Fuel cell system and fuel recirculation process including anode off-gas combustion system and independent heat recovery module

Abstract

An anode-off gas combustion system is provided, comprising: a burner chamber (100) physically separated into a lower cathode-off gas injection area (110) and an upper combustion area (120); an anode-off gas injection line (130) for directly injecting hydrocarbons or anode-off gas into the combustion area (120); and a cathode-off gas injection line (131) for injecting cathode-off gas into the injection area (110), wherein the cathode-off gas injected into the injection area (110) is injected into the combustion area (120) and the anode-off gas is combusted only in the combustion area (120).

Description

Technology Field

[0001] The present invention relates to a fuel cell system and a fuel recirculation process including an anode-off gas combustion system and an independent heat recovery module, and more specifically, to a fuel cell system and a fuel recirculation process including an anode-off gas combustion system and an independent heat recovery module that can be controlled independently from a power generation module in an SOFC fuel cell system, wherein the anode-off gas containing an excess amount of moisture, which is generated after passing through the process of the SOFC stack, a core component of the power generation module, is directly utilized as fuel for a burner without a cooling and condensation process (moisture separation process) to produce electricity, and wherein the control for recovering residual heat remaining at the final vent stage is independent from the module. Background Technology

[0002] Recently, efforts to develop and commercialize fuel cell systems capable of high-efficiency power generation as distributed energy source power generation systems are in full swing both domestically and internationally.

[0003] In these fuel cell systems, power generation proceeds either by directly supplying hydrogen as fuel or through hydrogen converted by reforming hydrocarbons. The fuel cell (SOFC) in such a system consists of an anode to which fuel is supplied and a cathode to which air is supplied. After consuming the fuel, the fuel cell emits Anode Off Gas (AOG), which contains residual fuel, and Cathode Off Gas (COG), which consists of air.

[0004] The anode-off gas emitted from these fuel cells contains residual hydrogen and unreacted fuel. Since the anode-off and cathode-off gases are produced at high temperatures, the utilization of the residual hydrogen and unreacted fuel, as well as heat recovery, are essential to increase the efficiency of the fuel cell system.

[0005] Therefore, in conventional technology, heat from high-temperature anode-off gas and cathode-off gas was recovered, and a process to remove moisture contained in the anode-off gas was required during the recovery process. A heat recovery system was implemented during the process of condensing the moisture contained in the anode-off gas.

[0006] This creates a problem where heat recovery must be performed continuously to operate the fuel cell power generation system, even when heat recovery is not desired. Additionally, the cooling and condensation processes to remove moisture contained in the anode-off gas are carried out in the gas-liquid separator, and the condensed water is removed from the separator. However, whenever the condensed water is discarded, negative pressure is applied to the piping from the separator to the burner, causing flashback of the burner flame, which leads to pipe damage or system failure.

[0007] Furthermore, cathode-off gas contains an excessive amount of air, making it unsuitable for use as combustion air. Consequently, supplying cathode-off gas to a standard burner results in the flame going out due to the excess air. Therefore, to resolve this issue, it is essential to supply air to the burner via a separate flow and to control the burner temperature by regulating the airflow of this air.

[0008] Figure 1 is a schematic diagram illustrating the flow of backfire occurring in a burner according to the prior art.

[0009] Referring to FIG. 1, a system according to the prior art includes a gas-liquid separator that receives anode-off gas discharged from a fuel cell stack, cools it, and condenses and removes moisture. After gas-liquid separation, the anode-off gas is supplied to a burner for combustion. At this time, separate air is supplied in addition to the cathode-off gas to divide the air supplied to the burner into two lines and supply them as separate flows. However, the air within the cathode-off gas cannot be utilized, and a separate air supply device is required for burner control. Furthermore, as the pressure of the gas-liquid separator decreases when condensate is discharged, pressure is applied in reverse from the burner, causing flashback to occur, which corresponds to the red part of FIG. 1. Prior art literature

[0010] 1. Republic of Korea Published Patent No. 10-2020-0135764 2. Republic of Korea Published Patent No. 10-2013-0037694 The problem to be solved

[0011] Accordingly, the problem to be solved by the present invention is to provide a fuel cell system including an independent heat recovery module capable of separating the power generation module and the heat recovery module by separate control to minimize heat loss to the outside that may occur during the process of condensing anode-off gas containing moisture and to use the recovered heat according to user requirements, an anode-off gas combustion system capable of solving the backfire problem caused by the pressure difference resulting from the discharge (drainage) of condensate, and a fuel cell power generation system including the same. means of solving the problem

[0012] To solve the above problem, the present invention provides an anode-off gas combustion system comprising: a burner chamber (100) physically separated into a lower cathode-off gas injection area (110) and an upper combustion area (120); an anode-off gas injection line (130) for directly injecting hydrocarbons or anode-off gas into the combustion area (120); and a cathode-off gas injection line (131) for injecting cathode-off gas into the injection area (110), wherein the cathode-off gas injected into the injection area (110) is injected into the combustion area (120) and the anode-off gas is combusted only in the combustion area (120).

[0013] In one embodiment of the present invention, a partition wall (140) is provided between the injection area (110) and the combustion area (120), and a plurality of holes (141) are formed in the partition wall (140).

[0014] In one embodiment of the present invention, the cathode-off gas is injected into the injection area (110) through the plurality of holes (141).

[0015] In one embodiment of the present invention, the anode-off gas and the cathode-off gas are each 500°C or higher.

[0016] In one embodiment of the present invention, the pressure of the injection area (110) is higher than the pressure of the combustion area (120).

[0017] The present invention also provides a fuel cell power generation system comprising the anode-off gas combustion system described above.

[0018] In one embodiment of the present invention, the fuel cell power generation system further includes a heat recovery module that recovers heat by heat-exchanging gas vented from the burner chamber (100).

[0019] The present invention also provides a fuel recirculation process using the fuel cell power generation system described above, characterized by comprising the steps of: heat-exchanging gas vented from the burner chamber; and condensing the heat-exchanged gas. Effects of the invention

[0020] The present invention directly mixes the high-temperature anode-off gas with the cathode-off gas and combusts it, without condensing or removing moisture contained in the anode-off gas. By doing so, the possibility of flashback occurring during the draining process is completely eliminated by directly mixing and combusting the high-temperature anode-off gas with the cathode-off gas, without using a separate gas-liquid separator for draining moisture. Furthermore, heat loss to the outside that may occur while cooling the anode-off gas temperature can be minimized, and the system volume can be reduced and the process simplified by not using a separate gas-liquid separator. Brief explanation of the drawing

[0021] Figure 1 is a schematic diagram illustrating the flow of backfire occurring in a burner according to the prior art. FIG. 2 is a schematic diagram of a system in which high-temperature hydrogen in an anode-off gas burns by spontaneous combustion according to one embodiment of the present invention. FIG. 3 is a plan view of a burner chamber (100) of a system in which high-temperature hydrogen in an anode-off gas and air in a cathode-off gas undergo a combustion reaction according to one embodiment of the present invention. Figure 4 is a schematic diagram illustrating a heat utilization process of burner off-gas according to conventional technology. FIG. 5 is a schematic diagram illustrating the heat utilization process of burner off-gas according to the present invention. FIG. 6 is a schematic diagram illustrating an anode-off gas heat recovery module according to the prior art. FIG. 7 is a schematic diagram illustrating a process for removing heat recovery module 2 using high-temperature anode-off gas and cathode-off gas according to the present invention. Specific details for implementing the invention

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0023] Before describing the invention in detail, the terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, and the inventor of the invention may appropriately define and use the concepts of various terms to best describe his invention.

[0024] Furthermore, it should be understood that these terms or words should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0025] In other words, the terms used in this specification are used merely to describe preferred embodiments of the invention and are not intended to specifically limit the content of the invention.

[0026] It should be noted that these terms are defined in consideration of the various possibilities of the present invention.

[0027] Additionally, in this specification, singular expressions may include plural expressions unless the context clearly indicates a different meaning.

[0028] In addition, you should be aware that even if it is expressed in the plural, it may contain a singular meaning.

[0029] Throughout this specification, where it is stated that a component "includes" another component, unless specifically stated otherwise, this may mean that it does not exclude any other component but may include any other component.

[0030] Furthermore, in cases where it is stated that a component "exists inside or is installed in connection with" another component, this component may be installed in direct connection with or in contact with the other component.

[0031] In addition, they may be installed spaced apart at a certain distance, and in the case where they are installed spaced apart at a certain distance, there may be a third component or means for fixing or connecting the component to another component.

[0032] Meanwhile, it should be noted that the description of the third component or means mentioned above may be omitted.

[0033] On the other hand, if it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there is no third component or means.

[0034] Likewise, other expressions describing the relationship between each component, such as “between” and “right between”, or “adjacent to” and “directly adjacent to”, should be interpreted as having the same intent.

[0035] In addition, terms such as “one side,” “other side,” “one side,” “other side,” “first,” “second,” etc., in this specification are used to ensure that one component can be clearly distinguished from another component.

[0036] However, it should be noted that the meaning of the component is not used restrictively by such terminology.

[0037] In addition, positional terms such as "top," "bottom," "left," and "right" used in this specification should be understood as indicating the relative position of the corresponding component in the drawing.

[0038] Furthermore, unless an absolute location is specified regarding their positions, terms related to these locations should not be understood as referring to absolute locations.

[0039] Furthermore, in the specification of the present invention, terms such as “…part,” “…unit,” “module,” and “device,” if used, refer to a unit capable of handling one or more functions or operations.

[0040] You should be aware that this can be implemented in hardware, software, or a combination of hardware and software.

[0041] In the drawings attached to this specification, the size, position, connection relationships, etc., of each component constituting the present invention may be described in a partially exaggerated, reduced, or omitted manner for the convenience of explanation or to sufficiently clearly convey the concept of the present invention, and therefore, the proportions or scale may not be strictly accurate.

[0042] In addition, in describing the present invention below, detailed descriptions of components that are deemed to unnecessarily obscure the essence of the invention, such as known technologies including prior art, may be omitted.

[0043] To solve the aforementioned problem, the present invention mixes the high-temperature anode-off gas directly with the cathode-off gas and burns it, without condensing or removing the moisture contained in the separate anode-off gas.

[0044] FIG. 2 is a schematic diagram of an anode-off gas combustion system according to one embodiment of the present invention.

[0045] Referring to FIG. 2, in one embodiment of the present invention, an anode-off gas or hydrocarbon containing hydrogen is directly injected into the combustion area (120) of the burner chamber (100) through an injection line (130).

[0046] In one embodiment of the present invention, the burner chamber (100) is physically divided into a lower cathode-off gas injection area (110) and an upper combustion area (120). As the stack reaction proceeds, the anode-off gas generated is mixed with fuel and injected directly into the upper combustion area (120) through the anode-off gas injection line (130), rather than the lower injection area (110). Subsequently, as the reaction proceeds, only the anode-off gas can be supplied to the combustion area (120) through the anode-off gas injection line (130).

[0047] In the injection area (110) of the lower section, cathode-off gas (COG) is injected from the fuel cell stack through the cathode-off gas injection line (131), and at this time, the cathode-off gas (COG) moves from the injection area (110) to the combustion area (120) through the separation partition (140) provided inside the burner chamber.

[0048] Accordingly, the above separation partition (140) disperses the supply of cathode-off gas to the combustion zone (120) and contacts the anode-off gas with combustion at an appropriate ratio, thereby enabling combustion even with an excess amount of air.

[0049] The present invention enables high-temperature supply by using cathode-off gas as the air for the burner, and utilizes the characteristic of the hydrogen component of the anode-off gas spontaneously igniting at a temperature of 500 to 580°C to allow the fuel and air to naturally react efficiently inside the burner. Accordingly, it is desirable that the temperatures of the anode-off gas and cathode-off gas be 500°C or higher without a separate cooling process.

[0050] Therefore, the present invention completely eliminates the possibility of flashback occurring during the draining process by directly mixing and burning high-temperature anode-off gas with cathode-off gas, without using a process for draining moisture from a gas-liquid separator where a cooling process is essential.

[0051] Furthermore, external heat loss occurring during the supply process of cooling the anode-off gas temperature can be minimized, and the system volume can be reduced and the process simplified by not using a separate gas-liquid separator.

[0052] FIG. 3 is a plan view of a burner chamber (100) of an anode-off gas combustion system according to one embodiment of the present invention.

[0053] Referring to FIG. 3, a burner chamber (100) according to one embodiment of the present invention includes a partition wall (140) having a plurality of holes (141) formed therein, and an anode-off gas injection line (130) extending from the center of the partition wall to the combustion area (120) of FIG. 2.

[0054] In addition, the cathode-off gas injected into the lower part of the burner chamber through the hole (141) formed in the separation partition (140) flows into the combustion zone (120) of Fig. 2 and causes an ignition reaction to occur.

[0055] As explained above, the present invention does not condense and remove moisture contained in a separate anode-off gas, but instead directly mixes the high-temperature anode-off gas with the cathode-off gas and combusts it. By doing so, without using a separate process for draining moisture from a gas-liquid separator, the high-temperature anode-off gas is directly mixed with the cathode-off gas and ignited, thereby completely eliminating the possibility of flashback occurring during the draining process.

[0056] Accordingly, a fuel cell power generation system including an anode-off-gas combustion system according to the present invention has the advantages of high thermal efficiency and low potential for flashback compared to conventional fuel cell power generation systems, as well as high spatial integration.

[0057] That is, the burner chamber of the present invention is divided into two regions, and cathode-off gas is dispersed and injected into each region. That is, a portion of the cathode-off gas is used for combustion, and the remainder is used to control the flame temperature within the combustion region.

[0058] To this end, the separating partition of the burner chamber may be provided with a plurality of holes through which cathode-off gas introduced into the injection zone enters the combustion zone, and the pressure in the injection zone is higher than the pressure in the combustion zone, thereby configuring the system so that cathode-off gas is injected from the injection zone into the combustion zone.

[0059] Furthermore, the above-mentioned separating partition may be in the form of a funnel with multiple holes of different heights.

[0060] In this case, the cathode-off gas entering through the relatively low-height hole comes into direct contact with the high-temperature anode-off gas, igniting and generating a flame, while the cathode-off gas entering through the high-height hole serves to regulate the temperature of the flame below to prevent it from rising excessively and to control the flame length so that it does not become excessively long. This is because if the burner temperature rises too high, it can cause problems with the internal materials, and there is a risk of damage due to heat concentration in the heat exchanger connected to the top.

[0061] In addition, the burner system according to one embodiment of the present invention prevents a pressure drop when the drain system is operated due to the omission of the gas-liquid separation process, so that the pressure in the injection area (110) of FIG. 2 is higher than that in the combustion area (120).

[0062] Furthermore, the present invention provides a fuel cell system comprising an independent module that recovers residual heat remaining at the final vent of the system through a combustion system as described above.

[0063] FIGS. 4 and 6 are fuel cell systems according to the prior art, including a heat recovery module (heat recovery module 2) that cannot be independently controlled, and FIGS. 5 and 7 are block diagrams of a fuel cell system that does not include the same.

[0064] Referring to FIGS. 4 and 5, in the case of the present invention, a separate heat recovery module (heat recovery module 1) that exchanges heat before discharging gas from the burner out of the power generation module may be separately included in the system.

[0065] FIG. 4 is a schematic diagram illustrating a heat exchange sequence according to the prior art, and FIG. 5 is a schematic diagram illustrating a heat exchange sequence according to an embodiment of the present invention.

[0066] Referring to FIGS. 4 and 5, in the prior art, the reformer was heated to a level of about 750°C using burner off-gas, and then the air and water supplied to the cathode were heated. However, the heat recovery method according to the present invention can heat the air and water supplied to the cathode directly without heating the reformer using burner off-gas.

[0067] The present invention can provide a fuel recirculation process using the fuel cell power generation system described above.

[0068] FIG. 6 is a block diagram of a power generation system according to the prior art, and FIG. 7 is a block diagram of a power generation system according to the present invention.

[0069] Referring to FIGS. 6 and 7, in the case of the present invention of FIG. 7, a condenser for cooling the anode-off gas is not used, and thus a heat recovery module 2 for cooling the condenser is not required, and independent heat recovery is possible only with the heat recovery module according to FIGS. 5 and 7.

[0070] That is, referring to FIG. 7, the anode off-gas generated in the stack heats the reformer directly, and the anode off-gas, cooled to a level of 350–400°C in the reformer, is burned directly in the burner without passing through the condenser. The burned burner off-gas is then heat recovered through the heat recovery module shown in FIG. 5.

Claims

Claim 1 An anode-off gas combustion system comprises: a burner chamber (100) physically separated into a lower cathode-off gas injection area (110) and an upper combustion area (120); an anode-off gas injection line (130) for directly injecting hydrocarbons or anode-off gas into the combustion area (120); and a cathode-off gas injection line (131) for injecting cathode-off gas into the injection area (110). A partition wall (140) is provided between the injection area (110) and the combustion area (120), and a plurality of holes (141) arranged at different heights are formed in the partition wall (140). Through the plurality of holes (141), the cathode-off gas is injected from the injection area (110) into the combustion area (120), and the cathode-off gas injected into the injection area (110) is in the combustion area (120). An anode-off gas combustion system characterized by being mixed with and combusted with an anode-off gas, wherein the anode-off gas and the cathode-off gas are each at a temperature of 500°C or higher, and the pressure of the injection area (110) is higher than the pressure of the combustion area (120). Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A fuel cell power generation system including an anode-off gas combustion system according to Article 1. Claim 7 In claim 6, the fuel cell power generation system further comprises a heat recovery module that recovers heat by heat-exchanging gas vented from the burner chamber (100). Claim 8 A fuel recirculation process using a fuel cell power generation system according to claim 6, characterized by comprising the step of heat-exchanging gas vented from the burner chamber; and the step of condensing the heat-exchanged gas.

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