JP2020149776A - Fuel cell system - Google Patents

Abstract

To provide a technology capable of restraining generation of condensate water in the circulation passage of exhaust gas of a fuel cell.SOLUTION: A fuel cell system includes a fuel cell, a gas circulation part having a circulation passage component through which exhaust gas emitted from the fuel cell flows, and circulating reaction gas contained in the exhaust gas to the fuel cell through the circulation passage component, a temperature detection part for detecting inlet gas temperature representing the temperature of the exhaust gas on the inlet side of the circulation passage component, and outlet gas temperature representing the temperature of the exhaust gas on the outlet side of the circulation passage component, and a control section for controlling the fuel cell to generate electricity, and executing warm-up operation for raising temperature of the circulation passage component. The control section ends the warm-up operation when the absolute value of the difference of the outlet gas temperature and the inlet gas temperature becomes equal to or below a predetermined threshold temperature.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a fuel cell system.

For example, as disclosed in Patent Document 1, the reaction gas remaining in the exhaust gas discharged from the polymer electrolyte fuel cell (hereinafter, also simply referred to as “fuel cell”) in the fuel cell system. Is circulated in a fuel cell and used for power generation.

Japanese Unexamined Patent Publication No. 2017-199564

The exhaust gas of a fuel cell usually contains a large amount of water generated in the fuel cell. Therefore, in a fuel cell system that circulates exhaust gas to a fuel cell, for example, in a low temperature environment such as below freezing point, a large amount of condensed water in which the moisture in the exhaust gas is condensed is generated in the parts constituting the exhaust gas circulation flow path. There was a case that it ended up. When a large amount of such condensed water is generated, there is a problem that the circulation flow path of the exhaust gas is blocked, the power generation efficiency of the fuel cell is lowered, and it becomes difficult to execute the scavenging treatment of the fuel cell. .. Further, if the scavenging process at the time of stopping the operation of the fuel cell system cannot be sufficiently performed, there is a problem that the water remaining in the system freezes and it becomes difficult to start the fuel cell.

In the technique of Patent Document 1 described above, when the temperature of the hydrogen pump for circulating hydrogen in the exhaust gas to the fuel cell is lower than the threshold value, hydrogen is generated by warm-up operation that increases the calorific value of the motor that drives the hydrogen pump. It suppresses the condensation and freezing of water in the exhaust gas in the pump. However, when the temperature of the hydrogen pump itself is measured, the temperature of the locally cooled part may not be sufficiently reflected in the measurement result depending on the temperature distribution in the hydrogen pump. Therefore, there is a possibility that the moisture in the exhaust gas may be condensed or the condensed water may be frozen in the locally cooled portion. These problems are common not only to hydrogen pumps but also to parts through which the exhaust gas of fuel cells is distributed.

Further, the conditions under which the water contained in the exhaust gas is condensed are influenced not only by the temperature of the parts through which the exhaust gas flows, but also by the temperature of the fuel cell, the flow rate of the exhaust gas, and the outside air temperature. Therefore, it is not possible to fully grasp the temperature change of the exhaust gas in the part only by measuring the temperature of the part itself to be prevented from freezing, and the condensation of the water in the exhaust gas in the part and the freezing of the condensed water are caused. It may not be sufficiently suppressed.

The technique of the present disclosure can be realized in the following forms.

In this form, a fuel cell system is provided. The fuel cell system of this form includes a fuel cell that generates power by receiving the supply of the reaction gas, a gas supply unit that supplies the reaction gas to the fuel cell, and a circulation flow path component through which the exhaust gas discharged from the fuel cell flows. The gas circulation unit that circulates the reaction gas contained in the exhaust gas to the fuel cell through the circulation flow path component, and the inlet gas temperature representing the temperature of the exhaust gas on the inlet side of the circulation flow path component. A temperature detection unit that detects the temperature of the exhaust gas on the outlet side of the circulation flow path component, and a warm-up operation that causes the fuel cell to generate power to raise the temperature of the circulation flow path component. It includes a control unit to execute. After the start of the warm-up operation, the control unit ends the warm-up operation when the absolute value of the difference between the outlet gas temperature and the inlet gas temperature is equal to or less than a predetermined threshold temperature.
According to this form of the fuel cell system, it is determined whether or not the temperature of the circulation flow path component has been raised by the warm-up operation based on the amount of temperature change of the exhaust gas before and after passing through the circulation flow path component. Therefore, the temperature state of the entire exhaust gas flow path in the circulation flow path component can be appropriately determined, and the warm-up operation ends without the exhaust gas flow path in the circulation flow path component being heated to a desired temperature. It is possible to prevent the exhaustion.

The schematic diagram of the fuel cell system in 1st Embodiment. The explanatory view which shows the flow of the warm-up process of 1st Embodiment. The schematic diagram of the fuel cell system in 2nd Embodiment. The explanatory view which shows the flow of the warm-up process of 2nd Embodiment.

1. 1. First Embodiment:
FIG. 1 is a schematic view showing the configuration of the fuel cell system 100 according to the first embodiment. The fuel cell system 100 is mounted on a vehicle, for example. The fuel cell system 100 includes a fuel cell 10 that generates electricity by being supplied with fuel gas and an oxidant gas, which are reaction gases. The fuel cell system 100 supplies the electric power generated by the fuel cell 10 to an external load connected to the fuel cell system 100 and auxiliary machinery constituting the fuel cell system 100.

The fuel cell 10 is composed of, for example, a polymer electrolyte fuel cell, and generates electricity by an electrochemical reaction between hydrogen, which is a fuel gas, and oxygen, which is an oxidant gas. The fuel cell 10 has a stack structure in which a plurality of single cells 11 are laminated. Each single cell 11 is a power generation element capable of generating electricity by itself, and includes a membrane electrode assembly, which is a power generator in which electrodes are arranged on both sides of an electrolyte membrane, and two separators sandwiching the membrane electrode assembly. Have. The electrolyte membrane is composed of a solid polymer thin film that exhibits good proton conductivity in a wet state containing water inside.

The fuel cell system 100 includes a control unit 20 that controls the operation of the fuel cell system 100. The control unit 20 is composed of an ECU (Electronic Control Unit) including at least one processor and a main storage device. The control unit 20 exerts various functions for controlling the fuel cell system 100 by executing a program or an instruction read by the processor on the main storage device. At least a part of the function of the control unit 20 may be configured by a hardware circuit.

The control unit 20 controls the gas supply unit 30, the gas circulation unit 40, and the gas supply / discharge unit 50, which will be described later, to control the power generation of the fuel cell 10. Further, as will be described later, the control unit 20 executes a warm-up process for warming up the components of the fuel cell system 100 when a predetermined condition is satisfied in a low temperature environment. The control unit 20 provides the fuel cell system 100 with information necessary for operating control of the fuel cell system 100, such as the temperature and pressure of the reaction gas, the outside temperature, the rotation speed of the circulation pump 44 and the compressor 52, and the like. Obtained from sensors not shown.

The fuel cell system 100 further includes a gas supply unit 30, a gas circulation unit 40, and a gas supply / discharge unit 50 as components for controlling the supply of reaction gas to the fuel cell 10. The gas supply unit 30 supplies fuel gas to the anode of the fuel cell 10. The gas supply unit 30 includes a tank 31 for storing high-pressure fuel gas, a fuel gas pipe 32 connecting the tank 31 and the anode inlet of the fuel cell 10, a main stop valve 33, a regulator 34, and a supply device 35. , Equipped with. The main check valve 33, the regulator 34, and the supply device 35 are provided in the fuel gas pipe 32 in this order from the upstream side, which is the tank 31 side. The main stop valve 33 is composed of a solenoid valve that opens and closes under the control of the control unit 20. The main check valve 33 controls the outflow of fuel gas from the tank 31. The regulator 34 is a pressure reducing valve and adjusts the pressure in the fuel gas pipe 32 on the upstream side of the supply device 35. Under the control of the control unit 20, the supply device 35 periodically opens and closes to send fuel gas to the fuel cell 10. The supply device 35 is composed of, for example, an injector which is an electromagnetically driven on-off valve that opens and closes at a set drive cycle.

The gas circulation unit 40 has a function of circulating the fuel gas contained in the exhaust gas discharged from the anode of the fuel cell 10 to the fuel cell 10 and a function of discharging the wastewater contained in the exhaust gas to the outside of the fuel cell system 100. Have. The gas circulation unit 40 includes an exhaust gas pipe 41, a gas-liquid separation unit 42, a circulation pipe 43, a circulation pump 44, a drainage pipe 45, and a drainage valve 46. The exhaust gas pipe 41 is connected to the anode outlet of the fuel cell 10 and the inlet of the gas-liquid separation unit 42, and gas-liquid exhaust gas on the anode side including fuel gas and wastewater that have not been used for power generation at the anode. It leads to the separation part 42. The gas-liquid separation unit 42 separates the gas component and the liquid component from the exhaust gas flowing in through the exhaust gas pipe 41, and stores the liquid component as drainage in the state of liquid water. One of the outlets of the gas-liquid separation unit 42 is connected to the circulation pipe 43. The circulation pipe 43 connects the outlet of the gas-liquid separation unit 42 with a portion of the fuel gas pipe 32 on the downstream side of the supply device 35. A circulation pump 44 is provided in the circulation pipe 43. The gas-liquid separation unit 42 guides the gas component separated from the exhaust gas to the circulation pipe 43. The circulation pump 44 is driven under the control of the control unit 20 and sends out the gas component including the fuel gas guided to the circulation pipe 43 to the fuel gas pipe 32. The gas-liquid separation unit 42 is provided with another outlet in the storage unit in which the wastewater is stored, and the drainage pipe 45 is connected to the outlet. The drainage pipe 45 is provided with a drainage valve 46 that opens and closes under the control of the control unit 20. Normally, the control unit 20 closes the drain valve 46 and opens the drain valve 46 at a predetermined timing set in advance, so that the drainage stored in the gas-liquid separation unit 42 is discharged to the fuel cell through the drain pipe 45. It is discharged to the outside of the system 100.

The gas supply / discharge unit 50 has a function of supplying the oxidant gas to the cathode of the fuel cell 10 and a function of discharging the exhaust gas discharged from the cathode of the fuel cell 10 to the outside of the fuel cell system 100. In the first embodiment, oxygen contained in the outside air is supplied to the fuel cell 10 as an oxidant gas. The gas supply / discharge unit 50 includes a supply pipe 51, a compressor 52, an on-off valve 53, an exhaust gas pipe 56, and a pressure regulating valve 58. One end of the supply pipe 51 communicates with the outside air, and the other end is connected to the cathode inlet of the fuel cell 10. Under the control of the control unit 20, the compressor 52 compresses the outside air taken in from one end of the supply pipe 51 and sends it out to the on-off valve 53 provided on the other end side of the supply pipe 51. The on-off valve 53 is normally closed and opens by the pressure of the compressed gas sent out from the compressor 52 to allow the compressed gas to flow into the cathode of the fuel cell 10. The exhaust gas pipe 56 is connected to the cathode outlet and guides the exhaust gas discharged from the cathode of the fuel cell 10 to the outside of the fuel cell system 100. The pressure regulating valve 58 is provided in the exhaust gas pipe 56, and adjusts the back pressure on the cathode side of the fuel cell 10 under the control of the control unit 20.

The fuel cell system 100 further includes a temperature detection unit 60. In the gas circulation unit 40, the temperature detection unit 60 includes an inlet gas temperature Tin indicating the temperature of the exhaust gas on the inlet side of the circulation flow path component RP through which the exhaust gas circulated in the fuel cell 10 flows, and an outlet of the circulation flow path component RP. The outlet gas temperature Tout, which represents the temperature of the exhaust gas on the side, is detected. In the first embodiment, the circulation flow path component RP is a gas-liquid separation unit 42. The circulation flow path component RP does not have to be the gas-liquid separation section 42, and in other embodiments, it may be, for example, a specific portion in the exhaust gas pipe 41 or the circulation pipe 43.

In the first embodiment, the temperature detection unit 60 calculates the inlet gas temperature Tin and the outlet gas temperature Tout as estimated values by using the information acquired from the control unit 20. The temperature detection unit 60 acquires the temperature of the fuel cell 10, the outside air temperature, and the flow rate of the exhaust gas from the control unit 20 as information for calculating the estimated value. The temperature and the outside air temperature of the fuel cell 10 are obtained by, for example, the control unit 20 from a temperature sensor (not shown). The flow rate of the exhaust gas is calculated by the control unit 20 based on the rotation speed of the circulation pump 44. The control unit 20 may acquire the flow rate of the exhaust gas from a flow meter (not shown) provided in the exhaust gas pipe 41 or the circulation pipe 43.

The temperature detection unit 60 stores in advance a map or a mathematical formula in which the inlet gas temperature Tin is uniquely determined with respect to the temperature of the fuel cell 10, the outside air temperature, and the flow rate of the exhaust gas, and uses the map or mathematical formula to set the inlet gas temperature Tin. get. This map and mathematical formula show heat transfer in the exhaust gas flow path between the fuel cell 10 and the circulation flow path component RP, such as the specific heat of the parts constituting the exhaust gas flow path between the fuel cell 10 and the circulation flow path component RP. It reflects the characteristics. Further, the temperature detection unit 60 stores in advance a map or a mathematical formula in which the outlet gas temperature Tout is uniquely determined with respect to the acquired inlet gas temperature Tin, the outside air temperature, and the flow rate of the exhaust gas, and uses the map or formula to determine the outlet gas temperature. Get Tout. This map and mathematical formula reflect the heat transfer characteristics in the exhaust gas flow path formed by the circulation flow path component RP, such as the specific heat of the circulation flow path component RP. In another embodiment, the temperature detection unit 60 may acquire the measured values of the temperature sensors provided at the inlet and the outlet of the circulation flow path component RP as the inlet gas temperature Tin and the outlet gas temperature Tout. ..

FIG. 2 is an explanatory diagram showing a flow of warm-up processing in the first embodiment. In the fuel cell system 100, the warm-up process is executed in order to prevent the flow path of the exhaust gas from being blocked due to the condensation and freezing of the moisture in the exhaust gas in the circulation flow path component RP of the gas circulation unit 40. Will be done. The control unit 20 executes this warm-up process when the fuel cell 10 is started in a low temperature environment such as below freezing point, or when the timing to start the execution of the scavenging process of the fuel cell 10 is reached. .. The timing for starting the execution of the scavenging process is, for example, the end of operation of the fuel cell system 100.

In step S10, a warm-up operation for raising the temperature of the circulation flow path component RP is started. As a warm-up operation, the control unit 20 performs idling in which the fuel cell 10 generates electricity and stands by while maintaining a state in which the exhaust gas flows into the circulation flow path component RP. In the warm-up operation, even if low-efficiency power generation is executed in which the ratio of the supply amount of the oxidant gas to the fuel gas is reduced as compared with the normal operation to increase the heat generation amount per unit time of the fuel cell 10. Good. Further, in the warm-up operation, a heater for raising the temperature of the circulation flow path component RP may be driven.

In step S20, the control unit 20 acquires the current inlet gas temperature Tin and the outlet gas temperature Tout from the temperature detection unit 60. In step S30, the control unit 20 determines whether or not the absolute value of the difference obtained by subtracting the inlet gas temperature Tin from the outlet gas temperature Tout is equal to or less than the threshold temperature α ° C. determined experimentally in advance. The threshold temperature α ° C. corresponds to an allowable value for the amount of temperature decrease of the exhaust gas when passing through the circulation flow path component RP, and may be, for example, a value of about 0 to 5 ° C.

When the absolute value of the difference between the outlet gas temperature Tout and the inlet gas temperature Tin is higher than the threshold temperature α ° C., the control unit 20 continues the warm-up operation as it is, and in steps S20 to S30 in a predetermined control cycle. Repeat the process. When the absolute value of the difference between the outlet gas temperature Tout and the inlet gas temperature Tin is higher than the threshold temperature α ° C, the temperature of the circulation flow path component RP is not sufficiently high, and the circulation flow path component RP and the exhaust gas This is because the amount of heat exchange between them is expected to remain large.

On the other hand, when the absolute value of the difference between the outlet gas temperature Tout and the inlet gas temperature Tin is equal to or less than the threshold temperature α ° C., the control unit 20 ends the warm-up process and shifts to the next control phase. If the warm-up process is executed, for example, when the fuel cell 10 is started, the control unit 20 starts normal operation control of the fuel cell 10 as the next control phase. If the warm-up process is executed as a preparatory process before the scavenging process, the control unit 20 starts executing the scavenging process as the next control phase. If the absolute value of the difference between the outlet gas temperature Tout and the inlet gas temperature Tin is equal to or less than the threshold temperature α ° C, the temperature of the circulation flow path component RP rises sufficiently and the heat between the circulation flow path component RP and the exhaust gas is increased. It is expected that the exchange amount will be smaller. Therefore, as the next control phase, even if the normal operation control and the scavenging process of the fuel cell 10 are started and the flow rate of the exhaust gas from the fuel cell 10 increases, the moisture in the exhaust gas in the circulation flow path component RP remains. Condensation beyond the permissible amount is suppressed.

As described above, according to the fuel cell system 100 of the first embodiment, the temperature difference of the exhaust gas between the inlet and the outlet of the circulation flow path component RP causes the exhaust gas in the circulation flow path component RP to be warmed up. It is determined whether or not the temperature of the circulation flow path component RP has been raised until the amount of heat exchange is sufficiently reduced. Therefore, it is possible to determine the temperature of the circulation flow path component RP that reflects the temperature state of the entire flow path of the exhaust gas in the circulation flow path component RP, and the temperature of the exhaust gas flow path in the circulation flow path component RP is desired. It is possible to prevent the warm-up operation from ending without raising the temperature. Further, since the temperature state of the entire flow path of the exhaust gas in the circulation flow path component RP can be determined, erroneous determination is suppressed as compared with the case where the temperature sensor is provided only at one part of the circulation flow path component RP. Therefore, the warm-up becomes insufficient, and in the normal operation of the fuel cell 10 or the scavenging process executed after the warm-up process, the exhaust gas flow path is blocked by the condensed moisture in the circulation flow path component RP. Scavenging is suppressed. Further, since the scavenging process can be effectively executed by suppressing the blockage of the flow path of the exhaust gas, it becomes difficult to start the fuel cell 10 due to the freezing of the water remaining in the fuel cell system 100. Is suppressed.

2. 2. Second embodiment:
FIG. 3 is a schematic view showing the configuration of the fuel cell system 100A in the second embodiment. The configuration of the fuel cell system 100A of the second embodiment is substantially the same as that of the fuel cell system 100 of the first embodiment except for the points described below. In the fuel cell system 100A, the circulation pump 44 is the circulation flow path component RP for which the inlet gas temperature Tin and the outlet gas temperature Tout are detected by the temperature detection unit 60. In the fuel cell system 100A, temperature sensors 61 and 62 for detecting the temperature of the exhaust gas are provided at the inlet and outlet of the circulation pump 44, respectively, and the temperature detection unit 60 uses the measured value of the inlet side temperature sensor 61 as the inlet gas. It is acquired as the temperature Tin, and the measured value of the outlet side temperature sensor 62 is acquired as the outlet gas temperature Tout.

FIG. 4 is an explanatory diagram showing a flow of warm-up processing executed in the fuel cell system 100 of the second embodiment. The warm-up process of the second embodiment is executed to raise the temperature of the circulation pump 44, which is the circulation flow path component RP, and the process of steps S23 and S25 is added, and instead of the determination in step S30. The warm-up process is almost the same as that of the first embodiment except that the determination in step S35 is executed.

In step S23, the control unit 20 acquires the adiabatic compression temperature rise amount ΔT representing the amount of temperature rise of the exhaust gas due to the adiabatic compression by the circulation pump 44. The control unit 20 uses, for example, an adiabatic compression with respect to the current rotation speed of the circulation pump 44 by using a pre-prepared map in which a unique relationship between the rotation speed of the circulation pump 44 and the adiabatic compression temperature rise amount ΔT is defined. The amount of temperature rise ΔT is acquired.

In step S25, the control unit 20 calculates the corrected outlet gas temperature TCout by correcting the outlet gas temperature Tout of the circulation pump 44 acquired in step S20 by using the adiabatic compression temperature rise amount ΔT. Specifically, the control unit 20 calculates the corrected outlet gas temperature TCout by subtracting the adiabatic compression temperature rise amount ΔT from the outlet gas temperature Tout.

In step S35, the control unit 20 determines whether or not the absolute value of the difference obtained by subtracting the inlet gas temperature Tin from the corrected outlet gas temperature TCout is equal to or less than the threshold temperature β ° C. determined experimentally in advance. When the absolute value of the difference between the corrected outlet gas temperature TCout and the inlet gas temperature Tin is higher than the threshold temperature β ° C., the control unit 20 continues the warm-up operation as it is, and steps S20 to S20 in a predetermined control cycle. The process of S35 is repeated. On the other hand, when the absolute value of the difference between the corrected outlet gas temperature TCout and the inlet gas temperature Tin is equal to or less than the threshold temperature β ° C., the control unit 20 ends the warm-up process and shifts to the next control phase. To do. The threshold temperature β ° C. corresponds to an allowable amount of temperature corresponding to the amount of heat of the exhaust gas absorbed by the circulation pump 44 when passing through the circulation pump 44, and may be, for example, a value of about 0 to 5 ° C.

The outlet gas temperature Tout is equivalent to the value obtained by subtracting the amount of temperature decrease of the exhaust gas due to heat exchange between the exhaust gas and the circulation pump 44 from the inlet gas temperature Tin and adding the amount of temperature rise due to the adiabatic compression of the exhaust gas by the circulation pump 44. To do. Therefore, the absolute value of the difference between the corrected outlet gas temperature TCout and the inlet gas temperature Tin, which is obtained by subtracting the adiabatic compression temperature rise amount ΔT from the outlet gas temperature Tout, is the exhaust gas excluding the influence of the adiabatic compression in the circulation pump 44. It is a value representing the amount of temperature decrease of the exhaust gas due to heat exchange between the gas and the circulation pump 44. In step S35, since the absolute value of the difference between the corrected outlet gas temperature TCout and the inlet gas temperature Tin is used, the temperature state of the circulation pump 44 can be determined more accurately. Therefore, it is possible to prevent the circulation pump 44, which is actually in a low temperature state, from being erroneously determined to have been sufficiently heated due to the temperature rise of the exhaust gas due to the adiabatic compression of the circulation pump 44.

In addition, according to the fuel cell system 100A of the second embodiment, various actions and effects similar to those described in the first embodiment can be obtained.

3. 3. Other embodiments:
In the fuel cell system 100A of the second embodiment described above, the warm-up process may be executed in the same flow as that of the first embodiment. In this case, it is desirable that the threshold temperature α ° C. is a value that reflects the amount of temperature rise due to adiabatic compression in the circulation pump 44.

10 ... Fuel cell, 11 ... Single cell, 20 ... Control unit, 30 ... Gas supply unit, 31 ... Tank, 32 ... Fuel gas piping, 33 ... Main stop valve, 34 ... Regulator, 35 ... Supply device, 40 ... Gas circulation Section, 41 ... Exhaust gas piping, 42 ... Gas / liquid separation section, 43 ... Circulation piping, 44 ... Circulation pump, 45 ... Drainage piping, 46 ... Drain valve, 50 ... Gas supply / exhaust section, 51 ... Supply piping, 52 ... Compressor, 53 ... On-off valve, 56 ... Exhaust gas piping, 58 ... Pressure regulating valve, 60 ... Temperature detector, 61 ... Inlet side temperature sensor, 62 ... Outlet side temperature sensor, 100 ... Fuel cell system, 100A ... Fuel cell system, RP ... Circulation Flow path parts

Claims (1)

It ’s a fuel cell system,
A fuel cell that generates electricity by receiving the supply of reaction gas,
A gas supply unit that supplies the reaction gas to the fuel cell,
A gas circulation unit having a circulation flow path component through which the exhaust gas discharged from the fuel cell flows, and circulating the reaction gas contained in the exhaust gas to the fuel cell through the circulation flow path component.
A temperature detection unit that detects an inlet gas temperature representing the temperature of the exhaust gas on the inlet side of the circulation flow path component and an outlet gas temperature representing the temperature of the exhaust gas on the outlet side of the circulation flow path component.
A control unit that executes warm-up operation to generate electricity in the fuel cell and raise the temperature of the circulation flow path component,
With
After the start of the warm-up operation, the control unit ends the warm-up operation when the absolute value of the difference between the outlet gas temperature and the inlet gas temperature is equal to or less than a predetermined threshold temperature. ..

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