JP2015082479A - Fuel cell cogeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means capable of removing a bubble generated in a heat exchanger at a low cost in a fuel cell cogeneration system.SOLUTION: A fuel cell cogeneration system 1 comprises: an exhaust passage 9 through which an exhaust gas from a fuel cell power generation module 5 flows; an exhaust heat recovery heat exchanger 11 which is disposed in the exhaust passage 9 and is for heat exchange between an exhaust gas after power generation and a heat medium; a circulation pump 36 for making the heat medium circulate in the exhaust heat recovery heat exchanger 11; and a control unit for performing bubble removal control of discharging a bubble generated inside a secondary side heat exchange path unit 11b of the exhaust heat recovery heat exchanger 11 from the exhaust heat recovery heat exchanger 11, by temporarily increasing a flow rate of the circulation pump 36 when a predetermined condition is established.

Description

  The present invention relates to a fuel cell cogeneration system, and more particularly to an improved heat exchange efficiency of a heat exchanger for exhaust heat recovery that performs heat exchange between exhaust gas from a fuel cell power generation module and hot water from a hot water storage tank.

  Conventionally, a fuel cell core that generates air by supplying air and a reformed fuel gas (hydrogen-containing gas) to the fuel cell stack, and recovers the heat generated secondaryly during the power generation as hot water. Generation systems are in practical use. A conventional fuel cell cogeneration system includes a fuel cell power generation device that generates power, a hot water storage hot water supply device having a hot water storage tank that stores hot water after heat exchange, and hot water between the fuel cell power generation device and the hot water storage hot water supply device. A hot water circulation circuit for circulation is provided.

  The fuel cell power generator described above is a fuel cell stack that generates power using air and reformed fuel gas, and reformed fuel gas that is supplied to the fuel cell stack is generated from pure water (steam) and fuel gas. A fuel cell power generation module having a vacuum chamber, an exhaust passage for exhausting exhaust gas from the fuel cell power generation module to the outside, and an exhaust gas from the fuel cell power generation module and hot water stored in a hot water storage tank A heat exchanger for exhaust heat recovery for heat exchange, a water treatment device for recovering and storing pure water supplied to the reformer from exhaust gas, and the like are provided.

  By the way, a plate heat exchanger is generally used for a heat exchanger for exhaust heat recovery that recovers exhaust heat of a fuel cell power generation module in order to reduce the size. However, since the circulation flow rate of the hot water used as the heat medium is small, the hot water may boil locally in the exhaust heat recovery heat exchanger and bubbles may be generated and remain. When bubbles are generated in the heat exchanger for exhaust heat recovery, there is a problem that heat exchange efficiency is lowered and corrosion occurs at the boundary between the gas and the liquid.

  As a means for removing the bubbles, for example, in the fuel cell power generation system of Patent Document 1, the warm water circulating in the middle of the circulation path for circulating the warm water between the heat exchanger and the fuel cell is used. A structure in which an air vent valve for excluding bubbles generated in the outside is installed is disclosed. Further, in the fuel cell system of Patent Document 2, a speed reduction part that reduces the flow rate of the heat medium and a bubble vent part that discharges the air bubbles in the speed reduction part to the outside are installed in the middle of the exhaust heat recovery flow path. The structure is disclosed.

JP 2003-223913 A Japanese Patent No. 4584337

  However, as in the fuel cell power generation system of Patent Document 1, an air vent valve is installed in the middle of the circulation path through which hot water flows, or in the middle of the exhaust heat recovery flow path as in the fuel cell system of Patent Document 2. If a speed reduction part and a bubble removal part are installed in the above, there is a problem that the number of parts increases and the cost becomes high.

  In addition, in the structures of Patent Documents 1 and 2, if the generated bubbles remain in the heat exchanger, the air vent valve or the air vent part cannot discharge the air to the outside, so the heat exchange efficiency in the heat exchanger is high. In addition, if the gas-liquid boundary portion is corroded and damaged in the heat exchanger, there is a problem in that the fuel cell power generation device has a problem.

  An object of the present invention is to provide a fuel cell cogeneration system that can remove bubbles remaining in a heat exchanger at low cost, and can remove bubbles without adding new components. Providing things, etc.

  The fuel cell cogeneration system according to claim 1 is an exhaust passage through which exhaust gas from the fuel cell power generation module flows, and an exhaust gas disposed in the exhaust passage and for exchanging heat between the exhaust gas after power generation and the heat medium. In a fuel cell cogeneration system including a heat recovery heat exchanger and a circulation pump for circulating the heat medium in the exhaust heat recovery heat exchanger, the flow rate of the circulation pump is set when a predetermined condition is satisfied. A pump control means for performing bubble removal control for discharging bubbles generated in the heat medium passage of the heat exchanger for exhaust heat recovery by temporarily increasing the bubbles from the heat exchanger for exhaust heat recovery; It is a feature.

  A fuel cell cogeneration system according to a second aspect of the present invention is the fuel cell cogeneration system according to the first aspect of the invention, further comprising determination means for determining a decrease in the amount of heat exchange in the exhaust heat recovery heat exchanger, wherein the predetermined condition is satisfied by the determination It is a case where it is determined that the heat exchange amount has been reduced by the means.

  The fuel cell cogeneration system according to a third aspect is the invention according to the first aspect, wherein the predetermined condition is established when a predetermined period is reached.

  According to the first aspect of the present invention, when a predetermined condition is satisfied, by temporarily increasing the flow rate of the circulation pump, bubbles generated in the heat medium passage of the heat exchanger for exhaust heat recovery are exchanged for heat recovery for exhaust heat recovery. Since it has a pump control means to control the removal of bubbles that are discharged from the inside of the chamber, it can be generated and remained in the heat exchanger for exhaust heat recovery at low cost by using the existing configuration without adding new parts. Thus, it is possible to surely remove the bubbles, and thus it is possible to improve the heat exchange efficiency of the heat exchanger for exhaust heat recovery and to operate the fuel cell power generator safely.

  According to the second aspect of the present invention, it is provided with a determination unit that determines a decrease in the heat exchange amount in the heat exchanger for exhaust heat recovery, and when the predetermined condition is satisfied, it is determined by the determination unit that the heat exchange amount has decreased. Therefore, it can be determined that bubbles have accumulated in the heat exchanger for exhaust heat recovery, and when the amount of heat exchange in the heat exchanger for exhaust heat recovery decreases, the bubble removal operation is executed reliably. can do.

  According to the third aspect of the present invention, since the predetermined condition is established when the predetermined period is reached, the bubbles generated in the heat medium passage of the heat exchanger for exhaust heat recovery are periodically removed. Can be removed.

It is a schematic block diagram of the fuel cell cogeneration which concerns on Example 1 of this invention. It is a schematic block diagram of a fuel cell power generator. It is a schematic block diagram of a hot water storage hot water supply apparatus. It is a front view of the heat exchanger for waste heat recovery. It is sectional drawing of the heat exchanger for waste heat recovery. It is a flowchart of bubble removal control. 10 is a flowchart of bubble removal control according to the second embodiment.

  Hereinafter, modes for carrying out the present invention will be described based on examples.

The overall configuration of the fuel cell cogeneration system 1 of the present invention will be described.
As shown in FIG. 1, a fuel cell cogeneration system 1 includes a fuel cell power generation device 2 that generates power, a hot water storage hot water supply device 3 that stores hot water (corresponding to a heat medium) after heat exchange, and a fuel cell power generation device. 2 and the hot water storage hot water supply device 3 are constituted by a hot water circulation circuit 25 for circulating hot water.

Next, the fuel cell power generator 2 will be briefly described.
As shown in FIG. 2, the fuel cell power generation device 2 is an external heat source of the hot water storage hot water supply device 3 for heating hot water. The fuel cell power generation module 5, the fuel reforming air blowing means 6, the cathode air blowing means. 7. Fuel gas boosting means 8, exhaust passage 9 for exhausting exhaust gas after power generation, plate-type exhaust heat recovery heat exchanger 11, water treatment means 12, inverter 13, desulfurizer 15, etc. The various means are integrally stored in the outer case 14.

  The fuel cell power generation module 5 includes a fuel cell stack 5a, an evaporator 5b, a fuel reformer 5c, an off-gas combustion chamber 5d, etc., and is used as reformed fuel gas and oxidant reformed by the fuel reformer 5c. Electric power is generated by chemically reacting air in the fuel cell stack 5a.

  The fuel cell stack 5a is composed of a plurality of fuel cells. The evaporator 5b generates water vapor for mixing with the fuel gas and supplies it to the fuel reformer 5c. The fuel reformer 5c has a reforming catalyst such as nickel or platinum, and generates a reformed fuel gas by mixing and reacting the desulfurized fuel gas, air, and water vapor.

  The DC power generated by the fuel cell power generation module 5 is converted into AC power via the inverter 13 and output to the outside. In the middle of the exhaust passage 9, the primary side heat exchange passage portion 11 a of the heat exchanger 11 for exhaust heat recovery is connected, and the exhaust gas discharged from the fuel cell power generation module 5 passes through the exhaust passage 9 and is exhausted. Heat is exchanged with hot water circulating in the hot water circulation circuit 25 in the heat recovery heat exchanger 11 and the temperature is lowered and then discharged to the outside.

Next, the hot water storage hot water supply apparatus 3 will be briefly described.
As shown in FIG. 3, the hot water storage and hot water supply device 3 has functions such as hot water storage, hot water supply, hot water supply to hot water heating terminals such as a floor heating panel, hot water supply to the bath, and reheating of the bath. Tank 21, auxiliary heat source device 22, first and second heat exchangers 23, 24, hot water circulation circuit 25, water supply passage 26, hot water supply passage 27, bath hot water supply circuit 28, hot water heating circuit 29, heat utilization circulation circuit 31 The control unit 32 and the like are provided, and most of them are integrally stored in the outer case 33.

  The hot water storage tank 21 is for recovering the exhaust heat in the fuel cell power generation module 5 and storing it as hot water, and is composed of a sealed tank capable of storing hot hot water (for example, 80 to 90 ° C.). The hot water storage tank 21 is covered with a heat insulating material in order to prevent heat dissipation of the stored hot water. The temperature of the hot water in the plurality of reservoirs in the hot water storage tank 21 is detected by the plurality of tank hot water temperature sensors.

  As shown in FIGS. 1 and 2, the hot water circulation circuit 25 is a closed circuit that circulates hot water between the heat exchanger 11 for exhaust heat recovery of the fuel cell power generator 2 that is an external heat source and the hot water storage tank 21. The upstream side of the forward passage 25a is connected to the lower part of the hot water storage tank 21, and the downstream end of the return side passage 25b is connected to the upper part of the hot water storage tank 21.

  A bypass passage 25c is bypassed from the middle portion of the forward passage 25a to the middle portion of the return side passage 25b, and a hot water storage switching valve 34 is installed at this branch portion. A radiator 35 capable of rapidly cooling hot and cold water is installed in the outward passage 25a. A circulation pump 36 for circulating hot water through the exhaust heat recovery heat exchanger 11 is installed on the fuel cell power generator 2 side of the forward passage 25a. The secondary side heat exchange passage portion 11b of the exhaust heat recovery heat exchanger 11 is connected between the forward side passage 25a and the return side passage 25b.

  The temperature of the hot water circulating in the hot water circulation circuit 25 is as follows: a circulating hot water temperature sensor 37a on the radiator inlet side, a circulating hot water temperature sensor 37b on the radiator outlet side, a circulating hot water temperature sensor 37c on the heat exchanger inlet side, and a heat exchanger outlet side. The temperature is detected by the circulating hot water temperature sensor 37d and the circulating hot water temperature sensor 37e in the return side passage 25b.

  In the normal exhaust heat recovery operation, as shown in FIG. 1, the hot water storage switching valve 34 is switched so as to block the bypass passage 25c, and hot water passes from the hot water storage tank 21 via the circulation pump 36 through the forward passage 25a. The heated hot water is sent to the secondary heat exchange passage portion 11b of the exhaust heat recovery heat exchanger 11 and heated, and the heated hot water is returned to the hot water storage tank 21 through the return side passage 25b.

  The fuel cell cogeneration system 1 is controlled by a control unit 32. Detection signals from various temperature sensors, various flow sensors, and the like are transmitted to the control unit 32, and the control unit 32 operates the fuel cell power generation device 2 and the hot water storage hot water supply device 3, operates and stops various pumps, and various valves. Control of switching of the opening / closing state and opening degree adjustment, etc., and various operations (hot water circulation operation, bath pouring operation, bath reheating operation, heating operation, hot water supply operation, etc.) are executed.

  Further, the control unit 32 temporarily increases the flow rate of the circulation pump 36 when a predetermined condition is satisfied, thereby corresponding to the secondary heat exchange passage portion 11b (corresponding to the heat medium passage) of the heat exchanger 11 for exhaust heat recovery. It is possible to perform bubble removal control for discharging bubbles generated in the heat exchanger 11 for exhaust heat recovery.

Here, a specific structure of the heat exchanger 11 for exhaust heat recovery will be described.
As shown in FIGS. 4 and 5, the exhaust heat recovery heat exchanger 11 includes a heat exchanger main body 41 and a plurality of partitions arranged at intervals in the heat exchange space in the heat exchanger main body 41. Plates 42 and 43. The plurality of partition plates 42 and 43 include a plurality of first flow paths 44 constituting the primary side heat exchange passage portion 11a through which exhaust gas flows and a plurality of second passages constituting the secondary side heat exchange passage portion 11b through which hot water flows. Two flow paths 45 are alternately formed.

  An exhaust gas inlet 46 opened in a rectangular shape is provided at the upper end of the heat exchanger body 41, and the upstream side of the plurality of first flow paths 44 is in communication with the exhaust gas inlet 46. The exhaust gas inlet 46 is connected to the downstream end of the upstream passage portion 9 a extending in the vertical direction of the exhaust passage 9.

  An exhaust gas outlet 47 opened in a rectangular shape is provided at the lower end of the heat exchanger body 41, and downstream sides of the plurality of first flow paths 44 are in communication with the exhaust gas outlet 47. The exhaust gas outlet 47 is connected to the upstream end of the downstream passage portion 9 b extending in the vertical direction of the exhaust passage 9.

  A hot water inflow pipe 48 extending in the horizontal direction is provided at the lower end of the side surface of the heat exchanger main body 41, and the lower end of the heat exchanger main body 41 communicates with each upstream side of the plurality of second flow paths 45. An inflow manifold 51 is provided. Upstream sides of the plurality of second flow paths 45 are connected to a hot water inflow pipe 48 via an inflow manifold 51. The hot water inflow pipe 48 is connected to the downstream end of a forward passage 25 a extending in the horizontal direction of the hot water circulation circuit 25.

  A hot water outflow pipe 49 extending in the horizontal direction is provided at the upper end of the side surface of the heat exchanger main body 41, and the upper end of the heat exchanger main body 41 communicates with each downstream side of the plurality of second flow paths 45. An outflow manifold 52 is provided. Downstream sides of the plurality of second flow paths 45 are communicated with a hot water outflow pipe 49 via an outflow manifold 52. The hot water outlet pipe 49 is connected to an upstream end of a return side passage 25 b extending in the horizontal direction of the hot water circulation circuit 25.

  When exchanging heat between the exhaust gas and hot water, the exhaust gas (for example, 200 ° C.) from the upstream passage portion 9a of the exhaust passage 9 flows into the plurality of first flow paths 44 from the exhaust gas inlet 46, The exhaust gas after heat exchange (for example, 20 to 30 ° C.) that flows downward through the plurality of first flow paths 44 and flows out from the exhaust gas outlet 47 passes through the downstream passage portion 9 b of the exhaust passage 9 to the outside. Discharged. Hot water (for example, 15 to 20 ° C.) from the forward passage 25a of the hot water circulation circuit 25 flows into the plurality of second flow paths 45 from the hot water inflow pipe 48 and flows upward through the plurality of second flow paths 45. Hot water (for example, 80 ° C.) flowing out from the outflow pipe 49 is returned to the hot water storage tank 21 through the return side passage 25 b of the hot water circulation circuit 25.

  Thus, the exhaust gas flows downward through the plurality of first flow paths 44 (primary side heat exchange passage portions 11a), and hot water flows into the plurality of second flow paths 45 (secondary side heat exchange passage portions 11b). As a result, the heat exchange is performed between the exhaust gas and the hot water. When heat exchange is performed by the heat exchanger 11 for exhaust heat recovery, the water vapor contained in the exhaust gas is cooled and condensed to become condensed water, and this condensed water is recovered by the water treatment means 12.

  By the way, the hot water sent from the hot water storage tank 21 through the outward passage 25a is heated by the exhaust heat recovery heat exchanger 11 as described above, and returned to the hot water storage tank 21 through the return side passage 25b. Dissolved oxygen or the like in the hot water heated by the exhaust heat recovery heat exchanger 11 becomes bubbles, and these bubbles return into the return heat passage 11 in the exhaust heat recovery heat exchanger 11 or in the vicinity of the exhaust heat recovery heat exchanger 11. It may stay in 25b. In this case, the heat transfer area of the heat exchanger 11 for exhaust heat recovery decreases, the amount of heat exchange in the heat exchanger 11 for exhaust heat recovery decreases, and the heat exchanger 11 for exhaust heat recovery and the return Corrosion occurs at the boundary between the gas and liquid in the side passage 25b. Therefore, the fuel cell cogeneration 1 of the present invention executes bubble removal control in order to discharge such bubbles.

  Next, the bubble removal control for discharging bubbles from the exhaust heat recovery heat exchanger 11 automatically performed by the control unit 32 during the operation of the fuel cell cogeneration system 1 is based on the flowchart of FIG. I will explain. In the figure, the symbol Si (i = 1, 2,...) Indicates each step. The control program for the bubble removal control is stored in the control unit 32 in advance.

  In the flowchart of FIG. 6, when this control is started, first, in S1, it is determined whether or not the fuel cell cogeneration 1 is in operation. If the fuel cell cogeneration 1 is in operation and the exhaust heat recovery operation is in progress, that is, if the determination of S1 is Yes, the process proceeds to S2, and if the determination of S1 is No, S1 is repeated.

  Next, in S2, the control unit 32 reads the detection signals of the circulating hot water temperature sensor 37c on the heat exchanger inlet side and the circulating hot water temperature sensor 37d on the heat exchanger outlet side, and recovers exhaust heat based on the detection signals. The inlet hot water temperature and outlet hot water temperature of the heat exchanger 11 are calculated, and a signal from an encoder provided in the circulation pump 36 is read, and the current rotational speed of the circulation pump 36 is calculated based on the encoder signal. To S3.

  Next, in S3, it is determined whether or not the heat exchange amount in the exhaust heat recovery heat exchanger 11 has decreased, and if the heat exchange amount in the exhaust heat recovery heat exchanger 11 has decreased (predetermined condition established) Time), that is, if the determination of S3 is Yes, the process proceeds to S4, and if the heat exchange amount in the heat exchanger 11 for exhaust heat recovery has not decreased, that is, if the determination of S3 is No, S1 Repeat S3.

  In S3, a decrease in the heat exchange amount in the exhaust heat recovery heat exchanger 11 is determined based on the calculated inlet hot water temperature, outlet hot water temperature, and the rotation speed of the circulation pump 36. For example, the rotational speed of the circulation pump 36 is controlled so that the outlet hot water temperature becomes 80 ° C., but the outlet hot water must be reduced unless the rotational speed of the circulation pump 36 is lowered from a predetermined value and the flow rate of the hot water circulation circuit 25 is lowered. When the temperature cannot be maintained at 80 ° C., it is determined that the heat exchange amount in the heat exchanger 11 for exhaust heat recovery has decreased. The control unit 32, the circulating hot water temperature sensor 37c on the inlet side of the heat exchanger, the circulating hot water temperature sensor 37d on the outlet side of the heat exchanger, the encoder of the circulating pump 36, the control program S2, S3 of the bubble removal control, etc. It corresponds to.

  Next, in S4, the output capacity of the circulation pump 36 is set to the maximum, the flow rate of the circulation pump 36 is temporarily increased, and the process proceeds to S5. That is, if bubbles remain in the exhaust heat recovery heat exchanger 11 or the return side passage 25b in the vicinity of the exhaust heat recovery heat exchanger 11, the heat transfer area in the exhaust heat recovery heat exchanger 11 is reduced. The amount of heat exchange in the exhaust heat recovery heat exchanger 11 decreases and the output capacity of the circulation pump 36 is set to the maximum, and bubbles are exhausted from the exhaust heat recovery heat exchanger 11 at once. To do.

  For example, during normal operation, the circulation pump 36 is controlled so that the flow rate of hot water flowing through the return side passage 25b of the hot water circulation circuit 25 is about 150 mL / min in the case of 80 ° C. control, for example. At the flow rate, there is no urging force to discharge the accumulated bubbles. Furthermore, if the amount of heat exchange in the heat exchanger 11 for exhaust heat recovery decreases, the flow rate of the return side passage 25b is reduced, so that it becomes more difficult to discharge bubbles. For this reason, when it is determined that the amount of heat exchange in the heat exchanger 11 for exhaust heat recovery has decreased, for example, the flow rate of hot water flowing through the return side passage 25b is about the flow rate of the circulating pump 36 so that the output capacity becomes maximum. It is controlled so as to be 5 L / min, and the bubbles are swept away into the hot water storage tank 21 at once. The flow rate value of the return side passage 25b is merely an example and can be changed as appropriate.

  Next, in S5, it is determined whether or not a fixed time has elapsed since the output capability of the circulation pump 36 was set to the maximum in S4. When the fixed time has passed, that is, the time (for example, about 5 seconds) during which bubbles are discharged from the exhaust heat recovery heat exchanger 11 or the return side passage 25b in the vicinity of the exhaust heat recovery heat exchanger 11 ) If it has elapsed, the determination in S5 is Yes and the process proceeds to S6. If S5 is No, repeat S5.

  Next, in S6, the circulation pump 36 is returned to the normal operation state. That is, the control unit 32 sets the circulation pump 36 to the rotation speed during normal operation, returns to S1, and repeatedly executes this series of control while the fuel cell cogeneration 1 is in the exhaust heat recovery operation.

Next, the operation and effect of the fuel cell cogeneration 1 of the present invention will be described.
During the operation of the fuel cell cogeneration 1, when it is determined that the heat exchange amount in the heat exchanger 11 for exhaust heat recovery has decreased, the control unit 32 executes bubble removal control to discharge bubbles. When the bubbles are discharged by the bubble removal control, it is possible to suppress the reduction of the heat transfer area of the heat exchanger 11 for exhaust heat recovery 11 and to prevent the gas-liquid boundary in the heat exchanger 11 for exhaust heat recovery. The position can be changed without always being constant.

  As described above, when the amount of heat exchange decreases, bubbles generated in the secondary heat exchange passage portion 11b of the heat exchanger 11 for exhaust heat recovery by temporarily increasing the flow rate of the circulation pump 36. Is provided with a pump control means for performing bubble removal control for discharging the heat from the heat exchanger 11 for exhaust heat recovery, so that heat for exhaust heat recovery can be obtained at low cost by using an existing configuration without adding new parts. Air bubbles generated in the exchanger 11 can be reliably removed, so that the heat exchange efficiency of the heat exchanger 11 for exhaust heat recovery can be improved and the fuel cell power generator 2 can be operated safely. Can do.

  In addition, a determination unit that determines a decrease in the amount of heat exchange in the heat exchanger 11 for exhaust heat recovery is provided, and the predetermined condition is satisfied when the determination unit determines that the amount of heat exchange has decreased. It can be determined that bubbles have accumulated in the heat recovery heat exchanger 11, and when the amount of heat exchange in the exhaust heat recovery heat exchanger 11 is reduced, the bubble removal operation can be executed reliably. .

  Next, Example 2 in which the fuel cell cogeneration 1 of Example 1 is partially changed will be described. In the first embodiment, the bubble removal control is executed based on the determination of the decrease in the heat exchange amount in the heat exchanger 11 for exhaust heat recovery. However, in the second embodiment, the bubble removal control is periodically executed. To do.

  The bubble removal control for discharging the bubbles from the exhaust heat recovery heat exchanger 11 automatically performed by the control unit 32 during the operation of the fuel cell cogeneration system 1 will be described with reference to the flowchart of FIG. . In the figure, reference sign Si (i = 11, 12,...) Indicates each step. The control program for the bubble removal control is stored in the control unit 32 in advance.

  In the flowchart of FIG. 7, when this control is started, it is first determined in S11 whether or not the fuel cell cogeneration 1 is in operation. If the fuel cell cogeneration 1 is in operation and is in the exhaust heat recovery operation, that is, if the determination in S11 is Yes, the process proceeds to S12, and if the determination in S11 is No, S11 is repeated.

  Next, in S12, time measurement by a timer is started, and the process proceeds to S13. In S13, it is determined whether a set time has elapsed. When the set time has elapsed, that is, when a preset periodic time (for example, 1 hour) has been reached (when a predetermined condition is satisfied), the determination in S13 is Yes, the process proceeds to S14, and the determination in S13 If No, repeat S13.

  Next, in S14, the control unit 32 sets the output capacity of the circulation pump 36 to the maximum, temporarily increases the flow rate of the circulation pump 36, and proceeds to S15 as in the second embodiment.

  Next, in S15, it is determined whether or not a certain time has elapsed since the output capability of the circulation pump 36 was set to the maximum in S14. If the fixed time has elapsed, that is, if the time (for example, about 5 seconds) during which bubbles are discharged from the return side passage 25b in the vicinity of the exhaust heat recovery heat exchanger 11 has passed, the determination in S15 Is Yes, the process proceeds to S16, and S15 is repeated when the determination of S15 is No.

  Next, in S16, the circulation pump 36 is returned to the normal operation state. That is, the control unit 32 sets the circulation pump 36 to the rotation speed during normal operation, resets the timer, returns to S11, and repeats this series of control while the fuel cell cogeneration 1 is in the exhaust heat recovery operation. Run.

  In this way, when the preset periodic time comes (for example, every hour), the secondary side heat exchange of the heat exchanger 11 for exhaust heat recovery 11 is temporarily increased by increasing the flow rate of the circulation pump 36. Since the control unit 32 that performs bubble removal control for discharging the bubbles generated in the passage portion 11b from the exhaust heat recovery heat exchanger 11 is provided, the secondary heat exchange passage portion of the exhaust heat recovery heat exchanger 11 is provided. The bubbles generated in 11b can be periodically removed. Other configurations, operations, and effects are the same as those of the first embodiment, and thus description thereof is omitted.

Next, a mode in which the above embodiment is partially changed will be described.
[1] If the determination means of the first embodiment can determine a decrease in the amount of heat exchange in the heat exchanger 11 for exhaust heat recovery, the sensors used for the determination are circulating hot water at the inlet side of the heat exchanger. It is not necessary to limit to the temperature sensor 37c, the circulating hot water temperature sensor 37d on the outlet side of the heat exchanger, the encoder of the circulation pump 36, and the like, and can be changed as appropriate, and the heat exchange amount calculation method can also be changed as appropriate.

[2] In the second embodiment, the bubble removal control by the control unit 32 is performed once a day as a predetermined periodic time regardless of the exhaust heat recovery operation of the fuel cell cogeneration 1. It may be executed about once a month, and the frequency and timing of the bubble removal control need not be particularly limited and can be changed as appropriate.

[3] In addition, those skilled in the art can implement the present invention in various forms with various modifications without departing from the spirit of the present invention, and the present invention includes such modifications. It is.

DESCRIPTION OF SYMBOLS 1 Fuel cell cogeneration system 5 Fuel cell power generation module 11 Heat exchanger 11b for waste heat recovery Secondary side heat exchange passage 21 Hot water storage tank 32 Control unit 36 Circulation pump

Claims (3)

An exhaust passage through which exhaust gas from the fuel cell power generation module flows, a heat exchanger for exhaust heat recovery disposed in the exhaust passage and for exchanging heat between the exhaust gas after power generation and the heat medium, and the exhaust heat In a fuel cell cogeneration system comprising a circulation pump for circulating the heat medium through a recovery heat exchanger,
Bubbles for discharging bubbles generated in the heat medium passage of the exhaust heat recovery heat exchanger from the exhaust heat recovery heat exchanger by temporarily increasing the flow rate of the circulation pump when a predetermined condition is satisfied A fuel cell cogeneration system comprising pump control means for performing removal control. A determination means for determining a decrease in the amount of heat exchange in the heat exchanger for exhaust heat recovery;
2. The fuel cell cogeneration system according to claim 1, wherein the predetermined condition is satisfied when the determination unit determines that the heat exchange amount has decreased. 2. The fuel cell cogeneration system according to claim 1, wherein the predetermined condition is established when a predetermined period is reached.