Fuel cell system

Abstract

Disclosed is a fuel cell system. The fuel cell system comprises: a fuel cell stack unit provided with a fuel cell stack; a main fuel supply unit supplying a main fuel gas to the fuel cell stack and provided with a first pipe that provides a path through which the main fuel gas flows; a fuel discharge unit provided with a second pipe that provides a path through which an off-fuel gas discharged from the fuel cell stack flows; a fuel recirculation unit branching from the second pipe and provided with a third pipe that provides a path through which a portion of the off-fuel gas flows; and a joining unit provided with a joining pipe structure. The joining pipe structure includes: an expansion pipe; first and second inlet pipes which are coupled to a first end surface of the expansion pipe, have parallel center axes, and are connected to the first and third pipes, respectively; a reducer pipe coupled to a second end surface of the expansion pipe; and an outlet pipe coupled to the reducer pipe.

Description

fuel cell system

[0001] The present invention relates to a fuel cell system that generates electrical energy using hydrocarbon fuel and air.

[0002] Fuel cells generate electricity through the reaction of hydrogen and oxygen. While fuel cells are most efficient when using hydrogen directly, installing hydrogen storage tanks directly where the fuel cells are installed poses significant safety concerns. Therefore, hydrocarbon fuels are currently reformed to produce hydrogen, which is then used as fuel for the fuel cells. Steam reforming, which involves reacting steam with the hydrocarbon fuel to produce hydrogen, is the most commonly used method for reforming hydrocarbon fuels.

[0003] Meanwhile, fuel cell systems have relatively low power generation efficiency. Therefore, extensive research has focused on methods to increase thermal efficiency by additionally utilizing the waste heat emitted from the fuel cell system. However, recently, demand has been growing for technologies that can improve power generation efficiency, rather than thermal efficiency. Consequently, technologies are being developed to recycle the anode off-gas emitted from the fuel cell stack into fuel gas to enhance power generation efficiency.

[0004] However, in a high-efficiency fuel cell system using anode off-gas recirculation technology, when the main fuel gas and the recirculated fuel gas join, a reverse flow of fluid may occur, and due to differences in pressure and flow rate of the main fuel gas and the recirculated fuel gas, they may interfere with each other, causing an uneven amount of fuel supplied to the fuel cell stack.

[0005] An object of the present invention is to provide a fuel cell system capable of uniformly supplying fuel to a fuel cell stack even though it has an off-fuel gas recirculation line.

[0006] A fuel cell system according to an embodiment of the present invention may include a fuel cell stack unit having a fuel cell stack; a main fuel supply unit having a first pipe for supplying main fuel gas to the fuel cell stack and providing a passage through which the main fuel gas moves; a fuel discharge unit having a second pipe for providing a passage through which off-fuel gas discharged from the fuel cell stack moves; a fuel recirculation unit having a third pipe branched from the second pipe and providing a passage through which some of the off-fuel gas moves; and a junction unit having a junction pipe structure including an expansion pipe, first and second inlet pipes coupled to a first end surface of the expansion pipe and having central axes parallel to each other and respectively connected to the first and third pipes, a reducer pipe coupled to a second end surface of the expansion pipe, and a discharge pipe coupled to the reducer pipe.

[0007] In one embodiment, the expansion pipe, the reducer pipe, and the discharge pipe have a central axis parallel to the central axes of the first and second inlet pipes, and the diameter of the expansion pipe may be two to three times larger than the diameter of the first and second inlet pipes.

[0008] In one embodiment, the length of the extension tube may be about two to three times the length of the discharge tube.

[0009] In one embodiment, the diameter of the discharge pipe may be smaller than the diameter of the expansion pipe and larger than the diameters of the first and second inlet pipes.

[0010] In one embodiment, the diameter of the discharge pipe may be 1.0 to 1.7 times the diameter of the first and second inlet pipes.

[0011] In one embodiment, the exhaust pipe may be connected directly to the fuel cell stack or may be connected to the fuel cell stack through a reformer that produces hydrogen from hydrocarbon fuel gas.

[0012] In one embodiment, the reducer tube may have a first end having the same diameter as a second end surface of the expansion tube and coupled to the second end surface of the expansion tube, and a second end having the same diameter as a diameter of the discharge tube and connected to the discharge tube.

[0013] In one embodiment, the angle between a line corresponding to a side surface of the reducer tube and the central axis of the reducer tube may be 30° to 60°.

[0014] In one embodiment, the main fuel supply unit may further include a first check valve installed in the first pipe.

[0015] In one embodiment, the main fuel supply unit may further include a first pump installed in the first pipe.

[0016] In one embodiment, the fuel recirculation unit may further include a second check valve installed in the third pipe.

[0017] In one embodiment, the fuel recirculation unit may further include a second pump installed in the third pipe.

[0018] In one embodiment, the fuel recirculation unit may further include a solenoid valve and a water trap installed in the third pipe.

[0019] According to the fuel cell system of the present invention, due to differences in pressure, flow rate, etc. between the main fuel gas supplied to the fuel cell stack and the recirculated off-fuel gas, it is possible to minimize uneven supply of fuel gas to the fuel cell stack due to interference with each other.

[0020] FIG. 1 is a drawing for explaining a fuel cell system according to an embodiment of the present invention.

[0021] Figures 2a and 2b are drawings for explaining the confluence pipe structure shown in Figure 1.

[0022] Figures 3a and 3b are drawings showing simulation results for a confluence pipe structure according to an embodiment.

[0023] Figures 4a and 4b are drawings showing simulation results for a confluence pipe structure according to a comparative example.

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention may be modified in various ways and may take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing each drawing, similar reference numerals are used to indicate similar components. In the attached drawings, the dimensions of structures are shown larger than actual size to ensure clarity of the present invention.

[0025] While terms like "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component."

[0026] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, step, operation, component, part, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, steps, operations, components, parts, or combinations thereof.

[0027] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0028]

[0029] FIG. 1 is a drawing for explaining a fuel cell system according to an embodiment of the present invention, and FIGS. 2a and 2b are drawings for explaining the confluence pipe structure illustrated in FIG. 1.

[0030] Referring to FIGS. 1 and 2, a fuel cell system (1000) according to an embodiment of the present invention may include a fuel cell stack unit (1100), a main fuel supply unit (1200), a fuel discharge unit (1300), a fuel recirculation unit (1400), and a merging unit (1500).

[0031] The fuel cell stack unit (1100) may include a stack of a plurality of single cells that generate electrical energy by utilizing the reaction of oxygen and hydrogen. The single cell may include an anode, an air electrode (cathode), and an electrolyte positioned therebetween, and when fuel gas containing hydrogen (H2) and air containing oxygen (O2) are supplied to the anode and the air electrode, respectively, reduced oxygen ions (O2) are generated at the cathode. 2- ) moves to the fuel electrode via the electrolyte, and the oxygen ions (O ) moved to the fuel electrode 2- ) reacts with hydrogen (H2) provided to the fuel electrode to produce water (H2O) and electrons (e - ) is generated, and the single cell can generate electrical energy using electrons generated through the reaction as described above. The reaction of oxygen and hydrogen is an exothermic reaction, and the fuel cell stack unit (1100) can release heat during the power generation mode in which it generates electrical energy.

[0032] The fuel cell stack unit (1100) may include one selected from a solid oxide fuel cell (SOFC), a molten carbonate fuel cell (MCFC), a polymer electrolyte fuel cell (PEMFC), etc., but is not limited thereto. Meanwhile, the fuel cell stack unit (1110) may include a stack of planar single cells, or may include a bundle of tubular or flat tubular single cells.

[0033] The above main fuel supply unit (1200) can supply main fuel gas to the fuel cell stack unit (1100).

[0034] In one embodiment, the main fuel supply unit (1200) may include a first pipe (1210), a first pump (1220), and a first check valve (1230).

[0035] The first pipe (1210) may be installed to connect the external fuel supply unit (10) and the junction unit (1500), and may provide a passage through which the main fuel gas supplied from the external fuel supply unit (10) moves to the junction unit (1500). The first pump (1220) may be installed in the first pipe (1210), and may move the main fuel gas toward the junction unit (1500) through the first pipe (1210). The first check valve (1230) may be installed in the first pipe (1210), and may prevent the main fuel gas from flowing backward in the opposite direction from the junction unit (1500).

[0036] The fuel discharge unit (1300) may include a second pipe (1310) that provides a passage through which off-fuel gas discharged after reaction in the fuel cell stack unit (1100) moves. The off-fuel gas may include unreacted hydrogen and hydrocarbon gases.

[0037] The above fuel recirculation unit (1400) is configured to branch from the second pipe (1310) of the fuel discharge unit (1300) and recirculate some of the off-fuel gas discharged from the fuel cell stack unit (1100) as fuel gas of the fuel cell stack unit (1100).

[0038] In one embodiment, the fuel recirculation unit (1400) may include a third pipe (1410), a second pump (1420), and a second check valve (1430), and may additionally include one or more selected from a solenoid valve (1440), a water trap (1450), and the like.

[0039] The third pipe (1410) may be connected to a portion of the second pipe (1310) located between the fuel cell stack unit (1100) and the combustor (1320) and branched from the second pipe (1310), and a portion of the off-fuel gas discharged from the fuel cell stack unit (1100) may be supplied to the combustor (1320), and another portion may be introduced into the third pipe (1410).

[0040] The second pump (1420) can move the off-fuel gas through the third pipe (1410).

[0041] The second check valve (1430) is installed in the third pipe (1410) and can prevent the off-fuel gas moving through the third pipe (1410) from flowing backward.

[0042] The above-described solenoid valve (1440) is installed in the third pipe (1410) and can be opened and closed, and the operation of the solenoid valve (1440) can be controlled according to a user's operation. For example, when a user opens the solenoid valve (1440), the off-fuel gas can be recycled by the fuel recirculation unit (1400), and accordingly, the fuel cell stack unit (1100) can generate electric energy by using both the main fuel gas supplied from the fuel supply unit (10) and the off-fuel gas supplied from the fuel recirculation unit (1400). In contrast, when a user closes the solenoid valve (1440), recirculation of the off-fuel gas does not occur, and as a result, the fuel cell stack unit (1100) can generate electric energy by using only the main fuel gas supplied from the fuel supply unit (10). In one embodiment, when the fuel cell stack unit (1100) can perform an autothermal reaction, the solenoid valve (1440) may be opened, and conversely, when the fuel cell stack unit (1100) cannot perform an autothermal reaction at the beginning of operation, the solenoid valve (1440) may be closed.

[0043] The above water trap (1450) can remove water vapor contained in the off-fuel gas by converting it into water. The configuration of the water trap (1450) is not particularly limited, and known water trap configurations for fuel cells can be applied without limitation.

[0044] The above junction (1500) is configured to merge the main fuel gas supplied through the first pipe (1210) and the off-fuel gas supplied through the third pipe (1410), and may include a junction pipe structure having a structure that can minimize interference between the main fuel gas and the off-fuel gas.

[0045] In one embodiment, as illustrated in FIGS. 2a and 2b, the confluence structure (1500a) may include a first inlet pipe (1511a), a second inlet pipe (1512a), an expansion pipe (1520a), a reducer pipe (1530a), and a discharge pipe (1540a).

[0046] The first inlet pipe (1511a) is connected to the first pipe (1210) and can receive main fuel gas from the first pipe (1210). In one embodiment, the first inlet pipe (1511a) may have a circular pipe structure having a first diameter, and may have a first end connected to the first pipe (1210) and a second end connected to a first region of the first end surface of the extension pipe (1520a).

[0047] The second inlet pipe (1512a) may be connected to the third pipe (1410) and may receive off-fuel gas from the third pipe (1410). The second inlet pipe (1512a) may have a circular pipe structure having the same diameter as the first inlet pipe (1511a), i.e., a first diameter, and may have a first end that is connected to the third pipe (1410) and a second end that is connected to a second region adjacent to the first inlet pipe (1512a) among the first end surfaces of the extension pipe (1520a).

[0048] In one embodiment, the first inlet pipe (1511a) and the second inlet pipe (1512a) may be coupled to the first end surface of the extension pipe (1520a) such that their respective central axes are parallel to each other and symmetrical to each other from the center of the first end surface of the extension pipe (1520a).

[0049] The above-described expansion pipe (1520a) may have a circular pipe structure having a second diameter larger than the first diameter. In one embodiment, the second diameter of the expansion pipe (1520a) may be at least twice the first diameter of the first and second inlet pipes (1511a, 1512a). For example, the second diameter may be larger than twice and smaller than three times the first diameter. The central axis of the expansion pipe (1520a) may be parallel to the central axes of the first and second inlet pipes (1511a, 1512a), and the central axes of the first and second inlet pipes (1511a, 1512a) may be positioned symmetrically with respect to the central axis of the expansion pipe (1520a) on the same plane. Meanwhile, the length of the expansion pipe (1520a) is not particularly limited and may be variously changed. For example, the length of the extension pipe (1520a) may be about 2 to 3 times the length of the discharge pipe (1540a).

[0050] The discharge pipe (1540a) may be disposed spaced apart from the expansion pipe (1520a) with the reducer pipe (1530a) therebetween, and the diameter of the discharge pipe (1540a), i.e., the third diameter, may be larger than the diameters of the first and second inlet pipes (1511a, 1512a), i.e., the first diameter, and smaller than the diameter of the expansion pipe (1520a), i.e., the second diameter, and the central axis of the discharge pipe (1540a) may be disposed to coincide with the central axis of the expansion pipe (1520a). For example, the third diameter of the discharge pipe (1540a) may be about 1.0 to 1.7 times the first diameter, and may be about 0.9 to 1.0 times the second diameter.

[0051] The above discharge pipe (1540a) may be directly connected to the fuel cell stack unit (1100) or may be connected to the fuel cell stack unit (1100) through a reformer (not shown) that generates hydrogen from hydrocarbon fuel gas.

[0052] The above-described reducer pipe (1530a) may be positioned between the expansion pipe (1520a) and the discharge pipe (1540a) to connect them. In one embodiment, the reducer pipe (1530a) may have a first end that has the same diameter as the second end surface of the expansion pipe (1520a), i.e., a second diameter, and is coupled to the second end surface of the expansion pipe (1520a), and a second end that has the same diameter as the third diameter of the discharge pipe (1540a) and is connected to the discharge pipe (1540a). The central axis of the reducer pipe (1530a) may be positioned to coincide with the central axes of the expansion pipe (1520a) and the discharge pipe (1540a). In one embodiment, in the center plane of the reducer tube (1530a), the angle between a line corresponding to the side surface of the reducer tube (1530a) and the center axis of the reducer tube (1530a) may be about 30° to 60°.

[0053]

[0054] According to the fuel cell system of the present invention, due to differences in pressure, flow rate, etc. between the main fuel gas supplied to the fuel cell stack and the recirculated off fuel gas, it is possible to minimize uneven supply of fuel gas to the fuel cell stack unit (1100) due to interference between them.

[0055]

[0056] Hereinafter, specific examples and comparative examples of the present invention will be described in detail. However, the following examples are merely some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[0057]

[0058] [Example]

[0059] As shown in Fig. 3a, a confluence pipe structure was fabricated, which consists of an extension pipe having a diameter of 1.2 inches, first and second inlet pipes having a diameter of 0.5 inches connected to a first end face thereof, a reducer pipe connected to a second end face of the extension pipe opposite to the first end face, and a discharge pipe having a diameter of 0.75 inches connected to an end of the reducer pipe.

[0060]

[0061] [Comparative example]

[0062] As shown in Fig. 4a, a confluence pipe structure was manufactured consisting of a first inlet pipe, a second inlet pipe, and an outlet pipe, all of which are connected to each other in a Y shape and have a diameter of 0.5 inches.

[0063]

[0064] [Experimental Example]

[0065] For the junction pipe structure according to the embodiment and the junction pipe structure according to the comparative example, city gas is supplied to the first inlet pipe at a rate of 0.00045 m 3 / s is supplied at a flow rate of 0.0006 m and the recirculated off-fuel gas is fed to the second inlet pipe. 3 The flow rate inside the confluence pipe structure was simulated by supplying it at a flow rate of / s.

[0066] FIGS. 3a and 3b are drawings showing simulation results for a confluence structure according to an embodiment, and FIGS. 4a and 4b are drawings showing simulation results for a confluence structure according to a comparative example.

[0067]

[0068] Referring to FIGS. 3a, 3b, 4a, and 4b, in the junction pipe structure according to the embodiment, as the voltage of the recirculation pump increases, the main fuel gas flow rate flows between a minimum of 18.45 lpm and a maximum of 18.5 lpm, resulting in an oscillation width of about 0.05 lpm, and the pressure flows between a minimum of 6 kPa and a maximum of 6.2 kPa, resulting in an oscillation width of 0.2 kPa. In contrast, in the junction pipe structure according to the comparative example, as the voltage of the recirculation pump increases, the main fuel gas flow rate flows between a minimum of 18.55 lpm and a maximum of 18.65 lpm, resulting in an oscillation width of about 0.1 lpm, and the pressure flows between a minimum of 6.1 kPa and a maximum of 6.6 kPa, resulting in an oscillation width of 0.5 kPa. Through these single-acting tests, it can be seen that the junction pipe structure according to the embodiment discharges fuel gas more stably than the junction pipe structure according to the comparative example.

[0069]

[0070] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

1. A fuel cell stack section having a fuel cell stack; A main fuel supply unit having a first pipe that supplies main fuel gas to the fuel cell stack and provides a passage through which the main fuel gas moves; A fuel discharge unit having a second pipe providing a passage through which off-fuel gas discharged from the fuel cell stack moves; A fuel recirculation unit having a third pipe branched from the second pipe and providing a passage through which some of the off-fuel gas moves; and A fuel cell system comprising a junction structure including an expansion pipe, first and second inlet pipes connected to a first end surface of the expansion pipe and having central axes parallel to each other and respectively connected to the first and third pipes, a reducer pipe connected to a second end surface of the expansion pipe, and a discharge pipe connected to the reducer pipe; 2. In paragraph 1, The above expansion pipe, the above reducer pipe and the above discharge pipe have a central axis parallel to the central axes of the first and second inlet pipes, A fuel cell system, characterized in that the diameter of the expansion pipe is 2 to 3 times larger than the diameter of the first and second inlet pipes.

3. In paragraph 2, A fuel cell system, characterized in that the length of the above extension pipe is 2 to 3 times the length of the above discharge pipe.

4. In paragraph 2, A fuel cell system, characterized in that the diameter of the discharge pipe is smaller than the diameter of the expansion pipe and larger than the diameters of the first and second inlet pipes.

5. In paragraph 4, A fuel cell system, characterized in that the diameter of the discharge pipe is 1.0 to 1.7 times the diameter of the first and second inlet pipes.

6. In paragraph 4, A fuel cell system, characterized in that the exhaust pipe is directly connected to the fuel cell stack or is connected to the fuel cell stack through a reformer that generates hydrogen from hydrocarbon fuel gas.

7. In paragraph 4, A fuel cell system, characterized in that the reducer tube has a first end that has the same diameter as the second end surface of the expansion tube and is coupled to the second end surface of the expansion tube, and a second end that has the same diameter as the diameter of the discharge tube and is connected to the discharge tube.

8. In paragraph 7, A fuel cell system, characterized in that the angle between a line corresponding to the side surface of the reducer tube and the central axis of the reducer tube is 30˚ to 60˚.

9. In paragraph 1, A fuel cell system, characterized in that the main fuel supply unit further includes a first check valve installed in the first pipe.

10. In paragraph 9, A fuel cell system, characterized in that the main fuel supply unit further includes a first pump installed in the first pipe.

11. In paragraph 1, A fuel cell system, characterized in that the fuel recirculation unit further includes a second check valve installed in the third pipe.

12. In paragraph 11, A fuel cell system, characterized in that the fuel recirculation unit further includes a second pump installed in the third pipe.

13. In paragraph 11, A fuel cell system, characterized in that the fuel recirculation unit further includes a solenoid valve and a water trap installed in the third pipe.

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