Control method of multi-stage fuel cell system and multi-stage fuel cell system

Abstract

The invention relates to the technical field of multi-stage fuel cell systems, and particularly discloses a control method of a multi-stage fuel cell system and the multi-stage fuel cell system.The control method of the multi-stage fuel cell system comprises the steps that the control method is started, specifically, air flows through a heating device at a first set air flow; starting a heating device; obtaining the cathode outlet temperature of the primary electric pile; when the temperature of the cathode outlet of the first-stage electric pile is not lower than the set purging temperature, the water tank supplies water to the steam generator and the second heat exchange runner at the same time for a set duration, and the water can be heated into water vapor and can purge the anode side, so that residual air on the anode side can be avoided, and the safety is ensured; compared with other inert gas purging, the water tank is fully utilized, the structure is simple, and the cost is low; in addition, water vapor output by the anode of the first-stage electric pile is condensed in the condensation water removal device, water is supplied to the second heat exchange runner of the heat exchanger through the water tank, and the water can absorb heat to be vaporized and directly enters the second-stage electric pile to be normally purged.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-stage fuel cell systems, and particularly to a control method for a multi-stage fuel cell system and a multi-stage fuel cell system. Background Art

[0002] Existing multi-stage fuel cell systems mainly consist of components such as a steam generator, a reformer, multiple fuel cells, a burner, a heat exchanger, and a waste heat recovery system. The steam generator mainly heats deionized water to evaporate it into steam; the reformer mainly performs steam reforming on hydrocarbon fuels such as natural gas and alcohols entering the system and steam to convert them into a mixed gas mainly composed of hydrogen, carbon monoxide, and carbon dioxide, thus being more conducive to the electrochemical reaction in the fuel cell; the burner mainly converts the unreacted fuel in the anode exhaust gas into heat and provides heat energy for the system; the heat exchanger conducts heat exchange, using a high-temperature heat source to heat a low-temperature medium.

[0003] For an existing multi-stage fuel cell system, during startup, the first-stage fuel cell is preheated first. When the startup temperature of the first-stage fuel cell is reached, the first-stage fuel cell is started, and all the anode exhaust gas of the first-stage fuel cell is introduced into the tail gas burner. The heat generated by combustion is used to preheat the second-stage fuel cell, and when the second-stage fuel cell reaches the startup temperature, the second-stage fuel cell is started. However, in this startup process, the situation where air may remain on the anode side is ignored, and safety accidents such as explosions are likely to occur during the startup process. Although there are existing technologies regarding the purging method for fuel cells during startup, they are usually designed for single fuel cells and cannot be applied universally in multi-stage fuel cell systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a control method for a multi-stage fuel cell system and a multi-stage fuel cell system to solve the problem that in the startup of an existing multi-stage fuel cell system, the situation where air may remain on the anode side is ignored, and safety accidents such as explosions are likely to occur during the startup process.

[0005] On the one hand, the present invention provides a control method for a multi-stage fuel cell system. The multi-stage fuel cell system includes a steam generator, a reformer, a first-stage fuel cell stack, a heat exchanger, a condensate removal device, a second-stage fuel cell stack, a heating device, a gas supplement mixer, and a water tank. The anode inlets of the steam generator, the reformer, and the first-stage fuel cell stack are connected in sequence. The heat exchanger has a first heat exchange flow channel and a second heat exchange flow channel. The two ends of the first heat exchange flow channel are respectively connected to the anode outlet of the first-stage fuel cell stack and the input end of the condensate removal device. The output end of the condensate removal device is connected to the first inlet of the gas supplement mixer. The second inlet of the gas supplement mixer is used to input supplementary fuel. The outlet of the gas supplement mixer is communicated with the second heat exchange flow channel. The second heat exchange flow channel is communicated with the anode inlet of the second-stage fuel cell stack. The water tank is used to supply water to the steam generator and is also used to supply water to the second heat exchange flow channel. The steam generator can generate water vapor from water. The reformer is provided with a reforming heat exchange flow channel. The heating device is used to heat air, and the heated air can flow through the reforming heat exchange flow channel, the cathode of the first-stage fuel cell stack, and the cathode of the second-stage fuel cell stack. The control method for the multi-stage fuel cell system includes a startup control method, and the startup control method includes:

[0006] Air flows through the heating device at a first set air flow rate;

[0007] Turn on the heating device;

[0008] Obtain the cathode outlet temperature of the first-stage fuel cell stack;

[0009] When the cathode outlet temperature of the first-stage fuel cell stack is not less than the set purging temperature, the water tank supplies water to the steam generator and the second heat exchange flow channel simultaneously and lasts for a set time.

[0010] As a preferred technical solution of the control method for the multi-stage fuel cell system, the heating device includes a burner and an air preheater. The first air inlet of the burner is connected to the anode outlet of the second-stage fuel cell stack. The second air inlet of the burner is connected to the cathode outlet of the second-stage fuel cell stack. The third air inlet of the burner is used to input external fuel. The waste gas generated by the combustion of the burner is used to provide heat for the air preheater. The air preheater is used to heat air;

[0011] Turning on the heating device includes:

[0012] External fuel enters the burner from the third air inlet of the burner and is ignited and burned.

[0013] As a preferred technical solution of the control method for the multi-stage fuel cell system, the startup control method further includes, after the water tank supplies water to the steam generator and the second heat exchange flow channel simultaneously:

[0014] Obtain the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack;

[0015] When both the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack are not less than T 1 the water tank stops supplying water to the second heat - exchange flow channel;

[0016] The inlet of the steam generator starts to introduce fuel and the first - stage stack and the second - stage stack do not generate electricity;

[0017] The flow rate of the external fuel introduced into the burner gradually decreases to not exceed the set flow rate.

[0018] As a preferred technical solution of the control method for a multi - stage fuel cell system, the startup control method further includes, after the flow rate of the external fuel introduced into the burner gradually decreases to not exceed the set flow rate:

[0019] Obtain the cathode outlet temperature of the first - stage stack;

[0020] When the cathode outlet temperature of the first - stage stack is not less than T 2 at this time, T 2 >T 1 ;

[0021] The first - stage stack starts to generate electricity.

[0022] As a preferred technical solution of the control method for a multi - stage fuel cell system, the startup control method further includes, after the first - stage stack starts to generate electricity:

[0023] Obtain the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack;

[0024] When the cathode outlet temperature of the first - stage stack is not less than T 3 , and the cathode outlet temperature of the second - stage stack is not less than T 2 at this time, T 3 >T 2 ;

[0025] Make - up fuel starts to be input from the second inlet of the air - supplement mixer;

[0026] The second - stage stack starts to generate electricity.

[0027] As a preferred technical solution of the control method for a multi - stage fuel cell system, the startup control method further includes, after the second - stage stack starts to generate electricity:

[0028] Obtain the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack;

[0029] When the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack are both not less than T 4 , T 4 >T 3 ;

[0030] Stop supplying external fuel to the burner;

[0031] The multi - stage fuel cell system is started up successfully.

[0032] As a preferred technical solution of the control method of the multi - stage fuel cell system, the control method of the multi - stage fuel cell system further includes a shutdown control method, and the shutdown control method includes:

[0033] Obtain a shutdown instruction;

[0034] The power generation power of the first - stage stack gradually decreases to zero, and the power generation power of the second - stage stack gradually decreases to zero;

[0035] The flow rate of the fuel introduced into the inlet of the steam generator gradually decreases to the minimum fuel flow rate;

[0036] The flow rate of the supplementary fuel input from the second inlet of the air - supplement mixer gradually decreases to zero.

[0037] As a preferred technical solution of the shutdown control method of the multi - stage fuel cell system, the shutdown control method includes, after the flow rate of the supplementary fuel input from the second inlet of the air - supplement mixer gradually decreases to zero:

[0038] Increase the flow rate of the air flowing through the heating device to the second set air flow rate;

[0039] Obtain the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack;

[0040] When the cathode outlet temperature of the first - stage stack and the cathode outlet temperature of the second - stage stack are both not greater than the oxidation temperature threshold;

[0041] Stop supplying fuel to the inlet of the steam generator.

[0042] As a preferred technical solution of the shutdown control method of the multi - stage fuel cell system, the shutdown control method further includes, after stopping supplying fuel to the inlet of the steam generator:

[0043] The water tank supplies water to the second heat - exchange flow channel;

[0044] After at least a set time period, the water tank stops supplying water to the second heat - exchange flow channel and the steam generator;

[0045] The flow rate of air flowing through the heating device is adjusted to zero.

[0046] On the other hand, the present invention provides a multi-stage fuel cell system for implementing the control method of the multi-stage fuel cell system described in any of the above solutions. The multi-stage fuel cell system includes a steam generator, a reformer, a first-stage fuel cell stack, a heat exchanger, a condensate removal device, a second-stage fuel cell stack, a heating device, a water tank, and a gas supplement mixer. The anode inlets of the steam generator, the reformer, and the first-stage fuel cell stack are connected in sequence. The heat exchanger has a first heat exchange channel and a second heat exchange channel. The two ends of the first heat exchange channel are respectively connected to the anode outlet of the first-stage fuel cell stack and the input end of the condensate removal device. The first inlet of the gas supplement mixer is connected to the output end of the condensate removal device. The second inlet of the gas supplement mixer is used for inputting supplementary fuel. The outlet of the gas supplement mixer is connected to the second heat exchange channel. The second heat exchange channel communicates with the anode inlet of the second-stage fuel cell stack. The water tank is used to supply water to the steam generator and to supply water to the second heat exchange channel. The steam generator can generate water vapor from water. The reformer is provided with a reforming heat exchange channel. The heating device is used to heat air, and the heated air can flow through the reforming heat exchange channel, the cathode of the first-stage fuel cell stack, and the cathode of the second-stage fuel cell stack.

[0047] The beneficial effects of the present invention are as follows:

[0048] The present invention provides a control method for a multi-stage fuel cell system and a multi-stage fuel cell system. The control method for the multi-stage fuel cell system includes a start-up control method. When starting the multi-stage fuel cell system, air is made to flow through a heating device at a first set air flow rate; the heating device is turned on; the cathode outlet temperature of the first-stage fuel cell stack is obtained; when the cathode outlet temperature of the first-stage fuel cell stack is not less than a set purge temperature, the water tank supplies water to both the steam generator and the second heat exchange channel simultaneously and for a set duration. The water is heated into steam and can purge the anode side, capable of blowing out the residual gas on the anode side, avoiding residual air on the anode side, which may cause safety accidents such as explosion when a reducing gas is subsequently input. Moreover, the multi-stage fuel cell system is originally equipped with a water tank, so purging the anode side with steam does not require the configuration of other inert gases, with a simple structure and low cost. Additionally, the supply amount of supplementary fuel is controlled by a gas replenishing mixer, and the condensation water yield of steam is controlled by setting a condensation water removal device. The combination of the two can adjust the fuel utilization rate of the second-stage fuel cell stack and the oxygen-carbon ratio entering the second-stage fuel cell stack. When the oxygen-carbon ratio is adjusted to the required range, it can ensure that the second-stage fuel cell stack can generate electricity efficiently. At the same time, the steam output from the anode of the first-stage fuel cell stack will condense in the condensation water removal device, resulting in very little steam on the anode of the second-stage fuel cell stack. In the present invention, the water tank supplies water to the second heat exchange channel of the heat exchanger, and the water absorbs heat and vaporizes into steam in the second heat exchange channel to ensure normal purging of the second-stage fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic structural diagram of the multi-stage fuel cell system in an embodiment of the present invention;

[0050] Figure 2 is a flow chart of the start-up control method in the control method of the multi-stage fuel cell system in an embodiment of the present invention Figure 1 ;

[0051] Figure 3 is a flow chart of the start-up control method in the control method of the multi-stage fuel cell system in an embodiment of the present invention Figure 2 ;

[0052] Figure 4 is a flow chart of the shutdown control method in the control method of the multi-stage fuel cell system in an embodiment of the present invention.

[0053] In the figure:

[0054] 1. Steam generator; 2. Reformer; 3. First-stage fuel cell stack; 4. Heat exchanger; 5. Tail gas cooler; 6. Gas replenishing mixer; 7. Second-stage fuel cell stack; 8. Condenser; 9. Water separator; 10. Water pump; 11. Water tank; 12. Air preheater; 13. Burner; 14. Shunt; 15. First mixer; 16. Second mixer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions, and the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or simply indicating that the first feature has a lower horizontal height than the second feature.

[0057] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0058] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0059] In the existing multi-stage fuel cell system, during startup, the first-stage fuel cell stack is preheated first. When the startup temperature of the first-stage fuel cell stack is reached, the first-stage fuel cell stack is started. All the anode exhaust gas of the first-stage fuel cell stack is introduced into the exhaust gas burner, and the heat generated by combustion is used to preheat the second-stage fuel cell stack. After the second-stage fuel cell stack reaches the startup temperature, the second-stage fuel cell stack is started. However, in this startup process, the situation of possible air residue on the anode side is ignored, and safety accidents such as explosion are likely to occur during startup. Although there are existing technologies for purging methods during the startup of fuel cell stacks, they are usually designed for single fuel cell stacks and cannot be applied universally in multi-stage fuel cell systems.

[0060] In view of this, the present embodiment provides a control method for a multi-stage fuel cell system to solve the above problems. The control method for the multi-stage fuel cell system is implemented by the multi-stage fuel cell system.

[0061] Among them, as Figure 1 shown, the multi-stage fuel cell system includes a steam generator 1, a reformer 2, a first-stage fuel cell stack 3, a heat exchanger 4, a condensation and water removal device, a second-stage fuel cell stack 7, a heating device, a gas supply mixer 6, and a water tank 11. In this embodiment, a scheme in which the multi-stage fuel cell system includes two fuel cell stacks is exemplarily given. In other embodiments, the multi-stage fuel cell system may further include three or more fuel cell stacks.

[0062] The anode inlets of the steam generator 1, the reformer 2, and the first-stage fuel cell stack 3 are connected in sequence. The water inlet of the steam generator 1 is used to input water, and the gas inlet of the steam generator 1 is used for fuel (such as natural gas). When the first-stage fuel cell stack 3 is generating electricity normally, the steam generator 1 can cause water to evaporate into water vapor and mix with the fuel. After the mixed gas enters the reformer 2, a reforming reaction occurs in the reformer 2, and hydrogen and carbon dioxide are partially generated, and then are transported to the anode of the first-stage fuel cell stack 3 to supply the reaction of the first-stage fuel cell stack 3.

[0063] The heat exchanger 4 has a first heat exchange flow channel and a second heat exchange flow channel. The two ends of the first heat exchange flow channel are respectively connected to the anode outlet of the first-stage fuel cell stack 3 and the input end of the condensate removal device. The output end of the condensate removal device is connected to the first inlet of the gas supply mixer 6. The second inlet of the gas supply mixer 6 is used for inputting supplementary fuel. The outlet of the gas supply mixer 6 is communicated with the second heat exchange flow channel. The tail gas output from the anode outlet of the first-stage fuel cell stack 3 can first pass through the first heat exchange flow channel of the heat exchanger 4 and then pass through the condensate removal device to condense and remove the water vapor in the tail gas, enter the gas supply mixer 6, and after being mixed with the supplementary fuel, enter the second heat exchange flow channel of the heat exchanger 4 to absorb heat and increase in temperature, and then enter the anode of the second-stage fuel cell stack 7. It can be seen that when the tail gas passes through the condensate removal device, most of it will be removed by the condensate removal device, so that the concentration of the gas part in the tail gas can be increased. And the second-stage fuel cell stack 7 can also be supplied with fuel through the gas supply mixer 6. Among them, by adjusting the condensate removal rate of the condensate removal device, the oxygen-carbon ratio of the second-stage fuel cell stack 7 can be adjusted, and by adjusting the flow rate of the supplementary fuel passing through the second inlet of the gas supply mixer 6, the fuel utilization rate of the second-stage fuel cell stack 7 can be adjusted.

[0064] Among them, the condensate removal device specifically includes a condenser 8 and a water separator 9 connected in series. The inlet of the condenser 8 is communicated with the first heat exchange flow channel, and the gas outlet of the water separator 9 is communicated with the first inlet of the gas supply mixer 6.

[0065] The water tank 11 is used to supply water to the steam generator 1 and is also used to supply water to the second heat exchange flow channel. It should be noted that an isolation valve and a proportional valve are also provided between the water tank 11 and the water inlet of the steam generator 1, and an isolation valve and a proportional valve are also provided between the water tank 11 and the second heat exchange flow channel. Among them, the isolation valve is used to control the on-off, and the proportional valve is used to control the opening.

[0066] Optionally, the multi-stage fuel cell system further includes a water pump 10. The water pump 10 is connected to the water outlet of the water separator 9 and is also connected to the water tank 11. The water separated from the water separator 9 can be recycled to the water tank 11 through the water pump 10, which can effectively save water resources.

[0067] It should be noted that in addition to being able to introduce fuel into the steam generator 1, an inert gas can also be introduced. Among them, when the inert gas is carbon dioxide or nitrogen, it can play the role of purging the anodes of both the first-stage fuel cell stack 3 and the second-stage fuel cell stack 7 at the same time; when the gas component is water vapor, it plays the role of purging the anode of the first-stage fuel cell stack 3, but when passing through the condensate removal device, most of the water vapor will condense into water and be removed, and cannot continue to enter the second-stage fuel cell stack 7. By supplying water to the second heat exchange flow channel through the water tank 11, after the water enters the second heat exchange flow channel, it absorbs heat and vaporizes into water vapor, which can continue to enter the anode of the second-stage fuel cell stack 7 and purge the anode of the second-stage fuel cell stack 7.

[0068] The reformer 2 is provided with a reforming heat exchange flow path. The heating device is used to heat air, and the heated air can flow through the reforming heat exchange flow path, the cathode of the first fuel cell stack 3, and the cathode of the second fuel cell stack 7. With such an arrangement, after the heating device heats the air, the air temperature rises, and then provides energy for the reforming reaction in the reformer 2, thereby heating the gas passing through the reformer 2, and then can heat the anode of the downstream first fuel cell stack 3, and heat the gas entering the second fuel cell stack 7 in the heat exchanger 4, and then can heat the anode of the second fuel cell stack 7.

[0069] In this embodiment, the heating device includes a burner 13 and an air preheater 12. The first air inlet of the burner 13 is connected to the anode outlet of the second fuel cell stack 7, the second air inlet of the burner 13 is connected to the cathode outlet of the second fuel cell stack 7, the third air inlet of the burner 13 is used to input external fuel, the waste gas generated by the combustion of the burner 13 is used to provide heat for the air preheater 12, and the air preheater 12 is used to heat air. Among them, one source of fuel for the burner 13 is external fuel, and the other is the anode tail gas of the second fuel cell stack 7. The oxygen source of the burner 13 is the cathode tail gas of the second fuel cell stack 7.

[0070] Optionally, the steam generator 1 is provided with a steam heat exchange flow path. The waste gas generated by the combustion of the burner 13 flows through the air preheater 12 and then enters the steam heat exchange flow path to provide heat for the steam generator 1 to vaporize the water vapor entering the steam generator 1.

[0071] Optionally, the heating device further includes a tail gas cooler 5, and the tail gas cooler 5 is used to heat air together with the air preheater 12. Specifically, the tail gas cooler 5 is a plate heat exchanger, which has a flow path for circulating air and a flow path for circulating a heat exchange medium. The two ends of the flow path for circulating the heat exchange medium are respectively connected to the first heat exchange flow path and the condenser 8. Thus, the high-temperature anode tail gas formed after the reaction of the first fuel cell stack 3 can heat the air when flowing through the tail gas cooler 5. In addition, by jointly heating the cold air by the tail gas cooler 5 and the air preheater 12, the heat exchange load of the air preheater 12 can be effectively reduced.

[0072] When the multi-stage fuel cell system generates electricity, natural gas and water are mixed and then heated up in the steam generator 1, and then enter the reformer 2 to undergo a steam reforming reaction to produce hydrogen, and then enter the anode of the first fuel cell stack 3 to generate electricity, and then are cooled down by heat exchange in the heat exchanger 4 and the tail gas cooler 5 in sequence, and then enter the condenser 8 for condensation, and then enter the water separator 9 to remove water, so that the gas concentration can be purified, and then enter the gas supplement mixer 6 and be mixed with the supplementary gas, and after being heated up by heat exchange in the heat exchanger 4, enter the anode of the second fuel cell stack 7 to continue generating electricity, and then enter the burner 13 for combustion. The tail gas after combustion heats the flowing air through the air preheater 12, and finally enters the steam generator 1 to heat the mixture of gas and water and then is discharged from the system.

[0073] The multi-stage fuel cell system further includes a diverter 14, a first mixer 15 and a second mixer 16. The inlet of the diverter 14 is for introducing air. The first outlet of the diverter 14 is connected to the first inlet of the first mixer 15. The second outlet of the diverter 14 is also connected to the air flow passage of the tail gas cooler 5 for air circulation. The third outlet of the diverter 14 is connected to the first inlet of the second mixer 16. The reforming heat exchange passage is connected to the second inlet of the first mixer 15. The outlet of the first mixer 15 is connected to the cathode inlet of the first-stage fuel cell stack 3. The cathode outlet of the first-stage fuel cell stack 3 is connected to the second inlet of the second mixer 16. The outlet of the second mixer 16 is connected to the cathode inlet of the second-stage fuel cell stack 7. After the cold air enters the diverter 14, it is divided into three paths. The first path is the main path and is diverted from the second outlet of the diverter 14. The second path is the bypass path and is diverted from the first outlet of the diverter 14. The third path is the bypass path and is diverted from the third outlet of the diverter 14. The first path of air can be heated up successively through the tail gas cooler 5 and the air preheater 12. The heated hot air enters the reformer 2 to provide heat for the reforming reaction. The hot air output from the reformer 2 is mixed with the cold air bypassed by the second path in the first mixer 15 and enters the cathode of the first-stage fuel cell stack 3. The hot air output from the cathode outlet of the first-stage fuel cell stack 3 is mixed with the cold air bypassed by the third path in the second mixer 16 and then enters the cathode of the second-stage fuel cell stack 7. The hot air output from the cathode outlet of the second-stage fuel cell stack 7 directly enters the burner 13 to provide oxygen for the combustion reaction.

[0074] Among them, the air is driven by a fan to enter the diverter 14. When the power of the fan changes, the amount of air entering the diverter 14 will also change, that is, the flow rate of the air heated by the heating device changes. When the power of the fan remains unchanged, the amount of air entering the diverter 14 remains unchanged, that is, the flow rate of the air heated by the heating device remains unchanged. At this time, by adjusting the diversion ratio of the diverter 14 and the mixing ratio of the first mixer 15, the air temperature entering the cathode of the first-stage fuel cell stack 3 can be adjusted. By adjusting the diversion ratio of the diverter 14 and the mixing ratio of the second mixer 16, the air temperature entering the cathode of the second-stage fuel cell stack 7 can be adjusted.

[0075] The control method of this multi-stage fuel cell system includes a start-up control method and a shutdown control method.

[0076] As Figure 2 and Figure 3 shown, the start-up control method includes the following steps.

[0077] S100: The air flows through the heating device at a first set air flow rate.

[0078] Among them, the air flowing through the heating device at the first set air flow rate means that the amount of air delivered to the heating device is stable. In this embodiment, after the air is delivered to the heating device, hot air is formed, and the hot air can successively pass through the reformer 2, the anode of the first-stage fuel cell stack 3, and the anode of the second-stage fuel cell stack 7 to supply heat to the multi-stage fuel cell system. Further, when the hot air enters the reformer 2, a part of cold air can be mixed. When the air coming out of the reformer 2 enters the cathode of the first-stage fuel cell stack 3, a part of cold air can also be mixed. Before the air output from the cathode of the first-stage fuel cell stack 3 enters the cathode of the second-stage fuel cell stack 7, a part of cold air can also be mixed. Of course, it is also possible that the hot air heated by the heating device does not mix with cold air when passing through the reformer 2, the first-stage fuel cell stack 3, and the second-stage fuel cell stack 7.

[0079] Specifically, in this embodiment, the cold air enters the diverter 14 driven by the fan. The diverter 14 divides it into three paths thereafter. The first path is the main path and is diverted from the second outlet of the diverter 14. The second path is a bypass path and is diverted from the first outlet of the diverter 14. The third path is a bypass path and is diverted from the third outlet of the diverter 14. The air in the first path can be heated up successively through the tail gas cooler 5 and the air preheater 12. The heated hot air enters the reformer 2 to provide heat for the reforming reaction. The hot air output from the reformer 2 is mixed with the cold air bypassed by the second path in the first mixer 15 and enters the cathode of the first-stage fuel cell stack 3. The hot air output from the outlet of the cathode of the first-stage fuel cell stack 3 is mixed with the cold air bypassed by the third path in the second mixer 16 and then enters the cathode of the second-stage fuel cell stack 7. The hot air output from the outlet of the cathode of the second-stage fuel cell stack 7 directly enters the burner 13 to provide oxygen for the combustion reaction.

[0080] S110: Turn on the heating device.

[0081] Specifically, the external fuel is input into the burner 13 from the third air inlet of the burner 13 and ignited for combustion.

[0082] S120: Obtain the temperature at the outlet of the cathode of the first-stage fuel cell stack 3.

[0083] The temperature at the outlet of the cathode of the first-stage fuel cell stack 3 can be detected by a temperature sensor.

[0084] S130: Compare the temperature at the outlet of the cathode of the first-stage fuel cell stack 3 with the set purge temperature.

[0085] When the temperature at the outlet of the cathode of the first-stage fuel cell stack 3 is not less than the set purge temperature, execute S140; when the temperature at the outlet of the cathode of the first-stage fuel cell stack 3 is less than the set purge temperature, return to S120.

[0086] S140: The water tank 11 supplies water to the steam generator 1 and the second heat exchange flow path simultaneously for a set duration.

[0087] By opening the isolation valve and the proportional valve between the water tank 11 and the steam generator 1, the water tank 11 supplies water to the steam generator 1. By opening the isolation valve and the proportional valve between the water tank 11 and the second heat exchange flow path of the heat exchanger 4, the water tank 11 supplies water to the second heat exchange flow path. Water is vaporized into water vapor in the steam generator 1, and further absorbs heat when passing through the reformer 2 and the first-stage stack 3, and can maintain the vapor state. When the water vapor passes through the first-stage stack 3, it enters the first heat exchange flow path of the heat exchanger 4 and exchanges heat with the water in the second heat exchange flow path, so that the water in the second heat exchange flow path is vaporized into water vapor. When the water vapor enters the anode of the second-stage stack 7, it can further absorb heat.

[0088] Since water vapor is likely to condense into water, there are certain requirements for the operating temperature environment. Therefore, purging is required when the cathode outlet temperature of the first-stage stack 3 is not less than the set temperature. At this time, the water vapor can flow smoothly on the anode side and is not easily condensed. Among them, when the water tank 11 supplies water to both the steam generator 1 and the second heat exchange flow path and lasts for a set time, it can ensure that the purging on the anode side is completed. The set time can be set according to the specific model of the multi-stage fuel cell system.

[0089] In this embodiment, by purging the anode side with water vapor at the initial stage of the startup process, the residual gas on the anode side can be blown out, avoiding the residual air on the anode side and causing safety accidents such as explosion when reducing gas is input subsequently. Moreover, the multi-stage fuel cell system is originally equipped with a water tank 11. Therefore, by purging the anode side with water vapor, there is no need to configure other inert gases, the structure is simple, and the cost is low. In addition, in this embodiment, by setting a condensing and water removing device to control the condensation water output rate of the water vapor, and controlling the supply amount of the supplementary fuel through the gas replenishing mixer 6, the two are combined to adjust the fuel utilization rate of the second-stage stack 7 and the oxygen-carbon ratio entering the second-stage stack 7. When the oxygen-carbon ratio is adjusted to the required range, it can ensure that the second-stage stack 7 can generate electricity efficiently when generating electricity. At the same time, the condensing and water removing device will cause most of the water vapor output from the cathode outlet of the first-stage stack 3 to condense into water and be discharged during purging, affecting the purging effect on the second-stage stack 7. By supplying water from the water tank 11 to the second heat exchange flow path of the heat exchanger 4, the condensing and water removing device can be avoided, and the water is vaporized into water vapor by absorbing heat in the second heat exchange flow path, ensuring normal purging of the second-stage stack 7.

[0090] Optionally, the startup control method further includes the following steps after S140:

[0091] S150: Obtain the cathode outlet temperature of the first-stage stack 3 and the cathode outlet temperature of the second-stage stack 7.

[0092] The temperature of the cathode outlet of the second-stage stack 7 can be detected by a temperature sensor.

[0093] S160: Compare the cathode outlet temperatures of the first - stage stack 3 and the second - stage stack 7 with T 1 in terms of magnitude.

[0094] When the cathode outlet temperatures of both the first - stage stack 3 and the second - stage stack 7 are not less than T 1 , execute S170; when the cathode outlet temperature of the first - stage stack 3 or the second - stage stack 7 is less than T 1 , repeat S150.

[0095] S170: The water tank 11 stops supplying water to the second heat - exchange flow path.

[0096] The isolation valve and the proportional valve between the water tank 11 and the second heat - exchange flow path can be closed to achieve the water tank 11 stopping supplying water to the second heat - exchange flow path.

[0097] S180: The intake port of the steam generator 1 starts to admit fuel and the first - stage stack 3 and the second - stage stack 7 do not generate electricity.

[0098] S190: The flow rate of the external fuel fed into the burner 13 gradually decreases to not exceed the set flow rate.

[0099] Among them, when the cathode outlet temperature of the stack is less than T 1 , after admitting fuel, it is likely to cause harmful substances such as nickel carbonyl to be produced. Therefore, when the cathode outlet temperatures of both the first - stage stack 3 and the second - stage stack 7 are not less than T 1 , fuel input can be carried out. Among them, T 1 is greater than the set purge temperature, and before fuel input, it is necessary to make the water tank 11 stop supplying water to the second heat - exchange flow path.

[0100] After fuel input, the fuel enters from the intake port of the steam generator 1, mixes with water vapor, then enters the reformer 2, and then enters the burner 13 to participate in combustion after passing through the first - stage stack 3 and the second - stage stack 7 in sequence, thereby reducing the external fuel supply to the burner 13 to avoid waste.

[0101] S200: Obtain the cathode outlet temperature of the first - stage stack 3.

[0102] S210: Compare the cathode outlet temperature of the first - stage stack 3 with T 2 in terms of magnitude.

[0103] When the cathode outlet temperature of the first - stage stack 3 is not less than T 2 , execute S220; when the cathode outlet temperature of the first - stage stack 3 is less than T 2 , repeat S200;

[0104] S220: The first - stage stack 3 starts to generate electricity.

[0105] When the cathode outlet temperature of the first - stage stack 3 is not less than T 2 it meets the minimum requirement for the first - stage stack 3 to start generating electricity. After the first - stage stack 3 starts generating electricity, the tail gas of the first - stage stack 3 has relatively high heat, which can be used to assist in heating the second - stage stack 7, and the hot air heated by the air pre - heater 12 can also heat the second - stage stack 7 to increase the temperature of the second - stage stack 7. Among them, T 2 > T 1 .

[0106] In addition, the fuel utilization rate of the first - stage stack 3 can be adjusted by adjusting the flow rate of the fuel input to the steam generator 1. Specifically, the fuel utilization rate is less than a certain value according to the performance requirements of the stack. By adjusting the water volume input from the water tank 11 to the steam generator 1, the oxygen - carbon ratio of the first - stage stack 3 can be adjusted. By making the oxygen - carbon ratio within the required range, a relatively high power generation efficiency can be ensured when the first - stage stack 3 generates electricity.

[0107] S230: Obtain the cathode outlet temperature of the first - stage stack 3 and the cathode outlet temperature of the second - stage stack 7.

[0108] S240: Compare the cathode outlet temperature of the first - stage stack 3 with T 3 and the cathode outlet temperature of the second - stage stack 7 with T 2 .

[0109] When the cathode outlet temperature of the first - stage stack 3 is not less than T 3 , and the cathode outlet temperature of the second - stage stack 7 is not less than T 2 , execute S250; when the cathode outlet temperature of the first - stage stack 3 is less than T 3 , or the cathode outlet temperature of the second - stage stack 7 is less than T 2 , repeat S230.

[0110] S250: Supplementary fuel starts to be input from the second inlet of the air - supplement mixer 6.

[0111] S260: The second - stage stack 7 starts generating electricity.

[0112] When the cathode outlet temperature of the first - stage stack 3 is less than T 3 and the cathode outlet temperature of the second - stage stack 7 reaches T 2 after that, the second - stage stack 7 meets the minimum requirement for power generation. At this time, supplementary fuel can be supplemented through the air - supplement mixer 6 to start the second - stage stack 7 generating electricity. Among them, T 3 > T 2 .

[0113] The fuel utilization rate of the secondary fuel cell stack 7 can be adjusted by regulating the flow rate of the supplementary fuel input to the gas replenishment mixer 6; by adjusting the condensation and water removal rate of the condensation and water removal device, the oxygen-carbon ratio of the secondary fuel cell stack 7 can be adjusted. By keeping the oxygen-carbon ratio within the required range, a high power generation efficiency can be ensured when the secondary fuel cell stack 7 generates electricity.

[0114] S270: Obtain the cathode outlet temperature of the primary fuel cell stack 3 and the cathode outlet temperature of the secondary fuel cell stack 7.

[0115] S280: Compare the cathode outlet temperature of the primary fuel cell stack 3 with T 4 and the cathode outlet temperature of the secondary fuel cell stack 7 with T 4 . Among them, T 4 > T 3 .

[0116] When the cathode outlet temperature of the primary fuel cell stack 3 and the cathode outlet temperature of the secondary fuel cell stack 7 are both not less than T 4 , execute S290; when the cathode outlet temperature of the primary fuel cell stack 3 is less than T 4 or the cathode outlet temperature of the secondary fuel cell stack 7 is less than T 4 , repeat S270.

[0117] S290: Stop supplying external fuel to the burner 13.

[0118] S300: The multi-stage fuel cell system has completed startup.

[0119] When the cathode outlet temperature of the primary fuel cell stack 3 and the cathode outlet temperature of the secondary fuel cell stack 7 are both not less than T 4 , at this time, the multi-stage fuel cell system can already operate stably. At this time, the power generation current of the primary fuel cell stack 3 and the power generation current of the secondary fuel cell stack 7 can be gradually increased, and the relevant control circuits can be enabled to supply power to other electrical components of the vehicle. At the same time, after the multi-stage fuel cell system operates stably, the anode-side tail gas is sufficient for the burner 13 to burn, so the supply of external fuel to the burner 13 can be stopped to save fuel.

[0120] As Figure 4 shown, the shutdown control method includes the following steps.

[0121] S1000: Obtain a shutdown instruction.

[0122] S1100: Gradually reduce the power generation power of the primary fuel cell stack 3 to zero and gradually reduce the power generation power of the secondary fuel cell stack 7 to zero.

[0123] S1200: Gradually reduce the flow rate of the fuel introduced into the intake port of the steam generator 1 to the minimum fuel flow rate.

[0124] S1300: The flow rate of the supplementary fuel input from the second inlet of the air supplement mixer 6 gradually drops to zero.

[0125] S1400: Increase the flow rate of the air flowing through the heating device to the second set air flow rate.

[0126] After receiving the shutdown instruction, the power generation of the two fuel cells can be stopped. First, stop the fuel supply of the air supplement mixer 6 that supplies fuel to the secondary fuel cell 7, but maintain the fuel supply of the steam generator 1, so that the anode side is in an atmosphere of reducing gas to prevent the oxidation of the electrodes. At the same time, increase the power of the fan so that more air passes through the heating device, thereby cooling the reformer 2, the primary fuel cell 3, and the secondary fuel cell 7.

[0127] It can be understood that the second set air flow rate is greater than the first set air flow rate.

[0128] S1500: Obtain the cathode outlet temperature of the primary fuel cell 3 and the cathode outlet temperature of the secondary fuel cell 7.

[0129] S1600: Compare the magnitude of the cathode outlet temperature of the primary fuel cell 3 with the oxidation temperature threshold, and the magnitude of the cathode outlet temperature of the secondary fuel cell 7 with the oxidation temperature threshold.

[0130] When the cathode outlet temperature of the primary fuel cell 3 and the cathode outlet temperature of the secondary fuel cell 7 are both not greater than the oxidation temperature threshold, execute S1700; when the cathode outlet temperature of the primary fuel cell 3 or the cathode outlet temperature of the secondary fuel cell 7 is greater than the oxidation temperature threshold, repeat S1500.

[0131] S1700: Stop supplying fuel to the air inlet of the steam generator 1.

[0132] S1800: The water tank 11 supplies water to the second heat exchange channel.

[0133] S1900: After at least the set duration, the water tank 11 stops supplying water to the second heat exchange channel and the steam generator 1.

[0134] S2000: Adjust the flow rate of the air flowing through the heating device to zero.

[0135] When the cathode outlet temperature of the primary fuel cell 3 and the cathode outlet temperature of the secondary fuel cell 7 are both not greater than the oxidation temperature threshold, the fuel supply to the steam generator 1 can be stopped. At this time, there is no oxidation risk. At the same time, turn on the water supply of the water tank 11. The water entering through the steam generator 1 can purge the primary fuel cell 3, and the water entering through the second heat exchange channel of the heat exchanger 4 can purge the secondary fuel cell 7, avoiding the residual reducing gas on the anode side and ensuring safety. After the purging is completed, the fan can be stopped to stop the air supply.

[0136] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A control method for a multi-stage fuel cell system, characterized in that: The multi-stage fuel cell system includes a steam generator, a reformer, a primary stack, a heat exchanger, a condensation and water removal device, a secondary stack, a heating device, an air supply mixer and a water tank. The steam generator, the reformer and the anode inlet of the primary stack are connected in sequence. The heat exchanger has a first heat exchange flow channel and a second heat exchange flow channel. The two ends of the first heat exchange flow channel are respectively connected to the anode outlet of the primary stack and the input end of the condensation and water removal device. The output end of the condensation and water removal device is connected to the first inlet of the air supply mixer. The second inlet of the air supply mixer is used to input supplementary fuel. The outlet of the air supplement mixer is communicated with the second heat exchange flow channel, the second heat exchange flow channel is communicated with the anode inlet of the secondary stack, the water tank is used to supply water to the steam generator, and is used to supply water to the second heat exchange flow channel, the steam generator can generate water vapor from water, the reformer is provided with a reforming heat exchange flow channel, the heating device is used to heat air, and the heated air can flow through the reforming heat exchange flow channel, the cathode of the primary stack and the cathode of the secondary stack, the control method of the multi-stage fuel cell system includes a startup control method, and the startup control method includes: Air flows through the heating device at a first set air flow rate; Turning on the heating device; Obtaining the cathode outlet temperature of the primary fuel cell stack; When the cathode outlet temperature of the first-level fuel cell stack is not less than the set purge temperature, the water tank supplies water to the steam generator and the second heat exchange channel at the same time and continues for a set period of time.

2. The control method of the multi-stage fuel cell system according to claim 1, characterized in that: The heating device includes a burner and an air preheater, wherein the first air inlet of the burner is connected to the anode outlet of the secondary stack, the second air inlet of the burner is connected to the cathode outlet of the secondary stack, the third air inlet of the burner is used to input external fuel, and the exhaust gas generated by the combustion of the burner is used to provide heat to the air preheater, and the air preheater is used to heat air; Turning on the heating device comprises: The external fuel enters the burner from the third air inlet of the burner and is ignited and burned.

3. The control method of the multi-stage fuel cell system according to claim 2, characterized in that: The startup control method further includes, after the water tank simultaneously supplies water to the steam generator and the second heat exchange flow channel: Obtaining the cathode outlet temperature of the primary fuel cell stack and the cathode outlet temperature of the secondary fuel cell stack; When the cathode outlet temperature of the first-stage fuel cell stack and the cathode outlet temperature of the second-stage fuel cell stack are both not less than T1, the water tank stops supplying water to the second heat exchange flow channel; The fuel starts to be introduced into the air inlet of the steam generator and the primary fuel cell stack and the secondary fuel cell stack do not generate electricity; The flow rate of the external fuel introduced into the burner is gradually reduced to not exceed the set flow rate.

4. The control method of the multi-stage fuel cell system according to claim 3, characterized in that: The startup control method further includes, after the flow rate of the external fuel introduced into the burner is gradually reduced to not more than the set flow rate: Obtaining the cathode outlet temperature of the primary fuel cell stack; When the cathode outlet temperature of the primary stack is not less than T2, T2>T1; The first-stage fuel cell stack starts to generate electricity.

5. The control method of the multi-stage fuel cell system according to claim 4, characterized in that: The startup control method further includes, after the first-level stack starts generating electricity: Obtaining the cathode outlet temperature of the primary fuel cell stack and the cathode outlet temperature of the secondary fuel cell stack; When the cathode outlet temperature of the first-stage stack is not less than T3, and the cathode outlet temperature of the second-stage stack is not less than T2, T3>T2; The supplementary fuel is inputted from the second inlet of the supplementary air mixer; The secondary fuel cell stack starts to generate electricity.

6. The control method of the multi-stage fuel cell system according to claim 5, characterized in that: The startup control method further includes, after the secondary stack starts generating electricity: Obtaining the cathode outlet temperature of the primary fuel cell stack and the cathode outlet temperature of the secondary fuel cell stack; When the cathode outlet temperature of the primary stack and the cathode outlet temperature of the secondary stack are both not less than T4, T4>T3; stopping the introduction of external fuel into the burner; The multi-stage fuel cell system startup is completed.

7. The control method of the multi-stage fuel cell system according to claim 5 or 6, characterized in that: The control method of the multi-stage fuel cell system further includes a shutdown control method, and the shutdown control method includes: Get shutdown instructions; The power generation power of the primary stack gradually decreases to zero, and the power generation power of the secondary stack gradually decreases to zero; The flow rate of the fuel introduced into the air inlet of the steam generator is gradually reduced to a minimum fuel flow rate; The flow rate of the supplementary fuel input from the second inlet of the supplementary air mixer gradually decreases to zero.

8. The control method of the multi-stage fuel cell system according to claim 7, characterized in that: The shutdown control method includes the following steps after the flow rate of the supplementary fuel input from the second inlet of the supplementary air mixer gradually decreases to zero: increasing the flow rate of air flowing through the heating device to a second set air flow rate; Obtaining the cathode outlet temperature of the primary fuel cell stack and the cathode outlet temperature of the secondary fuel cell stack; When the cathode outlet temperature of the primary stack and the cathode outlet temperature of the secondary stack are both not greater than the oxidation temperature threshold; The introduction of fuel into the air inlet of the steam generator is stopped.

9. The control method of the multi-stage fuel cell system according to claim 8, characterized in that: The shutdown control method further includes, after stopping the introduction of fuel into the air inlet of the steam generator: The water tank supplies water to the second heat exchange flow channel; After at least a set time, the water tank stops supplying water to the second heat exchange flow channel and the steam generator; The flow rate of air flowing through the heating device is adjusted to zero.

10. A multi-stage fuel cell system, characterized in that: A control method for a multi-stage fuel cell system for implementing any one of claims 1 to 9, wherein the multi-stage fuel cell system comprises a steam generator, a reformer, a primary stack, a heat exchanger, a condensation and water removal device, a secondary stack, a heating device, a water tank and an air supply mixer, wherein the steam generator, the reformer and the anode inlet of the primary stack are connected in sequence, the heat exchanger comprises a first heat exchange channel and a second heat exchange channel, the two ends of the first heat exchange channel are respectively connected to the anode outlet of the primary stack and the input end of the condensation and water removal device, the first inlet of the air supply mixer is connected to the anode outlet of the primary stack and the input end of the condensation and water removal device, and the first inlet of the air supply mixer is connected to the anode outlet of the primary stack and the input end of the condensation and water removal device. The output end of the condensation and water removal device, the second inlet of the air supplement mixer is used to input supplementary fuel, the outlet of the air supplement mixer is connected to the second heat exchange channel, the second heat exchange channel is connected to the anode inlet of the secondary fuel cell stack, the water tank is used to supply water to the steam generator, and is used to supply water to the second heat exchange channel, the steam generator can generate water vapor from water, the reformer is provided with a reforming heat exchange channel, the heating device is used to heat air, and the heated air can flow through the reforming heat exchange channel, the cathode of the primary fuel cell stack and the cathode of the secondary fuel cell stack.

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