Multi-stage fuel cell system, vehicle and starting method of multi-stage fuel cell system

Abstract

The invention relates to the technical field of vehicles, and particularly discloses a multi-stage fuel cell system, a vehicle and a starting method of the multi-stage fuel cell system.The system comprises a first-stage electric pile, a second-stage electric pile... an N-stage electric pile, a reformer and a steam generator, and the reformer is provided with a reforming flow channel and a first heat exchange flow channel; the steam generator is provided with a steam generation flow channel and a second heat exchange flow channel, an inlet of the steam generation flow channel is used for inputting external fuel gas and water, an outlet of the steam generation flow channel is communicated with an inlet of the reforming flow channel, an outlet of the reforming flow channel is communicated with an anode inlet of each electric pile, and an anode outlet of each electric pile is communicated with an inlet of the first heat exchange flow channel; an outlet of the first heat exchange runner is communicated with an inlet of the second heat exchange runner, reformed gas is directly supplied to anodes of all the electric piles through the reformer, the voltage efficiency of all the electric piles can be guaranteed, a nickel-based catalyst is prevented from being oxidized, a cooling water removal device does not need to be arranged between every two adjacent electric piles, the structure can be simplified, and the cost can be reduced.

Description

Technical Field

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

[0002] A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy. It does not require external power charging and can continuously output electrical energy as long as appropriate fuel is provided, and thus has a wide range of applications. Currently, the method of improving the power generation efficiency of a fuel cell system generally adopts the arrangement of multi-stage stacks. In this way, the fuel utilization rate of the system can be improved under the condition that the fuel utilization rate of a single-stage stack is not too high, and further the power generation efficiency of the system can be improved.

[0003] Taking the existing two-stage fuel cell system as an example, it includes a first-stage stack and a second-stage stack connected in series. Specifically, the fuel side is divided into two paths. One path of fuel is directly supplied to the first-stage stack, and then mixed with the other path of fuel and supplied to the second-stage stack. In this way, the fuel concentration entering the second-stage stack can be increased, and the fuel utilization rate of each single stack is improved. However, the most abundant component in the anode exhaust gas of the first-stage stack is water vapor, and its proportion can almost reach 50%. If it is directly mixed with external fuel, it will cause dilution of the fuel, and the fuel entering the second-stage stack will have a lower partial pressure than that of the first-stage stack, which will reduce the voltage efficiency of the second-stage stack and instead affect the overall efficiency of the two-stage fuel cell system. In addition, a large amount of water vapor entering the lower-stage stack will reduce the reducing atmosphere of the stack, cause oxidation of the nickel-based catalyst, lead to a decline in catalytic performance, and cause performance degradation of the stack.

[0004] In this regard, in the prior art, a multi-stage fuel cell system is provided. In adjacent two-stage stacks, the anode exhaust gas of the previous-stage stack is cooled to remove water and then mixed with external fuel and supplied to the subsequent-stage stack. In this way, the voltage efficiency of the subsequent-stage stack can be avoided from decreasing, and the catalyst of the subsequent-stage stack can be protected from oxidation; however, this also results in the need to set up a cooling and water removal device between each adjacent two-stage stacks, with a complex overall structure and high cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-stage fuel cell system, a vehicle, and a starting method for the multi-stage fuel cell system to solve the problem that in the existing multi-stage fuel cell system, in order to avoid the decrease in the voltage efficiency of the subsequent-stage stack and the oxidation of the catalyst, a cooling and water removal device needs to be set between adjacent two-stage stacks, resulting in a complex overall structure and high cost.

[0006] In a first aspect, the present invention provides a multi-stage fuel cell system, which includes:

[0007] N fuel cells, where the N fuel cells are a first - stage fuel cell, a second - stage fuel cell, …, an N - stage fuel cell respectively, and N is a positive integer greater than or equal to 2. The cathode inlet of the first - stage fuel cell is used to input hot air. The hot air output from the cathode outlet of the i - stage fuel cell is mixed with external air through a mixer and then input to the cathode inlet of the (i + 1) - stage fuel cell, where i is a positive integer greater than or equal to 1 and less than N;

[0008] A reformer, having a reforming channel and a first heat - exchange channel. The outlet of the reforming channel is respectively connected to the anode inlet of the first - stage fuel cell, the anode inlet of the second - stage fuel cell, …, the anode inlet of the N - stage fuel cell. The inlet of the first heat - exchange channel is respectively connected to the anode outlet of the first - stage fuel cell, the anode outlet of the second - stage fuel cell, …, the anode outlet of the N - stage fuel cell;

[0009] A steam generator, having a steam - generating channel and a second heat - exchange channel. The inlet of the steam - generating channel is used to input external gas and water. The outlet of the steam - generating channel is connected to the inlet of the reforming channel. The inlet of the second heat - exchange channel is connected to the outlet of the first heat - exchange channel.

[0010] As a preferred technical solution of the multi - stage fuel cell system, the multi - stage fuel cell system further includes:

[0011] A burner. The outlet of the second heat - exchange channel is connected to the fuel inlet of the burner. The cathode outlet of the N - stage fuel cell is connected to the air inlet of the burner;

[0012] An air pre - heater, having an air channel and a third heat - exchange channel. The exhaust gas outlet of the burner is connected to the inlet of the third heat - exchange channel. The inlet of the air channel is used to introduce external air. The outlet of the air channel is connected to the cathode inlet of the first - stage fuel cell.

[0013] As a preferred technical solution of the multi - stage fuel cell system, the multi - stage fuel cell system further includes a condensate water removal device disposed between the steam generator and the burner. The condensate water removal device includes a condenser and a gas - water separator. The outlet of the second heat - exchange channel is connected to the condenser. The condenser is connected to the inlet of the gas - water separator. The exhaust port of the gas - water separator is connected to the fuel inlet of the burner. The drain port of the gas - water separator is connected to the inlet of the steam - generating channel.

[0014] As a preferred technical solution of the multi - stage fuel cell system, the multi - stage fuel cell system further includes a circulation device, which is used to transport a part of the gas transported from the gas - water separator to the burner to the steam generator.

[0015] As a preferred technical solution of the multi-stage fuel cell system, the circulation device includes a circulation pump. The pump inlet of the circulation pump is communicated with the exhaust port of the gas-water separator, and the pump inlet of the circulation pump is communicated with the inlet of the steam generation flow channel; or,

[0016] The circulation device includes an ejector. The inlet of the ejector is used to input external fuel gas and water. The outlet of the ejector is communicated with the inlet of the steam generation flow channel, and the injection port of the ejector is communicated with the exhaust port of the gas-water separator.

[0017] As a preferred technical solution of the multi-stage fuel cell system, the multi-stage fuel cell system further includes N - 1 mixers. A mixer is provided between the cathode outlet of the i-th stack and the cathode inlet of the (i + 1)-th stack. One air inlet of the mixer is communicated with the cathode outlet of the i-th stack, the other air inlet of the mixer is used to introduce external air, and the air outlet of the mixer is communicated with the cathode inlet of the (i + 1)-th stack.

[0018] As a preferred technical solution of the multi-stage fuel cell system, each stack includes a distribution manifold and a plurality of sub-stacks, and the distribution manifold is respectively communicated with the cathode inlets of the respective sub-stacks;

[0019] The outlets of the heavy rectification channels are respectively communicated with the anode inlets of the respective sub-stacks of the first-stage stack, the anode inlets of the respective sub-stacks of the second-stage stack... the anode inlets of the respective sub-stacks of the N-th stack;

[0020] The inlets of the first heat exchange channels are respectively communicated with the anode outlets of the respective sub-stacks of the first-stage stack, the anode outlets of the respective sub-stacks of the second-stage stack... the anode outlets of the respective sub-stacks of the N-th stack;

[0021] The distribution manifold of the first-stage stack is used to input hot air. One air inlet of the mixer is communicated with the cathode outlets of the respective sub-stacks of the i-th stack, and the air outlet of the mixer is communicated with the distribution manifold of the (i + 1)-th stack.

[0022] In a second aspect, the present invention provides a vehicle, including the multi-stage fuel cell system in any of the above solutions, and the multi-stage fuel cell system is used to supply power to the electrical components of the vehicle.

[0023] In a third aspect, the present invention provides a starting method for a multi-stage fuel cell system, which is implemented by the multi-stage fuel cell system in any of the above solutions. The starting method for the multi-stage fuel cell system includes:

[0024] Input hot air into the cathode inlet of the first-stage stack;

[0025] Obtain the temperatures of each stack, and when the temperatures of each stack are not less than the first set temperature, input nitrogen into the steam generator at a set flow rate;

[0026] Obtain the temperatures of each stack, and when the temperatures of each stack are not less than the second set temperature, input water into the steam generator, and at the same time reduce the amount of nitrogen input into the steam generator, and keep the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator at the set flow rate, where the second set temperature is greater than the first set temperature;

[0027] Obtain the real-time temperature of the mixed gas transported by the steam generator to the reformer;

[0028] On the premise that the real-time temperature is not less than the set temperature value, gradually increase the amount of water input into the steam generator, and gradually reduce the amount of nitrogen input into the steam generator, and keep the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator at the set flow rate;

[0029] Obtain the amount of nitrogen input into the steam generator, and when the amount of nitrogen input into the steam generator drops to zero, perform a steam purge operation;

[0030] After the steam purge operation is completed, introduce external fuel into the steam generator, and each stack starts power generation operation.

[0031] As a preferred technical solution of the start-up method of the multi-stage fuel cell system, performing the steam purge operation includes:

[0032] Accumulate the total amount of water vapor transported into the reformer;

[0033] When the total amount reaches the preset flow rate, it is determined that the steam purge operation is completed.

[0034] The beneficial effects of the present invention are as follows:

[0035] The present invention provides a multi-stage fuel cell system, a vehicle, and a starting method for the multi-stage fuel cell system. The multi-stage fuel cell system includes a first-stage fuel cell stack, a second-stage fuel cell stack... an N-stage fuel cell stack, a reformer, and a steam generator. The reformer has a reforming channel and a first heat exchange channel, and the steam generator has a steam generation channel and a second heat exchange channel. The inlet of the steam generation channel is used to input external fuel gas and water, the outlet of the steam generation channel is communicated with the inlet of the reforming channel, the outlet of the reforming channel is respectively communicated with the anode inlets of each fuel cell stack, the anode outlets of each fuel cell stack are all communicated with the inlet of the first heat exchange channel, and the outlet of the first heat exchange channel is communicated with the inlet of the second heat exchange channel. The cathode inlet of the first-stage fuel cell stack is used to input hot air, and the hot air output from the cathode outlet of the i-stage fuel cell stack is mixed with external air through a mixer and then input to the cathode inlet of the (i + 1)-stage fuel cell stack, where i is a positive integer greater than or equal to 1 and less than N. For this multi-stage fuel cell system, the reformer directly supplies reformed gas to the anodes of each fuel cell stack, which can ensure the voltage efficiency of each fuel cell stack and will not cause the nickel-based catalyst of each fuel cell stack to be oxidized. Compared with the prior art, there is no need to set a cooling and water removal device between two adjacent fuel cell stacks, which can effectively simplify the structure and reduce the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of the multi-stage fuel cell system in an embodiment of the present invention Figure 1 ;

[0037] Figure 2 is a schematic structural diagram of the multi-stage fuel cell system in an embodiment of the present invention Figure 2 ;

[0038] Figure 3 is a schematic structural diagram of the multi-stage fuel cell system including two fuel cell stacks in an embodiment of the present invention;

[0039] Figure 4 is a schematic structural diagram of the multi-stage fuel cell system including two fuel cell stacks and each fuel cell stack including two sub-fuel cell stacks in an embodiment of the present invention;

[0040] Figure 5 is a flowchart of the starting method of the multi-stage fuel cell system in an embodiment of the present invention.

[0041] In the figure:

[0042] 1. Steam generator; 2. Reformer;

[0043] 31. First-stage fuel cell stack; 32. Second-stage fuel cell stack; 33. (N - 1)-stage fuel cell stack; 34. N-stage fuel cell stack; 301. Distribution manifold; 302. Sub-fuel cell stack;

[0044] 4. Burner; 5. Air preheater; 6. Condenser; 7. Gas-water separator; 8. Circulation pump; 9. Mixer. Detailed Implementation Modes

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. 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.

[0046] 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. It 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 of 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. Moreover, 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 "below", "under" and "beneath" 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.

[0047] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected" and "coupled" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may 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.

[0048] 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 denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0049] In an existing multi-stage fuel cell system, in adjacent two-stage fuel cell stacks, the anode exhaust gas of the previous-stage fuel cell stack is cooled to remove water and then mixed with external fuel and supplied to the next-stage fuel cell stack. In this way, water vapor in the anode exhaust gas of the previous-stage fuel cell stack can be removed, the voltage efficiency of the next-stage fuel cell stack can be improved, and oxidation of the nickel-based catalyst in the next-stage fuel cell stack can be avoided. However, this requires a cooling and water-removing device to be provided between every two adjacent fuel cell stacks, resulting in a complex overall structure and high cost.

[0050] In view of this, the present embodiment provides a multi-stage fuel cell system to solve the above problems, and this multi-stage fuel cell system can be applied to vehicles.

[0051] Please refer to Figures 1 to 3 , this multi-stage fuel cell system includes N fuel cell stacks, a reformer 2 and a steam generator 1. The N fuel cell stacks are arranged in sequence. The N fuel cell stacks are respectively a first-stage fuel cell stack 31, a second-stage fuel cell stack 32... an N-stage fuel cell stack 34. Each fuel cell stack uses a nickel-based catalyst, and N is a positive integer greater than or equal to 2. The steam generator 1 is used to generate water vapor from water, mix it with external fuel gas and supply it to the reformer 2. The reformer 2 can perform a reforming reaction on a part of the fuel gas (hydrocarbon) and water vapor entering it to generate hydrogen and carbon oxides, and mix the unreacted other part of the fuel gas and water vapor and supply them to the anodes of the N fuel cell stacks.

[0052] Among them, the anode side is arranged as follows: The reformer 2 has a reforming channel and a first heat exchange channel. The steam generator 1 has a steam generation channel and a second heat exchange channel. The inlet of the steam generation channel is used to input external fuel gas and water. The outlet of the steam generation channel is communicated with the inlet of the reforming channel. The outlet of the reforming channel is respectively communicated with the anode inlets of the first-stage fuel cell stack 31, the second-stage fuel cell stack 32... the N-stage fuel cell stack 34. The anode outlets of the first-stage fuel cell stack 31, the second-stage fuel cell stack 32... the N-stage fuel cell stack 34 are all communicated with the inlet of the first heat exchange channel. The outlet of the first heat exchange channel is communicated with the inlet of the second heat exchange channel.

[0053] The cathode side is arranged as follows: The cathode inlet of the first-stage fuel cell stack 31 is used to input hot air. The hot air output from the cathode outlet of the i-stage fuel cell stack is mixed with external air through a mixer 9 and then input to the cathode inlet of the i + 1-stage fuel cell stack, where i is a positive integer greater than or equal to 1 and less than N.

[0054] For the multi-stage fuel cell system provided by the present embodiment, by directly supplying reformed gas to the anodes of each fuel cell stack through the reformer 2, the voltage efficiency of each fuel cell stack can be ensured, and oxidation of the nickel-based catalyst in each fuel cell stack will not be caused. Compared with the prior art, there is no need to provide a cooling and water-removing device between two adjacent fuel cell stacks, which can effectively simplify the structure and reduce the cost.

[0055] In addition, in the prior art, usually, the anode exhaust gas of the fuel cell stack is burned by the burner 4 to generate hot exhaust gas to supply heat to the reformer 2 and the steam generator 1, or heat is supplied to the reformer 2 by the heated hot air. When the seal of the reformer 2 or the steam generator 1 is abnormal, leakage is likely to occur, and then it is easy to cause the oxygen in the exhaust gas or the oxygen in the hot air to leak into the high-temperature fuel gas, posing an explosion risk. In this embodiment, the anode exhaust gas of each fuel cell stack is used to supply heat to the reformer 2 and the steam generator 1. Even if leakage occurs, there is no explosion risk, which greatly improves the safety of the multi-stage fuel cell system. The principle of heating the reformer 2 and the steam generator 1 with the anode exhaust gas of the fuel cell stack is as follows: In the fuel cell stack, the oxygen on the cathode side will enter the anode side through the electrolyte and undergo an electrochemical reaction with the fuel gas to generate water. Therefore, this part of the oxygen will be discharged from the anode along with the exhaust gas of the electrochemical reaction. Therefore, the mass of the exhaust gas (including water vapor, unreacted fuel gas, and carbon oxides) at the anode outlet of the fuel cell stack is greater than the mass of the reformed gas at the anode inlet of the fuel cell stack. The mass of the reformed gas is the same as the mass of the fuel gas and water vapor entering the reformer 2 and is the same as the mass of the fuel gas and water flowing through the steam generator 1. Therefore, in the reformer 2 and the steam generator 1, the flow rate on the hot side is greater than that on the cold side, so the cold side can be heated to the system required temperature.

[0056] In addition, in the prior art, the cathodes of multi-stage fuel cells are usually connected in series in sequence. Due to the pressure drop between the fuel cell stacks, this will cause the air pressure requirement for the cathode of the first-stage fuel cell stack 31 to be particularly large, far exceeding the pressure on the anode side of the first-stage fuel cell stack 31, and leakage is likely to occur, which also poses a safety hazard. Moreover, the temperature of the cathode exhaust gas of the first-stage fuel cell stack 31 is relatively high. If it directly enters the cathode of the second-stage fuel cell stack 32, it is easy to cause the cathode of the second-stage fuel cell stack 32 to exceed the temperature upper limit. In this embodiment, hot air is directly introduced into the cathode of the first-stage fuel cell stack 31. In the second-stage fuel cell stack 32 to the Nth-stage fuel cell stack 34, among any two adjacent fuel cell stacks, the high-temperature exhaust gas of the cathode of the previous-stage fuel cell stack 31 is mixed with external air (normal-temperature air) and then enters the cathode of the next-stage fuel cell stack 31, which can effectively adjust the temperature of the air entering the cathode of the next-stage fuel cell stack 31, thereby avoiding the influence of the cathode temperature of the previous-stage fuel cell stack 31 on the cathode temperature of the next-stage fuel cell stack 31. At the same time, it can also effectively reduce the air pressure requirement at the cathode inlet of the first-stage fuel cell stack 31, avoid leakage, and ensure system safety. Since the air is driven and input by a fan, when the air pressure requirement at the cathode inlet of the first-stage fuel cell stack 31 is reduced, the power load on the fan can also be effectively reduced.

[0057] Optionally, the multi-stage fuel cell system further includes a burner 4 and an air preheater 5. The outlet of the second heat exchange channel is connected to the fuel inlet of the burner 4, and the cathode outlet of the N-stage fuel cell stack 34 is connected to the air inlet of the burner 4; the air preheater 5 has an air flow channel and a third heat exchange channel. The exhaust gas outlet of the burner 4 is connected to the inlet of the third heat exchange channel. The inlet of the air flow channel is used to introduce external air, and the outlet of the air flow channel is connected to the cathode inlet of the first-stage fuel cell stack 31. The waste gas generated by the combustion of the burner 4 can provide heat to the air preheater 5, thereby heating the air flowing through the air preheater 5. Among them, the number of air preheaters 5 can be set to one, or can be set to multiple according to needs. When multiple air preheaters 5 are provided, the air flow channels of the multiple air preheaters 5 are connected in series in sequence. External air flows through the air flow channels of the multiple air preheaters 5 in sequence and enters the cathode inlet of the first-stage fuel cell stack 31. The third heat exchange channels of the multiple air preheaters 5 are connected in series in sequence. The waste gas of the burner 4 flows through the third heat exchange channels of the multiple air preheaters 5 in sequence. In other embodiments, the air entering the cathode of the first-stage fuel cell stack 31 can also be heated by an electric heating device according to needs.

[0058] Optionally, the multi-stage fuel cell system further includes a condensate removal device disposed between the steam generator 1 and the burner 4. The condensate removal device includes a condenser 6 and a gas-liquid separator 7. The outlet of the second heat exchange channel is connected to the condenser 6. The condenser 6 is connected to the gas inlet of the gas-liquid separator 7. The exhaust port of the gas-liquid separator 7 is connected to the fuel inlet of the burner 4, and the drain port of the gas-liquid separator 7 is connected to the inlet of the steam generation channel. With such a setting, the purity of the fuel gas entering the burner 4 can be effectively improved; in addition, by supplying the water separated by the gas-liquid separator 7 to the steam generator 1, a water storage device does not need to be provided, realizing the effective utilization of water resources.

[0059] Optionally, the multi-stage fuel cell system further includes a circulation device for transporting a part of the fuel gas transported from the gas-liquid separator 7 to the burner 4 to the steam generator 1. With such a setting, the reuse of part of the fuel gas can be realized, and the power generation efficiency of the multi-stage fuel cell can be improved.

[0060] Specifically, please refer to Figure 2 , in this embodiment, the circulation device may include a circulation pump 8. The pump inlet of the circulation pump 8 is connected to the exhaust port of the gas-liquid separator 7, and the pump inlet of the circulation pump 8 is connected to the inlet of the steam generation channel. In this way, a part of the gas separated by the gas-liquid separator 7 can be transported to the steam generator 1 through the circulation pump 8.

[0061] As an alternative solution, the circulation device may further include an ejector. The inlet of the ejector is used to input external gas and water. The outlet of the ejector is communicated with the inlet of the steam generation flow channel. The injection port of the ejector is communicated with the exhaust port of the gas-water separator 7. In this way, a part of the gas separated by the gas-water separator 7 can be transported to the steam generator 1 through the ejector.

[0062] Optionally, the multi-stage fuel cell system further includes N-1 mixers 9. A mixer 9 is provided between the cathode outlet of the i-th stack and the cathode inlet of the (i + 1)-th stack. That is to say, between the second stack 32 and the N-th stack 34, a mixer 9 is provided between the cathodes of any two adjacent stacks. One air inlet of the mixer 9 is communicated with the cathode outlet of the i-th stack. The other air inlet of the mixer 9 is used to introduce external air. The air outlet of the mixer 9 is communicated with the cathode inlet of the (i + 1)-th stack. Among them, the amount of external air entering the mixer 9 can be adjusted. In this way, the temperature of the air entering the cathode inlet of the (i + 1)-th stack can be adjusted.

[0063] As Figure 1 The working principle of the anode side of the multi-stage fuel cell system shown in

[0064] As Figure 1The working principle of the cathode side of the multi-stage fuel cell system shown is as follows: External air enters the air flow channel of the air preheater 5, absorbs heat from the third heat exchange flow channel of the air preheater 5 and is heated, and then is transported to the cathode inlet of the first-stage fuel cell stack 31. Then, it undergoes an electrochemical reaction with the anode-side gas within the first-stage fuel cell stack 31. The tail gas is output through the cathode outlet of the first-stage fuel cell stack 31, and then after being mixed with external air, it is transported to the cathode inlet of the second-stage fuel cell stack 32. Then, it undergoes an electrochemical reaction with the anode-side gas within the second-stage fuel cell stack 32. The tail gas is output through the cathode outlet of the second-stage fuel cell stack 32... Then, after being mixed with external air, it is transported to the cathode inlet of the (N - 1)-stage fuel cell stack 33. Then, it undergoes an electrochemical reaction with the anode-side gas within the (N - 1)-stage fuel cell stack 33. The tail gas is output through the cathode outlet of the (N - 1)-stage fuel cell stack 33, and then after being mixed with external air, it is transported to the cathode inlet of the N-stage fuel cell stack 34. Then, it undergoes an electrochemical reaction with the anode-side gas within the N-stage fuel cell stack 34. The tail gas is output through the cathode outlet of the N-stage fuel cell stack 34 and supplied to the burner 4 for combustion. The waste gas generated by the combustion of the burner 4 is then transported to the third heat exchange flow channel of the air preheater 5 for heating air, and the waste gas is discharged to the atmosphere through the third heat exchange flow channel.

[0065] As Figure 2 shown, based on the working principle of the anode side of the multi-stage fuel cell system shown in Figure 1 After separating water and gas through the gas-water separator 7, part of the gas is pumped through the action of the circulation pump 8 to the pipeline for supplying water and external fuel gas to the steam generator 1, so that part of the fuel gas in the anode tail gas can be reused.

[0066] As Figure 2 shown, the working principle of the anode side of the multi-stage fuel cell system shown and Figure 1 the working principle of the anode side of the multi-stage fuel cell system shown are the same.

[0067] Optionally, each stack includes a distribution manifold 301 and a plurality of sub-stacks 302. The distribution manifold 301 is respectively connected to the cathode inlets of the respective sub-stacks 302. The outlets of the heavy rectifying channels are respectively connected to the anode inlets of the respective sub-stacks 302 of the first-stage stack 31, the anode inlets of the respective sub-stacks 302 of the second-stage stack 32... the anode inlets of the respective sub-stacks 302 of the N-stage stack 34; the inlets of the first heat exchange channels are respectively connected to the anode outlets of the respective sub-stacks 302 of the first-stage stack 31, the anode outlets of the respective sub-stacks 302 of the second-stage stack 32... the anode outlets of the respective sub-stacks 302 of the N-stage stack 34; the distribution manifold 301 of the first-stage stack 31 is used to input hot air. One air inlet of the mixer 9 is connected to the cathode outlets of the respective sub-stacks 302 of the i-stage stack, and the air outlet of the mixer 9 is connected to the distribution manifold 301 of the i+1-stage stack. Wherein, the number of sub-stacks 302 in each stack can be one or more. Exemplarily, please refer to Figure 4 , Figure 4 which shows a multi-stage fuel cell system including two stacks, and each stack includes a distribution manifold 301 and two sub-stacks 302.

[0068] It should be noted that the number of sub-stacks 302 in each stack needs to be kept consistent. This is because each stack has an air flow limit, for example, it cannot exceed 20 g / s. In a multi-stage fuel cell system, since the first-stage stack 31 to the N-stage stack 34 are arranged in series, if the number of sub-stacks 302 in a certain stack is inconsistent with the number of sub-stacks 302 in other stacks, it is very easy to cause the air flow of the stack with fewer sub-stacks 302 included to exceed the limit, thereby damaging the stack. For example, a multi-stage fuel cell system includes a first-stage stack 31 and a second-stage stack 32. The first-stage stack 31 includes four sub-stacks 302, and the second-stage stack 32 includes two sub-stacks 302. Then, for the second-stage stack 32, after the air flows out of the first-stage stack 31, it enters each sub-stack 302 of the second-stage stack 32, and the air flow of the sub-stacks 302 of the second-stage stack 32 is almost twice that of the sub-stacks 302 of the first-stage stack 31; similarly, if the second-stage stack 32 includes four sub-stacks 302 and the first-stage stack 31 includes two sub-stacks 302, since the flow rate of the external air entering the cathode of the first-stage stack 31 is determined by the stack with the largest number of sub-stacks 302, this will cause the air flow of the sub-stacks 302 of the first-stage stack 31 to be almost twice that of the sub-stacks 302 of the second-stage stack 32.

[0069] In the multi-stage fuel cell system in the prior art, the cathode side of the stack also adopts a pure parallel arrangement, that is, multiple stacks are connected in parallel, and each stack includes multiple sub-stacks 302 connected in parallel. This arrangement has poor flow uniformity on the air side, which may cause the temperature of individual sub-stacks 302 to be out of control, and may trigger system shutdown due to excessive temperature deviation between stacks. The multi-stage fuel cell system provided in this embodiment can effectively improve this situation and can greatly improve the uniformity of air distribution on the cathode side. Specifically, taking the example that the multi-stage fuel cell system includes a total of four sub-stacks 302. In this embodiment, the multi-stage fuel cell system uses two stacks connected in series, and each stack uses a scheme of two sub-stacks 302 connected in parallel; in the prior art, the multi-stage fuel cell system uses two stacks connected in parallel, and each stack uses a scheme of two sub-stacks 302 connected in parallel. Assuming that in the prior art solution, the amount of air entering the cathode of each stack needs to be 1, the overall air volume is 4; while in this embodiment, only making the amount of air entering each sub-stack 302 of the first-stage stack 31 be 1.2 to 1.5 can meet the air demand of the two stacks. This takes into account that part of the air entering the interior of the sub-stack 302 will enter the anode side to participate in the electrochemical reaction and be consumed. Even so, the overall air volume does not exceed 3, which can greatly reduce the required air volume.

[0070] This embodiment also provides a vehicle, including the above multi-stage fuel cell system, and the multi-stage fuel cell system is used to supply power to the electrical components of the vehicle.

[0071] This embodiment also provides a starting method for a multi-stage fuel cell system, and the starting method for the multi-stage fuel cell system is implemented by the above multi-stage fuel cell system.

[0072] Specifically, please refer to Figure 5 , and the starting method for the multi-stage fuel cell system includes the following steps.

[0073] S100: Input hot air into the cathode inlet of the first-stage stack 31.

[0074] Specifically, the burner 4 is also provided with a gas interface for inputting external gas, directly supplying external gas to the burner 4, and sending air to the air preheater 5 through a blower. When the air enters the burner 4, a combustion reaction occurs, and the generated high-temperature waste gas enters the air preheater 5 to heat the air, realizing the input of hot air into the cathode inlet of the first-stage stack 31.

[0075] During this process, the amount of external air mixed into each mixer 9 can be set to zero, so that the hot air can flow through the cathodes of each stack in sequence to increase the temperature of each stack with the highest efficiency.

[0076] S200: Obtain the temperatures of each fuel cell stack, and when the temperatures of each fuel cell stack are not less than the first set temperature, input nitrogen into the steam generator 1 at a set flow rate.

[0077] The temperatures of each fuel cell stack can be obtained through temperature sensors. Connect a nitrogen cylinder to the inlet of the steam generation flow channel of the steam generator 1 to supply nitrogen to the steam generator 1.

[0078] S300: Obtain the temperatures of each fuel cell stack, and when the temperatures of each fuel cell stack are not less than the second set temperature, input water into the steam generator 1, while reducing the amount of nitrogen input into the steam generator 1, and keep the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator 1 at the set flow rate.

[0079] A water pump can be connected to the inlet of the steam generation flow channel of the water tank and the steam generator 1 to supply water to the steam generator 1. The amount of supplied water and nitrogen are adjusted respectively through regulating valves provided on the pipelines for supplying water and nitrogen.

[0080] Among them, the second set temperature is greater than the first set temperature. When water vapor with a temperature less than the first set temperature is input into the fuel cell stack, it is easy to generate toxic nickel hydroxide at the anode. When the temperature of the fuel cell stack is higher than the second set temperature and remains unchanged, when nitrogen flows through the reformer 2 and the steam generator 1 at the current flow rate, it can vaporize all the water into water vapor and make the temperature of the water vapor not less than the first set temperature.

[0081] S400: Obtain the real-time temperature of the mixed gas transported from the steam generator 1 to the reformer 2.

[0082] The real-time temperature can be detected by a temperature sensor provided at the outlet of the steam generation flow channel of the steam generator 1.

[0083] S500: On the premise that the real-time temperature is not less than the set temperature value, gradually increase the amount of water input into the steam generator 1, and gradually reduce the amount of nitrogen input into the steam generator 1, and keep the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator 1 at the set flow rate.

[0084] The corresponding relationship between the increased amount of water and the reduced amount of nitrogen can be obtained through experiments when the real-time temperature is not less than the set temperature value and if the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator 1 is to be kept at the set flow rate, and the amount of water and nitrogen input into the steam generator 1 are adjusted according to the corresponding relationship.

[0085] During actual operation, the adjustable temperature value can be set. The adjustable temperature is greater than the set temperature value. When the real-time temperature reaches the adjustable temperature value, a unit quantity of water is added each time, and the corresponding quantity of nitrogen is reduced according to the corresponding relationship. Then, after an interval of the set time, a unit quantity of water is added again, and the corresponding quantity of nitrogen is reduced. This cycle repeats. Among them, the value of the set time can be determined through experiments. Specifically, as long as within the interval of the set time, under the heating of hot air, the real-time temperature of the fuel cell stack can reach or exceed the adjustable temperature value again.

[0086] S600: Obtain the amount of nitrogen input to the steam generator 1, and when the amount of nitrogen input to the steam generator 1 drops to zero, perform a steam purge operation.

[0087] Among them, the reason for choosing to perform the purge with steam is that the fuel gas introduced into the fuel cell stack is a hydrocarbon compound. When the temperature is above 300 °C and the water-carbon ratio is less than 2, carbonization will occur. Therefore, choosing to perform the purge with steam can ensure that a steam atmosphere is formed on the entire anode side, and it is not easy to cause carbonization at the initial stage of introducing the fuel gas.

[0088] Specifically, performing the steam purge operation includes: accumulating the total amount of steam transported into the reformer 2;

[0089] When the total amount reaches the preset flow rate, it is determined that the steam purge operation is completed.

[0090] S700: After the steam purge operation is completed, an external fuel is introduced into the steam generator 1, and each fuel cell stack starts to generate electricity and operate.

[0091] The startup method of the multi-stage fuel cell system provided in this embodiment first preliminarily heats each fuel cell stack with air, then raises the temperature of the cathode side with nitrogen, then gradually reduces the amount of nitrogen, and gradually increases the amount of steam, and then performs a purge with steam, which can ensure the safe startup of the multi-stage fuel cell system.

[0092] Obviously, the above embodiments of the present invention are only examples for clearly explaining the present invention, and are not intended to limit 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 list all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A multi-stage fuel cell system, characterized in that: include: N stacks, the N stacks are a first-level stack (31), a second-level stack (32) ... an N-level stack (34), N is a positive integer greater than or equal to 2, the cathode inlet of the first-level stack (31) is used to input hot air, the hot air output from the cathode outlet of the i-level stack is mixed with external air through a mixer (9) and then input to the cathode inlet of the i+1-level stack, i is a positive integer greater than or equal to 1 and less than N; The reformer (2) comprises a reforming flow channel and a first heat exchange flow channel, wherein the outlet of the reforming flow channel is respectively connected to the anode inlet of the first-stage battery stack (31), the anode inlet of the second-stage battery stack (32) ... the anode inlet of the N-stage battery stack (34), and the inlet of the first heat exchange flow channel is respectively connected to the anode outlet of the first-stage battery stack (31), the anode outlet of the second-stage battery stack (32) ... the anode outlet of the N-stage battery stack (34); A steam generator (1) comprises a steam generating flow channel and a second heat exchange flow channel, wherein the inlet of the steam generating flow channel is used to input external fuel gas and water, the outlet of the steam generating flow channel is connected to the inlet of the reforming flow channel, and the inlet of the second heat exchange flow channel is connected to the outlet of the first heat exchange flow channel.

2. The multi-stage fuel cell system according to claim 1, characterized in that: The multi-stage fuel cell system further comprises: A burner (4), wherein the outlet of the second heat exchange flow channel is connected to the fuel inlet of the burner (4), and the cathode outlet of the N-stage fuel cell stack (34) is connected to the air inlet of the burner (4); The air preheater (5) has an air flow channel and a third heat exchange flow channel, the exhaust gas outlet of the burner (4) is connected to the inlet of the third heat exchange flow channel, the inlet of the air flow channel is used to let in external air, and the outlet of the air flow channel is connected to the cathode inlet of the first-stage fuel cell stack (31).

3. The multi-stage fuel cell system according to claim 2, characterized in that: The multi-stage fuel cell system also includes a condensation and dehydration device arranged between the steam generator (1) and the burner (4), the condensation and dehydration device including a condenser (6) and a gas-water separator (7), the outlet of the second heat exchange flow channel is connected to the condenser (6), the condenser (6) is connected to the air inlet of the gas-water separator (7), the exhaust port of the gas-water separator (7) is connected to the fuel inlet of the burner (4), and the drain port of the gas-water separator (7) is connected to the inlet of the steam generation flow channel.

4. The multi-stage fuel cell system according to claim 3, characterized in that: The multi-stage fuel cell system further comprises a circulation device, wherein the circulation device is used to convey part of the fuel gas conveyed from the gas-water separator (7) to the burner (4) to the steam generator (1).

5. The multi-stage fuel cell system according to claim 4, characterized in that: The circulation device comprises a circulation pump (8), the pump inlet of the circulation pump (8) is connected to the exhaust port of the gas-water separator (7), and the pump inlet of the circulation pump (8) is connected to the inlet of the steam generating flow channel; or, The circulation device comprises an ejector, the inlet of the ejector is used to input external fuel gas and water, the outlet of the ejector is communicated with the inlet of the steam generating flow channel, and the ejection port of the ejector is communicated with the exhaust port of the gas-water separator (7).

6. The multi-stage fuel cell system according to claim 1, characterized in that: The multi-stage fuel cell system further comprises N-1 mixers (9), each of which is provided between the cathode outlet of the i-stage fuel cell stack and the cathode inlet of the i+1-stage fuel cell stack, an air inlet of the mixer (9) is connected to the cathode outlet of the i-stage fuel cell stack, another air inlet of the mixer (9) is used for introducing external air, and an air outlet of the mixer (9) is connected to the cathode inlet of the i+1-stage fuel cell stack.

7. The multi-stage fuel cell system according to claim 6, characterized in that: Each battery stack comprises a distribution manifold (301) and a plurality of sub-battery stacks (302), wherein the distribution manifold (301) is connected to cathode inlets of each sub-battery stack (302). The outlet of the reforming flow channel is respectively connected to the anode inlet of each sub-stack (302) of the first-stage stack (31), the anode inlet of each sub-stack (302) of the second-stage stack (32) ... and the anode inlet of each sub-stack (302) of the N-stage stack (34); The inlet of the first heat exchange flow channel is respectively connected to the anode outlets of each sub-stack (302) of the first-level stack (31), the anode outlets of each sub-stack (302) of the second-level stack (32) ... and the anode outlets of each sub-stack (302) of the N-level stack (34); The distribution manifold (301) of the first-level stack (31) is used to input hot air, an air inlet of the mixer (9) is connected to the cathode outlet of each sub-stack (302) of the i-level stack, and the air outlet of the mixer (9) is connected to the distribution manifold (301) of the i+1-level stack.

8. A vehicle, characterized in that: The multi-stage fuel cell system comprises the multi-stage fuel cell system according to any one of claims 1 to 7, wherein the multi-stage fuel cell system is used to supply power to electrical components of a vehicle.

9. A method for starting a multi-stage fuel cell system, characterized in that: The multi-stage fuel cell system is implemented by any one of claims 1 to 8, wherein the startup method of the multi-stage fuel cell system comprises: Inputting hot air into the cathode inlet of the first-stage fuel cell stack (31); Acquiring the temperature of each fuel cell stack, and when the temperature of each fuel cell stack is not less than a first set temperature, inputting nitrogen into the steam generator (1) at a set flow rate; The temperature of each battery stack is obtained, and when the temperature of each battery stack is not less than a second set temperature, water is input into the steam generator (1), while the amount of nitrogen input into the steam generator (1) is reduced, and the total flow rate of the mixed gas of water vapor and nitrogen output from the steam generator (1) is maintained at a set flow rate, and the second set temperature is greater than the first set temperature; Acquiring the real-time temperature of the mixed gas delivered from the steam generator (1) to the reformer (2); On the premise that the real-time temperature is not less than the set temperature value, gradually increase the amount of water input to the steam generator (1), gradually reduce the amount of nitrogen input to the steam generator (1), and maintain the total flow rate of the mixed gas of water vapor and nitrogen output by the steam generator (1) at the set flow rate; Acquiring the amount of nitrogen gas input to the steam generator (1), and when the amount of nitrogen gas input to the steam generator (1) drops to zero, performing a water vapor purge operation; After the steam purge operation is completed, external fuel is introduced into the steam generator (1), and each fuel cell stack starts to generate electricity.

10. The method for starting a multi-stage fuel cell system according to claim 9, characterized in that: Steam purge operations include: accumulating the total amount of water vapor transported into the reformer (2); When the total amount reaches the preset flow rate, it is determined that the steam purge operation is completed.

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