Fuel cell system, fuel cell generator set and regulation and control method of fuel cell generator set

Abstract

The invention discloses a fuel cell system, a fuel cell generator set and a regulation and control method thereof, and relates to the technical field of fuel cells. The fuel cell system comprises a first-stage fuel cell module, a second-stage fuel cell module, a separator, a fuel supply unit and an air supply unit, and the first-stage fuel cell module comprises at least one first-stage electric pile; the primary electric pile comprises a first air electrode, a first fuel electrode and an oxygen ion conductor electrolyte arranged between the first air electrode and the first fuel electrode; the secondary fuel cell module comprises at least one secondary electric pile, and the secondary electric pile comprises a second air electrode, a second fuel electrode and a proton conductor electrolyte arranged between the second air electrode and the second fuel electrode. The fuel supply unit provides fuel for the first-stage fuel cell module or the first-stage fuel cell module and the second-stage fuel cell module, and the air supply unit provides air for the first-stage fuel cell module and the second-stage fuel cell module.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a fuel cell system, a fuel cell power generation set and a control method thereof. Background Art

[0002] A fuel cell is a highly efficient energy conversion device that can directly convert the chemical energy stored in a combustible gas into electrical energy. Since it does not require an intermediate conversion from mechanical energy to electrical energy, it has a higher energy conversion efficiency.

[0003] The high-temperature operation of a high-temperature fuel cell increases the types of fuels that can be used. High-temperature fuel cells can use carbon fuels such as methane, gasoline, and diesel for power generation. The fuel electrode (anode) of a high-temperature fuel cell is composed of porous nickel metal and zirconia. Among them, the support material of the anode-supported cell is the same as the anode material, which is a mixture of nickel metal and zirconia. The thickness of the support is about 500 to 1500 micrometers. An anode functional layer with a thickness of 5 to 50 micrometers is between the support and the electrolyte. The thickness of the electrolyte is 2 to 30 micrometers. Subsequently, the air electrode (cathode) is coated and sintered on the other side of the electrolyte.

[0004] During the electrochemical reaction process of the fuel electrode, the fuel first diffuses into the porous structure of the electrode and then undergoes an electrochemical reaction. During the operation of the stack, the upstream part of the fuel inlet usually contains more fuel and has a higher partial pressure during the diffusion to the reaction surface. In the downstream part of the fuel outlet, a large amount of fuel is consumed by the battery, and the large amount of water vapor generated reduces the diffusion partial pressure and diffusion rate of the fuel in the fuel electrode, affecting the chemical reaction of the anode. Therefore, in the actual industrial application process, generally an excessive amount of fuel is introduced to ensure the fuel diffusivity in the downstream of the fuel flow channel, resulting in a low overall fuel utilization rate of the stack. In addition, the heat generated by the electrochemical reaction of the high-temperature fuel cell under high-temperature conditions is carried by the fuel fluid into the downstream of the fuel flow channel. Usually, the reaction temperature is relatively high in the downstream of the fuel flow channel. Water vapor has strong oxidizing properties at high temperatures, so the nickel metal inside the fuel electrode is very easy to be oxidized to nickel oxide. Nickel oxide agglomerates and its volume increases by about 60%. Therefore, under the condition of high fuel utilization rate, the fuel electrode is prone to expand and crack at the downstream of the fuel flow channel, resulting in the attenuation of the fuel electrode and the attenuation of the system performance.

[0005] In the prior art, a fuel circulation pump is added to a high-temperature fuel cell system to recycle a part of the tail gas at the outlet of the fuel flow channel of the stack to the inlet of the fuel flow channel. Generally, about 50% to 80% of the fuel tail gas is recycled to the inlet of the fuel flow channel. In this way, the fuel utilization rate inside the stack can be controlled to be 50% to 70%. There is still a large amount of unconsumed fuel near the support at the outlet of the fuel flow channel of the stack, which can increase the diffusion of fuel in the support and the functional layer. A large amount of fuel also inhibits the oxidation of nickel metal inside the support at the outlet of the fuel flow channel. At the same time, due to the presence of the fuel circulation pump, the overall fuel utilization rate of the high-temperature fuel cell system can be increased to more than 80%, greatly improving the system efficiency. However, adding a fuel circulation pump to the high-temperature fuel cell system greatly increases the complexity of the high-temperature fuel cell system. The fuel circulation pump operates under high-temperature conditions, and hydrogen and water vapor in the fuel easily corrode the blades and bearings of the fuel circulation pump, resulting in fuel leakage. Considering the long-term operation of the high-temperature fuel cell system, the use of the fuel circulation pump increases the maintenance cost of the high-temperature fuel cell system. Summary of the Invention

[0006] The purpose of the present invention is to provide a fuel cell system, a fuel cell power generation set and its control method, which can improve the fuel utilization rate of the fuel cell system, improve the power generation efficiency of the fuel cell power generation set, and reduce the maintenance cost of the power generation set.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] A fuel cell system, which includes:

[0009] A primary fuel cell module, including at least one primary stack, the primary stack includes a first air electrode, a first fuel electrode, and an oxygen ion conductor electrolyte disposed between the first air electrode and the first fuel electrode;

[0010] A secondary fuel cell module, including at least one secondary stack, the secondary stack includes a second air electrode, a second fuel electrode, and a proton conductor electrolyte disposed between the second air electrode and the second fuel electrode;

[0011] A fuel supply unit and an air supply unit, the fuel supply unit provides fuel for the primary fuel cell module or the primary fuel cell module and the secondary fuel cell module, at least a part of the first fuel tail gas after the reaction of the primary fuel cell module enters the secondary fuel cell module, and the air supply unit provides air for the primary fuel cell module and the secondary fuel cell module.

[0012] As an alternative of the fuel cell system, the fuel cell system further includes a separator disposed between the primary fuel cell module and the secondary fuel cell module for removing at least part of water and / or carbon dioxide in the first fuel tail gas, and the first fuel tail gas after removing water and / or carbon dioxide enters the second fuel electrode.

[0013] As an alternative of the fuel cell system, when the ratio of oxygen element to carbon element in the fuel entering the primary fuel cell module is 0.5 to 3, no carbon deposition occurs on the surface of the first fuel electrode.

[0014] As an alternative of the fuel cell system, the material of the first fuel electrode includes one of a mixture of transition metal and oxygen ion conductor, a mixture of noble metal and oxygen ion conductor, a mixture of transition metal, noble metal and oxygen ion conductor, and a mixture of transition metal, noble metal, oxygen ion conductor and conductive oxide.

[0015] As an alternative of the fuel cell system, when the ratio of oxygen element to carbon element in the fuel entering the secondary fuel cell module is 1 to 3, no carbon deposition occurs on the surface of the second fuel electrode.

[0016] As an alternative of the fuel cell system, the material of the second fuel electrode includes one or a mixture of more of a mixture of transition metal and alkali metal oxide, perovskite zirconate oxide doped with alkali metal element, perovskite cerate oxide doped with alkali metal element, perovskite titanate oxide doped with alkali metal element, perovskite ferrate oxide doped with alkali metal element, perovskite vanadate oxide doped with alkali metal element, perovskite chromate oxide doped with alkali metal element, perovskite manganate oxide doped with alkali metal element, perovskite cobaltate oxide doped with alkali metal element, perovskite nickelate oxide doped with alkali metal element, perovskite cuprate oxide doped with alkali metal element and proton conductor oxide; or,

[0017] a mixture of noble metal and one or a mixture of more of alkali metal oxide, perovskite zirconate oxide doped with alkali metal element, perovskite cerate oxide doped with alkali metal element, perovskite titanate oxide doped with alkali metal element, perovskite ferrate oxide doped with alkali metal element, perovskite vanadate oxide doped with alkali metal element, perovskite chromate oxide doped with alkali metal element, perovskite manganate oxide doped with alkali metal element, perovskite cobaltate oxide doped with alkali metal element, perovskite nickelate oxide doped with alkali metal element, perovskite cuprate oxide doped with alkali metal element and proton conductor oxide; or,

[0018] A mixture of one or more of transition metals, noble metals, and oxides of alkali metals, perovskite zirconate oxides doped with alkali metal elements, perovskite cerate oxides doped with alkali metal elements, perovskite titanate oxides doped with alkali metal elements, perovskite ferrate oxides doped with alkali metal elements, perovskite vanadate oxides doped with alkali metal elements, perovskite chromate oxides doped with alkali metal elements, perovskite manganate oxides doped with alkali metal elements, perovskite cobaltate oxides doped with alkali metal elements, perovskite nickelate oxides doped with alkali metal elements, perovskite cuprate oxides doped with alkali metal elements, and proton conductor oxides; or,

[0019] A mixture of one or more of transition metals, noble metals, conductive oxides, and oxides of alkali metals, perovskite zirconate oxides doped with alkali metal elements, perovskite cerate oxides doped with alkali metal elements, perovskite titanate oxides doped with alkali metal elements, perovskite ferrate oxides doped with alkali metal elements, perovskite vanadate oxides doped with alkali metal elements, perovskite chromate oxides doped with alkali metal elements, perovskite manganate oxides doped with alkali metal elements, perovskite cobaltate oxides doped with alkali metal elements, perovskite nickelate oxides doped with alkali metal elements, perovskite cuprate oxides doped with alkali metal elements, and proton conductor oxides.

[0020] As an alternative of the fuel cell system, the primary fuel cell module includes one or more primary stack groups, each primary stack group includes at least one of the primary stacks, and a plurality of the primary stack groups are connected in series, in parallel, or in a combination of series and parallel;

[0021] The secondary fuel cell module includes one or more secondary stack groups, each secondary stack group includes at least one of the secondary stacks, and a plurality of the secondary stack groups are connected in series, in parallel, or in a combination of series and parallel.

[0022] As an alternative of the fuel cell system, the fuel cell system includes a burner, the burner is disposed in the secondary fuel cell module, and the first air electrode, the second air electrode, the second fuel electrode, the fuel supply unit, and the air supply unit are all in communication with the burner.

[0023] As an alternative of the fuel cell system, the high-temperature exhaust gas generated after the burner burns provides heat for at least part of the fuel provided by the fuel supply unit and at least part of the air provided by the air supply unit through a heat exchange unit.

[0024] As an alternative to the fuel cell system, the heat exchange unit includes a first heat exchanger and a second heat exchanger. The first heat exchanger can transfer the heat of the high-temperature exhaust gas to at least part of the air provided by the air supply unit.

[0025] The second heat exchanger can transfer the heat of the high-temperature exhaust gas to at least part of the fuel provided by the fuel supply unit.

[0026] As an alternative to the fuel cell system, the high-temperature exhaust gas after combustion by the burner is in communication with the waste heat recovery unit.

[0027] As an alternative to the fuel cell system, the fuel supply unit provides high-temperature fuel and low-temperature fuel. The high-temperature fuel is in communication with the feed port of the first fuel electrode, and the low-temperature fuel is controllably distributed to the first fuel electrode and the second fuel electrode.

[0028] The air supply unit provides high-temperature air and low-temperature air. Both the high-temperature air and the low-temperature air are controllably distributed to the first air electrode and the second air electrode.

[0029] As an alternative to the fuel cell system, the air supply unit further includes a mixer group configured to mix the high-temperature air and the low-temperature air entering the first air electrode and the second air electrode.

[0030] As an alternative to the fuel cell system, the fuel cell system further includes a water supply unit and a reformer. Both the water supply unit and the fuel supply unit are in communication with the reformer. The reformer is used to reform the fuel provided by the fuel supply unit, and the reformed fuel enters the first fuel electrode.

[0031] As an alternative to the fuel cell system, the fuel cell system further includes a fuel circulation member disposed between the discharge port of the first fuel electrode and the reformer, so that at least part of the first fuel exhaust gas at the discharge port of the first fuel electrode enters the reformer for reforming.

[0032] As an alternative to the fuel cell system, the fuel cell system includes a first burner and a second burner. The first burner is disposed within the first-stage fuel cell module, and at least part of the high-temperature exhaust gas after the reaction of the first-stage fuel cell stack enters the first burner for combustion. The second burner is disposed within the second-stage fuel cell module, and at least part of the high-temperature exhaust gas after the reaction of the second-stage fuel cell stack enters the second burner for combustion.

[0033] As an alternative of the fuel cell system, all of the high-temperature tail gas after the reaction of the primary fuel cell module enters the second burner for combustion, and for the high-temperature tail gas after the reaction of the secondary fuel cell module, a part of it enters the second burner for combustion, and the other part enters the first burner for combustion.

[0034] As an alternative of the fuel cell system, a part of the high-temperature tail gas after the reaction of the primary fuel cell module enters the first burner for combustion, and the other part enters the second burner for combustion; all of the high-temperature tail gas after the reaction of the secondary fuel cell module enters the second burner for combustion.

[0035] A fuel cell power generation set, which includes the fuel cell system according to any one of the above solutions.

[0036] A control method for a fuel cell power generation set, which is applied to the fuel cell power generation set as described above. The control method for the fuel cell power generation set includes the following steps:

[0037] When the fuel cell system starts up, the air supply unit provides high-temperature air, and the high-temperature air enters the first air electrode and the second air electrode respectively. According to the temperature of the first air tail gas discharged from the first air electrode and the temperature of the second air tail gas discharged from the second air electrode, the fuel supply unit is controlled to supply fuel. When the temperature of the first air tail gas is higher than the start-up temperature of the primary fuel cell stack, the primary fuel cell stack is started up, and the fuel utilization rate of the primary fuel cell stack is controlled to meet the target that the fuel utilization rate of the primary fuel cell stack > 30%; when the temperature of the second air tail gas is higher than the start-up temperature of the secondary fuel cell stack, the secondary fuel cell stack is started up, and the fuel utilization rate of the secondary fuel cell stack is controlled to meet the target that the fuel utilization rate of the secondary fuel cell stack > 40%; and / or,

[0038] When the fuel cell system stops running, the temperature of the first air tail gas discharged from the first air electrode and the temperature of the second air tail gas discharged from the second air electrode are gradually decreased, and the current of the secondary fuel cell stack and the current of the primary fuel cell stack are gradually decreased to zero in sequence. When the temperature of the first air tail gas is lower than the start-up temperature of the primary fuel cell stack and the temperature of the second air tail gas is lower than the start-up temperature of the secondary fuel cell stack, the fuel supply unit stops supplying fuel.

[0039] As an alternative to the control method of the fuel cell power generation set, the fuel cell system further includes a separator, which removes water and / or carbon dioxide from at least part of the first fuel tail gas after the first fuel electrode reaction and then enters the second fuel electrode. When the fuel cell system is started, according to the temperature of the first air tail gas discharged from the first air electrode and the temperature of the second air tail gas discharged from the second air electrode, the steps of controlling the fuel supply unit to supply fuel include:

[0040] When the temperature of the first air tail gas is higher than the first set temperature, the fuel supply unit supplies fuel to the first-stage fuel cell stack, and the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack > 1; by adjusting the separation ratio of the separator and the fuel supplied by the fuel supply unit to the second-stage fuel cell stack, the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack > 0.5, and the first set temperature is lower than the start-up temperature of the first-stage fuel cell stack and the start-up temperature of the second-stage fuel cell stack.

[0041] As an alternative to the control method of the fuel cell power generation set, after starting the first-stage fuel cell stack, by controlling the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack and the current of the first-stage fuel cell stack, the target that the fuel utilization rate of the first-stage fuel cell stack > 30% is met.

[0042] As an alternative to the control method of the fuel cell power generation set, after starting the first-stage fuel cell stack, the method of controlling the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack and the current of the first-stage fuel cell stack to meet the target that the fuel utilization rate of the first-stage fuel cell stack > 30% includes:

[0043] By gradually increasing the fuel flow rate entering the first-stage fuel cell stack, the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack > 1, and at the same time gradually increasing the current of the first-stage fuel cell stack, so that the fuel utilization rate of the first-stage fuel cell stack > 30%.

[0044] As an alternative to the control method of the fuel cell power generation set, after starting the second-stage fuel cell stack, by controlling the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack and the current of the second-stage fuel cell stack, the target that the fuel utilization rate of the second-stage fuel cell stack > 40% is met.

[0045] As an alternative to the control method of the fuel cell power generation set, after starting the second-stage fuel cell stack, the method of controlling the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack and the current of the second-stage fuel cell stack to meet the target that the fuel utilization rate of the second-stage fuel cell stack > 40% includes:

[0046] By gradually increasing the fuel flow rate into the first-stage fuel cell stack and the fuel flow rate provided by the fuel supply unit to the second-stage fuel cell stack, the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack is made > 0.5, and the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack is made > 1. At the same time, gradually increase the current of the second-stage fuel cell stack so that the fuel utilization rate of the second-stage fuel cell stack > 40%.

[0047] As an alternative embodiment of the control method of the fuel cell power generation set, when the fuel cell system stops running, the method of gradually reducing the current of the second-stage fuel cell stack and the current of the first-stage fuel cell stack to zero in sequence includes:

[0048] First, gradually reduce the current of the second-stage fuel cell stack to zero, and at the same time reduce the fuel flow rate provided by the fuel supply unit to the second-stage fuel cell stack, and maintain the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack > 1;

[0049] Then increase the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack to > 1.5, and gradually reduce the current of the first-stage fuel cell stack to zero.

[0050] As an alternative embodiment of the control method of the fuel cell power generation set, when the fuel cell system is running, when the first air exhaust gas temperature is higher than the minimum steady-state operating temperature of the first-stage fuel cell stack, control the fuel utilization rate of the first-stage fuel cell stack between 40% and 95%; when the second air exhaust gas temperature is higher than the minimum steady-state operating temperature of the second-stage fuel cell stack, control the fuel utilization rate of the second-stage fuel cell stack between 50% and 95%.

[0051] As an alternative embodiment of the control method of the fuel cell power generation set, when the first air exhaust gas temperature is higher than the minimum steady-state operating temperature of the first-stage fuel cell stack, the method of controlling the fuel utilization rate of the first-stage fuel cell stack between 40% and 95% includes:

[0052] By adjusting the current of the first-stage fuel cell stack and the fuel flow rate into the first-stage fuel cell stack to satisfy that the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack > 0.5, and then adjusting the current of the first-stage fuel cell stack to control the fuel utilization rate of the first-stage fuel cell stack between 40% and 95%.

[0053] As an alternative embodiment of the control method of the fuel cell power generation set, when the second air exhaust gas temperature is higher than the minimum steady-state operating temperature of the second-stage fuel cell stack, the method of controlling the fuel utilization rate of the second-stage fuel cell stack between 50% and 95% includes:

[0054] Adjust the separation ratio of the separator, the current of the secondary stack, and the flow rate of the fuel provided by the fuel supply unit to the secondary stack to satisfy that the ratio of oxygen element to carbon element in the fuel entering the secondary stack > 1, and then adjust the current of the secondary stack to control the fuel utilization rate of the secondary stack between 50% and 95%.

[0055] As an alternative solution to the control method of the fuel cell power generation set, when the fuel cell system is operating, if the power of the fuel cell system is increased or decreased, by controlling the current of the primary stack and the fuel flow rate entering the primary stack; and / or, by controlling the current of the secondary stack and the fuel flow rate entering the secondary stack to increase or decrease the power of the fuel cell system, ensure that the fuel utilization rate of the primary stack is between 40% and 95%, and the fuel utilization rate of the secondary stack is between 50% and 95%.

[0056] As an alternative solution to the control method of the fuel cell power generation set, when increasing the power of the fuel cell system, by controlling the current of the primary stack and the fuel flow rate entering the primary stack; and / or, by controlling the current of the secondary stack and the fuel flow rate entering the secondary stack, and the method for ensuring that the fuel utilization rate of the primary stack is between 40% and 95% and the fuel utilization rate of the secondary stack is between 50% and 95% includes:

[0057] Keep the current of the primary stack unchanged, increase the fuel flow rate entering the primary stack and the fuel flow rate provided by the fuel supply unit to the secondary stack, increase the current of the secondary stack, and ensure that the fuel utilization rate of the primary stack is between 40% and 95% and the fuel utilization rate of the secondary stack is between 50% and 95%; or,

[0058] Increase the current of the primary stack, increase the fuel flow rate entering the primary stack, keep the current of the secondary stack unchanged, and ensure that the fuel utilization rate of the primary stack is between 40% and 95% and the fuel utilization rate of the secondary stack is between 50% and 95%; or,

[0059] Increase the current of the primary stack, increase the fuel flow rate entering the primary stack and the fuel flow rate provided by the fuel supply unit to the secondary stack, increase the current of the secondary stack, and ensure that the fuel utilization rate of the primary stack is between 40% and 95% and the fuel utilization rate of the secondary stack is between 50% and 95%.

[0060] As an alternative solution to the regulation method of the fuel cell power generation set, when reducing the power of the fuel cell system, by controlling the current of the first-stage stack and the fuel flow rate into the first-stage stack; and / or, by controlling the current of the second-stage stack and the fuel flow rate into the second-stage stack, and ensuring that the fuel utilization rate of the first-stage stack is between 40% and 95%, and the fuel utilization rate of the second-stage stack is between 50% and 95%, the method includes:

[0061] Keep the current of the first-stage stack unchanged, reduce the fuel flow rate into the first-stage stack and the fuel flow rate provided by the fuel supply unit for the second-stage stack, reduce the current of the second-stage stack, and ensure that the fuel utilization rate of the first-stage stack is between 40% and 95%, and the fuel utilization rate of the second-stage stack is between 50% and 95%; or,

[0062] Reduce the current of the first-stage stack, reduce the fuel flow rate into the first-stage stack, keep the current of the second-stage stack unchanged, and ensure that the fuel utilization rate of the first-stage stack is between 40% and 95%, and the fuel utilization rate of the second-stage stack is between 50% and 95%; or,

[0063] Reduce the current of the first-stage stack, reduce the fuel flow rate into the first-stage stack and the fuel flow rate provided by the fuel supply unit for the second-stage stack, reduce the current of the second-stage stack, and ensure that the fuel utilization rate of the first-stage stack is between 40% and 95%, and the fuel utilization rate of the second-stage stack is between 50% and 95%.

[0064] As an alternative solution to the regulation method of the fuel cell power generation set, when starting the fuel cell system, before controlling the fuel supply unit to supply fuel, introduce water vapor or inert gas into the fuel pipeline in the fuel cell system for purging.

[0065] Advantages of the present invention:

[0066] The fuel cell system provided by the present invention includes a primary fuel cell module, a secondary fuel cell module, a fuel supply unit, and an air supply unit. The electrolyte in the primary stack of the primary fuel cell module is set as an oxygen ion conductor electrolyte, and the electrolyte in the secondary stack of the secondary fuel cell module is set as a proton conductor electrolyte. The fuel supply unit supplies fuel to the primary stack or both the primary stack and the secondary stack, and at least part of the first fuel tail gas after the reaction of the primary stack enters the secondary stack. The air supply unit supplies air to the primary stack and the secondary stack. When fuel and air undergo an electrochemical reaction in the primary stack, oxygen ions in the oxygen ion conductor electrolyte are conducted from the first air electrode to the first fuel electrode to react with the fuel. The ratio of oxygen element to carbon element on the surface of the first fuel electrode is higher than that at the inlet of the fuel flow channel of the primary stack, which can ensure the diffusion partial pressure and diffusion rate of the fuel in the first fuel electrode, and improve the fuel utilization rate in the primary stack. When an electrochemical reaction occurs in the secondary stack, hydrogen ions in the proton conductor electrolyte are conducted from the second fuel electrode to the second air electrode to react with air to generate water vapor, and no water vapor is generated inside the second fuel electrode. Therefore, the nickel metal inside the second fuel electrode will not be oxidized to nickel oxide, avoiding the attenuation of the second fuel electrode caused by the expansion and cracking downstream of the outlet of the fuel flow channel. This fuel cell system not only improves the fuel utilization rate and effectively avoids the attenuation of the fuel electrode, but also does not require an increase in the maintenance cost of the fuel cell system.

[0067] The fuel cell power generation set provided by the present invention applies the above fuel cell system, improves the fuel utilization rate, and further improves the power generation efficiency of the fuel cell power generation set, and does not require an increase in the maintenance cost.

[0068] The control method of the fuel cell power generation set provided by the present invention is applied to the above fuel cell power generation set. When the fuel cell system starts and stops operating, the fuel supply unit is controlled to supply fuel and stop supplying fuel, the start and current of the primary stack and the secondary stack are controlled according to the temperature of the first air tail gas discharged from the first air electrode and the temperature of the second air tail gas discharged from the second air electrode, and the fuel utilization rates of the primary stack and the secondary stack are controlled within different ranges at different stages, realizing the effective control of the fuel utilization rates of the primary stack and the secondary stack in the fuel cell system at different stages, thereby improving the fuel utilization rate of the fuel cell system and finally improving the power generation efficiency of the fuel cell power generation set. Description of the Drawings

[0069] Figure 1 It is a schematic diagram of the working principle of the primary stack and the secondary stack in the fuel cell system provided by Embodiment 1 of the present invention;

[0070] Figure 2It is the schematic diagram of the first-stage stack group with the first structure in the fuel cell system provided by the first embodiment of the present invention;

[0071] Figure 3 It is the schematic diagram of the first-stage stack group with the second structure in the fuel cell system provided by the first embodiment of the present invention;

[0072] Figure 4 It is the schematic diagram of the working principles of the fuel supply unit, air supply unit, first-stage stack and second-stage stack in one of the fuel cell systems provided by the first embodiment of the present invention;

[0073] Figure 5 It is the schematic diagram of the working principle of one of the fuel cell systems provided by the first embodiment of the present invention;

[0074] Figure 6 It is the schematic diagram of the working principle of another fuel cell system provided by the first embodiment of the present invention Figure 1 ;

[0075] Figure 7 It is the schematic diagram of the working principle of another fuel cell system provided by the first embodiment of the present invention Figure 2 .

[0076] In the figure:

[0077] 100, first-stage fuel cell module; 200, second-stage fuel cell module;

[0078] 1, first-stage stack; 2, second-stage stack; 3, water separator; 4, carbon dioxide separator; 5, first flow control valve; 6, first flow distributor; 7, second flow control valve; 8, first mixer; 9, second mixer; 10, third mixer; 11, burner; 12, fuel source; 13, first flow controller; 14, fan; 15, second flow distributor; 16, first heat exchanger; 17, second heat exchanger; 18, third heat exchanger; 19, waste heat recovery unit; 20, water supply unit; 21, fourth mixer; 22, reformer; 23, second flow controller; 24, third flow distributor; 25, third flow controller; 26, fuel circulation part; 27, fourth flow distributor; 28, desulfurization tank; 29, filter;

[0079] 101, first air electrode; 102, first fuel electrode; 103, oxygen ion conductor electrolyte; 201, second air electrode; 202, second fuel electrode; 203, proton conductor electrolyte. Detailed implementation manners

[0080] Embodiments of the present invention will be described in detail below. 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 having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0081] 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 accompanying drawings. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply 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 limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0082] Unless otherwise clearly defined and limited, the terms "mounted", "connected", "connected to", "fixed" should be understood in a broad sense. For example, it can be a fixed connection or a detachable 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 or the interaction relationship between 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 circumstances.

[0083] Unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the first feature and the second feature being in direct contact, or may include the first feature and the second feature not being in direct contact but being in contact through additional features therebetween. 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 merely indicating that the first feature is at a higher horizontal level 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 merely indicating that the first feature is at a lower horizontal level than the second feature.

[0084] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific embodiments.

[0085] Embodiment 1:

[0086] As Figure 1As shown in the figure, this embodiment provides a fuel cell system, which includes a first - stage fuel cell module 100, a second - stage fuel cell module 200, a separator, a fuel supply unit, and an air supply unit. The fuel supply unit supplies fuel to the first - stage fuel cell module 100 or both the first - stage fuel cell module 100 and the second - stage fuel cell module 200. At least part of the first fuel exhaust gas after the reaction of the first - stage fuel cell module 100 enters the second - stage fuel cell module 200. The air supply unit supplies air to the first - stage fuel cell module 100 and the second - stage fuel cell module 200. Fuel and air enter the first - stage fuel cell module 100, and an electrochemical reaction occurs in the first - stage fuel cell module 100 to generate electric energy; fuel and air enter the second - stage fuel cell module 200, and an electrochemical reaction occurs in the second - stage fuel cell module 200 to generate electric energy.

[0087] The first - stage fuel cell module 100 includes at least one first - stage fuel cell stack 1. The first - stage fuel cell stack 1 includes a first air electrode 101, a first fuel electrode 102, and an oxygen - ion conductor electrolyte 103 disposed between the first air electrode 101 and the first fuel electrode 102.

[0088] Specifically, the first - stage fuel cell module 100 includes one or more first - stage fuel cell stack groups. Each first - stage fuel cell stack group includes at least one first - stage fuel cell stack 1, and multiple first - stage fuel cell stack groups are connected in series, parallel, or in a hybrid connection.

[0089] When a first - stage fuel cell stack group includes multiple first - stage fuel cell stacks 1, as Figure 2 shown, multiple first - stage fuel cell stacks 1 can be connected in parallel. As Figure 3 shown, multiple first - stage fuel cell stacks 1 can also be connected in series. Or, multiple first - stage fuel cell stacks 1 are connected in a hybrid connection, that is, multiple first - stage fuel cell stacks 1 are divided into at least two groups, each group includes at least two first - stage fuel cell stacks 1, and after at least two first - stage fuel cell stacks 1 in each group are connected in parallel, they are connected in series with other groups. Similarly, when the first - stage fuel cell module 100 includes multiple first - stage fuel cell stack groups, the multiple first - stage fuel cell stack groups are connected in series, parallel, or in a hybrid connection.

[0090] The first - stage fuel cell stack 1 includes at least one first - stage single - cell battery. The first - stage single - cell battery includes a first air electrode 101, a first fuel electrode 102, and an oxygen - ion conductor electrolyte 103. The first - stage single - cell battery can use the first air electrode 101, the first fuel electrode 102, or the oxygen - ion conductor electrolyte 103 as a support structure, and the thickness of the support structure is relatively large. Of course, a separate support can also be provided inside the first - stage single - cell battery, and the support is made of metal or oxide.

[0091] The oxygen - ion conductor electrolyte 103 is an oxygen - ion conductor (O 2-) During operation, oxygen ions are conducted from the first air electrode 101 to the first fuel electrode 102. When the fuel and air undergo an electrochemical reaction in the first fuel cell stack 1, the oxygen ions in the oxygen ion conductor electrolyte 103 are conducted from the first air electrode 101 to the first fuel electrode 102 to react with the fuel. The ratio of oxygen element to carbon element on the surface of the first fuel electrode 102 is higher than that at the inlet of the fuel flow channel of the first fuel cell stack 1, which can ensure the diffusion partial pressure and diffusion rate of the fuel in the first fuel electrode 102, and improve the fuel utilization rate in the first fuel cell stack 1.

[0092] The secondary fuel cell module 200 includes at least one secondary fuel cell stack 2, and the secondary fuel cell stack 2 includes a second air electrode 201, a second fuel electrode 202, and a proton conductor electrolyte 203 disposed between the second air electrode 201 and the second fuel electrode 202.

[0093] Specifically, the secondary fuel cell module 200 includes one or more secondary fuel cell stack groups, each secondary fuel cell stack group includes at least one secondary fuel cell stack 2, and multiple secondary fuel cell stack groups are connected in series, parallel, or in a hybrid connection.

[0094] When a secondary fuel cell stack group includes multiple secondary fuel cell stacks 2, the multiple secondary fuel cell stacks 2 can be connected in parallel. The multiple secondary fuel cell stacks 2 can also be connected in series. Or, the multiple secondary fuel cell stacks 2 are connected in a hybrid connection, that is, the multiple secondary fuel cell stacks 2 are divided into at least two groups, each group includes at least two secondary fuel cell stacks 2, and after the at least two secondary fuel cell stacks 2 in each group are connected in parallel, they are connected in series with other groups. Similarly, when the secondary fuel cell module 200 includes multiple secondary fuel cell stack groups, the multiple secondary fuel cell stack groups are connected in series, parallel, or in a hybrid connection.

[0095] The secondary fuel cell stack 2 includes at least one secondary single cell, and the secondary single cell includes a second air electrode 201, a second fuel electrode 202, and a proton conductor electrolyte 203. The secondary single cell can use the second air electrode 201, the second fuel electrode 202, and the proton conductor electrolyte 203 as a support structure, and the thickness of the support structure is relatively large. Of course, a separate support can also be provided inside the secondary single cell, and the support is made of metal or oxide.

[0096] The proton conductor electrolyte 203 is a hydrogen ion conductor (H + ) During operation, protons are conducted from the second fuel electrode 202 to the second air electrode 201. When the secondary fuel cell stack 2 undergoes an electrochemical reaction, the hydrogen ions in the proton conductor electrolyte 203 are conducted from the second fuel electrode 202 to the second air electrode 201 to react with air to generate water vapor, and water vapor will not be generated inside the second fuel electrode 202. Therefore, the nickel metal inside the second fuel electrode 202 will not be oxidized to nickel oxide, avoiding the attenuation of the second fuel electrode 202 caused by the expansion and cracking downstream of the outlet of the fuel flow channel.

[0097] The separator is disposed between the first - stage fuel cell module 100 and the second - stage fuel cell module 200, and is used to remove at least part of the water and / or carbon dioxide in the first fuel exhaust gas. The first fuel exhaust gas after removing water and / or carbon dioxide enters the second fuel electrode 202.

[0098] Specifically, the separator includes a water separator 3, which is disposed between the first - stage fuel cell module 100 and the second - stage fuel cell module 200 and is used to separate water in at least part of the fuel exhaust gas in the first - stage fuel cell module 100; and / or, the separator includes a carbon dioxide separator 4, which is disposed between the first - stage fuel cell module 100 and the second - stage fuel cell module 200 and is used to separate carbon dioxide in at least part of the fuel exhaust gas in the first - stage fuel cell module 100.

[0099] The fuel exhaust gas flowing out of the first - stage fuel cell module 100 includes hydrogen, carbon monoxide, carbon dioxide, water vapor and part of methane. After removing water and carbon dioxide through the separator, there are still hydrogen, carbon monoxide, methane and a small amount of carbon dioxide and water left, which enter the second - stage fuel cell module 200. At the same time, the fuel supply unit supplies part of the fuel to the second - stage fuel cell module 200 to carry out an electrochemical reaction. At least part of the first fuel exhaust gas after the reaction of the first - stage fuel cell stack 1 enters the second - stage fuel cell stack 2 for reaction after removing water and carbon dioxide through the separator, greatly improving the fuel utilization rate of the second - stage fuel cell stack 2.

[0100] The fuel cell system provided in this embodiment, by setting two - stage fuel cell stacks to consume fuel in stages, and setting the electrolyte in the first - stage fuel cell stack 1 as an oxygen - ion conductor electrolyte 103, increases the ratio of oxygen element to carbon element on the surface of the first fuel electrode 102, improves the fuel concentration. When supplying fuel to the first - stage fuel cell stack 1, there is no need to increase the ratio of oxygen element to carbon element of the fuel at the fuel inlet of the first fuel electrode 102, and the operating voltage of the first - stage fuel cell stack 1 under a constant current is improved. The electrolyte in the second - stage fuel cell stack 2 is set as a proton - conductor electrolyte 203. The water vapor generated in the second - stage fuel cell stack 2 has very little water vapor on the surfaces of the second air electrode 201 and the second fuel electrode 202, avoiding the expansion and cracking of the second fuel electrode 202 caused by the oxidation of nickel in the second fuel electrode 202, thus avoiding the attenuation of the second fuel electrode 202. Moreover, after pre - removing water and carbon dioxide in the first fuel exhaust gas of the first - stage fuel cell stack 1, the fuel utilization rate and the operating voltage under a constant current of the second - stage fuel cell stack 2 are improved, and the efficiency of the fuel cell system is greatly enhanced.

[0101] Of course, in other embodiments, the separator may not be provided, and the fuel in the secondary fuel cell module 200 is only provided by the first fuel exhaust gas after the reaction of the primary fuel cell module 100. Alternatively, a water separator 3 and a carbon dioxide separator 4 are provided. After the first fuel exhaust gas after the reaction of the primary fuel cell module 100 removes water through the water separator 3, it is then supplied to the secondary fuel cell module 200 after removing carbon dioxide through the carbon dioxide separator 4, and the fuel supply unit does not supply fuel to the secondary fuel cell module 200. Alternatively, only the water separator 3 is provided. After the first fuel exhaust gas after the reaction of the primary fuel cell module 100 removes water through the water separator 3, it is mixed with the fuel supplemented by the fuel supply unit and then enters the secondary fuel cell module 200. Alternatively, only the carbon dioxide separator 4 is provided. After the first fuel exhaust gas after the reaction of the primary fuel cell module 100 removes carbon dioxide through the carbon dioxide separator 4, it is mixed with the fuel supplemented by the fuel supply unit and then enters the secondary fuel cell module 200.

[0102] In the prior art, the surface anti-carbon deposition ability of the fuel electrode is weak, and water needs to be added to the fuel flow channel of the fuel electrode to ensure the ratio of oxygen element to carbon element in the fuel entering the fuel electrode. However, too much water in the fuel electrode is easily oxidized, which in turn causes attenuation of the fuel electrode.

[0103] Furthermore, when the ratio of oxygen element to carbon element in the fuel entering the primary fuel cell module 100 is 0.5 - 3, no carbon deposition occurs on the surface of the first fuel electrode 102. When the ratio of oxygen element to carbon element in the fuel entering the secondary fuel cell module 200 is 1 - 3, no carbon deposition occurs on the surface of the second fuel electrode 202. By changing the anti-carbon deposition ability of the first fuel electrode 102 and the second fuel electrode 202, the ratio of oxygen element to carbon element in the fuel entering the primary fuel stack 1 and the secondary fuel stack 2 can be reduced. In this way, the primary fuel stack 1 and the secondary fuel stack 2 can carry out electrochemical reactions when the ratio of oxygen element to carbon element in the fuel is lower, improving the efficiency of the fuel cell system.

[0104] In this embodiment, by changing the material of the first fuel electrode 102, the first fuel electrode 102 is ensured to meet the above conditions.

[0105] Specifically, the material of the first fuel electrode 102 includes one of a mixture of transition metal and oxygen ion conductor, a mixture of noble metal and oxygen ion conductor, a mixture of transition metal, noble metal and oxygen ion conductor, and a mixture of transition metal, noble metal, oxygen ion conductor and conductive oxide.

[0106] Similarly, by changing the material of the second fuel electrode 202, the second fuel electrode 202 is ensured to meet the above conditions.

[0107] Specifically, the material of the second fuel electrode 202 includes a mixture of one or more of a transition metal and an alkali metal oxide, a perovskite zirconate oxide doped with an alkali metal element, a perovskite cerate oxide doped with an alkali metal element, a perovskite titanate oxide doped with an alkali metal element, a perovskite ferrate oxide doped with an alkali metal element, a perovskite vanadate oxide doped with an alkali metal element, a perovskite chromate oxide doped with an alkali metal element, a perovskite manganate oxide doped with an alkali metal element, a perovskite cobaltate oxide doped with an alkali metal element, a perovskite nickelate oxide doped with an alkali metal element, a perovskite cuprate oxide doped with an alkali metal element, and a proton conductor oxide; or,

[0108] a mixture of one or more of a noble metal and an alkali metal oxide, a perovskite zirconate oxide doped with an alkali metal element, a perovskite cerate oxide doped with an alkali metal element, a perovskite titanate oxide doped with an alkali metal element, a perovskite ferrate oxide doped with an alkali metal element, a perovskite vanadate oxide doped with an alkali metal element, a perovskite chromate oxide doped with an alkali metal element, a perovskite manganate oxide doped with an alkali metal element, a perovskite cobaltate oxide doped with an alkali metal element, a perovskite nickelate oxide doped with an alkali metal element, a perovskite cuprate oxide doped with an alkali metal element, and a proton conductor oxide; or,

[0109] a mixture of one or more of a transition metal, a noble metal and an alkali metal oxide, a perovskite zirconate oxide doped with an alkali metal element, a perovskite cerate oxide doped with an alkali metal element, a perovskite titanate oxide doped with an alkali metal element, a perovskite ferrate oxide doped with an alkali metal element, a perovskite vanadate oxide doped with an alkali metal element, a perovskite chromate oxide doped with an alkali metal element, a perovskite manganate oxide doped with an alkali metal element, a perovskite cobaltate oxide doped with an alkali metal element, a perovskite nickelate oxide doped with an alkali metal element, a perovskite cuprate oxide doped with an alkali metal element, and a proton conductor oxide; or,

[0110] a mixture of one or more of a transition metal, a noble metal, a conductive oxide and an alkali metal oxide, a perovskite zirconate oxide doped with an alkali metal element, a perovskite cerate oxide doped with an alkali metal element, a perovskite titanate oxide doped with an alkali metal element, a perovskite ferrate oxide doped with an alkali metal element, a perovskite vanadate oxide doped with an alkali metal element, a perovskite chromate oxide doped with an alkali metal element, a perovskite manganate oxide doped with an alkali metal element, a perovskite cobaltate oxide doped with an alkali metal element, a perovskite nickelate oxide doped with an alkali metal element, a perovskite cuprate oxide doped with an alkali metal element, and a proton conductor oxide.

[0111] Exemplarily, the transition metal can be Ni, Fe, Co, Cu, etc. The oxygen ion conductor can be ZrO 2 , CeO 2 or LaGaO 3 , etc. The noble metal can be Ru, Pt, Pd, Au, Rh, Ir, etc. The conductive oxide includes cerium oxide doped with rare earth elements and transition metal elements, perovskite titanate doped with alkali metal elements, transition metal elements and rare earth elements, perovskite chromate doped with alkali metal elements, transition metal elements and rare earth elements, perovskite ferrate doped with alkali metal elements, transition metal elements and rare earth elements, perovskite manganate doped with alkali metal elements, transition metal elements and rare earth elements, perovskite nickelate doped with alkali metal elements, transition metal elements and rare earth elements, or perovskite vanadate doped with alkali metal elements, transition metal elements and rare earth elements.

[0112] One optional solution provided in this embodiment is that there is one fuel supply unit and one air supply unit. Both the primary fuel cell module 100 and the secondary fuel cell module 200 are connected to the fuel supply unit, and both the primary fuel cell module 100 and the secondary fuel cell module 200 are connected to the air supply unit; the fuel cell system includes a burner 11, the burner 11 is arranged in the secondary fuel cell module 200, and the first air electrode 101, the second air electrode 201, the second fuel electrode 202, the fuel supply unit and the air supply unit are all connected to the burner 11. One fuel supply unit and one air supply unit are arranged in the fuel cell system to supply air and fuel to the primary fuel cell module 100 and the secondary fuel cell module 200 respectively. One burner 11 is arranged in the fuel cell system. When the fuel cell system is started, the fuel supply unit supplies fuel to the burner 11, and the air exhausted from the primary fuel cell module 100 and the secondary fuel cell module 200 after the air supplied by the air supply unit enters them enters the burner 11 for combustion. The high-temperature exhaust gas after the burner 11 burns provides preheating heat for the entire fuel cell system. During the operation of the fuel cell system, at least part of the first air exhaust gas generated by the first air electrode 101, the second air exhaust gas generated by the second air electrode 201, and the second fuel exhaust gas generated by the second fuel electrode 202 can all enter the burner 11 for combustion, and the high-temperature exhaust gas after the burner 11 burns continuously provides preheating energy for the fuel and air in the fuel cell system.

[0113] The burner 11 generates high-temperature exhaust gas after combustion, and the high-temperature exhaust gas provides heat for at least part of the fuel provided by the fuel supply unit and at least part of the air provided by the air supply unit through the heat exchange unit.

[0114] Specifically, the heat exchange unit includes a first heat exchanger 16 and a second heat exchanger 17. The first heat exchanger 16 can transfer the heat of the high-temperature tail gas to at least part of the air supplied by the air supply unit to form high-temperature air. The second heat exchanger 17 can transfer the heat of the high-temperature tail gas to at least part of the fuel supplied by the fuel supply unit to form high-temperature fuel. The first heat exchanger 16 is used to transfer the heat in the high-temperature tail gas after the reaction of the burner 11 to at least part of the air supplied by the air supply unit, so that at least part of the air forms high-temperature air to enter the first-stage stack 1 and the second-stage stack 2 for reaction. The second heat exchanger 17 is used to transfer the heat in the high-temperature tail gas after the reaction of the burner 11 to at least part of the fuel supplied by the fuel supply unit, so that at least part of the fuel forms high-temperature fuel to enter the first-stage stack 1 and the second-stage stack 2 for reaction.

[0115] Furthermore, the high-temperature tail gas after the combustion of the burner 11 is communicated with the waste heat recovery unit 19. The waste heat recovery unit 19 recovers the excess heat of the fuel cell system and supplies it to the unit that demands heat externally, avoiding energy waste.

[0116] Specifically, the heat exchange unit further includes a third heat exchanger 18. The third heat exchanger 18 is used to transfer the heat in the entire fuel cell system to the waste heat recovery unit 19, and the waste heat recovery unit 19 recovers the heat. Of course, in other embodiments, a heat exchange component for exchanging heat with the high-temperature tail gas can also be provided in the waste heat recovery unit 19, and the high-temperature tail gas is discharged after exchanging heat with the heat exchange component.

[0117] Specifically, as Figure 4 and Figure 5 shown, the fuel supply unit includes a fuel source 12. The fuel source 12 is communicated with the burner 11 through a first flow controller 13, and the discharge port of the second fuel electrode 202 is communicated with the burner 11. The fuel source 12 is communicated with the first-stage stack 1, the second-stage stack 2 and the burner 11 through a third flow distributor 24. A third flow controller 25 is further provided between the third flow distributor 24 and the first-stage stack 1 and the second-stage stack 2. The third flow controller 25 is used to control the fuel flow rate entering the first-stage stack 1 and the second-stage stack 2.

[0118] The fuel in the fuel source 12 is desulfurized by a desulfurization tank 28 and then distributed by the third flow distributor 24 to supply the first-stage stack 1, the second-stage stack 2 and the burner 11 respectively. The first flow controller 13 is used to control the fuel flow rate entering the burner 11, and the third flow controller 25 is used to control the fuel flow rate entering the first-stage stack 1 and the second-stage stack 2. The fuel is desulfurized by the desulfurization tank 28, which can avoid the sulfur in the fuel from undergoing an oxidation reaction to generate sulfur dioxide and then polluting the environment after being discharged into the atmosphere.

[0119] The air supply unit includes a blower 14 and a second flow distributor 15. The blower 14 is communicated with the first air electrode 101 and the second air electrode 201 through the second flow distributor 15. The air outlets of the first air electrode 101 and the second air electrode 201 are both communicated with the burner 11. A filter 29 is also arranged in front of the blower 14 to filter impurities entering the blower 14, so as to avoid impurities entering the fuel cell system and affecting the efficiency of the fuel cell system.

[0120] The high-temperature tail gas generated by the reaction of the fuel and air entering the burner 11 transfers heat to the air supplied to the first stack 1 and the second stack 2 by the blower 14 through the first heat exchanger 16, heating the air into high-temperature air, and transfers heat to the fuel supplied to the first stack 1 and the second stack 2 by the fuel source 12 through the second heat exchanger 17, heating the fuel into high-temperature fuel.

[0121] Furthermore, the fuel supply unit supplies high-temperature fuel and low-temperature fuel. The high-temperature fuel is communicated with the feed port of the first fuel electrode 102, and the low-temperature fuel is controllably distributed to the first fuel electrode 102 and the second fuel electrode 202.

[0122] Specifically, the low-temperature fuel is respectively communicated with the feed port of the first fuel electrode 102 and the feed port of the second fuel electrode 202 through the first flow control valve 5. The high-temperature fuel is part of the fuel provided by the fuel source 12 that has been heat-exchanged with the high-temperature tail gas through the second heat exchanger 17, and the low-temperature fuel is part of the fuel that has not been heat-exchanged with the high-temperature tail gas through the second heat exchanger 17. After the low-temperature fuel passes through the first flow control valve 5, the first flow control valve 5 divides the low-temperature fuel into two parts. One part of the low-temperature fuel is mixed with the high-temperature fuel and then enters the first stack 1. After the first fuel tail gas of the first stack 1 separates water through the water separator 3 and then separates out part of the carbon dioxide through the carbon dioxide separator 4, it is mixed with the other part of the low-temperature fuel split by the first flow control valve 5 and then enters the second stack 2. The second fuel tail gas after the reaction of the second stack 2 enters the burner 11 for combustion.

[0123] The air supply unit supplies high-temperature air and low-temperature air, and both the high-temperature air and the low-temperature air are controllably distributed to the first air electrode 101 and the second air electrode 201.

[0124] Specifically, the high-temperature air is respectively communicated with the first air electrode 101 and the second air electrode 201 through the first flow distributor 6, and the low-temperature air is respectively communicated with the first air electrode 101 and the second air electrode 201 through the second flow control valve 7. The high-temperature air is part of the air provided by the blower 14 that has been heat-exchanged with the high-temperature tail gas through the first heat exchanger 16, and the low-temperature air is part of the fuel that has not been heat-exchanged with the high-temperature tail gas through the first heat exchanger 16.

[0125] Further, the air supply unit further includes a mixer group configured to mix the high-temperature air and the low-temperature air entering the first air electrode 101 and the second air electrode 201.

[0126] Specifically, the mixer group includes a first mixer 8 and a second mixer 9. Two inlets of the first mixer 8 are respectively communicated with an outlet of the first flow distributor 6 and an outlet of the second flow control valve 7, and an outlet of the first mixer 8 is communicated with an air inlet of the first air electrode 101. Two inlets of the second mixer 9 are respectively communicated with the other outlet of the first flow distributor 6 and the other outlet of the second flow control valve 7, and an outlet of the second mixer 9 is communicated with an air inlet of the second air electrode 201.

[0127] Further, the air supply unit further includes a third mixer 10. Two inlets of the third mixer 10 are respectively communicated with an outlet of the second mixer 9 and an air outlet of the first air electrode 101, and an outlet of the third mixer 10 is communicated with an air inlet of the second air electrode 201.

[0128] The high-temperature air is divided into two parts by the first flow distributor 6. One part of the high-temperature air enters the first mixer 8, and the other part of the high-temperature air enters the second mixer 9. The low-temperature air is divided into two parts by the second flow control valve 7. One part of the low-temperature air enters the first mixer 8, is mixed evenly with the high-temperature air in the first mixer 8, and then enters the first air electrode 101 of the first fuel cell stack 1. The other part of the low-temperature air enters the second mixer 9, is mixed evenly with the high-temperature air in the second mixer 9, then enters the third mixer 10, is mixed evenly with the first air exhaust gas, and then enters the second air electrode 201 of the second fuel cell stack 2. After the second air exhaust gas is discharged, it enters the burner 11.

[0129] Further, the fuel cell system further includes a water supply unit 20 and a reformer 22. The water supply unit 20 and the fuel supply unit are both communicated with the reformer 22. The reformer 22 is used to reform the fuel provided by the fuel supply unit, and the reformed fuel enters the first fuel electrode 102.

[0130] Specifically, the fuel cell system further includes a fourth mixer 21. The water provided by the water supply unit 20 and the fuel provided by the fuel source 12 are mixed in the fourth mixer 21 and then enter the reformer 22 for reforming. The water supply unit 20 and the fuel source 12 are respectively connected to two inlets of the fourth mixer 21, an outlet of the fourth mixer 21 is connected to the reformer 22, and the reformer 22 is connected to the first fuel electrode 102. A second flow controller 23 is further provided between the water supply unit 20 and the reformer 22, and the second flow controller 23 is used to control the water flow rate entering the fourth mixer 21.

[0131] When the fuel cell system operates in a steady state, the fuel from the fuel source 12 is split by the third flow distributor 24 and supplied to the first fuel cell stack 1 and the second fuel cell stack 2. The fuel enters the fourth mixer 21 at a first specific flow rate after being regulated by the third flow controller 25. The water supplied by the water supply unit 20 enters the fourth mixer 21 at a second specific flow rate after being regulated by the second flow controller 23. The fuel and water are mixed in the fourth mixer 21 and then enter the reformer 22 for reforming. At least part of the substances such as methane, ethane, and butane in the fuel are converted into hydrogen, carbon monoxide, and carbon dioxide, and then enter the first fuel cell stack 1 for an electrochemical reaction to generate electric energy. The reforming rate of the reformer 22 can be adjusted to regulate the conversion amount of the fuel. By reforming the fuel through the reformer 22, it is possible to further prevent carbon deposition on the first fuel electrode 102 of the first fuel cell stack 1 and improve the fuel utilization rate.

[0132] The first fuel exhaust gas of the first fuel cell stack 1 enters the carbon dioxide separator 4 and the water separator 3 to remove most of the carbon dioxide and water in the first fuel exhaust gas. The carbon dioxide separator 4 and the water separator 3 can be used simultaneously or only one of them can be used. The carbon dioxide separated by the carbon dioxide separator 4 and the water separated by the water separator 3 can be recycled into the water supply unit 20 for reuse. After most of the water and carbon dioxide are removed from the first fuel exhaust gas, it enters the second fuel cell stack 2 for an electrochemical reaction. The water vapor generated by the reaction of the second fuel cell stack 2 is on the second air electrode 201. The water vapor and the second air exhaust gas enter the burner 11 together. The second fuel exhaust gas also enters the burner 11 for combustion to release heat. The high-temperature exhaust gas after the burner 11 burns provides heat to the fuel cell system through the first heat exchanger 16 and the second heat exchanger 17.

[0133] Furthermore, the fuel cell system further includes a fuel circulation member 26. The fuel circulation member 26 is disposed between the outlet of the first fuel electrode 102 and the reformer 22, so that at least part of the first fuel exhaust gas at the outlet of the first fuel electrode 102 enters the reformer 22 for reforming.

[0134] Specifically, the fuel circulation member 26 is disposed between the outlet of the first fuel electrode 102 and an inlet of the fourth mixer 21, so that at least part of the fuel exhaust gas at the outlet of the first fuel electrode 102 enters the fourth mixer 21. Since the first fuel exhaust gas contains a large amount of water vapor, the fuel containing a large amount of water vapor enters the reformer 22 for reforming through the fourth mixer 21, reducing the amount of water supplied by the water supply unit 20. When the fuel cell system operates in a steady state, the fuel circulation member 26 can be used to circulate the first fuel exhaust gas to the front end of the first fuel cell stack 1, where it is mixed with the fuel or the fuel and water in the fourth mixer 21 and then enters the second heat exchanger 17, the reformer 22, and the first fuel cell stack 1 in sequence. By controlling the flow rate of the fuel circulation member 26, it is possible to achieve that the water supply unit 20 does not need to work or only needs to supply a small amount of water during steady-state operation, reducing the water supply amount of the water supply unit 20.

[0135] In this embodiment, the fourth mixer 21 includes three inlets and one outlet. The three inlets are respectively connected to the second flow controller 23, the third flow controller 25, and the fuel circulation member 26, and the outlet is connected to the second heat exchanger 17.

[0136] Specifically, a fourth flow distributor 27 is provided between the discharge port of the first fuel electrode 102 and the feed port of the second fuel electrode 202. The inlet of the fourth flow distributor 27 is connected to the discharge port of the first fuel electrode 102, and the two outlets of the fourth flow distributor 27 are respectively connected to the fuel circulation member 26 and the feed port of the second fuel electrode 202.

[0137] The first fuel tail gas is divided into two parts by the fourth flow distributor 27. One part enters the fuel circulation member 26 and circulates to the front end of the first-stage fuel cell stack 1, and the other part enters the second-stage fuel cell stack 2 after removing water and carbon dioxide through the carbon dioxide separator 4 and the water separator 3. In this embodiment, since the first fuel tail gas of the first-stage fuel cell stack 1 is shunted and then enters the fuel circulation member 26 for internal circulation, the flow rate entering the fuel circulation member 26 is relatively small, and the requirements for the fuel circulation member 26 are relatively low. The fuel circulation member 26 can be a pump or an ejector. In this embodiment, a pump is used as the fuel circulation member 26. Since the circulation volume is small, only a pump with a relatively small power is required to meet the requirements, and the maintenance cost is also relatively small compared with the circulation pump in the prior art.

[0138] In this embodiment, the flow control valve can not only control the flow rate but also distribute the flow rate. When used at low temperatures, the flow control valve can not only control the flow rate but also distribute the flow rate. However, when used at high temperatures, the quality requirements for the flow control valve are relatively high. Therefore, a flow distributor is used at high temperatures to distribute the flow rate, which reduces the cost.

[0139] Another alternative solution provided in this embodiment is that the fuel supply unit includes a first fuel supply unit and a second fuel supply unit. The first fuel supply unit supplies fuel to the first-stage fuel cell module 100, and the second fuel supply unit supplies fuel to the second-stage fuel cell module 200. The air supply unit includes a first air supply unit and a second air supply unit. The first air supply unit supplies air to the first-stage fuel cell module 100, and the second air supply unit supplies air to the second-stage fuel cell module 200. The fuel cell system includes a first burner and a second burner. The first burner is disposed in the first-stage fuel cell module 100, and at least part of the high-temperature tail gas after the reaction of the first-stage fuel cell stack 1 enters the first burner for combustion. The second burner is disposed in the second-stage fuel cell module 200, and at least part of the high-temperature tail gas after the reaction of the second-stage fuel cell stack 2 enters the second burner for combustion.

[0140] For a fuel cell system with a greater demand for power generation, the number of primary fuel cell stacks in the primary fuel cell module 100 is larger. To meet the supply of fuel and air, the first fuel supply unit and the first air supply unit are used to separately supply fuel and air to the primary fuel cell module 100. The second fuel supply unit and a second air supply unit are used to separately supply fuel and air to the secondary fuel cell module 200. A first burner is provided in the primary fuel cell module 100, and at least part of the high-temperature exhaust gas after the reaction of all the primary fuel cell stacks in the primary fuel cell module 100 enters the first burner for combustion. A second burner is provided in the secondary fuel cell module 200, and at least part of the high-temperature exhaust gas after the reaction of all the secondary fuel cell stacks in the secondary fuel cell module 200 enters the second burner for combustion. Of course, components such as a reformer 22 and a heat exchanger are also included in the primary fuel cell module 100 and the secondary fuel cell module 200. The fuel cell system may include more levels of fuel cell modules.

[0141] As Figure 6 shown, all of the high-temperature exhaust gas after the reaction of the primary fuel cell module 100 enters the second burner for combustion, and part of the high-temperature exhaust gas after the reaction of the secondary fuel cell module 200 enters the second burner for combustion to provide thermal balance for the secondary fuel cell module 200; another part enters the first burner for combustion to provide thermal balance for the primary fuel cell module 100.

[0142] As Figure 7 shown, part of the high-temperature exhaust gas after the reaction of the primary fuel cell module 100 enters the first burner for combustion to provide thermal balance for the primary fuel cell module 100; another part enters the second burner for combustion. All of the high-temperature exhaust gas after the reaction of the secondary fuel cell module 200 enters the second burner for combustion to provide thermal balance for the secondary fuel cell module 200.

[0143] This embodiment also provides a fuel cell power generation set, including the above-mentioned fuel cell system. This fuel cell system improves fuel utilization rate, thereby improving the power generation efficiency of the fuel cell power generation set, and there is no need to increase the maintenance cost.

[0144] Embodiment 2:

[0145] This embodiment provides a control method for a fuel cell power generation set, which is applied to the fuel cell power generation set provided in Embodiment 1. The control method for the fuel cell power generation set includes the following steps:

[0146] When the fuel cell system starts up, the air supply unit provides high-temperature air, which enters the first air electrode 101 and the second air electrode 201 respectively. According to the temperatures of the first air exhaust gas discharged from the first air electrode 101 and the second air exhaust gas discharged from the second air electrode 201, the fuel supply unit is controlled to supply fuel. When the temperature of the first air exhaust gas is higher than the starting temperature of the first fuel cell stack 1, the first fuel cell stack 1 is started up. By controlling the ratio of oxygen element to carbon element in the fuel entering the first fuel cell stack 1 and the current of the first fuel cell stack 1, the fuel utilization rate of the first fuel cell stack 1 is controlled to meet the target that the fuel utilization rate of the first fuel cell stack 1 > 30%; when the temperature of the second air exhaust gas is higher than the starting temperature of the second fuel cell stack 2, the second fuel cell stack 2 is started up. By controlling the ratio of oxygen element to carbon element in the fuel entering the second fuel cell stack 2 and the current of the second fuel cell stack 2, the fuel utilization rate of the second fuel cell stack 2 is controlled to meet the requirement that the fuel utilization rate of the second fuel cell stack 2 > 40%.

[0147] Specifically, it includes the following steps:

[0148] (1) First, the high-temperature air is respectively introduced into the first air electrode 101 and the second air electrode 201 to heat the first fuel cell stack 1 and the second fuel cell stack 2 respectively. The temperatures of the first air exhaust gas discharged from the first air electrode 101 and the second air exhaust gas discharged from the second air electrode 201 gradually increase.

[0149] (2) When the fuel cell system starts up, before controlling the fuel supply unit to supply fuel, steam or inert gas is introduced into the fuel pipeline in the fuel cell system for purging.

[0150] Specifically, when the temperatures of both the first air exhaust gas and the second air exhaust gas are higher than 200 °C, steam or inert gas is introduced into the fuel pipeline in the fuel cell system for purging.

[0151] By purging the air by introducing steam or inert gas into the fuel pipeline, it can avoid the easy explosion when high-temperature fuel is mixed with air after the high-temperature fuel is introduced. The volume of the steam entering the fuel cell system is more than 5 times the volume of the fuel pipeline in the fuel cell system.

[0152] (3) When the fuel cell system starts up, the steps of controlling the fuel supply unit to supply fuel according to the temperatures of the first air exhaust gas discharged from the first air electrode 101 and the second air exhaust gas discharged from the second air electrode 201 include:

[0153] When the temperature of the first air exhaust is higher than the first set temperature, the fuel supply unit supplies fuel to the first-stage fuel cell stack 1, and the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack 1 is >1; by adjusting the separation ratio of the separator and the fuel supplied by the fuel supply unit to the second-stage fuel cell stack 2, the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack 2 is made >0.5, and the first set temperature is lower than the start-up temperatures of the first-stage fuel cell stack 1 and the second-stage fuel cell stack 2.

[0154] The first set temperature is 300 °C. When the temperature of the first air exhaust is higher than 300 °C, the fuel supply unit starts to supply fuel into the fuel pipeline. The ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack 1 is >1. At this time, an electrochemical reaction starts to occur in the first-stage fuel cell stack 1. After the first fuel exhaust gas after the reaction is separated from most of the carbon dioxide and water by the carbon dioxide separator 4 and the water separator 3, it enters the second-stage fuel cell stack 2. At the same time, the fuel supply unit will supplement fuel to the second-stage fuel cell stack 2. By adjusting the separation ratio of carbon dioxide and the separation ratio of water, as well as the flow rate of the fuel supplemented by the fuel supply unit, the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack 2 is made >0.5.

[0155] (4) When the temperature of the first air exhaust is higher than the start-up temperature of the first-stage fuel cell stack 1, start the first-stage fuel cell stack 1. The start-up temperature of the first-stage fuel cell stack 1 is 400 °C. The methods for controlling the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack 1 and the current of the first-stage fuel cell stack 1 to meet the target that the fuel utilization rate of the first-stage fuel cell stack 1 is >30% include:

[0156] By gradually increasing the fuel flow rate entering the first-stage fuel cell stack 1, the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack 1 is made >1, and at the same time, gradually increasing the current of the first-stage fuel cell stack 1, so that the fuel utilization rate of the first-stage fuel cell stack 1 is >30%.

[0157] The first-stage fuel cell stack 1 generates electric energy after the electrochemical reaction. By controlling the output current of the first-stage fuel cell stack 1 through electrical components and controlling the ratio of oxygen element to carbon element in the fuel entering the first-stage fuel cell stack 1, the fuel utilization rate of the first-stage fuel cell stack 1 at the start of the fuel cell system is controlled to be >30%.

[0158] (5) When the temperature of the second air exhaust is higher than the start-up temperature of the second-stage fuel cell stack 2, start the second-stage fuel cell stack 2. The start-up temperature of the second-stage fuel cell stack 2 is 400 °C. The methods for controlling the ratio of oxygen element to carbon element in the fuel entering the second-stage fuel cell stack 2 and the current of the second-stage fuel cell stack 2 to meet the target that the fuel utilization rate of the second-stage fuel cell stack 2 is >40% include:

[0159] By gradually increasing the fuel flow rate into the first-stage stack 1 and the fuel flow rate provided by the fuel supply unit to the second-stage stack 2, the ratio of oxygen element to carbon element in the fuel entering the first-stage stack 1 is made greater than 0.5, and the ratio of oxygen element to carbon element in the fuel entering the second-stage stack 2 is made greater than 1. At the same time, the current of the second-stage stack 2 is gradually increased so that the fuel utilization rate of the second-stage stack 2 is greater than 40%.

[0160] After the second-stage stack 2 undergoes an electrochemical reaction, electrical energy will be generated. By controlling the output current of the second-stage stack 2 through electrical components, as well as the ratio of oxygen element to carbon element in the fuel entering the first-stage stack 1 and the ratio of oxygen element to carbon element in the fuel entering the second-stage stack 2, the fuel utilization rate of the second-stage stack 2 at the start of the fuel cell system is controlled to be greater than 40%.

[0161] It should be noted that since the first-stage fuel cell module 100 and the second-stage fuel cell module 200 are arranged in series, the high-temperature fuel first enters the first-stage stack 1 for electrochemical reaction, and the first fuel tail gas after the reaction then enters the second-stage stack 2. During the heat transfer process, a part of the heat will be lost before being transferred to the second-stage stack 2. Therefore, the temperature of the first air tail gas of the first-stage stack 1 reaches 400 °C first, and the temperature of the second air tail gas of the second-stage stack 2 reaches 400 °C later. The method for adjusting the current of the first-stage stack 1 and the second-stage stack 2 is already in the prior art and will not be elaborated here.

[0162] When the fuel cell system is operating, when the temperature of the first air tail gas is higher than the lowest steady-state operating temperature of the first-stage stack 1, the fuel utilization rate of the first-stage stack 1 is controlled between 40% and 95%; when the temperature of the second air tail gas is higher than the lowest steady-state operating temperature of the second-stage stack 2, the fuel utilization rate of the second-stage stack 2 is controlled between 50% and 95%.

[0163] Specifically, when the temperature of the first air tail gas is higher than the lowest steady-state operating temperature of the first-stage stack 1, the method for controlling the fuel utilization rate of the first-stage stack 1 between 40% and 95% includes:

[0164] By adjusting the current of the first-stage stack 1 and the flow rate of the fuel entering the first-stage stack 1 to satisfy that the ratio of oxygen element to carbon element in the fuel entering the first-stage stack 1 is greater than 0.5, and then adjusting the current of the first-stage stack 1, the fuel utilization rate of the first-stage stack 1 is controlled between 40% and 95%.

[0165] The output current of the first-stage stack 1 affects the number of electrons transferred during the power generation of the first-stage stack 1. The more electrons transferred during the power generation of the first-stage stack 1, the greater the power generation, the more fuel consumed, and the higher the ratio of oxygen element to carbon element in the fuel entering the first-stage stack 1. Therefore, the current of the first-stage stack 1 affects the ratio of oxygen element to carbon element in the fuel entering the first-stage stack 1 and also affects the fuel utilization rate of the first-stage stack 1.

[0166] When the temperature of the second air exhaust gas is higher than the minimum steady-state operating temperature of the second fuel cell stack 2, the method for controlling the fuel utilization rate of the second fuel cell stack 2 between 50% and 95% includes:

[0167] Adjust the separation ratio in the separator, the current of the second fuel cell stack 2, and the flow rate of the fuel provided by the fuel supply unit to the second fuel cell stack 2 to satisfy that the ratio of oxygen element to carbon element in the fuel entering the second fuel cell stack 2 > 1, and then adjust the current of the second fuel cell stack 2 to control the fuel utilization rate of the second fuel cell stack 2 between 50% and 95%.

[0168] The first fuel exhaust gas separates water and carbon dioxide through the separator. Adjusting the separation ratio of the separator can adjust the separation ratio of water and the separation ratio of carbon dioxide, and further adjust the ratio of oxygen element to carbon element in the first fuel exhaust gas entering the second fuel cell stack 2. The output current of the second fuel cell stack 2 affects the number of electrons transferred during the power generation of the second fuel cell stack 2. The more electrons transferred during the power generation of the second fuel cell stack 2, the greater the power generation, the more fuel consumed, and the higher the ratio of oxygen element to carbon element in the fuel entering the second fuel cell stack 2. Therefore, the current of the second fuel cell stack 2 affects the ratio of oxygen element to carbon element in the fuel entering the second fuel cell stack 2 and also affects the fuel utilization rate of the second fuel cell stack 2.

[0169] Furthermore, when the fuel cell system is operating, if the power of the fuel cell system is increased or decreased, by controlling the current of the first fuel cell stack 1 and the fuel flow rate entering the first fuel cell stack 1; and / or, by controlling the current of the second fuel cell stack 2 and the fuel flow rate entering the second fuel cell stack 2 to increase or decrease the power of the fuel cell system, ensure that the fuel utilization rate of the first fuel cell stack 1 is between 40% and 95%, and the fuel utilization rate of the second fuel cell stack 2 is between 50% and 95%.

[0170] Specifically, when increasing the power of the fuel cell system, the method for controlling the current of the first fuel cell stack 1 and the fuel flow rate entering the first fuel cell stack 1; and / or, by controlling the current of the second fuel cell stack 2 and the fuel flow rate entering the second fuel cell stack 2, and ensuring that the fuel utilization rate of the first fuel cell stack 1 is between 40% and 95%, and the fuel utilization rate of the second fuel cell stack 2 is between 50% and 95% includes:

[0171] Keep the current of the first fuel cell stack 1 unchanged, increase the flow rate of the fuel entering the first fuel cell stack 1 and the flow rate of the fuel provided by the fuel supply unit to the second fuel cell stack 2, increase the current of the second fuel cell stack 2, and ensure that the fuel utilization rate of the first fuel cell stack 1 is between 40% and 95%, and the fuel utilization rate of the second fuel cell stack 2 is between 50% and 95%; or,

[0172] Increase the current of the first - stage stack 1, increase the flow rate of the fuel entering the first - stage stack 1, maintain the current of the second - stage stack 2 unchanged, and ensure that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%; or,

[0173] Increase the current of the first - stage stack 1, increase the flow rate of the fuel entering the first - stage stack 1 and the flow rate of the fuel provided by the fuel supply unit for the second - stage stack 2, increase the current of the second - stage stack 2, and ensure that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%.

[0174] When reducing the power of the fuel cell system, by controlling the current of the first - stage stack 1 and the fuel flow rate entering the first - stage stack 1; and / or, by controlling the current of the second - stage stack 2 and the fuel flow rate entering the second - stage stack 2, and ensuring that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%, the method includes:

[0175] Maintain the current of the first - stage stack 1 unchanged, reduce the flow rate of the fuel entering the first - stage stack 1 and the flow rate of the fuel provided by the fuel supply unit for the second - stage stack 2, reduce the current of the second - stage stack 2, and ensure that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%; or,

[0176] Reduce the current of the first - stage stack 1, reduce the flow rate of the fuel entering the first - stage stack 1, maintain the current of the second - stage stack 2, and ensure that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%; or,

[0177] Reduce the current of the first - stage stack 1, reduce the flow rate of the fuel entering the first - stage stack 1 and the flow rate of the fuel provided by the fuel supply unit for the second - stage stack 2, reduce the current of the second - stage stack 2, and ensure that the fuel utilization rate of the first - stage stack 1 is between 40% and 95%, and the fuel utilization rate of the second - stage stack 2 is between 50% and 95%.

[0178] When the fuel cell system stops running, gradually reduce the temperatures of the first air exhaust and the second air exhaust, gradually reduce the current of the second - stage stack 2 and the current of the first - stage stack 1 to zero in sequence. When the temperature of the first air exhaust is lower than the start - up temperature of the first - stage stack 1 and the temperature of the second air exhaust is lower than the start - up temperature of the second - stage stack 2, the fuel supply unit stops supplying fuel.

[0179] Specifically, when the fuel cell system stops running, the method of gradually reducing the current of the second - stage stack 2 and the current of the first - stage stack 1 to zero in sequence includes:

[0180] Gradually reduce the current of the secondary stack 2 to zero, and at the same time, reduce the flow rate of the fuel supplied by the fuel supply unit to the secondary stack 2, while maintaining the ratio of oxygen element to carbon element in the fuel entering the secondary stack 2 > 1.

[0181] Then increase the ratio of oxygen element to carbon element in the fuel entering the primary stack 1 to > 1.5, and gradually reduce the current of the primary stack 1 to zero.

[0182] Specifically, the ratio of oxygen element to carbon element in the fuel entering the primary stack 1 can be increased by increasing the flow rate of water vapor, that is, increasing the flow rate of water supplied by the water supply unit 20 to the reformer 22, so that the ratio of oxygen element to carbon element in the fuel entering the primary stack 1 after being reformed by the reformer 22 increases.

[0183] The regulation method of the fuel cell power generation set provided in this embodiment is applied to the above fuel cell power generation set. When the fuel cell system starts, operates, and stops operating, control the fuel supply unit to supply fuel and stop supplying fuel, the start and current of the primary stack 1 and the secondary stack 2 according to the temperature of the first air exhaust gas discharged from the first air electrode 101 and the temperature of the second air exhaust gas discharged from the second air electrode 201. By controlling the ratio of oxygen element to carbon element in the fuel entering the primary stack 1, the ratio of oxygen element to carbon element in the fuel entering the secondary stack 2, as well as the current of the primary stack 1 and the current of the secondary stack 2, control the fuel utilization rates of the primary stack 1 and the secondary stack 2 within different ranges at different stages, achieving effective control of the fuel utilization rates of the primary stack 1 and the secondary stack 2 in the fuel cell system at different stages, thereby improving the fuel utilization rate of the fuel cell system and ultimately improving the power generation efficiency of the fuel cell power generation set.

[0184] The above content is only a preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. The content of this specification should not be construed as a limitation to the present invention.

Claims

1. A fuel cell system, characterized in that: include: A primary fuel cell module (100) comprises at least one primary fuel cell stack (1), wherein the primary fuel cell stack (1) comprises a first air electrode (101), a first fuel electrode (102), and an oxygen ion conductor electrolyte (103) disposed between the first air electrode (101) and the first fuel electrode (102); A two-stage fuel cell module (200) comprises at least one two-stage fuel cell stack (2), wherein the two-stage fuel cell stack (2) comprises a second air electrode (201), a second fuel electrode (202), and a proton conductor electrolyte (203) disposed between the second air electrode (201) and the second fuel electrode (202); A fuel supply unit and an air supply unit, wherein the fuel supply unit provides fuel to the first-level fuel cell module (100) or the first-level fuel cell module (100) and the second-level fuel cell module (200), and at least part of the first fuel tail gas after the reaction of the first-level fuel cell module (100) enters the second-level fuel cell module (200), and the air supply unit provides air to the first-level fuel cell module (100) and the second-level fuel cell module (200).

2. The fuel cell system according to claim 1, characterized in that: The fuel cell system also includes a separator, which is arranged between the first-level fuel cell module (100) and the second-level fuel cell module (200) and is used to remove at least part of the water and / or carbon dioxide in the first fuel tail gas. The first fuel tail gas after the water and / or carbon dioxide is removed enters the second fuel electrode (202).

3. The fuel cell system according to claim 1, characterized in that: The first fuel electrode (102) satisfies the requirement that when the ratio of oxygen to carbon in the fuel entering the first-stage fuel cell module (100) is between 0.5 and 3, carbon deposition does not occur on the surface of the first fuel electrode (102).

4. The fuel cell system according to claim 3, characterized in that: The material of the first fuel electrode (102) includes a mixture of a transition metal and an oxygen ion conductor, a mixture of a noble metal and an oxygen ion conductor, a mixture of a transition metal, a noble metal and an oxygen ion conductor, or a mixture of a transition metal, a noble metal, an oxygen ion conductor and a conductive oxide.

5. The fuel cell system according to claim 1, characterized in that: The second fuel electrode (202) satisfies the requirement that when the ratio of oxygen to carbon in the fuel entering the secondary fuel cell module (200) is 1 to 3, carbon deposition does not occur on the surface of the second fuel electrode (202).

6. The fuel cell system according to claim 5, characterized in that: The material of the second fuel electrode (202) includes a mixture of one or more of transition metal and alkali metal oxide, alkali metal element doped perovskite zirconate oxide, alkali metal element doped perovskite cerate oxide, alkali metal element doped perovskite titanate oxide, alkali metal element doped perovskite ferrite oxide, alkali metal element doped perovskite vanadate oxide, alkali metal element doped perovskite chromate oxide, alkali metal element doped perovskite manganate oxide, alkali metal element doped perovskite cobaltate oxide, alkali metal element doped perovskite nickelate oxide, alkali metal element doped perovskite cuprate oxide and proton conductor oxide; or, A mixture of a noble metal with one or more of an alkali metal oxide, an alkali metal doped perovskite zirconate oxide, an alkali metal doped perovskite cerate oxide, an alkali metal doped perovskite titanate oxide, an alkali metal doped perovskite ferrite oxide, an alkali metal doped perovskite vanadate oxide, an alkali metal doped perovskite chromate oxide, an alkali metal doped perovskite manganate oxide, an alkali metal doped perovskite cobaltate oxide, an alkali metal doped perovskite nickelate oxide, an alkali metal doped perovskite cuprate oxide and a proton conductor oxide; or, A mixture of one or more of transition metals, noble metals and alkali metal oxides, alkali metal doped perovskite zirconate oxides, alkali metal doped perovskite cerate oxides, alkali metal doped perovskite titanate oxides, alkali metal doped perovskite ferrite oxides, alkali metal doped perovskite vanadate oxides, alkali metal doped perovskite chromate oxides, alkali metal doped perovskite manganate oxides, alkali metal doped perovskite cobaltate oxides, alkali metal doped perovskite nickelate oxides, alkali metal doped perovskite cuprate oxides and proton conductor oxides; or, A mixture of one or more of transition metals, noble metals, conductive oxides and alkali metal oxides, alkali metal doped perovskite zirconate oxides, alkali metal doped perovskite cerate oxides, alkali metal doped perovskite titanate oxides, alkali metal doped perovskite ferrite oxides, alkali metal doped perovskite vanadate oxides, alkali metal doped perovskite chromate oxides, alkali metal doped perovskite manganate oxides, alkali metal doped perovskite cobaltate oxides, alkali metal doped perovskite nickelate oxides, alkali metal doped perovskite cuprate oxides and proton conductor oxides.

7. The fuel cell system according to claim 1, characterized in that: The primary fuel cell module (100) comprises one or more primary fuel cell stack groups, each of the primary fuel cell stack groups comprises at least one primary fuel cell stack (1), and a plurality of the primary fuel cell stack groups are connected in series, in parallel or in mixed connection; The secondary fuel cell module (200) comprises one or more secondary fuel cell stack groups, each of the secondary fuel cell stack groups comprises at least one secondary fuel cell stack (2), and a plurality of the secondary fuel cell stack groups are connected in series, in parallel or in mixed connection.

8. The fuel cell system according to any one of claims 1 to 7, characterized in that: The fuel cell system comprises a burner (11), wherein the burner (11) is arranged in the two-stage fuel cell module (200), and the first air electrode (101), the second air electrode (201), the second fuel electrode (202), the fuel supply unit and the air supply unit are all connected to the burner (11).

9. The fuel cell system according to claim 8, characterized in that: The high-temperature exhaust gas generated by the burner (11) after combustion provides heat to at least part of the fuel provided by the fuel supply unit and at least part of the air provided by the air supply unit through a heat exchange unit.

10. The fuel cell system according to claim 9, characterized in that: The heat exchange unit comprises a first heat exchanger (16) and a second heat exchanger (17), wherein the first heat exchanger (16) is capable of transferring heat of the high-temperature exhaust gas to at least part of the air provided by the air supply unit; The second heat exchanger (17) is capable of transferring the heat of the high-temperature exhaust gas to at least part of the fuel provided by the fuel supply unit.

11. The fuel cell system according to claim 9, characterized in that: The high-temperature tail gas after combustion in the burner (11) is communicated with the waste heat recovery unit (19).

12. The fuel cell system according to any one of claims 1 to 7, characterized in that: The fuel supply unit provides high-temperature fuel and low-temperature fuel, the high-temperature fuel is connected to the feed port of the first fuel electrode (102), and the low-temperature fuel flow rate is controllably distributed to the first fuel electrode (102) and the second fuel electrode (202); The air supply unit provides high-temperature air and low-temperature air, and the high-temperature air and the low-temperature air are both controllably distributed to the first air electrode (101) and the second air electrode (201).

13. The fuel cell system according to claim 12, characterized in that: The air supply unit further includes a mixer group configured to mix the high-temperature air and the low-temperature air entering the first air electrode (101) and the second air electrode (201).

14. The fuel cell system according to any one of claims 1 to 7, characterized in that: The fuel cell system further comprises a water supply unit (20) and a reformer (22), wherein the water supply unit (20) and the fuel supply unit are both connected to the reformer (22), and the reformer (22) is used to reform the fuel provided by the fuel supply unit, and the reformed fuel enters the first fuel electrode (102).

15. The fuel cell system according to claim 14, characterized in that: The fuel cell system also includes a fuel circulation component (26), which is arranged between the outlet of the first fuel electrode (102) and the reformer (22) so that at least part of the first fuel tail gas from the outlet of the first fuel electrode (102) enters the reformer (22) for reforming.

16. The fuel cell system according to any one of claims 1 to 7, characterized in that: The fuel cell system comprises a first burner and a second burner, wherein the first burner is arranged in the first-stage fuel cell module (100), and at least a portion of the high-temperature exhaust gas after the reaction of the first-stage fuel cell stack (1) enters the first burner for combustion, and the second burner is arranged in the second-stage fuel cell module (200), and at least a portion of the high-temperature exhaust gas after the reaction of the second-stage fuel cell stack (2) enters the second burner for combustion.

17. The fuel cell system according to claim 16, characterized in that: All high-temperature exhaust gas after the reaction of the first-stage fuel cell module (100) enters the second burner for combustion, and part of the high-temperature exhaust gas after the reaction of the second-stage fuel cell module (200) enters the second burner for combustion, and the other part enters the first burner for combustion.

18. The fuel cell system according to claim 16, characterized in that: Part of the high-temperature exhaust gas after the reaction of the first-stage fuel cell module (100) enters the first burner for combustion, and the other part enters the second burner for combustion; all of the high-temperature exhaust gas after the reaction of the second-stage fuel cell module (200) enters the second burner for combustion.

19. A fuel cell generator set, characterized in that: Comprising the fuel cell system according to any one of claims 1 to 18.

20. A control method for a fuel cell generator set, characterized in that: Applied to the fuel cell generator set according to claim 19, the control method of the fuel cell generator set comprises the following steps: When the fuel cell system is started, the air supply unit provides high-temperature air, and the high-temperature air enters the first air electrode (101) and the second air electrode (201) respectively. According to the temperature of the first air exhaust gas discharged from the first air electrode (101) and the temperature of the second air exhaust gas discharged from the second air electrode (201), the fuel supply unit is controlled to supply fuel, and when the temperature of the first air exhaust gas is higher than the start-up temperature of the first-stage stack (1), the first-stage stack (1) is started, and the fuel utilization rate of the first-stage stack (1) is controlled to meet the target of the fuel utilization rate of the first-stage stack (1) being greater than 30%; when the temperature of the second air exhaust gas is higher than the start-up temperature of the second-stage stack (2), the second-stage stack (2) is started, and the fuel utilization rate of the second-stage stack (2) is controlled to meet the target of the fuel utilization rate of the second-stage stack (2) being greater than 40%; and / or, When the fuel cell system stops operating, the temperature of the first air exhaust gas discharged from the first air electrode (101) and the temperature of the second air exhaust gas discharged from the second air electrode (201) are gradually reduced, and the current of the secondary stack (2) and the current of the primary stack (1) are gradually reduced to zero in turn. When the temperature of the first air exhaust gas is lower than the start-up temperature of the primary stack (1), and the temperature of the second air exhaust gas is lower than the start-up temperature of the secondary stack (2), the fuel supply unit stops supplying fuel.

21. The control method of a fuel cell generator set according to claim 20, characterized in that: The fuel cell system further comprises a separator, wherein the separator removes water and / or carbon dioxide from at least part of the first fuel tail gas after the reaction of the first fuel electrode (102) and then the first fuel tail gas enters the second fuel electrode (202). When the fuel cell system is started, the steps of controlling the fuel supply unit to supply fuel according to the temperature of the first air tail gas discharged from the first air electrode (101) and the temperature of the second air tail gas discharged from the second air electrode (201) include: When the temperature of the first air exhaust gas is higher than a first set temperature, the fuel supply unit passes fuel into the first-stage fuel cell stack (1), and the ratio of oxygen to carbon in the fuel entering the first-stage fuel cell stack (1) is greater than 1; by adjusting the separation ratio of the separator and the fuel supplied to the second-stage fuel cell stack (2) by the fuel supply unit, the ratio of oxygen to carbon in the fuel entering the second-stage fuel cell stack (2) is greater than 0.5, and the first set temperature is less than the start-up temperature of the first-stage fuel cell stack (1) and the start-up temperature of the second-stage fuel cell stack (2).

22. The control method of a fuel cell generator set according to claim 20, characterized in that: After starting the first-stage fuel cell stack (1), the ratio of oxygen and carbon elements in the fuel entering the first-stage fuel cell stack (1) and the current of the first-stage fuel cell stack (1) are controlled to meet the target of a fuel utilization rate of the first-stage fuel cell stack (1) greater than 30%.

23. The control method of a fuel cell generator set according to claim 22, characterized in that: After starting the primary stack (1), the method for controlling the ratio of oxygen and carbon in the fuel entering the primary stack (1) and the current of the primary stack (1) to meet the target of a fuel utilization rate of the primary stack (1) greater than 30% comprises: By gradually increasing the fuel flow rate entering the first-stage stack (1), the ratio of oxygen to carbon in the fuel entering the first-stage stack (1) is greater than 1, and at the same time, the current of the first-stage stack (1) is gradually increased, so that the fuel utilization rate of the first-stage stack (1) is greater than 30%.

24. The control method of a fuel cell generator set according to claim 20, characterized in that: After starting the secondary stack (2), the ratio of oxygen and carbon in the fuel entering the secondary stack (2) and the current of the secondary stack (2) are controlled to meet the target of a fuel utilization rate of the secondary stack (2) greater than 40%.

25. The control method of the fuel cell generator set according to claim 24, characterized in that: After starting the secondary stack (2), the method for controlling the ratio of oxygen and carbon in the fuel entering the secondary stack (2) and the current of the secondary stack (2) to meet the target of a fuel utilization rate of the secondary stack (2) greater than 40% comprises: By gradually increasing the fuel flow rate entering the primary stack (1) and the fuel flow rate provided by the fuel supply unit to the secondary stack (2), the ratio of oxygen to carbon in the fuel entering the primary stack (1) is greater than 0.5, and the ratio of oxygen to carbon in the fuel entering the secondary stack (2) is greater than 1. At the same time, the current of the secondary stack (2) is gradually increased, so that the fuel utilization rate of the secondary stack (2) is greater than 40%.

26. The control method of a fuel cell generator set according to claim 21, characterized in that: When the fuel cell system stops running, the method of gradually reducing the current of the secondary stack (2) and the current of the primary stack (1) to zero in sequence comprises: First, the current of the secondary stack (2) is gradually reduced to zero, and at the same time, the flow rate of the fuel provided by the fuel supply unit to the secondary stack (2) is reduced, so as to maintain the ratio of oxygen and carbon in the fuel entering the secondary stack (2) to be greater than 1; Then, the ratio of oxygen and carbon in the fuel entering the first-stage fuel cell stack (1) is increased to >1.5, and the current of the first-stage fuel cell stack (1) is gradually reduced to zero.

27. The control method of a fuel cell generator set according to claim 21, characterized in that: When the fuel cell system is in operation, when the first air exhaust temperature is higher than the lowest steady-state operating temperature of the first-stage fuel cell stack (1), the fuel utilization rate of the first-stage fuel cell stack (1) is controlled to be between 40% and 95%; when the second air exhaust temperature is higher than the lowest steady-state operating temperature of the second-stage fuel cell stack (2), the fuel utilization rate of the second-stage fuel cell stack (2) is controlled to be between 50% and 95%.

28. The control method of a fuel cell generator set according to claim 27, characterized in that: When the first air exhaust temperature is higher than the lowest steady-state operating temperature of the first-stage fuel cell stack (1), the method for controlling the fuel utilization rate of the first-stage fuel cell stack (1) to be between 40% and 95% comprises: By adjusting the current of the primary stack (1) and the flow rate of the fuel entering the primary stack (1), so as to satisfy that the ratio of oxygen element to carbon element in the fuel entering the primary stack (1) is greater than 0.5, and then adjusting the current of the primary stack (1), the fuel utilization rate of the primary stack (1) is controlled between 40% and 95%.

29. The control method of a fuel cell generator set according to claim 27, characterized in that: When the second air exhaust temperature is higher than the lowest steady-state operating temperature of the secondary fuel cell stack (2), the method for controlling the fuel utilization rate of the secondary fuel cell stack (2) to be between 50% and 95% comprises: The separation ratio of the separator, the current of the secondary stack (2) and the flow rate of the fuel provided by the fuel supply unit to the secondary stack (2) are adjusted to satisfy a ratio of oxygen to carbon in the fuel entering the secondary stack (2) greater than 1, and the current of the secondary stack (2) is then adjusted to control the fuel utilization rate of the secondary stack (2) between 50% and 95%.

30. The control method of a fuel cell generator set according to claim 27, characterized in that: When the fuel cell system is in operation, if the power of the fuel cell system is increased or decreased, the power of the fuel cell system is increased or decreased by controlling the current of the primary stack (1) and the fuel flow rate entering the primary stack (1); and / or, by controlling the current of the secondary stack (2) and the fuel flow rate entering the secondary stack (2), the power of the fuel cell system is increased or decreased to ensure that the fuel utilization rate of the primary stack (1) is between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is between 50% and 95%.

31. The control method of the fuel cell generator set according to claim 30, characterized in that: When increasing the power of the fuel cell system, the method comprises: controlling the current of the primary stack (1) and the fuel flow rate entering the primary stack (1); and / or controlling the current of the secondary stack (2) and the fuel flow rate entering the secondary stack (2), and ensuring that the fuel utilization rate of the primary stack (1) is between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is between 50% and 95%, comprising: The current of the primary stack (1) is maintained unchanged, the flow rate of the fuel entering the primary stack (1) and the flow rate of the fuel provided by the fuel supply unit to the secondary stack (2) are increased, the current of the secondary stack (2) is increased, and the fuel utilization rate of the primary stack (1) is ensured to be between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is ensured to be between 50% and 95%; or, Increasing the current of the primary stack (1), increasing the flow rate of fuel entering the primary stack (1), maintaining the current of the secondary stack (2) unchanged, and ensuring that the fuel utilization rate of the primary stack (1) is between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is between 50% and 95%; or, The current of the primary stack (1) is increased, the flow rate of the fuel entering the primary stack (1) and the flow rate of the fuel provided by the fuel supply unit to the secondary stack (2) are increased, the current of the secondary stack (2) is increased, and the fuel utilization rate of the primary stack (1) is ensured to be between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is ensured to be between 50% and 95%.

32. The control method of the fuel cell generator set according to claim 30, characterized in that: When reducing the power of the fuel cell system, the method of controlling the current of the primary stack (1) and the fuel flow rate entering the primary stack (1); and / or, controlling the current of the secondary stack (2) and the fuel flow rate entering the secondary stack (2), and ensuring that the fuel utilization rate of the primary stack (1) is between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is between 50% and 95% comprises: The current of the primary stack (1) is maintained unchanged, the flow rate of the fuel entering the primary stack (1) and the flow rate of the fuel provided by the fuel supply unit to the secondary stack (2) are reduced, the current of the secondary stack (2) is reduced, and the fuel utilization rate of the primary stack (1) is ensured to be between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is ensured to be between 50% and 95%; or, The current of the primary stack (1) is reduced, the flow rate of fuel entering the primary stack (1) is reduced, the current of the secondary stack (2) is maintained, and the fuel utilization rate of the primary stack (1) is ensured to be between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is ensured to be between 50% and 95%; or, The current of the primary stack (1) is reduced, the flow rate of fuel entering the primary stack (1) and the flow rate of fuel provided by the fuel supply unit to the secondary stack (2) are reduced, the current of the secondary stack (2) is reduced, and the fuel utilization rate of the primary stack (1) is ensured to be between 40% and 95%, and the fuel utilization rate of the secondary stack (2) is ensured to be between 50% and 95%.

33. The control method of a fuel cell generator set according to claim 20, characterized in that: When the fuel cell system is started, water vapor or inert gas is introduced into the fuel pipeline in the fuel cell system for purging before the fuel supply unit is controlled to supply fuel.

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