JP4880282B2 - Fuel cell system and fuel cell - Google Patents

Description

  The present invention relates to a fuel cell system having a solid oxide fuel cell and a gas supply system thereof, a fuel cell, and a fuel cell.

  Conventionally, the flow control of each gas supplied to a solid oxide fuel cell has utilized a proportional relationship between the output current of the fuel cell and the flow rate of the supply gas from the principle of electrochemical reaction. It was. For example, in Patent Literature 1, the output current of a fuel cell and the gas flow rate corresponding to the current amount are measured, the relationship is derived in advance by calculation, and the gas flow rate corresponding to the desired current amount based on the derived relationship. Control is performed to adjust the opening of the gas supply valve while measuring with a flow meter so as to become a predetermined amount.

  In Patent Document 2, an oxygen sensor that detects an increase in oxygen concentration caused by oxygen leakage into the fuel gas passage of the solid oxide fuel cell is provided, and the fuel gas supply amount increases as the oxygen concentration in the fuel gas passage increases. Control is performed to adjust the gas supply valve so as to increase.

Furthermore, in order to evaluate the power generation performance of a fuel cell, it is measured by directly monitoring the voltage of the electrode that is involved in the power generation of the battery, and battery performance degradation is a decrease in output measured directly from these electrodes. It was judged by.
Japanese Patent Laid-Open No. 10-302823 JP 2001-273915 A

  However, in the gas flow rate control method of Patent Document 1, the control is performed in order to control the gas valve while measuring the gas flow rate so as to match the gas flow rate obtained by measuring the current amount and then calculating the current amount. It is cumbersome and takes time at the same time. Therefore, there is a problem that in a situation where electric power changes every moment like a household power supply, the control takes time, so that the response is slow and cannot be handled. Furthermore, since the control is performed by an indirect method of the relational expression between the current and the gas flow rate, it is used at the last minute under the influence of some gas leak, and as a result, the fuel cell deteriorates. there were. In addition, the flow meter has a problem of high cost.

  Moreover, in the gas flow rate control method of Patent Document 2, an oxygen sensor is formed separately from the fuel battery cell, and is installed in the vicinity of the outlet side of the fuel gas passage. In this oxygen sensor, the same material as that of the solid electrolyte is formed in a tube shape, electrodes are provided on the inside and outside of the oxygen sensor, a lead wire for voltage extraction is connected, and a temperature sensor is also inserted in the tube. Such an oxygen sensor having a complicated structure is expensive to manufacture and requires a space for arranging the oxygen sensor.

  Furthermore, in the method of monitoring the voltage of the electrode involved in power generation for evaluating the power generation performance of the fuel cell, all the electrode surfaces are equipotential, and therefore there is a deterioration in a specific position in the cell or a distribution of deterioration conditions. In some cases, it is measured as if the entire appearance is deteriorated and cannot be distinguished. For example, when the fuel gas passage is deteriorated on the downstream side, it can be dealt with by changing the fuel flow rate. On the other hand, when the fuel gas passage is deteriorated on the upstream side, there is a possibility of leakage of the seal part. It is dangerous to increase.

  In view of the above situation, the object of the present invention is to detect the oxygen concentration in the fuel gas that has passed through the fuel gas passage of the solid oxide fuel cell, that is, the off-gas, and further to detect the oxygen concentration at an arbitrary position in the fuel gas passage. The fuel cell system is optimally operated by adjusting the flow rate of various gases supplied to the fuel cell using this detection means. To ensure proper maintenance.

In order to achieve the above object, the present invention provides the following configurations.
(1) A fuel cell system according to claim 1 is a fuel cell comprising a solid electrolyte layer sandwiched between a fuel electrode layer and an oxygen electrode layer, and a fuel gas passage provided along the solid electrolyte layer And a solid oxide fuel cell comprising an oxygen-containing gas introduction section for introducing an oxygen-containing gas, and a gas supply system for supplying a plurality of types of gases to the solid oxide fuel cell In the system,
An oxygen concentration measurement reference electrode formed as an electrode of the solid electrolyte layer in the vicinity of the outlet of the fuel gas passage;
The gas supply system comprises: a fuel gas supply means for supplying fuel gas to the fuel cell; an oxygen-containing gas supply means for supplying an oxygen-containing gas to the fuel cell; and the oxygen concentration measurement reference electrode. The fuel gas supply means and / or the control means for controlling the flow rate of each gas from the oxygen-containing gas supply means based on the output voltage.

(2) The fuel cell system according to claim 2 is characterized in that, in claim 1, the oxygen concentration measurement reference electrode is formed of the same material as the fuel electrode layer or the oxygen electrode layer.

(3) The fuel cell system according to claim 3 is characterized in that, in claim 1 or 2, a temperature sensor is provided in the vicinity of the oxygen concentration measurement reference electrode.

(4) A fuel cell system according to a fourth aspect is the fuel cell system according to any one of the first to third aspects, wherein the control means determines that the oxygen concentration in the fuel gas passage is based on an output voltage of the reference electrode for measuring oxygen concentration. The gas flow rate from the fuel gas supply means is controlled so as to be constant.

(5) A fuel cell system according to a fifth aspect of the present invention is the fuel cell system according to any one of the first to fourth aspects, further comprising a direct current sensor for detecting an output current from the fuel cell, wherein the control means is a signal of the direct current sensor. The flow rate of the gas from the fuel gas supply means is controlled based on the above.

(6) A fuel cell system according to a sixth aspect of the present invention is the fuel cell system according to any one of the first to fifth aspects, further comprising a direct current sensor for detecting an output current from the fuel cell, wherein the control means is a signal of the direct current sensor. The flow rate of the gas from the fuel gas supply means is controlled based on the above.

(7) A fuel cell according to claim 7 is a fuel cell in which a solid electrolyte layer is sandwiched between a fuel electrode layer and an oxygen electrode layer, and a fuel gas passage provided along the solid electrolyte layer. And a solid oxide fuel cell comprising an oxygen-containing gas introduction part for introducing an oxygen-containing gas, comprising an oxygen concentration measurement reference electrode formed as an electrode of the solid electrolyte layer in the vicinity of the outlet of the fuel gas passage It is characterized by that.

In the invention according to claim 1, the fuel cell system having the solid oxide fuel cell and the gas supply system thereof is provided as a fuel cell off-gas (a fuel gas that has passed through a fuel gas passage provided on the fuel electrode side of the fuel cell). ) Is provided with a reference electrode for measuring the oxygen concentration. The position where the oxygen concentration measurement reference electrode is provided is near the outlet of the fuel gas passage, that is, downstream of the fuel gas. The oxygen concentration measurement reference electrode is formed as a solid electrolyte layer electrode in the same manner as the fuel electrode layer or the oxygen electrode layer, but is provided independently of the fuel electrode or the oxygen electrode layer. The reference electrode for measuring oxygen concentration can be formed from, for example, a conductive ceramic.

  At the position of the oxygen concentration measurement reference electrode, a power generation reaction similar to that of the fuel battery cell is performed between the oxygen concentration measurement reference electrode and the counter electrode with the solid oxide interposed therebetween, whereby the oxygen concentration measurement reference electrode The output voltage taken out from the fuel cell reflects the difference in oxygen concentration between the fuel electrode side and the oxygen electrode side. For example, when the oxygen concentration measurement electrode is provided on the solid electrolyte on the oxygen electrode side, the fuel electrode itself can be used as the counter electrode, or a separate electrode can be provided on the solid electrolyte on the fuel electrode side. Good. In the type of fuel cell in which the oxygen-containing gas introduction part is installed outside the fuel cell, the oxygen concentration is generally regarded as substantially constant because the oxygen-containing gas is introduced outside the fuel cell. On the other hand, when the solid electrolyte layer is damaged and oxygen leaks into the fuel gas passage and the oxygen concentration in the fuel gas increases, the difference in oxygen concentration from the oxygen electrode side decreases, and this change is used for oxygen concentration measurement. This is because it appears as a change in the output voltage of the reference electrode.

  Since the oxygen concentration measurement reference electrode detects the difference in oxygen concentration between the oxygen electrode side and the fuel electrode side of the fuel cell, the installation position may be on the oxygen electrode side or the fuel electrode side.

As described above, in the present invention, a change in the oxygen concentration in the fuel gas passage is measured by providing the oxygen concentration measurement reference electrodes on both sides of the solid electrolyte layer of the existing fuel cell without providing a separate oxygen sensor. be able to. Thereby, it becomes possible to directly measure the power generation state of the fuel cell. The control means can control the valve opening degree of one or more gases based on the output voltage of the oxygen concentration measurement reference electrode so that the output voltage of the oxygen concentration measurement reference electrode becomes constant. . In this case, the response is fast and the load following is also fast. Furthermore, it can be formed at a low cost and is compact without taking up space.
The above-described effects are the same for the inventions according to claims 7 and 8.

  The adjustment of the fuel gas and the oxygen-containing gas can be controlled in two stages, for example, by first adjusting the flow rate of the fuel gas and further adjusting the flow rate of the oxygen-containing gas when the oxygen concentration in the fuel gas passage does not reach the target value. Specifically, when it is detected that the oxygen concentration in the fuel gas passage has increased (the difference in oxygen concentration between the fuel electrode side and the oxygen electrode side has decreased), the flow rate of fuel gas to the fuel gas passage is increased. As a result, the oxygen concentration in the fuel gas passage can be lowered and the oxygen concentration difference can be increased. As a next step, the oxygen concentration difference can be increased by increasing the flow rate of the oxygen-containing gas supplied to the oxygen electrode side in addition to or instead of this. Thereby, a constant power generation state can be maintained.

In the invention according to claim 2, the oxygen concentration measurement reference electrode is formed of the same material as the fuel electrode layer or the oxygen electrode layer of the fuel cell. Thereby, the reference electrode for measuring oxygen concentration can be formed simultaneously with any layer in the manufacturing process of the fuel cell. Therefore, an inexpensive and highly reliable oxygen concentration detection part can be constructed using a part of existing fuel cells.

In the invention according to claim 3, a temperature sensor is provided in the vicinity of the oxygen concentration measurement reference electrode. This may be replaced by a sensor that detects the temperature inside the fuel cell as well as the off-gas combustion temperature. In that case, it is possible to cope with this by obtaining in advance the temperature difference from the portion for measuring the oxygen concentration (the position where the oxygen concentration measurement reference electrode is installed). The oxygen concentration measurement reference electrode can be corrected based on the temperature detected by the temperature sensor, and an oxygen concentration change can be accurately detected.

In the invention according to claim 4, the control means controls the flow rate of the fuel gas so that the off-gas oxygen concentration becomes a preset value based on the output voltage of the oxygen concentration measurement reference electrode. Thereby, a constant power generation state can be maintained.

In the invention according to claim 5, the control means exceeds the preset value of the oxygen concentration in the off-gas based on the output voltage of the oxygen concentration measurement reference electrode (that is, the oxygen concentration difference becomes smaller than the preset value). A safety device for stopping the fuel cell system. Thereby, the fatal damage of the whole system can be prevented to the minimum.

The invention according to claim 6 has a direct current sensor for detecting the output current of the fuel cell, and when the output current is less than a preset value, the fuel gas is reduced so that the oxygen concentration in the fuel gas passage becomes low. Control is performed to increase the flow rate of the fuel gas from the supply means. Or it controls so that oxygen-containing gas increases. This is because the fuel cell generally has a tendency to deteriorate the utilization factor when the current is small, so that a constant utilization factor operation is realized.

In one aspect of the present invention, one or a plurality of oxygen concentration detection reference electrodes are provided as electrodes of the solid electrolyte layer between the inlet and the outlet of the fuel gas passage, and one or a plurality of reference electrodes are provided based on these output voltages. It is possible to adjust the valve opening of the gas and supply each necessary gas flow rate to the fuel cell. Thereby, it becomes possible to measure the state of the whole fuel cell directly. For example, since the oxygen concentration distribution over the entire fuel gas passage can be measured, it is possible to detect early whether the fuel cell has deteriorated only on the upstream side or the downstream side of the fuel gas. Become. As a result, it is possible to quickly perform the necessary maintenance for upstream deterioration that may lead to a dangerous situation.

In another aspect of the present invention, one or more temperature sensors are provided between the inlet and the outlet of the fuel gas passage. As a result, the temperature distribution over the entire fuel gas passage can be measured, and more accurate oxygen concentration distribution measurement can be performed regardless of the temperature change.

As described above, in the solid oxide fuel cell system of the present invention, the control is only performed by adjusting the opening of the fuel valve or the like according to the oxygen concentration of the fuel gas in the fuel gas passage, particularly the off-gas. A simple and fast response is possible. Furthermore, since the direct state of the fuel cell can be grasped, it is possible to cope with the deterioration of the fuel cell. The oxygen concentration measurement reference electrode may be made of the same material as any component of the fuel cell. Therefore, since the oxygen concentration detection part composed of the reference electrode, solid electrolyte, and counter electrode has the same structure as the fuel cell, it can be manufactured at the same time as the fuel cell, realizing an inexpensive and highly reliable sensor. can do.

Embodiments of the present invention will be described below with reference to the drawings showing examples of the present invention.
(1) Outline of Fuel Cell System FIG. 1 is a block diagram showing a simplified solid oxide fuel cell system of the present invention. The fuel cell system of the present invention includes a gas supply system 1 that supplies various gases, a fuel cell 2 that generates power using a plurality of gases, and an oxygen concentration for measuring the oxygen concentration of an off-gas of the fuel gas inside the fuel cell. A reference electrode for measurement 3 and a direct current sensor 4 for reading a direct current taken out from the fuel cell 2 as additional equipment are provided. Further, the gas supply system 1 is based on a gas calculation control unit 11 that issues a command of the flow rate of each gas to the gas supply system 1 by an output voltage from the reference electrode 3 for measuring oxygen concentration, and a command from the gas calculation control unit 11. The gas supply part 12 which adjusts the valve opening degree of each gas is comprised. The gas supply unit 12 includes at least a fuel gas supply unit 12a and an oxygen-containing gas supply unit 12b. The fuel gas supply unit 12 a supplies the fuel cell 2 with a fuel gas that may be hydrogen gas or a gas to be reformed. In the case of the reformed gas, it is reformed into fuel gas in the reforming case inside the fuel cell and flows into the fuel gas passage. The oxygen-containing gas supply unit 12b supplies air to the fuel cell 2, for example.

  The fuel cell system according to the present invention is characterized in that the gas supply system 1 includes a gas calculation control unit 11 and a gas supply unit 12 that issue commands for the respective gas supply amounts to the gas supply unit 12. 2 includes an oxygen concentration measurement reference electrode 3 for measuring the oxygen concentration of off-gas, and the gas calculation control unit 11 performs control based on the voltage output of the oxygen concentration measurement reference electrode 3 (arrow S1). This is the point at which the gas supply unit 12 operates (arrow C).

  Preferably, the fuel cell 2 further includes a temperature sensor 5, and based on this voltage output (arrow S2), the influence of the temperature on the voltage output of the oxygen concentration measurement reference electrode 3 is corrected.

  Further, preferably, a DC current sensor 4 for detecting the output current of the fuel cell 2 is also provided, and the gas calculation control unit 11 controls the gas supply unit 12 similarly based on this detection output (arrow S4). This will be specifically described below.

(2) Fuel Cell FIG. 2 is a perspective view schematically showing the main part of the fuel cell according to the present invention. For reference, the relationship between the gas calculation control unit 11 and the fuel gas supply unit 12a of the gas supply system 1 shown in FIG. 1 is also schematically shown.

  As shown in FIG. 2, the fuel cell 2 is configured by arranging four power generation units 56a, 56b, 56c and 56d in a housing (not shown). Although not shown, a plurality of oxygen-containing gas introduction pipes are disposed in the gaps between the power generation units 56a, 56b, 56c, and 56d, thereby introducing oxygen-containing gas.

  The power generation units 56a, 56b, 56c, and 56d have basically the same structure (however, the power generation units 56a, 56c and the power generation units 56b, 56d are arranged in the front-rear direction reversely). For example, the power generation unit 56a includes a rectangular parallelepiped fuel gas case 58a extending in the front-rear direction at the lower portion thereof. A cell stack 60a is mounted on the upper surface of the fuel gas case 58a that defines the fuel gas chamber. The cell stack 60a is configured by arranging a plurality of upright fuel cell cells 62 (hereinafter abbreviated as “cells”) extending in the vertical direction in the vertical direction.

  The power generation unit 56a also includes a rectangular shape (or cylindrical shape) reforming case 78a that is elongated in the front-rear direction above the cell stack 60a. The upper end of the fuel gas supply pipe 80a is connected to the front end surface of the reforming case 78a. The fuel gas supply pipe 80a extends downward, and its lower end is connected to the front surface of the fuel gas case 58a. One end of a reformed gas supply pipe 82a is connected to the rear end surface of the reforming case 78a. The to-be-reformed gas supply pipe 82a extends downward from the reforming case, extends under the housing, and extends out of the housing. The reformed gas is supplied from the fuel gas supply unit 12a of the gas supply system shown in FIG. 1 to the reformed gas supply pipe 82a. The reformed gas may be a hydrocarbon gas such as city gas. An appropriate reforming catalyst for reforming the gas to be reformed into a hydrogen-rich fuel gas is accommodated in the reforming case 78a.

  The reformed gas is supplied from the fuel gas supply unit 12a to the reforming cases 78a, 78b, 78c and 78d through the reformed gas supply pipes 82a, 82b, 82c and 82d, respectively, and reformed into hydrogen-rich fuel gas. Are supplied to the fuel gas chambers defined in the fuel gas cases 58a, 58b, 58c and 58d through the fuel gas supply pipes 80a, 80b, 80c and 80d, respectively, and then the cell stacks 60a, 60b, 60c and 60d. That is, the fuel gas flows in from the lower end of each cell 62, flows from the lower side to the upper side, and flows out as off gas from the upper end.

  The characteristic oxygen concentration measurement reference electrode 3 in the present invention is provided in the vicinity of the upper end of the cell 62 disposed at the foremost position of the cell stack 60a in FIG. The counter electrode of the reference electrode 3 is provided on the fuel electrode side in the cell 62 and may be shared with the fuel electrode itself or may be provided separately. The reference electrode 3 can measure the oxygen concentration of the off gas near the outlet of the fuel gas passage. Actually, the difference in oxygen concentration between the fuel gas passage inside the cell 62 and the outside of the cell 62 is output. Normally, since the oxygen-containing gas is supplied to the outside of the cell 62, it can be considered that the oxygen concentration is constant. In this case, the output of the reference electrode 3 indicates the oxygen concentration change in the fuel gas passage. The illustrated oxygen concentration measurement reference electrode 3 is provided on the solid electrolyte layer in the same manner as the oxygen electrode layer of the cell 62, but is provided electrically independent of the oxygen electrode layer. Moreover, it can form from a conductive ceramic similarly to an oxygen electrode layer. The reference electrode 3 for measuring oxygen concentration can be basically provided in the form of an electrode of a solid electrolyte layer, and may be provided on any pole side. The counter electrode is provided on the opposite pole side. Preferably, the manufacturing cost is reduced by forming the oxygen concentration measurement reference electrode 3 (including its counter electrode) with the same material as either the fuel electrode layer or the oxygen electrode layer.

  3A and 3B are cross-sectional views showing in detail the configuration of the cell according to the present invention. FIG. 3A is an X cross-sectional view of the cell stack 60a shown in FIG. 2, and shows a normal cell structure. FIG. 3B is also a Y cross-sectional view showing a cell structure of a portion where the oxygen concentration measurement reference electrode 3 according to the present invention is provided.

  As clearly shown in FIG. 3A, each cell 62 includes an electrode support substrate 64, a fuel electrode layer 66 that is an inner electrode layer, a solid electrolyte layer 68, an oxygen electrode layer 70 that is an outer electrode layer, and an interconnector 72. Has been. As shown in FIG. 2, the electrode support substrate 64 is a columnar plate-like piece that is elongated in the up-down direction, and has a cross-sectional shape having both flat sides and semicircular sides. The electrode support substrate 64 is formed with a plurality (six in the illustrated example) of fuel gas passages 74 penetrating therethrough in the vertical direction. Each of the electrode support substrates 64 is joined to a slit provided on the upper wall of the fuel gas case 58a of FIG. 2 by, for example, a ceramic adhesive having excellent heat resistance, and the fuel gas passes through the slit in the fuel gas passage 74. Flow into.

  The interconnector 72 is disposed on one flat surface of the electrode support substrate 64. The fuel electrode layer 66 is disposed so as to surround the other flat surface of the electrode support substrate 64 (the lower surface in the cell stack 60a in FIG. 3) and both side surfaces, and both ends thereof are joined to both ends of the interconnector 72. ing. The solid electrolyte layer 68 is disposed so as to surround the entire fuel electrode layer 66, and both ends thereof are joined to both ends of the interconnector 72. The oxygen electrode layer 70 is disposed on the outer flat portion of the solid electrolyte layer 68, and is positioned to face the interconnector 72 with the electrode support substrate plate 64, the fuel electrode layer 66, and the solid electrolyte layer 68 interposed therebetween.

  A current collecting member 76 is disposed between adjacent cells 62 in the cell stack 60a, and connects the interconnector 72 of one cell 62 and the oxygen electrode layer 70 of the other cell 62. Current collecting members 76 are disposed on both ends of the cell stack 60a, that is, on one side and the other side of the cell 62 positioned at the upper end and the lower end in FIG. Output current extraction means (not shown) is connected to the current collecting members 76 located at both ends of the cell stack 60a, and the output current extraction means extends outside the housing.

  Since the electrode support substrate 64 is required to be gas permeable in order to allow the fuel gas to permeate to the fuel electrode layer 66 and to be conductive in order to collect current via the interconnector 72, the electrode support substrate 64 is porous. The conductive ceramic (or cermet) can be used. In order to manufacture the cell 62 by co-firing the electrode support substrate 64 with the fuel electrode layer 66 and / or the solid electrolyte layer 68, it is preferable that the electrode support substrate 64 be formed of an iron group metal component and a specific rare earth oxide. In order to have the required gas permeability, it is preferred that the open porosity is in the range of 30% or more, in particular 35 to 50%, and the conductivity is also 300 S / cm or more, in particular 440 S / cm or more. Is preferred.

The fuel electrode layer 66 can be formed of a porous conductive ceramic, for example, ZrO ₂ (referred to as stabilized zirconia) in which a rare earth element is dissolved and Ni and / or NiO.

The solid electrolyte layer 68 has a function as an electrolyte for bridging electrons between the electrodes, and at the same time needs to have a gas barrier property in order to prevent leakage of fuel gas and oxygen-containing gas, Usually, it is formed from ZrO ₂ in which ₃ to 15 mol% of a rare earth element is dissolved.

The oxygen electrode layer 70 can be formed of a conductive ceramic made of a so-called ABO ₃ type perovskite oxide. The oxygen electrode layer 70 is required to have gas permeability, and the open porosity is preferably 20% or more, particularly preferably in the range of 30 to 50%.

Although the interconnector 72 can be formed from a conductive ceramic, it needs to have reduction resistance and oxidation resistance in order to contact the fuel gas and the oxygen-containing gas. For this reason, the lanthanum chromite perovskite type is required. An oxide (LaCrO ₃ -based oxide) is preferably used. The interconnector 72 must be dense to prevent leakage of fuel gas passing through the fuel gas passage 74 formed in the electrode support substrate 64 and oxygen-containing gas flowing outside the electrode support substrate 64, and 93% As described above, it is particularly desirable to have a relative density of 95% or more.

  The current collecting member 76 can be composed of a member having an appropriate shape formed from an elastic metal or alloy, or a member obtained by adding a required surface treatment to a felt made of metal fiber or alloy fiber.

In each of the cell stacks 60a, 60b, 60c and 60d, at the oxygen electrode,
1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte)
The electrode reaction of
O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻
The electrode reaction is generated and power is generated. As a result, an output current is taken out.

  Off-gas and oxygen-containing gas that have flowed upward from the cell stacks 60a, 60b, 60c and 60d without being used for power generation are appropriately burned by ignition means. As is well known, due to power generation and gas combustion, the power generation / combustion chamber becomes a high temperature of about 750 ° C., for example.

  Referring to FIG. 3B, the cell structure of the portion where the oxygen concentration measurement reference electrode 3 is provided is different from that of FIG. 3A only in that the oxygen concentration measurement reference electrode 3 is arranged instead of the oxygen electrode layer. The size of the reference electrode 3 for measuring the oxygen concentration is sufficient as long as it can cover the position to be measured and can provide a measurable voltage output. Is much smaller. The oxygen concentration measurement reference electrode 3 is installed near the outlet of the fuel gas passage 74, that is, downstream of the fuel gas. Therefore, also in the oxygen concentration measurement reference electrode 3, an electrode reaction similar to the electrode reaction at the oxygen electrode occurs. However, the output extracted from the oxygen concentration measurement reference electrode 3 is not a current signal but a voltage signal. By inputting this voltage signal to the gas calculation control unit 11 of FIG. 1, various gas flow rates are controlled. The output voltage of the oxygen concentration measuring reference electrode 3 reflects the oxygen concentration in the fuel gas passage 74 at the installation position. That is, since the oxygen concentration is considered to be substantially constant around the cell 62 because the oxygen-containing gas is abundantly supplied from the oxygen-containing gas introduction portion, the fuel gas passage 74 is leaked to the fuel electrode 66 side. This change in oxygen concentration appears as a change in the output voltage of the reference electrode 3 for measuring oxygen concentration.

  The application of the oxygen concentration measurement reference electrode in the present invention is not limited to the fuel cell having the structure shown in the drawing. For example, the present invention can be applied to a cell having a structure in which no electrode support substrate is provided, a cell in which a fuel electrode and an oxygen electrode are provided in reverse, and a cell having a different shape. In any fuel cell structure, a reference electrode for taking out the difference in oxygen concentration between the fuel electrode side and the oxygen electrode side as a voltage output may be attached on the solid electrolyte. The reference electrode is preferably formed of the same material as the fuel electrode and / or the oxygen electrode.

In the case of a solid oxide fuel cell, water vapor (H ₂ O) is generated on the fuel electrode side by an electrode reaction. Since the potential of the oxygen concentration measurement reference electrode 3 changes depending on the ratio of the water vapor, the ratio can be obtained. Now you can calculate the ratio of water vapor / hydrogen and find out how much fuel gas is consumed. For reference, a graph of water vapor ratio and electromotive force is shown in FIG. This is a general formula called the Nernst equation. The gas calculation control unit 11 in FIG. 1 adjusts the flow rate of the fuel gas so that this value becomes constant, thereby enabling operation with a constant fuel utilization rate.

  FIG. 3C is a cross-sectional view of a cell showing another embodiment of the present invention. In this embodiment, a temperature sensor 5 is further provided in the vicinity of the oxygen concentration measurement reference electrode 3 of the embodiment shown in FIG. 3B. The temperature sensor 5 measures the temperature of the oxygen concentration measurement reference electrode 3. By inputting the output of the temperature sensor 5 to the gas calculation control unit 11 of FIG. 1, the gas calculation control unit 11 corrects the influence of the temperature on the output voltage of the oxygen concentration measurement reference electrode 3 and derives an accurate output voltage. To do. Thereby, even if temperature changes, the oxygen concentration measurement by the oxygen concentration measurement reference electrode 3 can be accurately performed. The temperature sensor 5 does not need to be specially arranged only for the oxygen concentration measurement reference electrode 3 and can be replaced by another temperature sensor generally provided in the fuel cell. In that case, if the relationship between the output of the substitute temperature sensor and the temperature at the installation position of the oxygen concentration measurement reference electrode 3 is measured in advance, the oxygen concentration measurement reference electrode 3 is calculated from the output of the substitute temperature sensor. The temperature can be derived.

  FIG. 5 is a schematic perspective view of a power generation unit 56a showing still another embodiment of the present invention. The fuel gas F1 flows from the lower side to the upper side in the fuel gas passage such as the cell 62-1. On the other hand, the oxygen-containing gas F2 is supplied to the periphery of the cell by the oxygen-containing gas introduction pipe 21. The oxygen concentration measurement reference electrode 3 and the temperature sensor 5 are provided in the vicinity of the upper end of the cell 62-1 at the foremost position. As another example, another oxygen concentration measurement reference electrode 3a may be provided in the vicinity of the lower end of the cell. Thereby, the oxygen concentration in the vicinity of the inlet of the fuel gas passage, that is, the upstream side of the fuel gas can be measured. Thus, by providing another reference electrode 3a, the oxygen concentration distribution can be measured. For example, a plurality of oxygen concentration measurement reference electrodes 3a-1 to 3a-n are provided along the direction of the fuel gas passage for the cell 62-3 at the last position of the cell stack.

  The temperature distribution can be measured by providing a plurality of temperature sensors 5 along the direction of the fuel gas passage.

  As an example, the oxygen concentration measurement reference electrode 3 and / or the temperature sensor 5 may be provided in the cell 62-2 in the middle position of the cell stack. In other words, the oxygen concentration measurement reference electrode can be provided at any position of any cell in the cell stack as needed, and the oxygen concentration of the fuel gas passage at that position can be measured.

(3) DC Current Sensor The DC current sensor 4 shown in FIG. 1 is a sensor for measuring the current of DC power that is the output from the fuel cell 2. This sensor includes a so-called shunt resistor and a sensor using a Hall element. In either case, a direct current is converted into a voltage and further amplified and captured as a current value. The shunt resistor uses a characteristic in which a current is passed through a constant resistance and the voltage is proportional to the current, and the Hall element uses the Hall effect. Other than this, any DC current can be measured, and there is no particular limitation.

(4) Gas Supply System The gas supply unit 12 in the gas supply system 1 shown in FIG. 1 includes a water (water vapor) supply unit (not shown) in addition to the fuel gas supply unit 12a and the oxygen-containing gas supply unit 12b. Yes.

  The gas calculation control unit 11 of the gas supply system 1 basically reads the output voltage from the oxygen concentration measurement reference electrode 3 and measures the oxygen concentration in the fuel gas passage. More preferably, the measurement of the oxygen concentration is corrected based on the output from the temperature sensor 5. The gas calculation control unit 11 issues a command to the gas supply unit 12 so that the difference in oxygen concentration between the fuel electrode side and the oxygen electrode side becomes constant. For example, when the oxygen concentration in the fuel gas passage increases, the oxygen concentration is relatively lowered by increasing the gas flow rate from the fuel gas supply unit 12a to increase the fuel gas concentration in the fuel gas passage. Thus, the oxygen concentration difference between the two electrodes is returned to a predetermined value. Alternatively, by increasing the gas flow rate from the oxygen-containing gas supply unit 12b and increasing the oxygen-containing gas concentration outside the cell, the oxygen concentration difference between the two electrodes is returned to a predetermined value. Preferably, the control by the fuel gas supply unit 12a is first performed, and then the control by the oxygen-containing gas supply unit 12a is switched to or used together as a subsequent step. In this way, operation with a constant fuel utilization rate is possible.

  Further, the gas calculation control unit 11 determines that the oxygen concentration in the off-gas exceeds a preset value based on the output voltage of the oxygen concentration measurement reference electrode (that is, the oxygen concentration difference between the fuel electrode side and the oxygen electrode side is preset). A safety device is provided to stop the fuel cell system when it is smaller than Thereby, the fatal damage of the whole system can be prevented to the minimum.

  Further, the gas calculation control unit 11 is configured to increase the difference in oxygen concentration between the fuel electrode side and the oxygen electrode side when the output current of the fuel cell is smaller than a preset value based on the detection signal of the direct current sensor. The gas flow rate from the gas supply unit and / or the oxygen-containing gas supply unit is controlled. This is because the fuel cell generally has a tendency to deteriorate the utilization factor when the current is small, so that a constant utilization factor operation is realized.

  Here, although referred to as the gas calculation control unit 11, other control functions of the fuel cell 2, such as valve opening / closing, temperature measurement, gas leak detection, fire detection, pump operation, power management of various devices, A state notification function of the fuel cell 2 may be included.

It is a block diagram which simplifies and shows the solid oxide fuel cell system of the present invention. 1 is a perspective view schematically showing a main part of a fuel cell according to the present invention. It is X sectional drawing of FIG. 2 which shows the structure of the cell in this invention in detail. It is Y sectional drawing of FIG. 2 which shows the structure of the cell in this invention in detail. It is a figure of another Example corresponded in Y sectional drawing of FIG. 2 which shows the structure of the cell in detail in this invention. It is a graph of water vapor ratio and electromotive force (output voltage) of a reference electrode for measuring oxygen concentration. It is a schematic perspective view of the electric power generation unit which shows another Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas supply system 2 Fuel cell 3, 3a, 3a-1,. . 3a-n Reference electrode for measuring oxygen concentration 4 DC current sensor 5 Temperature sensor

Claims (7)

A fuel cell in which a solid electrolyte layer is sandwiched between a fuel electrode layer and an oxygen electrode layer, a fuel gas passage provided along the solid electrolyte layer, and an oxygen-containing gas introduction unit for introducing an oxygen-containing gas A fuel cell system comprising: a solid oxide fuel cell comprising: a gas supply system that supplies a plurality of gases to the solid oxide fuel cell;
An oxygen concentration measurement reference electrode formed as an electrode of the solid electrolyte layer in the vicinity of the outlet of the fuel gas passage;
The gas supply system comprises: a fuel gas supply means for supplying fuel gas to the fuel cell; an oxygen-containing gas supply means for supplying an oxygen-containing gas to the fuel cell; and the oxygen concentration measurement reference electrode. A fuel cell system comprising: a fuel gas supply unit and / or a control unit that controls a flow rate of each gas from the oxygen-containing gas supply unit based on an output voltage.   2. The fuel cell system according to claim 1, wherein the oxygen concentration measurement reference electrode is formed of the same material as the fuel electrode layer or the oxygen electrode layer.   The fuel cell system according to claim 1, wherein a temperature sensor is provided in the vicinity of the oxygen concentration measurement reference electrode.   The control means controls the gas flow rate from the fuel gas supply means so that the oxygen concentration in the fuel gas passage becomes a preset value based on the output voltage of the oxygen concentration measurement reference electrode. The fuel cell system according to claim 1.   The control means includes a safety device that stops the fuel cell system when an oxygen concentration in the fuel gas passage exceeds a preset value based on an output voltage of the oxygen concentration measurement reference electrode. The fuel cell system according to any one of claims 1 to 4, wherein A direct current sensor for detecting an output current from the fuel cell;
6. The fuel cell system according to claim 1, wherein the control unit controls a gas flow rate from the fuel gas supply unit based on a signal from the direct current sensor.   A fuel cell in which a solid electrolyte layer is sandwiched between a fuel electrode layer and an oxygen electrode layer, a fuel gas passage provided along the solid electrolyte layer, and an oxygen-containing gas introduction unit for introducing an oxygen-containing gas And a reference electrode for measuring oxygen concentration formed as an electrode of the solid electrolyte layer in the vicinity of the outlet of the fuel gas passage.

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