JPS62103983A - Fuel cell power generation system - Google Patents

Abstract

PURPOSE:To enhance the performance of a fuel cell and lengthen the life thereof, by providing a flow rate distribution orifice in a coupling metal located upstream as to the direction of passage of cooling water in an insulated coupling, and by performing electric connection so that the potential of the coupling metal provided with the orifice is lower than that of another coupling 27a comprises an anode and an cathode. CONSTITUTION:An insulated coupling 27a comprises an anode and an cathode meals 34, 35 and an insulation TEflon tube 33 connecting both the metals to each other. A flow rate distribution orifice for improving the balance of flow rates is provided in the anode metal 34 located upstream as to the direction of passage of cooling water in the insulated coupling 27a. Another insulated coupling 27b similarly comprises an anode and a cathode metals 34, 35 and an insulation Teflon tube 33 but is provided with no flow rate distribution orifice. Since the potential of the anode metal 34 provided with the orifice is lower than that of the cathode metal 35 provided with no orifice, a corrosion product does not clinging in the orifice. This results in preventing local overheating due to the decrease in the flow rate of the cooling water, to enable the very-efficient and stable operation of a fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell power generation system, and more particularly to an improvement of a fuel cell power generation system comprising a cooling water system for removing heat generated by a fuel cell.

[Technical background of the invention]

A fuel cell is a device that directly converts the energy released from the oxidation reaction into electrical energy by oxidizing the chemical energy of fuel through an electrochemical process. Power generation systems using fuel cells are expected to achieve power generation efficiency of 40 to 50% even on a relatively small scale, far exceeding new thermal power plants. Furthermore, SOx is a pollution factor that has become a major social problem in recent years.

In principle, high energy conversion efficiency can be expected due to extremely low NOX emissions, no combustion cycle is included in the power generation equipment, so large amounts of cooling water are not required, and vibration noise is small. Because it has such characteristics as having few problems and good responsiveness to load fluctuations, there are expectations and interest in research into its development and practical application.

Additionally, since this fuel cell power generation system can be modularized, it also has the advantage of shortening the construction period. In addition, the exhaust heat temperature of the fuel cell itself is within the range that can be used as a heat source for hot water supply, etc., and it is highly efficient, making it possible to create a heat supply power generation system, so it can be used as a large-scale power generation system to partially replace thermal power generation in the future. There are also high expectations and interest.

A small-scale fuel cell power generation system like this has already been prototyped and is now in the experimental operation stage. but,
The biggest technical problems in the practical application of large-capacity fuel cell power generation systems are miniaturization of individual fuel cells due to increased unit capacity, and how to efficiently arrange and install a large number of fuel cells. It all depends on how much space can be reduced and how efficiently the various piping and power terminal connection systems of the fuel gas cooling system can be made more efficient.

Now, a cross-sectional model diagram showing the principle of such a fuel cell is shown in Section 4.
Shown in the figure. That is, a single cell is formed by interposing an electrolyte layer 2 impregnated with an electrolyte such as phosphoric acid between the - set of porous electrodes 1, and hydrogen gas H, which is a fuel gas, is formed on both end faces of the single cell. and air A, which is an oxidant gas, are continuously supplied. In this way, reaction products and reaction residues are continuously removed to the outside, so power generation can be continued for a long period of time.

Further, the basic configuration of such a fuel cell is as shown in FIG. That is, a positive electrode 4 and a negative electrode 5 are arranged on both sides of an electrolyte matrix layer 3 to form a square plate-shaped unit cell, and in order to use this unit cell as a power generation device, a large number of unit cells are connected in series. Although it is laminated with
Ink connectors 6 having grooves for supplying gas are arranged between these single cells, and are stacked alternately with the above single cells. This ink connector 6 is provided with a plurality of grooves opening on two opposing side edges, and the hydrogen gas flow path 7 and the air flow path 8, which use the grooves on the side surfaces as flow paths, are arranged in directions orthogonal to each other. has been done.

By the way, the fuel cell N currently under development is the sixth
As shown in Figures (a) and (b), a cell stack 9 is constructed by stacking a plurality of cells as described above in a square column shape, and manifolds 10 for supplying reaction gas are attached to the four circumferential sides of the cell stack 9. There is. This manifold 10 includes a hydrogen gas supply pipe 11, a hydrogen gas discharge pipe 12, and an air supply pipe 1, respectively.
3 and an air exhaust pipe 14 are connected, and the hydrogen gas and air are designed to flow in the directions of arrows A and B in the cell stack 9. Further, although a higher operating temperature of the cell stack 9 is preferable in terms of reaction theory, it is desirable to maintain the operating temperature at around 200° C. due to constraints such as the heat resistance of the constituent materials and the vapor pressure of the electrolyte.

Therefore, the conduit (cooling pipe) buried in the cell stack 9
Cooling water is circulated inside the fuel cell to cool down the heat generated during fuel cell startup and during operation. That is,
In this type of fuel cell, a cooling water supply pipe 15 and a cooling water discharge pipe 16 are arranged as shown in FIG. 6(a), and the cooling water circulates within the cell stack 9 as shown by the broken line C. ing.

Furthermore, the output of the fuel cell N is direct current, which is connected to the tank 2 through a connecting conductor 19 and a bushing 20 from a power terminal (positive pole) 17 and a power terminal (minus pole) 18 arranged at the upper and lower ends of the cell stack 9. being pulled outside.

The main body of the fuel cell as described above is housed in the tank 21, and the tank 21 is filled with nitrogen gas or the like in order to suppress leakage of reaction gas from the manifold 10 and others. In order to maintain the cell stack 9 at an appropriate temperature and to effectively utilize the heat generated during operation through cooling pipes without dissipating it to the outside, a heat insulating material 22 is attached to the inner surface of the tank 21, etc. There is.

[Problems with background technology]

Now, fuel cells generate DC voltage through an electrochemical reaction, but heat is generated along with this reaction.

In order to operate this fuel cell efficiently and appropriately, it is necessary to control the temperature of the cell stack at a constant level, and for this purpose, a cooling water system is provided to perform cooling with water. In addition, since fuel cells connect a large number of single cells or cell stacks in series and parallel, it is necessary to balance the flow rate of cooling water in order to obtain a uniform temperature distribution. It is possible to use a general method of providing a. However, when there are many cooling systems connected in parallel, the number of apertures increases, which can lead to problems such as increased cost and reduced reliability due to increased space taken up or increased number of connection points during manufacturing. be.

On the other hand, the cooling water system of the fuel cell power generation system is provided with an insulating joint because it is necessary to electrically insulate the DC voltage generated by the fuel cell. Since the flow rate to each fuel cell is the same as the amount of R in this insulated joint, a method of balancing the flow rate at the insulated joint may be considered. That is, the above-mentioned problems can be solved by providing a restriction in the joint fitting in the insulated joint. However, some of these insulating joints receive a DC voltage of about 30'0 volts even within the cell stack, and several thousand volts between the cell stacks. When a DC voltage is applied to the insulated joint in this way, corrosion products generated in the cooling water piping, etc. will be attached to the inner surface of the joint fitting where the voltage has a positive polarity (regardless of the direction of water flow). ) was found to be. This relationship is shown in the table below, in which the leakage current of the joint fittings to which a positive voltage is applied is expressed as plus (+). This deposit adheres to the inner surface of the fitting in the form of a sharp orifice, increasing water flow resistance, and as a result, the cooling water base decreases and the cooling capacity decreases. Depending on the amount of this adhesion, the flow rate balance of the cooling water may become unbalanced, and if the adhesion adheres to the above-mentioned narrow constriction part of the water passage, even a small amount of adhesion may cause a blockage. This can cause overheating, leading to decreased performance and shortened fuel cell life.

Table 0) Relationship between the adhesion of corrosion products and leakage current [Object of the invention] The present invention was made to solve the above problems, and its purpose is to reduce the flow rate of cooling water due to the adhesion of corrosion products. Minimize the imbalance of silver? A small, inexpensive, and highly reliable fuel cell power generation system that reliably prevents local overheating due to ll reduction, improves fuel cell performance, and extends its service life, allowing for highly efficient and stable battery operation. The goal is to provide a system.

[Summary of the invention]

In order to achieve the above object, the present invention stores in a tank a cell stack formed by stacking a plurality of single cells each having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte, and A fuel cell configured to supply fuel gas to one electrode and oxidant gas to the other electrode, and extract electrical energy from between the electrodes through an electrochemical reaction that occurs, and an interior of the cell stack. A plurality of cooling pipes are buried in the cooling pipe, and cooling water supply and discharge pipes are respectively connected to the cooling pipe to circulate the cooling water, and the cooling pipe and the cooling water supply pipe are connected to each other. An insulating joint for electrical insulation consisting of two tubular joint fittings and an insulating tube connecting these joint fittings to each other is provided at each connecting portion between the cooling pipe and the cooling water discharge pipe. In a fuel cell power generation system comprising a cooling water system configured as described above, a fitting for distributing a flow rate is provided in a fitting fitting on the upstream side of the cooling water flow direction of the insulating joint, and a fitting fitting provided with the restriction. By making electrical connections so that the voltage on the other fittings is negative in polarity with respect to the other fittings facing it, imbalances in the cooling water flow rate due to corrosion-generating parts can be minimized and a uniform flow rate can be achieved. It is characterized by being able to perform cooling.

[Embodiments of the invention]

An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows an example of the configuration of a fuel cell power generation system according to the present invention, and this example shows a fuel cell power generation system consisting of two cell stacks. In the figure, the same parts as in FIGS. 6(a) and 6(b) are given the same reference numerals, and the explanation thereof will be omitted, and only the different parts will be described here.

In the figure, first, the cooling water system will be described. Each end of a plurality of cooling pipes 26 buried in each cell stack 9 is connected to a header 25 on the supply and discharge sides, respectively. In addition, the header 25 on the supply side is connected to an insulating joint 27a.
The header 25 on the discharge side is connected to the supply side manifold 23 via an insulating joint 27b, and the discharge side header 25 is connected to the discharge side manifold 24 via an insulating joint 27b. Furthermore, the supply side manifold 23 has an insulating joint 2 in the upper cell stack 9.
7a and directly in the lower cell stack 9.
They are connected to the cooling water supply pipes 15, respectively.

Further, the discharge side manifold 23 is connected to the cooling water discharge pipe 16 in the upper cell stack 9 via an insulating joint 27b, and directly in the lower cell stack 9. On the other hand, the cooling water enters from the cooling water supply pipe 15 side, is heated by the cooling pipe 26, and flows to the cooling water discharge pipe 16 side. This heated cooling water may flow as a so-called two-phase flow containing some water vapor, but this cooling water containing heat is cooled in the steam water separator 31 and adjusted to an appropriate temperature. After that, the water is sent through the cooling water piping 29 to the cooling water supply pipe 15 through the cooling water piping 30 by the circulation pump 28 . By circulating the cooling water in this manner, the fuel cell is maintained at an appropriate temperature.

On the other hand, the insulating joints 27a and 27k in the figure are provided to electrically insulate the pipes connected to them, and are necessary for the piping for cooling water passage of fuel cells that generate DC voltage. It is essential. This insulation joint 27a
By using 27b and 27b, it is possible to maintain the pipes connected thereto at different potentials. Also, Figure 2 (
1A is an enlarged view of the insulating joint 27a in FIG. 1, and FIG. 1B is a cross-sectional view thereof. In other words, the insulating joint 27a consists of two tubular joint fittings, namely a cathode and an anode fitting 34.35, and a Teflon insulating tube 33 that connects these cathodes and #I electrode fittings 34.35. Inside the cooling water passage device 34, a flow rate distribution throttle is provided as shown in the figure to improve the flow rate balance. In addition, the insulation joint 27b
Similarly, it consists of a cathode, anode fittings 34 and 35, and a Teflon insulating tube 33, and is constructed without the above-mentioned flow rate distribution restrictor. Here, the material of the cathode fitting 34 is a metal used for general piping (carbon steel, stainless copper,
Copper and copper alloys, etc.) can be used. On the other hand, as the material for the anode fitting 35, it is preferable to use copper, a copper alloy, or a metal other than carbon steel that does not easily cause electrolytic corrosion (high nickel or high chromium alloy such as stainless steel copper).

Next, to explain the electrical connections, the power terminal (negative pole) 18 of the lower cell stack 9 in FIG. Also connect. Further, the power terminal (plus tΦ) 17 is connected to the power terminal (minus pole) 18 of the upper cell stack 9,
The power terminal (negative pole) 18 is connected to a supply side manifold 23 and a discharge side manifold 24.

On the other hand, the power terminal (positive electrode) 17 of the upper cell stack 9
is connected to the other terminal of the load 32, and the electrical energy generated in the cell stack 9 of the fuel cell is consumed by the load 32. Furthermore, the cooling water supply pipe 15 of the cooling water system.
Cooling water discharge pipe 16. Cooling water piping 29 and 30. Steam water separator 31. The circulation pump 28 is electrically connected and grounded.

Here, between the cell stack and between the cell stack 9 and the load 3
Since a large current flows between the two, it is necessary to connect them with a power line, but a large current does not flow in the wire between the power terminal (negative pole) 18 and the supply side manifold 23 or the discharge side manifold 24, so it is necessary to use a power line. There isn't. That is, the leakage current of the insulated joints 27a and 27b flows through this electric wire.

In a fuel cell power generation system equipped with a cooling water system configured as described above, the voltage of the cathode metal fitting 34 with a restriction located on the upstream side in the cooling water flow direction of the insulating joint 27a provided on the cooling water supply side is However, since the polarity is on the negative side when viewed from the anode metal fitting 35 without a restriction which is opposite to this, there is no possibility that corrosion products will adhere to the inside of this restriction.

Further, adhesion occurs within the anode metal fitting 35, which is a joint fitting on the downstream side in the cooling water flow direction, but since this portion has a large inner diameter, the decrease in the inner diameter due to adhesion is small.

Furthermore, since the resistance due to the diaphragm is proportional to the rate of decrease in the cross-sectional area of the diaphragm, the rate of increase in resistance is very small compared to when it is attached inside the diaphragm.

As mentioned above, fuel cells usually obtain the necessary current capacity by stacking a large number of single cells, so the number of cooling pipes and insulating joints must be increased accordingly.

Size, length, etc. have a big effect on the overall space of the battery. In this regard, in the fuel cell power generation system according to the present embodiment, the throttle, which is used as a method for improving the flow balance of cooling water, is housed within the insulating joint 27a, which has an advantage in terms of space. By allowing corrosion products to adhere to the unrestricted area in the vicinity, the increase in flow path resistance due to adhesion can be suppressed to a low level, and local overheating due to a decrease in the flow rate of cooling water can be prevented, resulting in extremely high efficiency. It becomes possible to operate the fuel cell stably.

It should be noted that the present invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist thereof.

(a) In the above embodiment, the throttle was provided only in the joint fitting of the insulating joint provided at the connection part between the supply side manifold 23 and the header 25 for supplying cooling water.
As shown in the figure, the cooling water flows through the respective insulating joints provided at the connection parts between the supply side manifold 23 and the header 25 for cooling water supply and between the discharge side manifold 24 and the header 25 for cooling water discharge. Even if a throttle is provided in the joint fitting on the upstream side in the water direction, the same effects as described above can be obtained. In this case, each of the insulating joints 27a provided on the supply side and the discharge side is configured such that the voltage of the joint metal fitting provided with the throttle of the insulating joint 27a has a negative polarity with respect to the other joint metal fittings facing it, as described above. Electrical connections are made so that

(b) In the above embodiment, the case where the present invention is applied to a fuel cell power generation system composed of two cell stacks is described, but the present invention is not limited to this. The present invention can be similarly applied to a fuel cell power generation system composed of the following.

〔Effect of the invention〕

As explained above, according to the present invention, a cell stack consisting of a plurality of stacked cells each having a pair of porous electrodes arranged with an electrolyte layer impregnated in between is housed in a tank, and A fuel cell configured to supply fuel gas to one electrode and oxidant gas to the other electrode, and extract electrical energy from between the electrodes through an electrochemical reaction that occurs, and an interior of the cell stack. A plurality of cooling pipes are buried in the cooling pipe, and cooling water supply and discharge pipes are respectively connected to the cooling pipe to circulate the cooling water, and the cooling pipe and the cooling water supply pipe are connected to each other. An insulating joint for electrical insulation consisting of two tubular joint fittings and an insulating tube connecting these joint fittings to each other is provided at each connecting portion between the cooling pipe and the cooling water discharge pipe. In a fuel cell power generation system comprising a cooling water system configured as described above, a joint for flow distribution is provided in the joint fitting on the upstream side of the cooling water/water flow direction of the insulated joint, and the joint is provided with the restriction. Electrical connections are made so that the voltage of the metal fitting has negative polarity with respect to the other fittings facing it, minimizing imbalance in the cooling water flow rate due to the adhesion of corrosion products. A small, inexpensive, and highly reliable fuel cell that reliably prevents local overheating due to a decrease in flow rate, improves fuel cell performance, and extends its lifespan to ensure efficient and stable cell operation. Power generation system can be provided.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the fuel cell of the present invention, FIGS. 2(a) and 2(b) are enlarged views and cross-sectional views showing insulating joints applied to the same embodiment, and FIG. 3 is a diagram of the present invention. A configuration diagram showing another embodiment of the invention, FIG. 4 is a cross-sectional model diagram showing the principle of the fuel cell, and FIG. 5 is a vertical cross-sectional perspective view showing the basic configuration of the fuel cell.
FIG. 6(a) is a plan view showing a schematic configuration of a fuel cell currently under development, and FIG. 6(1) is a longitudinal sectional view thereof. N... Fuel cell, 1... Porous electrode, 2... Electrolyte layer, 3... Electrolyte matrix, 4... Positive electrode, 5
... Negative electrode, 6... Ink connector, 7... Hydrogen gas channel, 8... Air channel, 9... Cell stack, 1
0... Manifold, 11... Hydrogen gas supply pipe, 1
2... Hydrogen gas discharge pipe, 13... Air supply pipe, 14
...Air discharge pipe, 15...Cooling water supply pipe, 16...
・Cooling water discharge pipe, 17...Power terminal (positive pole), 1
8... Power terminal (negative pole), 19... Connection conductor, 20... Bushing, 21... Tank, 22...
・Heat insulation material, 23...Supply side manifold, 24...
Discharge side manifold, 25...header, 26...
Cooling pipe, 27a... (with orifice) insulation joint, 27b...
...(No throttle) Insulation joint, 28...Circulation pump, 2
9... Cooling water piping, 30... Cooling water piping, 31...
・Steam water separator, 32...Load, 33...Teflon insulation tube, 34...Cathode fitting (with aperture), 35...g
i-electrode alloy fitting 36...piping, A...air, H...hydrogen, L...reaction products and reaction residues. Applicant's representative Patent attorney Takehiko Suzue Figure 1 (a) (b) Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (3)

[Claims] (1) A cell stack consisting of a plurality of single cells stacked with a pair of porous electrodes sandwiched between an electrolyte layer impregnated with an electrolyte is housed in a tank, and one electrode is also supplied with fuel gas. A fuel cell configured to supply an oxidizing gas to each of the other electrodes and extract electrical energy from between each of the electrodes through an electrochemical reaction that occurs, and a plurality of cooling pipes buried inside the cell stack. At the same time, cooling water supply and discharge piping are respectively connected to the cooling pipe to circulate the cooling water, and between the cooling pipe and the cooling water supply piping and between the cooling pipe and the cooling water. A cooling water system comprising two tubular joint fittings and an insulating joint for electrical insulation consisting of an insulating tube that connects these joint fittings to each connection portion with the discharge piping. In the fuel cell power generation system, a throttle for flow distribution is provided in the joint fitting on the upstream side of the cooling water flow direction of the insulated joint, and the voltage of the joint fitting provided with the restriction is opposite to this. A fuel cell power generation system characterized in that the electrical connection is made so that the polarity is on the negative side with respect to the joint fitting. (2) The fuel according to claim (1), characterized in that a restriction is provided only in the joint fitting of the insulated joint provided at the connection portion between the cooling pipe and the cooling water supply pipe. Battery power generation system. (3) A restriction is provided in the joint fitting of each insulating joint provided at the connection portion between the cooling pipe and the cooling water supply pipe and between the cooling pipe and the cooling water discharge pipe. A fuel cell power generation system according to claim (1).