separating and removing oxygen molecules through filtering, and is an effect that is expressed using the post-filter oxygen concentration value as an index.

[0104] Furthermore, the graph shows that in the high gas flow rate range (e.g., over 1.0 L / min), the difference in post-filter oxygen concentration due to differences in the oxygen concentration of the inlet gas becomes larger. In other words, the lower the oxygen concentration of the inlet gas, the greater the filtering effect, even under conditions of high inlet gas flow rates. This also shows that using low-oxygen-concentration off-gas from a fuel cell as the inlet gas provides a greater filtering effect than using air as the inlet gas.

[0105] From the results of Example 1 and Experimental Example 1 described above, it can be seen that the "fuel cell" and the "filter" are highly compatible when combined with each other from the viewpoint of the pressure and oxygen concentration of the introduced gas (off-gas).

[0106] [Example 2] FIG. 4 is a graph for explaining Example 2 of the nitrogen gas generation process according to the present invention.

[0107] In Example 2, the results of which are shown in FIG. 4, the same "fuel cell" and "filter" configuration as in Example 1 of FIG. 2 was used, and the back pressure of the "fuel cell" was set to 0.10 MPa (atmospheric pressure), 0.15 MPa, 0.20 MPa, 0.25 MPa, 0.30 MPa, and 0.40 MPa. The relationship between the cell temperature of the "fuel cell" and the output power under each back pressure condition was investigated. Here, the "fuel cell" was operated with an air flow rate of 2.5 L / min and a hydrogen flow rate of 0.5 L / min, with the air electrode and hydrogen electrode sides at the same pressure (back pressure). Incidentally, hydrogen was supplied to the "fuel cell" from a hydrogen storage alloy cylinder in the hydrogen tank 104 (FIG. 1) at a maximum pressure of 0.4 MPa.

[0108] As can be seen from the graph in Figure 4(A), under each back pressure condition, the power output from the "fuel cell" increases as the cell temperature rises, and peaks (takes a maximum value) at a predetermined cell temperature (peak cell temperature) determined by the back pressure value. Moreover, the higher the back pressure, the higher this power peak value becomes. Furthermore, the higher the back pressure, the higher this peak cell temperature becomes. In other words, it shifts to a higher temperature side.

[0109] In this way, the greater the back pressure, the greater the output power (peak power value). This is because the chemical reaction between hydrogen and oxygen on the catalyst occurs as the hydrogen concentration [H(H + )] and oxygen concentration [O(O 2- This can be understood from the fact that the reaction proceeds as a monotonically increasing function (usually a directly proportional relationship) of the reaction rate constant k.

[0110] In other words, back pressure is an important quantity in the chemical reaction in the "fuel cell" related to the concentration of reactants, and basically, increasing the back pressure makes it possible to generate more power. Furthermore, as mentioned above, increasing the back pressure also improves the filtering effect of the "filter" of the nitrogen filter U12 (Figure 1), so ultimately it contributes to both the generation of large amounts of power and the generation of high-purity nitrogen gas.

[0111] For reference, Figures 4(B) and (C) show the relationship between cell temperature and voltage and current under various back pressure conditions. As can be seen from these figures, both voltage and current show variations in cell temperature dependence, especially at lower cell temperatures, compared to the power shown in Figure 4(A). This variation is thought to arise because the chemical reaction on the catalyst in the fuel cell has a history of temperature rise and fall. However, the variations in both voltage and current decrease near the peak cell temperature, and tend to converge to their respective peak voltage and current values.

[0112] As explained above in Example 2, by monitoring the cell temperature of the "fuel cell" and adjusting the cell temperature to near the peak cell temperature corresponding to the high back pressure (set to improve the filtering effect), it becomes possible to supply high purity nitrogen gas and also to supply greater power.

[0113] That is, when operating the "fuel cell," it is highly preferable to use a "temperature adjustment means" capable of controlling the cell temperature of the "fuel cell" to adjust the cell temperature of the "fuel cell" so that it falls within a cell temperature range (for example, "peak cell temperature" ±5°C) that is preset according to the pressure of the extracted off-gas and within which the output power peaks. Note that the "temperature adjustment means" can be a heat exchanger installed inside or around the "fuel cell," or a heat pipe connected to a separator with high thermal conductivity in the "fuel cell."

[0114] Next, FIG. 5 is also a graph for explaining Example 2 of the nitrogen gas generation process according to the present invention.

[0115] First, Fig. 5(A) is a graph showing the relationship between the back pressure of the "fuel cell" and the power peak value, i.e., the back pressure dependency of the power peak value, in Example 2. According to this graph, the higher the back pressure of the "fuel cell" is, the larger the power peak value of the power output from the "fuel cell" becomes, and the power peak value is a linear function of the back pressure with a positive coefficient.

[0116] This means that, for example, if the back pressure increases by ((N-1) x 0.1) MPa from 0.1 MPa (atmospheric pressure) to (N x 0.1) MPa, the oxygen density (number per unit volume) in the air on the air electrode side of the "fuel cell" and the hydrogen density (number per unit volume) on the hydrogen electrode side will both increase by (N-1) times the density at atmospheric pressure, and the two-dimensional (area) increase corresponding to this three-dimensional (volumetric) increase will contribute to the reaction in the electrolytic membrane (acting area-wise) in the "fuel cell," resulting in a linear increase in the amount of electricity produced by (N-1) times the cell reactant density.

[0117] Next, Figure 5(B) shows the relationship between the percentage increase in oxygen density and hydrogen density due to an increase in back pressure and the percentage increase in power. Here, all percentage increases are based on a back pressure of 0.1 MPa (atmospheric pressure). For example, if the back pressure is increased 1.5 times compared to 0.1 MPa (atmospheric pressure), the increase rate will be 50%. According to this figure, the power increase rate is a linear function with a positive coefficient for the oxygen density and hydrogen density increase rate, as expected from the results in Figure 5(A), and increases linearly as the oxygen density and hydrogen density increase rate increases.

[0118] Specifically, if the oxygen density / hydrogen density increase rate is increased to 200% (back pressure is increased to 0.3 MPa), the power generated by the fuel cell increases by approximately 20%. Furthermore, using this linear relationship, if the oxygen density / hydrogen density increase rate is increased to 600% (back pressure is increased to 0.7 MPa), the power generated by the fuel cell will increase by approximately 60%.

[0119] Finally, Figure 5(C) shows the relationship between fuel cell back pressure and peak cell temperature. As shown in Figure 5(C), the higher the back pressure, the higher the peak cell temperature. As mentioned above, by maintaining this peak cell temperature according to the set back pressure, it is possible to extract a large amount of power from the fuel cell, close to the peak power value.

[0120] Here, when the back pressure is increased to operate the "fuel cell" at a higher cell temperature, it is important to control the cell temperature so that it does not exceed the heat-resistant temperature (upper limit of operating temperature) of the electrolytic membrane of the "fuel cell." For example, it is preferable to use an electrolytic membrane with a heat-resistant temperature exceeding 120°C and maintain a higher peak cell temperature (i.e., a higher peak power value) (shifted to the higher temperature side) under a higher back pressure.

[0121] Next, an example will be shown in which an experiment was conducted to examine the balance of back pressure between the air electrode side and the hydrogen electrode side of a "fuel cell." In the examples described above, the back pressure was adjusted to be equal between the air electrode side and the hydrogen electrode side. In contrast, in Example 3 shown below, an experiment was conducted in which the back pressure on each side was changed in order to determine the design margin for back pressure application on the air electrode side and the hydrogen electrode side.

[0122] [Example 3] FIG. 6 is a graph for explaining Example 3 of the nitrogen gas generation process according to the present invention.

[0123] Figure 6 shows (Back pressure condition 1) The back pressure on the air electrode side and the back pressure on the hydrogen electrode side are both 0.1 MPa (atmospheric pressure), (Back pressure condition 2) The back pressure on the air electrode side is 0.2 MPa and the back pressure on the hydrogen electrode side is 0.1 MPa (atmospheric pressure), and (Back pressure condition 3) Condition where the back pressure on the air electrode side and the back pressure on the hydrogen electrode side are both 0.2 MPa The relationship between cell temperature and power for each of the above is shown in the graph.

[0124] According to these graphs, the relationship (back pressure condition 3) > (back pressure condition 2) > (back pressure condition 1) is established for both "peak power value" and "peak cell temperature." Here, if the difference between (back pressure condition 3) and (back pressure condition 1) in the peak power value is ΔW, then: (a) The difference in peak power value between (Back pressure condition 3) and (Back pressure condition 2) is also (b) The difference in peak power values ​​between (Back pressure condition 2) and (Back pressure condition 1) Both are ΔW / 2.

[0125] From this, it can be considered that, with regard to the cell reaction in the "fuel cell," under (back pressure condition 2), a reaction occurs that is exactly halfway between (back pressure condition 3) and (back pressure condition 1), and that, even though the hydrogen density is the same as under (back pressure condition 1), a greater amount of power is generated due to the higher oxygen density, and that, even though the oxygen density is the same as under (back pressure condition 3), a lesser amount of power is generated due to the lower hydrogen density.

[0126] Furthermore, in carrying out this Example 3, it was found that a very small amount of gas leakage may occur in some cases if a pressure difference of about 0.1 MPa or more exists between the air electrode side and the hydrogen electrode side. This is thought to be because, in the "fuel cell" used in the experiment, the outer periphery of the electrolytic membrane pressed against the grooved surface is sealed with silicone rubber, but differences in the force pressing against the silicone rubber create very small gaps, resulting in gas leakage.

[0127] From the above explanation, it can be understood that it is also highly preferable to adjust the pressure (back pressure) of the air (oxygen-containing gas) on the cathode side of the "fuel cell" of fuel cell U11 (Figure 1) and the pressure (back pressure) of the hydrogen gas (fuel gas) on the anode side using the back pressure valve of pressure control U123 (Figure 1) and the back pressure valve of pressure control U115 (Figure 1) so that the ratio (or difference) of these pressures falls within a predetermined pressure ratio range including 1 (or a predetermined pressure difference range including zero).

[0128] For example, a very suitable back pressure balance setting is to set the difference between the back pressure of air (oxygen-containing gas) and the back pressure of hydrogen (fuel gas) to at least less than 0.1 MPa, preferably ±0.0 MPa.

[0129] [Example 4] FIG. 7 is a graph for explaining Example 4 of the nitrogen gas generation process according to the present invention.

[0130] Figure 7 shows a graph showing the relationship between fuel cell temperature and power, which forms a hysteresis curve. In other words, the power output from a fuel cell changes depending on the cell temperatures it has experienced in the past.

[0131] Specifically, as shown in the graph in Figure 7, when the fuel cell is first started from a low temperature under back pressure conditions of "air electrode side back pressure: 0.35 MPa / hydrogen electrode side back pressure: 0.35 MPa," the power increases as the cell temperature rises, reaching a peak power value (approximately 8 W) when the cell temperature reaches around 95°C. After that, the fuel cell is stopped and water-cooled from the outside, lowering the cell temperature from around 95°C to around 84°C. When the fuel cell is then started again, the power curve appears in a different position from the previous power curve, indicating a history of experiencing high cell temperatures.

[0132] Here, as with the previous power curve, the power reaches its peak value (approximately 8 W) when the cell temperature is around 95°C, and in fact, it has been confirmed that the power behaves reversibly with respect to the cell temperature near the peak cell temperature (approximately 91°C to approximately 95°C).

[0133] Next, in the above operating mode, the "fuel cell" was initially operated under a back pressure of 0.1 MPa (atmospheric pressure), and the back pressure was gradually increased in stages or continuously as the cell temperature rose, and the power peak value (peak cell temperature) for each back pressure was passed, and the fuel cell was then moved to a higher power (cell temperature). As a result, the power history (variation) described above was suppressed, and it became possible to obtain the maximum power. Furthermore, it was found that gradually increasing the back pressure from 0.1 MPa (atmospheric pressure) allowed the cell temperature to rise more quickly and the peak power value to be obtained.

[0134] The graph in Figure 7 shows a power curve obtained when, immediately after the power reaches its peak value under the back pressure conditions of "air electrode side back pressure: 0.25 MPa / hydrogen electrode side back pressure: 0.25 MPa," the back pressure conditions are changed to "air electrode side back pressure: 0.30 MPa / hydrogen electrode side back pressure: 0.30 MPa," and when the power reaches its peak value under these back pressure conditions, the back pressure conditions are changed to "air electrode side back pressure: 0.35 MPa / hydrogen electrode side back pressure: 0.35 MPa." This curve shows that the power smoothly transitions to higher power after passing through the power peak value.

[0135] Incidentally, it has been experimentally shown that even in the process of lowering the cell temperature of a "fuel cell" by water cooling or the like, if the back pressure is reduced stepwise or continuously, and the power peak value (peak cell temperature) for the back pressure at each point is passed while transitioning to a higher power (cell temperature), a reversible operating state with suppressed history can be achieved.

[0136] In any case, it is important that the "fuel cell" of the fuel cell U11 according to the present invention is operated under high back pressure conditions. Here, considering the case where "electric power" is also supplied to the outside together with "high purity nitrogen gas", it is also preferable to quickly supply stable (reversible) power with suppressed history by controlling the high back pressure as described above.

[0137] In other words, a more suitable method for controlling the back pressure of this "fuel cell" is to sequentially increase the pressure (back pressure) of the air (oxygen-containing gas) and the pressure (back pressure) of the hydrogen gas (fuel gas) to multiple pressure levels preset based on the relationship between the pressure and the peak value of the output power, or to continuously increase the pressure at a preset pressure increase rate based on the relationship, until the target pressure (back pressure) is reached.

[0138] The above has explained the functions and actions of each component of the nitrogen gas generation system 1, as well as examples and experimental examples. As already pointed out, the nitrogen gas generation system 1 of this embodiment is characterized by the excellent combination of the high back pressure "fuel cell" in the fuel cell U11 and the "filter" in the nitrogen filter U12.

[0139] Here, in one embodiment that is considered to be very suitable for this combination, the "fuel cell" is as follows, taking into consideration the above description: (a) It has a high back pressure (e.g., 0.7 MPa) that is optimal for acting on the "filter"; (b) has a temperature control means suitable for controlling high temperatures (high cell temperatures) associated with high back pressure; (c) Equipped with a structure and components that can stably maintain high back pressure and high temperature, (d) It is possible to supply not only high-purity nitrogen gas but also large amounts of electric power and thermal energy to the outside. This is something that is distinct from conventional fuel cells, which are simply power generation devices that use fuel (hydrogen).

[0140] [Other embodiments of the nitrogen gas generator / system] FIG. 8 is a schematic diagram showing another embodiment of a nitrogen gas generating system according to the present invention.

[0141] The nitrogen gas generation system 1′ of this embodiment shown in FIG. 8 is different from the nitrogen gas generation system 1 shown in FIG. 1 in the following respects: (a) an oxygen tank 104' for temporarily storing oxygen generated by the hydrogen generation unit 103; (b) A gas mixer U106' mixes the taken-in air with oxygen gas introduced from the oxygen tank 104' and supplies a mixed gas (oxygen-containing gas) having a higher oxygen concentration than air to the air compressor U106. Furthermore, instead of using the pressure booster U124 (FIG. 1), (c) a pressure control U124' that controls the pressure of the high-pressure off-gas received from the off-gas buffer tank 122 to adjust it to a pressure (e.g., 0.7 MPa) suitable for introduction into the nitrogen filter U12; It is characterized by further comprising:

[0142] 1 except for the above configurations (a) to (c). That is, the nitrogen gas generation system 1' can also be considered as a nitrogen gas, electric power, and heat supply system, like the nitrogen gas generation system 1. It is also possible to configure a single nitrogen gas generation device that includes the components shown in FIG. 8, and further, it is also possible to configure a nitrogen gas generation device that includes at least a fuel cell U11 and components directly connected thereto, and a nitrogen filter U12, and that has at least a natural energy power generation system U101 external to the device.

[0143] Therefore, the nitrogen gas generation system 1' will be specifically described below, focusing on the above configurations (a) to (c). Incidentally, the material and energy transfers and the process flow shown by connecting the components with arrows in the system configuration diagram of Figure 8 can also be understood as one embodiment of the nitrogen gas generation method in the nitrogen gas generation system 1'.

[0144] Also in Figure 8, the Hydrogen Generator U103 is a high-pressure hydrogen gas generation unit that generates hydrogen gas at a pressure exceeding atmospheric pressure by electrolyzing water. Incidentally, the Hydrogen Generator U103 shown in Figure 1 can also be an electrolysis unit with the same configuration as the present Hydrogen Generator U103.

[0145] Specifically, the hydrogen generator U103 generates hydrogen and oxygen by electrolyzing water using electricity supplied from the renewable energy generator U101 or the like, and can supply high-pressure hydrogen gas by passing the generated hydrogen through a "high-pressure hydrogen passage." Here, this "high-pressure hydrogen passage" is a gas passage structured so that hydrogen ions that have migrated through an electrolytic membrane (e.g., a solid polymer membrane) placed between the electrodes of the electrolytic cell become high-pressure hydrogen gas at a pressure exceeding 1 atmosphere.

[0146] Generally, if electrolysis is continued in a sealed container, the gas pressure (hydrogen pressure, oxygen pressure) in the sealed container increases with the passage of current, resulting in the production of high-pressure hydrogen and oxygen. The hydrogen generator U103 basically utilizes this principle to produce high-pressure hydrogen (and high-pressure oxygen), but by adopting the structure described above, it is possible to supply even higher-pressure hydrogen gas. For example, the sealed structures described in JP 2005-180545 A and JP 2010-196133 A can also be adopted.

[0147] In any case, in the nitrogen gas generation system 1', the hydrogen generation U103 is used to generate high-pressure (for example, 0.7 MPa) hydrogen gas, which can be supplied to the "fuel cell" of the fuel cell U11.

[0148] 8, the gas mixer U106' is equipped with a known gas mixer, and oxygen gas produced in the hydrogen generator U103 is taken in through an oxygen tank 104' acting as a buffer, and mixed with the air taken in to produce oxygen-rich air having a higher oxygen concentration than air. By supplying this oxygen-rich air to the "fuel cell," the oxygen density in the cell reaction can be increased, making it possible to generate more electricity.

[0149] It is also preferable that the gas mixer U106' is equipped with a mass flow controller before oxygen gas is introduced into the gas mixer, so that the flow rate of the oxygen gas can be adjusted to mix the air and oxygen gas at the desired ratio. For example, as described above, if the nitrogen filter U12 uses a filter that has a higher filtering effect as the oxygen concentration of the gas decreases, the flow rate of the oxygen gas introduced may be reduced to reduce the oxygen concentration of the high-purity nitrogen gas to a target value (e.g., 0.1%). Alternatively, if the target value is easily achievable (e.g., when the target oxygen concentration is 0.99%), the flow rate of the oxygen gas introduced may be increased to supply more power.

[0150] Furthermore, by compressing and increasing the pressure of the oxygen-containing air using the air compressor U106, high-pressure (e.g., 0.7 MPa) oxygen-containing air can be supplied to the "fuel cell" of the fuel cell U11. Here, higher-pressure oxygen gas (as with hydrogen gas) may be extracted from the hydrogen generator U103 to generate the required amount of compression and pressure increase in advance. Alternatively, it is also possible to supply the high-pressure oxygen-containing air to the "fuel cell" simply by compressing and increasing the pressure using the air compressor U106.

[0151] In any case, by supplying such high-pressure oxygen-containing air, off-gas with a high back pressure (e.g., 0.7 MPa) can be introduced into the nitrogen filter U12, and therefore, in this embodiment, as described above, the pressure booster U124 (FIG. 1) is not required. Note that, as a modification, it is also possible to supply high-pressure (e.g., 0.7 MPa) air (compressed air) to the "fuel cell" instead of oxygen-containing air, as in the nitrogen gas generation system 1 of FIG. 1, without using the pressure booster U124 (FIG. 1).

[0152] 8, the pressure control U124' is a unit that has a known gas pressure control mechanism and adjusts the pressure of the higher pressure (e.g., 0.7 MPa) off-gas to a pressure suitable for acting on the "filter" of the nitrogen filter U12. Incidentally, if a certain pressure loss occurs in the mass flow controllers, regulators, etc. installed on the off-gas line of the nitrogen gas generation system 1', including this pressure control U124', it is also preferable to adjust the pressure of the off-gas introduced into the nitrogen filter U12 to a pressure (e.g., 0.8 to 0.9 MPa) that is the pressure suitable for acting on the "filter" (e.g., 0.7 MPa) plus the amount of the pressure loss.

[0153] It is preferable that the overall control U131' controls the mass flow controller of the gas mixer U106' described above to adjust the mixture ratio of air and oxygen gas, in addition to the control contents of the overall control U131 of the nitrogen gas generation system 1 shown in Figure 1. It is also preferable to control the pressure control U124' instead of the pressure booster U124 (Figure 1) to introduce high-pressure off-gas having a more suitable pressure into the nitrogen filter U12.

[0154] As described above, according to the nitrogen gas generation system 1' of this embodiment, off-gas having a pressure suitable for acting on the "filter" can be introduced into the "fuel cell" without using a mechanical pressure-increasing means immediately before introducing the off-gas into the nitrogen filter U12.As a result, high-purity nitrogen gas can be generated more efficiently and provided to the outside, and greater electric power can also be provided.

[0155] FIG. 9 is a schematic diagram for explaining still another embodiment of the nitrogen gas generation system according to the present invention.

[0156] The nitrogen gas generation system 1'' shown in FIG. 9 has a configuration in which a pressure equalizer U104e is provided instead of the hydrogen tank 104 and the air tank 107 in the nitrogen gas generation system 1' shown in FIG.

[0157] This pressure equalization U104e is (a) A high-pressure hydrogen chamber 104e1, which is a space for receiving and temporarily storing high-pressure hydrogen gas from the hydrogen generator U103 and is connected to a hydrogen supply pipe that supplies the hydrogen gas, which has reached the same pressure as oxygen-containing air (e.g., 0.7 MPa), to the flow controller U105; (b) a high-pressure air chamber 104e2, which is a space for receiving and temporarily storing high-pressure oxygen-containing air from the air compressor U106 (through a filter U107), and is connected to an air supply pipe that supplies the oxygen-containing air, which has reached the same pressure as hydrogen gas (e.g., 0.7 MPa), to a flow control U109; (c) A movable partition 104e3 that separates the high-pressure hydrogen chamber 104e1 and the high-pressure air chamber 104e2 in a spatially separated and insulated manner and that is movable to equalize the pressure of the gas contained in both chambers. It has the following characteristics.

[0158] Here, it is also preferable that the gas inlets and outlets of the high-pressure hydrogen chamber 104e1 and the high-pressure air chamber 104e2 are each provided with a control valve that can be driven and controlled by the overall control U131''. In this case, by controlling the opening and closing of these control valves, it is possible to apply the pressure of the high-pressure hydrogen chamber 104e1 and the pressure of the high-pressure air chamber 104e2 directly to the movable partition 104e3, thereby creating a situation in which pressure equalization processing can be performed.

[0159] The nitrogen gas generation system 1'' uses this pressure equalization U104e to generate air (oxygen-containing gas) and hydrogen (fuel gas) that are both above atmospheric pressure and have equal pressures (e.g., 0.7 MPa), and supplies these to the "fuel cell" of the fuel cell U11. As a result, even when the back pressure of the "fuel cell" is increased in this way, it is possible to automatically maintain a balance between the air electrode side and the hydrogen electrode side with respect to the back pressure.

[0160] Here, high-pressure hydrogen gas is introduced into the pressure equalization U104e from the hydrogen generation U103, while oxygen-containing air can be introduced at a lower pressure (for example, without passing through the air compressor U106). Even in this case, the oxygen-containing air can be compressed by the hydrogen gas in the pressure equalization U104e to become equal in pressure to the hydrogen gas. In other words, the pressure equalization U104e can perform the air compression process in place of the air compressor U106, or can assist the air compression process of the air compressor U106.

[0161] Incidentally, movable partition 104e3 may be, for example, a metal partition plate that moves parallel between high-pressure hydrogen chamber 104e1 and high-pressure air chamber 104e2 without deformation to equalize the pressure in both chambers. Alternatively, as a modified embodiment, movable partition 104e3 may be, for example, a resin plate or film-like member that has elasticity and that bulges toward one chamber rather than moving parallel to separate the two chambers to equalize the pressure.

[0162] As a modification of the nitrogen gas generation system 1'', the air compressor 106 provided upstream of the pressure equalizer 104e may be equipped with a booster valve, which may be used to increase the pressure of the oxygen-containing air. In this case, oxygen gas generated in the hydrogen generation 103 may be used as a support gas to drive the booster valve. Of course, the oxygen gas may be used as a support gas and then sent to the oxygen tank 104' for use in generating oxygen-containing air. Furthermore, hydrogen gas generated in the hydrogen generation 103 may also be used as the support gas, although care must be taken when handling it.

[0163] Furthermore, as another modification of the nitrogen gas generation system 1'', it is also possible to supply high-pressure (e.g., 0.7 MPa) air (compressed air) to the "fuel cell" instead of oxygen-containing air, similar to the nitrogen gas generation system 1 of Figure 1, without using the pressure booster U124 (Figure 1).

[0164] As described above in detail, the nitrogen gas generating device and method of the present invention allows off-gas (exhaust gas) discharged from a fuel cell and having a pressure exceeding atmospheric pressure (high back pressure) to act on a nitrogen filter capable of separating nitrogen and oxygen, thereby enabling efficient generation of highly pure nitrogen gas.

[0165] In this regard, fuel cells and nitrogen filters are well-suited to each other, and the low oxygen concentration and high temperature conditions in the off-gas from the fuel cell can also contribute to improving the filtering effect of the nitrogen filter.

[0166] 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 high-purity nitrogen gas. Naturally, it will also be possible to meet the need for on-site power supply. In other words, this invention is expected to greatly contribute 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 in the future.

[0167] 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.

[0168] 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]

[0169] 1, 1', 1'' Nitrogen Gas Generating System / Device 101 Renewable Energy Power Generation Unit (U) 102 Energy Storage U 103 Hydrogen Generation U 104 Hydrogen Tank 104' oxygen tank 104e Equal pressure U 104e1 High-pressure hydrogen chamber 104e2 High-Pressure Air Chamber 104e3 Movable partition 105, 125 Flow Control U 106 Air Compressor U 106' Gas Mixture U 107 Air Tank 108 Filter U 109 Flow Control U 11 Fuel Cell U 111, 112 Drain 113 Gas-liquid separation U 114 Hydrogen Recovery U 115, 123, 124' Pressure Control U 12 Nitrogen Filter U 121 Gas-liquid separation U 122 Off-gas buffer tank 124 Pressure Booster U 126 Nitrogen Tank 131, 131', 131'' Overall Control U

Claims

1. a fuel cell that operates by taking in air or an oxygen-containing gas including nitrogen and a fuel gas; a filter including hollow fibers capable of separating at least nitrogen and oxygen, wherein a lower limit pressure for obtaining a target nitrogen concentration in a filtered nitrogen-containing gas under a set gas flow rate of the introduced nitrogen-containing gas is determined by the use of the hollow fibers; a pressure increasing means for increasing the pressure of a filter-supply exhaust gas, which is exhaust gas extracted from the fuel cell and supplied to the filter; a pressure control means provided downstream of the fuel cell, which is capable of supplying the air or oxygen-containing gas having a pressure exceeding atmospheric pressure to the fuel cell, which is capable of supplying exhaust gas having a pressure exceeding atmospheric pressure discharged from the operating fuel cell to the pressure boosting means, and which is capable of supplying filter supply exhaust gas whose pressure has been increased by the pressure boosting means to the filter; a filter input / output section that introduces the filter-supply exhaust gas having increased pressure into the filter and extracts the exhaust gas having increased nitrogen concentration from the filter; an overall control means for causing the pressure control means to adjust the pressure of the filter-supplied exhaust gas to a pressure equal to or higher than the lower limit pressure, taking into account the pressure increase by the pressure increase means, and at which the nitrogen concentration in the exhaust gas with increased nitrogen concentration becomes a target high nitrogen concentration, under conditions where the oxygen concentration of the filter-supplied exhaust gas has been made a predetermined low oxygen concentration by the fuel cell; and for causing the pressure control means to adjust the pressure of the air or oxygen-containing gas supplied to the fuel cell to a pressure at which the oxygen concentration of the filter-supplied exhaust gas extracted from the fuel cell becomes the predetermined low oxygen concentration. and The predetermined low oxygen concentration is determined from the characteristics of the filter relating to the relationship between the oxygen concentration of the gas introduced and the oxygen concentration of the gas after filtering, and the target high nitrogen concentration. A nitrogen gas generator characterized by:

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

3. a fuel cell that operates by taking in air or an oxygen-containing gas including nitrogen and a fuel gas; a filter including hollow fibers capable of separating at least nitrogen and oxygen, wherein a lower limit pressure for obtaining a target nitrogen concentration in a filtered nitrogen-containing gas under a set gas flow rate of the introduced nitrogen-containing gas is determined by the use of the hollow fibers; a pressure increasing means for increasing the pressure of a filter-supply exhaust gas, which is exhaust gas extracted from the fuel cell and supplied to the filter; a pressure control means provided downstream of the fuel cell, which is capable of supplying the air or oxygen-containing gas having a pressure exceeding atmospheric pressure to the fuel cell, which is capable of supplying exhaust gas having a pressure exceeding atmospheric pressure discharged from the operating fuel cell to the pressure boosting means, and which is capable of supplying filter supply exhaust gas whose pressure has been increased by the pressure boosting means to the filter; a filter input / output section that introduces the filter supply exhaust gas with increased pressure into the filter and extracts the exhaust gas with increased nitrogen concentration from the filter; an overall control means for causing the pressure control means to adjust the pressure of the filter-supplied exhaust gas to a pressure equal to or higher than the lower limit pressure, taking into account the pressure increase by the pressure increase means, and at which the nitrogen concentration in the exhaust gas with increased nitrogen concentration becomes a target high nitrogen concentration, under conditions where the oxygen concentration of the filter-supplied exhaust gas has been made a predetermined low oxygen concentration by the fuel cell; and for causing the pressure control means to adjust the pressure of the air or oxygen-containing gas supplied to the fuel cell to a pressure at which the oxygen concentration of the filter-supplied exhaust gas extracted from the fuel cell becomes the predetermined low oxygen concentration. and The predetermined low oxygen concentration is determined from the characteristics of the filter relating to the relationship between the oxygen concentration of the gas introduced and the oxygen concentration of the gas after filtering, and the target high nitrogen concentration. A nitrogen gas generation system.

Images