JP2013105634A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system that makes maintenance work easier than conventional fuel cell systems and that, in the event of leakage of a check valve or the like, prevents emission of fuel gas to the exterior.SOLUTION: A fuel cell system 1 includes: a fuel cell 7; a reformer 8 that reforms fuel gas into anode reactant gas; a fuel gas supply path 5 through which fuel gas is supplied to the reformer 8; a cathode air supply path 3 through which air is supplied to the fuel cell 7; and a reforming air guide path 6 that guides the air into the fuel gas supply path 5. The air to pass through the cathode air supply path 3 and the reforming air guide path 6 is guided thereinto through a shared common inlet.

Description

  The present invention relates to a fuel cell system. The present invention is particularly suitable for a fuel cell system using a solid oxide fuel cell.

  A fuel cell is known as a power generation module. In this fuel cell, chemical energy generated by a chemical reaction between fuel (for example, hydrogen or methane) and air (oxygen) can be directly extracted as electric energy without performing heat conversion treatment. There is an advantage that the energy conversion efficiency is high compared with the generator using the engine.

  Among the fuel cells, solid oxide fuel cells (SOFC) have a higher temperature (operating temperature) suitable for operation (700 degrees Celsius to 1,000 degrees Celsius) than other fuel cells. Therefore, it is excellent in that it is not necessary to use an expensive platinum catalyst and that a reformed gas can be used.

The SOFC is a battery stack including a single cell (so-called single cell) formed by an anode (fuel electrode), a cathode (oxygen electrode), a solid oxide electrolyte sandwiched between the anode and the cathode, and a plurality of single cells. Composed.
Explaining the basic power generation principle of SOFC, oxygen reacts with electrons at the cathode to become oxide ions, and the oxide ions pass through the solid oxide electrolyte and react with hydrogen at the anode to generate water vapor and electrons. Further, carbon monoxide and oxide ions react at the anode to generate carbon dioxide and electrons. This solid oxide electrolyte passes oxide ions but does not pass water vapor, carbon monoxide, or electrons. Therefore, the electrons generated at the anode move in the external circuit connecting the anode and the cathode, reach the cathode, and oxygen is ionized again at the cathode, whereby a current flows through the external circuit.

  By the way, hydrogen and carbon monoxide supplied to the anode of SOFC can be obtained by reforming a fuel such as city gas, methanol, gasoline, propane gas, etc. with a reformer.

Conventionally, when reforming is performed, a partial oxidation reforming method (POX: Partial Oxidation Reforming) is performed until the SOFC starts up to a certain high temperature range (for example, 500 degrees Celsius or higher) (hereinafter also referred to as startup operation). ), Auto-thermal reforming (ATR), steam reforming (SR), and steam reforming (SR). After reaching a high temperature range (for example, 500 degrees Celsius or higher), steam reforming ( SR) only.
That is, since the reaction used in the steam reforming method is an endothermic reaction, the reaction is unlikely to occur unless the temperature is within a certain range. Therefore, until the SOFC starts up and reaches a certain high temperature range (for example, 500 degrees Celsius or higher), the three reforming methods are combined to form a hydrogen-rich condition, and the temperature is set using a burner or the like. It is rising.

Specifically, the following reaction (1) occurs when the partial oxidation reforming method (POX) is used, and the following reaction (2) occurs when the autothermal reforming method (ATR) is used, and the steam reforming method (SR). When is used, the following reaction (3) occurs.

  That is, since the partial oxidation reforming method (POX) and the autothermal reforming method (ATR) are used until reaching a high temperature range (500 degrees Celsius or higher), it is necessary to mix the fuel gas with air (oxygen). is there. Therefore, in a conventional fuel cell system using SOFC, a path for supplying air (oxygen) to the fuel cell from the outside (hereinafter also referred to as air supply path) and a path for supplying fuel gas to the fuel cell (hereinafter referred to as fuel gas) And a path for introducing reformed air into the fuel gas path (hereinafter also referred to as a reforming air path) is connected separately (for example, Patent Document 1). ).

JP 2011-76846 A

  For example, in the fuel cell system of Patent Document 1, auxiliary equipment such as an intake filter, a reforming air blower, a buffer tank, a flow sensor, a shut-off valve, and a check valve is provided in the reforming air path. . The air mixed with the fuel gas is introduced from the intake filter, passes through the reforming air blower, the buffer tank, the flow rate sensor, the shut-off valve, and the check valve, and is introduced into the fuel gas path.

  However, as described above, when the temperature reaches a high temperature range (500 degrees Celsius or higher) and SOFC power generation starts, only the steam reforming method is performed. That is, in the steam reforming reaction, only the fuel gas and steam react as shown in the reaction formula (3), and air (oxygen) does not participate in the reaction. Therefore, during the SOFC power generation, the above reforming air path is used. do not use.

  That is, during SOFC power generation, only the fuel gas is supplied to the downstream side (fuel gas path side) of the reforming air path, and the upstream side (reforming air blower side) of the reforming air path is Because it is not sucking air, it is atmospheric pressure. In other words, the reforming air path has a negative pressure relative to the fuel gas path. Therefore, if leakage occurs in the shut-off valve and the check valve during power generation of the SOFC, the fuel gas supplied into the fuel cell flows backward, and the fuel gas is discharged from the intake filter to the outside through the reforming air path. There was a fear.

  Further, since the reforming air path is provided separately from the air supply path, an intake filter must be attached to each of the paths although the supply gas is both air. Therefore, maintenance work for the intake filter must be performed separately, and workability is poor.

  Therefore, the present invention solves the above-mentioned problems, and improves the workability during maintenance work as compared with the prior art, and even if a check valve or the like leaks, fuel gas is discharged to the outside. An object of the present invention is to provide a fuel cell system capable of preventing this.

  The invention described in claim 1 for solving the above-described problems includes a fuel cell, a reformer for reforming the fuel gas into an anode reaction gas of the fuel cell, and a fuel gas for supplying the reformer with the fuel gas A supply path; a cathode air supply path for supplying air as a cathode reaction gas to the fuel cell; and a reforming air introduction path for supplying air used for reforming connected to the reformer or the fuel gas supply path; The reforming air introduction path is provided with reforming air intake means for taking in air into the reforming air introduction path, and the cathode air supply path has Cathode air intake means for taking in air is provided in the cathode air supply path, and the air introduced into the cathode air supply path and the reforming air introduction path is introduced from the same air introduction section. Is a fuel cell system characterized.

According to the configuration of the present invention, the air introduced into the cathode air supply path and the reforming air introduction path is introduced from the same air introduction section. That is, since the same air introduction part is used, it is not necessary to provide an intake filter in each of the reforming air introduction path and the cathode air supply path as in the prior art. Therefore, the cost for the intake filter can be reduced. Further, since the space for providing the intake filter can be omitted, the entire fuel cell system can be saved. Furthermore, since the air introduction part of the reforming air introduction path and the air supply path are the same, maintenance work such as replacement of the intake filter can be performed at the same time. That is, the time required for the maintenance work can be shortened, and the workability of the maintenance work is improved as compared with the conventional case.
Further, during power generation of the fuel cell, in the cathode air supply path, air as the cathode reaction gas is sucked from the air introduction unit by the cathode air intake means. Therefore, even if fuel gas leaks to the stop valve and the check valve during power generation of the fuel cell and the fuel gas flows back to the reforming air introduction path, the same air introduction part is used. The fuel gas flowing backward is sucked into the cathode air supply path at the air introduction portion. Therefore, it can prevent discharging from the air introduction part to the outside.

  According to a second aspect of the present invention, a check valve is provided between the air introduction part and the reforming air intake means, and the check valve is used for reforming from the air introduction part. The fuel cell system according to claim 1, wherein the fuel cell system allows distribution toward the air intake means.

  According to the configuration of the present invention, since the check valve enables the flow from the air introduction part toward the reforming air intake means, the backflow from the reforming air intake means side is prevented. can do. Therefore, it is less likely to flow backward from the fuel gas supply path side to the air introduction part side as compared with the conventional fuel cell system. In addition, when air is not flowing through the reforming air introduction path, even if dust or the like accumulates in the intake filter or the like of the air introduction section and becomes clogged, the suction force of the cathode air intake means It is possible to prevent the air in the reforming air introduction path from being taken into the cathode air supply path through the air introduction unit.

  According to the configuration of the present invention, since the cathode air supply path and the air introduction part of the reforming air introduction path are shared, the workability of the maintenance work is improved as compared with the conventional case, for example, a check valve or the like. Even if leakage occurs, the fuel gas can be prevented from being discharged to the outside.

It is an operation principle figure showing the fuel cell system concerning a 1st embodiment of the present invention. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1 and shows a cathode air supply path in black. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1 and a fuel gas supply path in black. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1 and shows a reforming air introduction path in black. It is a perspective view showing the air introduction part of FIG. 1, and has shown the flow of air with the arrow. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1, and is a diagram showing the flow of air and fuel gas at the start-up operation by arrows. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1, and is a diagram showing the flow of air and fuel gas at the time of power generation operation by arrows. FIG. 2 is an operation principle diagram of the fuel cell system of FIG. 1, and is a diagram showing the flow of combustion gas with arrows when it is assumed that the stop valve and the check valve are damaged. It is a top view showing the air introduction part of FIG. 8, and the flow of the fuel gas which flowed backward from the air introduction path | route for reforming is shown by the arrow. It is an operation principle figure used as a reference example of the fuel cell system of the present invention.

The fuel cell system 1 according to the first embodiment of the present invention will be described below.
As shown in FIG. 1, the fuel cell system 1 of the present invention includes a fuel cell module 2, a cathode air supply path 3, a fuel gas supply path 5, a reforming air introduction path 6, and an air introduction unit 20. ing.

The fuel cell module 2 includes at least a fuel cell 7, a reformer 8, and a temperature sensor 10 in a module housing 11. Further, a heating device such as a burner (not shown) is provided in the module housing 11.
The fuel cell 7 is not particularly limited, but an intermediate temperature or high temperature operation type fuel cell is preferable from the viewpoint that self-heating can be used for reforming. The medium temperature or high temperature operation type here refers to a fuel cell having an operation temperature of 500 degrees Celsius or higher. Examples of the medium temperature or high temperature operation type fuel cell include a molten carbonate fuel cell (MCFC) and a solid oxide fuel cell. In the present embodiment, a solid oxide fuel cell will be described.
The reforming device 8 is the same as a known device, and is a reforming device capable of reforming a fuel gas into an anode reaction gas. In the present embodiment, the fuel gas can be reformed to at least hydrogen and carbon monoxide.
The temperature sensor 10 is a sensor that senses the temperature inside the module housing 11, and is specifically a thermocouple.

The cathode air supply path 3 is a flow path that connects the air introduction unit 20 and the fuel cell module 2 as shown in black in FIG. 2. The cathode air supply path 3 is a fuel cell in the module housing 11. 7 is connected to the cathode.
The cathode reaction gas is a gas used as a reaction carrier at the cathode of the fuel cell 7 when the fuel cell 7 generates power, and specifically air.
The cathode air supply path 3 includes a cathode blower 12 (cathode air intake means), a flow rate sensor 15 and a flow sensor 15 in order from the upstream side in the air flow direction (air introduction unit 20 side) to the downstream side (fuel cell 7 side). A check valve 16 is provided.
The cathode blower 12 is a known booster blower and can control the flow rate of air.
The flow sensor 15 is a known flow sensor, and is a sensor that detects the flow rate of air passing through the cathode air supply path 3.
The check valve 16 is a known check valve, and is provided to prevent air from flowing backward from the fuel cell module 2 side. That is, it is possible to circulate from the upstream side in the air flow direction (air introduction unit 20 side) to the downstream side (fuel cell module 2 side).

Turning to the fuel gas supply path 5, the fuel gas supply path 5 is a flow path that connects the fuel gas introduction part 21 and the fuel cell module 2 as shown in black in FIG. It is a flow path through which gas passes. The fuel gas supply path 5 is connected to the reformer 8 in the module housing 11.
The fuel gas is a gas that is reformed by the reformer 8, and is a gas containing at least carbon in its composition. For example, city gas, propane gas, etc. are adopted.
The fuel gas supply path 5 has a flow rate adjusting unit 22, a flow rate sensor 23, and a desulfurizer 25 in order from the upstream side (fuel gas introduction unit 21 side) to the downstream side (reforming device 8 side) in the fuel gas flow direction. And a check valve 27 is provided.
The flow rate adjusting unit 22 is a part that adjusts the flow rate of the fuel gas, and is formed by combining a valve 61, a governor 62, a booster blower 63, and a buffer tank 64.
The flow sensor 23 is a known flow sensor, and is a sensor that detects the flow rate of the fuel gas passing through the fuel gas supply path 5.
The desulfurizer 25 is a known desulfurizer and is a device that removes sulfide components from the fuel gas.
The check valve 27 is a known check valve, and is provided to prevent fuel gas or the like from flowing back from the fuel cell module 2 side. That is, distribution from the upstream side in the fuel gas flow direction (fuel gas introduction part 21 side) to the downstream side (fuel cell module 2 side) is possible.

Turning to the reforming air introduction path 6, the reforming air introduction path 6 is a flow path that connects the air introduction unit 20 and the fuel gas supply path 5 as shown in black in FIG. 4. .
The reforming air introduction path 6 is connected downstream of the fuel gas supply path 5 in the fuel gas flow direction of the desulfurizer 25 and upstream of the check valve 27.
The reforming air introduction path 6 has a check valve 30 and a reforming air blower 31 (in order from the upstream side in the air flow direction (air introduction unit 20 side) to the downstream side (fuel gas supply path 5 side). Reforming air intake means), a flow sensor 32, a shut-off valve 33, and a check valve 35 are provided.
The reforming air blower 31 is a known booster blower and can control the flow rate of the reforming air.
The flow rate sensor 32 is a known flow rate sensor, and is a sensor that detects the flow rate of air passing through the reforming air introduction path 6.
The check valves 30 and 35 are known check valves, and are provided to prevent gas (including air) from flowing back from the fuel cell module 2 side. That is, gas (including air) can be circulated from the upstream side in the flow direction of the reforming air (air introduction unit 20 side) to the downstream side (fuel gas supply path 5 side).
The closing valve 33 is a known electromagnetic valve that is opened when energized.

Turning to the air introduction unit 20, the air introduction unit 20 is formed by partitioning a housing 50 having an opening 53 in one direction by a filter unit 51 as shown in FIG. 5. The cathode air supply path 3 and the reforming air introduction path 6 are connected in parallel in the width direction w to the inner wall 55 facing the opening 53 and the filter portion 51. A predetermined gap is provided between the inner wall 55 and the filter part 51, and an inner wall of the housing 50 and a space 52 closed by the filter part 51 are formed. That is, the cathode air supply path 3 and the reforming air introduction path 6 open to the inner wall 55 and communicate with the space 52 of the housing 50.
The filter unit 51 is a combination of a known cloth, activated carbon, or the like, and removes dust, dust, and the like from the air passing through the filter unit 51.

Next, the operation in the normal operation mode of the fuel cell system 1 of the present embodiment will be described. Note that the normal operation of the fuel cell system 1 of the present embodiment is almost the same as that of a known technique, and therefore the flow of air and fuel gas during the operation is only briefly described.
The fuel cell system 1 according to the present embodiment is divided into a start-up operation after starting and reaching a high temperature region (500 degrees Celsius or higher) and a power generation operation after reaching the high temperature region.

In the starting operation, air and / or fuel gas flows through the cathode air supply path 3, the fuel gas supply path 5, and the reforming air introduction path 6. That is, in the cathode air supply path 3, as shown by the arrow in FIG. 6, air is introduced from the air introduction unit 20 by the suction force of the cathode blower 12 and supplied to the cathode of the fuel cell 7 through the check valve 16. Is done.
In the fuel gas supply path 5, as indicated by the arrow in FIG. 6, the fuel gas is introduced from the air introduction unit 20 by the flow rate adjustment unit 22 and passes through the desulfurizer 25. On the other hand, in the reforming air introduction path 6, air is introduced from the air introduction unit 20 by the suction force of the reforming air blower 31, passes through the check valves 30 and 35, and the stop valve 33, and passes through the fuel gas supply path. 5 is introduced. Then, the fuel gas and air are mixed at the connection portion 36 between the fuel gas supply path 5 and the reforming air introduction path 6. Thereafter, the mixed gas passes through the check valve 27 and reaches the reforming device 8 inside the module housing 11, reformed by the reforming device 8 as described above, and supplied to the anode of the fuel cell 7. Is done.

On the other hand, in the power generation operation, as shown in FIG. 7, air or fuel gas flows through the cathode air supply path 3 and the fuel gas supply path 5, and air and fuel gas do not flow through the reforming air introduction path 6. . In other words, the reforming air introduction path 6 is closed by stopping the reforming air blower 31 and closing the closing valve 33.
In the fuel gas supply path 5, as shown by the arrows in FIG. 7, the fuel gas is introduced from the fuel gas introduction part 21 by the flow rate adjustment part 22, passes through the desulfurizer 25, and the connection part with the reforming air introduction path 6. At 36, the air is not mixed with air, passes through the check valve 27 and reaches the reformer 8. Then, as described above, it is reformed by the reformer 8 and supplied to the anode of the fuel cell 7.
The above is a description of the flow of air and fuel gas during the operation.

  Incidentally, as described above, air and fuel gas do not flow through the reforming air introduction path 6 in the power generation operation. Therefore, for example, in the fuel cell system 100 including the air introduction portions 101 and 102 in the cathode air supply path 3 and the reforming air introduction path 6 as shown in FIG. The inside is at atmospheric pressure, and the reforming air introduction path 6 has a negative pressure relative to the fuel gas supply path 5. That is, when a leak occurs in the check valve 35 and the stop valve 33, a part of the fuel gas introduced from the fuel gas introduction part 21 does not flow to the fuel cell module 2 side but flows to the reforming air introduction path 6 side. There was a fear. When flowing toward the reforming air introduction path 6, the anode reaction gas stays in the fuel cell 7, and the reaction proceeds in a deficient state of the anode reaction gas, so that the fuel cell 7 may be overloaded. .

Therefore, the fuel cell system 1 of the present embodiment has a function of detecting a failure of the check valve 35, the closing valve 33, and the check valve 30.
In the fuel cell system 1 of the present embodiment, the backflow of the fuel gas does not occur in principle because the backflow is prevented by the check valve 35, the closing valve 33, and the check valve 30 during power generation. Therefore, assuming that the check valve 35, the shutoff valve 33, and the check valve 30 are damaged due to external factors, the check valve 35, the shutoff valve 33, and the check valve 30 that are characteristic functions are broken down. The function to detect is demonstrated in detail using drawing.

The flow of the fuel gas when the check valve 35, the stop valve 33, and the check valve 30 are out of order will be described.
First, as shown by the arrows in FIG. 8, most of the fuel gas introduced from the fuel gas introduction section 21 and passing through the desulfurizer 25 in the fuel gas supply path 5 flows toward the reforming air introduction path 6. Then, it passes through the reforming air blower 31 and the check valve 30 and reaches the air introduction unit 20.
Here, during power generation, since the cathode blower 12 continues to suck the cathode air supply path 3 side, the fuel gas discharged into the space 52 of the air introduction unit 20 is discharged by the cathode blower 12 as shown in FIG. The air is sucked into the cathode air supply path 3.
Then, as indicated by the arrows in FIG. 8, the fuel gas sucked into the cathode air supply path 3 passes through the cathode blower 12 and the check valve 16 and reaches the fuel cell 7. In the module housing 11, the fuel gas is mixed and burned with air, causing abnormal combustion. When the temperature sensor 10 (abnormality detection means) senses a temperature increase of 10% or more with respect to the normal power generation temperature in the module housing 11, the operation of the fuel cell 7 is controlled to stop. More specifically, if the normal power generation temperature in the module housing 11 is 700 degrees Celsius to 800 degrees Celsius, it is recognized as abnormal when a temperature of 900 degrees Celsius or higher is detected, and the operation of the fuel cell 7 is stopped. So that it is controlled.

According to the fuel cell system 1, leakage of the check valve 35, the close valve 33, and the check valve 30 can be detected by detecting abnormal combustion that occurs in the module housing 11.
Further, according to the fuel cell system 1, the fuel gas discharged into the space 52 of the air introduction unit 20 is sucked into the cathode air supply path 3 by the cathode blower 12, so that the fuel gas is discharged outside the fuel cell system 1. Will not leak. That is, the fuel cell system 1 can be safely stopped.

According to the fuel cell system 1, when abnormal combustion is detected, the operation of the fuel cell 7 is stopped. Accordingly, it is possible to prevent the anode reaction gas from staying in the fuel cell 7 and the reaction from proceeding under the anode reaction gas deficiency state.
Further, according to the fuel cell system 1, during the power generation operation, even if dust or the like accumulates in the filter unit 51 of the air introduction unit 20 and clogging occurs, the fuel cell system 1 is used for reforming by the suction force of the cathode blower 12. It is possible to prevent the air in the air blower 31 from being taken into the cathode air supply path 3 through the air introduction unit 20.

  In the above-described embodiment, the temperature sensor 10 is used as the abnormality detection means, and the breakage of the valve is detected by the temperature change due to the abnormal combustion, but the present invention is not limited to this, and the output of the fuel cell is monitored, An abnormality may be detected by a change in the output per unit time of the fuel cell, and the valve breakage may be detected. For example, when a decrease in output of 5% or more with respect to the normal average output of the fuel cell is detected and the output continues to decrease for a predetermined time or longer, the operation of the fuel cell 7 is stopped. It is preferable that

DESCRIPTION OF SYMBOLS 1 Fuel cell system 3 Cathode air supply path 5 Fuel gas supply path 6 Reformation air introduction path 7 Fuel cell 8 Reformer 12 Cathode blower (cathode air intake means)
20 Air Introducing Unit 30 Check Valve 31 Reforming Air Blower (Reforming Air Intake Unit)

Claims (2)

Fuel cell, reformer for reforming fuel gas to anode reaction gas of fuel cell, fuel gas supply path for supplying fuel gas to reformer, cathode air for supplying air as cathode reaction gas to fuel cell A fuel cell system having a supply path and a reforming air introduction path for supplying air used for reforming connected to a reformer or a fuel gas supply path,
The reforming air introduction path is provided with reforming air intake means for taking air into the reforming air introduction path,
The cathode air supply path is provided with cathode air intake means for taking air into the cathode air supply path,
The fuel cell system, wherein the air introduced into the cathode air supply path and the reforming air introduction path is introduced from the same air introduction section. A check valve is provided between the air introduction part and the reforming air intake means,
2. The fuel cell system according to claim 1, wherein the check valve allows circulation from the air introduction portion toward the reforming air intake unit.

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