JPH04133271A - Fuel cell - Google Patents

Abstract

PURPOSE:To prevent a fuel cell from deteriorating by detecting an output of power generation of a fuel cell, regulating a gas quantity generated from an oxidizing agent gas controlling means and the opening degree of an intake port of the atmosphere corresponding to a generating current, and controlling oxygen content in oxidizing agent gas. CONSTITUTION:When oxygen content in an oxidizing agent gas is made high, it is necessary to start voltage control from a larger current value than that at the time when the ordinary atmosphere is fed. When the oxygen content enters such a region, a gas quantity generated from an oxygen enriching device 6 and an intake quantity of the atmosphere from an air intake port 63 are regulated by a controller 61, the oxygen content in the oxidizing agent gas to be fed into an oxidizing agent pole 13 is controlled, and a current region of voltage control which is performed by a means sending a current to a dummy load is made as small as possible, so as to make the oxygen content correspond to the current value. Since the oxygen content of oxygen-rich gas from the device 6 is made of constant value, the device 6 is regulated only for a flow rate of the generated gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the structure of a fuel cell that uses a fuel and an oxidizing agent and generates electricity through the reaction of these.

[Prior Art] A fuel cell has a power generation unit in which fuel electrodes and oxidizer electrodes are stacked alternately with an electrolyte and a separator in between, and generates electricity by supplying fuel and oxidizer to each electrode plate. It is a general term for things, and is classified into several types depending on the constituent materials, but from a practical standpoint, phosphoric acid fuel cells that use phosphoric acid as an electrolyte have reached technological perfection.

A system diagram of a conventional example of this phosphoric acid fuel cell is shown in FIG. 3, and the configuration of the power generation section is shown in FIG. 4.

This conventional example includes a power generation section 1, a reformer 2 for producing a fuel gas containing hydrogen as a main component to be supplied to the power generation section 1 from a raw material gas, and a burner 3 for operating the reformer 2 at a high temperature.
and a blower 4 which sends air to the gas 3 and also sends air as an oxidizing gas to the oxidizing electrode 13 of each cell of the power generation section 1, and a blower 4 which sends air to the raw material gas when producing the fuel gas. It has a steam generator 5 that supplies water vapor to be mixed.

The power generation section 1 is composed of a large number of cells (single cells) in which a fuel electrode 11 and an oxidizer electrode 13 are arranged with an electrolyte 14 in between, or a large number of cells are stacked with a separator 15 interposed therebetween, and a cooling plate is provided for each certain number of cells. 12, and each pole 11.13 is provided with an electrical output section 16. The cooling plate 12 is supplied as cooling water with water supplied from the water supply line 51 or through the steam generator 5 and the cooling water line 52, and after passing through the cooling plate 12, some of the cooling water becomes steam. It becomes water vapor in the generator 5. At this time, the heat collected by the power generation section 1 is used as heat necessary for steam generation. A raw material gas is supplied to the reformer 2 through a raw material gas supply line 21, and steam from the steam generator 5 is mixed into this raw material gas through a steam supply line 53. As a result, the raw material gas is reformed by the reformer 2 into a gas whose main component is hydrogen gas, such as methane gas, and this gas is uniformly sent to the fuel electrodes 11 of each cell through the fuel supply line 22. Extracted gas from the fuel electrode 11 of each cell is supplied as fuel to the burner 3 through the fuel gas exhaust line 31, and unreacted hydrogen in the exhaust gas is combusted with air from the blower 4. Blower 4 also serves as a blower for reaction air.
Air is supplied to the oxidizer electrode 13 of each cell of the power generation section 1 through an air supply line 41, and air after the reaction is discharged through an air discharge line 42.

As mentioned above, conventional phosphoric acid fuel cells use hydrogen obtained by reforming raw material gas as fuel, and use oxygen as an oxidizing agent, or use air as the oxygen source. has been done. In addition, the temperature of the power generation section 1 is approximately 190
Electrical energy is obtained through the reaction of hydrogen and oxygen under these temperature conditions. The power generation efficiency at this time was approximately 40%.

[Problem to be solved by the invention] By the way, in the above-mentioned fuel cell, if the conversion efficiency from the energy contained in the fuel to electrical energy is improved, the unit cost of power generation will be reduced, and as a result, the cost of power generation will be reduced. Therefore, improving the efficiency of fuel f-'+ batteries has become one of the important issues to be considered.

One effective measure for improving efficiency is increasing the oxygen partial pressure in the reaction air. Increasing the oxygen partial pressure means increasing the oxygen concentration itself in the oxidant gas, and in this case, the oxygen partial pressure increases from Pl to P,
The rise in the t4 voltage of a single cell when the voltage rises to t4 is expressed by the following equation (1).

Based on this equation (1), the voltage increase rate when an oxidant gas with an oxygen concentration of 50% is supplied is calculated.

If the atmosphere is used as is and the oxygen utilization rate is 50%, the amount of oxygen at the outlet is 10.5% in terms of the inlet, and the partial pressure of oxygen at the outlet is 0.09 considering the partial pressure of the water vapor produced.
5 atm, and the average oxygen partial pressure inside the oxidizer plate is 0153
It becomes atmospheric pressure. On the other hand, if the oxygen concentration at the inlet is 50% and the oxygen utilization rate is 20%, the amount of oxygen at the outlet is 40% at the inlet.
%, the oxygen partial pressure will be 0363 atm, and the average oxygen partial pressure within the oxidizer plate will be 0743 atm. Therefore, the voltage increase value and voltage increase rate per unit cell due to increasing the oxygen concentration are determined as follows. Note that the voltage per cell set of a phosphoric acid fuel cell under normal operating conditions is approximately 0.65 V, and that value is used here.

Voltage rise value (per cell set) △V=103・log=46.22
mV voltage increase rate 0.046+ 0.65 =
io7 times 0.65 In this way, increasing the oxygen concentration increases the average oxygen partial pressure between the inlet and the outlet, making it possible to increase the output of the fuel cell.

Incidentally, the output characteristics of a fuel cell are expressed by current (current density)-voltage (single cell output voltage) characteristics as shown in FIG. This current-voltage characteristic shows the output characteristics of a conventional fuel cell when an oxidant gas with a high oxygen concentration is supplied to the fuel cell, and (a) for comparison, air is directly supplied to the oxidizer electrode. In this case, (b) is the case where a gas with a high oxygen concentration is supplied. As is clear from this figure, when the oxygen concentration is increased, the output characteristic curve shifts to the higher voltage side overall. On the other hand, if we look at the normal operating conditions of fuel cells,
The upper limit of the current density is about 200 mA/cm', and it is used in the range below this. One of the reasons for this
The first reason is that even if the current density is increased excessively, the voltage will drop, so the output will not increase much, and the efficiency will not be good. On the other hand, when the current density is low, the output voltage of the cell increases, but there is an upper limit to the cell voltage in use due to the characteristics of the battery. This limit is greatly manifested in the rise in cell voltage, especially in the voltage rise at the oxidizer electrode, and this rise in voltage at the oxidizer electrode leads to elution of the catalyst dispersed on the electrode plate and corrosion of the carphone, which is the substrate of the electrode. Therefore, it was established to prevent this. Such a limit voltage in a phosphoric acid fuel cell is said to be 0.8V.

As mentioned above, there is an upper limit to the current density of fuel cells! Therefore, a lower limit also exists. Therefore, a pseudo load is usually installed at the output section of the fuel cell, and when the current flowing to the external load becomes small and the current density is likely to drop below the limit value, the power generation This increases the current and causes a current in excess of the load requirement to flow through this pseudo load, preventing the cell's output voltage from becoming excessively high. When a fuel cell is in operation, the discharge current is normally Since the output is often set close to the rated output, there is little need to take such measures. However, in standby conditions or when the output is low, such measures become necessary.

When an oxidant gas with increased oxygen concentration is fed into a fuel cell, the output voltage of the fuel cell increases as described above. In conventional fuel cells, there is only one blower, and this one
The blower 4 on the stand sends air to the burner 3 and also to the oxidizer electrode 13 in the power generation section 1, and it is not possible to increase only the oxygen concentration of the gas sent to the oxidizer electrode 13. There wasn't. Even if the air flow path to the burner 3 and the flow path to the oxidizer electrode 13 were separated and a dedicated flow path was provided for each, it would be impossible to simply feed the oxidizer gas with a higher oxygen concentration. With this configuration, when used in areas with low current density, the generated current will be increased as before, and if the current exceeds the required amount of the load, it will be passed through this pseudo load to increase the current density and increase the voltage. There is no other way than to let it fall. However, this method is only intentionally generating electricity at a value higher than the required current, and if the output is low or in standby mode, this means that fuel is wasted unnecessarily. This is a serious drawback from the viewpoint of the overall efficiency of the fuel cell.

The present invention was devised to improve these drawbacks, and aims to improve the efficiency of the fuel cell by increasing the oxygen concentration. An object of the present invention is to provide a fuel cell that prevents deterioration of the fuel cell by adjusting oxygen concentration and suppresses waste of fuel.

[Means for Solving the Problems] The structure of the fuel cell of the present invention for achieving the above object is as follows: a power generation section is constructed by stacking a large number of cells each consisting of a fuel electrode, an oxidizer electrode, and an electrolyte, and the fuel electrode supply fuel gas to
In a fuel cell that generates electricity by supplying an oxidizing gas to the oxidizing electrode, an oxidizing gas having an oxygen concentration higher than that of normal air is prepared at the entrance of an oxidizing gas supply passage to the oxidizing electrode; In addition to connecting the oxidant gas preparation means to be supplied, a normal atmospheric intake port is also provided, and the generated output from the oxidant gas preparation means is detected according to the generated current by detecting the power generation output of the fuel cell. The present invention is characterized in that it includes a control unit that adjusts the amount of oxygen and the degree of opening of the air intake port, and the oxygen concentration in the oxidant gas can be controlled according to the power generation output of the fuel cell.

[Function] The present invention increases the oxygen concentration by supplying an oxidant gas with an oxygen concentration higher than that of normal air from the supply path of the oxidant gas to the power generation section of the fuel cell using an oxygen enrichment device. In addition to improving the efficiency of the fuel cell, when the generated current is small and the output voltage of the cells that make up the power generation section becomes high, this condition is detected and a system is installed in parallel at the entrance of the oxidizing gas supply passage. The control section adjusts the opening degree of the normal atmospheric air intake according to the condition, adjusts the oxygen concentration in the oxidant gas, lowers the output voltage, and prevents deterioration of the fuel cell. Reduce fuel wastage.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is an overall system diagram of a fuel cell showing the configuration of an embodiment of the present invention. In this embodiment, instead of the configuration in which air from one blower 4 is directly introduced into the oxidizer electrode 13 of each cell of the power generation section 1 together with the burner 3 as shown in the conventional example shown in FIG. The air supply channel for the oxidizer electrode 13 of the cell and the air supply channel for the burner 3 are separated, and the oxidizer electrode 1
In contrast to 3, both oxidizing gas containing oxygen at a higher concentration than normal air and normal air are taken in, and the oxygen concentration can be adjusted according to the power generation output. The configuration of the power generation section 1 in this embodiment is the same as that of the conventional example shown in FIG. As for the cooling water supply system, the structure of the steam supply system for the reformer 2 in the fuel supply system is also the same as that of the conventional example, and each element in FIG. 1 is given the same reference numeral as in FIG. 3. It is.

In this embodiment, the oxygen concentration of the oxidant gas containing high concentration of oxygen can be adjusted in accordance with the power generation output of the fuel cell.
3, the power generation section 1 is
At the oxidant gas supply inlet to the oxidant electrode 13 of each cell, an oxygen enrichment device 6 for preparing an oxidant gas containing oxygen at a higher concentration than normal air is installed and connected. An air intake port 63 for adjusting the concentration of the oxidant gas containing high concentration of oxygen from the device 6 and a blower 62 for blowing air to the air intake port 63 are installed, while the power generation section 1 A current detector 64 for the generated current for detecting the generated output is inserted into the electric output part 16 of the 16, and the opening degree of the air intake port 63 and the blower are adjusted according to the generated current detected by the current detector 64. A controller 61 is added to control the operation of -62.

The operation and effect of the embodiment configured as above will be described.

FIG. 2 is an output characteristic diagram for explaining the method of controlling the output voltage of the fuel cell in this example, and (a) is a current density-cell voltage output characteristic when air is supplied as it is to the oxidizer electrode. (b).

(c) and (d) have oxygen concentrations of 30% and 40%, respectively.
The current density-cell voltage output characteristics are shown when an oxidant gas of 50% is supplied. When an oxidant gas with a high oxygen concentration is supplied to the fuel cell, the output characteristics of the fuel cell depend on the oxidation concentration, as shown by the output characteristic curves in (b), (c), and (d). As increases, the output voltage (b).

(c), (d) become higher (here, (d)
will be explained as the characteristics at an oxygen concentration of 50% and an oxygen utilization rate of 20%). Therefore, when generating electricity with the same current,
The output power can be increased by the amount that the voltage has increased. However, as mentioned earlier, the output voltage of the cells in the power generation section is 0.8
In a state exceeding v, deterioration of the oxidizer electrode occurs. Therefore, conventionally, in order to prevent the output voltage of the cell from exceeding such a value, current was intentionally passed through a pseudo load to increase the current generated by the fuel cell and thereby lower the voltage.

By the way, when the oxygen concentration of the oxidant gas is increased, the output characteristic curve shifts upward as explained in FIG. 5. Therefore, the starting current value for such voltage control moves from 11 to 14, and it becomes necessary to start voltage control from a larger current value than when normal air is being introduced. Therefore, in this embodiment, when such a region is reached, the amount of gas generated from the oxygen enrichment chemical device 6 and the amount of atmospheric air taken in from the air intake port 63 are adjusted so that the oxygen concentration corresponds to the current value. The controller 61 adjusts the oxygen concentration in the oxidizing gas fed to the oxidizing electrode 13 so that the current range of the voltage control performed by passing current through the pseudo load is made as small as possible. There is.

The specific relationship between the oxygen concentration in the supplied oxidant gas and the generated current when controlling the output voltage of the fuel cell in the above is as shown in FIG.

In this figure, the region where the current density is low is enlarged and displayed. As shown by curve (d), when the oxygen concentration is increased to 50%, the output voltage of the fuel cell increases from point DD to point D along curve (d) as the output current decreases. do. Therefore, at this point, measures are taken to suppress the voltage increase, and the oxygen concentration is adjusted as described above.

However, when switching from an oxidant gas with a high oxygen concentration to normal atmosphere in a short period of time, the output voltage transiently and rapidly decreases from point D to point AA, causing a large fluctuation in the output of the fuel cell. Therefore, in order to prevent such voltage fluctuations, in this embodiment, when the output voltage reaches point D, from then on,
The oxygen concentration is controlled so that the voltage shifts along the C-B-A path. Specifically, the curve (C) in Figure 2 is the voltage characteristic for an oxygen concentration of 40%, and the curve (b) is for an oxygen concentration of 3
Assuming the voltage characteristics for 0%, at the 0 point the oxygen concentration or 4
The flow rate of generated gas from the oxygen enrichment device 6 and the amount of air from the air intake port 63 are controlled so that the current density is 0% and 30% at the 8th point, and the output voltage is gradually lowered as the current density decreases. There is. Incidentally, in the case of FIG. 2, the ratio of the gas flow rate from the oxygen enrichment device 6 to the atmospheric amount from the air intake port 63 is as shown in Table 1. Therefore, this table 1
All you have to do is adjust the flow rate of each gas according to the following. Note that here, since the oxygen concentration of the oxygen-enriched gas from the oxygen enrichment device 6 is set at a constant value of 50%, the oxygen enrichment device 6 only needs to adjust the flow rate of the generated gas.

(Below, blank space) Table 1 1 pressure! ■! Popularity of oxidizing gas at the time and flow rate ratio of generated gas for a given element enrichment device. However, * indicates the volume percentage of atmospheric air and oxygen-enriched gas in the oxidizing gas required at each current. .

Note that oxidant gas containing high concentration of oxygen can be obtained, for example, with an oxygen enrichment device using a gas separation membrane.
In a small fuel cell, it is also possible to obtain such an oxidant gas using, for example, an oxygen cylinder, and the means for adjusting such an oxidant gas is not limited to these devices. Any method that can obtain an oxidant gas of a predetermined concentration can be applied. In addition, in the above embodiment, the voltage control method was described using a phosphoric acid fuel cell as an example, but even if the type of fuel cell is changed, it is basically the same except that the control value such as the output voltage is changed. Applicable to As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

[Effects of the Invention] As is clear from the above explanation, according to the fuel cell of the present invention, the oxidant gas containing a larger amount of oxygen than the normal atmosphere prepared by a preparation means such as an oxygen enrichment device is used as fuel. By feeding it into the oxidizer electrode of the battery, it is possible to increase the power generated under normal operating conditions of the fuel cell, and on the other hand,
The opening degree of the air intake port attached to the oxidant gas supply port of the oxidizer electrode of the fuel cell and the amount of gas generated from the preparation means such as the oxygen enrichment device are adjusted according to the power generation output of the fuel cell. This makes it possible to control the oxygen concentration in the oxidizing gas, and when operating conditions are such that the current taken out from the fuel cell is small and the current density per unit area of the electrode is low, the oxygen concentration can be controlled. It is possible to reduce the amount of current flowing through the pseudo load in order to lower the voltage, and as a result, the overall amount of fuel used is reduced, reducing unnecessary waste and reducing the operating costs of the fuel cell itself. can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram showing the configuration of an embodiment of the present invention;
Fig. 2 is an output characteristic diagram for explaining the operation and effect of the above embodiment, Fig. 3 is a system diagram showing the configuration of the conventional example, and Fig. 4 is a diagram showing the configuration of the conventional example.
The figure is a schematic perspective view showing the configuration of the power generation section of the above conventional example.
FIG. 5 is an output characteristic diagram of the conventional example. 1... Power generation section, 6-Oxygen enrichment device,] 1... Fuel electrode,
13...Oxidizing agent electrode, J4...Electrolyte, 16.Electrical output section, 61...Controller, 62...Blower 16
3.Air intake, 64.Current detector. tri-degree Figure 5 ImA/cm2)

Claims (1)

[Claims] (1) A power generation unit is constructed by stacking a large number of cells consisting of a fuel electrode, an oxidizer electrode, and an electrolyte, and power generation is generated by supplying fuel gas to the fuel electrode and supplying oxidant gas to the oxidizer electrode. In the fuel cell, an oxidant gas preparation means is connected to the inlet of the oxidant gas supply passage to the oxidant electrode, and an oxidant gas preparation means for preparing and supplying an oxidant gas having an oxygen concentration higher than that of normal air is connected. a control unit that also includes an air intake port and detects the power generation output of the fuel cell and adjusts the amount of gas generated from the oxidizing gas preparation means and the opening degree of the air intake port in accordance with the generated current; A fuel cell, comprising: an oxygen concentration in the oxidizing gas can be controlled according to the power generation output of the fuel cell.