Compact low-temperature direct ammonia fuel cell system

Abstract

The present invention relates to a fuel cell system, and specifically to a compact low-temperature direct ammonia fuel cell system. The system includes a fuel tank, an anode fuel feed subsystem, and a cathode fuel feed subsystem. The fuel tank is connected in sequence to the mixer and fuel heating pipeline of the anode fuel feed subsystem. The fuel heating pipeline is connected to the anode inlet of the stack. The anode outlet of the stack is connected in sequence to a condenser and a gas-liquid separator. The liquid output end of the gas-liquid separator is connected to the mixer, and the gas output end of the gas-liquid separator is connected in sequence to a back pressure regulator and an exhaust gas processor. The cathode fuel feed subsystem includes a compressor and a humidification tank connected in sequence. The humidification tank is connected to the cathode inlet of the stack, and the cathode outlet of the stack is connected in sequence to an expander and an exhaust gas processor. The fuel heating pipeline is placed inside the humidification tank. The system of the present invention combines the anode heating pipeline and the cathode humidification tank into one, reducing the system volume and realizing a compact low-temperature direct ammonia fuel cell system.

Description

Technical Field

[0001] The present invention relates to a fuel cell system, and in particular to a compact low-temperature direct ammonia fuel cell system. Background Art

[0002] A fuel cell is a device that converts chemical energy into electrical energy. Fuel cells can be categorized into various types based on their reaction principles, including proton exchange membrane fuel cells, alkaline anion membrane fuel cells, solid oxide fuel cells, and molten carbonate fuel cells. Among alkaline anion membrane fuel cells, low-temperature direct ammonia fuel cells (DAMFCs), which use liquid ammonia or ammonia gas as fuel, offer advantages such as fast startup and environmental friendliness, making them a promising new fuel cell technology. Currently, battery-powered power systems suffer from short operating times, long charging times, and poor safety. Hydrogen fuel cell-powered power systems are also beginning to enter the market, but the storage and transportation of hydrogen restrict their widespread application. In contrast, DAMFCs overcome the shortcomings of both batteries and hydrogen fuel cells, offering advantages in lightweight applications such as drones, bicycles, uninterruptible power supplies, and mobile power supplies.

[0003] In the existing technology, there is relatively little research on the technology of low-temperature direct ammonia fuel cells, and the research on the system in similar fields is not applicable to low-temperature direct ammonia fuel cells. The main reasons are that the low-temperature direct ammonia fuel cell system has the following problems: (1) the ammonia oxidation kinetics are slow; (2) the low-temperature direct ammonia fuel cell uses high-concentration ammonia fuel to improve the system energy density, and the ammonia fuel utilization rate is low; (3) the ammonia fuel on the anode side easily penetrates through the alkaline anion membrane to the cathode side, causing cathode flooding. Therefore, how to provide a compact system while solving the above three problems is of practical significance for the development of ammonia fuel cells. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low-temperature direct ammonia fuel cell system with a reasonable design, compact structure and high energy density. The main components used in the system include a fuel tank, an anode fuel feed subsystem, a cathode fuel feed subsystem, an exhaust gas processor and a stack. The fuel tank is completely sealed and contains high-concentration ammonia fuel, which can be at least one of liquid ammonia, an ammonia solution or other ammonia-alkali mixture. The fuel tank is connected to the anode fuel feed subsystem through a pipeline. The anode fuel heating pipeline passes through the inside of the cathode humidification tank and is heated by a water bath inside the humidification tank. It is then connected to the anode inlet of the low-temperature direct ammonia fuel cell stack. The anode outlet of the stack is connected to the anode fuel subsystem to form a loop. Air is connected to the cathode inlet of the stack through the cathode fuel feed subsystem, and the cathode outlet of the stack is connected to the cathode fuel cell subsystem to form a loop. The anode and cathode exhaust gases are respectively connected to the exhaust processor and discharged into the atmosphere after being treated by the exhaust processor.

[0005] The present invention specifically adopts the following technical solutions:

[0006] The present invention provides a compact low-temperature direct ammonia fuel cell system, which includes a fuel tank, an anode fuel feeding subsystem, a cathode fuel feeding subsystem, an exhaust gas processor and a fuel cell stack;

[0007] The anode fuel feeding subsystem includes a mixer, a fuel heating pipeline, a condenser, a gas-liquid separator, and a back pressure regulator; the fuel tank is connected to the mixer and the fuel heating pipeline in sequence, the fuel heating pipeline is connected to the anode inlet of the stack, the anode outlet of the stack is connected to the condenser and the gas-liquid separator in sequence, the liquid output end of the gas-liquid separator is connected to the mixer, and the gas output end of the gas-liquid separator is connected to the back pressure regulator and the exhaust gas processor in sequence;

[0008] The cathode fuel feeding subsystem includes a compressor and a humidifying tank connected in sequence, the humidifying tank is connected to the cathode inlet of the stack, and the cathode outlet of the stack is connected to the expander and the tail gas processor in sequence;

[0009] The fuel heating pipeline is placed inside the humidification tank.

[0010] In the above technical solution, further, a metering pump is provided on the pipeline between the fuel tank and the mixer.

[0011] In the above technical solution, further, the exhaust gas processor is a closed structure, and a solid adsorbent is loaded inside the exhaust gas processor to treat incompletely reacted ammonia fuel; the solid adsorbent is one of superphosphate, Prussian blue, silica gel, and activated carbon.

[0012] In the above technical solution, further, the stack is a low-temperature direct ammonia fuel cell stack, and its structure is a bipolar plate type fuel cell stack; the bipolar plate material is composite graphite or metal, and the metal is a stainless steel plate, a coated stainless steel plate or a titanium plate; preferably, the coating is a mixed coating of one or more of carbon, chromium, nickel, gold and silver.

[0013] In the above technical solution, further, the fuel tank is used to directly store high-concentration ammonia fuel; the high-concentration ammonia fuel is at least one of an ammonia aqueous solution or an ammonia-alkali mixture, and is stored at room temperature and pressure; the fuel tank is a closed structure, and the fuel tank material is one of polyethylene, polypropylene, polyethylene terephthalate or aluminum products.

[0014] In the above technical solution, further, the metering pump is one of a peristaltic pump, a gear pump, a centrifugal pump, a screw pump, a pneumatic diaphragm pump, and a spiral pump.

[0015] In the above technical solution, further, the fuel heating pipeline is a stainless steel pipeline, a tetrafluoroethylene pipeline, a polyvinylidene fluoride pipeline, a polyethylene pipeline, or a polypropylene pipeline; the heating method is to heat the anode fuel pipeline through a water bath inside the humidification tank.

[0016] In the above technical solution, further, the mixer is one of a propeller stirrer, a turbine stirrer, a paddle stirrer, and a ribbon stirrer.

[0017] In the above technical solution, further, the compressor is one of piston type, screw type, scroll type, centrifugal type, axial flow type, and jet type;

[0018] The expander is of piston type or turbine type.

[0019] Another aspect of the present invention provides a method for operating the aforementioned fuel cell system, wherein air passes through a compressor and enters a humidification tank. After humidification, the air enters the stack through the cathode inlet for reaction. Unreacted air and water in the stack flow out from the cathode outlet of the stack and enter the exhaust gas processor through an expander for discharge. Ammonia fuel is mixed in a mixer and enters a fuel heating pipeline in the humidification tank. After heating, the anode inlet of the stack enters the stack for reaction. Unreacted ammonia fuel flows out from the anode outlet of the stack and is cooled by a condenser. The coolant enters a gas-liquid separator. The liquid is mixed with the ammonia fuel in the mixer and continues to react in the next step. The gas passes through a back pressure controller and enters the exhaust gas processor for discharge.

[0020] The operating temperature of the fuel cell system is ≤200°C, preferably 80-120°C, and the system temperature is controlled by a fuel heating pipeline. Due to the slow kinetics of ammonia oxidation, a higher temperature is required to ensure a low overpotential in the anode ammonia oxidation process. The operating pressure of the fuel cell system is ≤3MPa, preferably 0.2MPa-0.4MPa. The system pressure is adjusted by a pressure controller and a compressor and an expander in combination. A higher operating pressure is beneficial to the mass transfer of the anode fuel.

[0021] Beneficial effects

[0022] (1) The system of the present invention has the advantages of compact structure and high energy density. The low-temperature direct ammonia fuel cell system provided by the present invention adds a condenser after the outlet of the anode side stack, condenses the unreacted ammonia fuel discharged from the anode into liquid for recovery, separates the product nitrogen and liquid ammonia fuel in the gas-liquid separator device, and the unreacted ammonia fuel is mixed with the introduced ammonia raw material through a mixer and then introduced into the stack, thereby solving the problem that the high-concentration ammonia fuel system has high energy density but low ammonia fuel utilization rate, improves the ammonia fuel utilization rate, and thus improves the system efficiency.

[0023] (2) The ammonia fuel on the anode side easily penetrates through the alkaline anion membrane to the cathode side, causing cathode flooding. The system provided by the present invention increases the operating pressure on the cathode side by using a compressor and an expander in combination on the cathode side, which is beneficial to the mass transfer of oxygen and improves the oxygen reduction kinetics. It solves the problem of cathode flooding caused by ammonia fuel penetrating into the cathode, which is not conducive to oxygen mass transfer; by arranging a back pressure controller at the tail end of the anode side, the operating pressure on the anode side is increased, which is beneficial for the ammonia fuel to reach the catalyst surface and improves the ammonia oxidation kinetics.

[0024] (3) The system provided by the present invention avoids the cooling effect caused by the low-temperature liquid ammonia fuel entering the fuel cell stack by heating the anode feed line, thereby increasing the operating temperature of the fuel cell stack, ensuring a low overpotential in the anode ammonia oxidation kinetic process, and improving the performance of the fuel cell.

[0025] (4) In the system provided by the present invention, the humidification tank humidifies the cathode gas, and at the same time, the anode heating pipeline passes through the sealed humidification tank to achieve heating of the anode pipeline. By placing the heating pipeline inside the humidification tank, the diffusion resistance of the cathode gas inside the humidification tank can be increased, thereby improving the humidification effect of the cathode gas; a single humidification tank heating auxiliary system can reduce the power output of the stack to the auxiliary system, effectively improving the energy efficiency of the system; the unreacted air discharged from the cathode outlet passes through the air expander and enters the tail exhaust device, and the gas separated in the gas-liquid separator is depressurized and enters the tail exhaust device, thereby fully utilizing the functions of each component and simplifying the system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a compact low-temperature direct ammonia fuel cell system in an embodiment;

[0027] In the figure, 1. air, 2. air compressor, 3. air expander, 4. humidification tank, 5. fuel stack cathode, 6. fuel stack anode, 7. exhaust water, 8. fuel tank, 9. metering pump, 10. mixer, 11. gas-liquid separator, 12. air condenser, 13. back pressure regulator, 14. exhaust gas processor, 15. exhaust gas, 16. water, 17. fuel heating pipeline.

[0028] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0030] Example 1

[0031] Figure 1 The present invention is a structural design diagram of a compact low-temperature direct ammonia fuel cell system using ammonia water or ammonia-alkali mixture as fuel.

[0032] The compact low-temperature direct ammonia fuel cell system includes a fuel tank 8, an anode fuel feeding subsystem, a cathode fuel feeding subsystem, an exhaust gas processor 14 and a fuel cell stack; ammonia water or an ammonia-alkali mixture is stored in the fuel tank;

[0033] The anode fuel feeding subsystem includes a mixer 10, a fuel heating pipeline 17, an air condenser 12, a gas-liquid separator 11, and a back pressure regulator 13. The fuel tank is connected to the mixer and the fuel heating pipeline in sequence through pipelines. The fuel heating pipeline is connected to the anode inlet of the stack. The anode outlet of the stack is connected to the condenser and the gas-liquid separator in sequence through pipelines. The liquid output end of the gas-liquid separator is connected to the mixer, and the gas output end of the gas-liquid separator is connected to the back pressure control valve and the exhaust gas processor in sequence. A metering pump is provided on the pipeline between the fuel tank and the mixer.

[0034] The cathode fuel feeding subsystem includes an air compressor 2 and a humidifier tank 4 connected in sequence through pipelines. The humidifier tank is connected to the cathode inlet of the stack, and the cathode outlet of the stack is connected in sequence through pipelines to an air expander 3 and an exhaust gas processor 13;

[0035] The fuel heating pipeline 17 is placed inside the humidification tank 4, which is filled with water and heated by the heat provided by the stack. The anode fuel pipeline is heated by the water bath temperature inside the humidification tank.

[0036] The exhaust gas processor is a closed structure, and a solid adsorbent is loaded inside the exhaust gas processor to treat incompletely reacted ammonia fuel; the solid absorbent can be one of superphosphate, Prussian blue, silica gel, and activated carbon.

[0037] The fuel cell stack is a low-temperature direct ammonia fuel cell stack, and its structure is a bipolar plate type fuel cell stack; the bipolar plate material is composite graphite or metal, and the metal is stainless steel plate, coated stainless steel plate or titanium plate.

[0038] The fuel tank is used to directly store high ammonia aqueous solution or ammonia-alkali mixture at room temperature and pressure; the fuel tank is a closed structure, and the fuel tank material is one of polyethylene, polypropylene, polyethylene terephthalate or aluminum products.

[0039] On the cathode side, air 1 is passed through the air compressor 2 and then connected to the humidification tank 4. After being humidified by the humidification tank, the air is connected to the cathode inlet of the stack. The unreacted air and water in the stack (diffused from the anode) flow out from the cathode outlet of the stack, connected to the air expander 3, and discharged into the atmosphere after passing through the exhaust gas processor 14. By using a compressor and expander in combination on the cathode side, the compressor draws gas into the system, and the expander controls the outflow of a small amount of gas, thereby increasing the pressure in the system and improving the operating pressure on the cathode side.

[0040] On the anode side, ammonia water or ammonia-alkali mixture 8 is connected to the mixer 10 through the metering pump 9. After being evenly mixed, it is connected to the anode inlet of the stack through the fuel heating pipeline. The fuel heating pipeline is heated by the water bath inside the humidifying tank to heat the ammonia fuel. The unreacted ammonia fuel flows out from the anode outlet of the stack and is connected to the air condenser 12 for cooling. The coolant is connected to the gas-liquid separator 11. The liquid coming out of the gas-liquid separator 11 is connected to the mixer 10 and mixed with the ammonia fuel to enter the stack again for reaction. The gas coming out of the gas-liquid separator 11 is connected to the back pressure regulator 13 and then passed into the exhaust gas processor 14 to absorb the unreacted ammonia fuel.

[0041] In this embodiment, the exhaust gas processor 13 is built with a solid adsorbent, using superphosphate, to absorb ammonia and water. The metering pump used in this embodiment is a peristaltic pump, the fuel heating pipeline is a stainless steel pipeline, the mixer is a propeller agitator, the compressor is a piston compressor, and the expander is a piston expander.

[0042] The operating temperature of the fuel cell system can be 80-120°C, and the operating pressure is controlled at 0.2MPa-0.4MPa.

[0043] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A compact low-temperature direct ammonia fuel cell system, characterized in that: The system includes a fuel tank, an anode fuel feeding subsystem, a cathode fuel feeding subsystem, an exhaust gas processor and a fuel cell stack; The anode fuel feeding subsystem includes a mixer, a fuel heating pipeline, a condenser, a gas-liquid separator, and a back pressure regulator; the fuel tank is connected to the mixer and the fuel heating pipeline in sequence, the fuel heating pipeline is connected to the anode inlet of the stack, the anode outlet of the stack is connected to the condenser and the gas-liquid separator in sequence, the liquid output end of the gas-liquid separator is connected to the mixer, and the gas output end of the gas-liquid separator is connected to the back pressure regulator and the exhaust gas processor in sequence; The cathode fuel feeding subsystem includes a compressor and a humidifying tank connected in sequence, the humidifying tank is connected to the cathode inlet of the stack, and the cathode outlet of the stack is connected to the expander and the tail gas processor in sequence; The fuel heating pipeline is placed inside the humidification tank; A metering pump is provided on the pipeline between the fuel tank and the mixer; The fuel tank is used to directly store high-concentration ammonia fuel; the high-concentration ammonia fuel is at least one of an ammonia solution or an ammonia-alkali mixture, and is stored at room temperature and pressure.

2. The system according to claim 1, wherein: The exhaust gas processor is a closed structure, and a solid adsorbent is loaded inside the exhaust gas processor to treat incompletely reacted ammonia fuel; the solid adsorbent is one of superphosphate, Prussian blue, silica gel, and activated carbon.

3. The system according to claim 1, wherein: The stack is a low-temperature direct ammonia fuel cell stack, and its structure is a bipolar plate type fuel cell stack; the bipolar plate material is composite graphite or metal, and the metal is a stainless steel plate, a coated stainless steel plate or a titanium plate.

4. The system according to claim 3, characterized in that The coating is a mixed coating of one or more of carbon, chromium, nickel, gold and silver.

5. The system according to claim 1, wherein: The fuel tank is a sealed structure, and the fuel tank material is one of polyethylene, polypropylene, polyethylene terephthalate or aluminum.

6. The compact low-temperature direct ammonia fuel cell system according to claim 1, characterized in that: The metering pump is one of a peristaltic pump, a gear pump, a centrifugal pump, a screw pump, a pneumatic diaphragm pump, and a spiral pump.

7. The compact low-temperature direct ammonia fuel cell system according to claim 1, characterized in that: The fuel heating pipeline is a stainless steel pipeline, a tetrafluoroethylene pipeline, a polyvinylidene fluoride pipeline, a polyethylene pipeline, or a polypropylene pipeline; The heating method is to heat the anode fuel pipeline through a water bath inside the humidification tank.

8. The compact low-temperature direct ammonia fuel cell system according to claim 1, characterized in that: The mixer is one of a propeller stirrer, a turbine stirrer, a paddle stirrer, and a ribbon stirrer.

9. The compact low-temperature direct ammonia fuel cell system according to claim 1, characterized in that: The compressor is one of piston type, screw type, scroll type, centrifugal type, axial flow type and jet type; The expander is of piston type or turbine type.

10. The operating method of the fuel cell system according to claim 1, characterized in that: After passing through the compressor, the air enters the humidification tank and then enters the stack through the cathode inlet for reaction. The unreacted air and water in the stack flow out from the cathode outlet of the stack and enter the exhaust gas processor through the expander for discharge. After being mixed in the mixer, the ammonia fuel enters the fuel heating pipeline in the humidification tank. After being heated, it enters the fuel cell stack through the anode inlet for reaction. The unreacted ammonia fuel flows out of the anode outlet of the fuel cell stack and is cooled by the condenser. The coolant enters the gas-liquid separator. The liquid is mixed with the ammonia fuel in the mixer and continues to react in the next step. The gas passes through the back pressure regulator and is discharged into the exhaust gas processor. The operating temperature of the fuel cell system is ≤200°C and the operating pressure is ≤3 MPa.

11. The operating method of the fuel cell system according to claim 10, characterized in that: The fuel cell system has an operating temperature of 80-120° C. and an operating pressure of 0.2-0.4 MPa.

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