JP6409368B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  As one type of fuel cell system, one shown in Patent Document 1 is known. As shown in FIG. 1 of Patent Document 1, in a fuel cell system, a fuel cell (1), a heat exchanger that performs heat exchange between exhaust gas generated by power generation of the fuel cell and water, and heat exchange A hot water storage tank (18) for storing hot water that has been heat-exchanged by the heat exchanger, and a circulation pipe (17) for circulating the hot water between the heat exchanger and the hot water storage tank.

  In the fuel cell system disclosed in Patent Document 1, when the temperature of the hot water flowing through the heat exchanger becomes equal to or higher than the set temperature, the flow rate of the hot water flowing through the circulation pipe is increased to increase the heat exchanger. The temperature of the hot water flowing in the interior is lowered to suppress evaporation of the hot water flowing in the heat exchanger. Thereby, precipitation of minerals, such as calcium contained in hot water storage, is suppressed, deposit (scale) is prevented from adhering to the heat exchanger, and corrosion of the heat exchanger is suppressed.

  When the temperature of hot water in the heat exchanger rises, the amount of air that can be dissolved in the hot water decreases, so the air dissolved in the hot water in the heat exchanger becomes bubbles and the heat exchanger Stays inside. If bubbles remain in the heat exchanger, it becomes impossible to exchange heat between the exhaust gas and the hot water in the heat exchanger. Even in such a case, if the technology of the fuel cell system disclosed in Patent Document 1 is used, when the temperature becomes such that bubbles are generated in the heat exchanger, the stored hot water flowing through the circulation pipe is used. By increasing the flow rate (hereinafter abbreviated as “bubble discharge control as appropriate”), bubbles remaining in the heat exchanger can be discharged outside the heat exchanger.

JP 2010-33880 A

  However, in the fuel cell system disclosed in Patent Document 1, since a hot water tank is connected with water, tap water having a low temperature, that is, water having a large dissolved amount of air is supplied to the hot water tank. In this way, when water with a large amount of dissolved water supplied to the hot water tank is supplied to the heat exchanger, the water with a large amount of dissolved air is heated in the heat exchanger, so that in the heat exchanger Bubbles continue to be generated. Then, the bubble discharge control described above is frequently executed, a high temperature layer in which hot hot water is retained is formed in the upper part of the hot water tank, and a low temperature layer in which low temperature hot water is retained is formed in the lower part of the hot water tank. The stratification will collapse.

  In this way, when the temperature stratification of the hot water in the hot water tank collapses, the low temperature hot water in the lower part of the hot water tank and the hot hot water in the upper part of the hot water tank are mixed, so there is a temperature forming layer inside the hot water tank. Compared with the time when it is formed, the temperature of the hot water stored in the upper part of the hot water tank is lowered. Then, the temperature of the hot water supplied from the upper part of the hot water tank to the place where the hot water is used is lowered as compared with the case where the temperature forming layer is formed. Moreover, since the temperature of the hot water stored in the lower part of the hot water tank rises, the temperature of the hot water supplied to the heat exchanger rises as compared with the case where the temperature forming layer is not collapsed. The heat recovery efficiency will decrease. As a result, the operating efficiency of the fuel cell system decreases.

  The present invention has been made to solve the above-described problem, and in a fuel cell system including a hot water tank, it is intended to suppress the collapse of the temperature stratification of the hot water in the hot water tank and improve the operation efficiency. And

  In order to solve the above problems, according to the invention of the fuel cell system according to claim 1, a fuel cell that generates power with fuel and an oxidant gas, a hot water storage tank that is a sealed space in which hot water is stored, A heat exchanger for exchanging heat between the exhaust gas exhausted from the fuel cell and the hot water, a first hot water circulation line for circulating the hot water between the hot water tank and the heat exchanger, and the first A hot water supply line provided between the hot water storage device and a pump provided in a hot water circulation line for circulating the hot water between the hot water storage tank and the heat exchanger, and the hot water storage device using the hot water. A closed-type second hot water circulation line through which the water circulates and the flow rate of the hot water discharged from the pump are adjusted, and the temperature of the hot water flowing out of the heat exchanger is set to a steady temperature to execute a steady operation. A steady operation part, Executes a temperature rise control for lowering the flow rate of the hot water discharged from the heat exchanger as compared to when the steady operation is being performed, and increasing the temperature of the hot water flowing out of the heat exchanger compared to the steady temperature. A temperature rise unit that performs, a bubble generation determination unit that determines whether or not bubbles are generated in the heat exchanger, and a case where the bubble generation determination unit determines that the bubbles are generated in the heat exchanger And a bubble discharge unit for performing bubble discharge control for discharging the bubbles from the heat exchanger by increasing a flow rate of the hot water discharged from the pump as compared with when the steady operation is performed. Have.

  In this way, temperature rise control is performed to raise the temperature of the hot water flowing out of the heat exchanger above the steady temperature. According to this, since the amount of air that can be dissolved in the hot water decreases as the temperature of the hot water increases, the temperature of the hot water rises, so that the air dissolved in the hot water is discharged from the hot water. Can be made. For this reason, the amount of dissolved air in the hot water can be reduced. In addition, since the second hot water circulation line in which hot water circulates between the hot water tank and the hot water storage equipment is a closed type, air is dissolved in the hot water tank, the first hot water circulation line, and the second hot water circulation line. Water does not flow continuously. For this reason, once temperature rise control is performed, the amount of dissolved air in the hot water can be kept small, and at least the generation of bubbles in the heat exchanger can be suppressed. Therefore, frequent execution of bubble discharge control is suppressed. As a result, the collapse of the temperature stratification of the hot water in the hot water tank can be suppressed, and the operating efficiency of the fuel cell system can be improved.

Furthermore , in the invention according to claim 1, in the temperature increasing section, the bubble generation determination section determines that the bubbles are generated while the steady operation is being performed, and the bubble discharge control is performed. After that, the temperature increase control is executed. As a result, when steady operation is performed, bubble discharge control is performed when bubbles are generated in the heat exchanger due to, for example, a decrease in the water pressure of the hot water flowing into the heat exchanger. Then, the temperature rise control is executed. For this reason, when bubbles are generated in the heat exchanger during steady operation, the generation of bubbles in the heat exchanger is suppressed by executing the temperature rise control so that the bubbles are hardly generated in the heat exchanger. be able to.

The invention according to claim 2, in the invention described in claim 1, wherein the temperature increase control is executed, it is determined that the bubble is not generated within the heat exchanger by the air bubble occurrence determination unit When the operating time exceeds the first specified time, a return unit for returning to the steady operation is provided.

  When the bubble discharge control is not executed during the first specified time, the dissolved air amount has already been reliably reduced by the temperature rise control. And since the 2nd stored hot water circulation line is a closed type, once the amount of dissolved air of hot water becomes low by temperature rise control, the stored hot water is maintained in a state where the amount of dissolved air is low. For this reason, even if the temperature of the hot water flowing out from the heat exchanger returns to the steady temperature, the state in which the generation of bubbles is suppressed in the heat exchanger is maintained. As described above, when the bubble discharge control is not executed during the first specified time, the temperature of the hot water flowing out from the heat exchanger is returned to the temperature before the bubble discharge control is executed. As a result, after the hot water is brought into a state where the dissolved air amount is low and the collapse of the temperature stratification of the hot water in the hot water tank is suppressed by the bubble discharge control being performed, the hot water flows out of the heat exchanger. The temperature of the hot water can be returned to the steady temperature. For this reason, after air bubbles are completely expelled from the heat exchanger, good temperature stratification is formed in the hot water tank. Therefore, the operation efficiency of the fuel cell system can be further improved.

The invention according to claim 3, in the invention of claim 1 or claim 2, the time of occurrence of the bubble in the temperature increase control the after run is determined by the bubble occurrence determination unit in said heat exchanger a storage unit for storing for, based on the time of occurrence of the bubble in the the heat exchanger which is stored in the storage unit, when the frequency of execution of the bubble discharge control after the temperature increase control execution is not reduced And an abnormality determination unit that determines that it is abnormal. Although the temperature rise control is executed, the amount of air dissolved in the hot water is reduced, the second hot water circulation line is closed, and the hot water is not mixed with a large amount of dissolved air. The fact that the frequency of occurrence of bubbles in the exchanger does not decrease means that the pressure in the hot water storage tank, the first hot water circulation line, or the second hot water circulation line is lower than the predetermined pressure due to water leakage or the like. This is an abnormal state in which air has entered either the first hot water storage line or the second hot water circulation line. The abnormality determination unit determines that there is an abnormality when the frequency of execution of the bubble discharge control after the temperature rise control is not reduced. Therefore, the water storage tank, the first hot water circulation line, and the second It is possible to detect whether any pressure in the hot water circulation line is lower than a predetermined pressure, or an abnormal state in which air is mixed into any of the hot water tank, the first hot water circulation line, and the second hot water circulation line.

The invention according to claim 4 is the invention according to claims 1 to 3 , wherein the hot water storage tank allows the outflow of air from the inside of the hot water storage tank to the outside of the hot water storage tank. An air vent valve that does not allow air to flow into the hot water storage tank from the outside of the tank is provided. Thereby, the air dissolved in the hot water is discharged to the outside of the hot water tank through the air vent valve. Moreover, since the intrusion of air from the outside of the hot water tank into the hot water tank is prevented, it is possible to prevent the air from being dissolved again in the hot water. For this reason, the amount of dissolved air in the hot water can be kept low.

It is a schematic diagram showing an outline of one embodiment of a fuel cell system according to the present invention. It is a graph showing the relationship between the temperature of hot water and the ratio of dissolved air of hot water. It is a flowchart of "circulation pump control processing" performed with the control apparatus shown in FIG. FIG. 4 is a charm chart when the “circulation pump control process” shown in FIG. 3 is executed. FIG.

  Hereinafter, an embodiment of the fuel cell system 100 according to the present invention will be described. As shown in FIG. 1, the fuel cell system 100 includes a power generation unit 10 and a hot water storage tank 21. The power generation unit 10 includes a housing 10a, a fuel cell module 11, a heat exchanger 12, an inverter device 13, a water tank 14, a control device 15, and a notification unit 17.

  The fuel cell module 11 includes a casing 31, an evaporation unit 32, a reforming unit 33, and a fuel cell 34. The casing 31 is formed in a box shape with a heat insulating material. The evaporating unit 32 is heated by a combustion gas to be described later, evaporates the supplied reforming water to generate water vapor, and preheats the supplied reforming raw material. The evaporation section 32 mixes the steam generated in this way and the preheated reforming raw material and supplies the mixture to the reforming section 33.

  One end of a reforming material supply pipe 11a is connected to the evaporation section 32. A supply source Gs is connected to the other end of the reforming material supply pipe 11a. The supply source Gs supplies a raw material for reforming. As reforming raw materials, there are gas fuels for reforming such as natural gas and LP gas, and liquid fuels for reforming such as kerosene, gasoline and methanol. The fuel cell system 100 of this embodiment will be described with respect to an embodiment using natural gas as a reforming raw material.

  A raw material supply pump 11a1 is provided in the reforming raw material supply pipe 11a. The raw material supply pump 11 a 1 is a supply device that supplies fuel (reforming raw material) to the fuel cell 34, and the amount of fuel supplied from the supply source Gs (supply flow rate (per unit time) per control current supplied from the control device 15. The flow rate)) is adjusted. The raw material supply pump 11 a 1 is a pressure feeding device that sucks the reforming raw material and pumps it to the evaporation unit 32.

  One end of a water supply pipe 11b is connected to the evaporation section 32. The other end of the water supply pipe 11b is connected to the water tank. The water supply pipe 11b is provided with a reforming water pump 11b1. With such a configuration, the reformed water is supplied from the water tank 14 to the evaporation unit 32. One end of a cathode air supply pipe 11 c is connected to the fuel cell 34 of the fuel cell module 11. A cathode air blower 11c1 is connected to the other end of the cathode air supply pipe 11c. With such a configuration, cathode air is supplied to the fuel cell 34.

  The reforming unit 33 is heated by the combustion gas described above and supplied with heat necessary for the steam reforming reaction, so that the reformed gas is generated from the mixed gas (reforming raw material, steam) supplied from the evaporation unit 32. Is generated and derived. The reforming unit 33 is filled with a catalyst (for example, Ru or Ni-based catalyst), and the mixed gas reacts with the catalyst to be reformed to generate a gas containing hydrogen gas and carbon monoxide. (So-called steam reforming reaction). The reformed gas contains hydrogen, carbon monoxide, carbon dioxide, steam, unreformed natural gas (methane gas), and reformed water (steam) that has not been used for reforming. As described above, the reforming unit 33 generates reformed gas (fuel) from the reforming raw material (raw fuel) and the reformed water and supplies the reformed gas (fuel) to the fuel cell 34. The steam reforming reaction is an endothermic reaction.

  The fuel cell 34 generates power using the fuel generated by the reforming unit 33 and cathode air (oxidant gas) supplied by the cathode air blower 11c1. The fuel cell 34 is configured by laminating a fuel electrode, an air electrode (oxidant electrode), and a plurality of cells 34a made of an electrolyte interposed between the two electrodes. The fuel cell of this embodiment is a solid oxide fuel cell, and uses zirconium oxide, which is a kind of solid oxide, as an electrolyte. Hydrogen, carbon monoxide, methane gas, etc. are supplied to the fuel electrode of the fuel cell 34 as fuel. The operating temperature is about 400-1000 ° C. It should be noted that power generation with a power generation below the rating is possible even at 400 ° C or lower. Not only hydrogen but also natural gas and coal gas can be used directly as fuel. In this case, the reforming unit 33 can be omitted.

  On the fuel electrode side of the cell 34a, a fuel flow path 34b through which the reformed gas as the fuel flows is formed. An air flow path 34c through which air (cathode air) that is an oxidant gas flows is formed on the air electrode side of the cell 34a.

  The fuel cell 34 is provided on the manifold 35. The reformed gas from the reforming unit 33 is supplied to the manifold 35 via the reformed gas supply pipe 38. The lower end (one end) of the fuel flow path 34b is connected to the fuel outlet of the manifold 35, and the reformed gas led out from the fuel outlet is introduced from the lower end and led out from the upper end. . The cathode air sent out by the cathode air blower 11c1 is supplied via the cathode air supply pipe 11c, introduced from the lower end of the air flow path 34c, and led out from the upper end.

  The first combustion unit 36 is provided between the fuel cell 34, the evaporation unit 32, and the reforming unit 33. In the first combustion unit 36, the anode off gas (fuel off gas) from the fuel cell 34 and the cathode off gas (oxidant off gas) from the fuel cell 34 are burned to heat the evaporation unit 32 and the reforming unit 33.

  In the first combustion section 36, the anode off gas is burned and a flame 37 is generated. The first combustion unit 36 is provided with a pair of ignition heaters 36a1 and 36a2 for igniting the anode off gas.

  The hot water storage tank 21 is a vertically long sealed container in which a sealed space in which hot water is stored is formed. The hot water tank 21 has a temperature stratification formed by hot water stored therein. That is, the temperature of the hot water stored in the upper part of the hot water tank 21 is the highest, the temperature of the hot water becomes lower as it is located from the upper part to the lower part of the hot water tank 21, and the temperature of the hot water stored in the lower part of the hot water tank 21 is the lowest. As described above, the hot water is stored in the hot water tank 21.

  An air vent valve 25 is provided in the upper part of the hot water tank 21. The air vent valve 25 is opened when the atmospheric pressure in the hot water storage tank 21 becomes equal to or higher than a predetermined value, and discharges the air in the hot water storage tank 21 to the outside of the hot water storage tank 21. That is, the air vent valve 25 allows the outflow of air from the inside of the hot water tank 21 to the outside of the hot water tank 21. The air vent valve 25 is a check valve that does not allow the inflow of air from the outside of the hot water tank 21 into the hot water tank 21.

  A first hot water circulation line 22 for circulating hot water between the hot water tank 21 and the heat exchanger 12 (circulating in the direction of the arrow in FIG. 1) is provided. The starting end of the first hot water storage line 22 is connected to the lower part of the hot water tank 21. A terminal end of the first hot water circulation line 22 is connected to an upper portion of the hot water tank 21. On the 1st hot water storage water circulation line 22, the circulation pump 22a and the heat exchanger 12 are arrange | positioned in order from the starting end side to the terminal end side. The heat exchanger 12 is connected to the start end of the condensed water supply pipe 12a. The terminal end of the condensed water supply pipe 12 a is connected to the water tank 14.

  The heat exchanger 12 is a device that is supplied with exhaust gas exhausted from the first combustion unit 36 (fuel cell 34) and is supplied with hot water from the hot water storage tank 21 to exchange heat between the exhaust gas and hot water. is there. In the heat exchanger 12, the exhaust gas from the fuel cell module 11 is introduced into the heat exchanger 12 through the exhaust gas introducing portion 12b, and is cooled by exchanging heat with the hot water. Thereby, the water vapor contained in the exhaust gas is condensed to generate condensed water. The exhaust gas after heat exchange passes through the exhaust pipe 12c, passes through the first exhaust port 10b provided in the housing 10a, and is discharged to the outside of the housing 10a. The condensed water obtained by cooling and condensing water vapor contained in the exhaust gas is supplied to the water tank 14 through the condensed water supply pipe 12a. The water tank 14 purifies the condensed water with ion exchange resin.

  The circulation pump 22 a circulates hot water between the hot water tank 21 and the heat exchanger 12. The controller 15 controls the discharge flow rate of the circulation pump 22a by controlling the amount of current supplied to the circulation pump 22a by linear current control. The linear current control mentioned here includes PWM control for changing the voltage DUTY ratio for driving the circulation pump 22a and changing the effective current.

  An exhaust heat recovery system 20 is configured from the heat exchanger 12, the hot water tank 21, and the first hot water circulation line 22 described above. The exhaust heat recovery system 20 recovers and stores the exhaust heat of the fuel cell module 11 in hot water storage. A first temperature sensor 12d that detects the temperature T1 of the hot water in the heat exchanger 12 and outputs a detection signal to the control device 15 is provided in the heat exchanger 12 of the first hot water circulation line 22. Yes. A temperature T2 of hot water flowing out from the heat exchanger 12 is detected near the outlet of the heat exchanger 12 in the first hot water circulation line 22, and a second temperature sensor 12e that outputs a detection signal to the controller 15. Is provided.

  A second hot water storage water circulation line 930 is provided between the hot water storage tank 21 and the hot water use device 910 in which the hot water is used (circulates in the direction of the arrow in FIG. 1). The starting end of the second hot water storage water circulation line 930 is connected to the upper part of the hot water storage tank 21. The terminal end of the second hot water storage water circulation line 930 is connected to the lower part of the hot water storage tank 21. A hot water supply pump 920 is provided in the second hot water storage water circulation line 930. The hot water supply pump 920 supplies hot hot water to the hot water use device 910 and returns the low temperature hot water flowing out from the hot water use device 910 to the hot water tank 21. In this way, the hot water supplied from the hot water tank 21 to the hot water storage device 910 is returned to the hot water tank 21 again. That is, the second hot water storage water circulation line 930 is a closed type. In other words, the fuel cell system 100 is a closed type in which tap water is not supplied from the outside at all times. The hot water storage device 910 includes an indoor heating device and a floor heating device.

  A second combustion section 28 is provided at a portion where the inlet of the exhaust gas introduction section 12 b of the heat exchanger 12 is connected to the casing 31, that is, at the outlet 31 a of the casing 31. The second combustion section 28 is a first combustion section off-gas which is a gas exhausted from the first combustion section 36, that is, an unused combustible gas (for example, hydrogen, methane gas, monoxide) exhausted from the first combustion section 36. Carbon etc.) is introduced and burned out. The 2nd combustion part 28 is comprised with the combustion catalyst which is a catalyst which burns combustible gas. Combustion catalysts include those in which a precious metal such as platinum or palladium is supported on a ceramic alone.

  Note that the combustion catalyst burns combustible gases such as hydrogen, methane gas, and carbon monoxide by the catalyst instead of flame combustion, so the combustion speed is high, a large amount of combustible gas can be burned, and the combustion efficiency is also high. Therefore, discharge of unburned gas can be suppressed. In a combustion catalyst, it is easy to ignite in order of hydrogen, carbon monoxide, and methane gas.

  The second combustion section 28 is provided with a combustion catalyst heater 28a for heating the combustion catalyst to the catalyst activation temperature and burning the combustible gas. The combustion catalyst heater 28 a is heated by an instruction from the control device 15.

  A DC voltage output from the fuel cell 34 is input to the inverter device 13. The inverter device 13 converts the input DC voltage into a predetermined AC voltage and outputs the AC voltage to the power supply line 16b connected to the AC system power supply 16a and the external power load 16c (for example, an electrical appliance). An AC voltage from the system power supply 16a is input to the inverter device 13 through the power supply line 16b. The inverter device 13 converts the input AC voltage into a predetermined DC voltage and outputs it to an auxiliary machine (each pump, blower, etc.) or the control device 15. The control device 15 controls the operation of the fuel cell system 100 by driving an auxiliary machine.

  The control device 15 performs overall control of the fuel cell system 100. The control device 15 adjusts the flow rate of the reforming raw material supplied to the evaporation unit 32 by the raw material supply pump 11a1, adjusts the flow rate of reforming water supplied to the evaporation unit 32 by the reforming water pump 11b1, The generated power generated by the fuel cell 34 is adjusted by adjusting the flow rate of the cathode air supplied to the fuel cell 34 by the cathode air blower 11c1. The control device 15 includes a storage unit 15 a that stores a time for storing the time of bubble generation in the heat exchanger 12.

  The notification unit 17 is a device that notifies an operator of the entry of air into at least one of the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930. The notification unit 17 includes a speaker and a display.

(Explanation of bubble discharge control and temperature rise control)
The “bubble discharge control” and the “temperature rise control” executed in the fuel cell system 100 will be described below using the graph shown in FIG. As shown in FIG. 2, the ratio of dissolved air in the hot water decreases as the temperature of the hot water increases. T0 is the temperature of tap water. T2a is a steady temperature. When the fuel cell system 100 is in steady operation, the temperature T2 of the hot water flowing out from the heat exchanger 12 is controlled to the steady temperature T2a by adjusting the discharge flow rate of the circulation pump 22a.

  When the fuel cell system 100 is first operated after the installation, the difference ΔA1a obtained by subtracting the dissolved air ratio A1a of the hot water at the steady temperature T2a from the ratio A1 of the hot water at the temperature T0 of the tap water. The air corresponding to is discharged from the stored hot water, and bubbles are generated in the heat exchanger 12. Then, the “bubble discharge control” is executed in which the flow rate of the hot water discharged from the circulation pump 22a to the heat exchanger 12 is increased compared to the time when the bubbles are generated, and the bubbles are discharged from the heat exchanger 12. The bubbles move to the hot water storage tank 21 through the first hot water storage water circulation line 22 and are discharged to the outside of the hot water storage tank 21 through an air vent valve 25 provided at the upper part of the hot water storage tank 21.

  In the present embodiment, since the second hot-water storage water circulation line 930 is a closed type, the tap water is basically the hot-water tank 21, the first hot-water storage water circulation line 22, and the second, except when the fuel cell system 100 is installed. It is not introduced into any of the two hot water circulation lines 930. That is, tap water with a high proportion of dissolved air is not mixed into the stored hot water. Thereby, if the ratio of the dissolved air in the hot water is made low, the ratio of the dissolved air in the hot water is kept low.

  As shown by the broken line in FIG. 2, when the water pressure of the hot water is lowered, the ratio of the dissolved air of the hot water is lowered. That is, bubbles are generated in the heat exchanger 12 as the stored hot water becomes lower. Therefore, in the present embodiment, after the “bubble discharge control” is executed, the temperature T2 of the hot water flowing out from the heat exchanger 12 is set to a temperature higher than the steady temperature T2a by adjusting the discharge flow rate of the circulation pump 22a. “Temperature rise control” for raising the temperature to the specified temperature T2b is executed. By this “temperature rise control”, the air dissolved in the hot water is forcibly discharged from the hot water, and the air is discharged from the air vent valve 25 to the outside of the hot water tank 21 to dissolve the hot water in the hot water. Is set to a lower state than before the “temperature rise control” is executed.

  And after execution of "temperature rise control", when the time which a bubble does not generate | occur | produce in the heat exchanger 12 after the 1st specified time tr1 mentioned later passes, the hot water storage tank 21, the 1st stored hot water circulation line 22, and Assuming that the air dissolved in the hot water in the second hot water circulation line 930 is sufficiently discharged, the temperature T2 of the hot water flowing out from the heat exchanger 12 is returned to the steady temperature T2a. The second hot water storage line 930 is a closed type, and water with a high proportion of dissolved air does not enter the hot water, so even if the temperature T2 of the hot water flowing out of the heat exchanger 12 is returned to the steady temperature T2a, The stored hot water in which the ratio of dissolved air is lowered by the “temperature rise control” is maintained in a state where the ratio of dissolved air is low. For this reason, even when the water pressure of the hot water stored in the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is reduced, the state in which bubbles are not easily generated in the heat exchanger 12 is maintained. Is done. Hereinafter, the “circulation pump control process” in which “bubble discharge control” and “temperature rise control” are executed will be described in detail using the flowchart shown in FIG.

(Circulating pump control processing)
The “circulation pump control process” executed in the fuel cell system 100 will be described below using the flowchart shown in FIG. When the fuel cell system 100 is activated, the program proceeds to step S11.

  In step S11, the control device 15 (steady operation unit) determines the temperature T2 of the hot water flowing out from the heat exchanger 12 (hereinafter, abbreviated as temperature T2 as appropriate) based on the detection signal from the second temperature sensor 12e. Then, a steady operation for adjusting the discharge flow rate of the circulation pump 22a is performed so that the steady temperature T2a (for example, 70 ° C.) is reached. As the discharge flow rate of the circulation pump 22a increases, the temperature T2 of the hot water flowing out of the heat exchanger 12 decreases. Further, the temperature T2 increases as the discharge flow rate of the circulation pump 22a decreases. When the temperature T2 of the hot water flowing out from the heat exchanger 12 is set to the steady temperature T2a, a temperature stratification is formed in the hot water tank 21 by the hot water. When step S11 ends, the control device 15 advances the program to step S12.

  If the control device 15 (bubble generation determination unit) determines in step S12 that bubbles have occurred in the heat exchanger 12 (step S12: YES), the program proceeds to step S13. On the other hand, if the control device 15 (bubble generation determination unit) determines that no bubbles are generated in the heat exchanger 12 (step S12: NO), the program returns to step S11.

  When bubbles are generated in the heat exchanger 12, the bubbles are heated by the exhaust gas flowing through the heat exchanger 12, and become high-temperature bubbles. When this high-temperature bubble comes into contact with the portion where the first temperature sensor 12d or the second temperature sensor 12e detects the temperature, the temperature T1 or the temperature T2 detected by the first temperature sensor 12d or the second temperature sensor 12e is changed. Get higher. Using this principle, the control device 15 allows the temperature T1 of the hot water stored in the heat exchanger 12 (hereinafter, appropriately abbreviated as temperature T1) to be equal to or higher than the first specified temperature Ta (eg, 90 ° C.), or When it is determined that the temperature T2 of the hot water flowing out from the heat exchanger 12 is equal to or higher than the second specified temperature Tb (for example, 90 ° C.), it is determined that bubbles are generated in the heat exchanger 12. Further, when the control device 15 determines that the temperature T1 is lower than the first specified temperature Ta and the temperature T2 is lower than the second specified temperature Tb, bubbles are not generated in the heat exchanger 12. to decide.

  It should be noted that the controller 15 may determine whether or not bubbles are generated in the heat exchanger 12 based on only one of the temperatures T1 and T2. Further, the control device 15 determines that bubbles are generated in the heat exchanger 12 when the temperature T1 is equal to or higher than the first specified temperature Ta and the temperature T2 is equal to or higher than the second specified temperature Tb. There is no problem.

  In step S <b> 13, the control device 15 (bubble discharge unit) executes “bubble discharge control” in which the discharge flow rate of the circulation pump 22 a is increased as compared with that during steady operation and the bubbles are discharged from the heat exchanger 12. This “bubble discharge control” is executed until the bubble discharge regulation time td elapses after the execution of “bubble discharge control” is started. Alternatively, when the temperature T1 or the temperature T2 drops to the specified temperature Td, the control device 15 may stop the “bubble discharge control”. The control device 15 advances the program to step S14.

  In step S14, the control device 15 (temperature riser) causes the temperature T2 of the stored hot water flowing out of the heat exchanger 12 to become the specified temperature T2b by feedback control based on the detection signal from the second temperature sensor 12e. In this manner, “temperature rise control” for adjusting the discharge flow rate of the circulation pump 22a is started. The specified temperature T2b is higher than the steady temperature T2a, and is 80 ° C., for example. In step S14, the control device 15 decreases the discharge flow rate of the circulation pump 22a when the temperature T2 of the stored hot water is the steady temperature T2a, that is, compared with the steady operation. Thereby, the temperature of the hot water flowing out from the heat exchanger 12 rises from the steady temperature T2a to the specified temperature T2b in step S12.

  By this “temperature rise control”, the temperature of the hot water flowing out of the heat exchanger 12 is set to a specified temperature T2b higher than the steady temperature T2a. Thereby, as shown in FIG. 2, the air corresponding to the difference ΔA1c obtained by subtracting the ratio A1b of the hot water stored water at the specified temperature T2b from the dissolved air ratio A1a at the steady temperature T2a is obtained from the hot water. After being discharged, the air is discharged to the outside of the hot water tank 21 through the air vent valve 25. As a result, the amount of dissolved air in the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is reduced, and bubbles are hardly generated in the heat exchanger 12. When step S14 ends, the control device 15 advances the program to S15.

  In step S15, if the control device 15 (bubble generation determination unit) determines that bubbles have occurred in the heat exchanger 12 (step S15: YES), the program proceeds to step S16. On the other hand, if the control device 15 (bubble generation determination unit) determines that bubbles are not generated in the heat exchanger 12 (step S15: NO), the program proceeds to step S31. The determination method of the control device 15 in step S15 is the same as the determination method of the control device 15 in step S12.

  In step S16, the control device 15 stores the time at which it is determined in step S15 that bubbles have occurred in the heat exchanger 12 in the storage unit 15a, and advances the program to step S17.

  In step S17, the control device 15 (bubble discharging unit) executes “bubble discharging control” similar to step S13, and advances the program to step S18.

  In step S18, the control device 15 (abnormality determination unit) determines that the generation frequency of bubbles has decreased based on the time when it is determined that bubbles have occurred in the heat exchanger 12 stored in the storage unit 15a. In the case (step S18: YES), the program is returned to step S14. On the other hand, when the control device 15 determines that the generation frequency of the bubbles is not reduced based on the time when it is determined that the bubbles are generated in the heat exchanger 12 stored in the storage unit 15a ( Step S18: NO), the program proceeds to Step S19. The bubble generation frequency here is the number of bubbles generated in the heat exchanger 12 per unit time and includes the bubble generation interval. The control device 15 may advance the program to step S19 when it is determined that the occurrence frequency of bubbles has not been reduced continuously (for example, twice) for a plurality of times.

  In Step S19, when the control device 15 (abnormality determination unit) determines that the time during which the frequency of occurrence of bubbles in the heat exchanger 12 is not reduced has passed the second specified time tr2 (for example, several tens of hours). (Step S19: YES), the program proceeds to Step S20. On the other hand, if the control device 15 determines that the time during which the frequency of occurrence of bubbles in the heat exchanger 12 does not decrease has not passed the second specified time tr2 (step S19: NO), the program is executed as a step. Return to S14.

  In step S <b> 20, the control device 15 (abnormality determination unit) is an “air mixing abnormality” in which air is mixed into at least one of the hot water storage tank 21, the first hot water circulation line 22, and the second hot water circulation line 930. judge. In this way, when the second specified time tr2 elapses after the “temperature increase control” is performed and the time during which the frequency of occurrence of bubbles in the heat exchanger 12 does not decrease has passed the second specified time tr2, the “air mixing abnormality” It is determined that there is. In step S14, “temperature rise control” is executed, the amount of air dissolved in the hot water is reduced, the second hot water circulation line 930 is closed, and the hot water contains a large amount of dissolved air. Nevertheless, the fact that the frequency of occurrence of bubbles in the heat exchanger 12 does not decrease means that the pressure of any one of the hot water storage tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is higher than a predetermined pressure. It can be considered that air is mixed in any of the hot water storage tank 21, the first hot water storage water circulation line 22, and the second hot water storage water circulation line 930. When step S20 ends, the control device 15 advances the program to S21.

  In step S21, the control device 15 causes the notification unit 17 to notify “abnormality” and advances the program to S14.

  In step S31, the control device 15 (returning unit) determines that no bubbles are generated in the heat exchanger 12 in step S15 after the execution of the “temperature rise control” is started in step S14. When it is determined that the first specified time tr1 (for example, several hours) has elapsed (step S31: YES), the program is returned to step S11. On the other hand, after the execution of the “temperature rise control” is started in step S14, the time during which it is determined in step S15 that no bubbles are generated in the heat exchanger 12 has passed the first specified time tr1. If it is determined that it has not been performed (step S31: NO), the program is returned to step S14.

  As described above, when it is determined that the first specified time tr1 has elapsed after the start of the execution of the “temperature rise control”, it is determined that no bubbles are generated in the heat exchanger 12. In step S11, the temperature T2 of the hot water flowing out from the heat exchanger 12 is returned to the steady temperature T2a. On the other hand, when the time when it is determined that no bubbles are generated in the heat exchanger 12 after the execution of the “temperature rise control” has not elapsed the first specified time tr1, In step S14, the temperature T2 of the hot water flowing out from the heat exchanger 12 is set to a specified temperature T2b higher than the steady temperature T2a, and the air dissolved in the hot water is discharged. The second stored hot water circulation line 930 is a closed type, and water such as tap water with a large amount of dissolved air may be mixed in any of the hot water storage tank 21, the first stored hot water circulation line 22, and the second stored hot water circulation line 930. Therefore, even if the temperature T2 of the hot water flowing out of the heat exchanger 12 is returned to the steady temperature T2a, the dissolved air amount (the ratio of dissolved air) of the hot water is reduced by the “temperature rise control”. State is maintained.

  The “temperature rise control” is executed, and the ratio of dissolved air in the hot water storage tank 21, first hot water circulation line 22, and second hot water circulation line 930 is reduced to A1b (1 in FIG. 2). If the water pressure of the stored hot water is lowered after the temperature of the stored hot water is set to the steady temperature T2a with the temperature maintained, the ratio A2a of the dissolved air in the stored hot water is reduced. It is lower than the dissolved air ratio A1b by a difference ΔA2a obtained by subtracting the dissolved air ratio A2a from the dissolved air ratio A1b. Then, air corresponding to the difference ΔA2a is discharged from the hot water, and bubbles are generated in the heat exchanger 12.

  Even in this case, if it is determined in step S12 that bubbles are generated in the heat exchanger 12, the “bubble rise control” in step S13 is executed, and then “temperature rise control” is performed in step S14. Is executed. As a result, as shown in FIG. 2, the ratio of the dissolved air in the hot water flowing out of the heat exchanger 12 is changed from the ratio A2a of the dissolved air at the steady temperature T2a at a low water pressure to the specified temperature T2b at a low water pressure. The ratio of dissolved air at A2b decreases. For this reason, air corresponding to the difference ΔA2b obtained by subtracting the dissolved air ratio A2b from the dissolved air ratio A2a is discharged from the hot water, and the air is discharged to the outside of the hot water tank 21 through the air vent valve 25. And even if the temperature T2 of the hot water flowing out from the heat exchanger 12 returns to the steady temperature T2a, the ratio of the dissolved air of the hot water is kept low. For this reason, generation | occurrence | production of the bubble in the heat exchanger 12 is suppressed, and execution of "bubble discharge control" is suppressed.

(Explanation of time chart)
A time chart when the “circulation pump control process” shown in FIG. 3 is executed will be described below with reference to FIG. The operation of the fuel cell system 100 is started, the “circulation pump control process” is executed, and the temperature T2 of the hot water flowing out from the heat exchanger 12 is set to the steady temperature T2a. If it is determined that bubbles have been generated in 12 (YES in step S12 of FIG. 3), “bubble discharge control” is started (step S13).

  When “bubble discharge control” ends at time t2, “temperature rise control” is started (step S14). Then, the temperature T2 of the hot water flowing out from the heat exchanger 12 is raised to the specified temperature T2b, and along with this, the dissolved air from the hot water flowing out from the heat exchanger 12 is discharged, and the air Is discharged to the outside of the hot water tank 21 through the air vent valve 25. As a result, the ratio of dissolved air in the hot water storage tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 gradually decreases, and the dissolved air in the hot water flowing into the heat exchanger 12 decreases. The rate gradually decreases.

  If it is determined that bubbles have occurred in the heat exchanger 12 at time t3 (YES in step S15), “bubble discharge control” is started (step S16). When the “bubble discharge control” ends at time t4, the “temperature rise control” starts again (step S14). Similarly, when it is determined at time t5 and time t7 that bubbles are generated in the heat exchanger 12 (YES in step S15), “bubble discharge control” is started (step S16). Similarly, when the “bubble discharge control” ends at time t6 and time t7, “temperature rise control” is started again (step S14). As described above, by executing the “temperature rise control”, the temperature T2 of the hot water flowing out from the heat exchanger 12 is raised to the specified temperature T2b, and the hot water tank 21, the first hot water circulation line 22, and The ratio of the dissolved air in the second hot water circulation line 930 is gradually decreased, and the ratio of the dissolved air in the hot water flowing into the heat exchanger 12 is gradually decreased.

  The ratio of dissolved air in the hot water storage tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is sufficiently reduced, and the ratio of the dissolved air in the hot water flowing into the heat exchanger 12 is sufficiently high. When it is lowered, it is difficult for bubbles to be generated in the heat exchanger 12, and it takes a long time to determine that bubbles are generated in the heat exchanger 12. Then, at time t9, when the time during which it is not determined that bubbles have occurred in the heat exchanger 12 has passed the first specified time tr1 (YES in step S31), the air flows out of the heat exchanger 12. The temperature T2 of the stored hot water is returned to the steady temperature T2a.

  The second hot-water storage water circulation line 930 is a closed type, and any of the hot water storage tank 21, the first hot-water storage water circulation line 22, and the second hot-water storage water circulation line 930 has a large proportion of dissolved air (dissolved air amount). Water does not flow in. Thereby, if the ratio (dissolved air amount) of the hot water stored in the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is reduced by the "temperature rise control", then the heat exchanger Even if the temperature T2 of the stored hot water flowing out from 12 is returned to the steady temperature T2a lower than the specified temperature T2b, the proportion of dissolved air (the amount of dissolved air) flowing into the heat exchanger 12 is kept low. Is done. For this reason, since it becomes difficult to generate bubbles in the heat exchanger 12 and the execution frequency of the “bubble discharge process” decreases, the collapse of the temperature stratification of the hot water in the hot water storage tank 21 is suppressed.

(Effect of this embodiment)
As is apparent from the above description, “temperature rise control” is executed to raise the temperature T2 of the hot water flowing out from the heat exchanger 12 when it is determined that bubbles are generated, that is, compared to the steady operation. (Step S14 in FIG. 3). According to this, the amount of air that can be dissolved in the stored hot water decreases as the temperature of the stored hot water increases, so by raising the temperature of the stored hot water, the air dissolved in the stored hot water is discharged from the stored hot water. And the amount of dissolved air in the hot water can be reduced.

  Further, since the second hot water circulation line 930 through which hot water circulates between the hot water tank 21 and the hot water storage device 910 is a closed type, the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line. Water in which air is dissolved in 930 does not continuously flow in. For this reason, once the “temperature rise control” is executed, the amount of dissolved air in the hot water can be kept small. As a result, at least the generation of bubbles in the heat exchanger 12 can be suppressed. Therefore, frequent execution of the “bubble discharge control” is suppressed, and the collapse of the temperature stratification of the hot water in the hot water tank 21 can be suppressed. As a result, hot water having a temperature lower than that of the upper part of the hot water tank 21 flows into the heat exchanger 12 from the lower part of the hot water tank 21. For this reason, the water vapor contained in the exhaust gas can be condensed in the heat exchanger 12, and the water in which the water vapor is condensed can be reused in the fuel cell system 100. Moreover, the fall of the heat recovery efficiency in the heat exchanger 12 is suppressed. As a result, the operation efficiency of the fuel cell system 100 can be improved.

  Further, the hot water pressure in the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is lowered, and the air dissolved in the hot water is discharged and bubbles are generated in the heat exchanger 12. Even if this occurs (determined as YES in step S12), the "temperature rise control" is executed (step S14), whereby the air dissolved in the hot water is discharged and the hot water is stored. The ratio of dissolved air is reduced, and the collapse of the temperature stratification of the hot water in the hot water tank 21 can be suppressed.

  The ratio of dissolved air in the hot water storage tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is sufficiently reduced, and the ratio of the dissolved air in the hot water flowing into the heat exchanger 12 is sufficiently high. When it is lowered, it is difficult for bubbles to be generated in the heat exchanger 12, and it takes a long time to determine that bubbles are generated in the heat exchanger 12. That is, when the bubble discharge control is not executed during the first specified time tr1, the dissolved air amount of the hot water is already reliably reduced by the “temperature rise control”. And since the 2nd stored hot water circulation line is a closed type, once the amount of dissolved air of hot water becomes low by temperature rise control, the stored hot water is maintained in a state where the amount of dissolved air is low. For this reason, even if the temperature T2 of the hot water flowing out from the heat exchanger 12 returns to the steady temperature T2a, the state in which the generation of bubbles is suppressed in the heat exchanger 12 is maintained. Therefore, when the “bubble discharge control” is not executed during the first specified time tr1 (determined as YES in step S31), the control device 15 (returning unit) determines the temperature of the hot water flowing out from the heat exchanger 12. T2 is returned to the steady temperature T2a. As a result, after the hot water is brought into a state where the amount of dissolved air is low and the collapse of the temperature stratification of the hot water in the hot water tank 21 due to the execution of “bubble discharge control” is performed, the heat exchanger The temperature T2 of the stored hot water flowing out from 12 can be returned to the steady temperature T2a. For this reason, after air bubbles are completely expelled from the heat exchanger 12, good temperature stratification is formed in the hot water storage tank 21. Therefore, the water vapor contained in the exhaust gas can be condensed in the heat exchanger 12, and the operating efficiency of the fuel cell system 100 can be further improved.

  Further, the control device 15 (abnormality notification unit) determines “abnormal” when the second specified time tr2 has elapsed (the determination is YES in step S19) when the frequency of execution of the “bubble discharge control” has not been reduced. The notification unit 17 notifies (step S20). For this reason, the operator determines whether the pressure of the hot water tank 21, the first hot water circulation line 22, and the second hot water circulation line 930 is lower than a predetermined pressure, the hot water tank 21, the first hot water circulation line 22, And the mixing of the air into at least any one of the 2nd hot water storage water circulation line 930 can be recognized.

  The hot water tank 21 allows air to flow from the inside of the hot water tank 21 to the outside of the hot water tank 21 but does not allow air to flow from the outside of the hot water tank 21 into the hot water tank 21. A valve 25 is provided. As a result, the air dissolved in the hot water is discharged to the outside of the hot water tank 21 through the air vent valve 25. Moreover, since the intrusion of air from the outside of the hot water storage tank 21 into the hot water storage tank 21 is prevented, it is possible to prevent the air from being dissolved again in the hot water storage water. For this reason, the amount of dissolved air in the hot water can be kept low.

(Another embodiment)
In the embodiment described above, in step S18 of FIG. 3, the control device 15 determines the occurrence frequency of bubbles based on the time when it is determined that bubbles are generated in the heat exchanger 12 stored in the storage unit 15a. It is judged whether or not it is reduced. However, in step S <b> 18, the control device 15 increases the bubble generation interval in the heat exchanger 12 based on the time when it is determined that bubbles are generated in the heat exchanger 12 stored in the storage unit 15 a. Even if it is embodiment which judges whether it was, it does not interfere. In the case of this embodiment, in step S18, the control device 15 determines the bubbles in the heat exchanger 12 based on the time when it is determined that the bubbles are generated in the heat exchanger 12 stored in the storage unit 15a. If it is determined that the generation interval has become longer (step S18: YES), the program proceeds to S14. On the other hand, based on the time when the control device 15 determines that bubbles are generated in the heat exchanger 12 stored in the storage unit 15a, the bubble generation interval in the heat exchanger 12 is shortened, or If it is determined that the interval is maintained (step S18: NO), the program proceeds to step S19.

  In step S12 and step S15 of FIG. 3, the control device 15 determines that the temperature T1 of the hot water in the heat exchanger 12 is equal to or higher than the first specified temperature Ta more than once, or the heat exchanger 12 There is no problem even in an embodiment in which it is determined that bubbles are generated in the heat exchanger 12 when it is determined a plurality of times that the temperature T2 of the hot water flowing out from the tank is equal to or higher than the second specified temperature Tb.

  In the embodiment described above, the steady temperature T2a during steady operation is constant. However, it may be an embodiment in which the steady temperature T2a is variable depending on the operation state of the fuel cell system 100.

  In the embodiment described above, “temperature rise” is executed after the steady operation and “bubble discharge control” are executed. However, there may be an embodiment in which “temperature rise control” is first executed when the fuel cell system 100 is installed.

  DESCRIPTION OF SYMBOLS 12 ... Heat exchanger, 12d ... 1st temperature sensor (temperature detection part), 12e ... 2nd temperature sensor (temperature detection part), 15 ... Control apparatus (steady operation part, temperature rise part, bubble generation | occurrence | production determination part, bubble discharge | emission 15a ... storage unit, 21 ... hot water tank, 22 ... first hot water circulation line, 25 ... air vent valve, 34 ... fuel cell, 22a ... circulation pump (pump), 100 ... fuel Battery system, 910 ... Hot water use equipment, 930 ... Second hot water circulation line

Claims (4)

A fuel cell that generates electricity using fuel and oxidant gas;
A hot water storage tank that is a sealed space in which hot water is stored;
A heat exchanger for exchanging heat between the exhaust gas exhausted from the fuel cell and the hot water,
A first hot water circulation line through which the hot water is circulated between the hot water tank and the heat exchanger;
A pump provided in the first hot-water storage water circulation line for circulating the hot-water storage between the hot-water tank and the heat exchanger;
A closed type second hot water circulation line in which the hot water circulates between the hot water storage device in which the hot water is used and the hot water tank;
A steady operation unit that adjusts the flow rate of the hot water discharged from the pump and sets the temperature of the hot water flowing out of the heat exchanger to a steady temperature to perform a steady operation;
Temperature increase control for lowering the flow rate of the hot water discharged from the pump as compared to when the steady operation is being performed and increasing the temperature of the hot water flowing out of the heat exchanger as compared with the steady temperature. A temperature riser to perform,
A bubble generation determination unit that determines whether or not bubbles are generated in the heat exchanger;
When it is determined by the bubble generation determination unit that the bubbles are generated in the heat exchanger, the flow rate of the hot water discharged from the pump is increased compared to when the steady operation is performed, A bubble discharger for performing bubble discharge control for discharging the bubbles from the heat exchanger;
I have a,
The temperature increasing unit is a fuel that executes the temperature increasing control after the bubble generation determining unit determines the generation of the bubbles and performs the bubble discharge control while the steady operation is being performed. Battery system. Wherein the temperature increase control is executed, if the time during which the air bubbles are determined not to be generated within the heat exchanger by the air bubble occurrence determination unit exceeds the first specified time, the steady operation The fuel cell system according to claim 1 , further comprising: a return unit that returns to the state. A storage unit for storing the time of occurrence of the bubble in the temperature increase control the after run is determined by the bubble occurrence determination unit in said heat exchanger,
Based on the time of occurrence of the bubble in the the heat exchanger which is stored in the storage unit, when the frequency of execution of the bubble discharge control after the temperature increase control execution is not reduced, indicating an abnormal The fuel cell system according to claim 1 , further comprising an abnormality determination unit that performs determination. The hot water storage tank has an air vent valve that allows air to flow from the inside of the hot water tank to the outside of the hot water tank, but does not allow air to flow from the outside of the hot water tank to the inside of the hot water tank. The fuel cell system according to any one of claims 1 to 3 , wherein the fuel cell system is provided.

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