JP2008192514A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of quick activation even under a low-temperature environment with a check valve of a circulation gas flow channel in danger of being frozen, in a system equipped with a plurality of ejectors. <P>SOLUTION: The fuel cell system is provided with, for instance, a solid polymer type fuel cell 1 and a small and a large ejectors 6, 5 connected in series. A suction port 6b of the small ejector 6 is connected with an outlet of an anode 1a. A discharge port 6c of the small ejector 6 is connected with a suction port 5b of the large ejector 5. A discharge port 5c of the large ejector 5 is connected with an inlet of the anode 1a. With such connection, a fuel gas circulation channel is formed from the anode outlet to the inlet of the anode 1a through the suction port 6b of the small ejector 6, the discharge port 6c of the small ejector 6, the suction port 5b of the large ejector 5, and the discharge port 5c of the large ejector 5. Hydrogen is directly supplied to the small ejector 6 from a hydrogen pressure control valve 3, and to the large ejector 5, hydrogen is supplied through a shutoff valve 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that improves the performance of a fuel gas circulation device that recirculates anode off-gas containing excess fuel gas discharged from an anode to the anode.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidant gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for a mobile body because it has a low operating temperature and is easy to handle.

  In the polymer electrolyte fuel cell, a catalyst layer containing platinum or the like is provided on both surfaces of a hydrogen ion conductive electrolyte membrane, and a gas diffusion layer having electronic conductivity and air permeability is provided thereon. The catalyst layer and the gas diffusion layer serve as a fuel electrode (anode or negative electrode) and an oxidant electrode (cathode or positive electrode) (for example, Patent Document 1). Then, a fuel gas containing hydrogen and an oxidant gas containing oxygen are supplied to the fuel electrode and the oxidant electrode from gas supply grooves provided in the separator, respectively, and electricity is generated by the following electrochemical reaction.

[Fuel electrode reaction]: H ₂ → 2H ⁺ + 2e ⁻ (Formula 1)
[Oxidant electrode reaction]: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (chemical formula 2)
Also, in the fuel cell system, in order to secure the supply amount of fuel gas to the electrolyte end of the fuel cell body, more fuel gas is supplied than the flow rate required for power generation, and the unreacted fuel gas (circulation gas) discharged Some of them are equipped with an ejector (jet pump) for supplying the fuel cell again.

By the way, in a fuel cell system for an electric vehicle, there is one in which two ejectors having different maximum flow rates are arranged in parallel in order to cope with a wide range of output from warm-up to rated output (for example, Patent Documents). 1, 2).
JP 2001-266922 A (6th page, FIG. 3) JP 2003-338302 A (Page 4, FIG. 1)

  However, when multiple ejectors are connected in parallel, when there is an ejector that is not operating, the gas boosted by the ejector that is operating does not operate. It is inevitable that the fuel flows backward without passing through the fuel cell. For this reason, at least the number of check valves or electromagnetic valves obtained by subtracting 1 from the number of ejectors must be provided to avoid backflow.

  This check valve or solenoid valve must be installed in the circulation channel before the intake port of the ejector. The fuel consumption deteriorates due to increased pressure loss caused by the valve, and the cost increases and the reliability increases due to the increase in the number of valves. There were problems such as decline. And as the biggest adverse effect, since a mechanical valve is provided in the anode circulation path which is in a humid environment, the liquid water remaining in the anode circulation path is frozen below freezing point, and the valve is also frozen and fixed. There was a problem that could not start below freezing.

  In order to solve the above problems, the present invention provides a fuel cell system including a fuel gas circulation device that adds hydrogen supplied from a hydrogen supply source to anode off-gas discharged from an anode outlet and supplies the hydrogen again to the anode inlet. The fuel gas circulation device comprises a plurality of ejectors arranged in series, the hydrogen supply source is connected to the drive inlet of each ejector, the anode outlet and the suction port of the uppermost ejector are connected, The gist is that the discharge port of the most downstream ejector is connected to the anode inlet, and the discharge port of the upstream ejector is connected to the suction port of the downstream ejector.

  In the present invention, since a plurality of ejectors for circulating the fuel gas are connected in series, it is not necessary to provide a valve for preventing the backflow of the fuel gas in the fuel gas circulation path.

  According to the present invention, there is no need to provide a valve for preventing check in the fuel gas circulation path which is a humid environment, and it is possible to avoid freezing and sticking of the valve due to an environment below freezing. There is an effect that it is possible to provide a fuel cell system that can be started quickly without providing time.

  In addition, there are effects that the cost can be reduced by reducing the number of valves, the reliability can be improved, and the deterioration of fuel consumption due to the pressure loss of the valves can be avoided.

All these effects can be achieved by controlling the number of ejectors that are operated according to the fuel cell load, that is, the effect obtained when the ejectors are connected in parallel. The effect that the operation can be performed in a choked state etc. can be realized with almost no deterioration. Here, meaning that it hardly deteriorates means that the supply hydrogen (fuel) input from the ejector operating upstream when the plurality of ejectors are operating is for the ejector operating downstream. Although the circulation performance of the ejector on the downstream side is reduced, the fluid of the increased load (the increased flow rate) is pure hydrogen, so the density is light and the medium pressure (before the fuel injection part) This means that the flow rate is a few hundreds [NL / min] in the environment where the pressure is high), so that the flow rate is not so high when converted to the volume under the anode operating pressure, so that it hardly causes a load increase.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In addition, although each Example described below is not specifically limited, it is a fuel cell system suitable for a fuel cell vehicle parked outdoors below freezing.

  As a first embodiment of the fuel cell system according to the present invention, a fuel cell system in which two ejectors are provided in series in a fuel circulation path will be described. In a fuel cell system in which two ejectors are connected in series, even if the two ejectors are the same without any difference in size and performance, high circulation performance can be ensured in a wider range than a single ejector system. In this embodiment, a system using two ejectors having different dimensions or performance, which is the most characteristic point of the present invention, will be described. Here, the difference in performance means that the circulating flow rate at which the maximum boost value is obtained, or the circulating flow rate at which the ratio of the circulating flow rate to the drive flow rate is maximum is different.

  In FIG. 1A, the fuel cell system according to the first embodiment includes, for example, a polymer electrolyte fuel cell 1, a large ejector 5, and a small ejector 6. The small ejector 6 and the large ejector 5 are connected in series.

  Next, the fuel gas path will be described. Hydrogen as a fuel gas is supplied to the anode 1 a of the fuel cell 1. The high-pressure hydrogen gas stored in the hydrogen tank 2 is depressurized to an appropriate pressure by the hydrogen pressure regulating valve 3. The decompressed hydrogen gas is supplied to the drive inlet 5a of the large ejector 5 through the shut-off valve 4, and is directly supplied to the drive inlet 6a of the small ejector 6 without passing through the valve. The suction port 6b of the small ejector 6 is connected to the outlet of the anode 1a. The discharge port 6 c of the small ejector 6 is connected to the suction port 5 b of the large ejector 5. The discharge port 5c of the large ejector 5 is connected to the inlet of the anode 1a. By these connections, fuel from the anode outlet to the inlet of the anode 1a through the suction port 6b of the small ejector 6, the discharge port 6c of the small ejector 6, the suction port 5b of the large ejector 5, and the discharge port 5c of the large ejector 5 is obtained. A gas circulation path is formed. Further, a purge valve (nitrogen purge valve) 7 is provided in a path branched from the path from the outlet of the anode 1 a to the suction port 6 b of the small ejector 6.

  Next, the oxidant gas path will be described. The compressor 8 compresses air as an oxidant gas and supplies the compressed air to the inlet of the cathode 1b. An air pressure adjusting valve 9 for adjusting the oxidant pressure of the cathode is provided at the outlet of the cathode 1b.

  A cooling system that keeps the temperature of the operating fuel cell 1 at an appropriate temperature and a power extraction control unit that controls power extraction from the fuel cell 1 are provided, but are not essential elements of the present invention. Illustration is omitted.

  Next, the internal structure of the ejector used in the present invention and the nozzle diameter and throat diameter for determining the ejector performance will be described with reference to FIG.

  In FIG. 2, the ejector 20 includes a drive inlet 21 to which a relatively high-pressure hydrogen gas is supplied as a drive flow. The driving inlet 21 communicates with a nozzle 22 through which the supplied hydrogen gas is injected. Here, let the inner diameter of the nozzle 22 be the nozzle diameter Dn. A space for a suction chamber 23 is provided around the nozzle 22, and the suction chamber 23 communicates with a suction port 24. A throat 25 is provided coaxially with the nozzle 22 in the injection direction of the nozzle 22. The throat 25 has a throat diameter Dt which is an inner diameter several times the nozzle diameter Dn. The throat 25 is connected to a diffuser 26 whose inner diameter is gradually increased in a tapered shape, and the diffuser 26 is connected to a discharge port 27.

  When relatively high-pressure hydrogen gas is supplied to the drive inlet 21 of the ejector 20, the nozzle 22 or a high-speed hydrogen gas flow is injected. The circulating gas in the suction chamber 23 is sucked by the negative pressure generated by the high-speed hydrogen gas flow. Then, a mixed flow of the hydrogen gas and the sucked circulating gas flows into the throat 25, and the flow velocity is reduced and the pressure is increased by the diffuser 26. As a result, a mixed flow having a pressure higher than that of the suction port 22 is discharged from the discharge port 27. In the present invention, a value obtained by subtracting the pressure value of the suction port 24 from the pressure value of the discharge port 27 is called a pressure increase amount.

  Next, referring to FIG. 3, a method for selecting the throat diameter of the small ejector will be described. The parameters that determine the ejector performance are the flow rate of hydrogen consumed by the fuel cell (equal to the flow rate of hydrogen supplied to the ejector in a steady state), the required circulation flow rate, the gas density of the circulation flow, and the ejector nozzle diameter. Dn (nozzle opening area Sn is proportional to the square of Dn) and ejector throat diameter Dt. If the ejector pressure increase amount becomes larger than the pressure loss of the whole anode system, a circulation flow rate higher than the required circulation flow rate is secured.

  In order to start the fuel cell system quickly and start a low load warm-up operation without waiting for thawing even below freezing, the circulating flow rate during the warm-up operation only needs to be secured by the ejector. During the warm-up operation, it is assumed that the hydrogen flow rate corresponding to the fuel cell output is supplied from the hydrogen pressure adjustment valve 3 only to the small ejector 6, the shutoff valve 4 is closed, and no hydrogen is supplied to the large ejector 5. When the optimum design of the small ejector 6 is performed with respect to the output during the warm-up operation, if only the throat diameter Dt of the small ejector 6 is changed while other conditions are fixed, the graph of the fine one-dot chain line in FIG. (Small ejector throat diameter sensitivity). The pressure increase amount of the small ejector during the warm-up operation peaks when the throat diameter is about Φ4 mm, and a value equal to or higher than the target pressure increase amount during the warm-up operation is obtained in the range of Φ3 mm to Φ10 mm in FIG. This is the first condition. However, when the throat diameter exceeds Φ10 mm, the target pressure increase amount during the warm-up operation is reduced.

  On the other hand, since the circulating flow rate increases during rated operation, the amount of pressure increase is positive (+) when the throat diameter exceeds Φ8.5 mm, as shown by the thick broken line graph (small ejector pressure loss throat sensitivity at the time of rating) in FIG. When the throat diameter is Φ8.5 mm, the pressure increase amount is 0, and when it is less than Φ8.5 mm, the pressure increase amount is negative (−), that is, pressure loss.

  However, since the large ejector is also operating during the rated operation, [the boost amount of the small ejector + the boost amount of the large ejector] = the total boost amount during the rated operation is a thick solid line in FIG. The total boost amount during the rated operation is equal to or greater than the target boost amount (thin solid line) during the rated operation when the throat diameter of the small ejector is Φ8 mm or more. This is the second condition.

  Accordingly, as a method of selecting the throat diameter of the small ejector, the throat diameter may be set from Φ8 mm to Φ10 mm, which is a range in which both the first condition and the second condition are satisfied. In order to operate the circulation performance higher even at a relatively high load point other than the rated time, the smallest one in the above range, that is, Φ8 mm may be selected.

  Here, the reason for selecting the smallest value (φ8 mm) in the establishment range of the throat diameter is that the smaller the throat diameter, the easier it is to operate optimally on the low load side. At low load, a low suction flow rate (circulation flow rate) is pulled with a low supply hydrogen drive flow rate. To obtain a high pressure increase in this state, mixing of the drive flow and the suction flow (after the merging of two fluids) It is necessary to do well (contact state). In other words, the smaller the diameter after merging, the easier it is to mix, and the momentum exchange can be performed efficiently. Therefore, if the optimum operation is to be performed on the low load side, the throat diameter should be smaller. However, if the throttle is too much, pressure loss will occur on the large flow rate side, so in a fuel cell system with a wide operating range (wide circulation flow range), you want to reduce the throat diameter to cover a low load. It is necessary to have a trade-off concept of not wanting to be a pressure loss factor during operation with a circulating flow rate.

  The reason for selecting φ8mm is that if the total boosted amount combined with other ejectors exceeds the target boosted amount at the rated output of the fuel cell (at the maximum circulating flow rate), the remaining conditions under the rated output are as much as possible. In order to increase the pressure by a small ejector, the smallest throat diameter in the throat diameter range indicated by the black double arrow in FIG. 3 is selected as the throat diameter of the small ejector.

  Next, a method for selecting the nozzle diameter will be described. FIG. 4 shows the supply hydrogen flow rate with respect to the hydrogen supply pressure for various nozzle diameters of the ejector and the supply hydrogen flow rate necessary for warming up. As shown in FIG. 4, a nozzle diameter φ0.8 mm that allows a supply hydrogen flow rate required during warm-up operation to flow by the hydrogen pressure (maximum source pressure) supplied from the hydrogen pressure adjustment valve 3 to the drive inlet 6 a of the small ejector 6. Choose a larger one. Further, as shown in FIG. 5, a nozzle smaller than the maximum nozzle diameter φ2.0 mm that satisfies the target pressure increase during warm-up operation is selected.

  Which nozzle diameter is to be selected within the range of φ0.8 mm to φ2.0 mm may be determined depending on where the point Pa where the operation of the large ejector is started is located as shown in FIG. If a nozzle with a small nozzle diameter between φ0.8 mm and φ2.0 mm is selected, the large ejector operation start point shifts to the low output side, and if a large nozzle diameter is selected, the large ejector operation start point shifts to the high output side. To do. This determination criterion is based on the pressure loss characteristic of the target anode circulation system. Basically, it is sufficient to set the nozzle diameter so that the entire region can be covered only by the ejector. In the graph of FIG. The nozzle diameter distribution may be such that the large ejector nozzle diameter is 1.5 mm and the small ejector nozzle diameter is 1.2 mm. When the nozzle diameter of the small ejector is determined, the nozzle diameters of the remaining large ejectors are inevitably determined.

  This is because the supply hydrogen flow rate required at the rated output is fixed and the hydrogen pressure (source pressure) supplied from the hydrogen supply source is the same, so the supply hydrogen flow rate distributed to the large and small ejector nozzles is If various losses due to friction and the like are ignored, the nozzle opening area ratio is allocated, so that when the small ejector nozzle is determined, the nozzle diameter of the large ejector is inevitably determined.

  Next, how the fuel cell output is continuously increased from the warm-up operation output (minimum output) to the rated output (maximum output) in the fuel cell system of FIG. FIG. 7 shows the operating state of the ejector according to a certain nozzle diameter distribution in all load regions of the fuel cell system including two series ejectors. The horizontal axis in FIG. 7 represents the fuel cell output (load), and the vertical axis represents the pressure increase amount of each ejector (negative value is pressure loss) and the total pressure increase amount of all ejectors.

  First, when the supply of hydrogen from the hydrogen tank 2 is started by starting the operation of the hydrogen pressure regulating valve 3, the small ejector 6, which is the first ejector from the minimum output, is operated. As the output gradually increases, the supply hydrogen flow rate increases, and the boosting performance of the small ejector 6 also increases accordingly. At this time, since no hydrogen is supplied to the large ejector 5, the large ejector 5 is merely a flow path and is a pressure loss element. The small ejector 6 needs to be boosted including the pressure loss of the large ejector 5.

  When the fuel cell output increases and reaches a certain output point Pa, the pressure before the nozzle of the small ejector 6 (the downstream pressure of the hydrogen pressure regulating valve 3), that is, the hydrogen supply pressure reaches the maximum original pressure, and the nozzle of the small ejector 6 The diameter comes to an output point where no more hydrogen can be supplied. This is recognized by detecting that the pressure value in front of the small ejector nozzle is equal to the maximum original pressure, and the shutoff valve 4 in front of the nozzle of the large ejector 5 is opened, and the operation of the large ejector 5 is started. From there, the large ejector 5 also starts boosting operation, and since the hydrogen is also supplied to the small ejector 6, the two ejectors simultaneously boost the pressure, and the total boosted amount exceeds the target boosted amount (anode pressure loss characteristic). The operation is performed.

  In this way, the low load region that is not circulated by one ejector is also covered up to the high load region. As a result, an effect equivalent to that of the ejector parallel connection can be realized without a check valve. Therefore, the check valve can be prevented from freezing and sticking, and the fuel cell system can be quickly started at a freezing point. Regarding the freezing of the ejector nozzle, since the hydrogen gas passing through the nozzle is dry, it is not necessary to consider the inside of the nozzle. On the outside of the nozzle, against the nozzle opening blockage due to freezing of the stack water (liquid water) adhering to the circulation gas flow path such as the suction chamber, the inside of the anode system is scavenged with dry hydrogen immediately before the operation is stopped. This can be avoided by putting operations such as removing them. If the system generates almost no liquid water, there is no need for such operation. In addition, there is a method to avoid by the ejector arrangement method and layout, and in the ejector layout where the nozzle faces downward, liquid water may drop on the tip of the nozzle and ice column-like freezing may occur, so the direction of the nozzle is It is also an effective means to lay out other than downward.

  Next, Example 2 will be described. FIG. 1B is a configuration diagram of the fuel cell system according to the second embodiment. The difference from the configuration of the first embodiment shown in FIG. 1A is that a mechanical fuel gas circulation pump 10 is added. Since other configurations are the same as those in FIG. 1A, the same reference numerals are given to the same components, and redundant description is omitted.

  The fuel gas circulation pump 10 is disposed between the outlet of the anode 1 a and the suction port 6 b of the small ejector 6 and upstream of the purge valve 7. The fuel gas circulation pump 10 is a mechanical pump of a type that does not block the gas flow path even when it cannot be operated due to freezing. This type of pump is generally referred to as a speed pump, and is a pump of a type in which kinetic energy is given to a fluid by rotating blades and the speed is changed to pressure. For example, a vortex pump, a centrifugal pump, or the like corresponds to this type of pump. .

  Then, the fuel gas circulation pump 10 is operated only in the circulation gas flow rate (or power generation output) region where the pressure increase amount (circulation flow rate) is partially insufficient. Thereby, since the operation frequency of the fuel gas circulation pump 10 can be significantly suppressed, the durability and reliability can be improved, and the effect of reducing pump operation noise and vibration can be obtained. Further, in the operation region where the anode operating pressure is low, when the nitrogen purge cannot be sufficiently performed, the space between the fuel gas circulation pump 10 and the small ejector 6 is temporarily increased by temporarily increasing the output of the fuel gas circulation pump 10. And the nitrogen purge flow rate can be secured.

  If the fuel gas circulation pump 10 cannot be started due to freezing of the movable part of the fuel gas circulation pump 10, power generation is performed by anode off-gas circulation using only the ejector, and the fuel cell output is output until the fuel gas circulation pump 10 is thawed. The fuel cell output is limited by the power extraction control unit so that the target circulation flow rate can be secured only by the ejector. While the fuel cell output is restricted, control such as thawing of the fuel gas circulation pump is performed. As described above, even if the fuel gas circulation pump 10 is frozen, power generation can be performed up to the fuel cell output that can be circulated only by the ejector. Therefore, when the present invention is applied to a fuel cell vehicle, a certain speed is obtained immediately after startup. This makes it possible to drive the vehicle with no uncomfortable thawing waiting time.

  By introducing such a fuel gas circulation pump, the circulation flow rate can be reduced in the fuel cell output range where the required circulation flow rate cannot be ensured by the ejector alone, depending on the system conditions, and the ability to control below freezing point, improve the freedom of fuel gas circulation control. There is an effect that it is possible to ensure both.

  In addition, when viewed from the fuel cell outlet side, by providing a fuel gas circulation pump in the uppermost stream, supply hydrogen supplied from the ejector is not added to the circulation flow rate of the fuel gas circulation pump. The pump load can be reduced, and there are effects such as a reduction in sound vibration, improvement in fuel consumption, and improvement in pump life due to the ability to operate at a reduced speed.

  In addition, a purge valve is provided downstream of the fuel gas circulation pump. When the anode system pressure is low, there is almost no pressure difference from the atmospheric pressure, so that sufficient nitrogen purge may not be performed. By increasing the pump output temporarily to increase the pump downstream pressure, there is an effect of enabling sufficient purge. Further, by providing a purge valve in front of the ejector, it is possible to avoid discharging hydrogen supplied from the ejector together outside the anode system, and to suppress a decrease in fuel efficiency due to the purge.

  Next, Example 3 will be described. The plurality of ejectors connected in series in the present invention is not limited to two, and can be applied to three or more ejectors. As the number of ejectors increases, the shape of each ejector can be finely adjusted, so that each ejector can be operated under conditions closer to the optimum operating point, and overall high circulation performance can be secured. The number is limited due to problems such as cost and space.

  FIG. 8 is a configuration diagram illustrating the configuration of a fuel cell system in which three ejectors are connected in series. In FIG. 8, the fuel cell system of Example 3 includes, for example, a polymer electrolyte fuel cell 1, a large ejector 5, a middle ejector 12, and a small ejector 6 connected in series.

  Next, the fuel gas path will be described. Hydrogen as a fuel gas is supplied to the anode 1 a of the fuel cell 1. The high-pressure hydrogen gas stored in the hydrogen tank 2 is depressurized to an appropriate pressure by the hydrogen pressure regulating valve 3. The decompressed hydrogen gas is supplied to the drive inlet 5a of the large ejector 5 through the shut-off valve 4, is supplied to the drive inlet 12a of the middle ejector 12 through the shut-off valve 11, and the drive inlet of the small ejector 6 is supplied. 6a is directly supplied without a valve.

  The suction port 6b of the small ejector 6 is connected to the outlet of the anode 1a. The discharge port 6 c of the small ejector 6 is connected to the suction port 12 b of the middle ejector 12. The discharge port 12 c of the middle ejector 12 is connected to the suction port 5 b of the large ejector 5. The discharge port 5c of the large ejector 5 is connected to the inlet of the anode 1a. With these connections, from the outlet of the anode 1a, the suction port 6b of the small ejector 6, the discharge port 6c of the small ejector 6, the suction port 12b of the middle ejector 12, the discharge port 12c of the middle ejector 12, and the suction port 5b of the large ejector 5 are provided. A fuel gas circulation path is formed through the discharge port 5c of the large ejector 5 to the inlet of the anode 1a. Further, a purge valve 7 is provided on a path branched from a path from the outlet of the anode 1a to the suction port 6b of the small ejector 6.

  Next, the oxidant gas path will be described. The compressor 8 compresses air as an oxidant gas and supplies the compressed air to the inlet of the cathode 1b. An air pressure adjusting valve 9 for adjusting the oxidant pressure of the cathode is provided at the outlet of the cathode 1b.

  A cooling system for keeping the temperature of the operating fuel cell 1 at an appropriate temperature and a power system for taking out electric power from the fuel cell 1 are provided, but these are not essential elements of the present invention, and are not shown. As in FIG. 1B, a mechanical fuel gas circulation pump 10 may be disposed between the outlet of the anode 1 a and the suction port 6 b of the small ejector 6 and upstream of the purge valve 7.

  Here, as for the nozzle opening area of each ejector, the nozzle opening area of the small ejector is the smallest, the nozzle opening area of the large ejector is the largest, and the nozzle opening area of the middle ejector is between the largest and the smallest.

  When operating a plurality of ejectors, the hydrogen supplied from the fuel injection portion of the ejector operating on the upstream side passes through (inhales) the circulation flow path of the ejector operating on the downstream side. Therefore, the ejector operating on the downstream side causes a load increase, and the amount of pressure increase is reduced. In the worst case, the downstream ejector is merely a pressure loss element. However, by providing an ejector from the upstream in order of increasing nozzle opening area, when a plurality of the ejectors are operating at the same time, more supply hydrogen always flows into the downstream ejector. As a result, performance can be ensured, and operation can be performed almost without being affected by an increase in load due to the supplied hydrogen flowing in from the upstream side.

  Next, with reference to FIG. 9, the control method of Example 3 is demonstrated. FIG. 9 is a diagram for explaining the operation state of each ejector with respect to the fuel cell output in the fuel cell system including three series ejectors. The horizontal axis in FIG. 9 represents the fuel cell output (load), and the vertical axis represents the pressure increase amount of each ejector (negative value is pressure loss) and the total pressure increase amount of all ejectors.

  The control method of the third embodiment is almost the same as in the case of two ejectors. First, only the small ejector 6 is operated while the output of the fuel cell is small from the warm-up operation, and the shutoff valves 4 and 11 are closed, and the middle ejector 11 and the large ejector 5 are simply circulation channels (pressure loss elements). It becomes. When the fuel cell output further increases and the pressure before the nozzle of the small ejector 6 reaches the maximum original pressure (the fuel cell output at this time is P1), the shut-off valve 11 before the nozzle of the middle ejector 12 is opened, Start the ejector. By operating the middle ejector 12, the pressure in front of the nozzle once decreases. When the fuel cell output further increases and the pressure just before the nozzle of the small ejector 6 (or the nozzle of the middle ejector 12) reaches the maximum original pressure (the fuel cell output at this time is P2), the shutoff valve 4 also Open to start supplying hydrogen to the large ejector 5 and operate all three ejectors.

  During operation of the fuel cell system, the drive inlet of the small ejector is not provided with a shut-off valve so that the ejector with the smallest nozzle opening area (small ejector) is always operated. Can be reduced by one, which has the effect of improving reliability and reducing costs.

  In addition, by always operating the ejector with the smallest nozzle opening area, the effect of the smallest ejector not becoming a pressure loss element even if the amount of pressure increase decreases when a large circulating flow rate flows at high loads. There is.

(A) It is a block diagram of the fuel cell system of Example 1 provided with two serial ejectors. (B) It is a block diagram of the fuel cell system of Example 2 provided with two serial ejectors and a mechanical fuel gas circulation pump. It is a schematic cross section of an ejector showing an example of the internal structure of the ejector used in the present invention. It is a figure explaining the design range of the throat diameter of the small ejector in Example 1. FIG. It is a figure explaining the relationship between the amount of supply hydrogen required at the time of warming-up in Example 1, and the nozzle diameter of a small ejector. It is a figure explaining the relationship between the pressure | voltage rise amount required at the time of warming-up in Example 1, and the nozzle diameter of a small ejector. It is a figure which shows the pressure | voltage rise amount and anode system pressure loss characteristic by each nozzle diameter of a small ejector and a large ejector with respect to the fuel cell output in Example 1. FIG. It is a figure explaining the operating condition of the small ejector and the large ejector with respect to the fuel cell output in Example 1. FIG. It is a block diagram of the fuel cell system of Example 3 provided with three series ejectors. It is a figure explaining each operating condition of the small ejector, the middle ejector, and the large ejector with respect to the fuel cell output in Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 1a Anode 1b Cathode 2 Hydrogen tank 3 Hydrogen pressure regulating valve 4 Shut-off valve 5 Large ejector 6 Small ejector 7 Purge valve 8 Compressor 9 Air pressure regulating valve 10 Fuel gas circulation pump

Claims (13)

In a fuel cell system including a fuel gas circulation device that adds hydrogen supplied from a hydrogen supply source to an anode off-gas discharged from an anode outlet and supplies the anode off-gas again to the anode inlet.
A plurality of ejectors arranged in series as the fuel gas circulation device;
Connecting the hydrogen source to the drive inlet of each ejector;
Connecting the anode outlet and the suction port of the uppermost ejector;
Connect the discharge port of the most downstream ejector and the anode inlet,
A fuel cell system comprising a discharge port of an upstream ejector connected to a suction port of a downstream ejector.   2. The fuel according to claim 1, wherein each of the plurality of ejectors has a different circulating flow rate at which a size or a maximum boost value is obtained, or a circulating flow rate at which a ratio of the circulating flow rate to the driving flow rate is maximized. Battery system.   The fuel cell system according to claim 1 or 2, wherein the nozzle opening area of the upstream ejector is smaller than the nozzle opening area of the downstream ejector.   A shutoff valve is not provided in the path from the hydrogen supply source to the drive inlet of the uppermost ejector, and a shutoff valve is provided in the path from the hydrogen supply source to the drive inlet of another ejector. The fuel cell system according to any one of claims 1 to 3, wherein the fuel cell system is characterized in that:   In the operation region where the amount of power generation is small, including when the fuel cell is warmed up, the drive flow is supplied from the hydrogen supply source to the drive inlet of the uppermost ejector, and the shutoff valve leading to the drive inlet of the other ejector is closed. The fuel cell system according to claim 4, wherein the ejector is not operated.   6. The number of ejectors to be operated in order from the smallest nozzle opening area when increasing the power generation amount of the fuel cell continuously from the minimum power generation amount. The fuel cell system described in 1.   When the pressure increase amount of the ejector, which is the pressure loss among the plurality of ejectors, is set to a negative value, the throat diameter of the uppermost ejector is the value of all ejectors in all flow regions of the fuel gas circulation flow rate of the fuel cell system. 7. The fuel cell system according to claim 5, wherein the minimum value is selected from a range of throat diameters in which the sum of the boost amounts is equal to or greater than the target boost amount.   Each nozzle opening area of the plurality of ejectors has a minimum area that is choked with the maximum hydrogen supply pressure at the minimum circulation flow rate circulated by the ejector, and the maximum hydrogen supply pressure at the maximum circulation flow rate circulated by the ejector. When the opening area to be choked is the maximum area, the area is set to the minimum area or more and the maximum area or less, and the throat diameter of each ejector is set so that the nozzle opening area is equal to the throat diameter of the maximum ejector. The fuel cell system according to any one of claims 1 to 7, wherein   2. The fuel cell system according to claim 1, wherein a mechanical fuel gas circulation pump is provided in series with the ejector so that the flow path is not blocked when the pump is not in operation.   10. The fuel cell system according to claim 9, wherein when viewed from the fuel cell anode outlet side, the fuel gas circulation pump is disposed first, and then a plurality of ejectors are disposed in order of increasing nozzle opening area. .   The fuel cell system according to claim 10, wherein a nitrogen purge valve is provided between the fuel gas circulation pump and the ejector.   The fuel cell system according to any one of claims 9 to 11, wherein when the target circulation flow rate cannot be achieved only by the ejector, the target circulation flow rate is achieved by operating the fuel gas circulation pump. .   When the fuel gas circulation pump cannot be started due to freezing of the movable part of the fuel gas circulation pump, power is generated by anode off-gas circulation of only the ejector, and the fuel cell output is output by the ejector until the fuel gas circulation pump is thawed. The fuel cell system according to claim 12, wherein the fuel cell system is limited to an output capable of ensuring a target circulation flow rate.

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