JPS61273872A - Fuel cell - Google Patents

Abstract

PURPOSE:To make as low as possible the poisoning of an electrode catalyst due to carbon monoxide included in a reformed gas, by disposing the fuel gas feed passages of each unit cell in a good state. CONSTITUTION:The concentration of carbon monoxide included in a reformed gas, which is used as fuel, the temperature of a fuel cell and the fall in the output of the cell are shown in the drawing. Separation plates 2 are provided on both the sides of a unit cell 1. A plurality of tunnels 5 for a coolant are provided in the inner portion of each of the separation plates 2. Other tunnels 3, 4 are provided over and under the tunnels 5 perpendicularly across them so that the tunnels 3, 4 function as fuel gas passages. A fuel gas inlet port and a fuel gas outlet port are provided near a coolant inlet port and a coolant outlet port, respectively, so that the temperature of the fuel gas near the fuel gas outlet port, at which the concentration of carbon monoxide is high because of the consumption of hydrogen, is higher than that of the fuel gas near the fuel gas inlet port. As a result, the fall in the output of the fuel cell due to the carbon monoxide is suppressed to be low.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

This invention is aimed at, for example, a phosphoric acid fuel cell, which generates electricity by reforming coal, petroleum, natural gas, methanol, or other hydrocarbon-based raw materials, and using the resulting hydrogen-rich reformed gas as fuel. , particularly regarding the fuel gas supply method.

[Prior art and its problems]

As is well known, in this type of fuel cell, a cell stack is constructed by laminating a large number of unit cells each consisting of an electrolyte layer and a pair of electrodes, an anode and a cathode, facing each other with the electrolyte layer in between. The hydrogen-rich reformed gas described above is supplied to the anode side of each unit cell, and air or oxygen as an oxidizing agent is supplied to the cathode side, thereby generating electricity through the cell reaction. By the way, this type of fuel cell can obtain higher output characteristics as its operating temperature is higher, but on the other hand, it is difficult to increase the operating temperature too high due to the corrosion resistance of the cell components including the fuel cell main body. In general, operation is carried out by limiting the operating temperature to 200°C or less, and in order to obtain a practical current within this operating temperature range, the anode,
The cathode ゛,゛(:・(Usually, a noble metal catalyst such as platinum is added to the electrodes 2' and 2' to promote the cell reaction at each electrode.):1,・□ On the other hand, as mentioned above, the fuel supplied to the fuel cell is: 1. □゛・The hydrogen gas is a hydrocarbon-based raw material that is reformed in a steam reformer. hydrogen lynch reformed gas obtained by

[5□ G'('> ・ is used. This reformed gas is mainly composed of hydrogen, and also contains carbon dioxide and a trace concentration of carbon monoxide, Of these, the carbon oxide component is known to have a poisoning effect that reduces the activity of the electrode catalyst. As shown in Figure 9, the lower the operating temperature of the fuel cell and the higher the concentration, the greater the effect, lowering the cell's output.Furthermore, the amount of decrease in output depends on the operating temperature. □ The reformed gas supplied to the anode side tends to increase in a quadratic curve, and since hydrogen is consumed by the cell reaction, the reaction gas □゛ discharge side of the fuel cell shows a tendency to increase in a quadratic curve. The concentration of carbon monoxide is relatively high compared to the above.Here, to give an example, for example, if the component is hydrogen 80 SO1%
, carbon dioxide 19 mo1%, -carbon oxide 1 mo1
% of reformed gas is supplied to the fuel cell, and if 80% of the hydrogen is consumed inside the fuel cell due to power generation, the gas components on the gas discharge side of the fuel cell will be 44% hydrogen, 53% carbon dioxide, - 3% carbon oxide, - the concentration of carbon oxide becomes significantly higher. On the other hand, since a fuel cell generates heat due to cell reactions during operation, forced cooling is required to remove the generated heat to the outside of the system in order to keep the battery below the above-mentioned operating temperature. In this case, one cooling method is to supply excess air as a reaction gas and exhaust the heat generated inside the battery to the outside of the system together with the excess air. The disadvantage is that the amount of escape is large. For this purpose, a cooling passage is formed that exclusively supplies a cooling medium such as water or air to a cooling plate or a separate plate installed in the cell stack independently of the reaction gas passage, and the cooling passage is passed through the cooling passage to one open end thereof. Water-cooling systems and air-cooling systems are widely used, in which a cooling medium is introduced through the opening end and discharged through the other open end to cool the battery body. However, when the coolant+2' body is passed through the cooling passage as described above, the low temperature cooling medium introduced from the passage entrance absorbs heat from the fuel cell side and gradually becomes hotter. Become. As a result, as shown in Fig. 10, inside the unit cell 1 along the flow direction C of the cooling medium, the temperature is low in the area near the cooling medium inlet side, and conversely -1, the temperature is low in the area near the cooling medium outlet side. The temperature distribution shows a temperature distribution in which the temperature increases in the near area.The figure shows the temperature distribution at each point when the unit cell is cooled to keep the temperature within 200℃ at maximum. ing. Note that in order to increase the power generation efficiency of fuel cells, unit cell 11. It is preferable to suppress the temperature difference in the plane direction within the tube as small as possible1, but on the other hand, it is necessary to pass a large amount of cooling and cooling medium for this purpose. °” Since the power of the lower, pump, etc. becomes large, the overall efficiency of the fuel cell decreases. Therefore, in actual operation, the unit cell is The area temperature distribution has the values shown in the figure. By the way, as can be seen from the explanations in Figures 9 and 10 above, when the fuel cell is in operation, the cooling medium is supplied to keep the maximum temperature below 200°C. In order to perform forced cooling, each unit cell that makes up the cell stack has a temperature distribution with high and low temperature differences in its area along the flow direction of the cooling medium, and on the other hand, carbon monoxide in the fuel gas The concentration gradually increases from the inlet side to the outlet side along the reactant gas supply passage.For this reason, if the fuel gas is uniformly supplied to an area with a temperature difference distribution for each unit cell, the temperature A region where a gas containing a high concentration of carbon monoxide flows occurs in a low surface area, and as a result, the poisoning effect of the electrode catalyst acts strongly in this region, resulting in a problem of a significant decrease in battery output. [Object of the invention] This invention has been made in consideration of the above points,
For fuel cells that are forcedly cooled by passing a cooling medium through them, we have successfully laid out the fuel gas supply passages formed in each unit cell to prevent the poisoning of the electrode catalyst by carbon monoxide contained in the reformed gas. It is an object of the present invention to provide a fuel cell in which high output characteristics of the fuel cell can be maintained by suppressing the output characteristics as low as possible.

[Key points of the invention]

In order to achieve the above object, the present invention provides a cooling passage for a fuel cell in which a cooling passage is formed in a cell stack for exclusive use of supplying a cooling medium separately and independently from a reaction gas passage formed for each unit cell. is formed perpendicular to the reaction gas passage for fuel gas, and the fuel gas is introduced from a surface area close to the inlet side of the cooling passage and discharged from a surface area close to the exit side of the cooling passage. A reaction gas passage is formed therein. With this configuration, hydrogen-rich fuel gas with a low carbon monoxide concentration flows in the low-temperature surface area of each unit cell, and exhaust-side fuel gas with a high carbon monoxide concentration flows in the high-temperature surface area. Therefore, the poisoning effect of carbon monoxide on the electrode catalyst by carbon monoxide can be suppressed to a low level over the entire area of the unit cell, and a decrease in battery output can be effectively prevented.

[Embodiments of the invention]

Fig. 1 is a schematic diagram showing the supply route of fuel gas and cooling medium of a unit cell showing the principle of this invention, and Fig. 2 is a monoxide in the fuel gas along the fuel gas passage corresponding to Fig. 1. Carbon concentration distribution diagrams, Figures 3 and 6 are block diagrams of specific examples of unit cells corresponding to Figure 1, and Figures 7 and 8 are further developments of Figure 1. Figure 3 shows a schematic diagram of another embodiment; In other words, in Fig. 1, for a rectangular unit cell l, the cooling medium is formed independently across two opposite sides a and b of the cell, as shown by arrow C. Flow is conducted through the passage from one open end to the other open end. On the other hand, the reaction gas passage for fuel gas is defined in a meandering manner in a direction perpendicular to the cooling passage, with an inlet and an outlet opening on the side C side perpendicular to the sides a and b, Here, the fuel gas is introduced through the reaction gas passage as shown by arrow F from a region near the inlet side of the cooling medium, and is discharged through a region near the exit side of the cooling medium. . Note that the reference numeral W in the figure represents a partition that defines the outgoing path and the incoming path of the meandering reaction gas passage. Therefore, the carbon monoxide concentration distribution of the fuel gas flowing through this reaction gas passage becomes as shown in FIG. 2 due to the consumption of hydrogen gas by the cell reaction. Here the second
As can be seen by superimposing the temperature distribution diagram due to forced cooling of the unit cell shown in Figure 10 on the carbon monoxide concentration distribution diagram in Figure 10, it is clear that a low concentration of carbon monoxide is introduced into the low-temperature area within the unit cell. The fuel gas on the side is flowing, 1,,
iAi′L771m9″-″(fs * T: tl
ao*b1$till(7)tM' Source gas will flow. As can be understood by comparing this condition with the characteristic diagram in Figure 9, fuel gas with a low concentration of carbon monoxide flows in the low-temperature area within the cell, so the effect of poisoning is small. −
The temperature of the area 1, where fuel gas with a high concentration of carbon oxide flows is high, so the effect of poisoning is also small.As a result, even when looking at the area of the unit cell as a whole,ゎ93. -ゎ6-ya1.ヮ8. Yo, -1. It can be seen that the influence of poisoning is small and that a decrease in battery output can be effectively prevented. Next, the specific structure of a fuel cell corresponding to the principle diagram shown in FIG. 1 is shown in FIGS. It consists of an anode electrode 1b and a cathode electrode lc which are sandwiched and overlapped on both sides, and there are lips on the top and bottom of this unit cell.
are layered. Here, as shown in FIG. 4, the rectangular separate plate 2 has openings on two opposing sides a and b of its four sides extending between the sides.゛Cooling passages 5 dedicated to supplying a plurality of tunnel-shaped cooling medium arranged in parallel are drilled, and are indicated by 1IvA) L fs
? ,? -O7゜)' 6 fil e74flR
1 (D □□□ The structure is such that air as a cooling medium is forced in and blown from the i system in the direction of arrow C. On the other hand, the anode electrode 1b of the unit cell is placed on both the upper and lower surfaces of the separate plate 2. Reactant gas passage 3 for fuel gas on the side opposite to
However, a reaction gas passage 4 for the oxidizing agent is also formed on the - side facing the cathode electrode 1c. Here, each reaction gas passage 3.4 is a separate,
The grooves are formed as a plurality of concave grooves lined up on the surface of the top plate 2, and the reaction gas supply and discharge ports thereof are on the other two sides C1d that are perpendicular to the side a+b where the cooling passage 5 is opened. It is formed to open on the □゛′ plane. In the illustrated embodiment, the reaction gas passage 3 for fuel gas is also used for supplying fuel gas. Both outlets are on the same side C (Fig. 5).
゛・), Supply of one air to the reaction gas passage 4,
The outlet is the same □゛i゛; on the side of the same side d (6th
Figure) Each reaction gas supply passage 3 is formed in a meandering manner by connecting the reaction gas supply port and the discharge port in a U-shape 2.
, 4 ゛, :′ −・:: Correspondingly indicated by the dashed line arranged on the side of the fuel cell; %gJ° q=*−t, F 7 , 8
, ilB-cM11yo") JF!lFi*
;゛□ Note that the hatched line in the center in FIG. 5 corresponds to the partition W shown in FIG. 1. The example shown in Figure 1 is an example in which cooling passages are formed in the separate plate 2.
Although shown, for example, a water cooling pipe may be installed in the cooling plate inserted for each of a plurality of cells. Next, FIGS. 7 and 8 show another embodiment that is a further development of the embodiment shown in FIG. 1. In the embodiment shown in FIG. On the other hand, in the embodiments shown in FIGS. 7 and 8, the number of partitions W defining the reaction gas passage in a meandering manner is increased to increase the corresponding surface area between the temperature distribution and the carbon monoxide concentration distribution in the unit cell. It is further divided into smaller pieces to achieve even higher effectiveness in preventing poisoning effects. In addition, in each illustrated example, the reaction gas passage is formed in a meandering shape with respect to the cooling passage, but this relative relationship can be reversed, and the reaction gas passage is formed in a straight line and the cooling passage is formed in a meandering shape. This can also be done in the same way.

【Effect of the invention】

As described above, according to the present invention, the cooling passage is formed perpendicular to the reactant gas passage for fuel gas, the fuel gas is introduced from a surface area close to the population side of the cooling passage, and the exit of the cooling passage is By forming the reaction gas passage for the fuel gas so that it is discharged from the area close to the side, the reformed fuel gas with a low concentration of carbon monoxide is discharged from the area with a low temperature within the unit cell.・、Since the fuel gas flows from the exhaust side where the carbon oxide concentration has increased, conversely, it flows to be discharged from the high temperature side, which causes battery fogging 1, The aim is to improve the output characteristics of fuel cells by suppressing the effects of poisoning of the electrode catalyst by carbon monoxide contained in the fuel gas, in which fuel cells are forcedly cooled to keep the operating temperature to around 200°C at most. You will be able to do this.

[Brief explanation of the drawing]

FIG. 1 shows the principle of the invention for a unit cell 'L:
FIG. 2 is a schematic diagram showing the flow path of the cooling medium and fuel gas, and FIG. 2 is along the fuel gas passage corresponding to FIG. 1. □IJ,, Fig. 3 is a carbon monoxide concentration distribution diagram of the fuel gas, Fig. 1 is a side view showing the specific configuration of the unit cell of the embodiment, Fig. 4 The figure is a cross-sectional view taken along the arrow EV-fV in Fig. 3.
5 and 6 are plan views respectively showing the reaction gas passages for the fuel and oxidizer formed in the separate plate in FIG. Schematic diagram, Figure 9 shows carbon monoxide concentration, battery temperature, 1
! Figure 1 is a characteristic diagram of a fuel cell showing the interrelationship of the amount of reduction in production power. Passage, 5: Cooling passage for supplying cooling medium, C: Supply direction of cooling medium, F:
Supply direction of fuel gas, W: partition defining a meandering passage for fuel gas. Figure 1 Figure 2 Figure 3 Figure 8

Claims (1)

[Claims] 1) For a cell stack that is a laminate of unit cells,
In a fuel cell in which a reaction gas passage for supplying a reaction gas of a fuel and an oxidizing agent for each unit cell, and a cooling passage through which a cooling medium exclusively flows separately and independently from the reaction gas passage, the cooling passage is provided. is formed perpendicular to the reaction gas passage for fuel gas, and the fuel gas is introduced from a surface area close to the inlet side of the cooling passage and discharged from a surface area close to the exit side of the cooling passage. A fuel cell characterized by forming a reactive gas passage. 2) In the fuel cell according to claim 1, the cooling passage is formed across two opposing side surfaces of the cell stack, whereas the reaction gas passage for fuel gas is formed between the cooling passages. A fuel cell characterized by being formed in a meandering manner in a direction perpendicular to a passage.