SoFC cogeneration system with simultaneous improvement of reliability and durability

Abstract

This invention belongs to the field of fuel cell technology. It discloses a SOFC (Solar-Fired Fuel Cell) combined heat and power system that simultaneously improves reliability and durability, including a fuel cell stack, auxiliary equipment, and a thermal management module. In terms of stack structural design, it introduces an integrated cooling channel for reforming and homogenization, and an alternating superimposed flow channel structure. In terms of stack material design, it employs gradient-hole electrode materials, coatings on the bipolar plate surfaces, and materials with low creep strength for the sealing layer. In terms of stack manufacturing process, it uses a multi-stage progressive continuous stamping method to prepare flexible connectors. In terms of auxiliary equipment design, it incorporates a series-connected fixed-bed desulfurizer and H2O... 2 The S-removal unit employs parallel reforming hydrogen production reactors, incorporating a water-steam shifter and a PSA unit. Regarding the thermal management module, multiple thermal balance management routes are established to link the high-temperature heat generated at the rear end of the fuel cell stack with the heat required at the front end. This invention is beneficial for simultaneously improving the reliability and durability of SOFC combined heat and power systems.

Description

SOFC combined heat and power system with simultaneous improvement in reliability and durability Technical Field

[0001] This invention belongs to the field of fuel cell technology, and particularly relates to a SOFC combined heat and power system that simultaneously improves reliability and durability. Background Technology

[0002] Fuel cells, which use H2, methane, methanol, and various organic wastes as fuel, are ideal energy conversion devices for future development. Fuel cells directly convert chemical energy into electrical energy, are not constrained by the Carnot cycle, and are the best choice for green energy. Among all fuel cells, solid oxide fuel cells have the highest theoretical power generation efficiency. The exhaust gas emitted from the stack is high-temperature and pollution-free, and can be used as a heat source to supply other parts of a combined heat and power (CHP) system, thus more effectively improving the overall system's energy utilization rate.

[0003] Combined heat and power (CHP) systems effectively alleviate energy consumption and environmental degradation. Based on the principle of energy cascade utilization, CHP first converts primary energy sources such as oil, coal, and natural gas into electricity using power generation technology, and then uses the waste heat from power generation for heating. Compared to separate heat and power generation, CHP offers advantages such as energy saving and emission reduction, smaller footprint, and higher heating quality, giving it a dominant position in power generation sectors that require high efficiency and long lifespan without frequent start-ups. Furthermore, it can also play a potential role in residential, public facility distributed power supply, and mobile power supply applications.

[0004] The key performance indicators affecting the durability of SOFC (SO2-fired combined heat and power) systems are continuous operating time, system lifespan, and the number of thermal cycles. System lifespan is primarily determined by the steady-state degradation rate, while the number of thermal cycles is determined by the thermal cycle degradation rate. The main indicators for ensuring the reliability of SOFC systems are system power generation, power generation efficiency, and combined heat and power efficiency. To simultaneously improve the reliability and durability of SOFC systems, the key is to ensure that they have both a low degradation rate and high output power and energy utilization efficiency.

[0005] SOFC (SOthermed Combined Heat and Power) systems comprise numerous pieces of equipment and components. The design, structure, and performance of each component all impact the reliability and durability of the entire system. These components are interdependent, and adjustments to their performance have varying effects on the overall system's reliability and durability. Therefore, it is necessary to identify the key modules and corresponding technical factors affecting the performance of SOFC systems, and to optimize the design of each module's technology to simultaneously improve system durability and reliability. Summary of the Invention

[0006] The purpose of this invention is to provide a SOFC combined heat and power system with simultaneously improved reliability and durability, effectively solving the problem of poor reliability and durability of current SOFC combined heat and power systems.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A SOFC combined heat and power system with simultaneously improved reliability and durability, the SOFC combined heat and power system comprising an SOFC stack, auxiliary equipment and a thermal management module.

[0009] The SOFC stack is a multi-layered overlapping component, including multiple individual cells, flexible connectors, sealing layers, and bipolar plates. The anode layer of each individual cell and the flexible connector form an anode fuel channel, and the cathode layer of each individual cell and the flexible connector form a cathode air channel. The anode layer of each individual cell has a gradient hole structure prepared by phase transformation casting method. An integrated cooling channel for reforming and homogenization is introduced between adjacent individual cells. The anode fuel channel and the cathode air channel adopt an alternating structure of cross-flow channels and counter-flow channels. The flow direction of the cooling channel is opposite to that of the adjacent anode fuel channel, and a reforming catalyst is impregnated on the surface of the cooling channel.

[0010] The flexible connector is prepared by a multi-step continuous stamping method, the sealing layer is made of a material with a creep strength coefficient and creep failure strain ratio smaller than that of the bipolar plate, and a composite spinel coating is introduced on the surface of the bipolar plate.

[0011] The auxiliary equipment includes a desulfurization unit, a reforming hydrogen production unit, a catalytic burner, multiple preheaters, and multiple heat exchangers. The desulfurization unit includes a fixed-bed desulfurizer and an H2S remover connected in series. The reforming hydrogen production unit includes a water-steam shift device, a PSA device, and two parallel reforming hydrogen production reactors. One of the two parallel reforming hydrogen production reactors is in operation, while the other is in standby mode. When the reforming efficiency of one reforming hydrogen production reactor decreases, the other reforming hydrogen production reactor is immediately started and put into operation.

[0012] The preheater includes a first preheater and a second preheater, and the heat exchanger includes a first heat exchanger, a second heat exchanger and a third heat exchanger;

[0013] Air enters the cathode of the SOFC stack through the first preheater. Liquid water is converted into high-temperature steam through the third heat exchanger and then enters the reforming hydrogen production reactor for reforming. Fuel passes through the first heat exchanger, the second heat exchanger, and the second preheater in sequence and then enters the desulfurization unit to remove sulfur impurities from the fuel before entering the reforming hydrogen production reactor to produce hydrogen. The hydrogen passes through the third heat exchanger and the second heat exchanger in sequence and then enters the water-steam conversion device. After passing through the first heat exchanger, it enters the PSA device and finally enters the anode of the SOFC stack.

[0014] A portion of the anode tail gas from the SOFC stack enters the reforming hydrogen production reactor after passing through the first and second preheaters for reforming reaction.

[0015] Another portion of the anode and cathode tail gas from the SOFC stack enters the catalytic burner for combustion. The water vapor produced after combustion enters the second preheater to preheat the fuel, and finally enters the reforming hydrogen production reactor for reforming reaction.

[0016] The thermal management module is configured with the following thermal balance management routes:

[0017] (1) A portion of the anode tail gas from the SOFC stack is reused in the steam reforming reaction at the front end of the SOFC stack.

[0018] (2) The other part of the anode tail gas from the SOFC stack is mixed and burned with the cathode tail gas to provide heat energy and steam to the front end of the SOFC stack. Part of the steam is used to heat the hydrogen, and the other part of the steam is used to provide heat for the front-end fuel reforming.

[0019] (3) After three stages of heat exchange, the fuel enters the desulfurization unit. First, it undergoes a first-stage heat exchange with the gas after passing through the water-steam shift device, then it undergoes a second-stage heat exchange with the gas after passing through the reforming hydrogen production reactor, and finally it undergoes a third-stage heat exchange with the water vapor produced after combustion in the catalytic burner.

[0020] (4) The heat generated after water vapor conversion is recovered and used for heating.

[0021] Furthermore, both the heat exchanger and the preheater are compact microchannel diffusion welding heat exchangers.

[0022] Furthermore, there are 1 to 2 catalytic burners.

[0023] Furthermore, the hydrogen entering the anode of the SOFC stack has a purity of over 95%.

[0024] Furthermore, the air reaches a temperature of over 600°C after passing through the first preheater.

[0025] Furthermore, the fuel is heated to 400-500°C after passing through the second preheater, and then sequentially enters the fixed-bed desulfurizer and H2S remover to remove sulfur impurities from the fuel.

[0026] The beneficial technical effects of this invention are:

[0027] (1) This invention, through the design of SOFC stack, auxiliary equipment and thermal management module, is conducive to simultaneously improving the reliability and durability of SOFC cogeneration system.

[0028] (2) By setting multiple thermal balance management routes in the thermal management module, this invention helps to link the high-temperature heat generated at the back end of the SOFC stack with the heat required at the front end, which helps to reduce the demand for air and the power consumption of the air compressor, improve the net power efficiency and cogeneration efficiency of the system, and at the same time avoid the outlet temperature of the catalytic burner being too high, reduce the requirements of SOFC cogeneration system on equipment materials, and improve the life and safety factor of SOFC cogeneration system. Attached Figure Description

[0029] Figure 1 is a technical roadmap of the present invention;

[0030] Figure 2 is a process flow diagram of the SOFC combined heat and power system of the present invention;

[0031] Figure 3 is a single-cell IVP curve of the embodiments and comparative examples of the present invention;

[0032] Figure 4 is a schematic diagram of the test results of the expected steady-state operation decay rate of the fuel cell stack in the embodiments and comparative examples of the present invention;

[0033] Figure 5 is a schematic diagram of the results of 50 cold and hot cycle decay tests of the fuel cell stack in the embodiments and comparative examples of the present invention. Detailed Implementation

[0034] Through extensive long-term continuous system operation and thermal cycling tests, as well as numerous numerical simulations and theoretical analyses, this invention reveals the main factors affecting the durability and reliability of the system, and forms an SOFC combined heat and power system with simultaneous improvement in reliability and durability as described below. This invention mainly includes three aspects: SOFC stack design, auxiliary equipment design, and thermal management module design. The specific technical route is shown in Figure 1.

[0035] (1) SOFC stack design includes three parts: stack structure design, stack material design and stack manufacturing process design.

[0036] In terms of stack structure design, the SOFC stack is a multi-layered overlapping component, including multiple individual cells, flexible connectors, sealing layers, and bipolar plates. The anode layer of each individual cell and the flexible connector form an anode fuel channel, while the cathode layer of each individual cell and the flexible connector form a cathode air channel. An integrated reforming and homogenization cooling channel is introduced between adjacent individual cells, and the surface of the cooling channel is impregnated with reforming catalyst material. Internal reforming removes heat from the cell, preventing the stack temperature from becoming too high. The anode fuel channel and the cathode air channel adopt an alternating structure of cross-flow and counter-flow channels to ensure uniform air intake and stack temperature. The flow direction of the cooling channel is opposite to that of the adjacent anode fuel channel.

[0037] In the design of fuel cell stack materials, for the anode layer, a gradient hole structure is prepared by phase transformation casting method to reduce redox stress and improve thermal cycling stability; for the bipolar plate, a composite spinel coating is introduced on the surface of the bipolar plate to reduce the mismatch thermal stress between the bipolar plate and the sealing layer, and improve the conductivity, oxidation resistance and chemical stability (inhibiting Cr volatilization) of the bipolar plate; for the sealing layer, a material with a creep strength coefficient and creep failure strain smaller than that of the bipolar plate is used, thereby greatly reducing the creep damage and failure probability of the sealing layer and improving the service life of the sealing layer.

[0038] In the design of the fuel cell stack manufacturing process, a multi-step progressive continuous stamping method is adopted to prepare the flexible connector, reduce the residual stress of the bipolar plate, and ensure the forming accuracy and thickness uniformity.

[0039] (2) In terms of auxiliary equipment design, the auxiliary equipment includes a desulfurization unit, a reforming hydrogen production unit, 1 to 2 catalytic burners, multiple preheaters and multiple heat exchangers.

[0040] The total number of preheaters and heat exchangers is 4 to 6. In this embodiment, there are 2 preheaters, including a first preheater 2 and a second preheater 3; and 3 heat exchangers, including a first heat exchanger 4, a second heat exchanger 5, and a third heat exchanger 6. In this embodiment, both the heat exchangers and the preheaters are compact microchannel diffusion welding heat exchangers.

[0041] The desulfurization unit includes a fixed-bed desulfurizer and an H2S remover connected in series to ensure the purity of sulfur impurities removed from the fuel.

[0042] The reforming hydrogen production unit includes a water-gas shift converter 7, a PSA unit, and two parallel reforming hydrogen production reactors. By introducing the water-gas shift converter 7 and the PSA unit, hydrogen production efficiency is improved, ensuring that the hydrogen purity entering the anode of the fuel cell stack is above 95%, thereby reducing the impact of fuel on stack performance degradation and improving stack durability. One of the two parallel reforming hydrogen production reactors is in operation, while the other is in standby mode. If the reforming efficiency of one reactor decreases, the other reactor is immediately started to enter operation, preventing carbon buildup and deactivation in one reactor from affecting the durability of the stack and the system.

[0043] As shown in Figure 2, the process flow of the SOFC cogeneration system of the present invention is as follows: Air enters the cathode of the SOFC stack through the first preheater 2; liquid water is converted into high-temperature steam through the third heat exchanger 6 and then enters the reforming hydrogen production reactor for reforming reaction; fuel passes through the first heat exchanger 4, the second heat exchanger 5, and the second preheater 3 in sequence, and then enters the desulfurization unit to remove sulfur impurities from the fuel before entering the reforming hydrogen production reactor to produce hydrogen; the hydrogen passes through the third heat exchanger 6 and the second heat exchanger 5 in sequence, and then enters the water-steam conversion device 7, then through the first heat exchanger 4, and then enters the PSA device, and finally enters the anode of the SOFC stack. A portion of the anode tail gas from the SOFC stack passes through the first preheater 2 and the second preheater 3 and then enters the reforming hydrogen production reactor for reforming reaction; another portion of the anode tail gas and cathode tail gas from the SOFC stack enter the catalytic combustor 1 for combustion; the water vapor produced after combustion enters the second preheater 3 to preheat the fuel, and finally enters the reforming hydrogen production reactor for reforming reaction.

[0044] The air reaches a temperature of over 600°C after passing through the first preheater 2, and the fuel reaches a temperature of 400-500°C after passing through the second preheater 3.

[0045] (3) Regarding the thermal management module design, a thermal balance management module is introduced. Its purpose is to link the high-temperature heat generated at the rear end of the fuel cell stack with the heat required at the front end, ensuring maximum combined heat and power efficiency through thermal balance calculations. The thermal management module is configured with the following thermal balance management routes:

[0046] ① A portion of the anode tail gas from the SOFC stack is reused in the steam reforming reaction at the front end of the SOFC stack.

[0047] ② Another portion of the anode exhaust gas from the SOFC stack is mixed and burned with the cathode exhaust gas to increase the exhaust gas temperature. The burned exhaust gas is then used to preheat air and fuel, providing heat and steam to the front end of the SOFC stack. Part of the steam is used to heat hydrogen, and the other part is used to provide heat for front-end fuel reforming.

[0048] ③ After the fuel reforming reaction, the CO and H2 in the gas are subjected to water vapor conversion. After the gas undergoes heat exchange with the fuel in the first step, it enters the PSA unit to purify high-purity H2.

[0049] ④ After three stages of heat exchange, the fuel enters the desulfurization unit. First, it undergoes a first-stage heat exchange with the gas after passing through the water-steam shift device 7, then a second-stage heat exchange with the gas after passing through the reforming hydrogen production reactor, and finally a third-stage heat exchange with the water vapor produced after combustion in the catalytic burner 1.

[0050] ⑤ The heat generated after water vapor conversion is recovered and used for heating (hot water, heating, etc.).

[0051] This solution significantly reduces the demand for air and the power consumption of the air compressor, which to some extent helps improve the net power efficiency of the SOFC cogeneration system, resulting in higher cogeneration efficiency. At the same time, it avoids excessively high outlet temperatures of the catalytic burner, reduces the material requirements of the SOFC cogeneration system, and improves the lifespan and safety factor of the SOFC cogeneration system.

[0052] The following description is based on specific embodiments and comparative examples.

[0053] Example:

[0054] Based on this invention, an 800W SOFC (Self-Powered Fuel Cell) cogeneration system using diesel fuel is designed. The SOFC stack of this cogeneration system comprises 24 individual cells, operates at a temperature of 750°C, and has a gradient aperture anode structure. The process flow of this cogeneration system is shown in Figure 2.

[0055] Comparative example:

[0056] Based on existing technology, an 800W SOFC (Self-Powered Central Fuel Cell) cogeneration system using diesel fuel is designed. The SOFC stack comprises 24 individual cells, operates at 750°C, and employs a cross-flow design internally. The anode has a through-hole structure, and the stack lacks an integrated cooling channel for reforming and homogenization. Flexible interconnects are etched and manufactured. The auxiliary equipment of this cogeneration system includes only one reforming hydrogen production reactor; it lacks a fixed-bed desulfurizer, H2S remover, water-gas shift converter, and PSA (Power Supply Alternating Current) unit. Fuel is directly fed into the SOFC stack after passing through the reforming hydrogen production reactor.

[0057] The IVP curves of the single cells in the test examples and comparative examples were tested according to the GB / T 34582-2017 standard. The test conditions were: heating rate: 0.5-1.0℃ / min, reduction with pure hydrogen at 800℃ for 2-3 hours, and test temperature: 750℃. The test results are shown in Figure 3. Compared with the comparative example, the IVP curve of the single cell in the test examples is flatter, and the peak power density is higher.

[0058] The expected steady-state operating attenuation rate of the fuel cell stack in the embodiment and the comparative example was predicted by numerical simulation. The results are shown in Figure 4. Compared with the comparative example, the steady-state operating attenuation rate of the embodiment is only 0.5% / kh, and the expected lifespan is 40,000h.

[0059] Both the example and the comparative example underwent 50 cycles of thermal cycling degradation tests on the fuel cell stack. Each thermal cycle consisted of 200℃→750℃→200℃, with 10 cycles constituting one period. During each period, the stack temperature was reduced to room temperature. The test results are shown in Figure 5. Based on the test results, the stable operation degradation rate of the example was only 0.15% / cycle @ 50 cycles.

[0060] The basic performance related to the reliability of the fuel cell stack in the test examples and comparative examples included power generation efficiency, fuel utilization rate, reforming efficiency, and cogeneration efficiency. The test temperature was 750℃, and the heating rate was 0.5-1.0℃ / min. The test results are shown in Table 1. The power generation efficiency, fuel utilization rate, reforming efficiency, and cogeneration efficiency of this example are all higher than those of the comparative example.

[0061] Table 1 Comparison of basic performance related to fuel cell stack reliability

[0062] Comparison Items: Power Generation Efficiency, Fuel Utilization Rate, Reforming Efficiency, Combined Heat and Power Efficiency; Example 38%, 62%, 80%, 82%; Example 51%, 73%, 91%, 89%. surface

[0063] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A SOFC (Solar-Fired Combined Heat and Power) system with simultaneously improved reliability and durability, characterized in that, The SOFC combined heat and power system includes an SOFC stack, auxiliary equipment, and a thermal management module. The SOFC stack is a multi-layered overlapping component, comprising multiple individual cells, flexible connectors, sealing layers, and bipolar plates. An anode fuel channel is formed between the anode layer of each individual cell and the flexible connector, and a cathode air channel is formed between the cathode layer of each individual cell and the flexible connector. The anode layer of each individual cell has a gradient hole structure prepared using a phase transformation casting method. An integrated reforming and homogenization cooling channel is introduced between adjacent individual cells. The anode fuel channel and the cathode air channel adopt an alternating structure of cross-flow channels and counter-flow channels. The flow direction of the cooling channel is opposite to that of the adjacent anode fuel channel. The surface is impregnated with reforming catalytic material; the flexible connector is prepared using a multi-stage progressive continuous stamping method; the sealing layer uses a material with a creep strength coefficient and creep failure strain ratio smaller than that of the bipolar plate; the surface of the bipolar plate is coated with a composite spinel coating; the auxiliary equipment includes a desulfurization unit, a reforming hydrogen production unit, a catalytic burner, multiple preheaters, and multiple heat exchangers; the desulfurization unit includes a fixed-bed desulfurizer and an H2S remover connected in series; the reforming hydrogen production unit includes a water-gas shift converter, a PSA unit, and two parallel reforming hydrogen production reactors, one of which is in operation and the other is in standby mode; when the reforming efficiency of one reforming hydrogen production reactor decreases, the other reforming hydrogen production reactor is immediately started. The system enters the working state; the preheater includes a first preheater and a second preheater, and the heat exchanger includes a first heat exchanger, a second heat exchanger, and a third heat exchanger; air enters the cathode of the SOFC stack through the first preheater, and liquid water is converted into high-temperature steam through the third heat exchanger and then enters the reforming hydrogen production reactor for reforming reaction; fuel passes through the first heat exchanger, the second heat exchanger, and the second preheater in sequence, and then enters the desulfurization unit to remove sulfur impurities from the fuel before entering the reforming hydrogen production reactor to produce hydrogen; the hydrogen passes through the third heat exchanger and the second heat exchanger in sequence, and then enters the water-steam conversion device, then through the first heat exchanger, and then enters the PSA device, and finally enters the anode of the SOFC stack; a portion of the anode tail gas from the SOFC stack passes through the first preheater. After the second preheater, it enters the reforming hydrogen production reactor for reforming reaction; another part of the anode tail gas and cathode tail gas from the SOFC stack enter the catalytic burner for combustion, and the water vapor generated after combustion enters the second preheater to preheat the fuel, and finally enters the reforming hydrogen production reactor for reforming reaction; the thermal management module is set with the following thermal balance management routes: (1) a part of the anode tail gas from the SOFC stack is reused for the steam reforming reaction at the front end of the SOFC stack; (2) another part of the anode tail gas from the SOFC stack is mixed and burned with the cathode tail gas to provide heat energy and water vapor for the front end of the SOFC stack, of which a part of the water vapor is used to heat hydrogen and the other part of the water vapor is used to provide heat for the front end fuel reforming;(3) After three stages of heat exchange, the fuel enters the desulfurization unit. First, it undergoes a first-stage heat exchange with the gas from the steam-water shift converter; then, it undergoes a second-stage heat exchange with the gas from the reforming hydrogen production reactor; finally, it undergoes a third-stage heat exchange with the steam generated after combustion in the catalytic burner. (4) The heat from the steam-water shift is recovered and used for heating.

2. The SOFC combined heat and power system with simultaneously improved reliability and durability according to claim 1, characterized in that, Both the heat exchanger and the preheater are compact microchannel diffusion welding heat exchangers.

3. The SOFC combined heat and power system with simultaneously improved reliability and durability according to claim 2, characterized in that, The number of catalytic burners is 1 to 2.

4. The SOFC combined heat and power system with simultaneously improved reliability and durability according to claim 1 or 3, characterized in that, The hydrogen entering the anode of the SOFC stack has a purity of over 95%.

5. The SOFC combined heat and power system with simultaneously improved reliability and durability according to claim 4, characterized in that, The air reaches a temperature of over 600°C after passing through the first preheater.

6. The SOFC combined heat and power system with simultaneously improved reliability and durability according to claim 5, characterized in that, The fuel is heated to 400-500°C after passing through the second preheater, and then enters the fixed-bed desulfurizer and H2S remover in sequence to remove sulfur impurities from the fuel.

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