JP5185589B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel gas supply system.

  In the fuel cell system, in order to prevent dust contained in the fuel gas or oxidant gas from adhering to the humidifier and deteriorating the humidifying performance, or from adhering to the valve and causing biting, malfunctions can be prevented. A filter is installed in the supply path and the oxidant gas supply path to remove dust (see, for example, Patent Document 1).

In the case of a vehicular fuel cell system, a fuel tank (hydrogen tank) is mounted on the vehicle. When the fuel tank is filled with hydrogen at a hydrogen station, the fuel tank is filled with high pressure, and when generating electricity with the fuel cell stack, the fuel tank. The hydrogen is reduced to a predetermined pressure by a regulator and supplied to the fuel cell stack.
JP 2007-109555 A

By the way, a compressor is generally used when the fuel tank is filled with hydrogen at a high pressure in the hydrogen station, but when the pressure of the hydrogen is increased by the compressor, a very small amount of the lubricating oil of the compressor is mixed into the hydrogen. Turned out to be. When oil is supplied to the fuel cell stack, the fuel cell stack is adversely affected.
However, it has been difficult to completely remove oil with a conventional filter for removing dust.

  Therefore, the present invention provides a fuel cell system that can reliably remove oil from fuel gas.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 is a fuel cell stack (for example, a fuel cell stack 1 in an embodiment to be described later) that is supplied with fuel gas and an oxidant gas to generate power, and a fuel that supplies fuel gas to the fuel cell stack. A gas supply path (for example, an anode gas supply path 23 in an embodiment described later) and a circulation path for circulating the fuel exhaust gas discharged from the fuel cell stack to the fuel gas supply path (for example, an anode in an embodiment described later) An off-gas flow path 29), an ejector provided between the circulation path and the fuel gas supply path (for example, an ejector 28 in an embodiment to be described later), and a fuel gas tank for supplying fuel gas to the fuel gas supply path ( For example, in a fuel cell system provided with a hydrogen tank 21) in an embodiment described later, a fuel gas upstream of the ejector. A first pressure reducing means (for example, a primary regulator 22 in an embodiment to be described later) and a second pressure reducing means (for example, a secondary regulator 26 in an embodiment to be described later) are provided in the gas supply path, The second pressure reducing means is installed downstream of the first pressure reducing means in the fuel gas supply path, and an oil filter (for example, an oil filter in an embodiment described later) is provided in the fuel gas supply path between the second pressure reducing means and the ejector. 27), the fuel gas is hydrogen gas, the first decompression means decompresses the fuel gas to a pressure higher than a critical pressure, and the second decompression means includes the fuel gas system in the operating region of the fuel cell system. The fuel gas is reduced to a pressure equal to or lower than the critical pressure.
By comprising in this way, the oil in fuel gas can be removed reliably.
In addition, since the oil filter is provided in the fuel gas flow path upstream of the ejector, the dried fuel gas can be circulated through the oil filter, the pressure loss in the oil filter can be kept low, and the oil filter Freezing can be prevented.

In addition, if the pressure of the fuel gas exceeds the critical pressure, the fuel gas becomes a supercritical fluid, and the oil becomes a dissolved state in the fuel gas, so it passes through the oil filter and the oil cannot be removed. By configuring as described above, the pressure reducing means reduces the pressure of the fuel gas to a pressure lower than the critical pressure in the operation region of the fuel cell system, so that the pressure of the fuel gas flowing through the oil filter becomes lower than the critical pressure. The oil can be separated from the fuel gas, and the oil can be removed by the oil filter.

  According to the first aspect of the present invention, since the fuel gas not containing oil can be supplied to the fuel cell stack, the fuel cell stack is not damaged by the oil. In addition, pressure loss in the oil filter can be kept low, and freezing in the oil filter can be prevented.

Further, in the operation region of the fuel cell system, the fuel gas from which the oil has been removed can be supplied to the fuel cell stack, and the fuel cell stack can be prevented from being damaged by the oil.

  Embodiments of the fuel cell system according to the present invention will be described below with reference to the drawings of FIGS. In addition, the fuel cell system in this embodiment is an aspect that is mounted on a fuel cell vehicle and is used as a power source for a traveling motor.

  The fuel cell stack 1 is a type that obtains electric power by chemically reacting a reaction gas. For example, a solid polymer electrolyte membrane made of a solid polymer ion exchange membrane or the like is sandwiched from both sides by an anode electrode and a cathode electrode, and a membrane electrode structure And a plurality of cells each having an anode gas channel 3 and a cathode gas channel 5 are stacked on both sides of the membrane electrode structure. The anode gas channel 3 has an anode gas (fuel gas). ) And gas containing oxygen as cathode gas (oxidant gas) is supplied to the cathode gas flow path 5, hydrogen ions generated by a catalytic reaction at the anode electrode pass through the solid polymer electrolyte membrane. Then, it moves to the cathode and generates electricity by causing an electrochemical reaction with oxygen at the cathode, generating water. Part of the generated water generated on the cathode side permeates the solid polymer electrolyte membrane and back diffuses to the anode side, so that the generated water also exists on the anode side. In FIG. 1, the anode gas channel 3 and the cathode gas channel 5 of a single cell are shown as representatives.

  Cathode gas (air) is pressurized to a predetermined pressure by a compressor (oxidant gas supply source) 7 such as a supercharger, and passes through a cathode gas supply channel (oxidant gas supply channel) 9 and a humidifier 11 to form a fuel cell stack. 1 cathode gas flow path 5 is supplied. After the cathode gas supplied to the fuel cell stack 1 is used for power generation, it is discharged from the fuel cell stack 1 together with the generated water on the cathode side into the cathode offgas flow path 13 as the cathode offgas, passes through the humidifier 11, and passes through the back pressure valve 15. Is introduced into the diluting device 35. The humidifier 11 includes, for example, a water permeable membrane. When the cathode gas and the cathode off gas are circulated with the water permeable membrane interposed therebetween, moisture contained in the cathode off gas permeates the water permeable membrane and becomes the cathode. It moves to gas and the cathode gas is humidified.

  On the other hand, the anode gas (hydrogen gas) supplied from the hydrogen tank (fuel gas tank) 21 includes a primary regulator 22, an anode gas supply channel (fuel gas supply channel) 23, a secondary regulator (decompression means) 26, an oil filter. 27, is supplied to the anode gas flow path 3 of the fuel cell stack 1 through the ejector 28.

The primary regulator 22 is directly connected to the header of the hydrogen tank 21, and depressurizes the hydrogen filled in the hydrogen tank 21 at a high pressure to a first predetermined pressure P1.
The secondary regulator 26 is installed downstream of the primary regulator 22 in the anode gas supply flow path 23, and the pressure of the anode gas supplied from the primary regulator 22 depends on the operating state of the fuel cell stack 1 ( In other words, the pressure is reduced to the second predetermined pressure P2 (in accordance with the load state of the fuel cell stack 1).
The oil filter 27 is installed downstream of the secondary regulator 26 in the anode gas supply flow path 23, and removes oil (oil) in the anode gas.
The ejector 28 is installed downstream of the oil filter 27 in the anode gas supply flow path 23, and the anode gas is supplied to the anode gas flow path 3 of the fuel cell stack 1 through the ejector 28.

Then, the anode gas that has not been consumed in the fuel cell stack 1 is discharged from the fuel cell stack 1 as an anode off-gas (fuel exhaust gas), sucked into the ejector 28 through the anode off-gas passage (circulation passage) 29, and supplied to the hydrogen tank. The fresh anode gas supplied from 21 is merged and supplied again to the anode gas flow path 3 of the fuel cell stack 1.
That is, the ejector 28 is provided between the anode gas supply channel 23 and the anode off-gas channel 29 (in other words, the junction). The oil filter 27 is provided in the anode gas supply channel 23 between the secondary regulator 26 and the ejector 28.

  An anode offgas discharge channel 33 having a discharge valve 31 branches off from the anode offgas channel 29. The discharge valve 31 is normally closed during power generation of the fuel cell stack 1 and opens when a predetermined purge condition is satisfied to introduce the anode off gas into the diluter 35. The anode off gas discharged from the discharge valve 31 is diluted by the cathode off gas discharged from the back pressure valve 15 in the dilution device 35.

  The hydrogen tank 21 is filled with hydrogen gas at an initial filling pressure P0 at a hydrogen station. Usually, in order to increase the hydrogen filling efficiency of the hydrogen tank 21, the initial filling pressure P0 is extremely high, for example, set to 35 MPaG (gauge pressure, hereinafter the same). Since the high-pressure hydrogen gas charged in the hydrogen tank 21 cannot be directly supplied to the fuel cell stack 1, the pressure is first reduced to the first predetermined pressure P 1 by the primary regulator 22, and further, by the secondary regulator 26. The pressure is reduced to a second predetermined pressure P2 corresponding to the operating state of the fuel cell stack 1 and supplied to the fuel cell stack 1 via the ejector 28.

  By the way, the flow rate characteristic of the ejector 28 is generally proportional to the supply pressure as shown in FIG. 3 when the supply flow rate and the differential pressure are constant. Here, the circulation flow rate is the anode off-gas flow rate flowing into the ejector 28 from the anode off-gas flow path 29, and the supply flow rate and supply pressure are the anode gas flow rate and anode gas pressure supplied from the secondary regulator 26 to the ejector 28, respectively. Yes, the differential pressure is the pressure difference between the supply pressure and the anode gas pressure at the outlet of the ejector 28.

Therefore, in order to increase the circulation capacity of the ejector 28, it is advantageous that the supply pressure to the ejector 28 is higher. That is, from the viewpoint of the circulation capacity of the ejector 28, it is better that the anode gas pressure after the pressure reduction of the secondary regulator 26 is higher.
However, in this fuel cell system, an oil filter 27 is provided downstream of the secondary regulator 26 in order to remove the oil contained in the anode gas. There is an upper limit to the anode gas pressure after depressurization of the next regulator 26. This will be described below.

  In some cases, oil is contained in the hydrogen gas filled in the hydrogen tank 21 by, for example, filling the hydrogen tank 21 with high pressure using a compressor at the hydrogen station. When this oil is supplied to the fuel cell stack 1, the fuel cell stack 1 is damaged, so an oil filter 27 is provided.

  By the way, as shown in FIG. 2, the substance takes three states of solid-liquid-gas depending on temperature and pressure conditions. Furthermore, each substance has a temperature and pressure unique to each substance called a critical point, and a state exceeding this critical point is called a supercritical state. In the supercritical state, no matter how much the gas is compressed, it does not become liquid but only the density increases, and it becomes a supercritical fluid comparable to liquid. A supercritical fluid has a solubility that easily dissolves a substance like a liquid and a high diffusibility like a gas.

  Therefore, when the hydrogen gas is a supercritical fluid, the oil is in a state dissolved in the hydrogen gas, and even if the hydrogen gas of the supercritical fluid is passed through the oil filter 27, the oil cannot be removed and passes through. . In order to remove the oil in the anode gas with the oil filter 27, hydrogen gas in a non-supercritical state must be passed through the oil filter 27. Here, the critical point of hydrogen is a critical temperature of minus 240 degrees and a critical pressure of 1.2 MPaG.

  The operating temperature range of the fuel cell stack 1 is higher than the critical temperature, and it is unrealistic to lower the temperature below the critical temperature to escape from the supercritical state. Therefore, in order to remove the oil in the anode gas with the oil filter 27, it is necessary to reduce the anode gas pressure to the critical pressure or less with the secondary regulator 26. That is, the upper limit value of the anode gas pressure after the secondary regulator 26 is depressurized is the critical pressure.

  Therefore, in this embodiment, the anode gas pressure after depressurization by the primary regulator 22 is set to 1.5 MPaG, which is higher than the critical pressure, and the anode gas pressure higher than this critical pressure is set to the critical pressure by the secondary regulator 26. The pressure is reduced to 1.1 MPaG or less, and the anode gas pressure in the anode gas supply channel 23 downstream of the secondary regulator 26 is 1.1 MPaG or less in the operating range of the fuel cell system. . In other words, the secondary regulator 26 always reduces the anode gas to a pressure equal to or lower than the critical pressure in the operation region of the fuel cell system.

By setting the outlet side pressures of the primary regulator 22 and the secondary regulator 26 in this way, the following operational effects are exhibited.
In the anode gas supply flow path 23 upstream of the secondary regulator 26, the anode gas pressure is higher than the critical pressure, so that even if oil is mixed in the anode gas, oil precipitation is small. As a result, the influence of oil on the operation of the device in the flow path can be extremely reduced.

  On the other hand, in the anode gas supply flow path 23 on the downstream side of the secondary regulator 26, the anode gas pressure is equal to or lower than the critical pressure, so the anode gas becomes a non-supercritical fluid, and oil is mixed in the anode gas. In this case, oil precipitates, and the oil can be reliably removed by the oil filter 27. Therefore, anode gas not containing oil can be supplied to the fuel cell stack 1, and damage to the fuel cell stack 1 due to oil can be prevented in advance.

  Further, the anode gas pressure on the downstream side of the secondary regulator 26 is a pressure close to the critical pressure while being equal to or lower than the critical pressure, and the pressure can be used as the supply pressure to the ejector 28. The capacity can be maximized and the circulation flow rate can be increased.

  The pressure reduction by the secondary regulator 26 is set to a pressure slightly higher than the critical pressure, and the anode gas pressure downstream of the ejector 28 is set to be equal to or lower than the critical pressure due to the pressure drop in the ejector 28 so that the ejector 28 and the fuel cell are reduced. The oil in the anode gas can also be removed by the oil filter 27 by providing an oil filter between the inlet of the stack 1. However, in this case, since the anode gas flowing into the oil filter 27 includes a high-humidity anode off-gas that is discharged from the fuel cell stack 1 and circulates through the anode off-gas passage 29, the oil filter 27 is humidified. The anode gas in the state will flow. When the humidified anode gas flows into the oil filter 27 in this way, the pressure loss in the oil filter 27 becomes large, which is disadvantageous, and the water may freeze in the oil filter 27 below the freezing point.

  On the other hand, when the oil filter 27 is disposed between the secondary regulator 26 and the ejector 28 and the anode gas is reduced below the critical pressure by the secondary regulator 26 as in this embodiment, the hydrogen tank Since only the dried anode gas supplied from 21 flows to the oil filter 27, it is advantageous in that the pressure loss in the oil filter 27 can be reduced, and the possibility of freezing in the oil filter 27 is extremely small.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, in the above-described embodiment, the anode gas is reduced to 1.1 MPaG or less by the secondary regulator 26. However, if the pressure on the outlet side of the secondary regulator 26 is less than the critical pressure, the pressure is particularly limited to 1.1 MPaG. Is not to be done.
Further, the initial filling pressure P0 to the hydrogen tank 21 is not limited to 35 MPaG, and the pressure P1 after the pressure reduction by the primary regulator 22 is not limited to 1.5 MPaG .

It is a block diagram which shows an example of the fuel cell system which concerns on this invention. It is a state figure (temperature-pressure diagram) of a substance. It is a flow characteristic figure of a general ejector.

Explanation of symbols

1 Fuel cell stack 21 Hydrogen tank (fuel gas tank)
22 Primary regulator (first decompression means)
23 Anode gas supply channel (fuel gas supply channel)
26 Secondary regulator ( second decompression means)
27 Oil filter 28 Ejector 29 Anode off-gas flow path (circulation path)

Claims (1)

A fuel cell stack that is supplied with fuel gas and oxidant gas to generate power; and
A fuel gas supply path for supplying fuel gas to the fuel cell stack;
A circulation path for circulating the fuel exhaust gas discharged from the fuel cell stack to the fuel gas supply path;
An ejector provided between the circulation path and the fuel gas supply path;
A fuel gas tank for supplying fuel gas to the fuel gas supply path;
In a fuel cell system comprising:
A first pressure reducing means and a second pressure reducing means for reducing the pressure of the fuel gas are provided in the fuel gas supply path upstream of the ejector, and the second pressure reducing means is installed downstream of the first pressure reducing means in the fuel gas supply path. An oil filter is provided in the fuel gas supply path between the second pressure reducing means and the ejector,
The fuel gas is hydrogen gas;
The first decompression means depressurizes the fuel gas to a pressure higher than a critical pressure,
The fuel cell system, wherein the second decompression means decompresses the fuel gas to a pressure equal to or lower than a critical pressure in an operation region of the fuel cell system.

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