JP3310412B2 - Fuel cell cooling device and control method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling system for a fuel cell in which a fuel cell stack is cooled by switching a three-way switching valve by a steam separator or a heat exchanger, and the passage of secondary cooling water to the heat exchanger. It relates to a 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 type fuel cell power generation device as an example. A fuel cell stack 1 composed of a stack of unit cells is provided for each of a plurality of unit cells. A cooling plate 7 having laminated water cooling pipes,
Between the water cooling pipe and the water cooling pipe, a circulating system for the battery cooling water 1W comprising a steam separator 4 having a three-way switching valve 8, a battery cooling water circulating pump 5, and an electric heater 6 is formed. Further, a heat exchanger 9 is provided which is switchably connected to the circulation system through the line C-B of the three-way switching valve 8. For example, a secondary cooling water system 10 having a shut-off valve 11 is connected to a low-temperature secondary cooling water 1.
It is configured to cool the high-temperature battery cooling water 1W by flowing 0W.

In operation of the water-cooled phosphoric acid fuel cell power generator constructed as described above, the battery cooling water 1W is supplied to the water-cooled pipe of the cooling plate 7 by the circulation pump 5 with the three-way switching valve 8 set to the A side. Circulating between the steam separators 4,
In this state, 1 W of the battery cooling water in the steam separator 4 is changed by the electric heater 6 to the operating temperature of the fuel cell (for example, 190 to 2).
The fuel cell stack 1 is preheated to around (00 ° C) to heat and raise the temperature of the fuel cell stack 1 to near its operating temperature. When the temperature of the fuel cell reaches an operable temperature, the electric heater 6 is turned off, the reaction air is supplied from the reaction air supply device 3 and the fuel gas is supplied from the fuel reformer 2 to the oxidizer electrode and the fuel electrode of the fuel cell. By supplying each of them, a power generation operation based on an electrochemical reaction is started. In addition, the electrochemical reaction is an exothermic reaction, and the cell cooling water 1W, which is heated by depriving the fuel cell stack 1 of power generation heat, is cooled by separating steam in the steam separator 4, and the cooled cell cooling water is cooled. Is returned 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 a steam reforming reaction, and also to collect waste heat (not shown) as heat recovery steam. The temperature of the battery cooling water 1W 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 reduced, 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 stopped. Open the shutoff valve 11 of the secondary cooling water 10W
Is passed through the heat exchanger to perform an operation mode (power generation cooling operation) for cooling the cell cooling water 1W. When the fuel cell temperature falls to a predetermined operation stop temperature, the current is cut off and the reaction is performed for the first time. The supply of the air and the fuel gas is stopped, and the operation as the fuel cell power generator ends. That is, when the output current of the fuel cell is cut off at the 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 is exposed to the high temperature open circuit voltage and shows a phenomenon of deterioration. It is known that after the power generation cooling operation is performed to lower the temperature of the fuel cell to a temperature at which the deterioration of the catalyst due to the open-circuit voltage does not become a problem, the current is cut off, and the supply of the reaction air and the fuel gas is stopped to thereby reduce the fuel. Battery deterioration can be prevented.

[0005]

According to the above-described operation method, the heat exchanger 9 is used only as a cooler for the battery cooling water during the power generation cooling operation, and the three-way switching valve 8 is set to the A during the steady operation. Side, the circulation of the battery cooling water 1W is stopped, and the shutoff valve 11 is also shut off so that the secondary cooling water 1W is shut off.
The flow of 0 W is also stopped, and the battery cooling water and the secondary cooling water stay in the heat exchanger. In this state, when the stationary power generation operation for cooling the fuel cell stack 1 by the steam separator 4 is continuously performed, the three-way switching valve 8 and the heat exchanger 9 are relatively close to each other and are connected by short piping. The heat exchanger is heated by heat conduction from the three-way switching valve to the heat exchanger, and the battery cooling water 1 retained in the heat exchanger 9
The temperature of W rises to 130 to 150 ° C., and at this time, the secondary cooling water 10W staying in the heat exchanger boils, and a mechanical shock is applied to the heat exchanger 9 by a bumping phenomenon, Impact sound is generated, and the accumulated secondary cooling water evaporates over time, and the impurities are concentrated and adhere to the heat exchange surface as a scale. The problem of causing stress corrosion cracking occurs.

When the three-way switching valve 8 and the heat exchanger 9 are relatively far apart, no bumping phenomenon occurs, but the accumulated secondary cooling water evaporates to concentrate impurities.
The phenomenon of sticking to the heat exchange surface as a scale occurs, causing a problem that the heat exchange capacity of the heat exchanger is reduced.
Therefore, in order to avoid the above problem, a method of continuously flowing secondary cooling water through the heat exchanger 9 even during the steady operation of the fuel cell to prevent the temperature of the heat exchanger from rising can be considered. At this time, since the temperature rise of the secondary cooling water is small and its heat utilization is difficult, there arises an irrationality of continuing to circulate the secondary cooling water of low added value.

An object of the present invention is to prevent a bumping phenomenon and a scale of secondary cooling water which are generated when the heat exchanger is stopped, and to prevent a trouble caused by these.

[0008]

According to the present invention, there is provided a fuel cell stack comprising: a cooling plate having a water cooling pipe laminated on a fuel cell stack for each of a plurality of unit cells; A circulating pump and a steam separator forming a circulating system for the battery cooling water through a three-way switching valve, and a high-temperature battery cooling water and a low-temperature secondary cooling which are switchably connected to the circulating system by the three-way switching valve. A heat exchanger that exchanges heat with water, wherein the cooling of the fuel cell stack is performed by switching to either the steam separator or the heat exchanger. It is assumed that a two-stage flow control mechanism for controlling in two stages is provided in the secondary cooling water system.

It is assumed that the two-stage flow control mechanism comprises a shut-off valve and a throttle mechanism connected in parallel to the shut-off valve. It is assumed that a two-stage flow control mechanism is composed of a pair of shut-off valves connected in parallel with each other and having different flow rates from each other. It is assumed that the two-stage flow control mechanism comprises one flow control valve having a control mechanism for controlling the flow in two stages.

A cooling plate having a water-cooled pipe laminated on a fuel cell stack for each of a plurality of unit cells; a circulating pump for forming a circulating system of battery cooling water between the water-cooled pipe and a three-way switching valve; The fuel cell stack, comprising: a separator; and a heat exchanger that is switchably connected to the circulation system by the three-way switching valve and exchanges heat between the high-temperature battery cooling water and the low-temperature secondary cooling water. In the cooling device for a fuel cell which switches the cooling of the fuel cell to either the steam separator or the heat exchanger, when the three-way switching valve is operated so that the cooling of the fuel cell stack is performed by the heat exchanger, the flow rate of the secondary cooling water is reduced. When the three-way switching valve is operated so as to perform heat exchange by controlling the flow rate to the large flow rate side and to cool the fuel cell stack by the steam separator, the secondary cooling water flow rate is reduced to the small flow rate side, and And to prevent overheating of the heat exchanger by conduction heat from the circulatory system.

[0011]

According to the present invention, a two-stage flow control mechanism for controlling the flow rate of the secondary cooling water in two stages, large and small, is provided in the secondary cooling water system. A large flow of secondary cooling water is passed through the heat exchanger to cool the battery cooling water, and during steady-state operation that does not require 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. Prevent overheating of the heat exchanger,
Since the boiling of the secondary cooling water staying in the heat exchanger can be prevented, the occurrence of mechanical shock and impact noise based on the bumping phenomenon of the secondary cooling water without wasteful circulation of the secondary cooling water is eliminated. The function of preventing the generation of scale due to the evaporation of the next cooling water and the prevention of problems such as a reduction in heat exchange efficiency and stress corrosion cracking of the heat exchanger can be obtained.

Further, the two-stage flow control mechanism is provided with a shut-off valve,
If a throttle mechanism connected in parallel with this is used, the flow rate of the secondary cooling water flowing through the heat exchanger can be increased or decreased by a simple operation of opening and closing the shut-off valve in synchronization with the switching of the three-way switching valve. In addition to being able to easily control in two stages, a function of stably holding the flow rate of the small amount of secondary cooling water without requiring special control by the throttle mechanism is obtained. Further, the two-stage flow control mechanism is constituted by a pair of shut-off valves connected in parallel with each other and having different flow rates from each other, or is constituted by one flow control valve having a control mechanism for controlling the flow in two stages. Can also obtain the same function as described above.

On the other hand, as a method of controlling the fuel cell cooling device, 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 heat exchange. With this configuration, after the power generation cooling operation that cools the temperature of the fuel cell stack to a predetermined temperature or less, the output current of the fuel cell is cut off, the supply of the reaction gas is stopped, and the operation can be stopped. Therefore, the function of stopping the operation of the fuel cell without causing an obstacle due to the high-temperature open circuit voltage is obtained. When the three-way switching valve is operated so that the fuel cell stack is cooled by the steam separator, the flow rate of the secondary cooling water is reduced to a small flow rate so as to prevent the heat exchanger from being overheated due to the heat transferred from the circulation system. With this configuration, it is possible to prevent the secondary cooling water retained in the heat exchanger from boiling due to the conduction heat from the three-way switching valve. Generation of mechanical shock and impact noise based on bumping phenomenon,
The function of preventing the generation of scale due to the evaporation of the secondary cooling water and the prevention of problems such as a decrease in heat exchange efficiency and stress corrosion cracking of the heat exchanger is obtained.

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

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a schematic system diagram showing a fuel cell cooling device according to an embodiment of the present invention. The same components as those of the prior art are denoted by the same reference numerals, and redundant 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 as a two-stage flow control mechanism 20 and a throttle mechanism 12 are provided in parallel with each other. Can be

In the cooling device for a fuel cell having the two-stage flow rate control mechanism 20 configured as described above, the start-up operation and the steady operation are performed by setting the three-way switching valve 8 to the A side and the battery cooling water in the steam separator 4. The temperature of 1 W is adjusted by the heater 6 or the cooling of the fuel cell stack 1 is adjusted by the amount of steam generated in the steam separator, and the fuel cell is maintained at the operating temperature. At this time, 2
The shutoff valve 11 of the stepped flow control mechanism 20 is closed, and the small amount of the secondary cooling water 10W whose flow rate is reduced by the throttle mechanism 12 is reduced.
Flows through the secondary cooling water system 10, the conduction heat is discharged from the three-way switching valve 8 to the heat exchanger 9, and the secondary cooling water 10 </ b> W accumulated in the heat exchanger can be prevented from boiling. Therefore, while avoiding unnecessary circulation of the secondary cooling water, the occurrence 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.
Obstacles such as a decrease in heat exchange efficiency and stress corrosion cracking of the heat exchanger can be prevented.

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 opening the shut-off valve 11 of the two-stage flow control mechanism 20 at the same time. When the battery 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 and cooled to a predetermined temperature or less, the output current of the fuel cell is cut off. By stopping the supply of the reaction gas and stopping the operation, each unit cell of the fuel cell stack 1 can be prevented from being exposed to the high-temperature open circuit voltage. It is possible to prevent the deterioration of the electrode catalyst occurring in the battery stack.

FIG. 2 is a simplified system diagram showing a different embodiment of the present invention. A two-stage flow control comprising a shut-off valve 11 and a throttle mechanism 12 in a secondary cooling water system 21 of a heat recovery heat exchanger 19 is shown. The point that the mechanism 20 is provided is different from the above-described embodiment. In the fuel cell cooling device configured as described above, the heat generated by the power generation of the fuel cell stack 1 is recovered by the heat recovery heat exchanger 19, and the heated secondary cooling water 21W is supplied to a heat utilization system (not shown). Thus, waste 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, and the shutoff valve 11 is opened to discharge the secondary cooling water 21W to the heat recovery heat exchanger 19. The heat exchange is performed by flowing the gas through the heat exchanger.

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, close the shutoff valve 11 and close the throttle mechanism 12 A small amount of secondary cooling water 21W squeezed by the above is passed through the heat recovery heat exchanger 19 to prevent overheating of the heat recovery heat exchanger 19 due to conduction heat from the three-way switching valve 8, and secondary cooling is performed. Obstacles caused by boiling and evaporation of the water 21W can be eliminated. 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,
By opening 1, the low-temperature secondary cooling water 21W flows through the heat recovery heat exchanger 19, thereby cooling the battery cooling water and preventing the deterioration of the electrode catalyst due to the high-temperature open circuit voltage.

FIG. 3 is a structural view of a main part showing another embodiment of the present invention. As a two-stage flow control mechanism 30, a shutoff valve 31 having a large flow rate and a shutoff valve 32 having a small flow rate are arranged in parallel with each other. This embodiment is different from the previous 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 shut-off valve 32 with a small flow rate is opened to exchange a small amount of secondary cooling water. When the three-way switching valve 8 is set to the B side when the three-way switching valve 8 is set to the B side, the shutoff valve 31 having a large flow rate is opened to allow a large amount of secondary cooling water to flow through the heat exchanger. Is obtained.

FIG. 4 is a block diagram of a main part showing another embodiment of the present invention. The two-stage flow control mechanism 40 controls a flow control valve 41 and the flow rate of the flow control valve in two stages. This embodiment is different from the above-described embodiment in that it is constituted by the control mechanism 42 and is connected to the secondary cooling water system of the heat exchanger. By switching the flow rate in two stages corresponding to the switching of the three-way switching valve 8, The same operation and effect as in the embodiment can be obtained.

[0022]

As described above, the present invention relates to a heat exchanger for use as a battery cooling water cooler or a heat recovery heat exchanger 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 control mechanism that controls the secondary cooling water flow in two stages, large and small, and a small amount of secondary cooling is used even when the battery cooling water to the heat exchanger is shut off by a three-way switching valve. It was configured to flow water. As a result, the problem of the prior art in which 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 bumping of the secondary cooling water is eliminated. There is no mechanical shock or impact noise due to the phenomenon, and scale generation due to concentration of impurities can be avoided, so that the heat exchange capacity can be maintained stably with low noise, and reliability such as stress corrosion cracking does not easily occur. It is possible to provide a fuel cell power generation device provided with a high-performance cooling device.

[Brief description of the 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 simplified system diagram showing different embodiments 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 different from the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell stack 1W Battery cooling water 2 Fuel reformer 3 Reaction 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) Reference Signs List 10 secondary cooling water system 10W secondary cooling water 11 shut-off valve 12 throttle mechanism 19 heat exchanger (heat exchanger for heat recovery) 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

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunsuke Oga 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. No. 1 Fuji Electric Co., Ltd. (56) References JP-A-59-176406 (JP, A) JP-A-61-10875 (JP, A) JP-A-5-41229 (JP, A) 41232 (JP, A) JP-A-7-83581 (JP, A) JP-A-58-92556 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/04 H01M 8 / 06

Claims (5)

(57) [Claims] A circulating pump for forming a circulating system of battery cooling water between a cooling plate having a water cooling pipe laminated on a fuel cell stack for each of a plurality of unit cells and a water cooling pipe via a three-way switching valve. And a steam separator, and a heat exchanger that is switchably connected to the circulation system by the three-way switching valve and that performs heat exchange 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, a secondary cooling water system is provided with a two-stage flow control mechanism for controlling the secondary cooling water flow in two stages, large and small. A cooling device for a fuel cell, comprising: 2. The fuel cell cooling device according to claim 1, wherein the two-stage flow control mechanism comprises a shutoff valve and a throttle mechanism connected in parallel to the shutoff valve. 3. The cooling device for a fuel cell according to claim 1, wherein the two-stage flow control mechanism comprises a pair of shut-off valves connected in parallel with each other and having different flow rates from each other. 4. The cooling device for a fuel cell according to claim 1, wherein the two-stage flow control mechanism comprises one flow control valve having a control mechanism for controlling the flow in two stages. 5. A circulating pump for forming a battery cooling water circulation system between a cooling plate having a water cooling pipe laminated on a fuel cell stack for each of a plurality of unit cells and the water cooling pipe via a three-way switching valve. And a steam separator, and a heat exchanger that is switchably connected to the circulation system by the three-way switching valve and that performs heat exchange between the high-temperature battery cooling water and the low-temperature secondary cooling water. In the cooling device for a fuel cell which switches the cooling of the cell stack to either the steam separator or the heat exchanger, when the three-way switching valve is operated so that the cooling of the fuel cell stack is performed by the heat exchanger, the secondary cooling is performed. When the water flow rate is controlled to the large flow rate side to perform heat exchange and 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, and 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.