A combined SOFC and PEMFC system using direct ammonia fuel

Abstract

The present invention discloses a combined SOFC and PEMFC system for direct ammonia fuel, belonging to the field of fuel cell technology. The system includes a liquid ammonia tank, a solid oxide fuel cell, a proton exchange membrane fuel cell, a burner, a condenser, an ammonia removal device, a heat exchanger, a vaporizer, a heat exchanger I, a heat exchanger II, and a heat exchanger III. The heat exchanger of the system uses the high-temperature tail gas from the SOFC anode to preheat the ammonia, and burns the unused hydrogen through the burner to preheat the air for the SOFC cathode, thereby realizing the recovery and utilization of waste heat and fuel. The system can form a cycle and has the advantages of low energy consumption and high system utilization. The present invention combines a solid oxide fuel cell with a proton exchange membrane fuel cell, fully utilizing the advantages of the two fuel cells, and can achieve zero carbon emissions by using ammonia as fuel.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a direct ammonia fuel SOFC and PEMFC combined system. Background Art

[0002] Hydrogen has long been considered the most ideal clean energy source, but its storage and transportation remain a major bottleneck hindering its development. Ammonia, a carbon-free compound, can also serve as a clean energy alternative to fossil fuels. Ammonia can be liquefied at -33°C under normal pressure, and its volumetric energy density is over twice that of liquid hydrogen. While ordinary liquefied gas cylinders can store ammonia, hydrogen requires specialized materials. Therefore, ammonia offers significant advantages in storage and transportation. As an alternative fuel to hydrogen, ammonia offers advantages such as easy liquefaction, high energy density, zero carbon emissions, enhanced safety, and low fuel costs.

[0003] Solid oxide ammonia fuel cell systems emit only water and nitrogen during operation, enabling clean power generation. Depending on the ammonia supply method, they can be divided into indirect ammonia fuel cells and direct ammonia fuel cells. Indirect ammonia fuel cells use an external reformer to decompose ammonia fuel into nitrogen and hydrogen, using the hydrogen as fuel. Direct ammonia fuel cells do not undergo external reforming; the ammonia fuel enters the fuel cell directly to generate electricity. Among various types of fuel cells, solid oxide fuel cells have good compatibility with ammonia fuel for the following reasons: First, the zirconium oxide-based solid electrolyte of solid oxide fuel cells is stable in an ammonia atmosphere; second, ammonia can be catalytically decomposed into hydrogen and nitrogen on a conventional nickel-based anode; and third, solid oxide fuel cells are high-temperature fuel cells, and the waste heat in the stack is conducive to the endothermic reaction of ammonia decomposition.

[0004] Existing ammonia fuel cell systems use external or internal reformers to reform ammonia. Both external and internal reformers have problems such as high energy consumption, increased system volume and cost. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to address the high energy consumption of the ammonia reforming module in existing ammonia fuel cells. To this end, the present invention provides a combined SOFC and PEMFC system that uses direct ammonia as fuel. Ammonia is decomposed into nitrogen and hydrogen on the SOFC's nickel-based anode at 800°C. Ammonia reforming is achieved using the SOFC's high-temperature waste heat and the anode's nickel-based catalyst.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides a combined SOFC and PEMFC system using direct ammonia fuel, the system comprising a liquid ammonia tank, a solid oxide fuel cell, a proton exchange membrane fuel cell, a burner, a condenser, an ammonia removal device, a heat exchanger, a vaporizer, heat exchanger I, heat exchanger II, and heat exchanger III;

[0008] The liquid ammonia tank is connected to the inlet I of the vaporizer;

[0009] The inlet I of the heat exchanger I is connected to the outlet I of the vaporizer, the outlet I of the heat exchanger is connected to the anode inlet of the solid oxide fuel cell, the outlet II of the heat exchanger I is connected to the inlet II of the vaporizer, and the inlet II of the heat exchanger is connected to the anode outlet of the solid oxide fuel cell;

[0010] The inlet I of the heat exchanger II is connected to the outlet of the burner, air is introduced into the inlet II of the heat exchanger II, the outlet I of the heat exchanger II is connected to the cathode inlet of the solid oxide fuel cell, and the outlet II of the heat exchanger II is used to discharge exhaust gas;

[0011] The inlet of the burner is connected to the anode outlet of the proton exchange membrane fuel cell and the cathode outlet of the solid oxide fuel cell respectively;

[0012] The inlet of the heat exchanger III is connected to the outlet II of the vaporizer, and the outlet of the heat exchanger III is connected to the condenser;

[0013] The condenser is connected to the ammonia removal device and the anode inlet of the proton exchange membrane fuel cell in sequence;

[0014] Air is introduced into the cathode inlet of the proton exchange membrane fuel cell, and the cathode outlet of the proton exchange membrane fuel cell is used to discharge air.

[0015] In the above technical solution, further, the system also includes a pressure valve; the liquid ammonia tank is connected to the inlet I of the vaporizer via the pressure valve.

[0016] In the above technical solution, further, the system also includes a control valve I and a control valve II; the outlet I of the heat exchanger is connected to the anode inlet of the solid oxide fuel cell via the control valve I, and the ammonia removal device is connected to the anode inlet of the proton exchange membrane fuel cell via the control valve II.

[0017] In the above technical solution, further, the system also includes a pressure pump I and a pressure pump II, the pressure pump I is connected to the inlet II of the heat exchanger II, and the pressure pump II is connected to the cathode inlet of the proton exchange membrane fuel cell.

[0018] In the above technical solution, further, the system also includes a pressure pump I and a pressure pump II, the pressure pump I is connected to the inlet II of the heat exchanger II, and the pressure pump II is connected to the cathode inlet of the proton exchange membrane fuel cell.

[0019] In the above technical solution, further, the solid oxide fuel cell anode material is nickel-based, and the support body includes yttria-stabilized zirconia YSZ or doped cerium oxide.

[0020] In the above technical solution, further, the operating temperature of the solid oxide fuel cell is 600-800°C.

[0021] Another aspect of the present invention provides a method for operating a combined SOFC and PEMFC system using direct ammonia fuel, the method comprising the following steps:

[0022] (1) Liquid ammonia in the liquid ammonia tank enters the vaporizer and is vaporized into ammonia gas. The ammonia gas is preheated to a preset temperature I through the heat exchanger I. The preheated ammonia gas serves as fuel and enters the solid oxide fuel cell through the anode inlet of the solid oxide fuel cell.

[0023] (2) The air is preheated to a preset temperature II through the heat exchanger II, and the preheated air enters the interior of the solid oxide fuel cell through the cathode inlet of the solid oxide fuel cell;

[0024] (3) The high-temperature exhaust gas discharged from the anode outlet of the solid oxide fuel cell includes hydrogen, nitrogen, water vapor and ammonia. The high-temperature exhaust gas first passes through heat exchanger I, vaporizer and heat exchanger III in sequence to cool the exhaust gas temperature to a preset temperature III;

[0025] (4) Part of the water vapor is liquefied into water through a condenser, and the remaining mixed gas including water vapor enters an ammonia removal device to remove ammonia;

[0026] (5) The treated mixed gas containing hydrogen, nitrogen and water vapor enters the interior of the proton exchange membrane fuel cell through the anode inlet of the proton exchange membrane fuel cell;

[0027] (6) Air enters the interior of the proton exchange membrane fuel cell through the cathode inlet of the proton exchange membrane fuel cell;

[0028] (7) The exhaust gas discharged from the anode outlet of the proton exchange membrane fuel cell and the air discharged from the cathode outlet of the solid oxide fuel cell enter the burner for combustion, and the heat generated is used to preheat the air at the cathode inlet of the solid oxide fuel cell.

[0029] In the above technical solution, further, unused air and water generated by electrochemical reaction are discharged to the outside through the cathode outlet of the proton exchange membrane fuel cell.

[0030] In the above technical solution, further, the preset temperature I is 700-750°C, the preset temperature II is 400-600°C, and the preset temperature III is 100-150°C.

[0031] The working principle of the direct ammonia fuel SOFC and PEMFC combined system of the present invention is as follows: ammonia is used as fuel, and ammonia is decomposed into nitrogen and hydrogen on the SOFC nickel-based anode at a high temperature of 600-800°C. A portion of the hydrogen is utilized by the SOFC to generate electricity, and the high-temperature tail gas (hydrogen, nitrogen, water vapor, ammonia) discharged from the anode has a high waste heat recovery value. The fuel ammonia at the anode inlet is preheated by a heat exchanger. The anode tail gas after heat exchange passes through a condenser and an ammonia removal device to condense and remove part of the water vapor and all the ammonia in the tail gas. The remaining mixed gas (hydrogen, nitrogen, water vapor) is introduced into the proton exchange membrane fuel cell, and the hydrogen is utilized by the PEMFC to generate electricity. The remaining hydrogen at the anode outlet is sent to the burner for combustion, and the heat generated is used to preheat the air at the SOFC cathode inlet.

[0032] The beneficial effects of the present invention are as follows:

[0033] The fuel cell combined system provided by the present invention reforms ammonia directly on the nickel-based anode of the SOFC, utilizing the high-temperature waste heat of the SOFC and the nickel-based catalyst of the anode to achieve ammonia reforming, thus solving the problems of high energy consumption of the ammonia reformer in the prior art, increased system volume and cost.

[0034] The present invention realizes the optimal utilization of waste heat and tail gas through waste heat recovery and tail gas recovery treatment, improves the overall efficiency of the system, and the fuel gas and air in the system can be recycled, which has the advantages of low energy consumption and high system utilization rate.

[0035] The present invention combines a solid oxide fuel cell with a proton exchange membrane fuel cell, fully utilizing the advantages of the two fuel cells and making up for the problem of insufficient power generation efficiency of a single fuel cell system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] Figure 1 This is a schematic structural diagram of a direct ammonia fuel SOFC and PEMFC combined system of the present invention;

[0038] In the figure: 1. Liquid ammonia tank, 2. Pressure valve, 3. Vaporizer, 4. Heat exchanger I, 5. Control valve I, 6. Anode inlet of solid oxide fuel cell, 7. Cathode inlet of solid oxide fuel cell, 8. Heat exchanger II, 9. Pressure pump I, 10. Air tank I, 11. Burner, 12. Cathode outlet of solid oxide fuel cell, 13. Anode outlet of solid oxide fuel cell, 14. Heat exchanger III, 15. Condenser, 16. Ammonia removal device, 17. Control valve II, 18. Anode inlet of proton exchange membrane fuel cell, 19. Cathode inlet of proton exchange membrane fuel cell, 20. Pressure pump II, 21. Air tank II, 22. Cathode outlet of proton exchange membrane fuel cell, 23. Anode outlet of proton exchange membrane fuel cell. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The specific implementation methods of the present invention are further described in detail below in conjunction with the drawings.

[0040] A direct ammonia fuel SOFC and PEMFC combined system, such as Figure 1 As shown, it includes a liquid ammonia tank 1, a solid oxide fuel cell, a proton exchange membrane fuel cell, a burner 11, a condenser 15, an ammonia removal device 16, a heat exchanger, a vaporizer 3, a heat exchanger I4, a heat exchanger II8, a heat exchanger III14, a pressure pump I9, a pressure pump II20, a pressure valve 2, a control valve I5 and a control valve II17;

[0041] The liquid ammonia tank 1 is connected to the inlet I of the vaporizer 3; the liquid ammonia is vaporized to obtain ammonia gas, which enters the solid oxide fuel cell as fuel.

[0042] The vaporizer 3 is used to vaporize liquid ammonia into ammonia gas, which enters the solid oxide fuel cell as fuel. The heat required by the vaporizer 3 is provided by the high-temperature tail gas at the anode outlet of the solid oxide fuel cell.

[0043] The inlet I of the heat exchanger I4 is connected to the outlet I of the vaporizer 3, the outlet I of the heat exchanger is connected to the anode inlet 6 of the solid oxide fuel cell, the outlet II of the heat exchanger I4 is connected to the inlet II of the vaporizer 3, and the inlet II of the heat exchanger is connected to the anode outlet of the solid oxide fuel cell; the heat exchanger I4 uses the high-temperature exhaust gas discharged from the anode outlet to preheat the ammonia to a preset temperature I, and the preheated ammonia enters the interior of the solid oxide fuel cell.

[0044] The inlet I of the heat exchanger II8 is connected to the outlet of the burner 11, air is introduced into the inlet II of the heat exchanger II8, the outlet I of the heat exchanger II8 is connected to the cathode inlet 7 of the solid oxide fuel cell, and the outlet II of the heat exchanger II8 is used to discharge exhaust gas; the heat exchanger II8 uses the high-temperature exhaust gas discharged from the burner 11 to preheat the air to a preset temperature II, and the preheated air enters the interior of the solid oxide fuel cell.

[0045] The inlet of the burner 11 is connected to the anode outlet 23 of the proton exchange membrane fuel cell and the cathode outlet 12 of the solid oxide fuel cell respectively; the air discharged from the cathode outlet 12 of the solid oxide fuel cell and the hydrogen discharged from the anode outlet 23 of the proton exchange membrane fuel cell enter the burner 11 and are burned, and the high-temperature exhaust gas generated is discharged into the atmosphere after passing through the heat exchanger.

[0046] The inlet of the heat exchanger III 14 is connected to the outlet II of the vaporizer 3 , and the outlet of the heat exchanger III 14 is connected to the condenser 15 ; the heat exchanger III 14 is used to cool the high-temperature exhaust gas from the solid oxide fuel cell to a preset temperature III.

[0047] Condenser 15 is sequentially connected to ammonia removal device 16 and the anode inlet 18 of the proton exchange membrane fuel cell. Condenser 15 is used to condense some of the water vapor in the anode exhaust of the solid oxide fuel cell. The condensed water is discharged from condenser 15, and the remaining water vapor and gases such as hydrogen enter the interior of the proton exchange membrane fuel cell. Ammonia removal device 16 is used to remove residual ammonia in the anode exhaust of the solid oxide fuel cell.

[0048] Air is introduced into the cathode inlet 19 of the proton exchange membrane fuel cell, and the cathode outlet 22 of the proton exchange membrane fuel cell is used to discharge air.

[0049] The liquid ammonia tank 1 is connected to the inlet Ⅰ of the vaporizer 3 through the pressure valve 2; the pressure valve 2 is used to control the flow rate of the liquid ammonia outlet, and the liquid ammonia enters the vaporizer 3 at a preset flow rate through the pressure valve 2.

[0050] The air is passed through the pressure pump I9 into the inlet II of the heat exchanger II8 and into the cathode inlet 7 of the solid oxide fuel cell. The pressure pump I is used to pressurize the air to a preset pressure, and the pressurized air enters the interior of the solid oxide fuel cell.

[0051] Air is introduced into the cathode inlet 19 of the proton exchange membrane fuel cell through the pressure pump II 20. The pressure pump II 20 is used to pressurize the air to a preset pressure, and the pressurized air enters the interior of the proton exchange membrane fuel cell.

[0052] Outlet I of heat exchanger I4 is connected to the anode inlet 6 of the solid oxide fuel cell via control valve I5, and ammonia removal device 16 is connected to the anode inlet 18 of the proton exchange membrane fuel cell via control valve II17. Control valve I5 is used to control the flow of fuel ammonia, and control valve II17 is used to control the flow of fuel hydrogen.

[0053] The anode material of the solid oxide fuel cell is nickel-based, and the support includes yttria-stabilized zirconia YSZ or doped ceria.

[0054] The operating temperature of solid oxide fuel cells is 600-800℃.

[0055] The working method of the above direct ammonia fuel SOFC and PEMFC combined system is as follows:

[0056] Liquid ammonia from ammonia tank 1 enters vaporizer 3 at a preset flow rate through pressure valve 2. The liquid ammonia is vaporized in vaporizer 3 into ammonia gas, which is then preheated to 700-750°C by heat exchanger 4. The preheated ammonia gas, acting as fuel, enters the solid oxide fuel cell through the anode inlet 6 of the solid oxide fuel cell. A control valve I5 controls the flow of the fuel ammonia gas. Air from air tank I10 enters pressure pump I9, where it is pressurized to 1.5 atmospheres. The pressurized air is then preheated to 400-600°C by heat exchanger II8. The preheated air enters the solid oxide fuel cell through the cathode inlet 7 of the solid oxide fuel cell. The solid oxide fuel cell converts the chemical energy of ammonia and oxygen into electrical energy through an electrochemical reaction. Ammonia decomposes into nitrogen and hydrogen at the SOFC's nickel-based anode at a high temperature of 600-800°C.

[0057] Solid oxide fuel cells are high-temperature fuel cells, and their high-temperature exhaust gas has a high utilization value. The high-temperature exhaust gas discharged from the anode outlet 13 of the solid oxide fuel cell contains four gases, namely hydrogen, nitrogen, water vapor and a small amount of residual ammonia. The high-temperature exhaust gas discharged from the anode outlet 13 of the solid oxide fuel cell first passes through the heat exchanger I4, part of its heat is used to preheat the ammonia, and then passes through the vaporizer 3, part of its heat is used by the vaporizer 3, and then passes through the heat exchanger III14 to cool the anode exhaust gas temperature of the solid oxide fuel cell to 100-150°C. The condenser 15 liquefies part of the water vapor into water, and the condensed water is discharged by the condenser. The remaining mixed gas including water vapor enters the ammonia removal device 16 to remove the remaining small amount of ammonia, and finally the mixed gas including hydrogen, nitrogen and water vapor enters the interior of the proton exchange membrane fuel cell through the anode inlet 18 of the proton exchange membrane fuel cell, wherein the control valve II 17 is used to control the circulation of the mixed gas including hydrogen, and the air in the air tank 21 enters the pressure pump II 20 to pressurize the air to 2 atmospheres. The pressurized air enters the interior of the proton exchange membrane fuel cell through the cathode inlet 19 of the proton exchange membrane fuel cell, and the proton exchange membrane fuel cell converts the chemical energy of hydrogen and oxygen into electrical energy through electrochemical reaction. Unused air and water generated by electrochemical reactions are discharged to the outside through the cathode outlet 22 of the proton exchange membrane fuel cell. The exhaust gas discharged from the anode outlet 23 of the proton exchange membrane fuel cell includes nitrogen and unused hydrogen. The exhaust gas discharged from the anode outlet 23 of the proton exchange membrane fuel cell and the air discharged from the cathode outlet 12 of the solid oxide fuel cell are sent to the burner 11, and oxygen and hydrogen are burned in the burner 11. The high-temperature exhaust gas generated by the combustion enters the heat exchanger II 8, which is used to preheat the air at the cathode inlet 7 of the solid oxide fuel cell. The exhaust gas after heat exchange in the heat exchanger is discharged into the atmosphere.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined SOFC and PEMFC system using direct ammonia fuel, characterized by: The system includes a liquid ammonia tank, a solid oxide fuel cell, a proton exchange membrane fuel cell, a burner, a condenser, an ammonia removal device, a heat exchanger, a vaporizer, a heat exchanger I, a heat exchanger II and a heat exchanger III; The liquid ammonia tank is connected to the inlet I of the vaporizer; The inlet I of the heat exchanger I is connected to the outlet I of the vaporizer, the outlet I of the heat exchanger is connected to the anode inlet of the solid oxide fuel cell, the outlet II of the heat exchanger I is connected to the inlet II of the vaporizer, and the inlet II of the heat exchanger is connected to the anode outlet of the solid oxide fuel cell; The inlet I of the heat exchanger II is connected to the outlet of the burner, air is introduced into the inlet II of the heat exchanger II, the outlet I of the heat exchanger II is connected to the cathode inlet of the solid oxide fuel cell, and the outlet II of the heat exchanger II is used to discharge exhaust gas; The inlet of the burner is connected to the anode outlet of the proton exchange membrane fuel cell and the cathode outlet of the solid oxide fuel cell respectively; The inlet of the heat exchanger III is connected to the outlet II of the vaporizer, and the outlet of the heat exchanger III is connected to the condenser; The condenser is connected to the ammonia removal device and the anode inlet of the proton exchange membrane fuel cell in sequence; Air is introduced into the cathode inlet of the proton exchange membrane fuel cell, and the cathode outlet of the proton exchange membrane fuel cell is used to discharge air; The solid oxide fuel cell anode material is nickel-based, and the support comprises yttria-stabilized zirconium oxide (YSZ) or doped ceria; The operating temperature of the solid oxide fuel cell is 600-800°C.

2. The system according to claim 1, wherein: The system further comprises a pressure valve; the liquid ammonia tank is connected to the inlet I of the vaporizer via the pressure valve.

3. The system according to claim 1, wherein: The system also includes a control valve I and a control valve II; the outlet I of the heat exchanger is connected to the anode inlet of the solid oxide fuel cell via the control valve I, and the ammonia removal device is connected to the anode inlet of the proton exchange membrane fuel cell via the control valve II.

4. The system according to claim 1, wherein: The system further comprises a pressure pump I and a pressure pump II. The pressure pump I is connected to the inlet II of the heat exchanger II, and the pressure pump II is connected to the cathode inlet of the proton exchange membrane fuel cell.

5. A method for operating a combined SOFC and PEMFC system using direct ammonia fuel according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: (1) The liquid ammonia in the liquid ammonia tank enters the vaporizer and is vaporized into ammonia gas. The ammonia gas is preheated to a preset temperature I through the heat exchanger I. The preheated ammonia gas is used as fuel and enters the solid oxide fuel cell through the anode inlet of the solid oxide fuel cell. (2) The air is preheated to a preset temperature II through the heat exchanger II, and the preheated air enters the solid oxide fuel cell through the cathode inlet of the solid oxide fuel cell; (3) The high-temperature exhaust gas discharged from the anode outlet of the solid oxide fuel cell includes hydrogen, nitrogen, water vapor and ammonia. The high-temperature exhaust gas first passes through heat exchanger I, vaporizer and heat exchanger III in sequence to cool the exhaust gas temperature to the preset temperature III; (4) Part of the water vapor is liquefied into water through the condenser, and the remaining mixed gas including water vapor enters the ammonia removal device to remove ammonia; (5) The treated mixed gas containing hydrogen, nitrogen and water vapor enters the interior of the proton exchange membrane fuel cell through the anode inlet of the proton exchange membrane fuel cell; (6) Air enters the interior of the proton exchange membrane fuel cell through the cathode inlet of the proton exchange membrane fuel cell; (7) The exhaust gas discharged from the anode outlet of the proton exchange membrane fuel cell and the air discharged from the cathode outlet of the solid oxide fuel cell enter the burner for combustion, and the heat generated is used to preheat the air at the cathode inlet of the solid oxide fuel cell.

6. The working method according to claim 5, characterized in that: Unused air and water generated by the electrochemical reaction are discharged to the outside through the cathode outlet of the proton exchange membrane fuel cell.

7. The working method according to claim 5, characterized in that: The preset temperature I is 700-750°C, the preset temperature II is 400-600°C, and the preset temperature III is 100-150°C.

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