WO2025009904A1 - Solid oxide fuel cell system including multi-functional bop components and operation method therefor - Google Patents

Abstract

The present invention relates to a solid oxide fuel cell system including multi-functional BOP components and an operation method therefor, the system comprising: a fuel supply unit that supplies a fuel to a fuel cell stack; an air supply unit that supplies air; a heat exchanger that increases the temperature of the fuel, supplied from the fuel supply unit, via a stack fuel electrode off-gas (fuel off-gas) discharged from the fuel cell stack, and supplies the fuel to a multi-functional steam reformer; a multi-functional catalytic burner that uses the stack fuel electrode off-gas (stack off-gas), discharged from the fuel cell stack, as fuel to increase the temperature of the supplied air; the multi-functional steam reformer that reforms NG into hydrogen by using the heat sources of the fuel electrode off-gas and the fuel heated to a higher temperature in the heat exchanger, and supplies the hydrogen to the fuel cell stack; and a recycle blower for recirculating the fuel off-gas discharged from the fuel cell stack.

Description

Solid oxide fuel cell system including multifunctional BOP components and its operating method

The present invention relates to a solid oxide fuel cell system including a multifunctional BOP component and an operating method thereof, and more particularly, to a solid oxide fuel cell system including an integrated multifunctional BOP component capable of maximizing thermal efficiency, enabling smooth fuel recirculation and stack replacement, and an operating method thereof.

A fuel cell is a generator that produces water and electricity through an electrochemical reaction of hydrogen (fuel) and oxygen. Fuel cells can be divided into an air electrode, a fuel electrode, and an electrolyte, and the name and operating temperature of the fuel cell are distinguished according to the electrolyte material. In a solid oxide fuel cell (SOFC), oxygen from the air electrode passes to the fuel electrode in the form of ions through a solid electrolyte, and usually operates at 650 to 900°C.

SOFCs must supply heterogeneous gases to the cell anode (air electrode, fuel electrode), and the separator and manifold perform this role, and the generated electricity is collected through the current collector and flows. In addition, a porous current collector is used to ensure that the heterogeneous gases supplied to the cell anode are smoothly supplied to each electrode.

The SOFC system is a device that smoothly supplies fuel and air to the SOFC stack and maintains a temperature of about 650 to 900℃ so that each cell can undergo an electrochemical reaction. Therefore, although it differs depending on the device, the representative mechanical parts that make up the SOFC system include a heat exchanger, a combustor, a reformer, a steam generator, and an air blower.

When fuel is supplied to the SOFC system, it meets oxygen through the combustor and undergoes a combustion reaction, and the heat generated at this time is used to increase the overall temperature of the SOFC system (including the stack) so that the SOFC cell reaches a temperature at which an electrochemical reaction can occur. In other words, the total energy of the fuel supplied to the SOFC system is the sum of the system temperature and the electrical energy generated by the stack.

The efficiency of these fuel cells can be calculated as shown in Equation (1) below.

Efficiency of fuel cell (%) = (stack power generation capacity - system power consumption capacity) / calorific value of fuel supplied to the system * 100 … (1)

In order to increase the efficiency of the system by the above equation (1), the amount of fuel supplied to the system must be reduced or the performance of the stack must be dramatically improved. However, if the amount of fuel supplied to the system is reduced, the temperature of the system will be lowered or the performance of the stack will be degraded.

Therefore, in order to increase the efficiency of the system in the system domain, there are two ways: ① to reduce the electrical capacity used by the system, or ② to reduce the amount of fuel supplied to the system without lowering the temperature.

① is a method to minimize power consumption of fuel supply devices, air supply devices (air blowers), and electric converters, and ② is a method to maximize thermal efficiency through thermal coordination, shortest distance arrangement, integration, etc. of mechanical devices such as heat exchangers, reformers, combustors, and stacks exposed to high temperature areas, thereby reducing the amount of fuel supplied to the system without lowering the temperature.

As a related prior art, a technology regarding a fuel cell system has been disclosed in Korean Patent Publication No. 10-2490704, etc. The above prior art reduces the number of conduits required to fluidically connect components of a fuel cell system and shortens their length, thereby reducing heat loss in fuel and air flowing through conduits in a fuel cell system, and has a configuration in which the cost and complexity of the fuel cell system are relatively low.

However, the above prior art has disadvantages in that the fuel flow cycle and the air flow cycle are configured separately in the upper and lower parts of the stack, which is not optimized for thermal efficiency, and in the case of the air heat exchanger, since a high-temperature air heat exchanger and a low-temperature air heat exchanger are each required, the number of components is large and thermal coordination between the components is difficult.

The present invention has been made to solve the above problems, and the purpose of the present invention is to provide a solid oxide fuel cell system including a multifunctional BOP component that maximizes thermal efficiency and facilitates the recycle flow of fuel through a recycle blower located inside a hot box.

In addition, the stack and BOP (Balance of Plant) in the hot box are installed in a modular form, enabling a customized stack design, and an integrated BOP module design for optimized heat management is possible, thereby providing a solid oxide fuel cell system that includes multifunctional BOP parts that enable stack replacement during maintenance.

In addition, the fuel off-gas of the stack, after being suctioned by the recycle blower, is primarily connected to a heat exchanger and is branched into two branch lines at the rear end of the recycle blower, the first branch line being provided to a fuel inlet line to supply newly supplied fuel and the stack, and the second branch line being provided to a catalytic combustor to provide a solid oxide fuel cell system including a multifunctional BOP component capable of maintaining the system temperature.

Through this structure, the present invention aims to provide a solid oxide fuel cell system including a multifunctional BOP component that can improve power generation efficiency by recirculating fuel and maximize thermal efficiency by consuming heat generated within the system within the system.

In addition, the purpose is to provide a solid oxide fuel cell system including multifunctional BOP components that can maximize thermal efficiency because the fuel off-gas discharged from the stack continues to circulate within the hotbox while carrying the heat formed by the exothermic reaction in the process of generating electricity, and can prevent stack performance degradation due to rapid and subtle temperature changes.

In addition, the purpose is to provide a solid oxide fuel cell system including multifunctional BOP components that minimize heat loss by minimizing the amount of fuel supplied to the system through the shortest distance arrangement and integration between components, thereby minimizing the fuel off-gas that did not participate in the reaction, thereby recirculating the fuel off-gas that is generated in the fuel electrode through the FC reaction with a recycle blower, thereby eliminating the need to separately supply water required for NG (Natural Gas) reforming, and which have excellent thermal coordination since mechanical devices such as a heat exchanger, reformer, combustor, and stack that are exposed to a high temperature area are tied together in one flow, and which can maintain a high fuel utilization rate by minimizing heat loss.

In order to achieve the above object of the present invention, the present invention provides a fuel recirculating solid oxide fuel cell system, comprising: a fuel cell stack; a fuel supply unit for supplying fuel to the fuel cell stack; an air supply unit for supplying air to the fuel cell stack; a heat exchanger for increasing the temperature of fuel supplied from the fuel supply unit through stack fuel off-gas discharged from the fuel cell stack and supplying the fuel off-gas to a multi-functional steam reformer; a multi-functional catalytic combustor for increasing the temperature of air supplied from the air supply unit and supplying the air to the multi-functional steam reformer by utilizing heat from a combustion reaction of stack cathode off-gas discharged from the fuel cell stack and fuel off-gas of a second branch line branched after passing through the heat exchanger; a multi-functional steam reformer for receiving heat required for a reforming reaction through a large amount of air whose temperature has been increased by a combustion reaction in the multi-functional catalytic combustor and reforming the fuel supplied from the heat exchanger into hydrogen and supplying it to the fuel cell stack, thereby performing heat exchange using heat generated from a gas flow of the cathode and the fuel electrode; and the fuel cell. A solid oxide fuel cell system is provided, comprising: a recycle blower installed in a fuel line to continuously recirculate stack fuel off-gas discharged from a stack; and a fuel line and an air line configured to use the fuel off-gas and air off-gas discharged from the fuel cell stack as a heat source for fuel and air supplied from the fuel supply unit and the air supply unit.

In the present invention, the fuel supply unit includes a hydrogen supply unit that supplies hydrogen, and a desulfurizer that removes sulfur in the fuel, and the fuel line is characterized in that the fuel off-gas passing through the recycle blower is mixed with the fuel supplied through the fuel supply unit and is re-supplied to the stack or supplied to the multi-functional catalytic combustor.

Here, the fuel off-gas passing through the recycle blower may be branched into two lines, the first branch line being connected to the fuel inlet line so as to be mixed with the fuel supplied through the fuel supply unit and re-supplied to the stack through the heat exchanger, and the second branch line may be connected so as to have the fuel off-gas flow to the multi-functional catalytic combustor.

The temperature of the stack can be controlled by adjusting the external/internal reforming ratio of the fuel cell stack by controlling the flow rate of the fuel supplied from the fuel supply unit.

The above fuel cell stack, heat exchanger, multi-functional catalytic combustor, multi-functional steam reformer and recycle blower are installed in a hotbox, and have a structure that maximizes thermal efficiency by continuously circulating fuel off-gas within the hotbox.

In the multifunctional catalytic combustor, the heat generated by the combustion reaction, that is, the combustion reaction in which the fuel and the air electrode off-gas supplied to the multifunctional catalytic combustor through the second branch line meet and combust in the multifunctional catalytic combustor, increases the temperature of a large amount of air newly supplied from the air supply section and is supplied to the multifunctional steam reformer.

The fuel recirculation flow of the above fuel line is characterized by being performed in the order of fuel cell stack → heat exchanger → recycle blower → heat exchanger → multi-functional steam reformer → stack.

In addition, the flow direction of the multifunctional catalytic combustor of the fuel line can be in the order of fuel cell stack → heat exchanger → recycle blower → multifunctional catalytic combustor → exhaust.

In the present invention, for additional stack temperature control, city gas (NG) is directly supplied separately to the fuel inlet pipe between the multi-functional steam reformer and the stack to force internal reforming of the stack, thereby controlling the stack temperature.

Meanwhile, the fuel cell stack and BOP (Balance of Plant) of the present invention are installed in a module form and each module is connected to a pipe so that each module can be separated during maintenance to replace the stack.

Meanwhile, in order to achieve the above object of the present invention, a method of operating a solid oxide fuel cell system comprises the steps of: supplying fuel from a fuel supply unit and introducing it into a heat exchanger; utilizing heat of stack fuel off-gas discharged from a fuel cell stack to increase the temperature of the fuel flowing into the heat exchanger and providing it to a multi-functional steam reformer; supplying reformed fuel through the multi-functional steam reformer to a fuel cell stack; suctioning by a recycle blower to continuously recirculate the fuel off-gas discharged from the fuel cell stack; branching the fuel off-gas suctioned by the recycle blower and providing it to a fuel inlet line and a multi-functional catalytic combustor; supplying air from an air supply unit to the multi-functional catalytic combustor; utilizing stack air off-gas discharged from the fuel cell stack and the fuel off-gas branched after passing through the heat exchanger as a heat source to increase the temperature of the air supplied from the air supply unit to the multi-functional catalytic combustor and supplying it to the multi-functional steam reformer. A method for operating a solid oxide fuel cell system is provided, characterized by including a step of supplying high-temperature air from the multi-functional steam reformer to the fuel cell stack, and a step of exhausting the stack air electrode off-gas introduced into the multi-functional catalytic combustor after combustion reaction with the fuel off-gas supplied by branching to the multi-functional catalytic combustor.

In the step of supplying the fuel off-gas suctioned by the recycle blower to the fuel inlet line and the multi-functional catalytic combustor by branching, the fuel off-gas passing through the recycle blower may be branched into two lines, the first branch line may be connected to the fuel inlet line so as to be mixed with the fuel supplied from the fuel supply unit and re-supplied to the stack through the heat exchanger, and the second branch line may be connected so as to have the fuel off-gas flow to the multi-functional catalytic combustor.

Here, the fuel off-gas that flows into the multifunctional catalytic combustor through the second branch line meets the stack air electrode off-gas in the multifunctional catalytic combustor to cause a combustion reaction, thereby increasing the temperature of a large amount of air supplied from the air supply unit and allowing it to be discharged.

In the present invention, the heat generated by the combustion reaction in the multifunctional catalytic combustor increases the temperature of a large amount of newly supplied air and is supplied to a multifunctional steam reformer and utilized as reforming reaction heat.

In addition, the stack heat generated by the FC reaction in the fuel cell stack, fuel off-gas, and hot steam are mixed with the fuel supplied from the fuel supply unit and supplied to a multi-functional steam reformer to be utilized as reforming reaction heat.

According to the present invention as discussed above, the fuel cell system of the present invention has the following effects.

① Maximize thermal efficiency

The fuel cell system of the present invention can maximize thermal efficiency by recycling (off-gas) the heat generated inside a hot box.

Specifically, the heat-generating part (FC reaction) and the heat-absorbing part (NG reforming) are connected as a single flow, resulting in high thermal efficiency, and the multi-functional catalytic combustor and multi-functional steam reformer have a heat exchange structure, thereby maximizing thermal efficiency.

② Smooth fuel recirculation

The fuel cell system of the present invention has the effect of helping smooth fuel recirculation by positioning a recycle blower inside the hot box.

③ Easy stack replacement

The stack and BOP parts are connected by piping, making stack replacement easy.

④ Prevent stack performance degradation

Stack fuel utilization can be reduced by fuel recirculation.

Fuel utilization rate is the actual applied current/electromotive force of the fuel x 100, that is, it is a numerical value of the degree to which the fuel's electrical properties are utilized as electricity.

A high fuel utilization rate means that the amount of fuel supplied is small, and a small amount of fuel leads to a lower voltage performance of the stack, which is associated with a high system power generation efficiency.

Figure 1 is a schematic diagram showing the configuration of a solid oxide fuel cell system according to the present invention.

FIG. 2 is a schematic diagram showing the overall flow of fuel and air in a solid oxide fuel cell system according to the present invention.

Figure 3 is a schematic diagram showing the flow of fuel in the solid oxide fuel cell system illustrated in Figure 2.

Figure 4 is a schematic diagram showing the flow of air in the solid oxide fuel cell system illustrated in Figure 2.

FIG. 5 is a diagram showing the temperatures of fuel and air as they pass through each component in a solid oxide fuel cell system according to the present invention.

FIG. 1 is a schematic diagram showing the configuration of a solid oxide fuel cell system according to the present invention, and FIG. 2 is a diagram showing the overall configuration of the flow of fuel and the flow of air in the solid oxide fuel cell system according to the present invention.

The present invention relates to a fuel recirculating solid oxide fuel cell system capable of maximizing thermal efficiency by recirculating fuel, comprising: a fuel cell stack (10); a fuel supply unit (20) for supplying fuel to the fuel cell stack (10); an air supply unit (30) for supplying air to the fuel cell stack (10); a heat exchanger (40) for increasing the temperature of newly supplied fuel by utilizing the heat of stack fuel electrode off-gas discharged from the fuel cell stack (10); a multi-functional catalytic combustor (50) for increasing the temperature of air supplied from the air supply unit by utilizing the stack air electrode off-gas discharged from the fuel cell stack (10) and the fuel off-gas branched off after passing through the heat exchanger (40) as a heat source and supplying the air to a multi-functional steam reformer; a multi-functional steam reformer (60) for reforming fuel, the temperature of which has been increased in the heat exchanger (40), into hydrogen and supplying the reformed fuel to the fuel cell stack (10); It is configured to include a recycle blower (70) installed in the fuel line to continuously recirculate stack fuel off-gas discharged from the fuel cell stack (10).

The above fuel cell stack (10) is a structure in which a number of cells are stacked, and is configured to increase output by connecting each cell in series. It is usually composed of repeatedly used parts such as cells, separators, current collectors, and sealants, a manifold for smoothly supplying gas to the fuel electrode and the air electrode, various types of stack fastening parts, and a busbar for connecting electricity.

In the fuel cell system of the present invention, the fuel cell stack (10) and BOP (Balance of Plant) are installed in a module form, enabling a stack-customized design, and are characterized by designing an integrated BOP module for optimized heat management.

That is, in the present invention, the fuel cell stack (10), heat exchanger (40), multi-functional catalytic combustor (50), multi-functional steam reformer (60), and recycle blower (70) are installed in a hotbox (80), and as shown in FIG. 1, the fuel cell stack (10) and BOP (Balance of Plant) are installed in a module form so that each module can be separated during maintenance, thereby enabling replacement of the stack (10) when necessary.

The above BOP (Balance of plant) module is a part related to supporting components and auxiliary systems necessary for power generation, such as transmitting energy, excluding the power generation device, and includes the heat exchanger (40), multi-functional catalytic combustor (50), multi-functional steam reformer (60), and recycle blower (70) in the present invention.

In the present invention, the fuel and air flow between the stack (10) and the BOP component is conducted only through the pipe, so that the stack can be easily replaced and a customized stack design is possible.

The fuel cell system of the present invention has a structure in which a fuel cell stack (10) and a BOP (Balance of Plant) are installed in a hot box (80) and stack fuel electrode off-gas is continuously circulated within the hot box (80) to maximize thermal efficiency.

Meanwhile, in the present invention, hydrogen is supplied through the fuel supply unit (20) to raise the system temperature to a temperature at which SOFC operation is possible, and since city gas is not externally reformed in the same manner as CPOx without a separate water supply device, hydrogen can be used as fuel in the warm-up stage of initial operation. Meanwhile, NG operation is possible when CPOx is used.

Accordingly, the fuel supply unit (20) includes a hydrogen supply unit that supplies hydrogen and a desulfurizer that removes sulfur in the fuel, and the hydrogen supply unit can be in any form that contains hydrogen, for example, a hydrogen tank, hydrogen piping, a hydrogen storage alloy system, a water electrolysis system, a hydrogen utility, a hydrogen multi-functional steam reformer, and a hydrogen supply device.

Fuel supplied from the above fuel supply unit (20) flows into the hot box (80) through the fuel inlet line (102), and fuel lines for the flow of fuel, including the fuel inlet line (102), are installed to connect each device.

Additionally, the air supply unit (30) may be formed of an air blower capable of supplying air into the hot box (80), and air lines for air flow are installed to connect each device.

The present invention is characterized in that the fuel line and air line are configured to use the stack fuel electrode off-gas and stack air electrode off-gas discharged from the fuel cell stack (10) as a heat source for the fuel and air supplied from the fuel supply unit (20) and the air supply unit (30).

FIG. 3 is a schematic diagram showing the flow of fuel in the solid oxide fuel cell system shown in FIG. 2, and FIG. 4 is a schematic diagram showing the flow of air in the solid oxide fuel cell system shown in FIG. 2.

Referring to FIG. 3, looking at the flow of fuel in the present invention, the fuel is supplied to the system through a desulfurizer outside the hot box (80), passes through a heat exchanger (40), enters a multi-functional steam methane reformer (60), and is then supplied to the stack (10).

At this time, fuel supplied from the fuel supply unit (20) flows into the heat exchanger (40) through the fuel inlet line (102), and a fuel line (106) is connected to the heat exchanger (40) to allow the stack fuel off-gas to flow in so as to increase the temperature of the fuel newly supplied from the fuel supply unit (20) by utilizing the heat of the stack fuel off-gas discharged from the fuel cell stack (10).

In order for the stack fuel off-gas discharged from the stack (10) to be continuously recycled after raising the temperature of the newly supplied fuel from the heat exchanger (40), in the present invention, a fuel line (107) for fuel recirculation is connected to the heat exchanger (40), and a recycle blower (70) is installed in the fuel line (107).

The fuel off-gas suctioned by the above-mentioned recycle blower (70) is branched to the fuel inlet line (102) and the multi-functional catalytic combustor (50) to provide recirculated fuel, which is a feature of the present invention.

That is, the fuel off-gas passing through the recycle blower (70) is branched into two lines (109)(110), and the first branch line (109) is connected to the fuel inlet line (102) so that it is mixed with new fuel supplied from the fuel supply unit (20) and re-supplied to the stack (10) through the heat exchanger (40), and the second branch line (110) is connected so that the fuel off-gas flows to the multi-functional catalytic combustor (50).

Fuel off-gas that flows into the fuel inlet line (102) through the first branch line (109) flows back into the heat exchanger (40), and fuel off-gas that flows into the multi-functional catalytic combustor (50) through the second branch line (110) meets air off-gas and is discharged after a combustion reaction, and a large amount of air supplied from the air supply unit receives the heat of combustion by the multi-functional catalytic combustor having a heat exchanger structure, thereby increasing its temperature.

The fuel recirculation flow of the fuel line in the present invention is in the order of fuel cell stack (10) → heat exchanger (40) → recycle blower (70) → heat exchanger (40) → multi-functional steam reformer (60) → stack (10).

In addition, the flow direction of the multifunctional catalytic combustor (50) of the fuel line can be in the order of fuel cell stack (10) → heat exchanger (40) → recycle blower (70) → multifunctional catalytic combustor (50) → discharge.

In this way, the fuel whose temperature has increased in the heat exchanger (40) is provided to a multi-functional steam reformer (60) that uses the heat of high-temperature air while performing heat exchange to increase the temperature of newly introduced fuel, and the fuel reformed through the multi-functional steam reformer (60) is supplied to a fuel cell stack (10).

In addition, the stack heat generated by the FC reaction in the fuel cell stack (10), the fuel off-gas, and the hot steam are first mixed evenly by a recycle blower and then mixed with NG (city gas) supplied from the fuel supply unit and reformed in a multi-functional steam reformer. By controlling the flow rate of NG (city gas) supplied from the fuel supply unit (20), the external/internal reforming ratio of the fuel cell stack (10) can be adjusted to control the temperature of the stack.

In the present invention, for additional stack temperature control, city gas (NG) is directly supplied separately to the fuel inlet line (105) between the multi-functional steam reformer (60) and the stack (10) to force internal reforming of the stack, thereby controlling the stack temperature.

Meanwhile, looking at the flow of air in the fuel cell system of the present invention, air is supplied from the air supply unit (30) and introduced into the multi-functional catalytic combustor (50).

The multi-functional catalytic combustor (50) receives fuel off-gas through the second branch line (110) and at the same time receives high-temperature stack cathode off-gas discharged from the stack, and uses the heat of the stack cathode off-gas to increase the temperature of the newly supplied air.

The multi-functional catalytic combustor (50) of the present invention uses the combustion reaction of anode off-gas and cathode off-gas as a heat transfer source to increase the temperature of the supplied air.

Thereafter, the air whose temperature has increased through the multi-functional catalytic combustor (50) is provided to a multi-functional steam reformer (60) that utilizes the heat of the high-temperature air.

The heat generated by the combustion reaction in the multifunctional catalytic combustor (50) increases the temperature of a large amount of air newly supplied from the air supply unit (30) and is supplied to the multifunctional steam reformer (60) to be utilized as reforming reaction heat together with the fuel off-gas to achieve thermal equilibrium.

High temperature air is supplied from the multi-functional steam reformer (60) to the fuel cell stack (10), and the stack off-gas discharged from the stack (10) is again introduced into the multi-functional catalytic combustor (50).

FIG. 5 is a diagram showing the temperatures of fuel and air as they pass through each component in a solid oxide fuel cell system according to the present invention.

Fuel supplied from the above fuel supply unit (20) flows into the hot box (80) through the fuel inlet line (102) and flows into the heat exchanger (40) that utilizes the heat of the stack fuel electrode off-gas discharged from the stack.

When the fuel supplied from the above fuel supply unit (20) flows into the hot box (80) through the fuel inlet line (102), the temperature of the fuel becomes about 100 to 300°C, and while exchanging heat with the stack fuel electrode off-gas in the heat exchanger (40), the temperature rises to 500 to 700°C.

Thereafter, the fuel whose temperature has increased in the heat exchanger (40) is provided to the multi-functional steam reformer (60).

Fuel reformed through the multi-functional steam reformer (60) is supplied to the fuel cell stack (10) at a temperature of 650 to 860°C, and fuel off-gas discharged from the fuel cell stack (10) is suctioned by a recycle blower (70).

The fuel off-gas, which is suctioned by the above-mentioned recycle blower (70) and undergoes heat exchange with the newly supplied fuel in the above-mentioned heat exchanger (40), is lowered in temperature to a temperature range of 350 to 550°C.

The above recycle blower (70) can be installed in the front and rear fuel lines of the heat exchanger (40), and the fuel off-gas passing through the recycle blower (70) is divided into two and provided to the fuel inlet line (102) and the multi-functional catalytic combustor (50), respectively.

The fuel off-gas that flows into the fuel inlet line (102) through the first branch line (109) flows back into the heat exchanger (40), and the fuel off-gas that flows into the multi-functional catalytic combustor (50) through the second branch line (110) undergoes a combustion reaction with the air electrode off-gas and is discharged. At this time, the temperature of a large amount of air supplied from the supply unit (30) is increased by the heat exchanger structure of the multi-functional catalytic combustor.

Meanwhile, air supplied from the air supply unit (30) is introduced into a multifunctional catalytic combustor (50) that utilizes the heat of stack off-gas, and the temperature rises in the multifunctional catalytic combustor (50) to be provided to a multifunctional steam reformer (60) as high-temperature air of 650 to 900°C.

Thereafter, high temperature air is supplied from the multi-functional steam reformer (60) to the fuel cell stack (10).

The stack air electrode off-gas discharged after the FC reaction in the above stack (10) is introduced into the multi-functional catalytic combustor (50), and the stack air electrode off-gas introduced into the multi-functional catalytic combustor (50) is discharged after undergoing a combustion reaction with the fuel off-gas supplied to the multi-functional catalytic combustor.

The solid oxide fuel cell system of the present invention maximizes thermal efficiency through a fuel recycling flow using fuel off-gas, and can maximize thermal efficiency because the fuel off-gas is continuously circulated within the hot box.

Additionally, the high-temperature steam generated by the FC reaction is continuously supplied to the fuel flow and utilized as a reactant ( _H2O ) and energy (heat or temperature) for the reforming reaction in a multi-functional steam methane reformer.

In this respect, the fuel cell system of the present invention has a simpler structure than that of other companies because it does not require a separate steam generator required for fuel reforming.

The heat capacity of a normal fluid can be calculated as shown in Equation (2) below.

Heat of fluid = Specific heat x Mass x Temperature difference… (2)

According to the equation (2) above, the heat capacity of a fluid is proportional to the fluid's specific heat, mass, and temperature difference. The specific heat is an inherent property of the fluid, and if the temperature difference is a process, the heat capacity of the fluid increases as the mass increases. In other words, it can be seen that air with a large flow rate moves with a large amount of heat in the system, and from this perspective, if the flow of air and the flow of fuel are crossed, the heat exchange efficiency can be increased.

Claims (15)

As a fuel recirculating solid oxide fuel cell system, fuel cell stack; A fuel supply unit for supplying fuel to the above fuel cell stack; An air supply unit for supplying air to the above fuel cell stack; A heat exchanger that increases the temperature of fuel supplied from the fuel supply unit through stack fuel off-gas discharged from the fuel cell stack and supplies it to a multi-functional steam reformer; A multifunctional catalytic combustor that increases the temperature of air supplied from the air supply unit by utilizing heat from the combustion reaction of stack air electrode off-gas discharged from the fuel cell stack and fuel off-gas from the second branch line branched off after passing through the heat exchanger, and supplies the air to a multifunctional steam reformer; A multifunctional steam reformer that supplies heat required for reforming reaction through a large amount of air whose temperature has increased by combustion reaction in the multifunctional catalytic combustor, reforms fuel supplied from the heat exchanger into hydrogen and supplies it to a fuel cell stack, thereby performing heat exchange using heat derived from the gas flow of the air electrode and the fuel electrode; and A recycle blower installed in a fuel line to continuously recirculate stack fuel off-gas discharged from the fuel cell stack; A solid oxide fuel cell system comprising: a fuel line and an air line configured to use fuel off-gas and air off-gas discharged from the fuel cell stack as heat sources for fuel and air supplied from the fuel supply unit and the air supply unit. In claim 1, The above fuel supply unit includes a hydrogen supply unit that supplies hydrogen, A solid oxide fuel cell system characterized by including a desulfurizer for removing sulfur in the fuel. In claim 1, The above stack fuel electrode off-gas is primarily connected to the heat exchanger and is branched into two branch lines. The first branch line is provided to the fuel inlet line, and the fuel supplied from the fuel supply section is supplied to the stack, thereby recirculating the fuel, thereby improving the power generation efficiency. A solid oxide fuel cell system characterized in that the second branch line is provided to the multi-functional catalytic combustor to maintain the system temperature. In claim 1, A solid oxide fuel cell system characterized in that the temperature of the stack is controlled by adjusting the external/internal reforming ratio of the fuel cell stack by controlling the flow rate of the fuel supplied from the fuel supply unit. In claim 1, A solid oxide fuel cell system characterized in that the fuel cell stack, heat exchanger, multi-functional catalytic combustor, multi-functional steam reformer, and recycle blower are installed in a hotbox, and have a structure in which fuel off-gas is continuously circulated within the hotbox to maximize thermal efficiency. In claim 1, A solid oxide fuel cell system characterized in that the heat generated by the combustion reaction in the multifunctional catalytic combustor increases the temperature of a large amount of air newly supplied from the air supply unit and is supplied to a multifunctional steam reformer to be utilized as reforming reaction heat, thereby achieving thermal equilibrium. In claim 1, A solid oxide fuel cell system, characterized in that the fuel recirculation flow of the above fuel line is in the order of the fuel cell stack → heat exchanger → recycle blower → heat exchanger → multi-functional steam reformer → stack. In claim 1, A solid oxide fuel cell system, characterized in that the flow direction of the multifunctional catalytic combustor of the above fuel line is in the order of the fuel cell stack → heat exchanger → recycle blower → multifunctional catalytic combustor → exhaust. In claim 1, A solid oxide fuel cell system characterized in that the stack temperature is controlled by forcing internal reforming of the stack by directly supplying separate city gas (NG) to the fuel inlet pipe between the multi-functional steam reformer and the stack for additional stack temperature control. In claim 1, A solid oxide fuel cell system characterized in that the fuel cell stack and BOP (Balance of Plant) are installed in a module form and each module is connected by a pipe so that each module can be separated during maintenance to replace the stack. A method of operating a solid oxide fuel cell system, comprising: A step of supplying fuel from the fuel supply unit and introducing it into the heat exchanger; A step of utilizing the heat of stack fuel off-gas discharged from a fuel cell stack to increase the temperature of NG (city gas) newly introduced into the heat exchanger and providing it to a multi-functional steam reformer; A step of supplying reformed fuel through the multi-functional steam reformer to a fuel cell stack; A step of suctioning by a recycle blower to continuously recirculate the fuel off-gas discharged from the fuel cell stack; A step of supplying the fuel off-gas suctioned by the above recycling blower by branching it to a fuel inlet line and a multi-functional catalytic combustor; A step of supplying air from an air supply unit to a multi-functional catalytic combustor; A step of using the combustion heat generated by the stack air electrode off-gas discharged from the fuel cell stack and the fuel off-gas branched after passing through the heat exchanger to meet and combust in a multi-functional catalytic combustor as a heat source to increase the temperature of air supplied to the multi-functional catalytic combustor from the air supply unit and supplying the air to a multi-functional steam reformer; A step of supplying high temperature air from the multi-functional steam reformer to the fuel cell stack; and A step in which the stack air electrode off-gas introduced into the multi-functional catalytic combustor is exhausted after combustion reaction with the fuel off-gas supplied by branching to the multi-functional catalytic combustor; A method for operating a solid oxide fuel cell system, characterized by including a. In claim 11, In the step of supplying the fuel off-gas suctioned by the above-mentioned recycle blower by branching it to the fuel inlet line and the multi-functional catalytic combustor, The first branch line is connected to the fuel inlet line so that the fuel supplied from the fuel supply unit is mixed and re-supplied to the stack through the heat exchanger. A method for operating a solid oxide fuel cell system, characterized in that the second branch line is connected to have a flow of fuel off-gas to the multi-functional catalytic combustor. In claim 12, A solid oxide fuel cell system operating method characterized in that the fuel off-gas introduced into the multi-functional catalytic combustor through the second branch line is discharged by exchanging heat through combustion reaction with the stack air electrode off-gas in the multi-functional catalytic combustor, thereby increasing the temperature of a large amount of air supplied from the air supply unit. In claim 11, A method for operating a solid oxide fuel cell system, characterized in that the heat generated by the combustion reaction in the multifunctional catalytic combustor increases the temperature of a large amount of newly supplied air, is supplied to a multifunctional steam reformer, and the temperature of the recycled fuel and newly supplied NG (city gas) is increased through heat transfer in a heat exchanger through which the fuel off-gas passes, and is supplied to the multifunctional steam reformer and utilized as reforming reaction heat. In claim 11, A method for operating a solid oxide fuel cell system, characterized in that stack heat generated by the FC reaction in the fuel cell stack is mixed with fuel supplied from a fuel supply unit and supplied to a multi-functional steam reformer to be utilized as heat for a reforming reaction.

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