JPS63168970A - Cooling device for fuel cell - Google Patents

Abstract

PURPOSE:To realize the reduction of the oxidation gas flow for cooling, by furnishing a recirculation line to lead a part of a fuel gas released from an anode to the gas feeding side, and furnishing a cooler at the recirculation line to recirculate and to cool the fuel gas. CONSTITUTION:At an anode 3 side, a recirculation line 31 is furnished to recirculate a part of a fuel gas FG released from the anode 3 to the gas feeding side, and on the way of the recirculation line 31, a blower 32 and a cooler for the recirculation purpose are furnished, while more fuel gas responding to the amount of the recirculation fuel gas flow is fed to the anode 3 side. In such a composition, the heating value which is cooled by the cooler at the cathode side conventionally can be cooled by the cooler 33 at the anode side, and in compliance with this the recirculation flow at the cathode 2 side can be reduced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a cooling device for a fuel cell used in the energy sector that directly converts chemical energy contained in fuel into electrical energy. This invention relates to a cooling device for a fuel cell that can reduce the amount of gas on the cathode side, which is often used for cooling, by cooling the cathode.

[Prior Art] Among the molten carbonate fuel cells that have been proposed to date, there is one as shown in FIG.

That is, an electrolyte plate (tile) 1 made of porous material impregnated with molten carbonate is sandwiched between a cathode (M cumulative) 2 and an anode (fuel electrode) 3 from both sides, and an oxidizing gas is applied to the cathode 2 side. While supplying OG, fuel gas (
A cell in which electricity is generated by the potential difference generated between the cathode 2 and anode 3 by supplying FG (hydrogen gas) is called one cell ■, and each cell ■ is separated by a separator 4.
Some have a structure in which they are laminated in multiple stages with .

The power generation system in which the fuel gas used in the molten carbonate fuel cell is modified from natural gas, that is, the natural gas reformed molten carbonate fuel cell power generation system is the fourth
As shown in the figure, in order to supply oxidizing gas to the cathode 2 side constituting the fuel cell, air A is compressed by multi-stage compressors 5 and 7, preheated by an air preheater 8, and then supplied to the cathode through line 9. The gas discharged from the cathode 2 is led to the turbine 13 via the line 12, and is further supplied to the air preheater 8. It is designed to be discharged through. on the other hand,
Since the gas discharged from the anode 3 contains moisture, some of the moisture in the fuel gas discharged from the anode 3 is separated from the gas, and then the separated water is reintroduced into the system. . For this purpose, the fuel gas discharged from the anode 3 passes through a heat exchanger 14 with the cooled gas and then into a preheater 15, 16 where it is exchanged with natural gas NG.
, passed through an evaporator 17, cooled and condensed in a condenser 18, and separated into gas and water in a gas-liquid separator 19. The gas is passed through a blower 20.
The reformer 1 is passed through the line 21 to the heat exchanger 14 at
Water (H2O) is pressurized by a pump 22 and sent to a feed water heater 23, where it is heated and turned into steam through a line 24 and an evaporator 17 to the reformer 11. The fuel gas produced in the reformer 11 is supplied to the inlet side and mixed with natural gas, and the fuel gas produced in the reformer 11 is supplied to the anode 3 of each cell through the pipe 25, and the oxidizing gas discharged from the reformer 11 is supplied to the anode 3 of each cell. , and are supplied to the cathode 2 of each cell of the fuel cell together with the gas flowing through the line 9.

50% of the oxidizing gas OG and fuel gas FG supplied to the cells (2) in each stage generate electricity, and the remaining 50% generate heat.

Therefore, it is necessary to cool the generated heat, and the conventional idea was to use oxidizing gas OG as this cooling medium. The flow ratio of oxidizing gas and OG was 1:10 in the natural gas reforming molten carbonate fuel cell, and 1:5 in the coal gasification molten carbonate fuel cell. That is, in the current natural gas reforming molten carbonate fuel cell, as shown in FIG.
By returning a part of the oxidizing gas OG discharged from the cathode 2 to the supply side by 7, the cell is basically cooled only on the oxidizing gas side, so the flow rate inside the cell is lower than that of the fuel gas. Therefore, the flow rate of oxidizing gas is about 10 times higher. In addition, in coal gasification molten carbonate fuel cells, the sixth
As shown in the figure, part of the fuel gas on the anode side is recirculated from the perspective of preventing carbon deposition at the anode 3, so the fuel gas side also has a part of the cooling function for the battery, so it is inside the battery. The flow rate ratio of fuel gas and oxidizing gas is 1:5.
It is in the position. 30 is a cooler.

On the other hand, the separator 4 of the stacked fuel cell has the function of partitioning each cell (2) to allow the oxidizing gas OG and fuel gas FG to flow in each cell, and also to uniformly press the cathode 2 and anode 3 against the electrolyte plate 1. Because it has
A gas passage for flowing the fuel gas FG and a gas passage for flowing the oxidizing gas OG are formed separately on both the front and back surfaces, and when the front side is in contact with the anode 3, only the fuel gas FG has one end on the front side. On the back side, only the oxidizing gas OG is allowed to flow from one end side to the other end side.

[Problems to be Solved by the Invention] However, as described above, the flow rate ratio of the fuel gas FG and the oxidizing gas OG supplied to each cell (2) has so far been around 1:10 or 1:5. In manufacturing the separator 4, the gas passages on one side for flowing fuel gas and the gas passages for flowing oxidizing gas on the opposite side are made to have different cross-sectional areas, and the oxidizing gas side has a flow rate 10 times the flow rate of the fuel gas. It must be possible to flow an amount of oxidizing gas, and the separator 4
When press-molding, it is necessary to press-form the front side and the back side separately using separate press machines, which requires two steps. Furthermore, even when attempting to form gas passages by etching, the cross-sectional areas of the gas passages on the front and back sides are different.
It is necessary to change the time for dissolving and corroding with a chemical solution on the front side and the back side. During molding, after etching both the front and back sides for the same amount of time, one side is covered with resist and etched again to increase the amount of corrosion on the other side. Two steps are required. Therefore, it takes a lot of effort to manufacture the separator 4, and currently, the fuel cell itself accounts for 30% of the total equipment cost that makes up the fuel cell power generation system, and nearly 50% of the cost is for the separator 4. The reality is that the cost is dominated by

Also, if the gas passage on the front side of the separator is different from the gas passage on the back side, the front and back will be asymmetrical and will not be interchangeable, so it is absolutely impossible to install the stacked fuel cell upside down when assembling it. There is a problem in that it is not allowed and must be handled with great care. Furthermore, increasing the flow rate of the oxidizing gas OG for cooling also increases the power consumption of the air blower for compressing the oxidizing gas.

Therefore, the present invention aims to make it possible to manufacture the above-mentioned separator at about half the current cost without lowering the overall plant efficiency, and to reduce the power consumption for compressing the oxidizing gas.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an electrolyte plate sandwiched between a cathode and an anode, and an oxidizing gas flowing through the cathode side and a fuel gas flowing through the anode side. A recirculation line is provided to guide a part of the fuel gas discharged from the anode of the fuel cell, which is formed by stacking one cell arranged to generate electricity in multiple stages via a separator, to the supply side. A cooling section is provided to recirculate and cool the fuel gas.

[Function] When a part of the fuel gas discharged from the anode is recirculated and cooled, the recirculated fuel gas acts to cool the cell, and some of the heat from the cathode side is removed by the anode side. It can be carried out. As a result, the flow rate of the oxidizing gas supplied to the cathode side can be reduced, and the flow rate ratio of fuel gas and oxidizing gas can be set to about 1:1 to 2. The cross-sectional area can be made the same.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows one embodiment of the present invention for a natural gas reforming molten carbonate fuel cell.

That is, both sides of the electrolyte plate 1 are sandwiched between a cathode 2 and an anode 3, and an oxidizing gas OG is supplied to the cathode 2 side from one end and discharged from the other end, and a fuel gas FG is supplied to the anode 3 side. The oxidizing gas OG is supplied from one end and discharged from the other end, and a part of the oxidizing gas OG discharged from the cathode 2 is guided to the supply side by a recirculation line 26, and a part of the oxidizing gas is supplied by a recirculation blower 27. In a configuration in which the gas is recirculated, the recirculated gas is cooled by the cooler 28, and a large amount of oxidizing gas is flowed to the cathode 2 side, the following configuration is adopted. That is, a recirculation line 31 is provided on the anode 3 side for guiding a part of the fuel gas FG discharged from the anode 3 to the supply side for recycling, and a recirculation line is provided in the middle of the recirculation line 31. Blower 32 and cooler 3
3, so that as much fuel gas as the flow rate of the recirculated fuel gas flows to the anode 3 side, the heat that was cooled by the cathode side cooler 28 in the conventional method shown in FIG. 5 is removed. 10 is cooled by a cooler 33 on the anode side as shown in FIG. 1, and the recirculation flow rate on the cathode 2 side is reduced by that much compared to the conventional system.

Note that the mechanism around the battery is the same as in the case of FIG. 4.

In the case where oxidizing gas OG is supplied to the cathode 2 side of the fuel cell and fuel gas FG is supplied to the anode 3 side, and power is generated by the potential difference generated between both electrodes, the anode 3
When the side recirculation blower 32 is operated, a part of the fuel gas FG discharged from the anode 3 passes through the recirculation line 31 and is cooled and recirculated to the anode 3. As a result, the flow rate of the fuel gas FG flowing on the anode 3 side is
Compared to the flow rate of fuel gas in conventional fuel cells, which was simply flowed for power generation, the amount is increased by the amount that is recirculated and flowed for cooling, and the cathode 2
The flow rate of the oxidizing gas that is recirculated can be reduced. Therefore, the flow rate ratio of the fuel gas flowing on the anode 3 side and the oxidizing gas flowing on the cathode 2 side can be increased from the current 1:10 to 1:1-2. When the flow rate of fuel gas and the flow rate of oxidizing gas in each cell sandwiching the separator 4 are approximately equal, the cross-sectional area of the gas passages formed on both the front and back sides of the separator 4 can be made the same, and the surface side of the separator 4 and the back side can be made symmetrical,
It becomes possible to manufacture the separator 4 by simultaneously forming gas passages on both the front and back sides.

Next, FIG. 2 shows another embodiment of the present invention, in which the flow rate ratio of fuel gas and oxidizing gas is changed from 1:5 to 1:1 in a coal gasification molten carbonate fuel cell. This allowed him to come in second place. That is, in the conventional fuel cell power generation system shown in FIG. 6, a cooler 35 is installed in the middle of the recirculation line 34 on the anode 3 side, and the flow rate of the fuel gas flowing through the recirculation line 312 is adjusted as shown in FIG. The ratio of the flow rates of fuel gas and oxidizing gas is increased to 1:1 to 2, and the oxidizing gas recirculation flow rate shown in FIG. 6 is significantly reduced.

When the recirculation rate of the fuel gas FG on the anode 3 side is increased, the flow rate of the fuel gas flowing on the anode 3 side from one end side to the other end side increases, so that the fuel gas flowing on the anode 3 side has a cooling effect on the cell. This makes it possible to perform part of the heat removal on the cathode 2 side on the anode 3 side, reducing the amount of recirculation of the oxidizing gas on the cathode 2 side, and reducing the flow rate ratio of the fuel gas on the anode side and the oxidizing gas on the canode side. can be changed from the conventional ratio of 1:5 to 1:1 to 2, as described above. Along with this, the separator can be made symmetrical on both sides,
This makes it easier to manufacture.

[Effects of the Invention] As described above, according to the present invention, instead of the current method of using only oxidizing gas as a gas to cool the heat generated in the fuel cell, a part of the fuel gas is recirculated to cool the anode side. increasing the flow rate of the flowing fuel gas and cooling the recirculated fuel gas to cool the battery;
By reducing the total flow rate of oxidizing gas, the flow rate ratio of fuel gas and oxidizing gas is increased from the conventional 1:10 to 1:1 for natural gas reformed molten carbonate fuel cells.
In addition, in the case of coal gasification molten carbonate fuel cells, the ratio can be reduced from the conventional 1:5 to 1:1 to 2. The flow rates of the fuel gas and oxidizing gas flowing through the separator of the type fuel cell can be made almost equal, and the gas passages formed on both the front and back sides of the separator can have the same cross-sectional area. can be formed at the same time in the same process, making the production of the separator easier than before, and the production cost of the separator can be halved compared to the conventional one, reducing the cost of the fuel cell itself. Moreover, since both the front and back sides of the separator can be made symmetrical, the separator itself is compatible, and there is no problem even when assembled with the front and back sides reversed, making it possible to create a separator that is convenient to handle. Furthermore,
Since the amount of oxidizing gas can be reduced compared to the conventional method, the power consumption for compressing the oxidizing gas can also be lowered, and the overall power generation efficiency of the plant can be increased.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing one embodiment of the present invention applied to a natural gas reforming molten carbonate fuel cell, and Fig. 2 is a schematic diagram showing another embodiment of the present invention applied to a coal gasification molten carbonate type fuel cell. FIG. 3 is a cross-sectional view showing an example of a conventional molten carbonate fuel cell; FIG. 4 is a schematic diagram of a conventional natural gas reforming molten carbonate fuel cell power generation system; FIG. This figure is a schematic diagram showing a cooling method for the fuel cell shown in FIG. 4, and FIG. 6 is a schematic diagram showing a cooling method for a conventional coal gasification molten carbonate fuel cell. ■... Cell, 1... Electrolyte plate, 2... Cathode,
3... Anode, 4... Separator, 11... Reformer, 31° 34... Recirculation line, 32... Recirculation blower, 33.35... Cooler, OG ... Oxidizing gas, FG...Fuel gas.

Claims (1)

[Claims] 1) An electrolyte plate is sandwiched between a cathode and an anode, and one cell is stacked in multiple stages with a separator in between to generate electricity by flowing oxidizing gas to the cathode side and flowing fuel gas to the anode side. A recirculation line is provided to guide a portion of the fuel gas discharged from the anode of the fuel cell to the supply side, and a cooler is provided in the recirculation line to cool the recirculated fuel gas, so that the fuel on the anode side is A fuel cell cooling device characterized by increasing gas flow rate.