Method and system for removal of high concentration of combustible hydrogen after fuel cell system operation

Abstract

The present invention relates to a method and system for removing flammable hydrogen gas discharged to the outside after the operation of a fuel cell system, and more particularly, to a method for removing flammable hydrogen gas in a high concentration from residual gas in a fuel cell system after operation, including the steps of detecting a specific condition in which the hydrogen concentration of the residual gas reaches a predetermined reference value or more after the operation of a fuel cell power generator; adjusting the opening of a hydrogen valve installed at the anode outlet of a fuel cell stack when the specific condition is detected; supplying air to the fuel cell stack by means of an oxygen supply unit of the fuel cell stack; and passing the supplied air together with the residual gas through a passive hydrogen removal catalyst module installed at the rear end of an exhaust pipe.

Description

Technical Field

[0001] This invention relates to a method and system for removing combustible hydrogen emitted to the outside after the operation of a fuel cell system, and more particularly to a method and system for removing and emitting high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the operation of the fuel cell system using a passive hydrogen removal catalyst. Background Technology

[0002] A fuel cell system, as a power generation system that converts the chemical energy of fuel into electrical energy within a fuel cell stack, is a useful system that generates electricity by reacting hydrogen (fuel) with oxygen from the air within the fuel cell stack. However, to minimize the risk of explosion or fire caused by hydrogen contained in the exhaust gases released after power generation, the hydrogen concentration in the exhaust gases needs to be controlled and maintained below a specified baseline value. Currently, residual gases containing high concentrations of hydrogen remaining in the fuel cell stack and hydrogen supply pipes after the fuel cell system has been running are diluted to an average of less than 4% using air supplied through blowers before being released to the outside. However, this still presents problems such as noise generation due to the operation of these blowers, and even with the high-concentration hydrogen diluted to an average hydrogen concentration of 4% and released, there is still a risk of explosion due to the accumulation of hydrogen concentration in areas with poor air circulation, such as underground parking lots.

[0003] Therefore, in order to dilute the residual gas remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has finished generating electricity, a large amount of dilution air is required. In order to ensure the dilution air, a large-capacity air supply device or multiple small-capacity air supply devices need to be operated. Thus, there is an urgent need for a solution that can solve the problems of noise generation caused by the operation of these supply devices and the fact that hydrogen is still emitted to the outside at a concentration that can spontaneously combust. Summary of the Invention

[0004] The present invention aims to solve the problems existing in the prior art. The purpose of the present invention is to provide a method for removing and discharging high concentrations of hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has been in operation.

[0005] Another object of the present invention is to provide a system for removing and discharging high-concentration hydrogen remaining in the fuel cell system after operation, without generating excessive noise due to the operation of a large-capacity air supply device or multiple small-capacity air supply devices used to dilute the high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe.

[0006] Another objective of this invention is to provide a method and system for removing 99.99% of the high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has been in operation, thereby minimizing the risk of explosion due to the accumulation of hydrogen concentration in enclosed areas where air circulation is difficult.

[0007] The purpose of this invention is to provide a method and system suitable for passive hydrogen oxidation devices, which removes 99.99% of the high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has finished operating, without requiring a large-capacity air supply device or multiple small-capacity air supply devices for hydrogen dilution, or even if required, can be replaced by a small-capacity air supplement supply device for hydrogen oxidation, and removes hydrogen at room temperature without a separate heat / energy source.

[0008] The technical issues to be addressed by this invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains will be able to further understand other technical issues not mentioned through the following description.

[0009] This invention provides a method and system for removing high concentrations of hydrogen gas remaining in a fuel cell system after power generation.

[0010] A method for removing high-concentration hydrogen from residual gas in a fuel cell stack and hydrogen supply pipe after operation, according to an embodiment of the present invention, may include: a step of detecting a specific condition where the hydrogen concentration of the residual gas reaches or exceeds a predetermined reference value after the fuel cell power generation is completed; a step of adjusting the opening of a hydrogen valve installed at the anode outlet of the fuel cell stack when the specific condition is detected; a step of supplying air to the fuel cell stack and / or exhaust pipe by means of an oxygen supply unit of the fuel cell stack; and a step of causing the residual gas to pass together with the supplied air through a passive hydrogen removal catalyst module installed at the rear end of the exhaust pipe.

[0011] As a method of supplying air to the exhaust pipe, air that is supplied to the cathode can be supplied to the exhaust pipe, or it can be supplied directly to the exhaust pipe without passing through the cathode through a separate valve.

[0012] If the air supplied through the oxygen supply unit is less than the amount of air required for hydrogen oxidation, a separate air supplement supply device can be used to supply sufficient air to the exhaust pipe. This air supplement supply device can be a small-capacity, low-noise blower or air compressor, and can be connected to the exhaust pipe via a valve as needed.

[0013] The amount of air required to oxidize the hydrogen contained in the residual gas can be determined in advance during system design. For example, if the goal is to oxidize all the hydrogen contained in the residual gas within a specific time and release it as exhaust gas, the corresponding hydrogen emission rate per minute can be calculated, and thus the amount of air required for oxidation can be calculated. This allows for the selection of an air supply device of appropriate capacity. If the capacity of the oxygen supply unit installed by default in the fuel cell stack is sufficient to meet the required air capacity, then an additional air supply device is not needed. Conversely, if the capacity of the oxygen supply unit is insufficient, an additional air supply device can be used to ensure the required air.

[0014] The residual gas, as a byproduct emitted from the fuel cell stack and hydrogen supply line, may contain air and hydrogen.

[0015] Furthermore, the moment when the concentration of hydrogen contained in the residual gas reaches or exceeds a specified benchmark value includes the moment when the fuel cell system finishes generating electricity. At the moment when the fuel cell system finishes generating electricity, the hydrogen valve is closed, air valve 1 is open to the cathode side, and air valve 2 is open.

[0016] According to one embodiment of the present invention, a system for removing high concentrations of hydrogen from residual gases remaining in the fuel cell stack and hydrogen supply pipe after operation in a fuel cell system may include: a fuel cell stack such that fuel, namely hydrogen, supplied to the anode via a hydrogen supply pipe through a hydrogen supply section reacts with oxidant, namely air, supplied to the cathode via an oxygen supply section through an air valve 1 to generate electricity; an exhaust pipe connected to the anode outlet of the stack via a hydrogen valve and connected to the cathode outlet via an air valve 2 to discharge residual gases to the outside; and a passive hydrogen removal catalyst module disposed at the rear end of the exhaust pipe.

[0017] In the passive hydrogen removal catalyst module provided by the system of the present invention, a hydrogen oxidation catalyst is filled with an active metal, namely platinum (Pt); or platinum (Pt) and palladium (Pd) coated on an alumina-based support. The hydrogen oxidation catalyst of the present invention can be configured into modules in various forms. Preferably, it is a honeycomb catalyst module that is coated onto a carrier after the support coated with active metal is made into a slurry.

[0018] In the system of the present invention, if the capacity of the oxygen supply section installed in the fuel cell stack is insufficient to meet the air capacity required for hydrogen oxidation by the passive hydrogen removal catalyst module, an air supplement supply device can be provided to supplement the air required for hydrogen oxidation by connecting to the exhaust pipe.

[0019] Furthermore, the air supply via the aforementioned air supply device can be achieved by opening a valve (not shown) installed on the exhaust pipe passage. The air supply device can be a blower or an air compressor. Additionally, when the gas in the anode and hydrogen supply pipe is discharged through the exhaust pipe by opening the hydrogen valve, a forced hydrogen emission device, such as a blower, can be installed on the exhaust pipe or the fuel cell stack.

[0020] Furthermore, the specific conditions may include the instantaneous occurrence of the hydrogen concentration in the residual gas reaching or exceeding a predetermined benchmark value. Preferably, the predetermined benchmark value refers to a situation where the average hydrogen concentration is 4% by volume or higher. Moreover, as mentioned earlier, even under conditions where the average hydrogen concentration is below 4%, a hydrogen explosion may still occur in a closed area with poor air circulation due to continuous hydrogen accumulation. Therefore, the conditions for hydrogen leakage, even in small amounts, are also included.

[0021] The forms described above are only a part of the preferred embodiments of the present invention. Those skilled in the art can deduce and understand various embodiments reflecting the technical features of the present invention based on the above detailed description of the present invention.

[0022] The effects of the method and system according to the present invention will be described next.

[0023] The present invention has the advantages of not requiring a large-capacity air dilution device for diluting the high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has been running, and not causing noise due to the operation of such a large-capacity air dilution device, but removing and discharging the high-concentration hydrogen simply through the hydrogen oxidation reaction.

[0024] Moreover, the present invention has the advantage of being able to almost completely remove the high concentration of hydrogen remaining in the fuel cell stack and hydrogen supply pipe after the fuel cell system has been running, thereby minimizing the risk of explosion due to the accumulation of hydrogen concentration in enclosed areas where air circulation is difficult.

[0025] Finally, the present invention can utilize a passive catalytic oxidation technology that removes hydrogen at room temperature through the exothermic reaction of hydrogen and oxygen without requiring a separate energy source, and the exothermic reaction can be used as the thermal energy required by the system, thus also having advantages in terms of energy efficiency.

[0026] The effects that can be obtained by the present invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains will be able to further understand other effects not mentioned through the following description. Attached Figure Description

[0027] Figure 1 This is a configuration diagram illustrating a fuel cell system according to one embodiment of the present invention.

[0028] Figure 2 This is a sequence diagram for illustrating a hydrogen removal method using a passive hydrogen removal catalyst module in a fuel cell system according to one embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram illustrating the hydrogen oxidation results using a platinum / palladium catalyst module.

[0030] Figure 4 This is a schematic diagram illustrating the results of hydrogen oxidation based on the hydrogen concentration in the residual gas. Detailed Implementation

[0031] The system and method to which embodiments of the present invention are applied will now be described in detail with reference to the accompanying drawings. definition The term "passive hydrogen oxidation catalyst" as used in this application refers to a catalyst that removes hydrogen at room temperature through the exothermic reaction of hydrogen and oxygen without a separate heat source. It is also referred to as a "hydrogen removal catalyst" in this application. The difference between this and an active catalyst, which requires a separate energy source to achieve the hydrogen oxidation reaction, is that hydrogen oxidation can be achieved at room temperature. The term "catalyst module" in this application is used in the same sense as a catalyst body or catalyst molding, and can be constructed in various forms. Preferably, it refers to an article in which a catalyst substance or catalyst composition is molded in a certain form or coated onto a carrier in a certain form. The catalyst substance is a composition of active substances such as precious metals coated onto a support with multiple pores. In this invention, high-concentration hydrogen is defined as hydrogen with a concentration of 4% by volume or more, which is self-igniting hydrogen. In this application, the gas remaining in the hydrogen supply pipe after the fuel cell power generation is completed, as well as the byproducts of the fuel cell stack, are collectively referred to as residual gas. In this invention, the high concentration of hydrogen contained in the residual gas can be almost completely oxidized to a hydrogen concentration of less than 0.01% at room temperature using a passive hydrogen oxidation catalyst module and then discharged to the outside as exhaust gas. Furthermore, the component connected to the fuel cell stack outlet side is defined as the exhaust pipe, which refers to the entire gas flow path connected to both the anode outlet and the cathode outlet.

[0032] Next, please refer to Figure 1 A brief explanation of the basic operation and structure of a fuel cell system is provided.

[0033] See Figure 1A fuel cell system equipped with the passive catalyst module for high-concentration hydrogen removal of the present invention may generally include: a fuel cell stack, including an anode and a cathode; a hydrogen supply unit connected to the anode via a hydrogen supply pipe; an oxygen supply unit connected to the cathode via an air valve 1; an exhaust pipe connected to the anode outlet of the stack via a hydrogen valve and to the cathode outlet via an air valve 2, thereby venting residual gas to the outside; an air supplement supply device connected to the exhaust pipe, thereby supplementing the supply of air required for hydrogen oxidation; and a passive hydrogen removal catalyst module disposed at the rear end of the exhaust pipe; however, this is only for the purpose of aiding understanding the present invention, and may of course include the general constituent elements required for a fuel cell system.

[0034] The reactor can generate electricity by reacting oxygen supplied through the oxygen supply unit with hydrogen supplied through the hydrogen supply unit. At the end of operation, the remaining air is discharged to the outside through the exhaust pipe as residual gas through the air valve 2 and the hydrogen is discharged through the hydrogen valve.

[0035] The air supplied to the exhaust pipe can be supplied from the oxygen supply unit through the cathode, or it can be supplied directly to the exhaust pipe without passing through the cathode by means of the operation of the air valve 1.

[0036] After the fuel cell system has finished operating, the concentration of hydrogen in the residual gas may exceed the prescribed baseline value. If high concentrations of hydrogen are released to the outside through the exhaust pipe, the risk of explosion and fire may increase.

[0037] To prevent the aforementioned danger, a fuel cell system equipped with a device for removing high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe after operation, according to one embodiment of the present invention, may include a passive catalytic module or a hydrogen oxidation module located at the rear end of the exhaust pipe. The passive catalytic module of the present invention is used to oxidize the high-concentration hydrogen remaining in the fuel cell stack and hydrogen supply pipe and discharge it to the outside as a harmless component. The air required for hydrogen oxidation is preferentially provided through an oxygen supply unit connected to the cathode side. However, if additional air is required for hydrogen oxidation, an air supplement supply device such as a blower or air compressor can be provided to supply additional air through a valve installed in the exhaust pipe flow path, or a separate air compressor within the fuel cell system can be used. The high concentration of hydrogen remaining in the fuel cell stack and hydrogen supply pipe can be mixed with the air required for hydrogen oxidation, and then decomposed and released into the atmosphere through the passive hydrogen oxidation module when the hydrogen concentration is reduced.

[0038] As an example, the control unit (not shown) can control the air supplement supply device to be switched on / off (ON / OFF) for a specified period of time after the fuel cell system operation has ended. If the air supplied by the oxygen supply unit is sufficient to completely oxidize the gases in the stack and hydrogen supply line via the passive catalyst module, the air supplement supply device may not be necessary. Conversely, if the amount of air supplied by the oxygen supply unit is insufficient for hydrogen oxidation, the air required for hydrogen oxidation can be supplied by turning on the air supplement supply device (ON), either together with the oxygen supply unit or separately. With the aid of the oxygen supply unit and the air supplied as needed by the air supplement supply device, the high concentration of hydrogen in the residual gas can be completely oxidized, thereby drastically reducing the maximum concentration of hydrogen emitted to the outside and the average concentration per unit time.

[0039] A valve (not shown) for enabling airflow using an air supplement supply device according to one embodiment may be added, which may be a solenoid valve, but is not limited thereto.

[0040] Typically, after a fuel cell system finishes operation, the concentration of hydrogen emitted through the exhaust pipe within 1 to 10 minutes can be very high. Therefore, according to one embodiment of the hydrogen removal system of the present invention, the hydrogen valve, oxygen supply unit, and air supplement supply device can be controlled at specific time points and / or under specific conditions to prevent hydrogen concentrations exceeding a specified baseline from being emitted through the exhaust pipe. It should be noted that the specific time points and / or specific conditions may include the time point when the system completely stops operating and the time point when it temporarily stops operating, etc., but this is only one embodiment, and the control time points can be adaptively set differently according to the characteristics and structure of the corresponding fuel cell system.

[0041] The fuel cell system of this invention uses a passive hydrogen oxidation catalyst module to reduce the concentration of high-concentration hydrogen. Specifically, it uses an active metal, platinum (Pt); or a catalyst module in which a catalyst slurry is prepared by coating platinum and palladium precursors onto an alumina-based support, such as alumina, and then partially or entirely coated onto a honeycomb-shaped molded body. The honeycomb-shaped molded body, as a carrier of the catalyst material, is formed by a regular arrangement of multiple through-cells with a roughly square cross-section along its length, and the through-cells are separated from each other by thin cell walls. The catalyst material is coated or supported on the surface of the cell walls or inside the pores. Specifically, 60 g / ft³ of platinum; or platinum and palladium precious metals are supported on the cell walls of the molded body. The optimal loading of precious metals may vary depending on the concentration and amount of hydrogen in the residual gas, the time required to remove hydrogen, etc.

[0042] Figure 2 This is a sequence diagram illustrating a method and operation process for removing high-concentration hydrogen from residual gas in a fuel cell system using a passive hydrogen oxidation catalyst according to one embodiment of the present invention.

[0043] In existing technologies, multiple dilution processes, such as using blowers, are required to dilute and release high-concentration hydrogen in residual gases in stages. However, as mentioned above, excessive operation of these dilution devices inevitably leads to noise, and even after multiple dilution processes, a relatively high concentration of hydrogen, averaging 4% by volume, is still emitted. Further dilution processes are needed when a further reduction in the emitted hydrogen concentration is required. Considering that the amount of air required to completely oxidize 100% hydrogen is only about 1 / 40th of the amount of air required to dilute hydrogen to 1% by volume, the inventors propose a hydrogen removal method based on hydrogen oxidation, rather than diluting high-concentration hydrogen before emission. Figure 2 A schematic illustration of the method for removing high-concentration hydrogen from fuel cell stacks and hydrogen supply pipes using the present invention is provided. The method discloses a method in which, after the fuel cell system is completed, residual gas containing high-concentration hydrogen in the fuel cell stack and hydrogen supply pipes, along with sufficient air, passes through a hydrogen oxidation catalyst module to achieve complete oxidation of excess hydrogen. Specifically, this may include: a step of detecting a specific condition where the hydrogen concentration of the residual gas reaches or exceeds a predetermined benchmark value after the fuel cell power generation is completed; a step of adjusting the opening of the hydrogen valve installed at the anode outlet of the fuel cell stack when the specific condition is detected; a step of supplying air to the fuel cell stack and / or exhaust pipe by means of the oxygen supply section of the fuel cell stack; and a step of causing the supplied air to pass together with the residual gas through a passive hydrogen removal catalyst module installed at the rear end of the exhaust pipe.

[0044] In the method of the present invention, the steps of discharging hydrogen by means of adjusting the opening of the hydrogen valve and supplying air to the fuel cell stack and / or exhaust pipe can be performed in parallel or sequentially in a time sequence.

[0045] Furthermore, the specific conditions include the instant when the fuel cell system stops generating electricity when the concentration of hydrogen contained in the residual gas reaches or exceeds a specified benchmark value. When the fuel cell system stops operating, the hydrogen valve on the anode outlet side of the fuel cell is closed, while the air valves 1 and 2 on the cathode inlet and outlet sides are open, allowing air supplied from the air supply unit to flow through the cathode to the exhaust pipe.

[0046] The air required for hydrogen oxidation can initially be supplied via the oxygen supply unit. If additional air capacity is needed, supplementary air supply devices such as blowers and air compressors connected to the exhaust pipe can be operated. Specifically, when the hydrogen valve is opened based on the amount of oxygen supplied via the oxygen supply unit, if the time required to completely vent hydrogen from the fuel cell stack is long, the amount of air supplied to the exhaust pipe via the supplementary air supply device can be increased to shorten the venting time. The amount of hydrogen vented can also be increased by adjusting the hydrogen valve, thereby regulating the venting time of residual hydrogen. Hydrogen can be vented to the exhaust pipe using the pressure difference between the hydrogen in the fuel cell stack and the exhaust pipe. However, for easier hydrogen venting, a forced venting device can also be installed on the fuel cell stack or exhaust pipe. Furthermore, after fuel cell operation ends, the air supplied via the oxygen supply unit will initially be supplied to the exhaust pipe through the fuel cell stack, but air can also be supplied directly to the exhaust pipe by closing air valve 1. In this invention, unlike the prior art which simply dilutes hydrogen and releases it to the outside, the high concentration of hydrogen in the residual gas is removed by means of hydrogen oxidation. At this time, the large amount of air required in the dilution process is not needed. Therefore, the air supplement supply device can be a small-capacity blower or air compressor.

[0047] Figure 3 The results of hydrogen oxidation using a platinum / palladium catalyst module are illustrated. Figure 4 The results of hydrogen oxidation based on the hydrogen concentration in the residual gas are illustrated.

[0048] See Figure 3 The heating at the rear end of a passive hydrogen oxidation catalyst module, filled with a catalyst containing platinum and palladium (weight ratio 10:1) as active metals, at 2.5 wt% and 9 times with a residual gas concentration of 12% by volume hydrogen, was confirmed. This indicates that the 12% hydrogen in the residual gas was almost completely oxidized. Furthermore, the hydrogen concentration at the front and rear ends of the catalyst module was confirmed using a mass analyzer, showing that the hydrogen concentration at the rear end of the catalyst module was less than 0.01%. See also... Figure 4 The heating temperature data under the condition that the hydrogen concentration in the residual gas is changed to 1, 5, 10, and 15% can also be used to confirm the residual gas with a hydrogen concentration of 1-15% based on the data from the mass analyzer. With the help of the system and method according to the present invention, 99.99% oxidation was obtained. Furthermore, while preferred embodiments of the present invention have been described above with reference to them, those skilled in the art should understand that the present invention can be modified and altered in various ways without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A method for removing highly concentrated combustible hydrogen from residual gases after operation in a fuel cell system, comprising: The step of detecting the hydrogen concentration of the residual gas after the fuel cell power generation is completed, under specific conditions, is to ensure that the hydrogen concentration reaches or exceeds a specified benchmark value. The steps include: adjusting the opening of the hydrogen valve installed at the anode outlet of the fuel cell stack when the specific conditions are detected; supplying air to the fuel cell stack via the oxygen supply unit of the fuel cell stack; and passing the residual gas along with the supplied air through a passive hydrogen removal catalyst module installed at the rear end of the exhaust pipe.

2. The method according to claim 1, further comprising, after the step of supplying air to the fuel cell stack via the oxygen supply unit of the fuel cell stack: The step of supplying additional air by means of an air supplement supply device connected to the exhaust pipe.

3. A system for removing highly concentrated combustible hydrogen from residual gases after operation in a fuel cell system, comprising: The fuel cell stack generates electricity by reacting fuel, namely hydrogen, supplied to the anode via a hydrogen supply unit with oxidant, namely air, supplied to the cathode via an oxygen supply unit through an air valve 1; an exhaust pipe is connected to the anode outlet of the stack via a hydrogen valve and to the cathode outlet via an air valve 2, thereby venting residual gases to the outside; and a passive hydrogen removal catalyst module is provided at the rear end of the exhaust pipe.

4. The system according to claim 3, further comprising: An air supplement supply device is provided to supplement the air required for hydrogen oxidation by being connected to the exhaust pipe.

5. The system according to claim 3, wherein the passive hydrogen removal catalyst module is filled with an active metal, namely platinum (Pt); or a hydrogen oxidation catalyst in which platinum (Pt) and palladium (Pd) are coated onto an alumina-based support.

6. The system according to claim 3, wherein the passive hydrogen removal catalyst module is provided as a honeycomb catalyst module in which a slurry composition of a hydrogen oxidation catalyst, in which an active metal, namely platinum (Pt); or platinum (Pt) and palladium (Pd) are coated on an alumina-based support, is coated onto a carrier.

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