CN103050723A - Cathode exhaust recirculating system for proton exchange membrane fuel cell - Google Patents

Abstract

An air system for a proton exchange membrane fuel cell belongs to the technical field of new energy vehicles, and is characterized in that an exhaust recirculation circuit is used to reintroduce the gas discharged from the cathode outlet of the electric stack to the inlet circuit of the electric stack. The total flow, total pressure and oxygen flow into the stack can be individually adjusted. While limiting the single-chip voltage of the stack, it can effectively avoid the phenomenon of water flooding or film drying of the stack; it can quickly dry the stack during shutdown. The internal liquid water prevents the stack from being damaged due to the residual water freezing in the low temperature condition; the entire pipeline can be filled with nitrogen during shutdown to avoid oxygen entering the anode and corroding the stack during long-term shutdown; Increases the amount of fresh air entering the system and reduces the load on mechanical and chemical filters. These measures can effectively improve the life and durability of fuel cells. At the same time, the bypass control of heat dissipation and humidification is introduced, which can speed up the warm-up speed of the stack under low temperature conditions.

Description

A cathode exhaust gas recirculation system for proton exchange membrane fuel cells

technical field

The invention relates to an air system of a proton exchange membrane fuel cell, in particular to an air system of an advanced proton exchange membrane fuel cell which introduces cathode exhaust gas recirculation technology, and belongs to the technical field of new energy vehicles.

Background technique

Proton Exchange Membrane Fuel Cell (PEMFC for short) is particularly favored by people for its advantages of high efficiency and zero emission. The fuel cell power generation system is an electrochemical device that directly converts chemical energy into electrical energy. The energy conversion process is not limited by the Carnot cycle, and the theoretical efficiency is relatively high. The fuel it consumes is hydrogen, the reaction product is water, and the harmful emissions are zero. It is one of the cleanest energy sources. Therefore, the fuel cell power generation system can be used in fields such as backup power stations, electric vehicles and mobile power supplies.

The fuel cell power generation system includes several main components, as shown in Figure 1, the fuel cell stack is its core, and the periphery of the stack also includes a hydrogen system, an air system, a humidification system, a cooling system, a power output system and a control system. system and other accessory systems. The hydrogen system is mainly responsible for providing hydrogen supply to the stack, and the pressure and flow of hydrogen entering the stack need to be adjusted according to the operating conditions; the air system is to provide an appropriate amount of oxidant, that is, air, for the stack, and the air entering the stack needs to be adjusted according to the working conditions The temperature, pressure and flow rate; the humidification system is to ensure that the humidity of the air entering the stack is within a certain range. Too dry and too humid will have adverse effects on the proton exchange membrane and the stack, so it is necessary to control the air entering the stack. Humidity control; the cooling system maintains the stack temperature at an appropriate level through coolant circulation to ensure stable and reliable operation of the stack; the power output system adjusts the output voltage and current of the stack through a DC/DC device. Change rate; the control system is the "brain" of the entire fuel cell power generation system, which optimizes and controls the various subsystems around the stack, so that the stack is in the best working condition and ensures long-term stable and reliable operation of the stack.

A typical fuel cell air system is composed of air compressor, radiator, humidifier, condenser and other parts, as shown in Figure 1. The ambient air enters the radiator after being compressed by the air compressor, and then enters the humidifier for humidification after being cooled by the radiator. After humidification, it enters the stack for electrochemical reaction, and the oxygen on the cathode side will chemically react with the hydrogen ions from the anode. , water (gas or liquid) is produced while outputting electric energy, and most of it flows out from the cathode air side, so the oxygen content of the cathode air after participating in the reaction decreases, and the water content (humidity) increases, and the air at the outlet of the stack is recovered by the condenser After the moisture is discharged into the environment through the flow control valve 2. The air system can control the air flow and air pressure entering the stack through the coordinated control of the air compressor and flow control valves 1 and 2, adjust the intake air temperature through the radiator, and control the intake air humidity through the humidifier.

According to the working principle and performance characteristics of PEMFC, the total amount of oxygen in the air entering the stack and the amount of oxygen participating in the reaction are called excess coefficient or equivalence ratio. The equivalence ratio of general vehicle fuel cells is between 1.5 and 3. . Obviously, the air flow rate and excess coefficient entering the stack are coupled with the total amount of air, and will vary with the output power of the fuel cell power generation system. At the same time, since the water (gas or liquid) generated by the internal reaction of the stack needs to be taken out through the cathode reaction channel, if the generated liquid water is not removed in time, the generated water will block the flow channel, which is the so-called flooding phenomenon, causing the stack to Performance decline affects the use of fuel cells. In order to improve the drainage capacity, it is necessary to increase the flow rate or velocity of the air in order to blow off the liquid water smoothly. At idle speed or light load, since the amount of water generated is relatively small, if the air flow rate is maintained at a high level, it is easy to dry up the water on the flow channel and the surface of the proton exchange membrane, resulting in the membrane being too dry and performance degradation; The small air flow rate is not easy to blow away the liquid water in the flow channel and cause flooding. Therefore, at idle speed or small load, the total amount of intake air cannot be reduced all the time, which leads to the total amount of oxygen or the equivalence ratio cannot be continuously reduced, and the excess coefficient is often kept at a high level, which also leads to fuel consumption at idle speed or small load. The battery voltage is high (0.9V~1.2V). According to related research, higher operating voltage (0.9V~1.2V) is extremely detrimental to the life of fuel cells. Studies have shown that under idling or light load conditions, if the oxygen equivalent ratio is reduced, the output voltage of the fuel cell can be effectively reduced, thereby ensuring the service life of the fuel cell.

How to make the cathode have a high gas pressure and flow rate, while ensuring its temperature and humidity are in the appropriate range, and also ensure that the oxygen content (partial pressure) in it is low, so that the output voltage of the fuel cell is at a low level , which contributes to fuel cell durability, is a challenge in air system design. In the current fuel cell air system shown in Figure 1, there is no ability to adjust the total air pressure and oxygen content separately.

Since the cathode reactant of the vehicle fuel cell is air from the atmosphere, and the humidity and temperature conditions of the atmosphere vary greatly with latitude, altitude and seasons, etc., high temperature and high humidity (close to 100% relative humidity) may occur, High temperatures and low humidity (near 0% relative humidity) can also occur. Another shortcoming of the air system shown in Figure 1 is that it cannot satisfy the ability of the fuel cell to flexibly adjust the temperature and humidity under extreme working conditions: in a high-temperature and low-humidity working environment, if the fuel cell works at idle speed and small Membrane drying is prone to occur under load conditions; in high temperature and high humidity working environments, fuel cells are prone to flooding if they work for a long time under heavy load conditions.

Another shortcoming of the air system shown in Figure 1 is that after shutdown, the oxygen in the entire air system pipeline cannot be completely removed, and the air system pipeline is in an oxygen-enriched state when the fuel cell is standing still. After the anode hydrogen is cut off, as the standing time increases, the oxygen on the cathode side gradually consumes the hydrogen in the anode, and then enters the anode through the proton exchange membrane, making the anode also in an oxygen-enriched state. This oxygen-rich state will accelerate the decline of the stack, making the life of the fuel cell significantly shortened.

Another disadvantage of the air system shown in Figure 1 is that, in order to ensure the stack drainage and other functions, more air from the atmosphere needs to enter the stack. Due to the presence of impurities such as particles and sulfur in the atmosphere, these impurities will speed up the stack. Therefore, special mechanical and chemical filters are required to filter out these impurities; increased air flow means that the volume and cost of mechanical and chemical filters increase, or the attenuation of their effective life is accelerated.

Contents of the invention

In view of the above problems, the present invention provides an air system design capable of realizing cathode exhaust gas recirculation, which can precisely control the condition parameters such as air pressure, total flow, temperature, humidity and oxygen content entering the stack, thereby providing a high level of support for the operation of the stack. Ideal working conditions can improve the stack efficiency and extend the life of the stack, accelerate the warm-up process of the stack under low temperature conditions, and improve the humidification effect of the stack under low humidity conditions.

One of the features of the present invention is:

A cathode exhaust gas recirculation system for a proton exchange membrane fuel cell is characterized in that it is based on computer-aided control to realize the control of air pressure, total air flow, air temperature, air humidity and air content entering the stack. The cathode exhaust gas recirculation system with synchronous control of the oxygen amount is suitable for the maximum working pressure greater than 1.5bar, including the control part and the cathode exhaust gas recirculation part, of which:

The control part includes: a controller, a vacuum pump and a vacuum tank, and seven control valves connected in series by solenoid valves and vacuum valves. There are also sensor groups composed of multiple temperature sensors, humidity sensors and pressure sensors. Denoted by S, the sensor signal is sent to the controller, where,

Each vacuum valve adopts a vacuum diaphragm valve, and a position sensor is installed on the valve stem to realize precise control of the valve flow; the signal input ends of each solenoid valve are connected in parallel and connected with the control signal input ends of the controller and the vacuum pump through a pressure sensor respectively. connected, the controller adjusts the duty cycle of each solenoid valve through the control end of each solenoid valve to adjust the vacuum degree of each vacuum valve;

Cathode exhaust gas recirculation section, including mechanical and chemical filtration devices, intake and exhaust circuits and exhaust gas recirculation circuits, where:

The intake and exhaust circuit includes an intake passage and an exhaust passage, where:

The air intake path starts from the air outlet of the mechanical and chemical filter device that is open to the atmosphere, and contains in sequence: the first sensor group S1, the air flow sensor, the first control valve V1, the second sensor group S2, the air compressor, the second Control valve V2, radiator, fourth control valve V4, humidifier and the air inlet of electric stack, there is also a third control valve V3 on the bypass circuit of the radiator, and the humidifier bypass There is also a fifth control valve V5 on the circuit, wherein the second control valve V2 and the third control valve V3 are an intake air temperature control valve group that realizes closed-loop control of the cathode gas temperature entering the stack, and the fourth control valve V4 and The fifth control valve V5 is a gas humidity control valve group that realizes the closed-loop control of the cathode gas humidity entering the stack;

The exhaust path starts from the air outlet of the electric stack, and sequentially contains the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4 and the seventh control valve V7;

The exhaust gas recirculation circuit is located before the air compressor, starting from the output end of the fourth sensor group S4, and ending at the inlet of the air compressor, communicating the intake circuit and the exhaust circuit, A line is formed from the air outlet of the stack to pass through the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4, the sixth control valve V6 on the branch road, and the air compressor , the second control valve V2, the radiator, the third control valve V3, the fourth control valve V4, the fifth control valve V6 and the humidifier reach the exhaust gas recirculation circuit of the stack air inlet, wherein:

The sixth control valve V6, the first control valve V1, and the seventh control valve V7 are a group that can flexibly distribute the gas volume flow and the ratio of oxygen components for recirculation, so as to adjust the total gas flow, total pressure, control valves for oxygen partial pressure purposes;

The sixth control valve V6, the first control valve V1, the air flow sensor and the oxygen sensor are components that realize the closed-loop feedback control of the oxygen content of the entire air circuit;

The first control valve V1 in the fully closed state, the seventh control valve V7 and the sixth control valve V6 in the fully open state constitute a shutdown control valve group with an exhaust gas recirculation ratio of 100%;

The first control valve V1, the sixth control valve V6, and the seventh control valve V7 in the normally closed state constitute a set of shutdown and storage control valve groups;

The second control valve V2 and the fourth control valve V4 in the fully closed state, the third control valve V3 and the fifth control valve V5 in the fully open state jointly constitute a low-temperature refrigerator quick start control valve group;

When the opening degree of the sixth control valve V6 is greater than the opening degrees of the first control valve V1 and the seventh control valve V7, the sixth control valve V6, the first control valve V1 and the seventh control valve V7 together constitute an idle speed and The high-potential control valve group under small load is also a control valve group to prevent water flooding when the stack is running for a long time under small load;

The fourth control valve V4 and the fifth control valve V5 whose openings have been adjusted during idle speed and light load operation together constitute a control valve group to prevent the stack film from drying out.

Two of the present invention's features are:

A cathode exhaust gas recirculation system for a proton exchange membrane fuel cell is characterized in that it is based on computer-aided control to realize the control of air pressure, total air flow, air temperature, air humidity and air content entering the stack. The cathode exhaust gas recirculation system with synchronous control of oxygen amount is suitable for the maximum working pressure less than or equal to 1.5bar, including the control part and the cathode exhaust gas recirculation part, of which:

The control part includes: a controller, a vacuum pump and a vacuum tank, and seven control valves connected in series by solenoid valves and vacuum valves. There are also sensor groups composed of multiple temperature sensors, humidity sensors and pressure sensors. Denoted by S, the sensor signal is sent to the controller, where,

Each vacuum valve adopts a vacuum diaphragm valve, and a position sensor is installed on the valve stem to realize precise control of the valve flow; the signal input ends of each solenoid valve are connected in parallel and connected with the control signal input ends of the controller and the vacuum pump through a pressure sensor respectively. connected, the controller adjusts the duty cycle of each solenoid valve through the control end of each solenoid valve to adjust the vacuum degree of each vacuum valve;

Cathode exhaust gas recirculation section, including mechanical and chemical filtration devices, intake and exhaust circuits and exhaust gas recirculation circuits, where:

The intake and exhaust circuit includes an intake passage and an exhaust passage, where:

The air intake path starts from the air outlet of the mechanical and chemical filter device that is open to the atmosphere, and contains in sequence: the first sensor group S1, the air flow sensor, the first control valve V1, the second sensor group S2, the air compressor, the second Control valve V2, radiator, fourth control valve V4, humidifier and the air inlet of electric stack, there is also a third control valve V3 on the bypass circuit of the radiator, and the humidifier bypass There is also a fifth control valve V5 on the circuit, wherein the second control valve V2 and the third control valve V3 are an intake air temperature control valve group that realizes closed-loop control of the cathode gas temperature entering the stack, and the fourth control valve V4 and The fifth control valve V5 is a gas humidity control valve group that realizes the closed-loop control of the cathode gas humidity entering the stack;

The exhaust path starts from the air outlet of the electric stack, and sequentially contains the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4 and the seventh control valve V7;

The exhaust gas recirculation circuit is located after the air compressor, starting from the output end of the fourth sensor group S4, and ending at the outlet of the air compressor, connecting the intake circuit and the exhaust circuit, A line is formed from the air outlet of the stack to pass through the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4, the sixth control valve V6 on the branch road, the air pump, The second control valve V2, the radiator, the third control valve V3, the fourth control valve V4, the fifth control valve V6 and the humidifier reach the exhaust gas recirculation circuit of the stack air inlet, where:

The sixth control valve V6, the first control valve V1, and the seventh control valve V7 are a group that can flexibly distribute the gas volume flow and the ratio of oxygen components for recirculation, so as to adjust the total gas flow, total pressure, control valves for oxygen partial pressure purposes;

The sixth control valve V6, the first control valve V1, the air flow sensor and the oxygen sensor are components that realize the closed-loop feedback control of the oxygen content of the entire air circuit;

The first control valve V1 in the fully closed state, the seventh control valve V7 and the sixth control valve V6 in the fully open state constitute a shutdown control valve group with an exhaust gas recirculation ratio of 100%;

The first control valve V1, the sixth control valve V6, and the seventh control valve V7 in the normally closed state constitute a set of shutdown and storage control valve groups;

The second control valve V2 and the fourth control valve V4 in the fully closed state, the third control valve V3 and the fifth control valve V5 in the fully open state jointly constitute a low-temperature refrigerator quick start control valve group;

When the opening degree of the sixth control valve V6 is greater than the opening degrees of the first control valve V1 and the seventh control valve V7, the sixth control valve V6, the first control valve V1 and the seventh control valve V7 together constitute an idle speed and The high-potential control valve group under small load is also a control valve group to prevent water flooding when the stack is running for a long time under small load;

The fourth control valve V4 and the fifth control valve V5 whose openings have been adjusted during idle speed and light load operation together constitute a control valve group to prevent the stack film from drying out.

Description of drawings

Figure 1 A typical fuel cell air system, the illustration is as follows:

Figure 2 Diagram of fuel cell air system with exhaust recirculation (recirculation loop before air compressor or fan)

Figure 3 Diagram of fuel cell air system with exhaust gas recirculation (recirculation loop after air compressor or fan)

Figure 4 Typical embodiment of fuel cell air system with exhaust gas recirculation (recirculation loop before air compressor or fan), the illustration is as follows:

Detailed ways

The two fuel cell air systems with exhaust gas recirculation of the present invention are shown in Figure 2 and Figure 3 respectively, and their working characteristics are as follows.

(1) Recirculation loop: use an exhaust recirculation loop to reintroduce the gas discharged from the cathode outlet of the stack to the inlet loop of the stack; according to the range of working pressure of the air system, there are two options to choose from; the first option As shown in Figure 2, for the scheme with high working pressure of component 11 (stack body) (high-voltage stack, for example, the maximum working pressure of the stack is greater than 1.5bar), the recirculation circuit (including pipelines and Component 15 (control valve V6) is arranged before component 3 (air compressor); the second solution is shown in Figure 3, and the working pressure of component 11 (stack body) is relatively small (low-voltage stack), The recirculation circuit (including pipeline and part 15, namely the control valve V6) can be arranged after part 3, and an air drive part 18 (air compressor or fan) can be added to the recirculation circuit at the same time, and the whole air system can be installed as required Necessary temperature, pressure and relative humidity sensors to respectively detect the atmosphere, the outlet of component 3 (air compressor or fan), the inlet and outlet of component 11 (the stack body), and the gas state before the inlet of component 15 (control valve V6) .

(2) Temperature control of the air circuit: As shown in attached drawings 2 and 3, in order to flexibly control the temperature of the gas passing through the compressor or fan, there are component 4 (control valve V2) and component 5 ( Control valve V3) can flexibly distribute the flow of gas flowing through the radiator to realize the closed-loop control of the cathode gas temperature entering component 11 (the stack body); the functions of flow control valves V2 and V3 can also be replaced by a three-way valve .

(3) Humidity control of the air circuit: As shown in Figure 2 and Figure 3, in order to flexibly control the humidity of the gas entering the stack, there are components 7 (control valve V4) and components 8 (bypass flow control valve V5), so that the flow of gas flowing through the humidifier can be flexibly distributed to achieve the humidity of the cathode gas entering part 11 (the stack body); the functions of flow control valves V4 and V5 can also be controlled by a three-way valve replace.

(4) Oxygen content adjustment mechanism: In attached drawings 2 and 3, part 15 (control valve V6) is provided on the exhaust gas recirculation circuit, respectively connected with part 2 (control valve V1) on the air inlet circuit. ) and the component 16 (control valve V7) on the outlet circuit can flexibly distribute the recirculated gas volume flow and the ratio of oxygen components, so as to flexibly adjust the total gas flow, total pressure and oxygen partial pressure entering the stack Purpose.

For example: when component 11 (stack body) is under the rated power (heavy load) working condition, component 2 (control valve V1) is fully open, component 15 (control valve V6) is fully closed, and the exhaust gas recirculation ratio is zero. , all the fresh air entering part 11 (the stack body) (the oxygen content is the oxygen content in the local atmosphere) supports the heavy load work of the stack; at this time, the working pressure and total flow of air can be controlled by part 3 (compressor or air Fan 1) and component 16 (control valve V7) to complete.

When the power of the stack is gradually reduced, the opening of part 2 (control valve V1) can be gradually reduced, and the opening of part 15 (control valve V6) can be gradually increased due to the corresponding decrease in the required oxygen flow rate, so that Gradually increase the proportion of exhaust gas recirculation, the effect is that the oxygen flow rate is reduced, and the total gas flow rate and pressure entering the component 11 (the stack body) can be adjusted; through the control system to adjust the opening of V1, V6 and V7, the entry can be realized The independent control of the total gas flow, total pressure and oxygen partial pressure (flow rate) of the stack realizes the solution of the output voltage of the stack (mainly affected by the partial pressure of oxygen) and the drainage of the stack (total flow and total pressure). coupling control.

(5) Closed-loop control of oxygen content: In order to accurately control the proportion of oxygen content entering part 11 (the stack body), part 1, that is, an air flow sensor, can be installed on the air inlet circuit, which can measure the flow through part 2, that is, control The fresh air flow of valve V1; on the air outlet circuit of the stack, there is a component 14, that is, an oxygen sensor, to measure the oxygen content in the exhaust gas; combined with the control of the gas flow through component 15, that is, the control valve V6, the entire air flow can be realized. Closed-loop feedback control of the oxygen content of the circuit; it is also possible to use no oxygen sensor, but to estimate the amount of oxygen consumed by the internal reaction of the stack according to the power and efficiency of the fuel cell, so that the amount of oxygen remaining in the exhaust gas can be estimated; the realization is based on physics Model oxygen content state estimation and closed-loop control.

(6) Shutdown control process: when part 2 (control valve V1) and part 16 (control valve V7) are fully closed and part 15 (control valve V6) is fully open, the proportion of exhaust gas recirculation is 100%. At this time, because the exhaust gas enters the component 11 (the stack body) through the recirculation loop many times, the oxygen in it is gradually reacted, so the oxygen content in the entire exhaust gas gradually decreases until it reaches zero, the reaction stops, and the stack enters the The natural state of the reaction; at this time, the gas components on the entire cathode side mainly include water vapor and nitrogen, without oxygen, the reaction stops naturally, and the stack no longer outputs high voltage, so it can be shut down naturally to protect the durability and life of the stack; The combination of space-time compressor and recirculation circuit can still produce the desired gas flow and pressure, and the residual liquid water in the stack can be discharged to ensure that the inside of the stack will not freeze due to residual water under low temperature conditions after shutdown resulting in damage to the stack.

Considering that the actuator is in a power-off state after shutdown, the control valves V1 and V7 connected to the atmosphere can be designed as normally closed valves, and the connection to the atmosphere can be automatically closed after power failure.

(7) Idling speed and small load process control: The idle speed and small load process control is similar to the above shutdown process, except that part 2 (control valve V1) and part 16 (control valve V7) will not be completely closed, but will be kept according to the power demand. Appropriate opening, that is, to ensure that there is an appropriate flow of gas to exchange with the surrounding atmosphere, and part 15 (control valve V6) can maintain a large angle, that is, the flow in and out of part 11 (the stack body) is kept large. At this time Oxygen concentration can be flexibly adjusted between 0% and 20%, ensuring that the output voltage and power of the fuel cell are at a low level, avoiding high voltage at idle speed and light load; Component 3 in 2 and component 18 in Figure 3) drive the recirculated gas flow to ensure that the liquid water generated during long-term operation is eliminated; thus avoiding the problem that component 11 (the stack body) is prone to flooding during long-term small-load operation ;By adjusting the opening of part 7 (control valve V4) and part 8 (control valve V5), the amount of air involved in humidification can be flexibly controlled, and the problem of dry film of the stack under idle speed and light load conditions can be avoided. Under the conditions of idling speed and partial load, through the adjustment function of the exhaust gas recirculation circuit, the amount of gas exchanged with the surrounding atmosphere can be ensured to be small, that is, the amount of fresh air entering from the mechanical and chemical filters is reduced, and the mechanical efficiency is improved. And the use efficiency of the chemical filter can effectively extend its service life.

(8) During parking and storage, part 2 (control valve V1) and part 16 (control valve V7) can be set to the state of power off and normally closed, because part 11 (stack body) and recirculation pipeline will The gas components are mainly nitrogen and water vapor without oxygen, so only nitrogen will permeate through the proton exchange membrane and enter the anode, and oxygen will not enter the anode side to cause chemical corrosion reactions, which can ensure that the vehicle will not damage the stack when it is stored for a long time performance.

(9) Quick start-up of low-temperature refrigerator: Under low temperature conditions, part 4 (control valve V2) and part 7 (control valve V4) can be closed at this time, and part 5 (control valve V3) and part 8 (control valve V5) can be closed. ) fully open, can pass through the recirculation circuit (component 15, control valve V6) and air drive components, for the part 3 air compressor in the accompanying drawing 2, and for the part 18 (air fan 2) in the accompanying drawing 3, due to The air compressor or the fan itself has the function of pressurizing and heating the air, or cooperates with a special air heating device (not shown in the figure), which can quickly heat the air entering the component 11 (the stack body) to above zero, so that the entire air The system heats up quickly to ensure that the electrochemical reaction can occur smoothly inside the stack, and then the heat produced by the stack itself is used to further accelerate the cold machine start-up process. After the temperature reaches a certain value (successful warm-up), the heat exchange and humidification process with the radiator and humidifier begins, which can greatly shorten the warm-up process of the fuel cell system.

The present invention adopts the above technical scheme and has the following advantages: 1. Due to the introduction of the exhaust gas recirculation function in this scheme, the total flow, total pressure and oxygen flow entering the stack can be adjusted independently, thereby achieving the limitation by controlling the oxygen content At the same time as the monolithic voltage of the stack, the total flow and total pressure can also be flexibly adjusted to achieve reliable drainage control, effectively avoiding the phenomenon of water flooding or membrane dryness caused by the reduction of the total amount of intake air under such working conditions. Improve the service life of the fuel cell; 2. In this scheme, the radiator and humidifier of the fuel cell air system are connected in parallel with the bypass pipeline and its control valve, which makes the system more flexible in the control of the intake air temperature and humidity, and is conducive to entering The gas of the stack can maintain the best humidity and temperature according to the condition of the stack, thereby improving the efficiency and durability of the stack; 3. This solution introduces the exhaust gas recirculation function, which can quickly dry the stack during shutdown The internal liquid water prevents the stack from being damaged due to the freezing of the residual water inside under low temperature conditions; 4. The exhaust gas recirculation and shutdown control strategy of this scheme makes the oxygen in the pipeline continuously reduce until it is exhausted; through Close the control valve connected to the ambient air to make the air system form a closed loop. During the shutdown process, the entire pipeline is filled with inert gas nitrogen to avoid the problem of oxygen entering the anode and corroding the stack during long-term shutdown, which can improve the life of the stack; 5. This program introduces the exhaust gas recirculation function, which reduces the amount of fresh air entering the system, reduces the load on mechanical and chemical filters, and improves their service life; 6. This program introduces the exhaust gas recirculation function and heat dissipation, increase The combination of wet bypass control can speed up the warm-up speed of the stack under low temperature conditions;

The present invention will be described in detail below with reference to the typical embodiment of the fuel cell air system with exhaust gas recirculation in FIG. 4 .

The flow control valves V1-V7 in the accompanying drawings 2 and 3 can be realized by different means, either an electronic throttle valve in a traditional engine control system or a butterfly valve driven by a motor. In this embodiment, a mature and reliable vacuum diaphragm valve with low cost and position feedback in the traditional automobile industry is used as the control valve. The relative position, that is, the equivalent flow cross-sectional area; a position sensor is installed on the valve stem to achieve precise control of the valve flow. The fuel cell air system using the vacuum diaphragm valve as the actuator is shown in Figure 4. The vacuum pump 19 (including the vacuum storage tank) generates a certain degree of vacuum, and the controller 20 of the fuel cell can adjust the electromagnetic valve respectively. The duty cycle of K1-K7 is used to adjust the vacuum degree of the vacuum diaphragm valve V1-V7, which also changes the valve stem position and equivalent flow cross-sectional area of V1-V7 to realize the flow adjustment of the air circuit. Signals of the position sensors installed on V1-V7 are connected to the controller 20 to feed back respective valve stem position signals so as to realize closed-loop control of the position of the control valves and precisely control their respective flow rates.

The air from the atmosphere first enters 17 (mechanical and chemical filtering device), is filtered out of particles and impurities, and after passing through the outlet of 2 (vacuum valve V1), it is connected in parallel with the outlet from the exhaust gas recirculation channel, and then connected to 3 (air Compressor) inlet; the outlet of air compressor 3 is connected to the inlet of two channels, one channel is connected to the inlet of 6 (radiator) through component 4 (vacuum valve V2), and the other channel is a parallel bypass pipeline, There is a flow control valve 5 (vacuum valve V3) on the pipeline, which can effectively regulate the gas flow into the radiator; the outlet of the radiator 6 is merged with the outlet of the parallel bypass, and connects the inlets of the two channels, one of which passes through 7 (vacuum Valve V4) is connected to the inlet of 9 (humidifier), and the other channel is a parallel bypass pipeline, and there is 8 (control valve V5) to control the flow on the pipeline; the outlet of humidifier 9 and its bypass pipeline After the outlet is combined, it is connected to the inlet of 11 (the stack body); the outlet of the stack 11 is connected to the inlet of 12 (condenser), and the condenser 12 is used to cool the outlet gas and recover water; the outlet of the condenser 12 passes through 14 (oxygen sensor), it will be divided into two pipelines, one is connected to the atmosphere through 16 (vacuum valve V7), which is the exhaust pipeline; the other enters the exhaust gas recirculation channel, which flows through 15 (vacuum valve V7) After V6), its outlet is connected in parallel with the outlet of 2 (vacuum valve V1), and then enters the inlet of 3 (air compressor) after merging. The vacuum pump 19 (including the vacuum tank) is respectively connected to the vacuum valves V1-V7 through solenoid valves K1-K7, and each solenoid valve is controlled by the fuel cell system controller.

According to the working pressure range of the air system, the exhaust gas recirculation circuit (including air pipeline and vacuum valve V6) can be arranged before the inlet of component 3 (air compressor); the recirculation circuit (including air pipeline and vacuum valve V6) can also be arranged Vacuum valve V6) is arranged after the outlet of component 3, and an air drive device 18 should be added to the exhaust recirculation circuit at this time; at this time, after the outlet of exhaust recirculation and the outlet of air compressor 3 are connected in parallel, then enter the Radiator for vacuum valves V2 and V3 and their bypass channels.

When the present invention is used in an actual fuel cell system to work, the controller monitors the voltage and current output by the stack in real time, as well as the gas temperature, humidity, and pressure state by receiving signals from various sensors, and realizes each vacuum through the control of each electromagnetic valve. The different openings of the valve can adjust the oxygen concentration, humidity, temperature, pressure and other state parameters of the intake air at any time, so that the stack can always work in the best state, the voltage is maintained between about 0.6V-0.8V, and there is no obvious flooding Or film drying phenomenon, so that the efficiency and life of the stack are optimized.

The optimization effect of the present invention on the fuel cell stack will be described in detail below in combination with the specific working conditions of the fuel cell stack.

Heavy load state: that is, the power demand is large, and the fuel cell stack is in a state of a better working point. At this time, there is no need to use exhaust gas recirculation to reduce the oxygen concentration in the intake air, so 15 (vacuum valve V6) is completely closed, and all exhaust gas is discharged into the environment through 16 (vacuum valve V7). And 2 (vacuum valve V1) is in a fully open state, which is beneficial to reduce air intake loss. At this time, the bypass loops that are parallel to the radiator 2 and the humidifier 3 are mainly effective, that is, the vacuum valves V2-V5.

When the outlet temperature of the air compressor 3 is normal, the 4 (vacuum valve V2) at the inlet of the radiator 6 is fully opened, and the 5 (vacuum valve V3) on the bypass circuit is completely closed, and all the gas passes through the radiator 6 for cooling. The airflow direction of the radiator part is shown in Figure 4, and the direction of the arrow is the airflow direction. When the outlet temperature of the air compressor is low, 5 (vacuum valve V3) on the bypass circuit of the radiator 6 is opened, and the corresponding control solenoid valves K2 and K3 cooperate with each other to control the opening of the vacuum valve V2 and vacuum valve V3. , to adjust the gas flow into the radiator 6. The lower the temperature, the greater the proportion of gas flow that flows through the radiator 6 bypass circuit. Thus, the temperature of the gas at the inlet of the humidifier 9 is controlled so that it is suitable for entering the electric stack.

When the ambient air humidity is low, the 7 (vacuum valve V4) at the entrance of the humidifier 9 is fully opened, and the 8 (vacuum valve V5) on the bypass circuit is closed, and all the gas is humidified through the humidifier 9, so that the inlet The air humidity can meet the stack requirements. When the ambient air humidity is high, the vacuum valve V5 on the bypass circuit of the humidifier 9 is opened, and the corresponding control solenoid valves K4 and K5 cooperate with each other to control the openings of the vacuum valve V4 and the vacuum valve V5 to coordinate and adjust Gas flow into humidifier 9. The greater the ambient humidity, the greater the proportion of gas flow that flows through the bypass circuit of the humidifier 9 . Thus, the humidity of the gas at the entrance of the 11 stack body is adjusted so that it is suitable for entering the stack.

Idle speed/light load: In idle speed or light load conditions, in addition to the bypass circuit connected in parallel with the radiator 6 and humidifier 9 and the vacuum valves V2-V5, the more important ones are the vacuum valves V1 and V6 , The mutual cooperation of V7 opening.

Under the condition of idling speed or light load, the fuel cell works in a state of low current and high voltage, which is not conducive to prolonging its service life. An effective way to reduce the voltage at this time is to use the concept of concentration overvoltage to reduce the excess coefficient of oxygen. One way is to reduce the power of the air compressor and reduce the total amount of intake air. This method makes the total amount of intake air linked to the degree of voltage drop, and the total amount of intake air is limited. However, due to the reduction of the total amount of gas, the ability of the gas to carry moisture is reduced, which may easily cause water flooding of the stack. In order to avoid this phenomenon, the present invention introduces an exhaust gas recirculation system into the air system of the fuel cell, which can effectively reduce the excess coefficient of oxygen without reducing the total amount of intake air, so as to achieve the purpose of limiting the voltage of the fuel cell. The total amount is still controllable and not limited by the degree of voltage drop.

When the idling voltage is high, the vacuum valve V6 for controlling exhaust gas recirculation is opened, and the dry exhaust gas with low oxygen content discharged from the outlet of the condenser 12 enters the intake pipe again. The larger the opening of the vacuum valve V6 and the smaller the opening of the vacuum valve V7, the greater the proportion of exhaust gas re-entering the intake pipe, and the smaller the proportion of exhaust gas, thus the greater the contribution to the reduction of oxygen content in the intake air. big. This ratio will be adjusted continuously until the voltage is limited below 0.8V.

Shutdown: The key during shutdown is to remove residual oxygen from the stack. The bypass circuit in which the radiator 6 and the humidifier 9 are connected in parallel, that is, the vacuum valves V2-V5 function normally. The vacuum valves V1 and V7 are gradually closed, and the vacuum valve V6 is opened to form a closed cycle. The exhaust gas flows back and forth in the entire air system until the oxygen is exhausted and then shut down. At this time, the air circuit of the fuel cell system only has nitrogen and a little water vapor, which can be considered as full of inert gas, which eliminates the corrosion effect of the oxygen stack during the fuel cell shutdown and storage process, and can effectively prolong the life of the stack.

Claims (2)

1. A cathode exhaust gas recirculation system for proton exchange membrane fuel cells, characterized in that: it is based on computer-aided control to realize the air pressure, total air flow, air temperature, air humidity and The cathode exhaust gas recirculation system with synchronous control of air oxygen content is suitable for a maximum working pressure greater than 1.5bar, including a control part and a cathode exhaust gas recirculation part, of which: The control part includes: a controller, a vacuum pump and a vacuum tank, and seven control valves connected in series by solenoid valves and vacuum valves. There are also sensor groups composed of multiple temperature sensors, humidity sensors and pressure sensors. Denoted by S, the sensor signal is sent to the controller, where, Each vacuum valve adopts a vacuum diaphragm valve, and a position sensor is installed on the valve stem to realize precise control of the valve flow; the signal input ends of each solenoid valve are connected in parallel and connected with the control signal input ends of the controller and the vacuum pump through a pressure sensor respectively. connected, the controller adjusts the duty cycle of each solenoid valve through the control end of each solenoid valve to adjust the vacuum degree of each vacuum valve; Cathode exhaust gas recirculation section, including mechanical and chemical filtration devices, intake and exhaust circuits and exhaust gas recirculation circuits, where: The intake and exhaust circuit includes an intake passage and an exhaust passage, where: The air intake path starts from the air outlet of the mechanical and chemical filter device that is open to the atmosphere, and contains in sequence: the first sensor group S1, the air flow sensor, the first control valve V1, the second sensor group S2, the air compressor, the second Control valve V2, radiator, fourth control valve V4, humidifier and the air inlet of electric stack, there is also a third control valve V3 on the bypass circuit of the radiator, and the humidifier bypass There is also a fifth control valve V5 on the circuit, wherein the second control valve V2 and the third control valve V3 are an intake air temperature control valve group that realizes closed-loop control of the cathode gas temperature entering the stack, and the fourth control valve V4 and The fifth control valve V5 is a gas humidity control valve group that realizes the closed-loop control of the cathode gas humidity entering the stack; The exhaust path starts from the air outlet of the electric stack, and sequentially contains the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4 and the seventh control valve V7; The exhaust gas recirculation circuit is located before the air compressor, starting from the output end of the fourth sensor group S4, and ending at the inlet of the air compressor, communicating the intake circuit and the exhaust circuit, A line is formed from the air outlet of the stack to pass through the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4, the sixth control valve V6 on the branch road, and the air compressor , the second control valve V2, the radiator, the third control valve V3, the fourth control valve V4, the fifth control valve V6 and the humidifier reach the exhaust gas recirculation circuit of the stack air inlet, wherein: The sixth control valve V6, the first control valve V1, and the seventh control valve V7 are a group that can flexibly distribute the gas volume flow and the ratio of oxygen components for recirculation, so as to adjust the total gas flow, total pressure, control valves for oxygen partial pressure purposes; The sixth control valve V6, the first control valve V1, the air flow sensor and the oxygen sensor are components that realize the closed-loop feedback control of the oxygen content of the entire air circuit; The first control valve V1 in the fully closed state, the seventh control valve V7 and the sixth control valve V6 in the fully open state constitute a shutdown control valve group with an exhaust gas recirculation ratio of 100%; The first control valve V1, the sixth control valve V6, and the seventh control valve V7 in the normally closed state constitute a set of shutdown and storage control valve groups; The second control valve V2 and the fourth control valve V4 in the fully closed state, the third control valve V3 and the fifth control valve V5 in the fully open state jointly constitute a low-temperature refrigerator quick start control valve group; When the opening degree of the sixth control valve V6 is greater than the opening degrees of the first control valve V1 and the seventh control valve V7, the sixth control valve V6, the first control valve V1 and the seventh control valve V7 together constitute an idle speed and The high-potential control valve group under small load is also a control valve group to prevent water flooding when the stack is running for a long time under small load; The fourth control valve V4 and the fifth control valve V5 whose openings have been adjusted during idle speed and light load operation together constitute a control valve group to prevent the stack film from drying out. 2. A cathode exhaust gas recirculation system for proton exchange membrane fuel cells, characterized in that: it is based on computer-aided control to realize the air pressure, total air flow, air temperature, air humidity and The cathode exhaust gas recirculation system with synchronous control of the oxygen content of the air is suitable for the maximum working pressure less than or equal to 1.5bar, including the control part and the cathode exhaust gas recirculation part, of which: The control part includes: a controller, a vacuum pump and a vacuum tank, and seven control valves connected in series by solenoid valves and vacuum valves. There are also sensor groups composed of multiple temperature sensors, humidity sensors and pressure sensors. Denoted by S, the sensor signal is sent to the controller, where, Each vacuum valve adopts a vacuum diaphragm valve, and a position sensor is installed on the valve stem to realize precise control of the valve flow; the signal input ends of each solenoid valve are connected in parallel and connected with the control signal input ends of the controller and the vacuum pump through a pressure sensor respectively. connected, the controller adjusts the duty cycle of each solenoid valve through the control end of each solenoid valve to adjust the vacuum degree of each vacuum valve; Cathode exhaust gas recirculation section, including mechanical and chemical filtration devices, intake and exhaust circuits and exhaust gas recirculation circuits, where: The intake and exhaust circuit includes an intake passage and an exhaust passage, where: The air intake path starts from the air outlet of the mechanical and chemical filter device that is open to the atmosphere, and contains in sequence: the first sensor group S1, the air flow sensor, the first control valve V1, the second sensor group S2, the air compressor, the second Control valve V2, radiator, fourth control valve V4, humidifier and the air inlet of electric stack, there is also a third control valve V3 on the bypass circuit of the radiator, and the humidifier bypass There is also a fifth control valve V5 on the circuit, wherein the second control valve V2 and the third control valve V3 are an intake air temperature control valve group that realizes closed-loop control of the cathode gas temperature entering the stack, and the fourth control valve V4 and The fifth control valve V5 is a gas humidity control valve group that realizes the closed-loop control of the cathode gas humidity entering the stack; The exhaust path starts from the air outlet of the electric stack, and sequentially contains the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4 and the seventh control valve V7; The exhaust gas recirculation circuit is located after the air compressor, starting from the output end of the fourth sensor group S4, and ending at the outlet of the air compressor, connecting the intake circuit and the exhaust circuit, A line is formed from the air outlet of the stack to pass through the fifth sensor group S5, the condenser, the oxygen sensor, the fourth sensor group S4, the sixth control valve V6 on the branch road, the air pump, The second control valve V2, the radiator, the third control valve V3, the fourth control valve V4, the fifth control valve V6 and the humidifier reach the exhaust gas recirculation circuit of the stack air inlet, where: The sixth control valve V6, the first control valve V1, and the seventh control valve V7 are a group that can flexibly distribute the gas volume flow and the ratio of oxygen components for recirculation, so as to adjust the total gas flow, total pressure, control valves for oxygen partial pressure purposes; The sixth control valve V6, the first control valve V1, the air flow sensor and the oxygen sensor are components that realize the closed-loop feedback control of the oxygen content of the entire air circuit; The first control valve V1 in the fully closed state, the seventh control valve V7 and the sixth control valve V6 in the fully open state constitute a shutdown control valve group with an exhaust gas recirculation ratio of 100%; The first control valve V1, the sixth control valve V6, and the seventh control valve V7 in the normally closed state constitute a set of shutdown and storage control valve groups; The second control valve V2 and the fourth control valve V4 in the fully closed state, the third control valve V3 and the fifth control valve V5 in the fully open state jointly constitute a low-temperature refrigerator quick start control valve group; When the opening degree of the sixth control valve V6 is greater than the opening degrees of the first control valve V1 and the seventh control valve V7, the sixth control valve V6, the first control valve V1 and the seventh control valve V7 together constitute an idle speed and The high-potential control valve group under small load is also a control valve group to prevent water flooding when the stack is running for a long time under small load; The fourth control valve V4 and the fifth control valve V5 whose openings have been adjusted during idle speed and light load operation together constitute a control valve group to prevent the stack film from drying out.

Images