JPH0794201A - Cooling apparatus for fuel cell and controlling method thereof - Google Patents

Abstract

PURPOSE:To prevent bumping of secondary cooling water and scale formation by installing a flow rate controlling mechanism to control the flow rate of the secondary cooling water in two stages of high and low and making a slight amount of secondary cooling water possible to flow even in the case the cell cooling water supply to a heat exchanger is shut by a three-way valve. CONSTITUTION:A three-way valve 8 is set on A side at the time of starting and normal driving of a cooling apparatus. At the time a shutoff valve 11 of a two-stage flow rate controlling mechanism 20 is closed and a slight amount of secondary cooling water 10W whose flow rate is throttled by a throttling mechanism 12 flows in the secondary cooling water system 10, so that heat is released from the three-way valve 8 to a heat exchanger 9 and boiling of the secondary cooling water 10W remaining in the heat exchanger 9 is prevented. Meanwhile, when the driving of a fuel cell power generating apparatus is stopped, the three-way valve 8 is switched to B side and at the same time the shutoff valve 11 of the two-stage flow rate controlling system 20 is opened, so that the cell cooling water 1W is cooled by a large amount of secondary cooling water 10W which flows in the secondary cooling water system and fuel cell stacks are cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell cooling device for cooling a fuel cell stack with a steam separator or a heat exchanger by switching a three-way switching valve, and a secondary cooling water passage to the heat exchanger. Flow control method.

[0002]

2. Description of the Related Art FIG. 5 is a schematic system diagram of a conventional cooling device showing a water-cooled phosphoric acid fuel cell power generator as an example. A fuel cell stack 1 composed of a unit cell stack has a plurality of unit cells. A cooling plate 7 having laminated water cooling pipes,
A circulation system for the battery cooling water 1W is formed between the water cooling pipe and the three-way switching valve 8, the battery cooling water circulation pump 5, and the steam separator 4 having the electric heater 6. Further, a heat exchanger 9 is provided which is connected to the circulation system through C-B of the three-way switching valve 8 so as to be switchably connectable. For example, a secondary cooling water system 10 having a shutoff valve 11 is connected to a low temperature secondary cooling water 1
It is configured to cool 1 W of high-temperature battery cooling water by flowing 0 W.

In the operation of the water-cooled phosphoric acid fuel cell power generator configured as described above, at the time of its start-up, the three-way switching valve 8 is set to the A side to circulate 1W of the cell cooling water by the circulation pump 5 to the water cooling pipe of the cooling plate 7 and Circulates between the steam separators 4,
In this state, the electric heater 6 supplies 1 W of the cell cooling water in the steam separator 4 to the operating temperature of the fuel cell (for example, 190 to 2).
The fuel cell stack 1 is heated to a temperature close to its operating temperature by preheating in the vicinity of 00 ° C. When the temperature of the fuel cell reaches the operable temperature, the electric heater 6 is turned off, and the reaction air is supplied from the reaction air supply device 3 and the fuel gas is supplied from the fuel reforming device 2 to the oxidizer electrode and the fuel electrode of the fuel cell. By supplying each, the power generation operation based on the electrochemical reaction is started. Further, the electrochemical reaction is an exothermic reaction, and the cell cooling water 1W that has been heated by depriving the fuel cell stack 1 of heat generated by power generation is cooled by separating water vapor in the water vapor separator 4 and cooled cell cooling water. Are circulated to the cooling plate 7 to cool the fuel cell stack 1 at the operating temperature. Further, the steam separated in the steam separator 4 is mixed with the raw fuel and supplied to the fuel reforming apparatus 2 to be used for the steam reforming reaction and also as exhaust heat recovery (not shown) as heat recovery steam. The temperature of the cell cooling water 1W supplied to the system is controlled to a constant temperature lower than the operating temperature of the fuel cell by controlling the supply amount.

On the other hand, when the power generation operation is stopped, the three-way switching valve 8 is switched to the B side while the output of the fuel cell is throttled, and the heat exchanger 9 is installed in the circulation passage of the battery cooling water 1W, and the secondary cooling water system 10 is connected. Open the shutoff valve 11 of the secondary cooling water 10W
Flow into the heat exchanger to carry out the operation mode (power generation cooling operation) of cooling the battery cooling water 1W, and the current is interrupted and the reaction is stopped only when the fuel cell temperature drops to the predetermined operation stop temperature. The supply of air and fuel gas is stopped to complete the operation of the fuel cell power generator. That is, when the output current of the fuel cell is cut off at its operating temperature, the potential difference between the electrodes of the unit cell rises to the open circuit voltage, and the electrode catalyst of the fuel cell may be exposed to the high temperature open circuit voltage and deteriorate. It is known that the fuel cell temperature is lowered to a temperature at which catalyst deterioration due to open circuit voltage is not a problem by performing a power generation cooling operation, then interrupting the current and stopping the supply of reaction air and fuel gas It is possible to prevent deterioration of the battery.

[0005]

According to the above operating method, the heat exchanger 9 is only used as a cooler for the battery cooling water during the power generation cooling operation, and the three-way switching valve 8 is set to A during normal operation. To the secondary cooling water 1W while the circulation of the battery cooling water 1W is stopped and the shutoff valve 11 is also shut off.
The 0 W flow is also stopped, and the battery cooling water and the secondary cooling water remain in the heat exchanger. In this state, when the steam generator 4 continues to perform a steady power generation operation for cooling the fuel cell stack 1, the three-way switching valve 8 and the heat exchanger 9 are relatively close to each other and are connected by a short pipe. If there is, the heat exchanger is heated by heat conduction from the three-way switching valve to the heat exchanger, and the battery cooling water 1 accumulated in the heat exchanger 9
The temperature of W rises to 130 to 150 ° C., at which point the secondary cooling water 10W remaining in the heat exchanger boils, and a mechanical shock is applied to the heat exchanger 9 by the bumping phenomenon, Impact noise is generated, and the secondary cooling water that has accumulated over time evaporates and impurities are concentrated, and adhere to the heat exchange surface as a scale, which reduces the heat exchange capacity of the heat exchanger. The problem of causing stress corrosion cracking occurs.

Further, when the three-way switching valve 8 and the heat exchanger 9 are located relatively far from each other, the bumping phenomenon does not occur, but the accumulated secondary cooling water is evaporated and the impurities are concentrated.
As a scale, the phenomenon of adhesion to the heat exchange surface occurs, which causes a problem that the heat exchange capacity of the heat exchanger is deteriorated.
Therefore, in order to avoid the above-mentioned problems, a method is conceivable in which the secondary cooling water is continuously passed through the heat exchanger 9 even during the steady operation of the fuel cell to prevent the temperature rise of the heat exchanger. At this time, the temperature of the secondary cooling water does not rise so much that it is difficult to use the heat.

An object of the present invention is to prevent the bumping phenomenon of secondary cooling water and the generation of scale that occur while the heat exchanger is stopped, and to prevent the troubles resulting from these.

[0008]

In order to solve the above-mentioned problems, according to the present invention, between a cooling plate having a water-cooling pipe laminated in a fuel cell stack for each unit cell and the water-cooling pipe. A circulation pump and a water vapor separator that form a circulation system of the battery cooling water through a three-way switching valve, and a circulation system that is switchably connected to the circulation system by the three-way switching valve, and the high-temperature battery cooling water and the low-temperature secondary cooling. A heat exchanger for exchanging heat with water, wherein the fuel cell stack is cooled by switching to either the steam separator or the heat exchanger, wherein the flow rate of the secondary cooling water is large or small. It is assumed that the secondary cooling water system is equipped with a two-stage flow control mechanism that controls in two stages.

It is assumed that the two-stage flow rate control mechanism comprises a shutoff valve and a throttle mechanism connected in parallel with the shutoff valve. The two-stage flow control mechanism shall be connected in parallel with each other and shall consist of a pair of shutoff valves with different flow rates. It is assumed that the two-stage flow rate control mechanism comprises one flow rate control valve having a control mechanism for controlling the flow rate in two stages.

A cooling plate having a water cooling pipe laminated in a fuel cell stack for each of a plurality of unit cells, and a circulation pump and steam for forming a circulation system of the cell cooling water through a three-way switching valve between the cooling plate and the water cooling pipe. A fuel cell stack including a separator and a heat exchanger switchably connected to the circulation system by the three-way switching valve to exchange heat between the high-temperature battery cooling water and the low-temperature secondary cooling water. In a cooling device for a fuel cell that performs cooling of either the water vapor separator or the heat exchanger, when the three-way switching valve is operated so that the fuel cell stack is cooled by the heat exchanger, the secondary cooling water flow rate When the three-way switching valve is operated so that the fuel cell stack is cooled by the steam separator to perform heat exchange, the secondary cooling water flow rate is reduced to the small flow rate side. And to prevent overheating of the heat exchanger by conduction heat from the circulatory system.

[0011]

In the present invention, the two-stage flow rate control mechanism for controlling the flow rate of the secondary cooling water in two steps, large and small, is provided in the secondary cooling water system, which is necessary for cooling the fuel cell during the power generation cooling operation. A large amount of secondary cooling water is passed through the heat exchanger to cool the battery cooling water, and during steady operation without the need for a heat exchanger, the secondary cooling water flow rate is reduced to a small amount and the conduction heat from the three-way switching valve is used. Prevents overheating of the heat exchanger,
Since it is possible to prevent the boiling of the secondary cooling water that accumulates in the heat exchanger, mechanical shock and impact noise due to the bumping phenomenon of the secondary cooling water can be generated without wasteful circulation of the secondary cooling water. It is possible to obtain a function of preventing the generation of scale due to evaporation of the secondary cooling water, and preventing a failure such as a decrease in heat exchange efficiency and stress corrosion cracking of the heat exchanger.

Further, a two-stage flow control mechanism is provided with a shutoff valve,
If it is configured with a throttling mechanism connected in parallel to this, the flow rate of the secondary cooling water flowing to the heat exchanger can be increased or decreased by a simple operation of opening and closing the shutoff valve in synchronization with the switching of the three-way switching valve. In addition to being able to easily control in two steps, it is possible to obtain a function of stably holding a small flow rate of the secondary cooling water by the throttling mechanism without requiring special control. Further, the two-stage flow rate control mechanism is configured by a pair of shutoff valves that are connected in parallel with each other and have different flow rates, or one flow rate control valve that has a control mechanism that controls the flow rate in two stages. Also, the same function as described above can be obtained.

On the other hand, as a method of controlling the cooling device for the fuel cell, when the three-way switching valve is operated so that the fuel cell stack is cooled by the heat exchanger, the secondary cooling water flow rate is controlled to the large flow rate side to perform the heat exchange. With this configuration, the output current of the fuel cell is cut off, the reaction gas supply is stopped, and the operation can be stopped after the power generation cooling operation of cooling the temperature of the fuel cell stack to a predetermined temperature or lower. Therefore, it is possible to obtain the function of stopping the operation of the fuel cell without causing any trouble due to the high temperature open circuit voltage. When the three-way switching valve is operated so that the fuel cell stack is cooled by the steam separator, the secondary cooling water flow rate is reduced to the small flow rate side to prevent overheating of the heat exchanger due to conduction heat from the circulation system. With this configuration, it is possible to prevent the secondary cooling water that has accumulated in the heat exchanger from boiling due to the conduction heat from the three-way switching valve, so that the secondary cooling water can be removed without wasteful circulation of the secondary cooling water. Generation of mechanical shocks and impact sounds based on bumping phenomenon,
The function of preventing the generation of scale due to evaporation of the secondary cooling water and preventing obstacles such as reduction of heat exchange efficiency and stress corrosion cracking of the heat exchanger can be obtained.

When the three-way switching valve is operated so that the fuel cell stack is cooled by the heat exchanger, the heat exchanger is operated by supplying the secondary cooling water whose temperature has been raised by heat exchange to the exhaust heat utilization device. The function of performing heat recovery also as a heat recovery heat exchanger is obtained.

[0015]

EXAMPLES The present invention will be described below based on examples. FIG. 1 is a schematic system diagram showing a cooling device for a fuel cell according to an embodiment of the present invention, and the same components as those in the prior art are designated by the same reference numerals, and a duplicate description will be omitted. In the figure, in a secondary cooling water system 10 of a heat exchanger 9 configured as a battery cooling water cooler, a shutoff valve 11 having a large flow rate and a throttle mechanism 12 are provided in parallel as a two-stage flow rate control mechanism 20. To be

In the cooling device for a fuel cell having the two-stage flow rate control mechanism 20 configured as described above, the three-way switching valve 8 is set to the A side for the starting operation and the steady operation, and the battery cooling water in the steam separator 4 is operated. It is performed by adjusting the temperature of 1 W with the heater 6 or by controlling the cooling of the fuel cell stack 1 by the amount of steam generated in the steam separator to keep the fuel cell at the operating temperature. At this time, 2
The shutoff valve 11 of the stepped flow control mechanism 20 is closed, and a small amount of the secondary cooling water 10W whose flow rate is throttled by the throttle mechanism 12
Flowing in the secondary cooling water system 10 exhausts the conduction heat from the three-way switching valve 8 to the heat exchanger 9 and can prevent the secondary cooling water 10W accumulated in the heat exchanger from boiling. Therefore, the generation of mechanical shock and impact noise based on the bumping phenomenon of the secondary cooling water and the generation of scale due to the evaporation of the secondary cooling water are prevented in a state in which the wasteful circulation of the secondary cooling water is eliminated.
It is possible to prevent problems such as a decrease in heat exchange efficiency and stress corrosion cracking of the heat exchanger.

When the operation of the fuel cell power generator is stopped, the power generation cooling operation is performed by switching the three-way switching valve 8 to the B side and simultaneously opening the shut-off valve 11 of the two-stage flow rate control mechanism 20, When the cell cooling water 1W is cooled by a large amount of the secondary cooling water 10W flowing in the secondary cooling water system and the temperature of the fuel cell stack 1 is cooled to a predetermined temperature or lower, the output current of the fuel cell is shut off. By stopping the supply of the reaction gas to stop the operation, it is possible to avoid exposing each unit cell of the fuel cell stack 1 to the high temperature open circuit voltage. It is possible to prevent the deterioration of the electrode catalyst that occurs in the battery stack.

FIG. 2 is a simplified system diagram showing a different embodiment of the present invention. A two-stage flow rate control including a shutoff valve 11 and a throttle mechanism 12 in a secondary cooling water system 21 of a heat recovery heat exchanger 19. The point that the mechanism 20 is provided is different from the above-described embodiment. In the fuel cell cooling device thus configured, the heat recovery heat exchanger 19 recovers the heat generated by the power generation of the fuel cell stack 1 and supplies the heated secondary cooling water 21W to the heat utilization system (not shown). Then, the exhaust heat can be used. At this time, the three-way switching valve 8 is switched to the B side to incorporate the heat recovery heat exchanger 19 into the circulation system of the battery cooling water 1W, the shutoff valve 11 is opened, and the secondary cooling water 21W is transferred to the heat recovery heat exchanger 19. Heat exchange is carried out by flowing it through.

When the heat recovery is stopped, the three-way switching valve 8 is switched to the A side to disconnect the heat recovery heat exchanger 19 from the circulation system of the battery cooling water 1W, and the shutoff valve 11 is closed to close the throttle mechanism 12. By passing a small amount of the secondary cooling water 21W squeezed by the heat recovery heat exchanger 19, it is possible to prevent the heat recovery heat exchanger 19 from being overheated due to the conduction heat from the three-way switching valve 8 and to perform the secondary cooling. It is possible to eliminate obstacles caused by boiling or evaporation of 21 W of water. Further, during the power generation cooling operation, the three-way switching valve 8 is switched to the B side to incorporate the heat recovery heat exchanger 19 into the circulation system of the battery cooling water 1W, and the shutoff valve 1
1 is opened to allow the low-temperature secondary cooling water 21W to flow through the heat recovery heat exchanger 19, whereby the battery cooling water can be cooled and the deterioration of the electrode catalyst due to the high temperature open circuit voltage can be prevented.

FIG. 3 is a block diagram of a main part showing another embodiment of the present invention, in which a shutoff valve 31 having a large flow rate and a shutoff valve 32 having a small flow rate are arranged in parallel as a two-stage flow rate control mechanism 30. It differs from the above-described embodiment in that it is connected to the secondary cooling water system of the heat exchanger. When the three-way switching valve 8 is set to the A side, the shutoff valve 32 with a small flow rate is opened to exchange a small amount of secondary cooling water with heat. When the three-way switching valve 8 is set to the B side, the shut-off valve 31 having a large flow rate is opened to allow a large amount of secondary cooling water to flow to the heat exchanger. Is obtained.

FIG. 4 is a block diagram of the essential parts showing another embodiment of the present invention. The two-stage flow rate control mechanism 40 controls the flow rate control valve 41 and the flow rate of this flow rate control valve in two stages. It is different from the above-mentioned embodiment in that it is constituted by a control mechanism 42 and is connected to the secondary cooling water system of the heat exchanger, and the flow rate is switched in two stages in response to the switching of the three-way switching valve 8 so that The same effects and advantages as in the embodiment can be obtained.

[0022]

As described above, the present invention provides a heat exchanger configured as a battery cooling water cooler or a heat recovery heat exchanger that is connected to a battery cooling water circulation system via a three-way switching valve. The secondary cooling water system is equipped with a two-stage flow rate control mechanism that controls the flow rate of the secondary cooling water in two steps, large and small, and a small amount of secondary cooling is achieved even when the battery cooling water to the heat exchanger is shut off by the three-way switching valve. It was configured to flow water. As a result, the problem of the prior art that the heat exchanger is overheated by the conduction heat from the three-way switching valve and the secondary cooling water accumulated in the heat exchanger boils or evaporates is eliminated, and the secondary cooling water bumps. There is no mechanical shock and impact noise due to the phenomenon, and the occurrence of scale due to the concentration of impurities can be avoided, so that the heat exchange capacity can be stably maintained with low noise, and damage such as stress corrosion cracking is unlikely to occur. It is possible to provide a fuel cell power generation device including a highly efficient cooling device.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing a cooling device for a fuel cell according to an embodiment of the present invention.

FIG. 2 is a system diagram showing a simplified example of a different embodiment of the present invention.

FIG. 3 is a configuration diagram of a main part showing another embodiment of the present invention.

FIG. 4 is a configuration diagram of a main part showing another embodiment of the present invention.

FIG. 5 is a schematic system diagram of a conventional cooling device showing a water-cooled phosphoric acid fuel cell power generator as an example.

[Explanation of symbols]

 1 Fuel Cell Stack 1W Battery Cooling Water 2 Fuel Reforming Device 3 Reactive Air Supply Device 4 Steam Separator 5 Battery Cooling Water Circulation Pump 6 Electric Heater 7 Cooling Plate 8 Three-way Switching Valve 9 Heat Exchanger (Battery Cooling Water Cooler) 10 Secondary Cooling Water System 10W Secondary Cooling Water 11 Shutoff Valve 12 Throttling Mechanism 19 Heat Exchanger (Heat Recovery Heat Exchanger) 20 Two-Stage Flow Control Mechanism 21 Secondary Cooling Water System (Connected to Heat Utilization System) 21W Secondary Cooling water 30 Two-stage flow control mechanism 31 Shut-off valve (large) 32 Shut-off valve (small) 40 Two-stage flow control mechanism 41 Flow control valve 42 Two-stage switching control mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunsuke Oga 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 inside Fuji Electric Co., Ltd.

Claims (5)

[Claims] 1. A circulation pump which forms a circulation system of cell cooling water between a cooling plate having a water cooling pipe laminated in a fuel cell stack for each of a plurality of unit cells and a three-way switching valve between the water cooling pipe. And a steam separator, and a heat exchanger that is switchably connected to the circulation system by the three-way switching valve to exchange heat between the high-temperature battery cooling water and the low-temperature secondary cooling water, In the one in which the cooling of the battery stack is switched to either the steam separator or the heat exchanger, the secondary cooling water system is provided with a two-stage flow rate control mechanism for controlling the flow rate of the secondary cooling water in two steps, large and small. A cooling device for a fuel cell characterized by the following. 2. A cooling device for a fuel cell according to claim 1, wherein the two-stage flow control mechanism comprises a shutoff valve and a throttle mechanism connected in parallel with the shutoff valve. 3. The cooling device for a fuel cell according to claim 1, wherein the two-stage flow rate control mechanism is connected in parallel with each other and comprises a pair of shutoff valves having different flow rates. 4. The cooling device for a fuel cell according to claim 1, wherein the two-stage type flow rate control mechanism comprises one flow rate control valve having a control mechanism for controlling the flow rate in two stages. 5. A circulation pump which forms a circulation system of cell cooling water through a three-way switching valve between a cooling plate having a water cooling pipe laminated in a fuel cell stack for each of a plurality of unit cells and the water cooling pipe. And a steam separator, and a heat exchanger that is switchably connected to the circulation system by the three-way switching valve to exchange heat between the high-temperature battery cooling water and the low-temperature secondary cooling water, In a cooling device for a fuel cell in which the cooling of the cell stack is switched to either the steam separator or the heat exchanger, secondary cooling is performed when the three-way switching valve is operated so that the heat exchanger cools the fuel cell stack. When the three-way switching valve is operated so that the water flow rate is controlled to a large flow rate for heat exchange and the fuel cell stack is cooled by the steam separator, the secondary cooling water flow rate is reduced to a small flow rate side. Control method of the fuel cell cooling device, characterized in that to prevent overheating of the heat exchanger by conduction heat from the circulatory system.