Exhaust heat recovery device

Abstract

To prevent malfunction of a pump by reducing deposition of copper oxide in a sliding part of the pump when circulating hot water between a tank and a heat exchange part by using the pump having the water lubrication sliding part.SOLUTION: An exhaust heat recovery device includes: a heat exchange part for exchanging heat between exhaust heat of a fuel cell system and hot water; a tank; a circulation passage that connects the heat exchange part and the tank; a pump installed on the downstream side of the tank in the circulation passage, having a water lubrication sliding part and circulating hot water between the tank and the heat exchange part; a temperature sensor installed on the downstream side of the pump in the circulation passage; and a control section that performs temperature rise control for raising a temperature of a heat generation part different from the pump in the circulation passage when a temperature detected by the temperature sensor becomes a predetermined temperature or higher during execution of the circulation control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present specification discloses an exhaust heat recovery device. [Background technology]

[0002] Conventionally, this type of exhaust heat recovery device has been proposed to include a heat exchanger that exchanges heat between hot water and exhaust heat (combustion exhaust gas) emitted from a power generation module including a fuel cell, a hot water storage tank that stores the hot water, a circulation pipe that connects the heat exchanger and the hot water storage tank, and a circulation pump installed downstream of the hot water storage tank on the circulation pipe (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-21725 Summary of the Invention [Problem to be solved by the invention]

[0004] Copper materials are commonly used for heat exchangers, circulation piping, etc., and it is known that copper ions are eluted from the materials into the circulating water. When the concentration of copper ions in the circulating water increases, copper oxide is precipitated under certain conditions. When a pump with water-lubricated sliding parts is used, the precipitation of copper oxide on the sliding parts may cause the pump to malfunction.

[0005] The exhaust heat recovery device disclosed herein uses a pump with water-lubricated sliding parts to circulate hot and cold water between a tank and a heat exchanger, and its main purpose is to reduce the deposition of copper oxide on the sliding parts of the pump and prevent the pump from malfunctioning. [Means for solving the problem]

[0006] The exhaust heat recovery device of the present disclosure employs the following measures to achieve the above-mentioned main object.

[0007] The exhaust heat recovery device of the present disclosure includes: An exhaust heat recovery device that recovers exhaust heat from a fuel cell system, a heat exchange unit that exchanges heat between exhaust heat from the fuel cell system and hot water; A tank for storing hot water, a circulation path connecting the heat exchange unit and the tank; a pump that is installed downstream of the tank in the circulation path and has a water-lubricated sliding part, and circulates hot and cold water between the tank and the heat exchange part; a temperature sensor installed downstream of the pump in the circulation path; a control unit that performs temperature increase control to increase the temperature of a heat generating unit other than the pump in the circulation path when the temperature detected by the temperature sensor becomes equal to or higher than a predetermined temperature during execution of circulation control that controls the pump so that the hot water in the tank circulates; The gist of the project is to provide the following:

[0008] After extensive research, the inventors of the present application discovered that when a pump with water-lubricated sliding parts, at least a portion of which is made of copper, is used to circulate hot and cold water, copper ions dissolve into the circulating water. As the concentration of copper ions in the circulating water increases, frictional heat from the sliding parts causes copper oxide to precipitate, potentially resulting in pump malfunction. Therefore, the presently disclosed exhaust heat recovery device performs temperature control to raise the temperature of a heat-generating part other than the pump on the circulation path when the temperature detected by a temperature sensor installed downstream of the pump exceeds a predetermined temperature. This promotes the precipitation of copper oxide in the heat-generating part other than the pump on the circulation path, thereby reducing the concentration of copper ions in the circulating water. As a result, the precipitation of copper oxide on the pump's sliding parts is reduced, preventing pump malfunction. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a schematic configuration diagram of a fuel cell system including an exhaust heat recovery device according to an embodiment of the present invention. [Figure 2] 10 is a flowchart illustrating an example of a control process. [Figure 3] 10 is a flowchart illustrating an example of a shaft portion copper oxide deposition suppression process. [Figure 4] 10 is a flowchart showing a shaft portion copper oxide deposition suppression process according to another embodiment. [Figure 5] 10 is a flowchart showing a shaft portion copper oxide deposition suppression process according to another embodiment. [Figure 6] 10 is a flowchart showing a shaft portion copper oxide deposition suppression process according to another embodiment. [Figure 7] 10 is a flowchart showing a shaft portion copper oxide deposition suppression process according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will be described with reference to the drawings.

[0011] 1 is a schematic diagram of a fuel cell system 10 according to this embodiment. As shown in the figure, the fuel cell system 10 includes a power generation module 11 including a fuel cell stack, various auxiliaries (not shown) for operating the fuel cell stack, an exhaust heat recovery device 20 according to this embodiment that recovers exhaust heat from the power generation module 11, and a control device 50 that controls the entire system.

[0012] The power generation module 11 includes a fuel cell stack that generates electricity using hydrogen in the fuel gas and oxygen in the oxidant gas, an evaporator that evaporates reforming water to produce steam, a reformer that reforms raw fuel (e.g., natural gas or LP gas) by steam reforming to produce fuel gas, a combustion unit that combusts off-gases (fuel off-gases, oxidant off-gases) not used for power generation in the fuel cell stack, and a heat-insulating module case that houses these components. The various auxiliary components include a raw fuel pump that supplies raw fuel to the reformer (evaporator), a flow sensor that detects the raw fuel supply flow rate, an air blower that supplies air as oxidant gas to the oxidant electrode of the fuel cell stack, a flow sensor that detects the air supply flow rate, a reforming water pump that supplies reforming water to the evaporator, and a power conditioner that converts the power generated by the fuel cell stack. A temperature sensor 44 that detects the indoor temperature (indoor temperature TH5) is installed in the auxiliary equipment room that houses the control device 50, the power conditioner, and other auxiliary equipment.

[0013] A gas microcomputer meter is installed in the raw fuel supply line, and if gas continues to flow continuously for a certain period of time, the gas microcomputer meter determines that a gas leak has occurred and cuts off the supply of raw fuel. In order to avoid the gas microcomputer meter determining that there is a gas leak, the fuel cell system 10 of this embodiment performs a periodic shutdown in which the system is temporarily stopped and restarted after a certain period of time has passed since the last time the system was started.

[0014] As shown in Figure 1, the exhaust heat recovery device 20 of this embodiment includes a heat exchanger 21, a hot water storage tank 22, a copper circulation pipe 23 that connects the heat exchanger 21 and the hot water storage tank 22 to form a circulation path, and a water pump 24 installed on the circulation pipe 23 downstream of the hot water storage tank 22.

[0015] Heat exchanger 21 is made of copper and exchanges heat between the exhaust heat of power generation module 11 and circulating water. To heat exchanger 21, combustion exhaust gas generated by combustion of off-gas in the combustion section may be introduced as the exhaust heat of power generation module 11, or fuel off-gas from the fuel cell stack may be introduced. In the latter case, the fuel off-gas after passing through heat exchanger 21 is supplied to the combustion section.

[0016] In this embodiment, the water pump 24 is configured as a submersible plain bearing pump having an impeller 24a that supplies and discharges circulating water by rotation, a shaft 24b, and a water-lubricated plain bearing 24c that rotatably supports the impeller 24a relative to the shaft 24b, as shown in Figure 1. The water pump 24 may be any pump that has a water-lubricated sliding part, and may be, for example, a piston (plunger) pump or a vane pump.

[0017] A circulating water outlet connected to the circulation pipe 23 is formed at the bottom of the hot water storage tank 22, and a circulating water inlet connected to the circulation pipe 23 is formed at the top of the hot water storage tank 22. When the water pump 24 is activated, the hot water stored in the hot water storage tank 22 is introduced into the heat exchanger 21, where it is heated by heat exchange with the exhaust heat (combustion exhaust gas and fuel off-gas) from the power generation module 11, and then returned to the hot water storage tank 22.

[0018] A water supply port connected to a water supply line 31 is formed at the bottom of the hot water storage tank 22, and a hot water supply port connected to a hot water supply line 32 is formed at the top of the hot water storage tank 22. A water supply valve 34 is installed on the water supply line 31. A bypass line 33 that bypasses the hot water storage tank 22 is also connected between the water supply line 31 and the hot water supply line 32, and a mixing valve 35 is installed at the connection between the hot water supply line 32 and the bypass line 33. Hot water discharged from the hot water supply port of the hot water storage tank 22 is mixed with low-temperature water supplied directly from the water supply line 31 by opening the mixing valve 35 as needed, and the mixed water is supplied to the hot water supply destination. Furthermore, a drain line 36 is connected to the hot water supply line 32 downstream of the mixing valve 35, and a drain valve 37 is installed on the drain line 36. The hot water in the hot water supply line 32 is discharged to the outside by opening the drain valve 37.

[0019] The exhaust heat recovery device 20 of this embodiment also includes a radiator 25 installed in the circulation pipe 23 between the heat exchanger 21 and the water pump 24, a radiator fan 26 that sends air to the radiator 25, and a heater 27 installed in the circulation pipe 23 between the water pump 24 and the radiator 25. The radiator fan 26 has an upper limit rotation speed set to prevent excessive noise and vibration, and is driven to rotate at or below the upper limit rotation speed. The heater 27 is, for example, a sheath heater, and is usually driven to consume a portion of the power generated by the fuel cell stack (for example, surplus power).

[0020] A temperature sensor 41 is installed in the circulation piping 23 near the outlet of the water pump 24 (downstream of the heater 27) to detect the temperature of the circulating water near the outlet of the water pump 24 (pump outlet water temperature TH10). Furthermore, a temperature sensor 42 is installed in the circulation piping 23 near the circulating water inlet of the heat exchanger 21 to detect the temperature of the circulating water near the circulating water inlet of the heat exchanger 21 (heat exchanger inlet water temperature TH1). Furthermore, a temperature sensor 43 is installed in the circulation piping 23 near the circulating water outlet of the heat exchanger 21 to detect the temperature of the circulating water near the circulating water outlet of the heat exchanger 21 (heat exchanger outlet water temperature TH3).

[0021] The control device 50 is configured as a microprocessor centered around a CPU 51, and in addition to the CPU 51, includes a ROM 52, a RAM 53, a timer 54, input / output ports, etc. Detection signals from temperature sensors 41, 42, 43, 44, flow rate sensors, etc. are input to the control device 50 via input ports. Drive signals are output from the control device 50 to the raw fuel pump, air blower, reforming water pump, water pump 24, radiator fan 26, heater 27, water supply valve 34, mixing valve 35, drain valve 37, etc. via output ports.

[0022] Next, the operation of the exhaust heat recovery device 20 of this embodiment configured as described above will be described.

[0023] Here, it has been found that when the heat exchanger 21 and circulation pipe 23 are made of copper and the water pump 24 has a water-lubricated plain bearing (sliding part) 24c, copper ions are eluted from the copper material into the circulating water, and when the shaft part 24b is heated by frictional heat of the plain bearing part 24c in a state where the concentration of copper ions in the circulating water is high, copper oxide (CuO) precipitates on the shaft part 24b. When copper oxide accumulates on the shaft part 24b, the clearance of the plain bearing part 24c decreases, which may result in the water pump 24 locking. This is thought to be due to the following factors: In water, the copper material corrodes (oxidation reaction of Cu shown in the following formula (1) and reduction reaction of O2 shown in the following formula (2)) and monovalent copper ions (CuO) precipitate on the shaft part 24b. + ) and hydroxide ions (OH - ) is generated. + When the concentration of copper ions (Cu) increases, the disproportionation reaction shown in the following formula (3) occurs. 2+ ) is then produced. Then, divalent copper ions (Cu 2+ ) and hydroxide ions (OH - ) reacts with copper hydroxide ions (Cu(OH)2) to generate copper hydroxide ions (Cu(OH)2). When copper hydroxide ions (Cu(OH)2) are heated to a certain temperature (e.g., 60°C) or higher, copper oxide (CuO) is precipitated by dehydration decomposition according to the following formula (5):

[0024] Cu → Cu + +e - …(1) 1 / 4O2+1 / 2H2O→OH - …(2) 2Cu + →Cu+Cu 2+ …(3) Cu 2+ +2OH - →Cu(OH)2…(4) Cu(OH)2 → CuO + H2O … (5)

[0025] Therefore, in this embodiment, the control device 50 executes a shaft copper oxide precipitation suppression process under certain conditions to suppress the precipitation of copper oxide (CuO) on the shaft portion 24b of the water pump 24 and prevent the water pump 24 from locking.

[0026] FIG. 2 is a flowchart showing an example of a control process executed by the CPU 51 of the control device 50. This process is repeatedly executed at predetermined time intervals (e.g., every several tens of milliseconds) while the power generation module 11 (fuel cell stack) is generating power and circulation control is being performed to circulate circulating water (hot water) between the heat exchanger 21 and the hot water storage tank 22 to recover exhaust heat from the power generation module 11. Here, the circulation control is performed by setting the duty of the water pump 24 using feedback control (proportional-integral control) based on the deviation between the heat exchanger outlet water temperature TH3 from the temperature sensor 43 and the control temperature TH3tag so that the heat exchanger outlet water temperature TH3 becomes the control temperature TH3tag, and then driving and controlling the water pump 24 at the set duty. The control temperature TH3tag is basically set to the normal water temperature TH3nor (e.g., 60°C or 65°C) and is changed as necessary by the process described below. Note that the control of the heat exchanger outlet water temperature TH3 may be controlled in conjunction with the control of the radiator fan 26 and the heater 27. The control process will be described in detail below.

[0027] When the control process is executed, the CPU 51 of the control device 50 first determines whether it is a predetermined time (e.g., several hours) before a system shutdown (regular shutdown) (S100). If the CPU 51 determines that it is not the predetermined time before the system shutdown (i.e., it is before the predetermined time before the system shutdown), the CPU 51 inputs the pump outlet water temperature TH10 from the temperature sensor 41 (S102) and determines whether the input pump outlet water temperature TH10 is equal to or greater than a threshold value TH10ref (S104). Here, the threshold value TH10ref is a threshold value for determining whether the pump outlet water temperature TH10 is in a temperature range where copper oxide (CuO) is likely to precipitate on the shaft portion 24b of the water pump 24, and is set to, for example, 60°C. If the CPU 51 determines that the pump outlet water temperature TH10 is not equal to or greater than the threshold value TH10ref, the CPU 51 terminates the control process. On the other hand, if the CPU 51 determines that the pump outlet water temperature TH10 is equal to or higher than the threshold value TH10ref, it determines whether or not this state has continued for a predetermined time (for example, several minutes or several tens of minutes) (S106). The predetermined time is the time required to determine that the pump outlet water temperature TH10 is in a temperature range in which copper oxide (CuO) is likely to precipitate on the shaft portion 24b. If the CPU 51 determines that the pump outlet water temperature TH10 is equal to or higher than the threshold value TH10ref but that this state has not continued for the predetermined time, it returns to S102. On the other hand, if the CPU 51 determines that the pump outlet water temperature TH10 is equal to or higher than the threshold value TH10ref and that this state has continued for the predetermined time, it executes shaft portion copper oxide precipitation suppression processing (S108) and ends the control processing.

[0028] If the CPU 51 determines in S100 that the predetermined time before system shutdown is reached, it inputs the indoor temperature TH5 from the temperature sensor 44 (S110) and determines whether the input indoor temperature TH5 is equal to or greater than a threshold value TH5ref (S112). The indoor temperature TH5 is a temperature correlated with the outside air temperature, and the threshold value TH5ref is a threshold value for determining whether the outside air temperature is in a temperature range where copper oxide (CuO) is likely to precipitate on the shaft portion 24b of the water pump 24. The threshold value TH5ref is set to, for example, 30°C. If the CPU 51 determines that the indoor temperature TH5 is not equal to or greater than the threshold value TH5ref, it waits until the system shutdown time arrives (S118), transitions to system shutdown control (S120), and terminates the control process. Note that a description of the system shutdown control is omitted as it is not relevant to the gist of this disclosure. On the other hand, if the CPU 51 determines that the indoor temperature TH5 is equal to or greater than the threshold value TH5ref, it determines whether this state has continued for a predetermined time (e.g., several tens of seconds) (S114). The predetermined time is the time required to determine that the indoor temperature TH5 (outdoor temperature) is in a temperature range where copper oxide (CuO) is likely to precipitate on the shaft portion 24b. If the CPU 51 determines that the indoor temperature TH5 is equal to or higher than the threshold value TH5ref but that this state has not continued for the predetermined time, the process returns to S110. On the other hand, if the CPU 51 determines that the indoor temperature TH5 is equal to or higher than the threshold value TH5ref and that this state has continued for the predetermined time, the CPU 51 executes shaft portion copper oxide precipitation suppression processing (S116), waits for the system shutdown time to arrive (S118), transitions to system shutdown control (S120), and ends the control processing.

[0029] Next, the shaft portion copper oxide deposition suppression process executed in S110 and S118 will be described. Fig. 3 is a flowchart showing an example of the shaft portion copper oxide deposition suppression process executed by the CPU 51 of the control device 50.

[0030] When the shaft copper oxide deposition suppression process is executed, the CPU 51 of the control device 50 first changes the control temperature TH3tag of the heat exchanger outlet water temperature TH3 from the normal water temperature TH3nor to a high water temperature TH3hi (e.g., 70°C or 75°C) that is higher than the normal water temperature TH3nor (S200). This causes the heat exchanger 21 to be heated until the heat exchanger outlet water temperature TH3 from the temperature sensor 43 reaches the high water temperature TH3hi. Next, the CPU 51 waits for a certain period of time to elapse (S202). Here, the certain period of time is the time required for the hot water stored in the hot water storage tank 22 to circulate once, and is determined in advance based on the capacity of the hot water storage tank 22, the length of the circulation pipe 23, the performance of the water pump 24, etc. When the CPU 51 determines that the certain time has elapsed, it returns the control temperature TH3tag of the heat exchanger outlet water temperature TH3 from the high water temperature TH3hi to the normal water temperature TH3nor (S204), and ends the shaft copper oxide deposition suppression process.

[0031] Thus, when the pump outlet water temperature TH10 remains above the threshold value TH10ref for a predetermined period of time and the copper ion concentration in the circulating water is expected to be high, the CPU 51 sets the control temperature TH3tag for the heat exchanger outlet water temperature TH3 to a high water temperature TH3hi, which is higher than the normal water temperature TH3nor, ​​for a certain period of time, and raises the temperature of the heat exchanger 21. As described above, when the copper ion concentration in the circulating water increases, copper oxide (CuO) is more likely to precipitate due to hydrolysis in the heat-generating portion at temperatures above 60°C. Therefore, by raising the temperature of the heat exchanger 21, copper oxide (CuO) is actively precipitated in the heat exchanger 21 (heat-generating portion) separate from the plain bearing 24c of the water pump 24, thereby reducing the copper ion concentration in the circulating water. This prevents copper oxide (CuO) from precipitating on the shaft portion 24b even if the shaft portion 24b is heated by frictional heat from the plain bearing 24c of the water pump 24, and prevents the water pump 24 from locking up.

[0032] Furthermore, in this embodiment, even if the indoor temperature TH5, which correlates with the outside air temperature, is equal to or higher than the threshold value TH5ref, a shaft copper oxide deposition suppression process is executed even a predetermined time before the system is shut down (scheduled shutdown). This is based on the fact that when the concentration of copper ions in the circulating water is high and the temperature of the circulating water drops to near room temperature as the system is shut down, copper oxide (CuO) deposition has been observed in the circulating water path, including the shaft portion 24b of the water pump 24. By executing the shaft copper oxide deposition suppression process, the concentration of copper ions in the circulating water can be reduced before the system is shut down, and copper oxide (CuO) deposition on the shaft portion 24b can be suppressed.

[0033] The above describes the forms for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms within the scope that does not deviate from the gist of the present disclosure.

[0034] For example, in the above-described embodiment, the CPU 51 performs control to cause copper oxide (CuO) to precipitate in the heat exchanger 21 through the shaft copper oxide precipitation suppression process. However, the CPU 51 may also perform control to cause copper oxide (CuO) to precipitate in the heater 27. In this case, the CPU 51 may execute the shaft copper oxide precipitation suppression process illustrated in FIG. 4 instead of the shaft copper oxide precipitation suppression process illustrated in FIG. 3.

[0035] In the shaft copper oxide deposition suppression process of FIG. 4, the CPU 51 of the control device 50 first turns on (energizes) the heater 27 (S210). Next, the CPU 51 starts circulating water flow rate feedback control, which controls the operation of the water pump 24 so that the pump outlet water temperature TH10 from the temperature sensor 41 becomes a heater deposition temperature at which copper oxide (CuO) deposits on the heater 27 (S212). Here, the heater 27 is installed downstream of the water pump 24 in the circulation pipe 23, and the temperature sensor 41 is installed downstream of the heater 27 in the circulation pipe 23. Therefore, the temperature sensor 41 can detect the water temperature around the heater 27. The heater deposition temperature is a temperature (TH10ref+α) higher than the above-mentioned threshold value TH10ref by a predetermined value α, and is set to, for example, 65°C or 70°C. Next, the CPU 51 waits for a certain period of time to elapse (S214). Here, similar to S202, the certain time is the time required for the hot water stored in the hot water storage tank 22 to circulate once. When the CPU 51 determines that the certain time has elapsed, it turns off the heater 27 (S216) and terminates the feedback control of the circulating water flow rate based on the pump outlet water temperature TH10 (S218), thereby terminating the shaft copper oxide deposition suppression process.

[0036] 4 , when the pump outlet water temperature TH10 remains above the threshold value TH10ref for a predetermined time and the copper ion concentration in the circulating water is estimated to be high, the temperature of the area surrounding the heater 27 is increased to actively precipitate copper oxide (CuO) on the heater 27 (heat-generating portion) separate from the plain bearing portion 24c of the water pump 24, thereby reducing the copper ion concentration in the circulating water. This prevents copper oxide (CuO) from precipitating on the shaft portion 24b even if the shaft portion 24b is heated by frictional heat from the plain bearing portion 24c of the water pump 24, thereby preventing the water pump 24 from locking. Furthermore, even if the indoor temperature TH5, which correlates with the outside air temperature, is above the threshold value TH5ref even a predetermined time before the system is shut down (regular shutdown), the temperature of the area surrounding the heater 27 is increased to reduce the copper ion concentration in the circulating water before the system is shut down, thereby preventing copper oxide (CuO) from precipitating on the shaft portion 24b.

[0037] In the above-described embodiment, the CPU 51 controls the shaft copper oxide deposition suppression process to raise the temperature of a heat-generating portion (heat exchanger 21 or heater 27) other than the shaft portion 24b of the water pump 24, thereby precipitating copper oxide (CuO) on the heat-generating portion. However, if the temperature of the circulating water continues to be 60°C or higher, the elution of copper ions from the circulation piping 23 is promoted. Therefore, the CPU 51 may control the temperature of the circulating water to decrease as the shaft copper oxide deposition suppression process of S110 to suppress the elution of copper ions into the circulating water. In this case, the CPU 51 may execute the shaft copper oxide deposition suppression process illustrated in FIGS. 5, 6, and 7 as the shaft copper oxide deposition suppression process of S110 when the pump outlet water temperature TH10 remains equal to or higher than the threshold value TH10ref for a predetermined period of time.

[0038] 5, the CPU 51 of the control device 50 first drains the hot water stored in the hot water storage tank 22 by opening the water supply valve 34, the mixing valve 35, and the drain valve 37 (S220). The hot water supplied from the hot water storage tank 22 to the hot water supply line 32 is mixed with water supplied from the water supply line 31 bypassing the hot water storage tank 22 by the mixing valve 35, and the low-temperature hot water is discharged to the outside via the hot water supply line 32 and the drain line 36 in that order. Next, the CPU 51 inputs the pump outlet water temperature TH10 from the temperature sensor 41 (S222) and waits until the input pump outlet water temperature TH10 becomes less than a predetermined temperature (TH10ref-β) (S224). Here, the predetermined temperature (TH10ref-β) is a temperature lower than the threshold value TH10ref by β, and is set to, for example, 50°C or 55°C. When CPU 51 determines that pump outlet water temperature TH10 has fallen below predetermined temperature (TH10ref-β), it closes water supply valve 34, mixing valve 35, and drain valve 37 to stop draining hot water from hot water storage tank 22 (S226), and ends the shaft copper oxide deposition suppression process. Note that drain valve 37 is installed in drain line 36 branching from hot water supply line 32, but it may also be installed downstream of radiator 25 in circulation piping 23. In this case, CPU 51 performs the shaft copper oxide deposition suppression process by opening water supply valve 34 and drain valve 37 to drain circulating water from circulation piping 23 and supply low-temperature water to hot water storage tank 22 while circulating water by water pump 24.

[0039] In the shaft copper oxide deposition suppression process of FIG. 6, the CPU 51 of the control device 50 first changes the control temperature TH3tag of the heat exchanger outlet water temperature TH3 from the normal water temperature TH3nor to a low water temperature TH3lo (e.g., 50°C or 55°C) that is lower than the normal water temperature TH3nor (S230). This causes the heat exchanger 21 to cool until the heat exchanger outlet water temperature TH3 from the temperature sensor 43 reaches the low water temperature TH3lo. Next, the CPU 51 waits for a certain period of time to elapse (S232). Here, the certain period of time is the time required for the hot water stored in the hot water storage tank 22 to circulate once. When the CPU 51 determines that the certain period of time has elapsed, it changes the control temperature TH3tag of the heat exchanger outlet water temperature TH3 from the low water temperature TH3lo back to the normal water temperature TH3nor (S234), and ends the shaft copper oxide deposition suppression process.

[0040] 7, the CPU 51 of the control device 50 first increases the rotation speed of the radiator fan 26 by a predetermined value γ above a predetermined upper limit rotation speed, thereby controlling the drive of the radiator fan 26 (S240). Next, the CPU 51 waits for a certain period of time to elapse (S242). The certain period of time is the time required for the hot water stored in the hot water storage tank 22 to circulate once. When the CPU 51 determines that the certain period of time has elapsed, it returns the rotation speed of the radiator fan 26 to the upper limit rotation speed (S244), thereby terminating the shaft copper oxide deposition suppression process. Here, while noise and vibration increase as the rotation speed of the radiator fan 26 increases, this does not pose a major problem because the increase in rotation speed is only for a certain period of time.

[0041] 5 to 7, when the pump outlet water temperature TH10 remains above the threshold value TH10ref for a predetermined period of time and the copper ion concentration in the circulating water is estimated to be high, the CPU 51 lowers the temperature of the circulating water. This makes it possible to suppress the elution of copper ions into the circulating water and prevent copper oxide (CuO) from precipitating on the shaft portion 24b of the water pump 24.

[0042] In the above-described embodiment, the water pump 24 is installed downstream of the hot water storage tank 22 and upstream of the radiator 25, but it may be installed downstream of the radiator 25. This allows the water pump 24 to draw in circulating water at a relatively low temperature, thereby preventing the shaft portion 24b from becoming too hot and preventing copper oxide (CuO) from being deposited. [Industrial Applicability]

[0043] The present disclosure is applicable to industries such as the manufacturing of fuel cell systems and exhaust heat recovery devices. [Explanation of symbols]

[0044] 10 fuel cell system, 20 exhaust heat recovery device, 21 heat exchanger (heat exchange section, heat generating section), 22 hot water storage tank (tank), 23 circulation piping (circulation path), 24 water pump (pump), 24c plain bearing section (sliding section), 27 heater (heat generating section), 41 temperature sensor, 43 temperature sensor (second temperature sensor), 50 control device (control section).

Claims

1. An exhaust heat recovery device that recovers exhaust heat from a fuel cell system, a heat exchange unit that exchanges heat between exhaust heat from the fuel cell system and hot water; A tank for storing hot water, a circulation path connecting the heat exchange unit and the tank; a pump that is installed downstream of the tank in the circulation path and has a water-lubricated sliding part, and circulates hot water between the tank and the heat exchange part; a temperature sensor installed downstream of the pump in the circulation path; a control unit that performs temperature increase control to increase the temperature of a heat generating unit other than the pump in the circulation path when the temperature detected by the temperature sensor becomes equal to or higher than a predetermined temperature during execution of circulation control that controls the pump so that the hot water in the tank circulates; An exhaust heat recovery device comprising:

2. The exhaust heat recovery device according to claim 1, the heat generating unit is a heater installed in the circulation path between the pump and the heat exchange unit, the control unit drives the heater as the temperature increase control when the temperature detected by the temperature sensor during execution of the circulation control becomes equal to or higher than a predetermined temperature. Exhaust heat recovery device.

3. The exhaust heat recovery device according to claim 1, a second temperature sensor disposed on an outlet side of the heat exchanger in the circulation path; The control unit controls the pump as the circulation control so that the temperature detected by the second temperature sensor becomes a first target temperature, and controls the pump as the temperature increase control so that the temperature detected by the second temperature sensor becomes a second target temperature higher than the first target temperature. Exhaust heat recovery device.

4. The exhaust heat recovery device according to any one of claims 1 to 3, The fuel cell system is periodically stopped and started, the control unit executes the temperature increase control for a predetermined period before the fuel cell system is stopped. Exhaust heat recovery device.

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