JP2005032652A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the operation of a fuel cell continuable even when an abnormality has occurred in a circulating pump for circulation of fuel offgas. <P>SOLUTION: A hydrogen circulating type fuel cell system which is provided with the fuel cell 1, an air feeding means and a hydrogen feeding means to feed air which is oxidant gas, and hydrogen which is fuel gas, to the fuel cell 1, a circulating path 6 and the fuel circulating pump 7 to feed the exhausted fuel offgas from the fuel cell 1 again to the fuel cell 1, is provided with an abnormality detecting means detecting any abnormality of the fuel circulating pump 7 and a valve 8 as a circulating path opening and closing means, for opening and closing the circulating path 6 are provided. Then, when an abnormality is detected in the fuel circulating pump 7 by the abnormality detecting means, the circulating path 6 is closed by the valve 8 so that the fuel offgas from the fuel cell 1 is not fed to the fuel circulating pump 7. Operation is carried out in a so called dead end method, in a state with the fuel offgas sealed inside the closed path. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system including a fuel circulation pump that circulates a fuel off-gas discharged from the fuel cell.

  As a countermeasure against environmental problems in recent years, particularly air pollution caused by exhaust gas from automobiles, global warming due to carbon dioxide, etc., fuel cell technology that enables clean exhaust and high energy efficiency has attracted attention. The fuel cell system is an energy conversion system that supplies hydrogen as fuel and air as an oxidant to the hydrogen electrode and air electrode of the fuel cell to cause an electrochemical reaction and convert chemical energy into electric energy.

  As a form of such a fuel cell system, unused hydrogen (fuel gas) that has not been used in the fuel cell is circulated and fuel is reused in order to realize high output of the fuel cell and improvement of hydrogen utilization efficiency. A hydrogen circulation type fuel cell system that is supplied to a battery and reused is known (see, for example, Patent Document 1).

In the fuel cell system described in Patent Document 1, the fuel off-gas discharged from the fuel cell is returned to the main path through the circulation path by driving the fuel circulation pump, and mixed with the fuel gas newly supplied from the fuel supply source Then, the fuel cell is supplied again.
JP 2002-289237 A

  By the way, in the hydrogen circulation type fuel cell system, if an abnormality occurs in the fuel circulation pump for circulating the fuel off gas, the fuel gas cannot be properly supplied, and it is difficult to continue the operation of the fuel cell. is there. For example, when considering an in-vehicle fuel cell system, it is a big problem that the entire fuel cell system goes down immediately when an abnormality occurs in the fuel circulation pump and the vehicle is stopped. In order to avoid a sudden stop of the vehicle, it is necessary to take some measures so that the operation of the fuel cell can be continued even when an abnormality occurs in the fuel circulation pump.

  The present invention was devised to eliminate the drawbacks of the conventional fuel cell system, and even when an abnormality occurs in the fuel circulation pump for circulating the fuel off-gas, the operation of the fuel cell is performed. An object of the present invention is to provide a novel fuel cell system that can be continued, for example, in an in-vehicle fuel cell system, in which a sudden stop of the vehicle can be avoided.

  The fuel cell system of the present invention includes a fuel cell, an oxidant gas supply means for supplying an oxidant gas to the fuel cell, a fuel gas supply means for supplying the fuel gas to the fuel cell, and a fuel off-gas discharged from the fuel cell. And a fuel circulation pump for supplying the fuel cell again to the fuel cell, and in such a fuel cell system, in order to achieve the object, an abnormality detection means for detecting an abnormality of the fuel circulation pump; Circulation path opening / closing means for opening and closing the circulation path is provided. When the abnormality of the fuel circulation pump is detected by the abnormality detection means, the circulation path is closed by the circulation path opening / closing means so that the fuel offgas from the fuel cell is not supplied to the fuel circulation pump, and the fuel offgas is closed. It was made to be in a state of being confined in the route.

  In the fuel cell system of the present invention as described above, when an abnormality of the fuel circulation pump is detected, the circulation path is closed, and the method of supplying the fuel gas is a dead end method in which circulation is not performed from the circulation method Will be moved to. In the dead end system, the amount of fuel gas flowing into the fuel cell is equal to the amount consumed by the power generation of the fuel cell, and the operation of the fuel cell is continued even if there is an abnormality in the fuel circulation pump.

  In the dead end system, the fuel gas utilization rate is 100%, and the operation in such a state where the fuel gas utilization rate is extremely high causes the output of the fuel cell to decrease. However, there is no problem as long as the driving is performed for a short time. For example, in a vehicle-mounted fuel cell system, the vehicle can be moved to a safe place by a short-time driving in a dead end system. Further, by performing appropriate control, it is possible to continue operation to some extent.

  According to the fuel cell system of the present invention, when an abnormality detecting means for detecting an abnormality of the fuel circulation pump and a circulation path opening / closing means for opening and closing the circulation path of the fuel off gas are provided, and an abnormality of the fuel circulation pump is detected, The circulation path is closed so that off gas from the fuel cell is not supplied to the circulation pump, and the fuel off gas is confined in the closed path, so even if an abnormality occurs in the fuel circulation pump, It is possible to continue the operation of the fuel cell by a so-called dead end system. Therefore, for example, in a vehicle-mounted fuel cell system, it is possible to avoid a sudden stop of the vehicle.

  Hereinafter, embodiments of a fuel cell system to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 shows a main configuration of the fuel cell system according to the present embodiment. As shown in FIG. 1, the fuel cell system of this embodiment includes a fuel cell 1 that generates power by supplying hydrogen as a fuel gas and air as an oxidant gas.

  The fuel cell 1 has a structure in which a power generation cell in which a fuel electrode to which hydrogen is supplied and an air electrode to which air is supplied is overlapped with an electrolyte / electrode catalyst composite interposed therebetween is stacked in a multistage manner. It converts chemical energy into electrical energy. At the fuel electrode of each power generation cell, hydrogen ions and electrons are dissociated when hydrogen is supplied, hydrogen ions pass through the electrolyte, electrons generate power through an external circuit, and move to the air electrode side. To do. In the air electrode, oxygen in the supplied air reacts with the hydrogen ions and electrons to generate water, which is discharged to the outside.

  As the electrolyte of the fuel cell 1, for example, a solid polymer electrolyte is used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte is made of an ion (proton) conductive polymer film such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.

  In the fuel cell 1, it is necessary to supply hydrogen, which is a fuel gas, or air, which is an oxidant gas, to a fuel electrode or an air electrode. The fuel cell system includes a hydrogen supply unit and an air supply unit as mechanisms for this purpose. Is provided.

  The hydrogen supply means includes, for example, a hydrogen storage means 2 that stores hydrogen as a fuel gas, a pressure control valve 3 that adjusts the hydrogen from the hydrogen storage means 2 to an arbitrary pressure, and a hydrogen path that supplies the fuel cell 1 And a hydrogen supply pipe 4. Then, the hydrogen supplied from the hydrogen storage means 2 that is a hydrogen supply source is decompressed by the pressure control valve 3 and sent to the hydrogen electrode of the fuel cell 1 through the hydrogen supply pipe 4. Further, a humidifying means 5 is provided at a position in front of the fuel cell 1 in the hydrogen supply pipe 4, and hydrogen supplied to the fuel cell 1 is humidified by the humidifying means 5.

  The fuel cell system of this embodiment is configured as a hydrogen circulation type fuel cell system, and hydrogen discharged from the fuel cell 1 without being consumed by the fuel cell 1 (fuel off-gas discharged from the fuel cell 1) is generated. It is circulated and newly mixed with hydrogen supplied from the hydrogen storage means 2 and supplied again to the hydrogen electrode of the fuel cell 1. As a mechanism for this, the fuel cell system of this embodiment is provided with a circulation path 6 and a fuel circulation pump 7 for supplying the fuel off-gas discharged from the fuel cell 1 to the fuel cell 1 again. .

  Further, a valve 8 capable of blocking the circulation path 6 and closing it is provided as a circulation path opening / closing means for opening and closing the circulation path 6 in the vicinity of the inlet side of the circulation path 6. By closing the valve 8, the circulation path 6 is closed so that the fuel off-gas from the fuel cell 1 is not supplied to the fuel circulation pump 7, and the off-gas is confined in the closed path (fuel cell 1). Become.

  The valve 8 operates to close the circulation path 6 when an abnormality occurs in the fuel circulation pump 7. Here, the determination of whether or not the fuel circulation pump 7 is abnormal may be performed by detecting, for example, the rotational speed of the fuel circulation pump 7 and detecting that the desired rotational speed is not reached. Alternatively, it may be performed by detecting the hydrogen pressure at the inlet / outlet of the fuel circulation pump 7 and detecting that the pressure difference at the inlet / outlet is not a desired value, or the hydrogen pressure at the outlet of the fuel circulation pump 7 may be changed. Detection may be performed by detecting that the pressure does not have a desired value. In any case, an abnormality detection means for detecting an abnormality of the fuel circulation pump 7 may be provided according to the detection method employed.

  Further, a hydrogen exhaust pipe 9 is provided on the outlet side of the fuel cell 1 so as to branch from the circulation path 6. The hydrogen exhaust pipe 9 is purged by opening the hydrogen exhaust pipe 9 as necessary. A purge valve 10 is provided for performing the operation. In the hydrogen circulation type fuel cell system, impurities such as nitrogen and CO accumulate in the circulation path 6 as the hydrogen circulates, and the hydrogen partial pressure decreases, so the efficiency of the fuel cell 1 decreases. Therefore, when the impurity concentration becomes high or when the fuel cell system is started, the purge valve 10 is opened and the gas in the circulation path 6 is purged to remove impurities from the circulation path 6. .

  On the other hand, although not shown, the air supply means includes a compressor for sucking outside air and pumping the air to the air electrode of the fuel cell 1, a filter for trapping microdust and sulfur, oil discharged from the compressor, and the like. It consists of an air supply pipe, an air exhaust pipe for discharging the air electrode exhaust gas, a pressure control valve for controlling the pressure of the supplied air to a desired pressure, etc., and air is fed into the air supply pipe by the compressor Thus, the fuel cell 1 is supplied to the air electrode. Further, oxygen and other components in the air that have not been consumed in the fuel cell 1 are discharged from the air exhaust pipe.

  The above is the schematic configuration of the fuel cell system of the present embodiment. In the fuel cell system of the present embodiment, when an abnormality occurs in the fuel circulation pump 7, the hydrogen supply method to the fuel cell 1 is changed from the circulation method. The system is shifted to the dead end system and the operation of the fuel cell 1 is continued. The control flow at this time is shown in FIG.

  The control flow in FIG. 2 is executed when an abnormality of the fuel circulation pump 7 is detected and determined to be abnormal in a program job executed during normal operation.

  In the fuel cell system of the present embodiment, during normal operation, hydrogen is circulated and used, so that the valve 8 is open and the purge valve 10 is closed, and hydrogen (fuel offgas) discharged from the fuel cell 1 is supplied as a fuel circulation pump. 7 is mixed with the hydrogen newly supplied from the hydrogen storage means 2 and supplied to the fuel cell 1 again. In addition, when the hydrogen concentration in the circulation path 6 is lowered, the purge valve 10 is opened as necessary, and control for performing a purge operation is executed in a timely manner.

  When the abnormality of the fuel circulation pump 7 is determined and the control flow of FIG. 2 is started, the flow path on the outlet side of the fuel cell 1 is closed by the valve 8 and the purge valve 10, and the hydrogen supply method is changed from the circulation method. Switching control for switching to a so-called dead end system in which circulation is not performed is performed.

  That is, in step S1, the valve 8 is closed, whereby hydrogen discharged from the fuel cell 1 is not circulated, and a closed path is formed by the valve 8 and the purge valve 10. As a result, the amount of hydrogen flowing into the fuel cell 1 is equal to the amount consumed for power generation of the fuel cell 1, and the utilization rate of hydrogen is 100%. Such operation with a very high hydrogen utilization rate may reduce the output characteristics of the fuel cell 1.

  For example, in the portion close to the outlet end of the hydrogen flow path in the fuel cell 1, the hydrogen flow rate there is slower than that at the inlet end, making it difficult to move the condensed water formed in the flow path. As a result, the reaction area is reduced, and the reaction may be worsened. Similarly, at the outlet side end of the hydrogen flow path, there is a possibility that the reaction is worsened due to the decrease in the hydrogen partial pressure due to the influence of an increase in components other than hydrogen.

  The latter deterioration of the characteristics of the fuel cell 1 when the hydrogen partial pressure is reduced becomes significant in a region where a certain current value is exceeded, and as a result, the voltage of the fuel cell 1 rapidly decreases. Therefore, in order to prevent the characteristics of the fuel cell 1 from drastically decreasing as much as possible, the operation conditions of the fuel cell 1 are changed, and the control content is switched so as to limit the output during the operation of the fuel cell 1. The contents will be described below.

  First, in step S2, the operating conditions of the fuel cell 1 are set so that the operating pressure of the fuel cell 1 is higher than when operating in the circulation system, and the operation control of the hydrogen supply means and the air supply means is performed accordingly. To be implemented. As a result, even if the total pressure of hydrogen flowing into the hydrogen electrode of the fuel cell 1 increases and the ratio of components other than hydrogen increases, the hydrogen partial pressure can be kept as high as possible, and the influence of diffusion polarization can be reduced. It becomes.

  As a method of increasing the operating pressure, if the system is operated with variable pressure according to the load, a method of increasing the operating pressure by a factor of a factor may be used in a region where low pressure operation is performed during normal operation. Alternatively, a method of operating at a constant maximum operating pressure allowed by the system, including the region where the low-pressure operation is performed, may be used.

  Next, in step S3, logic switching for determining the timing for purging is set, and thereafter, when it is determined that purging is necessary based on this logic, control for opening the purge valve 10 for a predetermined time is performed. . This is because the operation in the dead end system is more likely to accumulate condensed water on the gas flow path or to be affected by an increase in components other than hydrogen, compared with the case of operation while circulating hydrogen. This is intended to prevent the deterioration of the characteristics of the fuel cell 1 due to these factors.

  The purge determination after the logic switching may be obtained by multiplying a coefficient obtained in advance through experiments or the like on the basis of the periodic frequency in the case of the circulation method, or based on the operating conditions of the fuel cell 1 The frequency may be set to be higher by estimating the nitrogen concentration and lowering the reference value for determining purging as compared with the normal circulation operation. As a method of estimating the nitrogen concentration in the hydrogen path, the amount of nitrogen crossover from the air electrode is calculated from the specifications of the electrolyte membrane, the operating pressure, and the operating temperature, and compared with the volume in the hydrogen path. A method for obtaining the concentration can be exemplified.

  Next, in step S4, output restriction is performed when the fuel cell 1 is operated, and control is set so that the fuel cell 1 is not operated in a region where the output characteristics rapidly decrease. As a calculation method of the limited output value, the hydrogen partial pressure near the hydrogen path outlet in the fuel cell 1 during the dead-end operation is estimated, and the output voltage is calculated from the estimated hydrogen partial pressure using the Nernst equation. And a method of setting the current value before the output voltage rapidly decreases to the maximum current value. As a method for estimating the hydrogen partial pressure, the above-described nitrogen concentration may be estimated and obtained from the ratio of both gas components.

  Further, in step S5, control is performed so that the humidification amount of the humidifying means 5 is reduced or the humidification is stopped compared with the normal operation. This avoids excessive humidification, particularly near the outlet of the hydrogen flow path of the fuel cell 1, and prevents flooding in a large current region. In addition, the reduction of the humidification amount or the stop of the humidification may be performed only in a large current region or for a limited time, so that in an operation state where there is no possibility of flooding such as a low load region. It becomes possible to prevent shortage of humidification.

  As described above, in the fuel cell system according to the present embodiment, the hydrogen supply method is switched from the circulation method to the dead-end method even after an abnormality occurs in the fuel circulation pump 7 that circulates the hydrogen gas as the fuel. The operation of the fuel cell 1 can be continued. Further, when the hydrogen supply method is switched to the dead end method, the output characteristics of the fuel cell 1 are changed by switching the operation pressure, the purge frequency, the maximum extraction current value, the humidification control, etc. so as to correspond to this. The decrease can be suppressed, and the operation can be continued to some extent.

It is a figure which shows the principal part structure of the fuel cell system to which this invention is applied. 6 is a flowchart showing a control flow executed when an abnormality occurs in the fuel circulation pump in the fuel cell system to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Hydrogen storage means 5 Humidification means 6 Circulation path 7 Fuel circulation pump 8 Valve 10 Purge valve

Claims (5)

A fuel cell;
An oxidant gas supply means for supplying an oxidant gas to the fuel cell;
Fuel gas supply means for supplying fuel gas to the fuel cell;
A circulation path and a fuel circulation pump for supplying the fuel off-gas discharged from the fuel cell to the fuel cell again;
An abnormality detecting means for detecting an abnormality of the fuel circulation pump;
Circulation path opening and closing means for opening and closing the circulation path,
When the abnormality of the fuel circulation pump is detected by the abnormality detection means, the circulation path is closed by the circulation path opening / closing means so that the fuel off-gas from the fuel cell is not supplied to the fuel circulation pump, A fuel cell system in which fuel off-gas is confined in a closed path. When the circulation path is closed by the circulation path opening / closing means and the fuel off gas is confined in the closed path, the operating pressure of the oxidant gas and the fuel gas supplied to the fuel cell is high. The fuel cell system according to claim 1, wherein the oxidant gas supply unit and the fuel gas supply unit are controlled. A purge valve for performing a purge operation for discharging the fuel off-gas in the circulation path to the outside;
Controlling the opening and closing of the purge valve so as to increase the frequency of the purge operation when the circulation path is closed by the circulation path opening and closing means and the fuel off gas is confined in the closed path. The fuel cell system according to claim 1, wherein: When the circulation path is closed by the circulation path opening / closing means and the fuel off gas is confined in the closed path, output restriction is performed so as to reduce the power generation amount of the fuel cell. The fuel cell system according to any one of claims 1 to 3. Further comprising humidifying means for humidifying the fuel gas supplied to the fuel cell;
When the circulation path is closed by the circulation path opening / closing means and the fuel off gas is confined in the closed path, the humidification means is controlled so that the humidification amount to the fuel gas is reduced. The fuel cell system according to any one of claims 1 to 4, wherein

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