Fuel cell system with bypass flow rate adjustment

Abstract

The present invention relates to a fuel cell system capable of adjusting a bypass flow rate, which can automatically adjust the flow rate according to the temperature of exhaust gas discharged from a fuel cell stack, A fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention includes: The fuel cell stack is provided with an exhaust gas inlet flow path that supplies at least a portion of the exhaust gas discharged from the fuel cell stack to a membrane humidifier, an exhaust gas exhaust flow path that flows into the membrane humidifier and discharges the exhaust gas to the outside after moisture exchange, a bypass flow path that causes at least a portion of the exhaust gas discharged from the fuel cell stack to bypass the membrane humidifier and flow into the exhaust gas exhaust flow path, and a bypass flow rate adjustment unit that is formed in the bypass flow path and adjusts the opening degree of the bypass flow path depending on the temperature of the exhaust gas discharged from the fuel cell stack.

Description

[Technical field]

[0001] The present invention relates to a fuel cell system, and more specifically to a fuel cell system capable of adjusting a bypass flow rate, which can automatically adjust the bypass flow rate according to the temperature of exhaust gas discharged from a fuel cell stack. [Background technology]

[0002] A fuel cell is a power generating battery that produces electricity by combining hydrogen and oxygen. Unlike ordinary chemical batteries such as dry batteries and storage batteries, fuel cells can continue to produce electricity as long as hydrogen and oxygen are supplied, and because there is no heat loss, they have the advantage of being about twice as efficient as internal combustion engines. In addition, fuel cells emit less pollutants because they directly convert the chemical energy generated by the combination of hydrogen and oxygen into electrical energy, making them environmentally friendly and reducing concerns about resource depletion due to increased energy consumption. Depending on the type of electrolyte used, such fuel cells can be broadly classified into polymer electrolyte membrane fuel cells (PEMFCs), phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), alkaline fuel cells (AFCs), and the like. Although all of these fuel cells operate on the same principle, they differ in the type of fuel used, operating temperature, catalyst, electrolyte, etc. Among them, polymer electrolyte membrane fuel cells (PEMFCs) are known to be the most promising for use in small-scale stationary power generation equipment as well as transportation systems, as they operate at lower temperatures than other fuel cells, have a high power density, and can be made compact.

[0003] One of the most important factors in improving the performance of a polymer electrolyte fuel cell (PEMFC) is to maintain the moisture content by supplying a certain amount of moisture to the polymer electrolyte membrane (Polymer Electrolyte Membrane or Proton Exchange Membrane (PEM)) of the membrane electrode assembly (Membrane Electrode Assembly (MEA)). If the polymer electrolyte membrane dries out, the power generation efficiency drops sharply. Methods for humidifying a polymer electrolyte membrane include 1) a bubbler humidification method in which an internal pressure vessel is filled with water and the target gas is passed through a diffuser to supply moisture, 2) a direct injection method in which the amount of moisture required for the fuel cell reaction is calculated and moisture is supplied directly to the gas flow pipe via a solenoid valve, and 3) a humidification membrane method in which moisture is supplied to the gas flow layer using a polymer separation membrane. Among these, the membrane humidification method, which utilizes a membrane that selectively allows only water vapor contained in exhaust gas to pass through and provides water vapor to the air supplied to the polymer electrolyte membrane to humidify the polymer electrolyte membrane, is advantageous in that it allows the humidifier to be made lighter and smaller. The selectively permeable membrane used in the membrane humidification method is preferably a hollow fiber membrane with a large permeation area per unit volume when forming a module. That is, when a humidifier is manufactured using a hollow fiber membrane, it is possible to highly integrate hollow fiber membranes with a large contact surface area, and it is possible to sufficiently humidify a fuel cell even with a small capacity, and it is possible to use low-cost materials. It is also possible to recover moisture and heat contained in off-gas discharged at high temperature from a fuel cell and reuse them through a humidifier.

[0004] FIG. 1 is a diagram showing a fuel cell system according to the prior art. As shown in FIG. 1, the conventional fuel cell system includes a blower (B), a membrane humidifier 10, a fuel cell stack S, flow paths P1-P5 connecting them, and an adjustment valve 15. P1 is a dry gas supply flow path connecting the blower B and the membrane humidifier 10, and P2 is a stack flow path connecting the membrane humidifier 10 and the fuel cell stack S to supply humidified dry gas. P3 is an exhaust gas inflow flow path that supplies exhaust gas discharged from the fuel cell stack S to the membrane humidifier 10, and P4 is an exhaust gas discharge flow path that flows into the membrane humidifier 10 and discharges the exhaust gas after moisture exchange to the outside. P5 is a bypass flow path that causes a part of the exhaust gas discharged from the fuel cell stack S to flow to the exhaust gas discharge flow path P4 by bypassing the membrane humidifier 10. Here, "connection" includes not only direct connection but also indirect connection in which other parts are interposed in between. The membrane humidifier 10 comprises a humidification module 11 in which moisture exchange occurs between dry gas supplied from a blower B and moist air (exhaust gas) discharged from a fuel cell stack S, and caps (12: 12a, 12b) connected to both ends of the humidification module 11.

[0005] One of the caps 12, 12a, is formed with a dry gas inlet 13 through which dry gas supplied from the blower B is supplied to the humidification module 11, and the other, 12b, is formed with a dry gas outlet 14 through which air humidified by the humidification module 11 is supplied to the fuel cell stack S. The humidification module 11 includes a mid-case 11a having an off-gas inlet 11aa and an off-gas outlet 11ab, and a plurality of hollow fiber membranes 11b in the mid-case 11a. Both ends of the bundle of hollow fiber membranes 11b are fixed to a potting portion 11c. The potting portion 11c is generally formed by hardening a liquid polymer such as liquid polyurethane resin by a casting method. Dry gas supplied from blower B flows along the hollow of hollow fiber membrane 11b. Exhaust gas flowing into mid-case 11a through exhaust gas inlet 11aa comes into contact with the outer surface of hollow fiber membrane 11b, and is then discharged from mid-case 11a through exhaust gas outlet 11ab. When the exhaust gas comes into contact with the outer surface of hollow fiber membrane 11b, moisture contained in the exhaust gas permeates hollow fiber membrane 11b, thereby humidifying the dry gas flowing along the hollow of hollow fiber membrane 11b. The internal space of the cap 12 must only be in fluid communication with the hollow of the hollow fiber membrane 11b and must be completely isolated from the internal space of the mid-case 11a, otherwise air leakage due to pressure difference will occur, reducing the amount of humidified air supplied to the fuel cell stack and decreasing the power generation efficiency of the fuel cell.

[0006] On the other hand, depending on the need to control the system output value, adjust the pollution level of the external exhaust gas, etc., a portion of the exhaust gas discharged from the fuel cell stack S and supplied to the membrane humidifier 10 bypasses the membrane humidifier 10 via the bypass flow path P5, merges with the exhaust gas exhaust flow path P4, and is discharged to the outside. At this time, the bypass flow rate detouring through the bypass flow path P5 is adjusted by an adjustment valve 15 provided on the bypass flow path P5. The opening and closing degree of the adjustment valve 15 can be determined under the control of a controller (not shown). Such adjustment valve 15 must include a valve plate that is pivotally opened and closed, and an adjustment port that adjusts the opening and closing angle of the valve plate according to a user's operation or a signal from a controller, which results in a large number of parts, which increases costs and complicates the fuel cell system. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a fuel cell system capable of automatically adjusting the bypass flow rate according to the temperature of exhaust gas discharged from a fuel cell stack. [Means for solving the problem]

[0008] A fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention includes: The fuel cell stack is provided with an exhaust gas inlet flow path that supplies at least a portion of the exhaust gas discharged from the fuel cell stack to a membrane humidifier, an exhaust gas exhaust flow path that flows into the membrane humidifier and discharges the exhaust gas to the outside after moisture exchange, a bypass flow path that causes at least a portion of the exhaust gas discharged from the fuel cell stack to bypass the membrane humidifier and flow into the exhaust gas exhaust flow path, and a bypass flow rate adjustment unit that is formed in the bypass flow path and adjusts the opening degree of the bypass flow path depending on the temperature of the exhaust gas discharged from the fuel cell stack. In a fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the bypass flow rate adjustment unit may include a thermal expansion material that contracts in a first temperature range and expands in a second temperature range larger than the first temperature range. In the fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the bypass flow rate adjustment unit may be formed in a ring shape on an inner wall of the bypass flow passage. In the fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the bypass flow rate adjuster may be inserted in a ring shape into an annular fixing groove formed on an inner wall of the bypass flow passage. In the fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the exhaust gas inflow passage and the bypass passage may be formed in the same direction.

[0009] In a fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the membrane humidifier may include a mid-case having an exhaust gas inlet connected to the exhaust gas inlet flow path, a cap fastened to the mid-case, and a humidification module disposed within the mid-case and housing a plurality of hollow fiber membranes. In a fuel cell system capable of adjusting a bypass flow rate according to an embodiment of the present invention, the humidification module may include an inner case housing a plurality of hollow fiber membranes, and at least one cartridge having a potting portion formed at an end of the inner case. Further details, such as implementations of various aspects of the present invention, are included in the following detailed description. Effect of the Invention

[0010] In the fuel cell system according to the embodiment of the present invention, the bypass flow rate regulator can automatically adjust the opening of the bypass flow path according to the temperature of the exhaust gas discharged from the fuel cell stack without the need for additional components such as valves, etc. This reduces the number of components in the entire system, making it possible to reduce the size and manufacturing costs. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a fuel cell system according to the prior art. [Diagram 2] 1 is a diagram showing a fuel cell system according to an embodiment of the present invention; [Diagram 3] 4 is an enlarged view of a bypass flow rate regulator of a fuel cell system according to an embodiment of the present invention; FIG. [Figure 4] 4 is a diagram showing the operation state of the bypass flow rate regulator of FIG. 3 in a low output environment. [Diagram 5] 4 is a diagram showing the operation state of the bypass flow rate regulator of FIG. 3 in a high-output environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention can be modified in various ways and can have various embodiments, and a specific embodiment will be illustrated and described in detail in the detailed description. However, this is not intended to limit the present invention to the specific embodiment, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention. The terms used in the present invention are merely used to describe certain embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing a fuel cell system capable of adjusting a bypass flow rate according to one embodiment of the present invention (hereinafter, simply referred to as "fuel cell system"). As shown in FIG. 2, a fuel cell system according to one embodiment of the present invention may include a blower B, a membrane humidifier 100, a fuel cell stack S, flow paths P1-P5 connecting these, and a bypass flow rate adjustment unit (150, see FIG. 3). P1 is a dry gas supply flow path connecting the blower B and the membrane humidifier 100, and P2 is a stack flow path connecting the membrane humidifier 100 and the fuel cell stack S to supply humidified dry gas. P3 is an exhaust gas inflow flow path that supplies the exhaust gas discharged from the fuel cell stack S to the membrane humidifier 100, and P4 is an exhaust gas discharge flow path that flows into the membrane humidifier 100 and discharges the exhaust gas after moisture exchange to the outside. P5 is a bypass flow path that causes a part of the exhaust gas discharged from the fuel cell stack S to bypass the membrane humidifier 100 and flow to the exhaust gas discharge flow path P4. Here, "connection" includes not only direct connection but also indirect connection in which other parts are interposed in between.

[0013] The blower B collects air from the atmosphere and supplies it to the membrane humidifier 100. The output size of the blower B may be determined according to the output size of the fuel cell stack S. If desired, a filter (not shown) for removing fine dust may be provided at the front end of the blower B, and a cooler (not shown) for cooling the dry gas supplied to the membrane humidifier 100 may be provided between the blower B and the membrane humidifier 100. The membrane humidifier 100 humidifies dry gas and supplies it to the fuel cell stack S. The membrane humidifier 100 includes a humidification module 110 that humidifies the dry gas supplied from a blower B with moisture in the exhaust gas discharged from the fuel cell stack S. Both ends of the humidification module 110 are respectively coupled to caps (120: 120a, 120b). The humidification module 110 and the cap 120 may be formed separately or integrally. One of the caps 120, 120a, is formed with a dry gas inlet 130, which supplies dry gas supplied from the blower B to the humidification module 110, and the other, 120b, is formed with a dry gas outlet 140, which supplies air humidified by the humidification module 110 to the fuel cell stack S. The dry gas inlet 130 may be connected to a dry gas supply passage P1 that connects the blower B and the membrane humidifier 10. The dry gas outlet 140 may be connected to a stack passage P2 that connects the membrane humidifier 10 and the fuel cell stack S. The humidification module 110 is a device in which moisture exchange occurs between the dry gas supplied from the blower B and the exhaust gas, and includes a mid-case 111 having an off-gas inlet 111a and an off-gas outlet 111b, and a plurality of hollow fiber membranes 112 in the mid-case 111. Both ends of the bundle of hollow fiber membranes 112 are fixed to a potting portion 113.

[0014] Alternatively, the humidification module 110 may include at least one cartridge including a plurality of hollow fiber membranes 112 and a potting part 113 for fixing the hollow fiber membranes 112 to each other, and in this case, the hollow fiber membranes 112 and the potting part 113 may be formed in a separate cartridge case (inner case). In this case, the hollow fiber membranes 112 may be housed in the inner case, and the potting part 113 may be formed at an end of the inner case. When the humidification module 110 includes a cartridge, a resin layer for fixing the cartridge may be formed between both ends of the cartridge and the mid-case 111, or a gasket assembly for airtight coupling through mechanical assembly may be further included. The mid-case 111 and the cap 120 may each be independently formed of hard plastic or metal and may have a circular or polygonal widthwise cross section. A circular shape includes an oval shape, and a polygonal shape includes a polygonal shape with rounded corners. For example, the hard plastic may be polycarbonate, polyamide (PA), polyphthalamide (PPA), polypropylene (PP), etc. The hollow fiber membrane 112 may include a polymer membrane formed of polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, polyvinylidene fluoride (PVDF) resin, polyacrylonitrile (PAN) resin, polyimide resin, polyamide-imide resin, polyester-imide resin, or a mixture of at least two of these, and the potting portion 113 may be formed by hardening a liquid resin such as liquid polyurethane resin by a casting method such as dip potting or centrifugal potting.

[0015] The dry gas supplied from blower B flows along the hollow of hollow fiber membrane 112. The exhaust gas that flows into mid-case 111 through exhaust gas inlet 111a comes into contact with the outer surface of hollow fiber membrane 112, and is then discharged from mid-case 111 through exhaust gas outlet 111b. When the exhaust gas comes into contact with the outer surface of hollow fiber membrane 112, the moisture contained in the exhaust gas permeates hollow fiber membrane 112, thereby humidifying the dry gas that has been flowing along the hollow of hollow fiber membrane 112. Meanwhile, a portion of the exhaust gas discharged from the fuel cell stack S and supplied to the membrane humidifier 10 may have its flow rate adjusted by a bypass flow rate adjuster 150 that adjusts the opening degree of the bypass flow passage P5 according to the temperature of the exhaust gas discharged from the fuel cell stack S. The bypass flow rate adjuster 150 can automatically adjust the opening degree according to the temperature of the exhaust gas without requiring any additional parts. This reduces the number of parts in the entire system, making it possible to reduce the size and manufacturing costs. The bypass flow rate adjuster 150 will be described in detail with reference to FIG. 3. FIG. 3 is a diagram showing a bypass flow rate regulator 150 of a fuel cell system according to an embodiment of the present invention, and is an enlarged view of part "A" of FIG. 3, the bypass flow rate adjuster 150 is formed in the bypass flow path P5 and can adjust the opening degree of the bypass flow path P5 according to the temperature of the exhaust gas discharged from the fuel cell stack S. The bypass flow path P5 can be formed to be connected to the exhaust gas inlet flow path P3. In addition, the exhaust gas inlet flow path P3 can be formed to be connected to the exhaust gas inlet 111a. The exhaust gas inlet flow path P3 and the exhaust gas inlet 111a can be formed to form a predetermined angle, for example, a right angle. The bypass flow rate control unit 150 may be formed on the inner wall of the bypass flow passage P5. The bypass flow rate control unit 150 may be formed in a ring shape on the inner wall of the bypass flow passage P5. Alternatively, an annular fixing groove 151 may be formed on the inner wall of the bypass flow passage P5, and the bypass flow rate control unit 150 may be formed in a ring shape and inserted and fixed into the annular fixing groove 151.

[0016] The bypass flow rate control unit 150 may be made of a material that thermally expands depending on the temperature of the exhaust gas. The bypass flow rate control unit 150 may include a thermal expansion material that contracts in a first temperature range and expands in a second temperature range that is larger than the first temperature range. That is, the bypass flow rate control unit 150 may include a thermal expansion material that contracts at low temperatures and expands at high temperatures. The exhaust gas inlet flow passage P3 and the bypass flow passage P5 are preferably formed in the same direction. When the exhaust gas inlet flow passage P3 and the bypass flow passage P5 are formed in the same direction, the bypass flow rate control unit 150 faces the flow direction of the exhaust gas, so that contraction / expansion due to temperature can be effectively performed. The exhaust gas flowing through the exhaust gas inlet flow passage P3 is distributed to the exhaust gas inlet 111a and the bypass flow passage P5. At this time, the amount of exhaust gas supplied to the membrane humidifier 100 through the exhaust gas inlet 111a is determined by the amount of exhaust gas flowing through the bypass flow passage P5. In addition, the flow rate of the exhaust gas flowing through the bypass flow passage P5 is determined by the bypass flow rate adjustment unit 150. This will be described with reference to Figs. 4 and 5. 4 is a diagram showing the operation state of the bypass flow rate adjuster 150 in a low-power environment. When the output of the fuel cell stack S is less than about 40 kW, it can be said to be a low-power environment. In the low-power environment, a relatively low-temperature exhaust gas is supplied from the fuel cell stack S. Here, the low temperature can be a first temperature range of less than about 50°C.

[0017] Since the exhaust gas is low temperature, the bypass flow rate regulator 150 relatively contracts, and the opening diameter of the bypass flow path P5 becomes L1. Therefore, a relatively large amount of exhaust gas flows through the bypass flow path P5 compared to the high-output environment, and a relatively small amount of low-temperature exhaust gas is supplied to the membrane humidifier 100. 5 is a diagram showing the operation state of the bypass flow rate adjuster 150 in a high-power environment. When the output of the fuel cell stack S is approximately 40 kW or more, it can be said to be a high-power environment. In the high-power environment, a relatively high-temperature exhaust gas is supplied from the fuel cell stack S. Here, the high temperature is in the range of approximately 50 to 150°C, and can be a second temperature range that is higher than the first temperature range. Since the exhaust gas is at a high temperature, the bypass flow rate regulator 150 expands and the opening diameter of the bypass flow passage P5 becomes L2, which is smaller than L1. Therefore, a relatively small amount of exhaust gas flows through the bypass flow passage P5 compared to a low output environment, and a relatively large amount of high-temperature exhaust gas is supplied to the membrane humidifier 100. In the fuel cell system according to an embodiment of the present invention as described above, the bypass flow rate control unit 150 can automatically adjust the opening of the bypass flow path P5 according to the temperature of the exhaust gas discharged from the fuel cell stack S without the need for additional components such as a valve. This reduces the number of components in the entire system, making it possible to reduce the size and manufacturing costs. Although one embodiment of the present invention has been described above, a person having ordinary knowledge in the art would be able to modify and change the present invention in various ways by adding, changing, deleting, or adding components without departing from the concept of the present invention described in the claims, and this would also be considered to be within the scope of the claims of the present invention. [Explanation of symbols]

[0018] 100: Fuel cell membrane humidifier 110: Humidification module 111a: exhaust gas inlet 111b: exhaust gas outlet 120: Cap 150: Bypass flow rate adjustment section B: Blower S: Fuel cell stack P1: Dry gas supply passage P2: Stack passage P3: Exhaust gas inflow path P4: Exhaust gas exhaust path P5: Bypass flow path

Claims

1. an exhaust gas inlet flow passage that supplies at least a portion of the exhaust gas discharged from the fuel cell stack to the membrane humidifier; an exhaust gas exhaust flow path that discharges the exhaust gas after the exhaust gas flows into the membrane humidifier and is subjected to moisture exchange to the outside; a bypass flow path that causes at least a portion of the exhaust gas discharged from the fuel cell stack to flow into the exhaust gas discharge flow path, bypassing the membrane humidifier; a bypass flow rate adjusting unit that is formed in the bypass flow path and adjusts an opening degree of the bypass flow path depending on a temperature of exhaust gas discharged from the fuel cell stack, The bypass flow rate adjustment unit is a thermally expansive material that contracts in a first temperature range and expands in a second temperature range greater than the first temperature range; The bypass flow rate adjustment unit is The bypass passage is inserted in a ring shape into an annular fixing groove formed in an inner wall of the bypass passage. A fuel cell system with adjustable bypass flow rate.

2. 2. The fuel cell system capable of adjusting a bypass flow rate according to claim 1, wherein the exhaust gas inflow passage and the bypass passage are formed in the same direction.

3. The membrane humidifier comprises: A fuel cell system capable of adjusting a bypass flow rate as described in any one of claims 1 to 2, comprising a mid-case having an exhaust gas inlet formed therein and connected to the exhaust gas inlet flow path, a cap fastened to the mid-case, and a humidification module disposed within the mid-case and housing a plurality of hollow fiber membranes.

4. The humidification module includes:

4. The fuel cell system capable of adjusting a bypass flow rate according to claim 3, comprising an inner case housing a plurality of hollow fiber membranes, and at least one cartridge having a potting portion formed at an end of the inner case.

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