JPH0624136B2 - Fuel cell power generation system - Google Patents

Description

Description: 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 including a cooling water system for removing heat generated by the fuel cell.

[Technical background of the invention]

A fuel cell is a device that directly oxidizes the chemical energy of the fuel in an electrochemical process to directly convert the energy released along with the oxidation reaction into electrical energy. The power generation system using this fuel cell is expected to reach a power generation efficiency of 40 to 50% even on a comparatively small scale, and far surpass the new thermal power. Furthermore, SOx, N, which is a pollution factor that has become a big social problem in recent years,
In principle, high energy conversion efficiency can be expected, such as extremely low Ox emissions, no need for a large amount of cooling water because the power generator does not include a combustion cycle, and low vibration noise, as well as environments such as noise and exhaust gas. Since there are few questions and answers, and because it has characteristics such as good responsiveness to load fluctuations, expectations for and interest in research on its development and practical application are high.

In addition, since this fuel cell power generation system can be modularized, the construction work period is short. Furthermore, since the exhaust heat temperature of the fuel cell body is in a range that can be used as a heat source for hot water supply, etc., and it has high efficiency such as the ability to create a heat supply power generation system, it can be used as a large-scale power generation system to partially replace future thermal power generation. Is also expected and interested.

A small-scale fuel cell power generation system like this has already been prototyped and is in the stage of experimental operation. But,
The biggest technical problems in putting a large-capacity fuel cell power generation system to practical use are miniaturization of individual fuel cells by increasing the capacity of a single unit, and how efficiently multiple fuel cells are arranged and installed. It depends on how to reduce the space and improve the efficiency of the connection system of various pipes and power terminals of the fuel gas cooling system.

Now, a cross-sectional model diagram showing the principle of such a fuel cell is shown in FIG.
As shown in the figure. That is, a unit cell is formed by interposing an electrolyte layer 2 impregnated with an electrolytic solution such as phosphoric acid between a pair of porous electrodes 1, and hydrogen gas H, which is a fuel gas, is formed on both end faces of the unit cell. And air A, which is an oxidant gas, are continuously supplied. By doing so, the reaction product and the reaction residue L are continuously removed to the outside, so that power generation is continued for a long time.

The basic structure 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 the electrolyte matrix layer 3 to form a rectangular plate-shaped unit cell, and a large number of unit cells are connected in series in order to use the unit cell as a power generator. And then stacked,
The interconnector 6 is provided with a groove for supplying a gas between these unit cells, and is stacked alternately with the unit cells. The interconnector 6 is provided with a plurality of grooves that open at two opposite side edges, and the hydrogen gas flow path 7 and the air flow path 8 whose channels are grooves on one side face 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 FIGS. (A) and (b), a cell stack 9 is constructed by stacking a plurality of the above-mentioned unit cells in a square pole shape, and a manifold 10 for supplying a reaction gas is attached to the side surfaces of the four sides. There is. The manifold 10 includes a hydrogen gas supply pipe 11, a hydrogen gas discharge pipe 12, and an air supply pipe 1, respectively.
3 and the air discharge pipe 14 are connected to each other, and the hydrogen gas and the air are designed to flow in the cell stack 9 in the directions of arrows A and B in the drawing. Further, the higher the operating temperature of the cell stack 9 is from the viewpoint of reaction theory, but it is desirable to maintain the operating temperature at around 200 ° C. due to heat resistance of constituent materials and vapor pressure of electrolyte. Therefore, the cooling water is circulated through the conduit (cooling pipe) embedded in the cell stack 9 to cool the fuel at the time of starting the fuel cell and the heat generated during the operation. That is, in this type of fuel cell, the cooling water supply pipe 15 and the cooling water discharge pipe 16 are arranged as shown in FIG. 6 (a), and the cooling water flows in the cell stack 9 as shown by a broken line C in the drawing. It circulates. Further, the output of the fuel cell N is direct current, and from the power terminal (plus pole) 17 and the power terminal (minus pole) 18 arranged at the upper and lower ends of the cell stack 9,
It is drawn out of the tank 21 via the connection conductor 19 and the bushing 20.

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 the leakage of the reaction gas from the manifold 10 or the like. A heat insulating material 22 is attached to the inner surface of the tank 21 in order to keep the cell stack 9 at an appropriate temperature and to effectively utilize the generated heat during operation through the cooling pipe without radiating the heat.

[Problems of background technology]

Now, a fuel cell generates a direct current voltage by an electrochemical reaction, and heat is generated by the 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 that purpose, a cooling water system is provided for cooling with water. In addition, since a fuel cell has a large number of single cells or cell stacks connected in series and parallel, it is necessary to balance the cooling water flow rate in order to obtain a uniform temperature distribution. For this purpose, throttle the water passage. Can be used. However, when there are a large number of cooling systems connected in parallel, the number of throttles also increases, and there is a risk of problems such as increased cost and reduced reliability due to the space occupied by them or the increase in the number of joints during manufacturing. is there.

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 in the fuel cell. Since the flow rate to each fuel cell is the same as the flow rate inside this insulating joint, a method of balancing the flow rate at the insulating joint portion can be considered. That is, if the throttle is provided in the joint fitting in the insulating joint, the above-mentioned problems can be solved. However, some of the insulating joints may be applied with a DC voltage of about 300 V in the cell stack and several thousand V between the cell stacks. When a DC voltage is applied to the insulation joint in this way, corrosion products generated in the cooling water pipes, etc. adhere to the inner surface of the joint fitting where the voltage has a positive polarity (irrespective of the water flow direction). It turned out to be. Note that this relationship is shown in the table below, and in the table, the leakage current of the joint fitting to which the voltage on the plus side is applied is expressed as plus (+).
The deposit adheres to the inner surface of the fitting in the shape of a sharp orifice, which increases water resistance, resulting in a decrease in the amount of cooling water and a decrease in cooling capacity. Depending on the amount of this adhesion, the flow rate of the cooling water may be unbalanced, or if it adheres to the above-mentioned narrowed part of the water passage, even if the amount of adhesion is small, it may become blocked. Overheating, which leads to a decrease in fuel cell performance and a reduction in life. Of the two problems described above, the latter problem is the main problem.

[Object of the Invention] An object of the present invention is to prevent the risk of clogging of the cooling water system due to the adhesion of corrosion products to minimize the imbalance of the cooling water flow rate, and reliably prevent local overheating due to the flow rate decrease. To improve fuel cell performance and extend life,
It is to provide a small-sized, inexpensive and highly reliable fuel cell power generation system capable of performing highly efficient and stable battery operation.

[Outline of Invention]

In order to achieve the above object, in the present invention, while accommodating in a tank a cell stack formed by stacking a plurality of unit cells each having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte. A fuel cell configured to supply a fuel gas to one electrode and an oxidant gas to the other electrode to extract electric energy from between the electrodes by an electrochemical reaction occurring at this time, and an inside of a cell stack. A plurality of cooling pipes are embedded in the cooling pipe, and cooling water supply and discharge pipes are connected to the cooling pipes to circulate the cooling water, and the cooling pipe and the cooling water supply pipe are connected. And an insulating joint for electrical insulation including two tubular joint fittings and an insulating pipe connecting these joint fittings to each other at the respective connection portions between the cooling pipe and the cooling water discharge pipe. did An insulating joint provided with a waste water system and provided at a connection portion between the cooling pipe and the cooling water supply pipe, or between the cooling pipe and the cooling water supply pipe and between the cooling pipe and the cooling water discharge pipe. In each of the insulating joints provided in the connection part with the, a fitting for flow rate distribution is provided in the fitting fitting on the upstream side in the cooling water flow direction, and the voltage of the fitting fitting provided with the restriction opposes this. By making electrical connection so that the polarity of the fitting on the downstream side is negative, the risk of clogging of the cooling water system due to the adhesion of corrosion products is eliminated, and the imbalance of the cooling water flow rate is minimized. The cooling water system space and the number of joints can be reduced by installing the throttle in the joint fitting of the insulation joint to improve the reliability, downsizing and cost reduction. I can plan It has to.

[Embodiment of the Invention] In the present invention, in a fuel cell water cooling system in which a plurality of cooling pipes are embedded in a cell stack, clogging of the cooling water system can be prevented by attaching throttles for flow distribution at appropriate places. In addition to preventing it, the structure is rationalized.

That is, the throttle in the present invention is a joint metal fitting on the opposite side of the joint metal fittings at both ends of an insulating joint that is connected to electrically insulate between the cooling pipe and the cooling water supply or cooling water discharge pipe. Install it in the fitting (cathode fitting) on the side where a negative voltage is applied. In the fuel cell power generation system of the present invention, the throttle fitting is attached to the upstream joint fitting on the opposite side (downstream side) so that the throttle fitting can be attached to the upstream joint fitting in the cooling water flow direction of the insulating joint. Make electrical connections so that a negative voltage is applied to the metal fittings.

Here, the reason for mounting the diaphragm in the joint metal fitting (cathode metal fitting) to which a negative voltage is applied to the joint metal fitting on the opposite side is as follows.

(A) In the insulation joint of the fuel cell water cooling system, corrosion products generated in the cooling water pipes and the like adhere to the joint metal fitting (anode metal fitting) to which a positive voltage is applied to the joint metal fitting on the opposite side. , It was found that it does not adhere to the inside of the joint metal fitting (cathode metal joint) to which a negative voltage is applied to the joint metal fitting on the opposite side.

Therefore, the corrosion product contained in the inflowing cooling water does not adhere to the restrictor mounted in the joint metal fitting (cathode metal fitting) to which a negative voltage is applied to the joint metal fitting on the opposite side, resulting in clogging. The risk is eliminated.

(B) If there are many cooling pipes, the number of throttles required will also increase. Therefore, by mounting these throttles in the joint fittings of the insulation joint, the space of the cooling water system and the number of joints can be reduced, and the reliability can be improved. Can be improved, miniaturized, and cost can be reduced.

An embodiment of the present invention shown in the drawings based on the above concept will be described below. FIG. 1 shows an example of the configuration of a fuel cell power generation system according to the present invention.
A fuel cell power generation system consisting of two cell stacks is shown. In the figure, the same parts as those in FIGS. 6 (a) and 6 (b) are designated by the same reference numerals, and the description thereof will be omitted. Only different parts will be described here.

The cooling water system will be described first with reference to the drawing. Each of the plurality of cooling pipes 26 embedded in each cell stack 9 has its end connected to the headers 25 on the supply and discharge sides, respectively. In addition, the header 25 on the supply side is an insulating joint 27a.
The discharge side header 25 is connected to the discharge side manifold 24 via an insulating joint 27b. Further, the supply side manifold 23 has the 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. The discharge side manifold 23 is connected to the cooling water discharge pipe 16 via the insulating joint 27b in the upper cell stack 9 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. The heated cooling water may flow as a fluid containing a part of steam, that is, a so-called two-phase flow, but the cooling water containing this heat is cooled in the steam separator 31 and adjusted to an appropriate temperature. After that, it is sent to the cooling water supply pipe 15 through the cooling water pipe 29 by the circulation pump 28 through the cooling water pipe 29. By circulating the cooling water in this way, the fuel cell is kept at an appropriate temperature.

On the other hand, the insulating joints 27a and 27b in the figure are provided to electrically insulate the pipes connected thereto, and are indispensable for the pipes for passing the cooling water of the fuel cell that generates a DC voltage. It is something. By using the insulating joints 27a and 27b, it is possible to keep the pipes connected thereto at different potentials. Further, FIG. 2 (a) is an enlarged view of the insulating joint 27a in FIG. 1, and FIG. 2 (b) is a sectional view thereof. In other words, the insulating joint 27a is composed of two tubular joint fittings, the cathode and anode fittings 34 and 35, and the Teflon insulating pipe 33 that connects these cathode and anode fittings 34 and 35 to each other. Inside the cathode fitting 34 on the upstream side of the water flow, a flow rate distribution throttle for improving the flow rate balance is provided as shown.
In addition, the insulation joint 27b is similar to the cathode and anode fittings 34, 3
5 and a Teflon insulating tube 33, and is configured without the throttle for distributing the flow rate. Here, as the material of the cathode fitting 34, a metal used for general piping (carbon steel, stainless steel, copper and copper alloys, etc.) can be used.
On the other hand, as the material of the anode fitting 35, it is preferable to use a metal (high nickel, high chromium alloy such as stainless steel) which does not easily cause electrolytic corrosion, other than copper and copper alloy or carbon net.

Next, the electrical connection will be described. In FIG. 1, the power terminal (minus electrode) 18 of the lower cell stack 9 is connected to one end of the load 32 and the ground, and at the same time, to the supply side manifold 23 and the discharge side manifold 24. Also connect. The power terminal (plus pole) 17 is connected to the power terminal (minus pole) 18 of the upper cell stack 9, and the power terminal (minus pole) 18 is connected to the supply side manifold 2.
3 and the discharge side manifold 24. On the other hand, the power terminal (plus electrode) 17 of the upper cell stack 9 is connected to the other terminal of the load 32, and the electric energy generated in the cell stack 9 of the fuel cell is consumed by the load 32. Further, the cooling water supply pipe 15, the cooling water discharge pipe 16, the cooling water pipes 29 and 30, the steam separator 31, and the circulation pump 28 of the cooling water system are electrically connected and grounded to the ground. Here, since a large current flows between the cell stacks and between the cell stack 9 and the load 32, it is necessary to connect the power lines (minus electrode) 18 to the supply side manifold 23 or the discharge side manifold 24. There is no need to use a power line because a large current does not flow through. That is, this wire has insulation joints 27a and 27b.
Leakage current flows.

In the fuel cell power generation system including the cooling water system configured as described above, the voltage of the cathode metal fitting 34 with a throttle on the upstream side in the cooling water flow direction in the insulating joint 27a provided on the cooling water supply side. However, since it has a negative polarity when viewed from the anode metal fitting 35 that does not have a diaphragm facing it, corrosion products do not adhere to the inside of the diaphragm. Adhesion also occurs in the anode metal fitting 35, which is a joint metal fitting on the downstream side in the cooling water flow direction, but since this portion has a large inner diameter, the decrease in inner diameter due to the adhesion is small. Further, since the resistance due to the diaphragm is proportional to the reduction rate of the cross-sectional area of the diaphragm, the rate of increase of the resistance is very small as compared with the case where the resistance adheres in the diaphragm.

As described above, in a fuel cell, the required current capacity is usually obtained by stacking a large number of unit cells. It is very effective for In this respect, in the fuel cell power generation system according to the present embodiment, the throttle used as a method for improving the flow rate balance of the cooling water is
Since the insulating joint 27a is mounted in the joint fitting 34, the space of the cooling water system and the number of joints can be reduced, and the reliability can be improved, the size can be reduced, and the cost can be reduced. By attaching the corrosion product to the non-throttled part, the risk of clogging due to the attachment of the corrosion product can be eliminated, and the increase in flow path resistance due to the attachment can be suppressed to a low level. It is possible to prevent overheating, and it is possible to perform a highly efficient and stable operation of the fuel cell.

The present invention is not limited to the above-mentioned embodiments, but can be modified in various ways without departing from the scope of the invention.

(A) In the above embodiment, the throttle is provided only in the joint fitting of the insulating joint provided in the connection portion between the supply side manifold 23 and the cooling water supply header 25. However, as shown in FIG. The upstream side in the cooling water flow direction in each of the insulating joints provided at the connection portions between the supply side manifold 23 and the cooling water supply header 25 and between the discharge side manifold 24 and the cooling water discharge header 25. Even if a throttle is provided in the joint metal fitting, the same operation and effect as in the upstream can be obtained. In this case, the insulation joints 27a provided on the supply side and the discharge side have the same negative polarity as the voltage of the joint metal fitting provided with the throttle of the insulation joint 27a is opposite to the voltage of the other joint metal fitting facing this. The electrical connection is made so that

(B) In the above embodiment, the case where the present invention is applied to the fuel cell power generation system including two cell stacks has been described, but the present invention is not limited to this, and one cell stack or three cell stacks is used.
The present invention can be similarly applied to a fuel cell power generation system including one or more cell stacks.

〔The invention's effect〕

As described above, according to the present invention, while accommodating in a tank a cell stack formed by stacking a plurality of unit cells each having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte, Fuel gas is supplied to one electrode and oxidant gas is supplied to the other electrode, respectively, and a plurality of fuel cells are provided inside the cell stack and a fuel cell configured to extract electric energy from between the electrodes by an electrochemical reaction that occurs at this time. A book cooling pipe is buried, and cooling water supply and discharge pipes are connected to the cooling pipe to circulate the cooling water, and between the cooling pipe and the cooling water supply pipe. 2 at each connection between the cooling pipe and the cooling water discharge pipe.
And a cooling water system configured by providing an insulating joint for electrical insulation composed of two tubular joint fittings and an insulating pipe connecting each of these joint fittings, and between the cooling pipe and the cooling water supply pipe. Upstream of the cooling water flow direction in the insulating joints provided in the connection portion of each of the cooling pipes The flow path distribution throttle is provided in the joint metal fitting on the side, and the electrical connection is made so that the voltage of the joint metal fitting with the throttle has a negative polarity to the downstream joint metal fitting facing this. Since this is done, the risk of clogging of the cooling water system due to the adhesion of corrosion products is eliminated, the unbalance of the cooling water flow rate is minimized, and the local overheating due to the reduced flow rate is reliably prevented and the fuel cell performance is improved. Improved Achieving Rutotomoni long life, efficient stable and high fuel cell power generation system of inexpensive reliable compact capable of performing the cell operation can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fuel cell of the present invention, FIGS. 2 (a) and 2 (b) are enlarged views and sectional views showing insulating joints applied to the embodiment, and FIG. FIG. 4 is a configuration diagram showing another embodiment of the invention, FIG. 4 is a sectional model diagram showing the principle of the fuel cell, and FIG. 5 is a vertical 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 (b) 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 ... Interconnector, 7 ... Hydrogen gas passage, 8 ... Air passage, 9 ... Cell stack, 10 ... Manifold,
11 ... Hydrogen gas supply pipe, 12 ... Hydrogen gas discharge pipe, 1
3 ... Air supply pipe, 14 ... Air discharge pipe, 15 ... Cooling water supply pipe, 16 ... Cooling water discharge pipe, 17 ... Power terminal (plus pole), 18 ... Power terminal (minus pole), 19
...... Connecting conductor, 20 ... Bushing, 21 ... Tank,
22 ... Insulating material, 23 ... Supply side manifold, 24 ...
… Discharge side manifold, 25 …… Header, 26 …… Cooling pipe, 27a …… (with throttle) insulation joint, 27b ……
(No throttle) Insulation joint, 28 ... Circulation pump, 29 ...
Cooling water pipe, 30 ... Cooling water pipe, 31 ... Steam separator,
32 ... Load, 33 ... Teflon insulation tube, 34 ... (with diaphragm) cathode fitting, 35 ... Anode fitting, 36 ... Piping,
A ... Air, H ... Hydrogen, L ... Reaction products and reaction residues.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sumio Yamamoto 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Plant (72) Inventor Kiyoshi Fukui 2-cue, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Address: Toshiba Keihin Office (56) References JP-A-52-13637 (JP, A) JP-A-60-154473 (JP, A)

Claims (1)

[Claims] 1. A cell stack formed by stacking a plurality of unit cells each having a pair of porous electrodes sandwiching an electrolyte layer impregnated with an electrolyte is housed in a tank, and fuel gas is supplied to one of the electrodes. And a fuel cell configured to supply an oxidant gas to the other electrode and to extract electric energy from between the electrodes by an electrochemical reaction that occurs at this time, and a plurality of cooling tubes inside the cell stack. And a pipe for supplying cooling water and a pipe for discharging cooling water are respectively connected to the cooling pipe to circulate the cooling water, and between the cooling pipe and the cooling water supply pipe and the cooling pipe. Cooling water system in which insulating joints for electrical insulation, which are two tubular joint fittings and insulating pipes that connect these joint fittings to each other, are provided at respective connection portions between the cooling water discharge piping and the cooling water discharge piping. And Comprising an insulating joint provided at a connection portion between the cooling pipe and the cooling water supply pipe, or between the cooling pipe and the cooling water supply pipe and between the cooling pipe and the cooling water discharge pipe. In each of the insulated joints provided in the connecting portion, a throttle for distributing the flow rate is provided in the joint fitting on the upstream side in the cooling water flow direction, and the voltage of the fitting with the throttle is opposed to the downstream side. The fuel cell power generation system is characterized in that the electric connection is made so as to have a negative polarity with respect to the joint metal fitting.