JPS6298573A - Fuel cell - Google Patents

Abstract

PURPOSE:To increase pressure loss in the inlet and the outlet of a cell, reduce hydrostatic pressure effect caused by gas density difference, and make flow rate distribution uniform by arranging a resistance which produces flow resistance in the front of cell stack on fuel gas inlet side and/or the surface of cell stack on its outlet side. CONSTITUTION:A flow resistance 8 is arranged in the front of fuel gas inlet in a cell stack 1. The flow resistance 8 produces resistance to fuel gas supplied, and any resistance such as porous plate which produces large pressure loss compared with hydrostatic pressure effect can be used for the flow resistance 8. In pressure distribution in the inside of manifold of the inlet and outlet of fuel cell, since pressure difference between the inlet and the outlet is increased by the flow rate resistance plate, the upper part pressure difference DELTAPtop and the lower part pressure difference DELTAPbottom are increased, and the ratio of pressure difference in the upper part and the lower part (DELTAPtop/DELTAPbottom) becomes nearly 1. Therefore, the flow rate distribution in a cell height direction is made uniform.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to the main body structure of a fuel cell power generation device. There is growing interest in the use of power generation systems based on power generation systems as medium-sized distributed power plants in the suburbs of cities. The structure of the cell main body of this fuel cell is, for example, as shown in FIG. That is, a cell stack 1 assembled by stacking a plurality of single cells is fixed at the top and bottom using battery holders 2, and a fuel gas inlet port 4 and a rectifying plate 5 are fixed.
The battery main body is constructed by disposing a fuel gas inlet manifold 3 with a fuel gas inlet manifold 3 on one side of the battery, and disposing a fuel gas outlet manifold 6 with a fuel gas outlet port 7 on the opposite side.

In a fuel cell with such a configuration, it is important to know how many stages of cells the cell stack of the battery itself consists of, or in other words, how many AAA cells it consists of.
N becomes necessary. This is because the magnitude of the power generation output of a fuel cell is determined by the number of single cells. With the recent progress in cell stacking technology, it has become possible to achieve stacking heights of more than 2 meters for a single battery, but by increasing the height of a single cell stack, It has become possible to increase the firing output per cell stack. Generally, a system using fuel cells for power generation in the suburbs of a city is constructed by combining a plurality of cell stacks according to the demand. If the height of the cells in the cell stack can be made as high as possible based on stacking technology, the number of cell stacks in the system can be reduced, the piping system can be simplified, the control system can also be simplified, and the power generation system can be improved. The rational aspect is that the overall configuration is simple, and a compact, inexpensive, and highly reliable fuel cell power plant can be provided.

However, increasing the stacking height of the cell stack creates new technical problems.

It is a problem inherent in fuel cells used under gravity.

In a fuel cell, the composition of the fuel gas at the manifold inlet and outlet is different, so the density of the fuel gas at the manifold inlet and outlet is different. This difference in density also changes depending on the power generation load, and the higher the load, the larger the difference in si becomes. This is due to the following reason.

Hydrogen utilization rate is an indicator of the power generation load of batteries. This indicates how much of the hydrogen gas component in the fuel gas is used for power generation when passing through the battery, and the higher the hydrogen utilization rate, the higher the power generation load. For example, when the hydrogen utilization rate is 80, hydrogen gas in the fuel gas in the battery inlet manifold is 100 (mo
l/Hour), 80% of this is contained inside the battery, that is, 80 (mol/) (o u r
) is used in a chemical reaction with oxygen to generate electricity, leaving 20 (mol/
Hour ) refers to an operation in which hydrogen gas is discharged unused. Gas components other than hydrogen in fuel gas are gases with higher specific gravity than hydrogen, such as carbon dioxide and methane, so if the proportion of hydrogen in fuel gas decreases, the density of fuel gas increases. . Therefore, when the fuel gas in the inlet manifold is the same, the larger the power generation load, the more
In other words, the higher the hydrogen utilization rate, the greater the density of the fuel gas in the outlet manifold.

By the way, this difference in density between the inlet and outlet manifolds causes a problem in that fuel gas is not uniformly supplied to each unit cell. This will be explained using FIG. FIG. 6 shows the pressure distribution of the inlet manifold and the outlet manifold in the height direction of the pond. Hydrostatic pressure of fuel gas, i.e. (gas density ρ) × (
Due to the effect of gravitational acceleration, 'fg)X (high ah), the distribution is linear, and the pressure at the bottom of the 'μ battery becomes high. However, due to the difference in density between the inlet and the outlet, the slope of the straight line is larger on the outlet manifold side where the gas density is higher, and the pressure difference △P between the manifold inlet and outlet is greater than that at the top of the battery (above ΔP).
is large, and the bottom of the battery (below ΔP) is small.

Since the flow in the battery cell groove is laminar due to the low flow velocity, the flow rate and the pressure difference between the inlet and the outlet are approximately proportional. (However, as hydrogen is used during the flow, the physical properties change every moment, so the relationship is not completely proportional.) Therefore, the flow rate distribution in the battery height direction is as shown in Figure 7. , a large amount of fuel gas flows above the cell, and only less than the average flow of gas flows below, resulting in non-uniformity.

This 15 tf amount distribution becomes more non-uniform as the height of the cell stack becomes higher, the power generation load becomes higher, and the hydrogen utilization rate increases. As described above, if the supply of fuel gas to the lower part of the cell becomes insufficient, sufficient ignition cannot be performed. This is because the hydrogen gas in the fuel gas is used up, so to speak, a gas starvation situation occurs.

This will be explained in detail using figures. First, FIG. 8 schematically shows the gas reaction inside the battery.

If the hydrogen utilization rate is 80% and the flow rate is 100%, that is, the average flow rate passes through the cell, 80% of the hydrogen will be consumed, so 1006 hydrogen at the inlet manifold will be 200% at the outlet.
and is discharged. On the other hand, uneven flow distribution occurs in the cell stack height direction, and some cells have an average flow rate of 14
Let's consider the case where 0chi flows.

The amount of hydrogen at the inlet is 140 when the average flow rate is 100. Since the chemical reaction within the fuel cell is a heterogeneous reaction carried out via a catalyst, the degree of reactivity does not change depending on the concentration of hydrogen gas in the fuel gas. Therefore, even if the flow rate changes, the amount of hydrogen participating in the reaction is always 8
0, even if the flow rate is 140%, 60% hydrogen is discharged at the outlet, and if we focus only on this cell, the hydrogen utilization rate is 1×100#57%. In other words, the hydrogen utilization rate used as an index of the fuel cell load is determined from the average amount of hydrogen gas in the inlet and outlet manifolds, so when viewed locally, the hydrogen utilization rate of each cell is This may be due to non-uniform flow distribution. The problem here is that because the reaction form inside the fuel/cell is a heterogeneous reaction, if the amount of gas flowing into the cell is insufficient, all the hydrogen gas will be consumed. This is the occurrence of a deficiency phenomenon. This is also represented by the 60% flow rate line in FIG. At a flow i of 60%, the hydrogen gas component is completely consumed in the middle of the battery. When a single battery runs out of gas, the battery will no longer be able to generate the rated voltage. Since the batteries are connected in series, if even one single cell does not generate enough power, the entire fuel cell's 8 ton capacity will be insufficient. FIG. 9 shows the flow rate distribution in the height direction of the battery and the amount of hydrogen at the outlet, but there is a possibility that hydrogen gas may run out at the bottom of the battery. FIG. 10 shows the relationship between the fuel gas flow rate and the hydrogen concentration in the outlet manifold depending on the hydrogen utilization rate. As the power generation load is increased and the hydrogen utilization rate is increased, the lower limit of flow rate at which gas starvation occurs increases accordingly, which may cause a phenomenon in which the power generation voltage suddenly drops sharply.

As mentioned above, increasing the height of the cell stack increases the unevenness of the flow rate distribution of fuel gas in the cell height direction and causes problems such as hydrogen gas shortage and unstable power generation. Put it away.

For this reason, current fuel cells are made with a lower number of cell stacks, despite the fact that there is stacking technology that can create fuel cells that are advantageous in terms of system configuration.
In many cases, the configuration is such that non-uniformity of flow rate does not occur much. As described above, this increases the number of batteries, which complicates the system configuration, which is unfavorable from the viewpoints of cost, building area, and reliability.

[Purpose of the invention]

The present invention has been made to eliminate the problems of the prior art described above, and even if the cell stack of a fuel cell becomes high-rise, it can uniformly distribute the fuel gas flowing to each unit cell and supply hydrogen gas. The purpose of the present invention is to provide a fuel cell that is capable of stably generating electricity even under high loads, and is advantageous in terms of system configuration.

[Summary of the invention]

In order to achieve the above object, the present invention creates flow resistance on the front surface of the cell stack on the fuel gas inlet side, the cell stack surface on the outlet side, or both surfaces without changing the stacking height of the cell stack. To provide a fuel cell in which the pressure loss between the cell inlet and outlet is increased by installing a resistor, the hydrostatic pressure effect due to the difference in gas density is reduced, and the flow distribution is made uniform.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

composition FIG. 1 shows a configuration diagram of a fuel cell according to an embodiment of the present invention.

This embodiment differs from the conventional configuration shown in FIG. 5 in the point indicated by the arrow. That is, the flow resistor 8 is installed on the front surface of the cell stack 1 on the fuel gas inlet side. This flow resistor 8 acts as a resistance to the inflowing fuel gas,
Any resistor, such as a porous plate or a porous plate, can be used as long as it produces a large pressure loss compared to the hydrostatic pressure effect.

Operation: The pressure distribution within the manifold at the inlet and outlet of the fuel cell constructed as described above is shown in FIG.

In other words, since the pressure difference between the inlet and outlet has increased due to the flow resistance plate, when compared with the pressure distribution in the manifold of a fuel cell with a conventional configuration (Fig. 6), the pressure difference ΔP at the top of the cell has increased.
The pressure difference ΔP between the top and bottom of the battery is also increasing. As a result, when comparing the ratio of the pressure difference between the upper and lower parts of the cell (ΔP upper/ΔP lower), the value of (ΔP upper/ΔP lower) is 1 in the fuel cell of the present invention than in the conventionally configured fuel cell. Get closer. Therefore, the flow rate distribution in the battery height direction becomes nearly uniform. FIG. 3 shows the fuel gas flow rate distribution in the cell height direction of the fuel cell according to the embodiment of the present invention. There is no need to compare this with FIG. 7, which shows the flow rate distribution of the conventional structure, to see that the flow source of the fuel gas supplied to each unit cell is made uniform.

Effects According to this embodiment, since the flow rate distribution is made uniform as shown in FIG. 3, the hydrogen amount distribution in the outlet manifold is also as shown in FIG. This will not occur and stable power generation will be possible.

Other Examples In this example, the flow resistor was installed on the cell stack inlet side, but the flow resistor may also be installed on the cell stack outlet side, or it can be installed on both the inlet and outlet sides. effect can be obtained.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, there is no need to reduce the height of the cell stack or increase the number of cell stacks. It is possible to solve the problem of uniformity and provide a fuel cell that can stably generate power even during high hydrogen utilization rate operation. Furthermore, since the number of battery bodies can be kept to a minimum, the system can be simplified, making it possible to provide a fuel cell power plant that is advantageous in terms of reliability and cost.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a fuel cell showing an embodiment of the present invention;
FIG. 2 is a pressure distribution diagram in the inlet and outlet manifolds of a fuel cell having the configuration of an embodiment of the present invention, FIG. 3 is a flow rate distribution diagram in the same cell, and FIG. 4 is a diagram of the outlet manifold. Hydrogen amount distribution diagram, Figure 5 is a configuration diagram of a conventional fuel cell, Figure 6 is a pressure distribution diagram in the inlet and outlet manifolds of a conventional fuel cell, and Figure 7 is a flow rate distribution diagram in the same cell. , Fig. 8 is a schematic diagram showing the reaction process of hydrogen gas inside the cell, Fig. 9 is a hydrogen amount distribution diagram of the outlet manifold of a conventional fuel cell, and Fig. 10 is a diagram showing the hydrogen utilization rate as a parameter. FIG. 3 is a schematic diagram showing the relationship between the fuel gas flow rate and the amount of hydrogen in the outlet manifold. 1 Cell stack 3 ・Fuel gas inlet manifold 6 Fuel gas outlet manifold 8 Flow resistor agent Patent attorney Norihiro Chika Ken Yudo Hiroshi Mimata Large amount of water □ Large amount - 111 Figure 9 - Text - Material η゛ku Dot number 10 - Overthrowing

Claims (1)

[Claims] In a fuel cell in which a fuel gas inlet manifold is arranged on one side of a cell stack assembled by stacking multiple unit cells and a fuel gas outlet manifold is arranged on one side, the cell on the fuel gas inlet side A fuel cell characterized in that a resistor is installed on the front surface of the stack, on the surface of the cell stack on the outlet side, or on both sides of the cell stack on the inlet and outlet sides to create flow resistance to gas flow.