Fuel cell system

Abstract

To provide a fuel cell system capable of preventing freezing without using a freezing prevention heater.SOLUTION: A fuel cell system (1) includes: a power generation section (3) generating power using fuel gas supplied through a microcomputer meter (20); a hot water storage unit (10) performing hot water storage operation to store hot water heated using heat during power generation operation of the power generation section (3); control means (4) to control the power generation operation and the hot water storage operation; and communication means (19) to acquire weather information via an external communication network (21). The control means (4) sets a power generation stop period during which the power generation operation is periodically stopped to avoid activation of a gas cutoff function of the microcomputer meter (20) cutting off the supply of fuel gas if continuous supply of fuel gas exceeds a preset period, and predicts, based on weather information acquired by the communication means (19), a freezing prevention period during which freezing prevention operation for the hot water storage unit (10) is required, and if the interference between the power generation stop period and the freezing prevention period occurs, the power generation stop period is changed before the freezing prevention period.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel cell system configured to generate electricity using fuel gas, store hot water heated by heat generated during power generation, and use the stored hot water for hot water supply. [Background technology]

[0002] Conventionally, water heaters that use fuel gas to heat hot water and provide it have been widely used. The fuel gas is supplied to the water heater from a fuel gas supply source via a microcomputer meter. The microcomputer meter, as disclosed in Patent Document 1 for example, measures the amount of fuel gas used and monitors fuel gas leakage, pressure fluctuation, etc., and has a gas cutoff function that cuts off the supply of fuel gas if an abnormality is detected.

[0003] As a hot water supply device, for example, a fuel cell system equipped with a power generation section having a fuel cell and a hot water storage unit that performs a hot water storage operation in which a heat medium (hot water) heated by heat generated during power generation operation of the power generation section is stored in a hot water storage tank and the hot water in the hot water storage tank is used for hot water supply. This fuel cell system can improve energy efficiency because the hot water storage unit stores heat for hot water supply while the power generation section generates electricity for household use. If the heat in the hot water storage tank is insufficient, for example, a combustion-type auxiliary heat source unit heats the clean water to supply hot water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7082915 Summary of the Invention [Problem to be solved by the invention]

[0005] The microcomputer meter is configured to shut off the supply of fuel gas using the gas shutoff function if fuel gas is supplied continuously for a long period of time (e.g., 30 days). Since a long period of continuous fuel gas supply may result in fuel gas leakage from the equipment receiving the fuel gas, shutting off the fuel gas supply is a safety operation to prevent accidents.

[0006] In a fuel cell system, the power generation unit must be heated to a high temperature of, for example, 700°C or higher to generate electricity, and it is not easy to start and stop the power generation operation. Therefore, as in Patent Document 1, the system is usually configured to perform the power generation operation continuously, and to stop the power generation operation, for example, every 28 days, in order to avoid the gas cutoff function of the microcomputer meter. The power generation operation is generally stopped for a period of about 10 hours to 1 day.

[0007] In winter, as the outside temperature drops, there is a risk that the hot water in the water heater will freeze, but in a fuel cell system, the heat generated during power generation prevents freezing. However, when power generation is stopped to avoid the gas shutoff function, the temperature of the power generation section drops, and there is a risk that the heat transfer medium in the hot water storage unit and the hot water for hot water supply will freeze. Since freezing can induce breakdowns in the fuel cell system, when the outside temperature drops to the start temperature of the freeze prevention operation (for example, 3°C), the freeze prevention heater is activated to prevent freezing.

[0008] However, the anti-freeze heater only operates when the period when power generation is stopped overlaps with the period when there is a risk of freezing, and since this complicates the configuration of the fuel cell system and increases manufacturing costs, consideration has been given to omitting the anti-freeze heater. Therefore, an object of the present invention is to provide a fuel cell system that can prevent freezing without using an anti-freeze heater. [Means for solving the problem]

[0009] The fuel cell system of the invention of claim 1 is a fuel cell system having a power generation unit that generates electricity using fuel gas supplied via a microcomputer meter, a hot water storage unit that performs hot water storage operation to store hot water heated by heat generated during the power generation operation of the power generation unit, and a control means for controlling the power generation operation and the hot water storage operation, and further has a communication means for obtaining weather information via an external communication network, and the control means sets a power generation stop period during which the power generation operation is periodically stopped to avoid activation of the gas cut-off function of the microcomputer meter that cuts off the supply of fuel gas when continuous supply of fuel gas exceeds a predetermined period, predicts a freeze prevention period during which freeze prevention operation of the hot water storage unit is required based on the weather information obtained by the communication means, and if the power generation stop period and the freeze prevention period interfere with each other, changes the power generation stop period to before the freeze prevention period.

[0010] According to the above configuration, the fuel cell system generates power using fuel gas and stores hot water heated by utilizing heat generated during power generation. The fuel gas used for power generation is supplied via a microcomputer meter that cuts off the supply when continuous supply exceeds a predetermined period, so that the control means sets a power generation stop period so as not to activate this gas cut-off function, and stops power generation during this power generation stop period. The control means also predicts a period in which there is a risk of freezing of the hot water storage unit as a freeze prevention period to prevent freezing, based on weather information obtained by the communication means. Then, if the power generation stop period and the freeze prevention period interfere with each other, the power generation stop period is changed to before the freeze prevention period. Therefore, the power generation operation is stopped during the power generation stop period before the freeze prevention period to avoid activation of the gas cut-off function of the microcomputer meter, and the power generation operation is resumed during the subsequent freeze prevention period, and hot water storage operation is performed using the heat, so that the hot water storage unit can be prevented from freezing.

[0011] The fuel cell system of the invention of claim 2 is characterized in that, in the invention of claim 1, the control means controls the hot water storage operation so as to store the maximum amount of heat in the hot water storage unit before the power generation stop period. According to the above configuration, the maximum amount of heat is stored in the hot water storage unit before power generation is stopped, so the stored hot water can be used for, for example, hot water supply even during periods when power generation is stopped, and user convenience is not impaired. Also, even if, for example, weather conditions change and freeze prevention operation is required during periods when power generation is stopped, the stored heat can be used to prevent the hot water storage unit from freezing. Effect of the Invention

[0012] According to the fuel cell system of the present invention, freezing can be prevented without using an anti-freeze heater. [Brief description of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention. [Diagram 2] 4 is a flowchart of power generation suspension period adjustment according to the embodiment. [Diagram 3] 11 is a table showing an example of adjustment of a power generation suspension period according to an embodiment. [Figure 4] 3 is a flowchart of the power generation suspension period adjustment obtained by partially modifying FIG. 2. [Diagram 5] 5 is a table showing an example of adjusting the power generation suspension period in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the mode for carrying out the present invention will be described based on examples. EXAMPLES

[0015] 1, the fuel cell system 1 includes, within an exterior case 2, a power generation section 3 that performs a power generation operation, a hot water storage unit 10 that performs a hot water storage operation in which a heat medium (hot water) heated using heat from the power generation operation is stored in a hot water storage tank 11, and a control section 4 (control means) that controls the power generation operation and the hot water storage operation. Also housed within the exterior case 2 are a fuel gas supply section 5, a reforming water supply section 6, an oxidant gas supply section 7, and a power conditioner 8. The power conditioner 8 receives a supply of power for operating the fuel cell system 1 from the outside, and converts the power generated by the power generation section 3 into household power and supplies it to the outside.

[0016] The fuel gas supply unit 5 supplies fuel gas (e.g., city gas mainly composed of methane) supplied from an external fuel gas supply source via a microcomputer meter 20 as indicated by an arrow G to the power generation unit 3. The reforming water supply unit 6 supplies water for extracting hydrogen from the fuel gas by a steam reforming method to the power generation unit 3 by a reforming water pump 6a.

[0017] The oxidant gas supply unit 7 supplies air containing oxygen to be reacted with hydrogen to the power generation unit 3. The power generation unit 3 includes a fuel cell that generates electricity by reacting hydrogen extracted from the fuel gas with oxygen, which is an oxidant gas, in a high-temperature environment of, for example, 700° C. or higher, and sends the electricity generated during power generation operation to a power conditioner 8 via a power line (not shown).

[0018] The hot water storage unit 10 has a hot water storage tank 11, an exhaust heat recovery heat exchanger 12, a radiator 13, and a hot water supply heat exchanger 14. The hot water storage tank 11, the exhaust heat recovery heat exchanger 12, and the radiator 13 are connected to each other by a hot water storage circulation passage 15 equipped with a hot water storage pump 15a so that the heat medium can circulate. The hot water supply heat exchanger 14 and the hot water storage tank 11 are connected to each other by a hot water supply circulation passage 16 equipped with a hot water supply pump 16a so that the heat medium can circulate.

[0019] High-temperature power generation exhaust gas containing a large amount of water vapor generated by the reaction of hydrogen and oxygen in the power generation section 3 is supplied to the exhaust heat recovery heat exchanger 12. In addition, by operation of the hot water pump 15a, a heat medium is supplied from the lower part of the hot water storage tank 11 through the radiator 13 to the exhaust heat recovery heat exchanger 12. In the exhaust heat recovery heat exchanger 12, the high-temperature power generation exhaust gas is cooled by heat exchange with the heat medium that has been cooled by radiating heat to the air in the radiator 13.

[0020] Some of the water vapor in the power generation exhaust cooled by the exhaust heat recovery heat exchanger 12 condenses to become liquid water, and this water is sent to the reforming water supply unit 6. Impurities are removed from the water sent to the reforming water supply unit 6, and it is used as water for extracting hydrogen from the fuel gas, and unnecessary water is drained as shown by arrow D. In addition, the power generation exhaust, whose temperature has been reduced by being cooled, is discharged from the power generation exhaust passage 9 connected to the exhaust heat recovery heat exchanger 12, as shown by arrow E1.

[0021] The heat transfer medium heated by heat exchange with the high-temperature power generation exhaust gas in the exhaust heat recovery heat exchanger 12 is returned to the upper part of the hot water storage tank 11. In this manner, in conjunction with the power generation operation, the hot water storage unit 10 performs a hot water storage operation in which the heated heat transfer medium is stored in the hot water storage tank 11.

[0022] The fuel cell system 1 supplies hot water by utilizing the heat of the heat medium stored in the hot water storage tank 11. During hot water supply, clean water is supplied to the hot water supply heat exchanger 14 as shown by the arrow CW, and the heat medium in the upper part of the hot water storage tank 11 is sent to the hot water supply heat exchanger 14 by the operation of the hot water supply pump 16a. The hot water heated by heat exchange with the heat medium in the hot water supply heat exchanger 14 is then mixed with unheated clean water in the mixing valve 17 to adjust the temperature, and is supplied as shown by the arrow HW. The heat medium cooled by heat exchange in the hot water supply heat exchanger 14 is returned to the lower part of the hot water storage tank 11.

[0023] Since the power generation unit 3, which becomes hot during power generation, is housed in the exterior case 2, the air inside the exterior case 2 is ventilated by the ventilation fan 18 to suppress a rise in temperature inside the exterior case 2 during power generation operation. The air inside the exterior case 2 sent out by the ventilation fan 18 promotes heat dissipation from the radiator 13 and is also discharged to the outside of the exterior case 2 as shown by the arrow E2. Then, outside air is introduced into the exterior case 2 from the air intake port 2a as shown by the arrow A. The exterior case 2 is equipped with a temperature sensor (not shown), for example, near the air intake port 2a, so that the control unit 4 can obtain the outside air temperature.

[0024] The microcomputer meter 20 has a gas shutoff function that, when the continuous supply of fuel gas exceeds a preset period (e.g., 30 days), assumes that there is a fuel gas leak and shuts off the supply of fuel gas. To prevent this gas shutoff function from activating, the fuel cell system 1 periodically stops the power generation operation. The power generation unit 3 is hot when generating electricity, and drops to the outside air temperature when power generation is stopped, so it is not easy to stop and restart the power generation operation, and in order to avoid accelerating durability deterioration due to this temperature change cycle, the power generation operation cannot be stopped and restarted frequently.

[0025] Therefore, when the control unit 4 starts the power generation operation, it sets a power generation stop period for stopping the power generation operation before the gas cutoff function is activated, and continues power generation until the power generation stop period.The control unit 4 then stops the power generation operation when the power generation stop period begins, and starts the power generation operation when the power generation stop period ends.Therefore, the power generation operation is stopped periodically (for example, every 27 days) during the power generation stop period, the continuous supply of fuel gas is stopped, and the period of continuous supply of fuel gas, which is the activation standard for the gas cutoff function of the microcomputer meter 20, is reset to zero.

[0026] Furthermore, during the power generation stop preparation period before the power generation operation is stopped, the control unit 4 controls the hot water storage operation so that the hot water storage tank 11 is filled with the heat medium at the highest temperature that can be stored, i.e., so that the storage of the maximum amount of heat in the hot water storage unit 10 is completed. For example, starting six hours before the start of the power generation stop period, the hot water storage pump 15a is controlled to store hot water so that the temperature of the heat medium to be stored becomes a predetermined maximum temperature that can be stored. This allows hot water to be supplied by making maximum use of the heat of the stored heat medium even during the power generation stop period, so convenience is not lost.

[0027] During power generation operation, the temperature inside the exterior case 2 rises due to the heat from the high-temperature power generation section 3. In addition, the heat of the high-temperature power generation exhaust from the power generation section 3 is recovered to perform hot water storage operation. Therefore, even if the temperature drops in winter, for example, the hot water inside the hot water storage unit 10 is prevented from freezing during power generation operation. However, as described above, power generation operation is periodically stopped to avoid the activation of the gas cutoff function of the microcomputer meter 20, so the temperature inside the exterior case 2 drops while power generation operation is stopped, and there is a risk of freezing inside the hot water storage unit 10 in winter.

[0028] Therefore, the fuel cell system 1 is provided with a communication unit 19 (communication means) connected to an external communication network 21 (Internet), and is configured to adjust the power generation suspension period based on weather information acquired by the control unit 4 via the communication unit 19 in order to prevent freezing during power generation operation suspension. The weather information can be acquired from a weather information server 22 connected to the external communication network 21. The weather information server 22 may be, for example, a dedicated server installed by the provider of the fuel cell system 1, or may be one that provides weather information to the general public. The adjustment of the power generation suspension period by the control unit 4 will be described with reference to the flowchart of FIG. 2. In the figure, Si (i=1, 2,...) represents a step.

[0029] First, power generation operation is started in S1, and the process proceeds to S2. Then, in S2, a power generation stop period is set to avoid activation of the gas supply cutoff function of the microcomputer meter 20, and the process proceeds to S3. The gas supply cutoff function is activated when continuous supply of fuel gas exceeds a preset period (e.g., 30 days). Therefore, the power generation stop period is set, for example, on the 27th day from the start of power generation operation, to allow some leeway before the gas supply is cut off. The power generation stop period is set, for example, to start on the 27th day from the start of power generation operation. The length of the power generation stop period is, for example, 12 hours.

[0030] If the timing when the calendar date changes is set to the timing when the number of days since the start of power generation operation changes, if power generation operation is started at a time other than this date change, the power generation operation time on the first day of power generation operation will be less than 24 hours. This power generation operation time of less than 24 hours does not have to be included in the number of days since the start of power generation operation. The number of days since the start of power generation operation may also be counted based on the power generation operation time, in which case the date may change during a period when power generation is not being generated.

[0031] Next, in S3, weather information for a predetermined future period including the power generation suspension period is obtained via the communication unit 19, and the process proceeds to S4. The predetermined period is a period in which the current day is the first day and the date on which the initially set power generation suspension period ends is the last day. The weather information for the predetermined period is, for example, daily weather information, but since the weather information is updated, it is possible to obtain more accurate and more detailed weather information, for example, hourly weather information, the closer to the present.

[0032] Next, in S4, a freeze prevention period requiring freeze prevention operation is predicted based on the acquired weather information, and the process proceeds to S5. For example, on a day when the predicted minimum temperature included in the weather information is, for example, 3°C or lower, there is a risk of freezing inside the hot water storage unit 10 when the power generation operation of the fuel cell system 1, which is usually installed outdoors, is stopped, so this day is predicted as a freeze prevention period requiring freeze prevention operation. Note that the freeze prevention period can also be predicted based on not only the predicted minimum temperature, but also, for example, a water pipe freezing index, etc., included in the weather information.

[0033] In S5, it is determined whether the set power generation suspension period and the predicted freeze prevention period interfere with each other. If the determination in S5 is Yes, the process proceeds to S6, where the power generation suspension period set in S6 is changed to be before the predicted freeze prevention period, and the process proceeds to S7. For example, as shown in FIG. 3, since the predicted minimum temperature during the initially set power generation suspension period (27th day from the start of power generation) is below a predetermined temperature that requires freeze prevention operation (upper table), the power generation suspension period is changed to the 26th day from the start of power generation, where the previous predicted minimum temperature is equal to or higher than the predetermined temperature (lower table). If the determination in S5 in FIG. 2 is No, the power generation suspension period is not changed and the process proceeds to S7.

[0034] Next, in S7, it is determined whether the power generation operation stop preparation period for storing the maximum amount of heat before stopping the power generation operation has started. If the determination in S7 is No, the process returns to S3, and the power generation stop period is adjusted based on the updated weather information. If the determination in S7 is Yes, the process proceeds to S8, where the hot water storage operation is controlled to store the maximum amount of heat, and the process proceeds to S9.

[0035] Next, in S9, it is determined whether or not a power generation stop period has started. If the determination in S9 is No, the process returns to S8. If the determination in S9 is Yes, the process proceeds to S10, where the power generation operation is stopped and the process proceeds to S11. Then, in S11, the process waits until the end of the power generation stop period, and the power generation stop period adjustment is completed. The power generation stop period is set to a period in which it is predicted that anti-freeze operation is not necessary, and power generation operation is stopped, thereby preventing freezing of the hot water storage unit 10 while power generation operation is stopped.

[0036] For example, if the outside air temperature falls below a specified temperature during a power generation outage due to a change in weather conditions during the power generation outage or due to unavoidable interference between the power generation outage and the freeze prevention period, freeze prevention operation is performed. This freeze prevention operation prevents freezing without using a freeze prevention heater by intermittently operating the hot water pump 15a, hot water supply pump 16a, etc. to circulate the high-temperature heat medium stored in the hot water storage tank 11.

[0037] If the power generation stop period is changed many times, there is a risk that the duration of power generation operation will become too short. In addition, since weather information is updated, the closer to the present the weather information is, the more detailed and accurate the weather information that can be obtained, so that anti-freezing operation may no longer be necessary even on days that were previously predicted as anti-freezing periods. For this reason, for example, as shown in FIG. 4, if the power generation stop period set in S5 interferes with the predicted anti-freezing period and the determination is Yes, the process may proceed to S16, and the power generation stop period may be changed in S16 to a period that does not exceed the power generation stop period initially set and does not interfere with the anti-freezing period.

[0038] For example, as shown in FIG. 5, since the predicted minimum temperature during the initially set power generation suspension period (27th day from the start of power generation) is less than a predetermined temperature (e.g., 3°C) that requires anti-freezing operation (first table), the power generation suspension period is changed to the 25th day from the start of power generation, when the predicted minimum temperature is equal to or higher than the predetermined temperature (second table). If the weather information is subsequently updated and the predicted minimum temperature on the 25th day from the start of power generation becomes less than the predetermined temperature (third table), the power generation suspension period is changed again, but since the predicted minimum temperature on the 27th day from the start of power generation is equal to or higher than the predetermined temperature, the power generation suspension period is changed to this day (fourth table). Since the steps other than S16 for changing the power generation suspension period in FIG. 4 are the same as those in FIG. 2, a description thereof will be omitted, but the final power generation suspension period will be changed to before the anti-freezing period if the initially set power generation suspension period interferes with the predicted anti-freezing period.

[0039] Immediately after the start of power generation operation, the accuracy of weather information for the day on which the power generation suspension period is set is low, or weather information may not be available, so the power generation suspension period may be adjusted after a certain period of time (e.g., two weeks) has elapsed since the start of power generation operation. Also, from a few days before the power generation suspension period, the time (time period) corresponding to the anti-freezing period can be predicted based on detailed weather information, for example, every hour, and the power generation suspension period can be changed in hourly units. This makes it possible to change the power generation suspension period that is set to start late at night to start during the day when the temperature is rising.

[0040] The operation and effects of the above fuel cell system 1 will now be described. The fuel cell system 1 generates electricity using fuel gas and stores hot water heated by utilizing the heat generated during power generation. The fuel gas used for power generation is supplied via a microcomputer meter 20 that cuts off the supply when the continuous supply exceeds a predetermined period, so that the control unit 4 sets a power generation stop period so as not to activate this gas cut-off function, and stops power generation during this power generation stop period. Based on meteorological information obtained by the communication unit 19, the control unit 4 also predicts a period when there is a risk of the hot water storage unit 10 freezing as a freeze prevention period during which freezing must be prevented.

[0041] In the case where the power generation stop period and the freeze prevention period interfere with each other, the control unit 4 changes the power generation stop period to before the freeze prevention period. Therefore, power generation operation is stopped during the power generation stop period before the freeze prevention period to avoid activation of the gas cutoff function of the microcomputer meter 20, and power generation operation is resumed during the subsequent freeze prevention period, and the heat from the power generation operation can be used to prevent the hot water storage unit 10 from freezing.

[0042] In addition, since the maximum amount of heat is stored in the hot water storage unit 10 before power generation is stopped, the stored hot water can be used, for example, for hot water supply even during periods when power generation is stopped, and convenience is not lost. Furthermore, even if, for example, weather conditions change and freeze prevention operation is required during periods when power generation is stopped, the stored heat can be used to prevent the hot water storage unit 10 from freezing.

[0043] The present invention can also be applied to a fuel cell system configured to supply hot water from a hot water storage tank heated using heat generated during power generation. The communication unit 19 may be connected to an external communication network 21 via, for example, a home communication line, or may be connected to the external communication network 21 by a mobile communication device. In addition, a person skilled in the art can implement the present invention in a form in which various modifications are added to the above embodiment without departing from the spirit of the present invention, and the present invention includes such modifications. [Explanation of symbols]

[0044] 1: Fuel cell system 2: Outer case 2a: Air supply port 3: Power generation section 4: Control section (control means) 5: Fuel gas supply section 6: Reformed water supply section 6a: Reformed water pump 7: Oxidant gas supply section 8: Power conditioner 9: Generator exhaust passage 10: Hot water storage unit 11: Hot water tank 12: Waste heat recovery heat exchanger 13: Heat sink 14: Hot water heat exchanger 15: Hot water circulation passage 15a: Hot water pump 16: Hot water circulation passage 16a: Hot water pump 17: Mixing valve 18: Ventilation fan 19: Communication department (communication means) 20: Microcomputer meter 21: External communication network 22: Weather information server

Claims

1. A fuel cell system having a power generation section which generates power using fuel gas supplied via a microcomputer meter, a hot water storage unit which performs a hot water storage operation for storing hot water heated by using heat generated during a power generation operation of the power generation section, and a control means for controlling the power generation operation and the hot water storage operation, Further comprising a communication means for obtaining meteorological information via an external communication network; The control means sets a power generation stop period in which the power generation operation is periodically stopped to avoid activation of the gas cut-off function of the microcomputer meter, which cuts off the supply of fuel gas when continuous supply of fuel gas exceeds a predetermined period, and predicts a freeze prevention period during which freeze prevention operation of the hot water storage unit is required based on weather information obtained by the communication means, and if the power generation stop period and the freeze prevention period interfere with each other, changes the power generation stop period to before the freeze prevention period.

2. 2. The fuel cell system according to claim 1, wherein the control means controls the hot water storage operation so that a maximum amount of heat is stored in the hot water storage unit before the power generation stop period.

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