JP2020064808A - Fuel cell system - Google Patents

Abstract

To provide a technology for more securely preventing water from being frozen while improving an energy saving property of a fuel cell system.SOLUTION: A fuel cell system (100) comprises a fuel cell (3), a hot water storage tank (32), a heat recovery water channel (14) through which water in the hot water storage tank circulates, and a water pump (8). In a period in which the fuel cell (3) generates no power and an outside temperature is equal to or lower than a first temperature, a control unit (9) executes first freezing prevention operation of adjusting an operation condition of the water pump depending on the outside temperature until a water temperature difference between an upper part temperature and a lower part temperature in the hot water storage tank becomes equal to or lower than a predetermined value. When the water temperature difference becomes lower than the predetermined value during the first freezing prevention operation, the control unit shifts the operation to second freezing prevention operation of adjusting the operation condition of the water pump (8) depending on the lower part temperature.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to fuel cell systems.

  Fuel cell systems including reformers and fuel cells are well known. In the reformer, a hydrogen-containing gas is produced from a raw material such as city gas by a reforming reaction. The generated hydrogen-containing gas is supplied to the fuel cell together with oxygen (air) as an oxidant gas. In a fuel cell, electric power is generated by an electrochemical reaction between hydrogen and oxygen.

  For example, the fuel cell system 200 of FIG. 6 includes a fuel cell unit 51 having a fuel cell 50, a hot water storage unit 61 having a hot water storage tank 60 for storing hot water heated by the heat of the fuel cell 50, and heat exchange from the hot water storage tank 60. A cooling water path 62 is provided, which includes a forward path 62a for supplying water to the vessel 53 and a return path 62b for returning the water warmed by the heat exchanger 53 to the hot water storage tank. A cooling water path 62 is configured by the outward path 62a and the return path 62b, and water is circulated by a circulation pump 54 provided in the cooling water path 62. The heat medium passage 55 through which the heat medium generated during the power generation of the fuel cell 50 and the water flowing through a part of the cooling water passage 62 exchange heat with the heat exchanger 53, so that the heat generated by the power generation of the fuel cell is exchanged. It is effectively used. As described above, in the fuel cell system 200, various water flow passages such as the cooling water passage 62 of the fuel cell 50 and the drainage passage are provided. If the water freezes due to a decrease in the outside temperature, the fuel cell system cannot operate. There is also concern about damage to parts due to freezing of water. In particular, the outward path 62a connected to the hot water storage tank 60 may be damaged by freezing of water.

  Therefore, as described in Patent Document 1, in the winter or cold regions, when the outside air temperature decreases, the control unit 56 operates the circulation pump 54 to operate the cooling water path when the fuel cell 50 is not generating power. Freezing prevention operation is performed to fluidize 62 water and prevent freezing.

  Further, in Patent Document 2, in addition to fluidizing water in the circulation path, a heating device for heating the circulation path is provided. However, according to the technique of Patent Document 2, the power consumption of the heating device tends to increase.

JP, 2013-114851, A JP 2007-294186 A

  The configuration described in Patent Document 1 does not necessarily provide a sufficient antifreezing effect with respect to the suppression of freezing of water in the circulation path. Further, although the hot water in the hot water storage tank is used due to the fluidization of the circulation path, no measures are taken against the collapse of the temperature stratification of the hot water in the hot water storage tank in the process of using the hot water.

  The present disclosure provides a technique for more reliably preventing freezing of water while improving the energy saving of the fuel cell system.

This disclosure is
A fuel cell,
A hot water storage tank that stores hot water,
A circulation path through which the hot water stored in the hot water storage tank circulates;
A heat exchanger provided in the circulation path for exchanging heat between the exhaust heat from the fuel cell and the hot water stored in the hot water storage tank;
A water pump provided in the circulation path for circulating the hot water stored in the hot water storage tank through the circulation path;
An upper temperature detecting means and a lower temperature detecting means of the hot water storage tank;
An outside temperature detecting means for directly or indirectly detecting the outside temperature,
And a control unit,
In the period when the outside temperature is equal to or lower than the first temperature,
Until the difference between the temperature detected by the upper temperature detection means and the lower temperature detection means becomes less than or equal to a predetermined value, a first freeze prevention operation is performed to adjust the operating conditions of the water pump according to the outside air temperature,
When the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes smaller than the predetermined value during the first freeze prevention operation, the water is discharged according to the temperature detected by the lower temperature detecting means. Configured to transition to a second freeze prevention operation that adjusts the operating conditions of the pump,
Provide a fuel cell system.

  According to the technique of the present disclosure, it is possible to more reliably prevent freezing of water while improving the energy saving of the fuel cell system.

FIG. 1 is a configuration diagram of a fuel cell system according to an embodiment of the present disclosure. FIG. 2 is a flowchart shown as an example of the first freeze prevention operation and the second freeze prevention operation of the present disclosure. FIG. 3 is a diagram showing changes with time of the upper temperature and the lower temperature in the hot water storage tank when the water pump is operated at a predetermined speed while the fuel cell is stopped. FIG. 4 is a diagram illustrating an example of the first freeze prevention operation according to the embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of the second freeze prevention operation according to the embodiment of the present disclosure. FIG. 6 is a configuration diagram of the fuel cell system described in Patent Document 1.

(Findings that form the basis of this disclosure)
In the fuel cell system 200 shown in FIG. 6 of Patent Document 1, the high-temperature hot water heated by the heat generated by the fuel cell 50 is sequentially stored from the upper side to the lower side in the hot water storage tank 60 to form an upper layer of the hot water storage tank 60. From this, a temperature stratification is formed toward the lower layer. In reality, medium-low temperature hot water exists in the lower region of the hot water storage tank. In the fuel cell system, the medium- and low-temperature hot water is sent to the heat exchanger 53 by the circulation pump 54 through the cooling water path 62, and the high-temperature hot water heated by the heat generated by the fuel cell is stored therein from the upper part of the hot water storage tank. It is composed.

  By the way, in Patent Document 1, when the outside air temperature decreases, when the fuel cell 50 is not generating power, the control unit 56 operates the circulation pump 54 to fluidize the water in the cooling water path 62 and prevent freezing. We are doing preventive driving. When such an anti-freezing operation is executed, the medium- and low-temperature hot water existing in the lower portion of the hot water storage tank is stored in the hot water storage tank via the cooling water circuit 62 in a low outside temperature environment without heat supply from the fuel cell 50. It will be sent to the upper hot water region in 60. Therefore, the medium- and low-temperature hot water mixes with the upper-temperature high-temperature hot water, and the medium- and low-temperature hot water does not exist in the hot water storage tank 60. As described above, the configuration disclosed in Patent Document 1 does not necessarily mean the freeze prevention operation in which the hot water in the hot water storage tank is effectively used. Further, when the outside air temperature decreases and the risk of freezing of the cooling water passage 62 increases, it is necessary to heat the cooling water passage 62 by the heating device.

As a result of keen examination, the inventor of the present application has determined that the temperature stratification of the high temperature hot water formed in the upper part of the hot water storage tank is not destroyed by the mixing of the medium and low temperature hot water, and the temperature of the high temperature hot water in the hot water storage tank. By changing the method of controlling the circulating amount of hot water in the cooling water path depending on the period during which it can be determined that the distribution of hot water in the hot water storage tank has become almost uniform due to the stratification collapse, I noticed that I could more surely prevent freezing.
(Outline of One Aspect According to the Present Disclosure)
The fuel cell system according to the first aspect of the present disclosure is
A fuel cell,
A hot water storage tank that stores hot water,
A circulation path through which the hot water stored in the hot water storage tank circulates;
A heat exchanger provided in the circulation path for exchanging heat between the exhaust heat from the fuel cell and the hot water stored in the hot water storage tank;
A water pump provided in the circulation path for circulating the hot water stored in the hot water storage tank through the circulation path;
An upper temperature detecting means and a lower temperature detecting means of the hot water storage tank;
An outside temperature detecting means for directly or indirectly detecting the outside temperature,
And a control unit,
In the period when the outside temperature is equal to or lower than the first temperature,
Until the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes equal to or less than a predetermined value, a first anti-freezing operation of adjusting the operating conditions of the water pump according to the outside air temperature is executed,
When the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes smaller than the predetermined value during the first freeze prevention operation, the water is detected according to the temperature detected by the lower temperature detecting means. It is configured to shift to the second freeze prevention operation for adjusting the operating conditions of the pump.

  In the fuel cell system of the first aspect, when the urgency of freezing is high in view of the outside temperature detected by the outside temperature detecting means, the first freezing prevention operation is started. Prior to the start of the first freeze prevention operation, the hot water in the hot water storage tank had temperature stratification, but the fluidization of the circulation path stirs the hot water in the hot water storage tank, destroying the temperature stratification and increasing the temperature. Becomes uniform.

  According to the fuel cell system of the first aspect, the temperature detected by the upper temperature detecting means and the lower temperature detecting means of the hot water storage tank during the first freezing prevention operation of adjusting the operating condition of the water pump according to the outside air temperature. By detecting the difference, it is determined whether the hot water in the hot water storage tank maintains the temperature stratification or is uniformized. Since the urgency of freezing is judged from the outside temperature to adjust the operating state of the water pump, it is advantageous to maintain the temperature stratification of the hot water storage tank. Further, when it is determined that the hot water in the hot water tank has become uniform based on the difference in temperature detected between the upper temperature detecting means of the hot water storage tank and the lower temperature detecting means, the second freeze prevention operation is started and the temperature detected by the lower temperature detecting means is changed. Since the water pump is operated in accordance with the above, it is possible to reduce the power consumption supplied to the water pump, which is effective in improving energy saving.

  In the second aspect of the present disclosure, for example, the fuel cell system according to the first aspect includes a heating device which is provided directly or indirectly in the circulation path and heats water circulating in the circulation path, The control unit causes the heating device to generate heat when the temperature detected by the outside air temperature detection unit is equal to or lower than a second temperature lower than the first temperature when the first freeze prevention operation is performed.

  According to the second aspect, when the first freezing preventive operation is executed, when the urgency of freezing is high in view of the outside temperature detected by the outside air temperature detecting means, the heating device is caused to generate heat so that the circulation path Freezing can be reliably prevented. In addition, by intermittently operating the heating device or changing the set temperature according to the outside air temperature detected by the outside air temperature detecting means, the power consumption supplied to the heating device can be reduced, which is effective in improving energy saving. Is.

  In the third aspect of the present disclosure, for example, in the fuel cell system according to the second aspect, the control unit stops the heating device during the second freeze prevention operation.

  According to the third mode, in the second freeze prevention operation, the stratification of the hot water in the hot water storage tank is destroyed, and the temperature is substantially uniform. In the second freeze prevention operation, the heating device is stopped because hot water in the hot water storage tank is supplied to the circulation path. The power consumption supplied to the heating device can be reduced, which is effective in improving energy efficiency.

  In the fourth aspect of the present disclosure, for example, in the fuel cell system according to the second or third aspect, the control unit is configured to perform the upper temperature detection means and the lower temperature detection means during the first freeze prevention operation. When the difference in the detected temperature of is smaller than the predetermined value and the detected temperature of the lower temperature detection means is equal to or lower than the predetermined third temperature, the second freeze prevention operation is not performed and the first freeze prevention is performed. Shift to driving.

  According to the fourth aspect, the first freeze prevention operation is switched to the second freeze prevention operation based on the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means of the hot water storage tank during the first freeze preventing operation. At this time, the temperature of the lower temperature detecting means is confirmed. Even if it is confirmed that the stratification of the hot water temperature inside the hot water tank has collapsed due to the small temperature difference between the upper temperature and the lower temperature of the hot water storage tank, the temperature of the hot water inside the hot water tank prevents the circulation route from freezing. If it is determined that it is not possible, the freezing of the circulation path can be reliably prevented by shifting to the first freeze prevention operation.

  In the fifth aspect of the present disclosure, for example, in the fuel cell system according to any one of the first to fourth aspects, the control unit controls the lower temperature detection unit during the second freeze prevention operation. When the detected temperature becomes equal to or lower than the predetermined third temperature, the first freeze prevention operation is performed.

  According to the fifth aspect, when it is determined during the second freeze prevention operation that the temperature detected by the lower temperature detecting means of the hot water storage tank cannot prevent freezing of the circulation path due to a decrease in the temperature of the hot water in the hot water storage tank, Shift to the first freeze prevention operation. Then, in the first freeze prevention operation, when the urgency of freezing is high in view of the outside air temperature detected by the outside air temperature detecting means, the heating device is caused to generate heat. As a result, the freezing of the circulation path can be reliably prevented.

  In the sixth aspect of the present disclosure, for example, in the fuel cell system according to any one of the first to fifth aspects, the operating method of the water pump is that the water in the circulation path is continuously operated by continuously operating. It is configured to be switchable between a first operation in which the water in the circulation path is intermittently moved by intermittently operating it, and a second operation in which the water in the circulation path is intermittently moved. In operation, the circulating amount of the water pump and at least one of the operating methods are changed in accordance with the temperature detected by the outside air temperature detecting means, and in the second freeze prevention operation, in accordance with the temperature detected by the lower temperature detecting means. And at least one of the circulating amount of the water pump and the operating method is changed.

  According to the sixth aspect, when the first freezing prevention operation is executed, when the urgency of freezing is low in view of the outside temperature detected by the outside air temperature detecting means, the circulation amount of the water pump is reduced or the continuous operation is stopped. Switch to intermittent operation. Such an operation is advantageous for suppressing the power consumption of the circulation pump. Similarly, when the second freezing prevention operation is executed, when the temperature detected by the lower temperature detecting means of the hot water storage tank is relatively high and the effect of increasing the water temperature in the circulation path is high, the circulation amount of the water pump is reduced, Alternatively, the continuous operation is switched to the intermittent operation. Such an operation is advantageous for suppressing the power consumption of the circulation pump.

  In the seventh aspect of the present disclosure, for example, in the fuel cell system of the fourth aspect, in the second operation, the amount of water corresponding to the total volume of the circulation path is the time when the water pump operates once. It is time to make at least one round.

  According to the seventh aspect, the water temperature in each portion of the circulation path can be averaged by the water circulation by the water pump, which is advantageous in preventing the occurrence of local freezing in the circulation path.

  In the eighth aspect of the present disclosure, for example, in the fuel cell system according to any one of the first to seventh aspects, the control unit is executing the first freeze prevention operation or the second freeze prevention operation. When the fuel cell receives the start instruction, the first freeze prevention operation or the second freeze prevention operation that is being executed is stopped and the fuel cell is started.

  According to the eighth aspect, when the fuel cell is activated, the circulation path is heated by the heat generated by the fuel cell during power generation, so the freeze prevention operation is stopped. It is advantageous to prevent damage and deterioration of the elements (for example, water pump, heating device) for executing the freeze prevention operation.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.
(Embodiment)
(Fuel cell system configuration)
As shown in FIG. 1, a fuel cell system 100 according to this embodiment includes a fuel cell unit 1 including a housing 2, a fuel cell 3 and a reformer 4, a hot water storage tank 32, and a hot water storage tank housing 31. It has a hot water storage unit 30. The fuel cell 3 and the reformer 4 are housed in the housing 2. The hot water storage tank 32 is housed in the hot water storage tank housing 31. The outside air temperature sensor 10 is a temperature sensor using a thermistor or a temperature sensor using a thermocouple, and detects the outside air temperature.

The reformer 4 is a device for generating a hydrogen-containing gas by a reforming reaction such as a steam reforming reaction (CH ₄ + H ₂ O → CO + 3H ₂ ). The reformer 4 contains a reforming catalyst for advancing the reforming reaction. The reformer 4 uses the water and the raw material to generate a hydrogen-containing gas. The raw material is, for example, a hydrocarbon gas such as city gas or LP gas (liquefied petroleum gas). The hydrogen gas generated by the reformer 4 is supplied to the fuel cell 3. The fuel cell 3 uses the oxidant gas (air) and hydrogen gas to generate electric power. The fuel cell 3 is, for example, a solid polymer fuel cell or a solid oxide fuel cell. Hot water is generated by the exhaust heat of the fuel cell 3. The generated hot water is stored in the hot water storage tank 32.

  The fuel cell system 100 further includes a first water circuit 13, a second water circuit 12, a heat exchanger 5, and a heat recovery water passage (corresponding to a circulation passage) 14. The first water circuit 13 is connected to the fuel cell 3. The second water circuit 12 is connected to the reformer 4. The first water circuit 13 is a cooling water circuit in which cooling water for cooling the fuel cell 3 circulates. The first water circuit 13 is provided with the first tank 6 and the T-shaped joint 16. The second water circuit 12 is a water supply circuit for supplying water to the reformer 4. The second water circuit 12 is provided with the second tank 7 and the T-shaped joint 19. The water in the second tank 7 is supplied to the reformer 4. The heat exchanger 5 is arranged in the first water circuit 13.

  Further, the first tank 6 is provided with a heating device 11 (for example, a heater). Even when the fuel cell 3 is stopped, when the control unit 9 causes the heating device 11 to generate heat, the water in the first tank 6 is heated and the hot water flowing through the heat recovery water passage 14 via the heat exchanger 5 is heated. Can be heated.

  The heat recovery water channel 14 is a channel for recovering the exhaust heat of the fuel cell 3. The heat recovery water channel 14 includes heat recovery pipes 14a and 14b. The heat recovery pipes 14 a and 14 b are connected to the heat exchanger 5, respectively. The heat recovery pipe 14 a constitutes a downstream side portion of the heat recovery water channel 14. The heat recovery pipe 14b constitutes an upstream side portion of the heat recovery water channel 14. The heat recovery pipe 14 a is a pipe for guiding the water heated in the heat exchanger 5 to the hot water storage tank 32. The heat recovery pipe 14b is a pipe for guiding the water to be heated in the heat exchanger 5 to the heat exchanger 5. The heat recovery pipes 14a and 14b are metal pipes such as stainless pipes. The heat exchanger 5 is configured to exchange heat between the water flowing through the heat recovery water passage 14 and the water flowing through the first water circuit 13. That is, the heat exchanger 5 plays a role of heating the water to be stored in the hot water storage tank 32 by the heat of the cooling water of the first water circuit 13. The first water circuit 13, the second water circuit 12, the heat exchanger 5, and the heat recovery pipes 14 a and 14 b are also arranged inside the housing 2.

  The heat recovery pipe 14 a extends through the through hole 23 formed in the housing 2 to the heat recovery pipe 14 c formed outside the housing 2. The heat recovery pipe 14c is connected to the heat recovery pipe 14d through the through hole 24 formed in the hot water storage tank casing 31, and is connected to the high temperature water inlet at the upper part of the hot water storage tank 32. In detail, the high temperature side connector is attached to the through holes 23 and 24. Similarly, the heat recovery pipe 14 b extends through the through hole 21 formed in the housing 2 to the heat recovery pipe 14 f formed outside the housing 2. The heat recovery pipe 14f is connected to the heat recovery pipe 14e through the through hole 22 formed in the hot water storage tank casing 31, and is connected to the low temperature water inlet at the bottom of the hot water storage tank 32. In detail, the low temperature side connector is attached to the through holes 21 and 22. The heat recovery pipes 14 d and 14 e are arranged inside the hot water storage tank housing 31. The high temperature side connector and the low temperature side connector are made of resin or metal.

  On the other hand, the heat recovery pipes 14c and 14f are arranged outside the housing 2 and the hot water tank housing 31. The heat recovery pipe 14f through which the low-temperature water flows has a high risk of freezing at low outside temperatures.

  In order to fluidize the water in the heat recovery water channel 14 inside the housing 2, a water pump 8 is provided in the heat recovery pipe 14 b at the upstream side portion of the heat recovery water channel 14.

  The hot water storage tank 32 is provided with a plurality of temperature sensors 36a to 36f. The plurality of temperature sensors 36a to 36f detect representative temperatures in the respective regions 35a to 35f of the hot water storage tank 32. With this configuration, the temperature distribution of the hot water in the hot water storage tank 32 can be detected. Here, the temperature sensors 36a to 36f are temperature sensors using a thermistor or temperature sensors using a thermocouple. The temperatures of the hot water detected by the plurality of temperature sensors 36a to 36f are stored in the temperature management unit 38 as time-series data and are also sent to the control unit 9.

  Since the high temperature hot water is returned to the upper part of the hot water storage tank 32 from the heat recovery pipe 14d, the temperature stratification of the hot water is formed in the hot water storage tank 32. For example, the upper temperature of the hot water storage tank is detected by the temperature sensor 36a or 36b, and the lower temperature of the hot water storage tank is detected by 36e or 36f. For example, the upper temperature of the hot water storage tank is a temperature in the upper third of the vertical height of the hot water storage tank 32, and the lower temperature is a temperature in the lower third of the vertical height of the hot water storage tank 32. When the control unit 9 performs the boiling operation of the hot water storage tank 32 in accordance with the power generation of the fuel cell 3, for example, when the temperature sensors 35a and 35e reach a predetermined temperature or higher, the hot water storage tank 32 is filled with heat. It is determined that the boiling operation is completed. Therefore, even after completion of boiling, there may be cases where medium- and low-temperature hot water below the boiling temperature exists in a region below the lowest temperature sensor 36f in the hot water storage tank 32.

  A first drainage channel 17 is connected to the T-shaped joint 16 of the first water circuit 13. The first drainage channel 17 is a channel for draining water from the first water circuit 13. The first drainage channel 17 is typically composed of a resin pipe. A second drainage channel 20 is connected to the T-shaped joint 19 of the second water circuit 12. The second drainage channel 20 is a channel for draining water from the second water circuit 12. The second drainage channel 20 is typically composed of a resin pipe. In the present embodiment, a dedicated drainage channel is connected to each of the first water circuit 13 and the second water circuit 12. However, it is possible to combine the first drainage channel 17 and the second drainage channel 20 into one. The drainage channel may be connected to at least one selected from the first water circuit 13 and the second water circuit 12.

  A first water drain plug 18 is attached to the end of the first drainage channel 17. Specifically, a connector including the first water drain plug 18 is attached to a through hole formed in the bottom wall of the housing 2. A second drain plug 15 is attached to the end of the second drainage channel 20. In detail, a connector including the second drain plug 15 is attached to a through hole formed in the bottom wall of the housing 2. As a result, the first drainage channel 17 and the second drainage channel 20 each extend to the outside of the housing 2. The first water drain plug 18 and the second water drain plug 15 are, for example, screw-type plugs. The first water drain plug 18 and the second water drain plug 15 are located outside the housing 2. Therefore, it is possible to remove the first water drain plug 18 and the second water drain plug 15 from the outside of the housing 2. With such a structure, the water draining operation can be performed very easily.

The fuel cell system 100 further includes a controller 9. The control unit 9 is a device for controlling control targets such as the fuel cell 3, the reformer 4, and the water pump 8. The control unit 9 is configured by, for example, a DSP (Digital Signal Processor) including an A / D conversion circuit, an input / output circuit, an arithmetic circuit, a storage device, and the like.
(Freezing prevention operation)
In the fuel cell system 100 of FIG. 1, when the outside air temperature becomes equal to or lower than the temperature at which water is likely to freeze during the stop period including the standby period, the first freezing prevention operation of the heat recovery water channel 14 is executed.

Hereinafter, an example of the first freeze prevention operation will be described with reference to FIG. 2. As shown in FIG. 2, in step S1, the control unit 9 acquires information indicating the outside air temperature T ₀ detected by the outside air temperature sensor 10 and determines whether T ₀ is equal to or lower than the first temperature T ₁ . If the determination result in step S1 is negative, the process proceeds to step S14, and the control unit 9 executes a predetermined stop process of the first antifreezing operation. For example, in step S14, the control unit 9 stops the water pump 8 and turns off the heating device 11 when the heating device 11 is on. When the process of step S14 is completed, the first freeze preventive operation ends. The control unit 9 may return to step S1 after the process of step S14 is completed.

  On the other hand, if the determination result in step S1 is affirmative, the process proceeds to step S2, and the control unit 9 determines whether or not a startup instruction has been issued. In step S2, the control part 9 acquires the information regarding an alternating current power output command, for example. When the AC power command value shows a constant value other than 0, control unit 9 determines that a start instruction has been issued.

  If the determination result in step S2 is negative, the process proceeds to step S3, and the control unit 9 executes the first freeze prevention operation. Here, in the first freeze prevention operation, it is intended that the temperature stratification of the hot water stored in the hot water storage tank 32 is not destroyed as much as possible while executing the freeze prevention operation.

  When the first freeze prevention operation is being executed, the control unit 9 determines the operation mode of the water pump 8 based on the control map shown in FIG.

In FIG. 4, when the outside air temperature T ₀ is higher than T ₁ , it is determined that the possibility of freezing is considerably low, the operation of the water pump 8 is stopped, and the first freezing prevention operation is not performed.

Further, in FIG. 4, when the outside air temperature T ₀ is higher than T _{2 and} lower than T ₁ , it is determined that the possibility of freezing is relatively low, and the water pump 8 is intermittently operated to flow through the heat recovery water passage 14. Turn into. The ON time of the water pump 8 is set to be equal to or longer than the time when the amount of water corresponding to the total volume of the heat recovery water passage 14 makes at least one circulation in the heat recovery water passage 14. Thereby, the water temperature of the heat recovery water channel 14 is averaged and local freezing can be prevented. Further, by linearly correlating the outside air temperature T ₀ and the rotation speed of the water pump 8, the circulation amount of the heat recovery water channel 14 can be minimized. If the temperature of the hot water returned to the hot water storage tank 32 after circulating through the heat recovery water channel 14 is high, the temperature stratification in the hot water storage tank 32 collapses by reducing the circulation amount of the hot water, and the hot water in the hot water storage tank is substantially uniform. You can delay the time it takes to turn into.

Further, in FIG. 4, when the outside air temperature T ₀ is equal to or lower than T ₂ , it is determined that the possibility of freezing is relatively high, and the water pump 8 is continuously operated. For example, T ₁ is 5 ° C. and T ₂ is 0 ° C. Also in this case, the circulation amount of the heat recovery water channel 14 can be minimized by linearly corresponding the outside air temperature T ₀ to the rotation speed of the water pump 8. In this way, the power consumption of the water pump 8 can be suppressed by changing the operating state of the water pump 8 according to the outside air temperature T ₀ . After the operation mode of the water pump 8 in the first freeze prevention operation is determined, the process proceeds to step S4.

  On the other hand, if the determination result in step S2 is affirmative, the process proceeds to step S12, the control unit 9 stops the first freezing operation, and proceeds to step S13 to proceed to the startup sequence of the fuel cell system. When the fuel cell system is activated, the heat recovery water channel 14 is heated by the heat generated by the fuel cell 3 during power generation, so that the first freeze prevention operation can be stopped. As a result, it is possible to prevent the elements (for example, the water pump and the heating device) for executing the first freeze prevention operation from being damaged or deteriorated.

Next, in step S4, the outside air temperature T ₀ is compared with the predetermined temperature T ₃ . Here, T ₃ is a temperature at which it is determined that freezing is difficult only by fluidizing the heat recovery water channel 14. If the determination result in step S4 is affirmative, the process proceeds to step S6, and the heating device 11 is turned on. For example, _{T 3} is -3 ° C.. When the process proceeds to step S6, the control unit 9 determines that it is difficult to prevent freezing only by fluidizing the heat recovery water channel 14. Therefore, the heating device 11 is caused to generate heat intermittently or continuously. Even when the fuel cell 3 is stopped, when the control unit 9 causes the heating device 11 to generate heat, the water in the first tank 6 is heated and the hot water flowing through the heat recovery water passage 14 via the heat exchanger 5 is heated. Can be heated. As described above, when the urgency of freezing is high in view of the outside air temperature detected by the outside air temperature detecting means, the heating device 11 is operated intermittently or continuously to reliably prevent freezing of the heat recovery water channel 14. You can The heating device 11 may be intermittently operated or the set temperature may be changed according to the outside air temperature detected by the outside air temperature detecting means. Further, the rotation speed of the water pump 8 may be reduced as compared with the case where the outside air temperature T ₀ is T ₃ or more and less than T ₂ . By performing such setting, the power consumption supplied to the heating device 11 can be reduced and the energy saving property can be improved.

  On the other hand, if the determination result in step S4 is negative, the process proceeds to step S1 via step S5. At this time, it is determined in step S5 that the heating device 11 does not need to generate heat, and the control unit 9 turns off the heating device 11 when the heating device 11 is generating heat.

If the determination result in step S4 is affirmative, the process proceeds to step S7. Here, the determination content of step S7 will be described with reference to FIG. 3, the upper temperature _{T H} of the hot water storage tank 32 is the detection temperature of, for example, a temperature sensor 36a or 36b. The lower temperature T _L of the hot water storage tank 32 is, for example, the temperature detected by the temperature sensor 36e or 36f. When the water pump 8 is continuously operated at a predetermined rotation speed while the fuel cell 3 is stopped, as the medium- and low-temperature hot water is returned from the heat recovery water channel 14 to the high-temperature hot water in the upper part of the hot water storage tank 32, temperature T _H of the upper part of the high temperature hot water is reduced. Further, the water pump fluidizes the heat recovery water passage 14, whereby the hot water in the hot water storage tank 32 is agitated, the lower temperature _TL of the hot water storage tank 32 rises, the internal temperature is made uniform, and the temperature variations are uneven. Less hot water. For example, as shown in FIG. 3, when the temperature difference between the upper temperature T _H and the lower temperature T _L of the hot water storage tank 32 becomes equal to or less than _a predetermined temperature difference T _a after a lapse of time t ₀ from the start of operation of the water pump 8. It can be considered that the temperature distribution of the hot water in the hot water storage tank 32 is made uniform. For example, _TH is 60 ° C, _TL is 20 ° C, and _Ta is 5 ° C.

  That is, when the determination result in step S7 is negative, it is determined that the hot water in the hot water storage tank 32 maintains the temperature stratification, and the process returns to step S1 to continue the first freeze prevention operation.

On the other hand, if the determination result in step S7 is affirmative, it is determined that the temperature stratification of the hot water in the hot water storage tank 32 has collapsed, and the hot water temperature in the hot water storage tank 32 has been made substantially uniform, and the process proceeds to step S8. In step S8, control unit 9 determines whether lower temperature T _L of hot water storage tank 32 is lower than or equal to predetermined temperature T _b . For example, T _b is 15 ° C. If the determination result in step S7 is negative, that is, if the temperature distribution in the hot water storage tank 32 is not uniform yet, the process proceeds to step S1 and the control unit 9 continuously operates the water pump 8. By doing so, the hot water existing in the upper part of the hot water storage tank 32 can be stirred and the heat can be delivered to the lower part of the hot water storage tank 32. Even if there is no high temperature hot water in the upper part of the hot water storage tank, the water pump 8 is continuously operated, which is advantageous in terms of freeze prevention.

In the first freeze prevention operation, as shown in FIG. 4, the water pump 8 is continuously operated when it is determined that the possibility of freezing of the heat recovery water channel 14 is relatively high. For example, when the outside air temperature T ₀ is equal to or lower than T ₂ , the rotation speed of the water pump 8 may be set to increase according to the decrease in the outside air temperature T ₀ . By doing so, it is advantageous to prevent freezing of the heat recovery water channel 14.

Next, in step S8, it is determined whether or not to shift to the second freeze prevention operation for performing freeze prevention using hot water whose temperature is substantially uniformed in the hot water storage tank 32. That is, if the determination result of step S8 is affirmative (the lower temperature T _L of the hot water storage tank 32 is equal to or lower than the predetermined temperature T _b ), it is difficult to prevent freezing only by supplying the hot water in the hot water storage tank 32 to the heat recovery water channel. It is determined that there is, and the process returns to step S1 to execute the first freeze prevention operation. As a result, the freezing of the heat recovery water channel 14 can be reliably prevented.

  On the other hand, if the result of the determination in step S8 is negative, it is determined that the freezing can be prevented only by supplying the hot water in the hot water storage tank 32 to the heat recovery water channel, and the process proceeds to step S10 via step S9. At this time, it is determined in step S9 that the heating device 11 does not need to generate heat, and the control unit 9 turns off the heating device 11 when the heating device 11 is generating heat.

  If the determination result in step S8 is negative, the process proceeds to step S10, and the second freeze prevention operation is executed. In the second anti-freezing operation, the anti-freezing is performed by supplying the hot water in the hot water storage tank 32 to the heat recovery water channel 14 instead of not causing the heating device 11 to generate heat. This is intended to reduce the power consumption supplied to the heating device 11.

In the second freeze prevention operation, the control unit 9 determines the rotation speed of the water pump 8 based on the lower temperature T _L of the hot water storage tank 32 as shown in FIG. In the outside air temperature T ₀ without for controlling the rotational speed of the water pump on the basis of the lower temperature T _L of the hot water storage tank 32, the accuracy of the freezing prevention rises, the rotational speed of the water pump 8 than the first freeze prevention operation The power consumption can be further reduced. After determining the rotation speed of the water pump 8, the process proceeds to step S11.

Here, in the example of FIG. 5, the rotation speed of the water pump 8 is given as a linear function with respect to the lower temperature T _L of the hot water storage tank 32, but the invention is not limited to this. For example, the rotation speed of the water pump 8 may be changed stepwise with respect to the lower temperature T _L of the hot water storage tank 32. Further, instead of the operation method of rotating the water pump 8 at a low speed, the water pump 8 may be operated intermittently. As described above, when the second freezing prevention operation is executed, when the temperature detected by the lower temperature detection means of the hot water storage tank 32 is relatively high and the effect of increasing the water temperature of the heat recovery water passage 14 is high, the water pump 8 The power consumption of the water pump 8 can be suppressed by reducing the circulation amount or switching from continuous operation to intermittent operation.

Next, in step S11, it is determined whether or not to continue the second anti-freezing operation in which anti-freezing is performed using hot water whose temperature is substantially equalized in the hot water storage tank 32. That is, if the determination result of step S11 is affirmative (the lower temperature T _L of the hot water storage tank 32 is equal to or lower than the predetermined temperature T _b ), it is difficult to prevent freezing only by supplying the hot water in the hot water storage tank 32 to the heat recovery water channel. It is determined that there is, and the process returns to step S1 to execute the first freeze prevention operation. Then, in the first freeze prevention operation, when the urgency of freezing is high in view of the outside air temperature detected by the outside air temperature detecting means, the heating device 11 is operated intermittently or continuously. Thereby, it is possible to reliably prevent freezing of the heat recovery water channel 14.

On the other hand, when the determination result in step S11 is negative, the lower temperature _TL of the hot water storage tank 32 is higher than the predetermined temperature Tb, and the freezing prevention can be performed only by supplying the hot water in the hot water storage tank 32 to the heat recovery water passage. Then, the process proceeds to step S10 to continue the second freeze prevention operation.

As described above, according to the fuel cell system of the present embodiment, the upper temperature detecting means of the hot water storage tank 32 is executed during the first freeze prevention operation in which the operating condition of the water pump 8 is adjusted according to the outside air temperature T _0. By detecting the temperature difference between the lower temperature detecting means and the lower temperature detecting means, it is possible to determine whether the hot water in the hot water storage tank 32 maintains the temperature stratification or is made uniform. In addition, the operating condition of the water pump 8 is adjusted by judging the urgency of freezing from the outside air temperature, which is advantageous for maintaining the temperature stratification of the hot water storage tank 32. Further, when it is determined that the hot water in the hot water storage tank has become uniform based on the difference in temperature detected between the upper temperature detection means and the lower temperature detection means of the hot water storage tank 32, the second freeze prevention operation is started and the temperature detected by the lower temperature detection means is changed. Since the water pump is operated in accordance with the above, it is possible to reduce the power consumption supplied to the water pump and improve the energy saving property.

  According to the fuel cell system of the present embodiment, when the first freeze prevention operation is performed, the switching temperature of the operating state of the water pump 8 may have a range.

For example, the predetermined width δT is set before and after the temperature boundary value T ₁ at which the water pump 8 is switched from the stopped state to the intermittent operation. Then, the outside air temperature _{T 0} is from higher than _{T 1} until _T 1 -.DELTA.T to stop the operation. On the other hand, when the water pump 8 is intermittently operated in a state where the outside air temperature is T ₁ or less, the water pump 8 is not stopped and the intermittent operation is continued until the outside air temperature T ₀ becomes T ₁ + δT.

Similarly, a predetermined value δT is set around T ₂ which is a temperature boundary value at which the operating state of the water pump 8 is switched from intermittent operation to continuous operation. Then, the intermittent operation is continued until the outside air temperature T ₀ becomes higher than T ₂ until T ₂ −δT. On the other hand, when the continuous operation is performed in a state where the outside air temperature T ₀ is T ₂ or less, the continuous operation is continued until the outside air temperature T ₀ becomes T ₂ + δT.

  In this way, by making the temperature boundary value for changing the operating state of the water pump 8 wide (hysteris), the operation control of the water pump 8 can be stabilized. For example, δT is 1 ° C. Further, the predetermined width δT may be set for each temperature boundary value.

  From the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. The details of structure and / or function may be substantially changed without departing from the spirit of the invention.

  The techniques disclosed herein help prevent water from freezing in fuel cell systems. The technology disclosed in the present specification also contributes to improvement in energy efficiency of a fuel cell system.

100 Fuel Cell System 1 Fuel Cell Unit 2 Housing 3 Fuel Cell 4 Reformer 5 Heat Exchanger 6 First Tank 7 Second Tank 8 Water Pump 9 Controller 10 Outside Air Temperature Sensor 11 Heating Device 14 Heat Recovery Water Channels 14a, 14b , 14c, 14d, 14e, 14f Heat recovery piping 30 Hot water storage unit 31 Hot water storage tank housing 32 Hot water storage tanks 36a, 36b, 36c, 36d, 36e, 36f Temperature sensor

Claims (8)

A fuel cell,
A hot water storage tank that stores hot water,
A circulation path through which the hot water stored in the hot water storage tank circulates;
A heat exchanger provided in the circulation path for exchanging heat between the exhaust heat from the fuel cell and the hot water stored in the hot water storage tank;
A water pump provided in the circulation path for circulating the hot water stored in the hot water storage tank through the circulation path;
An upper temperature detecting means and a lower temperature detecting means of the hot water storage tank;
An outside temperature detecting means for directly or indirectly detecting the outside temperature,
And a control unit,
In the period when the outside temperature is equal to or lower than the first temperature,
Until the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes equal to or less than a predetermined value, a first anti-freezing operation of adjusting the operating conditions of the water pump according to the outside air temperature is executed,
When the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes smaller than the predetermined value during the first freeze prevention operation, the water is detected according to the temperature detected by the lower temperature detecting means. A fuel cell system configured to transition to a second freeze protection operation that adjusts pump operating conditions. Provided directly or indirectly in the circulation path, comprising a heating device for heating water circulating in the circulation path,
The control unit is
When the temperature detected by the outside air temperature detection means is equal to or lower than a second temperature lower than the first temperature when the first freeze prevention operation is performed, the heating device is caused to generate heat.
The fuel cell system according to claim 1.   The fuel cell system according to claim 2, wherein the control unit stops the heating device during the second freeze prevention operation. The control unit is
When the difference between the temperatures detected by the upper temperature detecting means and the lower temperature detecting means becomes smaller than the predetermined value during the execution of the first freeze prevention operation, the temperature detected by the lower temperature detecting means is the third predetermined value. The fuel cell system according to claim 2 or 3, wherein when the temperature is equal to or lower than the temperature, the second freeze prevention operation is not shifted to the first freeze prevention operation. The control unit is
The first freeze prevention operation is shifted to the first freeze prevention operation when the temperature detected by the lower temperature detection means becomes equal to or lower than the predetermined third temperature during execution of the second freeze prevention operation. The fuel cell system according to any one of claims. The operation method of the water pump includes a first operation in which water in the circulation path is continuously moved by continuously operating, and a first operation in which water in the circulation path is intermittently operated by operating intermittently. It is configured so that it can be switched to two operations,
The control unit is
In the first freeze prevention operation, the circulation amount of the water pump according to the temperature detected by the outside air temperature detection means, and at least one of the operating method is changed,
At least one of the circulating amount of the water pump and the operating method is changed according to the temperature detected by the lower temperature detecting means in the second freeze prevention operation. The fuel cell system described.   The fuel cell system according to claim 4, wherein in the second operation, the time for which the water pump operates once is a time for which the amount of water corresponding to the total volume of the circulation path makes at least one circulation in the circulation path.   The control unit, when the fuel cell receives a start instruction during execution of the first freeze prevention operation or the second freeze prevention operation, performs the first freeze prevention operation or the second freeze prevention operation in execution. The fuel cell system according to any one of claims 1 to 7, wherein the fuel cell system is stopped and the fuel cell is activated.

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