JP4519225B2 - Fuel cell system and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system using a hydrogen separation membrane and a control method thereof.
[0002]
[Prior art]
Currently, the fuel cell system being developed is mainly a polymer electrolyte fuel cell (PEFC) that generates electricity by reacting hydrogen with oxygen or air. Simultaneously with the stoppage, it is required that the power generation of the fuel cell stop.
In the case of a solid polymer electrolyte fuel cell, 1 mol of H ₂ reacts with 1/2 mol of O ₂ to produce 1 mol of H ₂ O.
As a result, the amount of hydrogen consumed on the fuel electrode side of the fuel cell is larger than the air (oxygen) on the oxidation electrode side of the fuel cell, and the pressure on the fuel electrode side is relatively reduced when the fuel cell system is stopped. Since it is greatly reduced, there is a problem that a large pressure difference is generated between the fuel electrode side and the oxidation electrode side sandwiching the electrolyte layer, and the cell components of the fuel cell are deteriorated.
[0003]
In order to eliminate these points, for example, in JP-A-7-272740, when the fuel cell system is stopped, the reaction gas (mainly hydrogen) in the fuel cell is changed to an inert gas (for example, N ₂ or the like) or the reaction. Japanese Laid-Open Patent Publication No. 11-111319 discloses a system for detecting the completion of substitution with an inert gas by a temperature sensor in order to prevent waste of the inert gas. Yes.
[0004]
In addition, the higher the concentration of hydrogen as the main component of the reaction gas used in the fuel cell, the higher the power generation efficiency of the fuel cell can be improved. As disclosed in Japanese Laid-Open Patent Application No. 4-121973, there is disclosed a system for supplying pure hydrogen gas obtained by purifying reformed gas using a hydrogen separation membrane and removing CO to a fuel cell.
[0005]
However, when a hydrogen separation membrane is applied to the fuel cell system, if the temperature is lowered in a hydrogen atmosphere, the hydrogen separation membrane deteriorates. Therefore, it is necessary to remove hydrogen from the hydrogen separation membrane when the fuel cell system is stopped. .
For this reason, when a hydrogen separation membrane is incorporated into a conventional fuel cell system (see Japanese Patent Laid-Open Nos. 7-272740 and 11-111319), hydrogen is supplied from both the reformed gas side and the permeate side of the hydrogen separation membrane. Since the fuel cell system must be removed, the fuel cell system becomes complicated and the cost increases.
In Japanese Patent Laid-Open No. 4-121973, sufficient consideration has not been given to stopping the power generation of the fuel cell simultaneously with the stop of the fuel cell system.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation, and an object of the present invention is to provide a hydrogen separation membrane that causes deterioration of the hydrogen separation membrane without using an inert gas when the fuel cell system is stopped. And a fuel cell system using a hydrogen separation membrane that can reliably and easily remove hydrogen and suppress the generation of a pressure difference between the electrodes of the fuel cell, which causes deterioration of the cell components of the fuel cell, and It is in providing the control method.
[0007]
[Means for Solving the Problems]
That is, according to the present invention, there is provided a fuel cell system that generates electric power by reacting hydrogen with oxygen or air, a reformer that generates reformed gas from fuel and air, and a reformer that is generated by the reformer. A hydrogen separation membrane that separates only hydrogen from the reformed gas, a hydrogen supply line that supplies purified hydrogen from the hydrogen separation membrane to the fuel cell, an air supply line that supplies air to the reformer, and a fuel cell An oxygen supply line for supplying oxygen or air to the fuel cell and a combustor connected to the hydrogen separation membrane and the exhaust line of the fuel cell, and when the fuel cell system is stopped, the supply of fuel to the reformer is stopped A fuel characterized by removing hydrogen on the reformed gas side and permeate side of the hydrogen separation membrane by closing the on-off valve of the hydrogen supply line and introducing air to the reformed gas side of the hydrogen separation membrane Battery system provided That.
At this time, when the fuel cell system is stopped, the supply of fuel to the reformer is stopped, the open / close valve of the hydrogen supply line is closed, and air is introduced to the reformed gas side of the hydrogen separation membrane, Hydrogen on the permeate side of the hydrogen separation membrane is preferably reversely permeated to the reformed gas side of the hydrogen separation membrane.
[0008]
In the present invention, it is preferable to replace the hydrogen in the fuel cell with air when the fuel cell system is stopped, so that the pressures on the fuel electrode side and the oxygen electrode side of the fuel cell are substantially equal. preferable.
[0009]
Further, according to the present invention, there is provided a control method for a fuel cell system using a hydrogen separation membrane that generates electricity by reacting hydrogen with oxygen or air, and reforming the hydrogen separation membrane when the fuel cell system is stopped. A fuel cell system characterized by removing hydrogen in a hydrogen separation membrane by introducing air to the gas side and reversely permeating hydrogen on the permeation side of the hydrogen separation membrane to the reformed gas side of the hydrogen separation membrane. A control method is provided.
[0010]
Furthermore, according to the present invention, there is provided a control method for a fuel cell system using a hydrogen separation membrane that generates electricity by reacting hydrogen with oxygen or air, wherein the hydrogen in the fuel cell is reduced when the fuel cell system is stopped. Hydrogen in the hydrogen separation membrane is replaced by air, introduced into the reformed gas side of the hydrogen separation membrane, and reversely permeated hydrogen on the permeation side of the hydrogen separation membrane to the reformed gas side of the hydrogen separation membrane. A control method for a fuel cell system is provided.
At this time, in the present invention, it is preferable to control the pressures on the fuel electrode side and the oxygen electrode side of the fuel cell to be substantially equal.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The fuel cell system of the present invention stops the supply of fuel to the reformer when the fuel cell system is stopped, closes the open / close valve of the hydrogen supply line, and supplies air to the reformed gas side of the hydrogen separation membrane. By introducing, hydrogen on the reformed gas side and permeate side of the hydrogen separation membrane is removed.
Thereby, when the fuel cell system is stopped, the hydrogen in the hydrogen separation membrane that causes deterioration of the hydrogen separation membrane can be reliably and easily removed, and the cell configuration of the fuel cell without using an inert gas It is possible to suppress the occurrence of a pressure difference between the two electrodes of the fuel cell that causes deterioration of the elements.
[0012]
Here, the main feature of the fuel cell system of the present invention is that, when removing hydrogen in the hydrogen separation membrane, the hydrogen remaining on the reformed gas side of the hydrogen separation membrane is replaced with air, so that the hydrogen separation membrane The hydrogen partial pressure on the reformed gas side is reduced, and the hydrogen on the permeate side of the hydrogen separation membrane is reversely permeated to the reformed gas side of the hydrogen separation membrane.
As a result, without introducing a purge line on the permeation side of the hydrogen separation membrane, it is only necessary to introduce air into the reformed gas side of the hydrogen separation membrane, so that the hydrogen separation membrane in the hydrogen separation membrane is deteriorated when the temperature is lowered. Hydrogen can be removed reliably and easily.
[0013]
In the fuel cell system of the present invention, it is preferable to replace hydrogen in the fuel cell with air when the fuel cell system is stopped.
As a result, when the fuel cell system is stopped, not only can the power generation of the fuel cell be stopped immediately, but also the generation of a pressure difference between the electrodes of the fuel cell (the fuel electrode and the oxidation electrode) that causes deterioration of the cell components of the fuel cell. Can be suppressed.
In addition, it is preferable to control so that the pressure of the fuel electrode side and the oxygen electrode side of a fuel cell may become substantially equal.
[0014]
Furthermore, the fuel cell system of the present invention preferably uses air instead of the inert gas as the replacement gas.
Thereby, since the cylinder which stores an inert gas is unnecessary, it can contribute to the weight reduction of a fuel cell system, and the reduction of a running cost.
[0015]
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of a fuel cell system of the present invention.
As shown in FIG. 1, an example of the fuel cell system of the present invention is a reformer 10 that generates reformed gas from fuel and air, and only hydrogen is separated from the reformed gas generated by the reformer 10. A hydrogen separation membrane 20, a hydrogen supply line 24 for supplying hydrogen purified from the hydrogen separation membrane 20 to the fuel cell 30, air supply lines 16 and 18 for supplying air to the reformer 10 and the fuel cell 30, hydrogen The separation membrane 20 and the combustor 40 connected to the exhaust lines 26 and 32 of the fuel cell 30 are provided.
The combustor 40 introduces excess hydrogen in the exhaust gas by introducing the exhaust gas from the reformer 10, the hydrogen separation membrane 20, and the fuel cell 30 into the combustion atmosphere of the reformed fuel and air. It treats oxygen and the like.
Further, the reformed fuel supply line 14 to the combustor 40 is not always necessary, and there is a problem if the operation temperature of the reformer 10 is maintained by combustion of the non-permeated gas of the reformed gas supplied from the exhaust line 26. Absent.
[0016]
Here, the fuel cell system described above is performed in the following procedure when the fuel cell system is stopped.
First, the first on-off valve 50 of the fuel supply line 12 is closed to stop the fuel supply to the reformer 10, and at the same time, the fifth on-off valve 54 of the hydrogen supply line 24 is closed to supply the fuel cell 30 to the fuel cell 30. Stop the hydrogen supply.
[0017]
Next, the fourth on-off valve 53 and the sixth on-off valve 55 are opened, air is introduced into the reformer 10 and the reformed gas side 21 of the hydrogen separation membrane 20, and the reformed gas in the reformer 10 is introduced. The functions of the reformer 10 and the fuel cell 30 are stopped by replacing the hydrogen in the hydrogen separation membrane 20 and the fuel cell 30 with air.
At this time, since the hydrogen partial pressure on the reformed gas side 21 of the hydrogen separation membrane 20 decreases, the hydrogen on the permeate side 22 of the hydrogen separation membrane 20 reversely permeates to the reformed gas side 21 of the hydrogen separation membrane 20. Hydrogen in the separation membrane 20 can be removed to a hydrogen partial pressure close to substantially zero.
The exhaust gas discharged from the reformer 10, the hydrogen separation membrane 20, and the fuel cell 30 is burned by the combustor 40 and then discharged out of the system.
[0018]
Finally, after the fourth on-off valve 53, the sixth on-off valve 55, and the seventh on-off valve 56 are closed, the second on-off valve 51 of the reformed fuel supply line 14 and the third on-off valve 52 of the air supply line 16 are turned on. The valve is closed, the combustor 40 is stopped, and the temperature of the fuel cell system is lowered.
[0019]
Each on-off valve 50 to 56, a fuel pump (not shown) connected to the fuel supply line 12, a reformed fuel pump (not shown) connected to the reformed fuel supply line 14, and an air supply line 16 , 18 are electrically connected to each other, and their operations are controlled by control means (not shown).
[0020]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not restrict | limited to these Examples.
(Example)
In order to verify the hydrogen removal method in the hydrogen separation membrane in the fuel cell system of the present invention, an experiment was conducted using the apparatus shown in FIG.
After the hydrogen separation membrane 60 was installed in the reaction tube 64 (stainless steel, internal volume: 0.5 l), the reaction tube 64 was heated to 400 ° C. in the electric furnace 62.
Next, the valve V1 is opened, and using the mass flow controller M1, 8 atmospheres (gauge pressure), 6 l / min methanol reforming simulation gas (hydrogen: 65%, carbon dioxide: 23%, carbon monoxide: 2%, Steam 10%) was fed into the reactor 64.
The supply gas line was heated to 130 ° C. with a ribbon heater so that water vapor was not condensed.
[0021]
At this time, the amount of permeated hydrogen was 3 l / min as a result of measurement with the flow meter M3, and the hydrogen recovery rate was 80%.
At the time of the above measurement, the valves V1, V3 and V4 were in an open state.
[0022]
Further, after operating the apparatus shown in FIG. 2 for 1 hour under the above experimental conditions, with the valve V4 opened, the valves V1 and V3 are closed, the valve V2 is opened, and the air is supplied with a gauge pressure of 0.2 atm. The mass flow controller M2 was introduced into the reactor 64 at 10 l / min.
At this time, when air was introduced into the reaction tube 64, as indicated by the pressure gauge P, the pressure on the permeate side of the hydrogen separation membrane 60 began to drop, and the absolute pressure reached almost 0 atm within 1 min.
[0023]
From the above, the hydrogen removal in the hydrogen separation membrane 60 significantly reduces the hydrogen partial pressure on the reformed gas side of the hydrogen separation membrane 60, and the hydrogen gas remaining at the atmospheric pressure on the permeation side of the hydrogen separation membrane 60. It was confirmed that this was performed by reversely permeating (concentration: approximately 99% or more) to the reformed gas side of the hydrogen separation membrane 60.
The hydrogen separation membrane used was a Pd thin film with a thickness of 5 μm formed by plating on the surface of an alumina porous substrate (pore diameter: 0.6 μm) having an outer diameter of 17 mm and a length of 100 mm.
[0024]
【The invention's effect】
The fuel cell system and the control method thereof according to the present invention reliably and easily remove hydrogen in the hydrogen separation membrane that causes deterioration of the hydrogen separation membrane without using an inert gas when the fuel cell system is stopped. In addition, it is possible to suppress the occurrence of a pressure difference between the two electrodes of the fuel cell, which causes deterioration of the battery components of the fuel cell.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a fuel cell system of the present invention.
FIG. 2 is a schematic diagram showing an example of an apparatus for removing hydrogen from a hydrogen separation membrane in the fuel cell system of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Reformer, 12 ... Fuel supply line, 14 ... Reformed fuel supply line, 16 ... Air supply line, 18 ... Air supply line (oxygen supply line), 20 ... Hydrogen separation membrane, 21 ... Reformed gas side ( (Hydrogen separation membrane), 22 ... permeate side (hydrogen separation membrane), 24 ... hydrogen supply line, 26 ... exhaust line, 30 ... fuel cell, 32 ... exhaust line, 40 ... combustor, 50 ... first on-off valve, 51 ... Second open / close valve, 52 ... third open / close valve, 53 ... fourth open / close valve, 54 ... fifth open / close valve, 55 ... sixth open / close valve, 56 ... seventh open / close valve, 60 ... hydrogen separation membrane, 62 ... electric furnace 64, reaction tubes, V1-V4, valves, M1-M2, mass flow controllers, M3, flow meters, P, pressure gauges.

Claims (7)

A fuel cell system that generates electricity by reacting hydrogen with oxygen or air,
A reformer that generates reformed gas from fuel and air; and
A hydrogen separation membrane for separating only hydrogen from the reformed gas generated by the reformer;
A hydrogen supply line for supplying hydrogen purified from the hydrogen separation membrane to the fuel cell;
An air supply line for supplying air to the reformer;
An oxygen supply line for supplying oxygen or air to the fuel cell;
A combustor connected to the hydrogen separation membrane and the exhaust line of the fuel cell;
When stopping the fuel cell system, the supply of fuel to the reformer is stopped, the open / close valve of the hydrogen supply line is closed, and air is introduced into the reformed gas side of the hydrogen separation membrane, A fuel cell system for removing hydrogen on a reformed gas side and a permeate side of a hydrogen separation membrane. When the fuel cell system is stopped, the supply of fuel to the reformer is stopped, the open / close valve of the hydrogen supply line is closed, and air is introduced into the reformed gas side of the hydrogen separation membrane , thereby 2. The fuel cell system according to claim 1, wherein hydrogen on the permeate side is reversely permeated to the reformed gas side of the hydrogen separation membrane.   The fuel cell system according to claim 1 or 2, wherein hydrogen in the fuel cell is replaced with air when the fuel cell system is stopped.   4. The fuel cell system according to claim 3, wherein pressures on the fuel electrode side and the oxygen electrode side of the fuel cell are made substantially equal. A control method for a fuel cell system using a hydrogen separation membrane that generates electricity by reacting hydrogen with oxygen or air,
When the fuel cell system is stopped, air is introduced into the reformed gas side of the hydrogen separation membrane, and hydrogen on the permeate side of the hydrogen separation membrane is reversely permeated to the reformed gas side of the hydrogen separation membrane, thereby A method for controlling a fuel cell system, comprising removing hydrogen. A control method for a fuel cell system using a hydrogen separation membrane that generates electricity by reacting hydrogen with oxygen or air,
When the fuel cell system is stopped, the hydrogen in the fuel cell is replaced with air, air is introduced into the reformed gas side of the hydrogen separation membrane, and the hydrogen on the permeate side of the hydrogen separation membrane is replaced with the reformed gas side of the hydrogen separation membrane. A method for controlling a fuel cell system, wherein hydrogen in the hydrogen separation membrane is removed by reverse permeation into the fuel cell.   The control method for a fuel cell system according to claim 6, wherein the pressures on the fuel electrode side and the oxygen electrode side of the fuel cell are controlled to be substantially equal.

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