JPS6223434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel cell stack consisting of a plurality of fuel cells electrically connected in parallel.

A basic fuel cell consists of a fuel electrode, an oxidant electrode, and an electrolyte defined in a compartment formed between the electrodes, each electrode having a catalyst layer on its electrolyte side. The non-electrolyte side of the fuel electrode is a reaction gas space for passing the fuel, and the non-electrolyte side of the oxidizer electrode is a reaction gas space for passing the oxidant. Both electrodes allow the reactant gas to diffuse through the electrodes,
Ions are configured to move from one electrode through the electrolyte to the other electrode by contacting the electrolyte in the catalyst layer and performing an electrochemical reaction. This flow of ions is basically the electrical current obtained by the fuel cell.

In fuel cell power generation equipment, a plurality of fuel cells are stacked with separators in between and electrically connected in series to form a fuel cell stack. These separators, together with the electrodes adjacent thereto, generally define a path for the reactant gas. The amount of current drawn by each cell is directly proportional to the amount of reactant gas available for the electrochemical reaction.

In conventional fuel cell stacks, fuel passes through each fuel cell in parallel only once, or passes through each fuel cell several times in parallel, and the fuel gas flow path is Both the upstream and downstream sides had approximately the same gas passage cross section. Therefore, approximately 80% of the fuel supplied to the fuel cell stack was consumed within the fuel cell, but the remaining approximately 20% was not utilized as fuel for the fuel cell. However, since phosphoric acid electrolyte fuel cells and molten salt electrolyte fuel cells are intended for use in electric power, and improvements in fuel utilization efficiency are particularly required, the fuel utilization rates mentioned above have not been sufficient. . In addition, in the above structure, on the upstream side of the fuel, the fuel concentration is high, so power can be generated efficiently and the calorific value is small, but on the downstream side, the fuel concentration is low, resulting in poor power generation efficiency. However, the disadvantage was that it generated a large amount of heat and was prone to thermal non-uniformity.

The present invention aims to improve the fuel utilization rate of a fuel cell stack and improve the overall efficiency of fuel cell power generation equipment. It is formed by stacking a plurality of unit structures each consisting of an electrolyte to be disposed via isolation means for a reaction gas space facing the first electrode and a reaction gas space facing the second electrode, In a fuel cell stack in which a reaction gas flows into a reaction gas space via a manifold, the reaction gas spaces of the plurality of stacked unit structures are connected in parallel and in series by the manifold,
A reaction gas space in which the number of parallel reaction gases on the downstream side is at least one less than the number of parallel connections on the upstream side connected in series with the reaction gas space, and partitioned by a partition structure that divides each into a plurality of parts, and the partition Each space partitioned by the structure is connected in parallel, in series, or in series and parallel by the manifold, and the width of the electrode to which the reaction gas is supplied by each partitioned space is determined by the width of the electrode to which the reaction gas is supplied. at least one downstream
The first feature is that at least one of the reaction gas spaces is narrower than the upstream side at the above points, and furthermore, a cooling pipe is provided every time a plurality of unit structures are stacked, The second feature is that it has a serial gas flow path that connects the reaction gas space located near the cooling pipe to the downstream side and the reaction gas space located far from the cooling pipe to the upstream side.

That is, the present invention prevents the density of the fuel gas from significantly decreasing by narrowing the passage width of the fuel gas as the reactant gas, for example, the fuel gas, decreases as it goes downstream. , the same power generation efficiency can be obtained on both the upstream and downstream sides of the fuel. In this way, as a means to narrow the width of the fuel gas passage, the defined fuel gas space is connected directly and in parallel by the manifold, and the number of parallels on the downstream side is made smaller than the number of parallels on the upstream side. This structure is effective. Another method of narrowing the fuel gas passage width on the downstream side is to provide partitions at uneven intervals in the fuel gas space, with the wide fuel gas space on the upstream side and the narrow fuel gas space on the downstream side. A structure in which gas is connected in series is also effective.

In order to clarify the basic concept of the present invention, a quantitative explanation will be given below in comparison with the prior art.

In the conventional technology, since the gas passage width is approximately the same on both the upstream and downstream sides of the fuel, the power generation efficiency is reduced by the amount that the fuel gas density is reduced on the downstream side. Fuel cells are normally operated in a region where the relationship between fuel gas density and power generation is almost proportional.
If the fuel gas density at a distance x from the inlet along the gas passage is n(x) and the gas passage width is l(x), fuel consumption occurs in proportion to n(x), so -d{ n(x)・l(x)・Δx}/dx =k・n(x)・l(x)・Δx……(1) Since l(x) is constant, n(x )=n ₀ e ^-kx ......(2). Here, n ₀ is the inlet fuel concentration, and k is a constant indicating the ease of reaction of the fuel cell.

This equation shows that the fuel gas density decreases exponentially along the gas path. Now, if a certain amount of fuel is passed through a fuel cell whose gas passage length is x ₅₀ , and 50% of the fuel supplied from the inlet is consumed and the remaining 50% is discharged from the outlet, then (2 )
From the formula It is. If only the length of the gas passage is lengthened and the same type of fuel cell with the same width is used, 80% of the fuel supplied from the inlet is consumed and only the remaining 20% is discharged from the outlet. By calculation similar to equation (3), It is. Therefore, the fuel utilization rate can be reduced from 50% to 80%.
To improve the fuel cell dimensions to 1.609/0.6
It must be increased by 93=2.32 times. When similar calculations are performed for fuel utilization rates of 90%, 95%, and 99%, dimensions that are 3.32 times, 4.32 times, and 6.64 times larger than those for a fuel utilization rate of 50% are required, respectively.
In other words, if the fuel utilization rate is to approach 100%, the size of the fuel cell will increase significantly.

Next, we will show the results of calculations for a fuel cell stack in which the fuel passage width is narrowed by the amount of fuel consumed to save the size of the fuel cell, that is, a fuel cell stack in which the fuel density is kept constant. If we use a fuel cell that is exactly the same as the fuel cell used in the calculation of the conventional technology except for the vertical and horizontal dimensions, the fuel density n(x) is constant, so l(x)=l ₀ e ^-kx ......(5 ) becomes. Here, l ₀ is the gas passage width at the inlet. When the fuel utilization rate is 50%, the width of the gas passage on the outlet side is 1/2 of the width of the gas passage at the inlet. Therefore, the gas passage length x′ ₅₀ at this time is It is. The area of the fuel cell at this time is ∫ ^x ′ ⁵⁰ ₀ l ₀ e ^-kx dx=0.5/k×l ₀ ………
(7). Since the fuel cell area required to obtain a fuel utilization rate of 50% with the conventional technology is x ₅₀ ×l ₀ =0.693/k×l ₀ (8), according to the present invention, This means that the size of the fuel cell can be reduced by 0.5/0.693=0.72 times compared to the method described above.

Similar calculations for fuel utilization 80%, 90%, 95%, 99
% case, and for the same utilization rate,
Comparing the case of the present invention and the case of the prior art, it is 0.497 times, 0.391 times, 0.317 times, respectively.
It is 0.215 times larger, which shows that the higher the fuel utilization rate, the greater the size reduction.

In addition, when comparing the fuel utilization rates of the present invention and the conventional technology using the same method as described above for fuel cells of the same size, it was found that even with the fuel cell size of the conventional technology, the fuel utilization rate was 63%. In the case of invention
This results in a fuel utilization rate close to 100%.

The present invention is based on such a basic concept, and will be explained in detail below using examples.

Figures 1 and 2 show a fuel cell stack (hereinafter referred to as
FIG. 1 shows the external appearance. The stack 1 consists of a plurality of fuel cells 2 electrically connected to each other in series. Manifolds 3, 4, and 5, 6 are provided on the outer periphery, facing each other,
The manifold 3 is provided with an inlet portion 7 and an outlet portion 8 for fuel gas, and the manifold 5 is provided with an inlet portion 9 and an outlet portion (not shown) for oxidizing gas. As shown in FIG. 2, each fuel cell 2 includes a fuel electrode 10, a fuel gas passage 11, an electrolyte 12, an air electrode 13, an air passage 14, and a separation plate 15. In this example, the fuel gas passage 11 and the air passage 14 are formed by defining a fuel gas space and an air space by ribs 16 and 17 formed by grooves on both sides of the separation plate 15. 18 in FIG. 2 indicates a cooler holder.

3 and 4 show a cross section of an embodiment of the fuel cell stack of the present invention, and the same parts as in FIGS. 1 and 2 are given the same reference numerals. In this example, the fuel cell 2 has cooling pipes 19, 20
They are stacked in six layers vertically across the cooler holder 18, which is provided with
is being pressed by. Manifolds 3 provided on both sides of the stack of fuel cells 2
and 4, the inside of the manifold 3 is divided into an inlet side gas chamber 22 and an outlet side gas chamber 23, and the inlet part 7 of the manifold 3 is divided into four fuel cells stacked vertically. 2, an inlet side gas chamber 221 configured to be connected to
222, and the outlet section 8 is connected to the outlet side gas chamber 23, which is configured to be connected to two fuel cells 2 stacked vertically.
The manifold 4 serves as a common gas chamber 24, and the inlet side gas chambers 221, 222
Therefore, the fuel gas that has passed through the eight fuel cells 2 in parallel passes through the common gas chamber 24, passes through the four fuel cells 2 in parallel, and flows into the outlet side gas chamber 23.

FIG. 4 shows the inlet side gas chamber 22 in the manifold 3 to realize such a flow of fuel gas.
This figure shows a structure for partitioning the gas chamber 2 and the outlet side gas chamber 23, and the same parts as in FIGS. 1, 2, and 3 are given the same reference numerals. As shown in this figure, the manifold 3 is pressed against the fastener 21 via the packing 25, but at this time, the packing 26, which is arranged so as to protrude from the cell surface of the fuel cell 2, comes into contact with the partition plate 27. It's becoming like that. A portion of this packing 26 is inserted into the surface of the fuel cell 2, and is fixed by tightening the stacked fuel cells 2 with the fasteners 21. This packing 26 partitions the inlet side gas chamber 222 and the outlet side gas chamber 23. Note that since the manifold 3 and the manifold internal partition plate 27 are insulated from the fuel cell 2 by the packing 25 and the packing 26, the fuel cell 2 is insulated by the manifold 3 and the manifold internal partition plate 27. The battery cells 2 are prevented from being short-circuited.

In a fuel cell stack having such a structure, the fuel gas flows in parallel through 8 cells on the upstream side where the amount of fuel is large, and the fuel gas flows through 4 cells on the downstream side where fuel is consumed and becomes less. Since the fuel cells flow in parallel, it is possible to prevent a decrease in battery performance due to a decrease in fuel density on the downstream side, and it is possible to achieve high performance with a small number of cells.

In other words, in a conventional fuel cell stack, the number of fuel gas paralleled on the upstream side and the downstream side is the same, so when the number of fuel cells is 16, 8 cells on the upstream side and 8 cells on the downstream side are connected. In contrast to this, in the fuel cell stack of this example, there are 8
Since the number of cells is reduced to 4, the gas concentration on the downstream side is doubled, and the battery performance per unit electrode area is also almost doubled, so even if the number of cells is reduced from 8 to 4, the battery Power output and fuel utilization can be approximately the same. That is, since the number of cells can be reduced, it is possible to downsize the fuel cell stack. In addition, assuming that 16 cells are used, which is the same as the conventional structure, and the gas flow path configuration of the present invention is configured such that 10 cells are arranged in parallel on the upstream side and 6 cells are arranged in parallel on the downstream side, and the gas is connected in series, the battery output and Fuel utilization can be improved.

In addition, this fuel cell stack is configured so that downstream gas is allowed to flow to the cells near the cooler and the upper and lower surfaces that are easily cooled, and upstream gas is allowed to flow to the cells that are difficult to cool. Therefore, as the fuel gas is heated and its temperature increases, it flows to a location where it can be easily cooled, which has the advantage that the temperature distribution within the fuel cell stack can be easily made uniform.

Furthermore, in the configuration shown in Fig. 4, the gas chambers on the inlet side and the outlet side are separated by bringing the packing protruding from inside the cell into contact with the manifold internal partition plate. It is effective in preventing the gas passage from being closed. The packing has poor dimensional accuracy and has a T-shaped cross section and a large area of the packing head so that the partition plate and the packing can come into contact even if the partition plate is misaligned. Note that this shape does not necessarily have to be a T-shape, but may be an inverted L-shape,
A simple sheet without a head is used for packing,
The contact surface of the partition plate may be T-shaped or inverted L-shaped.

Further, the packing 26 does not have to be entirely made of rubber-based material, but may be made of metal, carbon, or other materials, and may have a structure in which the packing is used only on the contact surface with the partition plate 27.

FIGS. 5 and 6 show other different embodiments, and in the fuel cell stack of the embodiment shown in FIG. In contrast, the fuel cell stack of this embodiment has a structure in which the gas flow path is folded back at the fuel cell surface.

In the embodiment shown in FIG. 5, a partition 28 is provided on two sides of the fuel cell, and this partition 28 is connected to the manifold 3.
On the side, the ratio of the length on the inlet side gas chamber 22 side and the length on the outlet side gas chamber 23 side is set to 8:4, and on the side of the common gas chamber 24 in the manifold 4, it is located in the center. There is. Note that 5 and 6 indicate the air side manifolds.

The gas passage partition 28 in the cell portion
It may be a rib structure provided on a separation plate as shown in the figure, or a structure in which the electrode portion is completely partitioned.

In this embodiment, the fuel gas passes from the inlet part 7 through the inlet side gas chamber 22 provided in the manifold 3 by a partition plate 27, and flows through the fuel gas passage of each cell parallel to the fuel cell 2 surface. Street common gas chamber 2
4, the gas flow is turned back at this common gas chamber 24, passes through the fuel gas passage, and flows into the outlet side gas chamber 23.

Therefore, the width of the electrode to which fuel gas is supplied is wide on the upstream side of the gas, and becomes narrower as it goes downstream. That is, as fuel is consumed,
Since the width of the fuel gas passage is narrowed, as described above, this is effective in reducing the size of the fuel cell stack and improving the fuel utilization rate. Furthermore, according to the structure shown in FIG. 5, the width of the electrode to which gas is to be supplied can be changed continuously as the gas flow moves from upstream to downstream.
It becomes possible to adjust so that all electrode surfaces can generate electricity efficiently.

Although FIG. 5 shows the manifolds 5 and 6 on the space side, the flow on the cell surface of the space passes through the air passage shown in FIG. 2 and flows in a direction perpendicular to the fuel gas. Also, in this figure, the air side does not have a folded flow, but like the fuel gas side,
By providing a partition and narrowing the electrode width to which downstream air is supplied, the oxygen utilization rate can be improved.

The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 5 in that all the partitions are provided parallel to the gas flow and that the gas flow is folded back three times. That is, partitions 291, 292, and 293 are provided parallel to the gas flow, and using partition plates 27 and 30, the electrode width to which gas is to be supplied is divided into four stages from upstream to downstream, with the width becoming narrower in order. It's summery. In this case as well, the effects of downsizing the fuel cell stack and improving the fuel utilization rate can be expected, as in the above-described embodiments. Moreover, since the partitions 291, 292, and 293 are all parallel compared to the embodiment shown in FIG. 5, if the ribs of the separating plate shown at 16 and 17 in FIG. When manufacturing the separator plate by continuous extrusion, this partition can also be formed at the same time, which has the effect of reducing manufacturing costs. Note that the separation plate 15 shown in FIG. 2 may be used as it is without providing any special ribs.

In the embodiment shown in Fig. 6, the width of the gas passage is changed into four stages, but the number of stages and the passage width of each stage are not limited. Even if it is, the effect of the present invention can be obtained as long as the width on the downstream side is narrower than the width on the upstream side as a whole.

In the embodiment shown in Fig. 3, the gas passages between stages of the fuel cell are divided, and in the embodiments shown in Figs. 4 and 5, the gas passages on the cell surface are divided. The effects of the present invention can also be obtained with a structure in which the gas passages in both directions are divided in the manifold and the gas passages are connected directly or in parallel.

Further, the effects of the present invention can be obtained even if a plurality of manifolds are connected in series and parallel for gas communication.

If it is desired to introduce the cooling pipes 19 and 20 of the embodiment shown in FIG. 3 into the structure of the embodiment shown in FIG. , the cooling pipe does not pass through the partition plate 30, but is divided into two, and the manifold 4 has:
A structure in which there are two inlets and two outlets for the cooling medium is easy to manufacture.

The present invention can be applied whether pure hydrogen or hydrogen gas containing an inert gas such as reformer gas is used as the fuel gas.
When using fuel gas containing inert gas,
Although the amount of hydrogen decreases on the downstream side of the gas flow, the inert gas component does not decrease, so as the electrode width to which gas is supplied becomes narrower, the gas flow rate increases, and the fuel gas remains unreacted. Inconveniences such as discharge or increased pressure loss may occur. If there are many such inert gas components, increase the depth of the upstream gas passage and make sure that the cross section of the gas passage does not become small even if the width of the electrode to which gas is supplied is narrowed as described above. Avoid increasing flow velocity. Thereby, the present invention can be effectively applied even if a fuel gas containing an inert gas is used.

In the above embodiment, as shown in FIG. 2, the fuel gas passage 11 and the air passage 14 are formed by forming grooves on both sides of the separation plate 15.
A fuel gas passage may be formed by forming grooves on the surface of the fuel electrode opposite to the electrolyte, and a fuel gas passage may be formed by forming grooves on the surface of the air electrode opposite to the electrolyte.
The present invention is applicable to any structure in which there is a fuel gas passage between the separation plate that separates fuel gas and air and the fuel electrode catalyst layer, and an air passage between the separation plate and the air electrode catalyst layer. be able to.

Further, in FIG. 2, a fuel gas space and an air space are defined by ribs 16 and 17 provided on both sides of the separation plate, and a fuel gas passage 11 and an air passage 14 are defined.
However, a zigzag gas passage may be formed by using a spacer made of a small piece instead of the rib. That is, the gas space defined by the partition of the present invention is not limited to the gas space defined by the rib structure, and the gas flow path structure within the defined space may be arbitrary.

As described above, the fuel cell stacks of these examples can achieve almost the same power generation efficiency on both the upstream and downstream sides of the fuel, thereby improving the fuel utilization rate of the fuel cell stacks and improving the overall efficiency of the fuel cell power generation equipment. Efficiency can be improved, and as a result, the size of the fuel cell stack can be reduced, and the temperature distribution in the fuel cell stack can be made uniform to prevent local overheating.

As described above, the fuel cell stack of the present invention improves the fuel utilization rate and the overall efficiency of fuel cell power generation equipment, and has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the appearance of a fuel cell stack, FIG. 2 is an exploded perspective view showing the structure of the fuel cell stack, and FIG. 3 is an embodiment of the fuel cell stack of the present invention. FIG. 4 is a vertical cross-sectional view of the main part of FIG. 3, and FIGS. 5 and 6 are cross-sectional views of other different embodiments. 2... Fuel cell, 3, 4, 5, 6... Manifold, 7... (fuel gas) inlet, 8...
... (Fuel gas) outlet section, 10 ... Fuel electrode, 11
... Fuel gas passage, 12 ... Electrolyte, 13 ... Air electrode, 14 ... Air passage, 15 ... Separation plate, 1
6, 17...Rib, 18...Cooler holder, 1
9, 20... Cooling pipe, 22, 221, 222...
Inlet side gas chamber, 23... Outlet side gas chamber, 24...
Common gas chamber, 27... Partition plate, 28, 291, 2
92,293...Partition, 30...Partition plate.

Claims (1)

[Claims] 1. A unit structure consisting of first and second electrodes constituting a fuel cell and an electrolyte disposed between the two electrodes, and a first unit structure disposed opposite to the first electrode. A fuel cell stack formed by stacking a plurality of fuel cells with a reaction gas space and a second reaction gas space provided opposite to the second electrode separated by an isolation means, and in which a reaction gas flows into the reaction gas space via a manifold. In the body,
The reaction gas spaces of the plurality of stacked unit structures are connected in parallel and in series by the manifold, and the number of parallel reaction gases on the downstream side is equal to the number of parallel connections on the upstream side connected in series. The reaction gas space is reduced by at least one space compared to the above, and each space is partitioned by a partition structure that divides the space into a plurality of spaces, and each space partitioned by the partition structure is connected in parallel, in series, or in series and parallel by the manifold. Among the reaction gas spaces, the width of the electrodes connected to each other and to which the reaction gas is supplied by the partitioned spaces is narrower at at least one point on the downstream side of the reaction gas than on the upstream side, A fuel cell stack comprising at least one. 2. The fuel cell stack according to claim 1, wherein the reaction gas space is a fuel gas space. 3. A unit structure consisting of first and second electrodes constituting a fuel cell and an electrolyte disposed between the two electrodes is placed in a reaction gas space opposite to the first electrode and in the second electrode. In a fuel cell stack, which is formed by stacking a plurality of fuel cells through isolation means for a second reaction gas space provided opposite to the fuel cell, and in which a reaction gas flows into the reaction gas space via a manifold, a plurality of the stacked fuel cells are stacked. The reaction gas spaces of the unit structure are connected in parallel and in series by the manifold, and the number of parallels on the downstream side of the reaction gas is at least one less than the number of parallels on the upstream side connected in series. The reaction gas space is divided into a plurality of spaces, and each space is partitioned by a partition structure that divides each space into a plurality of spaces, and each space partitioned by the partition structure is connected in parallel, in series, or in series and parallel by the manifold. the width of the electrode to which the reactive gas is supplied by each space is narrower at at least one location on the downstream side of the reactive gas than on the upstream side; A cooling pipe is provided for each stack of the unit structures, and a reaction gas space located near the cooling pipe is connected to the downstream side, and a reaction gas space located far from the cooling pipe is connected to the upstream side. 1. A fuel cell stack characterized by having a series gas flow path. 4. The fuel cell stack according to claim 3, wherein the reaction gas space is a fuel gas space.